Gas-and-steam emissions with some re-suspended ash in November 2020

Whakaari/White Island, located in the Bay of Plenty 50 km offshore of North Island, has been New Zealand’s most active volcano since 1976. Activity has been previously characterized by phreatic activity, explosions, and ash emissions (BGVN 42:05). The most recent eruption occurred on 9 December 2019, which consisted of an explosion that generated an ash plume and pyroclastic surge that affected the entire crater area, resulting in 21 fatalities and many injuries (BGVN 45:02). This report updates information from February through November 2020, which includes dominantly gas-and-steam emissions along with elevated surface temperatures, using reports from the New Zealand GeoNet Project, the Wellington Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity at Whakaari/White Island has declined and has been dominated by white gas-and-steam emissions during the reporting period; no explosive eruptive activity has been detected since 9 December 2019. During February through 22 June, the Volcanic Activity Level (VAL) remained at a 2 (moderate to heightened volcanic unrest) and the Aviation Color Code was Yellow. GeoNet reported that satellite data showed some subsidence along the W wall of the Main Crater and near the 1914 landslide scarp, though the rate had reduced compared to previous months. Thermal infrared data indicated that the fumarolic gases and five lobes of lava that were first observed in early January 2020 in the Main Crater were 550-570°C on 4 February and 660°C on 19 February. A small pond of water had begun to form in the vent area and exhibited small-scale gas-and-steam-driven water jetting, similar to the activity during September-December 2019. Gas data showed a steady decline in SO₂ and CO₂ levels, though overall they were still slightly elevated.

Similar activity was reported in March and April; the temperatures of the fumaroles and lava in the Main Crater were 746°C on 10 March, the highest recorded temperature to date. SO₂ and CO₂ gas emissions remained elevated, though had overall decreased since December 2019. Small-scale water jetting continued to be observed in the vent area. During April, public reports mentioned heightened gas-and-steam activity, but no eruptions were detected. A GeoNet report issued on 16 April stated that high temperatures were apparent in the vent area at night.

Whakaari remained at an elevated state of unrest during May, consisting of dominantly gas-and-steam emissions. Monitoring flights noted that SO₂ and CO₂ emissions had increased briefly during 20-27 May. On 20 May, the lava lobes remained hot, with temperatures around 500°C; a nighttime glow from the gas emissions surrounding the lava was visible in webcam images. Tremor levels remained low with occasional slightly elevated episodes, which included some shallow-source volcanic earthquakes. Satellite-based measurements recorded several centimeters of subsidence in the ground around the active vent area since December 2019. During a gas observation flight on 28 May there was a short-lived gas pulse, accompanied by an increase in SO₂ and CO₂ emissions, and minor inflation in the vent area (figure 96).

Figure 96. Photo of a strong gas-and-steam plume rising above Whakaari/White Island on 28 May 2020. Courtesy of GeoNet.

An observation flight made on 3 June reported a decline in gas flux compared to the measurements made on 28 May. Thermal infrared images taken during the flight showed that the lava lobes were still hot, at 450°C, and continued to generate incandescence that was visible at night in webcams. On 16 June the VAL was lowered to 1 (minor volcanic unrest) and on 22 June the Aviation Color Code had decreased to Green.

Minor volcanic unrest continued in July; the level of volcanic tremors has remained generally low, with the exception of two short bursts of moderate volcanic tremors in at the beginning of the month. Temperatures in the active vents remained high (540°C) and volcanic gases persisted at moderate rate, similar to those measured since May, according to an observation flight made during the week of 30 July. Subsidence continued to be observed in the active vent area, as well as along the main crater wall, S and W of the active vents. Recent rainfall has created small ponds of water on the crater floor, though they did not infiltrate the vent areas.

Gas-and-steam emissions persisted during August through October at relatively high rates (figures 97 and 98). A short episode of moderate volcanic tremor was detected in early August, but otherwise seismicity remained low. Updated temperatures of the active vent area were 440°C on 15 September, which had decreased 100°C since July. Rain continued to collect at the crater floor, forming a small lake; minor areas of gas-and-steam emissions can be seen in this lake. Ongoing subsidence was observed on the Main Crater wall and S and W of the 2019 active vents.

Figure 97. Photo of an observation flight over Whakaari/White Island on 8 September 2020 showing white gas-and-steam emissions from the vent area. Photo courtesy of Brad Scott, GeoNet.

Figure 98. Image of Whakaari/White Island from Whakatane in the North Island of New Zealand showing a white gas-and-steam plume on 26 October 2020. Courtesy of GeoNet.

Activity during November was primarily characterized by persistent, moderate-to-large gas-and-steam plumes that drifted downwind for several kilometers but did not reach the mainland. The SO₂ flux was 618 tons/day and the CO₂ flux was 2,390 tons/day. New observations on 11 November noted some occasional ash deposits on the webcams in conjunction with mainland reports of a darker than usual plume (figure 99). Satellite images provided by MetService, courtesy of the Japan Meteorological Agency, confirmed the ash emission, but later images showed little to no apparent ash; GNS confirmed that no eruptive activity had occurred. Initial analyses indicated that the ash originated from loose material around the vent was being entrained into the gas-and-steam plumes. Observations from an overflight on 12 November showed that there was no substantial change in the location and size of the active vents; rainfall continued to collect on the floor of the 1978/90 Crater, reforming the shallow lake. A small sequence of earthquakes was detected close to the volcano with several episodes of slightly increased volcanic tremors.

During 12-14 November the Wellington VAAC issued multiple advisories noting gas, steam, and ash plumes that rose to 1.5-1.8 km altitude and drifted E and SE, based on satellite data, reports from pilots, and reports from GeoNet. As a result, the VAL was increased to 2 and the Aviation Color Code was raised to Yellow. Scientists on another observation flight on 16 November reported that small amounts of ash continued to be present in gas-and-steam emissions, though laboratory analyses showed that this ash was resuspended material and not from new eruptive or magmatic activity. The SO₂ and CO₂ flux remained above background levels but were slightly lower than the previous week’s measurements: 710 tons/day and 1,937 tons/day. Seismicity was similar to the previous week, characterized by a sequence of small earthquakes, a larger than normal volcanic earthquake located near the volcano, and ongoing low-level volcanic tremors. During 16-17 November plumes with resuspended ash were observed rising to 460 m altitude, drifting E and NE, according to a VAAC advisory (figure 99). During 20-24 November gas-and-steam emissions that contained a minor amount of resuspended ash rose to 1.2 km altitude and drifted in multiple directions, based on webcam and satellite images and information from GeoNet.

Figure 99. Left: Photo of a gas observation flight over Whakaari/White Island on 11 November 2020 showing some dark particles in the gas-and-steam plumes, which were deposited on some webcams. Photo has been color corrected and straightened. Courtesy of GeoNet. Right: Photo showing gas, steam, and ash emissions rising above the 2019 Main Crater area on 16 November 2020. Courtesy of GNS Science (17 November 2020 report).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a total of eleven low-power thermal anomalies during January to late March 2020; a single weak thermal anomaly was detected in early July (figure 100). The elevated surface temperatures during February-May 2020 were detected in Sentinel-2 thermal satellite images in the Main Crater area, occasionally accompanied by gas-and-steam emissions (figure 101). Persistent white gas-and-steam emissions rising above the Main Crater area were observed in satellite imagery on clear weather days and drifting in multiple directions (figure 102). The small lake that had formed due to rainfall was also visible to the E of the active vents.

Figure 100. Low-power, infrequent thermal activity at Whakaari/White Island was detected during January through late March 2020, as reflected in the MIROVA data (Log Radiative Power). A single thermal anomaly was shown in early July. Courtesy of MIROVA.

Figure 101. Sentinel-2 thermal satellite images in the Main Crater area of Whakaari/White Island show residual elevated temperatures from the December 2019 eruption, accompanied by gas-and-steam emissions and drifting in different directions during February-May 2020. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 102. Sentinel-2 images showing persistent white gas-and-steam plumes rising from Main Crater area of Whakaari/White Island during March-November 2020 and drifting in multiple directions. A small pond of water (light blue-green) is visible in the vent area to the E of the plumes. On 11 November (bottom right), the color of the plume is gray and contains a small amount of ash. Images using “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brad Scott, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: https://twitter.com/Eruptn).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

July 1971 (CSLP 73-71)

New crater formed by small 19-20 July eruption

Card 1266 (28 July 1971) Small eruption on 19 July forms new crater and drops ash and blocks on the island

"A small tephra eruption took place from White Island, Bay of Plenty, New Zealand at approximately 1420 on 19 July 1971. The eruption produced an ash cloud 6,000 feet high and ejected large blocks (reported by local fisherman to be up to the size of a football) around the island, which exploded on impact with the water. A new Crater, about 200 feet across has been formed at the western end of 1933 crater. Professor R.H. Clark, who flew over the volcano on 20 July, reports that there is ash on the outer slopes of the volcano but only occasional bursts were being erupted from the new vent during the period he was over the island."

Card 1267 (28 July 1971) Eruption diminished by 20 July, but intermittend large explosions continuing

"The eruption occurred at White Island... at 1400 on 19 July 1971. The initial eruption ejected a large plume of steam as well as black ash and boulders, some of which reached the sea half a mile away. It was reported to be the largest eruption for some time. An aerial inspection on 20 July 1971 by R.H. Clarke, P.R.L. Browne, and the writer revealed that a new vent had formed to the south of Gilliver Crater (1966) and Rudolph Vent (1968). Fresh ash and debris were scattered over the entire W half of the crater and on the W outer slopes where Pohutukawa Forest was also dusted with ash. By 20 July the force of the eruption had considerably diminished though large explosive outbursts were occurring from time to time and fresh ash was falling from the steam cloud drifting to the WNW."

Information Contacts:
Card 1266 (28 July 1971) J.W. Cole, Department of Geology, Victoria University of Wellington, New Zealand.
Card 1267 (28 July 1971) J. Healy, New Zealand Geological Survey.

January 1977 (NSEB 02:01) Cite this Report

Explosive steam-and-ash eruptions form new craters

A visit on 13 and 15 December by a team of 10 scientists resulted in the following observations: "Continued bulging in the Noisy Nellie/1971 Crater area, the vigorous high-temperature fumaroles in the back wall of 1971 Crater, and generally higher ground temperature in the active part of the main crater all suggest further activity may occur. The situation is similar to that in 1967 prior to the eruption of Rudolf, and a phreatic eruption could occur in the next few months."

18 December: A fishing vessel reported an explosion from White Island at 1545. The White Island seismograph recorded a tremor.

20-21 December: Over 50 local earthquakes/day were recorded. At 1100 on 21 December a large steam plume rose 700 m.

25 December: Moderate-heavy tremor began, continuing for at least 3 days.

26 December: Discolored steam and some "rocks" were emitted for several hours prior to the eruption of a large, very dark ash cloud at 1545.

27 and 29 December: Steam and ash eruptions.

30 December: C. Hewson (DSIR Geophysics Division), S. Nathan, and E. Lloyd (NZGS) flew over White Island between 1033 and 1058. The E part of the island was sprinkled with mustard-green ash, which appeared thickest within the crater. Ash thickness may have exceeded l m near the active vent; several cm of ash coated the S rim. No impact craters were observed in the recent ash. The vent was located near the 1967 (Rudolf) crater (figure 1) and was about 20 m in diameter. Two nested craters appeared to have formed: the larger was saucer shaped and occupied the approximate position of the 1971 crater; the smaller inner crater was erupting a medium to dark gray steam and ash cloud, from which a very light ashfall was visible for 2-4 km downwind. The sea along the N coast was discolored by extensive orange-brown and milky precipitates. Several streams of water were visible on the crater floor and a particularly vigorous spring emerged at the base of the E crater wall.

Figure 1. Main crater of White Island Volcano, showing the locations of various vents and fumaroles. [After Browne and Cole (1973).]

6-7 January: Commercial pilots reported increased activity.

8 January: C. Hewson, S. Nathan, and two television reporters flew over White Island between 1450 and 1510. Light gray-brown ash was vigorously erupted. The vent appeared larger than on 30 December. Noisy Nellie was steaming strongly, but Donald Mound appeared less active, with only distinct fumaroles emitting steam. All visible parts of the island were mantled by light gray ash, estimated to be at least l cm thick on coastal vegetation; ash was much more widespread than on 30 December. The area within about 50 m of the vent was plastered with pale gray mud. No bomb craters were observed.

11 January: Victoria Univ. and NZGS scientists flew over White Island between 1110 and 1135. Steam, colored pale brown-gray by ash, billowed slowly to 800-900 m above sea level. The ash content of the eruption cloud was less than on 30 December. Since then, no more than l cm of ash appeared to have been deposited on the island. The active vents were larger and deeper, and covered the area of the 1971, Rudolf, and part of the 1933 craters [but see 2:2]. Minor fumaroles were noted on the outer slope of the volcano.

15 January: Two large eruptions were reported at 0830 and 1200, the eruption cloud from the latter reaching 1300 m.

17 January: J. Healy, B. Scott, and E. Lloyd (NZGS) overflew White Island between 1133 and 1146 and observed 1,000-m steam clouds containing some ash. The active vent seemed about the same size (150 m in diameter) as on 11 January. Although the observation period was brief, it appeared that the nature of the eruption had changed from continuous emission to one characterized by brief periods of little or no emission. The last eruption occurred 19-20 July, 1971.

[Reference. Browne, P.R.L., and Cole, J.W., 1973, Surveillance of White Island volcano, 1968-1972: New Zealand Journal of Geology and Geophysics, v. 16, no. 4, p. 959-963.]

Information Contacts: J. Cole, Victoria Univ., Wellington; D. Shackelford, Villa Park, CA.

February 1977 (NSEB 02:02) Cite this Report

Vigorous eruptions through mid-February

White Island was still erupting vigorously when visited on 25 January and inspected from the air on 12 February. The new crater (Christmas Crater) had increased slightly in size, but had not, as previously thought, engulfed Rudolf Crater.

25 January: Weak to moderate emission of ash in a moderately convoluting eruption cloud was occurring from a small vent (~10 m in diameter) within the new 160 m-diameter collapse crater (Christmas Crater). No incandescence was observed. Two scientists enveloped in the eruption cloud for about 30 seconds were covered by fine, dry ash and reported the cloud to be only "pleasantly warm". More than l m of fine- to moderate-grained tephra had been deposited on the E rim of Christmas Crater, but no large ejecta were observed. Noisy Nellie was much more active than on 13 December (02:01), emitting steam and SO₂ under high pressure.

12 February: A dense buff-brown plume of convoluting steam and ash rose 600-750 m from a small vent near one wall of Christmas Crater (figures 2, 3, and 4). The eruption cloud was considerably darker than on previous inspections because of a higher ash content, and ash cover within the crater appeared much thicker than on 25 January. Christmas Crater had increased 10 m in diameter and was 100 m deep, with steep, buttressed walls and a generally flat floor. Slump blocks had collapsed into the crater and pools of discolored water were on its floor. Mudflows covered the steep slopes around the crater.

Figure 2. Oblique aerial photo of Christmas Crater, 12 February 1977, showing steam and ash emission from the active vent. Courtesy of Ian Nairn.

Figure 3. Airphoto looking down into Christmas Crater, 12 February 1977, showing steam and ash emission from the active vent. Courtesy of Ian Nairn.

Figure 4. March 1978 map showing approximate boundaries of the new crater (Gibrus) and Christmas crater, tephra isopachs, and sites of measured sections (thicknesses in centimeters, measured 21 March, in parentheses). Courtesy of the NZGS.

Rudolf Crater was only a few meters deep, having been nearly filled with ash and slump debris. Noisy Nellie was steaming strongly, emission from Donald Mound was normal, and a little steam was issuing from the S wall of Gilliver. The crater floor around Noisy Nellie and Donald Mound was coated with sulfur.

Information Contacts: I. Nairn, NZGS, Rotorua; D. Shackelford, Villa Park, CA.

April 1977 (NSEB 02:04) Cite this Report

Ash eruptions continuing in late March-early April

White Island was inspected from the air on 25 March and 14 April, and visited on 4 April. On 25 March, a tan gas and ash cloud with an orange base was emitted from the vent, which had migrated from the wall to the N base of Christmas Crater, allowing access to the vent by runoff water for the first time. A glow had been observed during an 11 March overflight, but could not be confirmed on 25 March because of the large quantity of gas filling the crater. Many impact craters and large b1ocks, not present on 11 March, were seen S and E of Christmas Crater and on the floor of 1933 Crater, indicating that a major explosion had taken place between 11 and 25 March.

Observers reported a deep red glow above White Island during the night of 26 March, and clouds, frequently blackish, rising to 2000 m on 26-27 March.

On 4 April, a voluminous, moderately convoluting cloud of incandescent ash was rising to 600 m in brief puffs, and drifting to the SE. A comparison of 25 March airphotos with 4 April ground observations indicated that there had been no eruption of large ejecta since 25 March. The largest blocks from the 11-25 March eruption were composed of accidential material, but most of the tephra consisted of scoriaceous-essential lava ranging in size from ash, to blocks and bombs up to several m across. The 11-25 March eruption was the largest 20th-century explosion at White Island and the first to produce essential ejecta, but no eyewitness reports of a large eruption have been received. [A careful search by J.H. Latter of the records of regional seismic stations failed to detect any earthquakes at White Island during this period.]

By the 14 April overflight, activity had declined to low-volume emission of a dark fawn-colored, slowly convoluting steam cloud, containing a little ash. There was no evidence of major explosive activity postdating the 11-25 March eruption. A linear fumarole zone had developed, extending from the N end of Wilson Bay across the W end of Shark Bay to the crater wall.

Further Reference. Clark, R.H., Cole, J.W., Nairn, I.A., and Wood, C.P., 1979, Magmatic Eruption of White Island Volcano, New Zealand, December 1976-April 1977; New Zealand Journal of Geology and Geophysics, v. 22, no. 2, p. 175-190.

Information Contacts: I. Nairn and B. Scott, NZGS, Rotorua; J. Latter, DSIR, Wellington; R. Clark, Victoria Univ., Wellington.

May 1977 (NSEB 02:05) Cite this Report

Aerial inspection on 5 May revealed steam-and-ash column above Christmas Crater

The volcano was inspected from the air on 5 May. A steam and ash column, light tan and slowly convoluting, rose 600-900 m above Christmas Crater. No incandescence was observed, nor were there any new large ejecta, new impact craters, or major new ash deposits on the main crater floor. Christmas Crater appeared to be unchanged from 25 April.

Information Contacts: NZGS, Rotorua.

June 1977 (NSEB 02:06) Cite this Report

New ash deposits

Another aerial inspection on 24 May revealed two new ash deposits: the E half of the island was covered by gray-green ash erupted about 10 May, and the main crater contained red-pink ash that had fallen during the night 23-24 May. Steam was being emitted at low velocity from Christmas Crater. On another overflight 1 June, Christmas Crater was emitting a steam column containing some ash which rose slowly to 1,100 m, interspersed with occasional higher velocity ash pulses. Some ash adhered to the aircraft, for the first time since 28 March. No new large ejecta were observed during either inspection.

Observers in Whakatane (~55 km from White Island) reported eruption clouds during the early morning of 28 May and at 0627 on 1 June. An earthquake was felt in the Bay of Plenty at 0653 on 1 June.

Information Contacts: NZGS, Rotorua.

August 1977 (NSEB 02:08) Cite this Report

Entire island covered in ash in late July

There were inspections from the air on 5 and 26 July, and from the ground on 3 August. At 1117 on 5 July, Mr. Harvey, Civil Defence Whakatane, observed an ash column that rose rapidly to an estimated 1200 m. The crater and the base of the column appeared to be glowing. Mr. D. Thursby viewed White Island at 1150 from Te Kaha, about 50 km away, and reported a dense, red ash cloud that dispersed after rising about 300 m. The aircraft reached White Island at 1534. A pink, moderately convoluting cloud, interspersed with higher velocity ash pulses, was rising 300-400 m. A thick layer of deeply channeled red ash covered the main crater floor. No large ejecta or bomb craters were observed, nor was there any incandescence.

During the 26 July aerial inspection, ash content of the plume was reduced to an orange tint near the base. Brick-red ash, thought to be several days old, covered the island. No new impact craters were noted.

The 3 August ground inspection revealed that the gullied red ash seen from the air on 5 and 26 July had been covered by coarse gray tephra, field identified as glassy basaltic andesite, ranging from ash to blocks (up to l m in diameter) and bombs. Some of the gray tephra initially deposited on the main crater walls had been remobilized to form debris flows, about 3 m wide at their fronts and usually less than 100 m long, that had moved down pre-existing debris fans towards the crater floor. Pits dug at several locations in the main crater revealed that more than 82 cm of ash had fallen near Christmas Crater since 5 May. The gray tephra layer comprised 37 of the 82 cm, and was overlain by 2-5 mm of fine red ash.

The ash column on 3 August was light tan, and was emitted at moderate velocity to about 600 m. No incandescence was observed.

Information Contacts: J. Cole, Victoria Univ., Wellington; B. Scott and B. Houghton, NZGS, Rotorua.

September 1977 (NSEB 02:09) Cite this Report

Large eruptions on 25 August; lithic blocks ejected

White Island was inspected from the air on 25 August and from the ground on 28 August. A large but brief ash eruption from Christmas Crater began at 1445 on 25 August. Steam emission had been moderate to voluminous during the two previous weeks and a deep red glow was reported by pilots beginning about 1 week before the eruption. Pilot Bruce Black reported that the ash column, which included a few jets of incandescent material, rose rapidly to about 4,500 m before being blown NNW by a 40 km/hr wind. A few minutes later, a second explosion produced a cloud that reached 6,000 m altitude, but contained less incandescent material. Base surges from this cloud moved across the main crater, some of them against the wind. By 1515, activity had declined to steam emission.

Ground inspection revealed light gray ash, about half the thickness of the late July deposits containing lithic blocks up to 1 m in diameter. Impact craters with subdued outlines were common, the largest about 3 m in diameter and 1 m deep. Base surges had deposited moderately well-developed cross bedded transverse dunes. Slumping and a mudflow deposit were observed NW of Christmas Crater, and strong steam emission was occurring from the associated concentric cracks.

Information Contacts: I. Nairn, E. Lloyd, B. Houghton, and P. van der Werff, NZGS, Rotorua.

October 1977 (NSEB 02:10) Cite this Report

Weak ash column seen on 9 October, but no major explosions

No major explosions have occurred since the 25 August event. An aerial inspection on 9 October revealed a pink, moderately convoluting ash column rising about 900 m from Christmas Crater. Some rainwater channeling of the 25 August ash deposit had taken place.

Information Contacts: B. Scott, NZGS, Rotorua.

November 1977 (NSEB 02:11) Cite this Report

Ash eruptions continue during November

A 2,000-m brown ash cloud was observed over White Island on 7 November and eruption of additional ash was reported the next morning. An aerial inspection on 10 November revealed a white 600-m non-convoluting steam column emerging from a new fumarole in the N wall of Christmas Crater. Strong steaming, depositing sublimates, continued from several fumaroles.

White Island was visited on 20 November. Poorly sorted accessory ash and lapilli SE of Christmas Crater reached a maximum thickness of 330 mm above the 25 August deposits. A tongue of debris flow tephra, including blocks up to 1.6 m in diameter, extended 400 m SE from Christmas Crater. Base surge dunes were observed N of Christmas Crater.

Information Contacts: E. Lloyd, NZGS, Rotorua.

December 1977 (NSEB 02:12) Cite this Report

Seismogram analyses for 30 August-15 November

White Island seismograms for the period 30 August-15 November were analyzed (table 1). [About 2,700] small volcanic earthquakes have been counted and separated into four groups [for which the magnitude-frequency coefficient b was determined.] All the events interpreted as explosion earthquakes occurred during a [strong] swarm of A-type quakes between 1722 on 21 October and 0724 on 22 October. The largest, ML 2.6, occurred at 0104. [An eruption is known to have taken place between 9 October and 10 November (date unknown). From the explosion earthquakes, J.H. Latter suggests that the peak of this activity probably occurred at 0104 on 22 October.]

Table 1. Number [revised] and type of events recorded by White Island seismic stations, 30 August-5 November 1977.

Information Contacts: J. Latter, DSIR, Wellington.

January 1978 (SEAN 03:01) Cite this Report

19 January overflight shows mild steaming

White Island was inspected from the air on 19 January, the first observation since 20 November. No significant activity had been reported during the intervening period.

A 600-m column of weakly convoluting white steam was continuously emitted from Christmas Crater during the 20-minute overflight. A yellow-green pond, first noted in November, had grown to occupy much of the central floor of Christmas Crater, but was not steaming or otherwise active. Strong steaming continued from the new vent in the NW wall of Christmas Crater and from older fumaroles within the large main crater.

Information Contacts: I. Nairn, NZGS, Rotorua.

March 1978 (SEAN 03:03) Cite this Report

New collapse crater formed; strong explosive and seismic activity

White Island was visited on 16 February, and was viewed from the air on 23 February, 27 February, 2, and 16 March. Gas and a little ash were emitted at high pressure from a new vent in Christmas Crater on 16 February. . . . On 20 February between 1500 and 1800, observers about 55 km from the volcano noted a black ash column rising to about 1500 m, the largest seen since November 1977. During this activity, vigorous tremor and trains of apparent B-type earthquakes were recorded. Tremor intensified 21-22 February, accompanied by large-amplitude long-duration earthquakes.

During the 23 February overflight, a moderate amount of gray ash rose to about 1200 m altitude from the new Christmas Crater vent. Strong fumarolic activity continued from various vents. Ash emission from Christmas Crater was continuing on 27 February, and had begun from Gilliver (the November 1966-March 1967 eruption crater), about 200 m to the NW, which previously had only fumarolic activity during the current eruption.

Between 27 February and 2 March, the seismograph recorded periods (45 minutes to 6 hours) of semi-continuous 3-4 Hz vibration and several low-frequency, probable B-type shocks. Gray ash covered White Island on 2 March, but no impact craters were seen near the Christmas Crater vents, which emitted a moderate amount of dark brown ash that rose to about 900 m altitude at low velocity. Some ash was in the steam column from Gilliver Crater, but less than on 27 February. Strong fumarolic activity continued at other vents.

Semi-continuous 3-5 Hz vibration was recorded 2-10 March accompanied by numerous A-type and some B-type shocks. After the l0th, seismic activity was limited to a few 45-80-minute trains of A-type events recorded 13-16 March.

A thick blanket of light gray ash covered all of White Island on 16 March. A 350 m-diameter collapse crater had formed since the 2 March overflight, bounded by concentric cracks that developed in the spring of 1977. The collapse crater occupied the area of the new Christmas Crater vent and older craters Gilliver, Sulphur, and Big John. Strong steaming obscured the crater floor, but it appeared to have a maximum depth of about 100 m. Episodic emission of ash and blocks (to a maximum height of about 200 m) was occurring from the collapse crater, at the approximate former location of Sulphur Crater.

Information Contacts: I. Nairn and B. Scott, NZGS, Rotorua.

April 1978 (SEAN 03:04) Cite this Report

Eruptive and seismic activity decline after formation of new crater

White Island was visited on 21 March and inspected from the air on 5 April. The new collapse crater, provisionally named Gibrus Crater, is the largest new topographic feature to form on White Island since 1914 (average diameter is 325 m, depth about 100 m; figure 4). Its approximate volume was 6.7 x 10⁶ m³, more than 3x that of adjacent Christmas Crater.

Steam rising to 400 m obscured the new crater during most of the 21 March visit, but cleared briefly revealing steam vents, including the "active vent", which ejected ash and blocks during the 16 March overflight. A pair of 20 m-diameter vents near the NW wall had built small ash cones (figure 5). Hot gas (> 550°C) was emitted at high velocity from a new fumarole 50 m NNE of Noisy Nellie and temperatures of 370°C and 250°C were recorded in H₂S-rich gas from strongly active fumaroles on Donald Mound. Strong fumarolic activity deposited sulfur on the S wall of Christmas Crater.

Figure 5. Sketch by B. J. Scott showing the interior of Gibrus Crater on March, looking W from the E crater rim.

Numerous impact craters containing accessory blocks up to 0.6 m in diameter were found on 21 March up to 500 m from the new crater. Tephra thickness exceeded 85 cm near the crater rim. All tephra had been deposited as airfall.

Large black eruption clouds were observed at 0950 on 30 March (rising 3,000-4,500 m) and during the early morning of 4 April (visible from Tauranga, ~100 km away). However, no major new ashfall was seen on 5 April, nor were there any apparent changes in crater morphology (figures 6 and 7). Steam from Gibrus and Christmas craters rose 750 m, but other fumarolic activity had declined.

Figure 6. Oblique airphoto taken by J. Perrin on 11 March 1977, looking W, showing much of the W portion of White Island's main crater before the formation of the new (Gibrus) crater in March 1978. Compare with April photograph (figure 7). Courtesy of B.J. Scott, NZGS.

Figure 7. Oblique airphoto taken by E. F. Lloyd on 5 April 1978, looking WNW. The large vigorously steaming Gibrus Crater is behind the shallower, gently steaming Christmas Crater.

The formation of Gibrus Crater between 2 and 16 March was not observed, but numerous local earthquakes were recorded during this period. Larger events are tabulated below (table 2).

[J.H. Latter has corrected elements of this table and has rewritten the following paragraph based on more up-to-date information.]

Table 2. Larger seismic events 2-17 March 1978. Earthquake type is Minakami A-type (>3 Hz); type B, low-frequency (less than 1.75 Hz); C type, intermediate in frequency between A and B types. Type E indicates explosion event. J.H. Latter has corrected elements of this table.

[Volcanic tremor was conspicuous until 17 March. It was strong on 8 and 17 March, and ended immediately after the explosion earthquake at 2146 on 17 March.]

Information Contacts: B. Scott, E. Lloyd, and I. Nairn, NZGS, Rotorua; J. Latter, DSIR, Wellington.

May 1978 (SEAN 03:05) Cite this Report

Eruptions and seismicity resume in mid-May

Eruptions accompanied by seismicity resumed on 13 May after more than a month of weak to moderate fumarolic activity. Voluminous dark eruption clouds rising to about 3,000 m were reported by persons living near the Bay of Plenty (50-60 km from White Island) on 13 May, but poor weather hampered observations for the next several days. Visibility improved on the morning of 17 May, and a large cloud was seen from Whakatane, 55 km S of White Island. An aerial inspection early that afternoon revealed a 2,000-m steam cloud, containing little or no ash, fed by vigorous fumarolic activity from several sites, including a new, nearly horizontal fumarole on the SW wall of Christmas Crater. Fine dark gray ash mantling the main crater floor had been disrupted by rainfall on 15 May and probably 16 May. No coarse debris or impact craters were visible.

Subsidence, not seen during the previous overflight (2 May), was defined by arcuate scarps extending from the W wall of the new (Gibrus) crater to the SE wall of Christmas Crater. Vigorous steaming occurred from the collapse scarps, which were displaced about 1 m down to the NE.

Low-amplitude, low-frequency tremor began at about 2100 on 12 May and amplitude increased for about 22 hours. A similar tremor episode started on 15 May at about 0300, increased in amplitude until around 1900, then gradually subsided 16-18 May. Low-frequency B-type shocks accompanied the first period of tremor, but decreased noticeably during the second tremor episode.

Information Contacts: B. Scott, E. Lloyd, B. Houghton, NZGS, Rotorua.

July 1978 (SEAN 03:07) Cite this Report

Two harmonic tremor episodes, but no major new eruptions

Two brief periods of volcanic tremor, each followed by multiple earthquakes, were recorded during June. After low-frequency tremor between 0100 and 2000 on 8 June, multiple shocks occurred at 002645 on the 9th. Medium-frequency tremor lasting from 1200 on 22 June until 1100 on 24 June was succeeded by a high-frequency tremor episode beginning at 1518 on the 24th and culminating in a series of earthquakes at about 1646. Local seismicity was otherwise limited to a few small earthquakes per day.

White Island was inspected from the air on 28 June. No evidence of major eruptive activity since 17 May was observed. Voluminous steam emission from the new collapse crater (Gibrus) produced a convoluting steam column that rose about 600 m. Some new fumaroles were visible inside Gibrus, but other fumarolic activity had declined. A formerly hot (>550°C in late March) and vigorous fumarole NW of Noisy Nellie had declined to weak steaming. Two new pits were observed within Christmas Crater. The larger, 20-25 m in diameter, contained a pond of green water; the smaller, 15 m in diameter, was surrounded by a small amount of grayish ejecta.

Information Contacts: P. van der Werff, I. Nairn, and B. Scott, NZGS, Rotorua.

August 1978 (SEAN 03:08) Cite this Report

New impact craters and tephra deposits

White Island was inspected from the air on 26 July and visited on 6 and 9 August. Impact craters not present on 28 June were visible in 26 July airphotos. The time of the eruption that produced the craters is uncertain. However, a 4,500-m black eruption column was seen from the mainland by one observer, about 50 km away, at 1045 on 17 July.

Numerous impact craters from 0.5 to 2.0 m in diameter were found during the August visits, extending E from the active vent in Gibrus crater and reaching a concentration of about 1 crater/4 m² area. Geologists excavated a few of the craters, each of which contained an angular andesite block. Poorly sorted ash- to lapilli-sized gray tephra, 10-20 mm thick near the vent, mantled the surface. The tephra deposit contained no evidence of fresh magma. According to NZGS geologists, the tephra was probably deposited by a pyroclastic flow or base surge. The impact craters contained tephra deposits only on their distal rims, indicating that the tephra's movement included a substantial horizontal component.

The narrow ridge separating Christmas and Gibrus craters was virtually destroyed between 28 June and 26 July. The NW portion of the old Christmas Crater had deepened, and was occupied by vigorous fumaroles and a series of yellowish-green ponds. Continuous fumarolic activity was observed at other sites within this new composite crater, and weaker fumaroles were active NW of it.

Information Contacts: B. Houghton, E. Lloyd, B. Scott, NZGS, Rotorua.

October 1978 (SEAN 03:10) Cite this Report

Earthquake swarms, but no evidence of new explosions

At least 50 discrete high-frequency earthquakes were recorded between 0034 and 0608 on 5 October. Large events occurred at 0037, 0250, and 0424. With the possible exception of the second event, the shocks had very sharp onsets and were interpreted as A-type events. The earthquake swarm was followed by bursts of low-amplitude volcanic tremor, which continued sporadically through the rest of the day.

An aerial inspection on 5 October revealed no new tephra or impact craters. A white, gently convoluting steam cloud rose from fumaroles in 1978 crater and at the base of the main crater wall, north of Noisy Nellie. Yellow and white fumarole sublimates covered the walls of 1978 Crater.

Information Contacts: E. Lloyd, NZGS, Rotorua.

January 1979 (SEAN 04:01) Cite this Report

Renewed ash eruption, strongest since July

A period of renewed ash emission that began on 24 December 1978 has been one of the longest and most voluminous since the eruption began in December 1976. The ash emission was preceded by considerable local seismicity recorded since early November. The seismicity consisted of periods of continuous high-frequency tremor lasting up to 30 hours, separated by quiet periods of similar length, and other periods of similar total duration characterized by up to nine bursts of noise per minute.

Shortly after 1900 on 24 December, persons on the mainland (about 50 km from White Island) observed the ejection of a dark, billowing cloud to an altitude of about 3 km. This cloud drifted E and was followed by several smaller dark ash clouds. The eruption was accompanied by a brief seismic sequence (table 3).

Table 3. Sequence of seismicity accompanying the 24 December 1978 eruption at White Island.

The next morning, NZGS personnel flew over the volcano and observed new gray ash near the rim of 1978 Crater. Vapor rose from a cluster of small vents on the 1978 Crater floor, near the former site of Rudolf vent. Some block-sized ejecta surrounded the active vents, but no large ejecta could be seen outside 1978 Crater. Later that morning, pilot Graeme Bell saw blocks and ash ejected from these vents, with blocks rising 30-50 m.

Numerous small, high-frequency earthquakes occurred on 25 and 28 December, followed by periods of semi-continuous high-frequency tremor on the 28th and 29th. A few low-frequency B-type shocks were also recorded. Tremor became nearly continuous after about 0800 on 29 December. On the 31st, pilots reported block and ash eruptions.

During overflights on 1 and 9 January, columns of gas and ash rose 600-700 m from 1978 Crater. A few blocks and impact craters were visible near the crater rim on l January, but block ejection was not observed on either occasion. Between the lst and 9th, long periods of semi-continuous 3-7 Hz tremor were recorded on 6 days. Explosion-type earthquakes were recorded on 2 and 6 January and two large A-type events occurred on 8 January. Eruptive activity was visible from the mainland (~50 km away) on 4 January and five ash clouds, each rising about 1 km, were ejected in a 40-minute period the next morning. A 2-km-high cloud was seen during the late afternoon of 7 January, followed by 7 more large clouds in the next 35 minutes.

Ground inspection on 12 January showed four separate layers of fresh ash totalling 32 cm thick mantling the crater rim, underlain by a blocky layer that may have predated the 24 December activity. Ash thicknesses decreased to 6 cm about 200 m to the E. An ash column rose to about 450 m altitude from the active vent, about 70 m in diameter on the 1978 Crater floor.

Information Contacts: E. Lloyd, I. Nairn, B. Scott, NZGS, Rotorua; H. Palmer, Post Office, Rotorua.

February 1979 (SEAN 04:02) Cite this Report

Increased ash emission and accompanying seismicity persist

Increased ash emission and local seismicity were continuing in late January. Long periods of semi-continuous, moderate- to high-frequency tremor continued from the 12th, but were punctuated on 16 January by 19 possible explosion-type earthquakes between 0052 and 1738 (the largest at 0451). On 22 January there were 6 explosion events (maximum amplitude less than half that of the largest 16 January event) from 1158 to 1222, and tremor gradually declined to low levels after 0800 on the 23rd. Eleven hours later, however, tremor amplitude increased for 2 1/4 hours, then remained continuous at moderate to high frequency for over 5 days. A single explosion-type event occurred at 1015 on 26 January and tremor declined to a low level at 0500 on the 29th. [The largest B-type shock of the period, M 2.45, occurred during a 3-hour swarm of about 50 similar events on 24 February.]

On 23 and 25 January an ash column rose to about 600 m above sea level from the active vent, which was at least 50 m deep. About 40 cm of ash was measured at the rim of 1978 Crater on the 25th, 8 cm more than on 12 January. Blocks up to 1 m across, not observed on the 12th, were found about 200 m to the E. Fumarole temperatures of up to 535°C were recorded, similar to those measured on 7 December.

Information Contacts: B. Scott and I. Nairn, NZGS, Rotorua.

April 1979 (SEAN 04:04) Cite this Report

Continued ash emission

The morning of 12 April, a light tan, mildly convoluting eruption column rose from a deep vent in the floor of 1978 Crater. The column reached an altitude of about 500 m before drifting E and producing a fine ash fallout. No fresh impact craters or blocks were observed near the 1978 Crater rim, but brown ash covered the main crater floor. Strong vapor emission also occurred from a fumarole E of 1978 Crater. Almost continuous medium- to high-frequency tremor, had persisted for the past several weeks.

Information Contacts: B. Scott, NZGS, Rotorua.

May 1979 (SEAN 04:05) Cite this Report

At least two explosions since mid-April

At least two moderate explosive eruptions seemed to have occurred since 12 April. R. R. Dibble and E. Hardy observed recently ejected tephra deposits on 21-22 April. [J.H. Latter notes that the strongest period of volcanic tremor recorded between August 1977 and September 1979 started at 1800 on 29 April and continued until 1 May at 0856.] A newspaper article (Whakatane Beacon, 9 May) reported that an eruption at 2030 on 1 May produced a shock wave recorded by a vessel anchored off White Island and a thin layer of ash fell on the same vessel. At 1737 the next day, S. Harvey (Civil Defence, Whakatane, ~50 km from White Island) observed an eruption column that rose to 4-5 km altitude.

NZGS personnel overflew White Island on 18 May. A low, white gas column from the active vent in 1978 Crater obscured the W portion of the main crater floor. Strong steaming also occurred from fumaroles N and E of 1978 Crater. Reddish brown tephra covered much of the visible area of the main crater, and there were post-12 April impact craters up to 2 m in diameter 1/2 km E of the active vent.

Information Contacts: B. Houghton and I. Nairn, NZGS, Rotorua; R. Dibble and E. Hardy, Victoria Univ., Wellington; S. Harvey, Civil Defence, Whakatane; The Whakatane Beacon.

June 1979 (SEAN 04:06) Cite this Report

New ash measured; deflation continues

A NZGS team visited White Island on 28 May. The active vent, in the smaller SE section of the dumbbell-shaped 1978 Crater, emitted a weakly convoluting, ash-poor eruption column, punctuated by occasional pulses of more vigorous ash ejection. Bombs up to 1 m in diameter were infrequently thrown above the vent, breaking open to reveal incandescent interiors. Sharp detonations were heard as often as every 3-5 seconds, but appeared to be related to gas release, not bomb ejection. The bottom of the steep-sided active vent was not visible, but it appeared to be more than 100 m deep. Fumarolic activity continued at several locations, but appeared to be at lower pressures and temperatures than during other recent visits. The temperature at one fumarole a few hundred m E of 1978 Crater had decreased to 410°C from 535°C on 25 January.

The entire main crater floor was covered by red tephra from the April-May eruptions. A pit dug 5 m from the edge of 1978 Crater (but not along the E-W axis of heaviest deposition) revealed 230 mm of April-May tephra overlying 110 mm of older compacted gray ash. Large ejecta were abundant within about 300 m of the vent, forming a discontinuous layer along the axis of deposition. Most of the large ejecta were low-density, dark brown, flattened or fusiform bombs with a slaggy breadcrust surface and cowdung or ribbon shapes. Bomb sizes were commonly ~0.3 m, but reached 2 m in longest dimension. Some apparently fresh, dense, and vesiculated glassy bombs were also observed. Large dense blocks of altered lithic material were often associated with impact craters.

A levelling survey over the main crater floor showed deflation of both 1978 Crater (at the W end of the main crater) and the SE portion of the main crater, relative to the NE section. This represents a continuation of the trend seen between the surveys of 7 December 1978 and 21-22 April 1979.

Information Contacts: B. Houghton and I. Nairn, NZGS, Rotorua.

July 1979 (SEAN 04:07) Cite this Report

Explosion produces red ash

B. Adams reported a dark, pulsating tephra column that rose intermittently from White Island to about 1 km altitude. He first observed the eruption at about 0800 on 13 July from 50 km to the SSE. Ash appeared to be falling downwind from the vent. A white plume had been present over White Island for the previous several weeks.

NZGS personnel overflew the volcano on 16 July. An eruption cloud containing red ash emerged from the active vent in the SE section of 1978 crater, reaching about 600 m altitude before being blown N by a moderate wind. Much of White Island was covered by red ash, which was thick enough near the vent to cover the bombs ejected in April and May (04:5-6). No fresh impact craters were observed. Vigorous fumarolic activity continued at several sites within the main crater.

Information Contacts: E. Lloyd, NZGS, Rotorua.

August 1979 (SEAN 04:08) Cite this Report

Eruptions of fresh ash continue

NZGS personnel visited White Island on 6 August. Rapidly convoluting clouds of gas and fresh ash were ejected every 5-30 seconds, apparently from a magma column deep in the active vent. Ashfall rates at the 1978 Crater rim reached 1 mm/10-20 seconds. During the 3 1/2 hours of observations, a single more violent explosion threw 1-10 m-diameter blocks about 100 m above the crater.

Samples of the 6 August tephra were crystal-rich, containing plagioclase, pyroxene, olivine (?), both a pumiceous and nonvesicular (low-silica) andesitic glass, and limited amounts of altered lithic material.

Temperatures measured at the hottest accessible fumaroles (using a thermocouple) reached a maximum of 400°C, similar to those recorded during the last ground inspection, on 28 May. Since then, 213 mm of new tephra had fallen at a sampling site 20 m from the 1978 Crater rim, along the axis of maximum airfall.

A new level survey indicated that deflation in the direction of the vent continued (figure 8) although the deflation rate had slowed from a maximum of 40 µrad/month between December 1978 and April 1979 to 17 µrad/month since 28 May. A magnetic resurvey showed a substantial decrease in near-vent values, consistent with the change to magmatic activity since the last survey, in December 1978.

Figure 8. Tilt data 50 m E of Donald Mound, 28 August 1977-7 January 1983. [Originally from SEAN 08:01]. Courtesy of NZGS.

Seismic activity since 7 June (when the seismometer resumed operation) included long periods of medium-frequency volcanic tremor, interspersed with quiet periods. [An estimated 1,150 events occurred in a 6-hour period on 22 July.] Five low-frequency earthquakes (apparently B-type) were recorded 30-31 July. [Microearthquakes continued, with only minor breaks, until at least 30 September.]

Information Contacts: B. Houghton and I. Nairn, NZGS, Rotorua.

October 1979 (SEAN 04:10) Cite this Report

Moderate ash emission

NZGS personnel flew over White Island on 28 September. Since the previous inspection on 6 August, moderate ash emission had apparently been almost continuous. On 3-4 September, Sam Harvey of Whakatane observed a stronger ash eruption that produced a 2-km-high cloud. Seismic activity between the two inspections was characterized by prolonged bursts of high-frequency tremor [the most vigorous starting on 25 September at 1239 and lasting about 4.5 hours], interspersed with infrequent quieter periods of up to a few hours duration.

Eruptive activity during the 10-minute overflight consisted of spasmodic ejection of a pale brown, weakly convoluting gas and ash column that rose about 400 m before being blown NE by a light wind. Reddish-brown tephra appeared to uniformly mantle the main crater floor. No impact craters or other evidence of coarse ejecta were observed. Steam rose from a gully that enters 1978 Crater from the W, but pre-existing fumaroles on the main crater floor seemed unchanged.

Information Contacts: E. Lloyd, NZGS, Rotorua.

November 1979 (SEAN 04:11) Cite this Report

Mild fume emission

White Island was overflown 25 October, about a month after the previous aerial inspection. A weakly convoluting pink fume cloud rose to about 500 m from the eruption vent in 1978 Crater, and moderate steam emission occurred from fumaroles elsewhere in the main crater. Brown ash mantled the main crater floor, and a few blocks and apparent impact craters were visible near 1978 Crater.

Seismic activity between 28 September and 25 October typically consisted of intermittent to semicontinuous bursts of high-frequency tremor, with few quiet periods. Strong local earthquakes were rare.

Further Reference. Houghton, B.F., Scott, B.J., Nairn, I.A., and Wood, C.P., 1983, Cyclic Variation in Eruption Products, White Island Volcano, New Zealand, 1976-1979; New Zealand Journal of Geology and Geophysics, v. 26, p. 213-216.

Information Contacts: I. Nairn, NZGS, Rotorua.

February 1980 (SEAN 05:02) Cite this Report

Fresh ash and impact craters

The press reported that an eruption occurred during the late afternoon of 6 February. Records telemetered by the White Island seismograph showed a substantial increase in seismicity during the preceding week. Shortly after 1648 on the 6th, the seismograph recorded a high-amplitude, high-frequency event lasting about 3 minutes.

Personnel from the NZGS and Victoria Univ. flew over White Island on 7 February. A 500-m steam column emerged from deep within the active vent of 1978 Crater. Other fumarolic activity was at its weakest level since the eruption began. Extensive erosion, caused by heavy rainfall in mid-January, could be seen on the main crater floor. No fresh tephra was visible.

A second overflight on 25 February revealed fresh, pale brown ash mantling the main crater. Impact craters to about 1 m in diameter reached an estimated density of 1 per 10 m² at the E and SE rim of 1978 Crater, and could be seen, at reduced density, to ~200 m from the rim. Activity from 1978 Crater was similar to that observed on 7 February. High pressure fumarolic emission had begun at two sites on the main crater floor, but remained weak elsewhere.

Information Contacts: B. Houghton and E. Lloyd, NZGS, Rotorua.

April 1980 (SEAN 05:04) Cite this Report

Tephra eruptions

S. Harvey reported that continuous ash eruptions were visible from Whakatane beginning 9 April. The ash clouds were voluminous, but did not rise to great heights. During the first 2 days of the activity, the clouds were pinkish brown and were accompanied by emission of white vapor from a vent to the E. On 11 April, the ash clouds were black and vapor emission had apparently ceased.

At 1114 on 12 April, the White Island seismograph recorded a large-amplitude, high-frequency event with virtually instantaneous onset, against a background of the almost continuous high-frequency tremor that has characterized long periods of the seismic record in recent months. At about the same time, persons on the mainland saw a large ash eruption.

NZGS personnel flew over the volcano about 2 hours later. Red-brown ash rose from deep within 1978 Crater to about 700 m height. Impact craters were seen inside 1978 Crater and blocks littered the ground within 20 m of the SE rim. Much of the main crater floor was mantled by ash, including the area where the blocks were deposited. However, there was no ash on the blocks, which were therefore assumed to have been ejected quite recently, probably by the late-morning explosion. The interior of 1978 Crater has changed little since the present active vent was established in late 1978.

Information Contacts: E. Lloyd, NZGS, Rotorua.

May 1980 (SEAN 05:05) Cite this Report

Explosions continue; new fumaroles and renewed inflation

Geologists visited White Island on 26 May. During the first half of the 5-hour visit, eruptive activity was limited to emission of a white vapor column. After ash darkened the vapor column briefly, a small explosion ejected accessory blocks to a few tens of meters above the rim of 1978 Crater. A vigorously convecting gas and ash column deposited ash and lapilli-sized accessory material around the crater. Acidic, ash-charged water droplets fell within 400 m of the crater. A smaller explosion occurred about 40 minutes later. Both explosions were recorded by the White Island seismograph, which had recorded two similar but much larger events during the 2 previous days. One of the earlier explosions was observed from near Motiti Island, ~70 km away.

Since the previous ground inspection on 18 April, a line of 3 new fumaroles had formed NE of 1978 Crater, along a trend of pre-existing intense fumarolic activity. Temperatures in the new fumaroles ranged from 475 to 615°C. The largest vent, 10 m in diameter and 15 m deep, was surrounded by two small lobes of ejecta. Fumarolic activity elsewhere on the main crater floor had become substantially stronger, and several other new gas vents were observed. Divers found warm springs just off the NE and NW coasts of White Island, measuring a temperature of 45°C at a depth of 0.3 m at one of the sites.

A levelling survey revealed much more extensive and rapid uplift in the main crater since 18 April than had occurred in the 5 previous months. The maximum inflation values of 22-27 mm were measured in the portion of the survey area nearest 1978 Crater and the zone of intense fumarolic activity mentioned above. The inflation recorded since November 1979 was a reversal of steady deflation between February 1978 and August 1979. A magnetic survey of the main crater yielded no significant changes since 18 April. A pit dug about 200 m E of 1978 Crater went through 270 mm of tephra before reaching August 1979 deposits. Very little tephra had accumulated more than 400 m from 1978 Crater since August 1979.

Information Contacts: B. Houghton, E. Lloyd, and I. Nairn, NZGS, Rotorua; R. Dibble, Victoria Univ., Wellington.

June 1980 (SEAN 05:06) Cite this Report

New ash deposits, impact craters, and seismicity

NZGS personnel flew over White Island on 13 June. A vapor cloud produced by several fumarolic areas rose to a maximum height of about 1 km. A thin layer of gray ash mantled the main crater floor, obliterating footprints left by the 26 May survey party. A band of grey ash trending NE from 1978 Crater was particularly conspicuous on the outer slopes of White Island. Impact craters, numerous on the E side of 1978 Crater, extended several hundred meters to the ESE, farther than at any time during 1980. The distant impact craters appeared large (no size estimate given) but were widely spaced. Seismicity during the few days prior to the overflight was characterized by periods of moderate-amplitude, high-frequency tremor interspersed with longer periods when tremor was low in both amplitude and frequency or was entirely absent. Brief episodes of high-amplitude, high-frequency tremor were recorded on 11 June (4 minutes) and 13 June (1.5 minutes). Two A-type shocks occurred about 2.5 minutes apart on 13 June, about 3 hours before the 1.5-minute episode of intense tremor. None of the strong seismicity occurred during the overflight.

Information Contacts: B. Houghton, E. Lloyd, and I. Nairn, NZGS, Rotorua.

August 1980 (SEAN 05:08) Cite this Report

Ash eruption

On 19 July, residents of Whakatane observed a black ash column that rose about 3 km above the volcano. However, a 28 July NZGS overflight found it little changed from 13 June. The island was covered by red-gray ash, deeply gullied in places on the crater floor. Partly eroded impact craters extended up to 200 m from the SE rim of 1978 Crater. The latter was hidden by voluminous clouds of white steam and gas while the recently formed subsidiary gas vents to the E (05:02) were obscured by vapor from adjacent fumaroles. Other fumarolic activity farther to the N appeared to have declined since the previous inspection. The sea immediately off the NW coast was colored white, probably due to suspension of sulphur (and other precipitates from underwater hot springs; 5:05).

Seismicity during July was characterized by relatively low tremor levels and occasional earthquakes, some of low frequency (B-type). Periods of high-amplitude, high-frequency tremor were recorded 11-16 July. Some larger, high-frequency, probably A-type or regional earthquakes were recorded on 27 July. The seismograph was not operational during the 19 July eruption.

Information Contacts: I. Nairn, NZGS, Rotorua.

October 1980 (SEAN 05:10) Cite this Report

Minor ash emission; deflation slows

During 5 hours of observation by geologists and geophysicists on 21 October, the active vent in 1978 Crater emitted an ash-poor gas column of varying intensity which deposited no tephra. Gray ash postdating the 11 September inspection was 1 cm thick on the 1978 Crater rim, and less than 2 mm thick beyond 200 m from the rim. No fresh impact craters were observed. Fumarolic activity continued from the gas vents NE of 1978 Crater that were first observed in May and other gas vents remained vigorous. Fumarole temperatures were generally somewhat lower than in May and September with a maximum of 600°C.

A levelling survey showed that the relatively rapid rate of subsidence (as much as 2.3 mm/week) between May and September, which had followed 6 weeks of localized inflation, decreased to less than 1 mm/week in the 6 weeks since 11 September. Magnetic field intensity appeared to have fallen near the 1978 Crater rim since 11 September.

Information Contacts: B. Houghton, I. Nairn, NZGS, Rotorua.

January 1981 (SEAN 06:01) Cite this Report

Ash, impact craters, gas clouds, seismicity

NZGS personnel flew over White Island on the morning of 6 January. In the 10 minutes they were over the island, the voluminous convoluting emissions of white steam and gas clouds obscured their view around and into 1978 Crater. The lower portion of the 600-750-m-high eruption column was slightly ash-charged. The main crater was thickly covered with eroded brown-green ash. Impact craters extended a few hundred meters NE from 1978 Crater. Conspicuous blue fumes were associated with the steam-gas column rising in the 1914 landslide area just SE of 1978 Crater.

Seismicity since ground inspections in early December was characterized by four distinct periods of marked increase. Intervals of high-frequency, high-amplitude tremor were recorded for 32 hours on 15-16 December, for 35 hours on 22-23 December, and for 26 hours on 27-28 December. Strong ash emissions were likely during these periods. Large discrete earthquakes were recorded on 14 December and 2 January.

Information Contacts: B. Scott, NZGS, Rotorua.

March 1981 (SEAN 06:03) Cite this Report

Explosions and seismicity; tephra and tilt measured

NZGS personnel visited White Island on 17 January and 6 March, and overflew the volcano on 24 February after reports of explosive eruptions in January. On 17 January, a weakly convoluting gas column charged with light brown ash was issuing from the active vent in the S part of 1978 Crater. Gray tephra covered the main crater floor. Since the magmatic activity in early November, about 500 mm of ash had been deposited near the 1978 Crater rim, about 230 mm since 2 December. Two or possibly three generations of impact craters, the youngest perhaps less than a day or two old, were found 250-600 m NE of the active vent, with concentrations of up to 3 craters/m² 300-400 m away. Crater diameters ranged from 30 mm to 1.2 m. Blocks up to 0.7 m in diameter were found in some of the impact craters, but no fresh magma appeared to have been ejected. The apparent near-vertical final trajectory of the blocks in the impact craters was striking.

Seismic records showed that periods of high-frequency tremor occurred 7-13, 17-19, 22-23 and 25-28 January, and 30 January-11 February. Short bursts of harmonic tremor were recorded after the high-frequency tremor declined. Large discrete events (eruption sequences) were recorded on 24 and 29 January and 6, 12, 17, 23 and 24 February. The eruption accompanying the 24 January event produced ashfall at Cape Runaway (75 km E of White Island, on the mainland) and was witnessed by P. M. Otway (NZGS).

So little gas and tephra were being emitted during the 24 February overflight that viewing was excellent. The main crater floor appeared to be covered by a thick layer of red-brown principally fine-grained tephra. Impact craters formed since 17 January pocked the floor to 600 m E of the active vent, the greatest range since the March 1977 eruptions.

On 6 March, emissions from the active vent, entrenched in a subcrater at least 200 m deep, were very low. The rim of 1978 Crater showed no major changes, but a large portion of the crater floor N of the active vent had been raised several m by rapid accumulation of tephra between 17 January and 24 February. At the E edge of 1978 Crater rim, 410 mm of new tephra overlay earlier deposits. Within a kilometer to the E, the new tephra thinned to about 8 mm. The surface layer was a fine pink ash (mean diameter about 63 µm) containing abundant lithic clasts, subordinate crystals of pyroxene and olivine and minor amounts of glassy, weakly to moderately vesicular, essential, low-silica andesite. This layer was underlain by a finer green ash containing a greater percentage of essential clasts.

A few new impact craters had formed just outside 1978 Crater's E rim, some occupied by lithic blocks that were not coated with ash. Some of the older impact craters scattered across the main crater floor contained buried scoriaceous bombs, apparently of recent magmatic origin.

Fumaroles checked from the air in February were monitored in March. The inspection team measured minimum temperatures of 490°-650°C at 3 fumaroles formed within the past year E of 1978 Crater rim. One is the most energetic feature on the island other than the active vent.

The March levelling survey showed that subsidence had continued after the previous survey on 2 December. The volcano had deflated about 300 µrad since May, the peak of a 6-month period of inflation (figure 8). The greatest deformation, 12-13 mm since December and a total of 60 mm since May, was about in the center of the main crater, near the zone of fumarolic activity just E of 1978 Crater.

Information Contacts: B. Scott, B. Houghton, and I. Nairn, NZGS, Rotorua.

July 1981 (SEAN 06:07) Cite this Report

Volcanic seismicity declines; no sign of tephra ejection since May

A routine surveillance flight by NZGS personnel was made on 13 July from 1034 to 1057. Weak gas and steam emissions from the fumaroles and vents rose to 600 m and showed no sign of ash. The main crater floor appeared dark gray-brown near the active vent, but reddened away from it. Distinct yellow-green areas were visible both on the S side of the crater and on the N outer slopes. A tan area was also on the S side. Numerous impact craters of more than one generation extended about 600 m E of the active vent and were concentrated about 300 m from it. All the impact craters had subdued margins. Tephra deposits were extensively gullied. Although discrete explosive events had occurred, there had been little tephra emission since the previous visit on 21 May.

Seismic records revealed a contined decline in activity, apparent since early this year. Since 21 May a marked decline was evident in the number of low-frequency (B-type) events from more than 30/day to about 5/day. Volcanic tremor was recorded on 26 and 30 May; 3-4, 6, 12, and 28 June; and 2, 5-6, and 8 July. High-frequency (volcano-tectonic) events numbered fewer than 10/day except during 14-15 June, when several hundred per day were recorded. The increased high-frequency activity was accompanied by distinctive, medium-frequency seismic signatures which were symmetric and had emergent onsets. NZGS personnel interpreted these as volcanic earthquakes and, possibly, intrusive events.

Information Contacts: B. Scott, NZGS, Rotorua.

September 1981 (SEAN 06:09) Cite this Report

Little eruptive activity for six months; B-type events increase

On 18 September, NZGS personnel found that little eruptive activity had occurred in the last 6 months. The fine tephra evenly mantling the main crater floor showed rain wash, pitting, and considerable erosion along the main water courses. A small landslide near the midpoint of the main crater's S rim had sent several tongues of muddy, sulfur-rich, hydrothermally altered material onto the crater floor. A distinctive pink ash that had formed the surface on 6 March was at about 100 mm depth on the rim of 1978 Crater, but was only 30 mm below the surface in the center of the main crater 300 m to the E.

The active subcrater was 200 m wide and 150 m deep. A shallow green pond occupied most of its floor. A 20-30-m-wide vent on the NW side of its floor was emitting pink-tinged gas at high velocity. Throughout the visit this gas and other vapor from 1978 Crater formed a white column.

Fumaroles in a 300 m-wide zone across the main crater floor E of 1978 Crater appeared to be slightly less active than in March. Temperatures were 560°C in a large, reactivated vent; 550°C (100° lower than in March) in a smaller one nearby; and 340°C at a vent now so enlarged that the thermocouple could reach no more than halfway into the pit.

Except for inflation near the center of the main crater, the levelling survey showed no tilt change since May, in contrast to general subsidence earlier in the year. Significant inflation (115 µrad), had occurred just E of active fumaroles about 300 m E of 1978 Crater. The levelling survey team noted that this tilt reversal bears some resemblance to that in April 1980, which preceded the formation of three fumaroles in the same area.

Seismic records 1 August-20 September showed a marked increase in the number of low-frequency (B-type) events from fewer than 5 to more than 30 per day, reversing a decline from late May through mid-July. High-frequency (volcano-tectonic) events numbered fewer than 5/day except on 11 and 12 September, when ten were recorded each day. On 26 August, and 8 and 10 September, single distinctive seismic signatures (symmetric with emergent onsets) were recorded. The NZGS interpreted these as medium-frequency volcanic earthquakes, probably intrusive events. Volcanic tremor was recorded on 10 September.

Information Contacts: B. Houghton and I. Nairn, NZGS, Rotorua.

February 1982 (SEAN 07:02) Cite this Report

Localized inflation; decreased seismicity

Observers from Victoria Univ. and NZGS spent 4.5 hours the afternoon of 29 January inspecting the island and reactivating the seismograph. No tephra deposition had occurred since the last visit 2 December 1981. Tephra deposited between 18 September and December measured 46 and 23 mm at two sites on the crater rim, and was absent beyond 250 m from the active vent. Its fraction coarser than 250 µm was composed of roughly equal amounts of fresh glassy low-silica andesite (52 wt.%) and accessory, hydrothermally altered lithic material (48 wt.%).

Activity in 1978 Crater appeared less intense than in September. The depth of the active subcrater was 105 m. Vents on its floor and W wall emitted white steam. Numerous geysers jetted black muddy water to several m in the N part of the shallow bright-green pond that covered about half of the subcrater's flat floor. Many large lava blocks had fallen from the W walls; several rockfalls occurred during the observation period. The high-pressure gas vent that had been on the NW side of the subcrater floor in September was not present.

Fumaroles around Donald Mound, a 100 x 150-m area in the middle of the main crater, appeared more active than in September. Several had strong discharges of high-pressure, clear gas and some blue fume. Temperatures just E of the mound were 590°, 640°, and 655°C. Low-pressure gas in a fumarole W of it, where blue fume was condensing, had a temperature of 560°C. A large fumarole that had developed earlier on the N side of the main crater was at least 5 m deep and was emitting large volumes of white, superheated steam. Ephemeral minerals were collected on the last three visits. X-ray diffraction analysis indicated that these were predominantly unoxidized sulfur and anhydrous forms in the throats of fumaroles, and sulfate-hydrate and sulfate-hydroxide-hydrates surrounding fumaroles and their outwash areas.

The levelling survey found little tilt change between September and December, and none since December except in the vicinity of Donald Mound, where an 11-mm rise had been recorded. The inflated area was about 400 m across, centered at the E side of the Mound, about 200 m E of 1978 Crater. After a similar localized inflation, three small gas vents formed N of the Mound in May 1980.

Seismic records 21 September-19 January (when the seismograph stopped working) showed a gradual decline in the number of low-frequency (B-type) events from more than 40 to fewer than 5 per day by 10 December. The level has remained low. High-frequency (volcano-tectonic) events numbered fewer than 5/day except on: 25 November, 7 events; 16 December, 16; 21 December, 6 events; 8 January, 35 events; and 14 January, 7 events. Distinctive seismic signatures (symmetric, with emergent onsets) were recorded on 29 November, 1, 13, and 19 December, and 16 January. The NZGS interpreted these as medium-frequency volcanic earthquakes, probably intrusive events. Volcanic tremor was recorded weakly on 25-26 September, 8, 24, and 25 October, and 15 November.

Information Contacts: A. Cody, B. Houghton, I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS, Rotorua.

June 1982 (SEAN 07:06) Cite this Report

Localized inflation; no eruptive activity

NZGS personnel visited White Island on 1 June. No significant eruptive activity had occurred since January, but fumarolic activity in 1978 Crater appeared more intense. Vents on the walls and floor of the active subcrater emitted large white steam columns, and numerous small geysers jetted black muddy water. Rockfalls from the W wall had formed a fan onto the subcrater floor. A green lake occupied much of the SE sector of the subcrater floor.

Inflation localized around Donald Mound (a 100 x 150 m area in the middle of the main crater and ~150 m E of the edge of 1978 Crater) had continued, with a rise of 13 mm measured ~50 m to the E, and 18 mm about 100 m to the SE. The inflation started a year ago, but paused between September and December, 1981. Fumaroles near the Mound and about 200 m N of it were emitting large white steam columns. Fumarole temperatures around Donald Mound showed a general increase from 630°C on 2 December 1980, to 650°C in May 1981 and January 1982, and 690°C in June 1982. More sulfur appeared to have been deposited at the ground surface. For the area between 1978 Crater and Donald Mound and extending about 200 m to the N, magnetometer data showed increases in total magnetic field of between 64 and 326 nanoteslas (nT), compared to changes of less than 25 nT over the rest of the main crater since January.

Between 27 February and 2 June, more than 150 (and occasionally as many as 400) usually small, low-frequency (B-type) events were recorded per day during three periods of increased seismicity: 15-20 March, 26 March-8 April, and 22 May. No more than 39 low-frequency events were recorded on other days. High-frequency (volcano-tectonic) events usually numbered fewer than 5/day except for 6 on 4 and 13 March, 44 on 3 April, and 6 on 2 June. Volcanic tremor was recorded on 25-26 March, and 5 and 12 May.

Information Contacts: I. Nairn, C. Wood, and B. Scott, NZGS, Rotorua; P. Otway, NZGS, Wairakei; D. Sheppard, DSIR, Gracefield.

July 1982 (SEAN 07:07) Cite this Report

Eruption column and seismicity; new crater

On 1 July at 1413 a wide-band earthquake sequence indicative of an eruption was recorded, with peak-to-peak amplitude exceeding Full-Scale Deflection (FSD). From Whakatane, S. Harvey reported that a dark eruption column and ash fallout accompanied the earthquakes. Harvey observed an eruption column until 1517, by which time the seismicity had declined to 2-3 mm peak-to-peak, low-frequency, tremor-like activity. Two smaller wide-band earthquake sequences were recorded on 3 July at 0234 and 5 July at 0424.

About noon on 8 July NZGS personnel flew over the volcano. There was no sign of any new ash deposition or impact craters. A steam plume was rising to about 900 m from the SE part of 1978 Crater, and much smaller steam plumes were being emitted from the fumarole area in the center of the main crater. Emission was more intense than during the 1 June visit and during a photographic flight on 13 June. The green lake observed in the SE part of 1978 Crater during several previous visits was still present.

A sharp-walled pit had formed in the N part of 1978 Crater. It was filled with steam and opened into the gully that drains into the SE part. It had not been seen on March airphotos, but a small depression was noted in this area on 13 June photographs.

Between 2 June and 5 July the daily number of low-frequency (B-type) seismic events declined. Only on 24, 28 and 30 June were there more than 20 (maximum of 37 on 28 June), as compared to 27 February-2 June when the number of events often exceeded 150 per day. All were very small.

High-frequency (volcano-tectonic) seismic events numbered fewer than 3/day after 2 June. All events were small except on 2 July at 2027 when they exceeded FSD. On 21-22 June, 4 medium-frequency volcanic earthquakes were recorded. NZGS personnel interpret these as possible intrusive events. Tremor-like seismic activity was recorded 18-19 and 30 June, and 2, 3, and 4 July.

Information Contacts: I. Nairn and B. Scott, NZGS, Rotorua; P. Otway, NZGS, Wairakei.

October 1982 (SEAN 07:10) Cite this Report

Localized inflation continues

When NZGS personnel inspected the volcano on 8 October, two months after the last visit on 31 July, they found no new tephra deposits. There has been no significant tephra accumulation on the main crater floor since January 1982, the longest interval without deposition since the eruption began in December 1976. Much of the tephra cover in the W half of the main crater, where the fumaroles are, has been subjected to intense hydrothermal alteration.

Substantial steam columns were being emitted from vents on the floor and walls of 1978 Crater, and from Donald Mound and Noisy Nellie fumaroles. The strongest fumarolic activity was on the N side of 1978 Crater, near the new collapse pit. The small green pond in the SE part of the crater was still present; in a muddy black pond N of it, there was vigorous geysering. Fumarole temperatures measured at 4 places on the main crater floor ranged from 470°C in vents with low gas pressure to 695°C in high-pressure vents near Donald Mound.

Inflation of the Donald Mound area has continued at a steady rate. The E side had risen 9 mm since 31 July, and 58 mm since 21 May 1981 (figure 8), equivalent to 500 µrad of tilt. A deflationary trend was continuing about 200 m N of the Mound. The NZGS interpreted the inflation as a possible precursor of eruptive activity in this area.

Between 5 July and 1 October the number of low-frequency (B-type) seismic events did not exceed 10/day except in early July, when it increased to 31/day on the 9th and 10th, then declined. All the low-frequency events were small. High-frequency (volcano-tectonic) events usually numbered fewer than 5/day in this period, except as shown in table 4. These events were also generally small.

Table 4. Days between 5 July and 1 October 1982 when more than five high-frequency events were recorded at White Island.

Moderately high frequency volcanic tremor began about 2200 on 28 July and gradually increased in amplitude until 0800 on 30 July, when a distinct decline in amplitude was apparent; tremor ceased by 1600 that day. Wide-band earthquake sequences indicative of eruption were recorded on 9, 15, and 26 September, but no eruptions were reported. Medium-frequency volcanic earthquakes were recorded on 16, 17, and 26 July, 14 August, and 4 and 18 September. The NZGS interpreted these as possible intrusive events.

Information Contacts: I. Nairn and B. Scott, NZGS, Rotorua.

January 1983 (SEAN 08:01) Cite this Report

Abrupt deflation

Field work by NZGS personnel 7 January revealed no evidence of eruptive activity since their previous visit on 15 November. Only minor changes were observed in 1978 Crater. Temperatures were measured at three fumaroles. At vents E and NE of Donald Mound temperatures were 620°C and 630°C, 60-65°C lower than on 8 October. W of Donald Mound, a vent formed in 1980 had a temperature of 556°C, 86°C warmer than in October.

The center of the deflating area, near the E edge of 1978 Crater in November, had deepened and moved E several hundred meters to the Donald Mound area, which had been inflating from mid-1981 until November 1982. A site on the E side of the Mound area had subsided 16 mm since November. A nearby tiltmeter measured deflation of 50 µrad 8 October-15 November, and 170 additional µrad by 7 January (figure 8).

The inflation in the Donald Mound area had been interpreted by the NZGS as a possible precursor of minor eruptive activity, as in May 1980 when three new vents formed between there and the 1978 Crater. But the inflation rate was only 1/3 that of 1980, and the recent abrupt deflation is now thought to be the end of the 15-month inflationary episode.

Information Contacts: B. Scott, NZGS, Rotorua; P. Otway, NZGS, Wairakei.

March 1983 (SEAN 08:03) Cite this Report

No eruptive activity; B-type events increase

Aerial inspection by NZGS personnel on 10 March revealed no evidence of eruptive activity since 7 January. A white steam plume was rising to about 600 m altitude from the SE part of 1978 Crater. For 200 m to the N, there were moderate emissions from vents in deep gullies and from two fumaroles. Very little emission was originating from Donald Mound. Most of the Mound was covered with yellow sublimates, but a central zone was gray.

Since 7 January the number of low-frequency (B-type) events has increased, especially 9-15 February (more that 25/day; maximum, 42) and 22 February-4 March (more than 21/day). High-frequency (volcano-tectonic) events usually numbered fewer than 5/day, except for 6 on 29 January, 7 on 6 February, and 10 on 21 February. Wide-band seismic events were recorded on 19 and 24 February, and 2 and 6 March. They lasted 4-40 minutes with peak-to-peak amplitudes up to 70 mm.

Information Contacts: B. Scott, NZGS, Rotorua.

April 1983 (SEAN 08:04) Cite this Report

Deflation ends

When NZGS personnel visited the island on 14 April, they observed few differences in 1978 Crater. The small green ponds present during the previous visit on 22 March had enlarged and merged to cover 60-70% of the crater floor. Color ranged from orange adjacent to the fumaroles to lime green. Fumarolic activity continued on the W wall and up the NW-trending gully system. Activity at Donald Mound appeared to have declined, but no fumarole temperatures were measured. Very small changes in tilt were recorded: +8 mm about 150 m W of Donald Mound, and +9 mm about 100 m N of it. The NZGS noted that these changes indicated an end to the deflation of the Donald Mound area recorded between November 1982 and January 1983 (figure 8).

Information Contacts: P. Otway, NZGS, Waikarei; B. Scott, NZGS, Rotorua; G. Sorrell, DSIR, Wellington.

February 1984 (SEAN 09:02) Cite this Report

Tephra eruption from new vent

A tephra eruption began at White Island in late December 1983. No significant activity had been reported since late 1981.

NZGS personnel reported that a ground inspection on 23 November and an aerial inspection on 27 November 1983 had yielded no evidence of eruptive activity. Airborne COSPEC measurements on the 27th showed an SO₂ emission rate of 1,200 t/d. Voluminous steam colums above the island were observed from Pukehina Beach (~65 km SE) in late December-early January by two NZGS geologists. A pilot reported that the eruption column had changed from white to gray about 20 January. Photographs taken by a yachtsman who landed on White Island on 27 January showed a dense ash column.

During an aerial inspection on 2 February, crater conditions appeared similar to those shown in the 27 January photographs. Geologists who flew over the island (from 0944-1000) observed a gray-green ash layer on the main crater floor and the island's outer slopes. Ash appeared thickest on the N slopes. A white steam plume with a little light gray, fine ash was rising to 1.2-1.5 km above sea level. All eruptive activity appeared to come from a new vent (about 20 x 30 m and at least 50 m deep) that had formed at the site of a vigorous fumarole on the N margin of the older (SE) portion of the dumbell-shaped 1978 Crater complex. A small tuff ridge had been built up from the floor of 1978 Crater to the rim of the new vent. Impact craters and blocks up to 1 m in diameter were visible on the tuff ridge and throughout the complex, extending E to Donald Mound. Impact crater density decreased rapidly away from the vent. Fumarolic activity in other areas appeared to have declined from the level observed in November. At about 1200, after geologists left the area, a vigorous, dark eruption column was observed from many points along the coast of North Island, more than 50 km away.

During field work on 6 February, NZGS personnel observed little apparent change since their previous visit. No significant new ashfall was evident outside the rim of 1978 Crater. Small blocks (less than 10 cm in diameter) on the floor of the 1978 Crater complex were not ash-coated, suggesting recent ejection. All the blocks consisted of lithic andesite; some were altered. Moderate gas emission from the active vent was punctuated by occasional pulses of fine gray ash. More voluminous emissions occurred at about 1200 and 1530. Acid rain and a little ash fell on the geologists.

Post-November 1983 tephra thicknesses ranged from 60 mm about 150 m N of the new vent, to 15 mm about 350 m E, and 2 mm about 800 m E. Sand-sized material in new ash NE of the vent was dominated by abundant fresh plagioclase, pyroxene, some possible olivine crystals, and magnetite, with subordinate glass and minor amounts of lithic fragments. Considerable altered silt- and clay-sized material was also present in the ash. At a site closer to the vent, tephra from an earlier phase of the 1983-84 activity had the same crystal and glass components but a much larger proportion of altered lithic fragments.

At 762°C, the temperature of a fumarole E of Donald Mound was similar to that measured on 23 November 1983; temperatures below 700°C were measured on all other visits in 1983, 1982, and 1981. Inflation had continued in the Donald Mound area. The localized uplift area was about 400 mm across and centered on Donald Mound.

NZGS geologists returned to White Island on 17 February. Except for a small quantity of blocky ejecta around the E rim of the new vent, there was little evidence of recent eruptive activity. Fumarole temperatures remained high, and the Donald Mound area was still inflated.

Telemetry of seismic data, which stopped in late November, resumed 6 February. Between the 6th and 23rd, 6-30 low-frequency B-type volcanic earthquakes were recorded daily. There were more than 20 events/day, 9-15 February, and fewer than 15/day, 16-23 February. High-frequency volcano-tectonic earthquakes numbered fewer than 3/day except on 6, 7, 8, and 13 February when 13, 20, 12, and 11 events were recorded. Long-duration, wide-band, multiple-frequency earthquake sequences were recorded on 8, 9, 10, 11, 14, and 17 February. Similar sequences had previously been correlated with eruptive activity, but there was no visual confirmation of any eruption clouds associated with these events. Weak low- or medium-frequency tremor was recorded for 8-9 hours on 11 February.

Further Reference. Rose, W.I., Chuan, R.L., Giggenbach, W.F., Kyle, P.R., and Symonds, R.B., 1986, Rates of Sulfur Dioxide and Particle Emissions from White Island Volcano, New Zealand, and an Estimate of the Total Flux of Major Gaseous Species; BV, v. 48, p. 181-188.

Information Contacts: I. Nairn, NZGS, Rotorua; W. Rose, Michigan Tech. Univ.

November 1985 (SEAN 10:11) Cite this Report

Fumarole temperatures drop; magnetic anomaly

When geologists visited White Island on 13 November, there was no evidence that any eruptive activity had occurred since their visit on 21 May. Deflation of the Donald Mound area, roughly 100 m E of the 1978 Crater, continued. The area of subsidence was a NW-SE ellipsoid about 400 m long by 250 m wide, centered on Donald Mound. One station had dropped 112 mm since a small ash eruption in February 1984; stations immediately W of the area, which had dropped 15-25 mm May 1984-May 1985, had fully recovered by the November visit.

Magnetic data showed a small but high-amplitude anomaly centered N of Donald Mound, suggesting to geologists that substantial near-surface cooling had occurred in the area since the May magnetic survey. At one vent, fumarole temperatures had declined to 390°C from 523° in May. No low-frequency (B-type) events were recorded from February until late September, when they resumed following a M 7 event, 350-400 km NE of White Island. Since 25 October, 6-35 low-frequency events have occurred per day, with unusually large amplitudes (up to 50 mm peak to peak). The number of high-frequency (volcano-tectonic) earthquakes remained relatively constant in 1985, with 3-5 recorded on most days.

Information Contacts: I. Nairn, A. Cody, B. Scott, C. Wood, and W. Davis, NZGS, Rotorua; P. Otway, NZGS, Wairakei; D. Christoffel and E. Hardy, Victoria Univ. Wellington; W. Giggenbach, DSIR, Wellington.

February 1986 (SEAN 11:02) Cite this Report

New active vent produces tephra

Minor magmatic eruptive activity resumed ... about 1 February from a new vent within the 1978 Crater complex. On 3 February helicopter pilot Ian Johnson observed a new active vent and associated tephra fall.

About 15 low-frequency B-type earthquakes/day occurred from December into February with unusually large (50 mm p-p) amplitudes, although a gradual decline in amplitudes was apparent. Significant periods of volcanic tremor were recorded in January (11, 19, 20-21, 25-29) and February (1-5) but no vent-forming episode could be clearly recognized.

When geologists visited the volcano 10 February, there was a new vent ~ 25 m in diameter near the base of the E crater wall, farther E than any vent of the 1976-82 eruption sequence. The vent emitted vapor at a moderate rate and a small amount of very fine ash was occasionally present in the gas plume.

A fresh layer of ash, 10-15 mm thick, was on the main crater floor to 150-200 m E of the new vent and a small ejecta apron extended 30-50 m W of the vent. Small scoria bombs were sparsely scattered on the surface within 50 m of the new vent. Bombs were rarely larger than 100 mm in diameter. One had clearly flattened on impact, indicating it was still soft when it fell. The scoria is fresh, dark brown, vesiculated glassy andesite with phenocrysts of plagioclase and pyroxene. Recently deposited tephra comprise reworked crater-fill detritus, some fresh crystals, and brown glass.

Fumarole temperatures of 350-360°C were measured on 10 February, 25° cooler than on 13 November (10:11) and 15-25° cooler than on 7 February. COSPEC measurements on 7 February showed an SO₂ emission rate of 570 t/d, a substantial increase over the 320 t/d detected on 21 November 1984 and 350 t/d recorded on 7 January 1985.

Information Contacts: New Zealand Geological Survey (NZGS); P. Kyle, New Mexico Inst of Mining & Technology.

August 1986 (SEAN 11:08) Cite this Report

Continued minor phreatomagmatic activity

New ash layers indicated that small-scale phreatomagmatic activity has continued intermittently since May 1986 from "Congress Vent," which became active in February... . During a 1 August visit, geologists examined the 1986 tephra, which can be subdivided into three units. Layer 1, accumulated since 27 July, was 18 mm thick at the sampling site on the 1978 Crater rim, 50 m E of the vent. It consisted mostly of sub-millimeter ash, containing altered lithic fragments and many subrounded crystals. Some angular chips of dark gray fresh andesite and minor brown volcanic glass were also present. Layer 2 was very widespread, extending over most of the main crater floor, and was 120 mm thick at the sampling site. It appeared to have been deposited while damp. The dispersal axis of this layer probably trends N to NW from the vent and at least most of it was deposited since the last deformation survey, on 6 May. Layer 2 was similar to layer 1, but contained a larger proportion of more angular crystals and fresh andesite clasts, and less altered material. Layer 3, 155 mm thick at the sampling site, consisted of centimeter-bedded well-sorted very coarse gray ash and lapilli. Largely confined to within 50 m of the 1978 Crater rim, it was erupted in early 1986 and had formed the ground surface in early March.

Local volcanic seismicity since early May has been dominated by low-frequency (B-type) volcanic earthquakes. The number of events ranged from 15 to >40/day, and they appeared to have anomalously large amplitudes. High-frequency near-tectonic/volcano-tectonic events usually numbered < 5/day. Wide-band, long-duration volcanic earthquakes were recorded on 19, 26, and 30 June. An eruption column was reported by Geyserland Airways on 26 June.

The maximum temperature measured in the Donald Mound area (100 m E of the 1978 Crater rim) and the 1980 collapse pits to the NW was 665°C. Fumarole temperatures have generally declined in the Donald Mound area during the past eight months but have risen in the 1980 collapse pits. Temperatures and pressures of a fumarole in the easternmost collapse pit were particularly high, and the 594°C measured was well below the true temperature. The vent walls appeared slightly incandescent.

After 2.5 years, the persistent NW-SE trough of subsidence centered on Donald Mound has been virtually eliminated except for a narrow moat to the south. There appeared to be no significant height change near the eastern edge of 1978 Crater associated with the 1986 Congress Vent.

Information Contacts: B. Scott, NZGS Rotorua.

November 1986 (SEAN 11:11) Cite this Report

Ash emission and continuing seismicity

Geologists visited the crater 29-30 October. Ash emission, predominantly from Congress Vent (active since February) was heavy on 29 October but light the next day. The vent appeared to be inclined 40-50° toward the base of Donald Mound, several tens of meters to the E. A level survey showed that an area NW of Donald Mound had continued to subside, a pattern that has persisted since 1984 (SEAN 11:08).

Fumarole temperatures, measured in three vents on 29 October, ranged from 279 to 470°C, continuing a general decline since 6 May. During the evening, orange glow was visible in two fumaroles and a blue flame (caused by sulfur oxidation) in one. No glow was observed in Congress Vent.

Two layers of gray ash had accumulated on the W portion of the main crater since 1 August; 27 mm were measured at one site E of the 1978 Crater rim. The ash, much of which was thought to be reworked crater floor tephra, resembled the July ejecta but contained less fresh magma.

Since late October 1985, low-frequency (B-type) volcanic earthquakes have dominated seismicity, occurring at a rate of 5 to >50 events a day. High-frequency events were relatively rare (usually <3/day) but reached a maximum of 36/day. Wide-band, long-duration earthquake sequences were recorded on 3 days in August and September; weak-medium amplitude, low-medium frequency volcanic tremor was recorded on 17 days in August and 9 days in October. Seismic signatures could not be correlated with any of the numerous reported eruption columns in early October.

Information Contacts: J. Cole, Victoria Univ, Wellington; P. Otway and S. Sherburn, NZGS Wairakei; B. Scott, NZGS Rotorua; W. Giggenbach, Dept of Scientific and Industrial Research (DSIR), New Zealand.

January 1987 (SEAN 12:01) Cite this Report

Large explosion with no immediate seismic precursor

One of White Island's largest explosions of the last 10 years occurred on 25 January at [about] 2040. Ejecta up to 5 cm in longest dimension fell on a boat anchored roughly 1 km ESE of the vent (in Crater Bay); people on board heard rumbling. From another boat 5 km NW, ash and rocks were seen falling into the sea. A large black cloud rose from the main crater and lightning flashed in the eruption column. Seismicity associated with the eruption lasted for ~20 minutes (table 5). [An E-type earthquake accompanying the eruption began at 2044 but was relatively small, suggesting that the eruption was largely open-vent (Latter, 1988)]. There was no recognizable precursor to the eruption which occurred during a period of low seismic activity.

Table 5. Seismic activity during White Island's 25 January 1987 eruption. Times are in seconds after eruption onset (at 2041) except where otherwise noted.

An aerial inspection on 27 January showed that new ash had been dispersed mainly S of Congress Vent; 1-m ballistic blocks were abundant up to 0.5 km from the vent, and more widely dispersed 0.7 km away. The largest blocks appeared to be 1-2 m in diameter. Ash covered the floor of 1978 Crater and the main crater, coated the main crater's S wall, and extended over the rim onto the S flank. Vegetation on the edge of the ash did not appear to have been affected. At 1020 a weak gray ash column rose to 800 m from Congress Vent; fumaroles were emitting steam.

Since mid-November, seismicity has remained dominated by low-frequency (B-type) events. In mid-late November the number of B-type events declined from >20 to

A swarm of A-type earthquakes began at 2100 on 22 December and was followed by strong microearthquake activity (2,000-5,000/day) for 3 days. No eruptive activity was reported. Less intense microearthquakes occurred on 4-5 January. B-type events with anomalously large amplitudes usually numbered >30/day during January. On 20 January [at 0537-0538] a high-amplitude (>110 mm p-p), wide-band, long-duration, eruption (E-type) earthquake sequence was recorded. It is not known if eruptive activity accompanied this event. Weak, medium- to low-frequency volcanic tremor followed until 23 January. Tremor was banded and amplitude decreased with time. The 24-25 January seismic records were very quiet until the eruption.

Further Reference. Latter, J.H., 1988, Shallow seismicity of various volcanic areas during 1987: New Zealand Volcanological Record, no. 16, p. 35-44.

Information Contacts: I. Nairn and B. Scott, NZGS Rotorua.

February 1987 (SEAN 12:02) Cite this Report

Phreatic eruption ejected lapilli and blocks

The NZGS reported that the 25 January eruption that directionally ejected lithic lapilli and blocks over the SE part of the island appears to have been dominantly phreatic in origin. The NZGS noted that this interpretation is consistent with the lack of change in seismicity prior to the eruption, the continuing decline in fumarole temperatures (measured 13 days before the eruption), the apparent lack of associated inflation of the main crater floor (from surveys at 3-month intervals), and significant weekly rainfall (62 mm) that ended a period of drought before the eruption.

About 10 hours before the eruption (at 1000) a white steam plume was issuing from Congress Vent and no fresh ejecta were visible on the main crater floor. Comparison of photos taken before and after the eruption show that the mouth of Congress Vent approximately doubled in diameter and elongated N-S.

The January deposits had two main components: 1) a continuous tephra blanket of blocks and lapilli and 2) numerous large scattered ballistic blocks that fell up to 750 m from the vent. The lapilli and blocks were dispersed along a narrow SSE- trending axis with a maximum thickness of 0.4 m. Ash coated the main crater walls and outer flanks. Stratigraphic position indicated that the ballistic blocks were erupted after the lapilli/block bed. Ejecta volume was estimated at roughly 40,000 m³. Most clasts were andesitic/dacitic as in earlier eruptions.

December-February subsidence rates decreased substantially (to -4 mm at one site) and only very minor subsidence has occurred in the Donald Mound-Congress Vent area. Fumarole temperatures measured on 2 March ranged from 117 to >530°C. Since 1983 there has been a general trend of crater floor deflation and declining fumarole temperatures.

A M 4.7 earthquake occurred ~430 km N of White Island at 2037 on 25 January, 4 minutes before the onset of local seismicity and seven minutes before the eruption [at 2044]. The early phase that emplaced lapilli and blocks on the main crater floor is thought to have been associated with 8 minutes of continuous medium-frequency tremor (185-685 seconds after 2041 in table 5). About one minute of discrete (C-type) events soon followed, when most of the ballistic blocks may have been explosively erupted. Seismicity of higher amplitude and longer duration has accompanied smaller past eruptions and sometimes has occurred without an associated eruption.

Since 25 January, B-type events have continued to dominate the records, numbering 28-42/day. Small, high-frequency (A-type), volcano-tectonic events have numbered 1-3/day. Wide-band (E-type) 'eruption earthquake' sequences were recorded on 29 January at 1920, 1 February at 0214, and 2 February at 0958. The first was followed by 29 hours of low-amplitude, medium-frequency, volcanic tremor accompanied by moderate ash emissions. The other two events were unusually short and dominated by low frequencies. A M 6.2 earthquake centered ~60 km NNE of White Island on 2 March was not associated with any obvious change in volcanic activity.

Information Contacts: A. Cody, B. Houghton, I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS Rotorua; J. Latter, DSIR Geophysics, Wellington.

March 1987 (SEAN 12:03) Cite this Report

Continued ash emission

Several ash eruptions have occurred since geologists visited the crater on 3 February. Emissions occurred both before and after the M 6.3 earthquake on 2 March, and heavy steaming was observed on 3 March.

When geologists returned on 28 March, new ash covered at least the E half of the island to a maximum measured thickness of 20 cm, burying the 25 January block deposit E of 1978 Crater. Ash was predominantly lithic with a minor fresh magmatic component. Congress Vent had enlarged 2-3 times in diameter and expanded W across the floor of 1978 Crater, forming a vertical-walled, flat-floored, circular shaft ~50 m deep. On 28 March, ash and high-pressure gas emission was occurring from a several-meter-wide, sub-horizontal, pipe-like opening in the NW wall. The pipe remained incandescent red during an hour of observation. Temperatures of two fumaroles E of 1978 Crater were measured on 28 March: one had decreased from 343 to 180°C since 3 February and the second had increased from 244 to 280°C.

Significant tremor was recorded on the White Island seismograph 17 February-11 March and 21-22 March. Small to moderate low-frequency volcanic earthquakes (B-type) dominated activity during periods without tremor. A few high-frequency volcano-tectonic events accompanied the B-type events. Small earthquakes, possibly eruption (E-type) were recorded on 20 February, and 23, 26, and 27 March. On 28 March a small E-type earthquake that was followed by 10 minutes of low-amplitude tremor was associated with a moderate ash eruption between 1000 and 1020 during the geologists' visit.

Information Contacts: I. Nairn, NZGS Rotorua.

April 1987 (SEAN 12:04) Cite this Report

Continued ash emission

Intermittent ash eruptions have continued since 28 March fieldwork, although no significant change has occurred in vent morphology or crater floor conditions.

On 7 April at 1544, geologists visiting the island observed an ash column that rose >1.0 km and sent warm ash W of the crater. The gas/ash plume was jetted horizontally under high pressure from the active vent (Hitchhiker) in Congress Crater; bright incandescence was visible for 10-20 m. A low-frequency vibration accompanied the eruption. Small slabs of hydrothermally altered sediments (2-5 cm) were deposited within 100 m of the vent. A deformation survey conducted during the 7 April visit found 21 mm of uplift just E of the crater (in the Donald Mound area). Fumarole temperatures had not changed significantly and new ejecta remained lithic-dominated. Total ash accumulation since 25 January 1987 was 43 cm on the E rim of the 1978 Crater complex and 80 cm on the NE rim. Ash thickness decreased rapidly away from the rim.

Low-frequency (B-type) volcanic earthquakes numbered 13-33/day 28 March-13 April, while high-frequency (A-type) events remained rare. Levels of seismic activity were similar to those of 1986. Eruption (E-type) earthquakes were recorded on 1, 7, and 10 April. The 10 April event was the largest, with a maximum tremor amplitude of 15 mm and a duration of about 10 minutes.

A minor eruption was reported on 13 April by observers ... at Whakatane and Opotiki. A vertical steam column rose 1.5-3 km above the island and at least one discrete pulse of ash-laden steam was reported to "flow" laterally away from the eruption column over the sea. When geologists visited the crater on 15 April very little fresh tephra had accumulated on the main crater floor. The vent was more or less continuously emitting high-pressure gas with minor ash, and surging cauliflower clouds climbed the crater wall. Incandescence was seen intermittently during a period of poor visibility.

Information Contacts: I. Nairn and C. Wood, NZGS Rotorua.

May 1987 (SEAN 12:05) Cite this Report

Ash/block eruptions; inflation; seismicity

Eruptive activity 13-22 May was the most intense of 1987. New ash deposits on the island were voluminous (perhaps 104-10⁵ m³). The largest explosive eruptions threw ballistic blocks S and SSE of Congress Crater, and were similar in magnitude to the 25 January event (SEAN 12:01). On 16 May at 2036, blocks were incandescent and the ejection was accompanied by a shock wave. Major block eruptions appear to have occurred some time after heavy rain on 18-19 May, and have been followed by intermittent ash eruptions. Ash and steam eruptions were reported on 18 and 21 May.

A levelling survey on 12 May showed that inflation had continued E of Congress Crater (in the Donald Mound area), with 7 mm of uplift since mid-April and a total of 28 mm since 3 February. The area NW of Donald Mound, within 100 m of Congress Crater, continued to subside rapidly, falling 58 mm over the last year. Ground oscillations were observed during the levelling measurements, ~1 minute before an eruption. At 1134, an ash pulse was vigorously emitted from a vent in Congress Crater, forming a brown column. Lapilli of up to 50 mm were ejected and fell as far as 50 m from the rim of the 1978 crater complex. Tephra deposited prior to 12 May consisted of well-sorted lithic blocks and lapilli.

An aerial survey on 22 May showed that new, thick, light gray ash covered most of the E end of the island. A lobe of ashfall extended over the N crater wall, into the sea (N of Shark Bay). Blocks littered the flat SE of Donald Mound and were most abundant at the foot of the S crater wall. Impact craters were most abundant on the flatter slopes 60 m above the main crater floor. Blocks and impact craters extended down the S margin of the main crater floor.

Moderate medium-frequency tremor began 3 May and persisted until about 1200 on 22 May. Peak daily amplitude ranged from 11 to 40 mm. Some envelopes of pure harmonic tremor were recorded, especially on 13 May. "Strong" tremor was recorded during the 8.5 hours before tremor ceased on 22 May and larger E-type earthquake sequences occurred at both the commencement and cessation of the strong tremor. In the first 3 hours following the end of tremor, 100 C-type (medium-frequency) earthquakes occurred, the largest about M 1.5. Since 7 April, 2-30 low-frequency (B-type) volcanic earthquakes occurred/day, while high-frequency events (A-type) were rare. E-type eruption sequences had been recorded since 10 April and 18 were recorded 12-22 May, with the largest on 20 May at 2215. Two of the recorded E-type events were correlated with observed eruptions.

Information Contacts: J. Cole, Univ of Canterbury, Christchurch; I. Nairn and B. Scott, NZGS Rotorua.

June 1987 (SEAN 12:06) Cite this Report

Explosions weaken; inflation accelerates

Tephra emission and seismicity declined after the vigorous explosive activity of 13-22 May. Eruption (E-type) sequences were recorded on most seismograms between 22 May and 7 June. The largest event, at 1508 on 4 June, was accompanied by an eruption column clearly visible from the Bay of Plenty coast,>50 km away. Weak medium-frequency volcanic tremor was recorded 22-24 and 26 May, and lower-amplitude tremor bands, each lasting 4-10 hours, have dominated the background of most records since then. The number of low-frequency B-type earthquakes ranged from 3 to 15/day, but amplitudes were considerably lower than earlier in the year.

Geologists visited the crater on 11 June for the first time since the mid-May explosions. Only gas and minor ash emission was occurring from the active (Hitchhiker) vent on the floor of Congress Crater. Ballistic blocks probably ejected by the May explosions had fallen >700 m from the vent, and formed impact craters 0.5 m in diameter within 50 m of the coast (at Crater Bay). Since the 12 May visit, 900 mm of tephra had fallen at a site 60 m ESE of the rim of Congress Crater, but deposits thinned rapidly farther from the vent. All of the examined lapilli- to block-sized ejecta was lithic material, most altered, but some unaltered dense black andesite lava was found. The volume of the May-June tephra was in the order of 10⁵ m³, about half of the total volume of 1987 ejecta.

Rapid local inflation, centered ~200 m ESE of the vent (in the Donald Mound area) occurred between the 12 May and 11 June levelling surveys. Maximum uplift was 29 mm, compared to 7 mm the previous month. Magnetic data showed a sharp (-100 nT) anomaly N of Donald Mound and a broader +100 nT anomaly to the SE. The NZGS interpreted the combined deformation/magnetic data to suggest that local heating was occurring at depths of 200-300 m.

During a brief visit on 30 June, a steam plume containing a little ash rose from the vent, but less vigorously than on 11 June. No new ejecta were evident near the crater rim, but heavy rains within the previous 2-3 days had disrupted the ground surface.

Information Contacts: I. Nairn and B. Scott, NZGS Rotorua.

September 1987 (SEAN 12:09) Cite this Report

Ash eruption; tremor and eruption earthquakes

The largest eruption in 3 months occurred on 7 September. After a period of declining tremor, a short-duration C-type earthquake at 1014 was followed by 2 minutes of higher amplitude tremor of mixed frequency. This peaked at 1018 before returning to background levels at 1022. The time of the main eruption was interpreted from seismic records as being between 1015 and 1022. At 1100 the ash plume extended horizontally ~10 km NW at 1 km altitude. A steam and ash column was rising to 700 m above the island. Thickness of the new ash and lapilli layer was measured at 70 mm on the E part of the crater rim 1.5 hours after the eruption. All lapilli and block ejecta seen by geologists were altered lithic material derived from vent wall country rock.

Gas and ash emission was followed by moderate ejection of incandescent ash, observed 1120-1220 from a boat 900 m from the vent (in Wilson Bay). An observer on the coast (>50 km away) noted an ash column reaching 2,000 m. No seismicity accompanied the activity. A glow in the vent area had been observed from offshore the previous night.

Seismicity had been at moderate levels since 11 June, dominated by medium-frequency volcanic tremor. A number of E-type (eruption) earthquakes were recorded 2-5 September (and probably 30 August), the first significant discrete volcano-seismic events since June. Volcanic tremor often stopped at the time of an E-type event and gradually began again a few hours later. Tremor ceased after the 1015-1022 eruption on 7 September, and restarted at about 1900.

The recent eruption was similar to but smaller than the 25 January event that began the 1987 activity. It appeared to geologists to have been dominantly phreatic in origin.

Information Contacts: I. Nairn, NZGS Rotorua.

October 1987 (SEAN 12:10) Cite this Report

Explosions and ash emission; moderate seismicity

Intermittent ash eruption, with occasional larger explosive events, has continued since the last inspection on 7 September. An overflight on [15] October showed that the main crater floor was covered with dark ash. Congress Crater appeared to have deepened and the active vent emerged some distance above the crater floor.

Seismicity has remained at moderate levels since 7 September, dominated by medium- to high-frequency volcanic tremor. NZGS personnel thought it likely that episodes recorded 17-22 and 25-28 September accompanied significant ash emission. Several eruption-type earthquake sequences have been recorded since 7 September. These eruptive episodes, probably of similar size to the observed 7 September episode, have deposited block ejecta and left impact craters on the W part of the main crater floor. Volcanic earthquake events (E-type) that occurred between 7 September and 16 October were strongest on 12 and 13 September. Each event began with a sequence of C-type events followed 50-70 seconds later by a symmetric envelope of higher frequency (4-10 Hz) signal, interpreted as the time of the explosive eruption of ash and blocks from the vent (figure 9).

Figure 9. Typical example of an E-type volcanic earthquake at White Island, beginning with a sequence of C-type events. Courtesy of NZGS.

Information Contacts: A. Cody, I. Nairn, and B. Scott, NZGS Rotorua.

November 1987 (SEAN 12:11) Cite this Report

Ash emission continues; new vent

Intermittent ash emission continued in November and small eruption earthquakes were recorded on 31 October, and 8, 11(?), 15, 16, and 20 November. An eruption was observed at the time of the 31 October earthquake from Ohope (50 km S) and Matata (>55 km SW) at about 0810. A fast-rising "billowing" black column emerged to replace the usual white steam column and rose to >2,500 m. Ash fallout occurred N of the island.

During a 30 October inspection by geologists, minor to moderate ash emission was continuous and incandescent ash emerged at low pressure and without noise from Hitchhiker Vent in Congress Crater (on the E side of 1978 Crater). Since 7 September, 230 mm of fresh tephra had accumulated on the rim of 1978 Crater. Block ejecta consisted of altered country rock and smaller tephra were lithic-dominated with no fresh scoria component noted. Temperatures at sites ~120 m W of 1978 Crater (on Donald Mound) had continued to increase and generally ranged between 550 and 650°C.

Deflation continued near Congress Crater, with only a slight possible rise at the E end of Donald Mound, formerly an area of rapid inflation. Large changes had occurred in magnetic values since the last survey 11 June. Measurements indicated deep-seated (>700 m depth) heating below Donald Mound and in the areas N and S. A strong shallow (on the order of 100-200 m deep) heating center was found below the W edge. A general cooling was recorded over the remainder of the crater. A new small vent on the W edge of 1978 Crater floor was first sighted during a visit on 20 November, emitting a brown plume with fine ash. The 5-m-diameter vent had not been present on 15 October aerial photos nor was it noted during the 30 October visit. Hitchhiker Vent was emitting a light brown ash plume in semicontinuous pulses. Only a few meters of ash and a few new blocks (>0.2 m) had fallen on 1978 Crater rim since 30 October.

Information Contacts: I. Nairn, NZGS Rotorua; J. Cole, Victoria Univ, Wellington.

January 1988 (SEAN 13:01) Cite this Report

Seismicity increases; tephra columns

Eruptive activity from vents within 1978 Crater continued through January. In early December a marked increase in the number of A-type (high-frequency volcano-tectonic) earthquakes occurred, with events frequently numbering more than 5/day. The magnitude of larger events was ~2.5. E-type explosion/eruption earthquakes were recorded most days; amplitudes ranged from 20 to 200 mm. Eruption columns associated with 3 of the events were reported (table 6).

Table 6. Reported eruption columns from White Island, December 1987.

During a 14 January visit, ash emissions from both Hitchhiker vent (in Congress Crater, on the E side of 1978 Crater) and the November 1987 vent (on the W edge of the 1978 Crater floor) were observed. Enlargement had occurred at both vents since the November 1987 visit; the new vent was estimated at 10-15 m in diameter. The proportion of non-altered andesitic material in the tephra increased, but no magmatic material was recognized.

Information Contacts: B. Scott, NZGS Rotorua.

February 1988 (SEAN 13:02) Cite this Report

Minor tephra emission and seismicity

Eruptive activity has declined since 1987, accompanied by continuing deflation of the main crater floor. When geologists visited the volcano on 10 February, the small vent that had formed on the W edge of the 1978 Crater floor in November was not active. Gas and a little ash were being emitted at low pressure from Hitchhiker vent. At a site 350 m SE of the vent, 32-38 mm of new tephra had accumulated since 14 January and 310 mm since 30 October 1987. A few small bombs, probably ejected within the previous few days, were found 100 m SE of the vent; the bombs and associated ash were similar to those found on 14 January and 30 October. Temperatures at fumaroles SE and E of the vent (Donald Mound and Blue Duck areas) had increased in the past year, to a maximum measured value of 541°C, but had declined NE of the vent (Noisy Nellie area). Seismicity since 14 January has been characterized by sub-continuous volcanic tremor of low amplitude and medium-low frequency. E-type (eruption) volcanic earthquakes were recorded on 18 January at 1714, 19 January at 1209, and 21 January at 1713.

Information Contacts: I. Nairn, NZGS Rotorua.

March 1988 (SEAN 13:03) Cite this Report

Blocks and scoria bombs; incandescent fumarole

White Island's intermittent eruptions have continued, becoming slightly larger with an increasing magmatic component. Vigorous activity and sizeable eruption columns were reported [14 March at about 1615]; 29 March at 1640; 1 April at 0830 and 1100; and on 2 April through 1025 (when a column reached ~1,800 m altitude) before declining (to 640 m altitude by 1600).

Geologists briefly visited the island on 4 April [see also 13:4]. A weak steam plume that contained a little ash was emerging from the recent eruption (Hitchhiker) vent. New lithic lapilli and a few scoriaceous bomb fragments were scattered around the rim of South Crater, 700 m from Hitchhiker vent. Impact craters to 30 cm in diameter that contained dense lithic blocks were found at the base of the South Crater wall. Tephra deposited since 25 March was similar to earlier ejecta but contained a considerably greater proportion of highly vesiculated glassy scoria. High-pressure gas was emerging through two brightly incandescent openings from Fumarole 6, in the easternmost of three 1980 craters ~200 m E of Hitchhiker vent. The fumarole's cherry red glow suggested that its temperature exceeded 900°C. Temperatures of 541 and 655°C had been measured at the fumarole on 10 February and 12 March; it had not been incandescent on 25 March. Minor inflation measured in the area during a 10 February survey contrasted with the deflation that characterized the rest of the main crater floor.

Information Contacts: I. Nairn, NZGS Rotorua.

April 1988 (SEAN 13:04) Cite this Report

Strong explosion; inflation and heating

The largest explosive eruption since September 1987 occurred on 14 March at about 1615, when a dark eruption column rose to at least 3 km altitude. Eleven days later, geologists found altered lithic blocks up to meter-size scattered over the main crater floor, and ash covered the S slopes of the island. Some fresh, highly vesiculated andesitic bombs had also been ejected, probably comprising only a fraction of a percent of the large tephra, but were larger (to 25 cm) and more abundant than those found on 30 October 1987 and 10 February 1988. Samples of lapilli and ash were also lithic-dominated, but included a minor fresh magmatic component of dense, slightly vesiculated black glass. Intermittent explosive activity continued into early April.

When geologists visited the volcano on 14 April, ash emission was continuing but little new tephra had accumulated on the main crater floor since the previous visit 10 days earlier. A levelling survey showed a zone of very rapid shallow-sourced inflation on the main crater floor NE of the active (Hitchhiker) vent. Magnetic data indicated a broader zone of strong localized heating that included the rapidly inflating area, with cooling to the E. Within the area of inflation and heating, a fumarole that was incandescent in daylight had a measured temperature of 830°C. After repair of seismic instruments on 14 April, seismicity was characterized by sub-continuous medium-frequency volcanic tremor.

Information Contacts: I. Nairn, NZGS Rotorua.

June 1988 (SEAN 13:06) Cite this Report

Phreatomagmatic eruption; seismicity

White Island's activity has changed from continuous moderate gas and ash emission to episodic short-duration discrete eruptions. The largest eruption since September 1987 occurred at 1030 on 27 April; it was slightly larger than the 14 March explosion. The phreatomagmatic eruption emitted red ash, lithic blocks, and scoria bombs. A black plume (3.5 km high) was observed >50 km away, from the Bay of Plenty coast. Ash fell into the sea and moderate ash emission continued after the initial explosion.

The eruption followed 9.5 hours of relatively weak microseismicity. Its onset was marked by 2-3 minutes of relatively low-frequency (3-4 Hz) C-type seismicity that increased in frequency (6-7 Hz) and amplitude (60 mm) between 1031 and 1033, then declined to background by 1036. Twenty minutes of low-amplitude tremor followed, with lower frequency (2-3 Hz) than before the eruption. The tremor ceased after two high-amplitude/duration-ratio A-type volcano-tectonic events at 1058 and 1100. Two more volcano-tectonic events occurred at 1254 and 1301. Medium- to high-frequency tremor had dominated seismic records in the two weeks preceding the eruption.

Numerous swarm-like A-type events were recorded 4-6 May. Medium-frequency volcanic tremor was established by 7 May but declined to background by 0200 on 9 May. Small E-type (explosion) earthquakes occurred 7 May at 1821, 8 May at 1257, 12 May at 0357 and 2541, and 13 May at 0722. Tremor reappeared 11 May and dominated records in succeeding weeks.

When geologists visited the volcano on 27 May, impact craters probably produced by the 27 April eruption extended 750 m from Hitchhiker vent to Crater Bay. Numerous ash-covered scoria bombs deposited by the same eruption were found on the crater floor. Post-14 April ejecta at the crater rim consisted of 20 mm of fine pink ash, 25 mm of coarse dark ash, and lithic lapilli. The interior walls of Fumarole 6, 200 m E of Hitchhiker vent, were incandescent. A small eruption 10 m N of Fumarole 6 had ejected lithic blocks as large as 20 cm in size.

A 15 June visit revealed no changes apart from possible minor collapse along the rim of 1978 crater. Fumarole 6 was still incandescent and its temperature had declined only slightly, to 785 from 830°C two months earlier. Hitchhiker vent emitted gas that contained a little ash. A deformation survey measured deflation of the main crater, E and NE of Hitchhiker vent. Rapid local inflation had occurred around Fumarole 6 during its strongest activity.

Since 15 June, White Island seismicity has changed significantly. Tremor became more intermittent until it ceased 18 June. E-type earthquakes occurred at 0205 on 19 June (large), 1308 on 21 June (very small), 1026 on 22 June (medium), and 0705 on 23 June (large). Only the 23 June event was associated with an observed eruption, when pilots Morter and Ford (Air New Zealand) noted a "mushrooming" eruption column rapidly rising to 3.0 km at 0710.

Information Contacts: I. Nairn, NZGS Rotorua.

July 1988 (SEAN 13:07) Cite this Report

Continued ash ejections, fumaroles cool

Since the last visit ... on 15 June, ash ejections have continued but no major block/bomb-ejecting eruptions have occurred. Explosions on 23 June at 0710 and 19 July at 1507 produced eruption columns to 3,000 m. The June eruption was observed from an airplane and the July eruption was observed from the Bay of Plenty Coast ....

On 19 July, various areas along the crater rim were dusted with light-brown tephra and one location was densely littered with white lithic fragments up to 1 cm across. Sandy tephra was 8-10 mm thick in some places and overlaid fine dark-gray ash. The fine fraction of the deposit contained minor scoria in addition to abundant lithic/accessory material, suggesting that the eruption two hours earlier was phreatomagmatic with a minor magmatic component. No fresh impact craters were observed. A light-brown, weakly convoluting ash column rose from a vent above the crater floor on the N wall of Hitchhiker vent.

On 1 August, the main crater floor was covered with fine dark-gray wet ash, often clumped into aggregates, mantling all blocks and impact craters. A moderate volume of fine ash was discharged from Hitchhiker vent accompanied by loud detonations at 30-second to 2-minute intervals. These eruption sounds did not correlate with discernable changes in ash/gas emission (which remained fairly steady) and seemed to originate deep within the conduit beneath the vent. No incandescence was visible in Hitchhiker vent, and the ash plume rose in an expanded state. Ash erupted after 15 June was 70 mm thick on 1978 Crater rim. Some survey pegs were coated on vertical surfaces with up to 15 mm of gray ash deposited from wet ash clouds. Ash sampled from the crater rim contained mostly unaltered accidental lithic and essential crystal/glass fragments lacking scoriaceous material. The fragments presumably were derived from wallrock and solidified magma. No fresh scoriacous bombs were found in the sparse block-size ejecta on the ground surface, but the ash cover prevented examination of many of the new clasts. Blocks were dominantly lithic accessory material. NE of the eruption vent, the previously incandescent Blue Duck fumarole 6 and other thermal areas had cooled substantially (table 7) and vent pressures were much lower than on 15 June, probably due to recent heavy winter rainfalls.

Table 7. White Island fumarole temperatures measured with an infrared thermometer, April-August 1988.

Seismic records to 27 June recorded the first significant B-type events in 1988. Small A-types numbered 0-8/day and E-types (explosion events) were recorded most days after 18 June. No records were obtained 27 June-12 July. From 12 to 14 July, medium-frequency microearthquakes (2-3/minute) dominated. The activity was similar 18-20 July. Records 28-30 July showed a change to larger A-type events, still occurring at a rate of 2-3/minute. Since 1 August, weak medium-frequency volcanic tremor and continued discrete A-type events have dominated the seismic record.

Information Contacts: B. Scott and I. Nairn, NZGS Rotorua.

October 1988 (SEAN 13:10) Cite this Report

Ash emission; earthquake swarms

Since geologists last visited ... on 14 August, no eruptions have been reported although numerous E-type (explosion) earthquakes have occurred. During fieldwork on 14 October, a continuous expanded gas plume containing fine pink ash rose from Hitchhiker vent. Brick-red ash covered the island's E half and small impact craters were scattered ESE of the vent. Tephra ejected after 1 August was 70 mm thick at Congress Crater's rim and included altered lithic fragments, abraded crystals, and a few % fresh, light brown, highly vesicular scoria fragments. High pressure/temperature gas was emitted from fumaroles roughly 200 m E of Hitchhiker vent, including two new vents. Gas vents were surrounded by aprons of material ranging from anhydrite-cemented ash to lithic blocks.

Since early August, an average of seven B-type and fewer than five high-frequency A-type seismic events have been recorded/day. Earthquake swarms were detected 24-25 August (62 events), 7-8 September (38 events), and 23-24 September (57 events followed by E-type earthquakes). Of 20 E-type events recorded in August, 16 occurred 12-24 August. Four E-type events were recorded in September and one on 2 October, before ash accumulation on solar panels suspended operation of seismic instruments on 4 October.

Information Contacts: I. Nairn and B. Scott, NZGS Rotorua.

November 1988 (SEAN 13:11) Cite this Report

Ash emission continues; new fumarole

When geologists visited ... on 16 November, fine pink/red ash emerged from Hitchhiker vent, and moist acidic tephra fell near 1978 Crater. Since the last visit, on [14] October, up to 10 mm of ash had been deposited near its E rim. A new noisy fumarole (~1 m in diameter) discharged transparent blue vapor from the W edge of 1978 Crater's floor, near the location of the ephemeral vent documented 20 November 1987. Other fumaroles emitted gases at temperatures as high as 681°C. No incandescence was observed.

Information Contacts: E.F. Lloyd, NZGS Rotorua.

December 1988 (SEAN 13:12) Cite this Report

Minor ash emission; deflation; fumaroles cool

During 2 December fieldwork, geologists observed continued emission of fine red ash from Hitchhiker vent, similar to October and November. Near the vent, ~55 mm of ash had accumulated since 16 November, but only 1-2 mm of new ash had been deposited ~250 m to the SE. No fresh magma was detected in the ash; vesicular scoria fragments were last noted on 14 October. The new fumarole on the W floor of 1978 crater, first seen on 16 November, was emitting a jet of high-pressure white vapor at about a 45° angle. Small fumaroles were also noted for the first time on the floor of the western subcrater, below the 1914 landslide scar.

A deformation survey showed that subsidence had occurred in a broad zone, centered roughly 150 m E of Hitchhiker vent, since the previous measurements on 15 June. Magnetic data showed positive changes exceeding 200 nT in the same general area, interpreted to show significant cooling centered at 100-150 m depth. Temperatures of fumaroles in and near the area of subsidence had dropped substantially since June (Blue Duck, 775°C in June/565° in December; Donald Mound, 420/354°; Noisy Nellie, 280/226°). Seismicity has remained similar since mid-October, characterized by medium- to high-frequency volcanic tremor and microearthquakes. Maximum daily numbers of A-type (4) and B-type (23) events were associated with three small explosion earthquakes on 17-18 October.

Information Contacts: J. Cole, Univ of Canterbury, Christchurch; I. Nairn, B. Scott, P. Otway, and D. Christoffel, NZGS Rotorua; B. Christenson, DSIR Chemistry, Wairakei.

January 1989 (SEAN 14:01) Cite this Report

Vulcanian explosions; new crater

No unusual activity had been reported in the month following 2 December fieldwork. On 4 January, tourists found a few small lava bombs near the 1978 Crater rim. The previously active (Hitchhiker) vent emitted a pink plume containing fine ash. Between the 4th and the next visit at about 0800 on 12 January, a new pit vent had formed S of Congress Crater in 1978 Crater (figure 10). Both the new vent (named R.F.) and Hitchhiker vent emitted white steam plumes. At 1000, an incandescent jet was noted in the Blue Duck fumarole area, 200 m away.

Figure 10. Location of the new R.F. vent and height changes (in mm) at White Island, 15 June-2 December 1988. Courtesy of NZGS.

When geologists visited the crater on 14 January, the new vent was emitting voluminous clouds of light brown-red ash and appeared to be ~40 m in diameter. At 1039, a discrete eruption ejected a convoluting ash column to 1,500 m. Ash fell E into the sea. There was no emission from Hitchhiker vent. Light red-brown ash coated the E end of the island and reached 17 cm thickness at the 1978 Crater rim. Fumarole temperatures were similar to those measured 2 December. A vent (N of Fumarole 6) that had enlarged to 2 m in diameter and was surrounded by small blocks, may have been the source of the small eruption seen 12 January. Several similar eruptions were observed from Whakatane (50 km SSW) 14 and 15 January. The 12-14 January eruptions were among the largest since 1980.

Only limited seismic data were available after 2 December. Early December seismic records were dominated by weak, continuous, medium- to high-frequency volcanic tremor and small A-type volcanic events. After 4 January, microearthquake activity declined to a maximum of ~2,500/day, B-type events were rare, and A-types increased. Explosion earthquakes were registered 4 December and 7 January.

Information Contacts: B. Scott and I. Nairn, NZGS Rotorua.

February 1989 (SEAN 14:02) Cite this Report

January crater emits ash; new vents eject blocks

The new R.F. Crater, first observed 12 January, had enlarged to about the same size as Congress Crater when geologists visited the volcano 1 February. R.F. Crater emitted a pink-brown ash column, while the previously active Hitchhiker vent was dormant. Ejecta from the new crater was dominated by altered lithic material with a very small proportion of fresh vesiculated glass.

An apparently brief diversion of heat flow to a zone of thermal features (Blue Duck area) ~80 m E of 1978 Crater formed at least two new fumarolic vents (N of Donald Mound). The largest new vent, first noticed by tourists on 29 January, was 15-20 m in diameter and surrounded by an apron of block-sized ejecta that extended ~50 m, with isolated impact craters to 150 m. Its temperature was 630°C on 1 February.

The explosion that formed the new vent was apparently much larger than those that formed the 1980 pits, and larger than any explosion that has occurred on the main crater floor in 20 years. A new linear zone of fumaroles, ~20-30 m long and trending ENE, had also formed NE of the Blue Duck fumaroles.

Information Contacts: B. Scott, NZGS Rotorua.

March 1989 (SEAN 14:03) Cite this Report

Explosions continue from two new vents

Activity from R.F. Crater declined to intermittent ash emission in February and March. When helicopter pilot Robert Fleming visited White Island on 14 February, R.F. Crater was emitting ash. Additional tephra was found in the Blue Duck-Donald Mound area (figure 11) about 200 m to the E. On 19 February, R.F. Crater was quiet. Fleming's subsequent visits on 25 and 27 February and 5 March revealed that the new Donald Duck vent, about 40 m N of Donald Mound and first seen 29 January, had grown and ejected tephra. R.F. Crater was no longer emitting much ash during those visits.

Figure 11. Sketch map, showing recently active features on White Island, early 1989. The area shown is indicated by the box on the index map. Courtesy NZGS.

Vigorous explosions occurred 26 February and 14 March, producing tephra columns visible from the mainland (>50 km away). Both were accompanied by E-type earthquakes. The 14 March explosion, the largest magmatic event since early April 1988 (SEAN 13:04), scattered scoria bombs over the S margin of the main crater floor.

During geological fieldwork two days later, R.F. Crater emitted a light-pink steam plume. The Donald Duck vent was surrounded by new lithic blocks and had enlarged to 20 m in diameter and 10 m in depth. Vents on its floor emitted brown gas and intermittent ash.

Donald Duck vent erupted between 16 and 20 March, probably during a 25-minute E-type earthquake sequence that started at 1624 on 16 March. The blast was directed SSE, depositing gray-white coarse gravel near the vent and blocks up to 300 m away. No fresh scoria was found. The eruption enlarged the vent to 15 m deep and 30 m in diameter. Between 9 February and 20 March, >10 cm of new ash and lapilli had accumulated at the 1978 Crater rim. Red glow, probably caused by incandescent gas emission, was seen during the night of 21 March from Whakatane (50 km SSW ). No unusual seismic activity was recorded.

Fumarole temperatures declined after 9 February, probably due to heavy rainfall. Magnetic and crater floor deformation surveys suggested no significant rise of magma. Two months of inflation in the vicinity of the Donald Duck vent had ended, with deflation occurring between surveys on 9 February and 16 and 20 March.

Seismicity 9 February-16 March consisted of medium-to-strong high-frequency microearthquakes and persistent small A- and B-type events. Harmonic tremor and rare E-types were also recorded. After 22 February, B-type events averaged ~9/day. Low-amplitude, 1.5- to 2-Hz tremor was recorded 19 and 20 February. E-type shocks were recorded 22, 24, and 26 February, and 14 and 16 March.

Information Contacts: I. Nairn, NZGS Rotorua.

April 1989 (SEAN 14:04) Cite this Report

Tephra ejections continue

Donald Duck vent has intermittently ejected tephra since its formation in late January in a zone of strong fumarolic activity ~100 m NE of eruptive vents in 1978 crater (figure 11). Photographs by Geoff Green of a 4 March eruption (at about 1500-1530) show a 500-m, vigorously convoluting ash column with an incandescent base. The eruption continued for at least 45 minutes, and ash emission also began from R.F. Crater. A larger eruption between 16 and 20 March, apparently not witnessed, presumably generated a larger column. During April, Donald Duck vent continued to eject ash and threw lithic blocks to as much as 200 m S. Intermittent ash, block, and bomb ejections also continued from R.F. Crater during the month. Two bomb-ejecting eruptions from R.F. Crater since 20 March were followed by widespread ash deposition.

During 26 April fieldwork, Donald Duck vent emitted voluminous clouds of light gray gas from a vent at the base of its N wall. New ash-covered scoria bombs (first noted in early April) were present S of Donald Mound, reaching more than l m in diameter near the 1978 Crater rim. R.F. Crater (appearing deep with vertical walls) discharged a dilute cloud of gas and fine pink ash. Ash covered much of the main crater floor and walls. Impact craters and lithic blocks a few days old were abundant around Donald Mound and Donald Duck vent. Congress Crater was quiet.

Fumarole temperatures and emissions had decreased at most vents except Noisy Nellie, which continued to emit voluminous high-pressure gas. Geologists suggested that Donald Duck and R.F. Crater have been capturing heat from surrounding areas, which are cooling as a result. General deflation, in progress since mid-l987, continued with strong subsidence of the Donald Mound area. Seismicity through late April remained similar to previous months, with microearthquakes recorded most days. Activity was conspicuously banded, with individual bands lasting 1.5-24 hours, containing up to 10 medium-frequency events/minute. Activity was most prolonged around 1-2 April. Small E-type events were recorded in April on the 3rd (0854) and 8th (0115, 0931, and 2008), while small A-types occurred most days. Very few B-types were recorded.

Information Contacts: I. Nairn, NZGS Rotorua.

June 1989 (SEAN 14:06) Cite this Report

Explosions continue; craters enlarge

Eruptions of ash and blocks continued from R.F. Crater and Donald Duck vent in May and June. On 10 May, when R. Fleming visited White Island, R.F. Crater was erupting dark gray coarse ash, most of which fell into the crater. Donald Duck vent was emitting minor amounts of gas. A small (3 m diameter) new vent had opened 20-30 m NNE of Donald Duck, discharging gas and ash. On 1 June, Fleming observed similar conditions.

During geological fieldwork on 23 June, the main crater floor was covered with fine gray ash that thickened toward Donald Duck vent. Block-ejecting explosions (the largest yet from Donald Duck) had apparently also occurred since the 1 June visit. Fresh new impact craters and lithic blocks (up to 1 m in diameter) were abundant to ~200 m SW of Donald Duck, which had enlarged to 100 m in diameter and >200 m in depth. No fresh magma has been detected in the Donald Duck tephra. The new vent NNE of Donald Duck vent was no longer active. The pits that had formed in late January (SEAN 14:01) and the 1980 pits (W of Donald Duck) were quiet, but had recently collapsed (probably due to recent heavy rainfalls) and were deeper, with vertical walls.

Large scoria bombs (1 m) and blocks (>5 m in diameter near the 1978 Crater rim) had been erupted from R.F. Crater, which was emitting a dilute, green-brown ash column and a few small blocks. Coarse ash fell back into the crater. A total of 450 mm of ash had accumulated on the 1978 Crater rim since 26 April. Rare, vesiculated, brown glass was the only indication of fresh magma in the tephra. Hitchhiker vent (in Congress Crater) was slightly enlarged, but had not collapsed, suggesting reinforcement by local intrusions. Recent heavy rainfalls had triggered several debris flows of saturated ash from the 1978 Crater walls. The largest had flowed across the 1978 Crater floor and over the rims of R.F. and Congress Craters.

Fumarole temperatures in the Donald Mound area had dropped since 26 April, and tephra (ejected from Donald Duck) covered the vents. Deflation of the area had accelerated, with the W portion subsiding 21 mm and the NW portion >40 mm since 16 March. The area near the rim of 1978 Crater had subsided 300 mm since the small eruptions in early 1984 (09:02).

Intermittent seismic data after 26 April showed that seismicity had not significantly changed, other than an increase in E-type events (14 in May and 4 in June before transmission ceased). A- and B-type events were recorded most days, with maximum daily totals of 12 and 15 events respectively. Microearthquakes were recorded 26-31 April and 20-21 May, with 10 events/minute on 27 April.

Vegetation studies indicate that the post-l976 eruption is stronger than any in the last several hundred years at White Island (White Island 1976-82 Eruption [appendix by Clarkson and others]: New Zealand Geological Survey Bulletin, in press).

Information Contacts: I. Nairn and B. Scott, NZGS Rotorua; P. Otway, NZGS Wairakei.

July 1989 (SEAN 14:07) Cite this Report

Tephra emission declines

An explosion on 3 July, marked by an E-type earthquake at 1134, produced an eruption column 2,000-2,500 m high. E-type earthquakes were also recorded 25 June at 1002 and 17 July at 1015. Other seismicity generally remained similar to previous months, with A- and B-type events most days (~5-10), and minor high-frequency volcanic tremor 5-11 and 21-32 July.

When geologists visited the volcano on 31 July, there was little evidence of significant eruptive activity since previous fieldwork on 23 June. A small amount of fine gray ash may have originated from Donald Duck since the 23 June visit, but recent rainfall erosion made this difficult to assess. No new ejecta from R.F. crater had accumulated on the 1978 Crater rim, and no ash was found on the seismic solar panels. Tephra pits showed that Donald Duck had ejected nearly all the tephra deposited 26 April-23 June in the area ~150 m W and SW. Tephra from R.F. Crater was only significant ~200 m S of Donald Duck.

The new intermittently active vent 30 m NNE of Donald Duck (first noticed 10 May; 14:06) emitted white gas, as did R.F. Crater. Activity of R.F. and Hitchhiker vents seemed related; when emissions from R.F. Crater were strong, gases from Hitchhiker seemed to be drawn back into the vent. Dark blocks and numerous small fumaroles covered R.F. crater floor. Fumarole temperatures decreased in the Donald Mound/Noisy Nellie area. Deformation studies suggested that the pattern of continuous subsidence that began in February has ended.

Information Contacts: I. Nairn, NZGS Rotorua; J. Cole, Univ of Canterbury, Christchurch.

October 1989 (SEAN 14:10) Cite this Report

Tephra ejections; possible new vent

Phreatic block and ash ejections have continued since ... fieldwork on 31 July (SEAN 14:07). Small explosion-type earthquakes recorded 20 and 29 August, and periods of high-amplitude tremor in early-mid-September probably marked ejections of new lithic blocks, lapilli, and ash found on the crater floor in October. On 11 September, the crew of a fishing boat reported two dark mushroom clouds rising 500 m above the summit. This eruption coincided with low-amplitude tremor, but no discrete earthquakes were recorded.

When geologists visited the crater 11 October, new, gray, fine ash covered the main crater floor. Since 31 July, 280 mm of new tephra had accumulated on 1978 Crater rim, and 115 mm at a site roughly 200 m to the SE. No fresh magma was detected. Impact crater shapes suggested that blocks ejected to ~150 m E and SE of 1978 Crater had originated from a new vent within Congress Crater. This crater, previously funnel-shaped with walls dipping steeply into Hitchhiker vent, had deepened since July and had a flat floor. Gullies deepened to the E (away from Hitchhiker), suggesting that a new vent was obscured from view beneath the E crater wall.

Donald Duck crater was slightly enlarged and emitted clouds of light yellow gas, the first seen at White Island. The crater rim was lightly dusted with fine (<0.5 mm) bubble walls and spherules of yellow sulfur. Ash from the vent had largely buried the June 1989 block field as far as 100 m SE. R.F. Crater appeared unchanged since 31 July, with a near-flat floor and black, fountaining, muddy water, briefly visible through vapor clouds.

Background seismicity was steady in August with as many as 7 A-type and 16 B-type events/day. On 2 September a sequence of >100 high-frequency events (M < 3.5) were located ~13 km W of White Island at l-2 km depth. Medium-frequency tremor was recorded throughout September. By late September, seismicity had decreased to <3 A- or B-type events/day, and continued at a low level throughout October.

Deflation of the Donald Mound-1978 Crater area, almost continuous since mid-1987, has apparently resumed after a possible brief pause in July. Fumarole temperatures and gas emission had generally decreased, with only one fumarole (Noisy Nellie) showing high-pressure discharge of clear dry gas.

Information Contacts: I. Nairn, P. Otway, and B. Scott, NZGS Rotorua.

December 1989 (SEAN 14:12) Cite this Report

Mild explosions; new crater enlarged

Only mild eruptive activity has occurred since 11 October fieldwork revealed a possible new vent in Congress Crater. During a 4 November overflight, pilot R. Fleming witnessed ejection of tephra above 1978 Crater rim, and Bruce Christenson observed new blocks there on 9 November. No new tephra were found on the main crater floor during 12 and 18 November visits, but the new vent, named Corporate Crater, was clearly visible for the first time.

During 29 November fieldwork, geologists observed small amounts of new ash on the main crater floor, and 35 mm of new fine ash on 1978 Crater rim. Ash-covered lithic blocks (up to 0.2 m) had been ejected to 50 m from the E crater rim. Block distribution indicated a source in Corporate Crater (figure 12), now a deep vertical-walled pit that has grown to occupy the E half of Congress Crater. The remnant of Congress Crater's flat floor had been built up by ejecta and talus that infilled previously active Hitchhiker Vent. Scoriaceous bombs were found in the S part of the clast field, suggesting a source from R.F. Crater, which appeared unchanged since 11 October.

Figure 12. Sketch map showing recently active features at White Island, late 1989. Courtesy NZGS.

Most gas emissions originated from R.F. Crater, with a small amount of steam rising from Corporate Crater. Donald Duck vent emitted voluminous white clouds from active crater floor vents that had migrated NW. Noisy Nellie vent discharged a large volume of high-pressure clear gas.

Medium-frequency (3-4 Hz) volcanic tremor and rare small A-type events were recorded 11-14 October. Small A-types were the only clear events recorded 14 October- 21 November. Since 21 November, fewer than 5 small A- and/or B-type events/day have been recorded.

The 29 November deformation survey showed minor but uniform uplift of most of the main crater, reversing the strong subsidence (centered over Donald Mound) in the 10 weeks prior to 11 October. The inflation was interpreted as evidence of renewed heating at depth beneath Donald Mound, possibly the precursor of future increased activity from 1978 Crater. Magnetic data generally showed only small changes, suggesting modest shallow cooling that may have been associated with heavy recent rainfall.

Information Contacts: I. Nairn, NZGS Rotorua.

March 1990 (BGVN 15:03) Cite this Report

Minor ash emission; seismicity and thermal activity decline; deflation

Little eruptive activity has occurred since 29 November fieldwork revealed a new vent and fresh tephra on the main crater floor. Seismic activity has been at low levels, fumarole temperatures have decreased, and deflation on the main crater floor (centered in the Donald Duck area) suggests that heatflow has been redirected from Noisy Nellie fumarole westward to 1978 Crater. R. Fleming reported a small eruption of lithic accessory ejecta from Noisy Nellie in late January 1990, and further collapse of Corporate and Congress Craters.

Geologists from the RV Vulkanolog visited White Island 2-3 March. Only blue "flames" associated with fumarolic discharge were seen over fumaroles E of 1978 Crater (Donald Mound, Blue Duck, and Noisy Nellie) during the night of 2 March. The three most vigorous vents along a small cone on R.F. crater's floor glowed pale red (500-550°C) and a small eruptive episode on 3 March added pebble-sized material to the cone. A shallow green pond that occupied the rest of the crater floor was surrounded by yellow to orange precipitates.

On 6 March geologists found only 4 mm of fine green ash that had fallen since 29 November at a site 35 m E of 1978 Crater. No new ash was found on the 1978 Crater rim or to the SE (S of Donald Mound). Donald Duck emitted white gas/steam clouds, and low-pressure gas emerged from Noisy Nellie. Accessory blocks and smaller ejecta, first seen about a month earlier, extended 30 m SE from Noisy Nellie. Emissions from 1978 Crater obscured R.F. and Corporate craters, but small detonations from R.F. Crater were frequently heard.

Only ~10 small B-type events/day and an average of ~3 A-types/day were recorded in December, with small E-types recorded on the 7th and 21st. About 3-6 B-type events/day plus rare A-types were recorded during January and February, with tremor nearly absent.

A March deformation survey showed strong subsidence of the Donald Mound area following a period of brief uplift measured 29 November. Subsidence since then was centered E of 1978 Crater (between Noisy Nellie and Donald Mound), reaching 30 mm near Donald Duck vent, with a trough extending NW along the line of fumaroles. Noisy Nellie, near the apparent center of the 15+ mm uplift prior to 29 November, lies on the edge of this trough. The recent subsidence of 9 mm/month is similar to the rate observed since mid-1987.

Information Contacts: I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS Rotorua; W. Giggenbach, DSIR Chemistry, Petone.

March 1990 (BGVN 15:03) Cite this Report

Strong submarine hydrothermal activity at the Calypso Vents

The following observations, made by scientists from the USSR and New Zealand during a cruise of the RV Vulkanolog, are reported by W.F. Giggenbach and I. Menyailov.

"Calypso Mound is a white anhydrite cone some 6-8 m high, formed at 167 m depth by discharge of thermal waters at the ocean floor. It was discovered in February 1987 using the diving vessel Soucoup carried on the RV Calypso (Sarano and others, 1989). It lies within one of the 'bubble zones' extending in a line from White Island to Whale Island in the Bay of Plenty (Duncan and Pantin, 1969) [around 37.64°S, 177.10°E].

"The echograms indicated strong hydrothermal activity with a number of vents producing bubble curtains. However, an extended visual search under calm conditions from both the RV Vulkanolog and a rubber dinghy detected no bubbles at the surface. A possible explanation is re-dissolution of the gas in seawater. Similar gases, collected from more shallow submarine springs in the Bay of Plenty, S of Whale Island, and from Whale Island itself (see below), consisted predominantly of CO₂, which has a comparatively high solubility in water. Re-dissolution is also supported by the distribution of reflections recorded during a slow pass over the area. Most of the individual bubble swarms, now clearly separated, appeared to terminate at ~20 m depth.

"Close inspection of a video recording shows that the fluid discharged from two vents on Calypso Mound is very likely to contain a considerable free vapor phase, indicated by flame-like tongues of free vapor, rapidly quenched on contact with cold seawater. Water leaving the vapor-seawater interaction zone appeared clear and colorless except for schlieren indicating a density difference from seawater.

"The existence of free vapor at 167 m depth and about 18 bars pressure suggests that the temperature of the fluid discharged from Calypso Mound is close to 207°C. The high proportion of vapor, apparently present in the fluid mixture leaving the vents, would indicate high corresponding enthalpies of the fluid feeding Calypso Mound. The temperature of any initial single phase liquid, before flashing and possibly present at greater depth, may therefore be considerably higher. However, Sarano et al. (1989) consider it unlikely that the waters emitted from Calypso Mound were as hot as 160°C. The 'hydrothermal' nature indicated for the Calypso Mound system may also explain the enrichment in typically 'epithermal' elements such as As, Sb, Hg, and Tl, and the absence of a 'volcanic' trace metal signature (Giggenbach and Glasby, 1977) in clays recovered from near the main cone."

References. Duncan, A.R., and Pantin, H.M., 1969, Evidence for submarine geothermal activity in the Bay of Plenty: New Zealand Journal of Marine and Freshwater Research, v. 3, p. 602-606.

Giggenbach, W.F., and Glasby, G.P., 1977, The influence of thermal activity on the trace metal distribution in marine sediments around White Island, New Zealand: New Zealand Department of Scientific and Industrial Research Bulletin, v. 218, p. 121-126.

Sarano, F., Murphy, R.C., Houghton, B.F., and Hedenquist, J.W., 1989, Preliminary observations of submarine geothermal activity in the vicinity of White Island, Taupo Volcanic Zone, New Zealand: Journal of the Royal Society of New Zealand, v. 19, p. 449-459.

Information Contacts: I. Menyailov and A. Ivanenko, IV, Petropavlovsk; W. Giggenbach, DSIR Chemistry, Petone.

May 1990 (BGVN 15:05) Cite this Report

Ash emission from new vent; deflation reverses

Brown ash clouds rose from a new pit vent on the E side of R.F. Crater (near the SE wall of 1978 Crater) during 17 May fieldwork by geologists from NZGS and the Univ of Canterbury. The new pit appeared to be at the same location as three intense gas vents seen on 3 March (BGVN 15:03). Pulses of activity were observed at 1029, 1048, and 1436, and occasional light ashfalls occurred on the rim of 1978 Crater. Several detonations were heard, the strongest at 1041, but were not correlated with periods of visible tephra fall. Fumarole temperatures were similar to those observed during early March fieldwork, with a maximum measured value of 459°C.

Three new tephra layers had been deposited since early March. New material was 130 mm thick at one site on the 1978 Crater rim, consisting of two medium green, very fine to fine ash layers Separated by 8-10 mm of brick red, very fine ash. The deposits thinned rapidly with distance from the crater; only the two younger layers, totaling 14 mm, were found at a survey marker (peg XII) 180 m from the rim.

Deformation data showed a reversal of the general deflation, centered E of 1978 Crater, that was measured in March. Inflation had occurred since 6 March in the 1978 Crater area (in the vicinity of R.F. and Corporate Craters) although minor deflation persisted near the earlier deflation center. Magnetic data suggested a shallow cooling (up to 200 m deep) centered near the zone of persistent deflation, superimposed on widespread and possibly deep-seated heating that was strongest below the SW corner of the crater floor.

Information Contacts: J. Cole,Univ of Canterbury, Christchurch.

August 1990 (BGVN 15:08) Cite this Report

Block eruption; significant morphologic changes in 1978 Crater

Late-August fieldwork revealed significant morphologic changes to 1978 Crater, which had deepened and extended 30-50 m E since May. A narrow zone of newly erupted lithic blocks extended several hundred meters from a vent E of the 1978 Crater complex.

During a 29 May visit, Ashley Cody found no significant changes since 17 May fieldwork (BGVN 15:05). Fresh impact craters had apparently been formed by small blocks erupted from the new pit vent observed 17 May on the E side of R.F. Crater. Ash and "gravel" was reported falling on fishing boats anchored on the N side of White Island 29-30 June.

When geologists returned on 30 August, blocks had fallen in a zone ~100 m wide extending several hundred meters SE from Donald Duck vent (E of 1978 Crater). In the tephra-fall zone within 150 m of the vent, the ground was almost completely covered by blocks up to 1 m across. Farther from the vent, blocks to 0.3 m occupied scattered impact craters with the most distant blocks ~450 m away. A gray ash deposit thickened toward Donald Duck, from 20 mm roughly 100 m SW of the vent, to 330 mm at a site 5 m from the rim. No fresh magma was noted in any of the ejecta. Donald Duck vent had deepened and enlarged to a pipe 2-3 m in diameter extending down to the NW at a shallow angle to the horizontal. Moderate amounts of non-incandescent gas were being emitted from the vent. To the N, gas emission from Noisy Nellie was the strongest it had been in several years, causing ground vibration nearby. The vent had slightly enlarged and deepened, and had deposited a continuous coarse tephra cover that extended 30 m S. A minimum temperature of 370°C was measured (by Minolta-Land infrared sensor) during a 1 September visit, compared to 459° on 17 May. Activity at other fumaroles was at low intensity.

The 1978 Crater complex had deepened and enlarged considerably since May. No eruptive activity appeared to have accompanied the collapse episode and it was not associated with any unusual seismicity, suggesting that it was triggered by recent heavy rainfall. On 30 August, the crater's E wall was 30-50 m E of its 17 May position, and ground cracking extended ~10 m farther E from the nearly vertical crater wall, suggesting that further collapse was likely. Within the crater, the dividing wall between R.F. and Congress Craters had been removed. R.F. Crater was the deepest part of the complex, and was occupied by a green lake with a few small steaming areas around its edges. Material that had collapsed from 1978 Crater's E wall formed a landslide deposit across its E floor. A deformation survey revealed subsidence centered on Donald Mound (S of Donald Duck vent) exceeding 20 mm since 17 May, reversing two months of inflation. However, one site just S of Donald Duck vent showed a 289 mm decrease, suggesting incipient ground failure.

Seismic instruments resumed operation 20 May, recording 5-13 A-type (high-frequency) events daily until the onset of a swarm on 14 June. During the next two days, >120 A-type shocks were detected, reaching about ML 2.7. The swarm ended with an E-type eruption earthquake that had an unusually low dominant frequency and lasted ~45 minutes. Additional E-type episodes with durations of 28-35 minutes followed, again with lower-than-usual dominant frequencies. A-type events declined until 25 July, then increased again to ~10/day. Another swarm of >80 shocks (maximum ML 2.1) occurred 28 July, then A-type events declined to ~5/day. B-type (low-frequency) volcanic earthquakes were recorded on most days after 20 May, initially exceeding 20/day but soon declining to < 5/day. After the 14-16 June swarm, the number of B-type events increased sharply for two days, then dropped to 5-10/day, remaining at that level through August. Other E-type (eruption) earthquake sequences occurred at the end of May, with four of similar size, 6-15-minute durations, and lower-than-usual dominant frequencies shortly after seismic recording resumed. An isolated 7-minute E-type event on 13 July was of distinctly higher dominant frequency. Five E-type episodes have occurred since 13 August, most recently on the 24th, all with high-frequency codas but short (2-14-minute) durations. No tremor has been recorded.

Information Contacts: I. Nairn and B. Scott, NZGS Rotorua; P. Otway, DSIR, Wairakei.

September 1990 (BGVN 15:09) Cite this Report

Ash and block eruption; new crater formed; no juvenile material

An ash- and block-ejecting eruption occurred within the 1978/90 Crater Complex on 2 October, forming a new crater ~50 m in diameter at a site where high heat flow had been measured on 30 August. The eruption was well-recorded seismically and observed from fishing boats, commercial airliners, and coastal towns. The eruption column rose ~2,000 m above the crater, and was capped by an expanded cloud to >3,000 m.

Pre-eruption seismicity. Since early September the level of seismicity at White Island has been relatively low. Small A-type (high-frequency) volcanic earthquakes have been recorded most days but usually numbered <4/day. The number of B-type (low-frequency) volcanic earthquakes has declined, with only 2-3 events being recorded some days. E-type events were recorded on 10, 11, 13, 14, and 15 September, but no reports of associated eruptions have been received.

Eruptive episode. On 2 October, two seismic events were recorded. The first, at 1133, had an emergent high-frequency onset (3-5 Hz) lasting ~40 seconds. The dominant frequency then declined to 1-3 Hz, continuing for the next 10 minutes. No eruption accompanied this seismicity. The second event started at 1209, with an envelope of quite pure low-frequency tremor lasting for 20 seconds followed by another smaller sequence at 1210. The tail of this event led straight into a high-frequency signal that gradually increased in amplitude over the next 40 seconds (maximum 20 mm). The intense high-frequency signal lasted 5 minutes and was similar to past seismicity accompanying ash columns, as on 7 September 1987 (SEAN 12:09). During the high-frequency seismicity, the first reports of an eruption column were received from Whakatane, 50 km SSW (Brian Spake, Harbour Master); its first appearance was timed at between 1208 and 1209. Over the next 15 minutes the seismic signal gradually declined to background levels. Neither of the long-duration seismic events of 2 October are typical E-type events as described by Latter et al. (1989).

Crater observations. During fieldwork the day of the eruption, geologists observed a new crater some 50 m in diameter in the NE portion of 1978/90 Crater, merging with its sheer E wall. The new crater edge was scalloped and appeared to have a near-vertical inner wall of 10-20 m or more at the W side, the only part not obscured by steam. Much ejecta was thrown out during the crater-forming eruption, but its morphology suggests that significant collapse contributed to its present size. On 30 August, the new crater area had been a debris slope with intense fumarolic emission. Best views of the vent were obtained on 3 October, when it was quietly emitting voluminous clouds of ash-free white steam, tinged with yellow (possibly condensed sulfur vapor). The new vent was named TV1 Crater.

A continuous apron of ejecta extended ~30 m back from the lip of 1978/90 Crater directly above TV1 Crater. The ejecta, up to ~20 cm thick, was comprised of old rocks, gravel, and sand. Individual ballistic blocks fell far beyond the continuous ejecta apron to roughly 200 m away, where rocks up to 0.3 m across were embedded in impact craters 5 m or so apart. The blocks had fallen on near-vertical trajectories. At 1635 on 2 October, the largest blocks in the ejecta apron were still too hot to touch. There was no sign of any new coarse ejecta from Donald Mound. A sample of coarse gravel and sand collected 2 m from 1978/90 Crater rim was largely altered lava, breccia, and tuff, with a small amount of weakly consolidated bedded tuff. No fresh material was seen in this sample, and no new scoria bombs were seen anywhere in the ejecta apron.

The lake previously in the SE part of 1978/90 Crater had disappeared, and appeared to have been infilled by detritus. Another new vent, ~5 m in diameter, was visible under the SW wall of 1978/90 Crater (roughly opposite TV1 Crater). It was surrounded by a small, raised apron of ejecta, and was emitting low-pressure steam on 3 October.

Geologists noted that the E-type events on 10-15 September may have been associated with the formation of a vent, which has now developed into TV1 Crater, but there were no direct observations during that time. Seismic evidence suggests that it was largely or completely formed during the 2 October eruption.

Reference. Latter, J.H., Scott, B.J., and Dibble, R.R., 1989, Seismic activity associated with the 1976-82 eruption sequence at White Island volcano: New Zealand Geological Survey Bulletin, no. 103.

Information Contacts: B. Scott and C. Wood, NZGS Rotorua.

October 1990 (BGVN 15:10) Cite this Report

Strong thermal activity but no new eruptions

During a brief 17 October visit to the rim of 1978/90 Crater complex, white steam emissions were relatively voluminous. A lake had been re-established in the SE portion (R.F. Crater). The vent observed 3 October under the SW wall was apparently still present, although viewing conditions were poor. The margins of TV1 Crater appeared unchanged, and it was emitting white steam at low pressure. Strong, audible fumaroles were present in the area NW of the 20-m-high non-extrusive rock spine (first seen on 30 August and located 15 m W of TV1 Crater), where transparent vapors emerged from the crater floor, condensing to white steam above. East of 1978/90 Crater, Donald Duck vent was emitting wispy white vapor and its floor and vent area were clearly visible.

There was no evidence for further eruptive activity since 3 October from within 1978/90 Crater, TV1 Crater, or Donald Duck Crater.

Information Contacts: B. Scott, DSIR, Rotorua; S. Sherburn, DSIR, Wairakei.

December 1990 (BGVN 15:12) Cite this Report

Fumarolic activity; no tephra since 2 October

Fieldwork 28-29 November revealed no new ejecta that appeared to have been erupted from 1978/90 or Donald Duck craters since the 2 October ash emission. The 1978/90 crater rim had retreated since last precisely recorded on 30 August, and just intersected Donald Mound Crater. The collapse of 1978/90 crater rim had occurred over its entire length. Blocks ejected from both TV1 and Donald Duck craters had no ash cover. In 1978/90 Crater, a large green pond had been re-established in the R.F. Crater area, where only mild fumarolic activity was occurring. Strong fumarolic emission occured from the N wall of 1978/90 crater. Brecciated lava was exposed by the collapse of the E wall (above TV1 Crater) suggesting that Donald Mound is formed by a large lava body. Samples of this lava were collected for petrographic and geochemical study.

A levelling survey indicated >30 mm of deflation since 30 August. The 2 October ash emission appeared to have had little effect on deformation trends.

Recorded seismicity has been relatively low since the 2 October eruption. High- and low-frequency earthquakes (A- and B-types) rarely exceeded 2-3/day and all were very small. Two E-type (eruption) events were recorded (6 and 11 November), and a M 4.2 earthquake and six aftershocks, centered 20 km NNE of White Island, were recorded 24 November. Only two earthquakes were known to have been recorded by the portable seismographs operated during the 28-29 November fieldwork.

Information Contacts: J. Cole, Univ of Canterbury,Christchurch; I. Nairn and B. Scott, DSIR Geology & Geophysics, Rotorua; P. Otway and S. Sherburn, DSIR Geology & Geophysics, Wairakei.

February 1991 (BGVN 16:02) Cite this Report

Block/ash ejection from October vent

The first significant eruption on White Island since TV1 vent formed on 2 October took place on 8 February at about 2000. The tephra ejection episode was in the NE part of 1978/91 Crater and was associated with a 14-minute seismic signal that began at 2003 (table 8). Helicopter overflights by Robert Fleming had revealed no unusual activity on 4 February, but TV1 crater was emitting ash on the 6th. The 8 February eruption deposited a semi-continuous layer of blocks, generally 0.3-0.5 m across with some to 1 m, on the main crater floor within ~50 m of the 1978/91 Crater rim, and 5-20 mm of fine ash was spread over the E end of the island. Many blocks were almost ash-free, indicating that they had been ejected late in the episode. Blocks were more common in small gullies, where impact craters were rare, suggesting to geologists that they had been emplaced by lateral flow processes. No new scoria bombs were found, but many blocks showed evidence of high-temperature vapor-phase alteration and recrystallization, including cavities lined with specular hematite crystals. The top of the ash layer was an anhydrite-rich crust ~1 mm thick, suggesting that the ash was hot (>56°C) when deposited. The ash also included scattered 1-4 mm accretionary lapilli. Several meters of ash had ponded on the floor of R.F. Crater, and longitudinal dunes were evident on the surface of the ash deposit, again suggesting emplacement by a flow process. New impact craters, probably made by the 8 February activity, were visible high on the S wall of the main crater. Wooden pegs near the crater were burned by blocks and charred by gas and ash on the side facing the vent.

Table 8. E-type seismicity recorded at White Island, January-February 1991.

Fumarole temperatures were little changed since December. Deformation was concentrated NE of 1978/91 crater, where a maximum of 20 mm deflation had occurred since November and 50 mm since August.

Seismicity was characterized by 0-5 A-type and 0-3 B-type events/day after data collection resumed on 27 December. On 1 January, 31 A-type shocks (to ML 3.1) were recorded and up to ten B-type shocks/day occurred 26-28 January. Five episodes of E-type seismicity were detected, including the eruption event of 8 February (table 8). Weak, low-frequency tremor followed the 14-minute E-type episode on 4 February, which lacked an associated high-frequency cigar-shaped eruption signal. Tremor was strongest (but still only 1-2 mm peak-to-peak) on 6-7 February.

Information Contacts: I. Nairn, DSIR Geology & Geophysics, Rotorua.

March 1991 (BGVN 16:03) Cite this Report

Ash emission from new vent

Light ashfall was reported at 2000 on 20 March by the crew of a fishing boat on the S side of the island, and continued as of 22 March. Visits to the volcano on 21 and 22 March revealed that the emission originated from a new vent (Orca) in a gully on the W side of the 1978/91 Crater. When first noted 13 February, the 20-25-m-wide vent had been the site of high heat flow and strong emission of white vapor. The March ash was not pumiceous or highly vesiculated, but it was rich in fresh glass in comparison with February tephra from TV1 Crater. Geologists suggested that the relatively fresh glass and the westward progression of activity was possibly due to new magma near the surface in the area of the new vent. Activity at TV1 Crater and the fumarole area NW of TV1 (on the floor of 1978/91 Crater) had declined to weak vapor emission on 22 March.

Seismic records were limited to 7-14 March by equipment difficulties. One small E-type event was recorded on 11 March, but no tremor was detected. Post-21 March seismograms (after equipment repair) indicated no change in the level of seismicity.

Information Contacts: B. Scott, DSIR Geology & Geophysics, Rotorua.

April 1991 (BGVN 16:04) Cite this Report

Renewed ash emission; new collapse pit

There was no evidence, during fieldwork 21 April, of eruptive activity since the 20-22 March eruption that formed Orca vent and was probably responsible for up to 10 mm of ash deposited on the 1978/91 Crater rim since 13 February. An increase in gas emission (compared to visits during February and March) was noted at Orca vent and TV1 Crater. . . . Intense gas emission also occurred from an area of hot ground NW of TV1.

Several morphologic changes were observed in the crater area. A second, smaller vent (~5 m in diameter) was found on the slope NW of Orca vent. A new collapse pit, ~20 m in diameter and 50 m deep, was located above the conduit that had previously fed Donald Duck Crater. The new pit, a few meters NW of the crater, looked fresh, suggesting that it had formed shortly before the 21 April visit.

Ash-laden steam emission reportedly began 23 April and was continuing as of 3 May. No significant volcanic tremor or other seismicity was recorded during this period.

Information Contacts: I. Nairn and B. Scott, DSIR Geology & Geophysics, Rotorua.

May 1991 (BGVN 16:05) Cite this Report

Ash emission from new vent; continued deformation

Ash-laden steam emission was reported starting 23 April and continued as of 27 May. An 18 May visit revealed that activity was centered at a newly formed vent in the NE part of 1978/91 Crater (figure 13), near a zone of hot ground first observed on 21 April. Considerable ash accumulation had already occurred in the surrounding area.

Figure 13. Sketch map of White Island on 27 May 1991, showing the new May 91 Vent. Dots mark deformation bench marks. Contour interval, 40 m. Courtesy of DSIR.

During 27May fieldwork, the new vent (named May 91) almost continuously (>=1 pulse/second) emitted a column of gas and minor ash 500-600 m high, depositing dry material, plus some moist sub-millimeter aggregates. The vent, against the NE crater wall, was surrounded by a tuff cone 35-40 m in diameter and 8-10 m high, but no ballistic ejecta were visible. Orca and TV1 Craters quietly emitted weak steam.

Up to 95 mm of ash had accumulated since 21 May at a site 125 m SSE of May 91 vent, of which at least 25 mm was from the new vent. Tephra had infilled the small lake in the vicinity of R.F. Vent (near the SE wall of 1978/90 Crater), and small mudflows traveled across the crater floor. Ash contained a high proportion of fresh material, but lacked vesiculated clasts.

Little change was observed at the 40-45-m-deep collapse pit NW of formerly active Donald Duck Crater. Two passages (20-30 m wide) led from the pit; one connected to Donald Duck Crater (to the SE), and the other headed at least 50-60 m N towards Noisy Nellie. The SE passage contained large sulfur stalactites and stalagmites.

Deformation measurements on 27 May showed that subsidence centered at Donald Mound and Noisy Nellie continued, but at lower rates than the last measurements on 13 February. Minor uplift was measured ~200 m S of Donald Mound.

Seismicity (typically small A- and B-type earthquakes) remained at low levels since 21 April, with periods of 2-3 days without recorded events. One uncharacteristically large E-type event, similar to an event preceding the formation of TV1 Crater (BGVN 15:09) was recorded at 0538 on 23 May. Weak low-frequency tremor has been recorded since 10 May.

Information Contacts: B. Scott and B. Houghton, DSIR Geology & Geophysics, Rotorua; J. Cole, Univ of Canterbury, Christchurch.

August 1991 (BGVN 16:08) Cite this Report

Tephra emission; shock waves in crater

Emission of gas/tephra columns from May 91 vent continued through August. During early-August helicopter overflights, R. Fleming noted flashes and strong low-frequency detonations as a hot, dilute eruption column rose from the vent. Crumbly white lithic blocks and lapilli with rare juvenile scoriae had been deposited nearby. Larger-than-normal plumes were often visible from the North Island coast, roughly 50 km away.

During fieldwork 28-29 August, a convoluting pink-brown column was emitted from May 91 vent. It contained very little ash and no evident incandescent material. Visible shock waves emerged from the vent every few seconds as "flashing arcs," lighting clouds above with a flickering glow like that from a poorly-functioning fluorescent tube. The strongest shock waves were manifested as an instantaneous displacement of the plume at the vent, and could be felt 150 m away. Some could be seen to bounce off the crater walls and travel back through the clouds. The shock waves did not seem to affect the rate of plume emission. The activity was accompanied by dull booming and sloshing noises, and occasional sharp detonations. The sloshing sounds were much like those heard in 1988 at Yasur (Vanuatu), where large gas bubbles were bursting through the surface of an active lava lake. Geologists noted that the activity at May 91 vent was consistent with similar gas-bubble discharge through a liquid magma column.

About 200 mm of coarse and fine ash had been deposited just N of May 91 vent since the previous fieldwork on 27 May. Little new ash was evident elsewhere on the main crater floor, but small (< 0.3 m) lithic blocks and their impact craters were found >200 m SE of the vent and to its W. Scarce, widely scattered scoria bombs, most 0.1-0.2 m across but some reaching 0.3 m, were found on top of the May ash, with only a light ash coating. The bombs seemed most abundant a few hundred meters SE-NE of the vent. They had highly vesiculated interiors of black glass with large pyroxene and plagioclase phenocrysts. Internal vesicles were up to 30 mm across, but decreased rapidly to sub-millimeter size toward the surface.

The pattern of deformation between late May and late August was similar to that of the previous 3 months. Strong subsidence at roughly double the previous rate continued to be centered SE of May 91 vent, while relative inflation persisted ~200 m farther SE. A new zone of inflation was measured E of Noisy Nellie fumarole (NE of May 91 vent). Minor deformation associated with activity at May 91 vent is unlikely to be detected, as the nearest part of the levelling network is 100 m away. Most fumarole temperatures had changed little since May, although values at Noisy Nellie had increased from 240 to 411°C.

The volcano had remained seismically quiet until mid-June, when B-type events became more common, continuing at rates of 2-7/day through the end of the month. Very weak volcanic tremor was sometimes visible on seismic records. A sequence of >45 tectonic earthquakes (to ML 3.7) occurred near White Island 1-2 July. A- and B-type events increased markedly on 7 July, accompanied by a small increase in background volcanic tremor amplitude. E-type eruption earthquakes were recorded on 1, 7, and 11 July. Seismicity had declined by 15 July, but a 3-day swarm of >200 A-type events began on 20 July. Significant volcanic tremor also resumed and continued through mid-August, increasing again 21-28 August. Tremor varied from a nearly pure 1.8 Hz signal to a complex pattern with spectral peaks to 8 Hz. A-type events did not occur daily in August, but often numbered 8-10/day. B-type events were very rare after 24 July. E-type eruption shocks were recorded on 14, 15, 19, 20, 23, 27, 29, and 30 August.

Information Contacts: B. Houghton, I. Nairn, and B. Scott, DSIR Geology & Geophysics, Rotorua.

September 1991 (BGVN 16:09) Cite this Report

Continued explosions from May vent

Several explosions have been documented from May 91 vent since the 28-29 August fieldwork. The first occurred on 29 August at 2132, shortly after geologists left the island. A second, observed by R. Fleming on 5 September at 1149, produced a 2-km eruption column. Blocks larger than 1 m across fell 250 m SE of the vent and floating scoriae washed onto the shore at Crater Bay, roughly 800 m SE. A large eruption column that rose to 4-5 km altitude on 16 September at 1630, accompanied by intermittent block ejection, was observed from a nearby boat and from ~50 km away on the North Island coast (at Whakatane). Emission of ash continued overnight, with ash falling on a boat off the SE tip of the island, but tephra emission declined the next morning. Another eruptive episode was reported on 18 September at 1625, lasting 5-6 minutes and feeding a 2-km column.

When geologists returned to the island on 9 October, lithic blocks occupied scattered impact craters in a zone extending roughly 400-750 m SE from May 91 vent. Closer to the vent, blocks and craters became more common and fragments of slaggy scoria began to appear. Most of the scoriae were highly vesicular, but bombs of denser scoria, characterized by a smaller range of vesicle sizes (most <5 mm), were also found. Bombs reached 0.8 m in size and the largest observed lithic block was 1.3 m across. Most of the ballistic ejecta appeared to have fallen on the S side of the main crater floor, where it seemed to be directed by the vent configuration. Between 5 and 10 mm of fine gray ash was found at sites roughly 250 and 400 m SE of the vent, thickening toward the rim of the 1978/91 Crater complex.

Activity at May 91 vent on 9 October was similar to but less intense than that observed in late August, with emission of pink fume accompanied by loud roaring and occasional sharp detonations. The noises suggested that the top of the magma column was deeper in the conduit than at the end of August. Shock waves were visible about once a minute, less often than in late August, although conditions were less suitable for their observation. Low-pressure white gas emission from TV1 vent, roughly 50 m SE of May 91 vent, was similar to that of August, although its N wall had apparently migrated outwards 10-20 m by collapse. Voluminous gas emission continued from Noisy Nellie fumarole, on the main crater floor NE of the 1978/91 Crater complex.

Information Contacts: I. Nairn and B. Scott, DSIR Geology & Geophysics, Rotorua.

October 1991 (BGVN 16:10) Cite this Report

Tephra from new vent

A new active crater formed in the S part of the 1978/91 Crater complex between visits by geologists on 9 and 23 October. The crater (named Wade; figure 14) had developed at the site of the former R.F. Crater, active January 1989-mid 1990. The onset of activity at the new crater was not documented, but may have been marked by E-type seismic events recorded on 18 October. The captain of the Island Princess reported that red ash had been falling for at least four days before 23 October.

Figure 14. Map of White Island's Main Crater, showing the new (Wade) crater. The position of the 1978/91 Crater rim is as of 28 November 1990. Dots labeled with Roman numerals are levelling sites; only some are shown. Courtesy of B. Scott.

As geologists approached the island on 23 October, activity was initially limited to moderate steam emission. At about 1120, an eruptive episode sent a red-brown steam/ash column to ~1 km above sea level. Long trains of low- to medium-frequency, low-amplitude earthquakes were recorded between 1115 and 1127, with a burst of stronger, higher frequency tremor at about 1118. During field studies between about 1230 and 1500, quiet emission of reddish ash-rich gas continued from the new circular crater, roughly 30-50 m in diameter and at least 30 m deep. Recently fallen red-brown ash was visible on all of the outer slopes of White Island. About 4 cm of ash had fallen at a site roughly 200 m SE of the new crater, thickening to 14 cm on the S rim of 1978/91 Crater. No significant juvenile component was evident in the ash.

A small amount of recently fallen ballistic tephra, including andesitic scoriae that are probably juvenile and accessory blocks, was found within 20 m of the SE rim of 1978/91 Crater. The orientation of ash thrown from the impact craters suggested an origin for the ballistic clasts in the direction of TV1 crater (roughly 100 m NE of the new crater), perhaps during the late-morning eruptive episode. TV1 may also have been the source of a layer of lithic gravel within a gray ash matrix, deposited to its E between layers of reddish ash. TV1 emitted only white steam until about 1315, when it began to erupt voluminous clouds of gray-brown ash. Ash emission was continuous for at least the next 30 minutes, and the color of the ash was noticeably different from that emerging from the simultaneously erupting new crater. TV1 had formed on 2 October 1990 and erupted again in February 1991, but had been relatively quiet since then. Little gas emerged from May 91 crater during the 23 October fieldwork, although it was the site of vigorous gas emission during the previous visit on 9 October.

Information Contacts: C. Wood, DSIR Geology & Geophysics, Rotorua.

November 1991 (BGVN 16:11) Cite this Report

Tephra emission continues from new crater

An explosive episode on 24 November at 1400 ejected a tephra column and produced an E-type seismic event detected by a nearby seismometer. The tephra column was seen from the mainland by helicopter pilot R. Fleming, who estimated that it rose to 2,000 m.

Fieldwork on 28 November revealed fresh andesitic scoria bombs scattered over a wide area from 250 m NE to 500 m ESE of its probable source, the new crater (Wade) that had formed in mid-October (BGVN 16:10). Bombs ranged to 50 cm across and most were irregularly shaped. As much as 2 cm of gray ash covered the brick-red ash erupted by the new crater in late October and early November. During the 2-hour visit, emission of gas and fine, gray-brown ash from Wade crater was essentially continuous, accompanied by constant loud rumbling and occasional clattering noises that were probably caused by rocks striking the vent walls. The new crater was much larger than when first seen on 23 October, forming an oval to sub-rectangular slot extending across the floor of the 1978/91 Crater complex. TV1 crater, roughly 100 m NE of Wade, weakly emitted vapor and fine gray ash. May 91 crater appeared quiet.

Information Contacts: C. Wood, DSIR Geology & Geophysics, Rotorua.

December 1991 (BGVN 16:12) Cite this Report

Bombs and gas from deep October vent; occasional stronger explosions; deflation

During 5-6 December fieldwork, the new crater (Wade; figure 15) formed in mid-October continuously emitted a large white ash-poor gas plume. Booming and roaring noises were continuous, with some louder explosions that had only an occasional, delayed correlation with pulses of increased plume emission. Bombs (>1 m long) were ejected in near-vertical trajectories but rarely reached above the crater rim. Some of the few that landed on the rim were visibly incandescent on 6 December.

Figure 15. Sketch map of White Island's 1978/91 crater complex and adjacent parts of the main crater floor, showing positions of vents as of 6 December 1991. Courtesy of DSIR.

The observations suggested to DSIR geologists that Wade Crater's conduit was relatively straight, extending down to the top of the magma body beneath White Island, perhaps at 300-400 m below sea level. Although most of the bombs produced by the resulting Strombolian activity did not escape the deep cylindrical conduit, occasional larger eruptions had scattered bombs (to 0.5 m across) over the main crater floor to 500 m from the vent. Comparison of 5-6 December photos with those taken 28 November revealed many new bombs, but all were ash-coated and did not appear to have been erupted in the last few days. A few altered lithic blocks (to 0.3 m across) occupied fresh impact craters > 200 m SE of the vent. The blocks were not coated with ash and were probably from recent explosions.

Since activity began at Wade Crater, almost 180 mm of tephra had been deposited ~100 m SE of the vent, and 55 mm had fallen at a site 100 m farther SE. Gray scoriaceous ash, lapilli, and bomb layers from the magma column alternated with red, thermally altered ash derived from reworked crater-fill sediments reamed out of the conduit. Major and trace element analyses at the Univ of Canterbury showed no significant changes between bombs collected on 29 August 1991 and samples collected in 1977 and 1979.

Fumarole discharge in the main crater remained at pressures and temperatures that were lower than normal. The highest fumarole temperature measured on 5 December was 353°C (at Noisy Nellie); the same vent was 411°C on 29 August.

Deformation data showed that deflation E of the active vent (in the Donald Mound area) had continued since the previous survey in late August, at similar rates. Subsidence had resumed in areas NE and SE of Donald Mound that had registered inflation in the August survey.

In the days following the 24 November explosion seismic data showed only a few A- and B-type events. Periods of intermittent low-amplitude low-frequency tremor were associated with a pair of E-type (explosion) shocks on 29 and 30 November; the eruption associated with the 30 November event was observed at 1006. The next day, another E-type event and observed eruption occurred at 1103. A gradual onset of medium-frequency tremor was noted ~2 hours later. No more E-type events were recorded through 9 December. A portable seismograph operated during the 6 December fieldwork recorded 2-3-second bursts of tremor-like vibration with frequencies of about 5 Hz during three of the stronger booming sounds from Wade Crater (at 1053, 1101, and 1148). However, similar tremor-like bursts were also recorded during the visit without accompanying loud booms.

Intermittent low-amplitude tremor began 4-6 December, strengthened 7-8 December, and reached high intensity on the 9th, when an eruption was next observed. A column rose to ~2,000 m at about 1440, apparently causing substantial ashfall on the island. Transmission of seismic data was intermittent on 9 December, and no data were available during the eruption.

Information Contacts: I. Nairn and C. Wood, DSIR Geology & Geophysics, Rotorua.

February 1992 (BGVN 17:02) Cite this Report

Vigorous explosions; vent conduit collapse

Explosive activity continued through January. A large ash emission event on 17 January deposited ash 50 km S, and was associated with a large high-frequency seismic episode. The 17 January event marked a change from Strombolian ejections of scoriaceous bombs and juvenile ash, to emissions of ash-sized tephra dominated by lithics and altered glass.

Tephra ejection, December to mid-January. R. Fleming (Waimana Helicopters pilot) reported that Wade crater (formed in mid-October 1991) remained very active in late December and early January, emitting scoriae and bombs (to 30 m height) that were scattered over most of the W end of the main crater floor. The largest bombs were ejected after heavy rainfall at the beginning of January, but volcano noise (booming at 1-2-second intervals) heard during earlier visits had diminished after the rainfall. TV1 Crater (formed in October 1990) occasionally emitted ash, but no emissions were observed from May 91 vent.

B.J. Hogg and P. Horn reported observing an eruption from a boat 8 km E of the island shortly after 2000 on 16 January, coinciding with a recorded E-type earthquake. The initial gray-brown plume, ~150-180 m high, was followed by a separate brown ash column that rose ~900-1,500 m. Ashfall quickly obscured the W and S portions of the island. Roughly 15 minutes into the eruption, ash was observed cascading down the outer margins of the eruption column. Vigorous ash emission continued for at least an hour.

Strong explosion, 17 January. At 0932 on 17 January, seismometers registered the largest discrete seismic event ever recorded at the volcano (figure 16). Boats contacted at 1000-1015 reported limited visibility due to deteriorating weather, but that a "change to heavy ashfall had occurred within the last half hour." The New Zealand Herald reported that a yacht sailing close to the S coast of White Island at about 1100 had its sails coated with mud, and was later dismasted. Ashfall was reported 50 km S (in the Whakatane area) between 1115 and 1130. Geologists suggested that the 17 January explosion was probably caused by subterranean collapse of Wade Crater's conduit wall onto the top of the magma column at considerable depth. This resulted in a change from "open-vent" Strombolian eruptions of scoriaceous bombs, to "closed vent" phreatomagmatic eruptions of altered, lithic-dominated, mostly ash-sized ejecta.

Figure 16. Seismogram showing a large high-frequency event at White Island, 0932 on 17 January 1992. Ticks are at 1-minute intervals. Courtesy of DSIR.

Post-17 January fieldwork. Only a thin layer of light gray ash covered the island during fieldwork on 22 January, suggesting that most of the ash erupted on 17 January had been carried offshore by strong winds. About 32 cm of tephra had been deposited on the 1978/90 Crater rim (S of TV1) since 5 December, of which 11 cm were believed to be associated with 17-22 January activity. No surge deposits were recognized. The largest of the ash-covered blocks and bombs (up to 1.3 m long), found ~200 m E of Wade Crater, had been deposited before 17 January.

No significant changes had occurred to visible parts of the three recently active vents since fieldwork on 5 and 6 December. Wade Crater emitted a vigorously convoluting column of very fine dark gray-brown ash and white gas. White blocks (perhaps baked lithic material) were occasionally ejected. Most of the ash fell back into the vent. Noise from the crater was subdued, in comparison with 5 December, and the dull "booms" had no obvious correlation with emissions. TV1 Crater quietly emitted a small continuous plume of light gray ash that fell to ~100 m ENE, onto an area covered by a layer of recent ash and blocks.

During fieldwork on 23 January, Wade Crater erupted fine red ash, which became more predominant through the day. A distinctive gray-white ash deposit was apparent around the NE margin of 1978/90 Crater Complex, above TV1 Crater. Deposits of fine yellow-green ash, not apparent in photos taken on 22 January, mantled the ground elsewhere on Main Crater floor and on the outer SW slopes. Ash emissions from Wade Crater were stronger on 24 January and conspicuously redder. When geologists left the area at 1635, ash was falling at sea, downwind of the island.

On 31 January, a steam column with small quantities of pink ash from Wade Crater and a light gray column from TV1 combined to form a weakly convoluting pink-brown plume 400 m high. Solar panels 600 m SE of Wade had accumulated ~20 mm of ash since 22 January.

Seismicity. Before 9 December, episodic medium-frequency volcanic tremor accompanied open-vent Strombolian activity at variable, but low amplitude. Tremor declined after 12 December, and was replaced by more discrete, medium-frequency (C-type) events (~200/day) that lasted until 22 December. Relatively brief E-type (eruption) events were recorded on 11, 13, 16, and 17 December (at 1802, 1003, 1921, and 0723, respectively), and rare B-type events were recorded after 16 December. No signal was received 23-27 December.

B-type shocks and microearthquakes dominated the seismic records by 1 January, with 5-10/minute occurring in bursts lasting 3.5-8 hours. Microearthquake activity declined about 6 January, while the number of B-type earthquakes increased, peaking at >20/day on 11 January. A-type earthquakes remained constant, around 3-4/day. E-type sequences reappeared on 7 January, and occurred daily until 17 January, as B-type earthquakes decreased in number. A distinctly different, high-frequency, long-duration event (figure 16) occurred at 0932 on 17 January, shortly before reports of heavy ashfall. A sequence of 18 A-type earthquakes followed in the next 10 hours, and medium- to low-frequency volcanic tremor of variable but increasing amplitude commenced. After 18 January, 5-6 B-type and fewer A-type earthquakes were recorded daily. E-type events were recorded on 21 and 25 January (at 0312 and 1438, respectively), the latter accompanying a voluminous ash eruption. Increasing ash emission interrupted the seismic telemetry link on 26 January.

Information Contacts: I. Nairn and B. Scott, DSIR Rotorua.

March 1992 (BGVN 17:03) Cite this Report

Continued vigorous explosive activity

Explosive activity continued through early March from Wade and TV1 Craters.... Distinct emissions of gray and reddish ash were observed during regular visits to the island and from nearby fishing vessels. A larger event on 20 February produced a tall plume (estimates ranged up to 5,000 m) and ejected blocks and juvenile bombs. Numerous E-type seismic signals were recorded through mid-Mar.

Observations. On 3 February, R. Fleming (Waimana Helicopters) noted gray ash, not present during a 1 February visit, covering the W and SW walls of the main crater. Two eruption columns were reported the next day, the first at 0740 by R. Pollack (MV Pursuit), and a stronger one at 1318 by V. Froude (Dept of Conservation; MV Takapu). Froude observed another eruption column at 0737 on 5 February. TV1 Crater was the source of a light gray ash cloud, 50-100 m high, during an island visit at 1040-1730 on 7 February. Ash again emerged from TV1 during a 12 February visit. Light pink-brown ash emission began at about 1229, and increased slightly during the afternoon. The next day, Fleming reported the emission of red ash from TV1 (at 1530). Strong red ash emissions were reported at 1900-2000 by John Baker (MV Ma Cherie). Wade Crater, inactive earlier in the month, erupted light pink-red ash during a 17 February visit (1030-1546), while TV1 emitted only white steam.

The eruption on 20 February began abruptly at about 1004 without any visible precursors. The initial dark eruptive pulse rose rapidly from TV1 Crater, accompanied by an uprushing noise. Ballistics, white lithic blocks, and dark (not visibly incandescent) juvenile bombs, were ejected to 400-500 m height. Another 3-5 more-dilute, block-free pulses of activity occurred over the next 5 minutes, feeding a high convective plume that traveled SSE. By 1010, several observers along the Bay of Plenty coast had seen the eruption cloud, estimating heights of 1,600-5,000 m. R. Martin and M. Stringfellow (Bay of Plenty Regional Council staff) measured elevation angles of 4.8-5°, yielding column heights of 4,200-4,300 m. Fleming estimated that the initial eruptive pulse rose 1,700-1,800 m before expanding. By 1020, activity had decreased to an ash-free, very weakly convoluting, low eruptive plume. High levels of steam and gas emission continued for 1.5 hours after the explosion, before a dramatic decrease in mid-afternoon.

Voluminous light-brown ash emissions completely obscured the main crater during an afternoon visit on 27 February. On 1 March, thick dark ash emissions were reported by Pollack at 0847. Wade Crater erupted a cloud of pink/brown ash 500-700 m high while TV1 emitted white steam, during a visit at 1125-1515 on 3 March. Nearly continuous ashfall occurred E of the crater. Maximum particle sizes were ~1 mm. Occasional roaring and thumping noises were heard. Fumarole temperatures ranged to >300°C, and analyses of gas samples showed high gas/water ratios, with one sample yielding a strong magmatic signature. The floor of May 91 Crater was nearly flat, reaching 30-35 m below its SE rim. During a 5 March visit at 1020-1605, Wade emitted a weak ash-tinged plume and conspicuously blue fume, accompanied by loud, pulsating degassing noises. Dense ash-free steam from TV1 often obscured half of the 1978/90 Crater Complex. No ash was observed during a 10 March visit, although a steam plume rose to 300-400 m.

Seismicity. B-type seismicity increased from 5-6 events recorded daily 18-24 January to >15/day 1-5 February, while the daily number of recorded A-type earthquakes remained at 2-4. Medium-frequency volcanic tremor began on 6 February. B-type earthquakes declined sharply in number, and were absent from records on 12-17 February. Volcanic tremor amplitude increased after 11 February to a peak on 16 February, coinciding with an 11-hour period (15-16 February) when 4-6 microearthquakes were recorded per minute. Tremor, predominantly medium-frequency (4-7 Hz) with occasional lower frequency signals lasting 1-5 hours, declined to background levels by 21 February. The level of seismic activity remained similar (0-6 A-type and 0-5 B-type events daily) through 3 March, when a swarm of >40 B-type events was recorded.

E-type (eruption) events were recorded every several days during late January-early February [six from 30 January-4 February], were rare in mid-February [one on 14 February], then occurred almost daily from late February through mid-March [20 from 20 February-15 March, with seven on 29 February]. The event that accompanied the production of the large ash-laden column on 20 February was similar to, but larger than, the 17 January seismic event. Of the two predominant varieties of E-type signals during this period, the more common had a low-frequency onset followed by a high-frequency coda; the other was dominantly high-frequency and had a more impulsive onset.

Information Contacts: I. Nairn and B. Scott, DSIR Rotorua.

April 1992 (BGVN 17:04) Cite this Report

New collapse crater; ash emission

Continued eruptive activity in March and April was dominated by fine ash emission from Wade Crater (figure 17). Numerous E-type (eruption) earthquake sequences were recorded, but no new deposits of ballistic ejecta were evident. A new collapse crater (named Princess) developed in the SE part of the 1978/90 Crater complex in mid-April, and subsidence occurred over a substantial area nearby.

Figure 17. Sketch map of the 1978/90 Crater complex and adjacent parts of the Main Crater floor, mid-April 1992, showing the new Princess Crater and the neighboring subsided area. Contour interval, 40 m. Courtesy of DSIR.

During 15 April fieldwork, Wade Crater emitted a gas column that included a little ash, while dense white steam emerged from nearby TV1 Crater ... . Sounds from Wade Crater appeared to have a deeper origin than previously, suggesting that the level of the magma column had dropped. Fumarolic activity NW of the 1978/90 Crater complex occurred with a strong, high-pitched roar. Fine, green-brown ash coated much of the Main Crater floor and walls. Stratigraphy of a pit dug roughly 200 m SE of Wade Crater included 57 mm of fine ash overlying a block/lapilli layer erupted in early March. The coarsest fraction of surface ash collected at the site was dominated by fresh crystals of plagioclase, orthopyroxene, and clinopyroxene, with minor amounts of vesiculated brown glass and a little altered lithic material. Fewer than 10 fresh impact craters were observed near the tephra pit; one contained a scoriaceous bomb, the others dense lava blocks. A detailed infrared survey was flown over White Island, but no data were available at press time.

The new crater was not present during 15 April fieldwork, but collapse had occurred by the time R. Fleming visited the island during the late morning of 17 April. The only significant seismicity during the 2-day interval was a 37-minute E-type event, similar to many others recorded during 1992, that began at 0002 on 17 April. Light ash emission was occurring from Wade Crater on 17 April, and ash fallout N of the island was too heavy to sail through on 18-19 April. Red ash was emerging from Wade Crater on 20 April, and an eruption column rose ~1,500 m on 21 April at 1445.

The new collapse crater was 60-70 m in diameter with nearly vertical walls, when first observed by geologists on 23 April. No coarse ejecta appeared to have been erupted during its formation. More than 4,000 m² of the adjacent Main Crater floor had subsided and sagged toward the new crater. The head of the subsided area had a vertical scarp 1-1.5 m high, and its center had dropped an estimated 8-10 m. Given its shape, geologists suggested that the subsided area had previously been underlain by a SE-trending cavity.

Gray-brown ash collected near the subsided area on 23 April appeared to be mainly derived from crater-fill material involved in the formation of Princess Crater, with only a minor magmatic component. The sample's coarse fraction was dominated by white altered lithic material, although small amounts of black scoria and brown vesiculated glass were present. Many crystals had abraded surfaces and did not appear as fresh as those in the ash collected 15 April. Some fine pyrite clasts were also found in the sample.

Seismicity through 21 March was characterized by 2-5 A-type events/day. Significant volcanic tremor that was dominantly of medium frequency (3-5 Hz) resumed on 21 March. Individual tremor episodes lasting 2-9.5 hours continued through 31 March. A shallow ML 5 earthquake centered ~12 km NW of White island occurred on 26 March at 0527, followed by ~90 aftershocks in the next nine days. High-frequency A-type volcanic earthquakes began to increase on 29 March, averaging 7/day until a swarm of >150 events occurred on 3 April, with 58 more the next day; the largest reached ML 3.8. Seismicity remained elevated 5-12 April at >10 recorded events per day, then declined to more normal levels of 3-4/day. B-type events continued to be detected about every other day. No E-type earthquakes occurred from 18 March until one was recorded 2 April, but there were at least 20 from 6 to 16 April, sometimes accompanying the beginning or end of volcanic tremor episodes. Another E-type event was recorded on 21 April.

Information Contacts: B. Scott, DSIR Rotorua.

May 1992 (BGVN 17:05) Cite this Report

Continued tephra ejection from three vents

Voluminous emission of lithic-dominated fine ash continued into May from three vents in the 1978/92 Crater complex. No obvious changes have occurred to crater morphology since the formation of a new collapse crater (Princess) in mid-April.

No ash was being emitted during 5 May fieldwork. Most of the gas emission occurred from a crater (Wade) that had ... enlarged considerably since February 1992. It occupied much of the floor of the 1978/92 Crater complex, with only narrow divides separating it from neighboring craters TV1... and May 91. A few ash-free ballistic blocks, apparently erupted from Princess Crater since heavy rain two days earlier, had fallen within ~50 m of the 1978/92 crater rim.

When geologists returned on 12 May, voluminous clouds of steam and light-gray ash were emerging from Princess, Wade, and TV1 Craters. The Wade/Princess and TV1/Princess pairs were sometimes simultaneously active. Ash from Princess Crater collected at 1125 was in accretionary flakes 1-3 mm across, composed of silt- to sand-sized pulverized andesite, along with much hydrothermal opal-C, anhydrite, natroalunite, and pyrite. Additional blocks, probably from TV1 Crater, had been deposited in an arc extending 50-100 m E of the 1978/92 complex rim. Fine gray ash coated the blocks, about half of which were weakly vesicular to scoriaceous andesite with xenoliths of thermally altered lithic material. Fractures on the N side of the subsided area, which developed next to Princess Crater in mid-April, suddenly began emitting steam along a zone 20-30 m long at about 1100; Princess Crater was active at the time, but neighboring TV1 was not. Fresh-looking, tephra-free surfaces suggested that movement was continuing along new fractures at the S wall of Main Crater. A trench dug at the rim of the 1978/92 Crater complex revealed 1.5 m of tephra accumulation since April 1991.

Seismicity showed little change since late April. A-type events were recorded 1-11 times a day, while B-types were less than 6/day. Variable-frequency volcanic tremor continued until about 27 April in 2-18-hour episodes. No additional tremor was evident until 13 May, when medium-frequency, low-amplitude signals followed an E-type eruption signature at 0843 (see below). The occurrence of tremor continued to correlate well with observed ash emission. E-type eruption signatures were detected 21 April at 1758; 26 April at 0804, 1425, and 2008; 27 April at 0116; 2 May at 2157 and 2208; 8 May at 0816; 9 May at 0724; 10 May at 0905; 11 May at 0040; 13 May at 0843 and 0855; 14 May at 0452 and 0629; and 17 May at 0119 and 1135. The last event was associated with an ash eruption seen during a COSPEC survey, which yielded an average SO₂ emission rate of 350 t/d; see table 9 for a comparison with previous COSPEC data. The eruption, observed at 1139, fed a billowing cloud that rose 2,000 m. SO₂ in the leading edge of the cloud corresponded to an emission rate of 950 t/d.

Table 9. SO₂ emission measured by COSPEC at White Island, December 1983-May 1992. Courtesy of P. Kyle and W. Giggenbach.

Deformation data showed continued subsidence E of the 1978/92 Crater rim (in the Donald Mound area) at rates that were apparently only slightly lower than in 1991. No acceleration in deformation had been detected over the April 1992 subsidence area in the 16 months preceding December 1991. Magnetic and gravity changes were small. Fumarole temperatures measured by an IR pyrometer have declined since March. The maximum value in mid-May was 211°C, probably depressed by heavy rains the preceding week.

Information Contacts: I. Nairn, DSIR Geology & Geophysics, Rotorua.

September 1992 (BGVN 17:09) Cite this Report

Block ejection enlarges active crater

A new impact-crater field, extending to roughly 350 m ESE from the rim of the 1978/92 crater complex, was seen by helicopter pilot R.Fleming on 28 June. Morphology of the impact craters suggested that they were only a few days old, and that many of the ballistic blocks that had produced the craters had near-vertical trajectories. The eruption apparently occurred from the W part of the 1978/92 complex, substantially enlarging Wade Crater ... . NE of the 1978/92 complex, the wall separating the April 91 pit from Donald Duck Crater had been removed by the end of June, perhaps 1-2 weeks earlier.

None of the activity was witnessed, but seismic data suggest the possible timing. June-August volcanic seismicity was generally at low levels, with 2-5 A-type shocks/day. Geologists suspect that the wall dividing April 91 and Donald Duck craters collapsed on 17-18 June, when 17 A-type events were recorded daily. Wade Crater's eruption may have accompanied 13 E-type (explosion) events recorded 23-24 June, or it may have been triggered by a ML 5.6 tectonic earthquake on 21 June, centered ~20 km SW of White Island. Numerous aftershocks followed: 200 on 22 June, 150 on the 23rd, 40 on the 24th, and 10-20/day for the next 5 days. B-type events typically occurred at rates of 1-3 every other day, and there was no significant volcanic tremor.

Fieldwork by B. Scott on 2 September revealed that Wade Crater had enlarged substantially since May, and had developed 3 sub-craters. A western sub-crater, separated by a wall 15-20 m high, extended Wade 50-80 m W from its former rim. A bright-green crater lake filled the central portion, and a hummocky eastern section continued to erode until only narrow walls remained between it and two other steaming vents (May 91 and TV1). A pit dug just outside the SE rim of the 1978/92 complex showed an accumulation of ~55 mm of ash since May.

Information Contacts: B. Scott, Institute of Geological and Nuclear Sciences (IGNS), Rotorua [formerly DSIR].

December 1992 (BGVN 17:12) Cite this Report

Eruptive activity declines; rapid deflation

No significant eruptive activity has occurred since June 1992, although a minor ash emission was observed on 25 November. Observations are based on crater visits of 30 October, 19 November, and 8 December.

Within the 1978/92 Crater Complex, the three sub-craters observed on 2 September remained on 30 October (figure 18). The divide between May 91 and Wade Craters had collapsed, but two strong fumaroles were re-established through the collapse debris, creating a new "hot wall" in a horseshoe-shaped area on the N side of the former divide. The lake in the center of Wade Crater appeared to be deeper and slightly larger. A fumarole-vent in the western Wade subcrater (named Royce) had enlarged and was emitting white steam. A large SE-trending cavern was observed ~40-50 m below the rim of Princess Crater.

Figure 18. Sketch map of the main crater area of White Island showing crater and peg locations as of 5 May 1993. Crater locations unchanged since September 1992. Courtesy of the IGNS.

No changes were noted during the 19 November visit, but views were often obscured by strong steam emissions. A small crater lake remained in Wade Crater. Fumarolic activity on the main crater floor was weak, and there was no new ash.

Heavy rains in early December caused landsliding and sedimentation in the Crater Complex. Large landslides from various points around the steep crater wall were heard during fieldwork on 8 December. No new ash or other ejecta was recognized on the crater floor. Royce Crater, now mostly infilled, contained a small pond that was overflowing into the larger lake in Wade Crater. Extensive slumping along the N wall of Wade Crater had partially covered the crater floor. The most intense thermal feature on the island was a large new open vent in the slump deposits that was emitting colorless gas at high pressure. Little change was evident in the other craters.

A levelling survey completed on 8 December revealed that very rapid subsidence (maximum 130 mm), centered near the NE rim of the 1978/92 Crater Complex, had occurred since 13 May. Previous surveys indicate that major subsidence began about one year ago, but the rate has increased in the past 7 months. The deformation has been interpreted as a long-term pattern of steady deflation centered E of the 1978/92 Crater Complex (near Donald Mound). Based on chemical evidence, this deflation is believed to be associated with withdrawal of underlying brine fluids and reduced heat flow. The extremely rapid recent deflation is thought to reflect subterranean collapse.

Seismicity has remained consistently low since the last report, on 2 September, with 0-14 A-type events/day, very few B-type, and five E-type (explosion) events (figure 19). Short bursts of low-amplitude tremor were recorded, mostly in late September and early October. Low-frequency tremor was recorded for 12 hours on 22-23 November, just before helicopter pilot R. Fleming reported ash emission from Royce Crater.

Figure 19. Summary of 1992 seismic activity at White Island. Courtesy of IGNS.

Information Contacts: I. Nairn and B. Scott, IGNS Rotorua.

January 1993 (BGVN 18:01) Cite this Report

Minor ash ejections; rapid deflation continues

Minor ash emission was reported by helicopter pilot R. Fleming from a vent on the N floor of Wade Crater on 4 January. Eruption of blocks from a new vent under the S wall of the crater was observed on the same flight; no ejecta fell outside of the 1978/92 Crater Complex. The two vents were not significantly active the previous day, but gas emission was increasing. On 14 January, activity was observed from three sources in Wade Crater.

Fieldwork on 15 January revealed continuous ash coverage, with depths of 20-25 mm in some areas. No topographic changes within the 1978/92 Crater Complex were observed. An inclined vent on the S side of Wade Crater produced two types of activity. A steam column with minor ash content was emitted at about 1000, rising 200-500 m above the crater. Surtseyan style pulses with varying densities appeared at 1250 that rose 100-150 m. Individual blocks frequently broke away and could be heard rolling back into the vent. A steep unstable talus slope formed around the active vent. This vent appeared to occupy an area which showed some subsidence on 8 December.

There was no sign of new tephra or ejected blocks outside the 1978/92 Crater Complex during fieldwork on 21 January. A "lake" of viscous, black sludge in Wade Crater was erupting continuously from 3-4 points. The eruptions appeared to be generated by steam exploding through the sludge. Large lumps of sludge were thrown to 30 m, followed by larger explosions which sent debris up to 100 m high. No detonations were heard and there was no incandescence or fine ash emission observed at any stage of the eruptions. Fumaroles were active on the N and E sides of Wade Crater. TV1, Princess, and Royce craters were emitting fumes and low-pressure steam.

A levelling survey completed on 21 January again revealed rapid subsidence (-16.1 mm/month compared to -19.7 mm/month in the seven months prior to December) since 8 December on the W side of Donald Duck Crater. Geologists suggest a source depth of 100-150 m, with the rate of subsidence increasing since 1991. Medium-frequency volcanic tremors characterized seismicity through 15 January.

Information Contacts: B. Scott, C. Wood, and P. Otway, IGNS, Taupo.

May 1993 (BGVN 18:05) Cite this Report

Ash emissions stop; steaming doesn't

Weak ash emissions stopped in mid-February, although one explosion occurred near the end of the month. A crater lake was observed on the floor of Wade Crater near the end of March. Multiple visits were made by geologists from New Zealand and Japan to conduct microearthquake observations and make self potential measurements in the main crater.

Geologists noted no apparent changes on the crater floor during a 6 February visit, the first since 21 January. Conditions in the 1978/90 crater prevented observations. During a 16-17 February visit, observations were confined to the E end of main crater, where seismic recording equipment from the GSJ was installed, and from the NE rim. Light-brown, very fine ash emissions were rising ~150-200 m from unknown vents in the 1978/90 Crater Complex. Fallout from recent emissions had deposited ash between Donald Mound and Noisy Nellie (see figure 18), and farther N, filling all shallow erosion features in the area.

No ash emissions occurred during a visit to the rim of the 1978/90 Crater Complex at 1217 on 23 February. A deep, nearly continuous roaring noise was heard coming from deep in TV1 Crater, which was emitting steam. Recent landslide debris made up most of the floor of the 250-m-deep Wade Crater, though a small lake with geyser-type activity was present in the SW. A 50-80 m wide vent on the W side of the N crater wall was emitting gray fumes. There was no apparent activity in Royce or Princess craters. The N-facing wall of the flat area S of Princess Crater was severely cratered, with some of the impact craters producing small landslides. A lack of impact craters on the flat itself indicates a very directed blast, probably from the vent in Wade Crater. Increased steam emission was noted 25 February, originating from Wade, TV1, and possibly Princess craters. The steam column rose ~500 m before being blown to the E.

The rim of the 1978/90 Crater Complex was not visited on 2 March, when seismic monitoring equipment was installed and GPS observations were made, but no significant emissions were seen. A brief visit to the crater complex rim at 1237 on 9 March showed that activity was confined to Wade Crater, with no observable emissions from Royce, Princess, or TV1 craters. The only significant steam emissions were from vents on the E side of the collapsed wall in the May 91 Crater and deep in Wade Crater. Steam emission prevented a clear view of the floor of Wade Crater, but a lake was probably present.

A steam plume was rising ~500 m when geologists arrived on 15 March to retrieve the seismic equipment; emissions from the NE side appeared stronger. A visit to the rim of the crater complex at 1530 provided a clear view of the sub-craters. A gray-colored lake occupied the floor of Wade Crater, with conspicuous geysering and steaming in the SE. Waves from the SW suggested additional activity. The Royce Crater area had collapsed, filling any local vents. The most prolific steam emissions were coming from three fumaroles in the old SE wall of the May 91 Crater. Strong fumaroles were also present on the W wall of Wade Crater near the former May 91 Crater divide. Steam emissions were observed 16 March, but no one visited the crater rim.

Information Contacts: B. Scott, S. Sherburn, and C. Wood, IGNS Wairakei; Y. Nishi and T. Tosha, GSJ, Japan.

June 1993 (BGVN 18:06) Cite this Report

Ash eruptions; additional subsidence

Following the 16 March visit by IGNS geologists, ash eruptions were reported on 29 March and 2, 5, and 6 April by fishermen. An E-type earthquake at 1022 on 5 April lasted for 5 minutes, and may have been associated with one of the observed eruptions. Seismicity in April and May was generally low, with only a few A- and B-type events/day, and almost no volcanic tremor. Another E-type event on 20 April was preceded and followed by periods of microearthquake activity.

A visit to the island on 18 May revealed a few millimeters of gray rainwashed ash on the main crater floor. The primary gas emission site was a new fissure vent on the N wall of Royce Crater (figure 18), which was emitting moderate amounts of gray-tinted gas. Voluminous white steam clouds from TV1 Crater and vents high on the N wall of Wade Crater obscured views of those areas. Almost no emissions were coming from Princess Crater. Further wall collapse had occurred in Donald Duck Crater, enlarging it slightly and reducing the width of the dividing wall with the adjacent TV1 Crater. A green pond occupied the floor of Wade Crater.

About 5 mm of new gray ash was seen at peg M (~50 m SE of the Peg XII Sag) on top of the brown ash deposited in February. A total of 40 mm of fine ash has accumulated at this site since May 1992. Also since May 1992, ~100 mm of fine ash has accumulated at a site 20 m from the rim of the 1978/90 Crater on the SW wall of the Peg XII Sag, and 250 mm on the edge of Gibrus Ramp. Fumarole temperatures remained low in all areas, probably due in part to heavy rains in the three days before the visit.

Deformation since the January survey continues to be dominated by strong subsidence centered immediately SW of Donald Duck Crater. The maximum rate of -35 mm in 4 months (-9 mm/month) was registered at peg X, a significant reduction from the previous 5-week period when -20 mm/month was recorded. The subsidence near Donald Duck Crater is interpreted as continuing deflation associated with withdrawal of underlying brine fluids and a reduction of heat flow, possibly accompanied by some subterranean collapse. The subsidence rate has decreased substantially from the unusually high rate measured in 1992. There was also a 7 mm (2 mm/month) rise in the peg D-M area SE of Donald Mound, continuing the trend seen during the previous survey, and resulting in a minor elevated area. This uplift is thought to indicate a possible warming at depth, though no temperature or chemical effects are evident at the surface. Previous episodes of uplift in this area, of approximately half this magnitude, have occurred with no associated surface changes.

A magnetic survey was carried out by Victoria Univ geologists. Diurnal variation during the day was about 10 nT, and the magnitude of the measured changes was comparatively small (<80 nT). A positive trend was distinguished immediately NE of the 1978/90 Crater Complex, probably due to shallow cooling in the active vent area or an apparent increase in hot spring activity noted by the Victoria Univ team since 8 December 1992. This positive trend seems to be superimposed on a more widespread negative trend over most of the crater floor, and is thought to be caused by more deeply centered heating. A possible source of error in the magnetic differences is that the 8 December 1992 survey was done using a GEM GSM-19 rather than the usual Geometrics G8 magnetometer. December 1992 values were adjusted for the different staff lengths (the vertical magnetic gradient was also measured), and it is believed that residual errors would be small in magnitude.

Information Contacts: I. Nairn, B. Christenson, P. Otway, and C. Wood, IGNS Wairakei; E. Broughton and P. Rickerby, Victoria Univ, Wellington.

October 1993 (BGVN 18:10) Cite this Report

Phreatic eruption; crater lake and fumarole temperatures decline

During fieldwork on 30 July an active vent, ~30-40 m in diameter, at the base of the NW wall of Wade Crater on the divide with Royce Crater (figure 20), was emitting a nearly translucent fume under moderate-high pressure. The fume quickly condensed on expansion to vivid white steam without any apparent ash. The floor of Wade Crater was occupied by a bright green lake ~90 m below the rim of the 1978/90 Crater Complex. Neither TV1 nor Princess Crater was emitting much steam.

Figure 20. Sketch map of the 1978/90 Crater Complex of White Island showing crater locations as of 22 October 1993. Courtesy of IGNS.

A magnetic survey revealed relatively small changes (up to 53 nT) compared to the May survey. A pattern similar to the changes between the 8 December 1992 and 18 May 1993 surveys appeared: a broad negative anomaly occurring over most of the crater floor but with an area of positive change NE of the 1978/90 Crater Complex. The broad negative anomaly could be due to a deeply centered heat source, and the positive change could be interpreted as a magnetic anomaly arising from shallow cooling in the active crater area. A sharp anomaly appeared at Donald Mound, negative to the N, positive to the S, and represents a newly recognized trend. The trend is most likely due to the effect of shallow heating 50-100 m beneath Donald Mound.

A gravity survey showed little change from the May measurements. A very slight positive anomaly runs through the center of the crater along its axis, flanked on either side by small negative anomalies. This effect can be attributed either to a gentle warping along the crater axis or to the migration of fluids.

A visit on 22 October was made to sample fumaroles and to determine the effects of the 19 October phreatic eruption, the most significant activity reported in several months. An E-type seismic event commenced at 1102 on 19 October and lasted for about an hour. The captain of a fishing boat 3 km W of White Island described several eruptions starting around 1100 and lasting a total of ~45 minutes. The ash plume was very pale gray, rose ~1 km above the summit of Mt. Gisborne, and was blown to the SE. A resident at Te Kaha, on the coast 50 km SE of White Island, reported hearing explosions and feeling vibrations at 1100 while the volcano was erupting. Te Kaha is directly in line with the breached Main Crater of White Island.

The most active feature in October at the 1978/90 Crater Complex was the vent on the NE side of Royce Crater. The vent was continuously emitting voluminous, ash-free steam that completely obscured its shape (arbitrarily depicted on figure 20 as circular). Wade Crater was completely occupied by a lake that has changed color since the July visit to a brilliant orange-yellow. The water temperature was 23°C as measured remotely by radiometer. Visual comparisons with photographs taken on 30 July when the lake was pea-soup green suggest that the lake level has risen roughly 10 m. A large delta was building up where the stream draining the largely inactive NW area of the 1978/90 Crater Complex enters the lake near the divide between Royce and Wade Craters. A smaller outwash fan occurs where a small stream is eroding the gap between Royce Crater and the 1978/90 Crater Complex wall. Lake Wade was estimated to be 110-130 m below the edge of the 1978/90 Crater rim at the point just S of The Sag. Twin fumaroles were conspicuous high on the E wall of Wade Crater adjacent to TV1 Crater, which itself was only weakly steaming. Princess Crater was inactive.

Researchers dug a new pit close to the rim of 1978/90 Crater Complex, S of The Sag, and exposed 20-25 cm of finely layered, fine-grained, light- to dark-gray or brick-red ash. In addition, banded gray and red ash at the base of this sequence correlates to May 1992 from comparison with photographs of earlier pits. One pit ~15 m SW of Peg M had 6-7 cm of ash since May 1992, but only 1-2 mm of dark-gray fine ash since 18 May. Hence there has been little ash accumulation in the area S of Donald Mound in the past five months. The eruption on 19 October deposited little ash, consistent with the observation that the eruption clouds were mostly steam.

Ballistic ejecta were scattered across an area approximately as shown in figure 20. Blocks varied in size up to 20 cm across, but most were <10 cm. Impact pits were spread an average of 1-2 m apart. Many blocks had hit the ground surface (moderately compacted fine ash) and skipped a short distance (<50 cm) making a small impact scar; others were imbedded where they landed, protruding from the surface. There were no large craters typical of high-energy impacts, and only a few of the larger blocks were buried where they had hit a sloping surface facing towards the 1978/90 Crater Complex (on the E side of The Sag). Skip trajectories mostly projected back towards the vent in Royce Crater, the presumed eruption source. Many large blocks were visible on the delta in Lake Wade near the vent, and may have been ejected by the same eruption. The lack of impact craters suggests that the ballistic rocks landed with low energy from near the highest point of their trajectories (Royce vent is ~130 m lower elevation than the fall field). It seems likely that the eruption occurred as a phreatic, vent-clearing "cannon shot" directed to the ESE.

The most common types of blocks were fragments of old, partly altered andesitic lava, and lumps of gray, coarse, very poorly sorted vent breccia. The latter are of variable compaction, contain much hydrothermally altered clastic material, and were soaked with acidic, mineralized water; they probably represent recently accumulated vent fill detritus rather than ancient vent-wall rocks. Among the ejecta were irregular chunks of brine-soaked indurated volcaniclastic sandy-silty sediment showing intense folding and crenulation on a mm-cm scale; their origin and significance is not known. There were a number of andesitic scoriaceous bombs among the ejecta at the W end of the fall field. All were ash coated and none were found in impact scars. It is possible, but not proven, that they are juvenile bombs from the 19 October eruption.

Temperatures of springs and fumaroles have steadily decreased over the last four visits. Between 27 August and 27 October, the temperature at Noisy Nellie fumarole declined from 292 to 248°C, and the lake in Wade Crater went from 45.5 to 21.5°C.

Information Contacts: B. Christenson and C. Wood, IGNS Wairakei; J.L. Smellie, British Antarctic Survey, Cambridge.

December 1993 (BGVN 18:12) Cite this Report

Temperature rises in crater lake; no new eruptive activity

No eruptive activity has been reported through mid-December, although further collapse of the N and NE margin of the 1978/90 Crater Complex was noted on 1 December. There have been no ash emissions since a phreatic eruption on 19 October. Following that event, the lake in Wade Crater was generally yellow with a temperature around 22°C (table 10). By 27 November, the temperature was over 50°C, and there was geyser-like activity near the W shore. Lake color had changed to bright green or green-yellow by 1-2 December, with the temperature remaining high and strong bubbling and effervescence near the W shore. Examination of photographs indicated that the lake level may have risen 2-5 m between October and December.

Table 10. Summary of observations from the lake in Wade Crater at White Island, 30 July to 2 December 1993. A dash (--) signifies no measurement. Courtesy of IGNS.

Royce Crater was occupied by water on 1 and 2 December, a new development since 27 November, and the former fumarole vent was discharging through the pond. A tour operator reported possible impact craters in the Donald Mound-Donald Duck area on 12 December as well as a significant increase in steam emission and noise from vents in Royce Crater between visits on 10 and 12 December, indicating that the pond may have dried up around the active fumaroles. Fumarole temperatures declined slightly between 22 October and 2 December. During a visit on 3 November, the single circular fumarole on the E wall of Wade Crater above the twin fumaroles was an estimated 5-10 m in diameter and clearly visible.

Three precision proton magnetometers were installed on 3 November to provide continuous recording of magnetic field strength changes at frequent intervals. The instruments are located 22 m from the NE edge of the 1978/90 Crater Complex, just inside the SW sector of Noisy Nellie crater, and in the NE side of Main Crater ~100 m from the coast. A magnetic survey on 2 December measured 85 locations, including 10 new marker pegs. Most of the notable magnetic trends seen from the previous survey (30 August 1993) have continued at comparable rates. The most notable trends were a -90 nT anomaly N of Donald Mound and a +40 nT anomaly S of Donald Mound that indicated heating centered at a depth of ~50 m. A positive anomaly NE of TV1 Crater indicated continued shallow cooling in the active vent area.

Conditions during the deformation survey on 2 December were excellent, allowing good closures of all three circuits. Strong subsidence centered in the Donald Mound area continued to dominate the deformation pattern, although the rate had decreased since the exceptionally high rate recorded a year earlier in the Donald Duck-TV1 area. The subsidence was attributed to a combination of local cooling, withdrawal of underlying brine fluids, and subterranean collapse. An area centered ~200 m SE of Donald Mound has continued to inflate at a steady rate of 1.7 mm/month since first noted in January 1993. This inflation was tentatively attributed to increased heating at a depth of ~200 m.

Trial COSPEC measurements were attempted on 2 December from the crater floor and from a helicopter. Although SO₂ signals were recorded during ground-based measurements, calibration was impossible due to strong winds causing turbulent dispersal of SO₂ throughout the crater. Vertical measurements from the helicopter were also unacceptable due to interference from the main rotor. Measurements from a fixed-wing aircraft on 8 December were more successful; the plume was being displaced by a 5-knot wind. Seven passes were made beneath the plume at altitudes of 200-250 m above the ocean surface at ground speeds of 75-103 knots. The average SO₂ flux from three scans considered to be reliable was 171 ± 26 t/d.

Information Contacts: B. Scott and C. Wood, IGNS Wairakei.

March 1994 (BGVN 19:03) Cite this Report

Small ash eruptions and steam plumes

The lake in Wade Crater was first observed in March 1993. Following an ash-bearing phreatic eruption on 19 October 1993, the crater lake temperature decreased from ~45 to 22°C. By the end of November, lake temperature had again risen to >50°C, the water color was green-yellow, and there was strong bubbling and geyser-like activity near the W shore.

Fieldwork on 14 January 1994 revealed that the lake in Wade Crater had shrunk to a small pond of bubbling gray water at its former W end. Noise from the fumarole in the NW corner of Royce Crater, where a lake was present in early December, was loud enough to cause discomfort without ear protection. The next day, this fumarole emitted brown ash that formed a plume to 200 m above the main crater floor. Ballistic blocks up to 50 cm in diameter were thrown as high as 30 m above the vent. Noise levels were variable, but generally lower in intensity than on the day before. Maximum temperature of the pond, as measured by infrared pyrometer, dropped to 40°C on 15 January from 87°C on the 14th.

By 19 January, a thin layer of khaki-colored ash covered the Main Crater floor near the 1978/90 Crater Complex, and extended as far as peg E, ~380 m SE of the vent (figure 21). The pond in Wade Crater had disappeared, and a blocky tuff cone stood near the former active vent in the NW part of the crater. There was no sign of impact craters, even adjacent to the cone. The primary activity during the visit was geysering from a sludgy pool in the NW corner of Wade Crater. Bright white steam frequently burst through the surface of the pool immediately before upwelling commenced. Based on a strand line, the former lake had only been 2-5 m deep. The divide between Princess and TV1 craters had collapsed further, allowing clear views of the floor of Princess Crater.

Figure 21. Sketch map of the main crater area of White Island showing crater and peg locations as of 19 January 1994. Contour elevations are in meters. Courtesy of IGNS.

A deformation survey on 19 January suggested that local cooling, withdrawal of underlying brine fluids, and subterranean collapse were still operating beneath the Donald Mound area. Since 2 December 1993 an area centered W of Donald Mound-Donald Duck subsided at a rate similar to December 1992-December 1993 (4-5 mm/month). Possible deflation of ~3 mm SE of Donald Mound since last December, where inflation over the past year had averaged 1.7 mm/month, indicated that recent inferred heating in that area had stopped.

Lakes had reappeared in Wade and Royce craters by 29 January. A very sharp boundary could be seen within the Wade Crater lake. It was gray and steaming on the W side with a maximum temperature of 65°C, but the E side was greenish-yellow with a maximum temperature of 49°C. Steam discharges continued from the large vent at the W end of the crater, but noise levels were lower than on 15 January. A vigorously discharging superheated fumarole was observed on the N crater wall above the lake, but it was too small for a temperature measurement. Heavy rains on 4-5 February caused flash-flooding that stripped a large amount of ash from the surface and caused several landslides. A helicopter pilot noted that the lake level appeared 3-5 m higher, and that there was geysering and vigorous overturning in the lake.

A small eruption on 23 February was observed at about 1012, while scientists were in transit to the island. By 1018, the white, apparently ash-free steam plume had reached an altitude of 2 km (determined by an on-board altimeter), at which point the top of the plume was still vigorously convecting and ascending. Considering the temperature and ebullient nature of the crater lake, and because this was essentially a steam eruption, the vent in the crater lake was considered the most likely source for the eruption. A pulse of orange-brown ash was emitted from the 1978/90 Crater Complex at about 1155, followed by lesser amounts of pale gray ash for the rest of the afternoon. Because the vent area was almost totally obscured by steam, the source vent could not be determined.

The lake in Wade Crater again exhibited the two-tone coloration and similar temperatures as observed on 29 January, although the level was considerably higher. The turbid gray water in the W half of the lake appeared to descend beneath the comparatively suspension-free green water to the E. At least two sources of upwelling were apparent in the hotter gray water. Primary steam sources from the crater included the main fumarolic discharge from the NW part of Royce Crater, and increased discharges from fumaroles on the N wall immediately above the lake. Comments from a helicopter pilot indicated that this change in activity occurred after torrential rains about two weeks earlier. Combined noise levels from the fumaroles were moderate.

A small eruption near the location of a previous fumarole on Donald Mound had formed an elongate crater approximately 1 x 3 m in size and 50 cm deep. Two distinct low-temperature (98°C) discharges issued from this crater, one under high pressure. Preliminary analysis revealed fairly dry output gases with a high N₂/Ar ratio of ~1,300. Temperatures at Noisy Nellie fumarole ... were in the 201-208°C range in January and February. Other fumaroles ranged from 98 to 109°C during the same period.

Information Contacts: B. Christenson and B. Scott, IGNS, Wairakei.

July 1994 (BGVN 19:07) Cite this Report

No eruptive activity, but new shifts in leveling and magnetic data

Routine monitoring visits on 23 April and 28 June 1994 found no evidence of any eruptive activity. On 23 April the floor of Princess Crater was occupied by a muddy pond that contained fresh landslide debris (see figure 21). The divide between Wade and Royce craters had been destroyed. Active fumaroles included those in TV1 Crater, and those escaping from beneath landslide debris in the Royce area.

Scientists who made brief trips on 12 and 15 May noted 5-10 m subsidence of the lake occupying the active vent area on the floor of Wade Crater; the lowered lake level persisted until at least 29 May. A triangulation survey on 28 June determined the lake to be 56 m below sea level and 92 m below the rim of the 1978/90 Crater Complex.

Deformation was surveyed in nearly ideal conditions on 28 June, achieving a good error of closure; the results showed that since 19 January 1994 a subtle but significant crater-wide uplift, typically 5-10 mm, has taken place. Stronger uplifts occurred at Donald Mound (+15 mm) and SE of Peg M (+21 mm). This kind of crater-wide inflation was last seen in the three years preceding the 1976-93 eruptions.

A magnetic survey of established sites revealed a pattern of net magnetic changes very similar to the two previous periods of measurements in 1993. A negative anomaly lay to the N of Donald Mound (-100 nT), and a positive one to the S (+60 nT). P. Rickerby noted that "these anomalies could be interpreted as resulting from shallow heating under Donald Mound (~50 m deep) and shallow cooling under TV1."

Seismicity recorded during January-June 1994 has generally showed little change; tremor in this interval has remained near background, though it has been present on 54% of the obtained records.

Information Contacts: T. Hunt, B. Scott, T. Kabayashi, and T. Tosha, IGNS, Wairakei; P. Rickerby, Victoria Univ, Wellington.

September 1994 (BGVN 19:09) Cite this Report

Small eruption in late July ejects mud and blocks

A small eruption from Wade Crater on 28 July ejected mud and ballistic blocks. During a visit on 17 August, the floor of Princess Crater was occupied by a small green pond larger than on 28 June. The view of Wade Crater was restricted for most of the visit, but the gray lake was still present, and a small bench had formed on the E side of the lake. A mudflow deposit S of Wade Crater extended from the talus slope beneath the crater rim for 20-30 m towards The Sag. The deposit was ~20 cm thick, composed of fine mud with some small pebbles, and had a slightly yellow surface with a gray interior. The same deposit was seen on the divide between Wade and Princess craters, but thinned rapidly to the N, and disappeared before reaching TV1 Crater. Recent bombs and impact craters were observed SE of, but not within, the mudflow deposit. Additional bombs and impact craters were present N of TV1 Crater. The mud and block material was probably erupted at the same time from the lake bed of Wade Crater; the mud component was then remobilized and flowed down the talus slope. The blocks N of TV1 are assumed to be associated with the same eruption that formed the mudflow.

Leveling data showed a continuation of the uplift observed during January-June 1994. Total uplift at Peg M was 35 mm since January 1994. The uplift center was >100 m S of Donald Mound, although an area of relative subsidence persisted in the Donald Duck-TV1 Crater area to the N. Crater-wide inflation centered S of Donald Mound was clearly established. Inflation was also occurring N of Donald Mound, previously the most rapidly deflating area, but at a slower rate. The situation in mid-August was a significant reversal of the strong deflationary trend from 1987 to late 1993. These inflationary trends can be modelled as a doublet with a deep (500 m) source and a secondary shallow (200 m) source beneath Donald Mound, similar to the results observed in 1973-74 before the 1976-82 eruption. Volcanic seismicity continued at low levels during July-August compared to the April-June period, although volcanic tremor increased in late August.

Information Contacts: S. Sherburn, IGNS, Wairakei.

December 1994 (BGVN 19:12) Cite this Report

Lake persists in Wade Crater; rockslides; inflation continues

No evidence of eruptive activity was observed on 5 October, although clear conditions allowed for good views into the 1978/90 crater complex (figure 22). The floor of Wade Crater remained occupied by a lake that appeared light-gray with several dark-gray slicks; no convection or geysering was seen. On the rear wall below the May 91 embayment, there was a large audible fumarole. All traces of Royce Crater had been removed by landslide debris, and the floor of Princess Crater contained a small pond. The Wade Crater lake was still light-gray on 11 November with a bright green zone in the NW part. The ridge between TV1 Crater and Wade/Princess continued to fail. During a visit on 21 November the large lake in Wade Crater was covered by plates of gray scum in constant motion. Strong ebullition was occurring in the lake center to a height of 1-2 m. There was no sign of recent eruptions; a number of recent rockfalls had occurred from the steep walls of Wade, Princess, TV1, and Donald Duck craters. A small green lake was present in TV1 Crater.

Figure 22. Sketch map of Main Crater at White Island showing craters and peg locations as of 21 November 1994. Contour elevations are in meters. Courtesy of the IGNS.

A complete deformation survey on 21 November showed a continuation of the crater-wide uplift noted during the June and August surveys. The Donald Duck-TV1 area, previously rising much less rapidly than the area to the S, has recently been rising at a comparable rate. This uplift is interpreted by the IGNS as minor crater-wide inflation that began in early 1993, although the strong deflation that characterized the Donald Mound area persisted until mid-1994. Magnetic changes since 28 June 1994 showed a pattern similar to the three previous periods, with a positive anomaly NW of Donald Duck, a negative anomaly N of Donald Mound, and a positive anomaly S of Donald Mound. The magnitude of the changes is slightly less than for the 12 February 1993 to 28 June 1994 period, but the rate of change had increased slightly. These magnetic changes are again interpreted as resulting from a shallow heating under Donald Mound (~50 m deep) and shallow cooling under TV1.

Information Contacts: B. Scott and P. Otway, IGNS, Wairakei.

April 1995 (BGVN 20:04) Cite this Report

Currently non-eruptive but 2-year-long inflation continues

No eruptive activity occurred during January-March 1995. Wade Crater's floor remained occupied by an aqua-blue lake; photographs taken on 11 November 1994 and 27 February 1995 disclosed a lake-level rise of ~15-20 m. The lake appeared free of convection, but did contain conspicuous orange-colored material floating on its surface. The lake surface in March was thus considerably above the floors of Wade and Princess craters.

Dominant locations of fumaroles in or adjacent to Wade Crater included those high on the W wall, on the W side of the May 1991 embayment (particularly large and conspicuous fumaroles), and NE of Wade Lake on the divide between Wade and TV1 craters.

A 4 March leveling survey had a low error of closure (<=1.5 mm). The survey detected continued uplift, apparent since at least early 1993 (figure 23), with a maximum rate of 4.8 mm/month (58 mm/year) centered about 250 m SE of the middle of Wade Crater (Peg N). An area of shorter-term relative subsidence, apparent since at least August 1994, persists in the TV1-Donald Duck Crater area.

Figure 23. White Island deformation at leveling Peg C, ~750 m SE of the shore of Lake Wade, 1967-1995. Courtesy of IGNS.

The magnitudes of these upward and downward motions were as follows. For the interval 21 November 1994 to 4 March 1995 the motion was 15 mm (up at Peg N) and -1 to -16 mm (down near TV1). For the interval 19 January 1994 to 4 March 1995 the motion was about 64 mm (up at peg N) and 26 mm (up near TV1).

Continued uplift of the crater floor suggested a crater-wide inflation that has been in progress for more than 2 years (figure 23). This inflation bears a close resemblance to the 5-year inflation that led up to a noteworthy eruption beginning in December 1976. An early phase of the 1976 eruption "sprinkled mustard-green colored ash" up to 1 m or more thick, over the crater and lesser thickness over the E part of the Island (SEAN 02:01).

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

May 1995 (BGVN 20:05) Cite this Report

Fumarolic activity increases and lake level rises in Wade Crater

During April and May the fumarole emission rates increased in Wade Crater, but no significant eruptive activity occurred. On occasions, emissions from the large fumarole on the rear wall carried some fine ash. A ship anchored at the island was lightly coated with ash on 4 April. Donald Mound had some evidence for new tephra deposits, although this was hard to ascertain due to recent heavy rains.

By the time of the 26 May visit by IGNS scientists, the lake level in Wade Crater had risen ~12-15 m relative to March levels. This followed an ~15 m rise between 11 November 1994 and 27 February 1995 (BGVN 20:04). The lake appeared a gray-brown color with some small dark brown slicks on the surface. Despite the lack of convection during January-March, surface convection was observed in the central part of the lake near the W wall. The profuse area of fumaroles on the W wall, in the May 1991 embayment, had formed into one large, very audible vent. Fumaroles on the divide between Wade Crater and TV1 showed little change.

TV1 Crater was still occupied on 26 May by a calm, pale blue lake with several brown surface slicks. The water level in TV1 Crater was higher than in March. Princess Crater continued to shallow, due to the increased amount of debris washing into it.

The margin of the 1978/90 Crater Complex continued to structurally fail. Several small-scale mud and rock debris flows had moved down the Main Crater walls. Despite tour operator observations of weak ash emissions, there were no tephra preserved on the Main Crater floor.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

July 1995 (BGVN 20:07) Cite this Report

Rapid inflation, booming noises, and ashfall

A small ash eruption from an active vent within Wade Crater occurred around 29-30 June. Deformation and magnetic changes indicated inflation and warming, suggesting a possible progression into another eruptive cycle.

In contrast to recent visits, on 14 June the 1978/90 Crater Complex emitted continuous low-frequency booming noises. Wade Crater's lake had changed from light gray to bright emerald green, with gray slicks in the center near the beach below the fumarole. The lake in TV1 Crater was turquoise and at the same level as Wade Crater lake.

On 1 July a layer of light gray ash covered survey pegs C and J, and the walls of both the 1978/90 Crater Complex and Main Crater. The largest particles were 4-6 mm in diameter. As on 14 June, Wade Crater's lake was still bright emerald green. Following the 1 July observations, rainfall induced several landslides along Main Crater's walls.

Gas and condensate samples were taken from fumaroles ##1 and ##3, and temperatures measured 108 and 100°C, respectively. Both temperatures remained close to those seen over the last two years, although fumarole ##2 rose 6°C since November 1994. Water temperatures at Black Pot (93°C) were unchanged.

Inflation continued, although its center had moved slightly N, and was more symmetrical about Donald Mound with a steep downward gradient towards the TV1-Noisy Nellie area. Inflation rates have increased by 36% on the crater floor over the past 4 months, and by 136% at Donald Mound over the last 3.5 months. The current rates resemble those measured in the 5 years prior to the December 1976 eruption, although the present rate of uplift is 4-5x the rate 12 months prior to the 1976 event.

Ash collected on 6 July consisted of altered detritus and rounded, granular, clastic crystals and glass, an assemblage not directly from a vesiculating magma. This non-juvenile material possibly originated from a young, unaltered, solid andesitic body abraded by high-velocity gas. The sample contained euhedral, coarse-grained gypsum, which probably crystallized in the wet surface deposit near the air interface.

Magnetic surveys showed that since November 1994 there has been shallow cooling under TV1 crater, and heating at 50-100 m depth in the E side of Donald Mound. Similar results have been obtained since late 1993; however, the rate of magnetic change has more than doubled, suggesting that the heating rate has significantly increased.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

December 1995 (BGVN 20:11) Cite this Report

Sub-crater divides collapse, but no eruptive activity

The following summarizes observations between August and December 1995 made by pilot R. Fleming and IGNS scientists. No significant eruptive activity has occurred since minor ash emissions on 28-29 June (BGVN 20:07).

A new 30-m-diameter crater was noted on 12 August in the area of the May '91 embayment. It had destroyed a large fumarole and was ejecting mud at intervals of 2-5 seconds. By 3 October, Wade, TV1, and Princess craters were joined in a single lake, following the failure of their divides. On 13 November the rising lake level was encroaching on the area of fumaroles and hot ground. Several new fumarolic vents were noted 20-30 m above the lake level. No more crater changes were observed through 12 December. Very little seismicity was recorded: low-frequency tremor accompanied the formation of the 12 August vent. Seismicity revealed no evidence of eruptive activity since 28-29 June.

Ground deformation and magnetic surveys continued to record trends indicative of future eruptive activity. Inflation was localized in the Donald Mound area, in contrast with the earlier pattern of crater-wide inflation between November 1994 and July 1995. Inflation is occurring at a much greater rate than that observed before the 1976 eruption. Magnetic decreases under Donald Mound and on the NE side of the 1978/90 Crater Complex indicate shallow heating. Other indicators like heatflow and gas chemistry do not suggest an incipient eruption. Fumarole temperatures remain relatively low, and gas samples from fumaroles were richer in water than in the past, consistent with the rise of the water table. However, the influence of the rising water level and its possible masking effects remain uncertain.

Information Contacts: B.J. Scott, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

April 1996 (BGVN 21:04) Cite this Report

Uplift of the main crater floor and changes in the hydrothermal system

There has been no eruptive activity at White Island since the minor ash emission of 28-29 June 1995 ([corrected from] BGVN 20:07). A vent formed in August but no tephra was erupted (BGVN 20:11/12). Ground-deformation surveys continued to record uplift of the main crater floor. Magnetics showed a persistent decrease N of Donald Mound and an increase S of it. Changes were noticed in the hydrothermal system, but no significant variations were observed in seismicity. This report briefly summarizes several visits to the island from 27 December 1995 through 17 March 1996.

On 27 December, a slow but continuous rise in the water level of the combined crater lake was observed. Strong and audible fumarole activity was concentrated in the May 91 embayment area, on the N side of 1978/90 Crater Complex. During 22-24 January, scientists noted enhanced steam emissions, which may have been due to falling atmospheric pressure before a storm. The Dragon's Foot spring below fumarole 1 (SE of Donald Mound) reverted to being a fumarole after being a hot pool during most of 1995. Comparison of photographs suggested that the lake level had risen by 1-2 m since 12 December 1995.

During 9-12 February, fumarole temperatures in the May 91 area were 143°C, the lake level had risen, and the water temperature was 53°C. More intense fume emissions were observed from Donald Mound. In March, a new fumarole with a temperature of 100°C was found on Donald Mound and Noisy Nellie's temperature rose from 89°C on 7 March to 124°C on 17 March. Although there was no major increase in fumarole temperatures, heat flow had increased, as evident from expanded areas of sublimation, steaming ground, and mud pots. Gas discharge was very strong in the fumaroles along the S crater wall. Partially completed analysis from fumarole 13 showed increased HCl discharge.

Water analyses from the crater lake carried out between November 1995 and February 1996 showed decreasing pH values (from 0.58 to 0.23), increasing Cl concentrations (63,600 to 68,100 ppm), and decreasing Mg concentrations (6,060 to 5,600 ppm).

Observed ground deformation on 29 February suggested continuing strong inflation centered on Donald Mound, where the uplift rate since December had almost doubled compared to the previous five-month period (from 92 to 171 mm/year at peg F). Moreover, the uplift rate across the entire crater floor was twice that observed over the past two years (55 mm/year at peg C since December 1995, 28 mm/year at peg C from December 1993 to December 1995). This significant increase in the rate of inflation under both Donald Mound and the crater floor was interpreted as an indication that shallow (~100 m deep) heating is increasing under Donald Mound, and intrusion and/or heating is occurring in the whole area at a deeper level (~500 m). These observations suggested that water table changes were not the cause of the surface deformation (BGVN 20:11/12).

The magnetic survey on 23 January focused near Donald Mound where most of the recent changes took place. The dominant trends, decrease on the N side of Donald Mound and increase to the S, indicated shallow (50-100 m deep) demagnetization in this area.

No significant seismicity has occurred since September 1995. However, since 15 January 1996, high-frequency microearthquakes have appeared on the records in low numbers (50-300/ day). The occurrence of two E-type events did not produce any surface manifestation.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

September 1996 (BGVN 21:09) Cite this Report

Recent heating and deformation episode appears to have ended

Observations in April, May, and July indicated continued increases in heat flow and inflation of the Main Crater floor. Low-level volcanic tremor that began in late July continued through August. Since the tremor commenced it appears that heat-flow has decreased, as has the deformation. Measurements in late August indicated that the crater-wide deformation and heating of the last 2-3 years appears to have peaked without eruptive activity. Since the last report (BGVN 21:04), monitoring visits were made on 18 April, 16 May, 24 July, and 28 August 1996.

Crater observations. On 18 April, the lake occupied Royce, Wade, Princess, and TV1 craters, with the S part of the divide between Princess and Wade craters 2-3 m above the lake. The lake was light turquoise, with a few brown surface slicks. A fumarole in the N wall of Wade Crater was audible from the edge of the 1978/90 Crater Complex; it was the only significant steam source in the complex.

Donald Mound was steaming vigorously, with that part exposed in the wall of the 1978/90 Crater Complex and the SE slopes the dominant features. Sulfur deposits were obvious on Donald Mound and the 1978/90 wall. The area of mud pots at the base of Donald Mound was also steaming vigorously. The whole area was wet and some mud pots included areas of significant sulfur deposition. Collapse was actively occurring between the 1978/90 Crater Complex and Donald Duck, causing brown slicks on the lake surface.

An ejecta apron with material up to 12 m from the vent was observed by charter pilot J. Tait on 4 June. Calm and clear conditions on 9 June allowed a tall steam plume to develop above the island; it was mistaken as an eruption plume by several coastal observers and the media. However, pilots R. Fleming and J. Tait, on the island at the time, observed no unusual activity. On 11 June R. Fleming reported a dramatic rise in lake level (>5 m) in three weeks. Strong convection in the lake caused fountaining up to 3-4 m high in the embayment below the May '91 vent.

Fumarolic discharge continued to increase on the crater floor when measured on 28 August, although temperatures had moderated somewhat since May. Springs, consisting largely of steam condensate, continued to discharge, and two new such features had developed along the boundary between the E and central sub-craters. Maximum temperatures on Donald Mound were 311°C, down ~100°C from May. A large fumarole discharging a bright yellow, sulfur-laden plume had developed ~5 m below the inner crater rim that intersects Donald Mound. The crater lake was mostly obscured by steam, but it appeared gray in color; maximum temperature as recorded by pyrometer was 69°C.

Magnetic survey. A comprehensive survey of the magnetic network was conducted on 16 May with the exception of a few sites at Donald Mound that were inaccessible due to hydrothermal activity. Contouring the changes since the partial survey on 23 January 1996 showed that the decreases at Donald Mound with corresponding increases to the S were continuing. These results suggested continued shallow (50-100 m deep) heating. A weaker negative anomaly W of Noisy Nellie, presumably resulting from heating on the N side of the complex, continued the trend observed during 6 July-12 December 1995.

A positive anomaly E of Donald Mound (site D10b) showed a change of +518 nT, although the site is near a new mud hole, so the effect may be local. Positive changes at Site G (+126 nT) and nearby sites are unusual because decreases are usually recorded when there is heating at Donald Mound. This anomaly may suggest cooling, perhaps around 100-200 m deep, at the E edge of the area of hydrothermal activity, possibly related to the rising water table.

Deformation. Levelling surveys on 18 April and 16 May were conducted over the entire network except over Donald Mound due to intense steam and hot, soft ground. Both surveys revealed broadly similar patterns and rates of continuing uplift centered on Donald Mound and extending SE. Relative subsidence continued NW of Donald Duck Crater, although part of that may be due to slumping induced by encroachment from the 1978/90 Crater Complex. The inflation pattern during the previous five months remained similar to that since Donald Mound began rising in late 1993.

A partial levelling survey was done on 28 August; three pegs near Donald Mound could not be accessed, two were lost due to crater wall collapses, and one was buried under a landslide. Since about 1992-93, levelling surveys have shown a systematic crater-wide uplift. However, this survey showed a dramatic reversal of the uplift trend, with minor subsidence observed over much of the Main Crater floor. The larger subsidences were focused about the Donald Mound area and the margins of the 1978/90 Crater Complex. These changes are consistent with the thermal changes observed on 28 August and may indicate that the present inflationary-heating episode is over or declining.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

November 1996 (BGVN 21:11) Cite this Report

Inflating and heating trends cease and reverse

During 4-5 November, surveillance visits were made by scientists from the Institute of Geological & Nuclear Sciences (IGNS), Canterbury University, Otago University, Victoria University, Michigan Technology University, and California Institute of Technology.

Like monitoring results on 28 August (BGVN 21:09), these visits showed a continuation of the crater-wide deformation and heating reversal. This reversal suggested that a major long-term inflationary and heating pulse had peaked and that the probability of a significant eruption might be low in the short term.

Crater observations. A crater lake continued to occupy the floor of the 1978/90 Crater Complex (figure 24). Green coloration developed in the lake with blue-gray surface slicks. The coloration change from gray- brown to green in August-September suggested that there was less vigorous input into the lake with less or no convection. On 5 November, the water temperature of the lake was 58.2°C. A rapid fall of the lake level occurred, with the water level of the lake dropping 5-10 m during the week preceding the visit.

Figure 24. Relative height changes at White Island between 28 August and 4 November 1996. Numbers beside circles are relative height changes at individual pegs (in millimeters). Heavy contours (in millimeters) show relative height changes; light contours (in meters) show topography. Courtesy of B.J. Scott, IGNS.

The steep margins of the 1978/90 Crater Complex continued to fall, and several fresh landslide scars were visible around the crater wall. Similar activity also occurred in Donald Duck Crater.

Fumarole activity near Donald Mound continued to change. Many areas previously holding mud pots or pools had dried out and contained low-pressure fumaroles; maximum temperatures had decreased from 311°C on 28 August to 268°C. In contrast, beginning in late September, Noisy Nellie was almost full of water and sometimes overflowed. Several fluid seeps also developed in Noisy Nellie along with substantial landsliding off the Main Crater wall.

Deformation. A leveling survey of the White Island network was made on 4 November, with some sections repeated on 5 November. This survey revealed a continuation of the reversal of the inflationary trend first observed on 28 August (BGVN 21:09). Subsidence was apparent across the Main Crater floor, increasing toward the 1978/90 Crater Complex and Donald Mound (figure 24). Compared with the inflation from 1992, the recent subsidence was quite small (figures 24 and 25).

Figure 25. Relative height changes (in meters) with time at pegs C, F, and O in the White Island crater. Courtesy of B.J. Scott, IGNS.

Magnetic survey. Magnetic changes between 16 May and 4 November were dominated by a positive anomaly over most of the N part of the Main Crater centered just E of Donald Mound. A less intense anomaly occurred S of the Main Crater. These features suggested shallow (50-100 m deep) cooling on the E side of Donald Mound, probably a broadening of the cooling trend observed between 12 December 1995 and 16 May 1996 (BGVN 21:09).

Another significant trend was the negative anomaly to the N of Donald Mound, which appeared to be a continuation of the trend seen in this area since late 1995. These magnetic decreases might be due to shallow (100 m deep?) heating on the E side of the 1978/90 Crater or possibly to chemical demagnetization.

The overall magnetic pattern appeared to be the reverse of the trend from late 1993 to early 1995. However, the earlier trend did not reverse in magnitude, and lower temperatures on the E side of Donald Mound did not necessarily mean that the total heat flow was reduced. The continuing collapses along the E edge of the 1978/90 Crater Complex probably diverted more heat flow, and high temperatures (above ~450°C for significant thermo-magnetic effects to occur) were no longer sustainable near the surface.

Information Contacts: B.J. Scott, Colin Wilson, B.F. Houghton, and I. Nairn, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

February 1997 (BGVN 22:02) Cite this Report

Inflation peaked without eruptive activity

The 1993-96 inflationary and heating trend has peaked without eruptive activity, thus lowering the probability of a significant eruption in the short-term. However, since inflation is still higher than 1993 levels, eruptive activity in the medium- to long-term could still occur. The following summarizes a surveillance visit on 31 January and the report of a helicopter pilot in mid-December 1996.

Crater and fumarole observations. The water level of the lake in the 1978/90 Crater Complex continued to fall (BGVN 21:11). During 15-20 December, pilot R. Fleming reported the presence of a bank in the lake, which turned out to be a delta extending from the mouth of an E-W trending valley on the W side of the crater. The cyclonic activity of late December-early January resulted in an increase of the lake level and made the water turn dark gray. By late January an island appeared as the water level fell. Both the bank and the island were formed by sediment washed into the 1978/90 Crater complex from the valley.

Most of the crater lake was light blue-green with many bright orange-yellow slicks of sulfur at the edges of convection areas. The temperature was 69.5°C, similar to the last measurements. Vigorous geysering occurred from several vents NW of the island, in the May 91 Crater area. Enhanced fumarole emission also started near the Orca vent. Fumarole 13a temperature remained unchanged at 109°C.

Noisy Nellie was very quiet and had dried out; another fumarole appeared to the left of the main one. Two mud pots were near the main crater. Activity at fumarole 14 (80 m S of 13) had also decreased significantly to minor steam emission and a temperature as low as 75.3°C.

Deformation and magnetic surveys. A deformation survey revealed that the subsidence area observed in November 1996 (BGVN 21:11) had enlarged and clearly trended E-W. An elongated zone of subsidence became apparent on the Donald Mound where the subsidence rate was ~99 mm/month; an area of apparent uplift was observed across the E end of the main crater.

Magnetic changes observed between 4 November 1996 and 31 January 1997 were dominated by small increases (<20 nT), largely due to uncorrected diurnal changes or possibly broad or deep cooling. The only area with >50 nT change was around the N side of Donald Mound (+124 nT); at this site, however, the rate of change had decreased from 1.58 to 1.41 nT/day. A more dramatic change occurred close to the fumarole on the flat adjacent to Donald Mound, where the rate of change dropped from 5.95 nT/d to 0.48 nT/d. This suggested a higher temperature under this area and explained the higher level of fumarolic activity.

A significant magnetic decrease of -34 nT occurred NW of Donald Duck Crater, probably due to demagnetization under the E side of the 1978/90 Crater Complex.

Seismicity. In late July 1996 volcanic tremor was recorded for the first time after August 1995. The amplitude fluctuated during August before settling to a new background level, ~4x higher that the average levels earlier in 1996. Volcanic tremor continued to be recorded at this relatively higher level, but no significant trend was apparent.

Information Contacts: B.J. Scott, C. Wilson, B.F. Houghton, and I. Nairn, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

July 1997 (BGVN 22:07) Cite this Report

Surveys on 11 March and 6 May confirm that the deflation trend continues

Scientists from the Institute of Geological and Nuclear Sciences (IGNS) visited White Island on 11 March and 6 May. Prior to the visits, the 1993-96 inflationary and heating trend had peaked without eruptive activity, thus suggesting a lower probability of a significant eruption in the short-term. However, inflation remained above 1993 levels.

Crater and fumarole observations. The island was visited on 11 March by S. Sherburn who accompanied a UK-based film company. The lake in the 1978/90 Crater complex was emerald green and its level had change little since January (BGVN 22:02). Although some gray slicks on the lake surface were observed, there was no evidence of convection. A noisy fumarole on the N wall was noted.

On 6 May the lake level was lower than on 11 March, and several small banks or islands were emerging from it. Steam in the crater thwarted efforts to observe convection. The lake temperature was 66°C, three degrees cooler than the last measurement obtained on 31 January. Minor collapse of the crater margin continued, especially around the steeper N and NE margins. Both fumarole 13a and the fumarole centered in Donald Mound registered temperatures slightly lower than those previously reported.

Deformation and magnetic surveys. Visitors completed a full survey of the leveling network on the main Crater floor in good conditions. It indicated continued subsidence at an area subsiding since November 1996 (BGVN 21:11) (figure 26). It also revealed that in the center of Donald Mound there was a semi- elongated subsidence zone dropping at a rate of 9 mm/month; this subsidence was first noticed in January 1997 (BGVN 22:01) (figure 27).

Figure 26. Contour plot showing height changes at White Island between 31 January and 6 May. Height changes are in millimeters. Courtesy of B. J. Scott, IGNS.

Figure 27. Time series plot for White Island showing height of selected pegs. Refer to figure 26 for peg locations. Courtesy of B. J. Scott, IGNS.

In situ magnetism observed between 31 January and 6 May 1997 showed the smallest rates of change recorded in the last few years and no changes >50 nT. Most sites underwent a small field strength decrease. The only significant increases were on the N side of Donald Mound (a maximum recorded change of +46 nT at site S), indicating continuing shallow (~ 50 m deep) cooling. It was noted that at site S the rate of magnetic change had decreased significantly (0.48 nT/day, compared with 1.41 nT/day during 4 November 1996 to 31 January 1997). The widespread, small decreases could be due to an uncorrected diurnal variation or deep heating. The most recent data on the graph of the cumulative magnetic change at sites G and M (figure 28) may indicate that the trend at site G reversed. Such a reversal would imply heating; however, more time is required to confirm a trend reversal. Overall, the low rates of change in magnetism could indicate that temperature had stabilized and that the current level of surface hydrothermal activity will not greatly change in the short term.

Figure 28. Time series plot showing magnetic changes at White Island's pegs G and M. Refer to figure 26 for peg locations. Courtesy of B. J. Scott, IGNS.

Seismicity. Volcanic tremor had dominated the seismic records since July 1996 when it prevailed at a new background level ~4x higher that the average earlier that year. The ground motion for 1997 (figure 29) showed no diagnostic trend or clearly demonstrative pattern.

Figure 29. Time series plot showing White Island's volcanic tremor for 1997 (logarithm of tremor amplitude versus time). Courtesy of B. J. Scott, IGNS.

The uninhabited, 2 x 2.4 km White Island emerges at the summit of a 16 x 18 km submarine volcano. The island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Intermittent steam and tephra eruptions have occurred throughout the short historical period, but its activity is also prominent in Maori legends.

Information Contacts: B.J. Scott, C. Wilson, B.F. Houghton, and I. Nairn, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

April 1998 (BGVN 23:04) Cite this Report

Hydrothermal eruptions in late March

Minor hydrothermal eruptions occurred at White Island over the period 28-29 March. Lake floor mud, blocks, and tephra were ejected across the main crater floor and over the N flank of the 1978/1990 crater complex. Tephra was thickest around Noisy Nellie crater, and numerous impact craters were also observed. Small scale steam eruptions were continuing from a vent in the Crater Complex.

Deformation. A leveling survey on 8 April showed a decline in the subsidence rate; minor uplift was apparent across much of the crater floor. Figure 30 shows differences in height between 8 December 1997 and 8 April 1998. Figure 31 shows a time series of selected pegs. Some subsidence is continuing, particularly in the Donald Mound area.

Figure 30. Contour map of White Island showing height changes in millimeters between 8 December 1997 and 8 April 1998. Contours are in meters above sea level. Courtesy IGNS.

Figure 31. Time series showing height changes at selected pegs. Heights are meters above origin. Courtesy IGNS.

Seismicity. The recent hydrothermal activity was accompanied by an increase in the level of volcanic tremor. Figure 32 shows the daily average tremor for 1998. The dominant frequency did not change significantly.

Figure 32. Time series showing ground velocity (upper) and dominant frequency (lower) of volcanic tremor at White Island. Courtesy IGNS.

Gas and fumarole chemistry. Gas and water samples collected during recent visits initially showed a decrease in water content. Fumarole temperatures showed little change. During a COSPEC flight on 20 March only 140 tons per day of SO₂ were recorded; a flight 3 April indicated an increase to over 400 tons per day, consistent with the fumaroles drying out and allowing more gas to escape.

Magnetics. Three notable trends can be seen between 6 May 1997 and 8 April 1998 (figure 33). Magnetic increases N of Donald Mound correspond to decreases to the S: for example, an increase of 140 nT at site 'S' corresponds to a decrease of 43 nT at site 'P'. These may indicate shallow ( ± 50 m depth) cooling under Donald Mound. The decreases further N around Donald Duck and Noisy Nellie (e.g. -45 nT at site 'Y') could indicate deeper heating that is being masked by the shallow cooling. Both trends are continuations of those seen early in 1997 (BGVN 22:02). A third trend could be indicated by the decrease at 'CT5' (24 nT) and corresponding increase at 'CT3' (20 nT). These suggest localized, very shallow ( ± 20 m) heating in the vicinity of fumaroles SE of Donald Mound. Sites to the extreme N and S of the crater were not surveyed. Overall, the magnetic changes remain smaller than in 1995-96.

Figure 33. Contour map showing magnetic changes (in nT) between 6 May 1997 and 8 April 1998. Courtesy IGNS.

Summary. Monitoring data suggest the deflationary-cooling trends of the last 2-3 years are starting to reverse. This could lead to further eruptions. Should magmatic activity occur it would be stronger than the present hydrothermal activity and likely pose a risk to visitors on shore.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

August 1998 (BGVN 23:08) Cite this Report

Non-seismic eruptions confirmed during 31 August visit

On 21 August steam-and-gas plumes were reported rising to 1,500 m above White Island. There was no significant change in seismicity at that time, so the plume was taken to be atmospheric in nature (it is common for tall vapor plumes to form above the island on the first day of clear weather after a frontal system has passed). Visits by tour operators, however, indicated that on 22 August the plume was gray colored and presumably ash-laden, and on 23 August red colored. None of this activity was accompanied by seismic signals. A surveillance team visited on 31 August to confirm eruptive activity, make a ground deformation survey, and sample fumaroles and newly deposited ash. The hazard status was raised to Level 2.

A new active vent had arisen in the NW corner of the 1978/90 Crater Complex, in an area characterized by high-temperature fumaroles and gas vents over the last 2-3 years. This vent was in approximately the same area as one formed in May 1991. A maximum temperature of 463°C was measured for the venting ash column at the point of discharge. The progression from high-temperature fumarole, to active vent, and eventually active crater has been a common process at White Island. The lake on the floor of 1978/90 crater was greenish-brown in color, cool (20°C), and lacked visible zones of up-welling lake water.

Numerous impact craters had covered the mud flats adjacent to the lake. There were numerous fumarolic discharges on the crater floor, many of which appeared accessible since a collapse feature called "The Sag" had formed a rampart into the main crater. Visible cracking had appeared on the crater floor adjacent to The Sag and steam (at ~90°C) discharged through these cracks; sulfur was actively precipitating in the largest vents. This area is now unsafe to approach.

The ground-deformation survey revealed that inflation of the crater floor was reoccurring. Several survey marks that showed uplift until 1995-96, followed later by minor subsidence, had reversed again and uplift was observed. Experience from the 1976-82 eruption episode suggests that uplift occurs before eruptive episodes. Large-scale subsidence was apparent in The Sag area, with a drop of over 1,300 mm recorded (beyond Peg M). This subsidence overrode all deformation signals from the active vent in this area. Further collapse can be expected.

The volcanic ash deposit included two distinct layers. The lower one consisted almost entirely of varied and intensely altered fine white tuff together with altered lava chips; gypsum crystals were present as a minor component. This was interpreted as hydrothermally altered vent-filling detritus ejected during the opening phases of the newly active vent. The upper layer consisted of mixed altered fine detritus and fresh andesite crystals and matrix, but without pumiceous scoria clasts. Once cleared of altered debris, the vent appears to have discharged ash containing a high component of very fresh andesite. However, the lack of pumice or scoria suggested that the vent was not discharging directly from magma but possibly from the solidified carapace above a shallow degassing magma body.

Fumarole temperatures were generally lower than on previous visits, probably reflecting recent heavy rains. Fumarole 1 had a maximum temperature of 101.2°C (down from ~111°C in April), and the discharge remained CO₂-enriched (water depleted). All fumaroles on Donald Mound were at or below the boiling point with low discharge pressures. Noisy Nellie's temperatures had declined since April (from 153 to 126°C), but the pressures had apparently increased. Steam also discharged around the rim of Noisy Nellie flat, and a new fumarole discharged strongly on the E slope of the hill adjacent to Noisy Nellie crater. Fumarole 13a temperatures, at 105°C, were 8°C lower than in April and the discharges appeared to be CO₂-enriched.

Observations from the crater floor were generally consistent with increased degassing associated with new eruptive activity. It is anticipated that fumarolic discharge temperatures will increase as the hydrothermal system heats up. None of the eruptive activity had been accompanied by seismic signals; this is very unusual for White Island and if it persists it will be difficult to remotely assess activity.

The uninhabited 2 x 2.4 km White Island is the emergent summit of a 16 x 18 km submarine volcano. The island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE, where the shoreline conforms to several notches in the SE crater wall. Intermittent steam and tephra eruptions have occurred throughout the short historical period, but activity at White Island also forms a prominent part of Maori legends.

Information Contacts: B.J. Scott, Manager of Volcano Surveillance, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).

October 1998 (BGVN 23:10) Cite this Report

Minor gas-and-ash eruptions in August and October

A minor eruption at White Island in August (BGVN 23:08), which was investigated by volcanologists from the Institute of Geological and Nuclear Sciences (IGNS), persisted until late in September. Analysis of samples collected during the visits continued through September. Eruptive activity recommenced in late October, prompting another investigative visit on 2 November. The following reports is summarized from IGNS Science Alert Bulletins.

A new active vent in the NW corner of the 1978-1990 Crater Complex produced intermittent weak ash emissions during late August and early September that rose 100-1,500 m above the island. September ash contained more fresh volcanic glass than previous samples, but this failed to give clear indication of new magma being the source because the eruptions came from a crusted-over magma body.

Weak volcanic tremor on 10-11 September appeared on seismic records and impacted estimates of the Real-Time Seismic Amplitude (RSAM). The RSAM outputs a number of 'counts' over set time intervals. The higher the counts the stronger the volcanic tremor signal and the stronger the volcanic activity. The RSAM count level in mid-September was about 12-13, on a scale of several thousand, having risen from the typical background of 2-3 counts. There were no reports of ash after 18 September and seismicity was reduced to background levels. The Alert Level was reduced from 2 to 1 on 29 September.

Minor eruptive activity recommenced on 24 October. Small amounts of ash were emitted on 24-25 October, and on 31 October a steam-and-ash column rose in calm conditions to 1,500-1,600 m above the volcano. Weak volcanic tremor reappeared at about the same time as the ash eruptions recommenced; however seismicity remained low.

A surveillance visit was made on 2 November to assess the activity, conduct a deformation survey, and collect ash and gas samples. The level of activity varied during this visit, but the most energetic activity observed was not sufficient to raise the Alert Level. The active vent at the base of the NW wall of the 1978-1990 crater had grown slightly since August. A very weak ash-charged reddish-gray convecting plume was emitted. Occasional yellowish hues were present in the plume, consistent with the periodic eruption of hydrothermal sulfur from the vent. The maximum temperature measured in the ash column was 451°C.

Eruptive activity over previous days had deposited 15 mm of fine dark gray ash at the crater rim. Examination of the ash indicated no change in character from that of the July-August eruptions. Ground-deformation surveys showed a consistent trend of minor deflation across the main crater floor, with the largest changes (20-30 mm) near the crater rim. However, fumarole temperatures had increased nominally since August 31. Fumarole ##1 was at 113°C (up from 101°C), was moderately dry, and had molten sulfur in the orifice (indicating temperatures in excess of 119°C in the vent). Donald Mound continued to discharge only low-pressure steam from diffuse areas of steaming ground, and the cracks around Peg M continued to discharge steam close to the boiling point. Maximum temperature at Noisy Nellie was 140°C (up from 126°C), whereas pressures were similar to those observed in August. Fumarole 13a was 111°C, a slight increase from August (105°C). The plume from the island appeared to carry a heavier SO₂ burden than observed in August.

The uninhabited 2 x 2.4 km White Island is the emergent summit of a 16 x 18 km submarine volcano. The island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Intermittent steam and tephra eruptions have occurred throughout the short historical period, but its activity also forms a prominent part of Maori legends.

Information Contacts: B.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

November 1998 (BGVN 23:11) Cite this Report

Minor eruptive activity continues; alert level raised

Minor eruptive activity continued at White Island through November and early December. The level of activity varied, but observations during visits and instrumental indicators in early December were sufficient to raise the Alert Level from 1 to 2 on 3 December. The current style of activity was expected to continue for some time.

There was evidence that molten magma was the direct cause of eruptive activity, although only weak volcanic tremor accompanied the ash eruptions. A surveillance visit was made on 1 December to assess the ongoing activity, conduct deformation and magnetic surveys, and collect ash and gas samples.

Observations. The active vent at the base of the NW wall of 1978/90 Crater continued to erupt fine-grained volcanic ash during the 1 December visit. The vent size had not changed since the 2 November visit (BGVN 23:10). During the later visit, an ash-charged, tan-brown convecting plume rose to ~800 m before trailing downwind 10-15 km. The volume of ash in the plume was greater than that observed any time during November. The eruptive activity had deposited up to 45 mm of fine, dark gray and brown ash at the crater rim. Samples of ash that fell on 1 December showed a significant change from ash collected on 23 November and earlier. The 1 December ash samples contained fresh, vesiculated glass, suggesting that magma may have risen in the vent and was contributing directly to the eruption. Previously the ash was derived from solidified lava.

A ground-deformation survey showed a consistent trend of minor inflation across the main crater floor, with continued subsidence near the rim of 1978/90 Crater (figure 34). Large-scale post-1990 inflation was evident at the more distal sites (Pegs C and J), with only minor changes over the last 2-3 months. Collapse about the crater rim, which started in July, was continuing but at a lesser rate (Pegs M and W). Provisional results from the magnetic survey indicated heating at depth and shallow cooling about the crater rim area.

Figure 34. Contour plot from White Island showing the height changes (mm) between measurements made 2 November and 1 December 1998. Courtesy IGNS.

Fumarolic discharge pressures from sites 1, 6a (base of Donald Mound), and 13a were not significantly stronger than those observed on 2 and 16 November, and temperatures remained high at these features: site 1, 124°C; site 6a, 107°C; and site 13a, 120°C. Molten sulfur was found in vents at sites 1 and 13a, which is consistent with the temperatures in excess of 119°C. The sulfur mound at site 1 had grown over the vent during November, suggesting that sulfur was being remobilized from depth in response to elevated temperatures. The discharge at site 6a was mildly superheated, but of high pressure, indicating a relatively high gas content. These observations were consistent with general heating of the hydrothermal system.

The lake, which had reformed in the main crater, was the likely result of recent rains. The lake water was cool (~20°C) and had the brown color of the ash falling into it.

Information Contacts: B.J. Scott, Manager of Volcano Surveillance, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

December 1998 (BGVN 23:12) Cite this Report

New multiple-vent crater forms within 1978/90 crater

A multiple-vent crater, named Metra, took form on the floor of main 1978/90 crater during 7-11 January. The other active vent (PeeJay) in the main crater formed in August 1998 and continued to emit dense volcanic gas and steam with some volcanic ash. Volcanic tremor levels decreased with the decline in activity at Metra, but remain slightly above typical background for White Island.

A visit was made on 12 January to assess the ongoing activity, conduct a deformation survey, collect ash and gas samples, and service the seismic installation. Results from that visit are reported below. An Alert Level 2 remained; explosive eruptions producing ballistic ejecta are considered possible, particularly if Metra Crater reactivates.

PeeJay vent. The size of PeeJay vent, located at the base of the NW wall of 1978/90 crater (figure 35), had not changed appreciably since a visit in November 1998 (BGVN 23:10 and 23:11). During the January 1999 visit the only generally active vent was PeeJay. It emitted considerable volumes of gas and steam under high pressure, and carried a minor amount of dark gray ash. The plume rose to ~300-350 m before trailing off downwind 10-15 km. The volume of ash contained in the plume was less than that observed over the past month.

Figure 35. Sketch map of the crater area showing the position of the vents and ground deformation contours (heavy black lines; deformations in mm). Courtesy IGNS.

Measurements made near Peg Z, 140 m ENE of PeeJay, show that about 120 mm of fine ash had accumulated between 1 December 1998 and 12 January 1999, in at least 12 episodes of ashfall, mainly from PeeJay. Near Peg M, 280 m SE of PeeJay, only half that thickness was recorded.

Metra Crater. A considerable portion of the floor of 1978/90 Crater had collapsed, forming a multiple-vent, collapse-crater feature subsequently named Metra Crater (figure 35). The margins of this feature were characterized by scalloped areas that had subsided 5-10 m. On the N side were very fresh cracks in the ground; more collapse was deemed likely in this area. During the visit, Metra was essentially inactive but vivid white steam was emitted (figure 36). The deeper vents in Metra (15-20 m deep) contained pools of muddy, dark gray water and are likely the site of previously observed hydrothermal eruptions. Eruptions from Metra during the period from 7 January, when it was first seen, through 11 January produced a surrounding apron of closely spaced ballistic blocks on the 1978/90 crater floor. Scattered impact craters containing blocks up to 40 cm were seen on the 1978/90 crater rim in areas frequented by visitors, and isolated impacts were noted up to 350 m from Metra near Noisy Nellie. Observations on 17 January confirmed that no eruptions were occurring at Metra Crater; overnight rains had flooded the crater floor.

Figure 36. Close-up view of the new Metra crater at White Island, which appeared during January 1999. Courtesy IGNS.

Other observations. The ground deformation survey showed a consistent trend of minor deflation across the main crater floor, with continued subsidence near the rim of 1978/90 Crater. Data from two selected pegs (figure 37) show the large-scale post-1990 inflation and minor deflation over the last 2-3 months.

Figure 37. Plot showing temporal height changes of two selected pegs at White Island. Heights are in meters. Courtesy IGNS.

Volcanic tremor declined following the high that accompanied the formation of Metra (figure 38). Afterwards, tremor remained slightly higher than before the formation of the new vents. Tremor levels were low during 11-13 January before dramatically rising to a peak overnight on 14-15 January—the highest levels since those that accompanied the formation of the Metra Crater on 6-7 January. A further peak occurred on the evening of 15 January. Between 1030 and 1500 on 16 January explosive activity at Metra Crater tossed blocks up to 400 m from the crater. Observations from a helicopter operator, who was over the island during 1200-1220, suggested that multiple vents were active, each one erupting differently. Volcanic tremor levels reached a low on the morning of the 17th.

Figure 38. Plot showing volcanic tremor at White Island, 5-17 January 1999. Courtesy IGNS.

Discharge temperatures and characteristics for fumaroles on the main crater floor were little changed from previous measurements made on 1 December. Fumarole ##1 measured 111°C, but tubes removed from the vent were coated in molten sulfur, indicating temperatures in the conduit of at least 119°C. Elemental sulfur continued to accumulate near this and neighboring vents on the S crater wall at high rates. Discharges on Donald Mound and Gully were very weak. Noisy Nellie and ##13a discharge pressures were strong, with temperatures of 134°C and 115°C, respectively.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).

January 1999 (BGVN 24:01) Cite this Report

Eruptive activity declines, alert level lowered to Level 1

The eruptive activity on White Island (BGVN 23:10-23:12) continued but declined dramatically during the latter part of January. The alert level was lowered to Level One by the New Zealand IGNS.

Low volcanic-tremor levels rose overnight on 14-15 January to the highest levels recorded since the formation of the Metra Crater in early January (figure 39). Another tremor peak occurred during the evening of 15 January. On 16 January explosive activity in Metra Crater tossed blocks up to 400 m from the crater. Airborne observations during the explosive activity suggested multiple, differing eruptive events. Volcanic-tremor levels lessened on the 17th and later observations confirmed that no eruptions were occurring from Metra Crater. Overnight rains flooded the crater floor. A steam column rose 600 m above PeeJay Vent.

Figure 39. Seismic energy levels at White Island, January 1999. Courtesy IGNS.

Activity declined dramatically after 22 January (figure 39). By 3 February activity at Metra Crater and PeeJay Vent was hydrothermal, dominated by volcanic gas-and-steam emissions and minor geysering. The alert level was lowered to Level One based on aerial observations and a review of the seismic activity. Weak to moderate gas-and-steam emissions issued from PeeJay Vent, including 300 to 400 tons/day of SO₂ gas (2-3 times typical SO₂ background levels). Metra Crater area was dominated by shallow pits containing small ponds, fumaroles, and geysers. On 2 February a gas plume extended >30 km from the volcano.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).

February 1999 (BGVN 24:02) Cite this Report

Minor ash-and-steam emissions continue

Volcanic-tremor levels on White Island (BGVN 23:10-23:12 and 24:01) have remained low since 22 January and low-level eruptive activity continued through mid-March. On 12 February, the low-energy hydrothermal activity within Metra Crater was dominated by gas-and-steam emissions from small fumaroles on the N and W sides of the crater. Four small ponds had formed on the crater floor. A weak gas (SO₂) and steam plume from PeeJay Vent rose 400-500 m, forming haze visible 40-50 km away.

During a visit by C.P. Wood on 13 March activity was generally constant with the ash-and-steam column rising to ~ 1,060 m and drifting many kilometers downwind, with sea discoloration from fall-out evident to 1 km from the island. PeeJay Vent was continuously emitting ash-charged gray-brown steam, but with varying intensity. During peak discharges, observers standing on the 1978/90 Crater Complex edge noted a rumbling noise from PeeJay, but no block ejection was seen. The vent diameter appeared to have increased and was an obvious funnel shape lined with whitish sublimate deposits. Ash could not be collected because of the wind direction. Metra Crater was occupied by a lurid lime-green lake, which largely filled the original crater and peripheral scallops to ~ 1 m below the rim (the old lake floor). There was no sign of thermal disturbance in the Metra lakelet. The ash surface throughout Main Crater was rain-washed and smooth (except for the route used by tourist operators), with no sign of recent impact craters near the 1978/90 Crater Complex edge.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

April 1999 (BGVN 24:04) Cite this Report

Metra Crater excavated by 17 April explosions

Explosive eruptions on 17 April produced significant changes at Metra Crater. Institute of Geological & Nuclear Sciences (IGNS) scientists visited the volcano on 20 and 30 April to service the seismic installation and assess the effects of the explosive eruptions. These were the largest explosive eruptions since September 1992.

The whole island was blanketed with a thin layer of light-gray ash on 20 April. No single direction of dispersal was apparent, although ground thickness suggested that dispersal was toward the E. The lake in Metra Crater had disappeared and a steam plume traveled to the SE. During the 30 April visit a steam-and-gas plume, fed by emissions from PeeJay Vent and a new vent E of PeeJay, rose 750-900 m before traveling SW (figure 40).

Figure 40. Aerial view of 1978/90 Crater Complex on 30 April. Metra Crater is in the left foreground, while the two areas of steam emission in the center are PeeJay Vent and the new vent. Courtesy of IGNS.

Ballistic blocks and bombs had been ejected 450 m by the 17 April explosions; judging from changes in crater size and shape, they likely came from Metra Crater. The larger fragments fell mainly to the S and SW. Abundant centimeter-size fragments had impacted into new ash around the vents at distances of up to 600 m radius. At least 10 cm of fresh ash had fallen within a 200-m radius of the main crater by 20 April, but rain had caused some erosion and consolidation. The floor of 1978/90 Crater Complex was covered with ash and ballistic ejecta, and much of the original Metra Crater area had been excavated by the recent explosions. Metra was gently steaming and contained a few small puddles of yellow-green brine. Mud bubbling could be heard. No ash fell during the 20 April visit but PeeJay vent discharged white steam and gas. Collapse of the 1978/90 Crater Complex floor, especially between PeeJay and Donald Mound, left concentric cracks around the slumped margins of Metra Crater. A large fumarole had formed E of PeeJay vent. Output of the main fumaroles on the W and E walls did not appear to have changed. Noisy Nellie was producing almost colorless high-temperature steam and gas. Gas emissions around Donald Mound were weak.

Two features were formed by the 17 April explosive excavation of Metra Crater; the W embayment was the deeper and more active feature on 30 April. A small yellow-green lakelet had formed on its floor. The crater's western margins were still collapsing, and several large geothermal features were present, including geyser-like activity in some pools. The strongest fumaroles were on the NW side, emerging from the base of the crater wall, which was 8-10 m high. The E embayment was shallower and did not contain any active geothermal features. One small yellow-green lakelet was present at the W end of this feature. Several open concentric fractures extended around its margins, suggesting that further collapse may occur in this area.

Ballistic blocks reached a maximum of 2 x 2 m. Most of the larger ones were fresh, black, highly vesicular andesite, sometimes with internal plagioclase banding. No evidence of plastic deformation was seen and most blocks had an outer rim of red "baked" ash. The largest blocks had shattered on impact (figure 41). Dense (older, altered) lava was minor with blocks < 0.5 m in size. Lithified crater-fill sediment blocks were common and comprised either dark gray soft sandstone or harder red, yellow, or pale gray hydrothermally altered material. Ejection of the ballistics occurred largely after the main ashfalls, as evidenced by the thin layer of ash coating the blocks. Clear impact craters from small lapilli occurred at distances from the vents.

Figure 41. Remains of a large volcanic bomb near Metra crater. Courtesy of IGNS.

Approximately 12 cm of ash was present at Peg Z, but only 2 cm at Peg M on 20 April. A ground-deformation survey of the pegs that survived the April explosions was made on 30 April (figure 42). Seven pegs could not be found. The survey showed subsidence continuing around the ESE margin of 1978/90 Crater Complex, but at a lesser rate than in 1998. Over the remainder of the Main Crater floor weak inflation was apparent at many marks. Although deflationary trends have been observed at some marks since eruptions commenced in 1998, many remained elevated at this time (eg. Pegs C and J).

Figure 42. Contour map of the active center of White Island volcano. Heavy black lines plot height change in mm between 12 January and 30 April 1999. Courtesy of IGNS.

A white steam-and-gas plume rose 500-700 m above the 1978/90 Crater Complex during a visit by observers on 10 May. The plume was fed by emissions from PeeJay Vent and the new vent E of PeeJay. Emissions from the new vent were the stronger. The steam-and-gas plume formed acid rain, making conditions unpleasant under the plume and near the edge of the Crater Complex. Enlargement of the yellow-green lakelet within Metra Crater caused flooding into the crater's N embayment. There was no evidence of further explosive activity at Metra Crater.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).

June 1999 (BGVN 24:06) Cite this Report

Visit on 30 June reveals decreased activity

White Island was visited on 30 June by IGNS scientists who reported that no significant eruptive activity had occurred since the explosive activity in April (BGVN 24:04). PeeJay vent was inactive and the only significant emissions of steam and gas came from the vent that formed in early May (at a spot E of PeeJay vent).

As the group arrived on 30 June a weak white steam-and-gas plume was rising 500-700 m above the volcano and moving ENE (figure 43). The plume was being fed by emissions from within the 1978/90 Crater Complex; the new vent E of PeeJay was the plume's strongest contributing source. Most of the gas and steam emitted (at high velocity) from this vent was from an inclined orifice near the S side of the vent. Other prominent sources included fumaroles near the lakeshore and in the valley wall W of the lake. PeeJay vent was inactive and had been filled by sediment that formed a flat floor about 3 m below the vent's rim. Activity had stopped in late May or early June.

Figure 43. View of the 1978/90 Crater complex at White Island looking toward the NW on 30 June. Photograph courtesy of IGNS.

The light-green colored lake within Metra Crater had enlarged and flooded into the NNE embayments of this crater. There was no evidence of further explosive activity from Metra Crater. No strong ebullition or convection was observed in the lake.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

August 1999 (BGVN 24:08) Cite this Report

26 July visit reveals new erupting vent but no major ash accumulation

Several aircraft operators reported a plume extending 3 km above the island on 23 July. Tour operators noted that the ash ceased emitting after 0830 on 25 July. On 26 July steam and gas was observed over 40 km downwind of the volcano, and a visit by scientists indicated that minor activity had commenced from a new vent to the S of those active earlier this year. Thus, the source of the ash cloud was neither PeeJay vent nor the vent immediately E of it. Although the new, active vent emitted ash continuously, there was not evidence of significant ash accumulation.

Information Contacts: Brad Scott, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

November 1999 (BGVN 24:11) Cite this Report

Fumarolic activity continues; new crater lake

No eruptions have occurred at White Island since the minor ash emissions in July-August 1999 from the PeeJay vent area. This report includes observations following a visit on 23 November to service the seismic installation, conduct a deformation survey, collect volcanic gas samples, and assess the general status of volcanic activity on the island.

During the visit a weak steam-and-gas plume was rising 300-500 m. This plume originated from fumarolic vents NW of the former PeeJay vents. Since the last surveillance visit in July a crater lake has developed on the floor of 1978/90 Crater Complex, inundating Metra Crater and parts of the PeeJay vent area. A series of strand lines around the crater lake edge indicated a recent drop in the lake level. Small collapse pits had recently formed near the lakeshore, below the Sag area, and may have accompanied the recent drop in lake level. The lake is a lime green color, with minor convection evident. A temperature of 45°C was measured, down slightly from the previous measurements.

The strongest fumarolic vents were on the NW side of the PeeJay vents area, emerging from the vent wall, which is ~10-15 m high. There were three prominent vents, which were emitting steam and gas that were weakly transparent at the vent. At times the steam and gas plume appeared a yellow color. The emissions were audible from 2-300 m distance. Temperatures of Main Crater fumaroles ranged from 103-115°C, and are similar to previous measurements this year.

A ground-deformation survey was also made. Eight pegs were replaced, as these were damaged during the April-July 1999 eruptions. The survey results showed that subsidence continued at the E-SE margin of the 1978/90 Crater Complex, but at a lesser rate than observed in 1998. Over the remainder of the Main Crater floor weak subsidence was also apparent at many of the marks.

Information Contacts: Brad Scott, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

December 1999 (BGVN 24:12) Cite this Report

Report from 5 January visit by videographers

The following report from Stephen and Donna O'Meara relates their visit to White Island on 5 January 2000. They spent ~2.5 hours (0845 to 1115) around and inside the active central crater complex.

On an exceptionally clear day the steam plume rose 400-600 m above sea level before strong winds blew it to the E. The source of the main wind-blown plume came from the center of the active crater complex, though steam from fumaroles near the complex's base at the W and E walls added to the steam column's thickness at times. When seen from a distance at sea, the total column thickness changed from thick to thin at roughly 15-minute intervals.

A few bubbling springs in small ravines were observed on the floor of the active central crater complex near Donald Mound. A lime-green crater lake with slightly scalloped edges filled the 1978/1990 Crater Complex. A semicircular region around the PeeJay vent area and much of the adjacent wall to the N and S was active. The entire region produced vigorously jetting gas and steam from many single vents and craters with multiple vents. Veins of steam laced the entire lake and skated across the surface in the wind. The source of the steam appeared to be not only the highly active area on the NE side of the Complex, but submerged fumaroles in and around the entire crater lake.

Activity in and around the lake did not occur simultaneously. Individual vents turned on or shut down independently. When most vigorous, jetting from the PeeJay area could be heard several hundred meters away. The plume was very acidic and gas masks were required when the winds shifted. A videotape was made of the activity on the NE side of the crater. Photographs show small changes in activity around the entire lake circumference, including changes at submerged fumaroles on the W side of the Crater Complex. Exploration of the E side of the active Crater Complex found several small mud volcanoes, powerful fumaroles, and bubbling springs.

Information Contacts: Stephen and Donna O'Meara, Volcano Watch International, PO Box 218, Volcano, HI 96785, USA.

March 2000 (BGVN 25:03) Cite this Report

Minor ash emissions resume on 7 March, escaping from multiple vents

Minor eruptive activity recommenced on 7 March when a vent on the ridge SW of PeeJay vent began producing very weak ash emissions. Following reports from tour operators of ash emissions and the progressive failure of the transmission signal from the island, a visit by IGNS scientists was made on 9 March to ascertain the status of the eruptive activity and repair the seismic system.

When they arrived on the island, a weak, ash-charged gas plume rose ~1,500 m above the vent before being blown downwind >40 km. Viewing conditions within the Main Crater area were excellent. The steam-and-ash cloud was being fed from four vents on the ridge SW of the May 1991 embayment. PeeJay vent also was active in this area during 1999. Two of the vents on the ridge continuously emitted light brown ash while the other two emitted vivid white gas plumes. There was no evidence of ash accumulating on the Main Crater floor or on the outer flanks of the cone, indicating insignificant total ash emission; there was also no evidence of impact craters. Moderate convection was present in the crater lake, although there was no discoloration of the lake, which remained a bright green color with light gray surface slicks.

COSPEC flights were conducted on 10 and 17 March to measure the SO₂ flux within the gas plume. The results indicated an average estimated flux of 2,256 metric tons/day, the highest SO₂ values ever recorded from White Island. Despite a significant change in SO₂ flux, a prominent 1,500-m-high gas plume, and a phase of sustained but very minor ash discharge, there had not been any associated seismic activity or visible escalation of activity as of 21 March.

Information Contacts: Brad Scott and Brent Alloway, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

April 2000 (BGVN 25:04) Cite this Report

Continuous ash emissions in April; high SO₂ and fluctuating tremor

Starting on 7 March, White Island displayed minor eruptive activity, elevated seismicity, and higher than normal SO₂ gas flux (BGVN 25:03). Staff from the Institute of Geological & Nuclear Sciences (GNS) who visited on 18 April observed a gas plume, comprised of steam and small amounts of ash, being erupted to 1,300-1,700 m before being blown S. At distances of more than a few kilometers from the island no ash was visible in the plume, although reports from Whakatane indicated that trace amounts of ash fell during the night of 17-18 April. The erupting vent, named MH vent, is ~10 m across. The seismograph at White Island recorded volcanic tremor starting on 6 April 2000, the first significant tremor since April 1999. In addition, recent measurements of the SO₂ flux were well above typical background levels at White Island. This eruptive activity was sufficient to increase the Alert Level from 1 to 2.

Ash was erupted almost continuously during the weekend of 22-23 April, although there was no evidence that any larger blocks were erupted. During another visit by scientists on 26 April the activity level was much reduced from that of the previous two weeks, but minor eruptive activity continued. A weak gas plume, comprised almost totally of steam, was being erupted to 1,500 m before being blown NE. The plume was not visible more than a few kilometers from the island. The seismograph continued to record moderate to strong volcanic tremor, although the level fluctuated with time. It is unclear if there was a direct relationship between the intensity of the eruptive activity and the level of volcanic tremor. COSPEC measurements on 28 April recorded a SO₂ flux of 927 metric tons/day, down from previous measurements, but consistent with the activity.

Activity was similar during a monitoring visit on 2 May, with a weak gas and ash plume from MH vent. The ash plume was rising to 500 m, while the steam-and-gas plume rose to 760-900 m before being blown NNE. The plume was visible more than 10-15 km from the island. Ash emission was occurring continuously. The seismograph continued to record fluctuating moderate to strong volcanic tremor.

Information Contacts: Brad Scott, Brent Alloway, and Steven Sherburn, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

May 2000 (BGVN 25:05) Cite this Report

April-May seismicity and emissions appear independent

Staff from the New Zealand Institute of Geological & Nuclear Sciences (GNS) visited White Island on 8 June to assess the volcano status and do routine seismograph maintenance. The level of activity was similar to that reported over the last two months (BGVN 25:03 and 25:04). The MH-vent was producing a weak gas-and-ash plume, which was rising 800-1000 m before being blown to the NNW. The plume was visible 20-30 km from the island as a lightly colored haze.

Seismic activity had declined almost to background levels. Seismicity started to increase about 5 April, peaked about 12 May, and subsequently declined. Meanwhile, the nature and intensity of the eruptive activity had not changed significantly, confirming earlier assessments that no direct relationship existed between the intensity of the eruptive activity at MH-vent and the level of seismic activity.

White Island has now been at Alert Level 2 for ~50 days. While the intensity of the activity has varied slightly over this period, ash emission has occurred almost continuously and fresh ash now covers the island at thicknesses ranging from several millimeters to several centimeters. The style of eruptive activity has not changed during this time. The height of the ash-and-steam plume has varied with eruption intensity and wind strength, but 800-1000 m has been typical.

Information Contacts: Brad Scott and Steven Sherburn, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

July 2000 (BGVN 25:07) Cite this Report

New crater formed on 27 July during the largest eruption in about 20 years

This report covers June and July 2000. On 18 April 2000, the Institute of Geological and Nuclear Sciences (IGNS) increased the alert level from 1 to 2 (level 5 being the most severe) following minor eruptive activity that began on 7 March 2000 and included elevated seismicity and higher than normal SO₂ gas flux (BGVN 25:03).

The IGNS reported that for the week ending 16 June 2000, the active MH vent continued to emit an ash plume. This plume sometimes extended as far as 60 km downwind and deposited ash as far as 15 km away. Up to several centimeters of ash were deposited on White Island. Until 16 June, seismic activity was significantly less than in May.

Field observations on 12 July indicated little change in activity since April. Furthermore, no direct relationship between seismic activity during this time and the eruptive activity could be determined. The ash continued to be vented to an altitude of 800-1,000 m. By 19 July, strong NE winds had periodically blown the ash plume towards the mainland, resulting in minor ash deposition there. Ashfall at Turango airport led to landing and departure restrictions. Air traffic was also disrupted around the Bay of Plenty.

On 22 July IGNS staff noticed an increase in activity compared to previous observations. A yellowish-brown gas and an ash plume extending to a height of 1500 m were blown to the E and SE. This continued to disrupt air traffic and deposit ash on the mainland. In fact, the IGNS staff were unable to land due to ash accumulation at the landing site. However, they noted that yellowish-brown ash now covered the island with thicknesses ranging from several mm to several cm. They saw no evidence of ballistic bombs or evidence that the eruptive style had changed from the previous months. However, they did note that the height of the MH vent had decreased from its previous location above the acid lake to a height level with the lake.

On Thursday 27 July between 1700 and 2200, a period of strong seismic activity was recorded. Visual and satellite observations were not possible due to poor weather conditions. A tour operator arriving at the island the morning of 28 July, confirmed that there had been an eruption. IGNS staff arrived 29 July and discovered that a large explosive eruption formed a new crater 120 x 150 m wide in the site formerly occupied by a warm acidic lake in the 1978-90 Crater Complex. The eruption deposited as much as 30 cm of ash and pyroclastic material, including juvenile pumice blocks, over the eastern part of the island. This was the largest eruption at White Island in about 20 years; deposits from this eruption were found in areas frequently visited by tourists. The IGNS advised all visitors that similar eruptions pose serious risks to anyone on the island.

Observations on 31 July found the MH vent, which had enlarged to ~50 m, spewing a dark ash cloud while a reddish-brown ash cloud rose from the new 27 July vent. The plumes combined and rose as high as 1-1.2 km above the vents. After this event, activity returned to the level typical since April: minor eruptions that produced plumes of gas, steam, and volcanic ash.

Information Contacts: Brent Alloway, Brad Scott, and Steven Sherburn, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

August 2000 (BGVN 25:08) Cite this Report

Ash-and-steam emissions accompanied by magmatic eruption

The Alert Level for White Island was set to Level 2 on 19 April 2000 after it began to emit significant quantities of ash (BGVN 25:04). Ash continued to be produced from the MH vent at irregular intervals, and from April to June the ash emission was accompanied by a moderate level of seismic activity, although there was little correlation between the seismic activity and the amount of ash or steam coming from the volcano (BGVN 25:05). Ash emission continued during June and July; a short-lived magmatic eruption accompanied by strong seismicity produced a new explosion crater on 27 July 2000 (BGVN 25:07).

After the 27 July event, ash emission occurred from both active vents. However the ash content of the plume declined significantly in late August-early September. Staff from IGNS visited White Island on 19 September to assess the volcano status and reported that the current vents of White Island have not emitted any ash recently. The MH vent continued to emit steam and gas, but within the range of the normal fumarolic activity. Based on these observations, the Alert Level was reduced to Level 1.

Information Contacts: Brad Scott, and Tony Hurst, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

September 2001 (BGVN 26:09) Cite this Report

In early 2001, 145°C degassing and an ash plume to ~2 km height

This report describes venting of ash and gas that continued at White Island during November 2000 through May 2001. As previously reported, on 27 July 2000, strong seismicity accompanied a short-lived magmatic eruption and produced a new explosion crater. Following the event, the two active vents at White Island emitted an ash plume. The ash content of the plume declined significantly during late August-early September 2000 (BGVN 25:08).

On 9 November 2000 scientists visiting White Island found weak-to-moderate fumarole activity, with the two active vents producing a white steam-and-gas plume. By 16 November, a small new vent SE of the active MH was also steaming. Around that time, the noise from the MH vent was so loud that it could be heard from the beach in still conditions. By mid-December, the steam-and-gas plume rose to an altitude of ~1,250 m, and occasional bursts of low-level tremor occurred. The level of gas emission seemed to have stabilized after the increase that occurred during the previous month.

On 3 January 2001 a volcanologist visiting the site reported that the lake within the 78/90 Crater Complex had enlarged and had a yellowish-brown discoloration with surface slicks and noticeable areas of convection. Fumaroles appeared to be more extensive within the complex. A strong haze of sulphur dioxide gas was evident within the crater. By mid-January the water level near the vents had risen.

Based on reports from White Island tour operators, the Institute of Geological and Nuclear Sciences (IGNS) stated that on 19 February minor ash eruptions resumed. A light gray plume of fine ash rose ~2 km above the MH vent and drifted towards the mainland. Fine ash was deposited on and near White Island, but only an acid aerosol cloud reached the mainland near the town of Matata (~55 km SW).

During mid-March the steam-and-gas plume was not nearly as noisy as it had been, but it was still very hot, as indicated by the transparency of the bottom of the plume as it exited from the vent. The IGNS received reports from the public of an unusually large gas plume extending over White Island. This large plume, however, was attributed to still wind conditions and cooler air temperatures.

On 19 April a team from IGNS visited White Island and found no significant change from previous visits. The lake was still a yellow/green color, but was somewhat cooler at 28°C. The MH vent was still emitting a considerable volume of steam, but was not as noisy as it had previously been. Steam emerged from the vent at a temperature of 145°C, and reached a height of about 20 m before condensing. No ash was produced.

Heavy rain affected the area around the vents during May 2001 and changed the lake color to gray, but the volcanic activity was essentially unchanged. On 28 May, air waves were recorded by the seismometer, indicating a small surface explosion. Fumaroles continued to be active and produced a high level of water vapor in the crater area.

By July the gas pressure at White Island had decreased. A few isolated, small, low-frequency events were recorded in August. Weak volcanic tremor was recorded in September, but no changes occurred at the surface.

Information Contacts: Brad Scott and Tony Hurst, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

February 2003 (BGVN 28:02) Cite this Report

Increased SO₂ emissions since December, mud ejections in February

Minor volcanic tremor continued, and the plume of steam and gases from the vent remained unchanged through the end of November 2002, according to the Institute of Geological & Nuclear Sciences (IGNS). The output of SO₂ measured on 10 December was 112 ± 36 metric tons per day (t/d); in October the value was 63 t/d. Volcanic tremor continued and was accompanied by minor booming and explosions in the second week of December. After a brief period of increased activity at the start of the next week, volcanic tremor dropped to the weaker levels of tremor observed previously. Weak steam and gas emissions continued through 19 December, along with weak volcanic tremor.

An IGNS report on 7 February 2002 noted continuing minor volcanic tremor and a weak plume of steam and gases from the active vent. Activity increased slightly during 9-16 February. On 12 February mud was being thrown some tens of meters in the air, and ground vibrations could be felt. This corresponded to a period of slightly stronger volcanic tremor. Seismograph readings returned to normal by the 13th. Minor hydrothermal activity continued as of 21 February, and the output of SO₂ had increased to 269 t/d. Seismic tremor steadily declined to low background levels in the last week of the month, though a weak plume of steam and gases was still being emitted.

Seismic tremor levels at White Island remained low on 7 March, but mud was being ejected to low levels around the active vent and a steam plume remained. There were intermittent periods of weak tremor the next week, and SO₂ output was reported to be 267 t/d. Seismic tremor was at a very low level during the week ending on 21 March.

Information Contacts: Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

August 2003 (BGVN 28:08) Cite this Report

Large crater lake floods the active vent; new hazards identified

Following increased SO₂ emissions in December 2002 and mud ejections during February and early March 2003 (BGVN 28:02), the active vent at White Island continued to emit a small plume of steam and gases through 4 April, but seismic activity was at a very low level. Seismicity remained low through August 2003.

Scientists visited White Island during the week of 5-11 April for routine monitoring. This fieldwork included sampling high-temperature fumaroles, measuring carbon dioxide output, and geodetic surveying. The crater lake had grown in size and flooded the active vent, greatly reducing the emission of a gas plume from the vent and also reducing the seismicity to very low levels. A minor plume of steam and gases persisted through 20 June, but was not visible the week of 21-27 June; no further mention of a plume was made in reports through August.

Scientists from the Institute of Geological & Nuclear Sciences (IGNS) who visited the island during the week of 28 June-4 July noted striking changes in the crater lake, which had turned a light green color, and was very warm (58°C). The water level had risen several meters, to ~30 m below the crater rim, flooding all the active vents and spreading into all the areas of the crater floor. This lake is the largest to form within the 1978/90 Crater Complex. Fumarole temperatures ranged from 101 to 114°C.

By the first week of August the lake seemed to be semi-permanent, reaching a size of ~300 m long and somewhat less in width, with an unknown depth. As a result, a Science Alert Bulletin issued by the IGNS on 7 August 2003 noted that the existence of the lake created new hazards. Over the last 10-15 years many small ponds and lakelets have formed in topographic lows or the floors of small sub-craters within the 1978/90 Crater Complex. Their lives have typically been short as they have been filled in by the next eruption, or drained as new vents have formed. The small volumes of these lakes was such that they had no influence on eruptive activity.

However, the current lake volume is large enough that it could influence eruptive activity. Ejection of the lake in an eruption could cause flooding of the shallow stream valleys across the Main Crater floor, maybe as far as the sea. Should there be no significant eruptive activity within the next 18-24 months and the lake continues to fill, it may reach overflow level. In this situation water may overflow into drainage channels on Peg 12 Flat, S of the 1978/90 Crater Complex, and these channels may further erode if water is continuously flowing in them.

As of 29 August seismic and hydrothermal activity remained at the low levels recorded during the past four weeks. The lake level had risen since early July, and the temperature was 53°C, down slightly from 58°C on 2 July. The volcano monitoring team installed temporary benchmarks inside the main crater, so changes in the lake level could be observed from the safety of the crater rim. Although the development of the crater lake has been a concern, there is no significant change in volcanic activity on the island, so the hazard status for White Island remains at Alert Level 1.

Information Contacts: Brad Scott, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

March 2004 (BGVN 29:03) Cite this Report

Eruptions ceased in about 2002; crater lake rising

An April 2004 note from New Zealand geothermal geologist Ashley Cody noted that White Island had essentially ceased its eruptive episode since about 2002, when it began to emit only very weak gas (lacking ejecta). Accordingly, compared to several years ago, there has been little to report about it. However, the Institute of Geological & Nuclear Sciences (GNS) still monitors White Island seismically, and with the Geonet web camera (visible real-time on the net). This report contains a summary of their brief reports. An issue of current interest is the continued growth of the crater lake. Crater lake growth was previously reported in February and August 2003 (BGVN 28:02 and 28:08).

GNS reports warned that "should there be no significant eruptive activity within the next 18-24 months and the lake continues to fill, it may reach overflow level. In this situation water may overflow into drainage channels on Peg 12 Flat, S of the 1978/90 Crater Complex, and these channels may further erode . . . ."

Steve O'Meara of Volcano Watch International visited White Island on 8 February 2004 (figure 44) and noted considerably weaker fumarolic activity than during an earlier trip in 2000 (figure 45). Hydrothermal activity, though diminished, was still taking place in the crater and steam often lifted off the lake's surface, which effervesced. Scum was weakly present, especially around the lake's edges, but he did not see as much as during his 2000 visit. Volcanic bombs and explosion debris surrounded the crater. Although O'Meara's professionally-guided tour was conducted skillfully and with genuine regard for safety, he expressed concern about a sudden eruption from the lake catching onlookers off guard.

Figure 44. The rim of White Island's main crater taken looking W on 8 February 2004, showing the crater lake and the top of the E rim. Observers noted a small fresh landslide in the far crater wall (to the right of the fumaroles). Courtesy of Steve and Donna O'Meara, Volcano Watch International.

Figure 45. A wide-angle aerial shot of White Island taken 5 January 2000 amid much more vigorous degassing than present in February 2004. The then smaller, but more steam-covered crater lake appears in the center of the photo, directly behind the high point along the crater rim in the foreground. Courtesy of Steve and Donna O'Meara, Volcano Watch International.

A 13 February 2004 report from the GNS stated that heavy rainfall on White Island during the past few weeks triggered many small landslides inside the crater rim. They went on to note that the lake continued to fill steadily and last week all of the temporary marker posts were submerged or had washed into the lake. This week, GNS volcanologists had visited the island to install six more survey posts inside the main crater, so changes in the lake's level could continue to be monitored. The lake temperature was 57°C, similar to values measured during the last six months. A 26 March report noted a decrease in the rate of rainfall and consequent drop in the rate of filling of the crater lake. GNS reports on 2 April and 26 March also mentioned minor seismic activity, which was described in more detail in a 19 March report as "including a few very small, discrete earthquakes but no volcanic tremor."

The GNS report for 30 April 2004 stated that "seismic and hydrothermal activity at White Island remain at a low level. The crater lake was then [12-]13.6 m below the level at which it will overflow. White Island also remains at Alert Level 1 (some signs of volcano unrest)." An overview of late 2002-early 2004 GNS data appears on table 11. There were no HIGP-MODIS thermal alert warnings for White Island over the 12 months to April 2004.

Table 11. A summary of the Institute of Geological & Nuclear Sciences (GNS) reports discussing White Island, October 2002 to April 2004. Courtesy of GNS.

Information Contacts: Institute of Geological & Nuclear Sciences (GNS), Private Bag 2000, Wairakwi, New Zealand (URL: http://www.gns/cri.nz); GeoNet, a project sponsored by the New Zealand Government through these agencies: Earthquake Commission (E.C.), Geological & Nuclear Sciences (GNS), and Foundation for Research, Science & Technology (FAST). Geonet can be contacted at the above GNS address (their URL: http://www.geonet.org.nz/contact.htm); Steve and Donna O'Meara, Volcano Watch International, PO Box 218, Volcano, HI 96785.

May 2005 (BGVN 30:05) Cite this Report

Seismic and hydrothermal activity remain low through June 2005

White Island was last reported on in BGVN 29:03, covering the period to March 2004. At that time, approximately two years had passed since any significant eruption, but the New Zealand Institute of Geological and Nuclear Sciences (GNS) continues to monitor White Island. This report is a summary of their brief reports.

From April 2004 until June 2005, seismicity and hydrothermal activity at White Island remained at low levels, with some brief periods of weak to moderate volcanic tremor recorded during September to November of 2004. The level of the crater lake has risen significantly over this period, from 12-13 m below the overflow level in April 2004 to only 3-4 m below overflow level in June 2005 (figure 46). Some of this increase was caused by landslides in July 2004 and by heavy rains in May 2005. Steam and gas emissions have been minor, with the exception of a large plume visible from the mainland on 15 October 2004. The alert level remained at 1 (on a scale of 0-5), indicating some degree of unrest but no threat of eruption.

Figure 46. The crater lake on White Island, taken 9 January 2005, when the lake level was about 5 m below the overflow level and rising. Courtesy of Franz Jeker.

Information Contacts: Institute of Geological and Nuclear Sciences (GNS), Private Bag 2000, Wairakwi, New Zealand (URL: http://www.gns/cri.nz); GeoNet, a project sponsored by the New Zealand Government through these agencies:Earthquake Commission (E.C.), Geological and Nuclear Sciences (GNS), and Foundation for Research, Science and Technology (FAST). Geonet can be contacted at the above GNS address (URL: http://www.geonet.org.nz/contact.htm); Franz Jeker, Rigistrasse 10, 8173 Neerach, Switzerland.

December 2006 (BGVN 31:12) Cite this Report

Relative quite prevails during 2005-6

Between June 2005 and December 2006, seismic activity remained low at White Island. According to the Institute of Geological and Nuclear Sciences (GNS), observers have occasionally seen elevated levels of sulfur gases (sulfur dioxide, hydrogen sulfide) and carbon dioxide, as well as periods of micro-earthquakes and steam plumes. Minor changes in fumarole activity have also occurred. The crater lake has remained well below the overflow level. As of 15 December 2006, White Island remained at Alert Level 1 (some signs of volcano unrest).

Franz Jeker visited White Island on 9 January 2005 and took a series of photos showing some crater features (figures 47-49). Images from a web camera located on the crater rim show that no significant change in activity has occurred as of 9 February 2007 (figure 50).

Figure 47. Native sulfur deposits in a fumarolic environment at White Island, 9 January 2005. Courtesy of Franz Jeker.

Figure 48. Visitors standing on a high point in the crater at White Island, 9 January 2005. Courtesy of Franz Jeker.

Figure 49. Photo of the crater at White Island looking SE towards the ocean, 9 January 2005. Courtesy of Franz Jeker.

Figure 50. Webcam image taken from the crater rim at White Island, 9 February 2007. Courtesy of GeoNet.

Information Contacts: Institute of Geological and Nuclear Sciences (GNS), Private Bag 2000, Wairakwi, New Zealand (URL: http://www.gns.cri.nz/); GeoNet, a project sponsored by the New Zealand Government through these agencies: Earthquake Commission (E.C.), Geological and Nuclear Sciences (GNS), and Foundation for Research, Science and Technology (FAST) (URL: http://www.geonet.org.nz/); Franz Jeker, Rigistrasse 10, 8173 Neerach, Switzerland.

June 2007 (BGVN 32:06) Cite this Report

Falling water level in the crater lake, but no volcanic activity

According to Tony Hurst, reporting in the GNS Science Alert Bulletin of 6 March 2007, GeoNet conducted a visit to White Island on 23 February 2007 and found that the water level in the crater lake had fallen by 1.2 m in 10 days. The lake was 9 m below the overflow level, the result of rapid evaporation, with the lake temperature measured at 74°C. The falling level has reduced the area of the lake by about 10%, and volume by 20%, but there have been no indications of volcanic activity. However, the falling water level could reduce the pressure in the geothermal system, resulting in local boiling events at depth in the lake, and producing transient steam plumes.

Another Alert Bulletin prepared by Brad Scott on 3 May 2007 noted that the Alert Level for White Island remained at 1. The rapid decrease in the level of the crater lake seen over the last few months has continued. Recent observations confirmed that the lake was more than 28 m below overflow level, and the depth of water in the lake was likely to be about 10 m. The lake level fell very rapidly during April, significantly decreasing both the area and volume of the lake. The temperature of the lake declined from 74 to 64°C, probably due to less input from high-temperature steam vents, which are now above the lake. As the water level fell, many steam vents and fumaroles were exposed, producing transient steam plumes as high as 3 km sometimes mistaken as eruptions. However, no eruptions have occurred, and no changes in any of the monitoring data indicate potential increases in volcanic activity in the near future.

Information Contacts: GeoNet, a collaboration between the Earthquake Commission and GNS Science (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Earthquake Commission (EQC), PO Box 790, Wellington, New Zealand (URL: http://www.eqc.govt.nz/).

December 2008 (BGVN 33:12) Cite this Report

Gas and mud emissions, lake level shifts from May 2007 to January 2009

The water level in the White Island crater lake had decreased significantly, especially during April 2007, and the water temperature had fallen from 74° to 64°C (BGVN 32:06). However, this activity was not accompanied by any eruptions, and monitoring had not detected any increase in volcanic activity. This report discusses activity from May 2007 through January 2009.

By late October 2007, the lake had almost completely evaporated. Then, in December 2007, the lake began to rise. By mid-February 2008, the level had risen about 6 m. Accompanying the rise in lake level was a further drop in lake temperature, from 63° to 53°C, due to the greater volume of water. The lake color changed from a turbid gray to a light green, reflecting less suspended sediment.

On 21 November 2007, an earthquake swarm (the largest, M 4.2) occurred 10 km NW of White Island. On 13 June 2008 a tectonic earthquake (M 5.4) 10 km SW was widely felt in the Bay of Plenty. However, neither earthquake event was associated with increased volcanic seismicity. From 2 December 2008 through 31 January 2009 there were a few small earthquakes 5-10 km NW of the volcano. However, dozens of epicenters occurred just offshore N of the New Zealand mainland (near Whakatane and Matata), many to the SW of White Island.

By 23 October 2008 the lake had risen 15 m (within about 9 m of overflow), and was beginning to affect the geothermal features on the Main Crater floor. New springs formed on the floor and old springs flowed again. The lake temperature was 57°C, and the water color had changed to light green, reflecting a decrease in suspended sediment.

High-temperature fumaroles (101-103°C) were located on the S floor of the Main Crater. Steam, gas, and mud emissions had increased from the largest vent during the previous few weeks. The Alert Level remained at Level 1 (low on a scale of 0-5), indicating signs of unrest. Steaming continued into February 2009 (figure 51).

Figure 51. Photo of White Island crater taken 6 February 2009. Dinosaur toy in left foreground for scale. Courtesy of Geonet.

Information Contacts: GeoNet, a collaboration between the Earthquake Commission and GNS Science (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Earthquake Commission (EQC), PO Box 790, Wellington, New Zealand (URL: http://www.eqc.govt.nz/).

June 2012 (BGVN 37:06) Cite this Report

First ash emission in 10 years

After evaporating during 2011 and early 2012, White Island's crater lake rapidly rose on 28 July. Within two weeks, the first ash emissions from White Island in ~10 years occurred. This report summarizes GeoNet Alert Bulletins and provides selected photos of what "may represent the start of a new phase of activity at White Island."

Lake-level rise. During 2011-July 2012, White Island's crater lake slowly evaporated, exposing steam vents and leaving large mud pools on the lake floor (figure 52a). GeoNet reported intermittent volcanic tremor in early July 2012. One period of tremor lasted several hours in the early morning on 28 July; GeoNet stated that it may have been an indication than an eruption had occurred. Later that day, field observations revealed that the lake-level had rapidly risen 3-5 m sometime during the previous night or early morning (figure 52b). According to Brad Scott of GNS Science, rain and water derived from condensation within plumes were the sources of the lake-level rise.

Figure 52. Photos of White Island's crater lake taken on 6 March (a) and 28 July 2012 (b) illustrating the nearly dry lake floor during a period of evaporation in 2011-early 2012 and the newly refilled lake containing 3-5 m of water. The lake-level rose suddenly during 27-28 July 2012 (see text). The white asterisk marks the same location in each photograph. Courtesy of GeoNet.

The lake-level rise was accompanied by significant gas-and-steam emissions rising from the water. Gas measurements indicated an increase in SO₂ emissions compared to the last measurement three months prior, but CO₂ emissions were about the same. Ground surveys indicated that subsidence of the crater floor had stopped, and that the floor may have been slowly rising prior to the lake-level rise. Tremor was more continuous after 28 July 2012. As a result of the increased activity, the Aviation Colour Code was increased to Yellow (on a increasing scale of Green-Yellow-Orange-Red) on 2 August; the Alert Level remained at 1 (on a scale from 0-5).

First ash eruption in more than 10 years. An overnight episode of stronger tremor ended in a volcanic earthquake at 0454 on 5 August. Webcam images during the few minutes following revealed an accompanying plume rising from the crater lake (figure 53). As a result, the Alert Level/Aviation Colour Code was raised to 2/Orange.

Figure 53. An early morning webcam image of an eruptive plume at White Island on 5 August 2012. This was the first observed plume since the onset of the new episode of unrest in White Island's 1978/90 Crater Complex. Courtesy of GeoNet.

Two days later, on 7 August, tremor sharply decreased to levels seen prior to July 2012. A few hours later, however, the plume rising from the crater lake changed color from white to light brown, indicating the first observed ash erupted from White Island since February 2001 (BGVN 26:09). During a visit to the crater area, GeoNet volcanologists confirmed the ash emissions, and photographed the newly formed vent emerging in an area near the SW corner of the 1978/90 Crater Complex (figure 54). They described a 40-50-m-wide tuff cone forming around the vent and isolating the vent from the lake water. Impact craters around the tuff cone were the result of falling ejecta from explosions. The impact craters were confined to the 1978/90 Crater Complex.

Figure 54. A photograph of the new eruptive vent in the SW corner of White Island's 1978/90 Crater Complex. In this photograph, an ash laden plume is rising from the vent, and a 40-50-m-wide tuff cone is forming around the vent. Courtesy of GeoNet.

Through 13 August, weak volcanic tremor continued, along with steam-and-gas plumes that rose to 200-300 m above the crater and intermittently contained ash. A GeoNet Alert Bulletin released on the afternoon of 13 August announced the lowering of the Aviation Colour Code to Yellow "as a result of generally reduced ash emission." Four days later, on 17 August, the Alert Level was lowered to 1. GeoNet stated that "minor eruptive activity, which is required for Volcanic Alert Level 2, is no longer occurring and the Volcanic Alert Level is consequently reduced from 2 to 1." They noted that little-to-no ash was contained in steam-and-gas plumes, seismicity was low, and typical SO₂ levels were emitted during the previous week.

Information Contacts: GeoNet, a collaboration between the Earthquake Commission and GNS Science (URL: http://www.geonet.org.nz/); Brad Scott, GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Earthquake Commission (EQC), PO Box 790, Wellington, New Zealand (URL: http://www.eqc.govt.nz/).

February 2014 (BGVN 39:02) Cite this Report

Dome extrusion in late 2012 and further eruptions in 2012-2013

On 5 August 2012, White Island erupted, following rapid water level rises in the crater lake. Minor ash emission continued to as late as 17 August (BGVN 37:06). This report describes activity during September 2012-January 2014. Unless otherwise stated, information was compiled from GeoNet reports. Major events during the reporting interval include a spiny dome first viewed in December 2012, several months of explosive phreatic activity in early 2013, and discrete explosive eruptions during the latter half of 2013. Magma last surfaced at White Island in 2000 in an explosive eruption that ejected molten lava (BGVN 25:08). GeoNet, a monitoring project funded by the Earthquake Commission, is operated by New Zealand's GNS Science which produces an on-line Volcanic Alert Bulletin. It monitors volcano events by webcam, and acoustic and seismic instruments. Periodically, in situ temperature, fumarole and spring chemical sampling, deformation, gas data, and visual narratives were also recorded. Surveillance includes a mini DOAS network and may also airborne visual observations, photos, and IR images.

GeoNet currently describes White Island as the most active of New Zealand's volcanoes. During 2012 and 2013 normal seismic activity was interspersed with periods of heightened activity. GeoNet reported minor ash, seismicity, gas emissions, dome building, and changes at the crater and crater lakes. Two significant eruptions occurred after a period of reduced activity in 2013: one in August and the other in October. In January 2014, GeoNet volcanologists reported low seismicity. During a single year, tour companies estimated that over 10,000 tourists visited White Island from NZ's North Island ~45 km to the S. Safety of visitors to the island and surrounding waters depends on Volcanic Alert Bulletins. The NZ volcano alert levels ranged from 0 (low risk) to 5 (high risk); Aviation Alert colors ranged from Green (low risk), to Yellow, to Orange and then to Red (high risk). These two alert types were frequently updated, based on spikes in activity. For example in August 2013, Alert Levels ranged from 1 to 2 and Aviation Colour Codes shifted from Yellow to Green to Red to Orange and back to Yellow.

Ashfall in 2012 and a spiny lava dome. In a Volcanic Alert Bulletin issued on 12 December 2012, GNS reported that after the 5 August eruption, a spiny done was formed. In the 26 July 2013 report, phreatic and steam driven activity was observed beginning in December with minor ash emissions interspersed and continuing into the following year. Degassing and tremors were frequent with varying intensities (figure 55). The figure records seismicity as root square amplitude mean (RSAM) on the ordinate plotted along the time line abscissa from June 2007 to December 2013. The tremors were generally attributed to fluid movement (magma, geothermal water, and steam) at an undetermined depth in the crust.

Figure 55. White Island seismicity as root square amplitude mean (RSAM) on the ordinate plotted along the time line abscissa from June 2007 to December 2013. Figure by Brad Scott; courtesy New Zealand's Geological and Nuclear Sciences (GNS Science).

In December 2012, two airborne observations were conducted. GNS volcanologists on 10 December viewed for the first time a small spiny lava dome in the crater active during August 2012. The dome emerged in the vent active in a spot adjacent to two other venting areas (figure 56). GNS reporting attributed the dome morphology to a cooled carapace thrust upward by injection of magma deeper in the dome. Several spines protruded from the roughly 20-30 m diameter dome base (figure 57). Tour operators to the island commented that the dome was visible weeks before the volcanologists viewed it. The actual date of formation remained unstated and possibly unknown.

Figure 56. Aerial view of White Island's active crater. A lava dome juts up adjacent to the front edge of an active oval vent near the prominent lake in the center of the image. The image was taken from a helicopter on 10 December 2012 looking W at ~600 m from the active vents. Photo by Brad Scott; courtesy GNS Science.

Figure 57. Magnified view of the 10 December 2012 image showing the spiny lava dome (about 20-30 m diameter). The hot lake in the foreground sits adjacent to the active vent. Courtesy of GeoNet. Image by B. J. Scott, GNS Science.

Airborne observations on 20 December 2012 found the lava dome unchanged. Several small lakes occupied parts of the area formally covered by a large lake viewed before the August eruption. Infrared temperatures taken during the flight found the dome to be 187°C, the actively upwelling hot lake S of the dome to be 71°C, and the cool lake on the N side of the dome to be 35°C. 20 December airborne measurements resulted in a gas flux rate for SO₂ of 400 metric tons/day (t/d), for CO₂: 1,300 t/d, and for H₂S₂; 10 t/d.

Ashfall after the August 2012 eruption to the end of 2012 was unreported in the 2012 Volcanic Alert Bulletin archive. However, in the 26 July 2013 report, GeoNet summarized the December 2012-February 2013 activity as an eruption sequence interspersed with phreatic, steam driven activity and very minor ash emissions. Ashfall in December 2012 and January-February 2013 are reported in table 12. Exact ashfall dates were unreported due to the minor nature of ashfall events and irregular visits. Table 12 summarizes eruptive activity at White Island during this report period.

Table 12. December 2012-11 October 2013 eruptive activity at White Island. Column headings are eruptions, seismicity, and a brief eruptive narrative. Dates in the second column from the right came from Volcanic Alert Bulletin reports. Notes refer to image and video records found in the Reference section under GNS. Courtesy of GNS.

Ashfall in 2013, 20 August eruption, and 11 October eruption. On 1 January 2013, GNS volcanologists reported the spiny lava dome (figure 58) remained unchanged from December 2012. The lava dome temperature was 200-240°C, up from 187°C in December, and the nearby 'hot lake' was 70-80°C, unchanged from December.

GNS volcanologist Brad Scott, who visited the island, commented in the 22 January Volcano Alert Bulletin "the hydrothermal activity is some of the most vigorous I have seen at White Island for many years." Scott also reported the hot lake had disappeared, replaced by a small tuff cone. That cone was the main point of emission for steam and gas. On 30 January 2013, the active vent continued to produce intermittent vigorous bursts of mud, rock, steam, and gas rising 50-100 m high without detectable ash in the plume. On 31 January, gas fluxes were 2,000 metric tons per day (t/d) for carbon dioxide (CO₂), 600 t/d for sulfur dioxide (SO₂), and 19 t/d for hydrogen sulfide (H₂S).

Figure 58. This is the same photo seen in figure 56, but in this case it shows infrared temperatures of White Island's dome and lakes taken on 7 January 2013. The active vent continued to produce vigorous bursts of mud, rock, steam, and gas reaching 50-100 m high. Ash was not carried into the plume at the time of this photo. The small lake to the left is the cool lake (35°C) and the lava-dome crater is partially hidden under the steam plume. Courtesy of GeoNet. Image by Brad Scott, GNS Science.

On 7 February, SO₂ and CO₂ rates were similar to measurements in January: SO₂ was 560 t/d and CO₂ was 1,800 t/d. The main steam and gas plume came from the ash cone occupying the previous hot lake crater. Small explosive eruptions in the active crater and seismicity, which had been occurring for three weeks prior to the week of 11 February, became less intense.

During 23-24 February 2013 minor ash erupted from the active vent. Tremor was consistent with the level of unrest seen over the past month. On 25 February, the ash emissions had ceased and had been replaced by steam-and-gas explosions from the active vent. The level of volcanic tremor increased, associated with the reappearance of fluids in the vent area (figure 55). The unrest was among the most vigorous that Scott had observed during visits to White Island. He was quoted in the 25 February report to say "the unrest continues and we continue to see small scale explosive events. Larger explosive eruptions can occur at any time with little or no warning. As always a high level of caution should be taken if visiting the island."

The crater on 4 March 2013 contained an ash cone surrounded by water (figure 59), which replaced the previous hot lake as the primary source of steam in the crater. On 29 April 2013, GNS reported that ash had ceased being emitted at an undisclosed date during the first part of the month. In April, low to moderate seismic tremor was detected, while degassing continued. Rainfall during April caused the two lakes to combine. The maximum lake temperature was ~ 62°C. The lava dome temperature was ~200°C.

Figure 59. A 4 March 2013 image looking W ~600 m from the crater. A new ash cone formed at the hot lake emitted gas and steam. N of the ash cone sits the cool lake. Image by B. J. Scott, GNS Science.

During April, May, and June 2013 the crater lake reformed. On 9 July 2013 GNS reported small volcanic earthquakes occurred approximately every 70 seconds, with changing amplitude and frequency. GNS volcanologists visiting on 26 July observed gas venting through the small lake with debris ejected 20-30 m vertically. By 5 August this minor venting had declined and tremor had decreased to near-background levels (see figure 55).

A small eruption took place in August 2013 detected by a constellation of instruments on White Island which included audio receivers, seismometers, temperature sensors, and IR sensors. The eruption was captured on video media by several cameras near the crater rim and a camera stationed ~45 km S at NZ's North Island (figure 60). The eruption occurred at 1023 on 20 August 2013 (NZ local time) and continued for about 10 minutes. As seen from the mainland, it mainly produced a steam plume rising to ~4 km, and slowly trending W before dispersing (figure 61). The eruption originated from a vent in the active crater that had been experiencing very small mud eruptions in early to mid-August 2013. This eruption was preceded by strong tremor.

Figure 60. Map locating GNS video camera which resides at Whakatane on NZ's North Island ~50 km S of White Island. It recorded the 20 August 2013 eruption seen in the next figure. Map courtesy of 100% New Zealand (2014) and revised by GVP.

Figure 61. Image of White Island taken from Whakatane WebCam video of the 20 August 2013 eruption. The image was in the GNS 22 August 2013 report. Courtesy of Geonet.

The N rim webcam captured visual and thermal infrared images of the eruption. Both the N Island camera and the N rim camera video links were included in the GNS 22 August report. The 20 August eruption ejected mud and rocks a short distance from the vent and produced large volumes of white steam. Weather radar observations suggested that the steam also contained a small proportion of volcanic ash. The hazards posed by the eruption were restricted to the island or possibly vessels anchored nearby. By 21 August 2013, White Island activity had diminished. Volcanologists flying over the island on 23 August observed the return of a small lake. Steam emissions chiefly emerged from the cone area, but their intensity dropped as the small lake reformed. SO₂, CO₂, and H₂S gases recorded during the flight had diminished to pre-eruption levels.

The 7 October GNS report described the changes associated with the August 2013 eruption. A new basin further to the NE of the previous lake filled with water. The lava dome area appeared unchanged while nearby a small pond had formed. Landslides had altered several of the main crater walls, the result of processes most likely related to weather events. Daily SO₂ gas flux measured the previous month ranged from 117 to 662 t/d, typical of the last 12-18 months but higher than before July 2012. In early October it remained elevated.

A moderate but potentially dangerous eruption emerged on 11 October 2013. The eruption sequence began 4 October, with a small energetic steam emission followed by intensified tremor. On 8 October, a period of strong seismicity prevailed accompanied by acoustic signals, and a minor steam and mud eruption that produced a steam plume. During the evening of 11 October, a moderate explosive eruption lasted ~1 minute based on data from acoustic and seismic sensors. The N rim camera images showed that the eruption emerged from the crater's central vent. The explosive eruption produced an ash cloud that expanded across the main crater floor. New mud deposited on the crater floor was evident in the web camera images taken the following day (figure 63). The deposit was thick enough to bury much of the small scale topography on parts of the crater floor. This image and the muddy stratigraphic layer established the baseline for subsequent changes created by volcanism and erosion.

Figure 62. On 12 October 2013 at 0650, the crater floor and walls lie draped beneath fresh deposits of dark gray mud from the eruption the night before. Courtesy of Geonet.

The October 2013 mud eruption was the largest of recent events. GNS volcanologists estimated it would have been life threatening to people on the island. Volcanic tremor gradually decreased after 11 October returning to levels equivalent to the middle of the prior week (see figure 55). The mud deposited on 11 October 2013 had clearly begun to erode by early December 2013. Around this time a new camera on the W rim captured active steam-and-gas plumes from several vents and the large lake seen in 2012 (figure 63). On 23 December 2013 GNS reported an absence of eruptive activity since the 11 October eruption. Seismicity remained low; gas flux, variable. Average daily SO₂ flux ranged from 300 to over 1,000 t/d. Prior to 2012, daily averages were generally less than 300 t/d.

Figure 63. An 11 December 2013 image showing gullies and rills as erosion set in on the fresh mud coating within the crater formed by the 11 October 2013 eruption. Several vents produced active steam plumes and the lake had returned. Courtesy of GNS.

January 2014 changes to the crater and rate of gas emitted. During several January visits, GNS Science staff observed a continued rise in water level of the crater lake, reaching ~5 m higher than in late 2013. The average daily SO₂ flux ranged from 133 to 924 t/d. GNS volcanologists reported an absence of further eruptive activity since the 11 October 2013 eruption.

On 15 January 2014, a thermal infrared image was taken by a portable infrared sensor pointed W from the western crater rim (figure 64). The image shows part of the Crater Lake (oval labeled El1), the area of the 2012 lava extrusion below the lake (large rectangular box labeled Ar1), and a hot fumarole on the S edge of the Crater Lake (small rectangle in the center labeled Ar2). Maximum temperatures were 58°C at the lake, 285°C forAr1, and 297°C for Ar2. These observations confirmed that hot volcanic gases were still passing through these vents.

Figure 64. Thermal infrared image taken on 15 January 2014, with scale at right and areas with analysis at upper left. The oval area (El12) includes part of the Crater Lake, and the area of the 2012 lava extrusion (in rectangular Ar1). The smaller rectangle, Ar2, includes a hot fumarole on the southern edge of the Crater Lake. Courtesy of GeoNet.

References.

100% New Zealand, accessed 5 May 2014, New Zealand Map (URL: http://www.newzealand.com/int/map/).

GNS (22 August 2013), White Island eruption 20 August 2013 - 5x speed, (URL: http://info.geonet.org.nz/display/volc/2013/08/20/White+Island+Eruption.)

GNS (22 August 2013), White Island eruption 20 August 2013 Crater rim - 5x speed, (URL: http://info.geonet.org.nz/display/volc/2013/08/20/White+Island+Eruption).

GNS (14 October 2012), Un-named video clip URL reference in body of GNS report (URL: http://info.geonet.org.nz/pages/viewpage.action?pageId=7241739).

Information Contacts: GeoNet, a collaboration between the Earthquake Commission and GNS Science (URL: http://www.GeoNet.org.nz/); and GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/).

May 2017 (BGVN 42:05) Cite this Report

Ongoing unrest, with phreatic activity on 27 April and 13 September 2016

Following a period with frequent eruptions between 1995 and 2001, White Island (officially called Whakaari/White Island) was quiet until 2012, when plumes began rising from the crater lake on 5 August that included ash two days later (BGVN 37:06). Hydrothermal activity was vigorous, generating phreatic explosions and ash emissions through July 2013, followed by larger explosions in August and October (BGVN 39:02). No further eruptive activity was observed until 2016, when brief phreatic explosions took place on 27 April and 13 September. Monitoring by GNS Science is conducted under the GeoNet Project, the official source of geological hazard information in New Zealand. The following information comes from the GeoNet website.

GNS scientists visited in early February 2014 and measured the crater lake temperature of 57°C and that of fumarole F0, on the S part of the crater floor, at 147°C. The lake level was still rising, and had drowned one of the fumaroles on the southern lakeshore, causing occasional geysering in that area. A new Global Positioning System (GPS) station was installed on the crater floor to strengthen the deformation monitoring network. The average SO₂ gas flux remained below 500 metric tons per day; this was lower than the previous few months and may have been partly due to the higher lake level. On 28 August 2014 the GeoNet seismic network detected a sequence of small earthquakes near White Island, the largest event was magnitude 3.3 and located within 5 km of the island. All the quakes were shallow (less than 10 km depth).

Monitoring by plane, ground instruments, and visual observation throughout 2015 indicated that minor volcanic unrest continued. In October 2015, GNS Science volcanologists measured such factors are ground deformation, CO₂ soil gas, fumarole and crater lake temperature, lake level, and SO₂ gas. Seismometers continued to monitor volcanic tremors, and airborne monitoring measured CO₂, SO₂, and H₂S levels. Elevated amounts of CO₂ emitted from one of the large accessible fumaroles was detected on 1 October; temperatures and SO₂ emissions also increased. On 8 October volcanic tremor magnitude strengthened and became banded (the signal disappeared and reappeared every few hours), commonly noted during periods on unrest and eruptive periods.

Over two weeks in mid-April 2016 the lake level dropped by 2 m. Then, on the morning of 27 April, a brief eruption occurred (lasting about 90 minutes) accompanied by moderately elevated seismic activity. The eruption appears to have deposited material over the N side of the crater floor and up onto the N crater wall. The Volcanic Alert Level was raised to 3 (minor volcanic eruption) and the Aviation Colour Code (ACC) changed from Green to Orange. A subsequent lack of activity resulted in a lowering of the Volcanic Alert Level to 2 (moderate to heightened volcanic unrest) that evening. Observers who flew over the volcano the following day saw a dark-green ash covering at least 80% of the crater floor and up the sides of the crater wall on both N and S sides; the deposit was ~5 mm thick at a distance of 500 m from the eruption site (figure 65).

Figure 65. Ash from the White Island eruption on 27 April 2016 covering the monitoring station. Courtesy of GeoNet (Volcanic Alert Bulletin WI 2016/02).

An aerial inspection two days after the eruption revealed a new crater and vent in the NE corner of the 1978/1990 crater complex. Analysis of the deposit showed the ash to be strongly hydrothermally altered old rock; no evidence of new, juvenile lava was found, suggesting that the eruption was likely driven by steam and gas, like the eruptions in 2012 and 2013. The eruption did produce very energetic blasts and surges that broke survey pegs at ground level. The eruption sequence, as reported by GNS, was that the area around Donald Duck Crater collapsed and exploded (figure 66), then the former lake and sediments erupted, resulting in the blast and surge deposits. The lake floor dropped at least 13 m, and there was a collapse of the 1978/90 Crater walls.

Figure 66. Collapsed area in Donald Duck Crater at White Island as a result of the 27 April 2016 eruption. Courtesy of GeoNet (Volcanic Alert Bulletin WI 2016/07).

By 2 May, observations indicated no change in volcanic activity. As a consequence, the ACC was lowered to Yellow, and by 9 May the Volcanic Alert Level was lowered to 1. Although the April activity was a moderate steam and gas eruption, it did result in a new vent and ash deposits.

GeoNet reported that in the morning of 13 September 2016 a vent on the 2012 lava dome had a minor passive ash emission. The Volcanic Alert Level was raised to 3 from 1, and the ACC was changed from Green to Orange. Observations from a visit on 14 September found that the ash emissions had ceased; the Volcanic Alert Level was lowered to 2 and the ACC lowered to Yellow. The Alert Level was lowered to 1 on 19 September. The crater lake water level began to drop on 24 September, and by 26 September the lake was gone.

GNS has been using Unmanned Aerial Vehicles (UAV's; also known as drones), to monitor the volcano. In December 2016 the drone was used to obtain images of the active crater area, resulting in a new Digital Terrain Model (DTM) of the area (figure 67).

Figure 67. Digital Terrain Model of the White Island volcano crater floor as of December 2016. Courtesy of Geonet (Volcanic Alert Bulletin of December 2016).

According to a GeoNet report on 3 April 2017, visits to White Island over the previous 3-4 months confirmed that activity remained at low levels. Activity was confined to the gas-rich vents on the western side of the active crater. Hot, clear gas continued to be emitted. Some water had ponded on the floor of the active crater but no permanent lake had reformed. The seismic and acoustic activity generally remain low, and the SO₂ gas flux was slowly declining (figures 68 and 69).

Figure 68. View of the active crater area of White Island in early 2017. Note the gas vent (center-rear) and ponded rainwater. Courtesy of GeoNet (Volcanic Alert Bulletin WI-2017-01, 3 April 2017).

Figure 69. Close up view of a gas vent in the active vent area of White Island in early 2017. Courtesy of GeoNet (Volcanic Alert Bulletin WI-2017-01, 3 April 2017).

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/).

February 2020 (BGVN 45:02) Cite this Report

Explosion producing an ash plume and pyroclastic surge resulted in fatalities and injuries on 9 December 2019

Whakaari/White Island has been New Zealand's most active volcano since 1976. Located 48 km offshore, the volcano is a popular tourism destination with tours leaving the town of Whakatane with approximately 17,500 people visiting the island in 2018. Ten lives were lost in 1914 when part of the crater wall collapsed, impacting sulfur miners. More recently, a brief explosion at 1411 on 9 December 2019 produced an ash plume and pyroclastic surge that impacted the entire crater area. With 47 people on the island at the time, the death toll stood at 21 on 3 February 2020. At that time more patients were still in hospitals within New Zealand or their home countries.

The island is the summit of a large underwater volcano, with around 70% of the edifice below the ocean and rising around 300 m above sea level (figure 70). A broad crater opens to the ocean to the SE, with steep crater walls and an active Main Crater area to the NW rear of the crater floor (figure 71). Although the island is privately owned, GeoNet continuously monitors activity both remotely and with visits to the volcano. This Bulletin covers activity from May 2017 through December 2019 and is based on reports by GeoNet, the New Zealand Civil Defence Bay of Plenty Emergency Management Group, satellite data, and footage taken by visitors to the island.

Figure 70. The top of the Whakaari/White Island edifice forms the island in the Bay of Plenty area, New Zealand, while 70% of the volcano is below sea level. Courtesy of GeoNet.

Figure 71. This photo from 2004 shows the Main Crater area of Whakaari/White Island with the vent area indicated. The crater is an amphitheater shape with the crater floor distance between the vent and the ocean entry being about 700 m. The sediment plume begins at the area where tour boats dock at the island. Photo by Karen Britten, graphic by Danielle Charlton at University of Auckland; courtesy of GeoNet (11 December 2019 report).

Nearly continuous activity occurred from December 1975 to September 2000, including the formation of collapse and explosion craters producing ash emissions and explosions that impacted all of the Main Crater area. More recently, it has been in a state of elevated unrest since 2011. Renewed activity commenced with an explosive eruption on 5 August 2012 that was followed by the extrusion of a lava dome and ongoing phreatic explosions and minor ash emissions through March 2013. An ash cone was seen on 4 March 2013, and over the next few months the crater lake reformed. Further significant explosions took place on 20 August and 4, 8, and 11 October 2013. A landslide occurred in November 2015 with material descending into the lake. More recent activity on 27 April 2016 produced a short-lived eruption that deposited material across the crater floor and walls. A short period of ash emission later that year, on 13 September 2016, originated from a vent on the recent lava dome. Explosive eruptions occur with little to no warning.

Since 19 September 2016 the Volcanic Alert Level (VAL) was set to 1 (minor volcanic unrest) (figure 72). During early 2017 background activity in the crater continued, including active fumaroles emitting volcanic gases and steam from the active geothermal system, boiling springs, volcanic tremor, and deformation. By April 2017 a new crater lake had begun to form, the first since the April 2016 explosion when the lake floor was excavated an additional 13 m. Before this, there were areas where water ponded in depressions within the Main Crater but no stable lake.

Figure 72. The New Zealand Volcanic Alert Level system up to date in February 2020. Courtesy of GeoNet.

Activity from mid-2017 through 2018. In July-August 2017 GeoNet scientists carried out the first fieldwork at the crater area since late 2015 to sample the new crater lake and gas emissions. The crater lake was significantly cooler than the past lakes at 20°C, compared to 30-70°C that was typical previously. Chemical analysis of water samples collected in July showed the lowest concentrations of most "volcanic elements" in the lake for the past 10-15 years due to the reduced volcanic gases entering the lake. The acidity remained similar to that of battery acid. Gas emissions from the 2012 dome were 114°C, which were over 450°C in 2012 and 330°C in 2016. Fumarole 0 also had a reduced temperature of 152°C, reduced from over 190°C in late 2016 (figure 73). The observations and measurements indicated a decline in unrest. Further visits in December 2017 noted relatively low-level unrest including 149°C gas emissions from fumarole 0, a small crater lake, and loud gas vents nearby (figures 74 and 75). By 27 November the lake had risen to 10 m below overflow. Analysis of water samples led to an estimate of 75% of the lake water resulting from condensing steam vents below the lake and the rest from rainfall.

Figure 73. A GeoNet scientists conducting field work near Fumarole 0, an accessible gas vent on Whakaari/White Island in August 2017. Courtesy of GeoNet (23 August 2017 report).

Figure 74. GeoNet scientists sample gas emissions from vents on the 2012 Whakaari/White Island dome. The red circle in the left image indicates the location of the scientists. Courtesy of GeoNet (23 August 2017 report).

Figure 75. Active fumaroles and vents in the Main Crater of Whakaari/White Island including Fumarole 0 (top left). The crater lake formed in mid-2017 and gas emissions rise from surrounding vents (right). Courtesy of GeoNet (22 December 2017 report).

Routine fieldwork by GeoNet monitoring teams in early March 2018 showed continued low-level unrest and no apparent changes after a recent nearby earthquake swarm. The most notable change was the increase in the crater lake size, likely a response from recent high rainfall (figure 76). The water remained a relatively cool 27°C. Temperatures continued to decline at the 2012 dome vent (128°C) and Fumarole 0 (138°C). Spring and stream flow had also declined. Deformation was observed towards the Active Crater of 2-5 mm per month and seismicity remained low. The increase in lake level drowned gas vents along the lake shore resulting in geyser-like activity (figure 77). GeoNet warned that a new eruption could occur at any time, often without any useful warning.

In mid-April 2018 visitors reported loud sounds from the crater area as a result of the rising lake level drowning vents on the 2012 dome (in the western side of the crater) and resulting in steam-driven activity. There was no notable change in volcanic activity. The sounds stopped by July 2018 as the geothermal system adjusted to the rising water, up to 17 m below overfill and filling at a rate of about 2,000 m³ per day, rising towards more active vents (figure 78). A gas monitoring flight taken on 12 September showed a steaming lake surrounded by active fumaroles along the crater wall (figure 79).

Figure 76. The increase in the Whakaari/White Island crater lake size in early March 2018 with gas plumes rising from vents on the other side. Courtesy of GeoNet (19 March 2018 report).

Figure 77. The increasing crater lake level at Whakaari/White Island produced geyser-like activity on the lake shore in March 2018. Courtesy of Brad Scott, GeoNet.

Figure 78. Stills taken from a drone video of the Whakaari/White Island Main Crater lake and active vents producing gas emissions. Courtesy of GeoNet.

Figure 79. Photos taken during a gas monitoring flight with GNS Science at Whakaari/White Island show gas and steam emissions, and a steaming crater lake on 12 September 2018. Note the people for scale on the lower-right crater rim in the bottom photograph. Copyright of Ben Clarke, University of Leicester, used with permission.

Activity during April to early December 2019. A GeoNet volcanic alert bulletin in April 2019 reported that steady low-level unrest continued. The level of the lake had been declining since late January and was back down to 13 m below overflow (figure 80). The water temperature had increased to over 60°C due to the fumarole activity below the lake. Fumarole 0 remained steady at around 120-130°C. During May-June a seismic swarm was reported offshore, unrelated to volcanic activity but increasing the risk of landslides within the crater due to the shallow locations.

Figure 80. Planet Labs satellite images from March 2018 to April 2019 show fluctuations in the Whakaari/White Island crater lake level. Image copyright 2019 Planet Labs, Inc.

On 26 June the VAL was raised to level 2 (moderate to heightened volcanic unrest) due to increased SO₂ flux rising to historically high levels. An overflight that day detected 1,886 tons/day, nearly three times the previous values of May 2019, the highest recorded value since 2013, and the second highest since measurements began in 2003. The VAL was subsequently lowered on 1 July due to a reduction in detected SO₂ emissions of 880 tons/day on 28 June and 693 tons/day on 29 June.

GeoNet reported on 26 September that there was an increase in steam-driven activity within the active crater over the past three weeks. This included small geyser-like explosions of mud and steam with material reaching about 10 m above the lake. This was not attributed to an increase in volcanic activity, but to the crater lake level rising since early August.

On 30 October an increase in background activity was reported. An increasing trend in SO₂ gas emissions and volcanic tremor had been ongoing for several months and had reached the highest levels since 2016. This indicated to GeoNet that Whakaari/White Island might be entering a period where eruptive activity was more likely. There were no significant changes in other monitoring parameters at this time and fumarole activity continued (figure 81).

Figure 81. A webcam image taken at 1030 on 30 October 2019 from the crater rim shows the Whakaari/White Island crater lake to the right of the amphitheater-shaped crater and gas-and-steam plumes from active fumaroles. Courtesy of GeoNet.

On 18 November the VAL was raised to level 2 and the Aviation Colour Code was raised to Yellow due to further increase in SO₂ emissions and volcanic tremor. Other monitoring parameters showed no significant changes. On 25 November GeoNet reported that moderate volcanic unrest continued but with no new changes. Gas emissions remained high and gas-driven ejecta regularly jetting material a few meters into the air above fumaroles in the crater lake (figure 82).

Figure 82. A webcam image from the Whakaari/White Island crater rim shows gas-driven ejecta rising above a fumarole within the crater lake on 22 November 2019. Courtesy of GeoNet.

GeoNet reported on 3 December that moderate volcanic unrest continued, with increased but variable explosive gas and steam-driven jetting, with stronger events ejecting mud 20-30 m into the air and depositing mud around the vent area. Gas emissions and volcanic tremor remained elevated and occasional gas smells were reported on the North Island mainland depending on wind direction. The crater lake water level remained unchanged. Monitoring parameters were similar to those observed in 2011-2016 and remained within the expected range for moderate volcanic unrest.

Eruption on 9 December 2019. A short-lived eruption occurred at 1411 on 9 December 2019, generating a steam-and-ash plume to 3.6 km and covering the entire crater floor area with ash. Video taken by tourists on a nearby boat showed an eruption plume composed of a white steam-rich portion, and a black ash-rich ejecta (figure 83). A pyroclastic surge moved laterally across the crater floor and up the inner crater walls. Photos taken soon after the eruption showed sulfur-rich deposits across the crater floor and crater walls, and a helicopter that had been damaged and blown off the landing pad (figure 84). This activity caused the VAL to be raised to 4 (moderate volcanic eruption) and the Aviation Colour Code being raised to Orange.

Figure 83. The beginning of the Whakaari/White Island 9 December 2019 eruption viewed from a boat that left the island about 20-30 minutes prior. Top: the steam-rich eruption plume rising above the volcano and a pyroclastic surge beginning to rise over the crater rim. Bottom: the expanded steam-and-ash plume of the pyroclastic surge that flowed over the crater floor to the ocean. Copyright of Michael Schade, used with permission.

Figure 84. This photo of Whakaari/White Island taken after the 9 December 2019 eruption at around 1424 shows ash and sediment coating the crater floor and walls. The helicopter in this image was blown off the landing pad and damaged during the eruption. Copyright of Michael Schade, used with permission.

A steam plume was visible in a webcam image taken at 1430 from Whakatane, 21 minutes after the explosion (figure 85). Subsequent explosions occurred at 1630 and 1749. Search-and-Rescue teams reached the island after the eruption and noted a very strong sulfur smell that was experienced through respirators. They experienced severe stinging of any exposed skin that came in contact with the gas, and were left with sensitive skin and eyes, and sore throats. Later in the afternoon the gas-and-steam plume continued and a sediment plume was dispersing from the island (figure 86). The VAL was lowered to level 3 (minor volcanic eruption) at 1625 that day; the Aviation Colour Code remained at Orange.

Figure 85. A view of Whakaari/White Island from Whakatane in the North Island of New Zealand. Left: there is no plume visible at 1410 on 9 December 2019, one minute before the eruption. Right: A gas-and-steam plume is visible 21 minutes after the eruption. Courtesy of GeoNet.

Figure 86. A gas-and-steam plume rises from Whakaari/White Island on the afternoon of 9 December 2019 as rescue teams visit the island. A sediment plume in the ocean is dispersing from the island. Courtesy of Auckland Rescue Helicopter Trust.

During or immediately after the eruption an unstable portion of the SW inner crater wall, composed of 1914 landslide material, collapsed and was identified in satellite radar imagery acquired after the eruption. The material slid into the crater lake area and left a 12-m-high scarp. Movement in this area continued into early January.

Activity from late 2019 into early 2020. A significant increase in volcanic tremor began at around 0400 on 11 December (figure 87). The increase was accompanied by vigorous steaming and ejections of mud in several of the new vents. By the afternoon the tremor was at the highest level seen since the 2016 eruption, and monitoring data indicated that shallow magma was driving the increased unrest.

Figure 87. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 11 November to 11 December 2019 with the Volcanic Activity Levels and the 9 December eruption indicated. The plot shows the sharp increase in seismic energy during 11 December. Courtesy of GeoNet (11 December 2019 report).

The VAL was lowered to 2 on the morning of 12 December to reflect moderate to heightened unrest as no further explosive activity had occurred since the event on the 9th. Volcanic tremor was occurring at very high levels by the time a bulletin was released at 1025 that day. Gas emissions increased since 10 January, steam and mud jetting continued, and the situation was interpreted to be highly volatile. The Aviation Colour Code remained at Orange. Risk assessment maps released that day show the high-risk areas as monitoring parameters continued to show an increased likelihood of another eruption (figure 88).

Figure 88. Risk assessment maps of Whakaari/White Island show the increase in high-risk areas from 2 December to 12 December 2019. Courtesy of GeoNet (12 December 2019 report).

The volcanic activity bulletin for 13 December reported that volcanic tremor remained high, but had declined overnight. Vigorous steam and mud jetting continuing at the vent area. Brief ash emission was observed in the evening with ashfall restricted to the vent area. The 14 January bulletin reported that volcanic tremor had declined significantly over night, and nighttime webcam images showed a glow in the vent area due to high heat flow.

Aerial observations on 14 and 15 December revealed steam and gas emissions continuing from at least three open vents within a 100 m² area (figure 89). One vent near the back of the crater area was emitting transparent, high-temperature gas that indicated that magma was near the surface, and produced a glow registered by low-light cameras (figure 90). The gas emissions had a blue tinge that indicated high SO₂ content. The area that once contained the crater lake, 16 m below overflow before the eruption, was filled with debris and small isolated ponds mostly from rainfall, with different colors due to the water reacting with the eruption deposits. The gas-and-steam plume was white near the volcano but changed to a gray-brown color as it cooled and moved downwind due to the gas content (figure 91). On 15 December the tremor remained at low levels (figure 92).

Figure 89. The Main Crater area of Whakaari/White Island showing the active vent area and gas-and-steam emissions on 15 December 2019. Gas emissions were high within the circled area. Before the eruption a few days earlier this area was partially filled by the crater lake. Courtesy of GeoNet (15 December 2019 report).

Figure 90. A low-light nighttime camera at Whakaari/White Island imaged "a glow" at a vent within the active crater area on 13 December 2019. This glow is due to high-temperature gas emissions and light from external sources like the moon. Courtesy of GeoNet (15 December 2019 report).

Figure 91. A gas-and-steam plume at Whakaari/White Island on 15 December 2019 is white near the crater and changes to a grey-brown color downwind due to the gas content. Courtesy of GeoNet (15 December 2019 report).

Figure 92. The Whakaari/White Island seismic drum plot showing the difference in activity from 12 December (top) to 15 December (bottom). Courtesy of GeoNet (15 December 2019 report).

On 19 December tremor remained low (figure 93) and gas and steam emission continued. Overflight observations confirmed open vents with one producing temperatures over 650°C (figure 94). SO₂ emissions remained high at around 15 kg/s, slightly lower than the 20 kg/s detected on 12 December. Small amounts of ash were produced on 23 and 26 December due to material entering the vents during erosion.

Figure 93. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 1 November to mid-December 2019. The Volcanic Alert Levels and the 9 December eruption are indicated. Courtesy of GeoNet.

Figure 94. A photograph and thermal infrared image of the Whakaari/White Island crater area on 19 December 2019. The thermal imaging registered temperatures up to 650°C at a vent emitting steam and gas. Courtesy of GeoNet.

The Aviation Colour Code was reduced to Yellow on 6 January 2020 and the VAL remained at 2. Strong gas and steam emissions continued from the vent area through early January and the glow persisted in nighttime webcam images. Short-lived episodes of volcanic tremor were recorded between 8-10 January and were accompanied by minor explosions. A 15 January bulletin reported that the temperature at the vent area remained very hot, up to 440°C, and SO₂ emissions were within normal post-eruption levels.

High temperatures were detected within the vent area in Sentinel-2 thermal data on 6 and 16 January (figure 95). Lava extrusion was confirmed within the 9 December vents on 20 January. Airborne SO₂ measurements on that day recorded continued high levels and the vent temperature was over 400°C. Observations on 4 February showed that no new lava extrusion had occurred, and gas fluxes were lower than two weeks ago, but still elevated. The temperatures measured in the crater were 550-570°C and no further changes to the area were observed.

Figure 95. Sentinel-2 thermal infrared satellite images show elevated temperatures in the 9 December 2019 vent area on Whakaari/White Island. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Bay of Plenty Emergency Management Group Civil Defense, New Zealand (URL: http://www.bopcivildefence.govt.nz/); Auckland Rescue Helicopter Trust, Auckland, New Zealand (URL: https://www.rescuehelicopter.org.nz/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Ben Clarke, The University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom (URL: https://le.ac.uk/geology, Twitter: https://twitter.com/PyroclasticBen); Michael Schade, San Francisco, USA (URL: https://twitter.com/sch).

December 2020 (BGVN 45:12) Cite this Report

Gas-and-steam emissions with some re-suspended ash in November 2020

Whakaari/White Island, located in the Bay of Plenty 50 km offshore of North Island, has been New Zealand’s most active volcano since 1976. Activity has been previously characterized by phreatic activity, explosions, and ash emissions (BGVN 42:05). The most recent eruption occurred on 9 December 2019, which consisted of an explosion that generated an ash plume and pyroclastic surge that affected the entire crater area, resulting in 21 fatalities and many injuries (BGVN 45:02). This report updates information from February through November 2020, which includes dominantly gas-and-steam emissions along with elevated surface temperatures, using reports from the New Zealand GeoNet Project, the Wellington Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity at Whakaari/White Island has declined and has been dominated by white gas-and-steam emissions during the reporting period; no explosive eruptive activity has been detected since 9 December 2019. During February through 22 June, the Volcanic Activity Level (VAL) remained at a 2 (moderate to heightened volcanic unrest) and the Aviation Color Code was Yellow. GeoNet reported that satellite data showed some subsidence along the W wall of the Main Crater and near the 1914 landslide scarp, though the rate had reduced compared to previous months. Thermal infrared data indicated that the fumarolic gases and five lobes of lava that were first observed in early January 2020 in the Main Crater were 550-570°C on 4 February and 660°C on 19 February. A small pond of water had begun to form in the vent area and exhibited small-scale gas-and-steam-driven water jetting, similar to the activity during September-December 2019. Gas data showed a steady decline in SO₂ and CO₂ levels, though overall they were still slightly elevated.

Similar activity was reported in March and April; the temperatures of the fumaroles and lava in the Main Crater were 746°C on 10 March, the highest recorded temperature to date. SO₂ and CO₂ gas emissions remained elevated, though had overall decreased since December 2019. Small-scale water jetting continued to be observed in the vent area. During April, public reports mentioned heightened gas-and-steam activity, but no eruptions were detected. A GeoNet report issued on 16 April stated that high temperatures were apparent in the vent area at night.

Whakaari remained at an elevated state of unrest during May, consisting of dominantly gas-and-steam emissions. Monitoring flights noted that SO₂ and CO₂ emissions had increased briefly during 20-27 May. On 20 May, the lava lobes remained hot, with temperatures around 500°C; a nighttime glow from the gas emissions surrounding the lava was visible in webcam images. Tremor levels remained low with occasional slightly elevated episodes, which included some shallow-source volcanic earthquakes. Satellite-based measurements recorded several centimeters of subsidence in the ground around the active vent area since December 2019. During a gas observation flight on 28 May there was a short-lived gas pulse, accompanied by an increase in SO₂ and CO₂ emissions, and minor inflation in the vent area (figure 96).

Figure 96. Photo of a strong gas-and-steam plume rising above Whakaari/White Island on 28 May 2020. Courtesy of GeoNet.

An observation flight made on 3 June reported a decline in gas flux compared to the measurements made on 28 May. Thermal infrared images taken during the flight showed that the lava lobes were still hot, at 450°C, and continued to generate incandescence that was visible at night in webcams. On 16 June the VAL was lowered to 1 (minor volcanic unrest) and on 22 June the Aviation Color Code had decreased to Green.

Minor volcanic unrest continued in July; the level of volcanic tremors has remained generally low, with the exception of two short bursts of moderate volcanic tremors in at the beginning of the month. Temperatures in the active vents remained high (540°C) and volcanic gases persisted at moderate rate, similar to those measured since May, according to an observation flight made during the week of 30 July. Subsidence continued to be observed in the active vent area, as well as along the main crater wall, S and W of the active vents. Recent rainfall has created small ponds of water on the crater floor, though they did not infiltrate the vent areas.

Gas-and-steam emissions persisted during August through October at relatively high rates (figures 97 and 98). A short episode of moderate volcanic tremor was detected in early August, but otherwise seismicity remained low. Updated temperatures of the active vent area were 440°C on 15 September, which had decreased 100°C since July. Rain continued to collect at the crater floor, forming a small lake; minor areas of gas-and-steam emissions can be seen in this lake. Ongoing subsidence was observed on the Main Crater wall and S and W of the 2019 active vents.

Figure 97. Photo of an observation flight over Whakaari/White Island on 8 September 2020 showing white gas-and-steam emissions from the vent area. Photo courtesy of Brad Scott, GeoNet.

Figure 98. Image of Whakaari/White Island from Whakatane in the North Island of New Zealand showing a white gas-and-steam plume on 26 October 2020. Courtesy of GeoNet.

Activity during November was primarily characterized by persistent, moderate-to-large gas-and-steam plumes that drifted downwind for several kilometers but did not reach the mainland. The SO₂ flux was 618 tons/day and the CO₂ flux was 2,390 tons/day. New observations on 11 November noted some occasional ash deposits on the webcams in conjunction with mainland reports of a darker than usual plume (figure 99). Satellite images provided by MetService, courtesy of the Japan Meteorological Agency, confirmed the ash emission, but later images showed little to no apparent ash; GNS confirmed that no eruptive activity had occurred. Initial analyses indicated that the ash originated from loose material around the vent was being entrained into the gas-and-steam plumes. Observations from an overflight on 12 November showed that there was no substantial change in the location and size of the active vents; rainfall continued to collect on the floor of the 1978/90 Crater, reforming the shallow lake. A small sequence of earthquakes was detected close to the volcano with several episodes of slightly increased volcanic tremors.

During 12-14 November the Wellington VAAC issued multiple advisories noting gas, steam, and ash plumes that rose to 1.5-1.8 km altitude and drifted E and SE, based on satellite data, reports from pilots, and reports from GeoNet. As a result, the VAL was increased to 2 and the Aviation Color Code was raised to Yellow. Scientists on another observation flight on 16 November reported that small amounts of ash continued to be present in gas-and-steam emissions, though laboratory analyses showed that this ash was resuspended material and not from new eruptive or magmatic activity. The SO₂ and CO₂ flux remained above background levels but were slightly lower than the previous week’s measurements: 710 tons/day and 1,937 tons/day. Seismicity was similar to the previous week, characterized by a sequence of small earthquakes, a larger than normal volcanic earthquake located near the volcano, and ongoing low-level volcanic tremors. During 16-17 November plumes with resuspended ash were observed rising to 460 m altitude, drifting E and NE, according to a VAAC advisory (figure 99). During 20-24 November gas-and-steam emissions that contained a minor amount of resuspended ash rose to 1.2 km altitude and drifted in multiple directions, based on webcam and satellite images and information from GeoNet.

Figure 99. Left: Photo of a gas observation flight over Whakaari/White Island on 11 November 2020 showing some dark particles in the gas-and-steam plumes, which were deposited on some webcams. Photo has been color corrected and straightened. Courtesy of GeoNet. Right: Photo showing gas, steam, and ash emissions rising above the 2019 Main Crater area on 16 November 2020. Courtesy of GNS Science (17 November 2020 report).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a total of eleven low-power thermal anomalies during January to late March 2020; a single weak thermal anomaly was detected in early July (figure 100). The elevated surface temperatures during February-May 2020 were detected in Sentinel-2 thermal satellite images in the Main Crater area, occasionally accompanied by gas-and-steam emissions (figure 101). Persistent white gas-and-steam emissions rising above the Main Crater area were observed in satellite imagery on clear weather days and drifting in multiple directions (figure 102). The small lake that had formed due to rainfall was also visible to the E of the active vents.

Figure 100. Low-power, infrequent thermal activity at Whakaari/White Island was detected during January through late March 2020, as reflected in the MIROVA data (Log Radiative Power). A single thermal anomaly was shown in early July. Courtesy of MIROVA.

Figure 101. Sentinel-2 thermal satellite images in the Main Crater area of Whakaari/White Island show residual elevated temperatures from the December 2019 eruption, accompanied by gas-and-steam emissions and drifting in different directions during February-May 2020. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 102. Sentinel-2 images showing persistent white gas-and-steam plumes rising from Main Crater area of Whakaari/White Island during March-November 2020 and drifting in multiple directions. A small pond of water (light blue-green) is visible in the vent area to the E of the plumes. On 11 November (bottom right), the color of the plume is gray and contains a small amount of ash. Images using “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brad Scott, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: https://twitter.com/Eruptn).