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.

Geological Summary. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

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