Tarumai stratovolcano on the caldera's rim is site of 65 earthquakes

The number of volcanic earthquakes beneath Tarumai stratovolcano increased during the second half of August. A total of 65 earthquakes was recorded in August.

Information Contacts: Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.

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

June 1978 (SEAN 03:06) Cite this Report

Explosive eruption with small pyroclastic flow after 10 years of increasing seismicity

Tarumai exploded on 14 May at 2253, accompanied by volcanic tremor. A slight ashfall was observed 10 km NNE of the summit crater and a small pyroclastic flow consisting of pumiceous ash and blocks traveled 150 m SE from the vent. Sixteen hours after the eruption, geologists measured a temperature of 200°C at the base of the pyroclastic flow (30 cm below the surface). Smaller explosions occurred on 17 May, mantling the vent area with 1 cm of new ash. No further explosions had been observed as of 7 June.

Tarumai, which last erupted in 1955, is characterized by conspicuous earthquake swarms, followed by explosive eruptions of andesitic magma, then lava dome extrusion. The number of earthquakes at Tarumai has been increasing irregularly for the past 10 years and increased sharply in the first five months of 1978 (figure 1). No eruption was associated with the somewhat smaller peak in seismicity that occurred in 1975.

Figure 1. Monthly seismicity recorded at JMA's Tarumai Observatory, January 1978-June 1979. Arrows represent ash eruptions. Courtesy of JMA.

Further Reference. Katsui, Y., Onuma, K., Niida, K., Suzuki, T., and Kondo, Y., 1979, Eruption of Tarumai volcano in May 1978: Bulletin of the Volcanological Society of Japan, v. 24, no. 2, p. 31-40.

Information Contacts: JMA, Tokyo; D. Shackelford, CA.

July 1978 (SEAN 03:07) Cite this Report

No new explosions; seismicity declines to normal

As of early July, no eruptive activity had been observed since the explosions of 14 and 17 May. Seismicity decreased to its normal level in mid-June after a 10-year increase preceding the May explosions.

Information Contacts: JMA, Tokyo.

December 1978 (SEAN 03:12) Cite this Report

Two small ash eruptions

Tarumai erupted ash from 0910 to 0920 on 12 December. The ash cloud rose 200 m above the vent, which was also the source of small explosions on 14 and 17 May. Ash slightly darkened the snow in the summit area, but did not reach the foot of the volcano. A second ash eruption occurred on 16 December, with ashfall again restricted to the summit area. Seismicity remained at a low level (table 1).

Table 1. Monthly seismicity at Shikotsu (Tarumai) in 1978. Courtesy of JMA.

Information Contacts: JMA, Tokyo.

January 1979 (SEAN 04:01) Cite this Report

Ash eruptions continue

Ash eruptions continued through early January. Ash was ejected on 16, 26, and 29 December and on 5 January, falling on the summit area. Seismicity remained at normal levels through December.

Information Contacts: JMA, Tokyo.

February 1979 (SEAN 04:02) Cite this Report

Small ash eruptions continue; seismicity increases sharply

Ash eruptions continued through January. Ash was ejected on 5, 22, 23, and 27 January, darkening snow in the summit area, but no ash reached the foot of the volcano.

Local seismicity increased sharply about 10 January, after several months of relative quiet. An irregular increase in seismic activity has persisted since 1967.

Information Contacts: JMA, Tokyo.

March 1979 (SEAN 04:03) Cite this Report

Small ash eruptions and increased seismicity continue

Ash was ejected on 5, 8, 19, and 25-28 February, continuing the series of small explosions that resumed 12 December. The ash darkened snow in the summit area, but did not reach the foot of the volcano. The number of recorded local earthquakes increased from 201 in January to 427 in February.

Information Contacts: JMA, Tokyo.

April 1979 (SEAN 04:04) Cite this Report

More ash eruptions but declining seismicity

Ash eruptions continued in March. Ash fell on the summit area on 1, 2, 4, 6, and 8 March but did not reach the foot of the volcano. Seismicity declined considerably in March, but remained slightly above the monthly total for January.

Information Contacts: JMA, Tokyo.

May 1979 (SEAN 04:05) Cite this Report

Seismicity and number of explosions decline

Eruptive and seismic activity declined substantially in April. Only one [ash eruption] took place in April, on the 13th, causing a small ashfall in the summit area. The monthly number of recorded earthquakes dropped from 223 in March to 70 in April.

Information Contacts: JMA, Tokyo.

June 1979 (SEAN 04:06) Cite this Report

Small ash eruption but decline in seismicity persists

The decline in activity continued through May. A single small ash eruption occurred in May, on the 11th. Ash fell in the summit area but not reach the foot of the volcano. Monthly recorded earthquakes decreased slightly from 70 in April to 66 in May, but the number of tremor events dropped more sharply, from more than 40 to 9. The tremor events, each lasting a few minutes, were thought to be generated by vigorous activity at a vent. The strongest of this activity was visible from the base of the volcano.

Information Contacts: JMA, Tokyo.

July 1979 (SEAN 04:07) Cite this Report

Seismicity increases, but no explosions

No explosions or tremor events were recorded in June. However, the number of local earthquakes, which had been declining since March, increased in June.

Information Contacts: JMA, Tokyo.

August 1979 (SEAN 04:08) Cite this Report

No explosions; seismicity declines

The number of recorded earthquakes declined to 58 in July after rising sharply to 142 in June. No explosions were observed in July, nor were any tremor events, which are presumably generated by [ash ejection].

Information Contacts: JMA, Tokyo.

November 1979 (SEAN 04:11) Cite this Report

Brief increase in seismicity, but no eruption

An increase in the number of local earthquakes and a resumption of tremor events occurred in mid-September, but no eruption was observed. In October, seismicity returned to normal levels and no tremor events were recorded.

Information Contacts: JMA, Tokyo.

December 1980 (SEAN 05:12) Cite this Report

Seismicity increases

Seismic activity increased in November after about one and a half years of quiet.

Information Contacts: JMA, Tokyo.

January 1981 (SEAN 06:01) Cite this Report

Seismicity continues to increase

Seismic activity increased again to more than 400 recorded events during January. No eruption has yet been observed. About 200 events per month were recorded in November and December, after over a year of fewer than 50 events per month.

Information Contacts: JMA, Tokyo.

February 1981 (SEAN 06:02) Cite this Report

Sharp increase in seismicity

In February, 1,121 seismic events were recorded, the most in any month since 1967, when JMA began routine measurements at the volcano. Seismicity has irregularly but gradually increased in the past 14 years (figure 2). No eruption has occurred during the current increase in seismicity.

Figure 2. Yearly means of Tarumai's monthly seismicity, 1967-80. Courtesy of JMA.

Information Contacts: JMA, Tokyo.

March 1981 (SEAN 06:03) Cite this Report

Seismicity declines without expected eruption

Local seismicity began to increase in November 1980 and the number of events per month reached 1,211 in February 1981 (figure 3). Seismicity began a gradual decline in early March and by mid-March had reached the usual average of fewer than three recorded earthquakes per day.

Figure 3. Monthly numbers of days with eruptions (top), tremor events (center), and recorded earthquakes (bottom) at Tarumai, January 1978-March 1981. Courtesy of JMA.

Only 87 events were recorded in March. Although the December 1978-May 1979 eruption accompanied the last major increase in seismicity, no eruption has occurred during the current, much larger increase [but see 06:04].

Information Contacts: JMA, Tokyo.

April 1981 (SEAN 06:04) Cite this Report

Minor ash emission during February seismic peak

Seismicity declined to its usual level of fewer than three recorded earthquakes per day in March and remained at this level through April. Although no volcanic activity apparently had accompanied the peak of seismicity in February (1,211 events), subsequent investigation revealed that a weak steam explosion had occurred on 27 February or a few days earlier.

On the morning of 27 February an All Nippon Airways crew reported that they saw radially darkened snow on the SE part of the summit area. Yoshio Katsui visited the summit on 9 April and found a single layer of gray ash in the snow. The ash layer was only 0.3-0.6 mm thick at the crater rim. The total volume of ejecta was estimated to be no more than 400 m³.

Information Contacts: JMA, Tokyo; Y. Katsui, Hokkaido Univ.

February 1988 (SEAN 13:02) Cite this Report

Earthquake swarms

Local earthquake swarms occurred 24 January-18 February. The JMA seismometer, 1.1 km NE of the summit cone, recorded 30 events in January and 124 in February. Epicenters were located at the NW somma using data from five Hokkaido University seismometers. A white plume constantly rose ~100 m.

Tarumai's strongest earthquake swarm of the past two decades began in late 1980, peaking in February 1981, when more than 1,200 shocks were recorded. Late that month ~400 m³ of ash was deposited near the crater by a very small eruption. Seismicity then declined, and the number of local events has averaged <10/month in the last few years (figure 4).

Figure 4. Monthly number of earthquakes at Tarumai, January 1967-January 1988. Courtesy of JMA.

Information Contacts: JMA.

July 1996 (BGVN 21:07) Cite this Report

Seismic activity increases

The number of volcanic earthquakes beneath Tarumai stratovolcano (on the rim on Shikotsu caldera) increased in June and July. There were 13 events on both 8 and 10 June. A total of 64 earthquakes was recorded in July.

Information Contacts: Volcanological Division, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan

August 1996 (BGVN 21:08) Cite this Report

Tarumai stratovolcano on the caldera's rim is site of 65 earthquakes

The number of volcanic earthquakes beneath Tarumai stratovolcano increased during the second half of August. A total of 65 earthquakes was recorded in August.

Information Contacts: Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.