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Report on Asosan (Japan) — October 1992

Bulletin of the Global Volcanism Network, vol. 17, no. 10 (October 1992)
Managing Editor: Lindsay McClelland.

Asosan (Japan) Explosion produces 2500-m plume and wet ashfall; weak ejections from crater lake

Please cite this report as:

Global Volcanism Program, 1992. Report on Asosan (Japan). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199210-282110.

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Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


An eruption from Crater 1 occurred at 1340 on 26 October, the fourth this year and the first such activity since 29 September. A steam plume containing ash rose 2,500 m, and wet ash fell 1.5 km S of the crater. No blocks were jected. Eruption-tremor amplitude was 20 µm at the nearest seismometer, 0.8 km W of the crater (table 7).

Table 7. Eruptions at Aso during 1992. Courtesy of JMA.

Date Tremor Amplitude Plume Height Range of blocks (from center of crater)
01 Jul 1992 9 µm unknown 300 m N
08 Sep 1992 30 µm 2 km 600 m E
29 Sep 1992 30 µm 2 km 700 m S
26 Oct 1992 20 µm 2.5 km none

Steam was steadily emitted to a few hundred meters throughout October, and volcanic-tremor frequency was low. No changes in steam emission, tremor frequency, or earthquakes were noted before or after the eruption. Weak ejections of mud, blocks, and water to 15 m height continued in the crater lake, which ccupies half of the crater floor. Similar activity has continued through 14 November, without additional eruptions. The area within 1 km of the crater has been closed to tourists since 24 August. No damage was caused by the eruption.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.