Report on Asosan (Japan) — October 1995

Bulletin of the Global Volcanism Network, vol. 20, no. 10 (October 1995)
Managing Editor: Richard Wunderman.

Asosan (Japan) Isolated tremor; ejections of mud and water

Please cite this report as:

Global Volcanism Program, 1995. Report on Asosan (Japan). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 20:10. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199510-282110.

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Asosan

Japan

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

All times are local (unless otherwise noted)


During October the floor of Aso's active crater (Naka-dake Crater 1) remained covered by a pond of hot water. The pond's surface was disrupted by occasional fountaining up to 5-m high. Elevated tremor continued since last month, and some October days had over 200 earthquakes; the daily mean amplitude of continuous tremors sometimes reached over 0.5 þm. Personnel 800 m W of the crater (at Aso Weather Station) felt earthquakes at 1829 and 1909 on 11 and 22 October, respectively.

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 cu km 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 AD. 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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.