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Report on Asosan (Japan) — September 1992


Bulletin of the Global Volcanism Network, vol. 17, no. 9 (September 1992)
Managing Editor: Lindsay McClelland.

Asosan (Japan) Blocks ejected by explosive episode

Please cite this report as:

Global Volcanism Program, 1992. Report on Asosan (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199209-282110



32.8849°N, 131.085°E; summit elev. 1592 m

All times are local (unless otherwise noted)

An eruption from Crater 1 ejected blocks at 1223 on 8 September, the first such activity since a similar episode on 30 June-1 July. Another eruption at 1627 on 29 September scattered blocks 800 m SE and ejected a steam plume 2,000 m high. The number of blocks and the distance they fell from the crater were greater than for the eruptions of 8 September and 1 July. Eruption-tremor amplitude was 30.2 and 30.4 µm, respectively, for the September eruptive pisodes.

Steam was steadily emitted to a few hundred meters throughout September, and volcanic-tremor frequency was low. No anomalies in steam emission or tremor frequency were noted either before or after the eruptions. However, continuous-tremor amplitude increased for two days after the 8 September eruption. Weak ejections of mud, blocks, and water continued.

An area within 1 km of the crater has been closed to tourists since 24 August, and no damage was caused by the eruptions. Similar activity has continued through 14 October, but there have been no additional eruptions.

Geological Summary. 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.