Report on Asosan (Japan) — July 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 7 (July 1990)
Managing Editor: Lindsay McClelland.
Asosan (Japan) Sporadic eruptive activity stops; variable tremor amplitude
Please cite this report as:
Global Volcanism Program, 1990. Report on Asosan (Japan). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 15:7. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199007-282110.
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
. . . Ash clouds and blocks were ejected [from Crater 1] on 7 days in June 1990, most recently on the 18th. However, no eruptions occurred in July. Tremor amplitude increased from 22 June to 2 July, decreased, then gradually increased for the remainder of the month. The bottom of Crater 1 was covered with a pool of water.
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: JMA.