Report on Asosan (Japan) — September 1978
Scientific Event Alert Network Bulletin, vol. 3, no. 9 (September 1978)
Managing Editor: David Squires.
Asosan (Japan) Weak steam and ash emission in May and June
Please cite this report as:
Global Volcanism Program, 1978. Report on Asosan (Japan). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 3:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197809-282110.
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
Steam and ash emission from [Crater 1] of Naka-dake occurred 29 May-1 June, producing an ashfall on the N side of the crater. Rumbling accompanying the activity could be heard from [JMA's Asosan Weather Station] 1 km from [the crater of] Naka-dake. Mud and [block] spattering was observed in mid-June, but the ejecta rose only 40-50 m and remained within the crater. No further activity has been reported.
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; D. Shackelford, CA.