Report on Kujusan (Japan) — October 1995
Bulletin of the Global Volcanism Network, vol. 20, no. 10 (October 1995)
Managing Editor: Richard Wunderman.
Kujusan (Japan) Additional data on the sudden aseismic eruption of 11 October
Please cite this report as:
Global Volcanism Program, 1995. Report on Kujusan (Japan) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 20:10. Smithsonian Institution.
33.086°N, 131.249°E; summit elev. 1791 m
All times are local (unless otherwise noted)
On 11 October, aseismic phreatic eruptions started within the Kuju volcanic group, on Hosho (Hosyo) dome's E side (BGVN 20:09). On 12 October observers found an E-W trending line of vents ~300-m long; also, at that time an ash-bearing plume rose to ~1 km above the crater.
The eruption deposited a 100 m2 blanket of fist-sized volcanic clasts; it also emitted mud that flowed down an adjacent valley. After that, the volume and height of the plume gradually decreased until finally ash-bearing eruptions ceased at the month's end. Seismicity stayed low during October.
Geologic Background. Kujusan is a complex of stratovolcanoes and lava domes lying NE of Aso caldera in north-central Kyushu. The group consists of 16 andesitic lava domes, five andesitic stratovolcanoes, and one basaltic cone. Activity dates back about 150,000 years. Six major andesitic-to-dacitic tephra deposits, many associated with the growth of lava domes, have been recorded during the Holocene. Eruptive activity has migrated systematically eastward during the past 5000 years. The latest magmatic activity occurred about 1600 years ago, when Kurodake lava dome at the E end of the complex was formed. The first reports of historical eruptions were in the 17th and 18th centuries, when phreatic or hydrothermal activity occurred. There are also many hot springs and hydrothermal fields. A fumarole on Hosho lava dome was the site of a sulfur mine for at least 500 years. Two geothermal power plants are in operation at Kuju.
Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.