Report on Kusatsu-Shiranesan (Japan) — May 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 5 (May 1983)
Managing Editor: Lindsay McClelland.
Kusatsu-Shiranesan (Japan) 9 March activity was only seismic
Please cite this report as:
Global Volcanism Program, 1983. Report on Kusatsu-Shiranesan (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 8:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198305-283120.
36.618°N, 138.528°E; summit elev. 2165 m
All times are local (unless otherwise noted)
Tokyo Institute of Technology personnel visited the volcano on 12 March to investigate a report of a small phreatic explosion from Pit No. 7 on 9 March [originally reported in 8:4]. A brief swarm of volcanic earthquakes had been recorded at 0459 that day at the Maebashi District Meteorological Observatory. The Institute team found no fresh ash. Although ash was reported to have fallen on the frozen crater lake, another observer said that the lake was not frozen on 9 March. The team concluded that the 9 March activity had been only seismic.
Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.
Information Contacts: JMA, Tokyo.