Report on Kusatsu-Shiranesan (Japan) — March 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 3 (March 1991)
Managing Editor: Lindsay McClelland.
Kusatsu-Shiranesan (Japan) Brief peak in seismicity
Please cite this report as:
Global Volcanism Program, 1991. Report on Kusatsu-Shiranesan (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199103-283120.
36.618°N, 138.528°E; summit elev. 2165 m
All times are local (unless otherwise noted)
Seismicity continued at high levels through mid-April, after  recorded earthquakes and 11 tremor episodes in March. A sharp, brief increase in seismicity on 9 March (42 recorded earthquakes), prompted the JMA to issue a notice ("Extra Volcanic Information"), the first since August. No changes in surface activity were observed.
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.