JMA reported that anomalous temperatures and deformation of Kusatsu-Shirane’s crater, which began earlier in March, continued during 13-20 June. This activity has been focused in the area immediately of N of Mizugama crater. Elevated seismicity was also reported, although tremor was absent. The Alert Level was raised to 2 (on a scale of 1-5).

Geological Summary. 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.

Source: Japan Meteorological Agency (JMA) via the Volcano Research Center