Kusatsu-Shirane Mt., Japan, 1660s Eruption

Abstract

Mount Kusatsu-Shirane (36°37′N, 138°32′E) is an active, 2,171m high volcano in Kusatsu, Gunma, Honshu province, some 140 km northwest of Tokyo. It is called Kusatsu Shirane to differentiate it from the Mount Nikkö-Shirane on the other side of the Gunma Prefecture. In the historical times, frequent eruptions occurred there, the last event happened in 1989.

The summit of the Kusatsu-Shirane volcano, located north of the Asama volcano, consists of a series of overlapping pyroclastic cones separated by several crater lakes. The largest lake of them is Yu-gama, an acidic turquoise-colored lake with an overlay of yellow sulfur floating on its surface. The Kusatsu-Shirane volcano has an andesite–dacite body; the oldest sediments are of Pleistocene age. Southern and southeastern slopes of the volcano are covered by sintered tuffs and volcanic pumices. The crater was exploited during the intensive sulfur mining in the nineteenth and twentieth centuries. A number of fumaroles and hot springs, usually acidic, confirm the volcano's geologically young origin. Several volcanic eruptions occurred recently, the strongest one in the crater Yu-gama in October 1932.