Eruptive history of the Kusatsu Shirane volcano

Abstract

The eruptive history of the Kusatsu Shirane volcano is well described by means of 14 beds of tephra and intercalating loess soil. Three eruptive stages are recognized. During early or middle Pleistocene the Matsuozawa volcano was formed; this is the first stage. The second stage was initiated by effusion of the Horaguchi lava, which was followed by eruptions of the Oshi pyroclastic flow, older lava flows, 3P pumice fall, and Yazawahara pyroclastic flow. The third stage, which started about 14 000 years ago, is the formation of three pyroclastic cones on the summit and contemporaneous effusion of the younger lava flows, e.g. the Kagusa lava of 7000 years ago and the Sessyo lava of 3000 years ago. In historic times, phreatic explosions have frequently occurred on the summit crater, Yugama. -from English summary