草津白根火山の南東麓で見出された埋没岩屑なだれ堆積物
Year: 2016
Type: article
Abstract: A large-scale outcrop at the southeastern foot of Kusatsu-Shirane Volcano, Gunma prefecture, could be seen during the road construction along Route 292 in 2013 and 2014. Most of the deposit cropping out was poorly sorted and covered with alternating pyroclastic fall deposits and black humus soil. Since mega-blocks and deformed soft blocks characterize the heterogeneous matrix, the poorly sorted deposit is considered to be a debris avalanche deposit. The weathered ash and overlying thick pumice fall deposit is the 1.3ka Tsumagoi pumice fall (YPK) from neighboring Asama Volcano. The blocks contained in the debris avalanche deposit are mostly andesitic lava fragments. The bulk-rock major element compositions of the blocks in the debris avalanche deposit show similar K₂O contents to rocks from Kusatsu-Shirane Volcano, and higher than those exhibited by rocks from Asama Volcano. The chemical compositions of the blocks are similar to those of the late-stage of the Matsuozawa Volcano, which is a small-scale stratovolcano that formed in the early stage of Kusatsu-Shirane Volcano. Although Matsuozawa Volcano is topographically dissected and covered by younger deposits on its eastern flank, a horseshoe-shaped depression can be recognized on the southern upper flank suggesting past sector collapse. The buried debris avalanche deposit described in this study is considered to be the deposits of this sector collapse of Matsuozawa Volcano.
Language: Japanese
Subfield: Management, Monitoring, Policy and Law
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7145801239