長野県小谷村,土沢周辺の地質と地すべり

概要

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The active landslide of the Ohdaira Landslide is situated along the northern shore of the River Tsunzawa of the Otari Village, northwestern Nagano Prefecture, central Japan. The Ohdaira Landslide's max width is about 400m, the max length is about 750m and the height is about 350m. It is surrounded by the Tsunzawa Landslide. The Tsunzawa Landslide's max width is about 2.5km, the max length is about 1.8km and the height is about 500m. Some linear depressions are present on the head of this landslide. The Ohdaira Landslide is the daughter landslide of the Tsunzawa Landslide. The Lower Jurassic Kuruma Group is distributed along the streams on the middle reaches of the river Himekawa. The bed strikes east-west and dips 30 to 60° south. It shows monocline structure. But this structure is disturbed along the river Tsunzawa by the Tsunzawa Landslide activity. The Tsunzawa Gravel rests unconformably upon the Kuruma Group, furthermore the Shirouma-Oike Volcanic Rocks rests unconformably upon the Tsunzawa Gravel. It is composed of only pebble derived from the Kuruma Group. This layer distributes in this study area. It gives great influence on the landslides around middle reaches of the River Himekawa.They are cause of the Ohdaira Landslide activity.
信州大学の論文