One ancient large-scale landslide, which is tentatively named as the Oshinkoshin Slide, and some more ancient and recent landslides within the Oshinkoshin landslide-prone area in a dominant hard shale-bearing formation from the Middle to Upper Miocene Onnebetsugawa Formation in the Green Tuff region can be classified as an HAZL (hydrothermal alteration zone landslide) based on the bedrock geology. These HAZLs are dip slope type and can also be sorted as large-scale hydrothermally altered rockslides such as the Oshinkoshin Slide, middle-scale debris and earth slides such as the 2006 Oshinkoshin Slide, small-scale debris and earth slides such as the 1999 Oshinkoshin Slide, etc. based on the landslide body. The occurrence of these HAZLs is closely related to the thin beds of large amounts of smectite-bearing soft tuff within the thick hard shale.
View full abstract