Abstract
The Hokuyo A-160 Slide is one ancient greenstone landslide occurred at the Hokuyo-Toyomi landslide-prone area in Kitami City, northeastern Hokkaido, Japan, and is a large scale having approximately 250 m in width, approximately 300 m in length, and approximately 30 m in thickness. The slide is a weathered and hydrothermally altered rockslide, and the slide body consists primarily of weathered and hydrothermally altered rocks of accretionary greenstone and small amounts of their debris and earth. The inferred slip surface clay at depth of 21.25 m in core of a borehole excavated in the middle part of the slide body is tan in color, has shear planes, and is primarily composed of smectite and vermiculite, with lesser albite, laumontite, and goethite. Because this tan thin clay layer rich in swelling clay minerals such as smectite and vermiculite is considered to be the hydrothermal alteration and weathering products of the fault gouge in the crush zone based on the mode of occurrence and properties, this suggests a close relationship between the slide and the hydrothermal alteration and weathering of the fault gouge and fault breccia in the crush zone of greenstone.
