Spread-type landslides in volcanic terrains in Japan: A case study on the Edamatsu spread in Fukushima Prefecture

Records of spread-type landslides (STLs) in Japan, with their geomorphic and geologic characteristics, such as locations (coordinates of the center of the main scarp), heights of the top of the scarp and bottom of the slide, length and width of the landslide body, and lithology and age of the landslide, are summarized in a database. The sizes of the STLs range from 70–3200 m in length and 200–3000 m in width, and they occur mostly in the Oligocene to Pleistocene sedimentary and volcano-sedimentary formations. Some of the STLs are closely related to cap-rock geological structures developed in the volcanic terrains. The ages of their activities are mostly unknown, except for the STL in the Chiba Prefecture, which was active during the 1923 Great Kanto earthquake. The Edamatsu STL in the Fukushima Prefecture, Northeast Japan, developed in the Quaternary Tonohetsuri caldera, and it has a diameter of approximately 20 km. The sliding block, 1000 m long and 2500 m wide, is composed of massive andesitic lava overlying the lacustrine sediments accumulated in the caldera lake. In most cases, the boundary layer, i.e., siltstone, plays the role of a sliding surface.