Characteristics of Landslide Configurations and Recent Slope Disasters in the Shiretoko Peninsula, East Hokkaido, Japan

Abstract

In the Shiretoko Peninsula, totally 645 landslide configurations were identified through aerial photographs. The total area of landslide mass was counted at approximately 10, 000 hectares, and corresponds to 10% of the whole area of the Shiretoko Peninsula. The characteristics of landslide configurations in the Shiretoko Peninsula are summarized as follows:1) Small landslide configurations are found concentrically in the area underlain by Miocene strata. They consist mainly of “green tuffs” and shales interbedded with thin layers of tuff. Large and very large landslide configurations are arranged on the margins of Quaternary subaerial lavas overlying landslideprone Miocene strata, and both of them are found on the flanks of Quaternary stratovolcanoes.2) The landslide configurations are identified as debris slump, rock slump, debris slide, rock slide, earthflow, collapse (debris/rock fall) and debris avalanche types. Although debris slump and rock slump types predominate in this area, bedrock geology and caprock structures make difference in frequency of the type and scale of landslide configurations.3) In the Miocene area, most landslide configurations are debris slump type or debris fall type. Moreover, also recognized are large rock slump and rock slide types.4) On the margins of Quaternary subaerial lavas, making up caprock structures, large landslide configurations are rock slump, collapse and debris avalanche types.5) In the flank of Quaternary stratovolcanoes, there are large rock slumps and slides, giant collapses, and debris avalanches, which are so huge as to change remarkably the shape of volcanoes.Recently, partial sliding in old landslide mass and falling from old landslide scars were triggered by heavy rainfall and earthquakes. Therefore, paticular attention should be paid to landslide configurations near houses and roads from the viewpoint of landslide damage prevention.