Slope Evolution Processes of the Choja landslide, Southwest Japan

Abstract

Landform and geological structure of a landslide slope are deformed from those of original slope by landslide movement. Slope evolution processes of the Choja landslide which have been active for more than five hundred years are examined geologically.Owing to the comparison of the present location of Serpentine in the sliding mass with the original one, the landslide slope was formed retrogressive landslides of three stages (Figs. 9, 13). The movement of the first stage was originated in the middle part of the present landslide slope. The second stage was originated from the boundary between middle and upper part of the slope along the present slip surface, and mass of two retrogressive landslides entered into the landslide slope from. the side slopes. The upper part of the landslide slope began to move in the third stage. Total displacement of the latter two stages are around 300m.The present landslide has correspondent movement to the retrogressive slope evolution, mentioned above. The velocity of surface displacement of the upper slope is larger than that of middle and lower slope. Wide and thin distribution of Serpentine layers in the sliding mass is thought to be formed by ductile deformation around the slip surface, which is shown in the displacement data by borehole inclinometers.