Preliminary Report of the Crushing Type Landslide

Abstract

In Japan, without volcanic region, a great many active landslide areas coincide with the distribution of the Tertiary formations, faulted and fractured zones and metamorphic belts.These landslide areas are in general divided geologically into Tertiary type and Crushing type. Tertiary type landslide are mostly connected with mountainlands. Accordingly, on the landslide areas, the geological and geomorphological studies are extremely important.From this point of view, the writer applied technics of the geomorphology on the distribution of the Crushing type landslide which was shown in the topographic map of Kawaguchi 1: 50, 000. The results of this investigation are summurized as follows;1) The landslide areas abound in the fringe of residual erosion surface.2) The localities of the landslide areas abound in the 500m and 800m heights, and these heights are concerned with base level of erosion.3) The inclinations of the landslide areas are about 25° in general.4) The geology of the landslide areas consist of the metamorphic rocks rnd weakly metamorphosed rocks of the Palaeozoic formations. The localities of the landslides areas abound chiefly in crystalline schist of the Minawa formation, Koboke formation and Kawaguchi formation of the Sambagawa metamorphic belts, and are only a little on the weakly metamorphosed rocks so-called Mikabu greenrocks which compose of meta-gabblo, meta-diabase, basalt, and basaltic agglomerate.5) The landslide areas having closed on the fault line which is shown in the geological maps of the sheet Kochi-42 are little 20 percents.