Geomorphological Deformation due to Landslide

Abstract

It is important to judge accurately the geomorphological deformation due to landslide in each landslide area. Reflecting differences in both geological structure and geomorphological development in a landslide area, such deformation is considerably complicated.In a landslide area of mountainous district along the River Saigawa in northern part of Nagano prefecture, the aspect of deformation is rather simple in case the land consists mainly of mudstone. However, when pyroclastic deposits are mixed in the sedimentary rocks such as mudstone, sandstone, etc., the process of landslide is complicated. This report describes a case, as a typical example, on the deformation of landslide area at Kuranami District in Nagano city to investigate the relation between geological features and groundwater mechanism.In Kuranami Landslide Area. the groundwater flows down through debris accumulation on the upper reaches and is dammed by mudstone layer down at the village, where it makes the mudstone layer soften to cause sliding intra-stratum on the lower reaches. As the result, a remarkable three-stage cliff has been developed on the upper reaches, and a rolling slope unique in the landslide area has been formed on the lower reaches.