白馬岳東麓，長走沢・金山沢の地すべり地形と堆積物

Abstract

This paper describes landslide features observed in the Nagashirisawa Basin and Kanayamazawa Basin east of Mount Shiroumadake (central Japan), where mid- to late-Pleistocene mountain glaciers are thought to have developed. Geomorphological analyses accompanied by a study of airphoto interpretation and a geological survey show gentle slopes, low-relief ridges and mounds in the basins. In most cases, angular gravels in major deposits of these landforms comprise either one or a few kinds of bedrocks exposed near the slopes. No gravels originating from any other geology in the basins are found. Jigsaw-brecciated clasts and folded-elongated silt patches in the major deposits can also be distinguished. Landslide processes, including the gravitational deformation of bedrock (i.e., mass rock creep), are probable causes of these features. Chronological information suggests that a major landslide occurred during the period from late Pleistocene to late Holocene. The triggers of these landslides remain incompletely understood, glacial–interglacial climate changes along with precipitation variations, as well as paleoearthquakes originating from nearby active faults, might be important. Some landslides found in the basins overlap moraines identified by previous research. Historical geomorphology of this area requires further study.