Geomorphological Relationship between Multiple Ridges and Big Landslide in Akaishi Mountain Range

Abstract

There are some big landslides accompanied with double or multiple ridges in Akaishi mountain range, those high relief s are composed of mesozoic shale and sand stone affected by the tectonic movement from Median line and Itoigawa-Shizuoka line. The tectonic interpretation following geomorphologic surveying was carried out through the stereoscope to the aero-photographs of 1: ca 5000 scale that was taken at 1982. Some big landslides have the geomorphological connection with linear hollow and depressions. Their patterns are the direct shift from linear hollow to main scarp of slump, the indirect shift from linear hollow at backside slope to tension cracks of landslide, the orthogonal intersection of linear hollow to sliding plane, and the evolution from the end of arc multiple ridges to big collaps accompanied with rock slide. Because the linear hollows distribute alternately in parallel between multiple ridges, their number, length, and space interval have the high correlations with those of multiple ridges. Also they have the linear relations with width, area, and direction of big landslide. These relationships are useful as the basic information to forecast the big landslide in Akaishi mountain range. These facts lead to the guess that there is a kind of regular tendency between strain and destruction of slope basement that the force has acted on. The tectonic movement might promote the process of geomorphologic evolution that the big landslides were generated along the gravitational fault from the linear hollows. Based upon tha idea, the occurrence of big landslide can be discussed in the classification of evolutional stage. But this idea needs more data on dynamic properties of slope basement and the remove across linear hollow during long term.