Abstract
A landform continuum consisting of a cirquelike and a moraine-like topography is present on the eastern side of Mount Chogatake (2,664 m ASL), central Japan. There have been contrary and unresolved theories regarding the final morphogenetic process of these topographies : a Pleistocene glacier theory and a undated landslide theory. We therefore reevaluated the problematic topographies through a detailed redescription of the field geology and a geomorphological interpretation using aerial photos and 10 m DEM-generated shaded images. A thick (>100 m) deposit of brecciated and crackled clasts of sand and mud stones supported with fine matrices (sand to silt size) is evident around the moraine-like topographies. Unlike typical till or outwash, this deposit does not have subangular or subrounded gravels. No sedimentary structure indicating fluvial transport and deposition such as cross-bedding is found. Characteristic landforms such as linear to curved depressions and scarplets as well as valley side bulges indicating gravitational mass rock creeping or toppling are developed on and beside a ridge that encompasses the pseudo cirque-terminal moraine continuum. Judging from these geological and geomorphological characteristics, we conclude that the problematic topographies could be induced by large-scale slope failure (est., 3.2×107 m3). The age of the landsliding is uncertain. Although the direct trigger (s) of failure is also unspecified, it would appear that Holocene active faults and active volcano near Mount Chogatake as well as humid climates in the southern Hida Mountains may create be favorable conditions to generate the movement.
