Unsorted deposits discovered from southern Yokoo indicate possible advance of a glacier snout beyond the Iwagoya moraines in Kamikochi Valley

Abstract

In Kamikochi Valley, the lowest position of glacier snout has been believed to be located at 1695 m ALS along the Iwagoya moraines in MIS4. However, we found new information on unsorted debris-rich deposits (UDD) at Kurosawa 1.4 km (longitudinal) lower from Iwagoya. At Kurosawa, the UDD is composed of allochthonous igneous clasts derived from remote areas with high altitudes, despite the bedrock at Kurosawa is sedimentary rocks. We concluded that the UDD would be transported by glaciers from the accumulation areas where welded tuff is common. Rock avalanche and fluvial transportation seem to be inappropriate for explanation.