焼岳上々堀沢扇状地における土石流の堆積構造

Abstract

Spatial distribution of debris materials of debris-flow lobes was studied in relation to the deposi-tional process of debris flow at Kamikamihori Fan.At three lobes with different depositional conditions, several survey pits were dug in each lobe, to make the analysis of debris size of deposits on the ground surface and in the underground part.As for the formative processes of lobes at least of late years, it might be said that the swollen lobes inthe upper fan were the massive deposits of debris flow which had settled almost conserving the originalstructure of inverse grading in motion, while the flat lobes in the lower fan were the sandy deposits, almost having lost the original structure in motion, with scattered gravels lacking larger boulderswhich had settled along the running course of the debris flow.At the distal fan, thick strata by debris flows and thin strata by floods were found clearly in thealternation of the deposits, while in the upper and mid fan, the debris materials are assumed to havebeen supplied only by debris flow.