Journal of Natural Disaster Science

PRELIMINARY REPORT ON THE GAMAHARA TORRENT DEBRIS FLOW OF 6 DECEMBER 1996, JAPAN

Hideaki MARUI, Osamu SATO and Naoki WATANABE
Research Institute for Hazards in Snowy Areas, Niigata University

(Received 13 March, 1997 and in revised form 23 May, 1997)

Abstract

The background and process of the Gamahara Torrent debris flow of 6 December 1996 is reported. It is very unusual that the debris flow occurred at the beginning of December in terms of the necessary water supply. Clearly the debris flow was triggered by slope failure which occurred at the geological formation border at an elevation of about l,300m. The soil layer above the formation border probably contained very much water due to antecedent rainfall before the slope failure. Chemical analysis of the water contained in the debris flow deposit should provide an effective means of identifying the origin of this water. Chemical analysis results showed that the water in the debris flow deposit did not originate directly from rainfall and snow melt but came from stored groundwater.

Key words

debris flow, triggering slope failure, quaternary Kazafuki volcanics, snow melt, electric conductivity