Debris Movement by Heavy Rainfall during Snowmelt Season in Gullies of Tarumae Volcano, Hokkaido

Abstract

This paper describes debris movement due to heavy rainfall during snowmelt season in gullies of Tarumae Volcano, Hokkaido, northern Japan. A large amount of debris derived from slope surface, which had been loosen by freeze-thaw cycles, resulting from the heavy rainfall (total 162 mm) on April 22-23, 1990, deposited on valley bottom covered with snow. This debris was saturated by snowmelt water, thus turned into debris flow. The debris flows transported and deposited 340 m³ of fine materials (clay, silt, sand) with little coarse gravels. The sediment volume produced by this rainfall from slope surface was 400 m³. The volume is one order of magnitude greater in spring than in summer and in early winter. The return period of debris movement was estimated to be five years on the basis of the record of precipitation. The heavy rainfall during snowmelt season seems to play an important role on sediment production and transport processes in snowy subpolar zone.