Pulsation in Debris Flows and its Mechanism

Abstract

Discussions on pulsation in debris flows that rush down from Kamikamihorizawa torrent of Mount Yakedake, Japan, Jiang-jia torrent in Yunnan Province, China, and Aa torrent in Karakorum, Pakistan suggest that 1) periodic pulsation at Kamikamihorizawa is caused by flow instability, and non periodic one by response to rainfall intensity; 2) periodic pulsation at Jiang-jia is produced by both or one of two mechanisms: discrete mobilization of visco-plastic slurry deposits and instability in the flows; 3) pulsation in the flows at Aa torrent is brought about by drainage instability of melt water from glaciers. Its periodicity is brought about by both daily variation in solar radiation and storage capacity of melt water to a threshold for a drainage instability; 4) Non periodic pulsation is also brought about in a situation that multiple landslides are induced in succession to generate debris flows. The 20 August 2014 Hiroshima debris-flow disaster seems to have been enlarged by such a pulsation.