Depositional processes of the debris-flow and hyperconcentrated flow deposits, the Ebisutoge-Fukuda tephra (Karegawa volcanic ash) in the Tokai Group, Plio-Pleistocene boundary, central Japan

Abstract

Hyperconcentrated flow deposit, in the Ebisutoge-Fukuda tephra from Mie Prefecture, is thought to be deposited from dilution of the debris flow. Debris-flow deposit (facies A) is overlain by hyperconcentrated flow deposit (facies B). Typical hyperconcentrated flow deposit (facies B1 ; horizontal bedding part) changes upward into diluted hyperconcentrated flow deposit (facies B2 ; scour and fill structure part). These facies characteristics indicate that the debris flow changed through hyperconcentrated flow into normal streamflow by dilution during flow traveling.