[H-GM22] Geomorphology

[HGM22-04] Slope failure of the Oya-Kuzure and generation of the Akamizu Fall, upper reaches of the Abe River, Shizuoka Prefecture

*Masaaki SHIRAI¹, Mayo WATANABE¹, Takako UTSUGAWA¹, Ryo HAYASHIZAKI¹, Takayuki TAKAHASHI¹, Ryo OBI¹, Yuma KATO¹ (1.Dept. of Geography, Tokyo Metropolitan Univ.)

Keywords:debris flow deposit, shortcut, Abe River, Akamizu Fall, Oya-Kuzure

The “Oya-Kuzure” slope failure is located in the source area of the Abe River, Shizuoka Prefecture. It is estimated that many failure events had occurred repetitively around the area (e.g., Machida, 1959). The latest large-scale failure is estimated as occurring early 18th century. Deposits originated from the 18th century failure filled the Oya River and upstream of the Abe River (e.g., Tsuchiya, 2000).
Although origin of the Akamizu Fall, which is located on main stream of the Abe River with a height of 60 m has been inferred as that stream of the river eroded debris flow deposit filling the valley, that stream of the river flowed across a ridge, and so on, any opinion does not show evidence sufficiently.
As a result of survey, it were confirmed that distribution of debris flow deposits and paleo-current estimated from direction of gravel imbrication in the deposits imply meandering of the Abe River valley before burial by debris flow deposit. In addition, channel of the fall across a ridge of basement rock. We concluded that filling of a valley by debris flow deposit caused shortcut of stream of the Abe River across a ridge and generation of the Akamizu Fall.