[M-IS13] [JJ] Environmental changes in mountainous area

[MIS13-P08] Rockslide phenomenon occurred on the southern face of Mount Myojin and the origin of Myojin-ike Ponds in the Kamikochi Valley of the northern Japanese Alps, Central Japan

*Masayuki Morita¹, Yoshihiko Kariya² (1.Under Graduate, Department of Environmental Geography, Senshu University, 2.Department of Environmental Geography, Senshu University)

Keywords:Boulder, Rockslide, Maehotakadake welded tuff, Mountain landforms, Slope disaster

We describe the geological and geomorphological features (e.g., distribution, morphology, and lithofacies ) of boulder lobes in the Myojin-ike Pond area in Kamikochi Valley of northern Japanese Alps. Then we discuss the origin and cause of those boulders and Myojin-ike Ponds. Our main results are as follows: a) Boulders consisting of the lobes were supplied from the southern rock face of Mount Myojin, just north of Myojin-ike Ponds; b) Estimated transporting process of the rock debris was rockslide or rock avalanche from the rock wall composed of titled-welded tuff layer; c) Myojin-ike Ponds were formed by river course obstruction by accumulation of rock debris; d) the rockslide probably occurred before AD1693 based on the old document written by the Hotaka Shrine founded on the shore of Myojin-ike Ponds.