紀伊山地北部天川地域に分布する遷急線

Abstract

Distribution of convex slope breaks and fluvial knickpoints have been investigated in the Tenkawa district, northern Kii Mountains, southwest Japan. We found that paleosurface remnants are developed in higher elevations in the catchment of the Tennokawa River, which incises the paleosurfaces with a convex slope break, L1. The intersections of L1 and the tributaries of the Tennnokawa River coincide with knickpoints in 8 tributaries, suggesting that L1 was formed by knickpoint recession. 60% of landslides, or 75% of large landslides (>105 m2) in the study area involved L1 or occurred on slopes below L1, suggesting that they occurred on slopes destabilized by river incision. Paleosurfaces surrounded by slope breaks are widely developed in the Totsukawa catchment in the north and central Kii Mountains and we found that recent deep-seated catastrophic landslides have occurred on slopes with the slope breaks or newly incised slopes below the breaks.