Geomorphic Dynamics and Sediment Budget in the Southern Japanese Alps: Recent Studies and Prospects

Abstract

This review paper synthesizes geomorphic dynamics, sediment transport and resulting natu-ral hazards in mountains of the southern Japanese Alps and their drainage basins, where cli-matic and geological situations produce highly active landform dynamics. In alpine areas above the timber line, shallow diurnal freeze-thaw action operating in the thin topsoil produces small-scale periglacial forms, and gravitational spreading leads to numerous sackung features where snow-melt and heavy rain in places promote rockslides. In subalpine and montane areas, deep-seated landslides originate from fractured sedimentary rocks, deep V-shaped valleys, and heavy rain, while shallow landslides continue with historical forest clearance. Continuous slope fail-ures prevent vegetation recovery and maintain debris input to valleys. Steep valleys contribute to high-density debris flows. Frequent or repetitive occurrences of these mass movements pro-mote continuous denudation of slopes, rockfall accidents along hiking trails, and sedimentation at artificial dams. They occasionally cause significant hazards to villages further downstream. Predicting and mitigating slope hazards require distinguishing among annual, low-magnitude processes, episodic high-magnitude processes and geomorphic changes associated with long-term climate change.