有珠山の地形変動と侵食・土砂移動

概要

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Since the eruptions of Usu Volcano in August, 1977, the volcano has changed remarkably in shape during four years, caused by the volcanic crustal movement. On the northern part of the volcano, "U-shaped" block bounded by faults has appeared and displaced northeastward. The faults and flexure scarps have formed in and around the block. The deformation has resulted in landslides and gully erosions, both of which have produced much unstable debris. The debris flows and mudflows were caused by accumulation of the fall-deposits of the 1977-1978 eruptions and the unstable debris due to the deformation. In particular, the fine-ash deposits contributed to occurring of the flows by forming of the impermeable crust on the surface of the slope, which brought about overland flow of rain-water, and by making high fluidity of the flows containing water. Furthermore, rapid increase in the unstable debris has accelerated to frequent occurring of the debris flows and mudflows.
地学団体研究会の論文
1982-11-25