EROSION AND MASS MOVEMENTS ON MT. USU ACCELERATED BY CRUSTAL DEFORMATION THAT ACCOMPANIED ITS 1977-1982 VOLCANISM

概要

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The 1977-1982 volcanism, both by tephra eruption and crustal deformation, of Mt. Usu, Hokkaido, has accelerated erosion of slopes and downvalley mass movements. The upheaval of New Mountain on the summit atrio was followed by vigorous gullying that yielded the sediment at a rate of 130,000 m^3/km^2・yr during 1977-1981. On the upper slope of the northern somma which was continuously thrusting northeast, the gradient increased over time due to the contractile movements. This resulted in rapid expansion of landslide scars, leading to frequent rain-triggered debris flows during 1978-1981 in a watershed covered with only a few centimeters tephra. In April 1981,a debris avalanche was generated from the affected upper slope by melting of snow and rushed down at a maximum velocity of ca. 40m/s. Based on the field work and seismic record analysis, we reconstructed the dynamic processes of this event.
日本自然災害学会の論文