有珠山2000年噴火で発生した火砕サージ(<特集>2000年有珠山噴火 (2))

概要

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Small-scale pyroclastic surges were discharged at least three times during the 2000 eruption of Usu volcano. The first event was formation of dry surge derived from the collapse of low eruption column within initial 2 hours after the start of the eruption on March 31, 2000. This surge left moderately-sorted deposit with juvenile fragments. The second event occurred before the sunrise of April 7. The surge material was sticking on wall of buildings and tree trunks facing towards the source crater. An apartment house, which was located only within a few tens of meters from a new crater, was totally knocked down by the surge. Flow direction of the surge was controlled either by oblique discharge of the eruption column, wind direction or local topography. Maximum travel distance of this wet surge was about 600m from the source. Although exact date and source crater for the third event could not be specified, another wet surge was generated from a crater locating nearby residential area of Toyako hot-spring resort.
2002-09-17