野外爆発実験から見た有珠2000年噴火(<特集>2000年有珠山噴火 (2))

概要

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Usu volcano in SW Hokkaido began a lot of phreatic explosions, after 22 years of dormancy, on 31 March 2000. In the middle of April and May 2000, we observed an eruption using a piezo blast-sensor, visible and infrared image recorders for getting information on the volcanic blast, shape and scale of the ash cloud, distribution of ballistic fragments and the size of the volcanic crater. Based on a scaling-law established from the results of our field explosion experiments, the data were analyzed to clarify and understand the relations among explosion energy and depth, and the surface phenomena such as crater formation, propagation of volcanic blast and the ejection of ballistic fragment. A summary of the results is as follows. The scaling-law obtained from the field explosion experiment heldup well in the case of the Usu 2000 phreatic explosions. We could determine both the explosion energy and depth using observation data such as the maximum over-pressure of a volcanic blast and the duration time of the ash cloud ejection, and vice versa. The explosion energy of a firework type explosion ranged from 10^<10> J to 10^<12> J and that of jet type 10^8 J to 10^<12> J, respectively. It was also determined that the firework type occurred just beneath the ground surface, while the jet type occurred at a few tens meters to 100 meters deep.
特定非営利活動法人日本火山学会の論文
2002-09-17