粒度分布と凝集構造から見た有珠山2000年3月噴火の火山灰(<特集>2000年有珠山噴火 (3))

概要

論文の詳細を見る
Usu Volcano cornmenced the first eruption with a phreatomagmatic explosion at the western foot of the volcano on 31 March 2000. The total eruptive products during the March 31 eruption attained to 2.4×10^5 tons, which was the largest among the numerous number of eruptions in the following months. In this paper, transport and depositional processes, aggregate structure and whole deposit grain size population were investigated for the March 31 tephra of the phreatomagmatic eruption. Each sample of March 31 tephra dispersed to NE, reaching to Sapporo 80 km away from the vent, was analyzed in grain size. The grain size distribution of each sample was separated into a, b and c subpopulations, which are characterized by Log-normal distribution. The subpopulation-a (in sand and granule) decreases gradually in mean grain size with distance. Even in proximal area, however, subpopulations-b (coarse silt) and -c (fine silt to clay) occupy about 30 wt.%. Subpopulations-b and -c tend to increase gradually with distance. This is because the tephras fell out mainly as aggregate ash, as eyewitnessed on the day of the eruption and observed in the deposits.
特定非営利活動法人日本火山学会の論文
2002-11-29