火山灰のXRF化学組成分析に基づく本質物質寄与の見積もりー有珠火山2000年噴火を例としてー

概要

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XRF analysis of bulk ash composition offers information on magma contribution easily and quickly for monitoring temporal changes of eruptions. The 2000 eruption at Usu Volcano, North Japan, started at ca. 13 : 10 on March 31. Ash emitted on March 31, April 1, 2, and 4 were collected to investigate temporal changes in bulk compositions by XRF analysis. All the ash samples are plotted in a composition range between essential material and basement rocks. Among all of the ash, that of the March 31 eruption, the largest one, has the nearest composition to the essential material. These data indicate that the ash is a mixture of the essential material and basement rocks, and that the nearer the ash composition is to the essential material, the larger is the magma contribution to the eruption.