過去1万年間の噴出物にみる八丈島東山火山後期の活動と西山火山の成長

概要

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Hachijojima, 290 km south of Tokyo, is located on the volcanic front of Izu-Bonin Arc. The island consists of two volcanoes, Higashiyama (Miharayama) Volcano and Nishiyama (Hachijo-Fuji) Volcano built up mainly by basaltic lavas and pyroclastic deposits. Tsukui et al. (1991) divided eruption history of Higashiyama Volcano during the last 22,000 years into three stages : Sueyoshi Stage, Nakanogo Stage and Mitsune Stage. In this study, activities of the two volcanoes during past 10,000 years, Nakanogo and Mitsune Stages are revealled in details. The last eruption at the summit crater of Higashiyama Volcano occured in the last of Nakanogo Stage (about 10,000 years ago). Mitsune Stage (10,000-4,000 years ago) : in Higashiyama Volcano, six flank eruptions including four pumice eruptions, one eruption building a scoria cone and one phreatic explosions occured. The interval between each eruption is estimated to be about 1,000 yeras. On the other hand, Nishiyama Volcano possibly became active as a subaerial volcano in early Mitsune Stage. During the stage, seven or eight phreatomagmatic explosions and seventeen or more subaerial eruptions occured in the volcano and the eruption intervals should be shorter than 250 years.
特定非営利活動法人日本火山学会の論文
1993-09-30