カルデラ形成までの1万年間における伊豆大島火山の活動

概要

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Detailed stratigraphic study of the various kinds of the volcanic products of Izu-Oshima volcano prior to the summit caldera formation revealed the following: 1. Great eruptions have occurred every 145 years on an average during 10,000 years prior to the caldera formation. 2. The humus layer remains only in the fall deposits which were formed for the last 10,000 years or thereabout. 3. The predominant wind over Izu-Oshima Island has been in the northeast and in the southwest for the last 7,300 years. Before that, it was often in the east. 4. The eruptions which produce smaller amount of ejecta tend to occur more frequently for Izu-Oshima and Hakone volcanoes. Frequency distribution is expressed in an exponential curve. 5. About 7,300 years ago, a strong steam explosion occurred at the summit crater. A few eruptions immediately after that (O_<41>) produced large amounts of tephra but the successive eruptions formed decreasing amounts of it toward the caldera formation. Compared to the above temporal change in the mode of explosive eruptions beginning 7,300 years ago, the volcanic eruptions during the Younger Oshima age appear to correspond to the earlier half .
特定非営利活動法人日本火山学会の論文
1980-10-01