地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
論説
北海道屈斜路カルデラ中島火山の噴火年代
─中島軽石のテフロクロノロジー─
後藤 芳彦和田 恵治
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2018 年 127 巻 2 号 p. 157-173

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 Kutcharo caldera is situated in the eastern part of Hokkaido, Japan. It is subcircular with a diameter of 20-26 km and was formed by repeated violent rhyolitic explosive eruptions from 340 to 35 ka. The caldera has three post-caldera volcanoes: Atosanupuri, Nakajima and Mashu. Our new tephrostratigraphical survey suggests that a pyroclastic fall deposit (Nakajima pumice), which was extruded from Nakajima, is exposed at the western slope of Atosanupuri. The deposit comprises dacitic pumice clasts (< 9 cm across) in a fine-grained matrix. The pumice clasts are coated with fine-grained ash, suggesting the deposit was produced by a phreatomagmatic eruption. The deposit directly overlies a scoria-fall deposit, which was ejected from Mashu volcano at 17-12 ka, and is overlain by Ma-k tephra, which was extruded from Mashu volcano at 10 ka. The stratigraphy of the deposit suggests that a phreatomagmatic eruption occurred at Nakajima volcano between 17 and 10 ka.

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© 2018 公益社団法人 東京地学協会
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