浅間火山火車岩屑なだれ堆積物の再発見―浅間家畜育成牧場と周辺地域の火山地質―

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  • Rediscovery of the Higuruma Debris Avalanche Deposit in Asama Volcano

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Asama-Kurofu and Sennin volcanoes occupy the western part of the Asama volcano. The sector collapse occurred in the later stage of the volcano resulting a horseshoe-shaped caldera. A large-scale debris avalanche deposit was generated on the wide area and associated debris flow reached to the distant place more than 50 km. However, since the area closed to the volcanic edifice is thickly covered with the younger deposits from Asama-Hotokeiwa and Maekake volcanoes, little information on the debris avalanche deposit on the proximal area has been available. Hummocky topography is remark-able on the eastern area of the collapsed caldera. Geological survey in the proximal area was carried out especially in the Gunma Prefecture Asama Dairy Farm, the Nagakurayama National Forest, and its vicinity. Consequently, outcrops of the debris avalanche deposit were occasionally found in the valley bottom. In addition, a drilling core penetrated a thick debris avalanche deposit more than 27 meters. Whole-rock chemical composition of the blocks from the deposits are the same as those of the Asama-Kurofu and Asama-Sennin volcanoes. Long time ago, Yagi (1936) showed the distribution of “Higuruma debris avalanche” on his geologic map but few descriptions were made about it. The deposit confirmed in this study corresponds to the Higuruma debris avalanche and the description will be a clue for understanding the scale of the sector collapse.

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  • 研究紀要

    研究紀要 54 123-142, 2019-03-05

    日本大学文理学部自然科学研究所

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