東北日本, 白鷹火山の層序と歴史

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Shirataka Volcano (994 m in maximum altitude) is a small Pleistocene volcano situated behind the Quaternary volcanic front of the NE Japan Arc. This volcano lies on the Shirataka hilly land immediately west of the Yamagata Basin, and a much smaller Konpei rhyolite lava dome of 3.4 Ma neighbors on its west side. Shirataka Volcano is divided in ascending order into the lava flows and block-and-ash flow deposits of Kokuzo dacite, Numata andesitic pumice flow deposit, Hagino andesitic block-and-ash flow deposit, Hariu and Ojirafu debris avalanche deposit, Shiratakayama, Kitsunegoe and Nishikuromoriyama andesitic lava domes, Hataya debris avalanche deposit, and the Higashikuromoriyama lava dome. Shirataka Volcano was intermittently active during the past 0.2 million years from 1 to 0.9-0.8 Ma with a total eruption volume of 〓 5 km^3. Distributed on the flank and foot of Shirataka Volcano, the Hariu, Ojirafu and Hataya debris avalanche deposits contain mainly variably-shattered blocks of dacite and andesite with a matrix of their finer clasts. They demonstrate repeated sector collapse of Shirataka Volcano. The Hataya debris avalanche deposit, which is the youngest and largest among the three debris avalanche deposits, represents the last catastrophic event of Shirataka Volcano leaving a horseshoe-shaped caldera a few km wide and a large volume of deposit in excess of 2 km^3. Extruded within the collapsed caldera, the Higashikuromoriyama lava dome perhaps marks the last activity of Shirataka Volcano.
特定非営利活動法人日本火山学会の論文
2000-03-10

東北日本, 白鷹火山の層序と歴史

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