著者

南 裕介 伊藤 順一 草野 有紀 及川 輝樹 大場 司

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.2, pp.39-57, 2023-06-30 (Released:2023-07-27)

参考文献数

39

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Akita-Yakeyama Volcano is an active stratovolcano located on Northeast Honshu island, Japan. Recent eruptive activity has occurred on the flank of the volcano in May 1997 and in the summit crater (Karanuma vent) in August 1997. These events indicate that Akita-Yakeyama Volcano has a high potential for future eruptions. In order to better understand the hazards posed by Akita-Yakeyama Volcano, this study focused on the modern explosive activity of Akita-Yakeyama during the last 6000 years. The authors conducted field observations and excavation surveys at outcrops, whole-rock chemical analysis, volcanic glass chemical analysis, and radiocarbon dating for intercalated paleosol layers. As a result, at least nine layers of pyroclastic fall deposits derived from Akita-Yakeyama during the last 6000 years were recognized, ranging from Volcanic Explosivity Index (VEI) levels of 1 to 2. In chronological order, the major pyroclastic fall deposits consist of AKY8 (45th to 47th century BC), AKY7 (10th to 29th century BC), AKY6 (2nd to 8th century BC), AKY5 (1st century BC to 2nd century AD), AKY4 (5th to 9th century AD), AKY3 (1678 AD), AKY2 (1892 AD), AKY1 (1951 AD) and 1997 eruption ejecta. The decreasing proportion of juvenile materials in eruptive deposits over the last 6000 years is consistent with a reduced magma contribution. It indicates that the development of the hydrothermal system is likely to play an important role in future eruption scenarios for Akita-Yakeyama Volcano.

著者

南 裕介 中川 光弘 佐藤 鋭一 和田 恵治 石塚 吉浩

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.3, pp.211-227, 2021-09-30 (Released:2021-10-29)

参考文献数

30

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Meakandake Volcano is a post-caldera active stratovolcano located on the south-eastern rim of Akan Caldera, eastern Hokkaido, Japan. Recent eruptive activity has occurred in 1955-1960, 1988, 1996, 1998, 2006, and 2008 at Ponmachineshiri, which is one of several volcanic bodies that form the stratovolcano. These events indicate that Ponmachineshiri has a high potential for future eruptions. In order to better understand the hazards posed by Meakandake Volcano, this study focused on the modern eruptive activity of Ponmachineshiri during the last 1,000 years. The authors conducted field observations at outcrops in the summit area, excavation surveys on the volcanic flanks, component analysis for pyroclastic deposits, and radiocarbon dating for intercalated soil layers. As a result, at least four layers of pyroclastic fall deposits derived from Ponmachineshiri during the last 1,000 years were recognized, ranging from Volcanic Explosivity Index (VEI) levels of 1 to 2. In chronological order, the major pyroclastic fall deposits consist of Pon-1 (10th to 12th century; VEI 2), Pon-2 (13th to 14th century; VEI 2), Pon-3 (15th to 17th century; VEI 1), and Pon-4 (after AD 1739; VEI 1), with small-scale (VEI<1) phreatic and phreatomagmatic eruption deposits intercalated within Pon-1, Pon-2, and Pon-3 pyroclastic fall deposits. The presence of scoria and minor pumice in the Pon-1, Pon-2, and Pon-3 pyroclastic fall deposits suggests that these eruptions were phreatomagmatic events. On the other hand, the absence of juvenile materials in the Pon-4 pyroclastic fall deposits suggests that the activity was a phreatic eruption. The decreasing proportion of juvenile materials in eruptive deposits over the last 1,000 years is consistent with a reduced magma contribution and indicates that the development of the hydrothermal system is likely to play an important role in future eruption scenarios for Meakandake Volcano.