2018 Fiscal Year Final Research Report

Mechanism and the eruption process of rhyolitic phreatomagmatic explosions

Research Project

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Project/Area Number	16K05576
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Geology
Research Institution	Kobe University
Principal Investigator	Suzuki-Kamata Keiko 神戸大学, 海洋底探査センター, 教授 (20192544)
Co-Investigator(Kenkyū-buntansha)	山崎和仁神戸大学, 理学研究科, 講師 (20335417) 巽好幸神戸大学, 海洋底探査センター, 教授 (40171722) 中岡礼奈神戸大学, 海洋底探査センター, 特命助教 (40756673) 鹿野和彦鹿児島大学, その他部局等, 教授 (40356811)
Research Collaborator	KANO Kazuhiko
Project Period (FY)	2016-04-01 – 2019-03-31
Keywords	マグマ水蒸気噴火
Outline of Final Research Achievements	Mode of the rhyolitic phreatomagmatic eruptions in the different environment were researched at Mukaeyama volcano in Niijima Island, Tenjosan volcano in Kozusima Island and Hime-shima Island. Eruptive vent was located at the shallow sea area at Mukaeyama volcano in Niijima, shore area at Tenjosan volcano in Kozusima, and wet environment like a alluvial fan at Hime-shima. The amount of pyroclastics is correlated with the depth of vent location, deeper vent occurs the pyroclastics predominated eruption, and the shallower vent occur the lava predominated eruption. Phreatomagmatic eruptions can occur when high pressure fluids fracture and flow into magma and make contact with molten magma. Even if the direct contact of molten magma and water cannot occur, phreatomagmatic eruption of destruction of phase-equilibrium type may arise when the vapor reservoir with the equilibrium between vapor and water in the brecciated part of magma can form.
Free Research Field	火山地質学
Academic Significance and Societal Importance of the Research Achievements	珪長質マグマのマグマ水蒸気噴火の典型的事例として，発生環境の異なる向山火山（東京都新島），姫島火山群（大分県姫島），天上山火山（東京都神津島）の流紋岩質火砕堆積物を取り上げた. 現地調査と試料分析で得られるデータに基づいて，噴火機構と火砕密度流の流動定置機構を検討した結果、それぞれの事例に共通するマグマ水蒸気噴火噴出物の特徴が火口の水深と深く関わることが明らかになった.日本には流紋岩質マグマをはじめとする珪長質マグマを噴出する火山島が多く存在するため、それらの地域の将来の噴火様式を予測する上に火山防災にも役立つような情報を提供することが出来た。