Petrological investigation of pre-eruptive processes of Aso-5 magma reservoir

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05682
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Kumamoto University
• Principal Investigator: Hasenaka Toshiaki 熊本大学, くまもと水循環・減災研究教育センター, 特任教授 (50202429)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 阿蘇カルデラ / カルデラ噴火 / マグマ供給系 / 噴火準備過程 / メルト包有物 / 阿蘇中央火口丘軽石 / 先阿蘇火山岩類

Outline of Final Research Achievements

Is the present Aso volcano ready to make caldera-forming eruption? In order to answer this question, analyses of magma compositions, especially those of melt inclusions were conducted for volcanic products of pre-caldera stage (before 270 ka), caldera-forming stage (270 ka ~ 90 ka), and post-caldera stage (90 ka ~ present). Development of small silicic magma reservoir was detected for post-caldera Aso central Cone Pumice (ACP) -2, -3, -4, however, inhomogeneous reservoir was assumed for the youngest ACP-1 pumice. It was followed by dominant basaltic magma activities with trace of silicic magma. Compilation of analyzed magma indicate compositional range did not change through three stages. However, dominant composition changed from andesite (pre-caldera) to dacite (caldera-forming), then to basalt (Holocene~present), which probably reflect the distinct difference in magma plumbing system.

Free Research Field

火山岩岩石学

Academic Significance and Societal Importance of the Research Achievements

阿蘇４のような巨大カルデラ噴火が起こる可能性を科学的に見積もることは，社会インフラの建設，維持，管理において重要である．メルト包有物はマグマ供給系の各所の組成，温度，圧力などの情報をもたらす．後カルデラ期では中央火口丘軽石２，３，４で小規模で均質な珪長質マグマを検出したが，4千年前以降では，珪長質マグマの存在はほとんど検出されておらず，喫緊の巨大カルデラ噴火の可能性は低いと考えられる．