Remobilization timescale of mush-like magma and its correlation with eruption scale- Constraints from records of elemental diffusion in phenocrysts-

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K04000
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17030:Human geosciences-related
• Research Institution: Waseda University
• Principal Investigator: Suzuki Yuki 早稲田大学, 教育・総合科学学術院, 准教授 (00374918)
• Co-Investigator(Kenkyū-buntansha): 安田 敦 東京大学, 地震研究所, 准教授 (70222354)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 榛名火山 / マグマ供給系 / 噴火誘発過程 / マッシュ状珪長質マグマ / 苦鉄質マグマ / マグマ混合 / マグマの加熱 / 噴火規模

Outline of Final Research Achievements

We investigated the temporal change and the eruption triggering process of mush-like felsic magma focusing on younger Haruna volcano. The assemblage and composition of mineral species contained in the mush-like magmas are the same among the eruptions of different ages. However, the magmas of two eruptions at Futatsudake (5th~7th century) have lower crystallinities and lower bulk SiO2 contents than those of older four eruptions (45~10ka), indicating that the newer mush-like magmas had lower viscosities at the reservoir. We compared the Futatsudake-Shibukawa eruption with the subsequent Futatsudake-Ikaho eruption. The mush-like magma underwent only heating by mafic magma in the Shibukawa eruption, while the magma underwent not only heating, but also mixing with mafic magma in the Ikaho eruption. The amount of high-temperature mafic magma supplied to the mush-like felsic magma may have been larger in the Ikaho eruption, making it a larger eruption than the Shibukawa eruption.

Free Research Field

火山学、岩石学

Academic Significance and Societal Importance of the Research Achievements

マッシュ状珪長質マグマを対象に、噴火規模決定プロセスの理解をはかることを主な目的としていた。1火山の複数噴火を対象にしたため、噴火年代によるマッシュ状マグマの変化や、異なる特徴のマッシュの間の成因的関係も合わせて検討した。その結果、良く似たマッシュの関わる複数の噴火を選び出し、それらを比較することで、マッシュと高温の苦鉄質マグマとの相互作用の様式の違いが、最終的な噴火規模と関連を持っている可能性を指摘した。この研究を通じて、苦鉄質マグマを含むマグマの貯蔵深度についても整理した。その結果は地球物理学的手法等による観測的研究に還元され、榛名火山の火山活動の監視に役立てられる。