Does magma harden or soften with accelerating deformation? - Clarifying brittle fracture process of fluid for application to volcano dynamics

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H04039
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: The University of Tokyo
• Principal Investigator: ICHIHARA Mie 東京大学, 地震研究所, 准教授 (00376625)
• Co-Investigator(Kenkyū-buntansha): 山中 晃徳 東京農工大学, 工学(系)研究科(研究院), 准教授 (50542198) ; 亀田 正治 東京農工大学, 工学(系)研究科(研究院), 教授 (70262243)
• Research Collaborator: OHASHI masatoshi ; TAKEDA shiori ; YAMANISHI keita ; MARUYAMA shogo ; OTSUKI michio
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: レオロジー / マグマ / 噴火 / 流動 / 破壊 / 気泡 / 粘弾性

Outline of Final Research Achievements

To elucidate brittle fracture of fluid magma, theoretical, numerical, and experimental studies were performed. As a result of theoretical consideration, problems in the existing magma rheology constitutive equation are clarified. It is necessary to adequately describe nonlinear terms (field deformation / rotation effect and dissipation effect due to deformation). On the other hand, using a linear viscoelastic model, we performed a fracture simulation of the viscoelastic fluid by combining the phase-field method and the finite element method. We successfully reproduced the feature of the phenomenon seen in the experiment. A deformation experiment was performed using polyurethane foam in the foaming and solidification process as a magma analogue. A method was proposed to capture the deformation history just before magma fracture from the deformation degree of bubbles in products of volcanic eruptions.

Free Research Field

火山物理学

Academic Significance and Societal Importance of the Research Achievements

流体の破壊という未解明の問題について，理解が大きく進んだ．この問題は，火山噴火の爆発性を決める要因を明らかにするための基礎である．また，複雑な流体の製造・加工・応用を行う様々な工学分野でも重要である．本研究で得られた理論的知見や，数値計算手法は，まだ不完全であるが，今後進めるべき方向性について明らかになった．また，マグマ模擬物質としてポリウレタンフォームの変形実験を行ったが，実験手法や得られた結果は，火山学のみならず，ポリマーの分野でも新規性のあるものである．地球科学と工学の連携により，流体の破壊力学という新しい連続体力学への第一歩を踏み出すことができた．