Elucidation of runout process of large-scale pyroclastic density currents based on the view point of powder mechanics, and hazard evaluation

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K01246
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Natural disaster / Disaster prevention science
• Research Institution: The University of Tokyo
• Principal Investigator: MAENO Fukashi 東京大学, 地震研究所, 准教授 (20444078)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 火砕流 / 噴火 / 粉体 / 摩擦 / 火山

Outline of Final Research Achievements

The two-dimensional numerical model to represent the behavior of large-scale pyroclastic flows was improved. The roles of Manning-type friction law in the runout process and Coulomb-type friction law in the decelerating and stopping processes and the effects of their introduction were clarified. The model of cooling and welding of deposit, which depends on conditions such as temperature, thickness and gas amount of deposit, was improved, and applied to formation process of welding structure of large-scale pyroclastic flow and estimation of a time-scale of eruption. With regard to typical large-scale and small-scale pyroclastic flows, their generation, runout, sedimentary processes and physical parameters were clarified based on observation records and deposits, and the eruptive process was reconstructed. The elucidation of these pyroclastic flow phenomena contributes to advancement of understanding of entire eruption processes and to evaluation of hazards.

Free Research Field

火山学

Academic Significance and Societal Importance of the Research Achievements

数値モデル改良は、シミュレーションによる火砕流分布域の推定精度向上や、ハザード評価に貢献するものである。近年の噴火事例をもとに解明した中小規模火砕流の噴出量・噴出率と流走距離との関係は、数値モデル検証のためにも活用できる。鬼界カルデラの大規模噴火については、火砕流発生のタイミング、発生様式などが明らかになった。堆積物の溶結・冷却モデルと堆積物解析にもとづき、プリニー式噴煙柱崩壊後、大規模火砕流の発生に至るまで、日または週のオーダーのギャップがあった可能性を示した。この結果は、大規模噴火の推移の理解を進めるとともに、災害の規模や時間スケールの評価にも活用できるものである。