Understanding the preparation process of phreatic eruptions by seismic analyses at Ontake and Kusatsu-Shirane volcanoes

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K04016
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Nagoya University
• Principal Investigator: MAEDA Yuta 名古屋大学, 環境学研究科, 講師 (00728206)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 水蒸気噴火 / 御嶽山 / 地震波解析 / 数値シミュレーション / 草津白根山

Outline of Final Research Achievements

Phreatic eruptions of volcanoes are attributed to the sudden vaporization of shallow underground water. To understand the mechanisms and conditions for underground water to be heated to the boiling temperature, this study estimated the locations of fluid migration using seismic analyses. A numerical model for the heating of underground water was then developed using the results of the seismic analyses as constraints. The model showed that the injection of high-temperature water exsolved from magma into cold underground water layer results in an immediate pressure increase and may cause precursory seismicity. In contrast, the high-temperature region expands slowly, resulting in delayed occurrences of other precursors, or almost no precursors other than seismicity (as in the case of the 2014 eruption of Mt. Ontake) if the temperature of the injected water was relatively low.

Free Research Field

火山学

Academic Significance and Societal Importance of the Research Achievements

水蒸気噴火はマグマ噴火に比べ研究が少なく、地下のどこでどのような過程を経ていかなる条件で噴火が起きるのか、具体的なことがあまり分かっていない。本研究はその解明を試みたものであり、地震波解析に基づいて流体移動が起きる場所を推定したこと、その結果を用いて定量的な数値モデルを作成したことが特色である。御嶽山を対象とするモデルであるが他地域でも成り立ちうる物理的解釈を抽出しており、水蒸気噴火に関する火山学の発展に寄与し、将来的な火山活動推移予測にも寄与しうる。