Development of a flash-type volcanic gas composition automatic observation device and prediction of phreatic eruption

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05051
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 25030:Disaster prevention engineering-related
• Research Institution: Tokai University
• Principal Investigator: Ohba Takeshi 東海大学, 理学部, 教授 (60203915)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 水蒸気噴火 / 火山ガス / 噴気 / CO2 / H2S / 箱根山 / 草津白根山

Outline of Final Research Achievements

We developed a device to automatically measure the chemical composition of the fumarolic gas emitted in the geothermal area of active volcanoes. The device was installed on the slope of the Owakudani geothermal at Hakone volcano. The CO2/H2S ratio was successfully estimated from the correlation between the CO2 and H2S concentrations measured by the device. In parallel with the development of the device, the correlation with the frequency of volcanic earthquakes was investigated by repeated observations of direct sampling and chemical analysis of fumarolic gas at Hakone and Kusatsu-Shirane volcanoes. In August 2021, we detected an increase in the He/CH4 ratio in the fumarolic gas of Hakone volcano, and succeeded in detecting signs of increased volcanic activity. In the fumarolic gas at Kusatsu-Shirane volcano, a decreasing trend of He/CO2 ratio was obtained from around 2020. This is in harmony with the calming of volcanic activity that began in 2020.

Free Research Field

火山学

Academic Significance and Societal Importance of the Research Achievements

御嶽山では2014年に水蒸気噴火が突如発生し、登山客60名余りが犠牲になった。2018年の本白根山における水蒸気噴火では1名が犠牲になった。水蒸気噴火は、一般的に前兆としての火山性地震の発生頻度と地震の規模が小さいために、噴火の予測が困難である。日本の国土には100以上の活火山が分布し、活火山は観光地になっている場合が多い。そのため、水蒸気噴火の予測は防災の観点から重要視されている。本研究では、従来の火山性地震観測に加えて化学的な火山ガス観測を行うことで、水蒸気噴火を予測し、安心安全の社会作りに貢献することを最終的な目標としている。