Evaluation of phreatic eruption potential by the precise imaging of subsurface structure and the detection of ground deformation

2015 Fiscal Year Final Research Report

• Project/Area Number: 25350494
• 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: Tokyo Institute of Technology
• Principal Investigator: Kanda Wataru 東京工業大学, 火山流体研究センター, 准教授 (00301755)
• Co-Investigator(Kenkyū-buntansha): OGAWA YASUO 東京工業大学, 火山流体研究センター, 教授 (10334525) ; TANBO TOSHIYA 公益財団法人立山カルデラ砂防博物館, 学芸課, 主任学芸員 (10574311) ; KOBAYASHI TOMOKADU 国土地理院(地理地殻活動研究センター), 地理地殻活動研究室, 主任研究官 (40447991)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 火山災害 / 水蒸気爆発 / 比抵抗構造 / 地盤変動 / 熱水流体

Outline of Final Research Achievements

We conducted the resistivity surveys, the ground deformation analysis of InSAR images, the thermal observation, and the geochemical analysis of hot-spring waters in the Jigokudani valley of Tateyama volcano, where phreatic eruptions repeatedly occurred in the past and the volcanic activity has been increasing. These analyses revealed a typical cap structure consisting of near-surface cap rock overlying a gas reservoir, which has been detected in many volcanoes known to undergo repeated phreatic eruptions. We confirmed that the shallow subsurface of the Jigokudani Valley is in the pressurized and high-temperature state. In addition, we clarified that all hot springs are formed by the mixing of magmatic fluid and local meteoric water and have a common parent fluid that differentiates into three types in the shallow hydrothermal system. From these findings, we consider that the shallow ground of Jigokudani Valley is satisfying the requirements for causing a phreatic eruption.

Free Research Field

火山電磁気学