寄書
水準測量から明らかになった立山火山地獄谷の再隆起
—2020年9月～2021年9月—
2023 年 68 巻 2 号 p. 83-89
詳細
2023 年 68 巻 2 号 p. 83-89
Leveling surveys were conducted in Jigokudani valley, Tateyama volcano, since 2015. Subsidence was revealed to have started in 2017‒2018 when a new crater was formed at southwestern area of Jigokudani. Subsidence kept until 2020. During the one-year period from September 2020 to September 2021, ground of Jigokudani was revealed to have re-uplifted. We applied five types of deformation sources (Mogi-type spherical, finite spherical, penny-shaped, rectangular tensile fault and prolate spheroid sources) to the detected deformation. Using the grid search method and the weighted least squares method, we searched the optimal combination of the parameters of each model. Based on the c-AIC value, the penny-shaped deformation source was the best model among them. A penny-shaped inflation source with a radius of 375 m was located including southeastern area of Jigokudani valley where violent fumarole activities have been continued. Its depth was 50 m from the surface. The pressure change in the source of +0.8 MPa yields its volume change of +4800 m3. Inflation of the gas chamber beneath Jigokudani valley might have started due to increase in accumulation of volcanic gas/fluid or decrease in fumarolic activity.
