Precursory ground deformation of the 2018 phreatic eruption on Iwo-Yama volcano, revealed by four-dimensional joint analysis of airborne and spaceborne InSAR

Earth, Planets and Space

Shohei Narita¹  Youichiro Takada²  Masato Furuya²  Yosuke Aoki³  Makoto Murakami⁴  Masanobu Shimada⁵  Taku Ozawa⁶ 

[1]Aso Volcanological Laboratory, Institute for Geothermal Sciences, Kyoto University, 3028 Sakanashi, 869-2611, Aso, Kumamoto, Japan

[2]Department of Natural History Sciences, Graduate School of Science, Hokkaido University, N10W8, Kita‑ku, 060‑0810, Sapporo, Hokkaido, Japan

[3]Department of Earth and Planetary Sciences, Hokkaido University, N10W8, Kita-ku, 060-0810, Sapporo, Hokkaido, Japan

[4]Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, 113-0032, Tokyo, Japan

[5]Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, N10W8, Kita‑ku, 060‑0810, Sapporo, Hokkaido, Japan

[6]School of Science and Engineering, Division of Architectural, Civil and Environmental Engineering, Tokyo Denki University, 5 Senju Asahi-cho, Adachi-ku, 120-8551, Tokyo, Japan

[7]Volcano Disaster Resilience Research Division, National Research Institute for Earth Science and Disaster Resilience, 3-1 Tennodai, 305-006, Tsukuba, Ibaraki, Japan

关键词: InSAR;    Phreatic eruption;    Ground inflation;    Volcanic hydrothermal system;    Airborne SAR;    Iwo-yama;   

DOI  :  10.1186/s40623-020-01280-5

来源: Springer

【 摘 要 】

We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island, Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted an axisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to 2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggests that pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of the local ground inflation pattern just above the southern edge of the crack, which suggests the presence of a shallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of these deformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of the continuous fluid injection and formed another pressurized part directly above the southern tip of the crack. Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started around April 2017 for which thermal activity including a mud emission became pronounced around the location of the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue for predicting future eruption sites, as was also observed in the Hakone 2015 eruption.

【 授权许可】

CC BY