Posteruptive Thermoelastic Deflation of Intruded Magma in Usu Volcano, Japan, 1992–2017

Abstract

Secular ground subsidence at Usu volcano (Japan) has been reported around the eruption vents following the four eruptions in 1910, 1943, 1977, and 2000. However, the mechanisms accounting for the subsidence have not been well understood. In this study, we systematically investigated the posteruptive deformation at Usu volcano using interferometric synthetic aperture radar based on 111 JERS, ALOS-1, and ALOS-2 images acquired from 1992 to 2017. We also calculated quasi east-west and vertical ground displacements between 2006 and 2017. Our results show three localized deformation regions from west to east of Usu volcano with their locations corresponding to the 2000, 1977, and 1943 eruption vents, respectively. All the deformation sites show patterns of east-west contraction and subsidence. The extent and rate of posteruptive subsidence declined dramatically at the vent of the 2000 eruption site from 2006 to 2017, decreased gradually at the 1977 vent, and show a steady pattern for the 1943 site during 1992-2017. We ascribed the observed posteruptive subsidence to thermoelastic contraction of a sphere intruded at the time of the eruptions to constrain locations, depths, and volumes of heat sources with the assumption of the spherical source shapes. Thermoelastic modeling reveals that the heat sources are embedded at shallow depths not deeper than 400 m below sea level with volumes of about (8.72 ± 0.19) × 10 6 , (132.18 ± 5.21) × 10 6 , and (49.51 ± 2.02) × 10 6 m 3 for the 2000, 1977, and 1943 eruption sites, respectively. The modeling also highlights the importance of underground water in assessing the thermal diffusion process and the associated posteruptive deformation.

Assessment of Mitigation Strategies for Tropospheric Phase Contributions to InSAR Time-Series Datasets over Two Nicaraguan Volcanoes

“…Studies in volcanic regions have shown that GACOS captured broad atmospheric phase delays along the coastline of Bali Island in Indonesia and reduced the variance between 35-45% in interferograms spanning Bali Island in Indonesia [49], as well as improved upon previous estimates of ground displacement velocities at Agung volcano [53]. GACOS was also shown to reduce the standard deviation by at least 20% in 45% of the interferograms spanning the Usu volcano in Japan [51]. However, application of GACOS phase delays to interferograms spanning Cerro Azul volcano in the Galapagos showed that the standard deviations of the corrected interferograms were not significantly reduced and thus were not useful for further geodetic modeling [50].…”

“…Several Remote Sens. 2020, 12, 782 3 of 30 different GWMs have been used to remove tropospheric contributions from InSAR datasets, such as the North American Regional Reanalysis (NARR) [29,31,34,35,45,46], the Modern-Era Retrospective Analysis for Research and Applications (MERRA) [29,33,39], the Moderate Resolution Imaging Spectroradiometer (MODIS) [29,38,39,43], and weather reanalysis outputs from the European Centre for Medium-Range Weather Forecasts (ECMWF): ERA40 [25,31], ERA-Interim (ERA-I) [27,29,32-34, 36,46,47], ERA5 [21,47,48], high-resolution ECMWF (hereafter HRES ECMWF) [21,29,44,[49][50][51][52][53], and operational analysis [31]. From the GWMs, tropospheric phase delay maps that incorporate estimates of both the wet and dry phase delays can be created.…”

S-wave modeling of the Showa-Shinzan lava dome in Usu Volcano, Northern Japan, from seismic observations

“…Recent space geodetic observations reveal that Showa-Shinzan has been subsiding more or less constantly with a rate of about 16 mm/yr in the last ∼25 years (Aoyama et al 2009;Wang and Aoki 2019). Wang and Aoki (2019) suggested that this subsidence is due to the thermal contraction of the emerged lava dome. Indeed, the heat brought at the time of the dome emergence has not been wholly released; the temperature of the fumarole was still 190 • C as of early 1997, decreasing from 1000 • C in 1945 and ∼500 • C in 1960 (Minakami et al 1951;Yokoyama and Seino 2000).…”

Surface deformation of Asama volcano, Japan, detected by time series InSAR combining persistent and distributed scatterers, 2014‒2018

“…The NEF of Asama volcano exhibits continuous subsidence during the whole period. Recent studies have shown that continuous subsidence at active volcanoes may be explained by several mechanisms such as magma withdrawal (e.g., Lu et al 2010), consolidation of erupted deposits (e.g., Grapenthin et al 2010), viscoelastic relaxation of the host rock (Yamasaki et al 2018), thermal contraction of lava deposits or intruded magma body (e.g., Tallarico 2003;Wang and Aoki 2019), and the pore pressure drop associated with hydrothermal fluid circulations (Wauthier et al 2018). We first excluded the magma withdrawal and viscoelastic relaxation, because these two mechanisms generally induce broadly symmetric deformation around the magma source, inconsistent with the observed deformation.…”

“…We thus suggest that the thermoelastic contraction of the 1783 lava flow is unlikely to fully explain the subsidence at NEF of Asama, where subsidence with rates up to − 10 mm/year is observed. Moreover, considering that meteorological precipitation and groundwater flow would accelerate the cooling process (Chaussard 2016;Wang and Aoki 2019), some other mechanism must also contribute to the observed subsidence at NEF of Asama.…”