Imaging the Hydrothermal System of Kirishima Volcanic Complex, Japan with ALOS-1/2 InSAR Time Series

We present deformation measurements of the Kirishima volcanic complex from ALOS-1/2 Interferometric Synthetic Aperture Radar (InSAR) time-series during 2006-2019. Shinmoe-dake deflated ~6 cm during the 2008-2010 phreatic eruptions and inflated ~5 cm prior to the 2017 magmatic eruption. Iwo-yama inflated ~19 cm within the crater since January 2015 and ~7 cm around the southern and western vent since four months before the 2018 eruption. These deformations can be modeled as an ellipsoid at ~700 m depth beneath Shinmoe-dake and as a sphere on top of an ellipsoid at ~130 and ~340 m depths beneath Iwo-yama. Combining geodetic, geoelectric, geochemical and petrological analysis, we interpret the hydrothermal origin of the deflation at Shinmoe-dake and inflation at Iwo-yama; the hydrothermal-magmatic transition during the 2011 Shinmoe-dake eruption; water-boiling and bottom-up pressurization as driving mechanisms of the inflation at Iwo-yama. The study highlights the imaging potential of InSAR time-series on complex hydrothermal systems.