Imaging the Hydrothermal System of Kirishima Volcanic Complex With L-Band InSAR Time Series

Abstract

We present deformation measurements of the Kirishima volcanic complex from ALOS and ALOS-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 vents since 4 months before the 2018 eruption. These deformations can be modeled as ellipsoids 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; and 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.