Shallow Poroelastic Hydrothermal Deformation at Changbaishan Volcano Before the 2020 Unrest Revealed by Sentinel‐1 InSAR Time Series

Abstract

Ground deformation of dormant volcanoes provides critical insights into subsurface processes and potential hazards. Here we present Sentinel‐1 Interferometric Synthetic Aperture Radar (InSAR) time series (2015–2020) for Changbaishan volcano, the largest intraplate volcanic system in East Asia. We detect persistent subsidence of up to 3.5 mm/yr on the eastern flank of the summit prior to minor unrest in December 2020. Geodetic inversion locates the deformation source within a shallow hydrothermal system 2.7 ± 0.3 km beneath the summit. Constrained by independent CO ₂ ‐flux estimates, poroelastic models reproduce the observed deformation and indicate sustained discharge of an H ₂ O–CO ₂ mixture with vapor–liquid separation occurring above the hydrothermal system. We infer that long‐lived, mixture‐driven poroelastic compaction might have dominated the background deformation during the observed period. These findings underscore the need to integrate geodetic and geochemical observations to improve hazard assessments of future unrest at Changbaishan and analogous volcanic systems.