Observing Volcanic Activity at Mt. Merapi 2018-2023 with An Advanced InSAR Time – Series Method

Abstract

Surface deformation constitutes a key observable for constraining subsurface magma dynamics and assessing volcanic hazards. At Mount Merapi, deformation signals are commonly expressed as inflation and deflation; however, their interpretation remains uncertain in complex volcanic systems. This study employs time-series Interferometric Synthetic Aperture Radar (InSAR) analysis using the LiCSBAS framework, integrated with LiCSAR interferogram products from the COMET consortium, to quantify and characterize surface deformation at Mt. Merapi for the period 2018–2023. A total of 534 descending Sentinel-1 acquisitions and 902 interferograms covering ~88 km² were processed. The results indicate deformation rates ranging from −30 to 20 mm yr⁻¹, with deflation predominantly localized around the summit crater and inflation distributed across broader sectors of the volcanic edifice. The spatial and temporal deformation patterns are consistent with independent observations reported by the Center for Volcanology and Geological Hazard Mitigation (CVGHM). During January–April 2021, a period of rapid lava dome growth (11,000–15,000 m³ day⁻¹) coincided with detectable uplift signals of approximately 3.2–4.4 mm, suggesting a direct relationship between surface deformation and magma accumulation processes. These findings demonstrate that LiCSBAS-based InSAR time-series analysis provides robust, spatially continuous measurements of volcanic deformation.