Thawing State Monitoring of Retrogressive Thaw Slumps Using Time-Series Alos-2 and Sentinel-2 Data in MT. Fenghuoshan of Tibetan Plateau

Monitoring the deformation of retrogressive thaw slumps (RTSs) is important for understanding their evolution and future expansion trends. In this study, we utilized Japanese ALOS-2 PALSAR-2 data from 2015 to 2023 and European Sentinel-2 optical imagery from 2019 to 2023 to conduct long-term time-series evolution and surface deformation monitoring of two RTSs in the south of Mt. Fenghuoshan in the Tibetan Plateau. Analysis of the temporal Sentinel-2 imagery revealed that both RTSs exhibited a noticeable trend of rearward retreat, with annual rates of approximately 10 meters and 16 meters, respectively, from 2019 to 2023. Consequently, their areas increased by 4602 m
²
and 3513 m
²
, respectively. Interferometric Synthetic Aperture Radar (InSAR) monitoring results indicated obvious surface subsidence in these two RTSs, with deformation rates reaching -15 mm/year and -9 mm/year. The deformation rates exhibited distinct spatial distribution characteristics, with greater subsidence observed in the slump headwall compared to the scar region. The findings of this study show that headwalls remain unstable, with an ongoing risk of expansion.