Multi-sensor-based rock glacier detection over Sikkim Himalaya

Rock glaciers (RGs) are important permafrost landforms that store subsurface ice and influence mountain water resources, yet their distribution in the Eastern Himalaya is poorly documented. This study maps rock glaciers in the Sikkim Himalaya using Sentinel-1 SBAS InSAR time series (2022–2024) combined with high-resolution optical validation following IPA guidelines. SBAS-derived deformation signals were enhanced using Seasonal–Trend decomposition (STL), which isolates long-term displacement while confining snowfall- and moisture-related artefacts to seasonal and residual components. Glacier-covered areas were masked using RGI boundaries, and all candidates were validated using Google Earth Pro. A stable–moving point assessment confirmed millimeter-level stability at the reference site and ~35 mm LOS displacement at an active RG. We identified 626 active rock glaciers with LOS displacement rates of approximately −500 to +600 mm yr⁻¹. The results refine existing RG estimates for Sikkim and demonstrate the effectiveness of SBAS InSAR with STL filtering for robust RG detection and cryosphere assessment in the Eastern Himalaya