Multi-sensor-based rock glacier detection over Sikkim Himalaya

Rock glaciers (RGs) are important landforms that store subsurface ice and influence mountain water resources; yet, their distribution in the Eastern Himalaya (EH) remains limited. This study maps RGs in the Sikkim, EH using Sentinel-1 small baseline subset (SBAS) InSAR time series (2022-2024) combined with high-resolution optical validation following the RG Inventories and Kinematics guidelines. SBAS-derived deformation signals were enhanced using seasonal-trend decomposition using LOESS (STL), which isolates long-term displacement while confining snowfall and moisture-related artifacts 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 line-of-sight (LOS) displacement at an active RG. We identified 626 active RGs 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 EH.