Validation of remote sensing derived ice-thickness with in-situ Lake Bathymetry in the recently vacated area of gepang-gath glacier, Lahaul Himalaya, India

Field observations provide authenticity in remote sensing studies when it comes to glacierized areas where weather conditions and terrain are not accessible. This study is an attempt to validate the relation between the Randolph Glacier Inventory (RGI) ice thickness and DEM through a field survey in the recently vacated area occupied by the moraine-dammed proglacial lake of the rapidly retreating Gepang-Gath glacier in the Lahaul Himalaya. We used Randolph Glacier Inventory (RGI) version-6 data of ice thickness for Gepang-Gath glacier with SRTM digital elevation model (DEM) of the year 2000 and Sentinel-1 Synthetic Aperture Radar (SAR) interferometry-based DEM of the year 2020 to calculate the lake depth. This relation is validated with ground-based investigation and lake bathymetry data collected using a kayak and metallic nob tied with rope and measuring tape in June 2021 where the maximum depth of the lake is 48 m. The SRTM-DEM profile and ice thickness data suggested that the Gepang-Gath glacial lake will expand ~2 km with a maximum depth of ± 10 m measured near the snout. As this lake is potentially vulnerable, this type of study will help measure lake depth using snout height and vice-versa with the help of DEM data to avoid hazards in feeding glaciers retreating.