This study examines the glaciological changes that preceded the February 7, 2021, Chamoli disaster using multi-temporal satellite data. Glacier velocity, ice thickness, snow cover area (SCA), and mass balance were assessed for the Raunthi Hanging Glacier (RHG) and the Nanda Devi Group of glaciers. A sharp increase in velocity was observed during the pre-event period (January 31–February 5, 2021), with the RHG velocity rising from 8.44 m/day to 15.89 m/day, and the Nanda Devi glaciers from 17.24 m/day to 40.27 m/day. Ice thickness on the RHG increased from 24 m (30 Sep–16 Oct 2020) to 48 m just before the event, with a corresponding rise in average thickness from 10.25 m to 18.55 m. These thickness values are model-derived from surface ice velocity (SIV) and reflect apparent rather than actual physical changes, likely influenced by model sensitivity and seasonal accumulation. Following the disaster, the maximum and average thicknesses decreased significantly to 20 m and 3.9 m, respectively. The snow cover area increased from 37.95% to 99.65% on RHG and from 60.70% to 99.07% on Nanda Devi glaciers between September 30, 2020, and February 5, 2021, likely due to winter snowfall. Mass balance estimates indicate sustained glacier retreat, with values ranging from − 0.25 to − 1.20 m w.e. across the Nanda Devi glaciers. These results confirm significant preconditioning changes in glacial dynamics that contributed to the Chamoli disaster and underscore the critical need for continuous, remote-sensing-based glacier monitoring to facilitate early warning and risk mitigation in the Himalayan region.
Sivalingam et al. (Fri,) studied this question.