A preliminary assessment of the Chamoli rock and ice avalanche in the Indian Himalayas by remote sensing
Abstract
On 7 February 2021, a process chain disaster hit tributaries of the upper Alaknanda river in the Indian Himalayas referred to as the Chamoli disaster in the media. A large rock and ice avalanche was released from an elevation of approximately 5,100 m a.s.l.
The avalanche turned into a debris flow and further downstream into a flood, leaving behind four damaged hydropower projects and dozens of casualties. The initially dry flow, as indicated by dust observed on a satellite image, turned into a moist flow by entrainment of water from watercourses, snow and sediment.
Using satellite images from Sentinel-2 and PlanetScope, we were able to map the geometry of the event. Furthermore, satellite data allowed us to reveal a drop in the snow line elevation of approximately 1,500 m, which indicated a snow fall three days before the event.
We were also able to track the flood front propagation four days after the slope collapse. The analysis of temperature data from a near weather station indicated below zero temperatures in the detachment zone one month before the event and a temperature increase in the morning of the event.
We suggest that the weather conditions may have been the final trigger, whereas a heavy predisposition was given mainly by the structural and morphological aspects of the slope.