On 7 February 2021, a devastating flood severely impacted the Ronti Gad, Rishiganga, and Dhauliganga River Valleys in the northwestern District of Chamoli, India. The flood washed away two hydropower projects and caused more than 200 fatalities. This study assessed some of the causes and effects of this catastrophic flood event and aims to provide further documentation that the event was not caused by a glacial lake outburst flood, as many reports initially indicated. Analysis of high-resolution satellite imagery, digital elevation model (DEM) differencing, and precipitation and temperature data showed that an ice-rock avalanche was released as a result of a bedrock failure underneath a hanging glacier on Ronti Peak. Further GIS analyses revealed an approximate detachment volume of 26.2 million m3 of ice and rock. The ice-rock avalanche quickly transformed into a flood and caused widespread devastation. The disaster sparked debate about the viability of hydropower project developments in the Upper Ganges River Basin and highlights the importance of adequate early warning systems in fragile high-mountain systems.

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