THE MAKING OF A DISASTER

Satellite images suggest that the devastating flash floods in Uttarakhand’s Chamoli may have been triggered by a landslide in the upper reaches of Himalayas

1 A huge mass of snow and rock (about 200 metres) likely broke off the Trishul mountain on Saturday night or early Sunday morning, and slid down

2 The mass from the mountain slope hit the glacial snow and pushed it northwards with huge force into the 3.4km riverine that had likely accumulated ice from a 2016 avalanche.

3 The glacial water with boulders and debris surged down the steep slope and into Rishiganga river that originates from the end of the riverine.

4 Flowing downstream at a fast pace, river water and muck first hit the Rishi Ganga power plant near Raini village and washed it away, and then damaged the NTPC Tapovan hydel power plant (on the Dhauliganga river) about 7-8km northwards.*

“Due to freezing and thawing, rock mass has broken away and slid down...satellite imagery showed snow on February 6 and no snow on the slopes on February 7. So, it seems that it (landslide) was a mix of snow and rock avalanche, which led to the disaster.” — Pradeep Srivastava, Geologist, Wadia Institute of Geology

* Complete downstream flow not pictured in graphic. Image, data credit: Dr C Scott Watson, Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), University of Leeds, and Planet Labs