A massive rock and ice avalanche triggered February 7 Chamoli flashfloods: Study

A huge mass of ice and rock, that fell from a height of around 1,800 metres, led to the disaster which left over 200 people dead or missing in Chamoli district in Uttarakhand in February this year, an international team of researchers has reported in the Science journal.

The findings of the study carried out by over 50 scientists from institutions from Canada, Europe, India and the US actually corroborated the preliminary results submitted by a team of Indian scientists led by Prakash Chauhan, Director of the Indian Institute of Remote Sensing at Dehradun almost a month after the disaster struck.

The avalanche carried nearly 27 million cubic metres of rock and ice – almost equal to live water storage of a medium reservoir – setting off a chain of events that severely damaged two hydropower plants apart from the human calamities.

“As the avalanche tumbled down the valley, frictional heating melted nearly all of the ice contained therein, transforming it into an extraordinarily large, swift and powerful debris flow, which swept up boulders more than 20 metres in diameter and scoured the valley walls up to 220 meters above valley floors,” the authors of the Science paper said.

Deep analyses

The scientists put together the cascade of events by analysing satellite imageries, seismic records, numerical model results and eye witness records. According to them, the severity of the disaster was mainly because of three factors – the exceptional height from which the avalanche fell, the ratio of rock to ice in the initial cascade and the unfortunate location of downstream hydroelectric infrastructure.

“The disaster indicates that the long-term sustainability of planned hydroelectric power projects must account for both current and future social and environmental conditions while mitigating risks to infrastructure, personnel and downstream communities,” they argued.

The findings were very similar to what Chauhan and colleagues reported in the Journal of Indian Society of Remote Sensing on March 22. As per their account, a massive rockslide million cubic metre volume containing base rock, deposited ice, and snow got detached from the northern slopes of the Trishul mountain range near Ronti Glacier and created a vertical fall of almost 1,700 m before severely impacting the Ronti Gad valley located at 1.5 km downstream of the Ronti Glacier snout.

“One third of the mass was ice and two-thirds rocks and the instant melting of the ice created the slush which moved down the valley quickly,” said Anil Kulkarni, Distinguished Visiting Professor at the Davecha Centre for Climate Change at the Indian Institute of Science, Bengaluru.

“The region is tectonically very active region as shown by the Chamoli earthquake of 1991. Any construction activity in such zones should take all this into consideration. On top of it, there is climate change, which is causing glaciers to melt much more. So these kinds of hazards are expected to increase in future,” added Kulkarni, who is unconnected with either of the study.

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