Cause determined for India’s deadly disaster

An international coalition of 53 scientists has determined the cause, scope and effects of the devastating natural disaster that rocked northern India earlier this year, bringing attention to the increasing risks in the Himalayas due to climate change and development.

On 7 February 2021, a flood of water and winter debris barrelled down the Ronti Gad, Rishiganga and Dhauliganga river valleys. More than 200 people were killed or went missing in the flow, and two hydropower stations were destroyed.

Following the disaster, 53 scientists came together to find out how it happened. An open-access paper published in Science describes their results, based on satellite imagery, seismic records and eyewitness accounts.

“Our access to high-resolution satellite imagery and research software, and our expertise in satellite remote sensing were crucial to get a bird’s-eye view of how the event unfolded,” says Shashank Bhushan, a doctoral student in civil and environmental engineering at the University of Washington, US, and co-author on the paper.

“We worked with our French collaborators to coordinate satellite collections within days of the event and rapidly process the images to derive detailed topographic maps of the site.”

While initial suggestions thought a glacial lake outburst was the culprit, the team instead found that the flood came from a falling chunk of rock and glacier ice, high in the mountains. This chunk contained over 25 gigalitres of rock (80%) and ice (20%).

“The failed block fell over a mile before impacting the valley floor. To put this height in context, imagine vertically stacking up 11 Space Needles or six Eiffel Towers,” says Bhushan.

“As the block fell, most of the glacier ice melted within minutes. This resulted in a huge volume of water associated with the flooding,” he adds.

“This is highly unusual – a normal rock landslide or snow/ice avalanche could not have produced such huge volumes of water.”

Another co-author, Holger Frey from the University of Zurich, agrees that this was a rare event: “But it’s only a matter of time before the next such massive event will happen somewhere in the Himalayas.”

Researchers have previously warned that this event is related to climate change – because warming temperatures can melt underground ice that holds steep slopes of rock and ice together.

Bhushan says that this study has placed his own research into glacial dynamics in context: “Due to the scale of this disaster, my family and friends back in India were very curious to know how this event unfolded, and they were expecting me to come up with an answer. These interactions provided me with a sense of belonging and motivation that some of my research can be of such immediate use to society.”

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