A flash flood surged down a river in India’s Himalayan Uttarakhand state on February 7, killing at least 30 people and washing away two hydroelectric power stations.
As rescue workers search for more than 100 people who are still missing, officials and scientists are trying to unravel the causes of the sudden flood. Did a glacier high up in the mountains collapse, releasing a huge plug of frigid meltwater that spilled into the river? Or was the culprit a landslide that then triggered an avalanche? And what, if any, link might these events have to a changing climate?
Here are three things to know about what might have caused the disaster in Uttarakhand.
1. One possible culprit was the sudden break of a glacier high in the mountains.
News reports in the immediate wake of the disaster suggested that the floodwaters were caused by the sudden overflow of a glacial lake high up in the mountain, an event called a glacial lake outburst flood.
“It’s likely too early to know what exactly happened,” says Anjal Prakash, the research director of the Bharti Institute of Public Policy at the Indian School of Business in Hyderabad. Satellite images show that a section of a glacier broke off, but how that break relates to the subsequent floods is still unknown. One possibility is that the glacier was holding back a lake of meltwater, and that heavy snowfall in the region two days earlier added enough volume to the lake that the water forced its way out, breaking the glacier and surging into nearby rivers.
This scenario is certainly in line with known hazards for the region. “These mountains are very fragile,” says Prakash, who was also a lead author on the Intergovernmental Panel on Climate Change’s 2019 special report on oceans and the cryosphere, Earth’s icy places. But, he notes, there isn’t yet much on-the-ground data to help clarify events. “The efforts are still focused on relief at the moment.”
2. A landslide may be to blame instead.
Other researchers contend that the disaster wasn’t caused by a glacial lake outburst flood at all. Instead, says Daniel Shugar, a geomorphologist at the University of Calgary in Canada, satellite images snapped during the disaster show the telltale marks of a landslide: a dark scar snaking through the white snow and clouds of dust clogging the air above. “You could see this train of dust in the valley, and that’s common for a very large landslide,” Shugar says.
“WOW,” he wrote on Twitter the morning of February 7, posting side-by-side satellite shots of a dark area of possible “massive dust deposition,” contrasted against the same snowy, pristine region just the day before.