On the morning of Sunday, February 7, a wall of water and mud slammed its way down the valley of India’s Dhauliganga River. Nothing stopped it—not houses, ridges, or dams. As of February 12, 2021, more than 200 people were still listed as missing, 38 had been confirmed killed, and a massive rescue effort was still under way for 32 construction workers trapped by flood debris in a hydroelectric tunnel.

And the apparent cause? Glacier deterioration due to climate change.

The flood crushed five bridges, leaving 13 villages cut off. Two hydroelectric dams were destroyed and several other dams heavily damaged. Most of the missing come from those dams, or the areas directly around them where support towns have sprung up.

Looking for the cause of the flood, Dan Shugar, a geomorphologist at the University of Calgary, got to look at nearly live satellite imagery only 6 hours after the flood from the 130-strong fleet of tiny micro-satellites maintained by Planet Labs.

“They provide a snapshot of everywhere on Earth, every day,” Shugar said. And that surveillance provided the answer. An enormous hanging glacier (a glacier where one end has flowed over a cliff), roughly 75 times the size of a football field, had broken off a mountain above the Dhauliganga and had crashed down into the tributaries that carried glacial melt into the river.

“The health of Himalayan glaciers is deteriorating,” says Saurabh Vijay, a glaciologist from the Indian Institute of Technology. He says that melting in those glaciers from 2000 to 2020 has doubled compared to the previous measuring period, 1975 to 2000. Melting over the past several years, he learned from older satellite imagery, is what caused Sunday’s catastrophic collapse. This glacier developed a massive crack in 2017, but that wasn’t seen until after the collapse. Monitoring other hanging glaciers, he added, could help reduce the damage next time. And there will be a next time.

Photo: The Dhauliganga River is one of the six source streams of the Ganges river. It originates at an altitude of 5,070 m in the Niti Pass and merges with Alaknanda River in Chamoli District of Uttarakhand. Credit: Shutterstock