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On Feb. 7, 2021, the Chamoli district of Uttarakhand State in India experienced a humanitarian tragedy when a veritable wall of rock and ice slid down the Ronti Gad, Rishiganga, and Dhauliganga river valleys. The massive slide, caused when a wedge of rock carrying a steep hanging glacier broke off a ridge in the Himalayan mountain range, and the resulting debris flow led to the destruction of two hydropower generating facilities and left over 200 people dead or missing.

A self-organized coalition of 53 scientists came together in the days following the disaster to investigate the cause, scope, and impact of the flood and landslide. , which analyzed satellite imagery, seismic records, and eyewitness videos to produce computer models of the flow, was published June 10 in the journal Science.

Satellite imagery used to detect source of landslide

Dr. Dan Shugar, PhD, associate professor in the Department of Geoscience and the paper’s lead author, has been studying the glaciers and mountains of High Mountain Asia for a number of years, particularly as it experiences climate-related changes.

Using high-resolution satellite imagery, Shugar was able to determine the cause of the Uttarkahand landslide.

“High-resolution satellite imagery used as the disaster unfolded was critical to helping us understand the event in almost real time,” he says. “Using satellite images, we tracked a plume of dust and water to a conspicuous dark patch high on a steep slope. This was the source of a giant landslide that triggered the cascade of events, and caused immense death and destruction.”

Shugar says a dark triangular patch that was not there on Feb. 6 was visible on Feb. 7 in satellite imagery from PlanetLabs. In other words, part of the snow and ice on that slope had failed, taking along with it a huge volume of the bedrock underneath. The dark patch was the now-exposed bedrock under the failed surface, which had been previously covered in snow and ice.

“The mass fell so far and fast that friction melted nearly all the ice, turning a solid mixture into a debris flow and muddy flood,” says Jeffrey Kargel, senior scientist at the Planetary Science Institute, and co-author of the study.

Climate change, human activity major factors in Chamoli disaster

The Science paper provided satellite evidence that previous giant ice masses had been dislodged from the same ridge and struck the same valley area in recent years above the destroyed 13.2 megawatt Rishiganga and the 520 MW Vishnugad Tapovan hydropower facilities.

“The Vishnugad Tapovan project had a long history of repeated damaging flash floods and a rockfall,” Kargel says. “The much greater magnitude of this event certainly argues for avoiding development in these areas, especially given that we can expect global warming to increase their frequency.”

The Himalayan region is ecologically sensitive, and prone to flash floods and landslides. Glaciers in the Himalaya are also vulnerable to rising global temperatures due to climate change, which melt the ice and cause the glaciers to become unstable. Steep mountain slopes that previously were frozen solid year-round are also becoming less stable as permafrost, or permanently frozen ground, is thawing as a result of climatic warming.

Construction along the banks of the region’s rivers has also increased in recent years, bringing with it a growing number of hydroelectric dams, projects and infrastructure connecting them, such as roads and new developments.

Dr. Sara McBride, PhD, a social scientist with the United States Geological Survey, says contextualizing these kinds of events is critical.

“The avalanche and debris flow isn’t a disaster on its own, but its interactions with the built environment that makes it so."

McBride says that warning systems, drills, public education, and other mitigation efforts may have reduced the impacts of the event; the researchers explore this briefly in their paper for Science.

“While we may be fascinated by the physical aspects of the event, we can’t ignore the human tragedy it caused.”