On Feb. 7, 2021, the Uttarakhand region of India experienced a humanitarian tragedy when a veritable wall of rock and ice collapsed and formed a debris flow that barreled 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—led to the destruction of two hydropower generating facilities and leftover 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. Their study, which analyzed satellite imagery, seismic records and eyewitness videos to produce computer models of the flow, was published online today in the journal Science.
“People thought it was caused by a glacial lake outburst flood at first, but as scientists looked closer they realized that it was something different,” said Morgan McDonnell, a master’s student in the University of Utah’s Department of Geography and co-author of the paper. “This kind of collaborative effort across many disciplines is going to be essential to understand how regions like these are prone to more extreme hazards as the climate changes.”
Lead author Dan Shugar, an associate professor in the Department of Geoscience at the University of Calgary, used high-resolution satellite imagery provided by MAXAR Technologies, Planet Labs and the Centre National d’Etudes Spatiales to determine the cause of the Uttarakhand disaster. Shugar confirmed that there are no glacial lakes of any size large enough to produce a flood anywhere near the site.
“High-resolution satellite imagery used as the disaster unfolded was critical to helping us understand the event in almost real-time,” he said. “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.”
McDonnell provided crucial historical context. Using spy satellite imagery from the 1970s, she created historical digital elevation models and imagery to analyze how the landscape has changed. The historical imagery showed that this region was prone to mass wasting events in the past.
“To study mass wasting events, like landslides, you can observe changes in topography before and after the event,” said McDonnell. “With the historical elevation models and imagery, the group identified changes in the topography where rock and/or ice had been removed from higher elevations and deposited down the valley.”
The glacier in the valley is a hanging glacier that tends to break off and pile up, down the steep slope, then advance again over the steep slope and avalanche again. Usually, glacier avalanches don’t cause floods that move far down the valley. In this case, however, the rock underneath slid with it. If the ensuing avalanche is the right concentration of ice, rock and sediment, the ice will become water and cause a debris flow that moves far and fast.
“It was so surprising. It wasn’t the typical source—it wasn’t a lake burst, it wasn’t a cloud burst, and river levels were very low,” said Summer Rupper, associate professor of geography at the U and co-author of the paper. “Immediately following this really tragic event, a group of international scientists organically came together and rapidly started sharing ideas, insights, analyses. Morgan, myself and everyone put everything else on the back burner to figure out what happened with the hope of doing a better job informing people of the causes and to hopefully be better prepared to identify other high-risk areas.”
The researchers suggest that climate change is contributing to such events happening more frequently and that the magnitude of the latest disaster is an argument in favor of avoiding further developments in the area.
“Mountainous regions around the world are incredibly hazard-prone. And as climate change continues to warm mountain landscapes, it can increase these hazards,” said Rupper. “As development creeps more into the mountains, these increasing hazards have a higher probability for becoming human disasters.”
Adapted from a release by the University of Calgary.