Devastating debris flow

On February 7th, the Uttarakhand region of India experienced a humanitarian tragedy when a wall of rock and ice collapsed and formed a debris flow that barreled down the Ronti Gad, Rishiganga, and Dhauliganga river valleys. The disaster left more than 200 people dead or missing.

This massive slide was caused when a wedge of rock carrying a steep hanging glacier broke off a ridge in the Himalayan mountain range, leading to the destruction of two hydropower generating facilities, as well as massive loss of life.

Dr Stuart Dunning, Reader in Physical Geography, will join colleagues from the universities of Leeds and Hull, and leading Indian and North American partners, to estimate how quickly millions of cubic metres of new sediment deposited by the flood could be removed or modified by the river. The team will be led by Dr Matt Westoby from Northumbria University, and has just been awarded a Natural Environment Research Council (NERC) Urgency Grant to carry out the work.

Dr Dunning explained: “This new work will focus on the post-disaster legacy of the material left behind by the landslide and debris flood. The material is likely to be moved by monsoonal river flows and may present a short- and medium-term hazard to hydropower facilities as the fine-grained sediment can damage turbines. We also plan to model just how the river will behave through time, will the patterns of erosion and deposition present an ongoing risk to people and infrastructure in the immediate area.”

Speaking about this new project, Dr Westoby added: “The passage of this flood was a massive shock to the local river system. The next 12 months are a crucial period because this is when we predict that newly deposited sediments will be eroded and transported in vast quantities.

“These elevated sediment loads have implications for local hydropower operators and local authorities, who require forecast estimates of these loads to mitigate against further damage to key energy and transport infrastructure.

“We are using a state-of-the-art computer model to predict patterns and rates of river channel adjustment and are working closely with in-country partners to disseminate our findings to local stakeholders.”

In the days following the disaster, a team of 53 scientists came together to investigate the cause, scope, and impact of the flood and landslide. They analysed satellite imagery, seismic records, and eyewitness videos to produce computer models of the flow, and their findings have now been published online in the journal Science.

Lead author Dr Dan Shugar, Associate Professor in the Department of Geoscience at the University of Calgary, used high-resolution satellite imagery provided by MAXAR, PlanetLabs, and CNES to determine the cause of the Uttarakhand disaster.

While initial suggestions pointed to a glacial lake outburst flood, Dr 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.”

The Science paper provided satellite evidence that previous large ice masses had been dislodged from the same ridge and struck the same valley area in recent years. The researchers suggest that climate change is contributing to such events happening more frequently, and that the greater magnitude of the latest disaster is an argument in favour of avoiding further developments in the area.

Dr Dunning added: “This was a coming together of more than 50 scientists from around the world, bringing a diverse skillset to study the landslide disaster from both the physical and social viewpoints. A disaster is only a disaster when people, or things we value, are impacted by high mountain hazards such as the tragic event in February – in this case over 200 people and considerable infrastructure.

“This work brought together some highly experienced senior researchers, and showcased the work of the amazing next generation of scientists and cutting edge techniques that allowed so much to be done, in a very short time.

“It also showed the value of genuine partnership with Indian researchers, at a time when ‘parachute’ science is often still the case. Hopefully the quality of collaboration and the resulting science will become a template for researching high-mountain hazard cascades that are thought to becoming ever more frequent as climate warms.”

Reference: A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya by D. H. Shugar et al. Science, DOI: 10.1126/science.abh4455 

Press release adapted with thanks to Northumbria University