An avalanche of rock and ice set off the chain of events that severely damaged two hydropower plants and left more than 200 people dead or missing in Uttarakhand, India in February, according to a new study.
While earlier research had ruled that the disaster was caused by a massive rockslide, dismissing speculation that it was triggered by a glacial lake bursting, this study details the sequence of events that left a huge trail of destruction across the Himalayan landscape.
According to an international team of over 50 scientists, including those from India and the US, the findings highlight the increasing risks to people in the Himalayas due to both global warming and ever-increasing development projects.
In the research, the scientists assessed satellite imagery, seismic records, eyewitness videos and the results of mathematical models to gain an understanding of the sequence of events that led to the disaster in the Chamoli district of Uttarakhand.
The results of their analysis, published in the journal Science, revealed that a massive avalanche containing nearly 27 million cubic metres of rock and ice, weighing about 60 million tonnes, cascaded down the steep northern face of Ronti Peak on 7 February just before dawn, triggering massive flash floods in the region.
“A huge rock mass and overlying hanging glacier got snapped from the mountain at a height of 5,600 m in the high-slope Ronti peak, resulted into a ‘rock and ice avalanche’,” explained Kalachand Sain, director of the Wadia Institute of Himalayan Geology in Dehradun, India and a co-author of the study.
Based on the study, scientists say this massive chunk of rock and ice tumbled down the valley in a drop of elevation of nearly 3.7 km – for a portion of which it was airborne.
While several factors are linked to the rock and ice breaking off in the first place, scientists say the role of climate change cannot be ruled out.
“Due to global warming, glaciers are retreating or shrinking [in a way] that can destabilise the mountain flanks and alter the hydrological, thermal and stress regimes of underlying rock. This might have interacted in a complex way with the geologic and topographic setting to produce slope instability,” Sain told The Independent. An increased pattern of thawing, freezing and temperature variation could be the “major cause” of the ultimate detachment of the rock mass, he said.
The “mostly sedimentary” nature of the rocks in the Garhwal Range of the Himalayas where the Chamoli disaster happened also contributed to the rock and ice failure, according to Mohd Farooq Azam, another co-author of the study, from the Indian Institute of Technology Indore.
“Global warming is making this frozen soil, or permafrost, in the region more unstable that would result in more frequent mountain hazards including landslides. Climate change-derived extreme rainfall events also contribute to mountain hazards,” Azam told The Independent.
According to the study, the friction generated from tumbling down the mountain melted all the ice in the mass, transforming the avalanche debris into an “extraordinarily large, swift and powerful debris flow, which swept up boulders more than 20 metres in diameter and scoured the valley walls up to 220 metres above valley floors”.
The exceptional height from which the avalanche fell, the ratio of rock to ice in the initial cascade, and the unfortunate location of downstream hydroelectric infrastructure are three factors the scientists say contributed to the scale of the death and destruction.
With continued global warming, the researchers caution that the Chamoli disaster could prove to just be a “precursor” for more such rockslides in geologically sensitive parts of the world.
“Many glaciers on the high-slope mountainous regions have become hanging glaciers due to melting and receding. Further, rising temperatures could lead to development of cracks in these hanging glaciers that could lead to such [an] eventuality,” Sain told The Independent.
While the study calls for better early warning systems (EWS) that can provide close to 10-20 minutes for evacuation measures, the scientists say there is no straightforward “silver bullet” solution to prevent future loss of life from such disasters.
The EWS mainly consists of a network of seismic monitoring, automatic water level recording and weather stations that transmit data to a control room that allows for real-time assessments of the health of the rocks and glaciers.
However, activists question how all glaciers in the region could be extensively monitored using such warning systems.
“Every time a calamity happens scientists speak about early warning system. There are 1000s of glaciers in the Himalayas but how many eyes will you keep on all these? The government doesn’t have enough people or experts and equipment to assess these,” Vimal Bhai, a long-time activist with civil rights group Matu Jan Sangathan, told The Independent.
Study corresponding author Dan Shugar also added that an EWS may not offer much help.
“There are a lot of steep slopes and so it’s imperative to know which are most likely to be unstable. Even with an EWS though, workers at the Tapovan plant would only have had maybe 10 minutes of warning, or perhaps 20 if the system had been installed right at the failed slope,” Shugar, a geologist at the University of Calgary in Canada, told The Independent.
The effectiveness of an early warning system highly depends on the specific problem, adds Azam.
“For a disaster like Chamoli, it is extremely difficult to install EWS in advance as this particular disaster was extremely complex and very difficult to predict. Our rough estimate shows that if there would have been an EWS close to the disaster site, it would have allowed 6-10 minutes to the downstream population,” he added.
Based on the study, the scientists caution that large-scale development in such mountainous regions of the world, such as hydroelectric power projects, must account for current and future social and environmental conditions while mitigating risks to infrastructure, personnel and downstream communities.
“High mountain environments are by their nature dangerous environments, and so project proponents and governments need to be doing more thorough hazard assessments, taking into account the possibility of hazards cascades, where one type transitions or transforms into another, and climate change,” Shugar added.