- Jonathan Amos
- Science Correspondent, BBC
Nature often takes us by surprise. His power is too often underestimated, with catastrophic consequences.
This was the case with the Chamoli disaster in February, when the flank of a Himalayan mountain broke away and fell into the valley below.
The Avalanche claimed more than 200 lives and destroyed hydroelectric infrastructure for a worth hundreds of millions of dollars.
It is possible that you saw some of the images that were captured at that time that show the ghastly wall of mud running downhill, sweeping everything in its path.
An international group of more than 50 researchers has now published a detailed assessment of what happened. It is based on multiple data sources, from satellite images to field observations.
10 times the volume of the Great Pyramid of Giza
The disaster started near the top of the 6 km high Ronti Peak in the Chamoli district of Uttarakhand, a northern Indian state.
A wedge of rock covered by a glacier more than 500 meters wide and 180 thick suddenly dislodged.
The team estimates that thus began the descent of nearly 27 million cubic meters of material.
To put this volume in context, it is roughly 10 times that of the Great Pyramid of Giza in Egypt.
When the mass hit the bottom of the Ronti Gad valley, it released an energy equivalent to 15 Hiroshima atomic bombs.
“The ratio of rock and ice was about 80% and 20%. That ratio, combined with the incredible fall height of almost 2 km, was able to generate enough heat, through friction from the disintegrating rock, to almost completely melt the ice into water, “explained team leader Dr. Dan Shugar of the University of Calgary, Canada.
“This was instrumental in transforming what would otherwise have been a normal rock avalanche into something hypermobile and capable of traveling tens of kilometers at lower elevations,” he told BBC News.
On impact, the fallen material immediately sent large boulders, about 10 meters wide, onto the surrounding slopes. The gust of air destroyed 20 hectares of nearby forest.
In other cases, much of the pulverized mass would have been expected to remain in place. But it was not like that. With the consistency of a concrete mix, it descended further.
When the debris flow passed through the Rishiganga hydroelectric plant, located 15 km away, near the town of Raini, the frontal velocity was 25 m / s. That’s 90 km / h, the speed of a fast-moving car.
Even 10 km later, at the Tapovan hydroelectric power station, the flow was still moving at 16 m / s.
Almost all of those who died, 204 in all, were working or visiting power plants. They received no warning of what was coming.
At the time, it was speculated that much of the water in the stream could have come from a glacial lake.
In the Himalayas, large masses of meltwater form in front of glaciers, which can sometimes burst and cause a flash flood.
The team’s investigations rule it out definitively. No source of water could be identified.
The other big question in February was whether climate change may have played a role in the disaster.
That’s complicated. The team concludes that an event cannot be attributed to warm-up global, but they point out that the frequency of rockfall in the Himalayas increases as temperatures rise.
“Glacier contraction uncovers and destabilizes mountain flanks and strongly alters the hydrological and thermal regimes of the underlying rock,” the researchers write in their report for the journal. Science.
Co-author Professor Jeffrey Kargel of the Planetary Science Institute in Arizona, USA, told BBC News: “Identifying a specific trigger is very difficult.”
“What we do know is that this giant wedge of rock that eventually collapsed had started to slide in the previous four years. Satellite images (archive) showed that it had slid several tens of meters. Unfortunately, no human had noticed. this”.
Infrastructure at risk
The question now is what all this means for the people who live and work in the high mountains of Uttarakhand.
Kavita Upadhyay, a water policy expert and journalist from India who has written about the environment and hydropower in the region, says more needs to be thought before building large infrastructure projects in what is a very dynamic region, prone not to only to landslides, but also to floods and earthquakes.
“This is not the first time these power plants have been damaged,” he said.
“They were damaged in the floods of 2012, 2013, 2016. Therefore, you have to ask yourself how to put this infrastructure in such a fragile area. You can say that there should be no development, but governments are not going to listen to that.
“They are providing jobs, and for governments, hydropower is also about moving away from fossil fuels. But if we look for practical solutions, at least we have early warning systems,” he added.
This is repeated by landslide expert and co-author, Professor Dave Petley, from the University of Sheffield, UK.
“The Chamoli disaster highlights that we are underestimating the threat to the very expensive infrastructure that is being built in high mountain areas,” he said.
“The threat is greater than anticipated even in stable conditions. With climate change that problem is much worse,” he said.
“We need to better assess these threats or we will see high levels of human, economic, social and environmental costs associated with these projects,” he told the BBC.
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Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.