Avalanche: Uttarakhand Flood Debate Resolved, World Scientists Say, Hydropower Projects Are “Key Drivers” | India News

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Avalanche: Uttarakhand Flood Debate Resolved, World Scientists Say, Hydropower Projects Are "Key Drivers" |  India News


After months of debate about what led to the Uttarakhand floods in February of this year (eruption of a glacial lake or rock slide), a team of 53 scientists from around the world has confirmed that the cause was “an extraordinary avalanche of rocks and ice and a flow of debris”, using a computer model to reconstruct “in near real time” how the flood developed. But only part of the rock and ice mass collapsed from Ronti Peak in February, scientists warned, leaving a substantial part vulnerable.

A new lake was formed after the avalanche blocked a tributary of the Ronti Creek, but it was not a glacial lake. (Credit: Plant Labs Inc.

The findings, made by scientists from the universities of Calgary, Colorado, Washington, Zurich, Potsdam, Utah, Toulouse, Heidelberg, Geneva, Newcastle, Oslo and Utrecht, among several others, were published in the journal Science on Thursday. “There is no ambiguity that the event was a rock / ice avalanche,” co-author Dr. Irfan Rashid from the University of Kashmir told TOI.

A trajectory generated by a computer model of the Chamoli flood – Planet Labs Inc.
And it could happen again. “High-resolution Google Earth data on Ronti Peak suggests that only one larger hanging glacier collapsed in February. There is still a substantial chunk of ice with many cracks that could be vulnerable, ”Rashid said.

Annotated path of the rockslide at Ronti Peak that ultimately caused the flooding – Planet Labs Inc, Dan Shugar, University of Calgary
Lead author Dr Dan Shugar from the University of Calgary added: “If you’re just looking for dangerous glacial lakes, you will miss the dangerous slopes that could produce the highly mobile and destructive debris flow, like the one we saw.” . The document further stated: “The Chamoli event can be seen in the context of a change in geomorphological sensitivity and therefore could be seen as a precursor to an increase in events as global warming progresses.”

The Tapovan Vishnugarh project, 10 km downstream, was flooded when the increasing flow of water debris hit it at about 58 km / h (Credit: Plant Labs Inc.)

As for why the glacial lake blast was ruled out as a cause, Shugar said: “For GLOFs, there would normally be quite obvious signs or erosion and erosion downstream from the blast site. But at the Nanda Devi and Nanda Ghunti glaciers (where it was suggested that the glacial lake originated), no evidence of any change was observed in the days leading up to February 7 (when the floods passed through the Rishiganga and Dhauliganga rivers). There were no visible lakes in the previous days either. ”
What they found while recreating, with satellite images, seismic records, digital terrain models and videos, what happened on February 7 was a series of “extraordinary” events.
Seismic data from two stations, 160 km and 174 km from the source, indicated that around 10.21 a.m., a mass of 20 million m3 of rock (80%) and ice (20%) broke apart at an altitude of 5,500 m above sea level and hit the bottom of the Ronti Gad valley (stream) about 1,800 m below. The average speed of the avalanche was 205-216 kmph down the side of the 35 ° mountain. “The incredible frictional heat generated during the disintegration of the rock mass almost melted out of the ice during the descent. The liquid water is what allowed the debris to become so mobile, ”Shugar said. “Typical rock avalanches that don’t contain a lot of glacial ice or water tend to flow a great distance, maybe just a few kilometers, not the tens of kilometers that we saw here. This was a different event. ”
So the fall itself was exceptional. “The ~ 3700 m vertical drop to the Tapovan HPP is clearly exceeded by only two known events in the historical record, namely the Huascarán avalanches of 1962 and 1970,” the document said, referring to a 1962 avalanche in the slopes of an extinct volcano and a debris avalanche in 1970 caused by an earthquake in Peru. “The rock-to-ice ratio and the extreme height of the fall produced a ‘worst case’ scenario, where there was enough energy to melt the ice. If there had been more ice (relative to the rock), not enough heat would have been generated and less ice would have melted, ”Shugar added.
By analyzing the videos, they reconstructed that the flow was 25 meters per second (m / s) near the Rishiganga hydroelectric project (15 km downstream from the avalanche source), 16 m / s upstream of the Tapovan project (10 km downstream) and 12 m / s just downstream from Tapovan (26 km from the source), while the average between Raini and Joshimath (16 km downstream) was 10 m / s. The study also estimated the average discharge of the videos: 8,200-14,200 cubic meters per second (m3 / s) in the Rishiganga project and 2,900-4,900 m3 / s in the Tapovan project. Rashid said: “The maximum flood heights in certain areas of the river valley reached ~ 100 m, which is something that none of the team members expected.”
Because the flow was very mobile, another anomaly occurred. “In particular, and in contrast to most previously documented rock avalanches, very little debris is preserved at the base of the failed slope,” the document says. As the flow became more fluid down the valley, there were “very few large rocks that typically form the upper surface of rock avalanches.”
But one of the main drivers of the disaster, the newspaper said, was “the unfortunate location of multiple hydroelectric plants in the direct path of the flow.” Co-author Dr Mohd Farooq Azam from IIT-Indore told TOI: “The greater magnitude of the last Chamoli disaster it is an argument in favor of avoiding new developments in the fragile mountains of the Himalayas ”. The document concluded: “The disaster tragically revealed the risks associated with the rapid expansion of hydroelectric infrastructure in increasingly unstable territory.”

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