Glacier bursts: Chamoli
The events
How the glacier was struck
Ishita Mishra & Rohan Dua, February 10, 2021: The Times of India
A fivemember team of scientists deployed by the Centre to establish the chain of events that led up to the Uttarakhand flood on Sunday has found that a peak that “came loose” and a glacier perched precariously atop a cliff are most likely to have triggered the disaster.
The team from the Dehradun-based Wadia Institute of Himalayan Geology (WIHG) trekked to the glacial site in Uttarakhand’s Chamoli district and conducted field and aerial surveys on Tuesday. “The initial conclusion we’ve drawn is that Sunday’s incident was an episodic failure of rock mass (rockslide) and hanging glacier (that stops midway down a cliff) in the Raunthi glacier area,” WIHG director Kalachand Sain told TOI.
The origin was around two peaks — Raunthi and Mrigthuni. “It is possible a peak, a heavy and solid structure, broke off because of natural causes and fell on to a glacier beneath it, some 5,600m above sea level,” Sain said. That, in turn, fragmented the glacier and chipped off pieces were consolidated with the rock debris.
The rock-avalanche then surged over a sharp 37° slope for about 3km before hitting the Raunthi Gadhera stream’s floor at an altitude of about 3,600m. When it hit the river bed, the mix of heavy objects created a dam-like structure that stayed in place for some time because it was snowing. In the report, the scientists have attached photos of the accumulated water and those from September 28 last year, when it wasn’t present.
Then, for three days before the flood, the weather had been clear. “This caused freezing and thawing, leading to a massive slope failure,” the preliminary report said. Which means that the rock-ice mix that had accumulated melted, breached the area and came surging down to hit Tapovan Valley. “The flow contained rocks, snow, water,” said Sain. And the force it took on was because of this heavy mix, a scientist who prepared the report said. The downhill surge also generated heat, which may have melted the ice in the mix and added to the volume. A large part of what happened now understood, scientists are trying to figure out the root cause — what made the peak break off ?
“We believed the area the rock fell from had developed a weak zone. That happens only over a course of several years — it’s not the instant result of weather disturbance, like cloudburst or rains, as was the case with the 2013 floods. What we saw took decades to happen,” Sain said. “Continuous monitoring of glaciers — India has 26 — is vital. It could help avert such disasters, plan for remedial measures.”
The flood was initially believed to have been caused by a glacial lake outburst, when a glacial lake flows over. But satellite images from Indian Institute of Remote Sensing, shared with the Uttarakhand disaster management and mitigation centre on Monday, showed a landslide was more likely to have triggered the flood.
The Centre, taking Tuesday’s findings into account, said the probe will continue. Department of science and technology secretary Prof Ashutosh Sharma said, “This will be explored to ensure it’s helpful in managing our natural assets in the future.”
Behaviour of fish
Kautilya Singh & Shivani Azad, February 10, 2021: The Times of India
Did fish sense the oncoming deluge?
An otherwise slow Sunday morning in Lasu village was disrupted by a strange occurrence — the Alaknanda river, by which it lies, had turned silver with shoals of fishes close to the surface. It was around 9am. Within minutes, some hundred locals had gathered, ready with baskets, buckets, pots, pans to “pick up” the fish — they didn’t even have to drop a rod or net.
What they could not have known was that about 70km upstream, in another hour or so, disaster was about to strike. And this was a precursor.
In Raini, the surging Dhauliganga would ravage everything in its path after a landslide-triggered avalanche flooded it. The Dhauliganga is the Alaknanda’s tributary. And those downstream from the river, in places far away from Raini — Nandprayag, Langasu, Karnprayag — saw what those at Lasu had seen. Innumerable mahseers, carps and snow trouts had filled the waters, were not swimming too deep inside and were sticking to the banks. “Fish always swim in the middle of the stream. It was abnormal. They were only swimming along the edges,” Ajay Purohit, one of the first to spot the fish, told TOI.
At Girsa village, near Langasu, surprise gave way to pragmatism. “At least one person from each family in our village went to see what was happening. On any day, it would not be possible to catch fish with our hands. But they were so close, and so many. All of us brought back a lot of fish,” said Radha Krishna, a resident. Some of the fish caught weighed up to 2kg.
The one change they may have missed was that of the water. The clear green had turned grey, just like the slurry that had washed over Raini, Tapovan and other villages flooded in Chamoli.
How are the two related? Scientists said the subsurface vibrations of whatever it is that caused the floods may have ‘broken the sensors’ of fish upstream.
“Fish have a lateral line organ (a biological system in aquatic creatures that help them detect movement and pressure changes in water). It’s very sensitive. The slightest disturbance can set it off, sending the fish into a state of shock,” said K Sivakumar, senior scientist at Wildlife Institute of India. “In this case, it’s possible that a sound preceding the flood may have been picked up by the fish. It is also possible an electric wire or some source of power fell into the water and gave them electric shocks. There can be many reasons. This is why we keep saying that dynamite blasting should never be done on a river.”
