Source : INDIA TODAY NEWS
Rescue teams were searching on Thursday for people missing after catastrophic flooding along the Nepal-China border killed hundreds in Nepal and Tibet a day earlier. Many others are still unaccounted for, including scores of foreigners and pilgrims, as scientists studied satellite images to understand what caused the disaster and to assess the scale of the damage.
Earth scientists said clearer satellite images from Thursday suggest that the bedrock beneath a glacier on the Langtang Lirung peak, near the border with Tibet, collapsed. They said the failure brought down a massive chunk of ice and sent boulders and ice into the valley below, triggering the devastating flood.
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Geomorphologists Kristen Cook and Dan Shugar said initial images from Nepal on Wednesday were obscured by clouds and dust from the debris, and only showed that part of a glacier had broken off. In the clearer images from Thursday, they said the wider collapse was visible. “It shows the whole area without anything hidden, and we could see that, yes, it looked like there was not only this glacier that had failed, but a much larger chunk of the bedrock of the mountainside itself that had given way,” said Shugar, an associate professor at the University of Calgary. “You have this big bedrock failure that took part of the glacier with it.”
Shugar said it was heart-wrenching to look downstream in the images and see how debris had buried villages where people were living. After crashing into the valley floor, the mass continued through the steep and narrow valley as the ice melted, Cook of Universit Grenoble Alpes in France said. Water and mud several storeys high then swept through communities.
The Trishuli River surged during the flooding. Before-and-after satellite images of the Kolpurtar, Betrawati and Syapru Besi areas show the river is now much wider and has turned brown and black. Cook said the change in colour from greenish to very brown showed how much sediment the flow was carrying, with the water full of mud. Towns and villages along the river banks that were devastated now appear in the images as stretches of brown debris and mud, with some houses still visible in Betrawati.
The flooding also toppled and swept away buildings in Syapru Besi, a popular tourist spot where the trek to Langtang begins. In before-and-after images, a side river there is also wider because the flow was so powerful that it pushed upstream.
Alton Byers, a mountain geographer at the University of Colorado at Boulder, said the flooding “left a wasteland in its wake” and that recovery would take many years. Byers, who lived in Nepal and now visits every year to study glacial hazards and work with communities, said this was by far the largest glacier flood he had seen. He said he believed Wednesday’s flooding was linked to climate change, with warming melting glaciers and permafrost, the permanently frozen ground, and making high-altitude rock, ice and soil unstable. “All the indicators, to me, point to the impacts of warming trends,” he said. “In this case, the permafrost that for millennia has helped to hold together high-altitude rock and ice and soil and glaciers is now weakening and becoming unstable.”
Cook and Shugar said it was too early to say there was a direct link to climate change. Cook said slopes can fail and landslides do happen, although melting permafrost is destabilising mountainsides. “While we cannot at this point directly link this collapse to climate change, it is not unexpected to see more events of this type with a warming climate,” she said. “Not this big, hopefully not this big.” As the search for the missing continued, satellite images offered a clearer picture of how the collapse sent debris, mud and floodwater through the valley and devastated settlements along the river.
With PTI Inputs
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SOURCE :- TIMES OF INDIA
