This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As rescue teams searched for missing people following catastrophic flooding along the Nepal-China border, Earth scientists reviewed satellite imagery for clues to the cause and assessed the devastation. The flooding Wednesday killed hundreds of people in Nepal and Tibet, and hundreds more are missing, including foreigners and pilgrims.
Geomorphologists Kristen Cook and Dan Shugar said initial images from Nepal were obscured by clouds and dust from the debris, so they could only see that part of a glacier had broken off from Langtang Lirung peak, near the border with Tibet. In clearer images from Thursday, they said they could see that the bedrock underneath the glacier had collapsed, taking the massive chunk of ice down with it and sending boulders and ice into the valley. "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, associate professor at the University of Calgary.
"You have this big bedrock failure that took part of the glacier with it." Shugar said it's heart-wrenching to look downstream from there on the images, to where people were living, and see how the debris has buried villages. After slamming to the valley floor, the debris maintained its momentum through the steep, narrow valley as ice melted, said Cook, at the Université Grenoble Alpes in France. Water and mud several stories high swept through communities.
The Trishuli River surged during the flooding. Before and after satellite images of the Kolpurtar, Betrawati and Syapru Besi areas of Nepal show that the river is now much wider, and brown and black, because it overtopped its banks in some areas and filled with debris in others. The change in the color of the water shows how much sediment the flow was carrying, turning from greenish to very brown because it's full of mud, Cook said.
Towns and villages that were devastated along the river banks are submerged in debris and mud. They appear as areas of brown. Some houses are still poking through in an image of the Betrawati area.
The flooding toppled and swept away buildings in Syapru Besi, a popular tourist spot where a famous trek to Langtang begins. In before and after images, a side river is now wider too, because the flow was so powerful it pushed upstream. The flooding "left a wasteland in its wake" that will take many years to recover from, said Alton Byers, a mountain geographer at the University of Colorado at Boulder.
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