Rescue and Recovery Efforts Underway
Rescue teams searched Thursday for missing people following catastrophic flooding along the Nepal-China border, as Earth scientists reviewed satellite imagery for clues to the cause and assessed the devastation. The flooding killed hundreds of people in Nepal and Tibet on Wednesday. Many more are still missing, including scores of foreigners and pilgrims, according to reports.
Glacier Collapse Identified
Geomorphologists Kristen Cook and Dan Shugar said initial images from Nepal on Wednesday were obscured by clouds and dust from the debris, so they could only see that part of a glacier had broken off from the Langtang Lirung peak, near the border with Tibet. In clearer images from Thursday, 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. Towns and villages along the river are buried in debris and mud, with some houses still visible in the Betrawati area. Buildings were toppled and swept away in Syaprubesi, a popular tourist spot.
Climate Change Link
The flooding was made more severe because it happened during the heavy rains of the monsoon season, says Mohammad Farooq Azam, an expert at the International Centre for Integrated Mountain Development (ICIMOD). This flood is part of a trend, said Arun Bhakta Shrestha, an expert on climate change and the Himalayan glaciers. The world will see "more and more events like this," says Alton Byers, a faculty research scientist at the Institute of Arctic and Alpine Research at the University of Colorado Boulder. Permafrost on the mountains, the continuously frozen soil and sediment, is now changing, said Byers.
Scientists say glaciers in this region, and around the world, are increasingly unstable because of human-caused global warming. Across the mountains of Nepal and Tibet, climate change is causing glaciers to melt at an alarming rate. Planet-heating emissions from burning fossil fuels such as oil, gas and coal are the primary driver of climate change.
"There's no question that this event was made more likely because of climate change and that we're seeing more likely other similar glacier hazards occurring," says Twila Moon, deputy lead scientist at the National Snow and Ice Data Center.
Geomorphologists Kristen Cook and Dan Shugar said they cannot confirm a direct link between the flooding and climate change, but noted that such events are not unexpected with a warming climate. Dan Shugar said he believes Wednesday's flooding is related to climate change, as warming is melting glaciers and permafrost.
Flood Warning System Challenges
Preliminary reports indicate Nepal's flood warning system was not equipped to handle these floods, despite significant government investment in such systems over the last decade. Many flood-prone valleys in the country have warning alarms, but as NPR has reported, the government has struggled to keep up with the cost of maintaining the systems.