Washington, District of Columbia 2021-06-10 14:03:26 –
June 10, 2021
The state of Uttarakhand, India, experienced a humanitarian tragedy on February 7, 2021 when debris and water walls ran down the valleys of the Rontigado, Rishiganga and Dhauliganga rivers.
The event began when a glacier-carrying rock wedge broke from a steep ridge in the Himalayas. The resulting debris flow destroyed two hydropower facilities, killing or missing more than 200 people.
In the days following the disaster, a self-organized coalition of 53 scientists gathered to investigate the causes, extents and consequences. The team determined that the cause of the flood was not a lake or a diversion river, but a fall of melted rocks or glacier ice during its descent.
In this study, satellite images, seismic records, and witness videos were used to create a computer model of the flow. Released on June 10 In science.
“On the morning of the event, I was reading the news over a cup of coffee and saw a headline about the Himalayan disaster,” the co-author said. David scene, Associate Professor of Civil and Environmental Engineering, University of Washington. “I sat in front of the computer and took out the satellite imagery I got that morning. When I saw a cloud of dust moving down the valley, I told other scientists that they were this. I started writing an email asking if I was working on it. One mail thread quickly became five, then ten, and the effort of responding spent most of the wake-up time in the next two weeks. “
The first hypothesis about the cause of the event suggested a glacial lake outburst flood. However, the team decided that there was no glacial lake near the site large enough to cause a flood.
“Access to high-resolution satellite imagery and research software, as well as expertise in satellite remote sensing, was essential to get a bird’s eye view of how the event unfolded,” the co-authors said. Shashank Boushan, UW PhD student in civil engineering and environmental engineering. “We worked with a French collaborator to tune the satellite collection within days of the event and quickly process the images to derive a detailed topographic map of the site.”
The researchers compared the images before and after the event with the topographic map to document all changes and reconstruct the sequence of events.
“We tracked the dust and water plume to the prominent dark patches high up on steep slopes,” said the lead author. Dan Sugar, Associate Professor at the University of Calgary.
The dark patch turned out to be a scar left by 35 million cubic yards of lost rock and glacier ice. This is enough material to cover Washington DC with a layer 0.5 feet deep.
“This was the cause of a huge landslide that caused a series of events and caused huge deaths and destruction,” said Shugar, formerly an assistant professor at UW Tacoma.
Researchers also used maps to determine how far ice and rock blocks had fallen.
“The failed block fell more than a mile before hitting the bottom of the valley. Applying this height to the context, imagine stacking 11 Space Needles or 6 Eiffel Towers vertically. “Mr. Boushan said.
Larger teams were then able to quantify how the crushed rock and ice were redistributed downstream.
“When the block fell, most of the glacier’s ice melted within minutes, resulting in a large amount of water from the flood,” said Boushan. “This is very unusual. Normal rock landslides and snow / ice avalanches could not produce such a large amount of water.”
For Boushan, the job was personal.
“In general, PhD research projects are very niche. It can be difficult to explain to parents why it is important to measure glacier dynamics,” says Boushan. “But because of the scale of the disaster, my family and friends who returned to India wanted to know how this event unfolded. They expected me to give an answer. These interactions have given me a sense of belonging and motivation that some of my research may be immediately useful to society. “
The team also used satellite imagery archives to show that a former large ice block was removed from the same ridge and hit the same valley in recent years. Researchers suggest that climate change may be increasing the frequency of such events and that the larger scale of modern disasters should be considered before further infrastructure development in the region. I will.
“These alpine rivers are attractive for hydropower projects and we need to better understand the full range of potential alpine dangers,” says Shean. “We hope that the lessons learned from this effort will improve our ability to respond to future disasters and guide life-saving policy decisions.”
Shean, Bhushan and Shugar have 50 co-authors from 14 countries. In addition to geoscientists, the co-author list includes water policy experts and social scientists. Shean and Bhushan were funded by the NASA High Mountain Asia Team and the Future Investigators of the NASA Earth and Space Science Technology Fellowship. Other co-authors have been funded by various government agencies such as India, Canada, France, Germany and Switzerland. The satellite images used by the UW team were provided by MAXAR, Planet, ISRO, and CNES, the French government’s space agency.
UW Team Grant Numbers: 80NSSC20K1595, 80NSSC19K1338
Cause, scope determined for deadly winter debris flow in Uttarakhand, India Source link Cause, scope determined for deadly winter debris flow in Uttarakhand, India