2017-03-14. Glacial Outburst Flood near Mount Everest Caught on Video.

posted Mar 21, 2017, 4:02 PM by Alan Gould

By Katherine Kornei, Earth & Space Science News, EoS (AGU). For GSS Climate Change chapter 8. Excerpt: The black water, heavy with debris, came tumbling apparently out of nowhere, gushing over the rocky terrain and pushing boulders around like toys. This torrent is known as a glacial outburst flood, and it forms when water stored deep within a glacier is released without warning. A team of scientists witnessed this rare event firsthand as one spilled down the Lhotse Glacier near Mount Everest on 12 June 2016. Their view, captured on video, affords researchers and the public an up-close look at the mechanics of a glacial outburst flood.  ...In 2016, a team of American researchers was working in Nepal near Imja Lake, one of the region’s largest glacial lakes. They were collaborating with local communities to improve awareness of glacial lake outburst floods, a perennial danger for those downstream of Imja Lake.... On the morning of 12 June, some of the scientists were doing fieldwork near Lhotse Glacier, an avalanche-fed glacier that originates at the peak of Lhotse, the fourth-highest mountain in the world. Byers remembers hearing what sounded like a rock fall. She then saw a “black tongue of water, boulders, and silt” racing downhill toward the village of Chukhung.  She grabbed her camera and shot the video. “I felt powerless to help people…and at the same time experienced utter fascination at the geologic process unfolding before my eyes.” “I have never experienced such adrenaline,” Byers said. “I felt powerless to help people…and at the same time experienced utter fascination at the geologic process unfolding before my eyes.” The glacial outburst flood that Byers and her colleagues witnessed slowly subsided over the next hour. But the trail below the researchers had been washed away, and the only route to Chukhung was over the glacier itself, crossing an ice bridge with water still moving rapidly below it, Byers recalled. The scientists raced over the ice bridge and down into Chukhung. They found that all of the villagers were accounted for and that the community had lost only one outhouse. The large rock wall that the community had built 1 year ago—using donations from the scientists after the 2015 earthquake—had held. “It was twisted in some places but enough to keep the floodwaters from destroying the village,” said Byers. ...Within a glacier, water travels in conduits, which can be as large as several meters across. Swiss cheese is “a very good analogy” to explain a glacier’s interior structure, said David Rounce, a glaciologist at the University of Texas at Austin and a member of the research team. Sometimes those conduits can become blocked by ice or debris such as sand and boulders. When sufficient water pressure builds up behind the natural dam to cause it to burst, the torrent that’s released can be substantial.... “These floods are particularly difficult to prepare for because there is often no visual evidence of their threat,” said Duncan Quincey, a glaciologist at the University of Leeds who reviewed the paper....  https://eos.org/articles/glacial-outburst-flood-near-mount-everest-caught-on-video


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