One week the river was there — and the next it was not. And scientists blame global warming.
The event occurred after the vast Kaskawulsh Glacier in Yukon Territory retreated about a mile up its valley — and the water gushing from it reversed course and started draining into another river.
Rivers changing direction is relatively common, according to the scientists, but is usually caused by tectonic forces, landslides or erosion.
Scientists at the University of Washington Tacoma say the phenomenon is the first case of “river piracy” caused by global warming they have witnessed, according to the university’s website, UWTODAY.
“Geologists have seen river piracy, but nobody to our knowledge has documented it happening in our lifetimes,” said UWT geoscientist Dan Shugar. “People had looked at the geological record — thousands or millions of years ago — not the 21st century, where it’s happening under our noses.”.
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According to the website, its retreat reached the point in mid-2016 where the toe of ice that was sending meltwater toward the Slims River and then north to the Bering Sea retreated so far that the water changed course, joining the Kaskawulsh River and flowing south toward the Gulf of Alaska.
Shugar and his fellow researchers made the dramatic discovery when they visited the Slims River last summer and found that it was just not flowing. In addition, gauges showed an abrupt drop over four days from May 26 to 29.
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“There was barely any flow whatsoever. It was essentially a long, skinny lake,” Shugar told UWTODAY. “The water was somewhat treacherous to approach, because you’re walking on these old river sediments that were really goopy and would suck you in. And day by day we could see the water level dropping.”.
Shugar and his colleagues were shocked. “For the last 300 years, the Slims River flowed out to the Bering Sea,” he said, “and the smaller Kaskawulsh River flowed to the Gulf of Alaska. What we found was the glacial lake that fed Slims River had actually changed its outlet,” Shugar said.
The situation, said Shugar’s colleague John Clague of Canada’s Simon Fraser University, partly came about because the glacier’s toe was sitting on a geologic divide.
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“The event is a bit idiosyncratic given the peculiar geographic situation in which it happened, but in a broader sense it highlights the huge changes that glaciers are undergoing around the world due to climate change.” Clague told UWTODAY,.
“I always point out to climate-change skeptics that Earth’s glaciers are becoming markedly smaller, and that can only happen in a warming climate,” he added, referencing a UW study that shows a 99.5% probability that the glacier’s retreat is showing the effects of modern climate change.