Scientists said that an act of “river piracy” was to blame after the flow of water melting from a glacier in Canada’s Yukon reversed direction.
The term refers to one river capturing and diverting the flow of another.
It occurred last year at the Kaskawulsh Glacier, one of Canada’s largest, with a suddenness that “startled” scientists after a process thought to take thousands of years or more happened in just a few months.
Much of the meltwater from the glacier normally flows to the north into the Bering Sea via the Slims and Yukon rivers. A rapidly retreating and thinning glacier caused the water to redirect to the south and into the Pacific Ocean.
Last year saw melting waters cut a canyon through the ice, diverting more water into the Alsek River, which flows to the south and on into the Pacific, robbing the headwaters to the north.
Scientists said that the river theft “is likely to be permanent.”
Daniel Shugar, an assistant professor of geoscience at the University of Washington-Tacoma, and colleagues described the phenomenon in a paper published on Monday in the journal Nature Geoscience.
River piracy has been identified since the 19th century by geologists, but it has generally been said to happen with tectonic shifts and erosion over thousands or millions of years.
Glacial retreat has evidence of numerous abandoned river valleys.
Shugar and colleagues used technology, including drones, to survey the landscape and monitor the changes in the water coursing away from the Kaskawulsh Glacier.
The phenomenon is unlikely to occur so dramatically elsewhere, Shugar said in a telephone interview, because the glacier itself was forming a high point in the landscape and serving as a drainage divide for water to flow one way or another.
However, as climate change causes more glaciers to melt “we may see differences in the river networks and where rivers decide to go,” he said.
Changes in the flow of rivers can have enormous consequences for the landscape and ecosystems of the affected areas, as well as water supplies.
When the shift abruptly reduced water levels in Kluane Lake, the Canadian Broadcasting Corp reported, it left docks for lakeside vacation cabins — which can be reached only by water — high and dry.
The riverbed of the Slims River basin, now nearly dry, experienced frequent and extensive afternoon dust storms through the spring and summer of last year, the paper said.
The researchers said that the rerouted flow from the glacier shows that “radical reorganizations of drainage can occur in a geologic instant, although they may also be driven by longer-term climate change.”
“It’s a reminder that glacier-caused change is not always glacial-paced,” a writer for the Canadian Broadcasting Corp said last year in a story about the phenomenon.
The underlying message of the new research is clear, Shugar said.
“We may be surprised by what climate change has in store for us and some of the effects might be much more rapid than we are expecting,” he said.
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