Climate change reroutes a Yukon river in a geological instant

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In the blink of a geological eye, climate change has helped reverse the flow of water melting from a glacier in Canada's Yukon, a hijacking that scientists call "river piracy."

This engaging term refers to one river capturing and diverting the flow of another. It occurred last spring at the Kaskawulsh Glacier, one of Canada's largest, with a suddenness that startled scientists.

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 — accelerated by global warming — caused the water to redirect to the south, and into the Pacific Ocean.

Last year's unusually warm spring produced melting waters that 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.

The scientists concluded 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 Monday in the journal Nature Geoscience.

River piracy has been identified since the 19th century by geologists, and it has generally been associated with events such as tectonic shifts and erosion occurring thousands or even millions of years ago. Those earlier episodes of glacial retreat left evidence of numerous abandoned river valleys, identified through the geological record.

In finding what appears to be the first example of river piracy observed in modern times, Shugar and colleagues used more recent technology, including drones, to survey the landscape and monitor the changes in the water coursing away from the Kaskawulsh Glacier.

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 researchers concluded 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." Or, as a writer for the CBC put it in a story about the phenomenon last year, "It's a reminder that glacier-caused change is not always glacial-paced."


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