Modern River Piracy

The retreat of a massive Yukon glacier a mile up its valley has redirected meltwater from one river basin to another in the first modern case of “river piracy,” according to a new analysis by a team of researchers including Mike Willis, an assistant professor at the University of Colorado Boulder.

“We’ve seen this in the geological record, but this is the first time we’ve been able to document it happening in historic times,” said Willis, who is a CIRES Fellow, an assistant professor of Geological Sciences, and co-author of the new paper, published today in Nature Geoscience.

The massive Kaskawulsh Glacier in northern Canada has retreated about a mile in the past century, and in the spring of 2016, that retreat triggered a breakneck event, according to the new analysis. A 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.
Lead author Dan Shugar, a geoscientist at the University of Washington Tacoma, and several colleagues headed into the field and found a long skinny lake where there once was a flowing river, the Slims. "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,” Shugar said. “And day by day we could see the water level dropping."

Willis helped his colleagues by mapping, in precise detail (to 2-m resolution), the elevation of the landscapes through which the Slims flowed and now flows.