Glacier Retreat Hastened by Warming Enables Scientists to Study ‘River Piracy’ in Real Time

Apr 21, 2017

A case of “river piracy” accelerated by climate change …


For years now, scientists have been documenting changes under way throughout the far north that they say are being accelerated by the warming climate. Last week, a new study reported on an impressive example of such rapid change that took place in the geological equivalent of the blink of an eye. It was an act of so-called “river piracy” that occurred last year in the Yukon Territory.

Dan Shugar, a geoscientist with the University of Washington Tacoma, looks out on a dusty plain that previously was the delta where the Slims River flowed into Kluane Lake, in the Yukon Territory. Shugar and six coauthors recount their research of the event in an article published this week in the journal Nature Geoscience.
Credit Jim Best/University of Illinois

“It basically means one river is stealing the flow, the discharge, from another river,” says Dan Shugar, a geoscientist with the University of Washington-Tacoma.

Shugar is lead author of a study that recounts the piracy that occurred last year on the Yukon side of the St. Elias Mountains, just east of the Alaska Panhandle. That’s where the Kaskawulsh Glacier, one Canada’s biggest, had retreated about a mile up its valley over the past century – so that it no longer separated the Slims and Alsek rivers that were fed by the glacier’s meltwater.

“And last summer,” he added, “the source waters that were feeding the Slims were able to actually melt a channel through the terminus of the glacier, and drain in the opposite direction.”

A satellite image shows how meltwater from the Kaskawulsh Glacier fed the Slims River, which flowed north and empties into Kluane Lake( which in turn fed the Yukon River); and the Alsek River (via the Kaskawulsh River), which flows southward and empties into the Gulf of Alaska. Inset shows Yukon River drainage (pink) and Alsek drainage (blue).
Credit Dan Shugar/University of Washington

The meltwater that fed the Slims River previously flowed north into Kluane Lake and on to the Yukon River and the Bering Sea. After the breach, the Slims’ water was diverted into the Alsek, which empties into the Gulf Alaska. And it all happened over a few months, which stunned scientists, who’ve only studied river piracy from the last ice age – never in near-real time.

“It’s a super-dramatic change!” says Ken Tape, an ecologist who works for the University of Alaska Fairbanks. He says he was fascinated by the study coauthored by Shugar -- in part because he, Tape, was kayaking on the Alsek River and its tributary last summer.

“I think the reason that it’s of interest to scientists is because we are witnessing essentially a geologic event – something that’s occurring really quickly,” Tape said. “I mean, how many other examples do we have rivers drying up overnight?”

Next week: The river piracy's impact on Kluane Lake and the Yukon River, and the likelihood of more such events in the near future.