River piracy wasn’t supposed to happen in our lifetime, but here we are: Climate change, glaciers and a vanished river.

Posted on Monday, April 24, 2017

View across the lower part of Kaskawulsh Glacier in July 2016. The main drainage from the glacier used to occur through the Slims River (and ultimately to the Bering Strait), along the valley in the left-center background of the image. Today all of the glacier drainage occurs through the Kaskawulsh River (and ultimately Pacific Ocean) to the right. Photo: Luke Copland, University of Ottawa.

What happens when a massive glacier, like the Kaskawulsh Glacier in northern Canada, begins to melt due to climate change?

One might expect to see a flood when dealing with melted glaciers, but when researchers arrived at Slims River in the Yukon they were faced with a river that was no longer flowing. The Kaskawulsh Glacier retreated so far that it triggered a massive geologic event at breakneck speed. Meltwater now feeds the Kaskawulsh River and Gulf of Alaska, cutting off flow to existing river systems.

This capture of one river's flow by another, documented in a study led by the University of Washington Tacoma and published on April 17 in Nature Geoscience, is the first known case of "river piracy" in modern times.
River piracy, also known as stream capture, can happen due to tectonic motion of the Earth's crust, landslides, erosion or, in this case, the collapse of a glacial dam. The new study documents one of the less-anticipated shifts that can occur in a changing climate.

"Geologists have seen river piracy, but nobody to our knowledge has documented it happening in our lifetimes," said lead author Dan Shugar, a geoscientist at the University of Washington Tacoma. "People had looked at the geological record — thousands or millions of years ago — not the 21st century, where it's happening under our noses."

The research team used a mapping drone to create a detailed elevation model of the glacier tongue and headwater region. The resulting paper is a geological postmortem of the river's disappearance.

"The impacts of changes in the drainage from the Kaskawulsh Glacier have been immediate, especially to local communities around Kluane Lake who are having problems getting their boats in the water. The geologic event has redrawn the local landscape," said Luke Copland, co-author and University of Ottawa Research Chair in Glaciology.

Slims River crosses the Alaska Highway, and its banks were a popular hiking route. Now that the riverbed is exposed, Dall sheep from Kluane National Park are making their way down to eat the fresh vegetation, venturing into territory where they can legally be hunted. With less water flowing in, Kluane Lake did not refill last spring, and by summer 2016 was about one meter lower than ever recorded for that time of year. Waterfront land, which includes the small communities of Burwash Landing and Destruction Bay, is now farther from shore. As the lake’s level continues to drop, researchers expect this will become an isolated lake cut off from any outflow. "Shifts in sediment transport, lake chemistry, fish populations, wildlife behavior and other factors will continue to occur as the ecosystem adjusts to the new reality," explained Shugar.

View across the terminus of Kaskawulsh Glacier in August 2013, prior to the drainage of Slims Lake, visible on the right side of the image. When this lake drained in May 2016, it diverted all from flow the Slims River and Kluane Lake (right), and sent it along the Kaskawulsh River and Pacific Ocean (left). Photo: Luke Copland, University of Ottawa.

As rivers run dry and lakes turn to mud, this glacier's retreat is showing the effects of modern climate change.

"This isn’t something that can be stopped. The only way of stopping it would be to build a massive dam, but that’s unrealistic and extremely expensive," said Copland.

The University of Ottawa professor has been studying the Kaskawulsh Glacier for nearly a decade. Copland has watched the glacier terminus rapidly retreating and thinning using Canadian Space Agency imaging, running weather stations, flying over the area, and conducting fieldwork on the summit area of the Kaskawulsh Glacier with his Northern Field Research class.

Nature Geoscience article

The Slims River / Kluane Lake area

River piracy and drainage basin reorganization led by climate-driven glacier retreat authors:

  • Dan Shugar, University of Washington Tacoma
  • John Clague, Simon Fraser University
  • James Best, University of Illinois
  • Christian Schoof, University of British Columbia
  • Michael Willis, University of Colorado
  • Luke Copland, University of Ottawa
  • Gerard Roe, University of Washington Seattle

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