Photo: Dan Shugar / University of Washington
The remarkable pace of climate change has forced a Canadian glacier into such hasty retreat that a river of its meltwater has dried up and been diverted in a “geological instant.” Once drained by the Slims and Yukon Rivers — which flow north, eventually emptying into the Bearing Sea — the Kaskawulsh Glacier now feeds the Kaskawulsh River, which flows south into the Pacific Ocean.
The process of headwaters diverting from one river into another is known as “river piracy” or “stream capture.” It’s usually caused by plate tectonics, landslides or erosion and can take hundreds or even thousands of years to unfold. In this case, the gist of the diversion, caused by the failure of a weakening glacial dam, took four days.
A research team used a mapping drone to study the area after the Slims River mysteriously dried up in 2016. The results — which linked human-caused climate change to sudden geological events — were published Monday in the journal Nature Geoscience.
“What we found was the glacial lake that fed Slims River had actually changed its outlet,” said Dan Shugar, an assistant professor of geoscience at the University of Washington-Tacoma and lead author of the paper. “A 100-foot canyon had been carved through the terminus of the glacier. Meltwater was flowing through that canyon from one lake into another glacial lake, almost like when you see champagne poured into glasses that are stacked in a pyramid.”
It is the first time river piracy has been observed and studied as it occurred.
“Geologists have seen river piracy, but nobody to our knowledge has documented it happening in our lifetimes,” Shugar said. “People had looked at the geological record — thousands or millions of years ago — not the 21st century, where it’s happening under our noses.”
In addition to a dramatic rearrangement of the landscape, the diversion of meltwater led to severe dust storms on the dry riverbed in the spring and summer months. Kluane Lake, into which the Slims River once flowed, dropped by 3 feet. Researchers expect the water level to continue dropping until it becomes an isolated lake with no outflow. Dall sheep from Kluane National Park have also wandered onto the floodplain — where they can legally be hunted — to eat plants now growing there.
Looking into the future, events exactly like this one are unlikely. The disappearance of the Slims River is more notable for the attention it brings to the tenacious rate of global warming and, as a result, the rapid melting of glaciers. The Kaskawulsh Glacier, for instance, retreated a mile in the last century, leading to the eventual stream capture.
Speaking to the New York Times, Shugar issued an all-too-familiar warning. “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.”