Rare ‘river piracy’ reroutes glacier melt-off
WASHINGTON — Scientists have witnessed the first modern case of what they call “river piracy,” and they blame global warming. Most of the water gushing from a large glacier in northwest Canada last year suddenly switched from one river to another.
That changed the Slims River from a 10-foot-deep, raging river to something so shallow that it barely was above a scientist’s high top sneakers at midstream. The melt from the Yukon’s Kaskawulsh glacier now flows mostly into the Alsek River and ends up in the Pacific Ocean instead of the Arctic’s Bering Sea.
It seemed to all happen in about one day — last May 26 — based on river gauge data, said Dan Shugar, a University of Washington at Tacoma professor who studies how land changes. A 100-foot-tall canyon formed at the end of the glacier, rerouting the melting water, Shugar and his colleagues wrote in a study published in Monday’s journal Nature Geoscience.
The term “river piracy” is usually used to describe events that take a long, such as tens of thousands of years, to happen and had not been seen in modern times, especially not this quickly, said study co-author Jim Best of the University of Illinois at UrbanaChampaign. It’s different from something like the Mississippi River changing course at its delta. It involves more than one river and occurs at the beginning of a waterway, not the end.
The scientists had been to the edge of the Kaskawulsh glacier in 2013. Then the Slims River was “swift, cold and deep” and flowing fast enough that it could be dangerous to wade through, Shugar said. They returned last year to find the river shallow and as still as a lake, while the Alsek was deeper and flowing faster.
What had been a river delta at the edge of the Slims River had changed into a place full of “afternoon dust storms with this fine dust getting into your nose and your mouth,” Best said.
The lack of water in the Slims wasn’t because of changes in rainfall, Shugar said. They know that because it’s a river fed mostly by glacial melt, not rain, and the Alsek increased in amounts similar to what disappeared from the Slims.