Meltwater from one of Canada’s largest glaciers has been rerouted from draining northward into the Bering Sea to discharging southward into the Pacific Ocean, due to retreat of the glacier, reports a paper published online this week in Nature Geoscience. The so-called river piracy event is unique during the observational record, and the study concludes that the river rerouting was most likely caused by climate change.
River piracy events - rerouting of rivers through a different drainage basin - can have significant impacts on landscape evolution, ecosystems, water supply and hydroelectric power generation. These events have been documented in the geological record, and are believed to have occurred when the large ice sheets of the Last Glacial Maximum began to decay around 18,000 years ago. However, the impact of modern climate warming on river drainage networks has so far not been documented.
Daniel Shugar and colleagues use imagery obtained by drones and helicopters, along with satellite data and discharge data from river gauges, to reconstruct the drainage of Kaskawulsh Glacier in Yukon, Canada. They find that unusual surface melt on the glacier in spring 2016 led to the development of an ice-walled canyon across remnant ice that had become separated from the active glacier by earlier retreat. They show this rerouted the glacier’s meltwater from Sims River, which ultimately drains into the Bering Sea, to Alsek river, which drains into the Pacific Ocean. The authors then investigate the causes for the glacier retreat and attribute it with overwhelming likelihood to climate change.
In an accompanying News & Views, Rachel Headley writes that the study has “captured a unique impact of climate change: river piracy due to retreating and melting glaciers.”