First ever observed case of ‘river piracy’ saw the Slims river disappear as intense glacier melt suddenly diverted its flow into another watercourse
A view of the ice canyon that now carries meltwater from the Kaskawulsh glacier, seen here on the right, away from the Slims river and toward the Kaskawulsh river. Photograph: Dan Shugar/University of Washington Tacoma
An immense river that flowed from one of Canada’s largest glaciers vanished over the course of four days last year, scientists have reported, in an unsettling illustration of how global warming dramatically changes the world’s geography.
The abrupt and unexpected disappearance of the Slims river, which spanned up to 150 metres at its widest points, is the first observed case of “river piracy”, in which the flow of one river is suddenly diverted into another.
For hundreds of years, the Slims carried meltwater northwards from the vast Kaskawulsh glacier in Canada’s Yukon territory into the Kluane river, then into the Yukon river towards the Bering Sea. But in spring 2016, a period of intense melting of the glacier meant the drainage gradient was tipped in favour of a second river, redirecting the meltwater to the Gulf of Alaska, thousands of miles from its original destination.
The continental-scale rearrangement was documented by a team of scientists who had been monitoring the incremental retreat of the glacier for years. But on a 2016 fieldwork expedition they were confronted with a landscape that had been radically transformed.
The retreat of the Kaskawulsh glacier has resulted in a drastic change in the destination of its meltwater
“We went to the area intending to continue our measurements in the Slims river, but found the riverbed more or less dry,”
said James Best, a geologist at the University of Illinois.
“The delta top that we’d been sailing over in a small boat was now a dust storm. In terms of landscape change it was incredibly dramatic.”
Dan Shugar, a geoscientist at the University of Washington Tacoma and the paper’s lead author, added:
“The water was somewhat treacherous to approach, because you’re walking on these old river sediments that were really goopy and would suck you in. And day by day we could see the water level dropping.”
The team flew a helicopter over the glacier and used drones to investigate what was happening in the other valley, which is less accessible.
“We found that all of the water that was coming out from the front of the glacier, rather than it being split between two rivers, it was going into just one,”
said Best.
The Kaskawulsh River, seen here near its headwaters, is running higher now thanks to the addition of water that used to flow into the Slims River. Photograph: Jim Best/University of Illinois
Read more: The Guardian