The meltwater from the Kaskawulsh glacier flowing south in September 2016. (Dan Shugar. University of Washington)
A vast glacier-fed river which flowed from Canada’s Yukon province across Alaska to drain into the Bering Sea has disappeared in just four days in what scientists believe is the first observed case of “river piracy”.
High average temperatures in the first three months of 2016 caused a dramatic spike in the amount of meltwater flowing from the Kaskawulsh glacier, carving a deep canyon in the ice and redirecting the flow toward the Alsek River in the south, rather than the north-flowing Slims River.
That changed the Slims River from a three-metre-deep, raging torrent to a place where “massive afternoon dust storms occurred almost daily”, according to a sceintific paper in Nature Geoscience.
“We were really surprised when we got there and there was basically no water in the river,” lead author Daniel Shugar said of the Slims River.
“We could walk across it and we wouldn’t get our shirts wet.”
The scientists had previously been to the edge of the Kaskawulsh glacier in 2013 when the Slims River was “swift, cold and deep” and flowing fast enough that it could be dangerous to wade through.
Pinnacles are forming on the dry bed of Lake Kluane to the north of Kaskawulsh glacier. (Jim Best. University of Illinois)
The team, which published its observations in the journal Nature Geoscience, is blaming “post-industrial climate change” for average temperatures of as much as 4.3 degree Celsius above the 2007-2016 average in the three-months prior to the event, and say the switch will have dramatic implications for the lakes and rivers downstream.
“Ongoing thinning and retreat of the Kaskawulsh Glacier, caused by over a century of climate warming abruptly triggered the river piracy which was geologically instantaneous and is likely to be permanent.”
“The Slims, Kaskawulsh, and Alsek rivers must now all adjust to altered discharges,” the journal article stated.
“The large supply of sediment to Kluane Lake from Slims River has ended, with unknown effects on the structure and chemistry of the lake and its ecosystems.”
The south-flowing Alsek River, which is now receiving significantly increased flow from the glacier, is part of a UNESCO World Heritage region recognised for its “exceptional natural beauty” and plays a “pivotal” role in plant and animal migration.
It is a popular destination for tourists and white water rafting enthusiasts, and has stable populations of Dall sheep and mountain goats that are endangered elsewhere.
Although the Yukon is a sparsely populated region, the scientists suggest that massive and virtually instantaneous restructuring of entire river systems could be devastating to economic infrastructure if it occurs where people are reliant on the water flow.
“Most studies of the effects of climate change on glacial environments deal with enhanced melt or contributions to sea-level rise. We suggest that the effects can be more far reaching,” the paper stated.
Statistical analysis of their data gave a 99.5 per cent probability that the river piracy event was due to warming during the industrial era.
The Kaskawulsh glacier covers about 25,000 square kilometres. The front has retreated nearly 1.9 kilometres since 1899.