Sunday, 25 June, 2017

Glacial melt causing first observed case of 'river piracy'

Canada glacier melt rerouted in rare case of 'river piracy' Climate change causes glacial river in Yukon to change direction
Theresa Hayes | 19 April, 2017, 00:31

For the last 300-350 years, Slims River was fed by north-running meltwaters from one of Canada's largest glaciers, Kaskawulsh Glacier.

Scientists say as climate change causes more glaciers to melt, we may see differences in the river networks and changes in river flows.

This phenomenon, known as "river piracy", typically takes centuries but the study documented it over the course of one spring.

The Alsek River has flown water from its neighboring Slims River.

Kluane Lake, which was fed by water from the Slims, was about a metre lower by summer a year ago and is expected to fall further, to the point where there is no longer an outflow river.

The river piracy began at the edge of the massive Kaskawulsh Glacier, which spans some 15,000 square miles across Canada's Yukon territory.

Shugar and colleague James Best, a professor of geology and geography from the University of IL, travelled to the Slims River in the Kluane National Park and Reserve west of Haines, Yukon, last summer.

"I always point out to climate-change sceptics that Earth's glaciers are becoming markedly smaller, and that can only happen in a warming climate", Dr Clague says.

The beneficiary of the change, in hydrologic terms, the Alsek River - known for its whitewater rafting - saw far higher flows than normal as a outcome.

Images captured by the European Space Agency's Sentinel2 satellite in 2015 and 2016 show a dramatic drop in the Slims River's flow. When the shift abruptly reduced water levels in Kluane Lake, the Canadian Broadcasting Corporation reported, it left docks for lakeside vacation cabins - which can be reached only by water - high and dry.

Lead author Dan Shugar, a geoscientist at the University of Washington Tacoma, and several colleagues headed into the field and found a long skinny lake where there once was a flowing river, the Slims.

They traced its mysterious disappearance to the Slims River's headwaters, where they found a glacial barrier that once routed its flow northward into the Bering Sea had been breached in the spring. But when they arrived in the remote area of the Yukon where the glacier is situated, they heard the river was unusually low.

They returned past year to find the river shallow and as still as a lake, while the Alsek River was deeper and flowing faster. Kluane Lake, fueled by its waters, was so low that the residents had difficulty putting their boats into the water. The researchers expect the lake to become an isolated lake cut off from any outlet as its water levels continue to drop. The newly exposed riverbed is attracting sheep from a nearby national park to an area where they can be legally hunted.

The underlying message of the new research is clear, Shugar said. They therefore inferred that the events in question could be attributed to human-caused climate change. Since May 2016, a channel carved through one of northwestern Canada's largest glaciers has allowed one river to pillage water from another, new observations reveal. What's remarkable bout this particular study is that it documents the less than anticipated effects of climate change on our environment.

Richard Alley, a glacier expert at the University of Pennsylvania, who was not part of the study, told The Associated Press that the findings reconfirmed "that climate change has wide, widespread and surprising changes".