Wednesday April 19, 2017

How a Yukon river suddenly vanished in 4 days

Geoscientist Dan Shugar gazes out over exposed sediments and dust storms at Kluane Lake in the Yukon in summer of 2016 - a lake covered in water just months before.

Geoscientist Dan Shugar gazes out over exposed sediments and dust storms at Kluane Lake in the Yukon in summer of 2016 - a lake covered in water just months before. (Jim Best/University of Illinois)

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A new study suggests stark evidence of small increases in temperature lead to a rapid and extreme environmental consequence — the disappearance of the glacial Slims River in the Yukon.

According to scientists, climate change caused meltwater from the Kaskawulsh Glacier to change direction — the first documented case in modern times of a phenomenon known as "river piracy," meaning one river is stealing the flow of another river.

Dan Shugar, lead author of the study published in the journal Nature Geoscience, explains how the raging white water river stopped flowing.

"Essentially the tap was turned off if you want to boil it down," Shugar tells The Current's Anna Maria Tremonti.

The glacier which feeds into two rivers, neglected the Slims River and only fed into the Kaskawulsh River, in the opposite direction.

Kaskawulsh glacier map

Yukon's Kaskawulsh glacier in Kluane National Park. (CBC)

"Much of the water from the glacier, the meltwater would go via the Slims River into Kluane Lake and then eventually out to the Yukon River and in the Bering Sea. Whereas now the Kaskawulsh River joins the Alsek and then dumps into the Gulf of Alaska over a much, much shorter distance."

How did this happen?

Shugar says over the last 100 years as the glacier has been receding and spinning vertically, the two rivers — Slims River and Kaskawulsh River — have headwaters a couple kilometres apart and are on either side of a drainage divide set up by the glacier.

"The headwaters of the Slims River was at a higher elevation than the headwaters for the Kaskawulsh … and so as the glaciers pulled back and thinned, it's effectively reduced the obstruction, that height of land between them.

He says last summer the headwaters of the Slims carved a channel through the glacier in the direction of the Kaskawulsh River — "trying to seek that lower ground."

climate-change-yukon-river-piracy

An aerial view of the ice canyon that carries meltwater from the Kaskawulsh Glacier, seen here on the right, away from the Slims River and toward the Kaskawulsh River. (Dan Shugar/University of Washington Tacoma)

Slims river disappeared 'almost instantaneously'

Shugar tells Tremonti that the Slims river effectively dried up with water levels dropping by several meters vertically in just four days.

"It happened almost instantaneously, even on human time scales."

Shugar says it's likely that the canyon that was being cut through the glacier had been forming for the last year but the precipitous drop in water level was tracked in four days.

Last August, Shugar and a colleague went to Slims River only to find "there was barely a trickle hardly moving at all."

"We had no idea it was going to be essentially gone."

As a geoscientist Shugar says the phenomenon is "certainly academically interesting but it turns out to have quite an interesting and relevant story of climate change impacts."

Listen to the full segment at the top of this web post.

This segment was produced by The Current's Ines Colabrese, Shannon Higgins and Ashley Mak.