That Lake That Was Going to Fall Off a Cliff in Canada Actually Did

Decades of gradually rising temperatures culminated in two hours of "catastrophic" flooding in Canada's Northwest Territories, as a small lake burst through its melting embankment and sent tens of thousands of cubic meters of water crashing into a neighboring valley.

In a video released on Wednesday by the territorial government, the lake can be seen breaching a retaining wall weakened by thawing permafrost and dumping half its contents in a waterfall nearly five stories tall.

The drainage from the nameless lake, which is perched in the hills around the arctic hamlet of Fort McPherson, flowed several miles downstream into the Mackenzie River Delta and caused a slow slide of mud and debris that engulfed nearly two kilometers of the nearby landscape. The NWT Geological Survey issued warnings in June that a the lake would "drain catastrophically during 2015" and the flooding left the local First Nations community unscathed.

But a geographer who has been studying the lake says that this is just one small example of how the issues being grappled with at the United Nations Conference on Climate Change in Paris, which is set to close Saturday, are already having harrowing effects and altering the face of the far north.

"When people think about climate change, we hear a lot about trying to limit the increases over the next 50 or 100 years to a degree or two degrees celsius," Michael Pisaric of Brock University told VICE News. "This is an example of changes in the climate, just small changes, and they're enough to drive these pretty dramatic acts in the northern regions."

The 1.5-hectare lake is one casualty of rising global temperatures, which are already causing shifts in environmentally sensitive parts of Alaska, Siberia and Canada's north. Like much of the region, the terrain around Fort McPherson is covered in permafrost, often contained in icy headwalls up to 30 meters thick. This ice was deposited tens of thousands of years ago during the retreat of the Laurentide Ice Sheet, but over recent decades, warmer weather and heavier rains have accelerated thaws that mark the landscape with great slumps of earth and crater-like scars dozens of meters wide.

The process that led to the demise of the lake is known as a permafrost thaw slump. It begins when rain and heat melt headwall ice, exposing previously frozen soil and sediment that is in turn washed away to uncover more ice, driving a cycle that over decades or mere years can eat away entire hillsides. A single slump can displace up to 10-million cubic meters of ice and sediment — enough to fill the Toronto Blue Jays' stadium six times. The flow of this debris can create pools of sucking mud that behave like quicksand and have been known to trap large animals.

"The slumps we observe today develop in these landscapes and they are more abundant and much larger than they were in the recent past, so for northerners these are becoming increasingly important geohazards to be aware of," stated the NWT Geological Survey in a release.

On July 15, between 8 and 9 pm, the slumping permafrost that held back the unnamed lake finally gave way. The ensuing cascade gushed roughly 30,000 cubic meters of water in a flow that could have filled a dozen Olympic swimming pools. Although remote camera's captured the event, the extreme isolation of Fort McPherson, which sits roughly 1,800 miles due north of Vancouver, meant that news of the flood would not reach those studying the lake until weeks later.

In late July, VICE News and many other publications reported on the expected destruction of the lake that had actually drained a week earlier.

Until Wednesday, the NWT government had not informed the general public of the drainage. Pisaric, who does not work for the territorial government but retrieved the camera footage of the deluge, said that this was part of an effort to help the local Gwich'in community understand and cope with the event. And Steve Kokelj, a scientist with the NWT Geological Survey, said the four-month lag was partially due to a need to scrutinize the scientific data and prioritize informing the northern communities affected by the events reshaping their environment.

"This video is interesting, but the lake drainage is just one consequence of the intensification of this whole process," said Kokelj in an interview.

The remaining half of the lake may still drain as the newly exposed permafrost begins to melt, and the government advises people to avoid the area. Many other slumps throughout the region continue to alter the landscape and are clouding and clogging waterways with loads of sediment that scientists have found to have strong negative effects on aquatic ecology. According to Pisaric, these changes have provoked deep anxiety among the Gwich'ins of Fort McPherson, worries he said are shared among many communities across Canada's north.

"The processes that are driving these impacts of climate change up north are being produced elsewhere, and these lands and the people who live on these lands are being affected by things happening thousands kilometers away from where they live," said the professor.

Follow Jake Bleiberg on Twitter: @jzbleiberg