Permafrost slump to cause ‘catastrophic lake drainage’ near Fort McPherson

Permafrost slump to cause ‘catastrophic lake drainage’ near Fort McPherson
A lake 20 km from Fort McPherson is teetering on the edge of a cliff due to permafrost slumping.Photo: Scott Zolkos, University of Alberta.

Permafrost thaw in the area around Fort McPherson currently has a lake teetering on the edge of a cliff and waiting to flood the valley below.

The NWT Geological Survey recently put out an advisory of “catastrophic lake drainage” and potential debris flow in a valley west of Husky Lake, approximately 20 km from Fort McPherson in the Gwich’in Settlement Area.

A rapid flood of water and debris is expected to hit a small creek valley west of the lake, which could happen at any moment this summer or fall.

Land users are warned to avoid camping or traveling in the area, as there is no warning system in place, but Steve Kokelj, a permafrost scientist with the Survey, expects the impending flood will pose very little danger to residents or infrastructure.

“It’s a pretty isolated location,” he said. “In the summertime, from the accounts of the community, very few people use that area, actually; in fact, I would say almost nobody. In the wintertime, at the base of the stream channel that would accommodate the flow, there’s a skidoo route and a traveler’s cabin…but it’s very unlikely that the drainage would actually impact that cabin.”

The area outlined in red could be impacted by flash flooding and debris flows following the drainage of a small lake due to permafrost thaw at Husky Lake in Peel Plateau region.

Photo: NWT Geological Survey

The area outlined in red could be impacted by flash flooding and debris flows following the drainage of a small lake due to permafrost thaw at Husky Lake in Peel Plateau region.

Slumping impacting ecosystems

While slumping is a common occurrence in permafrost-rich areas around the globe, Kokelj said rising temperatures and increased rainfall have greatly accelerated slumping in the Peel region where, unlike along the coasts, the sediment sticks around in plain view, filling in valleys and disrupting locals’ traditional land use activities.

Typically, slumping is followed by a period of revegetation, whereby the exposed permafrost is gradually covered up by sediment and the ground stabilizes. But with the heavy rainfalls that have been increasing in the northern NWT over the past decade, those sediments are being washed away, keeping the ice exposed and fuelling the melting process.

“In the Peel Plateau, and other parts of the Western Arctic, we’ve noticed in particular over the last several decades that the size and number of slumps has increased significantly,” Kokelj said.

While slumping can be seen throughout the Peel Plateau region, this will be the first massive lake drainage to be captured and studied. The lake and slump are being monitored by cameras and possibly water level sensors as part of the Survey’s ongoing research on permafrost.

Kokelj expects the lake’s collapse will have a devastating impact on the stream valley below, which – like areas throughout the region – is already changing because of slumping.

As permafrost melts, not only does it dump hundreds of thousands of cubic metres of sediment into streams, lakes and rivers, drastically upping turbidity levels and changing the ecosystem; it also leaches minerals preserved over thousands of years into water bodies in potent concentrations.

Looking northeast at a permafrost thaw slump and small lake that is expected to drain catastrophically causing flash flooding near Husky Lake, Gwich’in Settlement Area.

Photo: Scott Zolkos, University of Alberta

Looking northeast at a permafrost thaw slump and small lake that is expected to drain catastrophically causing flash flooding near Husky Lake, Gwich’in Settlement Area.

The result has been a significant decrease in benthic invertebrates – a key indicator of ecosystem change – in impacted streams.

Kokelj expects the lake will wash a huge amount of this exposed sediment and its water-soluble minerals far downstream.

“The growing slump has already filled the valley with sediment, so there’s already a substantial impact,” he said. “If and when the lake drains, that debris flow would be eroded and moved much further down the valley.”

As part of their research, which has been ongoing since 2010 in partnership with local Aboriginal groups, universities and the territorial and federal governments, Kokelj said the team will be monitoring any changes on streams and lakes downstream, which will inform the larger research on the cumulative impacts of permafrost thaw in the North.

“One of the important opportunities we have is that it’s likely that with future warming, this phenomenon has the potential to become more common,” he said.

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