Northwest Territories lake finally falls off cliff
Thursday, December 17, 2015, 7:48 AM - Melting permafrost brought about by climate change has finally pushed a small lake in the Northwest Territories over the edge of a cliff. Experts have been waiting for the imminent demise of the lake for months.
On Wednesday, the Government of the Northwest Territories posted a video showing the lake collapsing into the valley below, creating a brief waterfall and splash of debris.
Steve Kokelj of the N.W.T. Geological Survey told The Canadian Press it "drained quickly."
"It was one of those things that you can get out of the way of but you can't stop," he added.
Not all of the water has drained. Kokelj says unfrozen sediment has stabilized the area and blocked further erosion. Still, authorities are asking people to avoid the vicinity, because there is a risk the rest of the lake will collapse.
What remains of the unnamed lake is situated near the community of Fort McPherson. It was previously at the top of a slope about 182 metres above the Mackenzie Valley.
WHAT IS CAUSING THE EROSION?
Much of N.W.T's melting permafrost is contained in ice headwalls that can be up to 30 metres thick. They have been in the area for 20,000 years.
Parts of the headwalls have become exposed from wind and rain erosion. That causes them to melt and forces the soil and rock that's on top to collapse.
That exposes even more ice, and the cycle starts again. The collapsed debris then moves down a slope, eroding the land.
“[The ice] thaws in the summertime and will continue to work its way back upslope until you run out of ice or the headwall gets covered by sediment,” Steve Kokelj of the Northwest Territories Geological Survey told the Canadian Press back in July.
Slumps are mass movements of debris that move a short distance either up or down an elevation. Experts say slumps are getting bigger in the area due to an increase in rainfall and warming temperatures.
The lake that recently toppled was atop a slump that's been wasting away for about a decade.
Source: The Canadian Press