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

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.

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