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YELLOWKNIFE — In a dramatic example of how climate change is altering the Arctic landscape, a small northern lake has fallen off a cliff after bursting through the melting earthen rampart that restrained it.

A video released Wednesday by the government of the Northwest Territories shows how the lake, undermined by melting permafrost, collapsed into a valley below and created a large temporary waterfall and an oozing tongue of mud and debris.

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“It drained quickly,” said Steve Kokelj of the N.W.T. Geological Survey.

It was one of those things that you can get out of the way of but you can’t stop

The lake, which has no name and sits in the territory’s northern corner near the community of Fort McPherson, is a victim of the region’s geology and changing climate.

Permafrost in this part of the N.W.T. contains a high percentage of ice in headwalls, which can be up to 30 metres thick. That ice has been there since the last ice age.

Trouble starts when the headwall tops are exposed by wind or rain. The ice melts, causing the soil and rock on top to collapse. That exposes more ice, which then melts and extends the collapse, and the cycle keeps repeating.