The Lake That Fell Off a Cliff

In a remote region of Canada’s Northwest Territories, north of Vancouver, a lake breached a retaining wall weakened by thawing permafrost and dumped enough water to fill a dozen Olympic swimming pools into an adjacent valley. The breach also caused a slow slide of sediment, creating pools of sucking mud. Environmentalists are worried the runoff could also make its way into nearby streams and lakes, killing fish and other aquatic life. Increased temperatures and rain in the region have led to permafrost thaw slump, a cycle that causes ice deposited tens of thousands of years ago to erode over several years.