(Photo: Northwest Territories Geological Survey)
This is what Peel Plateau Lake in the Northwest Territories of Canada looks like now.
It used to look like this. But now much of the lake has fallen off a cliff. That's because the natural wall that separated the lake from the cliff was made of permafrost. When the permafrost recently melted, the lake spilled over, as you can see in this time-lapse video:
Discovery quotes the Northwest Territories Geological Survey about the event:
"When the slump eroded to the edge of the lake, about half of the lake volume estimated to be about 30,000 m3 drained in about 2 hours by pouring over the slump headwall and forming a temporary waterfall 10 to 15 m high," the agency explains in a news release. "Peak flows lasted less than 30 minutes and flow rates reached at least 10 m3/second."
-via Jonah Goldberg