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... What is this hole in Siberia?

The Arctic is heating up faster than the rest of Earth, and that's quickly thawing the permafrost, which is a thick layer of soil that's permanently frozen -- at least, it used to be.

The Batagay crater isn't actually a crater at all. It's the world's largest "retrogressive thaw slump," which is a pit that forms when permafrost thaw causes the ground to cave in, creating a landslide as the earth at its edges slumps into the pit.

There are thousands of thaw slumps across the Arctic. But the size of the Batagay "crater" has earned it the title of megaslump. It's named for the nearby town of Batagay.

"Permafrost is not the most, let's say, photogenic of subjects," Roger Michaelides, a geophysicist at Washington University in St. Louis, told Business Insider.

"You're talking mostly about frozen dirt underground, which by definition you often can't see unless it's been exposed somehow, like in this megaslump."

That makes the Batagay pit a bit of a permafrost celebrity and an omen of what lies ahead. ...