A dramatic video filmed by a drone has revealed details of the one-kilometre-long Batagayka crater in Russia's Far East; This hole forms the largest frost depression in the world. According to Reuters: The video clip shows two explorers climbing with difficulty over the rugged terrain at the base of the depression, which is characterized by an irregular surface and small hills. This terrain began to form after the trees of the surrounding forest were cut down in the 1960s, and after the permafrost began to melt. Which caused the land to subside. “We locals call it a drop,” said Erel Struchkov, a local resident and explorer of the depression, standing at the edge of the depression. He added: "It began to appear in the 1970s, and first appeared in the form of a deep, narrow valley. Then it began to expand due to melting in the heat of sunny days."