: Last month a helicopter pilot spotted a wide, deep, circular crater as he flew over the Yamal Peninsula on Siberia's north coast. The crater's unusual size and shape prompted speculations that it might have formed as the result of a meteorite or missile hit. After visiting the crater, archeologist Andrei Plekhanov of Russia's Scientific Center of Arctic Studies has concluded that the release of methane from thawing permafrost was the culprit. Plekhanov found that the concentration of methane at the bottom of the crater was five orders of magnitude higher than the typical ambient value. At the crater's latitude, subsurface methane is usually frozen in the form of methane clathrate, which consists of methane molecules locked inside cages of water ice. According to Plekhanov, rising temperatures melted the clathrate and freed the methane, which turned to gas and exerted enough pressure to blow open the crater.