Aerial footage shows world's largest permafrost crater in Russia

An aerial footage of world's largest permafrost crater in Russia's Siberia has surfaced online. The 1-km-long crater began to form after the surrounding forest was cleared in the 1960s and the permafrost underground began to melt, causing the land to sink. "With an increasing air temperature, we can expect (the crater) will be expanding at higher rate," a scientist said.