The Tunguska event
The Tunguska event was a large explosion that occurred near the Stony Tunguska River in Russia on the morning of 30 June 1908. The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 km2 (770 sq mi) of forest (it caused no known casualties among humans). The cause of the explosion is generally thought to have been a meteor. It is classified as an impact event, even though no impact crater has been found; the meteor is thought to have burst in mid-air at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hit the surface of the Earth. Early estimates of the energy of the air burst range from 10–15 megatons of TNT (42–63 PJ), to 30 megatons of TNT (130 PJ), depending on the exact height of burst estimated when the scaling-laws from the effects of nuclear weapons are employed. Scientists have suggested close to one hundred different versions of the explosion.