The Tunguska event was a large explosion that occurred near the Stony Tunguska River, in Yeniseysk Governorate, now Krasnoyarsk Krai, Russian Empire, on the morning of 30 June 1908 (N.S.). The explosion over the sparsely populated Eastern Siberian Taiga flattened of forest and caused no known casualties. 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 rather than hit the surface of the Earth. Different studies have yielded varying estimates of the superbolide's size, on the order of , depending on whether the meteor was a comet or a denser asteroid. It is considered the largest impact event on Earth in recorded history.