Tunguska

On the morning of 30 June 1908, at about 07:17, something detonated five to ten kilometres above the Podkamennaya Tunguska river and flattened 2,150 square kilometres of forest in a pattern shaped like a butterfly. Estimates of the energy run from 3 to 50 megatons with most settling around 10 to 15, comparable to the Castle Bravo test. The cause was an air burst: a stony asteroid roughly 50 to 60 metres across that came apart in the atmosphere instead of hitting the ground, which is why there is no crater. Nobody scientific got there for thirteen years. Leonid Kulik surveyed it in 1921 and reached the blast site properly in 1927, and found the trees down in their millions and no hole at all. Krasnoyarsk Krai.