The Tunguska event

In 1908, a large explosion occurred near the Podkamennaya Tunguska River in Siberia, Russia. It flattened 2000 square kilometers of forest (that's over 80 million trees), and is generally attributed to an exploding meteoroid. Scientists believe that the meteoroid had an diameter between 50 and 200 meters, and that it didn't hit the earth, but exploded in a height of 5 to 10 kilometers.

The energy of the air burst was calculated to have been about 15 megatons of TNT, which is about 1000 times more than the atomic bomb dropped on Hiroshima in World War II.