Explosions (In The Sky?)

One hundred years ago, something leveled Siberia.

The Tunguska event was a massive explosion that occurred near the Podkamennaya (Lower Stony) Tunguska River in what is now Krasnoyarsk Krai of Russia, at around 7:14 a.m. on June 30, 1908.

USA Today, New Scientist, the astronomy blog Bad Astronomy, the BBC, Nature, and just about every sciency news outlet all have items devoted to the centennial. The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 km above Earth's surface. Different studies have yielded varying estimates for the object's size, with general agreement that it was a few tens of meters across.

Although the meteor or comet burst in the air rather than directly hitting the surface, this event is still referred to as an impact. Estimates of the energy of the blast range from 5 megatons to as high as 30 megatons of TNT, with 10–15 megatons the most likely - about 1000 times as powerful as the bomb dropped on Hiroshima, Japan and about one third the power of the Tsar Bomba, the largest nuclear weapon ever detonated. The explosion knocked over an estimated 80 million trees over 2,150 square km (830 square miles). It is estimated that the earthquake from the blast would have measured 5.0 on the Richter scale, which was not yet developed at the time. An explosion of this magnitude is capable of destroying a large metropolitan area, and had the Earth's rotation been four hours different, St. Petersburg. This possibility has helped to spark discussion of asteroid deflection strategies.

Further nerdening about Tunguska event on their wiki.