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Today in History: the Tunguska Event
The Tunguska event, sometimes referred to as the Tunguska explosion, was a massive explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai of Russia, between 7:00 and 8:00 AM on June 30, 1908.

The explosion was most likely caused by the airburst of a large (around 20 m (66 ft) across) meteoroid or comet fragment at an altitude of 5 to 10 kilometers (3-6 mi) above the Earth's surface. . . . The energy of the blast was estimated to be between 10 and 20 megatons of TNT, 1,000 times more powerful than the bomb dropped on Hiroshima, or equivalent to Castle Bravo, the most powerful nuclear bomb ever detonated by the US. . . .
Posted by: Mike 2009-06-30
http://www.rantburg.com/poparticle.php?ID=273244