Sunday, May 18, 2008

The Tunguska Event

The Tunguska Event, sometimes called the Tunguska explosion, 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. (0:14 UT, 7:02 a.m. local solar time) on June 30, 1908 (June 17 in the Julian calendar, in use locally at the time).

The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 3–6 miles 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 metres 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 Tsar Bomba. The explosion knocked over an estimated 80 million trees over 2,150 square kilometres (830 square miles). The earthquake from the blast measured 5.0 on the Richter scale. An explosion of this magnitude is capable of destroying a large metropolitan area. This possibility has helped to spark discussion of asteroid deflection strategies.

The Tunguska event is believed to be the largest impact event on land in Earth's recent history; impacts of similar size in remote ocean areas would have gone unnoticed before the advent of global satellite monitoring in the 1960s and 1970s.

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