The Tunguska event was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 07:14 KRAT (00:14 UT) on June 30 [O.S. June 17], 1908. The explosion, having the epicentre (60.886°N, 101.894°E), is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3–6 mi) above the Earth’s surface. Different studies have yielded widely varying estimates of the object’s size, on the order of 100 metres (330 ft). It is the largest impact event on or near Earth in recorded history. The number of scholarly publications on the problem of the Tunguska explosion since 1908 may be estimated at about 1,000 (mainly in Russian). Many scientists have participated in Tunguska studies, the best-known of them being Leonid Kulik, Yevgeny Krinov, Kirill Florensky, Nikolai Vladimirovich Vasiliev, and Wilhelm Fast.
Although the meteoroid or comet appears to have burst in the air rather than hitting the surface, this event still is referred to as an impact. Estimates of the energy of the blast range from 3 to as high as 30 megatons of TNT (13–130PJ), with 10–15 megatons of TNT (42–63 PJ) the most likely—roughly equal to the United States’ Castle Bravo thermonuclear bomb tested on March 1, 1954; about 1,000 times more powerful than the atomic bomb dropped on Hiroshima, Japan; and about two-fifths the power of the later Soviet Union’s own Tsar Bomba (the largest nuclear weapon ever detonated).
The Tunguska explosion knocked down an estimated 80 million trees over an area covering 2,150 square kilometres (830 sq mi). It is estimated that the shock wave from the blast would have 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.
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