The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia on a June morning in 1908.
The explosion is believed to have been caused by the air blast of a large meteoroid or comet fragment at an altitude of 5-10 kilometers (3-6 mi) above the Earth's surface.
Although it burst in the air rather than hitting the surface, this event is still referred to as an impact. It's estimated that the energy released was equal to about 1,000 Hiroshima bombs. The explosion knocked over an estimated 80 million trees covering 2,150 square kilometers (830 sq mi). An explosion of this magnitude would be capable of destroying a large metropolitan area. This possibility has helped to spark discussion of asteroid deflection strategies.
The Tunguska event is the largest impact event over land in Earth's recent history. Impacts of similar size over remote ocean areas would most likely have gone unnoticed before the advent of global satellite monitoring in the 1960s and 1970s.