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 June 30, 1908. The explosion is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 3-6 miles above the Earth's surface. Different studies have yielded varying estimates of the object's size, with general agreement that it was a few tens of metres across.