Footprint of the Tunguska meteorite explosion occurring in Siberia, Russia in 1908. The Tunguska event was a massive explosion that took place around 7:14 am on June 30, 1908. Although the cause is debated by some, the explosion is thought to be caused by the air burst of a large meteoroid or comet fragment at an altitude between 3 and 6 miles above Earth's surface. Expeditions to the area found immense damage with about 830 square miles of forest flattened.