Blast From the Past

"Early on the morning of June 30, 1908, a massive explosion shook central Siberia. Witnesses told of a fireball that streaked in from the southeast and then detonated in the sky above the desolate, forested region. At the nearest trading post, about 70 kilometers away from the blast, people were reportedly knocked from their feet. Seismic instruments in the area registered ground motions equivalent to those of a magnitude-5 earthquake."

more on Tunguska a hundred years later here:

http://www.sciencenews.org/view/generic/id/32892/title/Tunguska,_a_century_later