(June 30, 1908) Enormous aerial explosion that flattened about 500,000 ac (2,000 sq km) of pine forest near the Stony Tunguska River in central Siberia.
Its energy is estimated to have been equivalent to that of about 15 megatons of TNT . Uncertain evidence suggests that a meteoroid (see meteor ) 150300 ft (4590 m) in diameter or, less likely, a comet disintegrated in the atmosphere high above Earth's surface, creating a fireball and blast wave but no crater. Eyewitnesses spoke of a fireball lighting the horizon, initially visible from about 500 mi (800 km) away, followed by trembling ground and hot winds strong enough to throw people down and shake buildings. The object's vaporization scattered dust high into the atmosphere, causing abnormally bright nighttime skies in Siberia and Europe for some time afterward.