On June 30, 1908, something exploded over Siberia, leveling an area the size of Tokyo. The Tunguska Event has gone on to become a part of modern ‘dark’ lore, with mentions on The X-Files and other similar programs, through to spawning alternative theories ranging from an exploding extraterrestrial spaceship to human weapons testing. Orthodox scientists paint a more prosaic, but equally devastating scenario:
The explosion near the Podkamennaya Tunguska River on June 30, 1908, flattened some 500,000 acres (2,000 square kilometers) of Siberian forest. Scientists calculated the Tunguska explosion could have been roughly as strong as 10 megatons to 20 megatons of TNT — 1,000 times more powerful than the atom bomb dropped on Hiroshima.
The longstanding theory regarding the cause of the event is a cosmic impact from an asteroid or comet. In the last decade, researchers have conjectured the event was triggered by an asteroid exploding in Earth’s atmosphere and measuring roughly 100 feet wide (30 meters) and 617,300 tons (560,000 metric tons) in mass — more than 10 times that of the Titanic.
But recent supercomputer simulations suggest the asteroid that caused the extensive damage was much smaller.
Astrobiologist Dr David Morrison deflected the desire for a solution to the mystery in the direction of impending threat: “As interesting though Tunguska is, I’m more interested in the next Tunguska.”
The Space.com article also touches on other theories, such as Wolfgang Kundt’s speculation that the devastation may have been caused by an eruption of natural gas, as well as the more ‘imaginative’ scenarios. They also link to video from a mid-century newsreel which discussed Tunguska. The Wikipedia page on the Tunguska Event also has plenty of links to follow.