One of the most celebrated and bizarre events in history occurred on June 30, 1908 near the Podkamennaya Tunguska River in central Russia. At 7:40 am local time, a great swath was carved in the Siberian forest, probably by something hitting — or almost hitting — the Earth.
I say “almost hitting,” because despite an estimated detonation of 15-ish megatons (a thousand times the Hiroshima bomb) and the flattening of 770 square miles of forest, there appeared to be no impact crater from the Tunguska event. An impact crater would, of course, be expected in the case of a rocky or metallic meteor striking the Earth, which is why it’s long been proposed that the object in question was more like, say, a comet, or an unstable meteoroid that disintegrated about 5-10 kilometers up.
Maybe. National Geographic reports that scientists may have finally found the crater made in the Tunguska event. Recently, a team of Italian scientists “used acoustic imagery to investigate the bottom of Lake Cheko, about [eight kilometers] north of the explosion’s suspected epicenter.” The Italian team claims Lake Cheko might itself be the long-sought hole in the ground:
“When our expedition [was at] Tunguska, we didn’t have a clue that Lake Cheko might fill a crater,” said Luca Gasperini, a geologist with the Marine Science Institute in Bologna who led the study. “The funnel-like shape of the basin and samples from its sedimentary deposits suggest that the lake fills an impact crater.”
Unfortunately, Wikipedia reports that some eyewitness sources establish the pre-1908 existence of Lake Cheko, and a 1961 study dismissed the possibility of a modern origin for the lake due to the extensive silt on the lakebed.
The Tunguska Event featured prominently in “The X-Files” and has been a popular target of speculative theorists, who have suggested everything from an antimatter collision to a comet-based deuterium source detonation (a “natural H-bomb”) to a flying saucer crash to explain the event.
Photo from a 1927 expedition to the Tunguska site, via Wikipedia.