Trees were knocked down and burned over hundreds of square km by the so called Tunguska meteoroid impact

The largest impact in recorded history took place over Siberia on June 30^th, 1908. . Although it is believed that the meteor or comet burst prior to hitting the Earth's surface, this event, called the Tunguska Event, is referred to as an impact event. It is estimated that the Tunguska impact induced a blast of energy at the same magnitude as an explosion of 10-20 megatons of TNT. The explosion was 1,000 times more powerful than the nuclear explosion over Hiroshima, Japan and could have easily liquidated a large metropolitan area. This possibility helped spark the discussion of asteroid deflection strategies in recent years, and has inspired a number of Hollywood blockbusters. 

For the past century, many teams combed the Siberian impact site in an attempt to find the object that caused the explosion. Despite the efforts, none of the teams managed to discover even one fragment of an object that could have triggered the Tunguska event. The Cheko Lake is located along the most probable track of the cosmic body that caused the explosion. The unusual funnel-like shape of the lake's basin, which is extremely different than that of the neighboring lakes, may have been formed by compacted lake sediments or by a fragment of space rock. However, had pieces of space rock survived the impact with the atmosphere, they would have been too small and would have been traveling too slowly to have produced a crater the size of Lake Cheko. Also, an impact at the lake would have felled the trees all around the crater, yet there are trees older than 100 years old still standing around the lake today. 

Cheko Lake - image from space (Credit: Google Earth)

The scientists from the University of Bologna hypothesize that the cosmic body made a “soft crash” in the marsh terrain, splashing on the soft, swampy soil and melting the underlying permafrost layer, releasing carbon dioxide, water vapor and methane. This broadened the hole caused by the crash, and explains the shape and size of Lake Cheko's basin, which is unusual for an impact crater. So far, this is the only hypothesis that accounts for the unique, funnel-like morphology of the lake’s basin. According to the Italian team, only the topmost, one-meter-deep layer of debris actually came from the inflowing river. The deeper sediments predate 1908 and they were the target over which the impact took place, meaning Lake Cheko is only one century old. 

While the new findings are compelling, they do not address all of the questions about the Tunguska event. The last expedition of the Italian team to the area took place in 1999. The scientists are currently preparing for another expedition planned for 2008, during which they will drill probes up to 10m below the lake's bed in order to reach the geophysical anomaly and assess the nature of that rock. “We want to dig deeply in the bottom of the lake to definitively test our hypothesis and try to solve the Tunguska mystery,” said Luca Gasperini, a geologist with the Marine Science Institute in Bologna. 

TFOT recently covered the work of a team of U.S. and Czech researchers who claim to have discovered the origin of the dinosaur killing asteroid, and has also reported on the possibility of a space disease caused by an asteroid in Peru.