Message #265832

[Teri Charboneau]

Artemieva suggests an enormous plume resulted from the updraught, which was then followed by a cloud, "thousands of kilometres in diameter".

But Tunguska's story is not over. Even now, some other researchers have proposed that we have been missing an obvious clue to explain the event.

In 2007 an Italian team suggested that a lake 5 miles (8km) north-north-west of the explosion's epicentre could be an impact crater. Lake Cheko, they say, did not feature on any maps before the event.

Luca Gasperini of the University of Bologna in Italy, travelled to the lake in the late 1990s, and says it is difficult to explain the origin of the lake in any other way. "Now we are sure it was formed after the impact, not from the main Tunguska body but of a fragment of the asteroid that was preserved by the explosion."

    Any 'enigmatic' objects at the bottom of this lake could be easily recovered with minimal efforts

Gasperini firmly believes that a large piece of asteroid lies 33ft (10m) below the bottom of the lake, buried in sediment. "It would be very easy for Russians to get there and drill," he says. Despite heavy criticism of the theory, he still hopes someone will scour the lake for remnants of meteoric origin.

That Lake Cheko is an impact crater is not a popular idea. It is just another "quasi-theory" says Artemieva. "Any 'enigmatic' objects at the bottom of this lake could be easily recovered with minimal efforts – the lake is not deep," she says. Collins also disagrees with Gasperini's idea.

In 2008, he and colleagues published a rebuttal to the theory, stating that "unaffected mature trees" were close to the lake, which would have been obliterated if a large piece of rock had fallen close by.