In 1908 something exploded over Siberia and flattened a forest, leaving no crater.
One summer morning in 1908, a blinding fireball crossed the Siberian sky and exploded above the forest near the Tunguska River. The blast flattened trees over more than 2,000 square kilometres and knocked people off their feet far away. When scientists finally reached the site, there was no crater.
At about 7:14 local time on 30 June 1908, people northwest of Lake Baikal saw a bluish light, almost as bright as the Sun, streak across the sky, followed by a flash and a sound like artillery. The shock wave broke windows hundreds of kilometres away and registered on instruments across Eurasia and as far as Washington, D.C. For several nights afterwards, skies over Europe and Asia glowed so brightly that people reportedly took photographs at midnight without a flash.
It was the largest impact event in recorded history, with an energy estimated at somewhere between 3 and 50 megatons of TNT. The leading explanation is an air burst: a stony asteroid perhaps 50 to 60 metres wide, travelling at around 27 kilometres per second, that blew apart 5 to 10 kilometres above the ground. Because the region was so remote, eyewitness accounts suggest only up to three people may have died.
Russia's turmoil and the area's isolation meant no scientist reached the heart of the site until Leonid Kulik's 1927 expedition. Expecting a crater, his team found instead a zone where trees stood upright but stripped of branches, surrounded by a vast radial pattern of felled trunks pointing away from the centre. Later surveys mapped a butterfly-shaped area of flattened forest about 2,150 square kilometres in size. The often-repeated figure of 80 million trees felled rests on an early estimate that probably overstated the damaged area about fourfold.
Whether the object was an asteroid or a comet has been argued for a century. Comet supporters point to the glowing night skies; others note that a fragile comet should have broken up higher, and tiny particles found in tree resin resemble rocky asteroid material. Explosions this size are rare, perhaps once every few centuries to once in a thousand years, but one over a city would be devastating.
Source: Wikipedia — Tunguska event · Text summarised from Wikipedia (CC BY-SA 4.0)
