The mysterious aerial explosion occurred near the Tunguska River in Siberia, at about a quarter after seven on the morning of June 30, 1908, which felled an estimated 60 million trees over 2,150 square kilometres. Witnesses observed a huge fireball almost as bright as the Sun plunging across the Siberian sky, terminating in a huge explosion that registered on seismic stations all across Eurasia.
The size of the blast was later estimated to be between 10 and 15 megatons of TNT. The night sky had a strange orange glow as far away as Western Europe. The only proof that something happened was a quiver on a seismograph 1,000 miles away in the city of Irkutusk. Scientists did not come to the sight for another 19 years.
When they finally did come, what they saw was a place of utter devastation. They searched for a crater, a piece of an asteroid or meteorite but found nothing. They were able to find eyewitnesses in neighboring villages though. They recalled that there had been a fireball streaking through the sky, a horrifying noise, and an enormous blast. The parallel fallen trees indicate the direction of the blast wave.The first person to visit Tunguska was Leonid Kulik. When he first saw the vast area of charred trees, he thought that a huge fire had started all at once.
Kulik and his team photographed the area and searched for meteorite fragments but found nothing. Over the next 14 years, he lead four more expeditions to Tunguska, but turned up empty-handed. Kulik died in 1942 as a prisoner of war.
Since then, Russian scientists have gone to Tunguska every summer. One of the most useful things they did was map the entire 850 square mile region of tree fall. This task took them 35 years to do. This map has allowed scientist to calculate that the blast must have been four miles above the Earth with a force of 10 to 20 megatons of TNT. The precise cause of the explosion is still unexplained.