Tunguska meteorite, artwork. Depiction of the Tunguska meteorite approaching Siberia, Russia. In the early hours of 30 June 1908, a huge fireball was observed low in the sky over western Siberia. Shortly afterwards, an enormous explosion was heard. The explosion caused incredible damage, flattening over 3000 square kilometres of forests. The site of the explosion was near the town of Vanavara, in the Podkamennaya Tunguska River Valley. It is now thought that the event (estimated equivalence 2 million tonnes of TNT) was caused by a meteoroite about 50 metres in diameter breaking up and exploding in the atmosphere, although no major fragments or craters have been found.