At around 7:17am of the 30th of June 1908 near the Podkamennaya Tunguska River in Siberia, Russia a gigantic explosion took place. The force of the blast flattened around 80 million trees, and cleared an area more than 2,100 square kilometres (800 square miles) in size. For many years after this devastating impact, the true cause of the blast remained entirely unknown.