Tunguska Event

    The Tunguska event was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai,Russia, on June 30, 1908. Tunguska is the site of the largest-ever recorded explosion of a space object plunging to Earth. That blast is generally estimated to have been about 10 megatons. No injuries were reported, but some 80 million trees over 830 square miles were leveled in the blast. Scientists calculated the Tunguska explosion could have been roughly as strong as 20 megatons of TNT, or roughly 1,000 times more powerful than the atomic bomb dropped on Hiroshima. Dust from the explosion even hovered over Europe, reflecting light that was bright enough for Londoners to read at night by it! Because of the blast zone's remote location and the intrusion of worldly affairs (Aka WWI and the Russian Revolution), it wasn't until the 1920s that the first scientific expedition was sent to examine the area. Assuming that the blast had been caused by a falling meteor, the expedition expected to find a huge crater as well as pieces of the meteorite. They found neither. In the decades since this huge explosion, scientists and others have attempted to explain the cause of this mysterious event. The most commonly accepted scientific explanation now, is that either a meteor or a comet entered the Earth's atmosphere and exploded a couple of miles above the ground (which explains the lack of impact crater). Over a hundred years later, the exact cause of the Tunguska Event still remains a mystery. However, if the blast was in fact caused by a comet or meteor entering the Earth's atmosphere, it poses the serious possibility that in the future a similar meteor could once again enter Earth's atmosphere, but this time land on a populated area. The result would of that be catastrophic!
http://www.icr.org/research/index/researchp_sa_r05/