The Tunguska Event , or Tunguska explosion , was a powerful explosion that occurred not far from the PodkamennayaTunguska River in what is now Krasnoyarsk Krai in Russia, at 0 hours 13 minutes 35 seconds Greenwich Mean Time on June 30, 1908. Although the cause of the explosion is the subject of debate, it is commonly believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3.1–6.2 mi) above the Earth’s surface. Estimates of the energy of the blast range from 5 megatons of TNT to as high as 30 megatons of TNT with a decibel rating 300-315 making it the loudest sound known in the history of earth.