there are some dissenters. Astrophysicist Wolfgang Kundt has proposed that the Tunguska event was caused by the release and subsequent explosion of 10 million tons of natural gas from within the Earth's crust. The basic idea is that natural gas leaked out of the crust and then rose to its equal-density height in the atmosphere; from there, it drifted downwind, in a sort of wick, which eventually found an ignition source such as lightning. Once the gas was ignited, the fire streaked along the wick, and then down to the source of the leak in the ground, whereupon there was an explosion. The similar verneshot hypothesis has also been proposed as a possible cause of the Tunguska event. Other research has proposed a geophysical mechanism for the event. Similar event A smaller air burst occurred over a populated area on 15 February 2013, at Chelyabinsk in the Ural district of Russia. The exploding meteoroid was determined to have been an asteroid that measured about across. It had an estimated initial mass of 11,000 tonnes and exploded with an energy release of approximately 500 kilotons. The air burst inflicted over 1,200 injuries, mainly from broken glass falling from windows shattered by its shock wave. In popular culture See also Asteroid Day, annual global event held on June 30 Patomskiy crater, about to the east-southeast Sikhote-Alin meteorite, 1947 impact Tunguska Nature Reserve, protected area covering a portion of the site; ongoing scientific study of forest recovery References Bibliography Baxter, John; Atkins, Thomas; introduction by Asimov, Isaac. The Fire Came By: The Riddle of the Great Siberian Explosion, (Garden City, New York (state)) Doubleday, 1976. . (New York) Warner Books, 1977. . (London) Macdonald and Jane's, 1975. . Bronshten, V. A. The Tunguska Meteorite: History of Investigations, (Moscow) A. D. Selyanov 2000 (in Russian). . Brown, John C.; Hughes, David. W. "Tunguska's comet and the non-thermal carbon-14 production in the atmosphere", Nature, Vol 268 (May) 1977 pp. 512–514. Chaikin, Andrew. "Target: Tunguska", Sky & Telescope, January 1984 pp. 18–21. The Kresak/Sekanina debate, in a very widely available journal. Cited in Verma. Christie, William H. "The great Siberian meteorite of 1908", The Griffith Observer, (Los Angeles) The Griffith Observatory, Vol 6 (April) 1942 pp. 38–47. This review is widely cited. Crowther, J. G. "More about the Great Siberian Meteorite", Scientific American, May 1931 pp. 314–317. Cited in Verma. Furneaux, Rupert. The Tungus Event: The