TunGuSkaVideo: TunGuSka Explosion 1 of 3

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The Tunguska Event

The Tunguska Event, sometimes called the Tunguska explosion, was a massive explosion that occurred near the Podkamennaya (Lower Stony) Tunguska River in what is now Krasnoyarsk Krai of Russia, at around 7:17 a.m. on June 30, 1908 Julian (July 13 on Gregorian calendar).
The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometers (3–6 miles) above Earth's surface. Different studies yielded varying estimates for the object's size,[1] including 30 meters,[2] 50 metres,[3] 60 metres,[4] 90 to 190 metres,[5] and up to 1200 metres in diameter.[6] Although the meteor or comet is considered to have burst prior to hitting the surface, this event is still referred to as an impact event. Estimates on the energy of the blast include 3–5 megatons [7] and as high as 30 megatons[8] of TNT. 10–15 megatons has been considered the most likely to be accurate[8] — about 1,000 times more powerful than the bomb dropped on Hiroshima, Japan.[9] The explosion felled an estimated 80 million trees over 2,150 square kilometers (830 square miles). It is estimated to have measured 5.0 on the Richter scale.
The Tunguska event is the largest impact event in recent history. An explosion of this magnitude had the potential to devastate large metropolitan areas had it occurred over a large city.[10] This possibility has helped to spark discussion of asteroid deflection strategies.

History
There was little scientific curiosity about the impact at the time, possibly due to the isolation of the Tunguska region. If there were any early expeditions to the site, the records were likely lost during the subsequent chaotic years — World War I, the Russian Revolution of 1917, and the Russian Civil War.
The first recorded expedition arrived at the scene more than a decade after the event. In 1921, the Russian mineralogist Leonid Kulik, visiting the Podkamennaya Tunguska River basin as part of a survey for the Soviet Academy of Sciences, deduced from local accounts that the explosion had been caused by a giant meteorite impact. He persuaded the Soviet government to fund an expedition to the Tunguska region, based on the prospect of meteoric iron that could be salvaged to aid Soviet industry.

Photograph from the Soviet Academy of Science 1927 expedition led by Leonid Kulik.
Kulik's party reached the site in 1927. To their surprise, no crater was to be found. There was instead a region of scorched trees about 50 kilometres (30 miles) across. A few near ground zero were still strangely standing upright, their branches and bark stripped off. Those farther away had been knocked down in a direction away from the center.
During the next ten years there were three more expeditions to the area. Kulik found a little "pothole" bog that he thought might be the crater, but after a laborious exercise in draining the bog, he found there were old stumps on the bottom, ruling out the possibility that it was a crater. In 1938, Kulik arranged for an aerial photographic survey[16] of the area, which revealed that the event had knocked over trees in a huge butterfly-shaped pattern. Despite the large amount of devastation, there was no crater to be seen.
Expeditions sent to the area in the 1950s and 1960s found microscopic glass spheres in siftings of the soil. Chemical analysis showed that the spheres contained high proportions of nickel and iridium, which are found in high concentrations in meteorites, hinting that they were of extraterrestrial origin.
Detailed systematic eyewitness reports began to be gathered as late as 1959, when interviews were conducted with many of the indigenous people who had been within 100 kilometres (60 miles) of the explosion. Most of these accounts claimed that the local people had been covered with boils after the explosion, with whole families dying off.[citation needed] The medical scientists attached to the expedition concluded that there had been an epidemic of smallpox in the area at the time.[citation

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Monday, February 4, 2008

TunGuSka Explosion 1 of 3

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