|The Tunguska Event
Largest Impact Event over Land in Earth's Recent History
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, on June 30, 1908.
The leading scientific explanation for the explosion is the airburst of a meteoroid 6–10 kilometres (4–6 miles) above Earth's surface.
The U.S. Air Force's Defense Support Program indicate that such explosions occur high in the upper atmosphere more than once a year.
Although, Tunguska-like megaton-range events are much rarer and it is estimated that such events occur about once every 300 years.
The explosion is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3–6 miles) above the Earth's surface.
At around 7:17 a.m. local time, Tungus natives and Russian settlers in the hills northwest of Lake Baikal observed a column of bluish light, nearly as bright as the Sun, moving across the sky. About 10 minutes later, there was a flash and a sound similar to artillery fire.
Eyewitnesses closer to the explosion reported the sound source moving east to north. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away.
The majority of witnesses reported only the sounds and the tremors, and not the sighting of the explosion.
Eyewitness accounts differ as to the sequence of events and their overall duration. The explosion registered on seismic stations across Eurasia.
In some places the shock wave would have been equivalent to an earthquake of 5.0 on the Richter scale. It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain.
Over the next few days, night skies in Asia and Europe were aglow; it has been theorized that this was due to light passing through high-altitude ice particles formed at extremely cold temperatures, a phenomenon that occurred when the Space Shuttle re-entered the Earth's atmosphere.
In the United States, the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a decrease in atmospheric transparency that lasted for several months, from suspended dust.
Different studies have yielded varying estimates of the object's size, with general agreement that it was a few tens of metres across. The number of scholarly publications on the problem of the Tunguska explosion since 1908 may be estimated at about 1,000 (mainly in Russian).
Many scientists have participated in Tunguska studies, the best-known of them being Leonid Kulik, Yevgeny Krinov, Kirill Florensky, Nikolai Vladimirovic Vasily, and Wilhelm Fast. Various explanations have been discussed on what may have
caused such an event. These explanations range from comets, asteroids,
crashed UFOs, black holes, antimatter and a meteoroid airburst.
The leading scientific explanation for the explosion is the airburst of a meteoroid 6–10 kilometres (4–6 miles) above Earth's surface. Meteoroids enter Earth's atmosphere from outer space every day, usually travelling at a speed of more than 10 kilometres per second (6 miles/sec or 21,600 mph).
The Lost Archives: Tunguska
The Russian Roswell?
In Phenomenon: The Lost Archives –– Tunguska, the Russian Roswell,
viewers investigate the destruction of 200 square miles of Siberian
forest just prior to the Russian Revolution in 1908.
Was it, in fact,
the impact of an asteroid that caused the explosion? Or was it the crash
site of a UFO?
The heat generated by compression of air in front of the body (ram pressure) as it travels through the atmosphere is immense and most meteoroids burn up or explode before they reach the ground.
Since the second half of the 20th century, close monitoring of Earth's atmosphere has led to the discovery that such meteoroid airbursts occur rather frequently.
A stony meteoroid of about 10 metres (30 ft) in diameter can produce an explosion of around 20 kilotons, similar to that of the Fat Man bomb dropped on Nagasaki, and data released by the U.S. Air Force's Defense Support Program indicate that such explosions occur high in the upper atmosphere more than once a year.
Chemical analysis of peat bogs from the area revealed numerous anomalies considered consistent with an impact event.
The isotopic signatures of stable carbon, hydrogen, and nitrogen isotopes at the layer of the bogs corresponding to 1908 were found to be inconsistent with the isotopic ratios measured in the adjacent layers, and this abnormality was not found in bogs located outside the area.
The region of the bogs showing these anomalous signatures also contains an unusually high proportion of iridium, similar to the iridium layer found in the K–T boundary. These unusual proportions are believed to result from debris from the impacting body that deposited in the bogs. The nitrogen is believed to have been deposited as acid rain, a suspected fallout from the explosion.
Tunguska-like megaton-range events are much rarer. Eugene Shoemaker estimated that such events occur about once every 300 years.
Although the meteoroid or comet burst in the air rather than hitting the surface, this event is still referred to as an impact.
Estimates of the energy of the blast range from 5 to as high as 30 megatons of TNT with 10–15 megatons of TNT the most likely—roughly equal to the United States' Castle Bravo thermonuclear bomb tested on March 1, 1954, about 1,000 times more powerful than the atomic bomb dropped on Hiroshima, Japan, and about one-third the power of the Tsar Bomba, the largest nuclear weapon ever detonated.
The explosion knocked over an estimated 80 million trees covering 2,150 square kilometres (830 sq miles). It is estimated that the shock wave from the blast would have measured 5.0 on the Richter scale. An explosion of this magnitude is capable of destroying a large metropolitan area.
This possibility has helped to spark discussion of asteroid deflection strategies. The Tunguska event is the largest impact event over land in Earth's recent history. Impacts of similar size over remote ocean areas would most likely have gone unnoticed before the advent of global satellite monitoring in the 1960s and 1970s.