Location of the event in Siberia (modern map)
|Event||Explosion in forest area (10–15 Mtons TNT)|
|Time||30 June 1908|
|Place||Podkamennaya Tunguska River in Siberia, Russian Empire|
|Effects||Flattening 2,000 km2 (770 sq mi) of forest|
|Damage||Mostly material damages to trees|
|Cause||Probable air burst of small asteroid or comet|
Tunguska event is the name for a very large mid-air explosion that occurred on 30 June 1908 in Siberia. Most eyewitnesses talk about one or more explosions that happened around 7:15 a.m. local time. The cause of these explosions is unknown, but a meteorite impact has been suggested as a likely cause. About 30 kilometres (19 mi) around the place where the event happened, trees were uprooted. In Wanwara, a small settlement, about 65 km (40 mi) away, windows and doors were smashed. It is estimated, that in an area of about 2,000 km2 (770 sq mi), the trees were uprooted. Over 500 km (311 mi) away, bright light was seen, and an earthquake was felt.
Today, it is believed that the event happened about 7 to 15 km (4.3 to 9.3 mi) above ground, at 0:14 UTC (7:14 a.m. local time).
Energy involved[change | change source]
What happened is called air burst today. At the time, the energy involved was estimated to be between 10 and 30 megatons of TNT, depending on the height in which the air burst happened. Simulations that have been done with modern computers have found that the energy involved was probably between 3 and 5 megatons of TNT. Taking 15 megatons, this would mean that the energy involved was 1.000 times that of the atomic bomb dropped on Hiroshima, in 1945. The shock wave is considered to be that of an earthquake with a magnitude of 5.0 on the Richter scale. For these reasons, the Tunguska event is considered the largest impact event on Earth in recorded history.
Expeditions to the area[change | change source]
At first, there was no interest in the event. Over a decade after the event, Leonid Kulik, a Russian mineralogist led an expedition to the area. In his expedition of 1921 and 1922, he only got to Kansk, which is 600 km (373 mi) away from the "epicenter" of the event. In 1927, Kulik reached the region where the event happened, in 1938 he ordered aerial photos be taken.
Kulik's expedition is the first recorded expedition to the area. Since then, there were many expeditions; over 1,000 articles have been published on the event; most of them are in Russian language.
There were two other expeditions to the area: one in 1958, the other in 1963.
Theories[change | change source]
Today, there is no definite explanation for what caused the explosions, or for what happened. There are different theories, though.
Meteorite explosion[change | change source]
A meteorite hit the area. The most probable is an asteroid or comet of low density, and a diameter of between 30 metres (98 ft) and 80 metres (260 ft). The object exploded in a height of 7 to 14 km above ground; for this reason there is no impact crater. The problem with this theory is that meteorites of this type usually do not reach low levels of the atmosphere. Meteoroids, which contain more iron have a higher chance of reaching low levels of the atmosphere, but they do not cause such devastating explosions.
Lake Cheko[change | change source]
Lake Cheko is a small freshwater lake, about 8 kilometres (5.0 mi) from the center of the event. The lake does not show on maps of the area which are older than about 1928. Before 1908, it seems to be unknown. The lake is rectangular; it is 708 metres long, 364 m wide, and about 50 m deep. In 1999, Luca Gasperini did a study on the sediments in the lake, and found that the lake predates the event of 1908.. In 2007, National Geographic cites him as he states that it is possible the lake formed as an impact crater.
Geophysical theories: Volcanic eruption[change | change source]
The other theory is that the event has a geophysical cause: About 10 million ton of natural gas exploding would have the effect that was observed. The problem with this theory is that eyewitnesses spoke of a very bright light that could be seen from very far away. A natural gas explosion does not produce a bright light.
References[change | change source]
- Ian Ridpath: "Tunguska: the final answer". Published in: New Scientist. 11 August 1977, Vol. 75, No. 1064, page 346.
- C. Gritzner: "Human Casualties in Impact Events". Published in: WGN, Journal of the International Meteor Organization. October 1997, Vol. 25:5, pp 222-226.
- Geophysical/sedimentological study of a lake close to the epicenter of the great 1908 Siberian (Tunguska) Explosion, NGF Abstracts and Proceedings, no. 1, 2001 : « Although the morphology of the lake is compatible with an impact origin, several sedimentological and biological proxies indicate that its formation pre-dates the 1908 event. »
- Maria Cristina Valsecchi (7 November 2007). "Crater from 1908 Russian Space Impact Found, Team Says". National Geographic.