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Coordinates: 27°0′S 27°30′E / 27.000°S 27.500°E / -27.000; 27.500
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==Formation and structure==
==Formation and structure==
The [[asteroid]] that hit Vredefort is one of the largest ever to strike Earth (at least since the [[Hadean]]) and is estimated at {{convert|5|–|10|km|mi|abbr=on}} wide.<ref>{{cite web
The [[asteroid]] that hit Vredefort is estimated to be one of the largest ever to strike Earth (at least since the [[Hadean]] eon some four billion years ago). The asteroid's size has been calculated to be approximately {{convert|5|–|10|km|mi|abbr=on}} wide.<ref>{{cite web
| title = The Vredefort Dome: Centre of the World's Largest Meteorite Impact Structure!
| title = The Vredefort Dome: Centre of the World's Largest Meteorite Impact Structure!
| url = http://www.parys.co.za/dome/index.html
| url = http://www.parys.co.za/dome/index.html
| accessdate = September 2010
| accessdate = September 2010
}}</ref>
⚫
}}</ref> The crater has a diameter of roughly 250–300&nbsp;km (155–186&nbsp;mi),<ref name="current record"/> larger than the 200&nbsp;km (124&nbsp;mi) [[Sudbury Basin]] and the 170&nbsp;km (106&nbsp;mi) [[Chicxulub crater]]. This makes Vredefort the largest known impact structure on Earth. (The [[Wilkes Land crater]] in Antarctica, if confirmed to be the result of an impact event, is even larger at 500 kilometers across.) The Vredefort crater's age is estimated to be more than 2 [[1000000000 (number)|billion]] years (2,023 ± 4 million years), striking during the [[Paleoproterozoic]] era. It is the second-oldest known crater on Earth, a little less than 300 million years younger than the [[Suavjärvi crater]] in Russia.


⚫
The crater has a diameter of roughly 250–300&nbsp;km (155–186&nbsp;mi),<ref name="current record"/> larger than the 200&nbsp;km (124&nbsp;mi) [[Sudbury Basin]] and the 170&nbsp;km (106&nbsp;mi) [[Chicxulub crater]]. This makes Vredefort the largest known impact structure on Earth. (The [[Wilkes Land crater]] in Antarctica, if confirmed to be the result of an impact event, is even larger at 500 kilometers across.) The Vredefort crater's age is estimated to be more than 2 [[1000000000 (number)|billion]] years (2,023 ± 4 million years), striking during the [[Paleoproterozoic]] era. It is the second-oldest known crater on Earth, a little less than 300 million years younger than the [[Suavjärvi crater]] in Russia.
⚫
It was originally thought that the [[dome]] in the center of the crater was formed by a [[volcano|volcanic]] explosion, but in the mid 1990s evidence revealed that it was the site of a huge bolide impact, as telltale [[shatter cone]]s are often discovered in the [[stream bed|bed]] of the nearby [[Vaal River]].

⚫
It was originally thought that the [[dome (geology)|dome]] in the center of the crater was formed by a [[volcano|volcanic]] explosion, but in the mid 1990s evidence revealed that it was the site of a huge bolide impact, as telltale [[shatter cone]]s were discovered in the [[stream bed|bed]] of the nearby [[Vaal River]].


The Vredefort crater site is one of the few multi-ringed [[impact crater]]s on Earth, although they are more common elsewhere in the [[Solar System]]. Perhaps the best-known example is [[Valhalla (crater)|Valhalla crater]] on [[Jupiter]]'s moon [[Callisto (moon)|Callisto]], although Earth's [[Moon]] has a number as well. Geological processes, such as [[erosion]] and [[plate tectonics]], have destroyed most multi-ring craters on Earth.
The Vredefort crater site is one of the few multi-ringed [[impact crater]]s on Earth, although they are more common elsewhere in the [[Solar System]]. Perhaps the best-known example is [[Valhalla (crater)|Valhalla crater]] on [[Jupiter]]'s moon [[Callisto (moon)|Callisto]], although Earth's [[Moon]] has a number as well. Geological processes, such as [[erosion]] and [[plate tectonics]], have destroyed most multi-ring craters on Earth.
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The nearby [[Bushveld Igneous Complex]] (BIC) and [[Witwatersrand Basin]] were created during this same period, leading to speculation that the Vredefort bolide's mass and kinetics were of sufficient magnitude to induce regional volcanism. The BIC is the location of most of the world's known reserves of [[platinum group metals]] (PGMs), while the Witwatersrand basin holds most of the known reserves of gold.
The nearby [[Bushveld Igneous Complex]] (BIC) and [[Witwatersrand Basin]] were created during this same period, leading to speculation that the Vredefort bolide's mass and kinetics were of sufficient magnitude to induce regional volcanism. The BIC is the location of most of the world's known reserves of [[platinum group metals]] (PGMs), while the Witwatersrand basin holds most of the known reserves of gold.


==Threats to the site==
⚫
The Vredefort Dome World Heritage Site is currently facing threats from unstructured property developments and the Parys Sewage Treatment Plant, which are in a dilapidated state and are pumping untreated sewage into the Vaal River and the crater site.{{Citation needed|date=October 2009}}

[[Image:Vredefort crater.jpg|right|thumb|200px|Monochrome satellite view of the crater]]
[[Image:Vredefort crater.jpg|right|thumb|200px|Monochrome satellite view of the crater]]
⚫
The Vredefort Dome World Heritage Site is currently facing threats from unstructured property developments and sewage dumping into the Vaal River and the crater site.<ref>{{cite web

| title = River heading for the rocks
==See also==
| date = 23 August 2009
*[[Wilkes Land crater]]
| author = Momberg, Eleanor
*[[Bushveld Igneous Complex]]
| url = http://www.iol.co.za/news/south-africa/river-heading-for-the-rocks-1.456012
| accessdate = March 2011
}}</ref> The granting of prospecting rights around the edges of the crater have led to fears of destructive mining.


==References==
==References==

Revision as of 23:38, 21 March 2011

Vredefort Dome
UNESCO World Heritage Site
The multi-ringed Vredefort crater
CriteriaNatural: viii
Reference1162
Inscription2005 (29th Session)

Vredefort crater is the largest verified impact crater on Earth.[1][2] It is located in the Free State Province of South Africa and named after the town of Vredefort, which is situated near its centre. The site is also known as the Vredefort dome or Vredefort impact structure. In 2005, the Vredefort Dome was added to the list of UNESCO World Heritage Sites for its geologic interest.

Formation and structure

The asteroid that hit Vredefort is estimated to be one of the largest ever to strike Earth (at least since the Hadean eon some four billion years ago). The asteroid's size has been calculated to be approximately 5–10 km (3.1–6.2 mi) wide.[3]

The crater has a diameter of roughly 250–300 km (155–186 mi),[2] larger than the 200 km (124 mi) Sudbury Basin and the 170 km (106 mi) Chicxulub crater. This makes Vredefort the largest known impact structure on Earth. (The Wilkes Land crater in Antarctica, if confirmed to be the result of an impact event, is even larger at 500 kilometers across.) The Vredefort crater's age is estimated to be more than 2 billion years (2,023 ± 4 million years), striking during the Paleoproterozoic era. It is the second-oldest known crater on Earth, a little less than 300 million years younger than the Suavjärvi crater in Russia.

It was originally thought that the dome in the center of the crater was formed by a volcanic explosion, but in the mid 1990s evidence revealed that it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River.

The Vredefort crater site is one of the few multi-ringed impact craters on Earth, although they are more common elsewhere in the Solar System. Perhaps the best-known example is Valhalla crater on Jupiter's moon Callisto, although Earth's Moon has a number as well. Geological processes, such as erosion and plate tectonics, have destroyed most multi-ring craters on Earth.

The nearby Bushveld Igneous Complex (BIC) and Witwatersrand Basin were created during this same period, leading to speculation that the Vredefort bolide's mass and kinetics were of sufficient magnitude to induce regional volcanism. The BIC is the location of most of the world's known reserves of platinum group metals (PGMs), while the Witwatersrand basin holds most of the known reserves of gold.

Threats to the site

Monochrome satellite view of the crater

The Vredefort Dome World Heritage Site is currently facing threats from unstructured property developments and sewage dumping into the Vaal River and the crater site.[4] The granting of prospecting rights around the edges of the crater have led to fears of destructive mining.

References

  1. ^ "Vredefort". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton. Retrieved 2008-12-30.
  2. ^ a b "Deep Impact - The Vredefort Dome". Hartebeesthoek Radio Astronomy Observatory. 2006-08-01. Retrieved 2007-09-19.
  3. ^ "The Vredefort Dome: Centre of the World's Largest Meteorite Impact Structure!". Retrieved September 2010. {{cite web}}: Check date values in: |accessdate= (help)
  4. ^ Momberg, Eleanor (23 August 2009). "River heading for the rocks". Retrieved March 2011. {{cite web}}: Check date values in: |accessdate= (help)
Wikimedia Commons has media related to Vredefort.

27°0′S 27°30′E / 27.000°S 27.500°E / -27.000; 27.500

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