Vredefort crater
| Vredefort Dome | |
|---|---|
| Name as inscribed on the World Heritage List | |
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| Country | South Africa |
| Type | Natural |
| Criteria | viii |
| Reference | 1162 |
| UNESCO region | Africa |
| Inscription history | |
| Inscription | 2005 (29th Session) |
Vredefort crater is the largest verified impact crater to have existed on Earth, more than 300 km across.[1][2] It was located in the present-day Free State Province of South Africa and named after the town of Vredefort, which is situated near its centre. While the crater itself has long since eroded away, remaining geological structures at its centre are 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.
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Formation and structure [edit]
The asteroid that hit Vredefort is estimated to have been one of the largest ever to strike Earth (at least since the Hadean eon some four billion years ago), thought to have been approximately 5–10 km (3.1–6.2 mi) in diameter. The bolide that created the Sudbury Basin could have been even larger.[3]
The original crater was estimated to have a diameter of roughly 300 km (190 mi),[2] although this has been eroded away. It would have been larger than the 250 km (160 mi) Sudbury Basin and the 180 km (110 mi) Chicxulub Crater. The remaining structure, the "Vredefort Dome", consists of a partial ring of hills 70 km in diameter, and are the remains of a dome created by the rebound of rock below the impact site after the collision.
The crater's age is estimated to be 2.023 billion years (± 4 million years),[1] which places it in 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. In comparison, it is about 10% older than the Sudbury Basin impact (at 1.849 billion years).
The dome in the center of the crater was originally thought to have been formed by a volcanic explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River.
The crater site is one of the few multiple-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 multiple-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, while the Witwatersrand basin holds most of the known reserves of gold.
Conservation [edit]
The Vredefort Dome World Heritage Site is currently subject to property development, and local owners have expressed concern regarding sewage dumping into the Vaal River and the crater site.[4] The granting of prospecting rights around the edges of the crater has led environmental interests to express fear of destructive mining.
Community [edit]
The Vredefort Dome in the center of the crater is home to three towns, namely Parys, Vredefort and Koppies. Parys is the largest and a tourist hub; both Vredefort and Koppies mainly depend on an agricultural economy.
On 19 December 2011, a broadcasting license was granted by ICASA to a community radio station to broadcast for the Afrikaans- and English-speaking members of the communities within the crater. The Afrikaans name Koepel Stereo (Dome Stereo) refers to the dome and announces its broadcast as KSFM. The station broadcasts on 94.9 MHz FM.
References [edit]
- ^ a b "Vredefort". Earth Impact Database. University of New Brunswick. Retrieved 2008-12-30.
- ^ a b "Deep Impact - The Vredefort Dome". Hartebeesthoek Radio Astronomy Observatory. 2006-08-01. Retrieved 2007-09-19.
- ^ "The Vredefort Dome: Centre of the World's Largest Meteorite Impact Structure!". Retrieved December 2012.
- ^ Momberg, Eleanor (23 August 2009). "River heading for the rocks". Retrieved March 2011.
External links [edit]
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Wikimedia Commons has media related to: Vredefort |
- Impact Cratering Research Group- University of the Witwatersrand
- Earth Impact Database
- Deep Impact - The Vredefort Dome
- Satellite image of Vredefort crater from Google Maps
- Impact Cratering: an overview of Mineralogical and Geochemical aspects - University of Vienna
- google earth 3d .KMZ of 25 largest craters (requires google earth)
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Coordinates: 27°0′S 27°30′E / 27.000°S 27.500°E
