| Vredefort Dome * | |
|---|---|
| Country | South Africa |
| Type | Natural |
| Criteria | viii |
| Reference | 1162 |
| Region ** | Africa |
| Inscription history | |
| Inscription | 2005 (29th Session) |
| * Name as inscribed on World Heritage List ** Region as classified by UNESCO |
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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.
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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). The asteroid is thought to have been approximately 5–10 km (3.1–6.2 mi) in diameter.[3]
The crater has a diameter of roughly 250–300 km (160–190 mi),[2] larger than the 200 km (120 mi) Sudbury Basin and the 170 km (110 mi) Chicxulub crater. This makes Vredefort the largest known impact structure on Earth. If the Wilkes Land crater in Antarctica is an impact crater then it is the largest known at 500 km (310 mi) diameter. The Vredefort crater's age is estimated to be 2,023 ± 4 million years. It hit 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.
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.
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