Vredefort crater
Vredefort crater is the largest verified impact crater on Earth.[1] That means we know for certain it was caused by an asteroid or meteorite strike.[2][3] The crater is in the Free State Province of South Africa.
| Vredefort Dome (centre) | |
 Vredefort Dome, seen from space by STS-51-I | |
| Impact crater/structure | |
|---|---|
| Confidence | Confirmed |
| Diameter | 300 km (190 mi) |
| Age | 2,023 ± 4 mya Paleoproterozoic |
| Exposed | Yes |
| Drilled | Yes |
| Location | |
| Coordinates | 27°0′0″S 27°30′0″E / 27.00000°S 27.50000°ECoordinates: 27°0′0″S 27°30′0″E / 27.00000°S 27.50000°E |
| Country | South Africa |
| Province | Free State |
| Official name | Vredefort Dome |
| Includes |
|
| Criteria | Natural: (viii) |
| Reference | 1162 |
| Inscription | 2005 (29th Session) |
| Area | 30,000 ha (120 sq mi) |
In 2005, the Vredefort Dome was added to the list of UNESCO World Heritage Sites as a natural site of geologic interest.
Formation and structure
The asteroid that hit Vredefort was one of the largest ever to strike Earth since the Hadean eon. The Vredefort hit was some two billion years ago. The bolide is thought to have been about 5–10 km (3–6 miles) in diameter.
The crater has a diameter of roughly 250–300 km (160–190 mi),[3] 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 about two billion (109) years old, which puts it in the Palaeoproterozoic 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).
It was originally thought that the crater was formed by a volcanic explosion, but in the mid 1990s evidence showed that it was the site of a huge bolide impact.[4] 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 removed 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 bolide was big and fast enough to cause local volcanism. The BIC is where most of the world's known reserves of platinum group metals (PGMs) are found, while the Witwatersrand basin holds most of the known reserves of gold.
The Vredefort dome in the center of the crater is home to three towns: Parys, Vredefort and Koppies.
Vredefort Crater Media
Map of South Africa showing the location of the Vredefort Dome, the remains of a 2.023-billion-year-old impact structure. The interrupted line circle, 300 km (190 mi) in diameter, marks the extent of the original crater.
The view from the top of Aasvoëlkop in the heart of the Vredefort impact structure with the Vaal River and Venterskroon on its right in the background
A schematic diagram of a NE (left) to SW (right) cross-section through the 2.020-billion-year-old Vredefort impact structure and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is where the Witwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the impact structure's rim, on the left. Not to scale.
References
- ↑ It is sometimes called the Vredefort dome.
- ↑ Deep Impact - The Vredefort Dome. Earth Impact Database [1] Archived 2016-03-04 at the Wayback Machine
- ↑ 3.0 3.1 "Deep Impact - The Vredefort Dome". Hartebeesthoek Radio Astronomy Observatory. 2006-08-01. Retrieved 2007-09-19.
- ↑ Koeberl C. 1997. Impact cratering: The mineralogical and geochemical evidence. In: Proceedings, "The Ames structure and similar features", ed. K. Johnson and J. Campbell, Oklahoma Geological Survey Circular 100, 30-54 [2] Archived 2011-07-06 at the Wayback Machine
