Vredefort crater
Encyclopedia
Vredefort crater is the largest verified impact crater
on Earth. 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.
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 – in diameter.
The crater has a diameter of roughly 250–300 km (155.3–186.4 mi), larger than the 200 km (124.3 mi) Sudbury Basin
and the 170 km (105.6 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 (310.7 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 cone
s were discovered in the 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
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.
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
on Earth. It is located in the Free State Province of South Africa and named after the town of Vredefort
Vredefort
Vredefort is a small farming town in the Free State province of South Africa with cattle, peanuts, sorghum, sunflowers and maize being farmed. It is home to 3,000 residents....
, 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
UNESCO
The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations...
World Heritage Sites for its geologic interest.
Formation and structure
The asteroidAsteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
that hit Vredefort is estimated to have been one of the largest ever to strike Earth (at least since the Hadean
Hadean
The Hadean is the geologic eon before the Archean. It started with the formation of the Earth about 4.7 Ga and ended roughly 3.8 Ga, though the latter date varies according to different sources. The name "Hadean" derives from Hades, Greek for "Underworld", referring to the "hellish"...
eon some four billion years ago). The asteroid is thought to have been approximately 5 – in diameter.
The crater has a diameter of roughly 250–300 km (155.3–186.4 mi), larger than the 200 km (124.3 mi) Sudbury Basin
Sudbury Basin
The Sudbury Basin, also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geologic structure in Ontario, Canada. It is the second-largest known impact crater or astrobleme on Earth, as well as one of the oldest....
and the 170 km (105.6 mi) Chicxulub crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...
. This makes Vredefort the largest known impact structure on Earth. If the Wilkes Land crater
Wilkes Land crater
Wilkes Land crater is an informal term that may apply to two separate cases of conjectured giant impact craters hidden beneath the ice cap of Wilkes Land, East Antarctica...
in Antarctica is an impact crater then it is the largest known at 500 km (310.7 mi) diameter. The Vredefort crater's age is estimated to be 2,023 ± 4 million years. It hit during the Paleoproterozoic
Paleoproterozoic
The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
era. It is the second-oldest known crater on Earth, a little less than 300 million years younger than the Suavjärvi crater
Suavjärvi crater
Suavjärvi is a lake and impact crater in the Republic of Karelia, Russia about 50 km north of the town of Medvezhyegorsk...
in Russia.
It was originally thought that the dome
Dome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...
in the center of the crater was formed by a volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
explosion, but in the mid 1990s evidence revealed that it was the site of a huge bolide impact, as telltale shatter cone
Shatter cone
Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions...
s were discovered in the bed
Stream bed
A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...
of the nearby Vaal River
Vaal River
The Vaal River is the largest tributary of the Orange River in South Africa. The river has its source in the Drakensberg mountains in Mpumalanga, east of Johannesburg and about 30 km north of Ermelo and only about 240 km from the Indian Ocean. It then flows westwards to its conjunction...
.
The Vredefort crater site is one of the few multi-ringed impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s on Earth, although they are more common elsewhere in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. Perhaps the best-known example is Valhalla crater
Valhalla (crater)
Valhalla is the largest multi-ring structure on Jupiter's moon Callisto and in the Solar System. It was named after Valhalla, Odin's hall in Norse mythology. Valhalla consists of a bright central region 360 km across, an inner ridge and trough zone and striking concentric rings extending up...
on Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's moon Callisto
Callisto (moon)
Callisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
, although Earth's Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
has a number as well. Geological processes, such as erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, have destroyed most multi-ring craters on Earth.
The nearby Bushveld Igneous Complex
Bushveld igneous complex
The Bushveld Igneous Complex is a large layered igneous intrusion within the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin, the Transvaal Basin. Located in South Africa, the BIC contains some of the richest ore...
(BIC) and Witwatersrand Basin
Witwatersrand basin
The Witwatersrand Basin is a geological formation in South Africa holding the world's largest known gold reserves and having produced over 1.5 billion ounces. The basin straddles the old provinces of Transvaal and the Orange Free State and is of the same period as the Vredefort impact of 2.023 Ga...
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.
Conservation
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. The granting of prospecting rights around the edges of the crater has led environmental interests to express fear of destructive mining.External links
- 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)