Vredefort Crater



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.

The asteroid that hit Vredefort is one of the largest ever to strike Earth (at least since the Hadean) and is estimated at 5 to 10 km (3.1 to 6.2 mi) wide[3]. The crater has a diameter of roughly 250 - 300 km (155 - 186 miles), larger than the 200 km (124 miles) Sudbury Basin and the 170 km (106 miles) 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 three hundred million years younger than the Suavjarvi crater in Russia.

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 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.




In the News ...


Vredefort Dome   Thunderbolts - November 4, 2010

The largest crater on Earth might not have been created by a meteor impact.

Africa exhibits some of the most complex terrain on Earth. As has been suggested in past Picture of the Day articles, Africa appears to have been devastated in the recent past. From the Sahara Desert in the North to the vast dune fields of Namibia in the South, African topography resembles images taken by spacecraft in orbit around Mars.

There is more to the Martian connection than sand, however. Mars is home to some of the largest craters in the Solar System, while Africa plays host to the largest crater on Earth, otherwise known as Vredefort Dome. The "dome" is supposed to be a "rebound peak" where rocks in the crater's center melted from impact, consolidated into a single mass, and then bounced back after the explosion, freezing into an upraised mound. A similar process is thought to have formed the central peaks that can be seen in many lunar craters.

Vredefort Dome is located about 100 kilometers southwest of Johannesburg. It has been classified by geologists as the oldest and largest astrobleme on Earth: approximately 300 kilometers wide, ten kilometers deep, and nearly two billion years old. One of the characteristics shared by Vredefort and craters on other planets and moons is that it is a multi-ringed structure.

Among their common features, multi-ringed circular formations possess flat inner plains with vertical cliffs, some of which rise several kilometers. The outer rim of Vredefort is said to have eroded away over the eons, explaining why the crater was identified as a volcanic dome for decades. The vertical walls, such as those found around Popigai Crater in Siberia, are missing. It is possible that the rim was scoured away by wind and rain, but from an Electric Universe perspective the crater may not have had a rim from the moment of its inception.

In the northwestern arc of Vredefort is a secondary plain with a deep outer perimeter, like a V-shaped canyon, that also resembles the morphology of other concentric rings. Surrounding the secondary plain is another ring of cliffs with a gradual drop-off extending outward from the central uplift. That pattern is repeated several times, with shorter cliffs and broader plains, until they finally merge into the bedrock.

Was it a gigantic block of stone that formed Vredefort? Did a 10-kilometer-wide meteor strike Africa and excavate the giant crater in an explosion orders of magnitude greater than that which is supposed to have killed-off the dinosaurs? Alternatively, as has been previously proposed, did an electric arc of unimaginable force travel through the region, vaporizing the terrain and blasting out a hole along the path of a sinuous channel known as the Vaal River?

Some Electric Universe theorists think that many of the large rivers and their tributaries around the world are secondary to whatever it was that carved the beds in which they flow. In other words, rivers have "adopted" paths of least resistance through the landscape rather than founding their own courses. In the case of Vredefort Dome, the Vaal River cuts through many tiers of mountains that lie across its path as if they were not there.

This anomaly is significant, since there is no known way for a river to punch through a wall of solid rock, leaving a deep canyon. The river should have naturally gone around the barrier or gathered into a lake, not eaten away square kilometers of the hardest basalt in a clean cut.

Another anomaly within the crater is the chaotic magnetic fields that have been detected in the surface rocks, reminiscent of the intense crustal magnetism found in and around large basins on Mars. According to Rodger Hart of the iThemba Laboratory for Accelerator Based Science in South Africa, Vredefort's magnetic fields were imprinted by strong electric currents flowing in the ionized gases generated by the energetic impact.

Mineral deformations, such as shattercones, requiring pressures and temperatures far exceeding anything seen on Earth today are put forward as evidence for the impact theory. Indeed, diamonds are abundant in the region, conforming to the consensus opinion. Downstream from the crater, the Vaal River is mined for diamonds. The pressure waves released by whatever caused the crater are thought to have compressed gneiss formations and instantaneously transformed them into diamond. The blast that created the gems also threw them hundreds of kilometers to the West, where they can be found in the riverbed.

As Wal Thornhill wrote several years ago:

"The kinds of things to watch for are pitting, surface glassification or a burnt appearance, damage caused by the explosive release of trapped gases, shock metamorphism, and isotopic and elemental anomalies....One thing to look for if shocked crystals are found and their orientation determined, is the direction from which the blast originated. Electrical cratering has a blast center that moves below ground and around the crater's center. An impact has a stationary blast center above ground that coincides with the crater's center. An example on Earth of shocked minerals oriented to a subterranean moving blast center can be found in the giant Vredefort Dome structure in South Africa."




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