Geography and climate

The world's biggest meteor crater

Two billion years ago a meteorite 10km in diameter hit the earth about 100km southwest of Johannesburg, creating an enormous impact crater. This area, near Vredefort in the Free State, is now known as the Vredefort Dome.

It was voted South Africa's seventh World Heritage site at Unesco's 29th World Heritage Committee meeting in Durban in July 2005.

The meteorite, larger than Table Mountain, caused a thousand-megaton blast of energy. The impact would have vaporised about 70 cubic kilometres of rock - and may have increased the earth's oxygen levels to a degree that made the development of multicellular life possible.

The world has about 130 crater structures of possible impact origin. The Vredefort Dome is among the top three, and is the oldest and largest clearly visible meteorite impact site in the world.

The original crater, now eroded away, was probably 250 to 300 kilometres in diameter. It was larger than the Sudbury impact structure in Canada, about 200km in diameter.

At 2-billion years old, Vredefort is far older than the Chixculub structure in Mexico which, with an age of 65-million years, is the site of the impact that led to the extinction of the dinosaurs.

Vredefort's original impact scar measures 380km across and consists of three concentric circles of uplifted rock. They were created by the rebound of rock below the impact site when the asteroid hit. Most of these structures have eroded away and are no longer clearly visible.

The inner circle, measuring 180km, is still visible and can be seen in the beautiful range of hills near Parys and Vredefort. It is this area that was named a World Heritage site.

World Heritage in South Africa

Did you know that Table Mountain has more plant species than the British Isles? Or that the Vredefort Dome is the world's largest and oldest meteor impact crater? SA is home to seven Unesco World Heritage sites, places of "outstanding value to humanity".
Internationally, there are 851 World Heritage sites, in 141 countries. Africa has 77 sites and South Africa now a total of eight - four cultural, three natural and one of mixed cultural and natural heritage. The Vredefort Dome is a natural heritage site.

South Africa's other six World heritage sites are Robben Island, the Greater St Lucia Wetlands Park, the Mapungubwe Cultural Landscape, the Cradle of Humankind, the uKhahlamba Drakensberg Park and the Cape Floral Region.

"The Vredefort site is rich in the symbolic representation of our culture; it demonstrates the meeting between scientific and cultural philosophy and practice," Arts and Culture Minister Pallo Jordan said after the inscription of the site on the World Heritage list.

"At Vredefort, opportunities exist to engage in geological research and explore and understand more sensitively the rich culture of the Basotho, Batswana and Khoi-San and the early evidence of human cognitive and artistic endeavour their cultures boast.

"This demonstrates that heritage can be a tool for nation-building."

A map of the Vredefort Dome area A map of the Vredefort Dome area, clearly showing the topography of a large meteorite impact (Image: Council for Geoscience)

The Vredefort Conservancy

Further evidence of the meteorite impact site can be seen in the columns of granite that were injected into existing rock by the force and heat of impact.

In 1937, earth scientists John Boon and Claude Albritton Boon were the first to suggest that the Vredefort structure was the scar of an ancient meteorite impact. Since then the site has been studied extensively by earth scientists from around the world.

The Vredefort Dome Conservancy, as it is now known, is not just of scientific value. It also has great scenic beauty, making it an ideal tourist destination.

The Dome Conservancy contains a finely balanced ecosystem made up of open plains, bushveld, mountains and ravines with abundant flora and fauna. At least 99 plant species have already been identified, of which the world's largest olive wood tree forest is probably the best known.

The area is considered an important birding area, with over 450 species already identified. It also has as many identified butterflies as the whole of Great Britain, and is home to rare animals such as the rooikat, aardwolf, leopard and the endangered rock dassie.

The Vredefort Dome site fulfils all the criteria set by Unesco for a World Heritage site. It is of outstanding universal value from a scientific point of view, and is remarkable evidence of an important moment in the earth's geologic history.

Last updated: March 2008 SAinfo reporter

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Satellite image of the Vredefort Dome meteor impact crater Satellite image of the Vredefort Dome meteor impact crater (Photo: Lunar and Planetary Institute, Universities Space Research Association)  The inner circle of the Vredefort impact site is still visible and can be seen in the beautiful range of hills near Parys and Vredefort (Photo: The Dome Bergland Meander)  A cross-section of rock at the Vredefort Dome shows the dark grey granite that was melted by the impact and flowed, carrying chunks of unmelted granite within it. The vertical face seen here is two to three metres high (Photo: Hartebeesthoek Radio Astronomy Observatory)
South Africa's World Heritage sites

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