In search of South Africa’s meteor impact sites: craters and domes

AAs meteorites go, few come larger and more devastating than the 10km-wide chunk of space rock that hurtled towards Earth around 2-billion years ago, hitting the ground near what is today the town of Parys in South Africa’s Free State province. 

As it entered the atmosphere travelling at tens of thousands of kilometres per hour, the massive molten meteorite – larger than Table Mountain – exploded into the ground and shattered. It threw up a shower of rock, magma and dust that rained down over thousands of hectares, and the shockwaves rippled the landscape into concentric ridges for hundreds of kilometres around – some of which would form the Witwatersrand. 

It left a crater some 300km wide, and the dust that the impact threw up would have blanketed the planet for millennia, causing dramatic global cooling. 

In 2005, the Vredefort Dome – the rounded peak thrown up at the very centre of the impact by rebounding molten rock, which is the most visible remnant of the meteorite strike – became South Africa’s seventh World Heritage Site. Describing its global significance, the UNESCO World Heritage Site listing reads, ‘It is the site of the world’s greatest single known energy-release event.’ 

But the sheer size of the Vredefort crater surrounding the dome, not to mention 2-billion years of erosion and deposition, makes it hard to imagine the aftermath of the original impact. The most visible of the 4 major meteorite impact sites in South Africa lies 40km north of Pretoria and is called the Tswaing Crater. 

Tswaing, or ‘place of salt’ in Setswana (the language of the Tswana people), is a 1 946-hectare conservation area enclosing a crater caused by a relatively recent event – a much smaller meteorite between 30m and 50m wide that hit Earth less than 250 000 years ago. Just over a kilometre in diameter, the rim of the crater rises 100m high – in the centre is a small, salty lake from which the crater gets its name. 

Tswaing is a popular destination for birding enthusiasts, as it is located in dense African bush with a wetland nearby. 

The Kalkkop Crater in the Karoo in Eastern Cape, near Graaff-Reinet, is the impact site of another meteorite that hit Earth around 250 000 years ago. The impact left a crater 460m in diameter and more than 200m deep – evidence that it might have been somewhat smaller than the Tswaing meteorite, but travelling much faster. 

Located in the Kalahari Desert in North West province, the Morokweng Crater was formed around 145-million years ago and is estimated to be 70km in diameter. However, Morokweng is not visible from the Earth’s surface, and was only discovered in 1994 through magnetic and gravimetric surveys.