The world’s oldest and largest visible blast crater – probably caused by an asteroid impact – is centred on the Vredefort Dome, also known as the Vredefort Ring, or Structure. This is situated in central South Africa and its semi-circular shape is a remarkable feature of the landscape.
The blast occurred some 2.023 billion years ago (give or take a few million years). That is nearly half the age of the Earth, and today the crater is deeply eroded. The town of Vredefort is closest to the centre and has thus given its name to the feature, while Parys on the Vaal is the main tourism drawcard.
The “Dome” is not the crater, only the core of it. The Dome itself represents the central uplift, or upheaval dome, which rushed up to fill the hole made by the impactor. The central uplift is where molten granite surged up from below like a champagne cork popping out of a bottle, forming a plug. The Dome then collapsed to form the central depression. For a more detailed explanation of the Dome’s structure, with illustrations, read the Frequently Asked Questions. The article below is a summary of the main topics covered by this website.
In 2005, Unesco declared part of the structure as the Vredefort Dome World Heritage Site (WHS). Of the entire vast crater, some 260-300km across, only part of the central portion forms the WHS. The land is mostly in private hands and will be legally protected under the Protected Areas Act when government finally passes regulations for the area.
This site contains extensive background information and links to articles, books and videos. We are also on Facebook and Twitter for alerts. If you’d like to know more, contact us at Otters’ Haunt for the full briefing and location visits. We are the most up-to-date information centre in the area, specialising in briefings, excursions, research and publishing about the Dome.
Also see Frequently Asked Questions.
Major Dome themes
The Dome attracts scientists, students and the general public from all over the world for a great variety of reasons.
PLANETARY SCIENCE: Geology has made the Dome famous, not only because the crater is the biggest we can see on Earth, but because erosion has exposed the deep structure of a what is a complex and fascinating planetary science phenomenon.
CONTROVERSY: Despite its status as a WHS and the fact that it has been extensively studied, much remains puzzling about the Dome. A few scientists believe that the Vredefort structure was not caused by an asteroid strike but by a “cryptoexplosion” or “Verneshot” from within the crust of the earth. This seems unlikely but debates continue. There are several other issues in dispute – for example, how South Africa’s gold came to be so concentrated in the outer ring of the crater. The study of the Dome remains hugely interesting with new findings being produced every year.
GOLD: Most importantly from an economic aspect, the outer edge of the Dome – the so-called Arc of Gold marking the goldfields of the Witwatersrand and Free State – is directly a product of the Dome’s geology. The asteroid did not bring the gold, but the impact appears to have buried the gold-bearing reefs deep down. Gold would no longer have been found here (it would have eroded away) without the explosion which upended the gold-bearing strata and preserved the precious metal deep down for later mining.
LIFE & EXTINCTIONS: The crater is also notable for what it tells us about the evolution of life from simple bacteria which lie fossilised in rocks adjacent to the Dome. The birth of life, the creation of our atmosphere, and speculation about extinctions in the course of evolution, can all be discussed with reference to evidence in and around the Dome.
VAAL RIVER: The Vaal River is a notable feature, although much younger than the Dome. It is unique in being the only major river on Earth to flow through an impact crater – the biggest crater, at that. The Vaal itself is a very ancient Karoo system river whose watercourse has cut many channels in the underlying Dome granites, forming many islands which host a great variety of riverine wildlife.
HUMAN HISTORY: This landscape was certainly where primitive humans roamed in the course of our own evolution. Another WHS, the Cradle of Humankind, lies just to the north of the Dome and both regions shared the same grassland features where early humans are thought to have first emerged. The reason why no palaeontological remains of early man have been found here is that the Dome contains no limestone caves in which these remains could have been preserved.
BATTLEFIELDS: The entire crater from Johannesburg to Welkom is rich in archaeology and more recent history, with a great number of battlefields covering several epochs of conflict between tribes, nations and races. The region can truly be described as the central cauldron of South African history because this is where people from Africa and the world have struggled for possession and dominance over land and mineral wealth.
EDUCATION: many school and university groups come to the Dome to study geology, astronomy, geography, ecology and history. For youngsters, it is fascinating to hear about the forces of the blast and to speculate on when it is going to happen again.
ECOTOURISM: The area is extremely scenic with its peculiar ring of mountains, the Bergland, and the picturesque Vaal River running through it. Ecotourism in all its forms is flourishing, as the Dome attracts visitors who come to enjoy its adventure offerings, from whitewater rafting to horse-riding and hiking.