The Vredefort Dome

A UNESCO world heritage site

Once upon a time

The Vredefort crater is the largest verified impact crater on Earth, more than 300 km across when it was formed. What remains of it is located in the present-day Free State Province of South Africa and named after the town of Vredefort, which is situated near its center. Although the crater itself has long since eroded away, the remaining geological structures at its center are known as the Vredefort Dome or Vredefort impact structure. The crater is estimated to be 2.023 billion years old, with impact being in the Paleoproterozoic Era. It is the second-oldest known crater on Earth. In 2005, the Vredefort Dome was added to the list of UNESCO World Heritage Sites for its geologic interest.

A large shooting star

The asteroid is estimated to have been one of the largest ever to strike Earth thought to have been approximately 10–15 km in diameter. The original crater was estimated to have a diameter of roughly 300 km, although this has been eroded away. The remaining structure, consists of a partial ring of hills 70 km in diameter, and are the remains of a dome created by the rebound of rock below the impact site after the collision.

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Long Time Ago

A timeline of the earth's history indicating when the Vredefort crater was formed in relation to some of the other important South African geological events. The graph also indicates the period during which banded ironstone formations were formed on earth, indicative of an oxygen-free atmosphere. The Earth's crust was wholly or partially molten during the Hadean Eon.

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What's left

The dome in the center of the crater was originally thought to have been formed by a volcanic explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River. The crater site is one of the few multiple-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 multiple-ring craters on Earth. A schematic diagram of a cross-section shows the impact crater and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is located where the Witwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.

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