slow down and so they hit the ground at very high speed. (An 3. The Dome is only the central part of the impact After the impact Visitors to the World Heritage Site that hits the is called a . Thousands of crater. It is called a dome because the rock layers were bent into In total, the Vredefort probably lasted less than 10 The Vredefort Dome represents a unique opportunity to celebrate 1 small have already been found around the world.) the shape of an upside-down bowl 90km across by the impact minutes, although the melted rocks would have taken millions of the history of our planet extending back thousands of millions of The damage caused when a meteorite collides with the Earth is (see Figures 2 and 4). years to cool down and become solid again. For a time it would years and to marvel at the devastating forces that have shaped our massive. The speed of a meteorite is so high that it explodes when If we could look inside the Earth (imagine that it has been cut have looked like the crater in Figure 3, from the . Over many world. Apart from the unusual rocks in the dome, the area also has it hits the ground, blasting a giant hole (a crater) and causing open so that we can look at it from the side and see the different hundreds of millions of years more, rivers eroded the sides of the important historical, cultural and archaeological sites recording ANEXPLANATIONOFTHE intense heat of many thousands of degrees Celcius that can even layers of rock that make the Earth's crust, and even part of crater and most of the cooled melt-rock. This exposed the rocks human habitation over the past 200 000 years, together with a VREDEFORTDOME melt rock. In this way, the meteorite itself is completely destroyed. Earth's mantle underneath), Figure 2 is a drawing that shows that once lay underneath the crater (see Figure 4). In the rich scenic beauty. what geologists think must have happened. updomed centre (the Vredefort Dome), these rocks still show This is what happened in the near and Vredefort Whether it is scientific curiosity, historical or cultural interest, WORLDHERITAGESITE signs of shattering and melting from the impact (see Figure 5). millions of years ago. The explosion was so great that it was many ecotourism or adventure activities, the Vredefort Dome has millions of times more powerful than the biggest atomic bomb ever something special to offer each visitor. Welcome to our WhatisaWorldHeritageSite? built on Earth. If it happened today it would kill almost all living wonderland! A World Heritage Site is a place that has special importance for the things on Earth, including most people. people of the world and that is worthy of preservation and protection for future generations. A site may be chosen because important events in human history occurred there (such as at or Mapungubwe) or scientifically because it 2 contains special plants or animals or rocks, or is scenically spectacular (such as the uKhahlamba/ Park). Only Figure 3 is a crater from the Moon showing what the Vredefort crater 830 places around the world have so far been chosen as World would have looked like 2023 million years ago, before it was eroded. Heritage Sites. On 14 July, 2005, part of the Vredefort Dome was The crater was so big that it would have stretched from declared 's seventh World Heritage Site. This brochure on one side to Welkom on the other side. The Vredefort Dome would explains why the Vredefort Dome is such an important site. have lain under the hills in the middle of the crater. (Image courtesy of NASA/JPL) Shooting stars and meteorite impacts The geology of the Vredefort Dome “ Figure 1 is a photograph of a 33 km long giant asteroid called Eros in If we look up into the sky on a dark night we often see shooting Today, the rocks in the Vredefort Dome are exposed in several ” Outer Space. It is full of impact craters caused by collisions with other stars . These are bright streaks of light that move very fast across smaller . (Image courtesy of NASA/JPL-Caltech) rings (see Figure 4). The oldest rocks that were buried deep Figure 4 shows the upturned rings of different rock layers in the the sky for only a few seconds before they disappear. They are not within the crust before the impact event are found in the centre. Vredefort Dome, with the oldest in the centre. These rings are real stars - the streaks of light are caused by tiny pieces of burning The Vredefort These are mostly granite gneisses more than 3000 million years covered in the South by younger coal-bearing rock layers that rock, flying faster than bullets, that enter Earth's atmosphere from The meteorite impact that happened in the Free State made a old. Parys and Vredefort towns are built on these gneisses that formed long after the impact. Outer Space. Because they are moving so fast (more than 10 km in crater that was about 300 km wide (from Johannesburg to have been mined for their stone in many quarries. The hills of the 1 second, which means they would take only 30 seconds to fly from Figure5shows3signsoftheVredefortimpactevent Welkom!). This is the biggest meteorite impact that geologists Vredefort mountainland are made of hard white quartzite rock, Parys to Bloemfontein!), when they enter the atmosphere they thatarefoundintherocksoftheVredefortDome. have yet found on Earth and it is nearly twice as big as the impact with the valleys in-between made of softer shale. Some thin start to burn. (This burning is caused by friction with the air. When Vredefort Granophyre that killed the dinosaurs 65 million years ago. This makes it a site layers containing a little were once mined from these rocks 1. is the name given to the black 3 you rub your hands together very fast, they also get hot. To melt of great importance for scientists. It is also the oldest impact near Venterskroon. Beyond the hills towards Potchefstroom and crystallized impact melt-rock that flowed into cracks in the rocks rock, though, the temperature must reach more than 1000 °C!) crater that has been found on Earth. It is mainly for these reasons Fochville lie softer lava and dolomite rocks that form flatter land. underneath the crater (see Figure 2). It contains broken pieces There are many, many millions of such small pieces of rock in Outer that it has been made a World Heritage Site. All these rocks form part of the Vredefort Dome and are steeply from many different rock types, as well as very small chemical Space, left over from when our Sun and the planets were formed. dipping, but to the south they are covered by horizontal shale traces of the meteorite that caused the impact. Over many decades, geologists from South Africa and other parts Thousands of them become shooting stars every day. But among layers that only formed long after the impact and that contain of the world have been studying the broken and melted rocks 2. Shatter cones, which look like part of an ice-cream cone with them are also larger pieces of rock, ranging from football size to some coal. around Parys and Vredefort to understand this Vredefort Impact lines on it, were formed when the rock was cracked by the force of some up to many kilometres across. These asteroids (see Figure 1) Event. This is what they have found: Where exactly is the World Heritage Site? the impact shock wave. also sometimes fall into the Earth's atmosphere, but not as often as the smaller pieces. When they do, they are too big to burn up or 1. The meteorite impact happened about 2023 million years ago, Only a small part of the Vredefort Dome along the Vaal River, 3. Black veins of another crystallized melt-rock called at a time when there were no people or even animals or plants like Figure 2 shows how the Vredefort crater formed. The meteorite between the Parys - Potchefstroom and Vredefort - pseudotachylite look like Granophyre impact melt-rock, but they we see today. The only living thing was a type of algae, like the exploded in a fireball as hot as 20 000 °C and brighter than the Potchefstroom roads, has been declared a World Heritage Site contain no meteorite traces and the rock fragments only come Prepared for the Free State Province Department of green slime seen in dams today. Sun. This blasted rock, dust and melted rock into the air but also from rocks that are found next to the veins. Geologists are still not pressed the rock underneath the crater violently downwards for a (see Figure 4). Because the site needs to be protected, people Tourism, Environmental and Economic Affairs by R.L. sure whether the pseudotachylite formed because of the intense Gibson, School of Geosciences, University of the 2. To make a crater 300 km wide, the meteorite must have been short time. When this rock bounced back a few minutes later, it living in this area need to get special permission to build any new . Copyright R.L. Gibson, 12/2006 about 10 km across (as big as a mountain) and traveling at more formed the Vredefort Dome. The Vredefort Dome is only the houses, roads and fences. However, the evidence of the impact shock heat, or because large blocks of rock slid past each other than 10 km per second (36 000 km/h!). central part of a much bigger crater. is spread in the rocks over a much wider area. and were heated by friction when the dome was forming.