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Fun Facts About the Vredefort Crater

Born and raised in South Africa, Jana loves sharing the unique and special aspects about her home turf with the world.

only-in-south-africa-the-vredefort-crater

X Marks the Smash

Around 2,023 million years ago, a rock tumbled through space towards Earth. It was mountain-sized and measured approximately 10 kilometres (6.21 miles) across.

When it hit baby Africa, the meteorite was travelling at around 10 kilometres a second. The impact was mind-blowingly violent. As the world's biggest known energy-release event, it gauged a footprint 300 kilometres (185 miles) long and ten times deeper than the Grand Canyon.

Today, it can be found in South Africa's Free State province and the site is anything but dead. Apart from a lively tourist trade, the crater has its own inhabitants. Near the epicentre stands the town of Vredefort, home to around 15,000 people.

What Makes it Unique?

Compared to the other planets and moons in the solar system, Earth is remarkably free of craters. Only around 130 have been confirmed. No doubt more lies undiscovered but most were erased by geological processes such as erosion, volcanic activity and tectonics.

4 Reasons the Vredefort Site Is Special

  1. The Size and Age
  2. The Zircon Debate
  3. The Astrobleme Profile
  4. The Russian Connection
Vredefort was once huge—erosion made the crater a lot smaller but its original size is remarkable.

Vredefort was once huge—erosion made the crater a lot smaller but its original size is remarkable.

1. It Remains the Biggest and Oldest Crater

The Vredefort crater used to be a lot bigger. A lot. But centuries of erosion shrunk it to a radius of 190 kilometres (118 miles). Despite losing most of its original size, the Vredefort crater remains the world's oldest and largest impact site. Interestingly, the erosion also made it the deepest.

2. The Zircon Debate

After the meteorite hit, the immense heat melted the Earth's crust. A sea of magma, or melted rock, swelled up and filled the new crater. Scientists believed that all signs of this “lava ocean” have long since disappeared.

In the 1990s, a geochronologist named Desmond Moser was inside the crater, just doing what geochronologists do—trying to put a finer detail on the age of geological things. In this case, Moser wanted to narrow down the crater's age when he accidentally found a mineral called zircon.

The green-black rocks sparked a debate that rages to this day. Moser and like-minded researchers believed that the minerals are the only remains of the lost magma sea. They were found inside a rock called gabbronorite, which allegedly crystallized from local rock melted inside the magma and not the actual impact. However, not everyone is happy with the idea. Though the zircon minerals are both a lucky and rare find, some researchers feel that there isn't enough evidence to prove they didn't crystallize during the impact.

End of the Debate in Sight?

Science may, however, favour Camp Moser. A follow-up investigation yielded three positive clues that Moser had indeed found traces of the sea.

  • The distribution of zircon was random and interconnected with other kinds of minerals, an unlikely scene had they formed later than other types of minerals which were present before the impact
  • The zircons also crystallized at 725-928 Celsius (1,337-1,702 Fahrenheit). The same temperature range was identified at the Sudbury impact melt, a crater slightly younger and smaller than Vredefort
  • The presence of the element hafnium was a strong indication that the magma came from surface rocks and didn't well up from inside the Earth's crust.
An example of what zircon looks like (not those found at Vredefort).

An example of what zircon looks like (not those found at Vredefort).

3. The Only Complete Astrobleme Profile

In geological terms, the crater is also an astrobleme—the eroded remnant of an impact. Thus far, the Vredefort crater remains the only impact site with the complete geological profile of an astrobleme below the crater floor. These layers can one day help researchers understand how craters are formed during, and immediately after, the collision that shaped it.

4. The Russian Connection

When the meteorite violently connected with the planet's surface, not all of its consequences drove down into the earth. Some of them went up.

A cloud of particles was forced into the air by the powerful blast. The particles travelled 2,500 kilometres (1,550 miles) before they rained down on future Scandinavia and northwest Russia.

In modern times, scientists thought that the tiny spheres were mistaken ooids, something that forms in tropical waters. Further investigation, however, proved they were impact debris. The particles contained platinum and ruthenium, which are both rare elements that are linked to space. The spheres were also found in rock roughly dating back to the Vredefort event. However, scientists are keeping an open mind—another impact could also be responsible for the tiny rocks.

Did You Know?

  • The site has UNESCO status.
  • It's South Africa's seventh World Heritage Site.
  • The asteroid behind the Vredefort crater is believed to one of the largest to ever hit Earth.
  • There are around 100 plant species inside the dome, more than 70 kinds of butterflies and 300 species of birds.
  • The devastating global effects of the Vredefort event is believed by some scientists to have caused major evolutionary changes.
  • The unusual layered appearance of the crater's impact melt could help to identify older craters, especially those known only from faraway particles blasted into the air (if the Russian spheres did not come from the Vredefort incident, this would be one of those missing craters).

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2018 Jana Louise Smit

Comments

Devika Primić from Dubrovnik, Croatia on August 12, 2018:

Interesting to me and as a South African i find this fascinating and and must see when in South Africa.

Jana Louise Smit (author) from South Africa on August 12, 2018:

Visiting Vredefort is on my dream list as well :) Thanks for reading!

Jana Louise Smit (author) from South Africa on August 12, 2018:

Thank you, Liz!

Linda Crampton from British Columbia, Canada on August 07, 2018:

This sounds like it would be a very interesting place to visit. If I'm ever able to visit South Africa I'll make sure that I go to the dome.

Liz Westwood from UK on August 07, 2018:

This is a very detailed and interesting article.

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