Vredefort
The largest impact structure known on Earth.
Key facts
- When
- about 2.02 billion years ago
- Where
- Free State, near Johannesburg, South Africa
- What hit
- an asteroid probably 15 to 25 km across
- Era
- Deep time
- Location
- 27.00° S, 27.50° E
Very roughly several hundred million megatons of TNT, and possibly more: larger than Chicxulub.
Several times the Chicxulub impact; the original crater may have been about 250 to 300 km wide.
What happened
Vredefort is the biggest impact scar on our planet. The original crater, now worn down by about 2 billion years of erosion, may have spanned 250 to 300 km. What remains is the Vredefort Dome, the rebounded centre of the crater, where rock from deep in the crust was pushed up to the surface, and an arc of hills around it.
Earlier estimates gave the impactor a size of about 10 km. Studies published in the 2020s, modelling how the crater collapsed, suggest it may have been 20 to 25 km across and travelling at about 15 to 20 km per second.
Our full page on the crater describes what you can see there today.
Effects
At the time, life on Earth was entirely microbial and oxygen had only recently begun to build up in the air, so there was no mass extinction of animals to record. The blast would still have caused worldwide effects, including dust, heating and tsunamis.
The evidence
Shatter cones, shocked quartz, high-pressure minerals and veins of rock melted by friction, known locally as pseudotachylite, are found throughout the dome. Its rings and uplifted centre match the pattern of a giant impact crater.
Did you know?
Vredefort became a UNESCO World Heritage Site in 2005.
The impact helped preserve the rich gold deposits of the Witwatersrand basin nearby by pushing them down out of reach of erosion.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.