The Vredefort Dome
The largest impact structure on Earth is so old and worn down that it shows only as a ring of hills.
What was reported
South-west of Johannesburg, around the towns of Vredefort and Parys, a curved ring of hills marks the remains of the largest confirmed impact structure on Earth. When it formed, the crater may have been around 250 to 300 km across.
For a long time geologists argued over whether the dome was volcanic or caused by an impact. Shocked quartz and shatter cones, rock features formed only by sudden, extreme pressure, settled it.
Explanations offered
An asteroid perhaps 10 to 15 km across struck around 2 billion years ago. Erosion has since removed the original crater, leaving its uplifted centre, the dome. It became a UNESCO World Heritage Site in 2005.
- When
- Impact about 2 billion years ago
- Where
- Vredefort, Free State, South Africa
- Witnesses
- Geologists
- Status
- Explained
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.