Caves and Sinkholes of South Africa

South Africa's cave systems owe their existence largely to dolomite, a type of rock that dissolves slowly when exposed to slightly acidic groundwater over long periods of time. Where dolomite bands run beneath the surface, particularly in parts of Gauteng, North West, Limpopo and Mpumalanga, this slow dissolution has carved out extensive underground chambers, passages and, in some cases, dramatic sinkholes.

How dolomite caves form

Rainwater absorbs small amounts of carbon dioxide as it falls and moves through soil, making it mildly acidic. As this water seeps into dolomite rock, it gradually dissolves the stone along cracks and weaknesses, widening them over thousands to millions of years into tunnels and chambers. Where water continues to drip from the ceiling of these chambers, it can deposit dissolved minerals again, slowly building the stalactites, stalagmites and flowstone formations that make many show caves so visually striking.

In some areas, the dissolution process removes so much underlying rock that the ground above can no longer support its own weight. When this happens suddenly, it produces a sinkhole, a steep-sided depression or shaft that can appear with little warning. In other cases, the process is gradual, leading to slow subsidence rather than a sudden collapse.

The Cradle of Humankind

One of the best known dolomite cave regions in South Africa lies within the Cradle of Humankind, a UNESCO World Heritage Site northwest of Johannesburg. The caves in this area, including Sterkfontein, have been excavated for decades and have produced some of the most significant fossil discoveries related to early human ancestors anywhere in the world. These caves are notable not just for their geology but for what they have revealed about human evolutionary history, which is why the area attracts both scientists and visitors.

Show caves in Mpumalanga

Further east, in the Mpumalanga escarpment region near the Blyde River Canyon, dolomite caves have been developed into guided show caves open to the public. These typically offer walkways through natural chambers, pointing out dripstone formations and explaining the geological processes behind them. Visiting a developed show cave is generally the safest and most accessible way to experience this kind of underground environment, since routes are maintained, lit and supervised by guides familiar with the site.

Boesmansgat and deep sinkholes

In the Northern Cape, a different kind of underground feature has formed: deep, water filled sinkholes created where dolomite has collapsed and the resulting cavity has filled with groundwater. Boesmansgat, also known as Bushman's Hole, is among the best known examples and is recognised as one of the deepest freshwater sinkholes in the world. Its depth and clear water have made it a destination for experienced technical divers, though it has also been the site of serious diving incidents, underlining how demanding and dangerous deep cave diving can be.

Why these sites matter

They preserve a geological record of groundwater activity stretching back enormously long periods of time.
Several sites, particularly in the Cradle of Humankind, hold internationally significant fossil records.
They illustrate the risks of building on or near dolomite ground, since the same processes that create caves can also cause surface instability.

Visiting responsibly

Developed show caves with trained guides offer a practical way to see these formations without the risks associated with wild caving. Undeveloped caves and water filled sinkholes should only be approached by those with appropriate training, equipment and local knowledge, given the real hazards of unstable rock, confined spaces and, in the case of flooded sinkholes, deep water diving conditions.