Caves, Karst & Dolomite

A cave is a naturally formed underground void large enough for a person to enter. Karst is the wider landscape produced mainly as soluble rock is dissolved: caves are only one expression, alongside dolines, sinkholes, disappearing streams and springs.

How solution caves form

1. Rain absorbs carbon dioxide from the air and soil, becoming weakly acidic.
2. Water follows joints, bedding planes and fractures in limestone or dolomite.
3. Over long periods it dissolves carbonate minerals and enlarges pathways.
4. Underground drainage concentrates into conduits, chambers and cave streams.
5. Where mineral-rich water later releases carbon dioxide, calcite may be deposited as speleothems.

Speleothems include stalactites hanging from ceilings, stalagmites growing upward, columns, curtains, flowstone and many delicate crystal forms. Growth is often extremely slow and varies with water chemistry and climate.

Limestone and dolomite

The Council for Geoscience estimates that roughly 5–10% of South Africa’s land surface is underlain by dolomitic terrain. Not all carbonate outcrop contains enterable cave, and many voids never connect to the surface.

South Africa’s dolomite caves

Some of the country’s best-known fossil-bearing cave systems developed in ancient dolomite, especially in and around the Cradle of Humankind. Solution created voids; openings later admitted soil, rock, animal remains and traces of human activity. Over time these deposits were cemented and preserved. Their scientific importance depends on careful stratigraphic context, which is why unauthorised digging or collecting is destructive and may be unlawful.

Sandstone and other caves

South African cavers also explore caves in sandstone and other rock types. Sandstone caves may develop through weathering, erosion, joint widening, rock falls and removal of less resistant layers. Sea caves are cut by wave action; boulder caves form among collapsed blocks; lava and mine workings are different again. An underground opening should not be assumed to be natural or safe without assessment.

Karst landforms

Doline

A closed surface depression in karst, formed by solution, subsidence or collapse.

Sinkhole

A sudden or progressive ground collapse into an underlying void. In South African engineering practice, dolomite instability includes sinkholes, subsidence and ground cracks.

Swallow hole

A place where a surface stream drains underground.

Spring

A point where groundwater returns to the surface, sometimes carrying water from a large karst catchment.

Karst window

A collapse or opening that exposes an underground stream or cave segment.

Groundwater moves differently in karst

Water can move rapidly through open fractures and cave conduits rather than slowly through soil and porous rock. A pollutant entering a sinkhole may therefore reach a spring with little filtration. Protecting recharge areas, dolines and cave streams protects water resources used by people, farms and ecosystems.

Why sinkholes form

On dolomitic land, residual soil may bridge cavities in weathered rock. If material is washed downward—often where water concentrates—the arch can fail and the surface can subside or collapse. Leaking pipes, poor stormwater control, altered drainage and changes in groundwater may increase risk. The visible hole is not a reliable guide to the size of the affected ground.

Caves as archives and habitats

Cave deposits and speleothems can preserve records of former environments and climate. Caves also provide stable, humid habitats and bat roosts, and can support specialised invertebrates and microorganisms. The absence of obvious animals does not mean a cave is lifeless.

How SASA contributes

SASA’s member clubs explore and survey caves, record observations, publish work and support conservation and research partnerships. Cave maps and inventories can be valuable for science and management, but location data is handled carefully where disclosure could cause trespass, unsafe entry, vandalism or damage to sensitive heritage and wildlife.