How are caves made?

Caves are natural cavities formed under the Earth’s surface most commonly in limestone rock. Caves vary massively in size from gigantic caverns to tiny tubes and range from a few metres to several kilometres in length and depth.

Caves are formed when the limestone dissolves over a very long period of time. Rainwater collects carbon dioxide from the air and as it percolates through the soils it turns into a weak acid. Over thousands of years this water penetrates the joints, bedding planes and fractures of the limestone and dissolves the rock, eventually into passages large enough to explore.

As the surface topography changes the streams cut down to new and lower routes leaving the caves high and dry. These older passages often contain muddy sediments and breakdown boulders but also they may contain wonderful arrays of cave formations like stalactites, stalagmites and weird and wonky helictites.

The cave formations, or speleothems as they are collectively known, form when water saturated with calcium carbonate seeps down through the rock and enters the open passages. The drips deposit tiny amounts of the calcite which over time build up to create the stalactites on the roof and stalagmites on the floor below. Eventually some join to form columns.