Caves and Cave Formation

A cave is a natural underground void large enough for a person to enter. The most common caves form in soluble rock, especially limestone, in a process called karstification. Rainwater absorbs carbon dioxide from the air and soil to become a weak carbonic acid, which slowly dissolves the calcium carbonate in the rock. Over many thousands of years this enlarges cracks and bedding planes into passages, galleries and large chambers, sometimes producing extensive cave systems linked to sinkholes and underground rivers.

Inside a cave, the same chemistry that excavates the rock also builds delicate formations known collectively as speleothems. Water dripping from the ceiling deposits tiny amounts of dissolved mineral as carbon dioxide escapes, slowly growing icicle-like stalactites that hang downward and stalagmites that rise from the floor where the drips land. When the two meet, they form a column. Flowstone, curtains and rim pools develop where water films and pools redeposit minerals over long periods.

Caves have also been important to human history. Their stable, sheltered interiors preserved some of the oldest known art, the Paleolithic cave paintings and engravings made tens of thousands of years ago. Famous painted caves in Europe depict horses, bison, deer and other Ice Age animals rendered in ochre and charcoal. Because cave environments are fragile and easily damaged by light, humidity changes and human contact, many decorated caves are now strictly protected and studied through careful survey and replica.

Frequently asked questions

How do limestone caves form?

Slightly acidic groundwater, made acidic by dissolved carbon dioxide, gradually dissolves limestone along cracks and bedding planes. Over thousands of years this widens them into passages and chambers.

What is the difference between a stalactite and a stalagmite?

A stalactite hangs from the ceiling and grows downward from dripping mineral-rich water, while a stalagmite builds upward from the floor where those drips land. They can eventually join to form a column.

What is Paleolithic cave art?

It is prehistoric painting and engraving made during the Old Stone Age, often deep inside caves. The works frequently show Ice Age animals and are among the earliest known examples of human art.