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Doll's Theatre, Carlsbad Cavern
Doll's Theater, Carlsbad Caverns. Credit: NPS Photo by Peter Jones
Any chamber formed naturally in rock and, usually, open to the surface via a passage. Caves are found most often in limestone, where rainwater, rendered slightly acidic by dissolved carbon dioxide from the atmosphere, drains through joints in the stone, slowly dissolving it. Enlargement is caused by further passage of water and by bits of rock that fall from the roof and are dragged along by the water. Such caves form often in connected series; they may display stalactites and stalagmites and their collapse may form a gorge.

Caves are also formed by selective erosion by the sea of cliff bases. Very occasionally they occur in lava, either where lave has solidified over a mass of ice that has later melted, or where the surface of a mass of lave has solidified, molten lava beneath bursting through and flowing on (see lava tube).


The distinguishing feature of a pothole is that it is more or less vertical. Potholes generally occur in limestone rocks where water has enlarged a joint by solution. Potholes often provide the entrances to cave systems.

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