cavern

A cavern is a natural underground chamber or a connected system of chambers, usually large enough to be explored. The term is often used for expansive spaces within a cave and is sometimes distinguished from the more general word cave, with cavern implying greater size or complexity.

Most caverns form through the dissolution of soluble rocks, particularly limestone, by slightly acidic groundwater in karst landscapes. Other types arise from volcanic activity, such as lava tubes formed in flowing lava, or from tectonic and weathering processes that create voids in rock. Over time, circulating water and mineral deposition produce characteristic features that define many caverns.

Inside caverns, visitors commonly encounter stalactites and stalagmites, flowstones, columns, and underground rivers or lakes. These speleothems develop as minerals are dissolved, transported, and re-deposited by dripping water. Caverns also host unique ecosystems adapted to darkness, stable temperatures, and limited nutrients, studied by speleologists as part of cave biology and geology.

Exploration and research are coordinated by the disciplines of speleology and cave geology. Many caverns are protected as national or regional parks and require careful conservation to preserve delicate formations and underground habitats. Notable examples include Mammoth Cave in the United States and Carlsbad Caverns, which are studied for their geology, hydrology, and biology as well as for public education and recreation. The word cavern originates from Old French cavarne, from Latin cavern(a), meaning hollow or cavity.