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.
Doll's Theater, Carlsbad Caverns. Credit: NPS Photo
by Peter Jones
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
AND PLANETARY SCIENCE