DEFINITION OF CAVES

Underground openings and passageways in rock that

are larger than individual spaces between the constituent

grains of the rock. The term is often reserved for spaces that

are large enough for people to enter. Some scientists use the

term to describe any rock shelter, including overhanging

cliffs. Many caves are small pockets along enlarged or

widened cavities, whereas others are huge open underground

spaces. The largest cave in the world is the Sarawak Chamber

in Borneo, with a volume of 65 million cubic feet. The Majlis

Al Jinn (Khoshilat Maqandeli) Cave in Oman is the second

largest cave known in the world and is big enough to hold

several of the Sultan of Oman’s Royal Palaces, with a 747 flying

overhead (for a few seconds). Its main chamber is more

than 13 million cubic feet in volume, larger than the biggest

pyramid at Giza. Other large caves include the world’s third,

fourth, and fifth largest caves, the Belize Chamber, Salle de la

Verna, and the largest “Big Room” of Carlsbad Cavern,

which is a large chamber 4,000 feet (1,200 m) long, 625 feet

(190 m) wide, and 325 feet (100 m) high. Each of these has a

volume of at least 3 million cubic feet. Some caves form networks

of linked passages that extend for many miles in

length. Mammoth Cave in Kentucky, for instance, has at least

300 miles (485 km) of interconnected passageways. While the

caves are forming, water flows through these passageways in

underground stream networks.

The formation of caves and sinkholes in karst regions

begins with a process of dissolution. Rainwater that filters

through soil and rock may work its way into natural fractures

or breaks in the rock, and chemical reactions that

remove ions from the limestone slowly dissolve and carry

away parts of the limestone in solution. Fractures are gradually

enlarged, and new passageways are created by groundwater

flowing in underground stream networks through the

rock. Dissolution of rocks is most effective if the rocks are

limestone, and if the water is slightly acidic (acid rain greatly

helps cave formation). Carbonic acid (H2CO3) in rainwater

reacts with the limestone, rapidly (at typical rates of a

few millimeters per thousand years) creating open spaces,

cave and tunnel systems, and interconnected underground

stream networks.

See also KARST.

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