James Bloom, age 14, of Mesa, Ariz., for his question:
WHAT IS SPELEOLOGY?
Caves hold a fascination for adventurists and naturalists. Speleology is the scientific study of caves. Scientists who make such studies are speleologists while those who explore and map caves as a hobby are called spelunkers.
A cave is any natural hole in the earth that is large enough for a person to enter. Most caves are found in limestone or in a similar rock called dolomite. This type of rock dissolves easily in water.
Most caves form in limestone when water seeps through cracks and dissolves the rock, forming passages and rooms.
Caves have been used by animals and humans for shelter. Caves found in steep valley walls are called abris, a French word meaning shelters. In prehistoric times, abris were commonly used as homes and even today some people use them for permanent shelters.
Among the best known caves in the United States are Carlsbad Caverns in New Mexico, Floyd Collins Crystal Cave in Kentucky, Luray Caverns in Virginia, Mammoth Cave in Kentucky and Wayndotte Cave in Indiana.
When you list the most famous sea caves in the world you have to include the Blue Grotto on the Isle of Capri in Italy and the Scottish Fingal's Cave.
Deep, dark caves contain few living things, although often bats will roost in the caverns by day and fly out at night to hunt food. The bats in New Mexico's Carlsbad Caverns are especially famous.
Caves start to form when water seeps through cracks and rock is slowly dissolved. After many thousands of years, rooms are formed in sections of the rock where the material has dissolved quickly. Narrow passages are found where the rock dissolves more slowly.
When air enters the cave, often the water level falls. Water continues to drip from the ceiling and walls, carrying dissolved calcium bicarbonate into the cave. Often the dripping water produces interesting formations. A calcium curtain may form where water drips from a crack in the ceiling.
A stone column called a stalactite forms from the ceiling as a steady dripping of water falls. A stalagmite forms on the cave floor as a column builds up deposits of stone.
Too little is known about caves to say which is the longest, the deepest or the largest. Oil drillers, for example, have found flooded caves more than 10,000 feet below the earth's surface in Florida. Some of the deepest caves that have been explored are in France and they go down more than 3,000 feet.
Stone Age people left examples of the earliest art on the walls of caves in northern Spain and in southwestern France.