Illinois State Museum
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Karst Cave - Monroe County, 1673
Caves are natural openings into the Earth’s interior. They can be narrow crevices just big enough for a person to squeeze into, or tunnels large enough to drive a truck through. Caves are formed by the action of flowing water, and many Illinois caves have streams running through them. Erosion and deposition are often going on simultaneously in caves. Water is eroding limestone to create cave passages at the same time that it is depositing minerals to create cave formations.
Caves provide a unique habitat. Even where no light penetrates, caves can be surprisingly alive with unusual animals that have adapted to life in complete darkness. About 250 species of animals are permanent or part-time residents of Illinois caves.
There are more than 300 caves in Illinois. This reconstruction is based
on caves in the Ozark Division in the Mississippi River valley.