Cave Formation

Caves form with the deposition of rock, typically limestone. Limestone forms in a marine environment from the transgression and regression of the ocean. The lithification of the rock must take place relatively soon after deposition. Karst features begin to form after adequate amounts of acid rain have fallen. A Karst Landscape typically contains sinkholes, vertical shafts, and disappearing streams.

To form acid rain, carbon dioxide gas reacts with water vapor and forms carbonic acid. The carbonic acid in rain water reacts with limestone as it seeps through the ground to form calcium bicarbonate in solution. In a highly jointed limestone rock, the acidic water erodes the limestone, eventually creating crevices under ground. Over time the crevices enlarge to form caves. This is the process that occurred to form Crystal Cave.

A cave is defined as being large enough for a person to crawl into, naturally formed, and in complete darkness. Other requirements for cave formation include 80% or more of the rock to consist of calcium carbonate, the limestone to be located at or near the ground surface, and greater than 500 millimeters of annual rainfall.

Click animation to see cave formation over time.

Diagram illustrating cave formation and features (Christopherson, 2003).

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