What forces shape formation of caves? Humans have long been fascinated by caves and, eager to uncover their secrets, have sought to explore these chambers. Dissolution of soluble materials is a natural process that leads to cave formation around the world, giving humans a window on mysterious subterranean processes in intriguing karst environments.
Beginnings of Cave Formation: Acid in Water Dissolves Soluble Rock
Different forces contribute to cave formation, such as wave and volcanic action, glacial action or geological movement; however, many caves form in soluble rock, such as chalk, dolomite and gypsum, limestone, marble and salt. Caves that form out of soluble materials are called solution caves. The largest caves are formed in limestone, which dissolves through the action of both rainwater and groundwater charged with carbonic acid and other naturally occurring organic acids. This produces an environment scientists call karst, characterized by underground drainage systems.
Rainwater (containing carbon dioxide) trickles down through the soil layer to limestone beds. It picks up even more carbon dioxide as it works its way through the soil, which is rich in carbon dioxide by means of decaying organic matter. By a natural chemical process, the water and carbon dioxide form carbonic acid, which is a weak acid solution.
As this acidic water passes through hairline fractures and crevices in the ground and comes into contact with soluble minerals, rock, or more commonly, limestone bedrock, it dissolves these materials. Wherever the water runs, dissolution takes place, with the cracks widening and forming paths and a network of passageways.
Formation of a Cave at Water Table
Solution cave formation takes place at the water table. The water works its way downwards to where the ground is saturated. Once there, waters collect and channels form. Because these channels increasingly hold more water, this contributes to a faster rate of dissolution of surrounding soluble materials. As this process continues, formation of a tunnel or a cave or an actual cave system develops. If the water table drops, the active area of cave formation shows a corresponding drop.
Solution caves eventually become large enough for humans to enter. Some of these caves are mammoth in size, with numerous chambers and cave galleries offering a wealth of secondary formations such as stalactites and stalagmites.
Sources:
- Ford, D, Trevor, Limestones and Caves of Whales, Cambridge University Press, June 2, 2011
- Silvestru, Emil, The Cave Book, Master Books, April 30, 2008
- Waltham Tony, Great Caves of the World, Firefly Books, October 10, 2008
- Palmer, Arthur N., Cave Geology, CAVE BOOKS, July 1, 2007
- Davis, R.V., Limestone Caves, Dalesman Publishing Co Ltd, July 1978
Further Reading:
Burnham, Robert, Caves, Cliffs and Canyons, Discovery Communications, April 2000
Melody Rhodes - M. Rhodes is author of the Bedbug Books. She's been published in Canada, U.S. U.K. & NZ and has won awards for her poetry/prose.
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