In the darkness and depths of caves around the world, cavers have discovered incredible stone formations known as stalactites, mineral treasures hidden away in an underground world. In what scientists call a karst environment, caves and subterranean chambers form through the action of moving water and other natural forces, generated by solution of bedrock. This action also contributes to formation of stalactites, cave deposits or cave "decorations" that form over thousands of years.
What Are Stalactites and How Do They Form?
Stalactites are secondary mineral deposits known as speleothems. They are jagged cone-shaped formations, assuming varied lengths and sometimes incredible sizes, hanging from the ceilings and walls of limestone caves.
Stalactites form through a chemical reaction between water and limestone. Carbon dioxide in water acts to dissolve limestone. When a droplet of mineral-laden water falls from the ceiling or walls of a cave, a thin ring of calcite is left in its wake. As each droplet falls, this process is repeated. Over time, as deposits build up, a narrow tube forms. These tubes are known as soda straw stalactites. Soda straws can grow to a good length but they remain narrow, hollow tubes.
When one of these tubes becomes plugged, this opens the way for a larger stalactite to form. How so? Water is forced to run on the outside of the tube, which leads to a build up of deposits on the area of the soda straw. As more calcite is deposited, a larger stalactite forms and assumes the typical conical shape.
How Long Does it Take for Stalactites to Form and How Big Can They Get?
The growth rate of a stalactite is estimated to be about 1" (2.5 cm) for every 4000-5000 years. Many years must pass for formation of larger stalactites. Over time, stalactites may reach impressive lengths, such as the large 20' stalactite hanging in Doolin Cave in Ireland or--what is considered one of the largest stalactites discovered to date--the 27' foot specimen in Jeita's Grotto in Lebanon. Because these remarkable speleothems take so long to form, efforts are underway in some karst areas to protect stalactite cave formations for future generations.
Sources:
- P. M. Pedley, M. Rogerson, Tufas and Speleothems: Unravelling the Microbial and Physical Controls, Geological Society of London, 2010
- Tony Waltham, Great Caves of the World, Firefly Books, 2008
- Emil Silvestru, The Cave Book, Master Books, 2008
- Arthur N. Palmer, Cave Geology, Cave Books, 2007
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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