CavesA brief study of four main types of caves

Compiled by Kella Randolph M. Ed.

What is a cave?• A cave is a natural opening in the ground

extending beyond the zone of light and large enough to permit the entry of man. Occurring in a wide variety of rock types and caused by widely differing geological processes, caves range in size from single small rooms to interconnecting passages many miles long. The scientific study of caves is called speleology (from the Greek words spelaion for cave and logos for study). It is a composite science based on geology, hydrology, biology, and archaeology, and thus holds special interest for earth scientists of the U.S. Geological Survey.

• Left: View of a passage walkway in Wind Cave • 3dparks.wr.usgs.gov

Types of CavesA simple classification of caves includes four main types and several other relatively less important types.

• Solution caves are formed in carbonate and sulfate rocks such as limestone, dolomite, marble, and gypsum by the action of slowly moving ground water that dissolves the rock to form tunnels, irregular passages, and even large caverns along joints and bedding planes. Most of the caves in the world-as well as the largest-are of this type.

• lava caves are tunnels or tubes in lava formed when the outer surface of a lava flow cools and hardens while the molten lava within continues to flow and eventually drains out through the newly formed tube.

• Sea caves are formed by the constant action of waves which attacks the weaker portions of rocks lining the shores of oceans and large lakes. Such caves testify to the enormous pressures exerted by waves and to the corrosive power of wave-carried sand and gravel.

• Glacier caves are formed by melt water which excavates drainage tunnels through the ice. Of entirely different origin and not to be included in the category of glacier caves are so-called "ice caves," which usually are either solution caves or lava caves within which ice forms and persists through all or most of the year.

• USGS http://geomaps.wr.usgs.gov/parks/cave/#what

Solution CaveGround water dissolves certain rocks made of limestone, dolomite and gypsum, creating tunnels, passages and caverns below the surface of the ground.

Cave Geology | Missouri State Parks Less

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mostateparks.com

Solution Cave

The action of slowly moving ground water that dissolves the rock to form tunnels, irregular passages, and even large caverns along joints and bedding planes. Most of the caves in the world-as well as the largest-are of this type. Domica Cave is the most known and longest cave of the Slovak Karst National Park.

Domica Cave

http://www.ssj.sk/en/jaskyna/7-domica-cave

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Lava cavesLava caves are tunnels or tubes in lava formed when the outer surface of a lava flow cools and hardens while the molten lava within continues to flow and eventually drains out through the newly formed tube.http://geomaps.wr.usgs.gov/parks/cave/#what

www.flickr.com

Glacier CavesGlacier caves are formed by melt water which excavates drainage tunnels through the ice. Of entirely different origin and not to be included in the category of glacier caves are so-called "ice caves," which usually are either solution caves or lava caves within which ice forms and persists through all or most of the year.

Top: blue ice cave

http://www.123rf.com/search.php?word=glacier+caves&imgtype=&Submit=+&t_word=&t_lang=en&orderby=0&sti=mgvkuqmnwtkdsflmum|&mediapopup=6070282

Antarctic Glacier with cavities.

Karst Topography

• The degree of development of karst landforms varies greatly from region to region. Large drainage systems in karst areas are likely to have both fluvial (surface) and karst (underground) drainage components. As stated in the introduction, the term karst describes a distinctive topography that indicates dissolution of underlying rocks by surface water or ground water.

• Water falls as rain or snow and soaks into the soil. The water becomes weakly acidic because it reacts chemically with carbon dioxide that occurs naturally in the atmosphere and the soil. This acid is named carbonic acid and is the same compound that makes carbonated beverages taste tangy. Rainwater seeps downward through the soil and through fractures in the rock responding to the force of gravity. The carbonic acid in the moving ground water dissolves the bedrock along the surfaces of joints, fractures and bedding planes, eventually forming cave passages and caverns.

• Limestone is a sedimentary rock consisting primarily of calcium carbonate in the form of the mineral calcite. Rainwater dissolves the limestone by the following reaction: Calcite + Carbonic acid = Calcium ions dissolved in ground water + Bicarbonate ions dissolved in ground water. http://www.nature.nps.gov/geology/usgsnps/cave/karst.html

Permeable RockCracks and joints that interconnect in the soil and bedrock allow the water to reach a zone below the surface of the land where all the fractures and void spaces are completely filled (also known as saturated) with water. This water-rich zone is called the saturated zone and its upper surface is called the water table. The volume of void space (space filled with air or water) in soil or bedrock is termed porosity. The larger the proportion of voids in a given volume of soil or rock the greater the porosity. When these voids are interconnected, water or air (or other fluids) can migrate from void to void. Thus the soil or bedrock is said to be permeable because fluids (air and water) can easily move through them. Permeable bedrock makes a good aquifer, a rock layer that holds and conducts water. If the ground water that flows through the underlying permeable bedrock is acidic and the bedrock is soluble, a distinctive type of topography, karst topography, can be created. http://geomaps.wr.usgs.gov/parks/cave/#what

What’s in it for Me? Knowing where karst features are located could help city and town planners, as well as individual landowners, to make decisions on where to build houses and other structures. This information could save cities thousand of dollars in repairs to buildings that are built on unstable karst terrain.

Karst springs supply drinking water to millions of people. Knowledge of karst terrain and the movement of water in underground drainage systems is important for maintaining good quality and safe drinking water. Pollution of ground water is a major problem in karst terrain. http://www.nature.nps.gov/geology/usgsnps/cave/karst.html

www.publicdomainphotos.com

Sea CavesSea caves are formed by the constant action of waves which attacks the weaker portions of rocks lining the shores of oceans and large lakes. Wave action compresses air and exerts pressure in the cracks of rocks. After repeated crashes of waves. Water surges into cracks, joints and faults in the rock, causing pressure. Retreating water releases pressure and drags broken rock particles out to sea. Such caves testify to the enormous pressures exerted by waves and to the corrosive power of wave-carried sand and gravel.

Mourtos Sea Cave on Greek coast seen from sea. http://www.123rf.com/photo_2837168_mourtos-sea-cave-on-greek-coast-seen-from-sea.html?pdetail=1

Sea Cave FormationPhotos from The World's 16 Most Incredible Sea Caves Credit: Flickr/Daniel Gillaspia

Should we live there?

Human settlement in the area is likely to collapse into the sea over time, as the caves eventually are eroded enough to collapse the rock above, leaving a gap between what was once the side walls of the cave. Surface Subsidence and Collapse. ... Some sinkholes form when the roofs of caves collapse, ... Building cities in such areas aggravates the problem for several reasons. ww.tulane.edu/~sanelson/Natural_Disasters/subsidence.htm

Gallery.nen.gov.uk

Education Resources• USGS Geology of Caves • http://www.nature.nps.gov/geology/usgsnps/cave/cave.html• and USGS Geology in the Parks

http://geomaps.wr.usgs.gov/parks/cave/#what

• Karst Topography Computer animations and paper model (HTML), (PDF) USGShttp://www.nature.nps.gov/geology/usgsnps/cave/karst.html

• Photos credited on slides