A solutional cave, solution cave, or

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

cave is a

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

usually formed in a soluble rock like

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

(

Calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

, with chemical formula ''CaCO₃''). It is the most frequently occurring type of cave. It can also form in other rocks, including

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

, dolomite,

marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...

, salt beds, and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

Process

Bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

is dissolved by

carbonic acid Carbonic acid is a chemical compound with the chemical formula . The molecule rapidly converts to water and carbon dioxide in the presence of water. However, in the absence of water, it is quite stable at room temperature. The interconversion ...

in rainwater,

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

, or humic acids from decaying vegetation, that seeps through bedding planes, faults,

joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

, and the like. Over time, the surface terrain breaks up into clints separated by grikes and punctuated by

sinkholes A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

into which streams may disappear, crevices expand as the walls are dissolved to become caves or cave system. These may turn into large caverns or ''dolines'' when the roof collapses. The portions of a solutional cave that are below the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

or the local level of the groundwater are flooded.

Limestone caves

The largest and most abundant solutional caves are located in limestone. Limestone caves are often adorned with

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

formations produced through slow precipitation. These include

flowstone Flowstones are sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are typically found in "solution caves", in limestone, where they are the most common speleothe ...

stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...

stalagmite A stalagmite (, ; ; ) is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate, but may consist ...

helictite A helictite is a speleothem (cave-formed mineral) found in a Solution cave, limestone cave that changes its axis from the vertical at one or more stages during its growth. Helictites have a curving or angular form that looks as if they were gro ...

soda straw A soda straw (or simply straw) is a speleothem in the form of a hollow mineral cylinder (geometry), cylindrical tube. They are also known as tubular stalactites. Soda straws grow in places where water leaches slowly through cracks in rock, such ...

calcite rafts Calcite crystals form on the surface of quiescent bodies of water, even when the bulk water is not supersaturated with respect to calcium carbonate. The crystals grow, attach to one other and appear to be floating rafts of a white, opaque materia ...

, and

columns A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member ...

. These secondary mineral deposits in caves are called "

speleothem A speleothem (; ) is a geological formation made by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depen ...

s".

Carbonic acid dissolution

Limestone dissolves under the action of rainwater and groundwater charged with H₂CO₃ (

) and naturally occurring

organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are re ...

s. The dissolution process produces a distinctive landform known as "

", characterized by

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

s and underground drainage. Solutional caves in this landform—topography are often called karst caves.

Sulfuric acid dissolution

Lechuguilla Cave At , Lechuguilla Cave is the longest cave, eighth-longest explored cave in the world and the second deepest () in the continental United States. It is most famous for its unusual geology, rare speleothem, formations, and pristine condition. The ...

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

and nearby Carlsbad Caverns are now believed to be examples of another type of solutional cave. They were formed by H₂S (

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

) gas rising from below, where reservoirs of

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

give off sulfurous fumes. This gas mixes with ground water and forms H₂SO₄ (

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating to the surface.

Examples

Australia

Jenolan Caves The Jenolan Caves (Tharawal language, Tharawal: ''Binoomea'', ''Bindo'', ''Binda'') are limestone cave, limestone caves located within the Jenolan Karst Conservation Reserve in the Central Tablelands region, west of the Blue Mountains (New Sout ...

, New South Wales

Malaysia

* List of caves in Malaysia

Taiwan

* Black Dwarf Cave, Pingtung County

United States

Jewel Cave National Monument Jewel Cave National Monument contains Jewel Cave, currently the fifth longest cave in the world and second longest cave in the United States, with of mapped passageways as of May 2024. It is located approximately west of the town of Custer in ...

, South Dakota *

Mammoth Cave National Park Mammoth Cave National Park is a national park of the United States in south-central Kentucky. It encompasses portions of Mammoth Cave, the longest known cave system in the world. The park's are located primarily in Edmonson County, with sma ...

, Kentucky * Russell Cave National Monument, Alabama *

Wind Cave National Park Wind Cave National Park is a national park of the United States located north of the town of Hot Springs in western South Dakota. Established on January 3, 1903 by President Theodore Roosevelt, it was the sixth national park in the U.S. and t ...

, South Dakota * Oregon Caves National Monument and Preserve, Oregon * Cumberland Caverns, Tennessee

Vietnam

* Hang Sơn Đoòng,

Quảng Bình Province Quảng Bình was formerly a southern coastal Provinces of Vietnam, province in the North Central Coast region, the Central Vietnam, Central of Việt Nam, Vietnam. It borders Hà Tĩnh province, Hà Tĩnh to the north, Quảng Trị province, ...

Germany

* König-Otto-Tropfsteinhöhle

References

Sources

* * *

External links

* {{Authority control Karst caves