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, 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.

Process

Bedrock is dissolved by carbonic acid 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 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 flowstones, stalactites, stalagmites,

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 ...

s, calcite rafts, and columns. These secondary mineral deposits in caves are called " speleothems".

Carbonic acid dissolution

Limestone dissolves under the action of rainwater and groundwater charged with H₂CO₃ ( carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as "

", characterized by sinkholes 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, New South Wales

Malaysia

* List of caves in Malaysia

Taiwan

* Black Dwarf Cave, Pingtung County

United States

* Jewel Cave National Monument, South Dakota * Mammoth Cave National Park, Kentucky * Russell Cave National Monument, Alabama * Wind Cave National Park, South Dakota * Oregon Caves National Monument and Preserve, Oregon * Cumberland Caverns, Tennessee

Vietnam

* Hang Sơn Đoòng, Quảng Bình Province

Germany

* König-Otto-Tropfsteinhöhle

References

Sources

* * *

External links

* {{Authority control Karst caves