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Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite.

Due to subterranean drainage, there may be very limited surface water, even to the absence of all rivers and lakes. Many karst regions display distinctive surface features, with sinkholes or dolines being the most common. However, distinctive karst surface features may be completely absent where the soluble rock is mantled, such as by glacial debris, or confined by a superimposed non-soluble rock strata. Some karst regions include thousands of caves, even though evidence of caves that are big enough for human exploration is not a required characteristic of karst.

Various karst landforms have been found on all 6 major continents (see below: notable karst areas).

Background

Karst topography is charactarized by subterranean limestone caverns, carved by groundwater.The geographer Jovan Cvijić (1865–1927) was born in western Serbiamarker and studied widely in the Dinaric Kras region. His publication of Das Karstphänomen (1893) established that rock dissolution was the key process and that it created most types of dolines, "the diagnostic karst landforms". The Dinaric Kras thus became the type area for dissolutional landforms and aquifers; the regional name kras, Germanicised as "karst", is now applied to modern and paleo-dissolutional phenomena worldwide. Cvijić related the complex behaviour of karstic aquifers to development of solutional conduit networks and linked it to a cycle of landform evolution. He is recognized as "the father of karst geomorphology".

Different terms for karst topography exist in other languages—for example, yanrong in Chinese and tsingymarker in Malagasy. The international community has settled on karst, the German name for Kras, a region in Sloveniamarker partially extending into Italymarker, where it is called "Carso" and where the first scientific research of a karst topography was made. The name has a pre-Indo-European origin (from karra meaning "stone" ), and in antiquity it was called "Carusardius" in Latin. The Slovene form grast is attested since 1177, and the Croatian kras since 1230.

Chemistry



Karst landforms are generally the result of mildly acidic water acting on soluble bedrock such as limestone or dolostone. The carbonic acid that causes these features is formed as rain passes through the atmosphere picking up CO2, which dissolves in the water. Once the rain reaches the ground, it may pass through soil that may provide further CO2 to form a weak carbonic acid solution: H2O + CO2 → H2CO3 (the acid). Recent studies of sulfates, in karst waters, suggests sulfuric acid and hydrosulfuric acid may also play an important role in karst formation.

This mildly acidic water begins to dissolve the surface along with any fractures or bedding planes in the limestone bedrock. Over time, these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features.

Somewhat less common than this limestone karst is gypsum karst, where the solubility of the mineral gypsum provides many similar structures to the dissolution and redeposition of calcium carbonate.

Formations

The karstification of a landscape may result in a variety of large or small scale features both on the surface and beneath. On exposed surfaces, small features may include flutes, runnels, clints and grikes, collectively called karren or lapiez. Medium-sized surface features may include sinkholes or cenotes (closed basins), vertical shafts, foibe (inverted funnel shaped sinkholes), disappearing streams, and reappearing spring. Large-scale features may include limestone pavements, poljes and blind valleys. Mature karst landscapes, where more bedrock has been removed than remains, may result in karst towers or haystack/eggbox landscapes. Beneath the surface, complex underground drainage systems (such as karst aquifers) and extensive caves and cavern systems may form.

Erosion along limestone shores, notably in the tropics, produces karst topography that includes a sharp makatea surface above the normal reach of the sea and undercuts that are mostly the result of biological activity or bioerosion at or a little above mean sea level. Some of the most dramatic of these formations can be seen in Thailand's Phangnga Baymarker and Halong Baymarker in Vietnammarker.

Calcium carbonate dissolved into water may precipitate out where the water discharges some of its dissolved carbon dioxide. Rivers which emerge from springs may produce tufa terraces, consisting of layers of calcite deposited over extended periods of time. In caves, a variety of features collectively called speleothems are formed by deposition of calcium carbonate and other dissolved minerals.

A karst river may disappear underground a number of times and spring up again in different places, usually under a different name (like Ljubljanicamarker, the river of seven names).

An example of this is the Popo Agie River in Fremont Countymarker, Wyomingmarker. Simply named "The Sinks" and Sinks Canyon State Park, the river flows into a cave in a formation known as the Madison Limestone, and then rises again a half-mile down the canyon in a placid pool. When the river was dyed, it took two hours for the dye to reach the rising a short distance away.

Hydrology



Farming in karst areas must take into account the lack of surface water. The soils may be fertile enough, and rainfall may be adequate, but rainwater quickly moves through the crevices into the ground, sometimes leaving the surface soil parched between rains.

A karst fenster is where an underground stream emerges onto the surface between layers of rock, cascades some feet, and then disappears back down, often into a sinkhole.

Water supplies from wells in karst topography may be unsafe, as the water may have run unimpeded from a sinkhole in a cattle pasture, through a cave and to the well, bypassing the normal filtering that occurs in a porous aquifer. Karst formations are cavernous and therefore have high rates of permeability, resulting in reduced opportunity for contaminants to be filtered out.

Groundwater in karst areas is just as easily polluted as surface streams. Sinkholes have often been used as farmstead or community trash dumps. Overloaded or malfunctioning septic tanks in karst landscapes may dump raw sewage directly into underground channels.

The karst topography itself also poses difficulties for human inhabitants. Sinkholes can develop gradually as surface openings enlarge, but quite often progressive erosion is unseen and the roof of an underground cavern suddenly collapses. Such events have swallowed homes, cattle, cars, and farm machinery.

The Driftless Area National Wildlife Refugemarker in Iowamarker protects Discus macclintocki, a species of ice age snail surviving in air chilled by flowing over buried karst ice formations.

Pseudokarst

Pseudokarsts are similar in form or appearance to karst features, but are created by different mechanisms. Examples include lava caves and granite tors—for example, Labertouche Cave in Victoriamarker, Australia and paleocollapse features.

Notable karst areas

Africa

Madagascar



Asia



China



Georgia



Indonesia



Israel



Japan



Laos



Lebanon

Dunnieh mountains, North Lebanon


Malaysia



Philippines



South Korea



Thailand



Taiwan



Turkey



Vietnam



Europe

Albania



Austria



Bulgaria



Croatia



Czech Republic



England



Estonia



France



Germany



Hungary



Ireland



Italy



Montenegro



Poland



Romania



Scotland



Slovakia



Slovenia



Spain

El Torcal (Antequera - Spain)


Switzerland

  • Karst and Caves of Switzerland
  • , or 19% of the surface of Switzerland, is karst.
  • Within this area lies the majority of the 7,500 currently known Swiss caves, with an accumulated passage length of more than .


Wales



North America

Canada



United States



Mexico



Central America and the Caribbean

Belize



Cuba



Dominican Republic



Jamaica



Puerto Rico



Oceania

Australia



New Zealand



Papua New Guinea



South America



Notable pseudokarst areas

North America

Belize



United States



See also



References

  1. Jennings, ch.1 p.1
  2. Castleton, Karst hydrology By Christian Leibundgut, John Gunn, Alain Dassargues, International Association of Hydrological Sciences, 1998, ISBN 1901502406, accessed June 2009
  • Jennings, J.N., Karst Geomorphology, 2nd ed., Blackwell, 1985, ISBN 0631140328
  • Sweeting, M.M., Karst Landforms, Macmillan, 1973, ISBN 023103623X


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