AskDefine | Define Karst

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see karst

English

Alternative spellings

Pronunciation

  • IPA: /kɑɹst/

Noun

Karst
  1. A mountainous region in northeastern Italy and southwestern Slovenia.

Translations

a mountainous region

Extensive Definition

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 dolines or sinkholes 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.

Terminology and etymology

Different terms for karst topography exist in other languages - for example, yanrong in Chinese and tsingy in Malagasy (Jennings, Ch.1 p.1). The international community has settled on karst, the German name for Kras, a region in Slovenia partially extending into Italy 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 Slovenian form grast is attested since 1177, and the Croatian kras since 1230.

Chemistry of karst landscapes

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. Recent studies of sulfates in karst waters suggests sulfuric and hydrosulfuric acids may also play an important role in karst formation.
This mildly acidic water begins to dissolve the surface and 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 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.

Karst 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 dolines (closed basins), vertical shafts, foibe (inverted funnel shaped sinkholes), disappearing streams, and reappearing springs. 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 Bay and Halong Bay in Vietnam.
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 Ljubljanica, the river of seven names).
An example of this is the Popo Agie River In Fremont County, Wyoming. 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 ½ mile down the canyon in a placid pool. When the river was dyed, it took two hours for the dye to reach the rise such a short distance away.

Water drainage and problems

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. * Ankarana Reserve, Madagascar

Europe

United States

Caribbean

Mexico

South America

List of notable pseudokarst areas

North America

United States

References

  • Jennings, J.N., Karst Geomorphology, 2nd ed., Blackwell, 1985, ISBN 0631140328
  • Sweeting, M.M., Karst Landforms, Macmillan, 1973, ISBN 023103623X

External links

Karst in Bulgarian: Карст
Karst in Catalan: Relleu càrstic
Karst in Czech: Kras
Karst in Danish: Karst
Karst in German: Karst (Geologie)
Karst in Estonian: Karst
Karst in Spanish: Karst
Karst in Finnish: Karstimaa
Karst in French: Karst
Karst in Croatian: Kraško gorje
Karst in Indonesian: Karst
Karst in Italian: Carsismo
Karst in Hebrew: קארסט
Karst in Hungarian: Karszt
Karst in Dutch: Karst
Karst in Japanese: カルスト地形
Karst in Norwegian: Karst topografi
Karst in Polish: Kras (geologia)
Karst in Portuguese: Carste
Karst in Russian: Карст
Karst in Slovak: Kras
Karst in Slovenian: Kras
Karst in Swedish: Karst
Karst in Vietnamese: Carxtơ
Karst in Turkish: Karst
Karst in Chinese: 喀斯特地形
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