Share on Facebook Share on Twitter Email
Answers.com

Karst topography

 
Sci-Tech Encyclopedia: Karst topography
Home > Library > Science > Sci-Tech Encyclopedia

Distinctive associations of third-order, erosional landforms indented into second-order structural forms such as plains and plateaus. They are produced by aqueous dissolution, either acting alone or in conjunction with (and as the trigger for) other erosion processes. Karst is largely restricted to the most soluble rocks, which are salt, gypsum and anhydrite, and limestone and dolostone. See also Dolomite rock; Gypsum; Limestone.

The essence of the karst dynamic system is that meteoric water (rain or snow) is routed underground, because the rocks are soluble, rather than flowing off in surface river channels. It follows that dissolutional caves develop in fracture systems, resurging as springs at the margins of the soluble rocks or in the lowest places. A consequence is that most karst topography is “swallowing topography,” assemblages of landforms created to deliver meteoric water down to the caves.

Karst landforms develop at small, intermediate, and large scales. Karren is the general name given to small-scale forms—varieties of dissolutional pits, grooves, and runnels. Individuals are rarely greater than 10 m (30 ft) in length or depth, but assemblages of them can cover hundreds of square kilometers. On bare rock, karren display sharp edges; circular pits or runnels extending downslope predominate. Beneath soil, edges are rounded and forms more varied and intricate.

Sinkholes, also known as dolines or closed depressions, are the diagnostic karst (and pseudokarst) landform. They range from shallow, bowllike forms, through steep-sided funnels, to vertical-walled cylinders. Asymmetry is common. Individual sinkholes range from about 1 to 1000 m (3 to 3300 ft) in diameter and are up to 300 m (1000 ft) deep. Many may become partly or largely merged.

Dry valleys and gorges are carved by normal rivers, but progressively lose their water underground (via sinkholes) as the floors become entrenched into karst strata. Many gradations exist, from valleys that dry up only during dry seasons (initial stage) to those that are without any surface channel flow even in the greatest flood periods (paleo-valleys). They are found in most plateau and mountain karst terrains and are greatest where river water can collect on insoluble rocks before penetrating the karst (allogenic rivers).

Poljes, a Serbo-Croatian term for a field, is the generic name adopted for the largest individual karst landform. This is a topographically closed depression with a floor of alluvium masking an underlying limestone floor beveled flat by planar corrosion.

Karst plains and towers are the end stage of karst topographic development in some regions, produced by long-sustained dissolution or by tectonic lowering. The plains are of alluvium, with residual hills (unconsumed intersinkhole limestone) protruding through. Where strata are massively bedded and the hills are vigorously undercut by seasonal floods or allogenic rivers, they may be steepened into vertical towers.

Search unanswered questions...

Enter a question here...
Search: All sources Community Q&A Reference topics

Wikipedia: Karst topography
Top
Home > Library > Miscellaneous > Wikipedia
"Karst" redirects here. For other uses, see Karst (disambiguation).
A karst landscape in Minerve, Hérault, France.
The karst hills of the Burren on the west coast of Ireland

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.[1]

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).

Contents

Background

The geographer Jovan Cvijić (1865–1927) was born in western Serbia 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 tsingy in Malagasy.[2] 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[citation needed] (from karra meaning "stone"[clarification needed]), and in antiquity it was called "Carusardius" in Latin. The Slovene form grast is attested since 1177, and the Croatian kras since 1230.[citation needed]

Chemistry

Karst lake (Doberdò del Lago, Italy), from underground water springing into a depression. This lake has no surface inlet or outlet.

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

Limestone pavement in Dent de Crolles, France

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 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.

The Witch's Finger stalagmite in Carlsbad Caverns, USA

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 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.[citation needed]

Hydrology

A karst spring in the Jura mountains near Ouhans in eastern France at the source of the river Loue

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 Refuge in Iowa 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 Victoria, Australia and paleocollapse features.

Notable karst areas

Africa

Madagascar

Asia

Phong Nha Cave in Phong Nha-Ke Bang, Vietnam

China

Georgia

Indonesia

Israel

Japan

Laos

Lebanon

Dunnieh mountains, North Lebanon

Malaysia

Philippines

South Korea

Thailand

Taiwan

Turkey

Vietnam

Europe

El Torcal (Antequera - Spain)

Albania

Austria

Bulgaria

Croatia

Czech Republic

England

Estonia

France

Germany

Hungary

Ireland

Italy

Montenegro

Poland

Romania

Scotland

Slovakia

Slovenia

Spain

Switzerland

  • Karst and Caves of Switzerland
  • 7,900 square kilometres (3,100 sq mi), 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 1,200 kilometres (750 mi).

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. ^ "Glossary of Cave and Karst Terms". Speleogenesis.info. http://www.speleogenesis.info/glossary/. Retrieved 2009-05-04. 
  2. ^ Jennings, ch.1 p.1
  3. ^ "giants+hole"+castleton&as_brr=3#PPA63,M1 Castleton, Karst hydrology By Christian Leibundgut, John Gunn, Alain Dassargues, International Association of Hydrological Sciences, 1998, ISBN 1901502406, accessed June 2009
  4. ^ http://www.greenbrierriver.org/
  5. ^ http://www.nps.gov/maca/
  6. ^ www.nps.gov/ozar/skindeep.htm

External links

Search Wikimedia Commons Wikimedia Commons has media related to: Karst


This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
 

 

Copyrights:

Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Karst topography".  Read more