Karst topography

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Karst topography is a three-dimensional landscape shaped by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite. These landscapes display distinctive surface features and underground drainages, and in some examples there may be little or no surface drainage. Some areas of karst topography, such as southern Missouri and northern Arkansas in the USA, are underlain by thousands of caves.

Different terms for karst topography exist in other languages - for example, yanrong in Chinese and tsingy in Malagasy - a notable exception being English (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 Paleoeuropean origin (karra - stone) and in antiquity it used to be Carusardius. From 1177 the Slovenian form grast has been known and from 1230 the Croatian kras.

Contents 1 Chemistry of karst landscapes 2 Karst formations 3 Water drainage and problems 4 Pseudokarst 5 Partial list of karst areas 5.1 Africa 5.2 Asia 5.3 Caribbean 5.4 Europe 5.5 North America 5.6 Oceania 6 See also 7 References 8 External links

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, 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.

Karst river on its way can disappears underground a number of times and springs again at different places, usually under a different name (like Ljubljanica, the river of seven names)

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.

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. There is an example of this in Lycoming County, Pennsylvania.

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 some difficuties 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

Pseudokarst refers to landscape features that 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.

Partial list of karst areas

Africa

• Anjajavy Forest, western Madagascar
• Ankarana Reserve, Madagascar
• Madagascar dry deciduous forests, western Madagascar
• Tsingy de Bemaraha Strict Nature Reserve, Madagascar

Asia

• The Stone Forest (Yunnan Province, China)
• Area around Guilin and Yangshuo in Guangxi Zhuang Autonomous Region, China
• Zhangjiajie National Forest park, forming part of the Wulingyuan scenic area (a UNESCO World Heritage Site), Zhangjiajie Prefecture, Hunan, China.
• Ofra region, Israel.
• Akiyoshi plateau, Japan.
• El Nido, Palawan, The Philippines
• Sagada, Mountain Province, The Philippines
• Bohol, The Philippines
• Negros and Gigante Islands, Negros Oriental, The Philippines
• Vang Vieng, Laos
• Gunung Mulu National Park Malaysia
• Krabi region, Thailand
• Phangnga Bay Area, Southern Thailand
• Halong Bay, Vietnam
• Phong Nha- Ke Bang, Vietnam

Caribbean

• Limestone eastern foothills of Maya Mountains including parts of the Cockscomb Basin Wildlife Sanctuary
• Los Haitises National Park, Dominican Republic
• Cockpit Country, a region in Jamaica
• Limestone mountains of northwestern Puerto Rico
• Viñales Valley, Cuba

Europe

• The Herzegovina region of Bosnia-Herzegovina
• The regions of Dalmatia, Lika, Gorski kotar, Kvarner and the islands in Croatia
• The Moravian Karst
• The Central Rhodope karst in Bulgaria (Trigrad Gorge and caves), the Devnya Valley (karst springs)
• The Apuseni Mountains, Romania
• Slovak Paradise and Slovak Karst [1], Slovakia
• The region of Inner Carniola in Slovenia
• Kras, a plateau in southwestern Slovenia and northeastern Italy
• Murge, in Apulia and Basilicata, southern Italy
• The Picos de Europa and Basque mountains, northern Spain
• The Ciudad Encantada in the Cuenca province (Castilla-La Mancha)
• El Torcal de Antequera nature preserve, southern Spain
• The White Peak of the Peak District, UK, around Matlock, Castleton, and Thor's Cave
• Yorkshire Dales (including Malham Cove), England
• The Burren (Co.Clare, Ireland)
• Assynt, SE Skye and near Kentallen in Scotland
• The limestone region of the Southern Brecon Beacons National Park, Wales
• Hönnetal at Balve, Germany
• The Swabian Alb region in the federal state of Baden-Wuerttemberg in southern Germany
• The "Ares de l'Anie, in the southernmost part of Barétous valley, South-West of France

North America

• The Nahanni region in the Northwest Territories, Canada
• Monkman Provincial Park in the Northern Rockies, Canada
• Portions of the Niagara Escarpment, Ontario, Canada
• The Viñales Valley in Cuba
• The Cenotes of the Yucatan Peninsula, Mexico
• Huntsville, Alabama, and the North Alabama Region, U.S.A.
• Coulee Region in the American Midwest, U.S.A.
• The Florida peninsula, U.S.A.
• Mammoth Cave area and Bluegrass region of Kentucky, U.S.A.
• Southeastern Minnesota, U.S.A.
• The Ozark Plateau of Missouri and Arkansas, U.S.A.
• The Karst forest in Puerto Rico, U.S.A.
• The Cumberland Plateau in Middle Tennessee, U.S.A.
• The Hill Country of Texas, U.S.A.
• Central Pennsylvania
• Presque Isle County near and around Rogers City in northern Michigan
• The campus of the University of California, Santa Cruz
• The Shenandoah Valley of Virginia

Oceania

• Jenolan Caves, New South Wales, Australia
• Waitomo, Oparara regions of New Zealand
• The Nakanai Mountains, East New Britain, Papua New Guinea

See also

• Karst field
• Glaciokarst
• Speleothem
• Speleology
• Foiba
• Limestone pavement

References

Jennings, J.N. Karst Geomorphology 2nd ed. Blackwell 1985 Sweeting, M.M. Karst Landforms Macmillan 1973

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