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The word ''Karst'' is the German name for Kras , a region in Slovenia , partially extending to Italy , that rests on a limestone plateau. It was here that first scientific research of a karst topography was made. showing karst formations]] CHEMISTRY OF KARST LANDSCAPES Karst landforms are generally the result of mildly Acid ic Rainfall acting on soluble limestone or Dolostone Bedrock . The process of subsurface Rock dissolution results in a topography with distinctive features, including Sinkhole s or Doline s (closed basins), vertical shafts, disappearing streams, and Spring s. With a sufficiently low Base Level and sufficient time, complex underground drainage systems (such as karst Aquifer s) and extensive Cave s and cavern systems may form. 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 passes through the Soil , gathering up more CO2 to form a weak carbonic acid solution: H2O + CO2 → H2CO3. This mildly Acid ic water begins to Dissolve any fractures and 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. ).]] KARST FORMATIONS Erosion along limestone shores, common in the tropics, produces typical karst topography, including 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. stalagmite in Carlsbad Caverns ]] Calcium carbonate removed by water may deposit elsewhere. In caves, Stalactite s and Stalagmite s are formed by deposition of calcium carbonate and other dissolved minerals as the water drips from above. An example is the Gruta Rei Do Mato in the Lagoa Santa Karst formation around Sete Lagoas , Brazil with a stalactite of 20 meters height. Other formations consist of shields (where the flow is from a fissure rather than from a point), and Flowstone , which occurs when the flow of calcite-rich water is somewhat impeded and calcite is deposited in the flow. Helictite s are curlicue-shaped formations associated with the roofs and walls of caves. Larger flow-type formations are Rimstone Pool s and gours, which are bathtub-shaped and may contain large calcite or aragonite crystals as a result of slow Evaporation . Rivers which emerge from limestone caves may also produce Tufa terraces, consisting of layers of calcite deposited over extended periods of time as the water leaves the CO2-rich cave environment. WATER DRAINAGE AND PROBLEMS Farming in karst areas must take into account the excessive drainage. 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. Water supplies from Well s in karst topography are inherently hazardous, as the well water may simply run from a sinkhole in a cattle pasture through a cave and to the well, bypassing the normal filtering that occurs in a porous Aquifer . Groundwater in karst areas is just as easily Polluted as surface streams. All too often, sinkholes have been used as farmstead or even community Trash Dumps . In karst areas where Septic Tank s are the main Sewage disposal system, overloaded or malfunctioning systems 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 Ice Age Snail s surviving in air chilled by flowing over buried karst ice formations. PSEUDOKARST ''Pseudokarst'' occurs where the primary erosive agent is not rainwater, but there is underground drainage. This can occur in Basalt , where drainage is through Lava caves, or among Granite Tor s (for example Labertouche Cave in Victoria , Australia ). PARTIAL LIST OF KARST AREAS
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