Karst is a German name for an unusual and distinct limestone terrain in Slovenia, called Kras. The karst region in Slovenia, located just north of the
Adriatic Sea, is an area of barren, white, fretted rock. The main feature of a karst region is the absence of surface water flow. Rainfall and surface water (streams, for example) disappear into a subterranean drainage system characteristic karst areas. Another feature is the lack of topsoil or vegetation. In geology, the term karst topography is used to describe areas similar to that found in Kras. The most remarkable feature of karst regionsis the formation of caves.
Karst landscapes develop where the bedrock is comprised of such soluble rock as limestone, gypsum, or dolomite. Most karst regions develop in areas where the bedrock is limestone. The Mammoth cave system, Kentucky, is located in the largest karst landscape in the world. Other extensive karst regions are in southern France, southern China, Central America, Turkey, Ireland, and England.
Karst topography is formed when there is a chemical reaction between groundwater and bedrock. As rain, streams, and rivers flow over Earth’s surface, the water mixes with the carbon dioxide that naturally exists in air, and the soil becomes acidic and dissolves the calcium carbonate rock. In other cases, for example Carlsbad Caverns, New Mexico, sulfuric acid plays an important role in the dissolution of limestone to create caves. The carbonate solution seeps into fissures, fractures, crevices, and other depressions in the rock. Sinkholes develop and the fissures and crevices widen and lengthen. As the openings become larger, the amount of water that can enter increases. The surface tension decreases, allowing the water to enter faster and more easily. Eventually, an underground drainage system develops. The bedrock is often hundreds of feet thick, extending from Earth’s surface to depths below the water table. Solution caves can develop in karst regions by an extensive enlargement of the underground drainage structureinto a system of connecting passageways.
There are many variations of karst landscape, often described in terms of a particular landform. The predominant landforms are called fluviokarst,
doline karst, cone and tower karst, and pavement karst. Some karst regions were etched during the Ice Age and may appear barren and very weathered (pavement karst). Other karst areas appear as dry valleys for part of the year and after seasonal floods, as a lake (one example of fluviokarst). In tropical areas, karst regions can be covered with forests or other thick vegetation. Sometimes, the underground drainage structure collapses, leaving odd formations such as natural bridges and sinkholes (doline karst). Tall, jagged limestone peaks are another variation (cone or tower karst).