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By Jim Schrenkel, Certified Wildlife Biologist
Topography is topography, right? Wrong! Basic topography is just contour intervals and elevations, but Karst topography is not only above ground features such as sinkholes, but below ground features such as caves. So what exactly is Karst? Karst is defined as very distinctive landscape topography formed by the dissolving action of water on carbonate bedrock such as limestone. The word Karst derives from the German name Kras, (“meaning barren land”) a Slovenian region that rests on a limestone plateau. Karst features are very important because ten percent of the Earth’s surface is occupied in karst topography and they produce a quarter of the world’s water supply.
Karst features take many thousands of years to form. The slow dissolving action starts as rain falls through the atmosphere, picking up CO2. The CO2 and H2O chemically react to form a weak acid called carbonic acid (This is the same acid that makes carbonated drinks taste tangy). The acidic rain water leaches down through the soil into fractures in the bedrock. The carbonic acid in the moving ground water slowly dissolves the bedrock forming passageways and caves. This geological process results in unusual surface and subsurface features ranging from sinkholes, disappearing streams and springs to complex cave systems.
The most widely distributed karst landscapes are dolines, commonly called sinkholes. Sinkholes are surface depressions formed by either the dissolution of bedrock for a bowl shaped depression or the collapse of shallow caves. Sinkholes can range in size from a few feet to over 300 feet deep and several feet to thousands of feet wide. Sinkholes may fill up with water becoming ponds or lakes. The most popular karst feature is caves. Karst topography forms the longest cave system, the
Many animal species are associated with caves. Some species (called troglobites) have adapted exclusively to life in a cave. Troglobite species cannot survive outside the cave. These include diverse animals such as eyeless crayfish and fish, cave beetles and other unique insects and also the endangered
With all the benefits of Karst topography there are many concerns. Many karst areas have poor soils that do not retain water thus allowing it to go directly into underground water without proper filtration. Many sinkholes are beings used by individuals and even towns for trash dumps. Pollution is a main concern in karst terrain. Building on or near karst areas also pose potential problems. Sinkholes could form collapsing buildings or roads causing significant damage.
Some of the most beautiful and unique sites are a result of the Karst process as well as some unique and pressing land use problems. Public understanding and education of these crucial areas are necessary for the continued beauty and important wildlife habitat they provide to be maintained and properly managed.
The Alabama Department of Conservation and Natural Resources promotes wise stewardship, management and enjoyment of