Karst Topography

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 Mammoth Cave. This Kentucky cave is over 350 miles long. Alabama where Karst topography is prevalent boasts over two thousand caves. Many unique features are found in Karst caves. Stalactites (those features that hang from the ceilings of caves) and stalagmites (those features that rise from the floor of the cave) are formed by the deposition of slowly dripping calcium carbonate solutions.

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 Tennessee Cave salamander in Jackson County, Alabama. Other species such as bats, rats, and raccoons are just regular visitors to raise their young or hibernate. Several endangered bats reside in Alabama caves. Bats may be one of the most misunderstood but beneficial animals to people. The little brown bat can eat 600 mosquitoes an hour. Other bats are important as plant pollinators. The Mammoth Cave-Flint Ridge System in Kentucky has a biodiversity of 43 mammals, 15 reptiles, 19 amphibians and 3 fish.

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 Alabama’s natural resources through five divisions: Marine Police, Marine Resources, State Parks, State Lands, and Wildlife and Freshwater Fisheries.