Karst is a distinctive type of landscape or topography. Karst landscapes usually occur where carbonate rocks (limestone and dolostone) underlie the surface. Freely circulating slightly acidic rainwater and the water in the soil slowly dissolve the fractures in the limestone and create sinkholes, caves, and other features that characterize karst landscapes. These features are sensitive to contamination because most of the surface water flows directly into them and, therefore, is not filtered by soil and bedrock.
Two well-developed areas of karst landscape are present in Indiana. The first, the Mitchell Plateau, is a broad limestone karst plateau dissected by a few major stream systems and is located in southern Indiana. This plateau developed on Mississippian limestones and extends from the eastern part of Owen County southward to the Ohio River in Harrison County.
The second karst area is located in southeastern Indiana and is known as the Muscatatuck Plateau. This plateau developed on limestones of Silurian and Devonian age.
Solution Features Characteristic of Karst Terrains
- Springs are places where subsurface water flows from rock or soil onto the land surface.
- Sinkholes are funnel- or bowl-shaped basins on the land surface that formed where the limestone is dissolved and the soil layer above slopes into the resulting depression.
- Sinking or disappearing streams are surface streams in karst areas that flow directly into the ground-water system at a place called a swallowhole.
- Underground drainage systems, composed of conduits dissolved in the rock through which water may flow, are common in karst areas. Surface streams in a karst area are generally short and lose their water during dry periods.
Effect of Structure and Rock Type on Karst Features
The nature of the landforms and the movement and composition of the water in karst environments is controlled by the structure and rock type of the area. The Mitchell Plateau is underlain by limestone and dolomitic rocks of the Sanders and Blue River Groups, some of which are highly susceptible to chemical dissolution. In contrast, the Crawford and Norman Uplands, which flank the plateau to the west and east, are underlain predominantly by chemically resistant sandstone, shale, and siltstone. A layer of soil derived from rocks of the upland regions covers part of the Mitchell Plateau. This soil cover results in surface runoff that is diverted to underground drainage.
Ground water in karst terrains is contaminated easily because the surface waters are channeled rapidly into the subsurface at sinkholes and swallowholes. These waters then flow underground without the benefit of filtration or exposure to sunlight, which might remove or kill some organic contaminants. Eventually, the ground water exits at springs. Contaminants from livestock feeder lots, agricultural pesticides, poorly managed industrial plants, leaking gasoline tanks or spills, septic fields, and sewage plants may be discharged at these springs without being adequately diluted. Wastes located in sinkholes, including dead livestock, discarded chemical containers, waste oil, and batteries also can be washed into the underground conduit and cavern systems.
Ways to protect the karst environment
- Learn more about your karst environment. Talk with your educators or other providers of environmental information in your community.
- Don't dispose of trash in sinkholes.
- Check the regulations in your county before installing a septic system or animal waste lagoon. Always divert any contaminated runoff away from sinkholes.
- If your drinking water is from a well, be sure to have a sample of the water tested regularly for bacteria and nitrate content.
- Be aware that improper use of insecticides, herbicides, and fertilizers can contaminate the ground water. Read the instructions and do not overapply.