The term “karst” is defined as a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite, producing fissures, sinkholes, underground streams, and caverns. The dissolution of bedrock from percolating water can enlarge the fractures/bedding planes or form underground caverns in the carbonate bedrock. When unconsolidated materials (soil, gravel, sand, etc.) overlying the carbonate bedrock are thin, the potential exists for karst feature formation. These karst features can often be visible on the landscape as sink holes or fracture traces.
The formation of karst features limits the soil’s capacity to filter contaminants from percolating water. Furthermore, when karst features like sinkholes form in areas of concentrated flow like waterways or closed depressions, large volumes of surface water can directly enter groundwater with little to no filtration.
The potential for karst features to form increases as the thickness of soil above the bedrock decreases. Karst feature development has been observed with unconsolidated materials up to 50 feet in depth. Shown is a map of Wisconsin identifying areas where both carbonate bedrock is the uppermost bedrock unit and unconsolidated surface materials are less than 50 feet thick. These two factors combine to allow for karst formation.
The presence of karst landscapes is problematic in both rural and urban settings. Land management in these areas is critical to reducing the potential loss of nutrients, septic waste, and other contaminants to the fractured carbonate aquifers. Materials introduced to these types of aquifers can travel large distances in very short time periods as a result of fracture flow.
UW Discovery Farms staff recently attended an educational gathering of karst experts in Minnesota to help identify modern techniques used in karst feature mapping and management of landscapes prone to karst feature development. Many emerging geophysical techniques of monitoring karst aquifers are changing conceptual models of how water is moving in the fractured bedrock aquifers. This information will be utilized to increase the understanding of karst landscapes in Wisconsin and build upon information gained through initial research performed by the UW Discovery Farms Program.
The UW Discovery Farms Program has completed an initial phase of research to better understand karst landscapes in Wisconsin. These studies include depth to bedrock determination from well construction reports, verification of depth to bedrock with Geoprobe and seismic refraction, and feasibility of ground penetrating radar and electromagnetic pulsing equipment to determine depth to bedrock. These efforts have included two field days with soil scientists and geophysicists sharing information to better identify the thickness of soil and other unconsolidated materials over the fractured bedrock.
Multiple reports on various aspects of this research are in the final stage of production and should be available in early 2012 for reference. Future research is planned to better understand the land management challenges in karst landscapes to provide information for better informed land management decisions.
Written by Eric Cooley, firstname.lastname@example.org