6. Wisconsin Caves and Karst

Wisconsin’s caves and karst landscape are more widespread than is commonly appreciated and they merit greater attention. Roughly, 20% of the state exhibits karst landscape and carbonate-cemented sandstones contribute to carbonate-dominated groundwater underlying nearly 45% of the state. The caves and karst are formed primarily in Ordovician and Silurian dolostones and in underlying and interbedded Cambrian and Ordovician sandstones. Pleistocene glaciation has obscured much of the eastern, central, and south-central karst, leaving two main areas of exposure, in the Door Peninsula and adjacent counties of east-central Wisconsin and in the southwestern Driftless Area. In eastern, Wisconsin surface karst is essentially limited to Door County, where there are extensive open joints, sinkholes, sinking streams, karren, caves, and springs, plus glaciokarstic benches and steps. The caves are of dissolutional, littoral, and mechanical origin. Rapid karstic hydrologic connections between the surface and shallow groundwater pose serious threats of contamination, necessitating appropriate land use regulation. The karst hydrology of the Silurian aquifer south of Door County continues to be underappreciated but became manifest during construction of a deep tunnel stormwater management network in Milwaukee in the 1980s and 1990s. The southwestern karst is better known and escaped extensive Pleistocene glaciation. It may have evolved more-or-less continuously since the Paleozoic, but hypogenic contributions, long-term environmental episodicity and recent Pleistocene influences may all be involved. The karst is a fluviokarst, integrated into the fluvial landscape with a wide array of dry valleys, sinkholes, caves, and springs. Dissolution remains active, but the karst hydrogeology deserves greater study, as do the springs and caves, which have probably been influenced by hydrothermal processes, hypogenic dissolution, and possibly by dissolution under saline–freshwater mixing conditions. Lead ores were mined extensively from the Platteville and Galena formations during the nineteenth century and quarrying remains a significant industry. Land use has been dominated by small-scale agriculture, but intensive agriculture and sand mining have emphasized the potential for land-use conflicts and detrimental environmental impacts. Regional karst science has yet to be incorporated adequately into planning mechanisms, but the karst is becoming a central theme for NGOs and the regional press. There are also caves and karst developed in Paleozoic sandstones in southwestern and central Wisconsin, including pavements, natural bridges, and other fragile rock formations.