Introduction to Karst Landscapes Karst is a type of landscape formation which is common in areas with high concentrations of readily dissolvable rock, most often limestone, dolomite, and gypsum. It refers to the set of features created by the effect of water on these rocks over long periods of time. Around 450 million years ago, the land that makes up Kentucky today was covered by shallow seas where corals and other small animals thrived. The skeletal materials of these sea creatures built up on the seafloor over hundreds of millions of years, and the pressure of the seawater above compacted and solidified them into limestone. Limestone is a sedimentary rock composed of crystals of calcium carbonate (CaCO3), which primarily came from the skeletal remains of marine animals like corals. Geologic uplift at the end of the Paleozoic Era, about 250 million years ago, drained the seas and exposed this limestone in the Bluegrass Region. As portions of this limestone dissolved and soils built up on the surface, the unique rolling landscape of the Bluegrass was created. In a karst landscape, holes in the limestone where water disappears underground are called sinks or swallets. As cracks and fissures appeared in the limestone, water was able to dissolve the rock below the surface. As this dissolving action continued over time, a system of caves and underground streams were created. Features where the water reappears at the surface are called springs, or seeps. Water that flows through subterranean karst structures is considered part of an aquifer. An aquifer is an underground water resource in permeable rock structures that is recharged by the movement of surface water into the ground. Karst is not a static landscape. It is continually evolving as water continues to act on the stone. New sinkholes can appear and collapses can occur in caves and caverns. One easy place to see the action of water on karst is along the highway, where blasting and cutting through hillsides has exposed the underlying limestone. As water moves into the exposed karst, it weakens the landscape and the rock structures slowly crumble away. In addition, during cold periods, icicles will form where water seeps out of the limestone rock structures. Human activity can affect karst landscapes in important ways. One of the most significant is the contamination and pollution of the surface water that feeds underground streams. Litter, oils and greases, household hazardous wastes, pet feces, and other pollutants can be carried into subterranean karst structures where they are nearly impossible to remove or remediate. Movement of earth for urban development can expose previously buried limestone structures, and can cover or plug swallets and springs. This can cause issues for the health of the aquifer, for the movement of stormwater off the development site, and often can cause structural issues for the buildings on the site. In addition, impermeable surfaces created by urban development increase the volume and power of stormwater runoff, causing the erosion of topsoil, which exposes the limestone bedrock which can then erode further. Acid rain, often caused by the burning of fossil fuels, also speeds up the dissolving action of water on limestone and can negatively affect a karst landscape. Kentucky’s karst landscape has created great ecological and economic value for our state. It is up to us to protect this fragile and threatened asset. Sources Kentucky is Karst Country: What You Should Know About Sinkholes Springs by James C Currens http://kgs.uky.edu/kgsweb/olops/pub/kgs/ic04_12.pdf
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