The Karst Pages

INTRODUCTION -- What Is Karst?

The word ”karst” refers to a type of terrain, usually formed on carbonate rock (limestone and dolomite) where groundwater has solutionally- enlarged openings to form a subsurface drainage system. A mild carbonic acid produced from carbon dioxide in the atmosphere, particularly the soil atmosphere, is primarily responsible for the solvent power of groundwater on carbonate rocks.  Over millions of years, as flow routes are enlarged, carbonate aquifers change from diffuse-flow aquifers with water moving as laminar flow through small openings, to conduit-flow aquifers with water moving primarily as turbulent flow through well-developed conduit systems to discharge points at springs. As the water table lowers below the level of surface streams, the streams begin to lose water to developing cave systems below. As more and more of the surface drainage is diverted underground, stream valleys virtually disappear and are replaced by closed basins called sinkholes. Sinkholes vary from small cylindrical pits to large conical or parabolic basins that collect and funnel runoff into karst aquifers.  Groundwater flow in karst aquifers is significantly different from that of other aquifers because of the solutionally enlarged conduits. In porous media aquifers, groundwater moves very slowly as laminar flow, (usually only a few feet per year), but in karst aquifers, turbulently flowing underground streams have velocities approaching those of surface streams. The nature of the groundwater flow system causes karst areas to be extremely vulnerable to groundwater contamination. Other serious hydrogeologic problems include sinkhole flooding and sinkhole collapse.