The role of the epikarst in karst and cave hydrogeology: a review

The epikarst or subcutaneous zone is located at the top of the aerated or vadose zone in carbonate rocks. The vadose zone in karst comprises the soil (if there is any), the epikarst zone, and the transmission zone. From the epikarst, water percolates downwards through a zone dominated by transmission rather than storage that delivers recharge to the saturated or phreatic zone. In the sense of location, the epikarst is always present because it is the ‘skin’ of the karst; but in terms of hydrological function the detention and storage of recharge from rainfall in a subsurface aquifer the epikarst is often absent. These and other points were considered in the final discussion “What is Epikarst?” in Jones et al. (2004a). Although virtually all work on epikarst has been conducted on carbonate terrains, an epikarst aquifer may also exist in other karst rocks, such as gypsum, but has received little or no study. When subaerially exposed in arid or semi-arid climates, gypsum acquires a sealing crust from recrystallization following alternate wetting and drying (Klimchouk 1996, Macaluso & Sauro 1996), not unlike the case-hardened crust acquired by calcareous aeolianites (Jennings 1968). Such crusts have little water storage capacity.