Karst is a term applied to areas where extensive dissolution of
rock has led to the development of subterranean channels through
which groundwater flows in conduits (enclosed or semi-enclosed
channels). These conduits can vary in size from slightly
enlarged cracks to tunnels many meters in diameter and many
kilometers in length. Karst is produced mostly in areas
underlain by carbonate rocks, usually limestones and dolostones.
Limestones are usually composed of calcite (CaCO 3 ), and
dolostones are composed of dolomite (CaMg[CO 3 ] 2 ). More
rarely, other rocks such as evaporites, consisting of gypsum
(CaSO 4 · 2H 2 O) have been dissolved to produce karst features.
Carbonate rocks are relatively soluble in water that is mildly
acidified from dissolved carbon dioxide. Areas of karst
topography are characterized by natural features such as
sinkholes, which often are seen as circular ponds or
depressions, particularly from the air. Other common karst
features are caverns, springs, and few or no continuous surface