Sinkholes are cavities that form when water erodes easily dissolved, or soluble, rock located beneath the ground surface. Water moves along joints, or fractures, enlarging them to form a channel that drains sediment and water into the subsurface. As the rock erodes, materials above subside into the openings. At the surface, sinkholes often appear as bowl-shaped depressions. If the drain becomes clogged with rock and soil, the sinkhole may fill with water. Many ponds and small lakes form via sinkholes.

Abundant sinkholes as well as caves, disappearing streams, and springs, characterize a type of landscape known as karst topography. Karst topography forms where ground-water erodes subsurface carbonate rock, such as limestone and dolomite, or evaporite rock, such as gypsum and halite (salt). Carbon dioxide (CO₂), when combined with the water in air and soil, acidifies the water. The slight acidity intensifies the corrosive ability of the water percolating...