Karst topography and Florida sinkholes

Karst topography is caused by groundwater flowing through limestone strata. Groundwater is naturally slightly acidic and over time, the acid dissolves the limestone. This creates random openings in the rock. Over the course of time, these openings get larger and become caverns. Carlsbad Caverns, Mammoth Caves, Lewis and Clark Cavern are three such features. If the caverns are close to the surface or become large enough, the top collapses and produces a sinkhole. The locations and timing of sinkhole events are relatively random and unpredictable. In the case of the Florida sinkholes and the aquifer fluctuations, a full aquifer will exert upward pressure that helps support overlying rock and structures, but that support is ultimately temporary. In true geologic fashion, the full aquifer patiently continues to dissolve the limestone, thinning and weakening the rock, inevitably resulting in a sinkhole. It is estimated that >90% of Florida lakes are filled in sinkholes.

http://coastal.er.usgs.gov/publications/ofr/00-180/intro/karst.html