About 20% of our country is underlain by “karst terrain” and is susceptible to a sinkhole event. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.

In west-central Florida and elsewhere, their increasing frequency of sinkholes corresponds to the accelerated development of ground-water and land resources.
Most of Florida is prone to sinkhole formation because it is underlain by thick carbonate deposits that are susceptible to dissolution by circulating ground water. Florida’s principal source of freshwater, ground water, moves into and out of storage in the carbonate aquifers (most productive).
Development of these ground-water resources (municipal, industrial and agricultural water supplies) creates regional ground-water-level declines that play a role in accelerating sinkhole formation, thereby increasing susceptibility of the aquifers to contamination from surfacewater drainage. Such interactions between surface-water and ground-water resources in Florida play a critical and complex role in the long-term management of water resources and ecosystems of Florida’s wetlands
SINKHOLES ARE A NATURALLY OCCURRING IN FLORIDA LANDSCAPE
The exposed land mass that constitutes the Florida peninsula is only part of a larger, mostly submerged carbonate platform that is partially capped with a sequence of relatively insoluble sand and clay deposits.
In west-central Florida, the relation between the carbonate surface and the mantling deposits plays an important role in the circulation and chemical quality of ground water and the development of landforms. Sinkhole development depends on limestone dissolution, water movement, and other environmental conditions. Limestone dissolution rates (millimeters per thousand years) are highest in areas where precipitation rates are high.
DISSOLVING CARBONATE ROCKS CREATE SINKHOLES AND OTHER FEATURES
The soluble limestones and dolomites that constitute the carbonate rocks are sculpted by dissolution and weathering processes into a distinct geomorphology known as karst. karst terranes are directly related to limestone dissolution and ground-water flow and include sinkholes, springs, caves, disappearing streams, internally drained basins, and subsurface drainage networks.
CHANGES IN SEA LEVEL HELPED DEVELOP KARST TERRANES

Karst is well-developed in the carbonate rocks throughout the Florida carbonate platform. Throughout recent geologic time, fluctuations in sea level have alternately flooded and exposed the platform, weathering and dissolving the carbonate rocks.
Examples of these flooded features include the “blue holes” found in the Bahamas, the cenotes of the Yucatan, the springs of Florida, and numerous water-filled cave passages throughout these terranes. Many of the numerous lakes and ponds of west-central Florida formed as overburden materials settled into cavities in the underlying limestone. in west-central Florida, most of the soluble bedrock is below the water table. As ground water flows through the rock, geochemical processes continually modify both the rock and the chemical composition of the ground water. In many areas within the platform, the carbonates continue to dissolve, further enlarging cavities and conduits for ground-water flow.
The mantled karst of west-central Florida has resulted in a number of distinct geomorphic regions (White, 1970; Brooks, 1981), including several lake districts with numerous lakes created by subsidence of overburden into the buried karst surface. In other areas, especially where the mantling deposits are thick.

In the northern part of the region a thin (0 to 30 feet thick) mantle of highly permeable sediments overlies the carbonate rock. To the south, the overburden materials are generally thicker and less permeable. Where the overburden is 30 to 200 feet thick, sinkholes are numerous and two types are prevalent, cover-subsidence and cover-collapse. Where permeable sands are predominant in the overburden, cover-subsidence sinkholes may develop gradually as the sands move into underlying cavities. Where the overburden contains more clay, the greater cohesion of the clay postpones failure, and the ultimate collapse tends to occur more abruptly. In the southernmost part of the region, overburden materials typically exceed 200 feet in thickness and consist of cohesive sediments interlayered with some carbonate rock units. Although sinkhole formation is uncommon under these geologic conditions, where sinkholes do occur they are usually large-diameter, deep, cover-collapse type.
SINKHOLE DEVELOPMENT IS AFFECTED BY THE HYDROGEOLOGIC FRAMEWORK
The flow of subsurface water through sediments and eroded carbonate rocks affects how, where, and when sinkholes develop. Thus, formation of sinkholes is sensitive to changes in hydraulic and mechanical stresses that may occur naturally or as the result of human activity.
The chemistry of the ground water determines where dissolution and karst development occurs. Together, these hydrogeologic factors control the type and frequency of sinkholes that develop in west-central Florida.
AQUIFER SYSTEMS UNDERLIE
The hydrogeologic framework of west-central Florida consists of three layered aquifer systems that include both carbonate and siliciclastic rocks. The shallowest or “surficial” aquifer system generally occurs within unconsolidated sand, shell, and clay units.