Geohazards Geotechnical Consulting Gainesville, Florida


Sinkholes

Sinkholes are a natural and common geologic feature in areas underlain rock types that are soluble in natural water. In Florida, the most common of these soluble rock types are limestone and dolomite. The term sinkhole is used for closed depressions in the land surface that are formed by surficial solution or by subsidence or collapse of surficial materials owing to the solution of near-surface limestone or other soluble rocks.

Sinkholes occur in a variety of shapes from steep-walled "natural wells" to funnel-shaped or bowl-shaped depressions. Sinkholes are a product of solution-erosion processes and are analogous to valleys carved by rivers in areas underlain by insoluble clastic rocks. Just as rivers constantly erode the land surface by carrying away particles of rocks a grain at a time, limestone is carried slowly away in chemical solution an ion at a time. The ions are carried by water that percolates through cavities and conduits that were developed by solution of the limestone along fracture systems, bedding places, and other permeable zones in the rock. Surface erosion by rivers is well understood and subject to some control by man, but the detection of cavities at depth and predication of potential sinkhole collapse is inherently difficult.

Sinkholes are of interest in Florida because they are one of the predominant landform features of the State; because they may cause flooding during storms when the drainage capacity of natural subsurface conduits is exceeded; and because they may provide an avenue for pollutants on the land surface to move rapidly and possibly contaminate the groundwater. An important goal of geologic investigations is to describe the geologic and hydrologic features controlling the development of sinkholes so that sinkholes and their related problems may be better understood.

Sinkholes are also of interest in Florida because they have the potential to be a contributing cause of distress to a home or structure. Voids and cavities within the underlying limestone may result in surface depressions that can directly affect a structure's integrity. These voids and cavities within limestone may also result in a condition referred to as raveling. Raveling is the vertical and/or lateral migration of sediments to deeper voids or cavities within limestone. It is a mechanism for sinkhole formation.