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Subsurface Characterization of Selected Water Bodies in the St Johns River Water Management District, Northeast Florida

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Karst Development and Characterizaiton

Karst Devlopment | Types of Sinkholes

End-member classification of sinkholes.
Figure 11. End-member classification of sinkholes. Modified from Culshaw and Waltham (1987); Ogden (1984). Graph shows distribution relative to potentiometric and overburden controls. Click on image for a larger version.
Predicted sinkhole type in Florida.
Figure 12. Predicted sinkhole type in Florida. Modified from Randazzo and Jones (eds.), 1997. Click on image for a larger version.
Karst topography is the result of sinkholes: funnel, bowl or cylindrical-shaped depressions that form to accommodate loss of material due to dissolution in the underlying carbonate rock. Dissolution creates a subsurface conduit system that leads to collapse and sinkhole formation at the surface (Arrington and Linquist, 1987). In Florida, sinkhole type and lake development depend primarily on three factors: 1) proximity of the limestone rock to the surface; 2) thickness of the overburden (confining unit); and 3) location of the water table and potentiometric surface. Figure 11 shows a classification of sinkholes that has been developed based on these factors. When the water table is deep below the ground surface, dissolution of the rock occurs within the unsaturated rock, creating a conduit system that transports overlying material downward. If overburden is present, it is removed through the conduit system, causing subsidence at the surface (Fig. 11A). If no overburden is present, the self-accelerating process of dissolution eventually removes all the material at the surface and the conduit system develops progressively downward (Fig. 11B). Where the ground is close to the surface, fluctuations in the water table create a void system along the zone of fluctuation. Downward dissolution above the water table directly undermines the surface, eventually causing a collapse. If overburden is present it will slump into the hole, sometimes catastrophically (Fig. 11C). Lack of overburden will create a direct connection between the surface and any underground void or cave system (Fig. 11D). A transitional type of sinkhole (Fig. 11E) straddles the end member classification in that deposition of material in the depression created by dissolution can occur during subsidence or collapse, or after dissolution has ceased. In Florida this type of sinkhole can be found very near the surface with recent infilling, or deep in the subsurface from paleokarst development. Buried sinkholes can also reactivate since they continue to be preferential pathways for groundwater movement.

Figure 12 incorporates near surface geology (factors 1 and 2 mentioned previously) with depth to aquifer (factor 3) to map the distribution of sinkhole types in Florida. When compared to the surficial geology map (Fig. 5, Regional Geology), it is apparent that in areas where the competent overburden of the Miocene sediments overlie limestone that is in close proximity to the surface, there is the highest likelihood of cover-collapse sinkholes (Lake and eastern Marion counties). Areas of loose Quaternary fill typically experience the slower developing cover-subsidence sinkholes that are most commonly found along the eastern seaboard.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180 U. S. Department of the Interior | U.S. Geological Survey
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Updated May 06, 2013 @ 09:24 AM (JSS)