USGS Home - www.usgs.gov
Coastal and Marine Geology Program
Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

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

Northeast Florida Lakes and Rivers Home
North East Florida Atlas
About the Atlas:
Introduction
Methods
Regional Geology
Karst Development & Characterization You are at the Karst Development & Characterization sectin of the NE Florida Atlas
Sinkhole Lake Evolution & Effect of Urbanization
Identification of Karst Features from Seismic Patterns
Summary
Acknowledgements
References
Printable Version of the Atlas
Contacts
About the Atlas

Karst Development and Characterizaiton

Karst Devlopment | Types of Sinkholes

Carbonate dissolution process and karst formation.
Figure 9. Carbonate dissolution process and karst formation. Click on the image for a larger version.
Karst topography is created by a chemical dissolution process when groundwater circulates through soluble rock (Fig. 9). Carbon dioxide from the atmosphere is fixed or converted in the soil horizon to an aqueous state, where it combines with rainwater to form carbonic acid, which readily dissolves carbonate rock. Root and microbial respiration in the soil further elevates carbon dioxide partial pressure, increasing acidity (lowering pH). In tropical and subtropical regions such as Florida, abundant vegetation, high rainfall and high atmospheric CO2 values favor the rapid dissolution of the preexisting limestone.

Karst features develop from a self-accelerating process of water flow along well-defined pathways. As the water percolates downward under the force of gravity, it dissolves and enlarges any pore or fracture in the rock through which it flows. These pathways also include bedding planes, joints, and faults (Fig. 10). Enlarging the fracture allows it to carry more water, which increases the dissolution rate. As the fracture gets larger and transmits more water, it begins to pirate drainage from the surrounding rock mass. This process will create areas where the rock is highly eroded with very little dissolution around it, creating a very jagged appearance to the substructure.

Water will continue to percolate downward until it reaches the water table, below which all pore space is occupied by water. Since the rock is saturated with water at this point, water circulation is not as rapid and dissolution rates slow (the dissolution potential of the water is expended over time). However, the water table itself fluctuates up and down as a result of seasonal change, drought conditions and groundwater removal. This movement creates a zone of preferential dissolution along the zone of fluctuation. Over time this process creates pathways in the rock near the water table and provides a very efficient means to transport water. During wet cycles, the potentiometric surface of the confined aquifer may be higher than the ground surface. This allows water to flow through breaches in the confining unit and flow at the surface as springs.

Solution and collapse features of karst and karren topography.
Figure 10. Solution and collapse features of karst and karren topography. Click on the image for a larger version.

Water table fluctuations also occur on larger spatial and temporal scales related to sea-level change. Numerous sea-level cycles have occurred with lowstands extensive enough to expose most of the Florida peninsula and create extensive karst environments. These episodes of paleokarst development have been documented (Randazzo, 1972; Randazzo and Zachos, 1984) and can be identified in the rock record as cycles of shallowing-upward sequences. Geologic evidence includes the presence of evaporite deposits which form during the shallow phase of sea-level cycle. A diagenetic end-member of evaporites is hydrogen sulfide which, when oxidized to sulfuric acid, will greatly enhanced the carbonate dissolution process (Hines, 1997). The presence of paleokarst in the subsurface may influence the development of modern day karst.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

FirstGov.gov U. S. Department of the Interior | U.S. Geological Survey
Coastal and Marine Geology Program

email Feedback | USGS privacy statement | Disclaimer | Accessibility

This page is http://coastal.er.usgs.gov/publications/ofr/00-180/intro/karst.html
Updated December 05, 2016 @ 11:25 AM (JSS)