Geophysical applications to detect sinkholes and ground subsidence

The term sinkhole receives a lot of use, and equal amounts of abuse, in the popular media. Generally, anytime a hole or depression forms in the land surface, sometimes in a short period of time, it is called a sinkhole. Sinkholes are geologic features formed by movement of rock or sediment into voids created by the dissolution of water-soluble rock. Some sinkholes, such as the infamous Winter Park, Florida, sinkhole of 1981 (Figure 1), capture the attention of society as we view expensive homes and automobiles teetering on a precipice about to disappear into the underworld. Subsidence features caused by other processes, such as mine collapse and washouts resulting from broken water and sewer mains, are not true sinkholes, but may be equally as damaging. These features also result from rock or soil moving into a void, but the void was a result of human activities

Shallow Depressions in the Florida Coastal Plain: Karst and Pseudokarst

In Florida, shallow depressions (i.e., depressions \u3c1-2 m in depth) on the land surface are often attributed to sinkhole development. However, it has become evident that there are at least six different mechanisms through which these depressions can form in geologically young cover sediments. These mechanisms include: 1. Cover-subsidence sinkholes over shallow limestone; 2. Suffosion sinkholes over shallow limestone; 3. Cover settlement over shallow shell beds; 4. Large, aeolian deflation areas that resemble “Carolina bays;” 5. Depressions that mimic landforms developed on a shallow paleosol; and 6. Depressions created by pedodiagenesis (i.e., conversion of smectite to kaolinite) in a soil-forming environment. Of these, only the first two appear to represent traditional mechanisms for sinkhole development in eogenetic karst. Cover settlement over shell beds is poorly understood and incorrectly attributed to sinkhole development processes. This type of depression has serious limitations in terms of cover thickness and shell content of the substrate. The last three mechanisms are pseudokarst created by aeolian and soil-forming processes. In this paper we present examples of each and discuss their constraints and evidence

Photolinears, Fractures, and Fallacies: A \u3cem\u3ePost Hoc\u3c/em\u3e Study of Photolineaments, Hillsborough County, Florida

There is a misconception by some in the geologic and non-geologic communities of Florida that photolineaments and vertical bedrock fractures are one and the same. The main objectives of this paper are (1) to document a case study where a comprehensive geophysical and geotechnical exploration program was undertaken to verify a high-quality photolinear analysis; and, based on the case study, (2) evaluate the validity of photolinears as indicators of vertical bedrock fractures in the covered karst terrain of west-central Florida. The case study, an investigation by Upchurch et al. (1999), was an analysis of photolineaments at a 445-ha site intended for construction of an above-grade reservoir in west-central Florida. The photolineaments were ground truthed using ground penetrating radar (GPR), refraction and reflection seismic profiling, standard penetration testing (SPT), and cone penetrometer testing (CPT; Dobecki and Upchurch 2010). The post hoc review, based on the comprehensive site geophysical and geotechnical testing and resulting data, determined that fifty-eight percent of the photolinears do not correspond to vertical fractures in the limestone bedrock. This review demonstrates the fallacies of assuming all photolinears represent vertical bedrock fractures in the covered karst terrain of west-central Florida. Based on this case study and the post hoc review, it is our belief that in the covered karst terrains of Florida, all photolinear evaluations should have some form of field verification in order to equate them to vertical bedrock fractures or karst features

Shallow Depressions in the Florida Coastal Plain: Karst and Pseudokarst

In Florida, shallow depressions (i.e., depressions \u3c1-2 m in depth) on the land surface are often attributed to sinkhole development. However, it has become evident that there are at least six different mechanisms through which these depressions can form in geologically young cover sediments. These mechanisms include: 1. Cover-subsidence sinkholes over shallow limestone; 2. Suffosion sinkholes over shallow limestone; 3. Cover settlement over shallow shell beds; 4. Large, aeolian deflation areas that resemble “Carolina bays;” 5. Depressions that mimic landforms developed on a shallow paleosol; and 6. Depressions created by pedodiagenesis (i.e., conversion of smectite to kaolinite) in a soil-forming environment. Of these, only the first two appear to represent traditional mechanisms for sinkhole development in eogenetic karst. Cover settlement over shell beds is poorly understood and incorrectly attributed to sinkhole development processes. This type of depression has serious limitations in terms of cover thickness and shell content of the substrate. The last three mechanisms are pseudokarst created by aeolian and soil-forming processes. In this paper we present examples of each and discuss their constraints and evidence

Subbottom Profiling Investigation of Sinkhole Lake Structure in Bay and Washington Counties, Florida

pg(s) 207-21

Development of Sinkholes in a Thickly Covered Karst Terrane

pg(s) 273-27