Sinkholes are closed depressions in areas underlain by soluble rock such as limestone, dolostone, gypsum or salt. Sinkholes form when surface sediments subside into underground voids created by the dissolving action of groundwater in the underlying bedrock.
Other subterranean events can cause holes, depressions or subsidence of the land surface that may mimic sinkhole activity. These include subsurface expansive clay or organic layers which compress as water is removed; collapsed or broken sewer and drain pipes or broken septic tanks; improperly compacted soil after excavation work; and even buried trash, logs and other debris. Commonly, a reported depression is not verified by a licensed professional geologist to be a true sinkhole, and the cause of subsidence is not known. Such an event is called a subsidence incident. The Florida Geological Survey maintains and provides a downloadable database of reported subsidence incidents statewide. While this data may include some true sinkholes, the majority of the incidents have not been field-checked and the cause of subsidence is not verified.
Origins of the Subsidence Incident Reports
The database was started by the Florida Geological Survey (FGS) for scientific research purposes only. We are unsure what year (the FGS is over 100 years old). In the early 1980s, the database was moved to the newly formed and legislatively mandated Florida Sinkhole Research Institute (FSRI); however, in the early 1990s FSRI was eliminated and the database came back to the FGS. There was never a legal requirement that sinkhole occurrences or sinkhole insurance claims be entered into the database. Before being transferred to FSRI, the data collected came from citizens reporting sinkholes, cities, counties, and FDOT all voluntarily. FSRI did make an effort to increase the number of records entered into the database while it was under their tenure, but even those records were voluntary. Currently, a majority of the records come from the State Watch Office, which is the clearing house for emergency response calls involving man-made and natural disasters. The State Watch Office has a special reporting form that county, city and state dispatchers fill out (should they choose too) if a call comes in regarding a possible sinkhole occurrence. The second source is from citizens who either fill out and submit our Subsidence Incident Report form (via mail, email, fax) or by calling the FGS. The third source is via emergency situations where a swarm of sinkholes occurs and the FGS is called in by emergency officials to help survey the sinkhole hazard, such as after Tropical Storm Debby or the January 2010 frost/freeze event in the Plant City area. There are some records in the database that are associated with sinkhole insurance claims; however, those represent a small fraction of the total reports.
The Florida Department of Environmental Protection is the state’s lead agency for environmental management and stewardship – protecting our air, water and land. The vision of the Florida Department of Environmental Protection is to create strong community partnerships, safeguard Florida’s natural resources and enhance its ecosystems.