A sinkhole is a depression or hole in the ground surface that forms when underlying soluble bedrock, such as limestone, dissolves and collapses. These natural geological features are a common occurrence in Florida, a state widely recognized for its susceptibility to them.
Quantifying Florida’s Sinkholes
Quantifying the exact number of sinkholes in Florida presents challenges due to their varied nature and the continuous geological processes at play. Many sinkholes are small, go unnoticed in undeveloped areas, or are filled in over time. New sinkholes also form regularly, making a fixed number elusive.
The Florida Geological Survey (FGS) maintains a database of reported subsidence incidents, which includes events that may or may not be verified sinkholes. As of February 1, 2023, this database contained 4,159 records of such incidents. Another estimate suggests over 27,000 reported sinkhole incidences across 59 counties in Florida.
Central Florida, in particular, is often referred to as “Sinkhole Alley” due to a higher concentration of these features. The reported incidents tend to cluster in more populated areas, where they are readily observed and typically affect roads and dwellings.
Geological Factors Behind Sinkhole Formation
Florida’s abundant sinkholes are largely attributed to its underlying geology, specifically the presence of limestone bedrock, which forms what is known as karst topography. This allows for the formation of subterranean voids and cavities. Florida’s principal source of freshwater, groundwater, flows through these carbonate aquifers, continually modifying the rock.
Rainwater plays a significant role in this dissolution process. As rain falls through the atmosphere and seeps through decaying organic matter in the soil, it absorbs carbon dioxide, becoming mildly acidic. This acidic water then percolates downward, reacting with and slowly dissolving the limestone, enlarging existing cracks and creating new channels. These pores and cracks expand into extensive underground networks.
Sinkhole formation can be triggered by both natural and human-induced factors. Extreme weather events, such as prolonged droughts followed by heavy rainfall, can destabilize the ground. During droughts, groundwater levels may drop, removing the buoyant support for the roofs of underground cavities. Conversely, heavy rains can saturate the soil, increasing its weight and washing out sediments into voids, leading to collapse.
Human activities also contribute to sinkhole occurrences. Excessive pumping of groundwater can lower the water table, reducing the pressure that supports overlying soil and rock formations. Construction activities, including the weight of new buildings, changes in drainage patterns, and leaking utility pipes, can also place additional stress on the subsurface, accelerating the formation of sinkholes.
Living with Sinkholes in Florida
Living in a region prone to sinkholes requires awareness of potential signs. Property owners should look for indicators such as:
Cracks in walls, floors, or pavement
Doors or windows that suddenly become difficult to open or close
Depressions or sagging areas in the yard
Leaning fences or trees
Unexplained pooling of water or discolored well water
If a sinkhole is suspected, residents should secure the area by marking it off and keeping people and pets away. Documenting the situation with photographs and notes on its dimensions and changes over time is also helpful. If there is an immediate danger to life or property, local law enforcement should be contacted.
Individuals can contact their property insurance company, the Florida Geological Survey’s Sinkhole Helpline, or their local Water Management District. Florida law requires insurers to offer coverage for catastrophic ground collapse. Sinkhole insurance, which covers damage from broader sinkhole activity, is also available.
Research continues into better identification and mitigation strategies. Geological tests, such as ground-penetrating radar and soil borings, can assess sinkhole potential in certain areas. Mitigation techniques like grouting are used to stabilize compromised ground. The Florida Geological Survey also conducts research and mapping to understand the state’s vulnerability to sinkhole formation.