Sinkholes. Natural formations that are an integral part of Florida’s natural history and legends of terrifying headlines. Without sinkholes, Florida and it’s wildlife would be different. Sinkholes are a natural part of the geology that is the substrate of Florida. They also have become some of the state’s most scenic and ecologically significant landmarks.
Sinkholes result from the dissolution of limestone bedrock as rainwater seeps through soil. Water mixes with carbon dioxide to form a weak acid that slowly dissolves the limestone, creating underground cavities. Over time, the surface layer collapses, resulting in a sinkhole. Geology, a high-water table, and frequent rain, makes Florida one of the most sinkhole-prone regions in the United States.
Despite reputation, sinkholes play a critical role in ecology. A sinkhole’s evolution creates unique habitats supporting diverse plant and animal life. Aquatic environments, often a mix of fresh and saltwater, providing uniquely specific locations for native bird, fish, amphibians, insects, and even the endangered Florida manatee. Florida’s once wild, unaltered and thriving environment produced surprising flora, fauna, and wildlife in these pop-up sanctuaries for mating, feeding, and birthing new generations. Sinkholes, like the Everglades, were never the problem.
We can describe sinkhole evolution in stages. Each stage providing different ecological opportunities for plant and animal life. Formation, early stage, water accumulation, aquatic ecosystem, or terrestrial ecosystem development.
Rainwater and runoff combine with carbon dioxide, creating weak acid dissolving the underlying limestone bedrock. Underground cavities expand. As cavities grow larger, the surface layer eventually collapses, creating a sinkhole. Initially, the sinkhole can be dry or contain a small amount of water. During this stage, exposed limestone walls provide a habitat for various mosses, lichens, and ferns. Birds and small mammals may also seek shelter in the rocky crevices. This is the beginning of established wildlife lifecycles. Rainwater and groundwater accumulate in the sinkhole, creating a unique aquatic environment. Depending on the depth of the sinkhole and its connection to the surrounding water table, the water body may be ephemeral, semi-permanent, or permanent. In all categories, the evolving sinkhole offers further wildlife support for establishing changes.
Aquatic ecosystems are born from sinkholes successfully holding, filtering and feeding off surrounding groundwater and rainwaters becoming suitable habitat for plants such as water lilies, pondweeds. Submerged vegetation takes root, providing food and shelter for insects, crustaceans, and mollusks, and native fish and amphibians drawn to the new environment. Often a mix of fresh and saltwater, sinkholes formed with a resulting estuary tie to the gulf, Atlantic, or straits provide sanctuary to the endangered Florida manatee.
Conversely, terrestrial ecosystems can develop when the resulting sinkhole does not create a body of water, but new terrain for trees, shrubs, and grasses growing along the sinkhole’s edge and into the new basin supporting a diverse ecosystem for birds, reptiles, and mammals. The vegetation helps to stabilize the sinkhole’s walls, reducing the likelihood of further collapse.
Over time, a sinkhole’s ecosystem can undergo ecological succession, as plant and animal species change in response to evolving environmental conditions. Sinkholes of any age may eventually transition into a marsh or wetland, providing an even more diverse range of habitats for native flora and fauna. The entire evolutionary process contributes to the state’s ecological diversity. The interplay of fresh and saltwater in these environments allows for a rich mix of species promoting some of Florida’s most threatened and endangered inhabitants.
The specific conditions found in sinkhole environments, such as varying water levels, unique water chemistry, or submerged caves, meet the needs of some interesting wildlife residents. The Florida manatee is first to come to come to mind. The Blind cavefish, and the Dougherty Plain cave crayfish found in sinkholes connected to underground water systems, live in low-light or dark conditions, Dougherty Plain cave crayfish play an important role in the ecosystem by consuming detritus and organic material. The reticulated Flatwoods salamander relies on sinkhole ponds and other seasonal wetlands for breeding and laying eggs. The fluctuating water levels in sinkholes provide the ideal habitat for the development of these species.
Florida’s sinkholes provide the state with extraordinary natural landscapes. Like Sunken Gardens, in St. Petersburg. A historic botanical garden that began as a small sinkhole filled with water, and evolved into a lush, four-acre oasis of tropical plants and exotic birds. Visitors can meander through winding paths lined with over 50,000 plants while taking in the natural beauty of this unique landscape.
Some of Florida’s sinkholes are picturesque state parks providing a glimpse into the state’s geological past. Parks include Lake Jackson in Three Rivers State Park, De Leon Springs in De Leon Springs State Park, and Falling Waters in Falling Waters State Park. Visitors can kayak, canoe, swim, and hike, all while appreciating the geological marvels of sinkhole lakes.
The Devil’s Den, in Williston, is prehistoric. This fascinating geological feature has created a stunning underground spring that is popular among snorkelers and scuba divers. Crystal-clear water, ancient rock formations, and diverse marine life found in Williston present the evidence that sinkholes are not what the headlines would have you believe. The problem has never been sinkholes. The problem has always been developer’s and development practices.
Ever improving development practices and guidelines in Florida are addressing the potential for natural sinkhole formation as it pertains to agriculture and population dense residential planning. Technology and data can now minimize the risk of property damage and ensure the preservation of these unique geological features.
Geotechnical investigations and risk assessments identify potential sinkhole-prone areas. This process may involve ground-penetrating radar, electrical resistivity testing, or test drilling to determine the stability of the underlying limestone bedrock. Responsible land use planning and zoning regulations aim to minimize the risk of sinkhole damage by guiding development away from high-risk areas.
Sinkhole-resistant building design and construction techniques include the use of reinforced concrete slabs, structural reinforcement, and specialized foundation systems that can better accommodate ground movement and subsidence. Stormwater management is essential. Retention ponds, infiltration trenches, and rain gardens can reduce the risk of sinkhole formation and promote environmental sustainability.
In areas where sinkholes have already formed or are at risk of forming, developers may be required to implement monitoring and remediation measures including the installation of subsurface monitoring equipment, regular inspections, and the use of grouting or other stabilization techniques to prevent further sinkhole development. The state’s sinkhole risks vary throughout the state due depending on the quantity of dolostone.
The highest risk of formations exists in “Sinkhole Alley,” which covers parts of the west-central and north-central regions of the state, including Hernando, Pasco, Hillsborough, Pinellas, Marion, and Alachua counties. The underlying geology in these areas comprises thick layers of limestone and dolostone, which are easily dissolved by acidic rainwater, making them particularly susceptible to sinkhole formation.
The moderate-risk areas for sinkholes in Florida are in the northwestern and central parts of the state. Counties like Leon, Orange, and Osceola because of limestone bedrock but are less prone to sinkhole formation because of less or no dolostone found in bedrock.
The southeastern and southern regions of Florida, including Miami-Dade, Broward, and Monroe counties, have a relatively low risk of sinkhole formation. A combination of limestone and sand, which provides more stability and reduces the potential for sinkholes, characterizes the geology in these areas. Sinkhole formation can occur throughout the state because of the prevalence of limestone bedrock in Florida on the whole.
While sinkholes have garnered a reputation for destruction, they are, in fact, an essential component of Florida’s ecological tapestry and geological history. And for the scientific record, Sinkhole is a coined word for newspaper headlines to grab attention and breed a certain level of dread. Karst Terrain describes the overall geological landscape that would include a doline or individual sinkhole feature. Like volcanoes and tectonic plates, dolines and karst terrains will continue their lifecycles as prescribed by the Earth’s own lifecycle around the sun.