Florida has been known as a location where the formation of sinkholes is more common than in most other areas. The question is why does this happen? By analyzing the way sinkholes are formed and what causes them will lead to finding out why they are so predominant in the state of Florida.
Florida’s Natural Foundation
Throughout the state of Florida, there exist sand and clay deposits on top of an irregular surface of carbonate which varies in thickness and composition. The development of sinkholes depends on the certain environmental conditions along with water movement and limestone dissolution. In places where precipitation rates are high, limestone dissolution occurs more frequently. Sinkholes are created by dissolving carbonate rocks, which are made up of soluble dolomites and limestones. The formation that takes place by carbonate rocks being sculpted by weather processes and dissolution is called karst.
How Karst Works
Throughout the Florida platform of carbonate, karst is highly developed in the carbonate rocks. Presently in west-central Florida the majority of soluble bedrock is under the water table. Carbonates within the platform form larger cavities in the landscape as they continue to dissolve. Mantled karst is a distinctive terrain formed by the presence of buried karst. The composition and thickness of the overlying materials is directly related to sinkhole formation.
Types of Florida Sinkholes
There are three general types of sinkholes that occur in Florida.
1. Dissolution sinkholes are caused by the chemical erosion of limestone, these are sinkhole depressions in the limestone surface.
2. Cover-subsidence sinkholes are subsurface cavities are gradually in-filled from overburden materials.
3. Cover-collapse sinkholes are abruptly formed sinkholes created by the movement of cover materials into sub-surface voids.
Sinkholes by Location
In the northern part of west-central Florida, carbonate rock is dissolved by rainwater moving quickly into the subsurface, forming dissolution type sinkholes. In the southwest areas, the thickness and type of overburden materials are directly related to the frequency, location, and type of sinkholes. Moving to the south, overburden materials are typically less permeable and thicker. This is an area where cover-collapse and cover-subsidence sinkholes are very prevalent. Although sinkhole formation is not typical in areas where overburden materials exceed 200 feet in thickness, when they do occur they are normally cover-collapse type sinkholes that are deep and large in diameter.
How Sinkholes Form
While sinkholes have been divided into three basic types, they may form in different phases and can even be a combination of two types. The main answer as to why sinkholes form in Florida is because of the dissolution of soluble carbonate rocks by weakly acidic water. Water that falls through the air dissolves carbon dioxide when it sits on the surface. This forms a weak acid-carbonic acid which reacts easily with dolomite or limestone after contacting the surface of bedrock. As the dolomite or limestone is dissolved into bicarbonate, calcium, and magnesium, voids and cavities will develop.