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Sinkholes can be depressions in the land surface or may be hidden from view below the surface. Sometimes referred to as "sinks", they are widely distributed in Florida. They can be shallow or deep, small or large, but all are a result of the same general geologic processes.
Much of Florida's landscape is comprised of what's known as "karst." A karst terrain is a land surface produced by water dissolving the limestone bedrock and is characterized by sinkholes, cavern systems and springs. Sinkholes occur as a natural process of erosion of the limestone by water. Ancient cavities dissolved in the limestone need a triggering mechanism to cause the collapse. In pre-development times sinkholes were usually triggered by heavy rains or a flood that made the soil "roof" over the cavity very heavy, so that it eventually collapsed. Droughts also can lower the groundwater levels, reducing the buoyant support of a cavity roof and prompting a collapse.
Increased numbers of sinkholes can generally be attributed to changing or loading of the earth's surface with development such as retention ponds, buildings, changes in drainage patterns, heavy traffic vibrations or declining groundwater levels.
Sinkholes are of interest to Florida because they are one of the predominant land form features of the state. Their development may be sudden and may result in property damage or loss of life. Florida has more sinkholes than any other state in the nation. Florida's average sinkhole size is 3 to 4 feet across and 4 to 5 feet deep.
Based on historical evidence, the most vulnerable counties are located mostly in the center portion of the state and include: Hillsborough, Citrus, Pasco, Polk, Hernando, Marion, and Orange Counties. The least vulnerable counties, assumed by historical evidence, are in the panhandle, in the Northeast Jacksonville area and the Miami-Dade, Duval, Hendry, Holmes, Lafayette, Monroe and Walton counties.
Perhaps the most famous sinkhole in recent U.S. history is the one formed in May 1981, in Winter Park, Florida near Orlando. The sinkhole is roughly circular but elongated, (approximately 300 feet by 300 feet in size). It swallowed one house and shed, half of the municipal swimming pool, a Porsche sports car, several large oak trees, a section of the crossing street and adjoining street and an estimated 4 million cubic feet of soil. The sinkhole also damaged three other Porsche sports cars and a pick-up camper that slid into the crater, caused the rear of an auto shop to crack open and exposed the utility lines in the vicinity.
Lake Jackson in Tallahassee, a nationally known bass fishing lake, experienced a sinkhole on September 16, 1999. It suddenly drained more than half the lake of every last gallon of water, not to mention every fish and alligator. On July 12, 2001, emergency officials for Hernando County investigated 18 confirmed sinkholes that hit in one day across the area, affecting a 15- to 16-block residential area and causing extensive damage to one house. It was one of the largest holes measured, between 50 and 100 feet deep.
The best way to find out whether there is sinkhole activity in your area is to refer to maps on the Florida Department of Environmental Protection web site.
What to do if a Sinkhole forms? Refer to the Sinkhole Action Checklist, Checklist 11 in the Appendix in the Guidebook or on the checklist page of this site.
Though earthquakes are not likely to affect Florida, their effects have been felt throughout history. Of the earthquakes felt in Florida, only six are thought to have had epicenters in Florida. (State Profile, Florida Division of Emergency Management, 2003)
There is no historical evidence of landslide events in the state of Florida.