Why Sinkholes Form in Florida

Sections of a building at a resort near Orlando’s theme park district collapsed into a sinkhole on Aug. 12, forcing the evacuation of 105 guests in the structure and also dozens of visitors staying in two adjacent three-story buildings.
Sinkholes are as much a part of the Florida landscape as palm trees and alligators. Florida has more of them than any state in the nation. Earlier this year, a man near Tampa died when a sinkhole opened up underneath his bedroom.

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Experts say sinkholes aren’t occurring at a greater rate than usual but that the high-profile nature of recent one in populated areas has drawn attention to them. There also has been a rise in sinkhole claims in Florida, but insurance officials believe some of those claims are questionable. Here are some answers about why sinkholes form and their costs.

Why Are There Sinkholes in Florida?
Florida’s peninsula is made up of porous carbonate rocks such as limestone that store and help move groundwater. Dirt, sand and clay sit on top of the carbonate rock. Over time, these rocks can dissolve from an acid created from oxygen in water, creating a void underneath the limestone roof. When the dirt, clay or sand gets too heavy for the limestone roof, it can collapse and form a sinkhole. Sinkholes are caused naturally but they can be triggered by outside events.
What Triggers Sinkholes?
Although sinkholes are formed naturally, they can be triggered by heavy rainfall, drought followed by heavy rainfall, tropical storms and human activity. The most common actions by humans that cause sinkholes are heavy pumping of groundwater to spray on oranges and strawberries during freezes to keep them from being damaged, well drilling, excavating, creating landfills, leaking broken water lines and pounding or blasting from construction.
Where Are Sinkholes Most Common in Florida?
Three counties in the Tampa region are known as “sinkhole alley.” Two-thirds of the sinkhole damage claims reported to the state Office of Insurance Regulation from 2006 to 2010 came from Hernando, Hillsborough and Pasco counties. Sinkholes are less common in South Florida, home to the state’s two most populous counties — Broward and Miami-Dade.
How Many Sinkholes Occur in Florida?
The state Office of Insurance Regulation says reported claims from sinkholes have risen in recent years. More than 2,300 claims were reported in Florida in 2006 but that figure jumped to almost 6,700 claims in 2010. There is no geological explanation for the rise and state insurance officials believe many claims are questionable. There must be structural damage to a home for a policyholder to claim a loss from a sinkhole, but insurance officials say claims are often paid without that proof.
How Much Damage Do Sinkholes Do?
The state Office of Insurance Regulation says sinkhole claims in Florida cost insurers $1.4 billion from 2006 to 2010.
Sources: Florida Department of Environmental Protection and Florida Senate report.