Most sinkhole discoveries in Florida occur along a three-county swath known as "sinkhole alley" in central Florida, according to business media outlet Quartz. Hernando, Hillsborough and Pasco counties combined accounted for 68 percent of Florida's insurance claims regarding sinkholes in 2010. Sinkholes occur all over the state, but the populations of these three counties is growing faster than state levels, and new construction uncovers more sinkholes.
A state survey, which goes back to the early 1900s, keeps track of 3,500 sinkholes near urban areas and large population centers. Insurance claims for sinkholes topped 2,300 in 2006, and that figure rose to 6,700 in 2010. Some state insurance officials believe some of those claims are fraudulent, because they are paid without proof. Hernando County alone saw 200 new sinkholes in 2010 after Tropical Storm Debbie hit.
Florida has so many sinkholes due to the relatively young karst topography of the state. Limestone underneath the surface in Florida is weak and not compacted as much as other states. Water seeps into caves, which erodes the surface land. When the top layer of ground falls into the eroded cave, a sinkhole develops. Some of these water problems are caused by humans; Florida's citrus and strawberry growers use massive amounts of water to prevent freezing crops in cold weather.