In Florida, we frequently see headlines about sinkholes across the state. But what exactly are sinkholes? How do they occur?

According to the U.S. Geological survey, a sinkhole is “a depression in the ground that forms when groundwater circulates through rock and dissolves it.” Sinkholes appear in all sorts of shapes and sizes and can appear in many different places: roads, populated areas or out in the wilderness.

According to the U.S. Geological Survey, there are three common types of sinkholes: 1) dissolution, 2) cover-collapse, and 3) cover-subsidence. To understand how sinkholes work, let’s take a look at the cover-collapse formation type as an example.

Sinkholes normally occur in areas with carbonate bedrock like limestone, which is prevalent across Florida’s underground terrain. For the cover-collapse type of sinkhole, when groundwater moves through the limestone bedrock, it can slowly dissolve it over time and create underground tunnels or caves. The flowing groundwater can then erode soil and cause it to shift into this new open space. This process eventually leads to the sinkholes we see above the surface when this soil eventually caves in.

Sinkholes pop up the most in counties throughout Central Florida, like Pasco, Hernando, Hillsborough, Marion and Pinellas counties, to name a few. These areas’ sinkhole problems have dubbed this area “Sinkhole Alley.”

The state’s sinkhole research is largely handled by the Florida Geological Survey. In 2013, the group was contracted by the Florida Division of Emergency Management to make a map of areas most susceptible to sinkhole formation based on natural geology. Their findings fall along Sinkhole Alley and extend north.

If a small sinkhole opens in your yard, the Florida Department of Environmental Protection advises filling it with clean sand or soil. If it’s under a structure, talk to your insurance and keep people away. You can also call the Florida Geological Survey’s sinkhole hotline for advice on how to handle a sinkhole, and you can submit a subsidence incident report as well. But if you’re in immediate danger, always call 911 first.

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