Why Florida keeps falling in on itself

Q: I keep hearing in the news about sinkholes in Florida. What causes them?

A: Most of Florida is underlain by a rock called limestone. This rock base is covered with material laid down by the ocean over a great period of time, which becomes our soil and the subsoil material below.

florida-sinkhole

A sinkhole swallowing a house in Willow Sink, FL, in 2009. Photo by Richard Elzey (from flickr.com).

When the ocean receded, it left Florida high and dry. Limestone is a rock that dissolves easily. Over time water running through the rock (the water table or aquifer) can cut channels or caves or caverns in the rock. You then have a situation where there is a cave and a large weight of soil above the cave. Eventually the weight of the material above the cave is too much and it causes the top of the cave to collapse—then everything above the cave falls in. This forms a sinkhole.

The reason we see so many sinkholes open after a period of heavy rain is that the water in the soil makes the soil so much heavier that the extra weight is enough to collapse the cave’s ceiling. The most recent example is a motel close to Disney World that was swallowed by a sinkhole during the night. Luckily, due to the quick thinking of a security guard, all the guests were able to get out  without injury (http://mentalfloss.com/article/52187/what-causes-sinkholes).

A good diagram of how a sinkhole forms is found at http://21stcenturybuilder.org/sinkholes-causes-warning-signs-protection/.

–Answered by Nick Comerford, University of Florida

Have a question for Soils Matter? Post it here or email us at soils-matter@soils.org

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