There was widespread new coverage last week of a Tampa-area home that was swallowed up by a large sinkhole, killing a man inside. Shortly after that sinkhole occurred, the ground opened up between two homes just a few short miles away. Coincidence? Hardly. Thousands of sinkholes open up in the Sunshine State each year. There is even a large sinkhole in Florida that’s opened to tourists and divers, called “Devil’s Den”.
Sinkholes are naturally occurring works of nature in the landscape in Florida. They belong in the same land form classification as caves and underground drainage systems which also make up the Florida landscape. A sinkhole occurs when acidic rainfall seeps down through the surface soil where it eventually reaches a soluble bedrock such as limestone – which is what half the land mass of Florida is made up of.
The process of a sinkhole forming and then opening is one that can go on for centuries as water slowly dissolves small parts of the rock to enlarge its natural fissures and joints to create a cavity beneath. As the process unfolds, the loose soil above is slowly washed into the cracks and voids. As the hole underground expands, sooner or later the surface layer of soil will simply give way.
When a sinkhole collapses, the materials above it will funnel into the sinkhole and that material includes homes, businesses and whatever other types of things may be sitting atop the area. In sinkhole-prone areas such as Florida, geologists routinely carry out land surveys for builders and property owners who are worried about sinkholes.
The state of Florida is known as having a karst landscape. What this means is that the landscape is formed by underground erosion of rocks (limestone) which can be dissolved by water. With Florida’s average annual rainfall total of about 4 feet, the land making up the state is very susceptible to sinkholes. These naturally occurring works of nature are so common in fact that Florida is often called the “Sinkhole Capital”. When you couple that much rain with the limestone that half of the state is made up of, you get sinkholes and sometimes very large ones occurring all across the state.
So how do you know if you have sinkholes on your property? You can look for cracks in your foundation, fences & utility poles that wobble and window & door frames that suddenly don’t fit correctly. Warped fences and doors and windows that don’t close are other warning signs of a sinkhole lurking beneath the surface of the ground. There are tests which can be conducted to determine if there is a sinkhole present. One involves inserting a tube into the ground to see what the solidity of the rock is like in the soil. Ground-penetrating radar can also be used to determine if a property is at risk for a sinkhole.