While sinkholes are not the big problem in Alachua County that they are in Florida counties farther south--such as Pinellas, Hernando, and Hillsborough--they do happen here occasionally. The limestone underlayment of much of this area, called “karst,” is the root of the problem. Deterioration of the underground karst due to percolation of acidic rainwater through the soil causes voids to form, which collapse slowly, or sometimes abruptly, like in the dramatic newspaper photos of homes swallowed up overnight by a sinkhole.
The “Devil’s Millhopper” in northwest Gainesville is the largest sinkhole in Florida, and the state park’s stairs to the bottom is an enduring tourist attraction. Plus, many of the lakes in the area were formed by sinkholes.
But the more prevalent underground defect in this area is clay soil. The elasticity of clay causes it to shrink during dry spells, then swell during seasons with heavy rains. The swell/shrink cycle causes the ground under a home built over a layer of clay soil to heave up and down in seasons that are extra wet or dry. A hilly band of clay soil that geologists have labeled the “Hawthorn Formation” runs through the middle of Alachua County, roughly north-south along I-75 and east-west along Newberry Road.
Determining whether structural cracks in a home are due to sinkhole activity, clay soil, or erosion, is complicated. And engineering experts sometimes reach different conclusions about the cause of a structural problem when examining the same home.
But the determination of what’s causing a home to start cracking apart can a make a big difference as far as getting your homeowner’s insurance company to pay for repairs. Clay soil is considered an existing condition and is not covered, while sinkholes are. Or, at least, sinkholes can be covered, if you pay additional for it when the policy is written. They are typically excluded in standard policies nowadays.
To read more about clay soil and sinkholes, and view a map of the Hawthorn Formation, here’s a link to an April 14th, 2007, article in the Gainesville Sun, that covers the subject thoroughly:
Sinkhole claims have been on the rise over the past few years around the state, however, and here’s a recent Gainesville Sun commentary about the proliferation of insurance claims: