April 2013

With so many responsibilities with roads, bridges, drainage, plowing and more, the recent tragedy in Hillsborough County in Florida and the near tragedy on a golf course in Illinois are terrible reminders of yet another thing to worry about — sinkholes.

The area in western Florida where the deadly sinkhole occurred is known as “Sinkhole Alley.” According to the Florida Department of Environmental Protection’s Web site, sinkholes form in karst terrain from the collapse of surface sediments into underground voids. In that region of the country, solution sinkholes, cover-subsidence sinkholes or cover-collapse sinkholes may be spotted. The first two types will show only slight topographical disturbance to the naked eye, while the third shows an abrupt change in topography and is most associated with the idea of sinkholes.

Furthermore, a number of other factors can cause holes or depressions. Expansive clay layers in the earth may shrink upon drying, buried organic material, poorly-compacted soil after excavation work, buried trash or logs and broken pipes all may cause depressions to form at the ground surface. Experts also say sinkholes can occur almost anyplace where heavy rains or water bombard the ground. Regarding the golf course sinkhole in Illinois, geologists have recently stated that irrigation (the kind that frequently occurs on courses) can and will spawn sinkholes in areas of karst terrain.

The bottom line is, unfortunately, not much can be done ahead of time to prevent sinkholes from happening. However, geophysical instrumentations such as Ground Penetrating Radar (GPR), can detect cavities in the subsurface. In a sinkhole-prone area, it is wise to run such survey prior to any construction.

For more information on sinkholes, the Florida DEP has a very informative fact sheet on sinkholes (which includes warning signs) on its Web site at www.dep.state.fl.us/.

You can also view previous issues of Superintendent's Profile.