Sinkholes

Sinkholes -- sunken layers in the land caused by changes in material beneath the land's surface -- are a serious problem in some areas. Particularly in Georgia and Florida, sinkholes are a common landscape blight. Though most are only 10 to 12 feet in diameter, sinkholes have been known to expand to hundreds of feet in diameter and can appear with disturbing speed. Depending on the cause they can range from small, easily repairable nuisances to major landscaping problems.

What causes sinkholes

Most sinkholes occur where debris such as trash, stumps, tree branches and other building materials were buried during a construction project. Over time, the debris decays, leaving an empty space under the ground. Hidden under a layer of soil, this space goes unnoticed until it finally caves in, leaving in a sunken area in the landscape. Less commonly, sinkholes may be caused by broken water pipes or cisterns.

Georgia and Florida sinkholes
Georgia and Florida sinkholes have their own unique cause: sinkholes in this area are brought on by the slow, natural process of erosion in the area's underground limestone caves. Although the decay happens over thousands of years, when it reaches a critical level, land within a few hundred feet above the limestone collapses -- sometimes literally overnight.

How to recognize a sinkhole

If you discover that a section of your landscape is sinking, determining the cause is the first step in repairing it. Avoid walking onto the sunken area. From the stable edge of the sinkhole, use a shovel or stick to dig through the surface layer. If you continue to hit earth, rather than a hollow space, the problem is likely due to normal settling of the ground, rather than a sinkhole [See Repairing a sunken lawn for information on how to correct this problem]. If you can dig through, inspect the inside with a flashlight. If you see building materials or decaying branches, it is a construction sinkhole that you'll probably be able to take care of yourself. If there is standing water or a pipe, it may be a broken sewer line. (Needless to say, if it's the later contact the county or city water department immediately.)

How to repair a sinkhole

Different types of sinkholes require different treatments. Most small construction sinkholes can be repaired without a professional, while other types require a landscape contracter. Test the hole with a stick or garden tool to determine if the bottom and sides are solid. If they are, you'll be able to fill the hole yourself by simply adding layers of soil, a foot at a time, and packing each layer down firmly as you fill the hole. Once the area is refilled, you can safely plant on it again.