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"  Why They Appear Sinkholes most commonly occur in karst terrain: regions where limestone, gypsum, salt beds, or other carbonate rock can be dissolved. Water eats away at the rock until a pit is formed. When the roof\u2014the sediment layer that had been on top of the rock before it deteriorated\u2014no longer supports itself, it collapses into the pit. Sinkholes that occur on private property are the homeowner&amp;#039;s responsibility. Insurance may cover an evaluation and the repair if it is actually a sinkhole and not a subsidence incident\u2014a manmade problem caused by things like collapsed or broken sewer pipes and drainpipes, broken septic tanks and buried trash, or soil that wasn&amp;#039;t properly compacted after excavation work. There are two main types of sinkholes: cover subsidence and cover collapse. Cover-subsidence holes are usually found where thick, permeable sediment covers limestone or other soluble rock. As the rock wears away underground, the sediment slowly fills in the void. Eventually the ground surface will show a circular depression. Cover-collapse holes are more threatening. They can occur within minutes and are usually triggered by an event like heavy rainfall or drought that quickly sweeps away material, allowing the sediment covering the void to collapse suddenly. Property owners need to be especially vigilant if they live in an area prone to sinkholes. They should check frequently for small holes in the ground or cracks in a structure&amp;#039;s foundation. If you live in an area with soluble rock, check local and state geological surveys for more information about a specific area. What to Do If a sinkhole appears that is directly threatening a house or structure, get out immediately. Report the problem to emergency personnel as well as to a building inspector, and wait for an inspection to find out if it is safe to return. If a sinkhole occurs in the middle of the road, contact local law enforcement agencies. The area should be cordoned off immediately. But, if the sinkhole is not impacting a house or other structure, and if it is a manageable size\u20141 to 3 feet in both diameter and depth\u2014then it can be filled in. The Florida Department of Environmental Protection has these recommendations for filling the hole: \u2022 First, monitor the hole. If it does not get bigger over time, fill it in. \u2022 Add dry-mix concrete or a concrete plug at the bottom of the hole. This will provide a solid base. \u2022 After that, add clayey sand. Pure sand, with larger particles, feels gritty, while a fine-textured, clayey sand will feel sticky. Clayey sand will form a barrier that will help prevent water from seeping through the hole and enlarging it. Call a local contractor to find out where to buy clayey sand. If you can&amp;#039;t get any, it is okay to use pure, clean sand. \u2022 Finally, add sand and topsoil on top to blend in the area with other landscaping. Additional fill may be needed at a later date, but the hole should stabilize eventually. "^^<http://www.w3.org/2001/XMLSchema#string>
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