Sinkholes can form anywhere there is soluble rock present underground. This is known as "karst terrain," according to Randall Orndorff, Director at the Eastern Geology and Paleoclimate Science Center of the United States Geological Survey. Soluble rocks that could potentially lead to sinkhole formation include limestone, gypsum and salt.
More than 20 percent of the country is above "karst terrain," which can produce a sinkhole, according to the U.S. Geological Survey (USGS).
Sinkholes occur most often in Florida, Texas, Alabama, Missouri, Tennessee, Kentucky and Pennsylvania.
Earlier this year, a 20-foot sinkhole in Florida swallowed a house and its resident after developing while the man was sleeping.
On Aug. 11, 2013, a 60-foot-wide sinkhole formed under the Summer Bay Resort in Clermont, Fla., prompting the evacuation of its guests. Nobody was injured.
Content contributed by Molly Cochran.
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