Sinkholes are common in humid areas where limestone forms the underlying bedrock.
Geologists refer to these areas as karst.
Sinkholes are formed when ground water reacts chemically with the limestone and dissolves it over time, causing either a depression or a hole in the ground.
Large holes result when the dissolved limestone is part of the roof of a cave.
Sinkholes can be shallow depressions of about 3 feet (1 m) or so to straight-sided holes more than 100 feet (30 m) in diameter and more than 150 feet (46 m) deep.
Sinkholes are common and frequently cause property damage in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, Virginia, and Pennsylvania.