A sinkhole, also known as a sink-hole,[1] sink, swallow hole, shakehole,[2] swallet or doline, is a natural[citation needed] depression or hole in the ground caused by some form of collapse of the surface layer. Some are caused by karst processes—for example, the chemical dissolution of carbonate rocks[3] or suffosion processes[4] in sandstone. Other depressions formed as a result of the collapse of old mine workings close to the surface are not natural and therefore not sinkholes.[citation needed]
Sinkholes may vary in size from 1 to 600 m (3.3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may be formed gradually or suddenly, and are found worldwide. The different terms for sinkholes are often used interchangeably.[5]