"A sinkhole, also known as a sink-hole, sink, swallow hole, shakehole, swallet or doline, is a natural 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 or suffosion processes in sandstone. Others formed as a result of the collapse of old mine workings close to the surface are not natural and therefore not sinkholes.
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
Contributions by Vsmith, 188.8.131.52, and Altenmann."