Any closed depression in the land surface formed as a result of the collapse of the underlying soil or bedrock into a cavity. Sinkholes are common in areas where bedrock is near the surface and susceptible to dissolution by infiltrating surface water. Sinkhole is synonymous with doline, a term used extensively in Europe. The essential component of a hydrologically active sinkhole is a drain that allows any water that flows into the sinkhole to flow out the bottom into an underground conduit.

(also known as dolines) - A closed surface depression draining underground in karst landscape. Sinkholes are often "bowl-shaped" and can be a few to many hundreds of meters in diameter.

depressions in the ground surface where limestone rock has collapsed into underground caves hollowed out by running water.