maasisene karstivorm; lõhede kaudu või otse maapinnale avanev tunnel või selle laiend; tekkinud lõhede kohale salajõgede vooluteel, is a hollow place or void in the ground formed due to dissolution of rocks in the water. Over geological epochs smaller openings (faults, joint etc) expand as the walls are dissolved to become caves or even cave systems at several levels. The portions of a solutional cave that are below the water table or the local level of the groundwater can be flooded.