Panhole

A panhole is a depression or basin eroded into flat or gently sloping cohesive rock. The feature goes by several other names, including gnamma or rock hole in Australia, armchair hollow, and weathering pan or pit, as well as solution pan or pit. Some authors also call panholes potholes, but in fluvial geomorphology the word pothole is normally kept for a similarly shaped landform in a stream bed: a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, ground out by a stone or coarse sediment whirled around by eddies or the force of the current in one spot. The two features are therefore named alike in some usage, but the riverine pothole is the product of that grinding action in a channel bed.