Karst spring
A karst spring or karstic spring is a spring (exsurgence, outflow of groundwater) that is part of a karst hydrological system. == Description == Because of their often conical or inverted bowl shape, karst springs are also known in German-speaking lands as a Topf ("pot") which is reflected in names such as Aachtopf (the source of the Radolfzeller Aach) or Blautopf (the source of the Blau river in Blaubeuren).