Karstic spring

A karst spring is a spring that is part of a karst system. That includes the underground drainage of a much larger area, which means that karst springs often have a very large discharge. Because of their often conical or bowl shape, such water sources 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).

Karst springs are usually the end of a cave system at the place where a river cave reaches the Earth's surface. Thus, it is often possible to enter the caves at a karst spring and explore them. Large karst springs are located in many parts of the world. The world's largest karst springs are believed to be in Papua New Guinea, with others located in Mediterranean countries including Bosnia, Turkey, Slovenia and Italy.

An estavelle or inversac is a ground orifice which, depending on weather conditions and season, can serve either as a sink or as a source of fresh water. It is a type of sinkhole.

A Vauclusian spring is a spring that originates from a shaft or a cave system, with the water surging upwards under relatively high pressure. It is named after the Fontaine de Vaucluse in southern France.

Submarine karst springs, also known as vruljas, occur worldwide, and are most numerous in shallow waters of the Mediterranean Sea.

...
Wikipedia