Aachtopf

The Aachtopf ([ˈaːxtɔpf]) is Germany's biggest karst spring, south of the western end of the Swabian Jura near the town of Aach. It produces an average of 8,500 litres per second. Most of the water stems from the River Danube where it disappears underground at the Danube Sinkhole, 12 kilometres (7.5 mi) north near Immendingen and about 14 kilometres (8.7 mi) north near Fridingen. The cave system has been explored since the 1960s, but as of 2020 only a small part has been discovered due to a large blockage after a few hundred metres. The name Aachtopf is compounded from Aach (meaning "water" in Old High German); Topf can be translated as "bowl" and is commonly used for round, bowl-shaped springs. The Aachtopf is a karst spring, south of the western end of the Swabian Jura near the town of Aach. The spring is the source of the river Radolfzeller Aach, which flows southward into Lake Constance, and empties into the Rhine. The spring marks the southern end of a cave system that transports water from the western end of the Swabian Jura. It produces an average of 8,500 litres per second. Production varies seasonally and in response to the weather, but the spring never runs dry. Most of the water is derived from the Danube where it disappears underground at the Donauversickerung (Danube Sinkhole) near Immendingen and Fridingen. The Rhine's steeper gradient on its much shorter route to the North Sea creates stronger headward erosion than that of the much older River Danube (see the Danube upper river geology). This stream capture of the upper Danube and its surface tributaries is expected to cause the long-term disappearance of the Danube drainage entirely in favour of the Rhine. The Danube flows eastwards into the Black Sea, whereas the Rhine flows northwards to the North Sea. Therefore, the water of the Aach flows under the European watershed. This is a relatively common feature of karst stream captures. The karst spring is connected to a huge cave, which runs northwards. The cave is completely water-filled and can only be explored by cave divers.

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