Into the blue...

The Blautopf - definitely blue!

Thanks to its wonderful blue color, the Blautopf is the most famous attraction in Blaubeuren and one of the highlights of the Swabian Alb. But why is the blue pot so blue? In fact, the blue color is a physical phenomenon caused by the refraction of daylight in clear water. The blue, short-wave portion of daylight is refracted after immersion in water, diffuses and thus becomes visible to the human eye. The million-fold reflection of the blue light on the lime particles floating in the water intensifies the blue color impression to a wonderful turquoise.

Where the water comes from

Water is visibly and audibly oozing out of the blue pot. But where does the spring water come from? It collects in an extensive cave system in the belly of the Swabian Alb and emerges through the so-called nozzle at a depth of 22 meters before rising and flowing over the weir. Depending on the weather, the Blautopf pours an average of 2200 l/s, making it the second strongest karst spring in Germany. The amount of fill fluctuates extremely: after long phases without precipitation, only a trickle of a minimum of 290 l/s gurgles over the Schmiedekanal, whereas after intense and persistent rainfall, up to 32,000 l/s roars over the weir. Then in the people of Blaubeuren say: “the blue pot is boiling”.

Blue cave research

The Blautopf is the entrance gate to a huge cave system that roughly follows the course of the B28 northwest towards Bad Urach. Today, three research groups, the ARGE Blautopf, the Blaubeuren cave association and the ARGE Blaukarst, are conducting research together in the Blau catchment area. It was only in 1957 that Munich researchers managed to reach the entrance to the Blue Cave at the bottom of the Blautopf. From 1961, Jochen Hasenmayer conducted research in the Blautopf and in 1985, after diving 1,250 meters, he reached a 125-meter-long space above the karst water level, the Mörike Cathedral. In 2006, Jochen Malmann and Andreas Kücha from ARGE discovered the huge apocalypse: it would offer space for the nave of Ulm Minster. In 2010, a 17-meter-deep borehole was created next to the B 28 to create a dry land route into the blue cave system that is only accessible to speleologists. Expanding the Blauhöhle as a show cave would involve immense technical and financial effort and is therefore not currently being planned. Today, the Blautopf Cave has been explored up to a length of 16 kilometers, and it is estimated that it is well over 20 kilometers long. This would make the Blauhöhle the longest cave in Germany.

The Hammer Forge

In 1804, the blacksmith Abraham Friedrich converted a grinding mill on the Blautopf into a hammer forge, which was only in operation until 1900 because steam power had made it technically independent of water power. With increasing tourism in the 1960s, the city renovated the building and installed a tail hammer system from the Allgäu for show purposes. Water is fed via a canal under the water wheel, which drives a mighty corrugated tree. Depending on his needs, he can have the three tail hammers hit with weights of 100 kg and 120 kg.

Alb water supply

While there was always enough water in the valley thanks to the karst springs, the plateau of the Swabian Alb was an area of water shortage until the end of the 19th century: “Woe to the stranger who lives in one of the primitive Alb villages, where straw roofs predominate and people rely solely on rainwater is, a need arises for a glass of water. (…) The water that runs down from the thatched roofs has turned straw yellow to coffee brown. Only those who have grown accustomed to the sight of this water are able to put the glass to their lips without disgust” (In: Oscar Fraas, 1873). From 1870 onwards, construction of the Alb water supply began in the Kingdom of Württemberg. According to plans by the engineer and building inspector Karl von Ehmann (1827–1889), eight pumping stations in river valleys were to feed elevated tanks on the Alb via pressure pipes, from which the communities could be supplied with water via hydrants and house connections. However, many Alb communities initially rejected the project as unrealistic or too expensive. In 1951, a monument was erected to the three creators of the Albwasser supply, the engineers Karl von Ehmann, his cousin Hermann von Ehmann and Oskar Groß, at the Blautopf not far from the Albwasser supply III pump house.

What means "Karst"?

The Blautopf is a karst spring embedded in the landscape of the Swabian Alb, the largest karst area in Germany. The Swabian Alb consists of a limestone package several hundred meters thick that was deposited in the tropical Jurassic Sea around 200 to 140 million years ago and was lifted over 1000 meters during the formation of the Alps. Over the course of millions of years, fissures and passages, even huge caves, have formed in the so-called White Jurassic limestone through dissolution processes. As a result, precipitation no longer flows above ground, but seeps into the karst underground. In the extensive blue cave system, the water from a catchment area of 165 square kilometers flows together and forms the Blau, which emerges in the Blautopf and winds as a blue ribbon for around 20 kilometers through the picturesque Blautal before flowing into the Danube in the Ulm urban area.

Interesting Links

logo Blaubeuren