Into the blue...
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The Blautopf or Blue Pool - 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 where does the striking blue color come from? In fact, the blue color is a physical phenomenon caused by the refraction of daylight in clear water. Blue, which is the short-wave portion of daylight, is refracted shortly after immersing into water, it is diffused and thus becomes visible to the human eye. The reflection of the blue light on the calcium carbonate particles floating in the water intensifies the impression of the blue color to a wonderful turquoise.
Where the water comes from
Water visibly and audibly gushes out of the Blautopf. But where does the water come from? It accumulates in an extensive cave system in the belly of the mountain range of the Swabian Jura. It forces its way through the so-called nozzle at a depth of 22 meters before rising and flowing over the weir. On average, the Blautopf spills about 2200 l/s, which makes it the second strongest karst spring in Germany. The spillage, however, fluctuates significantly depending on the weather. After long phases without precipitation, only some 290 l/s gurgle into the small channel towards the water wheel, whereas after intense and persistent rainfall, up to 32,000 l/s roar over the weir. When this happens people of Blaubeuren tend to say: “The blue pot is boiling”.
Blue Cave research
The Blautopf is the entrance to a huge cave system that roughly follows the course of the B 28 northwest towards Bad Urach. Today, three research groups, the ARGE Blautopf, the Blaubeuren cave association and the ARGE Blaukarst carry out research in the Blue cave area. It was only in 1957 that researchers from Munich managed to reach the entrance to the Blue Cave at the bottom of the Blautopf. From 1961 onwards Jochen Hasenmayer conducted research in the Blautopf and in 1985, after diving about 1,250 meters into the belly of the mountain, he reached a 125 meters long cave. This cave hall is filled with air as it is above the karst water level. It was named Mörike Dom in remembrance of the romantic poet Eduard Mörike (1804 - 1875), who described such caves in his fairy tale "The story of the Beautiful Lau". In 2006, Jochen Malmann and Andreas Kücha from ARGE Blautopf discovered the huge cave hall called Apocalypse. Its gigantic size offers enough space for the nave of the Ulm Minster. Next to the B 28 a 17 meters deep manhole was drilled in 2010 to open a dry route into the Blue Cave system. However, only speleologists are allowed access. Currently there are no plans to transform the Blue Cave into a show cave as this would require immense technical knowhow and consume an enormous amount of money. Meanwhile the Blue Cave has been explored up to a length of 18 kilometers. The cave explorers expect it to be more than 20 kilometers long which would make it the longest cave in Germany.
The Drop Hammer Mill
In 1804, the blacksmith Abraham Friedrich converted a grinding mill at the Blautopf into a water-powered drop hammer mill, which was in operation until 1900 when the drop hammers were removed. It was the time when steam power replaced water power. However, with tourism increasing in the 1960s, the town bought three historic drop hammers and installed them here for show events. Like in the old days these drop hammers are powered by a water wheel, which turns a wooden shaft made of an oak tree trunk. The heavy heads of the three drop hammers weigh 80 kg, 100 kg and 120 kg.
The Swabian Jura water supply
While thanks to the karst springs there was always enough water in the valley, the plateau of the Swabian Alb was an area of water shortage until the end of the 19th century: “Woe to the stranger who comes to one of the primitive Alb villages, where straw roofs predominate and people rely solely on rainwater (...). The water that runs down from the thatched roofs is straw- and even coffee-colored. Only those accustomed to the sight of such water are able to put the glass to their lips without a feeling of disgust” (from: Oscar Fraas, 1873). Between 1870 and 1881 engineers designed water-powered pressure pumps to supply the villages on the plateau with water all year round. One of the old pumps dating from 1875 can still be seen in the old waterworks next to the Blue Pool.
What does "Karst" mean?
The Blautopf is a karst spring embedded in the landscape of the Swabian Jura, the largest karst area in Germany. The Swabian Jura consists of a several houndres meters thick layer of limestone that was deposited in the tropical Jurassic Sea around 200 to 140 million years ago and was lifted up 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. The water from a catchment area of 165 square kilometers gathers in the extensive Blue Cave system, gushes out into the Blautopf and then feeds the river Blau which meanders for about 20 kilometers through the picturesque valley of the Blau before flowing into the Danube in Ulm.
