Sinkhole in the Danube near Möhringen Schematic of the sinkhole locations and the route to Aachtopf Completely dry Danube riverbed right , Sink hole on the southern bank of the Danube, at the main sinkhole site below Immendingen Sign in Immendingen. Translation: "Sinkhole – Here the Danube sinks dry on about 155 days per year" The Danube Sinkhole (german: Donauversinkung or ) is an incipient underground stream capture in the

Upper Danube Nature Park The Upper Danube Nature Park (German: ''Naturpark Obere Donau''), founded in 1980, is located in the south of Baden-Württemberg in Germany and encloses primarily the districts of Tuttlingen and Sigmaringen. It encompassed initially 860 k ...

. Between

Immendingen Immendingen is a municipality in the district of Tuttlingen in Baden-Württemberg in Germany located on the Upper Danube. It is famous for the Danube Sinkhole. Geography Immendingen is located on the Upper Danube. On the municipal area are part ...

and Möhringen and also near

Fridingen Fridingen () is a town in the district of Tuttlingen, in Baden-Württemberg, Germany. It is situated on the Danube, 10 km east of Tuttlingen, and 23 km west of Sigmaringen. A large hoard of Bronze Age jewellery (mostly armlets and brac ...

(

Tuttlingen Tuttlingen ( Alemannic: ''Duttlinga'') is a town in Baden-Württemberg, capital of the district Tuttlingen. Nendingen, ''Möhringen'' and ''Eßlingen'' are three former municipalities that belong to Tuttlingen. Tuttlingen is located in Swabia ea ...

), the water of the

Danube The Danube ( ; ) is a river that was once a long-standing frontier of the Roman Empire and today connects 10 European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for , p ...

sinks into the riverbed in various places. The main

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...

is next to a field named ''Brühl'' between Immendingen and Möhringen. The term "sinking" is more accurate than "seeping", because, instead of just distributing into the soil, the Danube's water flows through

caverns A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

to the

Aachtopf The Aachtopf () 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 undergro ...

, where it emerges as the river

Radolfzeller Aach The Radolfzeller Aach (also known as Hegauer Aach) is a right or north tributary of the Rhine in the south of Baden-Württemberg (Germany). It is approximately 32 km long. Course The source of the river is the ''Aachtopf'' in Aach, the la ...

, a tributary of the

Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , so ...

Hydrography

The sinking Danube water disappears into a karst water system of the ''well-stratified limestone formation'', the ''ox2'' layer, of the White Jura and appears again in a horizontal limestone layer, the ''ki4'' layer, approximately twelve kilometers away at

. It then flows as

into Lake Constance at Radolfzell. Thus, a part of the Danube water also flows into the

. This geographical situation is a striking feature of the large European Watershed, which separates the catchment areas of the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

and the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...

. The water flows out through a variety of small to very small cracks and crevices; the karst in these places is apparently at an early stage of development. The cave system of Aachtopf, which is the underground river Danube is, however, probably already well developed; This can be inferred from the tight correlation in water temperatures of the Danube and the Aachtopf spring, which matches the behaviour of an underground river better than that of a branching system.

History

The first documented case of the Danube completely disappearing into the hole dates back to 1874. Since then, the number of days per year when this happens has risen sharply. Between 1884 and 1904, it happened, on average, 80 days per year. In 1922, it happened only on 29 days. In 1923, however, the number increased to 148. Between 1933 and 1937, the average was on 209; from 1938 to 1945, it was 270 days. The highest number so far, was in 1921, with 309 days. The relationship between the sinkhole and

spring was proven in October 1877. Geologist

Adolf Knop Adolf Knop (12 January 1828, in Altenau – 27 December 1893, in Karlsruhe) was a German geologist and mineralogist. He studied mathematics and sciences at the University of Göttingen, where he was a pupil of chemist Friedrich Wohler and ...

of the Karlsruhe Institute of Technology poured 10 kg of

sodium fluorescein Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used ...

, 20 tons of

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

, and 1200 kg of

shale oil Shale oil is an unconventional oil produced from oil shale rock fragments by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock (kerogen) into synthetic oil and gas. The resulting oil ca ...

into the Danube on 9 October. After 60 hours, all three substances emerged at the Aachtopf. The water at Aachtopf was described as "gorgeously green lit" by the fluorescein and tasting of creosote. Later, the connection of the individual sinkholes was explored. In 1908 an experiment of downing water in Fridingen in the presence of Baden and Württemberg Government representatives confirmed the assumption of Professor Endrist -Stuttgart that the Fridingen sinkhole not only leads to the Aach, but that large amounts of it could also be artificially induced. A German newspaper in the US reported about the event. In about 1908, a shaft was dug in Fridingen in an attempt to find out where the water of this sinkhole disappears to. In 1927, a case was brought before the Supreme Court of the German Reich between

Württemberg Württemberg ( ; ) is a historical German territory roughly corresponding to the cultural and linguistic region of Swabia. The main town of the region is Stuttgart. Together with Baden and Hohenzollern, two other historical territories, Würt ...

and

Prussia Prussia, , Old Prussian: ''Prūsa'' or ''Prūsija'' was a German state on the southeast coast of the Baltic Sea. It formed the German Empire under Prussian rule when it united the German states in 1871. It was ''de facto'' dissolved by an em ...

as the ruler of the

Hohenzollern Province The House of Hohenzollern (, also , german: Haus Hohenzollern, , ro, Casa de Hohenzollern) is a German royal (and from 1871 to 1918, imperial) dynasty whose members were variously princes, electors, kings and emperors of Hohenzollern, Brandenb ...

on the one hand, and the state of

Baden Baden (; ) is a historical territory in South Germany, in earlier times on both sides of the Upper Rhine but since the Napoleonic Wars only East of the Rhine. History The margraves of Baden originated from the House of Zähringen. Baden is ...

on the other hand, to decide the smoldering controversy over the quantitative impact of the Danube sinkhole, which is known as the Danube Sinkhole case (german: :de:Donauversinkungsfall).The Court rendered an interim decision and left the final settlement to an agreement between the parties. In January 1937, the "Donau-Aach-Gesetz" gave the Reich Minister the authority to decide on necessary measures and who was to pay the costs. After WWII, in 1967, a canal was built between Immendingen and Möhringen, which brings water to Tuttlingen during times of low water levels.

Outlook

As the karst is developing, future sinkhole stretches cannot be accurately predicted. The underground river Danube annually removes about 7,000 tons of lime, that is 2,700 m³ in volume, from the karst system. Future expansions or collapses in the underground system are conceivable, which would show above ground as

sinkholes A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...

ponor A ponor is a natural opening where surface water enters into underground passages; they may be found in karst landscapes where the geology and the geomorphology is typically dominated by porous limestone rock. Ponors can drain stream or lake wate ...

s. In the long run, today's upper Danube will probably be redirected entirely into the

, and thus to the

. This would mean that other tributaries that are currently insignificant would become the new headwaters of the Danube. The Danube has experienced a similar stream capture further upstream, during the

Würm glaciation The Würm glaciation or Würm stage (german: Würm-Kaltzeit or ''Würm-Glazial'', colloquially often also ''Würmeiszeit'' or ''Würmzeit''; cf. ice age), usually referred to in the literature as the Würm (often spelled "Wurm"), was the last g ...

, when the ''Feldberg-Danube'' was captured by the Wutach at the

Wutach Gorge The Wutach Gorge (german: Wutachschlucht) is a narrow, steep-sided valley in southern Germany through in the upper reaches of the River Wutach with three gorge-like sections, the lowest of which is also called the ''Wutachflühen''. The gorge cu ...

near

Blumberg For the town in South Australia previously called Blumberg, see Birdwood, South Australia. Blumberg is a municipality situated in the Schwarzwald-Baar region of Baden-Württemberg, Germany. Nineteen kilometres south of Donaueschingen, it lies ...

Coordinates

The water of the Danube is captured at the sinkholes in Immendingen () and Fridingen () and emerges at Aachtopf (). It flows into Lake Constance at Radolfzell (). The Rhine flows out of Lake Constance () and towards Basel, where it turns north (). When the Rhine captures the headwaters of the Danube through the karst, the new headwaters of the Danube will be the Krähenbach where it currently meets the Danube ( ) and the Elta where it currently meets the Danube ().

External links

Nachlese: Report on search for the underground river Danube

Testimony of the discovery of the Danube cave

Website about the construction of access to and further exploration of the Danube cave

Footnotes

{{Coord, 47.932173, N, 8.763528, E, display=title, type:landmark_region:DE-BW_dim:500 Danube Sinkholes of Europe Karst formations of Germany Landforms of Baden-Württemberg Rhine South German Scarplands Landforms of Germany