Furchenstein

from Wikipedia, the free encyclopedia
Crust stone on the Chiemsee shore - the furrowing becomes visible under the wiped away crust
Furchensteine ​​from Chiemsee
Hirnstein from Chiemsee

Furrows stones are sculptured limestone - attachment , the surface of more or less deep, often meandering sinuous groove-like channels are crossed, a series of bioerosion. The term crust stones is then common as long as the stones are covered with a lime crust made of so-called cyanobacteria . They occur in lime-rich inland lakes.

description

The conspicuous furrow stones, crisscrossed by labyrinthine canals and holes, are often found on the banks of calcareous lakes. Furchensteine ​​are widespread, for example finds from Switzerland, Austria, Denmark and Croatia are documented. This phenomenon was observed and scientifically described in Swiss lakes as early as the mid-19th century. In the first work on this topic, mussels or insect larvae were assumed to be the sole cause of the furrows. However, it was observed early on that these furrows always occur under a tuff-like, calcareous crust on the so-called crust stones. It was therefore assumed that this limestone crust was partly responsible for the formation of the furrows.

Mainly responsible for the formation of the lime crusts are the so-called cyanobacteria , which are able to form lime themselves, because they are able to use both CO 2 and HCO 3 - for photosynthesis. As a result, they increase the pH value and the alkalinity between their filaments considerably and promote the precipitation of lime, which only works if these dissolved carbonates are sufficiently available in the seawater. In pre-alpine lakes, for example, this is ensured by the water from the nearby limestone Alps as well as the limestone-rich glacial sediments of the area and their weathering products. In addition, a significant proportion of the lime crust is also due to trapped particles that get caught in the filaments or mucous coating of the cyanobacteria and contribute to an additional solidification of the crust. The result is a dense, chalky crust made up of small bumps and spots reminiscent of miniature reefs.

Between the individual cauliflower-like 'florets', corrosive processes within the crust are the best starting points that lead to the formation of the characteristic furrow pattern. The substrate is still the most vulnerable in these gaps, because the limestone crust at the base of the tufts is more solidified and therefore provides better protection.

The process of furrow formation is now initiated again by cyanobacteria. Some of these organisms involved in the formation of the calcareous crust are able to drill into calcareous rock under the crust. You will also be assisted by some boring mushroom species. These so-called endoliths create the prerequisite for the formation of the furrows, as they drill into the subsurface of the crust and weaken it decisively. Grazing animals that penetrate the crust, such as snails or some larvae, then further damage the subsoil. They quasi gnaw at the already loosened areas and thereby further hollow out the furrows. In addition, inorganic lime dissolution takes place in the cavities created. Rotting organic residues lead to local acidification of the water contained and thus develop additional corrosive forces.

Naming

If one follows that since the beginning of the 20th literature century the theme of Kalkinkrustation and Kalkkorrosion in lakes treated are initially following terms in the game: tuf lacustrine and galets Sculptes . In the meantime, the following names have become common.

Crust stone

With the work of Edith Kann Crust stones in lakes - a comparative overview , the term crust stone has been introduced in general. The document lists more than 20 European calcareous lakes for which studies and considerations regarding the occurrence of crustal stones are available.

The formation of crusts on stones is caused by lime-separating blue algae , the thickness of the layer can range from a few millimeters to centimeters. The crust stones form in the so-called eulitoral and also in the upper sublittoral . Crusts can form quite well on stones if the beach is wide and has a very small angle of approach . Fluctuations in water with brief drying out do not damage the crust, because its spongy structure can hold moisture for a long time. On the contrary, it can be observed that the crust formation becomes stronger in these cases.

Furchenstein

The first studies on limestone corrosion in lakes in connection with algae were carried out in Switzerland in the middle of the 19th century. By the beginning of the 20th century, different ways of explaining the origin of furrowing had emerged.

The most detailed studies are available, by Boysen-Jensen P. (1909) - About stone corrosion on the banks of Furesö. - Golubic S. (1962) - On the knowledge of lime incrustation and lime corrosion in the lake littoral.

The furrow stones are a type of crust stone as they are usually covered with crust. The furrows usually only become visible after the crust has been removed. They are of various kinds, curved and intertwined like a labyrinth, sometimes forming very fine channels and holes. Thin, sharp-edged ridges are characteristic between the furrows. The course of the furrows is mostly irregular in the depth (sublittoral), only in the eulittoral and in its vicinity they tend to be vertical.

Silicate rock never has furrows.

Brain stoa or brain stone

Locals at Chiemsee and Lake Constance call crust stones and furrow stones , whose surface structure resembles that of a brain , also brain stoa or brain stone .

Conditions for the random / meandering or vertical build-up of crusts / furrows

S. Golubic (1962) found in his investigations on Lake Vrana in Croatia that the crusts and furrows in the depths of the lake are mostly irregular. Whereas in the eulitoral the crusts and furrows tend to be arranged vertically.

On the Chiemsee , due to the heavy sedimentation of the Tiroler Ache (up to 300,000 m³ / year) in the catchment area when the snow melts / heavy rain, the crust stones and furrow stones occur only in the Eulitoral. However, calm zones can be identified in which the wave movements are greatly reduced. z. B. the " lagoon " west of the Seehäusl, the shallow water area at the observation point north of Chieming , a reed belt near Schützing, ....

Both manifestations, irregular / meandering and also vertical arrangement of the crusts / furrows on the Chiemsee are represented.

  • Crust stone / furrow stone with meandering / random arrangement

  • Furchenstein with vertical arrangement

Historical illustrations

  • ULE W. (1901) Crust stones from Lake Starnberg

  • BOYSEN-JENSEN P. (1909) Furchenstein from Furesö

  • BAUMANN E. (1911) Crust stones from Lake Constance

Web links

Commons : Furchenstein  - album with pictures, videos and audio files

literature

  • Eugen Baumann: The vegetation of the Untersee (Lake Constance). A floristic-critical and biological study by Dr. Eugen Baumann in: Archives for Hydrobiology and Plakton Studies. edited by Prof. Dr. Otto Zacharias, Supplement-Volume I, Stuttgart 1911, Chapter III c) Lime coatings on stones, furrow stones (“galets sculptes”) , book page 49 and Doc-page 59.
  • Willi Ule: The Würmsee (Starnbergersee) in Upper Bavaria. A limnological study by Willi Ule. In: Scientific publications of the Geography Association in Leipzig. Fifth volume published with the support of the Geography Association and the Carl Ritter Foundation in Leipzig, 1901, chapter Der Seegrund. , Book page 74 or doc page 98.
  • S. Golubic: On the knowledge of calcium incrustation and calcium corrosion in the lake littoral. In Switzerland. Z. Hydrobiol., 24: 1960, pp. 229-243.
  • P. Boysen-Jensen: About stone corrosion on the banks of the Furesö. Message. from the biolog. Freshwater rennet. Frederiksdal near Lyngby (Denmark) 1909.
  • Edith Kann: Crust stones in lakes. A comparative overview. In: Archives for Hydrobiology. Volume 37, 1941, pp. 504-532.

Individual evidence

  1. ↑ a b Gaudin, (1865). Note on certain galets des bords du lac de Geneve. Bull. De l. Soc.Geolog. Vaudoise.
  2. ↑ a b P. Boysen Jensen: About stone corrosion on the banks of Fureso. In: Int. Rev. Ges. Hydrobiol. , 2: 1909, pp. 163-173.
  3. ↑ a b c d Edith Kann: Crust stones in lakes. A comparative overview. In: Arch. Hydrobiol. 37: 1941, pp. 504-532.
  4. ↑ a b c d e f g S. Golubic: On the knowledge of calcium incrustation and calcium corrosion in the lake littoral. Switzerland. Z. Hydrobiol., 24: 1962, pp. 229-243.
  5. ↑ a b c H.G. Schröder: Biogenic benthic decalcification as a contribution to the genesis of limnic sediments. Example: Attersee (Salzkammergut; Upper Austria). Dissertation, Göttingen 1982. 179 pp.
  6. ^ Schneider, J. Schröder, HG & Le Campion-Alsumard, T. (1983). Algal micro-reefs: coated grains from freshwater environments. In Coated Grains (Peryt, TM, editor), 284-298. Springer, Berlin.
  7. ^ J. Schneider, T. Le Campion-Alsumard: Construction and destruction of carbonates by marine and freshwater cyanobacteria. In: Eur. J. Phycol. 34: 1999, pp. 417-426.
  8. ↑ E. Baumann: The vegetation of the Untersee (Lake Constance). In: Archiv f. Hydrobio. and plankton science. Volume I: Chapter III: 1911, pp. 49-54.
  9. ↑ a b c P. Boysen-Jensen: (1909). About stone corrosion on the banks of Furesö. In: Mitteil. biol. Freshwater rennet. Frederiksdal near Lyngby (Denmark). III: 1901, pp. 163 ± 173.
  10. ^ W. Ule: The Würmsee (Starnberger See) in Upper Bavaria. A Limnological Study. (= Scientific publication of the Geography Association in Leipzig. 5) 1901, pp. 74 ± 78.
  11. ↑ The Chiemgau Impact - a speculative bubble or the Tuttensee is NOT a comet crater
  12. ↑ Lake Constance - ... the furrowed rubble stones covered with blue-green algae ("furrow stones or brain stones")
  13. ↑ Chiemsee Conference 2014 - Landing of the Chiemsee