Karst

The karst is a landscape worked in carbonated soluble Roche S. It is not a rock but well a landscape which can develop in the Calcaire (mainly), the Marbre, the Dolomie or the Craie. The karstic landscapes are characterized by forms of corrosion of surface, but also by the development of cavities by subterranean water circulations.

The study of the karst is the Karstologie and the karstic adjective “ ” indicates what is relating to the karst.

The karst is the privileged ground of practice of the speleologists.

Etymology

The word karst comes from Kras, area Slovenien of plates limestones to the modelled characteristic. The word was germanisé in " karst" when the country was integrated into the Empire Austro-Hungarian.

The concept of karst was introduced in 1893 by Jovan Cvijic into its book Das Karstphänomen .

The karstification

The rock is worked by Dissolution, it is what is called the karstification.

The chemical reactions responsible for the dissolution of the Carbonate S are the following ones:

CO2 + H20 <-> H2CO3

  • aqueous Dissociation of the carbon Dioxide :

H2CO3 + H2O - > H3O+ + HCO3-

  • acid Attack of the carbonates (" calcaires") :

H3O+ + CaCO3 <-> Ca2+ + HCO3- + H20

  • Equation assessment:

CO2 + H20 + CaCO3 <-> Ca2+ + 2 HCO3-

It will be observed that in the content of Hydrogénocarbonate, a carbon atom comes from the calcareous matrix and that the other comes from carbonic gas (especially of biogenic origin because the concentration of this last in the ground is much more important than in the atmosphere). These two sources are differentiable besides by their contents of Isotope S of carbon (segregation of carbon 13 by the living beings).

Dissolution, and thus the formation of modelled karstic, are thus supported by:

  • the abundance of the Water;
  • content of water of CO2 (which increases with the pressure);
  • the low temperature of water (the colder one water is, the more it is charged out of gas thus in CO2);
  • the living beings (which reject of CO2 in the ground by breathing what reinforces its content considerably);
  • the nature of the rock (fracturings, composition of carbonates, etc);
  • the time of contact water-rock.

A cold, wet and calcareous area is likely thus more to develop a relief of karst. However, one finds this modelled on the whole of the sphere, as in hot and wet areas.

Formation of the stalactites and the stalagmites

When water, charged with gas and limestone dissolves, arrives in a cavity more important than the cracks by which it passed (cracks and diaclases caused by the movements Tectonique S or by the Gélifraction on the surface for example), it is degassed. Then, the calcium carbonate contained in each drop must be recristallized, either in the form of Stalactite with the ceiling of the cavity, or in the form of Stalagmite on the ground (average Mnémotechnique not to confuse both: the stalactite falls from the roof; the stalagmite goes up).

If you are attentive, you can observe stalactites in formation in the corridors of the Parisian subway. Obviously, they do not have the charm of those which one can see in the Grotte S! Moreover, they are often cleaned and thus not very bulky.

Forms of the karstic relief

The karstic areas comprise quite particular forms of relief like the Doline S and Ouvala S, the Polje S, the Ponor S, the Polje S the Canyon S, the lapié S, the Avens, the dry Vallées or the loss S and the Résurgence S.

One can also find Reculée S, even of the circuses of karstic erosion like the circus of Ramon, close to the Israeli city of Mitzpe Ramon.

The karst accounts for 20% of the emerged grounds.

In France, the modelled karstic one is present on almost half of the territory (the Alps, the Pyrenees, the Jura, Préalpes of Provence, Lorraine plate, Paris basin, Aquitanian Bassin,…).

Notable sites

Some modelled karstic are very famous, such as for example:
  • the Bay of Along in Vietnam (karst with turret ennoyé then by the sea);
  • the Cave Cosquer in France (the sea level was not always that which we know today. In glacial period, it was much lower: the Cosquer cave was not under water. Today, under water, near the Cosquer cave, one finds dolines, etc testifying to the karstification of the area at one former time);
  • the site of Montpellier-the-Old man where one can observe karstic arches and turrets (a sequence of the film the Great Ramble there was turned);
  • the lake of Stymphale in Greece (made famous for the fifth work of Hercules)
  • ares of the Annie in the valley of Barétous in France (64), one of the " déserts" Europeans
  • the Punt desert, in the mountains of Faucigny in Haute-Savoie in the natural reserve of Sixt-Passy, is one of the wide-area networks of cave of Europe.

Some karstic sites in the world

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