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GENERALITY
Presentation

The subterranean environment represents one of the biggest ground ecosystems of the planet. It is made up of natural cavities in the calcareous mountains but also more generally of underground shelters dug by man, old mines, piles of fallen rocks, tubes of lava or the cracks formed by streams. When we talk about a cave, it is necessary to differentiate between the subterranean environment in general and the karst in particular.

Karst

The origin of the word comes from a limestone region of Slovenia, Karst. It refers to all space dug out in calcareous rocks, the penetrable cavities of which reveal some of its aspects. Under the combined action of water, carbon dioxide and time, limestone gives birth to an organized and hierarchical basic structure of cracks, galleries and chambers.

Subterranean heritage

Contrary to the natural environment outside, where the vegetation dies back and regenerates every year, the karstic environment shelters a heritage which builds up over the course of millenniums. Particularly stable, it is able to give back to us in a state of remarkable preservation so much the works of our distant ancestors, as well as vestiges of the fauna of the quaternary age (cave bears, mammoths, bisons) and even the tertiary age, with the speleothems that formed bit by bit and became integrated into the landscape.

Speleothems

The speleothems arise from deposits of matter transported in a dissolved state through the rocky mass, and result from the action of water and carbon dioxide on the soluble limestone. Of this reaction are born crystalline deposits of calcite, aragonite or gypsum, which, according to the various forces to which they are subjected, take the shape of stalactites, stalagmites, columns, etc.

Scientific interest

For science, the study of speleothems in caves remains a relatively unexplored domain. Only a very restricted part of the karst has been approached, still leaving in the shade whole areas of research. The study of karst requires complex and expensive, indirect methods, putting it out of reach for many researchers. Nevertheless the mineralogical, geochemical paléoclimatical interest is considerable. Today, a speleothem constitutes a natural record of the environmental conditions which presided over its forming and then over its preservation. A speleothem is the climatic memory of the Earth going back hundreds of thousand years.

Fragile heritage

This heritage is not only exceptional, it is also of a fragility beyond compare, both the modifications of the environment and the pollution connected with the presence of humans, direct (footprints, damage done by walking) and indirect (effects of human metabolism on the atmosphere in the cave) endanger the preservation of the karstic environment. For some years now, regular visits to subterranean sites, which often become damaged, voluntarily or not, have made the saving of caves and their contents a difficult but major task.

 

Text elaborated largely by Michel Bakalowicz, HydroSciences Montpellier – France

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