> THE KARST - How the karst was formed
The karst is the result of the action of acid water on limestone rock.. Highly acid water dissolves the carbonates of which limestone is made and this leaves empty spaces that are sometimes extremely large.
At first sight, these contorted empty spaces are scattered here and there and seem be randomly distributed in the limestone layers...
However recent studies show that they are very well organised with the links between them following structural rules with a well defined sequence of events which arise from the conditions under which they are created.
Two elements are needed for this process: limestone rock and acid water.
Limestone rock.
These rocks are very widespread throughout the world and are of two kinds: sedimentary – formed from pre-existing rocks; or biochemical – constructed by organisms such as coral or some seaweeds.
In France, they make a third of the land mass...
Limestone is mainly made up of calcium carbonates (CaCO3). The main minerals that are created are “calcite” and “aragonite”.
Sometimes magnesium carbonate is combined with calcium carbonate and the resulting rock is known as “dolomite” or “dolomite limestone”. The corresponding mineral is “dolomite” (MgCaCO3).
Limestone and dolomite are usually very hard rocks which are found in compact layers, known as strata, separated by various substances..
Although folds are sometimes found, they are very brittle and fissures are easily formed when they are subjected to mechanical stress.
Being impermeable, they dissolve very slowly in acid solutions.
Acid water.
Rainwater is not normally acid. Water becomes acid when it falls through the atmosphere, and then, when it percolates through the ground, it becomes charged with carbon dioxide (CO2), that results from bacteriological action on the organic matter (plants and animals) present in the ground.
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