How many litres of rainwater is required to dissolve a few milligrams of limestone?
To dissolve a few milligrams of lime we need one litre of rainwater.
A karst landscape can appear only where there are water-soluble rocks like limestone and dolomite. Another name for them is carbonate rocks, after the main mineral they contain – calcium carbonate. Both rocks appeared as sea sediment. Karst stone has been used by man for building since prehistoric times. In some areas of the Kras, the traditional karst houses are built almost fully from stone cut by hand.
Limestone is a rock primarily made up of water soluble calcium carbonate, CaCO3. One litre of pure rainwater can dissolve a few milligrams of lime. A similar rule applies to dolomite rock. The solubility increases when carbon dioxide (CO2) from the air or the soil also dissolves in the water, creating a mild carbonic acid (H2CO3). The acid dissolves the carbonate rock, resulting in the appearance of calcium (Ca2+) and hydrogen carbonate ions (HCO3). This process takes place in both directions. One litre of rainwater percolating through the soil to the limestone can thus dissolve up to a few hundred milligrams of calcium carbonate.
The Kras is the area between the sources of the River Ljubljanica and Bay of Trieste, which thanks to its famous caves, intermittent lakes, sinking rivers and river sources, rocky surface and dolines, has always aroused interest among both locals and travellers. As this is where the first scientific research of karst landscapes and phenomena took place, the Kras, or “classical karst” has become the “locus typicus” of such landscapes around the world, giving its name to this natural phenomenon.
Authors: Andrej Mihevc, PhD and Slavko Polak