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THE KARST SYSTEM All exogenous phenomena are generally grouped under the name of karsts. This is the result of the effect of predominantly chemical erosion of carbonate rocks (dolomite, limestone, crai, etc.) and of some sulphuric rocks (gypsum, anhydride) and saline rocks (rock salt, etc.). These rocks are dissolved by water, especially rainwater, in corresponding measure to their solubility, the highest solubility being in salt rock and the lowest in carbonate rocks that have a largely magnesian content (dolomite).As far as carbonate rocks are concerned, the phenomenon occurs because rainwater contains a significant amount of dissolved CO of atmospheric origin in the form of dissociated carbonic acid, and so in practice it is weakly acidic. This intensifies the chemical dissolution of the carbonate as the carbonic acid converts calcium carbonate into bicarbonate as shown in the following chemical formula: | H2O + CO2 | H2CO3 | CaCO3 + H2CO3 | ↔ | Ca (CO3H)2 | | Water + Carbon Anhydride | Carbonic Acid | calcite+ Carbonic Acid | ↔ | Calcium Bicarbonate |
As you can see, bicarbonate is soluble and therefore removable and transportable in a dissociated form from water. The dissolution caused by the acidulous water is most evident in the widening of the fissures of the rock, at first on the surface and then in depth. This phenomenon results in morphological surface details (epiges) and underground details (hypoges.)Among the epigeic forms, let us mention the great depressions called polje and the smaller ones called ùvala; the dolinas, funnel-shaped depressions that are more or less symmetrical at the base; the sinks, of the same type as the dolinas, but characterized by vertical wells that are very deep; the karst fields or ploughed fields, which correspond to sloping rock surfaces on which the water flows and shows its dissolving action producing a series of furrows that are more or less parallel.Among the hypoge karst forms are galleries and caves or cave systems which usually consist of a series of chambers which are often very large, linked by slightly sloping narrower galleries. It is not uncommon for the large chambers to house true and proper lakes in their depths. Normally hypoge karst systems house subterranean streams. Bibliography: - F. Ippolito, P. Nicotera, P. Lucini M. Civita R. de Riso “Geologia Tecnica per ingegneri e geometri” Tipografia ISEDI Istituto editoriale Internazionale Milano
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