Case Studies from the Dinaric Karst of Slovenia

GeomorphologyAndrej MihevcIn folk language, “karst” meant “barrenstony land.” This term often occurred in localtoponyms and could denote an entire landscape.Today, the word “karst” means a landscapewith specific relief, water, and undergroundfeatures that formed in long geologicalperiods on water-soluble rock, mostly limestoneand dolomite (Gams 1973; Kranjc 1998).Relief on impermeable non-karst rock isprimarily sculpted by water that runs on thesurface in river networks. Rivers sculpt fluvialvalleys that dissect the surface into valleys,slopes, and ridges. The valleys are deepenedby the mechanical erosion of rivers, which isgreater where the inclination is steeper andthere is more water. The slopes above valleysare shaped by sheet erosion or denudation.As a rule, closed depressions do not form inthis relief, but if they do, they are immediatelyfilled by water or sediment.On karst, however, relief is formed by waterthat chemically dissolves the limestoneand carries the solution away. Gravel thereforedoes not form on the surface and very littleinsoluble debris remains on the limestone.Gravel and insoluble debris could fill nascentdepressions in the relief, cover the bedrock,and be the basis for the formation of soil. Sincethis is not the case, the karst surface is rockyand hollowed.Pure water can dissolve only a little limestoneor its main component, the mineral calcite.Solubility increases when CO 2from theair or soil is dissolved in the water resultingin weak carbonic acid. Dissolving or corrosionis further accelerated by acids produced byplants or the decomposition of organic matterin the soil.The dissolution of karst rock is strongest onthe surface or a few meters below the surface,but water remains aggressive for a long timeand can form caves underground. Sheet erosionand the lowering of the surface results inkarst denudation. Various methods have determinedthat denudation has amounted tobetween twenty and fifty meters in a millionyears in Slovenia’s karst regions (Gams 1974).This also means that surface denudation hasalready reached individual caves and removedtheir ceilings to create roofless caves (Mihevc2007)Rivers flow onto karst areas and form undergroundstreams. Because they carry largeamounts of water and sediment from impermeableneighbouring areas, they are capableof dissolving a considerable amount of limestone,but their effect is limited only to the vicinityof the watercourse (Gams 1962; Mihevc2001).Karst rock featuresSome dolomites and most of the limestoneare mechanically very resistant types ofrock, but they are all subjected to dissolution.Precipitations start to dissolve them as soonas they get into contact with the karst rocks.Intensity of the corrosion depends on propertiesof the rock, aggressively of the water andthe way in which water flows on the surface ofthe rock. Small corrosion features that form onthe rock make its surface uneven and rough orform different shapes.Karen is common term used for dissolutionfeatures on exposed soluble rock surfaces.(Gines 2009). Two basic processes controltheir formation, the dissolution by thin water30