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Kras and Karst
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Karst Investigations in Slovenia

The Karst presents a distinctive type of earth with special karstic phenomena getting the name after the region Kras in the background of the Trieste Bay. The name has Paleoeuropean origin (karra - stone) and in Antiquity it used to be Carusardius. From 1177 the Slovenian form "Grast" has been known and from 1230 the Croatian "Kras". In the international terminology the German version -(Karst) - has remained in use, obviously after the place name Kras.

Information about the features of Kras, especially about the spring of Timavo river, Reka river and ękocjanske caves (jame), was spread all over the world by the Greeks and the Romans (Strabo, Virgil, Plinius). From the 16th to the 19th century the periodic Lake of Cerknica was the most famous and the best described karst phenomenon (Valvasor, Steinberg). In the past two centuries several caves and other karst forms and curiosities were explored on the Kras, presenting today the properties of "Classical Karst" from where not only the name of karstology derives but the roots of speleology are found.

Rakov Skocjan - A Copper Engraving by Franc Anton Steinberg in "Gruendliche Nachricht von dem in dem Inner-Crein gelegenen Czirknitzer-See", 1758
Photo by Arne Hodalic

Schmidl (1854, 1858) contributed to the knowledge of the caves in Notranjsko (Inner Carniola) and introduced some Slovenian popular names for the most impressive karst features into the literature (jama, dolina, ponor). These names were adopted later in the international use.

The discovery of new parts of the Postojna Cave in 1818 marks a new period of speleological and karstological investigations in Slovenia. Thus the Postojnska jama is often called the cradle of speleobiology.

Karst in Slovenia

According to all documentation collected till now, some 9000 km2 or 44% of the territory of Republic of Slovenia can be classified as karst area. Over two thirds of this territory (6300 km2) consist of limestones, mainly Mesozoic, whereas karst areas on other rocks (dolomite, conglomerate, calcarenite and breccia) occupy some 30% of the entire karst areas of Slovenia. The karst in Slovenia is commonly divided in relation to geological, hydrological and geomorphological characteristics into three major units:

Karst in Slovenia
Authors: Dr. Peter Habic and eng. Vili Kos.
The Encyclopedia of Slovenia, Vol. 5, Reference KRAS

The Alpine karst

The Alpine karst (the Julian Alps, the Karavanke, the Kamnik and Savinja Alps) can be classified as the fractured orogenetic karst.

The Alpine karst region is dissected by deep valleys, lying between ridges at an altitude from 1000 to 2800 m. The plateau-like segments below the highest peaks are small but quite extensive in Komna, Pokljuka, Jelovica, Mezakla etc. in the border part of the Alps. At high levels of the Alpine karst we can find all karst forms known in the Northern and Southern Limestone Alps (big dolines - kontas, small dolines with vertical walls - kotlic (sing.), all kind of karren). Recently the 11 km long alpine cave Poloska jama and some potholes with the depth between 700 and 1200 m (the Cernelsko brezno 1198 m, Skalarjevo brezno 911 m, Brezno pri Gamsovi glavici 817 m, Poloska jama 704 m) have been discovered.

In other Alpine karst areas the karstic hydrology is often the karst phenomenon. The underground waters can rise to the impervious ground but flow out to normal valleys. Karst waters come out as the sources in the Quaternary deposits at the bottoms of the valleys or directly from the steep rocky slopes in the form of waterfalls (the Savica, Boka, Soca). The Alpine karst waters are comparatively pure because the surface is barren, without thicker layers of soil, and less populated.

The Dinaric karst

The Dinaric karst includes continuous karst areas in western and southern Slovenia. It can be divided into three elongated parallel belts according to geological, geomorphological and hydrological characteristics. They are the Littoral Karst, the Karst of Notranjsko and the Karst of Dolenjsko.

The Littoral Karst, extending along the Adriatic coast, is further divided into original Kras areas (called also Trieste Karst or Carso di Trieste) in the background of the Timavo spring, and, second, the karst of northern Istria.

The longest blind valley in Kras area is that of the Notranjsko Reka - Vremska dolina with its terraced bottom. The river Reka sinks into the caves Skocjanske jame. There are two fresh collapse dolines and many older collapse dolines there.

Cave research organizations of Slovenia have till now registered more than 700 caves and potholes in the area of ca. 500 km2 of the Classical Kras.

The Karst of Notranjsko (Inner Carniola) belongs to the central highest Dinaric belt. It is high, wooded and scarcely populated karst plateaus at an altitude of 800 to 1700 m with intermediate lower valley-like karst depressions at an altitude between 400 and 600 m are predominant in this area. The high out-flow karst can be subdivided in relation to structural tectonicand morphogenetic charateristics into more or less coherent hydrogeological units: the Banjsice, Trnovski gozd, Hrusica, Nanos, Javorniki, Sneznik, Krim, Velika gora, Kocevski Rog and the central part of the Gorjanci mountains. Karst waters flow out from these units to several directions and feed the karst springs in their border zones.

Lying between these high areas of out-flow karst is the central part of the through-flow karst of Notranjsko. Across it the surface and underground waters flow forming intermittently flowing streams that flood the karst poljes. A considerable part of the through-flow karst belongs to the drainage basin of the Ljubljanica river, but some waters drain also towards the Kolpa and Krka rivers.

There is the famous polje of Cerknica with its periodic lake, numerous springs on the southeastern part, and ponors in the central part and in the nortwestern side. In the year 1971 a sluice was built at the entrance of the ponor cave Karlovica which has prolonged the lake phase from 6 to 7 months yearly. The purpose of that is to intensify the fishing season on the lake, and tourism. The alternation of the dry and the flood phases, which was in early modern times a matter of admiration for so many scientists still persists.

In the Notranjsko podolje only the polje of Postojna - Pivka contains a bigger flysch area. The rivers draining the flysch have shaped many caves in Cretaceous limestone. The longest is Postojnska jama (19.5 km). On the 30 km2 the triangle territory among Postojna, Loz, and Logatec, there are 60 km of cave channels and this is the greatest cave density in Slovenia. The second valley-like depression includes the western part of Dolenjsko. Waters drain both to the Krka and to the Kolpa rivers. The polje of Kocevje (about 60 km2) is the greatest polje in Slovenia; it has also the character of a peripheral polje.

The karst of Dolenjsko belongs to the shallow out-flow through-flow karst of the inner Dinaric or Peripanonnian belt. The surface is covered with the thicker layer of the red karst soil, the typical terra rossa, which has made possible denser population in more continuous tracts of agricultural land-use. Gentler forms, dolines, uvala like depressions, even small karst poljes and rounded hills, are predominant in the karst relief. Waters derive from the impervious and dolomitic rims of the karst areas and flow only at small depth under the surface or even in shallow open canyons.

The isolated karst

The isolated karst in sub-Alpine and sub-Dinaric Slovenia is subdivided into several homogenous isolated units. The hydrographical significance of the isolated karst depends on the location and size of carbonate rock. The isolated patches of the karst are important natural reservoirs of underground water for local supply.

In 1818 Luka Cec a native of Postojna discovered the interior parts of the Postojna Cave. The photo shows the reconstruction of the then cave and the costumes of the visitors. His discovery wide opened the door to Postojna tourism.
Photo by Arne Hodalic
Massive natural bridge in Rakov Skocjan / a 2,5 km long sunken valley between Cerknica and Planina polje is a real Karst gem
Photo by Arne Hodalic
Planina polje - a world-famous example of a perfect polje in the karst
Photo by Bogdan Kladnik
Planina polje
Photo by Bogdan Kladnik
Planina jama
Photo by Bogdan Kladnik
Cerknica Lake
Photo by Bogdan Kladnik
Losko polje
Photo by Arne Hodalic
The watery Krizna jama
Photo by Arne Hodalic
Franci Bar: In boats at Calvaria in Kriżna jama
Photo by Bogdan Klad

According to "Slovenia - Geographic Aspects of a New Independent European Nation", Ljubljana, 1992 By Peter Habic, Ph..D. Research Associate, The Institute of Karst Research, Centre of Scientific Research of the SAZU

Postojna Cave / Drawing by Janez Vajkard Valvasor in "In Praise of the Duchy of Carniola" 1689
Photo by Arne Hodalic