Case Studies from the Dinaric Karst of Slovenia

dolomite barrier along the Idrija wrench faultzone, which crosses the polje, forces the karstwaters to overflow from higher karstified limestonebackground to the surface, and aftercrossing Planinsko polje toward the northeastthey can sink into the underground again. Theprincipal Unica springs, with mean annual discharge24 m 3 /s (min. 0.3 m 3 /s, max. 100 m 3 /s),are situated in the southern polje’s part in Cretaceouslimestone, where the confluence ofwaters from Cerknica, Javorniki Mt. and Pivkais located. Main spring is 6,656 m long cavePlaninska jama.The principal Unica swallow-holes are disposedat the northern edge, where mostlymedium and high waters are sinking. At lowwaters the whole Unica is disappearing inswallow-holes at eastern polje’s border. Upto 160 m long ponor caves are known, butthere are several horizontal caves in vicinityof the polje, where water oscillations canbe observed. Larger caves behind the ponorsare over 5,110 m long Najdena jama cave andLogarček.Rakov ŠkocjanRakov Škocjan is a karst depression about1,5 km long and 200 m wide. It is situatedbelow the N side of Javorniki Mountain at elevationabout 500 m between Planinsko andCerkniško polje. Through the depression flowsthe permanent river Rak. The Rak springsfrom Zelške jame cave, bringing water fromCerkniško polje. Zelške jame are about 5 kmlong; the end of the cave is in huge collapsedoline Velika Šujca, where from the other sidethe Karlovica cave system ends. In Karlovicasystem is the main outflow from Cerkniškopolje. Numerous collapse dolines are situatedaround the entrance of Zelške jame. In oneof them the small natural bridge is present.Downstream, the valley widens and severalsprings bring additional water to the Rak River.The valley narrows at the Great Natural Bridgeand afterwards the Rak sinks into Tkalca jamacave, from where the water flows towardsthe cave Planinska jama at Planinsko polje.The connections of the Rak with water fromCerkniško polje and with the Unica springs atPlaninsko polje were proved by water tracing.From 1949 Rakov Škocjan has been a LandscapePark.Cerkniško polje (Cerknica polje)Cerkniško polje (Cerknica polje; Fig. 42) isthe biggest karst polje in Slovenia. Often it iscalled just Cerkniško jezero (Lake of Cerknica),because of its regular floods, or intermittentlake. The intermittent lake covers 26 km 2 whenis full; it is 10.5 km long and almost 5 km wide.Its hydrological properties caused that alreadyin the beginning of New Age scholars from allround Europe were attracted to it. The lake becomesstill more known through the Valvasor’sdescription in 1689. Bottom of Cerkniško poljecovers 38 km 2 in elevation of about 550 m. Inflowsare on E, S, and partly on W polje’s side.The largest tributary to polje is Cerkniščica,drained about 45 km 2 large mostly dolomitecatchment area. The important karst springsare Žerovnica, Šteberščica and Stržen. Strženflows on the W side of polje towards theponors in the middle of the polje, from wherewater flows directly to Ljubljanica springs, andtowards NW side of polje, from where the waterflows to Rakov Škocjan. From the foot ofJavorniki mountain to the contact with dolomitein the polje bottom are 12 ponor caves.They are connected to Karlovica cave system,to which also the highest waters from poljeflows. The system there is more the 7 km ofpassages. Passages are generally low, becausethey are filled by alluvia. Thickness of alluviain Jamski zaliv, before the caves entrances, isabout 8 –15 m.Cerkniško polje is a karst polje developed inthe important regional fault zone – Idrija fault.Idrija fault has the “Dinaric” direction (NW-SE);in the same fault zone are developed: Planinskopolje, Loško polje and Babno polje. Bottomof polje is formed on Upper Triasic dolomite,which is presented also on the N, E and SE side54