Case Studies from the Dinaric Karst of Slovenia

KrasThe Kras is a distinct plateau, especiallywhen viewed from the seaward side. The Krastrends NW–SE between Trieste Bay, the northernmostpart of the Adriatic Sea, Vipava valleyin north-east, and the Friuli–Venezia Giulialowlands and river Soča in northwest (Fig. 40).The 45°45´´N and 14°00´´E lines of latitudeand longitude cross the Kras near Divača village.There are steep limestone slopes a fewhundred meters high rising directly from thesea or from the neighbouring lowlands to thenorthwest. Higher relief on flysch in the eastseparates the Kras from the Pivka region. Inthe southeast, the border of Kras is again welldefined by contact with the non-carbonateflysch of the Brkini hills and the valley of theReka river. Toward the south, the transition tokarst ridges and Matarsko podolje karst plateauis less obvious. The climate is sub-Mediterraneanwith warm dry summers. Cold winters,with most of the precipitation, show thestrong influence of the continent.The Kras belongs to the Adriatic–DinaricCarbonate Platform of the External Dinarides,composed of shallow marine fossil-bearingCretaceous and Palaeogene carbonates. Eoceneflysch rocks encircle the carbonate plateau.Kras and Matarsko podolje tectonicallybelong to Komen thrust sheet (Placer 1999),which is thrust over Eocene flysch and Palaeocene/Eocenelimestone of the Podgorski kras,a part of Kras imbricated structure (beforeknown as Čičarija imbricated structure; Placer2007). The whole structure is sub-thrust by theIstria unit.The main part of the plateau is essentiallylevelled, inclined slightly towards the northwest,with numerous dolines, caves and otherkarst features. There is a belt of slightly higherrelief in the central part of the plateau, formedby conical hills-like Grmada (324 m a.s.l.), Volnik(545 m a.s.l.) and Stari tabor (603 m a.s.l.), anddissected by large depressions. The higherrelief divides the Kras into two separatedlevelled surfaces. The southern one is namedNabrežinsko podolje. In the northwestern part,the plateau descends to below 50 m a.s.l. onthe edge of the Friuli Plain; on its south-easternedge altitudes are about 500 m a.s.l There areabout 300 m of accessible vadose zone withcaves formed at all altitudes from the surfaceto the sea level and below it. No superficialstreams occur on the Kras surface because allrainwater immediately infiltrates to carbonaterocks. There are two dry valleys crossing theplateau and some NW–SE-trending belts oflower relief which were believed to representprimary river valleys also because they containremnants of fluvial sediments dated to a prekarstificationphase (Melik 1955; Radinja1985).Geomorphologic and speleogenetic studiesand especially new interpretations of fluvialsediments from the Kras surface as the fluvialfill of now unroofed caves have enabled a newexplanation of the evolution of the Kras (Mihevc1996, 1998, 1999a-c, 2001b, 2007; ZupanHajna et al. 2008a).Nabrežinski krasNabrežinski kras (Nabrežina Karst) is thenorth-western part of the Kras around thevillage of Nabrežina (Aurisina in Italian). It isonly about 150–180 m a.s.l. There are severalold collapse dolines on the surface, morethan 300 m wide and to 50 m deep. Smallersolution dolines are less abundant, most ofthe surface having plain or slightly undulatingrelief. Toward the north-east, the surface ofthe Nabrežinski kras gradually transforms intothe slopes of the Volnik (545 m a.s.l.) hills andGrmada (324 m a.s.l.). An abrupt change of50