Karst geomorphology, hydrogeology and caves in the areas of the Prespa Lakes, at the Albania-Macedonia-Greece border

The lakes of Prespa and Ohrid represent a very important hydrogeological system shared between Albania, FYR of Macedonia and Greece, and are the largest tectonic lakes in Europe. Prespa Lake is about 150 m higher in elevation than Ohrid, and the twos are separated by high mountains (Mali Thate, 2,287 m, and Galičica Mt., 2,262 m a.s.l.), built up during the Pliocene-Quaternary tectonic events. These mountains mainly consist of Upper Triassic–Lower Jurassic limestones, with wide graben to the E (Prespa) and the W (Ohrid). Pliocene clays, sandstones, and conglomerates fill most of the lakes. In 2002, an artificial tracer experiment physically demonstrated the underground connection between them (Amataj et al., 2007). In the past, periodical oscillations of the level at Prespa Lake were in the 1-3 m range. After middle 1980’s, a steady decrease of water level has been recorded, producing serious disturbance to its ecological balance. Shape of Lake Prespa is quite irregular: the narrow sandy isthmus Gladno Polje separates it into Macro and Micro Prespa. In the recent past, Micro Prespa was a gulf of Macro Prespa, but then, due to erosion and sedimentation processes, the isthmus has been formed and the lakes separated (Popovska & Bonacci, 2007). In this contribution we illustrate the main karst geomorphological characters, also providing updated information on its hydrogeology. In Galičica Mt. the most important surface karst forms are the Petrinska Plateau, a 20 km2 feature developed at elevation of 1500 m a.s.l., and the Samari blind valley, about 7 km long, in the NE part at about 1300–1400 m a.s.l. At least 12 high elevation caves have been documented, the longest being Samoska Dupka with length of 279 m. Numerous small caves are also situated along the Prespa Lake coastline near the villages of Stenie and Gollomboc; the longest is Treni cave (315 m long) at the W point of MicroPrespa Lake (Trocino et al., 2010). The Zaver swallow hole is situated at the Prespa W border, near Mala Gorica, with an extensive karst cave just uphill. Other smaller swallow holes are near Gollomboc; about in the same area, several caves of limited size (up to some tens of meters) are present, too. All these elements are important to describe the Prespa Lakes area as a sector of potential interest for further karstological studies, addressed to a better comprehension of the karst phases that interested this trans-boundary sector.   References Amataj S. et al., 2007, Tracer methods used to verify the hypothesis of Cvijic about the underground connection between Prespa and Ohrid lake. Environ. Geol. 51 (5), 749-753. Eftimi R., Stevanovic Z. & Stojov V., 2021, Hydrogeology of Mali Thate–Galičica karst massif related to the catastrophic decrease of the level of Lake Prespa. Environ. Earth Sci. 80, 708. Popovska & Bonacci O., 2007, Basic data on the hydrology of Lakes Ohrid and Prespa. Hydrol. Proc. 21, 658-664. Trocino A., Parise M. & Rizzi A., 2010, Ricerche speleologiche in Albania: primi dati sulle cavità nei pressi del lago di Prespa. XII Reg. Meeting Speleology “Spelaion 07”, 246-259.