Hypothetic age of Vrana Lake on Cres Island, Croatia

Zavala Vranskog jezera bila je reljefna osnova za postanak krškog polja. Sljedeća faza bilo je slatkovodno jezero. Budući da jezerska voda potječe od padalina, njihova promjenljivost odražava se u promjenljivosti godišnjih vodostaja. U 40-godišnjem razdoblju 1929.-1968. srednja razina jezera iznosila je 13.73 m iznad morske razine. Za toliko je razina jezera uvijek bila viša od razine Jadranskog (odnosno svjetskog) mora. Polazeći od poznatih visina morske razine određena je razina Vranskog jezera. Na početku holocena, prije 10 000 godina, Vransko jezero bilo je 17.26 m niže od morske razine danas (odnosno od nulte izobate u jezeru). Ako je najdublja točka u jezeru 61.50 m ispod razine mora (ili 75,23 ispod današnje razine jezera) onda bi Vransko jezero bilo staro 17 900 godina. Gornjem virmu pripada 7 900 godina, a holocenu 10 000 godina. Prema tome, Vransko jezero je gornjevirmsko - holocensko jezero.The older depression was a relief predisposition for the origin of Vrana Lake. The next phase was a fresh water karst lake. Since the lake water originates of atmospheric precipitation water (rainfall and underground inflow) the variability of the lake level corresponds in essence to precipitation annual changes. In the 40 years period 1929-1968 mean lake level was 13.73 m above the mean sea level. This difference was maintained even in the past. Comparison with the known world sea level curve in certain critical dates it is possible to calculate the Vrana Lake levels. At the beginning of holocene period, 10,000 years ago, Vrana Lake level was 17.26 m lower than present sea level. Supposing that the deepest point in the Vrana lake is 61.50 m below sea level (or 75.23 m below the present lake level) it was calculated that Vrana Lake is 17.900 years old. About 7.900 years belong to the Upper Wurm period and 10.000 years to the Holocene period. Accordingly, Vrana Lake is of Upper Wurm and Holocene age