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Our two beautiful true karst rivers (which means they spring and end in other rivers or the sea in the karst area) Mrežnica and Zrmanja belong in areas where speleogenesis is significant, where there are such conditions which allow quantitative speleogenesis which can be considered classic in the speleologic sense of the word. Here its about numerous speleologic objects (caves and pits), which where created in soluble carbonate rocks tectonically broken with the presence of large quantities of aggressive subterranean and surface waters.
Mrežnica and Zrmanja and their tributaries, all spring out of speleologic sites (caves). The river Mrežnica, Zvečaj (there is also Zagorska Mrežnica which flows along Ogulin field) and springs in the vicinity of Primišlje on Kordun from a cave which is explored in the length of several hundred meters. The cave is complicated and ends with few siphons which have to be dived through. In the vicinity of Mrežnica (in its basin) there are 350 speleologic objects (caves and pits). Its Suvača, Rudnica, Kukača, Tounjčica, Globornica and other basins. The longest cave in the area is in the quarry Tounj, with over 8487 meters. Here we have to mention Mijat's pit at Mateško village on the right bank of Mrežnica. The significant ones are Tounjčica, Tamnica, Zala, Bistrac, Mandelaja, Rudnica, and so forth.
Mijat's pit is actually a cave with a pit entrance which is impressive (20 x 20 meters, 54 meters deep). You can enter Mijat's pit only with speleologic equipment, which means, after speleologic education. The cave is full of big halls, stalactites and stalagmites, and it has a short subterranean flow. It has been explored in a length of 1204 meters.
The river Zrmanja also springs out of a speleologic object, but deeper diving into its spring is impossible because of stone blocks. The spring is on the eastern slopes of south Velebit, near the village Zrmanja Vrelo. IN the vicinity of the river Zrmanja there is 150 known speleologic objects. WE are speaking about Krupa, Krnjeza, Dobarnica and other basins. The longest cave in the vicinity of Zrmanja, not observing the objects which are located in the Velebit area, is the cave Čude not far from Muškovci near Obrovac. Čavle, Vratolomka, Krnjeza, Kusa, and Milića are also significant.
The cave Čude has been explored for more than a kilometer, and exploring goes on. It is a very complicated speleologic object where there are many siphons, cave heaps, cave lakes, etc. For visiting this cave you have to have completed speleologic education, because it is a very dangerous speleologic object.
In canyons of our mentioned rivers there are over 500 speleologic objects what speaks about speleologic riches of these areas.
If you are interested in speleologic education you can contact us at:
Hrvatski speleološki savez Nova Ves 66 10000 Zagreb