The confluence of the Pazinčica, popularly called “potok” (stream) by the inhabitants of Pazin covers the surface of 83 square kilometres and the length of 16.5 km. It almost entirely lies on the impermeable flysch rocks giving the water flows a very flood-like character. Reaching the permeable rock in the cave, the Pazinčica becomes a subterranean river.
Due to large precipitations, floods are characterized by the creation of big quantities of water. When the inflow of waters of the Pazinčica exceeds the capacity of disappearing underground, the cave witnesses the flooding of the abyss.
The Pazinčica used to flow underground-near Beram, Kringa and Dvigrad to the sea- forming the Lim Valley.
In the hydro-geological sense, the Cave of Pazin is an abyss created on the junction of the impermeable flysch base of the confluence of the Pazinčica and the permeable limestone that makes up the whole area of southwest Istria. Right behind the impressive gorge of the abyss is a long hall with a large cave lake- Martel’s lake. By means of a siphon, it is connected with the nearby Mitar’s lake.
Research indicates that the water bearer whose waters also include the Pazinčica directs its waters towards springs in the east and the south part of the Istrian peninsula (Raša and Blaz).
The share in the formation of the Cave of Pazin equally belongs to tectonic and hydrologic influences, so that it can be called the speleological object of polygenetic type.
Layers of upper-Cretaceous limestone included in the large NW-SI crevices provided a tectonic predisposition for the creation of the cave itself and the final canyon of the Pazinčica. The once opened passage into the underground was enlarged and shaped as a consequence of later influence of water.
The largest flood in the cave occurred in 1896. It was noted by E. A. Martel, renowned French speleologist. On that event, the water in the cave reached 30 metres under the city walls of the Castle. The last big floods happened in 1964 and 1993.