The underground world of karst: Speleology

There are about a hundred caves and pits along the course of the Krka River, some 40 of which are within the boundaries of Krka National Park.

The largest number of cave structures has been recorded in the Promina deposits and Upper Cretaceous rudist limestone. These structures were created from tectonic fissures that expanded over time under the corrosion and erosion influences of water. Cave structures from the Quaternary also include travertine barriers and are typically of smaller dimension.

Miljacka cave spring

The longest cave is found near the Miljacka slap waterfall

There are five known cave-springs (Miljacka I, II, III, IV and V). The largest, Miljacka II, is also the largest within the park bounds, and is situated on the right bank of the river, just a hundred metres downstream from the waterfall.

During periods of high water, a subterranean river flows through the cave, thought to be water from the Zrmanja River that sinks at Mokro Polje. During periods of low water, the cave contains a 200 m long lake of unknown depth, ending in a siphon. The cave has been investigated to a length of 1,750 m. The ceiling, floor and walls of the cave are ornamented with numerous eroded stalagmites, which indicate the frequent changes in water levels in the cave. The caves around Miljacka slap are exceptional underground habitats, with 36 subterranean species recorded to date, the majority of which are endemic to Croatia and/or the Dinaric karst area. The Miljacka II cave is a known habitat for the endemic olm (Proteus anguinus) and 8 species of bats. During the summer bats, bat colonies with up to 9,000 individuals take shelter here, the most abundant of which is the long-fingered bat (Myotis capaccinii) with about 7,000 individuals.

Pit opposite Torak Lake

There is an exceptionally interesting pit just opposite the Torak spring, situated about 20 m above the river valley on the right bank of the Čikola River.

The pit is about 20 m deep and 10 m long. The upper part of the structure has been formed in conglomerate, while the lower in marly limestone. There is no doubt that the pit was submerged with the raising of the lake following the growth of travertine barriers at Skradinski buk. At the bottom of the pit are three small lakes at the level of the water of the Čikola River. The largest is 17 m deep. The second is a known habitat for the olm in Krka National Park and also contains submerged stalactites that are grown over with colonies of the endemic cave polychaete (Marifugia cavatica).

Oziđana pećina and Jazinka

Traces of human settlements have been found in two caves, Oziđana pećina cave and Jazinka cave

Oziđana pećina is situated on the left bank of the Krka River, just above Roški slap, near the very top of the canyon. The cave opens towards the southwest, in the middle of a 20 m high, vertical cliff. It was named after a stone wall (Oziđana pećina roughly translated means walled cave), a sort of rampart, constructed at the entrance into the cave. The cave is tunnel-shaped and is 59 m long, up to 7 m wide and 2.5 m high, with two ‘chimneys’ at the rear. Fragments of ceramic dishes, flint knives, stone tools, a large number of different animal bones, mussel shells and two skeletons of childhood age, dating back to the period of the Danilo culture, have been discovered within.

Jazinka cave is situated on the left bank of the Krka River, near the medieval fortress Nečven. The cave is a simple structure, 42 m long, up to 6 m wide and about 4 m high. Fragments of various ceramic dishes, animal bones, bronze arrows and bronze fibulas, and human bones dating to the transition between the Bronze and Early Iron Ages, have been unearthed here.

Nameless cave

Traces of industrial archaeology have been found in a nameless cave on the left bank of the Krka River next to Skradinski buk, on the northwestern side of the ruins of the Jaruga I hydroelectric plant.

The cave was discovered in 1894 at the time of construction of the plant. According to the available information, at that time, the cave was about 150 m long, 80 m wide and with a total area of 1,200 m2, richly ornamented with fantastic dripstones, with a small lake at the bottom. The cave was formed by the deposition of travertine. Today, the lower parts of the cave have been filled in, and it is now only 24 m long and 10 m deep. The dripstones have since lost their shine and the lake has dried up due to the diversion of the river during the construction of the hydroelectric plant. Remnants of the foundation of the hydroelectric plant can be seen in part of the cave.

Other speleological structures near the Park

Other notable speleological structures near the national park are the pits Stara jametina and Martina jama

Stara jametina is found east of the village of Koštani, near the settlement of Konjevrate. This is the deepest known pit along the course of the Krka River. It is 188 m long, and has been investigated to a depth of 85 m, as further study is not possible due to the very narrow fissures. Martina jama, though called a pit, is actually a cave with a vertical entrance. It is found on the right bank of the Krka Rvier, south of Skradin, near the village of Bićine. The cave is 120 m long and 27 m deep. Flowstones of varying colour separate the underground cavern into two separate halls adored with stalagmites and stalactites. The halls are also richly ornamented with calcite structures of exceptional beauty, making this the most spectacular pit in the Krka River region.