Karst and hydrological phenomena

The richly developed and often somewhat specific karst phenomena in the Idrija region are the reflection of complex rock composition, as well as tectonic and morphological stratification, of the highly variegated Idrija region. In a broader sense, the karst territory in Idrija may be divided into the high karst and the solitary karst, which includes the other »nonkarst« territory in the Idrija region (Čar, 2010).

The high karst comprises the area of Pevec, Idrijski Log, Zadlog, the central part of the Črni vrh plateau, Predgriž and Lom, as well as part of Hotenjsko podolje near Godovič. It continues southward and westward along the boundary of the Trnovo forest, Javornik and Hrušica. Owing to the geological conditions existing on the other side of the Idrijca River valley, the high karst passes into shallower limestone karst at Zagrebenc, Gladke skale and the valley of the Nikova stream. From the geological aspect, the high karst and the shallower limestone karst are built of Lower and Upper Cretaceous limestones of the Koševnik horse and Upper Cretaceous rudist limestone of the Hrušica nappe, which comes to light in Bevk's tectonic window and in the Strug tectonic window. Typical of the high karst are deeply karstified carbonate rocks, particularly limestones, with all the characteristics of classical karst. On the surface, numerous sinkholes can be found in various geological structures (Čar, 2001), whereas the underground karst is characterised by deep abysses, occasional subhorizontal short caves, as well as short sinking streams and swallow holes ('covered karst') along the thrust edges. Special mention should be made of the 400 m-deep Habe shaft, the famous boiling spring of Divje jezero (Wild Lake), and the powerful Podroteja springs.

Wild lake boiling

All the remaining parts of the Idrija territory where the high karst has not developed is formally classified as the »nonkarst« world, but certain individual or group karst phenonema found here are classified as solitary karst. This type of karst is usually developed in limestones and dolomites of varying age found in the middle of impermeable rocks (shales, calcareous sandstones, etc). The size and development of karst phenomena depend on geological conditions, i.e. the petrographic features of rocks, thickness of permeable rocks, tectonics, hydrological conditions, and climatic conditions. The solitary karst is more extensively developed on Krnice, the Ledina plateau, Vojsko plateau, and in Srednja Kanomlja.

Idrijca river valley

The entire valley is a very narrow and in some parts barely accessible gorge with steep cliffs. Numerous interesting plant species thrive in the valley, including protected and endangered
plants. Several historical and technical monuments are situated in the valley.

Stičišče dolin Idrijce (levo spodaj) in Belce (desno zgoraj)

Valley of the Belca stream

The valley of the Belca stream is a narrow water gap running in the direction of the Dinaric
Alps. Very steep cliffs rise up from the bottom of the valley, in many places these are vertical, overhanging walls. Several botanical particularities can be found in the valley. This is home to the Soča trout. Several technical monuments are preserved in the valley.

Suha Idrijca

Represents the lower part of Črni potok, a torrential stream. By its bedding, this is a special type of water channel that was formed at the contact of dolomite and limestone. It runs  beneath the fault in the Suha Idrijca gorge. Visible here is bedded dolomite (from Cordevolian upwards), which laterally alternates with limestone of Julian age containing Clypeina besici algae.


Gačnik stream, right tributary of the Trebušica, with waterfalls and profiles of Upper
Triassic rocks and the fossil shells Myophora and Pachycardia, fossils of the bivalve mollusc Solenomorphora, and marsh meadows.

Springs in Podroteja

A karst spring lying near the confluence of the Idrijca and Zala rivers. Water is used to supply the town.

Springs at Podroteja Divji potok (Wild spring)

Divji potok

On the left bank of the Idrijca River above the klavže (water barriers) is a strong tectonic spring, Divji potok. The spring rises at an altitude of 737 m from a fissure in the dolomite.


In the riverbed above Lajšt are natural water pools called bučke. These pools are formed in rocks with inclusions of softer materials that are easily carried away by water. The initial hole begins to broaden and deepen until several meter-deep hollows are formed.

Waterfall at Bizjak's mill

A strong karst spring connected to the nearby cave.Waterfall at Črna, the left tributary of the Poljanska Sora near Podklanec.

Ponor and gorge In Klame

A barely accessible gorge in Klame located within the Kanomlja triple tectonic window. The Idrija fault runs nearby. During low water levels, the Kanomljica stream disappears into a swallow hole.

Anžičk and Pagon ponikve

Anžičkove in Pagonove ponikve

A typical example of underground streams on dolomite, forming part of a complex geographic
natural area, a rare ecosystem, habitat of endangered plant and animal species.

Spring near Šinkovčeva žaga

A strong karst spring connected to the nearby cave.

Cave above Kobila

A horizontal cave that is also a boiling stream; after rainfall a mighty waterfall roars and flows out from the cave, discharging into the Idrijca River.

Habečkov brezen

The deepest natural shaft in the municipality of Idrija (400m), a true rarity because of its natural bridge at the entrance and the springs in the shaft. Water colouring has shown that waters from the shaft flow towards the springs at Podoroteja and Wild Lake.

Snežna jama below Štrangel

A step-like, inclined shaft. Occasionally used for visits.

Kalar glacier

The cave is 45 m deep, on the bottom of which is an open area where ice remains all year. The ice was exploited in the past.

Matjaževe kamre

Together with the Sora River, this labyrinth of caves represents a speleological site of regional
importance. These are the remains of an active water cave carved by the Sora River. It is home to several rare and protected cave animals, and a paleolithic station.


Zadlog is a special karst polje formed entirely on dolomite. It is comprised of vast, wet meadow with typical vegetation and fauna.




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