Čolniči - Obrh

virtual excursion

The Čolnici–Obrh Cave, functioning both as a karstic vauclusian spring (obrh) and as the source of the Obrh (Jezerščica) stream on the eastern margin of the Cerkniško polje near the village of Gornje Jezero, represents an exceptional example of an active karst system shaped by complex hydrogeological and geomorphological processes. Its position at the transition between the subterranean drainage of the Javorniki Mountains and the surface hydrology of the polje long concealed its entrance beneath collapsed rock and sediment. Only in 2007 did a team of cavers from the Society of Karst Cave Enthusiasts (DLKJ), led by geographer Matej Kržič, remove the rocky barrier above the spring and reveal the first accessible passage. Further exploration was immediately halted by a fully flooded epiphreatic zone, indicating pronounced seasonal water-level fluctuations and a highly dynamic subterranean flow regime.

A decisive breakthrough occurred in September 2011, when exceptionally low water levels opened a narrow temporal window for exploration. An interdisciplinary team of cavers—biologists, chemists, karstologists, and geographers—entered the system. Their diverse expertise enabled a comprehensive interpretation of the cave’s geological, hydrological, and biological features. The team crawled through tight epiphreatic conduits, swam across cold subterranean lakes, navigated an unknown labyrinth of passages, and simultaneously mapped the cave’s floor plan, producing the first coherent spatial documentation of the system.

A detailed visualization created during this phase depicts approximately 1500 meters of the cave. It begins at the entrance, where intertwined tree roots hang from the ceiling, and continues through narrow passages carved into dolomite coated with black manganese oxide and yellowish clay. The walls and ceiling of the dry subterranean channel are covered with micro-chimneys—fine relief structures formed by long-term dissolution and mineral precipitation under fluctuating hydrological conditions.

After nineteen hours of continuous crawling, swimming, and surveying, the researchers entered a vast subterranean chamber. A distinct horizontal black manganese line ran across the chamber’s walls at roughly half its height—a clear geochemical marker of the former water level when the epiphreatic zone was completely inundated. Above this line rose abundant speleothem formations, which could only develop during prolonged periods when the chamber was above the water table and exposed to dripping and ventilation.

Dominating the central part of the chamber was a massive rockfall, which later provided the key to understanding a remarkable paleontological discovery: numerous skeletons of cave bears. The spatial context and condition of the remains indicate that during the last glacial period, large bears sought shelter in the cave to escape harsh winter conditions. However, a catastrophic collapse sealed the main entrance, trapping the animals inside and confining them to the subterranean karst environment for tens of thousands of years. Their fate remained hidden until the modern expedition uncovered this isolated paleontological archive.

The members of the research team thus became the first humans to witness this preserved subterranean world and the geological and biological consequences of the cave bears’ tragic end. The discovery of an additional 1000 meters of passages—including large chambers and richly decorated speleothem galleries containing bear remains—significantly expanded the understanding of the cave’s geomorphological evolution and its role within the broader hydrological system of the Cerkniško polje.

The expedition and visualization of the Čolnici–Obrh Cave stand as a compelling example of contemporary speleological research, where fieldwork, interdisciplinary expertise, and advanced documentation techniques converge to produce a holistic interpretation of karst environments. The cave remains a living system, still concealing unknown spaces, while simultaneously serving as a valuable archive of geological, hydrological, and biological processes that have shaped its development over millennia.