Enormous Dimensions in the Cave Matejeva jama
A Newly Discovered Giant Chamber in the Heart of the Sežana Karst area - 2025-03
Newly discovered caves with large entrances have become extremely rare in the past decade. Cavers typically find them in hard-to-reach terrains or areas that have yet to be explored. Caves with smaller entrances are more common but are also becoming increasingly rare in thoroughly examined regions. Today, the search for new caves is made easier by freely accessible LiDAR surface measurements of Slovenia. Explorers can identify potential cave entrances from their computers. However, LiDAR is not all-powerful. The search for breathing holes and small crevices that may conceal caves is still carried out the old-fashioned way—by inspecting the terrain.
For over a century, researchers in the Orlek area, at the heart of the Sežana Karst, have been searching for vast underground chambers carved by an ancient subterranean river. The underground course of this river has changed over geological eras, making it mysterious. The underground path of the Reka River has been partially known since the mid-19th century and continues to intrigue explorers. Because of the ongoing search for caves that could lead explorers to the Reka River, the terrain from Divača to Trieste is one of the most thoroughly examined in Slovenia. Nevertheless, cavers are constantly in the field, searching for new breathing holes that might lead them to the underground stream.
Matej Husu, a caver from Orlek and a member of JD Sežana, discovered a small breathing hole near the Italian border during winter when temperature differences make such holes “breathe” most strongly. The hole was located at the edge of a large collapse doline, where cave entrances are more likely, though often buried deeper at the bottom. Matej excavated the breathing hole, revealing a narrow entrance to a vertical shaft. He then teamed up with Claudio Bratos, an experienced local caver (Sancinova jama), along with Trieste-based cavers Mauro Kraus, Gianni Benedetti, and Lorenzo Slama. Within a few days, they widened and cleared the entrance, eventually breaking through to a massive chamber. The passageway leading from the chamber maintains nearly the same dimensions and descends to a large window, where they had to stop due to a lack of equipment. Judging by the echoes, the spaces beyond extended into an immense black void.
On the next expedition, the team descended into the enormous chamber. It was found to be 40 by 80 meters at the bottom, with a ceiling estimated to be over 100 meters high. The chamber is characterized by large rock collapses and is not particularly rich in stalagmites. The most significant cluster of speleothems is in a large stalactite niche on the opposite side of the chamber and near the entrance slope. Here, some stalagmites have been severely eroded due to changes in the water’s chemical composition, and the rock show grooves up to a meter deep. Due to the unstable collapse floor, most stalagmites are fractured, with the largest one already visibly broken.
The first continuation was discovered below the stalactite niche, where the team descended another twenty meters into a second chamber. Its floor is covered with a thick calcite deposit, and at the edge, another passage is already visible. The cavers identified an entrance to a new large shaft in a narrow crevice, but it will need to be widened for access. They are also attempting to climb a chimney higher up, while in the main chamber, a richly decorated passage was discovered in a window along the wall. There is also hope for another chimney, which continues at the same elevation as the entrance passage, though climbing to it will likely be challenging.
Matejeva jama currently reaches a depth of 175 meters and a length of over 300 meters. Its entrance is on the Slovenian side of the border, but the main passage runs southward into Italy. The massive chamber itself is already on the Italian side, and above it, Matej discovered a new breathing hole. After initial widening, he confirmed airflow with the Trieste-based cavers, suggesting a possible second entrance to Matejeva jama. Once the cavers widen the narrow passages, they will be able to descend directly into the center of the giant chamber. This would be a unique case of a cave with two entrances in two different countries in this region.
Caves of such dimensions are discovered only rarely in the Sežana and Trieste Karst, usually just once in several decades. This time, only three years after the discovery of Sancinova jama, another giant has emerged. The hope is that Matejeva jama has not yet revealed its final secrets.
A huge thank you to my team (Mojca and Boštjan Vrviščar, Gregor Karlovšek, and Janez Ferreira-Stražišar) for helping with the transport of equipment and the creation of photographs, and for being, as always, wonderful company.
