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Postojna Cave ‘Extended’ by 3.5 Kilometres

The Latin inscription on the building of the Jamski Dvorec Mansion, located at the entrance into Postojna Cave, Immensum ad antrum aditus means ‘Enter, traveller, this endless cave!’ The inscription dating back to 1928 gives visitors who are waiting to enter the cave, unaware of what it is awaiting them, an inkling of the vastness of underground halls behind the cave entrance. Postojna Cave, which has – with the splendours and mightiness of its halls and the length of its passages – been amazing visitors for two centuries, is now even longer. Since last week, it has been known that its length is actually 3.5 kilometres more than what was previously believed.

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The fact that Postojna Cave, Black Cave, Pivka Cave and Planina Cave are part of the same cave system has been known for a century and a half, as the caves are interconnected through the same underground river. However, according to speleology rules this has not been proven unless passages and siphons connecting the caves have been swum and walked through by man. Thus, the network of passages between Postojna Cave and Planina Cave still remains largely mysterious, however, the mystery behind it is on a good way of becoming uncovered.

Following the initiative of Mr Marjan Batagelj, the Chairman of the Postojna Cave Management Board, to provide moral and, especially, financial support for all explorations of the subterranean areas between Postojna Cave and Planina Cave, the best Slovenian cavers started intense exploration earlier this year. Last year, this had not been possible due to the weather conditions, as the safety of the whole team always takes absolute priority, which is something that the Postojna Cave operator insists on.

For four decades, cavers have been working hard on overcoming the last remaining obstacles, i.e. just over 2 kilometres of the air distance between the Postojna Cave and the Planina Cave systems. Initially, the exploration began as early as 1852, following the idea of routing the Southern Railway through Postojna Cave. The most extensive exploration activities took place in 1976, 1983 and 1998, whereas in the years after they unfortunately died out almost completely.

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Therefore, it was not until earlier this year that the groundbreaking discoveries took place, the result of which are the 3.5 kilometres of new explored and measured passages. This was no mean feat and an achievement considered exceptional on a worldwide scale too, even more so since the exploration was carried out in the system of the longest and most important show cave in Europe under extreme conditions. To be able to dive into siphons, divers need to maintain an extremely high level of physical, and even more so, mental fitness. During a dive, they carry approximately 50 kg of equipment each, and the underwater visibility in complete darkness is typically reduced to half a metre or less.

The most recent exploration of outflow siphons took place on Saturday, 20 June 2015, and lasted twelve hours, during which the primary aim was to explore the main passage from Pivka Cave to Planina Cave. A number of side passages were also discovered on this occasion and the cavers are planning on conducting more exact measurements in the future. The abundance of the subterranean life is exceptional; in fact, cavers reported that they had found fish in the siphon lakes and that had been accompanied by a large proteus colony all the way. The exploration was conducted 250 metres below the earth’s surface and for the sake of comparison it should be pointed out that the ceiling of the Great Mountains inside Postojna Cave is ‘a mere’ 60 metres in thickness.

The biggest obstacle to such exploration are the water siphons. On this occasion, the cavers-divers were successful in breaking through a very difficult fourth siphon, where the cave continues with a mighty passage that moves away from the direction of Planina Cave and runs north. This had been one of the reasons for cavers’ concerns whether they were actually on the right track towards Planina Cave. It was explorers’ persistence that led to the discovery that there was a turn in the direction towards southwest and the right way towards Planina Cave. Here, there is another (the fifth) siphon awaiting the explorers and will be tackled during the next expedition. This is the location of the previously unexplored side passage, the old riverbed of River Pivka, where halls with an abundance of speleothems are supposedly located. Now, there are a mere 400 metres of air distance remaining to Planina Cave, and if this – hopefully the very last – obstacle has been overcome, Slovenia will get a cave system that is more than 31 kilometres in length (the expected length is between 31 and 35 kilometres).

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Working together, divers Igor Vrhovec, Sebastjan Gantar and Matej Koršič, alongside their support team which consisted of Izidor Šantek, Aleš Konobelj, Matjaž Milharčič (cave exploration society DZRJ Luka Čeč Postojna), Matej Zalokar, Simon Hiti, Uroš Frlan and Franjo Drole (speleological society JD Rakek), Mitja Prelovšek (cave exploration society DZRJ Ljubljana) and Marjan Temovski (SK Zlatovrv – Macedonia), Marjan Vilhar (Postojna Cave), explored and documented that the Postojna Cave system is longer by 3.5 kilometres and is currently 24,120 metres in length.

Further exploration activities depend on a number of circumstances, in particular weather conditions and the River Pivka water levels. Although cavers will gladly admit that cave exploration and measurement alone make for a very interesting activity, their pursuits are additionally inspired by a great desire to achieve their target and connect the Postojna-Planina cave system, which explorers have been endeavouring to do for 170 years.

The company Postojnska jama, d.d. provides both moral and financial support for these endeavours, as this is considered to be the company’s mission. Connecting the two cave systems will make this the longest cave system in Slovenia and one of the longest ones in Europe, which is of great importance for further development of speleology as such and the International Union of Speleology. The Union celebrated its 50th anniversary only a few weeks ago, and had actually been founded in the Dance Hall of Postojna Cave. And since Postojna Cave is a cave that boasts countless superlatives and milestones, all these exploration activities are undoubtedly another step towards a new notable achievement.