The history of exploring Velebit’s underground

The first written records of Velebit’s pits date back to the 18^th century, when they first appear on topographic maps. At the time, the strong north-easterly winds sweeping down Velebit's slopes were believed to originate in deep pits.

Explorations of Varnjača, Crikvena and Hajdučka špilja pits in Northern Velebit are described in Planinarski vodič (Hikers’ Guide) from 1929.

In late 1960s, members of the speleology department of the Željezničar, a Zagreb-based hiking society, arrived in Northern Velebit to explore pits in Lomska duliba and Rožanski kukovi. Among other sites, they explored the pit known as Ledena jama in Lomska duliba, making their way down to the ice plug at the depth of 58 m.

Exploration continued in 1980, when members of Zagreb-based speleological society Ursus spelaeus joined their colleagues from the Željezničar. They discovered a 143 m deep pit, the deepest one thus far discovered on Velebit, and named it Jama 22. The speleologists explored a dozen other subterranean structures, some deeper than 100 m.

Stories about the allure of Northern Velebit and its pits attracted Slovak speleologists from the Speleology Club of the Comenius University in Bratislava to the area in 1990. They made their way down into pits that had already been discovered, but while surveying the terrain, they also discovered a snow cave near Rossijev kuk, and noticed a small crack that started to open at its floor, made of ice. Breaking through between the rock and the ice, they descended to the depth of 157 m, where they were stopped by a second large ice plug. They named the pit Punoleda (literally “Lots of Ice”). It was the deepest pit discovered in Northern Velebit thus far.

The same group of speleologists returned in 1992, when they discovered a large entrance to a pit on Hajdučki kukovi. They began their exploration and made it to the depth of 190 m when heavy rain and underground waterfalls forced them to turn back. The pit, which was given the working name “Manuel I”, became the deepest known pit on Velebit. Slovak speleologists shared the data on the pits they explored with their Croatian colleagues.

As early as 1993, Croatian speleologists, led by Branko Jalžić, continued the exploration of this pit and made it to a depth of 600 m, which made Manuel I the deepest known pit in Croatia at the time. They named the pit Lukina jama in honour of Ozren Lukić “Luka”, geologist and long-standing member of the Željezničar speleological society, who was killed on Velebit in the Croatian War of Independence. Even though they only had very basic gear, Damir Lacković, Siniša Rešetar and Robert Dado continued their descent to the floor, at the depth of 1355 m, during the same expedition, discovering a syphon lake. Photographs were taken, geological prospecting was completed, and Lukina jama claimed the title of the deepest pit in Croatia. Croatian speleologists also entered Ledena jama that same year, making their way through the newly formed cracks in the ice plugs, and descending to the depth of 451 m.

The exploration of Lukina jama continued next year, when speleologists discovered the entrance to another pit, which they named Trojama (roughly translates as “Triple Pit”), in immediate vicinity of the entrance to Lukina jama. Exploring the new pit, they discovered that it was connected with Lukina jama at the depth of 558 m. The pit, which has two entrances, was then named Lukina jama –Trojama. This expedition included the exploration of the syphon lake in the lowest segment of the pit, at the depth of 1355 m. Cave divers Zoran Stipetić “Patak” and Teo Barišić descended into the lake and dived across the syphon passage, to the length of 57 m and the depth of 6 m. They only had very basic gear, small oxygen bottles and wetsuits, and water temperature was 4°C. This was the greatest depth at which a dive was ever performed in a subterranean structure in history. The dive across the syphon and the discovery of another, higher entrance into Trojama revealed that the Lukina jama – Trojama system was in fact 1392 m deep. Another passage was discovered on the floor of the lake syphon.

The syphon on the floor of Lukina jama is today known as Patkov sifon (“Patak's Syphon”) in honour of Zoran Stipetić “Patak”, member of the speleology department of the Velebit hiking society, who was killed in 1996 while testing new diving equipment for further exploration of the syphon lake in Lukina jama.

An unknown endemic leech species, which was named Croatobranchus mestrovi and is now known as the Meštrov's leech, was discovered in Lukina jama, along with many other animal species that have adapted to life in eternal darkness and moisture.

In 1996, Slovak speleologists made it through the ice plug in the Xantipu pit on Vratarski kuk, and descended into a new pit, 516 m deep, in Mali kuk, which was named Slovačka jama.

Next year, speleologists from the speleology department of the Velebit hiking society, led by Darko Bakšić, joined their Slovak colleagues in another descent into Slovačka jama, making it to the depth of 1000 m. The Croatobranchus mestrovi leech was discovered there too.

In 1997, speleologists discovered and explored a new pit on Gornji kuk, which is almost completely vertical, from the entrance to the floor, located at the depth of 553 m. They named it Patkov gušt (“Patak’s Joy”) in honour of Zoran Stipetić Patak, the cave diver who explored Lukina jama.

In the following years, speleologists discovered new subterranean structures in addition to further exploring the already discovered ones. Speleologists from Karlovac discovered a pit they named Olimp on Begovački kuk in 1998, and Slovak speleologists discovered Meduza pit and a number of other pits near Crikvena. Large speleological expeditions were mounted, many of them international. The deepest underground speleological camp was set up in Slovačka jama in 1999, at the depth of 1254 m. By 2020, 617 subterranean structures were discovered and explored in the Northern Velebit National Park

Measuring equipment was set up in select pits to keep track of microclimate parameters, hydrological characteristics, and water quality. Sediment samples were taken for chemical analysis, along with fauna samples to determine species, and many other studies were conducted.

For each subterranean structure they explore, speleologists produce a detailed 1:500 map, keep an exploration log and record all their observations, along with microclimate and structural element measurement results, identify biological samples in situ, collect samples for further analyses, and more.