كهف كروبيرا

At the beginning of the 20th century, Arabika was visited by French speleologist Édouard-Alfred Martel, who published several works about the massif.[6] In 1909–10 Russian karst scientist Alexander Kruber, a founder of the study in Russia, performed some field studies in Arabika. He published his observations in a series of Arabika-specific papers[7][8][9] and several أفرودةs. During the subsequent 50 years no special studies were undertaken of the karst and caves in the region, although the karst of Arabika was referred to in many works dealing with regional geology and hydrogeology.

In the early 1960s, Georgian speleologists led by L. Maruashvili began exploring caves in the high sector of the massif.[10][11][12] Among several other caves, they made the first exploration of an open-mouthed 60 m shaft in the Ortobalagan Valley and named it after Alexander Kruber. The first explorers were stopped by impassable squeezes at −95 m in a meandering passage which led off from the foot of the entrance shaft. The cave remained largely neglected over next 20 years, although occasionally visited by cavers from various caving clubs. Before 1980 there were no caves deeper than 310 م (1,020 قدم) known in Arabika.

The new epoch in cave explorations in the Arabika massif began in 1980 when the Kiev Speleological Club, led by Alexander Klimchouk, started exploring caves there. They adopted an approach to cave search and exploration which included thorough investigations in a defined area and systematic testing of cave limits, through digging in boulder chokes and enlarging squeezes which had previously obstructed exploration. The Ortobalagan Valley had been selected as a primary focus for the Ukrainian efforts. This approach, followed in subsequent years by other caving clubs which joined exploration activity in different parts of Arabika, resulted in the discovery of many deep caves including five caves deeper than 1,000 m.

In the Ortobalagan Valley, the Ukrainian cavers made breakthroughs in Kujbyshevskaja Cave at −160 m and pushed it to −1,110 م (−3,640 قدم) by 1986 through a series of massive boulder chokes. They broke through an impassable squeeze at −120 m in Genrikhova Bezdna Cave and eventually connected it to Kujbyshevskaja at −956 m in 1987. The resultant system has been named the Arabikskaja System.

From 1982 onwards, the Kiev cavers started systematically working in Krubera Cave, located less than 200 metres from the Kujbyshevskaja entrance, hoping to connect with the Arabikskaja System and increase its total depth by 60 m. Exploration progressed slowly because critically tight meanders between the pits required enormous amounts of work to widen them to a passable size. The cave was pushed to −340 m during 1982–1987. Two "windows" in a vertical shaft at depths of 220–250 m were documented on the cave map but remained unexplored. During this time the cave received its second, alternative name Voronja (Crows') Cave, owing to the number of crows nesting in the entrance shaft.

The political and ethnic conflict in Abkhazia during 1992–94 resulted in instability and border problems which continued over subsequent years. This suspended speleological explorations in Arabika. Some stabilization of the situation in 1998 has since enabled a renewal of exploration effort to take place in the region.

In 1999, the expedition of the Ukrainian Speleological Associations (Ukr.S.A.) led by Yury Kasjan made a major breakthrough in Krubera Cave by discovering and exploring two branches behind the windows at a depth of 220–250 m. These branches stretched in two different directions. The "Main Branch" was explored to −740 m and the "Nekujbyshevskaja Branch" to −500 m.

In 2000, the Main Branch was quickly pushed by the multi-stage expedition of the Ukr.S.A. in August to −1,200 m and in September to −1,410 m.

In January 2001, the Ukr.S.A. expedition explored the cave to −1,710 م (−5,610 قدم) making it the deepest cave in the world. For the first time in the history of speleology, the deepest cave in the world had been established outside of western Europe. Since 2001, the Krubera explorations by the Ukr.S.A. have been undertaken within the frame of the multi-year project named "The Call of the Abyss", coordinated by A. Klimchouk, Y. Kasjan, G. Samokhin and K. Markovskoy. Besides the Ukrainian speleologists, cavers from many countries such as France, Spain, Russia, Moldova, Bulgaria, Great Britain, Ireland, Israel and Lithuania have taken part in different expeditions of the Ukr.S.A.

The major events in the exploration of Krubera Cave in subsequent years were as follows (see Figure 4 for spot locations):

• August: the Ukr.S.A. expedition led by Yury Kasjan. Four underground camps established in the cave: in the Main Branch at −500, −1,200 and −1,400 m and in the Nekujbyshevskaja Branch at −500 m. Systematic inspection and probing of potential leads in the deep sections of the Main Branch; climbing in the Lamprechtsofen tributary; digging in the boulder choke in the Nekujbyshevskaja Branch.

• August: the expedition of the Kiev Speleological Club and the CAVEX team. Tested and passed a sump at −1,440 m (now known as Sump 1), explored the post-sump section to roughly −1,660 m, continued climbing in the Lamprechtsofen tributary.

• July: the CAVEX team started their separate explorations, beyond the Ukr.S.A. project, in Krubera Cave. Continued exploring a section beyond Sump 1 at −1,410 m and reached the next sump (Sump 2 – "Blue Lake") at depth claimed to be −1,840 m. The depth of that point according to the subsequent Ukr.S.A. survey is −1,775 m.
• August: the Ukr.S.A. expedition led by Nikolay Solovjov and Alexander Klimchouk. In the Main Branch, surveyed the post-sump series, established a camp at −1,640 m, discovered a lead to a new section ("The Way to the Dream") and explored to −1,840 m. Explored the Uzhgorodskaja Series in the upper part of Krubera by climbing an 80 m high shaft in the Meander Krym. Continued working in the Nekujbyshevskaja Branch.
• October: the Ukr.S.A. expedition led by Yury Kasjan. In the Main Branch, discovered a lead into a new section beyond the Big Junction at −1,790 m. Explored this section named "Windows" to a blind chamber called "Game Over" at −2,080 m. The depth mark of 2,000 m had been passed for the first time in the history of speleology.

• February–March: the Ukr.S.A. expedition led by Yury Kasjan. In the Main Branch, continued exploring the "Windows" series where many side leads and several sumps were tested. A sump at −1,980 m called "Kvitochka" was passed by Nokolay Solovyov, and a continuation found behind it.
• July: the CAVEX team expedition. Explored the section beyond the Kvitochka Sump to a further sump called Dva Kapitana ("Two Captains") at −2,140 m.
• August: the Ukr.S.A. expedition led by Nikolay Solovyov. Continued digging and broke through the boulder choke at −500 m in the Nekujbyshevskaja Branch, explored it to the next boulder choke at −640 m.
• October: the Ukr.S.A. expedition led by Yury Kasjan. The exploration beyond the Kvitochka Sump had been cancelled due to a sudden flood. Established a camp at −1,960 m. Performed a verification survey to −1,200 m by hydrolevelling to assess the precision of the standard Ukr.S.A. survey (the الجمعية الجغرافية الروسية group). Continued climbing in the Lamprechtsofen tributary to +210 m relative to the junction.

• August–September: the Ukr.S.A. expedition coordinated by Yury Kasjan. In the Main Branch the terminal sump called Dva Kapitana ("Two Captains") was tested by Gennadiy Samokhin to depth of 17 m, which extended the total depth of Krubera Cave to 2,158 م (7,080 قدم). In the Nekujbyshevskaja Branch, a group led by Kyryl Markovskoy broke through the boulder choke at −640 m and explored a continuation to −1,004 m.

• January: the CAVEX team expedition. Performed a dive in the terminal "Dva Kapitana" sump and claimed it to reach −30 m depth below the water table. However, characteristics of morphology of the underwater passage reported by the team were not confirmed by the subsequent exploration, and no safety line was found deeper than 16 m.
• August–September: the Ukr.S.A. expedition led by Yury Kasjan. In the Main Branch, Gennadiy Samokhin dived the terminal "Dva Kapitana" Sump for a length of 140 m and depth of −46 m, which set the new depth for Krubera Cave at 2,191 م (7,188 قدم). After an elbow at -35 m the underwater passage continues to depth under steep angle. Also in the deep parts of the Main Branch, several side passages and sumps at various depths were explored. In a side branch which previously ended at −1,775 m by the "Blue Lake" sump, a series of air-filled passages was explored behind the sump, separated by six intermediary sumps. The farthest sump, "Yantarny", was explored for 130 m in length and 19.5 m in depth and continues. The deepest point in this branch has been reached at −1,841 m. In the Nekujbyshevskaya Branch, a group led by Kyryl Markovskoy continued exploring new leads and extended the depth of this branch to −1,293 m.

• September: the Ukr.S.A. expedition led by Yury Kasjan. Explored the Nekujbyshevskaya Branch to depth of 1,390 م (4,560 قدم). An international scientific expedition "Towards the Centre of the Earth", led by ليتوانيون Aidas Gudaitis (Aenigma), descended the main branch as far as −1,800 م (−5,906 قدم), placing water level loggers at siphons here and in the "Chamber of Soviet Speleologists" at −1,710 م (−5,610 قدم).[13]

• August–September: the Ukr.S.A. expedition led by Yury Kasjan has further pushed the Nekujbushevskaya Branch to a siphon at depth of 1,557 م (5,108 قدم). The international "Towards the Centre of the Earth" expedition led by Aidas Gudaitis returned to the main branch to collect data from water level loggers, swap their locations and push exploration in the "Spanish branch" near camp 1400.[13] 2008–2009 data collected from 1,710 m and 1,800 m indicated that the sump levels rose in two distinct periods: continuously from May–July 2009 and with an isolated pulse in October 2008, both sumps reaching a maximum flood depth of 12 m. New logger locations at depths of 1,800 m, 1,980 m (Kvitochka sump) and 2,140 m (Dva Kapitanas sump).[13]

• July–August: The CAVEX Team Summer expedition led by Konstantin Mujin performed the first biospeleological studies in the Krubera-Voronya cave. The biospeleological studies led by the cave biologists Ana Sofia Reboleira and Alberto Sendra, provided the deepest subterranean arthropods of the Earth.[14]
• August: During "Towards the Centre of the Earth" expedition led by Aidas Gudaitis, Lithuanian member of Aenigma caving club Saulė Pankienė became the first woman to dive Kvitochka sump at 1,980 m, and subsequently to descend to the "Two Captains" sump at a depth of 2,140 م (7,020 قدم). Water level measurement results of 2009–2010, collected during this expedition, showed that the water level rose up to 228 م (748 قدم) above the sump "Two Captains" during June 2010. Data logging devices were installed by Irish members of the expedition near to the entrance of the cave, to log surface conditions and enable correlation of data between surface and underground locations. "Spanish Branch" exploration was completed and a limit was reached with 131 m total passage surveyed.[15]

• August: A team of 59 spent 27 days exploring Krubera. Including members from nine different countries, the team set up a series of camps underground. Ukrainian cave diver Gennadiy Samokhin was responsible for reaching a new world depth record of −2,197 متر (−7,208 قدم).[4][16]