Misplaced Pages

#256743

85-485: The difference in elevation of the highest cave entrance (Arbaika) and its deepest explored point is 2,199 ± 20 metres (7,215 ± 66 ft). It became the deepest-known cave in the world in 2003 when the expedition of the Ukrainian Speleological Association reached a depth of 1,910 m (6,270 ft) which exceeded the depth of the previous deepest-known cave, Lamprechtsofen , in

170-734: A geologic formation , such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons . Highly fractured rocks can make good aquifers or hydrocarbon reservoirs , since they may possess both significant permeability and fracture porosity . Fractures are forms of brittle deformation. There are two types of primary brittle deformation processes. Tensile fracturing results in joints . Shear fractures are

255-480: A = half crack length. Fracture mechanics has generalized to that γ represents energy dissipated in fracture not just the energy associated with creation of new surfaces Linear elastic fracture mechanics (LEFM) builds off the energy balance approach taken by Griffith but provides a more generalized approach for many crack problems. LEFM investigates the stress field near the crack tip and bases fracture criteria on stress field parameters. One important contribution of LEFM

340-451: A car windshield or a highly ductile crack like a ripped plastic grocery bag. Rocks are a polycrystalline material so cracks grow through the coalescing of complex microcracks that occur in front of the crack tip. This area of microcracks is called the brittle process zone. Consider a simplified 2D shear crack as shown in the image on the right. The shear crack, shown in blue, propagates when tensile cracks, shown in red, grow perpendicular to

425-445: A constant of proportionality within geology. σ n is the normal stress across the fracture at the instant of failure, σ f represents the pore fluid pressure. It is important to point out that pore fluid pressure has a significant impact on shear stress, especially where pore fluid pressure approaches lithostatic pressure , which is the normal pressure induced by the weight of the overlying rock. This relationship serves to provide

510-473: A fixed function of θ {\displaystyle \theta } . With knowledge of the geometry of the crack and applied far field stresses, it is possible to predict the crack tip stresses, displacement, and growth. Energy release rate is defined to relate K to the Griffith energy balance as previously defined. In both LEFM and energy balance approaches, the crack is assumed to be cohesionless behind

595-437: A fracture forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. Fractures also play a significant role in minerals exploitation. One aspect of the upstream energy sector is the production from naturally fractured reservoirs. There are a good number of naturally fractured reservoirs in

680-405: A large area of the eastern sector of the massif (the hypothetical "Eastern Karst Hydrological System"). It is not clear where Sarma Cave (−1,550 m) drains to, Goluboje Ozero to the southeast or Reprua to the southwest, at the shore. The results of the dye-tracing tests demonstrated that groundwater flow is not subordinate to the fold structure but is largely controlled by faults that cut across

765-526: A low overall hydraulic gradient of 0.007-0.008. Low- TDS groundwater is tapped by boreholes in the shore area at depths of 40–280, 500, 1,750, and 2,250 m below sea level, which suggests the existence of a deep flow system with vigorous flow. Submarine discharge along the Arabika coast is reported at depths up to ~400 m b.s.l. It is difficult to interpret these facts in terms of the development of karst systems controlled by contemporary sea level, or within

850-611: 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 Kuybyshevskaya Cave at −160 m and pushed it to −1,110 m (−3,640 ft) by 1986 through

935-413: A remote tensile stress, σ n , is applied, allowing microcracks to open slightly throughout the tensile region. As these cracks open up, the stresses at the crack tips intensify, eventually exceeding the rock strength and allowing the fracture to propagate. This can occur at times of rapid overburden erosion. Folding also can provide tension, such as along the top of an anticlinal fold axis. In this scenario

SECTION 10

#1732852564257

1020-403: A result from shear or tensile stress. Some of the primary mechanisms are discussed below. First, there are three modes of fractures that occur (regardless of mechanism): For more information on this, see fracture mechanics . Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined. The first form is in axial stretching. In this case

1105-418: A result, any differences in hydrostatic balance down the well can result in well control issues. If a higher pressured natural fracture system is encountered, the rapid rate at which formation fluid can flow into the wellbore can cause the situation to rapidly escalate into a blowout, either at surface or in a higher subsurface formation. Conversely, if a lower pressured fracture network is encountered, fluid from

1190-475: A rod under uniform tension Griffith determined an expression for the critical stress at which a favorably orientated crack will grow. The critical stress at fracture is given by, σ f = ( 2 E γ π a ) 1 / 2 {\displaystyle \sigma _{f}=({2E\gamma \over \pi a})^{1/2}} where γ = surface energy associated with broken bonds, E = Young's modulus , and

1275-636: A role in guiding groundwater flow; the latter guide flow across the strike of major plicative dislocations, from the central sector toward the Black Sea . The cave has six entrances, in the gallery below they are arranged by altitude, highest to lowest, after the main one. All are situated above the tree line . Major on-shore karst springs with individual average discharges of 1 to 2.5 m/s (35 to 88 cu ft/s) are located at altitudes ranging from 1 m (3.3 ft) (Reprua Spring) to 540 m (1,770 ft) (Gega waterfall). Two of them are located in

1360-703: A series of massive boulder chokes. They broke through an impassable squeeze at −120 m in Genrikhova Bezdna Cave and eventually connected it to Kuybyshevskaya at −956 m in 1987. The resultant system has been named the Arabikskaya System. From 1982 onwards, the Kiev cavers started systematically working in Krubera Cave, located less than 200 metres from the Kuybyshevskaya entrance, hoping to connect with

1445-507: A weakened section of rock. This weakened section is more susceptible to changes in pore pressure and dilatation or compaction. Note that this description of formation and propagation considers temperatures and pressures near the Earth's surface. Rocks deep within the earth are subject to very high temperatures and pressures. This causes them to behave in the semi-brittle and plastic regimes which result in significantly different fracture mechanisms. In

1530-422: Is called cataclastic flow, which will cause fractures to fail and propagate due to a mixture of brittle-frictional and plastic deformations. Describing joints can be difficult, especially without visuals. The following are descriptions of typical natural fracture joint geometries that might be encountered in field studies: Faults are another form of fracture in a geologic environment. In any type of faulting,

1615-535: Is less than force required to fracture and create new faults as shown by the Mohr-Coulomb diagram . Since the earth is full of existing cracks and this means for any applied stress, many of these cracks are more likely to slip and redistribute stress than a new crack is to initiate. The Mohr's Diagram shown, provides a visual example. For a given stress state in the earth, if an existing fault or crack exists orientated anywhere from −α/4 to +α/4, this fault will slip before

1700-422: Is observed. To fully understand the effects of applied tensile stress around a crack in a brittle material such a rock, fracture mechanics can be used. The concept of fracture mechanics was initially developed by A. A. Griffith during World War I. Griffith looked at the energy required to create new surfaces by breaking material bonds versus the elastic strain energy of the stretched bonds released. By analyzing

1785-572: Is one of the deepest caves in the world. Before the discovery of the Krubera Cave in Georgia , it was the deepest-known cave in the world. Lamprechtsofen is located 2 km (1.2 mi) northwest of Weißbach bei Lofer ( Salzburg ), Austria , in the Leogang Mountains . The cave has been known for centuries. In 1701 it was walled up to prevent the intrusion of treasure seekers, who were lured to

SECTION 20

#1732852564257

1870-428: Is one of the two known caves on Earth deeper than 2,000 metres. Georgian speleologists from "Kipiani group" who discovered the cave in the 1963 named it for Russian geographer Alexander Kruber and explored it to -57 m. In 1980's the cave was rediscovered by another group and called "Siberian cave'. And then it was rediscovered for the third time by Ukrainian speleologists in 1980s' and called "Voronya" (Crows' cave) for

1955-462: Is the stress intensity factor , K, which is used to predict the stress at the crack tip. The stress field is given by σ i j ( r , θ ) = K ( 2 π r ) 1 / 2 f i j ( θ ) {\displaystyle \sigma _{ij}(r,\theta )={K \over (2\pi r)^{1/2}}f_{ij}(\theta )} where K {\displaystyle K}

2040-513: Is the Peak of Speleologists (2,705 m (8,875 ft)) but the dominant summit is a typical pyramidal horn of the Arabika Mount (2,695 m (8,842 ft)). Some middle- to low-altitude ridges covered with forest lie between the central sector and the Black Sea . A plateau-like middle-altitude outlier of the massif in its south sector is Mamzdyshkha, with part of the plateau slightly emerging above

2125-423: Is the stress intensity factor for Mode I, II, or III cracking and f i j {\displaystyle f_{ij}} is a dimensionless quantity that varies with applied load and sample geometry. As the stress field gets close to the crack tip, i.e. r → 0 {\displaystyle r\rightarrow 0} , f i j {\displaystyle f_{ij}} becomes

2210-547: 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

2295-565: The Austrian Alps , by 80 metres (260 ft). In 2006, for the first time in the history of speleology , the Ukrainian Speleological Association expedition reached a depth greater than 2,000 metres (6,600 ft), and explored the cave to −2,080 m (−6,824 ft). Ukrainian diver Gennadiy Samokhin extended the cave by diving in the terminal sump to 46 metres' depth in 2007 and then to 52 m in 2012, setting successive world records of 2,191 m and 2,197 m, respectively. Krubera

2380-540: The Black Sea and plunge below the modern sea level. To the northwest, north, northeast, and east, Arabika is bordered by the deeply incised canyons of Sandripsh, Kutushara, Gega and Bzyb rivers. The Bzyb River separates Arabika from the adjacent Bzybsky Massif, another outstanding karst area with many deep caves, including the Snezhnaja-Mezhonogo-Iljuzia System (−1,753 m or −5,751 ft) and Pantjukhina Cave (−1,508 m or −4,948 ft). To

2465-568: The coulomb failure envelope within the Mohr-Coulomb Theory . Frictional sliding is one aspect for consideration during shear fracturing and faulting. The shear force parallel to the plane must overcome the frictional force to move the faces of the fracture across each other. In fracturing, frictional sliding typically only has significant effects on the reactivation on existing shear fractures. For more information on frictional forces, see friction . The shear force required to slip fault

2550-403: The Arabikskaya 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

2635-621: The Gega canyon (1 m/s or 35 cu ft/s; 540 m or 1,770 ft a.s.l.). There are also several smaller springs in the Gagra town. The Reprua River , one of the shortest rivers in the world, about 60 feet (18 m) long, starts in the cave and flows toward the Black Sea . Some boreholes located along the shore of the Black Sea yield karstic groundwater from depths of 40–280 m below sea level. Other much deeper boreholes tapped low-salinity karstic waters at depths of 500 and 1,750 m in

Krubera Cave - Misplaced Pages Continue

2720-485: The Khashupse Valley near Gantiadi and 2,250 m near Gagra. This suggests the existence of a deep karst system and vigorous karst groundwater circulation at depth. Submarine springs are known in the Arabika area, emerging from the floor of the Black Sea in front of the massif. Shallow springs at depths of 5–7 m can be reached by free dive near Gantiadi. Tamaz Kiknadze (1979) reported submarine springs near

2805-580: 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. Kasyan, G. Samokhin and K. Markovskoy. Besides the Ukrainian speleologists, cavers from many countries such as France, Spain, Russia, Moldova , Bulgaria , United Kingdom, Ireland, Israel and Lithuania have taken part in different expeditions of

2890-669: The Kujbyshevskaja Cave and the Iljukhina System were detected in the Kholodnaja Rechka and Reprua springs, proving groundwater flow to the south-southwest across major tectonic structures over a distance of 13–16 km as the crow flies (Figure 1). The tracer from Kujbyshevskaja Cave was also detected in a borehole located between these two springs, which yields groundwater from a depth of 200 m (660 ft) below sea level. This has been interpreted as an indication of

2975-573: 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 m (−5,610 ft) 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,

3060-460: 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 the next 20 years, although occasionally visited by cavers from various caving clubs. Before 1980 there were no caves deeper than 310 m (1,020 ft) known in Arabika. The new era in cave explorations in

3145-506: The Ortobalagan Valley likely belong to a single hydrological system, connected to large submarine springs at the Black Sea shore. The Ortobalagan Valley extends along the crest of the Berchil'sky anticline , which gently plunges northwest. The cave entrances are aligned along the anticlinal crest (Figure 2) but the caves are controlled by longitudinal, transverse, and oblique fractures and faults and exhibit complex winding patterns in

3230-457: 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): Lamprechtsofen Lamprechtsofen (also called Lamprechtshöhle , Lamprechtsofenhöhle or, together with a connected cave, Lamprechtsofen-Vogelschacht ) is a limestone karst river cave in Austria . With a depth of 1,735 m (5,692 ft), it

3315-485: The United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production. The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates. One of

3400-607: The Upper Jurassic succession resting on the Bajocian Porphyritic Series, which includes sandstones , clays and conglomerates at the top, and tuff , tuffaceous sandstones , conglomerates and breccia , porphyry and lava . The Porphyritic series forms the non-karstic basement of Arabika, which is exposed only on the northern and eastern outskirts, locally in the bottoms of the Kutushara and Gega River valleys. In

3485-485: The Zhovekvara River mouth, which has dimensions of about 5 x 9 km and a maximum depth of about 380 m (1,250 ft). The Arabika Submarine Depression is a closed feature with internal vertical relief of about 120 m (390 ft) (measured from its lowest rim) separated from the abyssal slope by the bar at a depth of about 260 m (850 ft). It has steep northern and northeastern slopes (on

Krubera Cave - Misplaced Pages Continue

3570-412: The active fracture experiences shear failure, as the faces of the fracture slip relative to each other. As a result, these fractures seem like large scale representations of Mode II and III fractures, however that is not necessarily the case. On such a large scale, once the shear failure occurs, the fracture begins to curve its propagation towards the same direction as the tensile fractures. In other words,

3655-469: The anticline roughly coincides with the ridge bordering the Gelgeluk Valley to the north. Located on the southwestern flank of the major anticline is another large one (Berchil'sky), in which the crest is breached by the Ortobalagan Valley. There are several smaller sub-parallel anticlines and synclines farther southwest, between the Berchil' Ridge and the coast. The plicative dislocation structure of

3740-836: The birth of true horizontal drilling in a developmental context. Another example in South Texas is the Georgetown and Buda limestone formations. Furthermore, the recent uprise in prevalence of unconventional reservoirs is actually, in part, a product of natural fractures. In this case, these microfractures are analogous to Griffith Cracks, however they can often be sufficient to supply the necessary productivity, especially after completions, to make what used to be marginally economic zones commercially productive with repeatable success. However, while natural fractures can often be beneficial, they can also act as potential hazards while drilling wells. Natural fractures can have very high permeability , and as

3825-485: The cave by legends of wealth hidden by a knight named Lamprecht after the Crusades . In 1905, several human skeletons were found in the cave, probably the remains of treasure hunters. At the same time, a 600-metre (2,000 ft) portion of the cave was opened to the public as a show cave . The exploration of Lamprechtsofen has been primarily conducted from the bottom (from the resurgence of its cave river ), rather than

3910-497: 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

3995-419: The cavity to reach the depth of 1735 m. Today, about 700 m (2,300 ft) are open to visitors, a portion of the cave that covers a 70-metre (230 ft) altitude difference. Because of the cave's river, it is subject to flooding from heavy rain and melting snow. As such, visitors and explorers have been occasionally trapped in the cave. Fracture (geology) A fracture is any separation in

4080-674: The central part of Arabika the Cretaceous cover ( Valanginian and Hauterivian limestones, marls and sandstones) is retained only in a few ridges and peaks, but it lies intact through the low-altitude ridges to the south-west of the central part. There the Cretaceous succession includes Barremian and Aptian – Cenomanian limestones and marly limestones with abundant concretions of black chert . The Upper Jurassic succession begins with thin-bedded Kimmeridgian – Oxfordian cherty limestones, marls, sandstones and clays , which are identified in

4165-423: The connection of the cave with the submarine discharge. The large "Central Karst Hydrologic System", which encompasses most of the southeastern flank of the Arabika anticline, had been identified in this way. The system became the deepest in the world with its overall vertical range of about 2,500 m (8,200 ft) (measuring to the borehole water-bearing horizon) or even 2,700 m (8,900 ft) (measuring to

4250-405: The crack tip. This provides a problem for geological applications such a fault, where friction exists all over a fault. Overcoming friction absorbs some of the energy that would otherwise go to crack growth. This means that for Modes II and III crack growth, LEFM and energy balances represent local stress fractures rather than global criteria. Cracks in rock do not form smooth path like a crack in

4335-464: The crows nesting in the entrance pit. Only later exchange of information between the caving clubs allowed them to discover they explored same cave. The Arabika Massif , the home of Krubera (Voronya) Cave, is one of the largest high-mountain limestone karst massifs in the Western Caucasus. It is composed of Lower Cretaceous and Upper Jurassic limestones that dip continuously southwest to

SECTION 50

#1732852564257

4420-502: The deepest part of the Krubera Cave (at the depth of −2,175 metres). At the beginning of the 20th century, Arabika was visited by French speleologist Édouard-Alfred Martel , who published several works about the massif. 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 and several monographs . During

4505-602: The deepest reported submarine discharge points). Another tracer was injected in the Moskovskaja Cave (−970 m) and detected at the Gegsky Vodopad spring, indicating the presence of a karst hydrologic system comprising the northeastern flank of the Arabika anticline (the "Northern System"). No connections have been revealed with yet another major spring, Goluboje Ozero in the Bzyb River canyon, although it apparently drains

4590-417: The direction of the least principal stresses. The tensile cracks propagate a short distance then become stable, allowing the shear crack to propagate. This type of crack propagation should only be considered an example. Fracture in rock is a 3D process with cracks growing in all directions. It is also important to note that once the crack grows, the microcracks in the brittle process zone are left behind leaving

4675-598: The dramatic sea level drop of ~1,500 m is well established. The biocenosis of Krubera-Voronja is composed of more than 12 species of arthropods of several groups, such as pseudoscorpions , spiders , opiliones , crustaceans , springtails , beetles and dipterans . Krubera-Voronja cave is inhabited by endemic species, including four springtails discovered during the CAVEX Team expedition of 2010: Anurida stereoodorata , Deuteraphorura kruberaensis , Schaefferia profundissima , and Plutomurus ortobalaganensis ;

4760-410: The eastern part of Gagra at depth of 25–30 m and Buachidze and Meliva (1967) revealed submarine discharge at depths up to −400 m by hydrochemical profiling. Recently an outstanding feature of the sea floor topography near Arabika has been revealed from a digital bathymetric map that combines depth soundings and high-resolution marine gravity data. This is a huge submarine depression in front of

4845-411: The fault typically attempts to orient itself perpendicular to the plane of least principal stress. This results in an out-of-plane shear relative to the initial reference plane. Therefore, these cannot necessarily be qualified as Mode II or III fractures. An additional, important characteristic of shear-mode fractures is the process by which they spawn wing cracks , which are tensile cracks that form at

4930-527: The first initial breaks resulting from shear forces exceeding the cohesive strength in that plane. After those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults. Most often, fracture profiles will look like either a blade, ellipsoid, or circle. Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults . Fractures may also be

5015-422: The fracture face is actually touching the other face. The cumulative impact of asperities is a reduction of the real area of contact' , which is important when establishing frictional forces. Sometimes, it is possible for fluids within the fracture to cause fracture propagation with a much lower pressure than initially required. The reaction between certain fluids and the minerals the rock is composed of can lower

5100-467: The last of these is the deepest terrestrial animal ever found on Earth , living 1,980 metres (6,500 ft) below the cave entrance. The beetle Catops cavicis inhabits Krubera-Voronja cave and also several caves around the Ortobalagan Valley . The subterranean amphipod crustacean Kruberia abchasica caught by Gennady Samokhin in August 2013, during dives in the siphon 'Dva Kapitana', dwells at

5185-408: The least principal normal stress, σ n . When this occurs, a tensile fracture opens perpendicular to the plane of least stress. Tensile fracturing may also be induced by applied compressive loads, σ n , along an axis such as in a Brazilian disk test. This applied compression force results in longitudinal splitting. In this situation, tiny tensile fractures form parallel to the loading axis while

SECTION 60

#1732852564257

5270-422: The load also forces any other microfractures closed. To picture this, imagine an envelope, with loading from the top. A load is applied on the top edge, the sides of the envelope open outward, even though nothing was pulling on them. Rapid deposition and compaction can sometimes induce these fractures. Tensile fractures are almost always referred to as joints , which are fractures where no appreciable slip or shear

5355-533: The lower part of Krubera Cave. Above lies the thick Tithonian succession of thick-bedded limestones with marly and sandy varieties. Sandy limestones are particularly abundant through the upper 1,000 m sections of deep caves of the Ortobalagan Valley. The tectonic structure of Arabika is dominated by the axis of the large sub-Caucasian anticline (oriented NW–SE), with the gently dipping southwestern mega-flank, complicated by several low-order folds, and steeply dipping northeastern flank (Figure 3). The axis of

5440-497: The massif is severely complicated by faults, with the fault-block structure strongly controlling both cave development and groundwater flow. Major faults of the sub-Caucasian orientation delineate several large elongated blocks that experienced uplift with different rates during Pliocene and Pleistocene . This had a pronounced effect on the development of deep groundwater circulation and of Krubera Cave in particular. Both longitudinal and transverse faults and related fracture zones play

5525-542: The most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas. The chalk had very little porosity, and even less permeability. However, tectonic stresses over time created one of the most extensive fractured reservoirs in the world. By predicting the location and connectivity of fracture networks, geologists were able to plan horizontal wellbores to intersect as many fracture networks as possible. Many people credit this field for

5610-463: The non-Kujbyshevskaja branch of Krubera Cave, etc.). The deep parts of Krubera display a more pervasive conduit pattern with a mixture of phreatic morphology, characteristic of the zone of high-gradient floods, which can be up to 400 m above the low-flow water table, and vadose downcutting elements that are observed even below the water table. The core part of the Arabika Massif is composed of

5695-485: The plan view, remaining largely within and near the anticlinal crest zone. The caves are predominantly combinations of vadose shafts and steep meandering passages, although in places they cut apparently old fossil passages at different levels (e.g., at −2,100–2,040 m (−6,890–6,690 ft) in Kujbyshevskaja and Krubera caves, −1,200–1,240 m (−3,940–4,070 ft) and −980–1,150 m (−3,220–3,770 ft) in

5780-407: The plastic regime cracks acts like a plastic bag being torn. In this case stress at crack tips goes to two mechanisms, one which will drive propagation of the crack and the other which will blunt the crack tip . In the brittle-ductile transition zone , material will exhibit both brittle and plastic traits with the gradual onset of plasticity in the polycrystalline rock. The main form of deformation

5865-417: The propagation tip of the shear fractures. As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the σ h-max , which is the direction of maximum principal stress. Shear-failure criteria is an expression that attempts to describe the stress at which a shear rupture creates a crack and separation. This criterion is based largely off of

5950-530: The range of its Pleistocene fluctuations (up to −150 m). In combination with the existence of the Arabika Submarine Depression, all these facts point to the possibility that karst systems in Arabika could have originated in response to the Messinian salinity crisis (5.96–5.33 Ma) when the Black Sea (Eastern Paratethys ) could have almost dried up, as did the adjacent Mediterranean , where

6035-565: The region. In 1999, the expedition of the Ukrainian Speleological Associations (Ukr. S.A.) led by Jurij Kasjan (also spelled Yuriy Kasyan) 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 "Nekuybyshevskaya Branch" to −500 m. In 2000,

6120-445: The seashore. Since 1980, Ukrainian cavers have been undertaking systematic efforts in exploring deep caves in the Ortobalagan Valley, resulting in exploration of the Krubera Cave to its current depth and of the surrounding caves, now mostly connected to it. Another deep cave in the valley, located in its very upper part and explored by Moldavian and Ukrainian cavers is Berchilskaya Cave, 770 m (2,530 ft) deep. All large caves of

6205-503: The shore area; these are Reprua (average discharge 2.5 m/s or 88 cu ft/s; altitude 1 m or 3 ft 3 in above sea level) and Kholodnaja Rechka (1.2 m/s or 42 cu ft/s; 50 m or 160 ft a.s.l.). Two more major springs are located in the river canyons bordering Arabika to the east: Goluboe Ozero in the Bzyb canyon (2.5 m/s or 88 cu ft/s; 90 m or 300 ft a.s.l.) and Gega waterfall in

6290-567: The side of the massif) and gentle south and southwestern slopes. Its formation is apparently karstic. Presently this depression seems to be a focus of submarine discharge of the karst systems of Arabika. The speleological explorations and a series of dye tracing experiments conducted during the 1980s under the coordination of Alexander Klimchouk have radically changed previous notions of the hydrogeology of Arabika, revealed its outstanding speleological perspectives and strongly stimulated further efforts for exploration of deep caves. Tracers injected in

6375-526: The southwest, Arabika borders the Black Sea . The Arabika Massif has a prominent high central sector with elevations above the tree line at ~1,800–1,900 m (5,900–6,200 ft). This is an area of classical glaciokarstic landscape, with numerous glacial trough valleys and cirques, with ridges and peaks between them. The bottoms of trough valleys and karst fields lie at elevations of 2,000–2,350 m (6,560–7,710 ft), and ridges and peaks rise to 2,500–2,700 m (8,200–8,900 ft). The highest peak

6460-444: The strength of the rock is reached and a new fault is formed. While the applied stresses may be high enough to form a new fault, existing fracture planes will slip before fracture occurs. One important idea when evaluating the friction behavior within a fracture is the impact of asperities , which are the irregularities that stick out from the rough surfaces of fractures. Since both faces have bumps and pieces that stick out, not all of

6545-456: The stress required for fracture below the stress required throughout the rest of the rock. For instance, water and quartz can react to form a substitution of OH molecules for the O molecules in the quartz mineral lattice near the fracture tip. Since the OH bond is much lower than that with O, it effectively reduces the necessary tensile stress required to extend the fracture. In geotechnical engineering

6630-426: The strike of major folds, and that the large part of the central sector of Arabika is hydraulically connected to the springs along the seashore and with submarine discharge points. Krubera Cave has an extremely steep profile and reveals a huge thickness of the vadose zone. The lower boundary of the vadose zone (the top of the phreatic zone) is at an elevation of about 110 m (360 ft) at low flow, which suggests

6715-427: 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 geographers led by Levan Maruashvili began exploring caves in the high sector of the massif. Among several other caves, they made the first exploration of an open-mouthed 60 m shaft in

6800-407: The tensile forces associated with the stretching of the upper half of the layers during folding can induce tensile fractures parallel to the fold axis. Another, similar tensile fracture mechanism is hydraulic fracturing . In a natural environment, this occurs when rapid sediment compaction, thermal fluid expansion, or fluid injection causes the pore fluid pressure, σ p , to exceed the pressure of

6885-457: The top-down exploration typical for vertical caves. On August 19, 1998, a team led by Polish caver Andrzej Ciszewski discovered a connection between Lamprechtsofen and the PL-2 cave system, which established the height difference of the united cave system as 1,632 m (5,354 ft). This new discovery made Lamprechtsofen the deepest-known cave in the world for less than three years, as Krubera

6970-408: The tree line. Among several hundred caves known in the Arabika Massif, fifteen have been explored deeper than 400 m and five deeper than 1,000 m. Krubera Cave is located at 2,256 m above sea level in the Ortobalagan Valley, a perfectly shaped, relatively shallow, glacial trough of the sub- Caucasian stretch, which holds the advanced position in the Arabika's central sector relative to

7055-551: The wellbore can flow very rapidly into the fractures, causing a loss of hydrostatic pressure and creating the potential for a blowout from a formation further up the hole. Since the mid-1980s, 2D and 3D computer modeling of fault and fracture networks has become common practice in Earth Sciences. This technology became known as "DFN" (discrete fracture network") modeling, later modified into "DFFN" (discrete fault and fracture network") modeling. The technology consists of defining

7140-409: The work of Charles Coulomb, who suggested that as long as all stresses are compressive, as is the case in shear fracture, the shear stress is related to the normal stress by: σ s = C+μ(σ n -σ f ), where C is the cohesion of the rock, or the shear stress necessary to cause failure given the normal stress across that plane equals 0. μ is the coefficient of internal friction, which serves as

7225-572: Was discovered in June 2001 to be 2,197 metres (7,208 ft) deep. As of 2014, Lamprechtsofen is the fourth-deepest cave in the world, as two more Georgian caves have since been discovered to be deeper. Sarma Cave is 1,830 m (6,000 ft) and Illyuzia-Mezhonnogo-Snezhnaya Cave is 1,753 m (5,751 ft). On August 14, 2018 a Polish expedition connects the CL3 chasm to the Lamprechtsofen allowing

#256743