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– the Rudice Swallow Hole, Bull Rock and Bar caves
Vojtěch A. Gregor
VAG Geoscience Specialists, P.O. Box 192 A, Prince George, BC V2L 4S1, Canada,
Vojtěch A. Gregor
| 19.1.2015 17:13 |
I dedicate this study to the memory of my great friend and colleague, geologist, hydrologist, hydrogeologist and speleologist-karstologist RNDr. Dušan Hypr aka Klobouk († July 1st, 2014)
The Moravian Karst is a typical fluviokarst. It is built over and in Devonian limestones the age of which ranges from the Middle Devonian to the Lower Carboniferous. The series of strata consist of several depositional (sedimentary) cycles. The limestone massif is folded, faulted and fractured. The structure is a result of several tectonic events, mainly the Variscan orogeny and the Saxon tectogenesis.
The Rudice Plateau is situated in the central part of the Moravian Karst. It is noted for a well-developed fossil (Lower Cretaceous) tropical karst as well as the second longest cave system in the Czech Republic – that of the underground Jedovnice Creek. The system includes the Rudice Swallow Hole Cave, Bull Rock Cave, Bar Cave and the Josefov karst springs.
The system provides a continuous view of the geological setting of the limestone in an 8 km long and up to 150 m high cross-section beneath the ground surface. It consists of several geomorphological units, each with characteristic features. The sedimentary fill reveals several phases of the system development during the Quaternary period. In addition, it contains rich bone (skeleton) remnants of Pleistocene fauna (Bar Cave) and artifacts of sixteen cultures ranging from 13,000 yrs. BCE to 16th century AD (Bull Rock Cave).
Key Words: Moravian Karst, Rudice Plateau, Jedovnice Creek, Rudice Swallow Hole, Bull Rock Cave, Bar Cave, geology, stratigraphy, tectonics, geochemistry, hydrology, geomorphology, speleogenesis, paleontology, archeology.
Moravian Karst (Moravský kras)
Physiography. The Moravian Karst (Fig. 1, 2) is situated at the southeastern margin of the Bohemian Massif (Český masív), north of the Moravian capital of Brno. The NNE-SSW strip of partly barred Paleozoic limestone that forms the Moravian Karst is approx. 24 km long, 2 to 6 km wide and occupies an area of ca. 96 km2. The surface of the limestone forms a shallow depression that is surrounded by highs of the Brno Massif (Brněnský masiv) to the west and those of the Drahany Upland (Drahanská vysočina) to the north and east. It is generally flat, averages 450 m a.s.l. in elevation and dips gently to the south.
Fig. 1. Czech Republic, Drahany Upland (shaded), and Moravian Karst (black strip) north of the city of Brno. (Golec 2015, with permission)
Fig. 2. Protected Land Area Moravian Karst, self-explanatory map (Internet, public domain).
The Moravian Karst is a typical fluviokarst. A network of up to 140 m deep, mostly dry karst valleys (glens, gorges) dissects the surface into a number of karst plateaux. They commonly feature karst dolines and, in places, karren. Allogenic streams flowing from the borderland highs submerge at the margin of the limestone area in numerous caves, sinkholes and ponors (swallets). They emerge in karst springs at the bottom of the valleys.
The area of the Moravian Karst is geographically divided into three parts, namely the northern, central (middle) and southern part. The northern part is drained by the river of Punkva to the west, into the river of Svitava. The central part is drained by the Křtiny Creek (Křtinský potok) also to the west and the Svitava River. The Říčka Creek drains the southern part to the east, into the drainage basin of the Svratka River. The Punkva River is fed by three main headwaters, namely the Sloup Creek (Sloupský potok, the western branch), the White Water Creek (Bílá voda, the eastern branch) and the Lopač, Krasovský potok and Vilémovický potok creeks (the southern branch). In the central part, the Jedovnice Creek (Jedovnický potok) is the major tributary to the Křtiny Creek. The Hostěnice Creek (Hostěnický potok) is the main tributary to the Říčka Creek in the southern part.
Some 1400 caves are known in the Moravian Karst. The Amateur Cave (Amatérská jeskyně) in the northern part is the longest cave; the total length of its passages exceeds 32 km. The caves of the Jedovnice Creek in the central part – the Rudice Swallow Hole (Rudické propadání), Bull Rock (Býčí skála) and Bar (Barová) caves – with the total length of the passages in excess of 12 km follow. The Macocha Chasm (-187.2 m) with the Punkva Caves (Punkevní jeskyně) are the most outstanding karst landforms.
Geologic setting – stratigraphy. The Moravian Karst limestone complex exceeds 1000 m in true and 2800 m in apparent thickness and ranges from the Middle Devonian to the Lower Carboniferous in age. It is underlain by Lower to Middle Devonian siliciclastic rocks that in turn overlie the Proterozoic basement – the intrusive body of granitoid rocks of the Brno Crystalline (Igneous) Massif. The complex consists of two stratigraphic units, namely the Macocha Formation and the Líšeň Formation (Zukalová, Chlupáč 1982, Dvořák et al. 1993). To the north and east, the limestone sequence is overlain by Lower Carboniferous flysh – Culm – sequence (shale, graywacke, and conglomerate) of the Protivanov series of strata.
The Macocha Formation ranges from the Eifelian to the Lower Famenian in age. Itcomprises four major (mega) and a number of minor depositional cycles, each of which contains dark-gray limestone (summarily “Lažánky Lm.”) at the base and light-gray limestone (summarily “Vilémovice Lm.”) at the top (Hladil 1983a, b, 1986; Hladil, Vít 2000). The series of strata consists of several units (maximum true thickness measurements):
- Vavřinec Limestones: Eifelian to Lower Givetian, 30 m. This unit represents the “Vilémovice Lm.” of the 1st megacycle.
- Josefov Limestones: Givetian, 50 m.
- Lažánky Limestones: Givetian, > 400 m. These deposits consist of the “Lažánky Lm.” of the 2nd megacycle – Lažánky Lm. ss, 3rd megacycle – Habrůvka Lm., and 4th megacycle – Hostěnice Lm.
- Vilémovice Limestones: Givetian to Lower Famenian, > 600 m. These deposits include the “Vilémovice Lm.” of the 2nd megacycle – Sloup Lm., 3rd megacycle – Vilémovice Lm. ss, and 4th megacycle – Mokrá Lm.
The units are distinguished by the following characteristics:
- Vavřinec Limestones: light gray to gray micritic but locally also micro- to fine-grained laminated and platy limestones with clayey admixture and intercalated clayey beds. Locally, this unit contains dark gray lenticular layers with abundant stromatoporoids, corals and rare trilobites. In the northernmost part of the Moravian Karst, the Vavřinec Limestones are represented by pinkish-gray and pink micritic to medium-grained calcarenites with quartz admixture, biocalcarenites, and sparite biocalcarenites, informally called the Petrovice limestones.
- Josefov Limestones: dark, bluish-gray micritic to microcrystalline but locally also micro- to fine-grained platy limestones and dolomitic limestones with a variable content of clayey and sandy admixture. The faunal content includes abundant lumachelles of thick-walled brachiopods (Bornhardtina sp.) and, in places, massive stromatoporoids. The dolomitization is post-depositional, probably resulting from the diagenetic process. The Josefov Limestones are considered a facies of the Lažánky Limestones.
- Lažánky Limestones: dark-gray to gray, locally bluish-gray and bituminous, usually thin-bedded and in the lowermost layers strongly dolomitized limestones. Characteristic are micritic to microcrystalline layers alternating rhythmically with biomicritic and biodetrital layers rich in liptocenoses of branching stromatoporoids, particularly those of genus Amphipora. Spherical stromatoporoids, stachyodes, rugose corals and locally also thick-walled brachiopods are abundant.
- Vilémovice Limestones: gray to light-gray micrites and sparites to very fine-grained biosparites and biomicrosparites, usually poorly bedded or massive, locally rich in bioherms of benthic fauna (corals, stromatoporoids and, in places, also brachiopods).
The limestone density ranges from 2.61 g/cm3 to 2.81 g/cm3 with an average of 2.72 g/cm3. Higher density values are associated with dolomitized limestones whereas lower values are characteristic of limestones with clastic admixture. The limestones are tight, without significant intergranular porosity (helium, 0-1.0 %) and permeability (air, 0-0.1 mD).
Tables 1 and 2 show the chemical composition of limestones comprising the Macocha Formation.
The Líšeň Formation ranges from the Frasnian to the Lower Viséan in age. It consists of the Křtiny Lm. (Upper Frasnian to Tournaisian, 40 m) and the Hády-Říčka Lm. (Famenian to Lower Viséan, 150 m). The Vavřinec, Josefov, Křtiny and Hády-Říčka limestones combined form less than 20 % of the outcropping limestone mass. The units are characterized as follows:
- Křtiny Limestones: varicoloured nodular limestones with a variable content of clay, usually well-bedded and containing clayey interbeds. The faunal content includes trilobites, cephalopods, ostracodes and abundant conodonts.
- Hády-Říčka Limestones: dark-gray to black micritic to biodetrital but locally also micro- to fine-grained platy limestones with a variable content of clayey to sandy admixture and with clayey-sandy interbeds. In places, chert nodules occur. The faunal content is of mixed pelagic and neritic nature, highly fragmented and redeposited, probably by the action of currents.
Geologic setting – fold and fracture tectonics. The limestone complex is folded and fractured. Syndepositional gravity folds belong to the earliest deformations noted in the limestone strata. The main deformation, however, took place during the Uppermost Viséan (Sudetian) phase of the Variscan (Hercynian) orogeny (Dvořák, Pták 1963, Dvořák et al. 1993). The fold structure of the Moravian Karst is a product of this event.
In the northern and central parts of the Moravian Karst, the fold pattern is monovergent: all macrofolds display more or less obvious vergency to the east. This indicates a W→E oriented principal horizontal tectonic stress, the source of which is the compressive push of the Brno Igneous Massif to the west. Round and sinuous open folds are dominant. The main (B) fold axes predominantly follow NNE-SSW to NE-SW directions. The bedding dip ranges from ca. 5° to 90°, the most common dips being 10° to 45° to the east. The fractures include thrust faults, high angle normal and strike-slip faults, joints and joint zones, and calcite veins (Tab 3, 4-6). They are classified into five orders (Gregor 1976):
(1) First order fractures, particularly high angle faults and en echelon joint zones that persist from the basement through the entire Phanerozoic sequence.
(2) Fractures of the 2nd to 5th orders are limited to the limestone strata. The vertical extent of these features ranges from
(a) the maximum thickness of the outcropping section (≥ 100 m, 2nd order) to
(b) thinner layers (< 100 m, 3rd order) to
(c) packages of several beds (4th order) to
(d) single beds (5th order).
Fractures of the 2nd to 5th orders include joints bc (compression joints, more or less parallel to the fold axial plane B; also termed “axial joint cleavage”) and ac (tension joints, more or less perpendicular to the fold axial plane). Joints ac are usually filled with calcite. Faults typically contain calcite, calcite and calcite-limestone breccias, gouge and mylonite.
The fracture network is thought to have resulted from several tectonic events (Tab. 3; Gregor 2012, 2013). These include pre-Variscan (syndepositional) movements, the main deformation and the following late Variscan tectonic adjustments; the Upper Jurassic to Upper Cretaceous effects of the Saxon tectonics; and the Paleocene to Upper Miocene effects of the Alpine orogeny. The youngest generation of tectonic movements is called “neotectonics” and is post-Upper Miocene in age (Gregor 1976a, b, 2014a). The hierarchy of individual fracture systems is based on their geometry, mutual relationship, and physical and chemical properties of fracture calcite fills (so-called primary calcite, Tab. 4 to 6).
Tectonics and karst landforms. The majority of the karst landforms are developed in the Macocha Formation, especially in the Vilémovice and Lažánky limestones. The cave network consists of a number of cave levels (Gregor 1977, 2014a, b). Major structural controls on the cave network are, in a descending order of both magnitude and frequency: bedding planes and joints; bc joints, ac joints and other 4th to 2nd order fractures; and 1st order fractures. Karst dolines and sinkholes also show an affinity for the fracture network. Many of these features are aligned in straight lines that follow fracture directions, and thus form what is termed morphostructural or morphotectonic linears.
Sediments – surface deposits. Most of the Moravian Karst limestone complex is covered by non-carbonate overburden that ranges from the Lower Cretaceous to the Recent in age and varies in origin, lithology and thickness (Kettner 1970, Bosák 1980, 1984; Dvořák et al. 1993). It includes Lower Cretaceous clays, silts, sands and iron ore minerals of the Rudice Formation (also called Rudice beds); Upper Cretaceous (Cenomanian to Turonian) freshwater and marine sands, sandstones and marlstones; Tertiary (Paleogene and Neogene) sediments including the Middle Miocene (Lower Badenian) fill of the Lazanky Valley, and a variety of Quaternary sediments including gravel, loess, loess loam, and different types of soils.
Sediments – Cave fills comprise two distinct cave sediment facies: cave entrance facies and intra-cave facies. Both facies consist of allochthonous and autochthonous deposits. Allochthonous deposits include fluvial sediments (gravel, sand, silt and clay, mostly of the Culm, Drahany Upland provenience); infiltration sediments (gravel, sands, silts and clays derived from overburden); eolian deposits (loess, occurrences are limited to cave entrances); and colluvial deposits (entrance soil and talus). Infiltration sediments also contain materials from weathered Mesozoic and Tertiary cover sediments, e.g. quartz grains and pebbles, subangular quartzites and chert detritus. In the central part of the Moravian Karst (Rudice Plateau, Rudice Swallow Hole and Bull Rock caves) these deposits also contain redeposited sediments of the Rudice Formation, synsedimentarily sunken into depressions of the Rudice paleokarst. Autochthonous deposits include weathering detritus (chiefly residual soils), foam sinter, cave breakdown and speleothems.
Paleokarst – mostly fossil karst depressions of Lower Cretaceous to Paleogene in age – is preserved in some areas. Depressions with Paleogene fills occur at the NW margin of the Moravian Karst, in the area of the Žďárská plošina Plateau (Gregor 2013a). A fossil depression forms the upper, “doline” section of the Macocha Chasm; it was established during the Lower Cretaceous and deepened during the Paleogene. The Lower Cretaceous karst is best-developed on the Rudice Plateau, especially within the Rudice sunken block (Burkhardt 1974; Burkhardt, Gregor and Hypr 1975; Bosák 1976, 1980, 1981a, b, 1984, 1995; Bos8k et al., 1976; Bosák, Horáček and Panoš 1989).
Rudice Plateau (Rudická plošina)
The Rudice Plateau occupies most of the central (middle) part of the Moravian Karst. The plateau is delineated by the Lažánky Valley to the north, the Devonian (limestone) - Culm (silicates) geological boundary to the east, the Josefov-Křtiny Valley to the south, and the NNW-SSE striking western marginal fault of the Blansko Graben to the west (Fig. 3 and 4). The plateau contains two subunits, the Olomučany and Habrůvka plateaux (Demek 1993; Balák 1988, 1990; Balák et al. 1997). The average elevation of the proper Rudice Plateau is ca. 515 m a.s.l.; the Habrůvka Plateau reaches 546 m a.s.l.
Fig. 3. Rudice Plateau, self-explanatory map. The irregular red line between the Rudické propadání (Rudice Swallow Hole) and the Býčí skála (Bull Rock Cave, below the name-caption “Josefov”) represents the Jedovnice Creek cave system (author unknown, probably Administration of the Protected Land Area Moravian Karst, Ivan Balák).
Fig. 4. Rudice Plateau with the RSH Cave, BRC and BAC, before the discovery of the Easter Cave, BIRC and SRC. Explanatory notes: 1-granitoids of the Brno Igneous Massif, 2-Culm, 3-Rudice ceramic clays mining sites, 4-Blansko Graben western marginal fault – the western boundary of the plateau, 5-Old Slavic mining works, 6-historical mining claims, 7-unused alternatives of mining claims, 8-old mining works or karst dolines?, 9-modern fire/heat-resistant clays and foundry sands mining sites, 10-karst springs (Burkhardt 1977, Gregor 2014b).
Geologic setting. The surface of the Rudice Plateau is a product of the pre-Jurassic peneplanation, further re-formed during the Lower Cretaceous denudation – tropical weathering and erosion. The plateau is built by limestones of the Macocha Formation, namely by (from the base up) the Josefov Lm. (the lowermost layers of the Lažánky Habrůvka Lm.), the Habrůvka Lm. proper, and the Vilémovice (ss) Lm. (Hladil 1983a, b, 1986; Tab. 1 and 2). The package includes so-called transitional strata between the Vilémovice and Habrůvka limestones. This unit consists of alternating light-gray and dark-gray layers (on the order of centimeters to meters), or rather by an increasing presence of dark-gray layers in light-gray limestone, and may exceed 120 m in total thickness.
The limestone massif features fractures of the 1st to 5th order. They belong to two systems – the older, Variscan system (primaries ESE-WNW, 120°-140°, orthogonals NE-SW, 30°-50°) and the younger, Saxon-Alpine system (Tab. 3, 4-6). Saxon faults and joint zones, especially the primaries (NNW-SSE, 160° ± 10°), are the most prominent tectonic lines. They are part of, or parallel with, the Blansko Graben – a trench-like structural low that contains tectonically sunken deposits of Upper (Late) Cretaceous sediments of the Cenomanian and Turonian stage. The graben’s western marginal fault (Fig. 4) displays an apparent vertical displacement (AVD) of ca. 100 m. To the east, this displacement is counterbalanced by five faults, each with 15-20 m amplitude of the AVD (Bosák 1976, 1984).
Saxon-Alpine primaries – NNW-SSE striking fractures of the 1st and 2nd order – both delineate and are most notably present in the Rudice sunken block. A horst of this orientation separates the block from the Blansko Graben (Fig. 5). The block is noted for well-developed cockpit fossil karst (paleokarst) of the Lower Cretaceous age, with depressions (geological organs) up to 140 m deep.
Fig. 5. Rudice Plateau, general geologic setting and the RSHCave. Explanatory notes (symbol column, from top to bottom): 1-Devonian limestones, 2-Culm silicates, 3-Neogene sediments, 4-tectonic fractures (SA primaries), 5-caves, 6- development phases of the surface drainage (1-3); Rudická pokleslá kra-Rudice sunken block, hrásť-horst, jádro Blanenského prolomu-core of the Blansko Graben (Burkhardt, Gregor and Hypr 1975).
Sedimentary cover. The karstified limestone surface of the Rudice Plateau is covered with Mesozoic, Tertiary and Quaternary sediments.
The Mesozoic deposits, namely the Jurassic (Callovian-Oxfordian) sandy limestone, covered most of the Moravian Karst area in the pre-Cretaceous time. As a result of widespread denudation – intense weathering and erosion during the Lower Cretaceous and, to a lesser extent, also during the Paleogene – the limestone is preserved only in erosional remnants. A small relic is exposed near the village of Olomučany (Bosák 1978). The limestone is strongly silicified. It contains spongolite and chert. Spongolite is a rock composed almost entirely from siliceous sponges with silica spicules. Chert, dark gray to black in color, forms up to several centimeters thick intercalations in the limestone. It consists of microcrystalline to cryptocrystalline and microfibrous silicon dioxide, SiO2, mostly in the form of chalcedony. It also contains glauconite, an iron potassium phyllosilicate, and its disintegration product, limonite. Chert is a replacement substance, resulting from some type of diagenesis. The accumulation of silicon dioxide is attributed to disintegration of siliceous shells of organisms (including the spicules of siliceous sponges) or hydrothermal solutions rich in SiO2. Weathering-resistant chert nodules and their fragments (chert detritus) form extensive sheets on the plateau. Both the nodules and fragments vary in color, from white to black, most usually grayish white, light gray, gray, dark gray, brown, grayish brown, and black. Conchoidal fracturing makes chert a suitable material for lithic reduction. Chert tools from local resources form a significant part of the Upper Paleolithic Magdalenian stone industry found in the Bull Rock Cave (Golec 2014, with two discussion comments by the present author; Ref. 1, www.byciskala.cz/MaRS/index.php?show=clanek&id=541).
Rudice geodes, in the decreasing order of occurrence quartz, kasholong, kasholong-chalcedony and amethyst ones, are siliceous concretions derived from the Jurassic limestone. These concretions were probably formed in small cavities of biogenic origin (vugs remaining after disintegrated parts of sea urchins and siliceous sponges) that were gradually filled with colloidal SiO2 from infiltrating solutions (Kaplan (2005; photo Ref.2, www.byciskala.cz/MaRS/index.php?show=galerie&id=75&celkem=25).
Most of the Rudice Plateau is covered with sediments of the Rudice Formation, commonly known as Rudice beds (Bosák 1976, 1980). These varicolored, iron-rich terrestrial sediments – clays, silts and sands – are a redeposited product of intense tropical kaolinic-lateritic weathering of the siliceous Jurassic limestone as well as that of the Lower Carboniferous siliciclastic rocks of the Drahany Upland (Culm) and the granitoids of the Brno Igneous Massif during the Lower Cretaceous epoch. Synsedimentarily, they sunk into the deepening karst depressions (Fig. 6). The color of these deposits covers almost the entire spectrum of the visible light. It is controlled by the content of iron, the warm hues (red, orange, yellow) indicating the presence of oxidation iron (Fe3+) and the cold ones (green, blue) that of reduction iron (Fe2+). Iron ore deposits – mostly limonite (goethite) and hematite – precipitated at the basis of the Rudice beds, usually at the contact with the limestone substratum, from descendent vadose solutions percolating through the Fe-rich overlying sediments. At the contact with the substratum, metasomatic replacement of the limestone occurred. The iron deposits were exploited since the 8th century CE: historical and prehistorical (Old Slavic Krhút) mining claims extend over a large part of the plateau (Fig. 4). The Rudice beds have been locally mined for use in the foundry (foundry sands) and ceramic (ceramic clays) industry. In places, Rudice beds contain brown-reddish calcitic concretions called Rudice or Olomučany doughnuts (rudické koblížky).
Fig. 6. Rudice Plateau, fossil karst depressions, 3D model. Explanatory notes: 1-villages (Rudice), 2-main road, 3-dirt roads, 4-contours based on well (borehole) data, 5-approx. contours; contour interval 10 m (Bosák 1980, 1984, with permission).
Quartz grains, rounded to spherical quartz pebbles, and mostly subangular quartzites, the latest including varicolored “sluňáky”, (silcrete stones, “sunstones”), represent redeposited remnants of siliceous crusts that formed after the regression of the Upper (Late) Cretaceous sea (Burkhardt 1974a, Dvořák et al. 1993). These crusts originated during a relatively long period of terrain exposition, in a warm and dry climate with the amount of rainfall lesser than the rate of evaporization. They precipitated from SiO2-rich solutions ascending (capillary lift) from the underlying rocks and sediments. Weathering of these crusts began in the uppermost Cretaceous time and culminated during the Paleogene (Oligocene silcrete stones).
Quartz grains and pebbles are probably of Neogene age. They are thought to have originated within the tidal zone of the Tortonian-Badenian sea (Burkhardt 1974a; Gregor 2013b, 2014a, b).
Quaternary sediments include Young Pleistocene (the Würm Glacial) loess and loess loam, the latter being loess redeposited by the action of water. The uppermost layers are formed by Holocene and Recent soils with a variable content of humus.
Sedimentary overburden, namely loess loam, chert detritus and sediments of the Rudice beds, sink and/or are washed down into the Jedovnice Creek cave system by means of cave chimneys. This process began in the course of the Pleistocene and continues to the present day (Gregor 2013b, 2014a, b).
Karst landforms. The Rudice Plateau features numerous karst landforms including gullies with or without ponors, and dolines (closed karst depressions-sinkholes) that commonly act as ponors of autogenic (atmospheric or meteoric, rain and thaw) waters. Exploration shafts were sunk in several dolines without considerable success (i.e., cave discoveries). Finding karst dolines on the plateau proves to be difficult since they are easily confused with ancient iron mine works. The most striking karst features of the Rudice Plateau, however, are the rock amphitheatre Kolíbky (Cradles, Img. I and II), the blind Jedovnice-RudiceValley (Jedovnicko-rudické údolí) with the closure wall and the Rudice Swallow Hole (Rudické propadání) at its foot (Img. III and IV), and the Jedovnice Creek cave system.
Jedovnice Creek (Jedovnický potok) and its cave system
The Jedovnice Creek (Jedovnický potok) is a water stream of the 7th hydrological order (in reference to the Black Sea, that being of the zero order). The 12 km long surface stream submerges at the foot of ca. 40 m high closure wall of the blind Jedovnice-RudiceValley (Img. III). Absolon (1970) regards the swallow hole (the proper Rudice Swallow Hole, as the deepest katavothron (chasmal sinkhole) in the Moravian Karst. The drainage area amounts to 28.7 km2 at the gullet of the swallow hole and ca. 38.2 km2 at the karst springs near the settlement of Josefov in the Josefov (Josefov-Křtiny) Valley. The flow rate Q ranges from 0 to 8.9 m3/s at the stream gauge above (upstream) the swallow hole, with an average of 0.13 m3/s. At the Josefov springs, the flow rate fluctuates between 0.021 m3/s and 8.5 m3/s, with an average of 0.16 m3/s. The average flow rates roughly correspond to 330-daily flow. The velocity of the flow depends on the flow rate; at low water levels it can be as low as 0.5 m.s-1in torrential stretches and 0.01 to 0.05 m.s-1 in limnic stretches (data from the Easter Cave of the Rudice Swallow Hole Cave). Flow rates during floods 1883 and 1927 exceeded 10 m3.s-1 with flow velocities as high as 1.9 m.s-1. The 1972 flood culminated at 8.5-9 m3.s-1 and 0.97 m.s-1, respectively.
Additional data on the hydrography and hydrology of the Jedovnice Creek were presented by Burkhardt (1953), Burkhardt, Gregor and Hypr (1975, 1977), Gregor (1977a, 2010), and Knížek (2006).
The Jedovnice Creek cave system – or, more precisely, the subterranean course of the Jedovnice Creek – begins at the gullet of the Rudice Swallow Hole (RSH) and comes to an end in the Josefov karst springs. The system includes the RSH Cave (jeskyně Rudického propadání), the Bull Rock Cave (BRC, jeskyně Býčí skála), and the Bar Cave (Barová jeskyně, BAC). Estimates of the length of the entire system range from 6 km to ca. 18 km depending on what is taken into consideration – the length of the main survey traverse, the length of the underground water course, the length of the main passage, the total length of all horizontal passages or the total métrage including cave verticals (chimneys, pits, etc.). Gregor (2014a, b) reports 13.5 km as the total length of all horizontal passages, both water and dry, with the exception of upper cave levels and storeys. The length of the RSHCave is 3,690 m without, and 4,010 m with, the 320 m long Tipeček Gallery. The remaining 9,010 m are shared by the BRC complex, the passages between the BRC and the BAC, the BAC itself, and the water channels between the BAC and the Josefov springs. The length of the underground stream is estimated at some 7 km, thus bringing the total length of the creek, both surface and underground, to 19 km. The gradient of the underground drainage falls from ca. 340 m a.s.l. (W-M Dome) to ca. 302 m a.s.l. (the confluence of the Jedovnice and Křtiny creeks), thus amounting to 0.57 %.
The Jedovnice Creek cave system (Fig. 7) is the second longest in the Moravian Karst as well as the Czech Republic. In addition, it is the first and so far the only cave system in the Moravian Karst that cavers-cave divers passed continuously through, from the point of submergence (Rudice Swallow Hole Cave) to the point of emergence (the main spring at Josefov). This historical event took place on May 1st, 1991 (vide Pekárek 2005, Dvořáček 2013).
Fig. 7. Jedovnice Creek cave system. Explanatory notes: Rudické propadání-RSH Cave, Proplavaná skála-SRC, Prolomená skála-BIRC, Nová Býčí skála-NBR, Býčí skála-OBR, Barová j.-BAC, Rudický dóm-Rudice Dome, Obří dóm-Giant Dome, Velikonoční j.-Easter Cave, Srbský sifon-Serbian Siphon, Sifon dřiny-Inflow Siphon (NBR), Kaňony-Canyons (NBR), Šenkův sifon-Schenk Siphon (Musil et al. 1993; Gregor, Havlík and Mikeš 2014).
Rudice Swallow Hole Cave (jeskyně Rudického propadání)
Geologic setting. The Rudice Swallow Hole Cave, also called the Rudice Swallet Cave, RSC (Rudické propadáni or jeskyně Rudického propadání, Fig. 7, Ref. 3 – www.byciskala.cz/MaRS/index.php?show=clanek&id=535, vide map) is carved in the Vilémovice (ss) Limestone and the transitional strata between the Vilémovice and Habrůvka limestones (Burkhardt, Gregor, Hypr 1975, 1977; Hypr 1976, Gregor 2014b). In general, the stratigraphic change – the transition from the Vilémovice Lm. (higher in the stratigraphic column) to the Habrůvka Lm. (lower in the stratigraphic column) – occurs along the course (gradient) of the underground Jedovnice Creek, i.e., along the incision (downcutting) of the streambed into stratigraphically and structurally deeper positions. The lithologic change – the transition from generally light-gray to dark-gray limestone – occurs in the same downstream direction. However, this overall trend is locally complicated by Saxon block tectonics: the sunken blocks expose only the light-gray Vilémovice Lm. whereas the transitional strata and possibly also the uppermost layers of the underlying dark-gray Habrůvka Lm. occur mainly within the uplifted (upthrown) blocks – e.g. within the horst between the Rudice and Giant domes. In general, the limestones form a flat anticline the SE limb of which is complicated by the tectonic contact with the Culm in the east (Burkhardt, Gregor and Hypr 1975, 1977). The NW limb is marked for a mosaic of lifted (NW) and sunken (SE) fault blocks.
Figures 8, 9 and 10 portray the geological (structural) setting of the RSC. The Saxon-Alpine fractures (SA, Tab. 3) – specifically faults and joints following the orientation of SA primaries (NNW-SSE, 160° ± 10°) – are common in the cave section beneath the Rudice sunken block, that is, between the entrance (the proper swallow hole) and the Rudice Dome (Rudický dóm). They control most of the course of the Rudice arm (rudické rameno) of the canyon section – the section between the Tipeček Gallery and the Old River Gallery (Chodba Staré řeky) – as well as that of the Tipeček Gallery, and also appear between the Old River Gallery and the Rudice Dome. The section between the Rudice Dome and the Giant Dome (Obří dóm) passes through the horst. It follows the strike of the bedding; SA primaries are practically absent. The Giant Dome, a ca. 80 m long and 50 m high cave room, is built on a SA primary fault 160°/80° SW. Fractures of this orientation also appear in, and partly control the course of, the 900 m long passage between the Giant Dome and the semi-siphon (half-siphon) Black Loams (U Černých hlín) and, to a lesser extent, the end part of the RSC, the 386 m long Velikonoční jeskyně (Easter Cave; Fig. 10). According to Fig. 5, this part is associated with the core of the Blansko Graben (Burkhardt, Gregor, Hypr, op. cit.).
Fig. 8. Schematic geological (structural-tectonic) map of the Rudice Swallow Hole Cave. Explanatory notes: 1-cave passages, 2-surface and underground water courses, 3-surface erosional cuts filled w/Quaternary sediments, 4-Quaternary gravel terraces and alluvia, 5-outcrops of Devonian lms, 6-Neogene valley fills, 7-Culm, 8-Devonian lms, 9-joint zones, strike and dip, 10-faults, strike and dip, 11-inferred tectonic lines, 12-limestone beds, strike and slip, 13-overturned recumbent fold, 14-levelling points (above sea level elevations in meters. Sets of joint zones and microfaults-mostly joints bc and bedding joints (Burkhardt, Gregor and Hypr 1975, 1977, modified).
Fig. 9. Schematic geological map of the RSH Cave, section between the Giant Dome and the Black Loams semi-siphon (detail). Explanatory notes: vide Fig. 7 and 8. Numbers 7-13 – locations of explored chimneys (Gregor 2014b).
Fig. 10. Schematic topographical (D. Hypr, P. Čížek and A. Nejezchleb, 1974) and geological (V. A. Gregor, 1974) map of the Easter Cave. Explanatory notes (symbol column, from top to bottom): 1-dry parts, 2-wide and slow flow, 3-rapid flow, 4-prominent joints, strike and dip, 5-joint zones, strike and dip, 6-parallel joints (2 to 3), strike and dip, 7- bedding, strike and slip, 8-traverse points; Nos. 1 to 3, bold print in topo map-semi-siphons, Polosifon U Černých hlín-Black Loams semi-siphon, Dóm s komíny-Dome with chimneys, Srbský sifon-Serbian Siphon (Gregor, Havlík and Mikeš, 2014).
Geomorphology. In principle, the RSC consists of a single cave corridor (passageway) enlarged by several more or less spacious cave domes (Ref. 3). The Giant Dome is the largest of these features. Structural elements – bedding planes and high angle fractures – are the major controls on the origin of these rooms. In addition, the domes are usually associated with chimneys and thus, vertical influx of atmospheric water. Corrosion by this water is another important factor in the development of these rooms and so is cave breakdown.
The RSC can be classified into several geomorphological units, namely:
(1) The ponor section (Fig. 11). It consists of the Lower Passage (Dolní chodba, the proper water swallow hole, ca. 86 m deep); the Upper Passage (Horní chodba, a paleoponor drainage conduit, ca. 111 m deep); and the Wankel-Mládek Dome (Wankel-Mládkův dóm, W-M Dome, also called the Hugon Dome – Hugonův dóm).
(2) The canyon section. The narrow, ca. 650 m long and up to 10-15 m high canyon passage between the W-M Dome and the Old River Gallery (Chodba Staré řeky). The passage consists of two “arms” – the Jedovnice arm (jedovnické rameno) and the Rudice arm (rudické rameno, Ref. 3). The arms form an acute angle the vertex of which is the mouth of the Tipeček Gallery. The canyon passage developed as a result of a/the deepening of the Jedovnice-Rudice Valley (vide the profile of higher gravel terraces on Fig. 11) to the present level. The passage represents the youngest part of the RSC. It was produced by relatively rapid incision (downcutting) of the Jedovnice Creek to the local erosion base level – the genetically older tunnel passage.
Fig. 11. Schematic cross-section of the ponor area of the Jedovnice Creek in the blind Jedovnice-Rudice Valley. Explanatory notes: Horní chodba-Upper Passage (dry), Dolní chodba-Lower Passage (water), W-M dóm-Wankel-Mládek Dome (Burkhardt, Gregor and Hypr 1975, Gregor 2014b).
(3) The Tipeček Gallery. The 160 m long (until 1975), high and narrow, fracture-predisposed gallery was in 1976 prolonged to the present length of 310 m. A chimney in the new part led to the discovery of a 150 m long, generally east-striking upper cave storey 10-12 m above the active stream. The unbalanced, step-like gradient curve of the gallery floor – mostly exposed rock bottom – is a result of rapid incision down to the local erosion base level – the active stream of the Jedovnice Creek in the canyon passage.
The gallery is a streambed of an eponymous water stream with a more or less constant flow rate of 3.0 ± 0.25 l/s. The stream is fed by atmospheric (precipitation) water via minor surface streams. These streams originate in the drainage area on the Culm substratum, east of the limestone massif (Fig. 5, 8). They submerge in small depressions-sinkholes in the proximity of the Culm/limestone geological boundary. In the late 1980s, a 137 m deep borehole was drilled from the surface into the gallery. Since then, the water is pumped out and utilized as a source of drinking (potable) water for the village of Rudice (Gregor 2014b).
Less than 100 m downstream from the mouth of the Tipeček Gallery, the ceiling at the NE wall of the Rudice arm gives way to the Fountain chimney (Chimney above the Fountain, Komín nad Kašnou). The 147 m high chimney serves as episodic karst drainage of the Gully (Žlíbek) – a gully that is located south of the village of Rudice (Burkhardt 1966). The chimney is built on fractures 130º/60º SW (fault w/10 m thick calcite breccia) and 160º/70-85º SW (NW prolongation of the Tipečekfracture zone, Fig. 8). Small fracture channels in the lower part of the chimney, 12-26 m above the Jedovnice Creek, are the source of a constant sintering water influx. This influx nourishes the stalacto-stalagmitic Fountain, the best known sinter form in the RSC (Ref. 3-photos, Fig. 12 and 13). As a result of drilling the Tipeček water well, the white surface of the sinter was temporarily colored with brownish-red clays of the Rudice Formation provenience. This phenomenon indicates that the Fountain is part of the Tipečekhydrogeological system – a new, unexpected finding (Gregor 2014b).
Fig. 12. The Fountain (Balák et al. 1997, Gregor 2014b).
Fig. 13. The Fountain and the ladder (Balák et al. 1997, Gregor 2014b).
(4) The tunnel section. The predominantly low and wide tunnel passage begins with the Old River Gallery and extends to the Serbian Siphon (Srbský siphon) of the Easter Cave (Velikonoční jeskyně) – Ref. 3, Fig. 8. Fluvial sediments of the Old River Gallery contain Culm material from the Quaternary fill of the Jedovnice-RudiceValley. In addition, rounded pebbles of Culm rocks up to 25 cm in size are wedged in chimneys – vertical ponor drainage conduits – at the end of the gallery. The sedimentary fill also contains redeposited calcareous clay and fossil fauna – Foraminifera and siliceous sponge spicules – from the Neogene Lower Badenian fill of the Lažánky Valley (Burkhardt, Gregor, Hypr 1975, 1977). According to the results of water tracing tests, the gallery communicates with the Svažná studna (Hoist Well) Cave, a ponor cave of a small intermittent creek in the upper part of the Lažánky Valley (Otava, Kahle 2003; Otava et al. 2003, Šimíček, Otava 2004). The cave was excavated downward from a doline (sinkhole) that is situated in the upper part of the valley; it is 90 m deep and the total length of the passages exceeds 500 m. The 32 m deep vertical entrance shaft – partly in loose limestone debris blocks – follows a karstified fracture that is pre-Badenian in age. Lower Badenian fauna was found in the sedimentary fill of the shaft, in the upper part (10-12 m) redeposited, in the bottom part (25-32 m) in situ (Otava et al. 2003). The proper cave is apparently younger, with three points of water influx.
The tunnel passage is locally rejuvenated by deeper-cut water channels. The incision is an ongoing process that results from lowering of the local erosional base level – the floor of the KřtinyValley. The down-cutting is most noticeable in neotectonically uplifted blocks, especially within the section between the Giant Dome and the Black Loams semi-siphon (Fig. 9).
Fig. 14. Serbian Siphon in the Easter Cave – the terminal point of the Rudice Swallow Hole Cave (Gregor, Havlík and Mikeš 2014).
Fig. 15. Easter Cave, low ceiling passage (Gregor, Havlík, Mikeš 2014).
Cave chimneys and upper storeys. The RSC complex incorporates generally vertical karst conduits – cave chimneys. The Glossary of Karst and Cave Terms of the Commission for Karst Hydrogeology and Speleogenesis of the International Union of Speleology (UIS) defines “chimney” as “nearly circular shaft rising upwards from the ceiling of a cave towards the surface of the ground”. The present author re-defines cave chimney as “generally vertical shaft rising from a cave towards the surface of the ground” (Gregor 2014a). The morphology (shape) and the ceiling are not a necessary condition.
The RSC is situated 130-220 m beneath the ground surface. The highest chimneys in the RSC exceed 100 m in height (Fig. 17). The Fountain chimney is connected with the ground surface by a 6 m deep excavated shaft, thus forming the 153 m deep Rudice Pit (Rudická propast, Fig. 18). The Rudice or Thirsty chimney (Rudický or Žíznivý komin) in the Rudice Dome is 150 m high (Fig. 19). Two independent water injection tests demonstrated that the chimney communicates with a sinkhole-ponor that opened on the terrain high “Tumperk” during a torrential rainfall and the following flash flood in the summer of 2010 (Šebela 2011). Once physically connected (an ongoing exploration and excavation project), they will form a cave pit ca. 190 m deep – the deepest “dry” cave pit in the Czech Republic.
Fig. 17. Schematic longitudinal cross-section of the Rudice Swallow Hole Cave (Ivan Balák, with permission; Gregor 2014b).
Fig. 18. Fountain chimney – Rudice Pit, schematic cross-section (A. Nejezchleb and P. Glozer 1982; Gregor 2014b).
Fig. 19. Rudice (Thirsty) chimney in the Rudice Dome, schematic cross-section (Ivan Balák, with permission; Gregor 2014b).
Some chimneys in the RSC are associated with upper cave storeys – short subhorizontal passages of vadose origin (Gregor 2014b). Some of these passages were later employed by the Jedovnice Creek – for example the Squeeze of Sights (Chodba vzdechů), the channel crossing the 1922 siphon at a higher level and episodically functioning as a flood overflow (Gregor 2014b).
Sediments. The sedimentary fill of the RSC consists mainly of allochthonous fluvial sediments: gravel (mostly rodlike pebbles of Culm shale), sandy gravel, quartzy sand with Culm material, silty sand, silt, silty clay and clay (Burkhardt, Gregor, Hypr 1975). Other allochthonous sediments include infiltration sediments, largely loess loam and silty clay loam, chert detritus, and materials of the Rudice beds – all being re-deposited by the action of gravity and/or water. The occurrence of these sediments is associated with some of the chimneys and upper cave storeys (étages), that is, former and/or present conduits of surface (atmospheric) water. Autochthonous deposits include cave breakdown (predominantly in domes) and chemogenic mineral deposits – iron hydroxides and oxides (Gregor, 2010, 2013, 2014a) and, above all, secondary calcite forms – stagmalite speleothems (sinter forms, “dripstones”).
Fluvial sediments – namely the gravel fraction – contain a substantial amount of anthropogenous material – human waste – such as fragments of bricks, concrete, metals and plastics and, above all, slag. The slag comes from a large deposit in the Rudice-Jedovnice Valley; it is a remnant of the Salm Hugon’s iron works that operated there from 1746 to 1890. As a result of rainwater erosion, the slag is loosened and washed down to the cave. The material contains oxides (30-50 % SiO2, 7-20 % Al2O3, 25-42 % CaO, 1-12 % MgO, 0.5-15 % FeO, 2-10 % MnO and 1.0-1.5 % TiO2) with an admixture of sulphur, phosphorus and metal particles; it is hard and the metal particles are sharp. Slag causes corrasion (abrasion) of speleothems within the hydrodynamic zone of horizontal circulation and the zone of seasonal and flood fluctuation (Gregor, 1986); moreover, it contributes to sediment accumulation in, and plugging of, low profile passages. The worst of all the anthropogenous deposits, however, is sewage from the poorly designed treatment plant in the village of Rudice.
From July to November 2014, a new ponor developed in the sediments – mostly slag – of the surface streambed of the Jedovnice Creek: a sinkhole that is located ca. 15 m in front of the proper swallow hole (gullet). The sinkhole is 2 m deep and exposes the limestone bedrock. As a result, the creek now enters the Lower Passage (Fig. 11) at some 10 m below the gullet. During this event, at least 100 m3 of slag were eroded and washed down into the karst underground.
Speleothems. The frequency of speleothem occurrence in the RSC decreases in the downstream direction, that is, along the transition of the Vilémovice Lm. into the transitional strata (Habrůvka Lm). According to Tab. 1, the Habrůvka (Lažánky) Lm. contains up to 13-times more MgO than the Vilémovice Lm. and thus, it is less soluble than the Vilémovice Lm. Owing to this fact, the section between the Wankel-Mládek Dome and the Giant Dome, i.e. the stretch that is carved in the Vilémovice (ss) Lm. and the upper section of the transitional strata, contains more speleothems than the stretch between the Giant Dome and the Serbian siphon (transitional strata and the uppermost section of the Habrůvka Lm.). The great thickness of the overlying limestone mass is another important factor. The photographs in Ref. 3 were taken in the downstream direction, from the Wankel-Mládek Dome to the underground Vyvěračka spring beyond the Giant Dome. The decreasing presence of speleothems is apparent.
Speleothems in the main passage are, almost exclusively, stalactiforms (Ref. 3, photos – www.byciskala.cz/MaRS/index.php?show=clanek&id=535; Fig. 12, 13, 20; Audy and Audyová 1993). They are rather bulky shapes – draperies, baldachins (canopies), stalactitic flowstones and sinterfalls (type codes 188.8.131.52 to 184.108.40.206 according to a classification by Gregor, to be published). Genetically, they are related to chimneys and karstified fractures and bedding joints – that is, “open” karst and fracture conduits with a substantial and continuous or at least continual influx of autogenic (atmospheric) water. The ladder at the Fountain was erected in 1922. In 1972, the sinter crust on the right (southern) stringer (Fig. 13) was ca. 5 cm thick. This indicates an average growth rate of 1.0 mm/a. According to the present author (unpublished data), recent (1890-1989) annual growth rates for the fastest growing stagmalite speleothems in the Moravian Karst range from ca. 0.1 to 3.2 mm/a in either height (length) or diameter (thickness), with an average of 0.69 mm/a. These rates are 0.1-1.1 mm with an average of 0.26 mm/a for stalagmiforms and 0.2-3.2 mm with an average of 1.12 mm/a for stalactiforms.
Fig. 20. Complex stagmalite (sinter) form in the tunnel passage (photo Igor Audy, with permission).
The occurrence of stalagmites is limited to inactive (flood) passages and upper cave storeys. Speleothems are rare in the stretch between the Giant Dome and the Serbian siphon – this passage is carved in the lower section of the transitional strata and in the uppermost layers of the proper Habrůvka Lm. (Burkhardt, Gregor and Hypr 1975, Gregor 1977).
Speleohistory. Altgraf (Old Count) Hugo Franz zu Salm-Reifferscheidt is the first historically known person to attempt a descent into the RSC, via the Lower Passage, in 1802. The attempt ended at the depth of 11 m. In 1810, Salm discovered, and reached the depth of 40 m in, the Upper Passage (Absolon 1970).
Heinrich (Jindřich) Wankel and Antonín Mládek are credited with the first full descent to the bottom of the RSC and the discovery of the Wankel-Mládek Dome. This was the result of a number of partial descents through the Lower and Upper passages during the years 1856-1863 (Wankel 1882, Absolon 1970). The following three descents by Florián Koudelka and companions in 1883-1884 did not cross the point reached by the Wankel-Mládek expeditions, that is, the outflow siphon of the Wankel-Mládek Dome. Karel Absolon’s expeditions in 1900-1921 followed, without any tangible results (Absolon, 1970).
In 1921, a group of Rudice residents lead by František Sedlák overcame the siphon by blasting its roof and as a result discovered a new passage – the ca. 650 m long canyon passage with the Jedovnice and Rudice arms – and the 160 m long Tipeček Gallery. This section of the RSC is called the Old Rudice Swallet Cave (Staré propadáni); and it is terminated by another siphon (1922).
A new etape in the exploration of the RSC began in 1957. It was launched by members of the Speleological Group at the Czech Kolben-Daněk (ČKD) Machine Works Blansko in cooperation with the Speleological Club in Brno and mountain climbers from the Alpine Club at the Zbrojovka Brno Firearms Company. In January 1958, climbers František Plšek and Josef Jirůšek ascended into a previously unknown “window” – the mouth of an upper cave storey that is now called the Squeeze of Sighs (Chodba vzdechů) or the Passage of Whores (Chodba kurev). The 60 m long squeeze – an overflow channel crossing the 1922 siphon at a higher level – lead to 18 m deep pithole and the active stream beyond the siphon. Subsequently, the team discovered the 2.5 km long tunnel passage between the Old River Gallery and the then terminal Black Loams semi-siphon (Burkhardt 1958, 1959).
The 42 m long semi-siphon was deemed penetrable in June 1973 when V. A. Gregor crawled half-way through (Burkhardt, Gregor, Chaloupka 1974). During a second attempt in the spring of 1974, Dušan Hypr, Alois Nejezchleb and two other cavers penetrated the entire semi-siphon, and thus discovered the Easter Cave and the Serbian Siphon (Hypr 1976; Burkhardt, Gregor and Hypr 1975, 1977; Gregor 2014b; Gregor, Havlík and Mikeš 2014).
Since the foundation of the Czech Speleological Society (ČSS) in 1978, the group operates as one of the fundamental organizations of the society, ZO 6-04 Rudice (vide www.jeskynar.cz/rudice). Currently, Rudice cavers focus on exploration of chimneys and underground tributaries of the Jedovnice Creek, especially in the area of the Rudice Dome – the Rudice/Thirsty chimney and the Žegrov waterfall.
Bull Rock Cave (jeskyně Býčí skála, Býčí skála)
The Bull Rock Cave (jeskyně Býčí skála, Img. V) in the Josefov-Křtiny Valley represents an underground streambed of the Jedovnice Creek and, inpart, also a paleoresurgence cave of the stream. At high floods the paleoresurgence part – the main passage of the Old Bull Rock Cave – becomes a flood streambed and the cave entrance(s) an active karst spring.
The cave (Ref. 4, www.byciskala.cz/MaRS/index.php?show=mapa&id=10) consists of several units. They are named, from the entrance to the Serbian Siphon, Entrance Hall (Předsíň), Old Bull Rock Cave (OBR, Stará Býčí skála), New Bull Rock Cave (NBR, Nová Býčí skála), Broken-in Rock Cave (BIRC, Prolomená skála) and Swum-through Rock Cave (SRC, Proplavaná skála).
Geological setting and implications. In the downstream direction from the Serbian siphon to the Josefov springs, the Bull Rock Cave passes through the transitional strata, the Habrůvka Lm., and the underlying Josefov Lm. (Tab. 1, 2). The cave crosses the core of the Blansko Graben (Fig. 5). Both the number and prominence of SA primaries (NNW-SSE, 160° ± 10°) decrease in the same direction – they appear as joints (fractures of the 2nd and 3rd order) rather than faults (fractures of the 1st order). The Bull Rock Cave is dominated by the older, Variscan fracture system (Tab. 3, 4-6), namely fractures striking NNE-SSW to NE-SW (VA orthogonals) and ESE-WNW to NW-SE (VA primaries). These features control much of the course of the cave and, locally, are outstanding in the cave morphology – e.g. the fault Gothic passage (Gotická chodba in the SRC, Fig. 21, vide also Ref. 6).
Fig. 21. Gothic passage (photo by Michal Piškula; Piškula 1986, www.byciskala.cz).
Bedding – bedding joints and bedding planes – along with the axial fold cleavage (compression joints bc) exercise principal structural control over the cave. The bedding angle (dip) ranges from horizontal or subhorizontal (5°-10°) to almost vertical (80°, Fig. 22).
Fig. 22. “Vertical beds” (photo by Michal Piškula; Piškula 1986, www.byciskala.cz).
Breakdown (ceiling and wall collapse) led to the formation of several spacious rooms (cave domes), namely the Breakdown Dome (Řícený or Zřícený dóm in the BIRC) and the Rotunda in the Flood Passage (Povodňová chodba) of the SRC. They can be classified as block breakdown and slab breakdown (White and White 2000). The cause of breakdown is mechanical failure within or between rock beds or fracture-bounded rock masses. The Rotunda (www.byciskala.cz/MaRS/index.php?show=clanek&id=486, Ref. 5; and www.byciskala.cz/MaRS/index.php?show=galerie&id=77&celkem=22, Ref. 6) with its breakout cupola is an example of breakdown due to failure in the tension (stress) dome. It is generated in steeply inclined beds so that the classical, separate beam or cantilever model of a tension dome in well-bedded horizontal strata (Ford and Williams 1989, White and White 2000) is not fully applicable. In addition, the model is based strictly on vertical, static stress – the weight of the overlying rock mass (Fig. 23). The present author suggests that the Rotunda is the morphological envelope of a deformation (strain) ellipsoid or rather elliptic paraboloid created by two principal stress vectors: the dominant generally W → E oriented horizontal tectonic stress and the vertical static stress.
Fig. 23. Stress dome model. A-distribution of vertical (static) stress lines around a cave and tension dome. B-relationship between passage width (or span) and the breaking thickness of limestone beds (based on limestone samples and bedding stress 1.6 x 107 Pa). C-formation of theoretical breakdown dome in steep-inclined strata. D-pressure release spalling where load is maximum, e.g. at a pillar or the foot of a cave wall (Ford and Williams 1989, White and White 2000, with permission).
Similarly to the RSC, cave domes in the BRC are controlled by structural elements, namely the dip of limestone beds (bedding planes and bedding joints) and high angle fractures. Since the majority of the domes are associated with chimneys, it is obvious that, in addition to breakdown, corrosion by autogenic (atmospheric) waters of the zone of vertical circulation (vadose zone) descending through the chimneys is another important factor in the formation of the domes.
Of the entire Bull Rock Cave complex, the Old Bull Rock Cave and the New Bull Rock Cave (Fig. 24, Ref. 4) are the best known units from the geological, geomorphological and speleological point of view. According to Burkhardt (1973; also Burkhardt, Gregor and Chaloupka 1973) and Gregor (2013b, 2014a), the OBR and NBR are developed in the Josefov Lm. and the overlying Lažánky (Habrůvka) Lm. (Fig. 25, Tab. 1, 2).
Fig. 24. Map of the Old and New Bull Rock caves at a normal hydrographical situation. Explanatory notes: Vchody-entrances, Předsíň-Entrance Hall, Brunina jeskyně-Bruna Cave, Skalní zámek-Rock Castle, Obří komín-Giant Chimney, Býčí (Šenkův) sifon-Schenk Siphon, Kaňony-Canyons, Odtokový sifon-Outflow Siphon, Vysoký komín-High chimney, Velká síň-Great Hall, Přítokový sifon-Inflow Siphon (Gregor 2015).
The High Dome (Vysoký dóm) in the NBR, including the Old Adit (Stará štola) and the Dead Snail’s Head (Hlava mrtvého šneka), provide a detailed insight into the interior of a prominent fault – the so called SE fault (Southeast fault, JV zlom, Fig. 25, 26). The fault is one of the most prominent tectonic features of this type in the entire BRC. It is a deep-seated, 1st order fracture. It extends from the Precambrian crystalline basement (the Young Cadomian Brno Igneous Massif) through the entire Phanerozoic sedimentary sequence to the surface of the Rudice Plateau. The fault is of Variscan origin – a VA primary that originated during post-Variscan tectonic adjustments – and was reactivated in the course the Saxon-Alpine tectogenesis, during the formation of the Blansko Graben (Tab. 3). In the cave, the fault is oriented ca. 120°/80° NE, the first number indicating the strike (NW-SE) and the second the dip. It contains up to 3 m thick fill of zonal calcite and calcite breccia (Tab. 4-6). The estimated apparent vertical displacement (AVD) along the fault is ≥ 12 m, and the NE block is the downthrown block (Gregor 2013b, 2014a). Later neotectonic (post-Upper Miocene, post-Badenian) movements reactivated the fault again and resulted in a further 4-6 m downthrow of the NE block. This strongly affected the development of the main, tunnel passage (corridor). It lead to the formation of the Inflow Siphon (Přítokový sifon) and the paragenetic stretch northeast of the Great Hall (Velká síň) – the Trunk or Case (Kufr) and the entrance Semi-siphon (Polosifon, Fig. 27, 28). The Blansko Graben fault zone is still active, and so is the SE fault. Episodic movements along the faults are related to seismic activity (earthquakes) at the ESE margin of the Bohemian Massif and their magnitude is on the order of 0.001 to 0.1 mm. They might have contributed to young breakdown (angular limestone and calcite blocks) in the Old Adit and the Dead Snail’s Head at the NW end of the fault (Fig. 29; Gregor 2013b).
Fig. 25. Schematic geological cross-section of the Old and New Bull Rock caves. Explanatory notes: the substratum of the Habrůvka Lm. is formed by the Josefov Lm. (the later pictured as blocks w/double/lined sides). Brunina-Bruna Cave, Skalní zámek-Rock Castle, Obří komín-Giant Chimney, Šenkův sifon-Schenk Siphon, Kaňon-Canyons, Horolezecká-Mountain Climbers Gallery, JV zlom-SE fault, Zufluss Sifon-Inflow Siphon (Burkhardt 1973, Gregor 2013b).
Fig. 26. New Bull Rock Cave and the SE fault. Explanatory notes: 1 to 6-locations of surveyed chimneys and upper cave storeys, 4-High chimney, 5-Mountain Climbers Gallery, 6-Loathsome chimney; JV zlom-SE fault, Šenkův sifon-Schenk Siphon, Kaňony-Canyons, Velká síň-Great Hall, Přítokový sifon-Inflow Siphon (Gregor 2014a).
Fig. 27. Schematic SW-NE cross-section of the New Bull Rock Cave from the Canyons to the Inflow Siphon (vertically exaggerated). Explanatory notes: měřítko délek-horizontal scale, měřítko výšek-vertical scale, also in meters a.s.l.; upper horizontal line-1972 flood water level, Kaňon-Canyons, JV zlom-SE fault (High Dome), Velká síň-Great Hall, Kufr-Trunk (Burkhardt 1975, Gregor 2013b).
Fig. 28. Geological map of the Trunk. Vide Fig. 8 and 10 re explanation of symbols of geological structural elements (Burkhardt 1975, Gregor 2013b).
Fig. 29. Breakdown in the Old Adit, SE fault – calcite and limestone blocks (photo Martin Vágner, 2011, with permission; Gregor 2013b).
The fault and with it associated (sub-) parallel fractures control approximately 100 m long stretch of the New Bull Rock Cave to the height of > 50 m. Two chimneys – the High chimney (Vysoký komín, Fig. 26-No. 4, Fig. 30-32) and the Loathsome chimney (Odporný komín, Fig. 26-No. 5, Fig. 33, 34) – are associated with the fault. The fault also controls a section of an upper cave storey (étage), the Mountain Climbers Gallery (Horolezecká chodba, Fig. 26-No. 6; Fig. 35-38; Gregor 2013b, 2014a).
Fig. 30. High chimney, plan and SE-NW cross-section (Gregor 1972, in Gregor 2014a).
Fig. 31. High chimney, entrance part (Gregor 1972, in Gregor 2014a).
Fig. 32. High chimney, ceiling, diffusion corrosion forms (Gregor 1972, in Gregor 2014a).
Fig. 33. Loathsome chimney, ground plan, NE-SW cross-section and SE-NW cross-section (Gregor 1972, in Gregor 2014a).
Fig. 34. Loathsome chimney, bottom part (Gregor 1972, in Gregor 2014a).
Fig. 35. Mountain Climbers Gallery, ground plan, an upper cave storey. Explanatory notes: JV zlom-SE fault, vstup-entrance, excentrika-helictites and influx of atmospheric water from a small chimney, propast-open pit hole, Mauglího okno-Maugli Window, vide Fig. 37 (Gregor 1972, in Gregor 2014a).
Fig. 36. Mountain Climbers Gallery, entrance passage and southern branch, cross-section. Vertical scale in meters a.s.l. (Gregor 1972, in Gregor 2014a).
Fig. 37. Mountain Climbers Gallery, NE branch and Maugli Window, cross-section. Explanatory notes: SV odbočka-NE branch, Komínovitá propast-Chimney pit (open pit hole), Mauglího okno-Maugli Window, Výsoký komín-High chimney. Vertical scale in meters a.s.l. (Gregor 1972, in Gregor 2014a).
Fig. 38. Mountain Climber Gallery, entrance (Gregor 1972, in Gregor 2014a).
Influx of meteoric water – dropfall to trickle, depending on the meteorological situation – occurs along the fault and is characteristic of the Loathsome chimney. Owing to rapid penetration through the overlying strata, the water is still aggressive on the limestone as witnessed by sharp, honeycomb corrosion forms in the chimney.
Mesozoic and Cenozoic cover sediments sink and/or are washed down along the fault and through the chimneys. Pleistocene loess (loess loam) is the most common deposit. Clays and silts of the Rudice beds form the basis of, and millimeters thin intercalations within, the loess loam deposits. Chert detritus and geodes occur in the Loathsome chimney, Old Adit, and the Dead Snake’s Head (Gregor 2013b, 2014a).
Another major tectonic dislocation, one striking NE-SW with 80° SE dip, predisposes and controls the course of the Loamy Rooms (Hlinité síně) and the Gallery of Adamov cavers (Chodba adamovských jeskyňářů) with its NE prolongation, the Violet Gallery (Fialová chodba) above the Outflow Siphon (Odtokový sifon) of the Canyons (Kaňony). The Violet Gallery (Ref. 7, www.byciskala.cz/MaRS/index.php?show=clanek&id=517; also called Purple Gallery; Skoupý and Kukla 2014) is the name of an upper cave storey that opens from the Gallery of Adamov cavers at the elevation of ca. 32 m above the normal water level. At the time of this presentation, the gallery is ca. 30 m long and its NE heading is situated some 25 m from the Dead Snake’s Head and thus, from the presumed intersection of the NE fault with the SE fault. Corrosion by descending atmospheric water and breakdown have been the major factors in the development of the gallery. Water influx from vertical karst conduits associated with the dislocation amounts to units of l/s (Skoupý and Kukla 2014).
Geomorphology. The main passage of the Bull Rock Cave is nothing else but the continuation of the main, tunnel corridor of the Rudice Swallet Cave. The passage is well-defined through the entire BRC, especially through the SRC and BIRC. The trend of rejuvenation of the passage by deeper-cut water channels, as observed in the RSC, continues in the BRC. A noteworthy feature of this kind is the Ugly Passage (Škaredá chodba) with the Ugly siphon (Škaredý sifon) in the SRC. This channel bypasses the normally dry Flood Passage (Povodňová chodba) between traverse points # 52 and # 38/37 (Ref. 4). The twinning occurs in a neotectonically uplifted block – one that is adjacent to the neotectonically sunken block of the Serbian Siphon (the Library and the Easter Cave).
The Canyons and the Narrow Channels (Busgang, Úzké kanály, Ref. 4, Fig. 24) in the New Bull Rock Cave are the most prominent features as far as the rejuvenation process is concerned. Their genesis might have been synchronous with, or postdate, that of the canyon passage – the Jedovnice and Rudice arms and the Tipeček Gallery – of the RSC. The Canyons channel complex has diverted the active flow toward the WNW, to the present-day Bar Cave and the springs at Josefov. As a result, the Jedovnice Creek abandoned the Old Bull Rock Cave that now serves only as a floodwater streambed and outlet (Ref. 8, www.byciskala.cz/MaRS/index.php?show=galerie&id=256&celkem=8, photographs of the Canyons).
The main passage incorporates several sections, or stretches, of paragenetic origin. The Library (Knihovna), a chamber within the Serbian Siphon (Fig. 39-41), was described in detail by Gregor, Havlík and Mikeš (2014). The Stretch of Preliminary End (Úsek předběžného konce, ÚPBK), roughly between traverse points # 24 and # 23 on the map in Ref. 4, is another paragenetic stretch; and so is the Semi-siphon @ No. 7 (Polosifon u č. 7, Semi-siphon at traverse point # 7, Ref. 4). In the New Bull Rock Cave, the Trunk (Ref. 9, www.byciskala.cz/MaRS/index.php?show=galerie&id=191; Fig. 42; Kosina 2010) with the Inflow Siphon (later renamed Siphon of Drudgery) and the Entrance semi-siphon (Fig. 43-45), represent an amplified analogy to the Library with its entrance semi-siphon Jukadlo (Fig. 39) and the Serbian Siphon. In 1973, a 25 m long passageway was blasted by ripping off the ceiling trough the Semi-siphon into the Trunk (Fig. 46; Gregor 2013b; vide also Ref. 10).
Fig. 39. Library, ground plan. Explanatory notes (symbol column, from top to bottom): 1-limestone, 2-sediment (mostly fluvial), 3 (dashed line)-estimated contours, 4 (dotted line)-edge of sediment, Δ1 to 3-chimneys; oblast Srbského sifonu-Serbian siphon, odtržený stropní blok-ceiling breakdown block, počátek polosifonu-arch of the entrance semi-siphon (Gregor, Havlík and Mikeš 2014).
Fig. 40. Library, Serbian siphon (Gregor, Havlík and Mikeš 2014).
Fig. 41. Library, downstream view (Gregor, Havlík and Mikeš 2014).
Fig. 42. Trunk and the Inflow Siphon (photo Karel Kosina, 2010, with permission; Kosina 2010, Gregor 2013b).
Fig. 43. Great Hall, a view toward the Entrance semi-siphon (photo Igor Audy, 1966, with permission; Gregor 2013b).
Fig. 44. Entrance semi-siphon, streambed of the Jedovnice Creek, original condition (photo V. A. Gregor, 1972).
Fig. 45. Entrance semi-siphon, subhorizontal ceiling beds and breakdown, original condition (photo V. A. Gregor, 1972).
Fig. 46. Adit in the (former) Entrance semi-siphon (photo Karel Kosina, 2010, with permission; Kosina 2010, Gregor 2013b).
The main passage is throttled by three siphons. They are, in the downstream direction from the Serbian Siphon, the Divers’ siphon (Sifon potápěčů) between the SRC and BIRC, the Inflow Siphon between the BIRC and NBR, and the Schenk Siphon (Šenkův sifon) between the NBR and OBR. Structural and petrographic factors were the main controls on the genesis of these features.
The dynamics of water flow and sediment movement in siphons was well-observed in the downstream arm of the Inflow Siphon during diving attempts and the Project UFO. Project UFO was the codename for a rocket-type device that was jet-propelled by a mixture of compressed air and water and functioning on the principle of action and reaction (Ref. 10, www.byciskala.cz/MaRS/index.php?show=galerie&id=219; Fig. 47). It was designed as a potentional vehicle for remote (cable controlled) survey equipment. The device was tested in January 1974, with the assistance of three cave divers. The flow rate in the open channel below the siphon (in the Trunk) was ca. 210 l/s and the flow velocity 0.4-0.6 m/s. In the open channel the device was able to move upstream. In the throttled neck of the siphon (Gregor 2013b), the flow velocity ranged from 2 to 3.5 m/s. The water was effervescent with ejected sediment – sand, granular and pebble gravel, and slag – and the device was also ejected. The sediment plugged the suction openings and, in addition, disabled the divers’ aqualung regulators.
Fig. 47. Project UFO water rocket, test 1974 (photo author’s archive).
The cross-section (A) of the neck – the flow area of the siphon elbow – in the Inflow Siphon is a function of the flow rate (Q): A = f (Q). It is directly proportional to the flow rate: it decreases with decreasing Q and vice versa. Low Qs result in sediment accumulation and thus, dwindling of the flow area. High Qs lead to sediment erosion and transport, thus enlarging of the flow area; however, the moving sediment makes any human advance impossible. A suction dredge and a sliding crate were the technical means that allowed for the first exploration of the siphon by divers.
The Schenk Siphon (Šenkův sifon) is both the oldest and best known siphon in the Bull Rock Cave (Ref. 11, www.byciskala.cz/MaRS/index.php?show=clanek&id=430; Gregor 2015). It represents the terminal point of the historical Bull Rock Cave (Old Bull Rock Cave) and the dividing point between the OBR and the NBR (Fig. 24, Ref. 4). With the development of the Narrow Channels and the Canyons, the siphon and the OBR were gradually abandoned by the active stream; presently, they function only as flood water conduits.
Under normal hydrological conditions, the siphon is fed with atmospheric (meteoric) water dripping or trickling from two chimneys that are located in the proximity of the siphon. The most substantial influx, however, comes from the so-called Chapel (Kaple); this source, in turn, is sustained by meteoric waters descending from the surface to karst and fracture conduits that are associated with the Augeias Dome (Augiášův dóm, Fig. 48, 49; Gregor 2015).
Fig. 48. Detailed geological map of the Schenk Siphon (Chapel passage – Map of the Republic). Explanatory notes (symbol box in the upper left corner, from top to bottom): 1- limestone beds, strike and slip, 2-fractures (mostly joints), 3-shear movement along fractures, relative lateral strike-slip (Dušan Hypr 2002, in Gregor 2015).
Fig. 49. Schenk Siphon and Augeias Dome, ground plan. Explanatory notes: Šenkův sifon-Schenk Siphon, Kaple-Chapel, Augiášův dóm-Augeias Dome (Dušan Hypr 2002, in Gregor 2015).
The normal, naturally stabilized water level in the Schenk Siphon rests at 308.5 m a.s.l. – that is, at the level of the Watershed (Divide, Rozvodí) in the NBR (Fig. 24, Ref. 4). The Watershed is the highest point between the mouth of the Canyons and the siphon. During floods, however, water may overflow the Watershed, fill up the siphon and eventually rise to ca. 311 m a.s.l., to the divide Loams (V hlínách) in the OBR. A further increase in the water level leads to an overflow into the main passage of the OBR and, as the case may be, discharge from the cave entrances.
Since 1947, an electrical submersible pump has kept the water in the siphon at a navigable level of 305.5 ± 0.5 m a.s.l. Nowadays, the siphon is pumped-out and dry most of the time (Fig. 50-52).
Fig. 50. First full-steel boat passage over the Schenk Siphon, October 12th, 1963 (archives of ZO ČSS 6-01 Býčí skála-Bull Rock, Gregor 2015).
Fig. 51. Boats on the Schenk Siphon (undated photo Igor Audy, with permission; Gregor 2015).
Fig. 52. Emptied (pumped-out) Schenk Siphon, 2013 (photo Igor Harna, with permission; Gregor 2015).
The overflow of the Watershed and flooding (filling up) of the Schenk Siphon occurs more frequently (twice in 2006, and once in 2014) than the flood flow through the main, normally dry passage of the OBR. The last such event occurred in 1972 (Fig. 53). It was preceded by floods in 1947, 1883 and, possibly, also in 1832 (Burkhardt 1974b, Gregor 2013b, 2015). The siphon may partially drain to the Jedovnice Creek in the Canyons by means of infiltration through sediments and/or karst-fracture conduits in the limestone bedrock. After the 2014 flooding, a substantial natural decline in the flood water level in the siphon occurred. The subsequent pumping exposed sinkholes in the floor sediment, probably communicating with karst drains (Gregor 2015).
Fig. 53. Bull Rock Cave (OBR and NBR), flood 23. 7. 1972. Explanatory notes: 1-dry parts (rooms); 2-rapid stream flow, Q ≈ 0.25 m3/s; 3-slow flow, depth in meters; 4-temporary (flood) siphons; 5-water reservoirs (“lakelets”, incl. Schenk Siphon) at a normal hydrographical situation; 6-local water table under pressure due to air trapped in closed ceiling cavities, up to 1.3 atm (1.34 kg/cm2, 132 kPa-N/m2); 7- new erosional cuts, up to 2 m deep; 8- new accumulations of fluvial sediments, mostly sandy gravel; 9- local water table and depth of Schenk Siphon at navigable level 305.5 m a.s.l.; 10-local water table and depth of Schenk Siphon after the flood, at a naturally stabilized level 308.5m a.s.l.; 11-water level at the flood culmination. Sifon 1 to 5-flood siphons; vchod(y)-cave entrance(s); Předsíň-Entrance Hall; Obří komín-Giant Chimney; Šenkův sifon-Schenk Siphon, Rozvodí-Watershed; Kaňony-Canyons, Velká síň-Great Hall; Přítokový sifon-Inflow Siphon (Burkhardt 1974, Gregor 2013b, 2015).
Cave chimneys. In the Bull Rock Cave complex, there are more than 200 chimneys of which most remain unsurveyed (A. Pekárek, private communication). The spacious, ca. 95 m high Giant Chimney (Obří komín) in the OBR is the most spectacular feature of this type. The chimney provides an access to the Low Passages (Nízké chodby). To the SW, the Low Passages merge with the Rock Castle (Skalní zámek) – an upper cave passage that is situated ca. 26 m above the floor of the main passage, and ca. 32 m above the normal water level of the Jedovnice Creek at the mouth of the Canyons (the latter at 306 m a.s.l.; vide Fig. 24 and Ref. 4). The Pagan Chimney (Pohanský komín) leads to a complex of short, subhorizontal passages that are interconnected by chimneys (pits) – the Bruna Cave (Brunina jeskyně, Brunagrotte). The Low Passages-Rock Castle complex represents the longest known upper cave passage in the Old Bull Rock Cave. Chimneys and upper passages in the New Bull Rock Cave were documented in detail by the present author in 1970-1972 (Gregor, 2013b, 2014a; vide also Fig. 26 and 30-38).
Cave levels and cave storeys. In Czech speleological literature, two terms exist to describe caves and cave passages that are situated above each other: cave levels (jeskynní úrovně) and cave storeys (jeskynní patra).
A cave level is a system of hydrographically or paleohydrographically interconnected caves (cave passages) that are genetically related to a temporarily stabilized surface of the permanently saturated body of karst-fracture water (top of the phreatic zone), the local erosion base level, and the valley floor (Gregor 1977b, 1986, 2005; Hypr 1981). [Note: the term “water table” is not the best choice to describe the hydrogeological setting of the Moravian Karst] Cave levels are subhorizontal – their course follows the gentle section of the gradient curve of the underground karst stream. They usually extend over long distances – the recently active ones span a number of kilometers in the Moravian Karst. Typically, they are represented by underground stream beds of allogenous streams (paleostreams) that begin beneath the ponors and end in points of issue – points of emergence, karst springs. For example, the main passage of the RSC, beginning in the Wankel-Mládek Dome at the bottom of the RSH and including the BRC with the NBR and the Canyons, the May Cave, the Bar Cave and the Josefov springs is the lowest and youngest cave level of the Jedovnice Creek. Cave levels commonly contain fluvial sediments – in the Moravian Karst characteristically gravel, sand and silt of the Culm (Drahany Upland) provenience. The vertical extent of a cave level is given by thickness of the zone of horizontal circulation, the zone of seasonal and flood fluctuation, and the zone of siphon circulation (Fig. 54, 55; Gregor 1977b, 1986, 2005). Cave levels correspond to, and thus can be correlated with, valley development phases – valley forms and accumulation (sedimentary, gravel) terraces. The main passage (corridor) of the RSC and the BRC is an example of a mature cave level.
Fig. 54. Vertical hydrodynamic zoning in carbonate rocks. Explanatory notes: 1-zone of aeration: 1.1-zone of surface and shallow subsurface (subcutaneous) circulation, 1.2-zone of vertical descendent circulation (in this presentation includes the transit of allogenic waters), 1.2.1-subzone of perched waters. Zones 1.2 and !.2.1 are part of the vadose zone. 2-transitional zone of seasonal and storm (flood) fluctuation. The dashed line indicates the maximum free water level in karst conduits. 3-zone of intense local circulation: 3.1-zone of horizontal circulation, 3.1.1-subzone of channel (accelerated) flow, 3.1.2-subzone of sheet (retarded) flow, 3.2-zone of siphon circulation, 3.3-zone of sub-valley (sub-river) circulation. Zone 3 is part of the phreatic zone. 4-zone of intense regional circulation (includes water movement in paleokarst conduits). 5-zone of impeded circulation (includes deep artesian circulation and ascending circulation of mineral-thermal brines. I-zone of active circulation, II-zone of impeded circulation: semi-confined zone, III-zone of very impeded circulation: confined zone (Gregor 1986).
Fig. 55. Vertical hydrodynamic zoning in the limestone massif of the Macocha Plateau with respect to the Macocha Chasm and Punkva Caves, Moravian Karst. Explanatory notes. Vertical hydrodynamic zones of karst waters: Z1-zone of surface and shallow subsurface (subcutaneous) circulation; Z2-zone of vertical descendent circulation; Z3-zone of seasonal and storm (flood) circulation; Z4-zone of horizontal circulation; Z5-zone of siphon circulation; Z6-zone of subvalley circulation. Pustý žleb-Pustý žleb Gorge, Štajgrovka-Štajgr Cave, vrt HV 103-borehole HV 103, Vodní Punkevní jeskyně-flooded part of the Punkva Caves (Vodní plavba, Water navigation), Macocha-Macocha Chasm (Gregor 2005).
Cave storeys (étages) are more or less horizontal cave passages that are not mutually interconnected. They are limited to comparatively short distances and their origin is not related to either the phreatic zone, the local erosion base level, or valley forms and terraces. Rather, cave storeys are controlled by structural-tectonic features (Štelcl 1963, Gregor 1977b). The origin of cave storeys in the Moravian Karst is usually ascribed to autogenic waters of the vadose zone – descending waters of the zone of vertical circulation (Gregor 1986, 2005, 2014a, b). They commonly contain allochthonous infiltration sediments that sunk in or were washed down from the surface. The Mountain Climbers Gallery in the New Bull Rock Cave is a typical cave storey (Fig. 35-38; Ref. 12, www.byciskala.cz/MaRS/index.php?show=galerie&id=153, photos of the gallery, the High chimney, etc.).
Five different elevations of cave passages higher than the present-day water channel and the flood passage can be recognized in the Jedovnice Creek cave system (Gregor 2014a, b). They are situated at 6-8 m, 10-12 m, 18-22 m, 26-34 m, and 45-50 m above the normal water level of the Jedovnice Creek. Some of them might be fragments of upper cave levels, particularly those at 18-22 m, 26-34 m, and 45-50 m. The sedimentary fill of these passages contains Culm sand and gravel (pebbles of Culm shale and, to a lesser amount, of Culm graywacke). Deposited in situ (primarily, not redeposited by floods), they are indicative of paleoflow of the Jedovnice Creek. The Rock Castle in the OBR is the longest known fragment of the 26-34 (32) m cave level in the BRC.
The exploration of a chimney in the Loamy Rooms (above the Outflow Siphon of the Canyons, Fig. 24, Ref. 4) led to the discovery of the Carriage Gallery (Kočárová chodba; Ref. 13, www.byciskala.cz/MaRS/index.php?show=clanek&id=550; Skoupý 2014). The gallery is situated some 50-60 m above the active stream of the Jedovnice Creek; it is approximately 100 m long, 1 m wide, 2-5 m high, and ends in a 12 m high dome with floor plan dimensions 7 x 20 m. The sedimentary fill is mostly autochthonous – limestone breakdown and speleothems – with a minimum presence of infiltration sediments, namely loess loam. The absence of fluvial sediments indicates that the Carriage Gallerywas formed by atmospheric waters. It is the highest known cave storey in the NBR-OBR complex.
Sediments – speleothems. Similarly to the Rudice Swallow Hole cave complex, the sedimentary fill of the BullRockCave consists of allochthonous (fluvial, infiltration and anthropogenous) and autochthonous deposits. Autochthonous sediments are represented by breakdown and chemogenous deposits. Regarding the latter, calcite speleothems (also termed secondary calcite forms, stagmalite, dripstones and sinter) are scarce in the cave. This is due to the same factors that control speleothems in the RSC, namely:
(1) the cave is formed, for the most part, by water passages with active continual or episodic (flood) streamflow, the water restricting the development of stalagmiforms;
(2) great thickness the overlying limestone rock, 120-200 m;
(3) geochemical character of the overlying strata (Table 1 and 2).
The main passage, however, contains stagmalite formations, mainly stalactiforms (Audy and Audyová 1993). An almost 8 m high, at the base several meters wide sinterfall in a place called the Dripstone (U krápníku, Tábor), is an example. Other stagmalite forms occur in the Dripstone Gallery (Krapníková galerie) in the Dome of Surprise (Dóm překvapení), and the Map of the Republic (Mapa republiky). Comparatively rich and in places also multicolored dripstone decoration can be found in tributary branches of the main passage – karst conduits with the influx of atmospheric water – such as the Sinter Passage (Sintrová chodba), Colorful Passage (Barevná chodba) and the Sinter Waterfall (Sinterfall, Sintrový vodopád), and the Passage of Old Fools (CHSV, Chodba starých volů) – vide Ref. 4. Sinter forms also occur in most chimneys and upper cave storeys, e.g. in the Mountain Climbers Gallery (vide Ref. 12), the Svozil Cave (Svozilka; www.byciskala.cz/MaRS/index.php?show=galerie&id=86, Ref. 14; Správce 2009), the Violet and Carriage galleries (Ref. 7 and 13) and some others.
According to historical accounts (in Burkhardt, Zedníček 1951-1955 and others), there was some dripstone decoration in the main passage of the OBR in the 17th to 19th centuries. However, it fell victim to exploitation by the Lichtenstein owners of the land and also to theft by visitors.
Iron (Fe) mineralization is common in the Bull Rock Cave (Gregor 2010, 2013b; Gregor, Havlík and Mikeš 2014). Iron streaks, trickles, coatings and crusts in the Trunk and Rudolf’s Adit (Ref. 9, Fig. 56; Kosina 2010)are related to calcareous, usually ocher to light rusty-brown colored clay interbeds (intercalated or interstratified beds) within the flat-laying limestone strata.
Fig. 56. Fe-mineralization in Rudolf’s Adit (photo by Karel Kosina, 2010, with permission; Ref. 9, Gregor 2013b).
Fe-mineralization in Rudolf’s Adit begins at the 18th running meter, the distance being measured from the entrance in the Trunk. Some of the deposits are 1 to 2 cm thick. This section of the adit was blasted during the years 1982 to 1984. A growth rate of 0.4-0.8 mm/a can be inferred from these data. According to Bartoň (1986, 2010), at the 18th meter the adit encountered siliceous limestone with up to 45 % content of SiO2. Next running meters pass through limestone with thick interbeds of clayey shale and yellow clay. Apparently, the richest Fe-mineralization is related to these interbeds. Siliceous limestone with intercalated clay and shale might represent the uppermost section of the underlying carbonate sedimentary cycle. It might also have been the petrographic factor in the origin of the Inflow Siphon (Gregor 2013b).
Fe-deposits in both the Trunk and the adit are formed by limonite – an amorphous mineraloid consisting of a mixture of hydrated Fe3+ oxide-hydroxides in varying composition (Fig. 57). The generic formula is written as FeO (OH).nH2O, although the ratio of oxide to hydroxide can vary quite widely. Limonite usually forms from the hydration of hematite and magnetite, and also from the oxidation and hydration of Fe-rich sulfide minerals such as pyrite. The main component of the mixture is goethite, FeO (OH), a yellowish to reddish to dark brown orthorhombic bipyramidal iron oxyhydroxide (also written as HFeO2). Goethite (Fig. 58) forms through weathering of other iron-rich minerals such as hematite and magnetite. The formation is marked by the change of Fe2+ to Fe3+. The low-temperature cave environment with the pH-factor between 6 and 8 is favorable to the formation of this mineral. Hematite, Fe2O3, a trigonal hexagonal Fe3+ iron oxide with scalenohedral symmetry, is also present in the deposits (Fig. 59).
Fig. 57. Limonite (Wikipedia, public domain).
Fig. 58. Goethite (Wikipedia, public domain).
Fig. 59. Hematite (Wikipedia, public domain).
Gypsum, a monoclinic prismatic hydrous calcium sulfate, CaSO4.nH2O, was found in clayey interbeds between subhorizontal limestone banks in the entrance Semi-siphon to the Trunk (the part ripped off in 1973). This mineral probably originated from weathering of pyrite, FeS2 (Fig. 60), in the calcareous clays and/or at contact with limestone (CaCO3). Micro- to macroscopic grains of pyrite were found in the interbeds that also contain rare chalcopyrite (CuFeS2), galenite (galena, PbS) and sphalerite (ZnS).
Fig. 60. Pyrite (Wikipedia, public domain).
Archeology. Allochthonous sediments of the Old Bull Rock Cave contain osteologic remnants of Pleistocene and Holocene mammals as well as artifacts of sixteen cultures or rather episodes of human occupancy, each with its own characteristics. According to Golec (2013a, b; Ref. 15, www.byciskala.cz/MaRS/index.php?show=clanek&id=456), they are:
 Magdalenian (Upper Paleolithic, 13,000-10,000 BCE);
 Linear pottery culture (Lower Neolithic, 5,700-4,900 BCE);
 Pricked (punctured) pottery culture (Middle Neolithic, 4,900-4,700 BCE);
 Moravian painted pottery culture (Upper Neolithic, 4,700-3,700 BCE);
 Jordanian culture, the Boleráz type (Early Eneolithic, Late Copper Age, 3,700-3,400 BCE);
 Fluted pottery culture (Middle Eneolithic, 3,400-3,200 BCE);
 Jevišovice culture (Late Eneolithic, 3,200-2,600 BCE);
 Unětice culture (Early Bronze Age, BA1-BA2, 1,550-1,300 BCE);
 Middle Danube Tumulus culture (Middle Bronze Age, BC1-BC2, 1,550-1,300 BCE);
 Middle Danube culture of Urn Fields (Velatice culture, Late Bronze Age, BD-HA2, 1,300-1.000 BCE);
 Middle Danube culture of Urn Fields (Podolí culture, Late Bronze Age, HB1-HB3, 1,000-800 BCE);
 Horákov culture (Hallstatt culture, Early Iron Age, HC1-HD3, 800-450 BCE);
 Vekerzug culture (Scythian culture, Early Iron Age, HD2, 550-500 BCE);
 Latenian period (Celtic culture, Late Iron Age, LB1-LD2, 370-0.0 BCE);
 Roman period (Germanic people, 0.0-375 CE);
 Late (Uppermost) Middle Ages-Medieval period (15th to 16th century).
The Paleolithic and Horákov-Hallstatt cultures are the most renowned episodes of human occupancy or presence, as well as artifact and human (skeleton) remains deposition in the OBR. The Paleolithic was discovered in the Jižní odbočka (Southern Branch) by Heinrich (Jindřich) Wankel in 1870, and excavated and studied by Jan Knies, Martin Kříž, brothers Rudolph and Wilhelm Czizek, F. R. Czupik and, finally, by Karel Absolon (in 1936). Later summary studies were published by Karel Absolon, Karel Valoch and most recently by Martin Oliva. Local material – chert from the Rudice Plateau – was used for manufacturing of some stone tools by the Magdalenian occupants (Ref. 1; Golec 2014, Gregor in Golec 2014). The famous “Hallstatt Burial” in the Entrance Hall (Předsíň) of the BRC (OBR) was discovered by Wankel in 1872 (Ref. 16, www.byciskala.cz/MaRS/index.php?show=clanek&id=362; Wankel 1882 and Absolon 1970; numerous articles by Martin Golec and Petr Kos on www.byciskala.cz; Kos 2012a, b).
Speleohistory. Karel Absolon (1970) calls the Bull Rock Cave “the most memorable cave in the Moravian Karst”. This statement is quite truthful in regard to both the prehistory (Golec 2013a, b) and history (also Golec 2015) of the Old Bull Rock Cave. Concerning the latter, the oldest signature so far discovered in the OBR dates to 1650 – one of Krasl (M. Golec, personal com., 2013). Martin Alexander Vigsius, a Premonstratensian monk and the canon of the Zábrdovice Abbey, authored the first published reference in 1663 (Vallis Baptismi alias Kyriteinensis, etc.). Absolon considers Vigsius the first geographer of the Moravian Karst. Johann Ferdinand Hertod von Todtenfeld is the second author who, in his work Tartaro Mastix Moraviae etc. (1669), mentions the BRC (OBR) and describes his visit to the cave – the Entrance Hall, the main passage of the OBR and the Schenk Siphon. Signatures on the cave walls, most of them from the 19th century, are the subject of ongoing research by Martin Golec (a number of articles on www.byciskala.cz; also Čermáková and Golec 2014).
The history of speleological exploration of the OBR is probably as old as late 1790s. Exploration efforts of that time as well as those of the 19th century consisted, for the most part, of attempts to cross the Schenk Siphon on a watercraft – a small boat or raft (Golec, op. cit.; Gregor 2013c, 2015).
Systematic exploration of the Bull Rock Cave began in 1902. It was carried out by members of the VDT (VdT) – Verein der deutschen Touristen in Brünn (Club of German Tourists in Brno). First by the DAV – Deutscher Alpen Verein (German Alpine Club), the alpine branch of the VDT. The DAV activities are closely associated with the name of Hermann Bock, an outstanding mountain climber of that time, and to the discovery of the Brunagrotte (Bruna Cave; Gregor 2014a). The exploration of the Giant Chimney in 1909 resulted in the discovery of the Low Passages and the Rock Castle. This effort was carried out by the joint forces of the DAV and the GfH Sd VDT – the Gruppe für Höhlenforschung, Section des Vereines deutscher Touristen – a German caving group in Brno under Bock’s leadership (1901-1907). The activities of the German cavers have been extensively studied by Martin Golec and Vladimír Šebeček on www.byciskala.cz.
In 1912, the German cavers, now under the leadership of Günther Nouackh, focused their attention on the key problem – the then terminal point of the cave, the Schenk Siphon. This included diving (Nouackh), water pumping and, finally, drilling and blasting off parts of the siphon roof. In 1920, their effort was crowned with a success – the overcoming of the siphon and the discovery of the New Bull Rock Cave with the underground Jedovnice Creek.
An extraordinary flood in 1927 filled up the Schenk Siphon to the natural water level, and closed it for the next 20 years (Gregor 2013c, 2015).
During the years 1944-1945 the Entrance Hall and the front part of the OBR were drastically modified in order to accommodate an aircraft engine factory for Hitler’s Luftwaffe (Air force). Fortunately, the factory was never completed and operational.
In 1945, shortly after WWII, the Czech Speleological Club in Brno, an umbrella for Moravian cavers and speleologists, was founded. In 1947, members of the club, in cooperation with firefighters, pumped the Schenk Siphon, lowered the water level, and thus reopened the NBR. Subsequently, electrical power was brought into the cave and a submersible pump was installed that kept the water at a navigable level.
In 1952-1953, members of the club attempted – unsuccessfully – to lower the water level in the Inflow Siphon by means of deepening the streambed between the siphon and the mouth of the Canyons via an excavated trench (Golec 2014, Gregor in Golec 2014; Ref. 17, www.byciskala.cz/MaRS/index.php?show=clanek&id=521).
In 1954, a speleological group was established at the Adamov Machinery Works (Adast Adamov), under the auspices of the factory’s Revolutionary Trade-Union Movement social club and the Speleological Club in Brno. After 1978, the group became a member – that is, one of the fundamental organizations – of the national Czech Speleological Society (ČSS): ZO ČSS 6-01 Býčí skála (Bull Rock).
During the years 1969 to 1972, the geological and speleological foundation was laid and technical preparations were made for a decisive attack on the Inflow Siphon. The project was a joint effort, in partnership with the Department of Karst Research of the Moravian Museum in Brno (Rudolf Burkhardt and V. A. Gregor; vide Burkhardt, Gregor and Chaloupka 1973, 1974; Burkhardt 1975). The extraordinary flood of 23rd July, 1972, caused damages to the compressed-air pipeline and the electrical cable. At the beginning of 1973, with all the necessary repairs completed, a 25 m long passageway was blasted (by ripping off the roof) trough the entrance Semi-siphon into the Trunk. In the course of the years 1973-1975, a 14 m long adit was blasted in the rock massif of the Inflow Siphon. Work was resumed in 1982, after a 7-year pause. With the assistance of cave divers from the ZO ČSS 6-09 Labyrint, the adit (now called Rudolf’s Adit) was completed in 1984 at the total length of 39 m. As a result, the Broken-in Rock Cave (BIRC, Prolomená skála) was discovered. Subsequently, divers penetrated the Divers’ Siphon at the end of the BIRC and discovered the Swum-through Rock Cave (SRC, Proplavaná skála) and reached the Serbian Siphon (1985; Bartoň 1986/2010, Piškula 1986/2010). Later on, the Divers’ Siphon was bridged by an adit that is 57.5 m long (1985-1989).
On May 1st, 1991, the first and so far the only passage through the RSC-BRC system took place. Cave divers Miroslav Měkota, Libor Laus and Jaroslav Nečas passed through the whole system in the downstream direction, and Aleš Pekárek, solo, in the upstream direction.
From 1988 to1991, speleodivers from the Labyrint Group, namely Petr Gryc and Miroslav Měkota overcame the Outflow Siphon of the Canyons and discovered the May Cave (Májová jeskyně), the Dome of Silence (Dóm ticha) and the Cross Dome (Křížový dóm) – vide Ref. 4 and 18. They also found the connection with the Bar Cave. [Ref. 18, www.byciskala.cz/MaRS/index.php?show=galerie&id=257&celkem=8]
Present exploration activities focuson the OBR and the NBR. The purpose is twofold: first, to find a “dry way” to the Bar Cave; second, to solve the remaining speleological problems of the resurgence area of the Jedovnice Creek. The discovery of the Access Passage (Přístupová chodba) from the Entrance Hall of the OBR led to the discovery of the Svozil Cave (Ref. 14) and the Windy Tunnel (Větrný tunel). The present end of the tunnel is located in the proximity of the Dome of Silence. Most recent (2013-2014) explorations of the chambers and chimneys in the Outflow Siphon area (Canyons) brought on the discovery of the Violet (Ref. 7) and Carriage (Ref. 13) galleries.
Bar Cave (Barová jeskyně, Barovka)
The Bar Cave is located between the New Bull Rock Cave (the Outflow Siphon of the Canyons) and the karst springs of the Jedovnice Creek at the settlement of Josefov in the Josefov-Křtiny Valley (Ref. 4). The cave is also known as the Raven Rock Cave (jeskyně Krkavčí skála; Img. VI and VII, also Ref. 30), and the Sobol Cave (Sobolova jeskyně, after the official discoverer Antonín Sobol).
The cave (Ref. 4; Ref. 19,www.byciskala.cz/MaRS/index.php?show=mapa&id=16, map; Ref. 20, www.byciskala.cz/MaRS/index.php?show=galerie&id=251&celkem=19, photos) is carved in the Josefov Lm. and the lowermost layers of the overlying Habrůvka Lm. (Tab. 1, 2). The general course of the cave as well as its overall morphology are controlled, in addition to the bedding strike and dip, by fractures striking NE-SW to ENE-WSW and, to a lesser extent, WNW-ESE to NW-SE.
The cave consists of two levels. The vertical extent of the upper level (with the roof at ca. 18 m above the normal water level) is approximately 15 m; it represents a paleo-streambed of the Jedovnice Creek (Hypr 1977a, b). The level is filled with fluvial sediments that are overlain by infiltration sediments, namely loess loam (loess redeposited by the action of water), clays and fine sands of the Rudice beds, and limestone debris. A cross section of the deposit at the Pit No. 1 (Propast I; R. Musil 1959 in Hypr 1977a) shows, from the base up, loess loam with intercalations of fine-grained Culm sand (fluvial sediment); stratified red-brown loam with limestone debris, fragments of stagmalite (sinter forms) and skeleton remnants of Pleistocene mammals; and sterile yellow-brown loess loam with limestone debris on top (Fig. 61).
Fig. 61. Bar Cave, cross-section of sedimentary fill at Pit I. Explanatory notes: 1-loess loam w/intercalations of fine-grained sand (fluvial sediment); 2-stratified red-brown loam w/limestone debris, stagmalite fragments and bones of Pleistocene fauna; 3-yellow-brown loess loam w/limestone debris, almost sterile (Rudolf Musil 1959, in Hypr 1977a).
The lower level, with ca. 50 m long active stream of the Jedovnice Creek, is part of the lowermost cave level in the resurgence area, the latter including the Canyons in the NBR, the May Cave, the Dome of Silence, and the Cross Dome. Downstream from the Bar Cave, an approximately 150 m long water channel leads to the main spring (outlet) in the Josefov quarry.
In places, especially those affected by fracture tectonics and/or associated with paleo-influx of atmospheric water such as chimneys and other karst conduits within the zone of vertical descendent circulation, the thin rock partition between the upper and lower level collapsed. This resulted in the formation of six generally vertical pits, Pit I to VI (Propast I to VI), numbered in the order of discovery (Ref. 19, Fig. 62 and 63).
Fig. 62. Bar Cave, ground plan and petrography of cave floor. Explanatory notes: 1 to 3-fluvial sediments: 1-sandy gravel, 2-sand, 3-fine-grained sand and silt, 4-redeposited (washed down) sediments and limestone waste, 6-sinter, 7-rock bottom (floor), 8-mixture of fluvial and infiltration sediments. Numbers in circles-local nomenclature: 1-lower cave level, 2-entrance area, 6-Pit IV, 7-Pit I, 8-Pit II, 9-Pit III, 10-Pit IV, 11-Pit V (Hypr 1977a, with permission).
Fig. 63. Bar Cave, sedimentary fill cross-sections (top and bottom sections SW-NE). Explanatory notes: 1-pit numbers, 2-sediment profile numbers, 3-sample numbers, 4-sandy gravel, 5-sand, 6-fine-grained sand and silt, 7- redeposited (washed down) sediments and limestone waste, 8- mixture of fluvial and infiltration sediments, 9-limestone blocks, 10-water level, Jedovnice Creek (Hypr 1977a, with permission).
The paleontological (bone, skeleton) content of the infiltration sediments in the upper level has been studied since the discovery of the cave in 1947, most recently by Vlastislav Káňa and Martina Roblíčková:
Recent excavations yielded a large number of cave lion (Panthera spelaea) bone remnants, including one incomplete skeleton of a subadult female and an almost complete skull; and long bones of at least six other individuals, six lower jaws and nearly two hundred other bones (Káňa and Roblíčková 2013, 2014). The most abundant bones, however, belong to cave bear, Ursus ex gr. spelaeus. Other taxa include cave hyena (Crocuta crocuta spelaea), gray wolf (Canis lupus), fox (Vulpes sp.), reindeer (Rangifer tarandus), red deer (Cervus sp.), wild goat-Alpine ibex (Capra ibex), hare (Lepus sp.), and bird clade Columbidae, pigeon (Aves gen. sp.) – vide Káňa and Roblíčková (2013). This assembly is typical for the last glacial period, the Upper Pleistocene Würm Glacial – the Vistula (Weichsel) glaciation.
The Bar Cave was discovered in 1947 by Antonín Sobol, a high school professor of chemistry (Sobol, 1948, 1952). Later exploration advances and discoveries are credited to Sobol’s students – the Sobol’s Caving Group, under the auspices of the Speleological Club in Brno. In 1975, the group merged with the Bull Rock Caving Group, ZO ČSS 6-01 Býčí skála.
Present exploration activities concentrate on the lower level, namely the siphons and water caves between the Bar Cave and the Bull Rock Cave (OBR and NBR). They include pumping, moving volumes of sediments by means of digging and hydraulic mining, climbing and exploration of chimneys, etc. The purpose is the same as that of recent explorations in the Bull Rock Cave: to connect the Bar and Bull Rock caves via dry or semidry access; and to solve the remaining speleological problems of the resurgence area (“resurgence delta”) of the Jedovnice Creek. Exploration activities between the Bar and May caves enabled a temporary access to the Cross Dome and the Dome of Silence (Ref. 4). The prolongation of a neglected, narrow side branch in the western wall of the Entrance Hall of the OBR led to the discovery of the Svozil Cave (Ref. 14) and the Windy tunnel (Větrný tunel). However, after some 75 m, the tunnel ended in an impassable sump. Some photographs can be found on the following websites:
Karst springs of the Jedovnice Creek – the Josefov springs
The underground Jedovnice Creek emerges at the foot of a limestone outcrop at the eastern edge of the village -- or rather settlement – of Josefov in the Křtiny-Josefov Valley (Ref. 29, www.byciskala.cz/MaRS/index.php?show=clanek&id=142; Ref. 30, www.byciskala.cz/MaRS/index.php?show=galerie&id=504&celkem=15).
The outcrop is formed by the Josefov Lm. (Tab. 1, 2) – dark, bluish-gray micritic to microcrystalline but locally also micro- to fine-grained platy limestone and dolomitic limestone with a variable content of clayey and sandy admixture. The faunal content includes abundant lumachelles of thick-walled brachiopods of the Bornhardtina genus, particularly the Bornhardtina onychophora species and, in places, also massive stromatoporoids. The dolomitization is post-depositional, probably resulting from the diagenetic process. The Josefov Lm. is considered a facies of the Lažánky Lm. The bank structure of the outcrop is folded, the major features being open folds on the order of one to a few meters. Dense axial fold cleavage – bc joints with a western dip – is the dominant fracture element.
A thick-walled brachiopod of the Bornhardtina genus, probably Bornhardtina onychophora sp., in the Josefov Lm., the Bull Rock Cave. Photo by Zuzana Zazza Součková, 2015 (with permission).
The appearance of the spring area changed substantially within the past hundred or so years. A small-scale limestone quarry established in 1920s, and the construction of the Josefov-Křtiny highway in the valley strongly affected the original morphology of the outcrop and the setting of the springs. The original spring (spring # 1, Fig. 64) was disabled. The quarry opened and exposed springs # 2 (under the rock, pod skálou) and # 3 (flood spring). At the present time, the function of these springs depends on the water level (flow rate) and changes in the configuration of the cave sediments. All the three springs were active during the flood of 1972. Figure 65 portrays the main spring that is active all year round – the former flood spring # 3.
Fig. 64. Karst spring of the Jedovnice Creek (Josefov springs) between WWI and WWII (photo in Golec 2010b, with permission).
Fig. 65. Josefov springs, main spring today (photo by Martin Golec, Golec 2010b, with permission).
Analyses of water emerging from the main spring indicate that some 49.5 m3 (100 t) of dissolved carbonate, both CaCO3 and MgCO3, are removed from the limestone (karst) area between the Rudice Swallow Hole and the spring per year (Burkhardt 1953, Demek 1962, Gregor 2015).
Under the Josefov-Křtiny highway bridge, the Jedovnice Creek empties into the Křtiny Creek (Křtinský potok), a tributary to the Svitava River.
Img. I. Rudice Plateau, rock amphitheatre Kolíbky-Cradles (photo Igor Audy, with permission).
Img. II. Kolíbky (Cradles), limestone “hřebenáče”-ridges, mogotes (photo Internet, author unknown).
Img. III. Closure wall of the Jedovnice-Rudice blind valley with the Rudice Swallow Hole at the foot (photo Internet, author unknown).
Img. IV. Rudice Swallow Hole, gullet – entrance to the Lower Passage (photo Internet, author unknown).
Img. V. Majestic face of the Bull Rock in the Josefov-Křtiny Valley. Entrances to the Bull Rock Cave are located at the foot of the wall (photo Internet, author unknown).
Img. VI. Raven Rock in the Josefov-Křtiny Valley. The entrance to the Bar Cave is situated at the foot of the valley face (photo archive of Czech Geological Survey, with permission).
Img. VII. Raven Rock (photo Internet, author unknown).
The author is grateful to Martin Golec for editing, formatting and publishing the manuscript on the Bull Rock Cave web pages. The manuscript benefited from a peer review by Marta N. Gregor. Authors of photographs and other graphics are acknowledged in figure captions.
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