6.6 Karstification by Geothermal Waters

Transcription

1 6.6 Karstification by Geothermal Waters YV Dublyansky, University of Innsbruck, Innsbruck, Austria r 2013 Elsevier Inc. All rights reserved Introduction Zonation and Settings of Hydrothermal Karst in the Earth s Crust Diagnostics of Thermal Water Caves Cave Minerals Isotope Alteration of Bedrock Indirect Evidence Macromorphology of Hydrothermal Caves Simple Forms: Individual Rooms and Single-Conduit Caves Individual rooms and chambers Single conduit caves Bush-Like Caves or Caves with Cupolas Maze Caves Mesomorphology of Hydrothermal Caves Features Created by Phreatic Rising Flow Features Characteristic of Near-Stagnant Phreatic Conditions Features Related to the Free Convection Micromorphology of Hydrothermal Caves Polygenetic Forms Subaqueous Forms Water-Level Forms Subaerial Forms Forms related to air movement Forms related to uniform surface attack Forms related to condensation runoff and dripping Conclusions 69 References 70 Glossary Euhedral (crystal) Refers to crystals possessing welldeveloped external facing (syn. panidiomorphic). Partly faceted crystals are called subhedral (syn. hypidiomorphic), and those with no crystallographically defined faces anhedral (syn. allotriomorphic). Fluid inclusions Microscopic cavities in crystals, filled with liquid and gas (collectively called fluid ). Inclusions may form during crystal growth (primary inclusions) or during healing of fractures in previously formed crystals (secondary inclusions). Fluid inclusions represent natural samples of the medium from which a crystal grew, or to which it was exposed at later stages. Studies of fluid inclusions provide information on the chemistry of mineral-forming solutions and their temperatures. Hypergene (caves, processes, speleogenesis) In karst studies refers to formation of caves by water that recharges the soluble formation from overlying or immediately adjacent surface (an antonym for hypogene). In karst literature, the term (syn.) epigenic is now strongly entrenched, whereas the pair of terms hypergene hypogene (processes, minerals, and deposits) discriminating between the deep-seated and surficial phenomena is in wide use elsewhere in geological sciences. From ancient Greek ńpér huper, over. Hypogene (cave, processes, speleogenesis) In karstrelated literature refers to formation of caves by water that recharges the soluble formation from below, driven by hydrostatic pressure or other sources of energy, independent of the recharge from the overlying or immediately adjacent surface. It is one component of dual system of karst, the other component being hypergene (or epigenic) karst. From ancient Greek ńpo combining form of ńpó hypó, under. Micrite (micritic) Constituent of a limestone composed of calcareous particles ranging in diameter up to 2 4 mm, formed by the recrystallization of lime mud. From MICRocrystalline calcite. Phreatic (zone, karstification, cave, morphology) Refers to matters relating to groundwater below the water table. The phreatic zone (syn. zone of saturation, saturated zone) Dublyansky, Y.V., Karstification by geothermal waters. In: Shroder, J. (Editor in Chief), Frumkin, A. (Ed.), Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 6, Karst Geomorphology, pp Treatise on Geomorphology, Volume

2 58 Karstification by Geothermal Waters is the area in an aquifer, below the water table, in which all pores, fractures, and cavities (including karst caves) are filled with water. From Greek phrear, phreat well, spring. Scalenohedral (crystal) A crystal whose faces are scalene triangles (triangles whose three sides are unequal in length). One of the characteristic morphologies of natural lowtemperature hydrothermal calcite. Sparite (sparitic) Constituent of a limestone composed of crystalline grains with size exceeding 2 4 mm (i.e., coarser than micrite). From spar a crystal that has readily discernible faces. Vadose (zone, karstification, cave, morphology) Refers to matters relating to groundwater occurring above the water table. The vadose zone (syn. unsaturated zone) is the area between the Earth s surface and water table, in which pores, fractures, and cavities (including karst caves) are filled with both water and air. From Latin vadōsus, vadum a shallow, ford. Abstract Thermal waters moving through soluble rock may create voids ranging in sizes from enlarged porosity and cavernosity to extensive two- and three-dimensional cave systems. Hydrothermal caves develop in a number of settings including deepseated phreatic, shallow phreatic (near-water table), and subaerial (above the thermal water table). Speleogenesis in each setting involves specific mechanisms, resulting in diverse features of cave macro-, meso-, and micromorphology. Mechanisms most characteristic of the hydrothermal speleogenesis are the free convection (in both subaqueous and subaerial conditions) and the condensation corrosion. This chapter describes the morphology of hydrothermal caves Introduction The concept that some caves could have been formed by ascending thermal waters rather than by cold descending, gravity-driven ones was first introduced as early as in the midnineteenth century (Nöggerath, 1845; Desnoyers, 1845; as reported in Shaw (1992) and Bosák (2000)). Subsequently, it has been suggested that Pb Zn ores in some of the European deposits in carbonate rocks were emplaced in dissolution cavities and that the latter owe their existence to the same solutions from which, at later stages, the ores were deposited (Pošepný, 1893). In his capital Treatise on Metamorphism, Van-Hise (1904) provided explanations for how and why hydrothermal solutions move advectively through the rocks, and what causes their aggressiveness. He conjectured that most hydrothermal solutions originate as common meteoric waters that become heated during their circulation deep in the Earth s crust. These early works laid a foundation for the concept of hydrothermal karst. Hydrothermal karst is defined as the process of dissolution and possible subsequent infilling of cavities in the rock by the action of thermal water (Dublyansky, 1990, 2000a). This definition requires an additional definition of what water should be called thermal. In hydrogeology, water is considered thermal if its temperature at the resurgence point is significantly warmer than the mean average air temperature in the region. The qualifier may have significantly different numeric values ranging between 4 and 8 1C (Schoeller, 1962; Waring, 1965). Such temperatures cannot be caused by exogenic sources of energy (solar radiation) and, therefore, indicate the input of the hypogene (i.e., from within the Earth) energy. The definition appears adequate in many geographical settings (excluding climatic extremes), but cannot be applied to deepseated environments, neither modern (e.g., waters tapped by boreholes) nor fossil (e.g., mineral deposits in caves). Alternatively, Ford (1995) proposed a formal boundary of 20 1C to distinguish between normal and thermal karst. This boundary is appropriate for regions with temperate climates, but not in hot climates where the mean annual temperature may be greater than 20 1C. In the Earth s crust the temperature increases with depth according to geothermal gradient, which means that starting from certain depth any karst falls under definition of hydrothermal karst. The isotherm of 20 1C lies at m in areas of active volcanism, at about 500 on platforms, and plunges to as deep as m in permafrost areas (Frolov, 1976). Many mountainous karst massifs are overcooled by descending karst water circulation and ventilation, and normal geothermal gradient in them begins to control the rock mass temperature only at significant depth. Geothermal gradient can be significantly increased as a result of the focused upward flow of thermal waters. In such local thermal anomalies, hydrothermal karst could develop closer to topographic surface (anomalous hydrothermal karst; Andreychouk et al., 2009). Elevated temperature of water affects the development of karst in a number of ways, which can broadly be subdivided into chemical and physical ones. Chemical effects pertain to aggressiveness of water and can be realized through: increase in solubility of rock, speeding up reactions, and introducing additional dissolution mechanisms (e.g., thermal mixing corrosion). Physical effects are mostly concerned with the facilitating or intensifying circulation of water. Again, several mechanisms such as decrease of water viscosity, specific mechanisms of water movement (free convection), and specific mechanisms of karstification (e.g., condensation corrosion) can operate. Elevated temperature, thus, is not the main agent of speleogenesis, but, rather, its catalyst. Hydrothermal karst commonly develops in those zones of the Earth s crust where the heat flux is enhanced. Origin of the increased heat flux can vary (volcanism, magmatism, thinning of the lithosphere, etc.). The end result, however, is that heat is being redistributed upward by moving water. Importantly, it is not only heat, which is transported, but also hypogene matter, most notably dissolved CO 2 and H 2 S, the presence of which enhances the aggressiveness of rising water with respect to carbonates.

3 Karstification by Geothermal Waters 59 Waters rich in carbon dioxide and hydrogen sulfide define two major chemical varieties of hydrothermal karst in carbonate rocks. The varieties are associated with both common and specific solution mechanisms (Palmer, 1991; Dublyansky, 2000b). Rising and gradually cooling fluids saturated with CO 2 maintain aggressiveness along most of the deep-seated flow path. Only close to the surface (hydrostatic depth of m) dissolved CO 2 begins to form a separate phase, which leads to the drop in carbonate solubility. Respectively, in such a system cavities form at significant depth, whereas at shallower depth deposition of calcite prevails. In contrast to carbon dioxide-rich water, aggressiveness of the hydrogen sulfide-rich water is generally limited in the deep-seated settings but increases dramatically where such water mixes with oxygenated water or contacts with the atmosphere, which results in rapid oxidation of H 2 StoH 2 SO 4. Such situations tend to occur at shallow levels, both below and above the (thermal) water table. Although pure carbonic acid hydrothermal karst may be common, sulfuric acid karstification is almost always a mixed process. Most natural H 2 S-rich groundwaters have also elevated contents of CO 2 ; in addition, CO 2 is produced by dissolution of carbonate rocks by sulfuric acid. Under certain circumstances, this additional CO 2 could significantly enhance carbonate dissolution (Palmer and Palmer, 2000). When waters containing different amounts of dissolved CO 2 or H 2 S mix, the aggressiveness of the resulting solution is greater than that of each of the initial solutions. Even when mixing waters are saturated with respect to carbonate, the resulting water can be aggressive. Because situations in which waters with varying chemistry mix are rather common in hydrogeology, mixing corrosion is an important speleogenetic mechanism. Both chemical varieties of hydrothermal karst are known to be associated with subaerial dissolution of carbonate rocks. The enlargement of voids above a thermal water table occurs through a series of processes, involving evaporation of water, degassing, convection of vapor- and gas-enriched air, condensation, and corrosion of rock by films of condensate. In addition to the direct dissolution by water films, upward enlargement of cave chambers in sulfuric acid caves can occur through replacement of calcite by gypsum and subsequent falling of the replacement rinds or dissolution of gypsum Zonation and Settings of Hydrothermal Karst in the Earth s Crust Distribution of hydrothermal karst in the Earth s crust is vertically zoned, and these zones could be defined on the basis of different parameters (Andreychouk et al., 2009). The two schemes that are most pertinent to the subject of this chapter are given below. According to the medium in which the karstification takes place, hydrothermal karst may be subdivided into subaerial and subaqueous. When discussing karst morphology, it may be convenient to distinguish in addition the zone intermediate between the two settings (i.e., the near-water table zone). Based on temperatures, hydrothermal karst may be subdivided into two broad zones (Dublyansky, 1997, 2000a). The near-surface high-gradient zone exists where thermal waters occur close to the Earth s surface, resulting in elevated temperature gradients. This zone encompasses areas below and above the thermal water table. In this zone, hypergene factors (e.g., influx and mixing of oxygen-rich surface-derived water) may play an important role in the karst development. The deep-seated zone is located deeper beneath the Earth s surface. It is characterized by significantly smaller thermal gradients and is little affected by hypergene factors. Two very distinct, end-member settings of hydrothermal karst can be defined on the basis of the prevailing gross geotectonic and hydrogeological structure of the karstified area. One end member corresponds to basinal structures characterized by horizontal bedding, gentle dip of the strata, contrasting permeability properties of some strata, and, commonly, large lateral extent of the karstifiable formations. Another end member is that of strongly deformed strata, where karstifiable rocks are folded, faulted, dip at steep angles, and commonly have restricted lateral extent (e.g., steeply dipping soluble layers sandwiched between impermeable rocks). This setting is typical of the fold belts. Differences in overall permeability architecture in these two settings lead to distinct gross morphology of caves. In layered basinal formations, the guiding roles of disjunctive structures (joints and faults) and bedding planes in the propagation of caves are comparable. The mechanism of transverse speleogenesis (see Klimchouk, 2007, 2009; Chapter 6.19) tends to produce laterally extensive maze caves, restricted to certain karst-productive layers. By contrast, caves in folded strata are predominantly structurally guided. Although bedding planes can control the cave propagation to some extent, the most common guiding structures are joints (Osborne, 2009). To become available to observations, hydrothermal caves formed in a deep-seated setting must first be brought close to modern topographic surface. This happens in areas that underwent tectonic uplift. If uplift occurred after the cessation of the hydrothermal karst process, the deep-seated hydrothermal caves can be brought to the surface in well preserved state. If, however, the uplift and hydrothermal speleogenesis occur simultaneously, the cave formed at deep levels could move into the shallow phreatic, then the near-water table, and finally into the subaerial setting. As a result, the initial morphology of the deep-seated cavities can be overprinted, or even completely obliterated, by morphs resulting from shallower hydrothermal speleogenetic processes (which are commonly much more powerful than their deep-seated counterparts). This multiphase development can result in very complex aggregate cave morphologies. For example, Osborne (2007) demonstrated at least six distinct phases of hypogene (likely thermal) speleogenesis for the Cathedral Cave in Eastern Australia. Being brought near the topographic surface, hydrothermal caves can be truncated and exploited by descending meteoric waters, resulting in overprint by conventional karst morphology. Conversely, thermal water could invade the preexisting conventional karst caves. Prominent examples are the Kugitang-tau cave in Turkmenistan (Bottrell et al., 2001) and the main ore body of the Tyuyua-Muyun U-V deposit in Kirghizstan, where the preexisting vadose cave was lined or entirely

4 60 Karstification by Geothermal Waters filled with minerals (Dublyansky, 1990). To sum up, almost all imaginable temporal relationships between morphologies produced by different phases of hypogene (hydrothermal) and hypergene (conventional) karst have been reported in the literature. ascertained: examples are known when hydrothermal solutions invaded preexisting conventional karst passages and deposited minerals there (e.g., the main ore body of the Tyuya Muyun U-V deposit in Kirghizstan) Isotope Alteration of Bedrock Diagnostics of Thermal Water Caves As it is apparent from brief discussion above, hydrothermal karst is but a special case within a broader category of hypogene karst (see Chapter 6.19). The invariant of the hydrothermal karst is its development at elevated temperatures, whereas hypogene karst can also develop at ambient temperatures. This means that significant similarity between the morphology of hypogene caves in general and that of the hydrothermal caves is to be expected. Significant progress has recently been made in defining the morphological features of hypogene speleogenesis (Klimchouk, 2007, 2009; Audra et al., 2009a, b; Osborne, 2009). Nevertheless, unambiguous diagnosis of such origin typically involves additional, nonmorphological considerations. An important argument in support of the hypogene origin of caves is the absence of any obvious relationships with the surface hydrology, including lack of surface karst forms. Most hypogene caves have been discovered after they have been intersected by nonkarst processes, such as surface or slope erosion, valley incision, roof collapse, as well as construction and mining activities. Supportive evidence with regard to hypogene origin includes lack of cave morphs and cave deposits indicative of the running (or, more generally, gravitydriven) water. In most cases, discrimination between the nonthermal and the hydrothermal hypogene caves on the basis of morphological features alone is ambiguous. Additional indicators are typically needed for confident interpretations. In short, one should look for footprints of thermal waters left in caves or in the surrounding rock Cave Minerals Some hydrothermal caves contain minerals, which can be related to speleogenetic process. The most common example is euhedral calcite: many known hydrothermal caves are lined with scalenohedral crystals of this mineral (commonly called dogtooth spar in cave literature). Other caves contain crystals of gypsum. In some areas, typically associated with mineralized regions, caves host other hydrothermal minerals, such as fluorite, barite, quartz, and sulfides. If such minerals are present, then by studying fluid inclusions in them it is possible to determine the temperature of paleowaters and, thus, verify their thermal character. The temperatures characterize the stage of infilling of hydrothermal karst cavities. In the case of calcite deposited on the walls of a hydrothermal cave in carbonate rock, this would imply that water circulating through the cave was not aggressive any more. The temperature of waters determined from fluid inclusions in calcite would, therefore, correspond to the postsolution stage. Another caveat is that genetic continuity of the processes must be Movement of heated waters through carbonate rocks commonly causes isotopic alteration of the latter. It has been found that cave walls of some hydrothermal carbonate caves carry an oxygen isotope alteration halo (Spötl et al., 2009). The extent of the isotopic alteration can provide information on the temperature of altering water (Dublyansky and Spötl, 2009). The caveat here is that not all hydrothermal caves carry this isotopic signal. Isotopic alteration of bedrock occurs as propagation of the alteration front from cavity wall into the bedrock. The speed of propagation depends on a number of factors, such as matrix permeability of the rock and temperature. If water on the contact with the cave wall is aggressive, then the removal of the material from the rock surface by dissolution competes with the propagation of the alteration into the rock. An alteration halo could form only if dissolution is very slow, or absent. The absence of alteration halo, therefore, does not necessarily indicate the nonthermal character of karst Indirect Evidence Some general geologic features, although not indicative of the hydrothermal origin of a given cave could, nevertheless, support it. Such evidence includes the proximity of studied caves to known thermal activity (hydrothermal mineralization and thermal springs) or to travertine deposits Macromorphology of Hydrothermal Caves Macromorphology refers to gross morphology of individual hydrothermal caves. Hydrothermal caves display a broad range of morphologies, ranging from very simple, such as individual rooms, single chambers, or single-conduit caves, to very complex two- and three-dimensional systems Simple Forms: Individual Rooms and Single-Conduit Caves Individual rooms and chambers Individual rooms are isolated chambers or rooms with sizes ranging from 0.5 to 15 m. The shapes of the rooms are commonly isometric, but may also be elongated along one or two directions. This form is characteristic of the phreatic karstification, commonly at significant depth (hundreds of meters). Such cavities are commonly lined with large euhedral crystals of calcite or gypsum, deposited from hydrothermal solutions (cf. isolated geode of Audra et al. (2009a)). In most cases, individual rooms are produced by pure dissolution. Dissolution may be by CO 2 -charged water, H 2 S water, or in response to mixing of waters with differing chemistry and/or temperature.

5 Karstification by Geothermal Waters 61 Vadose shaft Khod Koniom in Crimea, Ukraine, intersects at a depth m of several isometric cavities 0.5 and 8 m in diameter, hosting clay and scalenohedral crystals of calcite up to 80 cm in size. Fluid inclusion studies demonstrated that calcite crystallized from waters with T ¼ C (Dublyansky, 1990). Another spectacular example is horizontally elongated (length 8 m, width 1.8 m, and height 1.7 m) room of the Geode of Pulpí in Almería, Spain (Figure 1). The cavity is lined with euhedral gypsum crystals up to 2 m in size. Both dissolution of the chamber and deposition of secondary minerals are attributed to hydrothermal solutions (Fernandez-Cortes et al., 2006). The presence of large individual crystals attests for a very stable, essentially stagnant, hydrodynamic conditions. Individual rooms can also develop in shallow phreatic setting. For example, an isometric room c. 17 m in diameter was discovered by SCUBA divers in Héviz lake (Hungary). The cave is developed in sandstone, and its bottom is 45 m below the lake surface. The cave was formed (and is being formed) by mixing corrosion, as two springs with temperature of 17 and 40 1C emerge in this underwater chamber (Plózer, 1977). Individual chambers are distinguished from individual rooms discussed above by their larger dimensions, ranging from tens to hundreds of meters. Such chambers may have a variety of shapes, ranging from simple isometric, near-spherical ones, to more complex hemispherical, funnel, or invertedfunnel ones. In plan view, individual chambers may be isometric or somewhat elongated. Unlike individual rooms, for which the concave floor is typically observable, floor in larger individual chambers is commonly covered with the breakdown material, and in most cases it cannot be readily observed. Whether or not such chambers had originally spherical, or upward convex hemispherical, shape is not always clear. Specific speleogenetic processes leading to the development of the individual-chamber morphology need to be deciphered on a case-by-case basis. According to Audra et al. (2002, 2009a), some of such cavities form in subaerial setting through coalescence of spherical niches developing by mechanism of condensation corrosion above thermal lakes. Examples of individual chambers developing in shallow phreatic setting are cenotes Caracol and La Pilita in Mexico (Figure 2). Caves, which have nearly spherical shapes and diameters of m, are filled with moderately thermal water (29.6 and C). Active convection in these caves can be inferred from constant character of temperature and water conductivity measured in these caves through the whole depth of water column (c. 70 and 100 m, respectively; Gary and Sharp, 2009). Bolshaya Baritovaya cave in Kirghizstan provides an example of a chamber formed in the deep-seated phreatic settting. The cave is lined with large euhedral crystals of calcite (up to 50 cm) and barite (up to 15 cm) deposited at C. Frumkin and Fischhendler (2005) attributed individual chambers in Israel to convection in phreatic zone. Although vigorous dissolution is a necessary prerequisite for creation of such large underground voids, the role of gravitational breakdown (roof and wall collapse) increases with increasing sizes of cavities. For large individual chambers, the role of collapse may be comparable to, or even exceed that of dissolution. Besides cavity dimensions, the breakdown is E Caracol La Pilita W Plan view Profile view Figure 1 Schematic presentation of the 8 m long Geode of Pulpí in Almería, Spain. This individual room is carved in Triassic dolomite, which around the cave was replaced by siderite. The room is lined with gypsum crystals. Adapted from Fernandez-Cortes, A., Calaforra, J.-M., Garcia-Guinea, J., The Pulpí gigantic geode (Almeria, Spain): geology, metal pollution, microclimatology, and conservation. Environmental Geology 50, , with permission from Geological Society. Figure 2 Individual chamber morphology of cenotes of the Sistema Zacatón, Mexico. The graph is generated from underwater sonar data (color) and laser scanning data above the water surface (white). These large chambers were opened by roof collapse. These cenotes are filled with thermal water (29.6 1C in Caracol and C in La Pilita). Adapted from Gary, M.O., Sharp, Jr. J.M., Volcanogenic Karstification: Implications of this Hypogene Process. NCKRI Symposium 1, Advances in Hypogene Karst Studies. National Cave and Karst Research Institute, Carlsbad, NM, pp Scale ¼ 100 m.

6 62 Karstification by Geothermal Waters controlled by the structure and mechanical properties of the rock. The fate of this collapsed material depends on the setting under which the cave is formed. If collapse occurs within cavity filled with aggressive water, the (soluble) collapsed material continues to be dissolved and, eventually, removed from the cave. The cave, thus, preserves its, largely solutional, morphology and only volumetrically small amounts of insoluble residue could accumulate at the floor of the cave. If intense collapse occurs in a cavity developing above water table, by coalescence of condensation corrosion cupolas (Audra et al., 2009a), the collapsed material is removed from zone of dissolution. This may lead to accumulation of thick gravitational deposits at the floors of chambers, which commonly occupy significant part of the cave volume (Figure 3) Single conduit caves As implied by the name, the single conduit caves are composed of a single long, typically tube-shaped passage. The passage can be aligned horizontally, parallel to water table, or at a steep angle to it. These two geometric alignments may reflect different speleogenetic processes. The near-horizontal single conduit caves typically develop at the thermal water table. Prominent examples are Hellespont, Spence, and Kane caves in Wyoming, USA. The caves are tube-shaped conduits m long, through which thermal springs discharge (Egemeier, 1981). Conduits were developed in subaerial setting, where rising thermal H 2 S- charged water contacted with air inducing replacement of limestone by gypsum (replacement corrosion) which was subsequently removed. Steeply dipping single conduit caves develop in phreatic setting. Narrow tubular chimney of the Grotte de Chat, France was interpreted as a being due to the rise of thermal water along the major fault (phreatic chimneys of the early phase; Audra et al., 2009b). Caves with larger tube diameters are commonly called deep phreatic shafts (Audra et al., 2009a). A spectacular example of such single conduit cave is the Pozzo del Merro in Italy the deepest explored underwater cave of the world. Klimchouk (2007) interpreted it as a rising shaft an outlet of a deep hydrothermal system, presumably formed by rising thermal water charged with CO 2 and H 2 S. Another prominent example of deep phreatic shaft is the cenote Zacatón in Mexico, which exhibits staked cylindrical pit morphology (Figure 4) Bush-Like Caves or Caves with Cupolas Such caves typically consist of a basal chamber from which a branching pattern of rising passages develops. The branches are composed of coalesced spherical cupolas with typical sizes of m, and cupolas form blind termination of branches. Such caves are known in Hungary (Müller and Sárváry, 1977) with two prominent examples being Sátorköpuszta and Bátori caves. Such types of caves are thought to be due to the delivery of hot water to a single input point at the base of carbonate rock having low fissure density (Ford and Williams, 1989). Two competing hypotheses attribute this specific cave morphology either to natural convection of thermal waters in phreatic conditions (Rudnicki, 1978) or to convective movement of moist air above thermal lakes and condensation corrosion (Szunyogh, 1982, 1989; Audra et al., 2007). It is possible that both processes play a role at different stages of speleogenesis Maze Caves Maze caves represent perhaps the most common type of hydrothermal cave systems. They develop where many interconnected openings enlarge at comparable rates. Maze caves may have two- and three-dimensional architecture. Palmer (1991) distinguished network, spongework, anastomotic, and E W S Cross section N Zacatión Entrance Plan view Profile view 0 50 m Figure 3 Individual chamber, Grotte aux Champignons, France. Note that gravitational deposits occupy most of the cave volume. Adapted from Audra, P., Bigot, J.-Y., Mocochain, L., Hypogenic caves in Provence (France). Specific features and sediments. Acta Carsologica 31(3), Figure 4 Cylindrical pit morphology of cenote Zacatón, Mexico. The graph is generated from underwater sonar data (color) and laser scanning data above the water surface (white). Adapted from Gary, M.O., Sharp, Jr. J.M., Volcanogenic Karstification: Implications of this Hypogene Process. NCKRI Symposium 1, Advances in Hypogene Karst Studies. National Cave and Karst Research Institute, Carlsbad, NM, pp Scale ¼ 100 m.

7 Karstification by Geothermal Waters 63 ramiform mazes. Abundant examples of all these maze varieties can be found in caves of the Guadalupe Mountains, New Mexico, USA (Palmer and Palmer, 2000). Network mazes represent angular grids of intersecting passages formed by the widening of nearly all major fractures within favorable areas of soluble rocks. Closed loops and relatively high and narrow passages are common. Twodimensional rectilinear maze systems are formed where rising thermal water flows through densely jointed carbonate rock below a relatively impervious bed (Ford and Williams, 1989). Prominent examples of such hydrothermal morphology are Cserszegtomaji-kut and Acheron-cut caves in Hungary (Kárpát, 1982, 1983) developed in Triassic dolomite under the cover of the Miocene sandstone aquitard. Three-dimensional hydrothermal rectilinear network caves are exemplified by caves of Buda Hills, Hungary (Pál-völgyi, Szemlö-hegy, Ferenchegy) and caves of the Black Hills, South Dakota, USA (Wind Cave and Jewel Cave). Many carbonate-hosted hydrothermal zinc lead ore deposits exhibit a network pattern of solutionenlarged fractures filled, partly or entirely, with ore minerals (e.g., Jefferson City mine, Tennessee, USA and Devil s Hole mine, UK). Spongework mazes consist of solution cavities of varied sizes interconnected in a seemingly random three-dimensional pattern. Such caves form by coalescence of intergranular pores and minor interstices (Palmer, 1991). Quite commonly, such mazes originate in mixing zones, where the aggressiveness of water is high, flow velocity is low, and flow itself is diffuse rather than concentrated. In downflow directions from these sites, where aggressiveness is weakened, the maze passages tend to transform into single conduits (Palmer and Palmer, 2000). Anastomotic caves consist of curvilinear tubes that intersect in a braided pattern with many closed loops. They commonly form a two-dimensional array along a single favorable parting or low-angle fracture. The three-dimensional arrays follow more than one geologic structure. An example of the supposedly hydrothermal three-dimensional anastomotic cave is Pobednaya cave in Kirghizstan with its 1.5 km or very narrow tube-shaped crawlways (Mikhailev, 1989). Ramiform caves consist of irregular rooms and galleries wandering three dimensionally with branches extending outward from the main areas of development. Passage interconnections are common, producing a continuous gradation with spongework and network caves Mesomorphology of Hydrothermal Caves Mesomorphology refers to elements of cave morphology similar in scale to the cave passage diameter Features Created by Phreatic Rising Flow The concept of the morphologic suite of rising flow was introduced by Klimchouk (2007) as a tool to identify caves with confined transverse origin (see Chapter 6.19 for details). The suite comprises three major components: (1) feeders (inlets), (2) transitional wall and ceiling features, and (3) outlet features. Feeders or inlets correspond to sites of input of rising water into hypogenic caves. Typical feeders are vertical or subvertical conduits, either individual or forming small networks. The feeder conduits can be tubular, providing point inputs of water into the cave; alternatively, they can be rift-like features, providing input of water along their entire length. They vary in sizes from tens of centimeters to many meters in cross section. Dimensions of feeders are commonly smaller in their lower parts, and they widen near the connection points with the main cave galleries. In multistory systems, typical of the basinal setting, feeders for upper stories serve as outlets for lower stories. Extensive maze caves forming in basinal setting commonly have multiple feeders distributed more or less uniformly through the network. In folded setting caves, the number of feeders is typically smaller. Transitional wall and ceiling features form in response to rising flow, with a considerable role of buoyant effects (upward-focused dissolution associated with rising limbs of free convection cells). They include: rising wall channels, ceiling channels (half-tubes), ceiling cupolas, and rising sets of coalesced ceiling cupolas or arches. These forms will be discussed in Section Outlet features represent channels of varying morphology and origin, connecting the cave to the next upper story or discharging water out of the cave-development zone. Typically, they are represented by cupolas and domepits (vertical tubes) that rise from the ceilings of cave passages and rooms. Outlet channels vary in sizes from less than a meter to many meters in cross section and can reach tens of meters in the vertical extent. Closely spaced individual outlets may merge, forming linear rather than point openings to the upper contact Features Characteristic of Near-Stagnant Phreatic Conditions Laughöhle passages have flat ceilings (Laugdecke) and inward inclined walls with a slope of c. 451, resulting in triangular cross section (Kempe et al., 1975). Passages with such profiles are thought to develop in standing phreatic water that allows development of slowly moving density-driven convection cells. The driving mechanism for this type of convection is the difference in density between saturated water in the boundary layer near cave wall and the aggressive body of water. This difference, which may be as high as 30% for halite and 0.1% for gypsum, leads to sliding of denser mineralized water down and displacement of less dense aggressive water upwards. As a result, the upper part of cavity is continuously exposed to more aggressive waters than its lower parts. Although such forms are more common in evaporates, smaller variants are also known from limestones (Figure 5) (Lauritzen and Lundberg, 2000). It is thought that Laughöhlen form within the upper 1 2 m of the phreatic zone, closely below the water table. Whether or not the Laughöhle morphology could develop in thermal water bodies remains unclear. It would appear that water circulation related to thermal convection cells should overwhelm convection due to density difference

8 64 Karstification by Geothermal Waters 1 m (a) (b) (c) Figure 5 Laughöhle morphology. (a) Profile formed by convection cells driven by density currents. The flat ceiling Laugdecke is formed closely below the water table (indicated as shaded surface). Modified from Kempe, S., Brandt, A., Seeger, M., Vladi, F., Facetten and Laugdecken, the typical morphology of caves developing in standing water. Annales de Spéléologie 30(4), , and adapted from Lauritzen, S.-E., Lundberg, J., Solutional and erosional morphology. In: Klimchouk, A.B., Ford, D.C., Palmer, A.N., Dreybrodt, W. (Eds.), Speleogenesis: Evolution of Karst Aquifers. National Speleological Society, Huntsville, AL, pp (b, c) Laughöhle Laugdecke morphology in presumably hypogene Kozak cave, Austria. Photo: A. Desch and C. Spötl. caused by dissolution. Quantitatively, however, these effects have not been compared Features Related to the Free Convection In hydrothermal caves, particularly those in the near-surface high-gradient zone, free convection is an entirely expected process. Convection cells could develop in thermal water bodies, as well as in warm moist air above the surface of underground thermal ponds. Both types of convection result in cave forms which, despite difference in mechanisms of dissolution, can be strikingly similar. Cupolas are solution cavities with dome-shaped ceiling and a circular to elliptical plan with a diameter or long axis in plan 41.5 m (Osborne, 2004). Synonyms are solution domes (Hill, 1987) and convection cupolas (Lauritzen and Lundberg, 2000). Smaller cavities of the same shape are called bellholes or ceiling pockets (see Section 6.6.6). Many cupolas, particularly large ones, contain speleothems or sediments at their floors obscuring the true solution shape of the void. In other cases, lower parts of cupolas are removed by later cave

9 Karstification by Geothermal Waters 65 processes. An important question is whether the cupolas represent features developing upward from ceilings of caves, or they are stand-alone solution forms subsequently intersected by cave passages. This question needs to be answered on the case-by-case basis. At least two distinct speleogenetic processes can be responsible for the appearance of cupolas. In the phreatic setting, cupolas result from slow movement of water caused by natural convection (Rudnicki, 1978). The reason for convection could be temperature and/or density difference; forced convection also cannot be excluded. In the subaerial setting, cupolas are thought to have been developing above the thermal water surfaces by mechanism of condensation corrosion. Convection of moisture-laden air is involved, but in this case the matter is removed by a film flow of condensate (Szunyogh, 1982, 1989; Dreybrodt et al., 2005; Audra et al., 2007). Although condensation corrosion can be an important speleogenetic factor in certain nonthermal hypergene setting (e.g., Tarhule-Lips and Ford, 1998), this process is particularly active in hydrothermal caves, where temperature gradients are high due to the presence of thermal water, and concentrations of carbon dioxide and/or hydrogen sulfide could be significantly elevated. Osborne (2004) discriminated between the following morphological types of cupolas: elliptical cupolas, cathedrals, hemispherical cupolas, conical cupolas, and spherical niches. Elliptical cupolas are elongated along vertical or dipping guiding structures (joints or beds in steeply dipping limestones). In plan view, elliptical cupolas have a length to width ratio ranging up to 4:1. Cathedrals are much less frequently observed shape in which horizontal axis is longer than vertical. Cathedrals are tens of meters long and high, and 10 m or more wide. Conical cupolas are usually elongate features with a basal diameter or long axis of 2 m or less and a vertical axis extending for several meters. Conical cupolas may be circular or elliptical in plan. Conical cupolas occurring in both limestone and gypsum caves show little morphological difference. Hemispherical cupolas are characterized by a circular plan and a hemispherical cross section (Figure 6). Many hemispherical cupolas show no apparent guidance by geological structures. Spherical cupolas are relatively rare forms of cupolas approximately 1 3 m in diameter. They commonly connect to the rest of the cave or to other spherical cupolas by an opening at an angle ranging from 01 to about 451 to the perpendicular, and form a complex spongework of niches projecting outward and upward from the vertical axis. A characteristic feature is the presence of the necks between the adjacent niches that have diameters smaller than those of the niches. Cupolas may be the dominant morphology in some caves, for example, Sátorköpuszta and Bátori caves in Hungary composed of a basal chamber and a combination of numerous partly coalesced cupolas (see Section ). In other cases, they are restricted to certain parts of the caves. A good example is the Azérous in Northern Algeria. Hydrothermal caves there have various macromorphologies, from a single passage (Rhar Figure 6 Cupolas: (a) cupola-shaped room with smaller hemispherical cupolas in Zwergelloch cave, Austria and (b) cupolas in Kraus cave, Austria. Photo: L. Plan. Sidi Bacou cave) to three-dimensional network and ramiform mazes (Rhar Mejraba and Rhar Amalou caves). The cupolas have relatively regular diameters of c. 1 m, commonly coalesce, and develop in massive Cretaceous host limestone without any apparent guidance by fissures. The cupolas appear to form at advanced stages of speleogenesis, and in most cases are restricted to the uppermost parts of caves (Collignon, 1989) Micromorphology of Hydrothermal Caves Micromorphology refers to small-scale morphological features (forms that are much smaller than passage diameter) and rocky relief features (cf. speleogens of Osborne (2004)), as well as nonaccessible karst forms, such as karst porosity. These forms can develop in either subaqueous or subaerial settings; some forms are known to form in both (polygenetic forms) Polygenetic Forms These are forms that can develop both subaqueously and subaerially and, thus, cannot be used to discriminate between these settings.

10 66 Karstification by Geothermal Waters Partitions is the collective term referring to various remnants of bedrock that at some time in the past separated the adjacent cavities. Hydrothermal caves commonly develop by quasi-independent enlargement of individual cavities (e.g., cupolas) and their eventual aggregation into larger caves. Because of that partitions are particularly abundant in hydrothermal caves. Partitions, thus, result from geometric relationships between adjacent cavities (Figure 7) and are not necessarily related to the locally increased resistance of the bedrock to solution. In some cases, partitions are associated with solution-resistant bodies, such as lithified fracture fill or resistant beds in stratified sequences. Pillars with concave wall shapes may remain between adjacent solution chambers or passages, which did not merge completely. Juts are bedrock projections from the cave walls (Slabe, 1995). They have curved sides and their connections with the main rock mass are circular in sections. Ceiling pendants are juts that project downward from cave ceilings or overhanging portions of cave walls. Blades are elongate projections of bedrock rising from the cave floors or projecting from the cave ceiling with a narrowing, blade-like edge (Osborne, 2007). Projecting corners are narrow bedrock projections into the cave (Osborne, 2007). Cusps are pointed bedrock projections. They form through aggregation of more than two individual spheroid cavities (Figure 8). Arches and rock bridges represent broadly horizontal partitions and form through aggregation of cavities stacked vertically. They are particularly common in hydrogen Figure 8 Cusp formed by intersection of three spheroid cavities. Kozak cave, Austria. Photo: C. Spötl. Pillar Ceiling pendant, jut Projecting corner, cusp Blade Aggregation Rock bridge, arche Terrace Wall half-tube Aggregation Low Pseudo notch Figure 7 Schematic representation of evolution of partitions in process of advancing aggregation of independently enlarging cavities. The earlier-stage morphology is shown by dashed line. Modified from Audra, P., Mocochain, L., Bigot, J.-Y., Nobécourt, J.-C., 2009b. Morphological indicators of speleogenesis: hypogenic speleogenesis. In: Klimchouk, A., Ford, D. (Eds.), Hypogene Speleogenesis and Karst Hydrogeology of Artesian Basins. Special Paper 1. Ukrainian Institute of Speleology and Karstology, Simferopol, pp

11 Karstification by Geothermal Waters 67 sulfide maze caves (e.g., in Guadalupe Mountains, New Mexico (Palmer and Palmer, 2000)). Terraces are remnants of horizontal partitions. They may or may not be related to solution-resistant beds Subaqueous Forms Solution porosity or cavernosity is represented by solutionenlarged pores and small anastomotic cavities. Layers of rock with solution-enhanced transmissivity are commonly reported in deep borehole cores from geothermal deposits and oil fields. These small voids may form extensive zones or horizons and in places become parts of oil and gas reservoirs. According to Belkin and Medvedsky (1989) in some deep oil reservoirs of Western Siberia, at a depth exceeding 4 km, where the temperature exceeds 100 1C, solution voids can account for 5 15% of rock volume. In places the cavities become lined with secondary minerals (calcite, dolomite, quartz, etc.). Zones of solution-enhanced transmissivity develop under slow flow conditions (millimeters per year or less), in places where hydraulic structures capable of focusing the flow (faults) are absent. Zones of solution porosity can also develop in places where the transmissive faults intersect porous beds in basinal settings. As these two structures may host waters with different chemistry, solution porosity and cavernosity develops by mixing corrosion mechanism. In this case, the aggressive waters may or may not be thermal. Half-tubes are long and narrow depressions having semicircular or semi-oval cross sections (Figure 7). Half-tubes occur on ceilings (ceiling half-tubes) or run up the cave walls (rising half-tubes). The latter variety commonly connect with small cupolas or pipes in the cave ceilings. Pipes are vertical to subvertical tubes with a circular to oval cross section and, typically, blind terminations that cut through the rock mass. Rising half-tubes can result from pipes being intersected by later cave development. Pseudonotches are elongated indentations in the cave walls, similar to a notch, but they are really a smaller tube with circular cross section that has been intersected by later cave development (Osborne, 2004). Pseudonotches may merge with bridges or with tubular passages that have not been intersected. Rising channels of thermal water are medium-scale channels in the overhanging walls of caves, with internal surface sculptured by scallops (Figure 9), indicating rising flows of water. Example of such channel is reported in shaft OX 655 in French Pyrénées by Audra et al. (2009b). Bubble trails are small-scale rising solution channels curved in the overhanging walls. Their origin is attributed to the corrosive action of bubbles of CO 2 (Chiesi and Forti, 1987). Effervescing from the water, the bubbles move up along the overhanging walls. In order to cut a channel, the bubbles must follow exactly the same path; it is more likely, therefore, that bubble trails will develop at the location where there is point input of degassing water (e.g., lateral fracture joining the passage). An alternative mechanism for development of bubble trails is the oxidation of sulfur deposits (oxidation vents; De Waele and Forti, 2006). Figure 9 Rising channel with large scallops in OX 655 shaft, France. Photo: J.-Y. Bigot; adapted from Audra, P., Mocochain, L., Bigot, J.-Y., Nobécourt, J.-C., 2009b. Morphological indicators of speleogenesis: hypogenic speleogenesis. In: Klimchouk, A., Ford, D. (Eds.), Hypogene Speleogenesis and Karst Hydrogeology of Artesian Basins. Special Paper 1. Ukrainian Institute of Speleology and Karstology, Simferopol, pp Thermo-sulfuric discharge slots represent feeders supplying aggressive water into the sulfuric acid caves. They are laterally restricted and narrow at shallow depth. Larger cave forms, such as chambers, typically develop above the slots, commonly through corrosion occurring above the water table (Audra et al., 2009b). Anastomoses are small-diameter (mostly, centimeters) channels with circular or elliptical cross section. They form in phreatic setting, developing along guiding structures, such as bedding planes or joints. Most commonly, they are exposed by collapse of a block on one side of the guiding structure. Spongework is a highly complicated three-dimensional arrangement of interconnected pockets, tubes, and cavities of various shapes and sizes. The dimensions of cavities are nevertheless relatively small, so that this micro-morphological term should not be confused with spongework caves (described in Section 6.6.5). The type locality is the Carlsbad Caverns, New Mexico, USA (White, 1988). Scallops and other flow indicators are generally absent, suggesting slow or stagnant flow regime. Development of spongework is explained by differential corrosion under nearly stagnant flow of water that is close to chemical equilibrium. Experiments of Rauch and White (1977) suggest that rocks with slightly varying chemical properties could dissolve with drastically different relative

12 68 Karstification by Geothermal Waters corrosion rates. It is to be noted that spongework morphology is also known from nonhypogenic and nonthermal settings, such as the fresh-salt water mixing zone within poorly consolidated carbonate rocks on carbonate platforms (Mylroe and Carew, 1990) Water-Level Forms Notches are water-level features represented by elongate indentations in the cave walls. Well-developed notches are characterized by planar sloping lower surface (facet) that commonly dips at approximately 451; the upper part of the notch cross section is typically semicircular (Osborne, 2007). Less-developed notches appear as incipient indentations. Wall convection niches form immediately above the surface of thermal ponds (Audra et al., 2009b). The shapes and sizes (diameter of cm) of niches are generally uniform at a given location, and they are aligned along the same level (Figure 10). The shape of each niche represents portion of a spheroid, with a steep overhang at the top. Deeply incised into the cave wall, laterally coalesced niches could produce a notch-like feature Subaerial Forms Two important physico-chemical processes occur above the surface of thermal cave pools: evaporation and degassing (CO 2 and H 2 S). Vapor-saturated air becomes involved in the convective movement in which warm air moves up, then cools down in upper parts of the cave or cave chamber, and returns back toward the thermal pool surface. Warm water vapor condensing on cooler cave walls in the presence of significant amounts of acid gases becomes strongly aggressive with respect to carbonate rocks. The condensed water then returns back to the thermal water pool by either capillary or laminar flow along the wall, or by dripping. Subaerial forms developing in response to these complex processes can reflect the dominant process (e.g., air movement, focused sulfuric acid corrosion, dripping, etc.) Forms related to air movement Vents are small-scale near-vertical chimneys with circular or more complex (e.g., two or more coalesced circles) cross section. They typically connect parts of the cave located at different levels and are commonly associated with peculiar calcite deposits riming its upper opening (Audra et al., 2007). In hydrothermal caves, vents readily develop when the lower of the connected cave passages hosts thermal water. The latter initiates convective upward movement of moist air, which carves the vent by mechanism of condensation corrosion. Condensation corrosion channels with megascallops are relatively rare forms developing on the overhanging walls in high cave chambers (Audra et al., 2009b). Such channels were found to initiate at the level of the supposedly thermal water table (e.g., Kraus cave, Austria) and develop prominently above the warm rivers (Audra et al., 2009b). The channels can be incised to a depth of a half-tube. Following on the shape of the walls, they can change the direction or even bifurcate. The surface of the channels commonly bears megascallops. Giant scallops or megascallops are rounded concavities in cave walls, typically arranged in a polygonal pattern (Figure 11). Similarly to scallops caused by flowing water, megascallops develop in response to transition from laminar to turbulent flow in the convecting air, resulting in eddy currents (Forti et al., 2006). Feeder (?) Notch Figure 10 Sulfuric acid notch marking former position of the water table and wall convection niches developed above the pond. Kraus cave, Austria. Photo: L. Plan.

13 Karstification by Geothermal Waters 69 Figure 11 Mega scallops in an ascending channel. Kraus cave, Austria. Photo: L. Plan Forms related to uniform surface attack The condensation corrosion process attacks the bedrock uniformly in zones where condensation occurs. Specific conditions of dissolution are typically similar in individual caves, but may vary drastically between the caves, resulting in diverse micromorphology. Dissolution of rock can be presented as interplay of the two processes: (1) surface reactions (chemical dissolution per se) and (2) mass transport of dissolved matter from surface through the diffusion boundary layer into the bulk of solution (Rickard and Sjöberg, 1983). In the case of carbonate dissolution, another rate-limiting reaction, slow reaction between H 2 O and CO 2 producing H þ ions must be taken into account (Dreybrodt and Eisenlohr, 2000). The overall dissolution rate is controlled by the slowest of these components. When surface reaction is slow (kinetic regime), dissolution will strongly depend on the chemistry of the bedrock. Local differences in the chemical purity, degree of crystallinity, and sizes of mineral grains (micrite, sparite, etc.) may result in different rate of dissolution producing prominent microrelief of cave walls. Conversely, when surface reaction is fast, the overall dissolution rate can be controlled by slow diffusion of matter through boundary layer (diffusion regime). In this case, materials with slightly variable solubilities will dissolve uniformly, and the resulting cave surface will be smooth. Boxwork and wall hieroglyphs were described as an indicative suite of condensation corrosion in Grotte du Chat, France (Audra et al., 2009b). Under conditions in this cave, crystalline carbonate veinlets were less susceptible to dissolution under condensation corrosion than the fine-crystalline matrix of the host limestone (i.e., kinetic dissolution regime). Networks of intersecting veinlets remain protruding from cave walls as the surrounding material is removed, producing a boxwork. Conversely, in fissured rocks, condensation corrosion can widen the cracks, resulting in wall hieroglyphs. In many other caves, condensation corrosion cavities cut through the substrate with different properties (e.g., bedrock limestone and speleothems) in a single smooth curved surfaces (Lauritzen and Lundberg, 2000). The process, thus, seems to be diffusion controlled. Weathered walls are produced by selective dissolution of micritic cement in the limestone while leaving behind sparitic calcite grains. In dolomitic rocks, dissolution is most active along crystalline grain boundaries, so that dolomite grains become detached. By this process, soft weathered layer up to several centimeters thick develops on the cave wall, built-up of the loosely attached microcrystals. Microcrystals disjointed by dissolution can also be removed by gravity Forms related to condensation runoff and dripping Drip tubes are cylindrical channels in the floors of caves with vertical walls forming in places where condensation is vigorous, and downward-oriented projections are present on cave walls and ceilings, which serve as permanent drip sites. Other forms, such as sulfuric karren, sulfuric cups, and corrosion tables, have been reported from sulfuric acid caves, which could have been developed in the presence of slightly thermal waters. Because these morphs reflect primarily chemistry of water rather than its thermal character, they will not be discussed here (the reader is referred to Chapters 6.4 and 6.20 of this monograph) Conclusions There exist only a limited number of indicators allowing unequivocal identification of the thermal origin of caves. These include: 1. The presence of thermal waters in cave. Obviously, this indicator is only relevant in presently active hydrothermal karst caves.

14 70 Karstification by Geothermal Waters 2. The presence of hydrothermal minerals deposited on the cave walls. Hydrothermal character of mineralization is inferred from mineralogical and/or geochemical evidence (the fluid inclusion microthermometry is particularly informative). It is also necessary to demonstrate that the two speleogenetic processes (stages), cave development and mineralization, are related to the same process. 3. The presence of isotopic alteration of the cave walls. Character and degree of alteration must correspond to the water/rock interaction at elevated temperature, which is inferred on the basis of isotopic calculations. The morphology of caves formed under action of thermal water can exhibit a number of characteristic features: features indicating very slow water movement; features indicating free convection of water; and features indicating active enlargement of caves in subaerial setting (air convection and condensation corrosion mechanism). Suggestive evidence includes: lack of morphological features and deposits indicating running water environment; lack of association with the surface features of conventional karst; and spatial association with hydrothermal activity (including extinct one). The cave morphology per se rarely provides a smoking gun evidence of the hydrothermal origin of caves. Yet, combined with other lines of evidence, it may provide important insights not only into the origin of caves (hydrothermal or conventional karstic), but also into the specific settings and processes of hydrothermal speleogenesis. References Andreychouk, V., Dublyansky, Y., Ezhov, Y., Lisenin, G., Karst in the Earth s Crust: Its Distribution and Principal Types. University of Silezia Ukrainian Institute of Speleology and Karstology, Sosnovec-Simferopol, 72 pp. Audra, P., Bigot, J.-Y., Mocochain, L., Hypogenic caves in Provence (France). Specific features and sediments. Acta Carsologica 31(3), Audra, P., Hoblea, F., Bigot, J.-Y., Nobecourt, J.-C., The role of condensation corrosion in thermal speleogenesis: study of a hypogenic sulfidic cave in Aix-Les-Bains. France. Acta Carsologica 36(2), Audra, P., Mocochain, L., Bigot, J.-Y., Nobécourt, J.-C., 2009a. Hypogene cave patterns. In: Klimchouk, A., Ford, D. (Eds.), Hypogene Speleogenesis and Karst Hydrogeology of Artesian Basins. Special Paper 1. Ukrainian Institute of Speleology and Karstology, Simferopol, pp Audra, P., Mocochain, L., Bigot, J.-Y., Nobécourt, J.-C., 2009b. Morphological indicators of speleogenesis: hypogenic speleogenesis. In: Klimchouk, A., Ford, D. (Eds.), Hypogene Speleogenesis and Karst Hydrogeology of Artesian Basins. Special Paper 1. Ukrainian Institute of Speleology and Karstology, Simferopol, pp Belkin, V.I., Medvedsky, R.I., Deep-Seated Karst and the Problem of Interconnected Ore- and Oil-Forming Process. Ore-Bearing Karst of Siberia. 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15 Karstification by Geothermal Waters 71 Müller, P., Sárváry, J., Some aspects of development in Hungarian speleology theories during the last 10 years. Karszt és Barlang (Hungary), Special Issue, Mylroe, J.E., Carew, J.L., The flank margin model for dissolution cave development in carbonate platforms. Earth Surface Processes and Landforms 15, Nöggerath, J., Ueber sogennante natürliche Schluchten oder geologische Orgeln in verschiedenen Kalksteinbildungen. Archiv für Mineral., Geogn., Bergbau Hüttenkunde, 513. Osborne, R.A.L., The Troubles with Cupolas. Acta Carsologica 33/2(1), Osborne, R.A.L., Cathedral Cave, Wellington Caves, New South Wales, Australia. A multiphase, non-fluvial cave. Earth Surface Processes and Landforms 32, Osborne, R.A.L., Hypogene caves in deformed (fold belt) strata: observations from Eastern Australia and Central Europe. In: Klimchouk, A., Ford, D. (Eds.), Hypogene Speleogenesis and Karst Hydrogeology of Artesian Basins. Special Paper 1. Ukrainian Institute of Speleology and Karstology, Simferopol, pp Palmer, A.N., Origin and morphology of limestone caves. Geological Society of America Bulletin 103, Palmer, A.N., Palmer, M.V., Hydrochemical interpretation of cave patterns in the Guadalupe Mountains, New Mexico. Journal of Cave and Karst Studies 62(2), Plózer, I., Situation of Hungarian cave diving in Karszt és Barlang (Hungary), Special Issue, Pošepný, F., The genesis of ore deposits. Transactions of American Institute of Mining Engineers (New York) 22, Rauch, H., White, W.B., Dissolution kinetics of carbonate rocks: 1. Effect of lithology on dissolution rate. Water Resources Research 13, Rickard, D.T., Sjöberg, E.L., Mixed kinetic control of calcite dissolution rates. American Journal of Science 283, Rudnicki, J., Role of convection in shaping subterranean karst forms. Kras i Speleologia (Katowice) 11(2), Schoeller, H., Les eaux souterraines. Masson and Cie, Paris. Shaw, T., History of Cave Science. Sydney Speleological Society, Sydney, pp Slabe, T., Cave Rocky Relief and Its Speleologenetical Significance. Zbirka ZRC, Ljubljana. Spötl, C., Dublyansky, Y., Meyer, M., Mangini, A., Identifying low-temperature hydrothermal karst and palaeowaters using stable isotopes: a case study from an alpine cave, Entrische Kirche, Austria. International Journal of Earth Sciences 98, Szunyogh, G., A hévizes eredetü gömbfülkék kioldodásának elméleti vizsgálata (Theory of the dissolving of spherical cavities formed by thermal water). Karszt és Barlang (Budapest) 2, Szunyogh, G., Theoretical investigation of the development of spheroidal niches of thermal water origin second approximation. Proceedings of the 10th International Congress of Speleology. Budapest, August 1989, pp Tarhule-Lips, F.A.R., Ford, D.C., Condensation corrosion in caves on Cayman Brac and Isla de Mona. Journal of Cave and Karst Studies 60(2), Van-Hise, C.R., Treatise on Metamorphism. Monograph US Geological Survey. US Government Printing Office, Washington, DC, vol. 47, 1289 pp. Waring, G.A., Thermal springs of the United States and other countries of the world. US Geological Survey Professional Paper No. 492, 383 pp. White, W.B., Geomorphology and Hydrology of Karst Terrains. Oxford University Press, New York, NY, 464 pp. Biographical Sketch Yuri Dublyansky was born in 1960 in Simferopol, Crimea, Ukraine to a family of geologists. He visited his first cave at the age of 3, and between the ages of 7 and 16 he always spent 1 or 2 summer months in field expeditions with either his father or mother. Not surprisingly, after finishing school in 1977, he enrolled at the University in Odessa, Ukraine, to study hydrogeology and geological engineering. After graduating in 1982, Yuri enrolled with in the PhD program in geochemistry at the Institute of Geology and Geophysics in the Academy of Science s Research Center in Akademgorodok (Academy Town) near the city of Novosibirsk one of the most renowned centers of science in the Soviet Union. During the next 2 decades, the central theme of Yuri s studies became hydrothermal karst. After completion of his PhD in 1985, he was offered a permanent position at the Institute. He studied hydrothermal karst at many sites in the Soviet Union (Crimea, Caucasus, Altai Mountains, Kyrgyzstan) and abroad (Hungary, Czech Republic, USA), and chaired the working group Hydrothermal Karst at the International Speleological Union (UIS UNESCO). Between 1995 and 2000, Yuri was involved in studies of the proposed high-level nuclear waste disposal site in Nevada, USA. Since 2006, he has resumed studies of hypogene karst at the University of Innsbruck, Austria.