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Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

Speleology in Kazakhstan

Shakalov on 11 Jul, 2012
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That compaction, specific is the decrease in thickness of deposits, per unit of increase in applied stress, during a specific period of time [21]. see also compaction; compaction, residual.?

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Karst environment, Culver D.C.
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Your search for feedback (Keyword) returned 36 results for the whole karstbase:
Showing 16 to 30 of 36
Development and Evolution of Epikarst in Mid-Continent US Carbonates, 2005, Cooley Tony L. , P. E.

This paper presents the basic elements of a conceptual model for the development of epikarst in US mid-continent, horizontally-bedded carbonates in which flow is largely confined to secondary and tertiary porosity. The model considers the development of epikarst regimes in carbonate sequences beginning shortly after non-carbonate rocks are eroded away to expose the underlying carbonates and follows this through capture of the shallow flow by deeper dissolution conduits with reorientation of the epikarst to a more vertical form. The model does not require an underlying zone of vadose flow and in many cases considers development of such a zone to depend on the water supply provided by prior development of the epikarst. It is not claimed that all epikarsts form in the accordance with this model; rather this paper presents a viable additional model for epikarst formation under appropriate starting conditions. Factors influencing the development of epikarst are a combination of: 1) the pre-karst topography and modifications to this as the system evolves, 2) the original distribution and aperture of fractures as well as the distance and orientation of physically favorable fractures relative to potential discharge points, such as existing dissolutionally-enhanced channels with low head or nearby valleys, 3) character of soil cover as this affects percolation of water to the rock, erodability of the soil, sediment filling of conduits, and transport of sediment 4) variations in availability of dissolutionally aggressive water with time and location, and 5) low solubility layers, such as shale or chert, that promote lateral flow until a penetration point can be found. These interact to form an epikarst and deeper karst system that progressively increases its capacity both by internal improvement of its flow routes and extension into adjacent areas. The availability of water needed to promote dissolution also often has a positive feedback relationship to epikarst, in which locations of most active dissolution modify their vicinity to progressively increase capture of water, which promotes further dissolution. In early stages, lateral flow through the overlying soils and along top-of-rock must dominate the groundwater flow because the relatively intact carbonates have insufficient transmissivity to convey the available recharge through the body of the rock. Top-of-rock runnels developed by a combination of dissolution of their floors and piping erosion of their roofs would carry a significant portion of the flow. Horizontally-oriented epikarst develops with discharge to local drainage. Cutters and pinnacles, collapse-related macropores, and areas of concentrated recharge would begin to form at this stage. Initial downward propagation of this system would occur mostly due to lateral flow. Mixing corrosion could occur in sumps in these lateral flow routes when fresh, percolating rainwater mixes with older water with a higher dissolved load. Should conditions be suitable, leakage from this system promotes the migration of deeper karst conduits into the area by Ewers multi-tiered headward linking. Other sources of water may also bring in such deeper conduits. Once such deeper conduits are present, the epikarst can evolve into a more vertically oriented system, at least in the vicinity of master drains into this deeper system. Former shallow epikarst routes may then plug with sediment. In some areas, deeper systems may never develop due to unfavorable conditions. The epikarst may be the only significant system in these cases. This includes the case of poor karst formers such as interbedded shales and carbonates that may have very shallow horizontal epikarst flow paths that channel shallow subsurface flows.


Dominant Microbial Populations in Limestone-Corroding Stream Biofilms, Frasassi Cave System, Italy, 2006, Macalady Jennifer L. , Lyon Ezra H. , Koffman Bess, Albertson Lindsey K. , Meyer Katja, Galdenzi Sandro, Mariani Sandro,
Waters from an extensive sulfide-rich aquifer emerge in the Frasassi cave system, where they mix with oxygen-rich percolating water and cave air over a large surface area. The actively forming cave complex hosts a microbial community, including conspicuous white biofilms coating surfaces in cave streams, that is isolated from surface sources of C and N. Two distinct biofilm morphologies were observed in the streams over a 4-year period. Bacterial 16S rDNA libraries were constructed from samples of each biofilm type collected from Grotta Sulfurea in 2002. {beta}-, {gamma}-, {delta}-, and {varepsilon}-proteobacteria in sulfur-cycling clades accounted for [≥]75% of clones in both biofilms. Sulfate-reducing and sulfur-disproportionating {delta}-proteobacterial sequences in the clone libraries were abundant and diverse (34% of phylotypes). Biofilm samples of both types were later collected at the same location and at an additional sample site in Ramo Sulfureo and examined, using fluorescence in situ hybridization (FISH). The biomass of all six stream biofilms was dominated by filamentous {gamma}-proteobacteria with Beggiatoa-like and/or Thiothrix-like cells containing abundant sulfur inclusions. The biomass of {varepsilon}-proteobacteria detected using FISH was consistently small, ranging from 0 to less than 15% of the total biomass. Our results suggest that S cycling within the stream biofilms is an important feature of the cave biogeochemistry. Such cycling represents positive biological feedback to sulfuric acid speleogenesis and related processes that create subsurface porosity in carbonate rocks

Modle dvolution de paysages, application aux karsts en cockpit de Jamaque, 2007, Fleurant Cyril , Tucker Gregory, Viles Heather
LANDSCAPE EVOLUTION MODEL, EXAMPLE OF COCKPIT KARST TERRAINS, JAMAICA. A model of cockpit karst landscape evolution is presented. After explaining implementation of dissolution processes of limestone in the landscape evolution model CHILD, we develop a model of limestone denudation based on epikarst theory processes. The model takes into account an anisotropic dissolution in space and time according to what is observed in reality or described by scenarios of cockpit karst landscape evolution. This model requires a fractures network to take into account subsurface flow. Then, dissolution and thus fractures widening are computed and show a positive feedback between dissolution and flow. The relation between subcutaneous dissolution of fractures and denudation of the topography is introduced by means of an empirical equation associated with epikarst processes: the denudation is taken to be proportional to the dissolution in the subcutaneous zone. Simulated cockpit karst terrains are compared with real landscapes by means of morphometric criteria. Results of the model are very close to reality which hence confirms the importance of anisotropic dissolution processes and above all could be a numerical validation of the epikarst processes to describe cockpit karst genesis.

Hypogene Speleogenesis: Hydrogeological and Morphogenetic Perspective., 2007, Klimchouk A. B.

This book provides an overview of the principal environments, main processes and manifestations of hypogenic speleogenesis, and refines the relevant conceptual framework. It consolidates the notion of hypogenic karst as one of the two major types of karst systems (the other being epigenetic karst). Karst is viewed in the context of regional groundwater flow systems, which provide the systematic transport and distribution mechanisms needed to produce and maintain the disequilibrium conditions necessary for speleogenesis. Hypogenic and epigenic karst systems are regularly associated with different types, patterns and segments of flow systems, characterized by distinct hydrokinetic, chemical and thermal conditions. Epigenic karst systems are predominantly local systems, and/or parts of recharge segments of intermediate and regional systems. Hypogenic karst is associated with discharge regimes of regional or intermediate flow systems.

Various styles of hypogenic caves that were previously considered unrelated, specific either to certain lithologies or chemical mechanisms are shown to share common hydrogeologic genetic backgrounds. In contrast to the currently predominant view of hypogenic speleogenesis as a specific geochemical phenomenon, the broad hydrogeological approach is adopted in this book. Hypogenic speleogenesis is defined with reference to the source of fluid recharge to the cave-forming zone, and type of flow system. It is shown that confined settings are the principal hydrogeologic environment for hypogenic speleogenesis. However, there is a general evolutionary trend for hypogenic karst systems to lose their confinement due to uplift and denudation and due to their own expansion. Confined hypogenic caves may experience substantial modification or be partially or largely overprinted under subsequent unconfined (vadose) stages, either by epigenic processes or continuing unconfined hypogenic processes, especially when H2S dissolution mechanisms are involved.

Hypogenic confined systems evolve to facilitate cross-formational hydraulic communication between common aquifers, or between laterally transmissive beds in heterogeneous soluble formations, across cave-forming zones. The latter originally represented low-permeability, separating units supporting vertical rather than lateral flow. Layered heterogeneity in permeability and breaches in connectivity between different fracture porosity structures across soluble formations are important controls over the spatial organization of evolving ascending hypogenic cave systems. Transverse hydraulic communication across lithological and porosity system boundaries, which commonly coincide with major contrasts in water chemistry, gas composition and temperature, is potent enough to drive various disequilibrium and reaction dissolution mechanisms. Hypogenic speleogenesis may operate in both carbonates and evaporites, but also in some clastic rocks with soluble cement. Its main characteristic is the lack of genetic relationship with groundwater recharge from the overlying or immediately adjacent surface. It may not be manifest at the surface at all, receiving some expression only during later stages of uplift and denudation. In many instances, hypogenic speleogenesis is largely climate- independent.

There is a specific hydrogeologic mechanism inherent in hypogenic transverse speleogenesis (restricted input/output) that suppresses the positive flow-dissolution feedback and speleogenetic competition in an initial flowpath network. This accounts for the development of more pervasive channeling and maze patterns in confined settings where appropriate structural prerequisites exist. As forced-flow regimes in confined settings are commonly sluggish, buoyancy dissolution driven by either solute or thermal density differences is important in hypogenic speleogenesis.

In identifying hypogenic caves, the primary criteria are morphological (patterns and meso-morphology) and hydrogeological (hydrostratigraphic position and recharge/flow pattern viewed from the perspective of the evolution of a regional groundwater flow system). Elementary patterns typical for hypogenic caves are network mazes, spongework mazes, irregular chambers and isolated passages or crude passage clusters. They often combine to form composite patterns and complex 3- D structures. Hypogenic caves are identified in various geological and tectonic settings, and in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in cave patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Presence of the characteristic morphologic suites of rising flow with buoyancy components is one of the most decisive criteria for identifying hypogenic speleogenesis, which is much more widespread than was previously presumed. Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world.

The refined conceptual framework of hypogenic speleogenesis has broad implications in applied fields and promises to create a greater demand for karst and cave expertise by practicing hydrogeology, geological engineering, economic geology, and mineral resource industries. Any generalization of the hydrogeology of karst aquifers, as well as approaches to practical issues and resource prospecting in karst regions, should take into account the different nature and characteristics of hypogenic and epigenic karst systems. Hydraulic properties of karst aquifers, evolved in response to hypogenic speleogenesis, are characteristically different from epigenic karst aquifers. In hypogenic systems, cave porosity is roughly an order of magnitude greater, and areal coverage of caves is five times greater than in epigenic karst systems. Hypogenic speleogenesis commonly results in more isotropic conduit permeability pervasively distributed within highly karstified areas measuring up to several square kilometers. Although being vertically and laterally integrated throughout conduit clusters, hypogenic systems, however, do not transmit flow laterally for considerable distances. Hypogenic speleogenesis can affect regional subsurface fluid flow by greatly enhancing initially available cross- formational permeability structures, providing higher local vertical hydraulic connections between lateral stratiform pathways for groundwater flow, and creating discharge segments of flow systems, the areas of low- fluid potential recognizable at the regional scale. Discharge of artesian karst springs, which are modern outlets of hypogenic karst systems, is often very large and steady, being moderated by the high karstic storage developed in the karstified zones and by the hydraulic capacity of an entire artesian system. Hypogenic speleogenesis plays an important role in conditioning related processes such as hydrothermal mineralization, diagenesis, and hydrocarbon transport and entrapment.

An appreciation of the wide occurrence of hypogenic karst systems, marked specifics in their origin, development and characteristics, and their scientific and practical importance, calls for revisiting and expanding the current predominantly epigenic paradigm of karst and cave science.


Hydrodynamic aspect of caves, 2008, Prelovek M. , Turk J. And Gabrovek F.
From a hydrological point of view, active caves are a series of connected conduits which drain water through an aquifer. Water tends to choose the easiest way through the system but different geological and morphological barriers act as flow restrictions. The number and characteristics of restrictions depends on the particular speleogenetic environment, which is a function of geological, geomorphological, climatological and hydrological settings. Such a variety and heterogeneity of underground systems has presented a challenge for human understanding for many centuries. Access to many underground passages, theoretical knowledge and recent methods (modeling, water pressure-resistant dataloggers, precise sensors etc.) give us the opportunity to get better insight into the hydrodynamic aspect of caves. In our work we tried to approach underground hydrodynamics from both theoretical and practical points of view. We present some theoretical background of open surface and pressurized flow in underground rivers and present results of some possible scenarios. Moreover, two case studies from the Ljubljanica river basin are presented in more detail: the cave system between Planinsko polje and Ljubljansko barje, and the cave system between Bloko polje and Cerkniko polje. The approach and methodology in each case is somewhat different, as the aims were different at the beginning of exploration. However, they both deal with temporal and spatial hydrodynamics of underground waters. In the case of Bloko polje-Cerkniko polje system we also explain the feedback loop between hydrodynamics and Holocene speleogenesis.

Conduit evolution in deep-seated settings: Conceptual and numerical models based on field observations, 2008, Rehrl C. , Birk S. , Klimchouk A. B.

To examine the interrelation between hydrogeological environment and conduit development in deep-seated settings, a conceptual model is tested by numerical modeling. Based on field observations, simplified model settings are designed and crucial parameters are varied. A coupled continuum-pipe flow model is employed for simulating conduit development within the soluble unit of a multilayer aquifer system. In agreement with field observations, the evolving cave patterns are characterized by pronounced horizontal passages and multiple vertical conduits at the bottom of the soluble unit but only few at the top. The frequency distribution of conduit diameters is found to be bimodal if the permeability of the rock formation is sufficiently high to allow competitive conduit development governed by the feedback between increasing flow and dissolution rates. This feedback, however, is suppressed in low-permeability formations. As a consequence, conduit development is uniform rather than competitive.


Alteration of fractures by precipitation and dissolution in gradient reaction environments: Computational results and stochastic analysis, 2008, Chaudhuri A. , Rajaram H. , Viswanathan H.

Precipitation and dissolution reactions within fractures alter apertures, which in turn affects their flow and transport properties. Different aperture alteration patterns occur in different flow and reaction regimes, and they are also influenced by preferential flow resulting from spatial variations in the aperture. We consider the alteration of variable-aperture fractures in gradient reaction regimes, where fluids are in chemical equilibrium with a mineral everywhere but precipitation and dissolution are driven by solubility gradients associated with temperature variations. The temperature field is defined by a geothermal gradient corresponding to a conduction-dominated heat transfer regime. Monte Carlo simulations on computer-generated aperture fields vividly illustrate pattern formation resulting from two-way feedback between fluid flow and reactive alteration. In dissolution-controlled systems, distinct dissolution channels develop along the dominant flow direction, while elongated precipitate bodies form perpendicular to the mean flow direction in precipitation-controlled systems. Aperture variability accelerates the increase and decrease of effective transmissivity by dissolution and precipitation, respectively. The dominance of precipitation versus dissolution is determined by the angle between the mean hydraulic gradient and solubility/temperature gradient. Development of pronounced anisotropy with oriented elongate features is the key feature of aperture alteration in gradient reaction regimes. A stochastic analysis is developed, which consistently predicts general trends in the aperture field during reactive alteration, including the mean, variance, and spatial covariance structure. Our results are relevant to understanding the long-term diagenetic evolution of fractures in conduction-dominated heat transfer regimes and related problems such as emplacement of ocean bed methane hydrates.


Hydrodynamic aspect of caves, 2008, Prelovek M. , Turk J. , Gabrovek F.

From a hydrological point of view, active caves are a series of connected conduits which drain water through an aquifer. Water tends to choose the easiest way through the system but different geological and morphological barriers act as flow restrictions. The number and characteristics of restrictions depends on the particular speleogenetic environment, which is a function of geological, geomorphological, climatological and hydrological settings. Such a variety and heterogeneity of underground systems has presented a challenge for human understanding for many centuries. Access to many underground passages, theoretical knowledge and recent methods (modeling, water pressure-resistant dataloggers, precise sensors etc.) give us the opportunity to get better insight into the hydrodynamic aspect of caves. In our work we tried to approach underground hydrodynamics from both theoretical and practical points of view. We present some theoretical background of open surface and pressurized flow in underground rivers and present results of some possible scenarios. Moreover, two case studies from the Ljubljanica river basin are presented in more detail: the cave system between Planinsko polje and Ljubljansko barje, and the cave system between Bloško polje and Cerkniško polje. The approach and methodology in each case is somewhat different, as the aims were different at the beginning of exploration. However, they both deal with temporal and spatial hydrodynamics of underground waters. In the case of Bloško polje-Cerkniško polje system we also explain the feedback loop between hydrodynamics and Holocene speleogenesis.


PRINCIPAL FEATURES OF HYPOGENE SPELEOGENESIS, 2009, Klimchouk A. B.

Hypogenic and hypergenic (epigenic) karst systems are regularly associated with different types, patterns and segments of flow systems, which are characterized by distinct hydrokinetic, chemical and thermal conditions. Epigenic karst systems, which had long been the focus of most karst/speleogenetic research, are predominantly local systems receiving recharge from the overlying or immediately adjacent surface. Hypogenic karst is associated with discharge regimes of regional or intermediate flow systems dominated by upward flow, although mixing with local systems is commonly involved. Hypogenic speleogenesis tends to operate over long time spans, continuously or intermittently. Its main characteristic is the lack of genetic relationship with groundwater recharge from the overlying or immediately adjacent surface. Hypogenic karst may not be expressed at the surface and is largely climate-independent. Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending through a cave-forming zone from below. It develops in leaky confined conditions although it may continue through unconfined ones. Vertical hydraulic communication across lithological boundaries and different porosity systems allows deeper groundwaters in regional or intermediate flow systems to interact with shallower and more local systems, permitting a variety of dissolution mechanisms. There is a specific hydrogeologic mechanism inherent in hypogenic transverse speleogenesis (restricted input/output) that suppresses the positive flow-dissolution feedback and speleogenetic competition seen in the development of initial flowpath networks in hypergene cave genesis, accounting for the more uniform and pervasive conduit development found in the hypogene. Hypogenic caves are found in a wide range of geological and tectonic settings, basinal through folded, being formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, the resulting caves tend to display remarkable similarity in their patterns and meso-morphology, strongly suggesting that the type of ?ow system is the primary control. Hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising ?ow across the cave-forming zone, with distinct buoyancy dissolution components. Cave patterns in hypogenic speleogenesis are guided by the initial permeability structure, its vertical heterogeneities (discordance in the permeability structure between adjacent beds) and the mode of water input to, and output from, the cave-forming zone. The latter again depends on relationships between permeability structures in the cave-forming zone and formations that lie below and above. Because of its “transverse flow” nature hypogenic speleogenesis has a clustered distribution in plan view, although initial clusters may merge during further development and extend over considerable areas. Recognition of the wide occurrence, significance and specific characteristics of hypogenic speleogenesis represents a major paradigm shift in karst science that answers many questions not satisfactorily addressed previously.


On the essence of karst, 2010, Klimchouk, O. B. , Andreychouk, V. N.

The long-lasting uncertainty with the central for karstology notion of karst hinders synthesis of knowledge and the development of a theoretical basis of this scientific discipline. This paper analyses the essence of karst, based on generalization of the modern ideas about regularities of the origin and evolution of conduit permeability in soluble rocks, viewed in the light of ideas of synergetics and non-equilibrium thermodynamics of I.P.Prigogine regarding self-organization in open systems and formation of ordered dissipative structures.

The presence of soluble rocks in the sedimentary environment determines a phenomena of self-organization of the flow structure, which brings the water-rock system into a new capacity-state, namely karstic. The property of self-organization of this geosystem realizes via specific (speleogenetic) mechanism of permeability development, which action radically changes (organizes in a special manner) the structure and functioning of the flow system.

The mechanism of self-organization of flow and of the formation of the karst geosystem (speleogenesis) includes: 1) early speleogenesis, positive feedback between flow and the rate of enlargement of initial flow paths (revealing of proto-conduits), 2) speleogenetic initiation: a cascade breakthroughs of proto-conduits to the condition of rapid dissolution kinetics, with accelerated growth of initiated conduits, hydrodynamic competition, respective destabilization and reorganization of the flow pattern and change in boundary conditions, and, 3) speleogenetic development: stabilization of the system at dynamic equilibrium at the expense of increased energy exchange with the environment, and further growth of conduits. As a result of this specific evolution the geosystem acquires new, karstic, capacity and more complex of organization, with the establishment of one more level of permeability, the most contrast one.

The notion of karst is derived from the essence of progressive evolution of the geosystem containing permeable soluble rocks, driven by water exchange and speleogenetic mechanism of self-organization of the permeability structure. Regressive evolution of the karst geosystem includes processes of gravitational destruction and various accumulations, which lead to fragmentation and demolition of relict structures of karst permeability. Based on this new approach to definition of the notion of karst, criteria of distinction between proper karst and similar but not identical phenomena (merokarst, pseudokarst) are discussed.


Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers, 2011, Hubinger B. , Birk S.

Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete pathways along fractures or bedding planes, thus creating highly conductive solution conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving conduit systems the aperture-size frequency distributions resulting from generic models of conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoconduits are represented by tubes with log-normally distributed aperture sizes with a mean of 0.5 mm. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a conduit pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a conduit pathway is inhibited and the conduit pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that conduit development under suppressed flow conditions may significantly enhance the permeability of the formation e.g. in deep-seated carbonate settings.


The significance of turbulent flow representation in single-continuum models, 2011, Reimann T. , Rehrl C. , Shoemaker W. B. , Geyer T. , Birk S.

Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete pathways along fractures or bedding planes, thus creating highly conductive solution conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving conduit systems the aperture-size frequency distributions resulting from generic models of conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoconduits are represented by tubes with log-normally distributed aperture sizes with a mean ?0 = 0.5 mm for the logarithm of the diameters. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a conduit pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a conduit pathway is inhibited and the conduit pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that conduit development under suppressed flow conditions may significantly enhance the permeability of the formation, e.g. in deep-seated carbonate settings.


Computational Investigation of Fundamental Mechanisms Contributing to Fracture Dissolution and the Evolution of Hypogene Karst Systems, 2011, Chaudhuri A. , Rajaram H. , Viswanathan H. S. , Zyvoloski G. , Stauffer P. H.

Hypogene karst systems evolve by dissolution resulting from the cooling of water flowing upward against the geothermal gradient in limestone formations. We present a comprehensive coupled-process model of fluid flow, heat transfer, reactive transport and buoyancy effects to investigate the origin of hypogene karst systems by fracture dissolution. Our model incorporates the temperature and pressure dependence of the solubility and dissolution kinetics of calcite. Our formulation inherently incorporates mechanisms such as “mixing corrosion” that have been implicated in the formation of hypogene cave systems. It also allows for rigorous representation of temperature-dependent fluid density and its consequences at various stages of karstification. The model is applied to investigate karstification over geological time scales in a network of faults/fractures that serves as a vertical conduit for upward flow. We considered two different conceptual hydrogeologic models. In the first model, the upward flow is controlled by a constant pressure gradient. In the second model, the flow is induced by topographic effects in a mountainous hydrologic system. During the very early stages of fracture growth, there is a positive feedback between fluid flow rate, heat transfer and dissolution. In this stage the dissolution rate is largely controlled by the retrograde solubility of calcite and aperture growth occurs throughout the fracture. For the first model, there is a period of slow continuous increase in the mass flow rate through the fracture, which is followed by an abrupt rapid increase. We refer to the time when this rapid increase occurs as the maturation time. For the second model of a mountainous hydrologic system, the fluid flux through the fracture remains nearly constant even though the fracture permeability and aperture increase. This is largely because the permeability of the country rock does not increase significantly. While this limits the fluid flux through the system, it does not impede karstification. At later stages, forced convection and buoyant convection effects arise in both models due to the increased permeability of the evolving fracture system. Our results suggest that there is s strong tendency for buoyant convection cells to form under a wide range of conditions. A modified Rayleigh number provides a unified quantitative criterion for the onset of buoyant convection across all cases considered. Once buoyant convection cells are set up, dissolution is sustained in the upward flow portions of the cells, while precipitation occurs in the regions of downward flow. We discuss the implications of this type of flow pattern for the formation of hot springs and mazework caves, both of which are characteristic of hypogene karst environments. We also investigate the sensitivity of karst evolution to various physical and geochemical factors.


A holistic approach to groundwater protection and ecosystem services in karst terrains, 2012, Goldscheider, Nico

A holistic conceptual approach to groundwater and natural resources protection, surface and subsurface biodiversity conservation and ecosystem services in karst terrains is presented. Karst landscapes and aquifers consist of carbonate rock in which a part of the fractures has been enlarged by chemical dissolution. They are characterised by unique geomorphological and hydrogeological features, such as rapid infiltration of rainwater, lack of surface waters, and turbulent flow in a network of fractures, conduits and caves. Karst terrains contain valuable but vulnerable resources, such as water, soil and vegetation, and they provide a great variety of habitats to many species, both at the surface and underground, including many rare and endemic species. Karst systems deliver various ecosystem services and act as natural sinks for carbon dioxide (CO2) thus helping to mitigate climate change. It is demonstrated that all these resources and ecosystem services cannot be considered in an isolated way but are intensely interconnected. Because of these complex feedback mechanisms, impacts on isolated elements of the karst ecosystem can have unexpected impacts on other elements or even on the entire ecosystem. Therefore, the protection of natural resources, biodiversity and ecosystem services in karst requires a holistic approach


A holistic approach to groundwater protection and ecosystem services in karst terrains, 2012, Goldscheider, Nico

A holistic conceptual approach to groundwater and natural resources protection, surface and subsurface biodiversity conservation and ecosystem services in karst terrains is presented. Karst landscapes and aquifers consist of carbonate rock in which a part of the fractures has been enlarged by chemical dissolution. They are characterised by unique geomorphological and hydrogeological features, such as rapid infiltration of rainwater, lack of surface waters, and turbulent flow in a network of fractures, conduits and caves. Karst terrains contain valuable but vulnerable resources, such as water, soil and vegetation, and they provide a great variety of habitats to many species, both at the surface and underground, including many rare and endemic species. Karst systems deliver various ecosystem services and act as natural sinks for carbon dioxide (CO2) thus helping to mitigate climate change. It is demonstrated that all these resources and ecosystem services cannot be considered in an isolated way but are intensely interconnected. Because of these complex feedback mechanisms, impacts on isolated elements of the karst ecosystem can have unexpected impacts on other elements or even on the entire ecosystem. Therefore, the protection of natural resources, biodiversity and ecosystem services in karst requires a holistic approach.


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