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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. ...

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That soddy karst is see subsoil karst.?

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Your search for aperture variability (Keyword) returned 9 results for the whole karstbase:
Influence of aperture variability on dissolutional growth of fissures in karst formations., 1998, Hanna R. B. , Rajaram H.

Influence of aperture variability on dissolutional growth of fissures in karst formations, 1998, Hanna R. B. , Rajaram H. ,
The influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two-dimensional numerical simulations. The logarithm of the fissure aperture before dissolution begins is modeled as a Gaussian stationary isotropic random field. The initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure (the breakthrough time). The breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field (sigma/mu) increases. In comparing uniform and variable aperture fissures in limestone, the breakthrough time with sigma/mu = 0.1 is about a factor of 2 smaller than that in a uniform fissure. The breakthrough time is reduced by about an order of magnitude with sigma/mu = 2.0. The mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow. Dissolution channels are narrower and more tortuous as sigma/mu. increases. Investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock. In uniform fissures in rapidly dissolving minerals, breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path. However, in variable aperture fissures, breakthrough occurs rapidly because of selective growth along preferential flow channels, which progressively capture larger fractions of the total flow. These results partly explain why conduits develop rapidly in gypsum, although previous one-dimensional studies suggest that conduit growth will not occur

Potential influence of aperture variability on the dissolutional enlargement of fissures, 1999, Rajaram H. , Cheung W. , Hanna B.

Structure, flow, and generalized conductivity scaling in fracture networks, 1999, Margolin G. , Berkowitz B. , Scher H.

We present a three-dimensional (3-D) model of fractures that within the same framework, allows a systematic study of the interplay and relative importance of the two key factors determining the character of flow in the system. The two factors of complexity are () the geometry of fracture plane structure and interconnections and (2) the aperture variability within these planes. Previous models have concentrated on each separately. We introduce anisotropic percolation to model a wide range of fracture structures and networks. The conclusion is that either of these elements, fracture geometry and aperture variability, can give rise to channeled flow and that the interplay between them is especially important for this type of flow. Significant outcomes of our study are (1) a functional relationship that quantifies the dependence of the effective hydraulic conductivity on aperture variability and on the network structure and fracture element density, (2) a relation between aperture variability and the Peclet number, and (3) a basis for a new explanation for the field-length dependence of permeability observed in fractured and heterogeneous porous formations.


Toward a better understanding of fissure growth in karst formations: Investigations from genesis to maturation and the influence of fracture-matrix interactions., 2002, Cheung, Wendy Wai Wan

There has been interest in quantitative modeling of early karstification with the objectives of estimating time-scales of conduit growth and understanding the nature of cave patterns. In particular, the initiation phase has been studied in great detail because it is the slowest phase in the development of caverns. In this study aperture variability in a two-dimensional framework and fracture matrix interaction are studied to better understand their role in time estimations of aperture growth. The initial phase of karst development is studied from its nascent stage as a fissure into the early stages of turbulence. In uniform fissures in rapidly dissolving minerals, the concentration reaches the solubility limit within a short distance along the flow path. However, the variability in the aperture field inherently provides instabilities to the system and growth is propagated along these perturbations. Flow is focused into preferential channels which are enlarged at a faster rate than surrounding regions of slow flow. As a result, a positive feedback mechanism takes place and creates growth in a highly selective manner. Only in large domains (>25 correlation lengths), can the instabilities create competition for flow at the solution front as well and lead to significant branching. It is this branching which creates the non-monotonic behavior in breakthrough times (defined as the point in which turbulent flow is first encountered). It has been observed that the non-monotonic behavior is scale dependent. Smaller domains do not exhibit this behavior because there are only a few correlation lengths between
the fingertip and the lateral domain boundaries. Aperture variability significantly impacts dissolution patterns in a two-dimensional framework. While aperture variability speeds up growth, the inclusion of the porous bedrock can inhibit growth. The porous matrix serving as a large low - conductive reservoir can significantly influence the development of the fracture by slowing down dissolution growth through matrix diffusion. In a one dimensional model, this issue is further explored. Although the focus of the study is on modeling of early karstification, there are many common themes between this problem and other reactive transport problems that this model can be made suitable for exploring.


Dissolution of limestone fractures by cooling waters: Early development of hypogene karst systems, 2005, Andre Bj, Rajaram H,

[1] Fracture dissolution in the early stages of karstification under hypogene conditions is investigated using a coupled numerical model of fluid flow, heat transfer, and reactive transport. Dissolution of calcite in the H2O-CO2-CaCO3 system along a cooling flow path is investigated using both equilibrium and kinetic models. During the very early stages of fracture growth, there is a positive feedback between flow, heat transfer, and dissolution. In this stage the dissolution rate is largely controlled by the retrograde solubility of calcite, and aperture growth is relatively uniform along the fracture length. 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. As the flow rate continues to increase after maturation, forced convective effects lead to higher fluid temperatures in the fracture, resulting in a negative feedback that slows the rate of fracture growth. The behavior of aperture growth before the maturation time can be described by a simple ordinary differential equation. The solution of this differential equation provides an estimate of the maturation time, in terms of the initial aperture, hydraulic and thermal gradients, and the change in solubility with temperature. The behavior before maturation in two-dimensional variable aperture fractures is investigated using a simplified model. The maturation time is shown to decrease with the degree of aperture variability due to highly selective growth along preferential flow paths


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.


SIMULATING THE DEVELOPMENT OF SOLUTION CONDUITS IN HYPOGENE SETTINGS, 2009, Rehrl C. , Birk S. , Klimchouk A. B.

Karst aquifers develop where an enlargement of fractures due to dissolution creates highly permeable conduits. These conduits are embedded in the much less permeable fissured system of the surrounding rock. The hydrogeological characterisation of these heterogeneous, dualistic flow systems requires a deep understanding of the processes involved in karstification. During the last two decades many numerical models have been developed to simulate conduit evolution in karst terrains and to understand and analyze the mechanisms of speleogenesis. In this study, conduit development within a soluble unit of a multi-layer aquifer system is examined by process-based numerical modeling. The dual flow system is adequately represented by a coupled continuum-pipe flow model; the flow model is coupled to a module calculating dissolution rates and the corresponding widening of conduits depending on flow conditions. The simplified model scenarios are largely based on field observations compiled from the gypsum karst terrain of the Western Ukraine. It is demonstrated that the hydraulic conductivity of the rock formation is a crucial factor that controls the frequency distribution of conduit diameters in hypogene speleogenesis. If the permeability of the rock formation is sufficiently high, conduit development is found to be competitive and leads to bimodal aperture distributions. Otherwise flow in low-permeability formations is suppressed and as a consequence, there is a smooth transition from scarcely developed proto-conduits to well-developed conduits rather than a clear and distinct separation. This work further examines the influence of the variability of the initial apertures on dissolutional growth of fissures and the evolving cave patterns. The initial apertures were not spatially correlated and log normally distributed. The influence of the aperture variability was investigated in several scenarios. It is found that in an ensemble average sense the degree of heterogeneity determines the temporal development of the cave patterns, i.e. higher aperture variability generally decelerates the karstification process. The aperture variability, however, appears to be of minor relevance regarding the general structure and geometric properties of the evolving cave patterns.


Influence of initial aperture variability on conduit development in hypogene settings, 2010, Rehrl C. , Birk S. , Klimchouk A. B.

The development of gypsum maze caves in hypogene settings is examined by process-based numerical modelling using a coupled continuum-pipe flow model. The model scenarios are largely based on field observations compiled from the gypsum karst terrain of the Western Ukraine. This area hosts the world\'s largest maze caves in gypsum and provides a well documented example of hypogene speleogenesis under artesian conditions. Building on previous studies that revealed the basic speleogenetic mechanisms in this type of setting, this work aims to examine the influence of the variability of the initial apertures on dissolutional growth of fissures and the evolving cave systems. To this end, the initial apertures were spatially uncorrelated and lognormally distributed and the influence of the coefficient of variation of the aperture data (?/?) was investigated in several scenarios on the basis of a set of four realisations. It is found that a small degree of heterogeneity leads to cave patterns similar to those obtained with uniform initial apertures. However, with increasing heterogeneity the karstification process decelerates and a significant amount of variability between the different realisations follows. In an ensemble average sense, the aperture variability is determining the temporal development of the cave patterns and generally decelerates the karstification process, but appears to be of minor relevance regarding the general structure and geometric properties of the evolving cave patterns.


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