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. ...

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,

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. ...

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 driphole is 1. hole in rock or clay produced by fast-dripping water. 2. hollow space surrounded by precipitated material, such as the bottom of a stalactite [10].?

Most concepts of conduit development have focused on telogenetic karst aquifers, where low matrix permeability focuses flow and dissolution along joints, fractures, and bedding planes. However, conduits also exist in eogenetic karst aquifers, despite high matrix permeability which accounts for a significant component of flow. This study investigates dissolution within a 6-km long conduit system in the eogenetic Upper Floridan aquifer of north-central Florida that begins with a continuous source of allogenic recharge at the Santa Fe River Sink and discharges from a first-magnitude spring at the Santa Fe River Rise. Three sources of water to the conduit include the allogenic recharge, diffuse recharge through epikarst, and mineralized water upwelling from depth. Results of sampling and inverse modeling using PHREEQC suggest that dissolution within the conduit is episodic, occurring only during 30% of 16 sampling times between March 2003 and April 2007. During low flow conditions, carbonate saturated water flows from the matrix to the conduit, restricting contact between undersaturated allogenic water with the conduit wall. When gradients reverse during high flow conditions, undersaturated allogenic recharge enters the matrix. During these limited periods, estimates of dissolution within the conduit suggest wall retreat averages about 4 × 10−6 m/day, in agreement with upper estimates of maximum wall retreat for telogenetic karst. Because dissolution is episodic, time-averaged dissolution rates in the sink-rise system results in a wall retreat rate of about 7 × 10−7 m/day, which is at the lower end of wall retreat for telogenetic karst. Because of the high permeability matrix, conduits in eogenetic karst thus enlarge not just at the walls of fractures or pre-existing conduits such as those in telogenetic karst, but also may produce a friable halo surrounding the conduits that may be removed by additional mechanical processes. These observations stress the importance of matrix permeability in eogenetic karst and suggest new concepts may be necessary to describe how conduits develop within these porous rocks.

Mixtures of two saturated H2O/1bCO2/1bCaCO3 solutions of different chemical composition gain renewed capability of dissolving calcite. This is an important mechanism in the solution processes of limestone during karstification. Using recent data on the kinetics of calcite dissolution, dissolution rates in mixture corrosion are calculated. In the region of the chemical composition of natural karst waters the solution rate is approximated by:R=-[alpha]([Ca2] - [Ca2]s where [Ca2], [Ca2]s are the concentrations of the Ca2 ion in the solution and at saturation, respectively. [alpha] ranges from 10-4 to 3[middle dot]10-4 cm s-1.This result is applied to the solution of limestone in karst water mixtures flowing in cylindrical conduits. The saturation length, i.e. the length xs which the solution has to travel to drop to 37% of its renewed dissolving capability, is calculated in the region of turbulent flow. This region starts at conduit radii R of several millimeters. At the onset of turbulent flow the saturation length is 260 m, increasing with R1.665. The increase of conduit radii is calculated from the dissolution rates of calcite solution to be on the order of 10-3 cm yr.-1.The results are discussed for a comprehensive model of karstification and cave development, which for the first time gives a realistic theoretical time region for cave development, in agreement to experience

Limestone caves form along ground-water paths of greatest discharge and solutional aggressiveness. Flow routes that acquire increasing discharge accelerate in growth, while others languish with negligible growth. As discharge increases, a maximum rate of wall retreat is approached, typically about 0.01-0.1 cm/yr, determined by chemical kinetics but nearly unaffected by further increase in discharge. The time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width, discharge, gradient, and P(CO2). Most caves require 10(4) - 10(5) yr to reach traversable size. Their patterns depend on the mode of ground-water recharge. Sinkhole recharge forms branching caves with tributaries that join downstream as higher-order passages. Maze caves form where (1) steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or (2) discharge or renewal of undersaturation is uniform along many alternate routes. Flood water can form angular networks in fractured rock, anastomotic mazes along low-angle partings, or spongework where intergranular pores are dominant. Diffuse recharge also forms networks and spongework, often aided by mixing of chemically different waters. Ramiform caves, with sequential outward branches, are formed mainly by rising thermal or H2S-rich water. Dissolution rates in cooling water increase with discharge, CO2 content, temperature, and thermal gradient, but only at thermal gradients of more than 0.01-degrees-C/m can normal ground-water CO2 form caves without the aid of hypogenic acids or mixing. Artesian flow has no inherent tendency to form maze caves. Geologic structure and stratigraphy influence cave orientation and extent, but alone they do not determine branch-work versus maze character

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated nonstoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25-degrees-C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer approximately 60 angstrom on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer approximately 25 angstrom (as much as 26 mol% SrCO3 on aragonite and 44 mol% CaCO3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO3)2) than in solutions spiked with the more soluble component (Ca(HCO3)2), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a nonstoichiometric surface reactive zone significantly decreases dissolution rates

The geochemistry of regional groundwater flow along the Aladag karstic aquifer indicates a remarkable correlation between the hydraulic and geochemical conditions. The Aladag. karstic aquifer, in between the recharge area and the regional ero¬sion base, comprises unconfined and confined sections. A transition zone along which semi-confined flow conditions dominate also occurs between these sections. The parts of the aquifer in which unconfined and confined flow conditions dominate seem to be anal¬ogous of geochemically open and closed systems of carbonate dissolution, respectively. The varition of physical and chemical properties of the karstic effluents implies that although the carbonate dissolution is perpetual along the flow system, dissolution rates decrease where confined flow conditions start to prevail. However, gypsum dissolution along the regional flow path seems to be independent of hydraulic conditions.

Dissolution of CaCO3 in the system H2O-CO2-CaCO3 is controlled by three rate-determining processes: The kinetics of dissolution at the mineral surface, mass transport by diffusion, and the slow kinetics of the reaction H2O CO2 = H HCO3-. A theoretical model of Buhmann and Dreybrodt (1985a,b) predicts that the dissolution rates depend critically on the ratio V/A of the volume V of the solution and the surface area A of the reacting mineral. Experimental data verifying these predictions for stagnant solutions have been already obtained in the range 0.01 cm < V/A < 0.1 cm. We have performed measurements of dissolution rates in a porous medium of sized CaCO3 particles for V/A in the range of 2 . 10(-4) cm and 0.01 cm in a system closed with respect to CO2 using solutions pre-equilibrated with an initial partial pressure of CO2 of 1 . 10(-2) and 5 . 10(-2) atm. The results are in satisfactory agreement with the theoretical predictions and show that especially for V/A < 10(-3) cm dissolution is controlled entirely by conversion of CO2 into H and HCO3-, whereas in the range from 10(-3) cm up to 10(-1) cm both CO2-conversion and molecular diffusion are the rate controlling processes. This is corroborated by performing dissolution experiments using 0.6 mu molar solutions of carbonic anhydrase, an enzyme enhancing the CO2-conversion rates by several orders of magnitude. In these experiments CO2 conversion is no longer rate limiting and consequently the dissolution rates of CaCO3 increase significantly. We have also performed batch experiments at various initial pressures of CO2 by stirring sized calcite particles in a solution with V/A = 0.6 cm and V/A = 0.038 cm. These data also clearly show the influence of CO2-conversion on the dissolution rates. In all experiments inhibition of dissolution occurs close to equilibrium. Therefore, the theoretical predictions are valid for concentrations c less than or equal to 0.9 c(eq). Summarising we find good agreement between experimental and theoretically predicted dissolution rates. Therefore, the theoretical model can be used with confidence to find reliable dissolution rates from the chemical composition of a solution for a wide field of geological applications

Numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior. If the lengths of the fractures are large and hydraulic heads are low, as is the case in nature, dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow, which after a long gestation time by positive feedback accelerates dramatically within a short time span. Mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time, when this happens, in excellent agreement with the results of a numerical model. This expression quantifies the geometrical, hydraulic, and chemical parameters determining such karat processes. If the lengths of the enlarging channels are small, but hydraulic heads are high, as is the case for artificial hydraulic structures such as darns, it is the widening at the entrance of the flow path which determines the enlargement of the conduit. Within the lifetime of the dam this can cause serious water losses, This can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged. Thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems. As a further important result, one finds that minimum conditions, below which karstification cannot develop, do not exist

Experiments with gypsum in aqueous solutions at 25 degrees C, low ionic strengths, and a range of saturation states indicate a mixed surface reaction and diffusional transport control of gypsum dissolution kinetics. Dissolution rates were determined in a mixed flow/rotating disc reactor operating under steady-state conditions, in which polished gypsum discs were rotated at constant speed and reactant solutions were continuously fed into the reactor. Rates increase with velocity of spin under laminar conditions (low rates of spin), but increase asymptotically to a constant rate as turbulent conditions develop with increasing spin velocity, experiencing a small jump in magnitude across the laminar-turbulent transition. A Linear dependence of rates on the square root of spin velocity in the laminar regime is consistent with rates being limited by transport through a hydrodynamic boundary layer. The increase in rate with onset of turbulence accompanies a near discontinuous drop in hydrodynamic boundary layer thickness across the transition. A relative independence of rates on spinning velocity in the turbulent regime plus a nonlinear dependence of rates on saturation state are factors consistent with surface reaction control. Together these behaviors implicate a 'mixed' transport and reaction control of gypsum dissolution kinetics. A rate law which combines both kinetic mechanisms and can reproduce experimental results under laminar flow conditions is proposed as follows: R = k(t) {1 - Omega(b)() zeta [1 - (1 2(1 - Omega(b)())(1/2)]} where k(t) is the rate coefficient for transport control, and Omega(b)() is the mean ionic saturation state of the bulk fluid. The dimensionless parameter zeta(=Dm(eq)()/2 delta k() where m(eq)() = mean ionic molal equilibrium concentration, D is the diffusion coefficient through the hydrodynamic boundary layer, delta equals the boundary layer thickness and k() is the rate constant for surface reaction control) indicates which process, transport or surface reaction, dominates, and is sensitive to the hydrodynamic conditions in the reactor. For the range of conditions used in our experiments, zeta varies from about 1.4 to 4.5. Rates of gypsum dissolution were also determined in situ in a cavern system in the Permian Blaine Formation, southwestern Oklahoma. Although the flow conditions in the caverns were not determinable, there is good agreement between lab- and field-determined rates in that field rate magnitudes lie within a range of rates determined experimentally under zero to low spin velocities A numerical model coupling fluid flow and gypsum reaction in an idealized circular conduit is used to estimate the distance which undersaturated solutions will travel into small incipient conduits before saturation is achieved. Simulations of conduit wall dissolution showed-member behaviors of conduit formation and surface denudation that depend on flow boundary conditions (constant discharge or constant hydraulic gradient and initial conduit radius. Surface-control of dissolution rates. which becomes more influential with higher fluid flow velocity, has the effect that rate decrease more slowly as saturation is approached than otherwise would occur if rates were controlled by transport alone. This has the effect that reactive solutions can penetrate much farther into gypsum-bearing karst conduits than heretofore thought possible, influencing timing and mechanism of karst development as well as stability of engineered structures above karst terrain

The development of cave systems in carbonate rocks depends on a variety of boundary and initial conditions. Among the cave systems, two main types of geometries can be distinguished: the dendritic and maze pattern. A numerical model has been developed capable of modeling the genesis of karst systems in complex geological environments. It is applied to simulate the development of the above mentioned two different types of cave geometries. The results confirm that a prerequisite for the development of maze caves is evenly distributed recharge (White 1969). However more important for the development of maze caves is that flow through the system is restricted by an overlying less conductive horizon, e.g. a sandstone caprock. Thus the feed back mechanism of higher flow rates leading to higher dissolution rates and therefore the preferential development of a small number of tubes does not dominate the evolution of the karst aquifer. This hydraulic restriction furthers the development of other conduits also to achieve a significant diameter.

Two-dimensional nets of initial fractures are constructed on a square-lattice by occupying the lines between nearest neighbour sites by a water leading fissure of width a"SUBo" and length l with an occupation probability p. For p > 0.5 percolating nets occur which lead water. To simulate cave genesis we calculate the water flow rates driven by the hydraulic head h through all fissures. By employing nonlinear dissolution rates of the type F=k"SUBn"(l-c/c"SUBeq")'"SUPn" the widening of the fractures is obtained. At the onset of karstification flow is evenly distributed on all fractures. As the system develops solutional widing creates preferred pathways, which attract more and more flow, until at breakthrough both widening and flow increase dramatically. We discuss the evolution of karst aquifers for natural conditions and also upon human impact at dam sites where steep hydraulic gradients may generate water leading conduits below the dam in times comparable to the lifetime of the structure.

Dissolution rates of single calcite crystals, limestones, and compressed calcite powders were determined from sample weight loss using free-drift rotating disk techniques. Experiments were performed in aqueous HCl solutions over the bulk solution pH range -1 to 3, and at temperatures of 25 degrees, 50 degrees, and 80 degrees C. Corresponding rates of the three different sample types are identical within experimental uncertainty. Interpretation of these data using equations reported by Gregory and Riddiford [Gregory, D.P., Riddiford, A.C., 1956. Transport to the surface of a rotating disc. J. Chem. Sec. London 3, 3756-3764] yields apparent rate constants and H diffusion coefficients. The logarithms of overall calcite dissolution rates (r) obtained at constant disk rotation speed are inversely proportional to the bulk solution pH, consistent with r = k(2') a(H,b), where k(2)' stands for an apparent rate constant and a(H,b) designates the hydrogen ion activity in the bulk solution, This variation of dissolution rates with pH is consistent with corresponding rates reported in the literature and the calcite dissolution mechanism reported by Wollast [Wollast, R., 1990. Rate and mechanism of dissolution of carbonates in the system CaCO3-MgCO3. In: Stumm, W. (Ed.), Aquatic Chemical Kinetics. Wiley, pp. 431-445]. Apparent rate constants for a disk rotation speed of 340 rpm increase from 0.07 0.02 to 0.25 0.02 mol m(-2) s(-1) in response to increasing temperature from 25 degrees to 80 degrees C. H diffusion coefficients increase from (2.9 to 9.2) x 10(-9) m(2) s(-1) over this temperature range with an apparent activation energy of 19 kJ mol(-1). (C) 1998 Elsevier Science B.V. All rights reserved

Comparison of field- and laboratory-derived rates of chemical weathering is generally regarded as unsatisfactory. However, laboratory dissolution rates for calcite derived under realistic conditions which simulate the field situation compare well with field rates of measured limestone erosion, provided appropriate adjustments are made for periods of wetting. For physical and biological weathering there are far fewer field and laboratory studies available, and the range of different processes and process interactions makes comparisons difficult. However, period of wetting seems also to be a vital factor in more realistic comparisons between laboratory and field results. Experiments and field observations that look at the combined action of chemical physical and biological weathering are increasingly required

The relative dissolution kinetics of the Lirio Limestone and the Isla de Mona Dolomite were determined by dissolving discs of various samples in CO2 -saturated solutions. Rate curves for carbonate dissolution were determined by monitoring pH and specific conductance as a function of time. Dissolution rates for limestone samples were distinctly higher than rates for dolomite samples but the rate curves had similar shapes. Initial rates for limestones averaged 12.53 mmol m-2 sec-1 compared with 8.53 for dolomite. The limestone rates are comparable with those measured on single crystal calcite but the dolomite rates are higher than rates measured on Paleozoic dolomites. The relative dissolution rates are sufficient to be a factor in explaining the concentration of caves at the limestone/dolomite contact but may not be the only controlling factor