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Community news

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. ...

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 rivulet is a very small stream [16].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms


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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for inversion (Keyword) returned 36 results for the whole karstbase:
Showing 16 to 30 of 36
Recent active faults in Belgian Ardenne revealed in Rochefort Karstic network (Namur Province, Belgium), 2001,
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Vandycke S. , Quinif Y. ,
This paper presents observations of recent faulting activity in the karstic network of the Rochefort Cave (Namur Province, Belgium, Europe). The principal recent tectonic features are bedding planes reactivated as normal faults, neo-formatted normal faults in calcite flowstone, fresh scaling, extensional features, fallen blocks and displacement of karstic tube. The seismotectonic aspect is expanded by the presence of fallen blocks where normally the cavity must be very stable and in equilibrium. Three main N 070degrees fault planes and a minor one affect, at a decimetre scale, the karst features and morphology. The faults are still active because recent fresh scaling and fallen blocks are observable. The breaking of Holocene soda straw stalactites and displacements of artificial features observed since the beginning of the tourist activity, in the last century, also suggest very recent reactivation of these faults. This recent faulting can be correlated to present-day tectonic activity, already evidenced by earthquakes in the neighbouring area. Therefore, karstic caves are favourable sites for the observation and the quantification of recent tectonic activity because they constitute a 3-D framework, protected from erosion. Fault planes with this recent faulting present slickensides. Thus a quantitative analysis in term of stress inversion, with the help of striated faults, has permitted to reconstruct the stress tensor responsible for the brittle deformation. The principal NW-SE extension (sigma(3) horizontal) is nearly perpendicular to that of the present regional stress as illustrated by the analysis of the last strong regional earthquake (Roermond, The Netherlands) in 1992. During the Meso-Cenozoic, the main stress tectonics recorded in this part of the European platform is similar to the present one with a NE-SW direction of extension. The discrepancy between the regional stress field and the local stress in the Rochefort cave can be the result of the inversion of the sigma(2) and sigma(3) axes of the stress ellipsoid due to its symmetry or of a local modification at the ground surface of the crustal stress field as it has been already observed in active zones

The application of Time-Lapse Microgravity for the Investigation and Monitoring of Subsidence at Northwich, Cheshire, 2003,
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Branston Mw, Styles P,
Peter Street is an area of terraced houses in Northwich suffering from subsidence, thought to be related to salt extraction in the 19th century. Microgravity and resistivity profiling have been used as non-invasive techniques to investigate the cause of this subsidence. Repeat (or time-lapse) microgravity has been used to assess the stability and evolution of the low-density areas. Time-lapse microgravity uses the characteristics of anomaly size and gradient to track the development of cavities as they propagate to the surface. It is possible to monitor the change in gravity with time and to model the increase in cavity volume and/or depth. A gravity low was found to be coincident with the area experiencing subsidence. Integratedmodelling techniques including Euler deconvolution, Cordell & Henderson inversion and GRAVMAG modelling have been used to investigate the depth and size of the body responsible for this anomaly. Resistivity imaging has been used to investigate the conductivity of the near surface and constrain the gravity models. Results from both techniques suggest that low density ground is now present at a depth of 3-4 m below the surface in the subsidence affected area. The use of time-lapse microgravity has shown that there has been an upwardmigration of a low-density zone at gravity anomaly C over the monitoring period

Stalagmite growth and palaeo-climate: an inverse approach, 2004,
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Kaufmann G. , Dreybrodt W. ,
The growth of stalagmites is controlled by climatic conditions such as temperature, soil activity, and precipitation. Hence, a stalagmite stratigraphy reflects fluctuations of palaeo-climate conditions on various time scales, from annual variations to ice-age cycles. However, no attempt has been made to infer palaeo-climate fluctuations from the stratigraphy itself We describe the complicated growth of a stalagmite with a simple mathematical model, in which both the growth rate and the equilibrium diameter of stalagmites are functions of palaeo-climate variables. Hence, inverting a given stalagmite stratigraphy in terms of growth rate and equilibrium diameter can in principle recover the palaeo-climate signal. The strongly nonlinear dependence of these two geometrical parameters, however, limits the success of a formal inversion of stratigraphical data. In this paper, we explore the resolving power of both growth rate and equilibrium diameter data for the palaeo-climate signals temperature, carbon-dioxide concentration, and precipitation. We use numerically generated stalagmite stratigraphies as observational data, thus we know beforehand the palaeo-climate signal contained in the stratigraphic record. Our results indicate that both variations in carbon-dioxide concentrations (as a proxy of soil cover) and drip interval (as a proxy of precipitation) can be recovered from the stratigraphy. However, temperature variations are poorly resolved. (C) 2004 Elsevier B.V. All rights reserved

Inversion strategy in crosshole radar tomography using information of data subsets, 2004,
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Becht A, Tronicke J, Appel E, Dietrich P,
Detecting discrete anomalies, such as cavities or tunnels, is an important application of crosshole radar tomography. However, crosshole tomographic inversion results are frequently ambiguous, showing smearing effects and inversion artifacts. These ambiguities lead to uncertainties in interpretation; hence, the size and position of anomalies can only be interpreted with limited accuracy and reliability. We present an inversion strategy for investigating discrete anomalies with crosshole radar tomography. In addition to the full traveltime data set, we use subsets of specified ray-angle intervals for tomographic inversion. By analyzing inversion results from different ray-angle intervals, a more accurate interpretation of anomalies is possible. The second step of our strategy is to develop a good inhomogeneous starting model from joint interpretation of the inversion results from different subsets. The third step is to invert the full data set using this new starting model and to evaluate the inversion results by analyzing the distributions of mean square traveltime residuals with respect to the ray angles. We use a synthetic model with two discrete anomalies located roughly at the same depth to demonstrate and evaluate our approach. This inversion strategy is also applied to a field data set collected to investigate karst cavities in limestone. From the inversion results of both examples, we show that horizontal smearing of anomalies can be reduced by eliminating near-horizontal rays. A good starting model can be obtained based on the joint interpretation of the inversion results of the different subsets; it leads to a high-resolution final image of the full data set

Spatiotemporal analysis of air conditions as a tool for the environmental management of a show cave (Cueva del Agua, Spain), 2006,
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Fernandezcortes A, Calaforra Jm, Sanchezmartos F,
We recorded the air temperature and carbon dioxide concentration within the Cueva del Agua, a cave in Spain, under natural conditions prior to the cave being opened to tourists. Geostatistical tools are useful techniques for characterizing microclimate parameters with the aim of adopting measures to ensure the conservation and sound environmental management of tourist caves. We modelled the spatial distribution of these microclimatic parameters over an annual cycle using iterative residual kriging, revealing the stratification of air related to the cave's topography. Replenishment of the cave air is activated by convective circulation that accompanies the development of inversions in the thermal gradient of the air. Comparison of the spatial distribution of each microclimatic parameter over time enables us to characterize the exchange of air between the cave interior and the outside, as well as identify potential areas that could be opened to tourists and determine suitable visiting schedules

Using 2D inversion of magnetic resonance soundings to locate a water-filled karst conduit, 2006,
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Boucher M, Girard Jf, Legchenko A, Baltassat Jm, Dorfliger N, Chalikakis K,
SummaryA new methodology for magnetic resonance sounding (MRS) data acquisition and interpretation was developed for locating water-filled karst cavities. This methodology was used to investigate the Ouysse karst system in the Poumeyssens shaft in the Causse de Gramat (France). A new 2D numerical MRS response model was designed for improved accuracy over the previous 1D MRS approach. A special survey performed by cave divers confirmed the accuracy of the MRS results. Field results demonstrated that in favourable conditions (a low EM noise environment and a relatively shallow, large target) the MRS method, used with a coincident transmitter/receiver loop, can be an effective tool for locating a water-filled karst conduit. It was shown numerically that because an a priori orientation of the MRS profile with the karst conduit is used in the inversion scheme (perpendicular for instance), any error in this assumption introduces an additional error in locating the karst. However, the resulting error is within acceptable limits when the deviation is less than 30[deg]. The MRS results were compared with an electrical resistivity tomography (ERT) survey. It was found that in Poumeyssens, ERT is not able to locate the water-filled karst. On the other hand, ERT provides additional information about heterogeneities in the limestone

tude des transferts de masse et de chaleur dans la grotte de Lascaux: le suivi climatique et le simulateur., 2007,
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Lacanette D. , Malaurent Ph. , Caltagirone J. P. , Brunet J.
Study of heat and mass flows in Lascaux cave: the climatic monitoring and the simulation tool. The cave of Lascaux, discovered in 1940 and located in the Dordogne area in France, is inscribed on the Unesco World Heritage List. It is considered as one of the major prehistoric caves in the world. Since its discovery, several problems have occurred, due to the huge amount of visitors, and their release of vapour and carbon dioxide by their breath, causing the formation of calcite and the apparition of green algae and mosses. The Ministry of Cultural Affairs had the cave closed in 1963. Since then, prehistorians, archaeologists, geologists, hydrogeologists, have tried hard to maintain the cavity in the most stable state as possible, using remote metering to record the variations in temperature, hygrometry, and carbon dioxide gas pressure. The biological equilibrium remained fragile and, in 2001, colonies of micro-organisms, mushrooms and bacteria developed on the rock edges and on the floor. This attack made the authorities and the Minister of Culture and Communication create the scientific international comity of the Lascaux cave, a multidisciplinary comity (composed of archaeologists, physicists, geologists, hydrogeologists, conservators working altogether) to understand the mechanisms of apparition of the micro-organisms in order to stop their propagation. Among the measures taken by the comity, a better understanding of the flows in the cave has appeared very important, and has induced the creation of a simulation tool, the "Lascaux Simulator". The non intrusive character of simulation is one of the major assets of this method. Thus, the numerical simulation in fluid mechanics is here dedicated to the conservation of the cave of Lascaux. The simulator is based on a computational fluid dynamics code named Aquilon. A three dimensional survey has been leaded in the cave using laser scanning and an accurate topology of the environment is incorporated in the simulator. Starting from this point, governing equations of the fluid mechanics are solved and parameters such as temperature, velocity or moisture content are known in every point of the cavity. Thermal conditions are chosen, basing on the analysis of the calculated and measured temperature data for more than 50 years. In this article, two configurations are chosen, the first one in September 1981, period during which the cave remained in a stable state regarding condensation, and the other one in December 1999; at this time, temperature were reversed, the ground of the cavity was colder than the vaults. This phenomenon implied an inversion of the air flow in the cave. Finally, the removal of the dividing wall of the Bauer airlock has been simulated, and it has been showed that the impact on the cavity would be negligible.

Navier-Stokes flow and transport simulations using real fractures shows heavy tailing due to eddies, 2007,
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Cardenas M. B. , Slottke D. T. , Ketcham R. A. , Sharp Jr. J. M.

Two-dimensional Navier-Stokes flow and transport simulations are conducted for a 15-cm long fracture mapped via X-ray computed tomography. (1) The actual fracture with irregular aperture, (2) a truncated fracture where the largest aperture area is excluded from the domain, (3) the truncated fracture with further thinning of other large aperture areas, and (4) a fracture with uniform vertical aperture equal to the actual fracture’s mean aperture, are subjected to the same pressure gradient. Slight variations in fracture characteristics result in significantly different flow and transport behavior. Flux is much larger for the uniformaperture fracture compared to the actual fracture. A pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power-law tail absent in other cases. The uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1D analytical model. The analytical model fit to the other cases is not as robust as in the uniform aperture case


VEGETATION OF THE DOLINES IN MECSEK MOUNTAINS (SOUTH HUNGARY) IN RELATION TO THE LOCAL PLANT COMMUNITIES, 2009,
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Csiky Jnos Erd?s, Lszl, Morschhauser Tams, Trk Pter & Krmczi Lszl
This paper deals with the forest vegetation of the lower part of the dolines in Mecsek Mts. (South Hungary). In order to char-acterize this vegetation type, samples were compared to the 6 plant communities occurring in the neighbourhood of the dolines. Considering the vegetation texture and species com-position, the vegetation of the dolines resembles mainly the extrazonal beechwoods (Helleboro odori-fagetum) and local ravine forests (Scutellario altissimae-Aceretum) that preserve several mountain, subatlantic relict species in this area. Our study revealed that the plant communities characteristic of the karst surface of Western Mecsek are arranged along a moisture and nutrient gradient. In this system, the habitat conditions of the dolines are similar to those of the beech forests and the lo-cal ravine forests, fresh and relatively rich in nutrients. In the karst, dominated by oak-hornbeam and beech forests, effects of the thermal inversion are the most spectacular where beech forests follow turkey oak-sessile oak forests and oak-hornbeam forests on the lower part of the doline slopes. The described vegetation type of these depressions is developed by edafic fac-tors; its identification as a separate association is not supported by the analyses.

ASSESSING THE RELIABILITY OF 2D RESISTIVITY IMAGING TO MAP A DEEP AQUIFER IN CARBONATE ROCKS IN THE IRAQI KURDISTAN REGION, 2009,
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Aziz B. , Baban E.

A more accurate model of the subsurface is a two-dimensional (2-D) model where the resistivity changes in the vertical direction as well as in the horizontal direction along the survey line. Our survey was carried out by a new modern computerized static type resistivity meter, “SYSCAL Jr switch-72”. The interpretation of the 2D ?eld model was performed by the latest version of the software package “RES2DINV” version 3.54v and “RES2DMOD” version 3.01w, which perform smoothness constrained inversion using ?nite difference and ?nite elements forward modeling. The measurements were carried out by using Roll-along technique in 69 2-D soundings distributed over two pro?les. The area is characterized by quite homogenous and relatively thin recent sediments. The isopach map constructed shows generally about 10-80 m of these sediments. Excellent aquifers were detected in the Pila Spi limestones, which have wide ranges of resistivities between 22-700 ?.m due to lateral and vertical facies changes from low resistivity chalky limestone to compact high resistivity dolomite. This aquifer is buried beneath 10-80 m of sedimenst, and greater depths were detected in a few limited locations due to existence of particular structural features. The isopach map of the Pila Spi aquifer shows that thickness ranges between (20-135) m. In addition, three important structural features were identi?ed within the Pila Spi strata, a strike slip fault near Dargazen village, the “Hayasi Horst” which extends NE-SW close to Hayasi village, and a graben “Ibrahim Awa graben” close to Ibrahim Awa village. These structural features form natural obstacles below the surface and have great in?uence on the groundwater movements.


Inversion for the Input History of a Dye Tracing Experiment, 2011,
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Field M. S. , Li G.

The advection-dispersion model (ADM) is a good tool for simulating transport of dye or solutes in a solution conduit. Because the general problem of transport can be decomposed into two problems, a boundary-value problem and an initial-value problem, the complete solution is a superposition of the solutions for these two problems. In this paper, the solution for the general problem is explained. A direct application of the solution for the boundary-value problem is dye-tracing experiments. The purpose is inclusion of the input history of a solute dye into the ADM. The measured breakthrough curve of a dye-tracing experiment is used to invert for the release history of the dye at the input point through the ADM. It is mathematically shown that the breakthrough curve can not be directly used to invert for the boundary condition at a tracer release point. Therefore, a conductance-fitting method is employed to obtain the input history. The inverted history for a simple example is then shown to be a step function with amplitude of 420 mg/L and a duration of 10 minutes. Simulations illustrate that the breakthrough curves at downstream springs provide a means for understanding the migration of dye. A discussion of the implication of the solution for an initial-value problem (e.g., simulating transport of preexisting solutes such as dissolved calcium carbonate in solution conduits) is also included.


Pit cave morphologies in eolianites: variability in primary structure control, 2011,
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Moore Paul J. , Seale L. Don, Mylroie John E.

The landforms of San Salvador, Bahamas, demonstrate extensive karst development, in particular epikarst features called pit caves. Studies on Hog Cay, an interior dune ridge located north of the San Salvador International Airport runway, indicate that some pit caves have morphologies controlled by bedding. These pit caves, initiating within the vadose zone, have a tendency to follow the foreset beds of the dune for some distance and are analogous to solution chimneys found in continental settings. These solution chimneys are distinguished from vertical shafts, which propagate vertically into the vadose zone of the
subsurface with little, if any, horizontal offset.

Previous field observations have described how eolian deposits can be sorted by grain size into alternating coarse-grained and fine-grained strata. The alternating strata undergo selective cementation, where the coarse-grained strata become poorlycemented and the fine-grained strata become well-cemented because of retention of pore waters. This is observed in weathered outcrops as poorly-cemented micro-recesses and well-cemented micro-ledges. In the subsurface, the coarse-grained, poorlycemented strata are the preferred flow path for vadose water. This water is perched upon and flows laterally along the foreset beds on the well-cemented, fine-grained strata. Pit caves forming under these conditions are described as solution chimneys. Also found on Hog Cay are pit caves that extend from the surface down to near sea level. These vertical shafts are generally found on the crests of dunes, with the deepest shaft being over 15 meters. They commonly display a near-perfect cylindrical shape and extend vertically with no horizontal offset. The walls of vertical shafts exhibit micro-ledge and micro-recess morphology; however, the vertical shafts have no indication of bedding control, which may be due to cementation in the fine-grained layers
being less complete in certain areas, facilitating vertical shaft development.

Preliminary XRD analysis of the pit caves shows that the top and bottom wall rocks of one pit is almost entirely calcite, but the wall rocks in the middle of the pit have a high aragonite content. These observations are consistent with long residence time of meteoric water in the epikarst at the top of the pits, and in the fill material at the base of the pits, such that aragonite was inverted to calcite. However, the rapid transit time of the vadose water along the pit walls allowed dissolution to enlarge the pit, but without inversion of the primary aragonite.


Structural and host rock controls on the distribution, morphology and mineralogy of speleothems in the Castanar Cave (Spain), 2011,
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Alonsozarza A. M. , Martinperez A. , Martingarcia R. , Gilpena I. , Melendez A. , Martinezflores E. , Hellstrom J. , Munozbarco P.

The Castanar Cave (central western Spain) formed in mixed carbonate-siliciclastic rocks of Neoproterozoic age. The host rock is finely bedded and shows a complex network of folds and fractures, with a prevalent N150E strike. This structure controlled the development and the maze pattern of the cave, as well as its main water routes. The cave formed more than 350 ka ago as the result of both the dissolution of interbedded carbonates and weathering of siliciclastic beds, which also promoted collapse of the overlying host rock. At present it is a totally vadose hypergenic cave, but its initial development could have been phreatic. The cave's speleothems vary widely in their morphology and mineralogy. In general, massive speleothems (stalactites, stalagmites, flowstones, etc.) are associated with the main fractures of the cave and bedding planes. These discontinuities offer a fairly continuous water supply. Other branching, fibrous, mostly aragonite speleothems, commonly occur in the steeper cave walls and were produced by capillary seepage or drip water. Detailed petrographical and isotope analyses indicate that both aragonite and calcite precipitated as primary minerals in the cave waters. Primary calcite precipitated in waters of low magnesium content, whereas aragonite precipitated from magnesium-rich waters. Differences in isotope values for calcite (-5.2‰ for ?18O and -9.6‰ for ?13C) and aragonite (?18O of -4.5‰ and ?13C of -3.5‰ ) can be explained by the fact that the more unstable mineral (aragonite) tends to incorporate the heavier C isotope to stabilize its structure or that aragonite precipitates in heavier waters. Changes in the water supply and the chemistry and instability of aragonite caused: (1) inversion of aragonite to calcite, which led to the transformation of aragonite needles into coarse calcite mosaics, (2) micritization, which appears as films or crusts of powdery, opaque calcite, and (3) dissolution. Dolomite, huntite, magnesite and sepiolite were identified within moonmilk deposits and crusts. Moonmilk occurs as a soft, white powder deposit on different types of speleothems, but mostly on aragonite formations. Huntite and magnesite formed as primary minerals, whereas dolomite arose via the replacement of both huntite and aragonite. Owing to its variety of speleothems and location in an area of scarce karstic features, the Castanar Cave was declared a Natural Monument in 1997 and is presently the target of a protection and research programme. Although the main products formed in the cave and their processes are relatively well known, further radiometric data are needed to better constrain the timing of these processes. For example, it is difficult to understand why some aragonite speleothems around 350 ka old have not yet given way to calcite, which indicates that the environmental setting of the cave is still not fully understood. 


Speleogenesis of the Buco dei Vinchi inactive swallow hole (Monte Croara karst sub-area, Bologna, Italy), an outstanding example of antigravitative erosion (or paragenesis) in selenitic gypsum. An outline of the post-antigravitative erosion , 2012,
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Pasini, Giancarlo

Inactive swallow hole Buco dei Vinchi developed along a plane dividing selenitic gypsum stratum and an underlying shale interlayer, mostly by antigravitative erosion and by post-antigravitative erosion. It formed through six speleogenetic phases starting from a phreatic phase followed by several antigravitative erosion (= paragenetic) and post-antigravitative erosion phases and vadose phase. During first antigravitative erosion phase, the phreatic protoconduits evolved into small antigravitative conduits with typical cross-section in shape of an inversed U or a bulb. At the end of this phase the small antigravitative conduits converged and merged together in successive stages to form ever-bigger conduits, until – at a certain point – most of them flowed into a single, much wider antigravitative conduit, which later evolved into a composite conduit. Wwe demonstrate that the subhorizontal flat ceilings are not a characteristic feature of the antigravitative passages tout court – as claimed by most authors –, but instead they evolved in caves during periods when the piezometric surface was tangent to the vault of the cave (post-antigravitative erosion phenomenon). Thus these flat ceilings are traces of ‘paleo-piezometric surfaces’; moreover these flat ceilings, being sub-horizontal originally, can provide important information on possible tectonic movements or breakdowns occurred after their formation. The possible ages of the karstic phenomena in the selenitic gypsum near Bologna are discussed. This paper points out that the Buco dei Vinchi and the Cava a Filo swallow holes, presently located in “topographic highs”, were very probably in “topographic lows” at the time of their hydrologic activity, and that this is evidence of a relief inversion started at least 127,000 years ago. Therefore the beginning of the first karstic phenomena in the Bologna karst area is much older than this date. It is explained why the absolute altimetrical lowering of the Monte Croara karst sub-area (with respect to the present sea level) should be of about – 0.39 mm/year.


An electrical resistivity imaging-based strategy to enable site-scale planning over covered palaeokarst features in the Tournaisis area (Belgium), 2012,
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Kaufmann O. , Deceuster J. , Quinif Y.

Since the beginning of the 20th century, more than 150 sinkhole occurrences, mainly dropout (or covercollapse)sinkholes, have been reported in the Tournaisis area (south-eastern Belgium). Land-use planning in such a context has to take into account hazards linked with sinkhole subsidence and collapse. Management maps, drawn at a regional scale, point out zones where karstic risks have to be taken into account when dealing with infrastructure or building projects. However, karst hazard is highly variable in three dimensions at the local scale. Therefore, for such purposes, an accurate methodology is needed to detect and delineate covered karst features, especially when located in urbanized areas. As geophysical investigations are sensitive to contrasts in physical properties of soils, these methods can be useful to detect such targets. The specific karstic context encountered in the Tournaisis area strongly guides the choice of investigation techniques. Electrical resistivity imaging (ERI) methods were tested on a wellknown site where dropout sinkholes occurred formerly. This site was also studied using static cone penetration tests (CPT) and boreholes. A 3D inverted resistivity model was computed based on the 2D ERI models obtained after inversion. Resistivity profiles were extracted at each CPT location and compared to geotechnical results to determine an empirical and site-specific resistivity law that allows discrimination between weathered zones and sound limestone. Performance tests were conducted to evaluate the potential of the proposed methodology for two typical engineering problems based on two current hypotheses. Borehole data were used as ground truth. Similar performance tests were also computed using the CPT depth to bedrock model. The results of these performance tests are compared and discussed. Finally, an ERI-based investigation strategy is proposed to assess karst hazard in palaeokarstic context, such as encountered in the Tournaisis area, at the scale needed for building and infrastructure purposes. 


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