Digital elevation models (DEM) are digital representations of topography that are especially suitable for numerical terrain analysis in earth sciences and engineering. One of the main quantitative uses of DEM is the automatic delineation of flow networks and watersheds in hydrology and geomorphology. In these applications (using both low­resolution and precision DEM) depressions hinder the inference of pathways and a lot of work has been done in designing algorithms that remove them so as to generate depression­free digital elevation models with no interruptions to flow. There are, however, geomorphological environments, such as karst terrains, in which depressions are singular elements, on scales ranging from centimetres to kilo­metres, which are of intrinsic interest. The detection of these depressions is of significant interest in geomorphologic map­ping because the development of large depressions is normal in karst terrains: potholes, blind valleys, dolines, uvalas and poljes. The smallest depressions that can be detected depend on the spatial resolution (pixel size) of the DEM. For example, depressions from centimetres to a few metres, such as some types of karren, cannot be detected if the raster digital eleva­tion model has a spatial resolution greater than, say, 5 m (i.e., square 5m pixel). In this work we describe a method for the au­tomatic detection and delineation of terrain depressions. First, we apply a very efficient algorithm to remove pits from the DEM. The terrain depressions are then obtained by subtract­ing the depression­free DEM from the original DEM. The final product is a digital map of depressions that facilitates the cal culation of morphometric features such as the geometry of the depressions, the mean depth of the depressions, the density of depressions across the study area and the relationship between depressions and other variables such as altitude. The method is illustrated by applying it to data from the Sierra de las Nieves karst massif in the province of Málaga in Southern Spain. This is a carbonate aquifer that is drained by three main springs and in which the depressions play an important role in the recharge of the aquifer. A doline density map, produced from a map of 324 detected dolines/uvalas, identifies three main recharge areas of the three springs. Other morphometric results related to the size and direction of the dolines are also presented. Finally the dolines can be incorporated into a geomorphology map.

The main objective of this study is to analyse the effect of tendencies in the meteorological variables on the water quality on the example of five lakes in the Aggtelek and Slovak karst. The data set used eleven water quality parameters (oxygen saturation, chemical oxygen demand, nitrate, nitrite, orthophosphate, total phosphorus, ammonium, pH, conductivity, iron, manganese), as well as daily data of six climatic parameters from the period 2008­2010. A cluster analysis is performed in order to determine the climate impact on the water quality parameters. Furthermore, factor analysis with special transformation, as a novelty in the study, is implemented to find out the weight of the climate parameters as explanatory variables and hence their rank of importance in forming the given water quality parameter as an influencing variable. The study introduces a methodology for analysing the climate impact on the water quality parameters. In order to reduce the number of the water quality parameters, a so called two­stage factor analysis was performed, which is a novel procedure. Application of the two­stage factor analysis involves both benefits and disadvantages. Its benefit is that it substantially reduces the number of resultant variables. In this way, information loss of the retained factors is around 20%. As a result, we received that both positive and negative extreme values of water quality parameters can be associated with weak or breaking­up warm fronts passing through over the region. On the contrary, the role of anticyclones or anticyclone ridge weather situations is supposed to be irrelevant. Unstable and extreme weather conditions act in the direction of breaking up the balance that would support the good water quality. This process does not benefit the water use nor the sensitive karst hydrogeological system

The epikarst is a permeable boundary between surface and subsurface environments and can be conceptualized as the vadose critical zone of epigenic karst systems which have not developed under insoluble cover. From a hydrologic perspective, this boundary is often thought of as being permeable in one direction only (down), but connectivity between the flow paths of water through the epikarst and the root systems of woody plants means that water moves both up and down across the epikarst. However, the dynamics of these flows are complex and highly dependent on variability in the spatial structure of the epikarst, vegetation characteristics, as well as temporal variability in precipitation and evaporative demand. Here we summarize insights gained from working at several sites on the Edwards Plateau of Central Texas, combining isotopic, hydrogeochemical, and ecophysiological methodologies. 1) Dense woodland vegetation at sites with thin to absent soils (0-30 cm) is in part supported by water uptake from the epikarst. 2) However, tree transpiration typically becomes water-limited in dry summers, suggesting that the plant-available fraction of stored water in the epikarst depletes quickly, even when sustained cave drip rates indicate that water is still present in the epikarst. 3) Flow paths for water that feeds cave drips become rapidly disconnected from the evaporation zone of the epikarst and out of reach for plant roots. 4) Deep infiltration and recharge does not occur in these systems without heavy or continuous precipitation that exceeds some threshold value. Thresholds are strongly correlated with antecedent potential evapotranspiration and rainfall, suggesting control by the moisture status of the epikarst evapotranspiration zone. The epikarst and unsaturated zone in this region can be conceptualized as a variably saturated system with storage in fractures, matrix porosity, and in shallow perched aquifers, most of which is inaccessible to the root systems of trees, although woody vegetation may control recharge thresholds.

Archaeological investigations of the Overlook Rockshelter in the Caves Branch River Valley of central Belize offer a unique view of ancient Maya cave ritual through the complete recovery and analysis of all artifacts within the site’s two small activity areas. In general, the assemblage contains many of the same types of objects documented from other nearby caves and rockshelters. However, the nearly 1700 ceramics sherds showed almost no refits, demonstrating that sherds were deposited at the site individually, rather than as complete vessels. The human bone assemblage represents three or four individuals, with the majority of the bones comprising a single individual, and all of these were deposited as incomplete secondary interments. Analogies for this depositional behavior based on archaeological and ethnographic studies suggest that this rockshelter may represent a waypoint within a ritual circuit composed of multiple locations over which fragments of complete items such as ceramic vessels and secondary burials were spread.  

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The early stage of hypogene karstification is investigated using a coupled thermohydrochemical model of a mountain hydrologic system, in which water enters along a water table and descends to significant depth (_1 km) before ascending through a central high-permeability fracture. The model incorporates reactive alteration driven by dissolution/ precipitation of limestone in a carbonic acid system, due to both temperature- and pressuredependent solubility, and kinetics. Simulations were carried out for homogeneous and heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded at some stage. Buoyant convection is then initiated and controls the evolution of the system thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses large buoyant convection rolls, although a large number of smaller rolls form. Even after the onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths by retrograde solubility and by additional ‘‘mixing corrosion’’ effects closer to the surface. Aperture growth patterns in the fracture are very different from those observed in simulations of epigenic karst systems, and retain imprints of both buoyant convection and preferential flow. Both retrograde solubility and buoyant convection contribute to these differences. The paper demonstrates the potential value of coupled models as tools for understanding the evolution and behavior of hypogene karst systems.

The early stage of hypogene karstification is investigated using a coupled
thermohydrochemical model of a mountain hydrologic system, in which water enters along a
water table and descends to significant depth (1 km) before ascending through a central
high-permeability fracture. The model incorporates reactive alteration driven by dissolution/
precipitation of limestone in a carbonic acid system, due to both temperature- and pressuredependent
solubility, and kinetics. Simulations were carried out for homogeneous and
heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass
Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture
growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded
at some stage. Buoyant convection is then initiated and controls the evolution of the system
thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant
convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses
large buoyant convection rolls, although a large number of smaller rolls form. Even after the
onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths
by retrograde solubility and by additional ‘‘mixing corrosion’’ effects closer to the surface.
Aperture growth patterns in the fracture are very different from those observed in simulations
of epigenic karst systems, and retain imprints of both buoyant convection and preferential
flow. Both retrograde solubility and buoyant convection contribute to these differences. The
paper demonstrates the potential value of coupled models as tools for understanding the
evolution and behavior of hypogene karst systems.

The early stage of hypogene karstification is investigated using a coupled thermohydrochemical model of a mountain hydrologic system, in which water enters along a water table and descends to significant depth (_1 km) before ascending through a central high-permeability fracture. The model incorporates reactive alteration driven by dissolution/ precipitation of limestone in a carbonic acid system, due to both temperature- and pressuredependent solubility, and kinetics. Simulations were carried out for homogeneous and heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded at some stage. Buoyant convection is then initiated and controls the evolution of the system thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses large buoyant convection rolls, although a large number of smaller rolls form. Even after the onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths by retrograde solubility and by additional ‘‘mixing corrosion’’ effects closer to the surface. Aperture growth patterns in the fracture are very different from those observed in simulations of epigenic karst systems, and retain imprints of both buoyant convection and preferential flow. Both retrograde solubility and buoyant convection contribute to these differences. The paper demonstrates the potential value of coupled models as tools for understanding the evolution and behavior of hypogene karst systems.

Microorganisms have shaped the world around us, yet their role in karst processes and speleogenesis remains poorly understood. Biospeleogenesis is the formation of subsurface cavities and caves through the activities of microorganisms, by either respiratory (redox) or metabolic chemistries. In carrying out energy acquisition and the metabolic processes of growth, microorganisms change the local geochemistry of the environment. Such activities can dramatically accelerate speleogenesis and even lead to cave formation in geochemical environments that would otherwise not be conducive to dissolution. The aim of this chapter is to help the reader understand the importance of microbial activity in geochemistry and how such activity can lead to the formation and morphology of caves. The chapter then describes the role that microorganisms are known to have in speleogenesis (carbonic and sulfuric acid biospeleogenesis), hints that such activity may be occurring in newly described cave systems (iron biospeleogenesis), and a potential role in other cave systems (quartzite biospeleogenesis). It is hoped that the reader will gain an understanding of what motivates microorganisms to dramatically change their environment, understand the potential geochemical conditions where such activity could occur, and allow the informed geologist to make predictive statements as to the potential of, and for, biospeleogenesis

The Carboniferous Limestone at Bullslaughter Bay hosts some of the most notable examples of deep weathering in  the British Isles as well as two members of an enigmatic suite of breccias known as the Gash Breccias. The weathered limestone has  been investigated thoroughly in order to identify the process responsible for the weathering. In this paper it is demonstrated that the  weathering is isovolumetric but the weathering profile is not characterised by a vertical gradient and its depth suggests that meteoric  waters did not contribute significantly to the weathering process. The weathered limestone has lost significant amounts of calcium and  parts are virtually decalcified. It is seen that the dominant primary minerals of illite and quartz have been preserved while secondary  clay minerals are generally absent. The weathered limestone cannot be a saprolite sensu stricto as it has been subjected to only restricted  chemical processes. It is, therefore, interpreted as a “ghost-rock”. This type of weathering results from chemical dissolution by slow  moving waters in the saturated zone. It is suggested that the weathering may have taken place during periods of emergence in the  Carboniferous, at the same time as the cyclothem tops were exposed to subaerial modification, as evidenced by omission surfaces and  palaeokarstic solution features. This is the first time that ghost-rock weathering has been reported from the British Isles.

The historical approach of the karst always gave preferential treatment to the study of the superficial phenomena or underground cavities explored by human. However as demonstrated by hydrogeologists, the main karst development keep out of reach because of the too small sizing of drains or due to its filling. Consequently appears the question about the inception drain, the way used by the water from the sink hole to reach its resurgence. Some authors consider this primary link as obvious when the practice demonstrates clearly that the hydrodynamic continuity results of a very long, complex and selective evolution, essentially geochemical. This is the field of the drain inception stages, that we can spell “prekarst” or “primokarst”. Those stages include the successive fields of isalterite and alloterite. This last one opens by compaction a free space and allows a concentrated hydrodynamic flow. These processes, at the origin of the endokarst initiation, can develop on the side of synchronous mechanical dynamics if in the same drain or under a regolith coverage, something divides the bedrock and the quick flow. Without any doubt, this is the purview of the cryptokarst and of the cave walls under filling. We can observe it in the progradation front of the introduction karst or in the retrogradation front of the restitution karst.

The Devils Hole Ridge, a small block of Paleozoic carbonate rocks surrounded by the Amargosa Desert in southern Nevada, is located at the discharge end of the Ash Meadows regional groundwater flow system.
Continuous, long-term presence of slightly thermal (33.6°C) groundwater and the extensional tectonic setting, creating underground thermal lakes in open fractures, lead to intense dissolution above the water table. The morphology of the subaerial parts of the tectonic caves was slightly modified by condensation corrosion, and the Devils Hole Prospect Cave was almost entirely created by condensation corrosion. Caves and cavities in the Devils Hole Ridge are an interesting example of a hypogene speleogenesis by mechanism by condensation corrosion, operating above an aquifer which was demonstrably supersaturated with respect to calcite for hundreds of thousands of years.

Most models of cave formation in limestone that remains near its depositional environment and has not been deeply buried (i.e. eogenetic limestone) invoke dissolution from mixing of waters that have different ionic strengths or have equilibrated with calcite at different pCO2 values. In eogenetic karst aquifers lacking saline water, mixing of vadose and phreatic waters is thought to form caves. We show here calcite dissolution in a cave in eogenetic limestone occurred due to increases in vadose CO2 gas concentrations and subsequent dissolution of CO2 into groundwater, not by mixing dissolution. We collected high-resolution time series measurements (1 year) of specific conductivity (SpC), temperature, meteorological data, and synoptic water chemical composition from a water table cave in central Florida (Briar Cave).We found SpC, pCO2 and calcite undersaturation increased through late summer, when Briar Cave experienced little ventilation by outside air, and decreased through winter, when increased ventilation lowered cave CO2(g) concentrations.We hypothesize dissolution occurred when water flowed from aquifer regions with low pCO2 into the cave, which had elevated pCO2. Elevated pCO2 would be promoted by fractures connecting the soil to the water table. Simple geochemical models demonstrate that changes in pCO2 of less than 1% along flow paths are an order of magnitude more efficient at dissolving limestone thanmixing of vadose and phreatic water.We conclude that spatially or temporally variable vadose CO2(g) concentrations are responsible for cave formation becausemixing is too slow to generate observed cave sizes in the time available for formation. While this study emphasized dissolution, gas exchange between the atmosphere and karst aquifer vadose zones that is facilitated by conduits likely exerts important controls on other geochemical processes in limestone critical zones by transporting oxygen deep into vadose zones, creating redox boundaries that would not exist in the absence of caves.

The conduit system of mature karstified carbonate aquifers is typically characterised by a high hydraulic conductivity and does not impose a major flow constriction on catchment discharge. As a result, discharge at karst springs is usually flashy and displays pronounced peaks following recharge events. In contrast, some karst springs reported in literature display a discharge maximum, attributed to reaching the finite discharge capacity of the conduit system (flow threshold). This phenomenon also often leads to a non-standard recession behaviour, a so called “convex recession”, i.e. an increase in the recession coefficient during flow recession, which in turn might be used as an indicator for conduit restricted aquifers. The main objective of the study is the characterisation and modelling of those hydrogeologically challenging aquifers. The applied approach consists of a combination of hydrometric monitoring, a spring hydrograph recession and event analysis, as well as the setup and calibration of a non-linear reservoir model. It is demonstrated for the Auja spring, the largest freshwater spring in the Lower Jordan Valley. The semi-arid environment with its short but intensive precipitation events and an extended dry season leads to sharp input signals and undisturbed recession periods. The spring displays complex recession behaviour, exhibiting exponential (coefficient α) and linear (coefficient β) recession periods. Numerous different recession coefficients α were observed: ∼0.2 to 0.8 d−1 (presumably main conduit system), 0.004 d−1 (fractured matrix), 0.0009 d−1 (plateau caused by flow threshold being exceeded), plus many intermediate values. The reasons for this observed behaviour are the outflow threshold at 0.47 m3 s−1 and a variable conduit–matrix cross-flow in the aquifer. Despite system complexity, and hence the necessity of incorporating features such as a flow threshold, conduit–matrix cross-flow, and a spatially variable soil/epikarst field capacity, the developed reservoir model is regarded as relatively simplistic. As a number of required parameters were calculated from the hydrogeological analysis of the system, it requires only six calibration parameters and performs well for the highly variable flow conditions observed. Calculated groundwater recharge in this semi-arid environment displays high interannual variability. For example, during the 45-year simulation period, only five wet winter seasons account for 33% of the total cumulative groundwater recharge.

The Cova des Pas de Vallgornera is the longest cave of Mallorca (Balearic Islands, Western Mediterranean) and one of the 30 longest caves in the world. The exploration of one of the galleries allowed the discovery of a fossiliferous deposit of vertebrate remains in a remarkable preservation state. The fossil faunal complex found in this gallery is composed of up to 5 mammalian species (Myotragus aff. kopperi, Hypnomys onicensis, Nesiotites aff. ponsi, Rhinolophus aff. mehelyi and Pipistrellus sp.), at least 14 bird species (among them two Mallorcan endemic taxa: Pica mourerae and Athene vallgornerensis), one reptile (Podarcis aff. lilfordi) and one amphibian (Discoglossus sp.). This faunal composition is similar to the one recorded in the Pedrera de s’Ònix, a well known deposit from the Early Pleistocene of Mallorca, and shared morphological characteristics between taxa of both deposits suggest that the chronology of the Cova des Pas de Vallgornera should be considered Early Pleistocene as well. Both taxonomical analysis and chronology of this fauna furnished information on some speleological aspects of the cave.

The data set presented in this paper includes the fossil fauna collected in the cave named Cova des Pas de Vallgornera (CPV), located on the southern coast of Mallorca (Balearic Islands, Spain). It holds 1481 catalogued items, 97.5% identified at species level. Mammalia, Aves, Reptilia, and Amphibia are represented in the Database. The fauna collected in the cave includes the three endemic mammals present on Mallorca during the Early Pleistocene (Myotragus aff. kopperi, Hypnomys onicensis, and Nesiotites aff. ponsi). There are also represented two taxa of Chiroptera (Rhinolophus aff. mehelyi and Pipistrellus sp.), 16 taxa of birds (6 of them identified at species level), one Reptilian taxon (Podarcis sp.) and one Amphibian taxon (Discoglossus sp.). Most of fossils were collected during a single excavation campaign of 3 days (28-30th May, 2010). A few remains were obtained in two previous visits to the cave, in 2006 and 2009. All the specimens are curated and documented at the Vertebrate Collection of the IMEDEA [Institut Mediterrani d'Estudis Avançats (CSIC-UIB)]. The assemblage of CPV fossils is a part of the paleontological collection IMEDEA-PALEOVERT, included at the GBIF portal.