Water-filled Cave Research Articles

Mechanism, mode, and prediction of karst caves collapse in the deep marine carbonate fracture-cavity reservoir

Tahe oilfield in the Tarim Basin of China is a typical deep marine carbonate fracture-cavity type reservoir. Large paleokarst caves are the important storage space types in this reservoir. Drilling data reveals that most of the caves have varying degrees of collapsed breccia filling. A better understanding of cave collapse mechanism, modes, and distribution is crucial for highly efficient production. In this study, large karst caves in the Ordovician of Tahe oilfield are taken as research objects, and several types of typical cave conceptual models are established based on similarity theory. Physical tests and numerical simulation methods are used to reveal the collapse mechanism under different depths, shapes, filling types, and tectonic stresses of different periods. Collapse modes are established based on the revealed mechanism, morphology, and damage zone of simulated karst caves. Seismic prediction methods of different types of collapsing caves are explored according to their reflection characteristics. The results reveal that compaction and shearing damage are the main reasons for cave collapsing. The roof and surrounding rock of the cave sink in during the collapse process, with a shear-slip damage zone of 2–3 times larger than the cave diameter. The sand/mud-filled cave is shown to be more stable than the water-filled cave, and the unfilled cave is the least stable. Tectonic stresses acting in the early Hercynian period are the primary reason for the current collapsed caves. Two cave collapse modes are established, type Ⅰ being mainly affected by overlying gravity and type Ⅱ mainly affected by shear stress. There are local differences in seismic reflection characteristics between these two types. The prediction of the two types of collapsed karst caves can be realized by combining the seismic attribute of colored inversion, frequency division energy, GR inversion and coherent energy gradient, etc. The comprehensive prediction results of collapsed karst caves in Tahe oilfield show a good correspondence with oil well productivity.

Study on Propagation Characteristics of Ground Penetrating Radar Wave in Dikes and Dams with Polymer Grouting Repair Using Finite-Difference Time-Domain with Perfectly Matched Layer Boundary Condition

Non-aqueous reactive polymer grouting technology has been widely used in the repair engineering of dikes and dams with shallow diseases. By using the finite difference time-domain method and perfectly matched layer boundary conditions, the calculation model of dikes and dams with shallow diseases such as water-filled cave, air-filled cave and incompact area is established. The propagation process of electromagnetic waves of ground-penetrating radar in dikes and dams with shallow diseases using polymer grouting repair is simulated, and the forward simulation profiles and single-channel waveforms are obtained. The propagation characteristics such as waveform amplitude, waveform shape, transmission time, and reflection time are compared and analyzed. The results show that the forward simulation profiles of dikes and dams with water-filled caves before and after polymer grouting repair present two clusters of hyperbolas, but three clusters of hyperbolas with different amplitudes were observed at 50% repair. The amplitude of the hyperbola and the single-channel reflected waves before repair and 50% repair of the cave and incompact area are greater than those of 100% repair. The propagation characteristics of ground-penetrating radar can effectively explain the degree of polymer grouting repair for dikes and dams with shallow diseases, and provide a theoretical basis for using the ground-penetrating radar to evaluate the effect of polymer grouting technology to repair dikes and dams with shallow diseases.

The Whole-Space Modeling of the Hazardous Geological Body ahead of the Tunnel Face by the Transient Electromagnetic Method

Karst caves are widely distributed in southwest China, causing difficulties and disasters for tunnel construction. To better detect the krast caves in front of the tunnels under construction using the transient electromagnetic method, in this paper we propose a 3-D finite element method to simulate the multi-parameter transient electromagnetic response of unfavorable geological bodies in a whole-space. First, the models of vertical water-filled faults, water-filled caves and complex geological bodies in front of the tunnel face are established. The horizontal electric field component and the vertical magnetic field component at different time in the whole-space are researched. Secondly, the electromagnetic response features of the caves with different resistivity, buried depths and scales are studied. We found that the resistivity of the target body is 10 times larger than that of the surrounding rocks, and the anomaly amplitude increases obviously with the growing distance from the target body. The deeper the buried depth, the later the anomaly appears and the smaller the anomaly amplitude. The larger the target size, the longer the transient electromagnetic response delay and the larger the anomaly amplitude. We arranged a measuring line on the tunnel face. The full-time apparent resistivity section shows the position and characteristics of the low-resistivity anomalous body, indicating that the transient electromagnetic method (TEM) has obvious advantages in detecting the low-resistivity body in front of the tunnel face. Finally, the TEM is successfully applied to the advanced detection of a karst tunnel to get the electrical distribution of the surrounding rocks in front of the tunnel face. According to the geological conditions of the excavated tunnel, the validity of the TEM in the tunnel advanced prediction is verified.

Experimental Study on the Mix Proportion and Mechanical Properties of New Underwater Cementitious Filling Materials

Considering that it is difficult for traditional materials to simultaneously meet the requirements for filling grouting of water-filled karst caves and subsequent shield tunneling, an environmentally friendly and controllable new underwater cementitious filling material (NUC-FM) is developed, with abandoned shield mud as the basic raw material. Through laboratory tests, the mechanical property parameters of NUC-FM are tested, and its micromechanism is analyzed. The research results show that there is excellent synergistic interactions among shield mud, cement, flocculant, fly ash and other raw materials. The NUC-FM grouting filling material with superior performance can be prepared when the water binder ratio is between 0.45 and 0.6 and the water consumption is between 270 and 310 kg/m3. It has the characteristics of non-dispersion underwater and moderate consolidated body strength. The compressive strength of the NUC-FM consolidated body samples under each mix proportion is much higher than 0.5 MPa, which meets the technical strength requirements of a construction site, and the microstructure shows that there is an obvious dense and stable block structure inside. The cost of the NUC-FM prepared with an optimized mix proportion is only 34.57 dollars/m3, which is far lower than the market purchase price of concrete and cement mortar. It can be predicted that the NUC-FM is an ideal filling grouting material for water-filled karst caves in shield tunnels in water-rich karst areas.

Evolution Pattern and Matching Mode of Precursor Information about Water Inrush in a Karst Tunnel

The water inrush of the Shangjiawan karst tunnel is used to study the evolution pattern of precursor water inrush information in water-filled caves and to further reveal the matching mode of the information. The three-dimensional numerical method FLAC3D was used to simulate the evolution process of water inrush after damage to a water-blocking rock mass structure in a water-filled cave and to obtain the evolution pattern of precursor water-inrush information caused by the damage. The results show that the multifield response to the characteristic precursor information of the water-inrush pattern after the fracture of the water-blocking rock mass follows the order of stress-field displacement-field seepage-field. Further, the matching pattern of the information shows that the stress field increased first and then decreased, the displacement field always increased, and the seepage field increased first and then decreased.

Study on multi-field catastrophe evolution laws of water inrush from concealed karst cave in roadway excavation: a case of Jiyuan coal mine

Coal is the major energy source in China. Many coal mines in Southwest China have arranged the excavation roadway system in the Maokou limestone in coal seam floor because of its special hydrogeological conditions. Since karst is widely distributed in Maokou limestone and water-filled karst caves are also developed commonly there, once a strongly water-filled karst cave is exposed during roadway excavation, the water inrush disaster occurs easily. In order to reveal the phenomenon of water inrush disasters from covered karst caves more effectively, the water inrush that occurred during the roadway excavation process of Jiyuan coal mine in northern Guizhou was taken as a research object in this study. Based on the regional geological structure, the hydrogeological condition and the fluid-structure interaction theory, a fluid-structure interaction model of water inrush in the roadway excavation was established, and variation laws of stress field, displacement field and seepage field of surrounding rock during the process of water inrush from karst cave were analyzed. Besides, the influence of different geological conditions on water inrush from karst cave was discussed from aspects of the size of karst cave, the water pressure of karst cave and the thickness of aquiclude.

Experimental study of the precursor information of the water inrush in shield tunnels due to the proximity of a water-filled cave

A water-filled cave can easily result in the deterioration of the surrounding rock when a shield tunnel passes through the urban karst area, resulting in engineering disasters such as water inrush, ground collapse, and shield machine malfunction. To study the surrounding rock stability due to the proximity of a cave with confined water, we carried out a large-scale three-dimensional geo-mechanical model test on a tunnel that was excavated by a compound EPB (Earth Pressure Balance) shield machine based on the metro tunnel in the “spring city” of Jinan. We developed a new 3D printing technology for a water-filled cave and a new method for the 3D laser reconstruction of surface settlement monitoring. The multi-physics evolution information, including the soil moisture content of the muck, the displacement, the stress, and the seepage pressure, were obtained and proven consistent with each other. The results showed that the water inrush mainly resulted from a shield tunneling disturbance in conjunction with the confined water in the cave. The process of water inrush in the surrounding rock could be divided into three stages, which included the initial stable period, the variation period with the shield tail passing through, and the final stable period. The rock ahead of the excavation face was characterized by two stages, which included the initial stable period and the sudden collapse of the water-resistant slab. Compared with the tunnel excavated by drilling and with the blasting method, the water inrush triggered by the EPB shield machine tunneling was observed to be more hidden and catastrophic. The displacement and the seepage pressure comprised the most intuitive precursor information. These test results can provide a theoretical basis and guidance for the water inrush prediction for being triggered by a single confined cave with no inter-connections.

Study on the treatment materials of urban rail transit water-containing caves

With the sustained and rapid development of the national economy and the accelerating urbanization process, the contradiction between urban basic design, especially urban transportation facilities and urbanization, has become increasingly prominent. Rail transit has become the main public transport in major cities with its advantages of large capacity, fast speed, safety and reliability, and on-time comfort. Most of the rail transit lines are underground tunnels. When the tunnel crosses the karst area, it may encounters caves with different sizes, different locations, different filling levels and different water content. The existence of these caves will seriously affect the surrounding rock in tunnel construction. To carry out research on the typical disaster of water-filled caves, different types of filling materials were compared and analysed. And the applicable scope, advantages and disadvantages of various filling materials were also analyzed. Aiming at the treatment method of cement-water glass as filling material for the water-soluble cave, the relationship between the setting time of cement-water glass and the water inflow time was studied. The research shows that the effect of injecting the cave near the cement-water glass is the best.

Reconstruction and Measurement of Irregular Karst Caves Using BLST along the Shield Metro Line

This study investigated the application of the borehole laser scanning technology (BLST) method in the detection of both dry and water-filled karst caves. In order to solve the problem of excessive laser attenuation during the detection, we designed a test for the characteristics of multiwavelength laser attenuation in water-filled karst caves and studied the influence exerted by various factors, including different wavelengths, different laser power levels, different suspended media, and effect of turbidity on the attenuation coefficient. During the test, we discovered the existence of a “blue-green window” with low turbidity and a “near infrared window” with high turbidity in karst cave water environments. Based on the general survey results of drilling and comprehensive geophysical prospecting, a quantitative method using targeted drilling was proposed to detect the spatial morphology of karst caves in complex environments. We also investigated the effects of complex environmental factors such as suspended media and high turbidity on the laser detection distance and accuracy in karst caves, and established a quantitative matching model of laser wavelengths, laser power, and complex environmental parameters. Based on this, we obtained the best acquisition mode for detecting lasers in different karst development environments. A high-precision, three-dimensional visualized model of a real karst cave was established to quantitatively obtain the characteristic parameters, such as accurate position, three-dimensional shape, space volume, and cave filling type, which was applied to the detection of karst caves along the Jinan subway line.

Catastrophe analysis of deep tunnel above water-filled caves

To explore the influence of karst cavity pressure on the failure mechanisms of rock layers above water-filled caves, novel blow-out and collapse mechanisms are put forward in this study. The proposed method uses the nonlinear optimization to obtain the failure profiles of surrounding layered rock with water-filled cave at the bottom of the tunnel. By referring to the functional catastrophe theory, stability analysis with different properties in different rock layers is implemented with considering the incorporation of seepage forces since the groundwater cannot be ignored in the catastrophe analysis of deep tunnel bottom. Also the parametric analysis is implemented to discuss the influences of different rock strength factors on the failure profiles. In order to offer a good guide of design for the excavation of deep tunnels above the water-filled caves, the proposed method is applied to design of the minimum effective height for rock layer. The results obtained by this work agree well with the existing published ones.

An iterative inversion method using transient electromagnetic data to predict water-filled caves during the excavation of a tunnel

The correct interpretation of full-space transient electromagnetic data has always constituted a critical safety problem during tunnel excavation projects. Targeting the interpretation of water-filled caves under narrow tunnel conditions, we have developed an iterative inversion method based on 3D finite-difference time-domain (FDTD) forward calculations and a direction algorithm. In total, 125 groups of 3D FDTD forward calculation results are analyzed to identify the correlations between the response data and the geometric conditions of the cave. A direction algorithm is established based on the correlations, thereby increasing the iterative inversion convergence speed. Using the proposed iterative inversion method, the location and volume of the water-filled cave in front of the tunnel face are successfully inverted. Through an iterative program, the inversion results of simulations involving the detection of water-filled caves under tunnel conditions are accurately analyzed, and the relative error is less than 10%. The application of the iterative inversion method to the Mingyue Mountain Tunnel project suggests that this method is capable of interpreting the size of water-filled caves and it is valid for a narrow tunnel face with only a single available measurement point. The proposed iterative inversion method can be used alone or in combination with other detection techniques, thereby providing engineers with a better early warning system for detecting water-filled caves in tunnels.

New 3D failure analysis of water-filled karst cave beneath deep tunnel

In this study, both 2D and 3D failure shapes of rock mass above the water-filled cavity are put forward when the surrounding rock mass cannot bear the pressure caused by the water-filled cavity. Based on the analytical expressions derived by kinematic approach, the profiles of active and passive failure patterns are plotted. The sensitivity analysis is conducted to explore the influences of different rock parameters on the failure profiles. During the excavation of the deep tunnels above the karst cavity, the water table always changes because of progressive failure of cavity roof. Therefore, it is meaningful to discuss the effects of varying water level on the failure patterns of horizontal rock layers. The changing laws of the scope of the failure pattern obtained in this work show good consistency with the fact, which could be used to provide a guide in engineering.

Radar spectral analysis and evaluation of the effect of grouting treatment in karst caves and soil caves

This paper studies karst cave and soil cavity development in the process of karst collapse as a means of disaster prevention and control. Using the karst area of the Shandong section of the Beijing–Shanghai high-speed railway as a test area, a numerical simulation method is presented as well as the model test to study the characteristics of typical radar images of different types of karst caves and soil cavities. By combining theoretical analysis with field test results, the method and characteristic standards for nondestructive testing using ground-penetrating radar to determine the grouting effect on a karst roadbed are given. The radar spectrum characteristics are analyzed for a cave, water-filled cave, clay-filled cave, karst cave with dense grouting and karst cave with grouting that is not dense. Comprehensive analysis of the results of indoor model testing and numerical analysis, combined with the engineering practice of evaluating the effect of grouting treatment in the selected section of the Beijing–Shanghai high-speed railway, clarifies the basic characteristics of map recognition of radar detection of karst grouting. The morphological characteristics of the karst caves in the geological radar images are usually composed of many hyperbolic strong reflection waves. Multiple-reflection wave groups of high amplitude, low frequency, and equal distance indicate the side wall of the cave. The bottom interface of the cave is not obvious, although when the bottom part of the cave is filled with water or clay, silt, sand and gravel material. The bottom of the reflection wave will be enhanced. When the cave is filled with material, the electromagnetic wave energy decays rapidly, the high-frequency part is absorbed, and the reflection is mostly low frequency wave. The characteristics of radar images of the slurry distribution area are obvious in the grouting zone. A horizontal direction results in arc-shaped distribution, and a vertical direction has more regular distribution. The results of the study are helpful in the exploration of karst caves and soil caves, and the evaluation of the effect of grouting treatment in mitigating karst collapse.

The remarkable remipedes

This presentation will be a very general look at the exciting history of the crustacean class Remipedia, from discovering them in a water-filled cave in the Bahamas in 1979 to today. I will begin with an introduction to the beautiful remipede cave habitat. We will explore where these fascinating animals live and what other cave crustaceans inhabit their community. I will review remipede research since publishing their description in the first volume of the Journal of Crustacean Biology in 1981 through 37 years of research. Several interesting remipede species will be highlighted for their unusual morphology. In closing I will propose questions to encourage future research with these interesting crustaceans.

Trace metal cycling in karst aquifers subject to periodic river water intrusion

River water that enters critical zone aquifers can deliver metals and alter groundwater redox potential, resulting in precipitation and/or dissolution of metal oxides. These effects on metal concentrations should be particularly dynamic in karst critical zones where surface water and groundwater are linked through preferential flow paths (e.g., caves and conduits). Metals can be either toxins or micronutrients and thus their concentrations are important to water quality. To evaluate trace metal dynamics in karst critical zones, we measured Pb and Sr isotopic ratios and major and trace metal concentrations of Fe,Mn-oxide deposits collected from two water-filled cave networks (Madison Blue and Peacock springs) in the carbonate upper Floridan aquifer (Florida, USA). We also measured dissolved and total metal concentrations in water from conduits of both cave networks during three river water intrusion events and subsequent flood recessions. The Fe,Mn-oxides contain anthropogenic Pb that increases in concentration from interior to exterior of the oxides, indicating they formed and continued to grow over the past several decades. Sr isotope ratios of the Fe,Mn-oxides are intermediate between flood water and groundwater values and indicate they form during intrusion events. This result is corroborated by variations in Fe and Mn concentrations in water during intrusion and recession. The Fe,Mn-oxide interiors are more altered than exteriors as shown by depletion of Mn concentrations and the lack of a positive Ce anomaly in the interior of the Fe,Mn-oxides. Most trace metal concentrations correlate with Mn concentrations suggesting remobilization of trace metals over time periods longer than individual intrusion events. Cycling between accumulation and dissolution of Fe,Mn-oxides presents challenges for evaluation and remediation of trace metal contamination of carbonate critical zones.

River–groundwater connectivity in a karst system, Wellington, New South Wales, Australia

The characterization of river–aquifer connectivity in karst environments is difficult due to the presence of conduits and caves. This work demonstrates how geophysical imaging combined with hydrogeological data can improve the conceptualization of surface-water and groundwater interactions in karst terrains. The objective of this study is to understand the association between the Bell River and karst-alluvial aquifer at Wellington, Australia. River and groundwater levels were continuously monitored, and electrical resistivity imaging and water quality surveys conducted. Two-dimensional resistivity imaging mapped the transition between the alluvium and karst. This is important for highlighting the proximity of the saturated alluvial sediments to the water-filled caves and conduits. In the unsaturated zone the resistivity imaging differentiated between air- and sediment-filled karst features, and in the saturated zone it mapped the location of possible water- and sediment-filled caves. Groundwater levels are dynamic and respond quickly to changes in the river stage, implying that there is a strong hydraulic connection, and that the river is losing and recharging the adjacent aquifer. Groundwater extractions (1,370 ML, megalitres, annually) from the alluvial aquifer can cause the groundwater level to fall by as much as 1.5 m in a year. However, when the Bell River flows after significant rainfall in the upper catchment, river-leakage rapidly recharges the alluvial and karst aquifers. This work demonstrates that in complex hydrogeological settings, the combined use of geophysical imaging, hydrograph analysis and geochemical measurements provide insights on the local karst hydrology and groundwater processes, which will enable better water-resource and karst management.

Predicting multifarious behavioural divergence in the wild

Many animals show complex behaviours that can have important ecological and evolutionary consequences. Environmental variation can lead to divergent selection that consistently favours particular behaviours in different environments; but how predictably multiple aspects of animal behaviour diverge in response to different environmental conditions remains unclear. We tested whether populations evolving under different levels of predation risk show predictable and repeatable population-level behavioural differences in all five primary components of animal personality: aggression, sociability, boldness, activity and exploration. We formulated and tested a priori predictions of divergence for each behaviour using the adaptive radiation of Bahamas mosquitofish, Gambusia hubbsi (family Poeciliidae), inhabiting vertical water-filled caves (blue holes) where they have evolved for thousands of years in either the presence or absence of predatory fish. Mosquitofish behaviours differed consistently, and largely predictably, between predation regimes: low-predation mosquitofish showed reduced sociability and greater exploration of a novel environment compared to high-predation counterparts. However, some differences were sex dependent: only females showed greater boldness and only males displayed reduced aggressiveness in low-predation populations. Activity levels did not differ between predation regimes. All populations showed a behavioural syndrome characteristic of either proactive or reactive stress-coping styles with regard to exploration. Exploration behavioural syndromes were more similar among populations that evolved in similar predation regimes, regardless of genetic relatedness. Using laboratory-born, high-predation mosquitofish, we confirmed that exploratory behaviours have a genetic basis and show significant within-individual repeatability. Our results suggest that environmental variation, such as chronic predation risk, can lead to repeatable, and often predictable, changes in multifarious animal behaviours, and that various aspects of behaviour can diversify more or less independently of one another. Considering the ecological importance of these behaviours, the ability to forecast behavioural shifts in a rapidly changing world could serve as a valuable conservation tool.

A New Fossil Land Tortoise in the Genus Chelonoidis (Testudines: Testudinidae) From the Northern Bahamas, With an Osteological Assessment of Other Neotropical Tortoises

An extinct tortoise, Chelonoidis alburyorum n. sp., is described from nearly complete, beautifully preserved fossils from Sawmill Sink, a deep inland blue hole and cave system, on Great Abaco Island, Little Bahama Bank, in the northern Bahamas. This tortoise is part of an extensive fossil fauna in peat deposits associated with an immense debris cone in the entry shaft of this water-filled cave. The peat fauna also includes intact skeletons, skulls, and isolated bones of Cuban crocodiles (Crocodylus rhombifer), large birds, native rodents (Geocapromys ingrahami), and bats. The turtle remains include the first complete skull, first intact shells, and first associated vertebrae and appendicular skeletons of a tortoise from The Bahamas and/or West Indies. A morphological assessment of this tortoise and other Neotropical tortoises shows greater similarity of this new species with modern Chelonoidis nigra from the Galápagos Islands and fossils from the greater Caribbean area, than with the Cuban Chelonoidis cubensis or living and fossil continental Chelonoidis. AMS radiocarbon dates obtained from bones from the holotype and female paratype of the new tortoise, and from three Cuban crocodiles from Sawmill Sink, indicate a late Holocene age (2,580-3,820 yrs BP) for the peat deposits that produced the fossils of Chelonoidis alburyorum. Two other fossil faunas from this sink are thought to be older, possibly Pleistocene in age. These older fossils lack sufficient carbon to permit reliable radiometric dating. Chelonoidis alburyorum is one of a series of tortoise fossils recently found in blue holes, caves, and archaeological sites in the Bahamian archipelago, including the Turks and Caicos Islands, BWI. Two other fossil species from Abaco and the Turks and Caicos Islands, both in the genus Chelonoidis, are also new to science and will be described elsewhere. Affinities of the fossils from other Bahamian banks remain unstudied. A morphological asssessment of Neotropical tortoises shows greater similiarities between the new species, modern Cheolonoidis nigra, and to a lesser degree fossils from the greater Caribbean than with the Cuban Chelonoidis cubensis and continental Chelonoidis.

DIVERGENT SELECTION, NOT LIFE-HISTORY PLASTICITY VIA FOOD LIMITATION, DRIVES MORPHOLOGICAL DIVERGENCE BETWEEN PREDATOR REGIMES INGAMBUSIA HUBBSI

We recently tested the hypothesis of ecological speciation in a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi) inhabiting inland blue holes (vertical, water-filled caves) on Andros Island, the Bahamas (Langerhans et al. 2007). Combining morphological, molecular, and behavioral data, our results suggested that enhanced premating isolation evolved as a byproduct of differences in body shape between predator regimes, due to assortative mating for body shape. Our results strongly supported the hypothesis of ecological speciation, and parallel results were observed across species within the genus, suggesting a past history of such ecological speciation within the Gambusia lineage. Downhower et al. (in press) question the morphological results described for G. hubbsi in our paper, contending that prior work on life-history variation in G. hubbsi (primarily Downhower et al. 2000, 2002) invalidates our conclusions. Here we show that this contention is based on a mischaracterization of our study, inaccurate quotation of our paper, and misinterpretation of the relevance of their life-history data for morphological results observed in our study. Downhower et al. (in press) suggest—without providing any direct evidence—that differences in body shape between predator regimes in G. hubbsi reflect correlative effects of phenotypic plasticity in life-history traits in response to variation in food availability. To make such a conclusion, we would have to set aside the following facts: (1) morphological differences were observed in adult males, who do not exhibit the life-history traits in question (e.g., number and size of offspring), (2) results matched well-supported a priori predictions of body shape variation based on divergent selection on locomotor performance, (3) results matched empirical results observed in other fish presumably experiencing similar forms of divergent selection between predator regimes, (4) the observed morphological differences are known to influence swimming performance in Gambusia fish and consequently influence endurance and survival with predators, (5) consistent results were observed for males both within and between Gambusia species, (6) any differences in food availability among blue holes are unknown, and (7) available evidence to date indicates that differences in body shape partly reflect genetic divergence, and not solely phenotypic plasticity. The criticisms in Downhower et al. (in press) can be summarized as three arguments: (1) incorrect attribution of evidence for divergent selection between predator regimes in G. hubbsi to several previous

Detection and 2d modelling of cavities using pole–dipole array

The resistivity method is often used in cave prospecting. In this paper the pole–dipole array ability to detect cavities at different depths and with different water contents is investigated. The research was performed using analogical and numerical modelling. According to the results, empty caves at a depth less than four times its diameter can be easily detected. The ability of the pole–dipole array to detect water-filled caves reaches a minimum at filling percentages of 30–50%. Overburden effects research shows that low resistivity overburden reduces the resolution capability of the array. This study shows that equivalent results can be obtained by modelling the empty caves as infinite resistivity bodies or, alternatively, as very high resistivity ones. The analysis of field data acquired in the Macico Calcario Estremenho (Portugal) shows the practical importance of the pole–dipole array in cavities prospecting.