Rock Cavities Research Articles

Palaeoenvironmental reconstruction of the Late Pleistocene to Early Holocene Robertson Cave sedimentary deposit, Naracoorte, South Australia

Sedimentological investigations and geochemical analyses of the Robertson Cave deposit, 7 km south of Naracoorte, South Australia, document a palaeoenvironmental record for the Late Pleistocene and Early Holocene. Three distinct depositional episodes spanning the interval 32 – 8 ka are represented by over 4 m of sediments exposed in the chamber 2 excavation pit. The oldest of the three, the lower unit (>30 ka BP) is dominated by reddish and brown sandy silts. A 20 cm band of red silt horizons that cap this unit contain enriched δ15N values (12 – 15‰), low C/N ratios, significant SO3 (20%) and CaO (18.5%) contents, a high alkyl-C component and phosphorus-rich mineralogy. These unique sediment horizons are interpreted as being derived from the accumulation of bat guano and degraded cave rock fragments. Their presence suggests a period of low sediment input into the cave, possibly reflecting the existence of a stable geomorphic environment prior to 30 ka. The time period 30 – 27 ka saw the rapid deposition of the middle unit, a sequence of coarser homogeneous sands that resulted in the entrance to chamber 2 becoming blocked. These horizon-less sediments, with clear aeolian features, are most likely representative of the drier conditions associated with the Last Glacial Maximum, which peaked at 20 – 17 ka. Deposition into the chamber recommenced at approximately 13 ka and continued until 8 ka, resulting in the accumulation of the upper unit, a sequence of silt, charcoal and organic matter rich horizons. Here, a shift to more 13C-depleted values (−25‰ to −27‰) is evident in the bulk soil organic matter and charcoal between 11 and 10 ka, possibly reflecting a shift from the dry Last Glacial Maximum to the wetter environs of the Holocene. The upper unit may also be a record of burning practices associated with Aboriginal migration to the area.

Nature of the scattered seismic response from zones of random clusters of cavities and fractures in a massive rock

ABSTRACTThe scattering of elastic energy by random clusters of fractures and/or cavities in a massive rock is studied. The interpretation of the scattered seismic response reveals crucial information about the clusters of inhomogeneities (fractures/cavities), which may correspond to reservoirs. The study is based on a new two‐dimensional numerical‐modelling method that relaxes the constraints on the location and orientation of the inhomogeneities, accounts for inhomogeneities that have almost no volume but a finite surface area (fractures) and improves the accuracy of the calculation when the size of the inhomogeneities is comparable to the mesh size.It is shown that the nature of the seismic response of zones of diffuse fracturing and/or cavities is associated with the non‐uniformity of micro‐inhomogeneities in such zones; accumulations of these micro‐inhomogeneities are known as clusters.The relationship between the non‐uniformity of micro‐inhomogeneities and the strength of the seismic response has been established and measured.Considerable differences in the structure of the seismic response of zones of diffuse fracturing and diffuse cavities have been identified. Converted PS‐waves dominate in the scattered wavefield associated with fractures. This is explained, as the modelling results show, by a greater transparency of fluid‐filled fractures, which reduces the reflected energy of compressional waves. The wavefield associated with cavities is characterized by the predominance (in terms of strength) of compressional PP‐waves. The strength of converted PS‐waves in the scattered wavefields for both media is approximately the same.On the whole, according to the results of the modelling, the energy of the scattered response of fractured reservoirs is considerably less (about two times) than that of cavernous reservoirs.

Cronstedt’s zeolite

Abstract Axel F. Cronstedt (1722–1765), famous Swedish mineralogist, was the first scientist to describe, 250 years ago, the distinctive property of zeolites, i.e., the unique frothing characteristics when heated in a blow-pipe flame. Cronstedt examined two specimens: one from Svappavaara in Northern Sweden and one that was said to come generically from Iceland. From Cronstedt’s indications, the occurrence of the first specimen was near the mining area of Kiruna. The morphological characteristics of the specimen suggested that the zeolite species is stilbite which would make it the first discovered zeolite mineral. This paper is devoted to the description of the structure and microstructure of that first discovered natural zeolite from Svappavaara (Northern Sweden). The SEM investigation of all the sample rock cavities filled with the zeolite crystals and the optical observation of the separated zeolite crystals revealed that the sample is mainly composed of stellerite with subordinate stilbite crystals which are present only in a few cavities together with stellerite. The chemical formula of the stellerite crystals derived from the EPMA and TG analyses is (Ca4.03Mg0.01Na0.03K0.11) [Si27.81Al8.19O72]·28.6H2O. The results of the structure refinement confirm that the investigated specimen is actually stellerite and evidenced no ordering in the tetrahedral sites. The structure refinement evidenced no ordering in the tetrahedral sites. The extraframework cation Ca is located in the centre of the main channel parallel to the a axis, on the mirror plane and is surrounded by water molecules with no contact with framework oxygen atoms. The coordination of Ca is 6-fold. A number of short water–water distances are possible by considering the different possible schemes around the Ca atom. Considering the short water–water distances and the partial occupancy of water sites, a number of octahedral coordinations around Ca are possible.

Leroi‐Gourhan and the Emergence of PrehistoryAutour de l’homme: Contexte et actualité d’André Leroi‐Gourhan. Edited by Françoise Audouze and Nathan Schlanger. Antibes: APDCA, 2004. 442 pp.

Leroi‐Gourhan and the Emergence of Prehistory<i>Autour de l’homme: Contexte et actualité d’André Leroi‐Gourhan</i>. Edited by Françoise Audouze and Nathan Schlanger. Antibes: APDCA, 2004. 442 pp.

Effects of intermediate principal stress on rock cavity stability

The linear Mohr-Coulomb and nonlinear Hoek-Brown failure criteria, which neglect the effects of intermediate principal stress, are widely used in soil and rock engineering. However, much experimental data shows that the failure envelope relates to the intermediate principal stress. Employing the failure criterion and the generalized plastic potential function, the stability of rock cavity driven in an isotropic and homogeneous medium was investigated under the condition of plane strain considering the effects of intermediate principal stress. The closed-form solutions for stresses and displacement around a rock cavity were given in the elastic and plastic zones. Based on the closed-form solutions, the intermediate principal stress has an important effect on cavity stability.

Culturable Microbial Diversity and the Impact of Tourism in Kartchner Caverns, Arizona

Kartchner Caverns in Benson, AZ, was opened for tourism in 1999 after a careful development protocol that was designed to maintain predevelopment conditions. As a part of an ongoing effort to determine the impact of humans on this limestone cave, samples were collected from cave rock surfaces along the cave trail traveled daily by tour groups (200,000 visitors year-1) and compared to samples taken from areas designated as having medium (30-40 visitors year-1) and low (2-3 visitors year-1) levels of human exposure. Samples were also taken from fiberglass moldings installed during cave development. Culturable bacteria were recovered from these samples and 90 unique isolates were identified by using 16S rRNA polymerase chain reaction and sequencing. Diversity generally decreased as human impact increased leading to the isolation of 32, 27, and 22 strains from the low, medium, and high impact areas, respectively. The degree of human impact was also reflected in the phylogeny of the isolates recovered. Although most isolates fell into one of three phyla: Actinobacteria, Firmicutes, or Proteobacteria, the Proteobacteria were most abundant along the cave trail (77% of the isolates), while Firmicutes predominated in the low (66%) and medium (52%) impact areas. Although the abundance of Proteobacteria along the cave trail seems to include microbes of environmental rather than of anthropogenic origin, it is likely that their presence is a consequence of increased organic matter availability due to lint and other organics brought in by cave visitors. Monitoring of the cave is still in progress to determine whether these bacterial community changes may impact the future development of cave formations.

Numerical Modelling and Assessment of Excavation Damaged Zone around the Underground Excavations: A Case Study

This paper presents a study on the quantification of the degree of damage from the microseismic event data, for assessment of excavation damaged zone of anisotropic rock in Jinchuan mine and presents numerical simulation and prediction on the deformation and failure of the rock masses surrounding laneway under rock mass properties and excavating conditions. Following an introduction to the engineering geology and mechanical properties of the rock mass in the Jinchuan mine areas, this paper reveals the features of the measured in situ stresses and puts emphasis on an analysis of the mechanism of underground opening and damage induced by the underground mining. Stress and AE redistribution induced by excavation of underground engineering results in the unloading zone in parts of surrounding rock masses. A micromechanics-based model has been proposed for brittle rock material undergoing irreversible changes of their microscopic structures due to microcrack growth. A systematical numerical modeling analysis method was completed. Based on numerical modelling, a series of predicting curves for rock mass response and deformation are obtained, which provides the basis of guiding the design and construction of anisotropic rock cave in Jinchuan mine. The use of the in situ stress field results in enhanced modeling of the stress concentrations and potential failures at the mines has also been reviewed. Knowledge of the prevailing rock stress field at the mines is a critical component for such modeling which has led to improved rock mechanics understanding and operations at Jinchuan mines.

Mechanical degradation of emplacement drifts at Yucca Mountain—A modeling case study: Part II: Lithophysal rock

This paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at Yucca Mountain, which is the designated site for the proposed US high-level nuclear waste repository. The welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties: nonlithophysal and lithophysal units, based on the relative proportion of lithophysal cavities. The term ‘lithophysal’ refers to hollow, bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine-grained alkali feldspar, quartz, and other minerals. Lithophysae are typically a few centimeters to a few decimeters in diameter. Part I of the paper concentrated on the degradation behavior of the generally hard, strong, and fractured nonlithophysal rock. Part II concentrates on the host rock in the lithophysal units. Lithophysal rock is characterized by lithophysal cavities interconnected by fracturing. Fracture sets are not as clearly defined as in the nonlithophysal rock. The rock mass porosity in the lithophysal units has been shown to be the primary physical factor that governs elastic and strength properties. The degradation behavior of the tunnels in the lithophysal rock is controlled by the spalling of the surrounding rock mass. A discontinuum material model has been developed to represent the drift scale rock mass properties in which slip and separation of contacting rock blocks can be estimated. Two-dimensional discontinuum analyses were developed with the consideration of in situ, thermal, and seismic loads. Time-dependent degradation was also considered. In this study, field and laboratory data and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation.

Mechanical degradation of emplacement drifts at Yucca Mountain—A modeling case study—Part I: Nonlithophysal rock

This paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at Yucca Mountain, which is the designated site for the proposed US high-level nuclear waste repository. The factors leading to drift degradation include stresses from the overburden, stresses induced by the heat released from the emplaced waste, stresses due to seismically related ground motions, and time-dependent strength degradation. The welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties: nonlithophysal units and lithophysal units, based on the relative proportion of lithophysal cavities. The term ‘lithophysal’ refers to hollow, bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine-grained alkali feldspar, quartz, and other minerals. Lithophysae are typically a few centimeters to a few decimeters in diameter. Part I of the paper concentrates on the generally hard, strong, and fractured nonlithophysal rock. The degradation behavior of the tunnels in the nonlithophysal rock is controlled by the occurrence of keyblocks. A statistically equivalent fracture model was generated based on extensive underground fracture mapping data from the Exploratory Studies Facility at Yucca Mountain. Three-dimensional distinct block analyses, generated with the fracture patterns randomly selected from the fracture model, were developed with the consideration of in situ, thermal, and seismic loads. In this study, field data, laboratory data, and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation.

Non-marine radiaxial fibrous calcites—examples of speleothems proved by electron backscatter diffraction

The occurrence of radiaxial fibrous calcites (RFC) in speleothems is documented for the first time using the new electron backscatter diffraction (EBSD) method. Up to now, in speleothems these precipitates have only been observed as Mg-containing calcites in close association with aragonite, in caves of the temperate to cool Central European regions with mean annual temperatures between 4 and 16 °C. As the four studied occurrences are located in caves in dolomitic and/or ankeritic host rocks, magnesium is considered to be of particular importance for triggering the formation of radiaxial fibrous (Mg-) calcite.

Níveis de radioatividade natural decorrente do radônio no complexo rochoso da Serra de São Vicente, SP

OBJETIVO: Realizar monitoração passiva e integrada do radônio em várias amostras de águas, solos e locais fechados do complexo rochoso da Serra de São Vicente, SP, com o intuito de avaliar a distribuição de ocorrência deste gás radioativo naquele local. MATERIAIS E MÉTODOS: A técnica utilizada consistiu em expor detectores plásticos policarbonatos (SSNTD) do tipo Makrofol E, na geometria de copo fechado, ao radônio emanado das amostras de águas coletadas dos solos e ao acumulado em ambientes internos (residências e cavidades nas rochas) existentes no complexo rochoso de São Vicente. RESULTADOS: Os valores obtidos para os teores de radônio variaram entre 8,1 e 36 Bq/l para as fontes de água natural, entre 68 e 610 Bq/m³ nas residências, entre 0,41 e 3,46 kBq/m³nos solos e entre 0,72 e 5,85 kBq/m³ nas cavidades do Maciço de São Vicente. CONCLUSÃO: Para algumas residências e na maioria das fontes de água estudadas, os teores de radônio encontrados neste trabalho estiveram acima dos limites máximos propostos por organismos internacionais. Recomenda-se, portanto, que ações de intervenção sejam implementadas para a dissipação do radônio, tanto nessas residências como durante a coleta das águas para fins de consumo.

Salt ingestion caves

Large vertebrate herbivores, when they find a salt-bearing layer of rock, say in a cliff face, can produce sizable voids where, over generations, they have removed and consumed salty rock. The cavities formed by this natural animal process constitute a unique class of caves that can be called salt ingestion caves. Several examples of such caves are described in various publications. An example in Mississippi U.S.A., Rock House Cave, was visited by the authors in 2000. It seems to have been formed by deer or bison. Perhaps the most spectacular example is Kitum Cave in Kenya. This cave has been excavated to a length over 100 meters by elephants. An ancient example is La Cueva del Milodon in Chile, which is reported to have been excavated by the now extinct milodon, a giant ground sloth. Still other possible examples can be cited. This class of caves deserves a careful definition. First, the cavity in rock should meet the size and other conventions of the locally accepted definition of a cave. Of course this requirement differs in detail from country to country, particularly in the matter of size. The intent is to respect the local conventions. The characteristic that human entry is possible is judged to be a crucial property of any recognized cave definition. Second, the cavity should be significantly the result of vertebrate animal consumption of salt-bearing rock. The defining process is that rock removed to form the cave is carried away in the digestive track of an animal. While sodium salts are expected to be the norm, other salts for which there is animal hunger are acceptable. Also some other speleogenesis process, such as solution, should not be excluded as long as it is secondary in formation of a cave in question.

Geochemical Constraints on the Genesis of the Scheelite Dome Intrusion-Related Gold Deposit, Tombstone Gold Belt, Yukon, Canada

The Scheelite dome intrusion-related gold deposit, western Selwyn basin, Yukon, is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid-Cretaceous Tombstone-Tungsten magmatic belt, Tintina gold province, Alaska and Yukon. A variety of mineralization styles occur throughout a 10- × 3-km east-trending corridor and include reduced Au- and W-rich skarns, Au-, W- and Ag-Pb-Zn-Sb–rich quartz tension-vein arrays, and multiphase fault veins and isolated zones of Au-rich sericite-carbonate altered rock. Integrated U-Pb SHRIMP data for magmatic zircon and Ar-Ar data for magmatic and hydrothermal biotite indicate that gold mineralization occurred within 1 to 2 m.y. of magma emplacement. Fluid inclusion, oxygen isotope, and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550°C. High-temperature Au-rich skarns formed at >400°C, whereas vein-hosted mineralization formed at 280° to 380°C. In skarns, Au is strongly associated with enrichments of Bi, Te, W, and As, whereas a variety of Au-rich veins occur, with As-rich (type 1), and Te- and W-rich (type 2) end members. Silver-Pb-Zn-Sb veins are typically Au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis. The fluid inclusion data indicate that all mineralization styles were formed from low-salinity (≤4 wt % NaCl equiv) aqueous-carbonic fluids, consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks. However, the nonaqueous fluid was predominantly CH 4 in skarn, CO 2 in Au-Te and Au-W veins, and a fluid with roughly equal amounts of CO 2 , CH 4 , and N 2 in Au-As and Ag-Pb-Zn-Sb veins. Oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive δ 18 O values during interaction with 18 O-enriched metasedimentary strata. Sulfur isotope data suggest two possible sources of sulfur, a magmatic source characterized by δ 34 S values of approximately −5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative δ 34 S values of approximately −15 to −10 per mil. Collectively the data indicate that gold at Scheelite Dome was deposited from a magmatic-hydrothermal system. Interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids, higher CH 4 /CO 2 ratios, and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels. Progressive reduction and cooling of hydrothermal fluids, in addition to phase separation in vein-hosted mineralization, were the mechanisms for gold deposition. Compared to other intrusion-related gold deposits associated with the Tombstone-Tungsten magmatic belt magmatism, exposed mineralization at Scheelite Dome is predominantly hosted by hornfelsed metasedimentary rocks. This results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data.

Numerical Study on the Fracture Evolution around Cavities in Rock

By using numerical code RFPA2D (Rock Failure Process Analysis), the evolution of fracture around cavities subjected to uniaxial and polyaxial compression is examined through a series of model simulation. It is shown from the numerical results that the chain of events leading to the collapse of the cavity may involve all or some of the fractures designated as primary tensile, shear and remote fracture. Numerical simulated results reproduce the evolution of three types of fractures. Under the condition of no confining pressure, the tensile mode dominates with collapse coinciding with the sudden and explosive appearance of the secondary tensile fracture; at moderate higher confining pressure, the tensile mode is depressed, comparatively, the shear effect is strengthened. Nevertheless, tensile fractures especially in remote fractures stage still play a role; at higher pressure, the shear fracture dominates the remote fractures. In addition, the evolution and interact of fractures between multiple cavities is investigated, considering the stress redistribution and transference in compressive and tensile stress field.

Modeling of Area-End Ore Drawing under Caved Rocks

The results of modeling the technology of area-end ore drawing under caved rocks are adduced. The advantages of the new method over the end ore drawing are shown. A method of calculating losses and impoverishment depending on sublevel and breaking parameters as well as on ore drawing mode is presented.

Vertical motion of ground water in bed rock induced by earth tide and its influence on a repository for burnt nuclear fuel: a theoretical calculation

Earth tide induced by the Moon and the Sun makes the volume of pores or the apertures of fractures of the bed rock vary, which in turn makes the ground water move. The flow equation of ground water, complete with the tide effect, and its solution, shows that the diffusive propagation of pore pressure is decisive for the response of the perturbation of gravity. Moreover the solution shows that diffusive flow dominates in the Fennoscandian Precambrian rock. The analysis shows that a constitutive coefficient relating the varying perturbation gravity and porosity of bed rock can be determined by field measurements of the level of water in boreholes. Water in a cavity in the bed rock is exposed to an oscillatory interaction with the surrounding pore water. If the cavity is a repository for nuclear waste, this interaction deserves attention. The analysis shows that the magnitude of the oscillatory motion of water between a repository for nuclear waste and its. surrounding groundwater is much less than the vertical motion of the phreatic surface.

Preliminary Screening of Residual Soil Stability in Karst Terrain

The stability of the residual soils that overlie cavitose limestone is often a concern during the siting, construction, and maintenance of facilities in karst terrain. Voids or domes often form in the residual soil above the rock cavities, and unless the thickness of the residual soil is sufficient for the development of arching, the soil may collapse and sinkholes may form. A preliminary screening method is proposed to estimate the thickness of residual soil required to provide stability for a given range of potential soil-void diameters. The method considers two modes of instability for sites with shallow (less than 25 m) overburden. Stability with respect to the first mode (cover collapse) depends on the development of arching in the residual soil and suggests a minimum allowable cover thickness for stability. Stability with respect to the second mode (cover subsidence) corresponds to the yielding and plastic flow of the soils into the soil and/or rock void and suggests a maximum cover thickness above which subsidence should be evaluated. Sites with very thick overburden (more than 25 m) are generally not considered problematic. The limiting conditions for the first stability mode are compared with estimated sinkhole dimensions reported in the literature and the application of the stability chart is demonstrated by an example.

Geomechanical Substantiation of Ore-Block Breaking Schemes Taking into Account Static Stress Field Redistribution under the Short-Delay Blasting

The features of the static stress field redistribution in a rock mass are established for schemes of blasting that form a sinusoid-shaped ore block without a free surface on the contact with caving zone. The influence exerted by caved rocks on the dimensions and location of tension zones in a broken block is estimated.

Den Characteristics of Black Bears in Southwestern Virginia

Abstract Proper den sites are crucial to the reproduction of female black bears (Ursus americanus). We monitored 31 bears for 39 bear winters in the Southern Appalachians with 95% of the bears confirmed to have denned. Bears denned in trees (41%), rock cavities (32%), excavations (14%), snags (8%), and ground nests (5%). Chestnut oak (Quercus prinus; n = 9), red oak (Q. rubra; n = 8), and tulip-poplar (Liriodendron tulipifera; n = 1) were used as tree dens. Habitat characteristics did not differ between ground dens and tree dens; however, older bears used ground dens more frequently than tree dens (Z = −2.484, P = 0.013). We documented one instance of den reuse. Our results provide managers with more accurate information about black bear dens.

Simulating the growth of tafoni

AbstractThroughout the world, large caves in rocks (tafoni) are found, which originate from salt weathering. The mechanisms that control their development are poorly understood. The growth of tafoni has been studied with a model that describes how a rock surface, containing a small pit, disintegrates by salt crystallization during wetting/drying cycles. In the model the rock is mapped on a grid. The migration and crystallization of salts are simulated explicitly in the drying phase of a cycle. At the end of each wetting/drying cycle the amount of salt deposited at the grid nodes is evaluated and the shape of the rock surface is adjusted by removing nodes. The length of the drying period in a single cycle proved to be the key parameter. For short drying periods the amount of crystallized salt at the surface is proportional to the drying rate. Therefore, for short drying periods most salts are deposited at the more exterior parts of the rock surface. As a result, most damage will develop at these parts of the surface, which results in smooth surfaces. Due to the characteristics of the drying process for long drying periods, most salts accumulate at regions with low evaporation rates, which are the sheltered parts of the rock surface. These parts are not exposed to the wind or the sun. As a result, the pit grows and a tafone develops. Copyright © 2004 John Wiley &amp; Sons, Ltd.