using resistivity measurements for dam safety evaluation at enemossen tailings dam in southern sweden internal erosion is a major reason for embankment dam failures resistivity measurements is an essentially non destructive technique which may have the possibility of detecting internal erosion processes and anomalous seepage at an early stage before the safety of the dam is at stake this paper presents results from part of a dam safety investigation conducted at the enemossen tailings dam in southern sweden longitudinal resistivity sections 2d measurements along the dam crest provided an overview of the whole dam and served to detect anomalous zones in selected areas additional cross sectional 2d surveys gave detailed information about the geo electrical situations in the embankments this information is valuable for similar investigations as information about resistivity in embankment construction material is scarce known problem areas were associated with low resistivities even though the resistivity measurements alone did not provide enough information to confidently come to a decision about the status of the dams

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

experiments on piping in sandy gravels tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory the probable explanation is that a major part of the overburden load is carried on a framework of gravel particles leaving the sand under relatively small pressures by contrast piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient the tests broadly confirm kenney s criterion for the internal stability of granular materials des essais realises sur des graves sableuses a instabilite interne importante montrent qu une proportion non negligeable du sable est lessivee pour des gradients hydrauliques bien inferieurs au gradient critique donne par les theories classiques l explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au reseau des particules graveleuses le sable n etant alors plus soumis qu

geochemical evolution of uraniferous soda lakes in eastern mongolia extremely high concentrations of uranium u were discovered in shallow groundwater fed hyperalkaline soda lakes in eastern mongolia a representative groundwater sample in this area is dilute and alkaline ph 7 9 with 10 mm tic and 5 mm cl in contrast a representative lake water sample is ph 10 with tic and cl each more than 1 000 mm groundwater concentrations of u range from 0 03 to 0 43 m l 1 lake water u ranges from 0 24 to 62 5 m possibly the highest naturally occurring u concentrations ever reported in surface water strontium isotopes 87sr 86sr varied in groundwaters from 0 706192 to 0 709776 and in lakes 87sr 86sr varied from 0 708702 to 0 709432 high concentrations of u na cl and k correlate to radiogenic sr in lake waters suggesting that u is sourced from local cretaceous alkaline rhyolites uranium rich groundwaters are concentrated by evaporation and u vi is chelated by co 3 2 to form the highly soluble uo2 co3 3 4 modeled evaporation of lakes suggests that a u mineral phase is likely to precipitate during evaporation

laboratory technique for measurement of spectral induced polarization response of soil sampies1 abstract laboratory measurements of soil samples are necessary to assess the effect of mineralogy grain size distribution moisture content and electrolyte composition on the resistivity spectrum of soil material laboratory results are also required for the interpretation of field data induced polarization phenomena in glacial soils are poorly understood and so far no convenient laboratory techniques are available for its measurement coarse grain size and the need to measure unsaturated samples and to monitor the homogeneity of the sample require a sample holder electrode construction that differs from those presented in clay mineral studies this study presents a spectral induced polarization laboratory system that is suitable for measuring fine and coarse grained and both saturated and unsaturated soil samples the noise caused by the electrode electrolyte interface is studied in detail it is shown that easy to use platinum or acid free steel potential electrodes are convenient over a broad frequency band ranging from 0 016hz up to more than 1000 hz the laboratory experiments and comparisons between laboratory and field results also indicate that sampling and sample packing procedures have only a minor influence on the phase spectrum of glacial soils

localization and quantification of leakages in dams using time lapse self potential measurements associated with salt tracer injection the self potential method is the only non intrusive method that is directly sensitive to the flow of the pore water in a porous material we propose the use of a new protocol of self potential measurements associated with a brine injection to locate leakages in earth dams and to quantify their permeability indeed a brine solution injection upstream of an earth dam in the assumed leakage zone is able to change the electrical conductivity of the medium in turn this decreases the magnitude of the electrokinetic contribution of the self potential signals that are related to the flow of the seepage water the evolution of this anomalous self potential signal expected to be positive with respect to a reference state prior the salt injection can be measured at the ground surface with a network of non polarizing electrodes the seepage flow inside the dam is localized from the evolution in space and time of the resulting transient self potential signals associated with the transport of the brine the mean permeability of the preferential flowpath can be determined this method is first applied to a laboratory test to show how the passage of a salt tracer affects the self potential response then we apply this new methodology to a field test site a dam with a proven leakage located in the south of france at this test site self potential mapping was first performed to locate the preferential flow path then a network of non polarizing electrodes was used to perform time lapse self potential measurements at the dam crest during a brine injection occurring upstream of the seepage zone we used two lines of 16 non polarizing electrodes each from the time lapse data the permeability of the leaking area was estimated inside one order of magnitude

seasonal formation of ikaite caco3 6h2o in saline spring discharge at expedition fiord canadian high arctic assessing conditional constraints for natural crystal growth abstract spring discharge at expedition fiord pollard et al 1999 on axel heiberg island in the canadian high arctic produces a variety of travertine forms in addition to a diverse collection of mineral precipitates this paper focuses on clusters of thermally unstable crystals believed to be the mineral ikaite caco3 6h2o growing seasonally along two spring outflows at colour peak this form of calcium carbonate mineral occurs along small sections of discharge outflow as white euhedral crystals up to 0 5 cm in length difficulty in sampling storage and transport of the samples for analysis has hampered attempts to confirm the presence of ikaite by x ray diffraction however various field observations and the remarkable instability of these crystals at normal ambient temperatures strengthens our argument this paper provides a description of these particular caco3 6h2o crystals and their environmental surroundings and attempts to determine the validity of ikaite precipitation at this site by theoretical geochemical modeling these results are compared with other reported observations of ikaite to both understand their occurrence and help delineate their geochemical characteristics it is believed that the restrictive combination of spring water chemistry and long periods of low temperatures characteristic of arctic climates are necessary for ikaite growth at this site the fact that ikaite is not forming at a second group of saline springs 11 km away allows us to more specifically outline conditions controlling its presence

ground penetrating radar investigation of a lake bonneville deita provo level brigham city utah field experiments carried out in the brigham sand and gravel company pit near brigham city utah show an impressive similarity between observed gravelly deltaic foreset facies in highwall exposures and inclined reflections detected by ground penetrating radar gpr beneath the pit floor the radar indicates additional inclined strata more than 30 m deep in a test to compare different antenna frequencies 50 100 and 200 mhz using a 400 v transmitter 50 mhz antennas are capable of detecting gravel facies in excess of 30 m whereas signal loss for the 100 and 200 mhz antennas occurs below 23 and 17 m respectively though providing higher resolution

computation of optimized arrays for 3 d electrical imaging surveys 3 d electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2 d models might suffer from artefacts many 3 d surveys use a grid where the number of electrodes along one direction x is much greater than in the perpendicular direction y frequently due to limitations in the number of independent electrodes in the multi electrode system the surveys use a roll along system with a small number of parallel survey lines aligned along the x direction the compare r array optimization method previously used for 2 d surveys is adapted for such 3 d surveys offset versions of the inline arrays used in 2 d surveys are included in the number of possible arrays the comprehensive data set to improve the sensitivity to structures in between the lines the array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set comparisons of the conventional consisting of dipole dipole and wenner schlumberger arrays and optimized arrays are made using a synthetic model and experimental measurements in a tank the tests show that structures located between the lines are better resolved with the optimized arrays the optimized arrays also have significantly better depth resolution compared to the conventional arrays

potential of ikaite to record the evolution of oceanic δ18o a challenge in the quest to understand the sensitivity of the climate system is the separation of the competing effects of ice volume or sea level salinity and temperature on foraminiferal 18o we present precipitation experiments on the mineral ikaite a hydrated form of calcium carbonate found in organic carbon rich deep marine sediments that show that the hydration waters within the ikaite crystal capture the 18o of seawater 18 osw with a fractionation factor of 1 0029 0 0002 the 18osw measures the volume of continental ice with an overprint of local salinity isolation of 18osw by analysis of the hydration waters of sedimentary ikaite preserved at temperatures 4 c could be exploited to create a record of sea level during the pleistocene preliminary data of 18osw from hydration waters of ikaite at the last glacial maximum agree with estimates from modeling of pore waters that antarctic bottom water was 1 4 0 2 heavier 2006 geological society of america

glendonites as a paleoenvironmental tool implications for early cretaceous high latitude climates in australia glendonites calcite pseudomorphs after the metastable mineral ikaite caco3 6h2o occur in the late aptian interval of the bulldog shale in the eromanga basin australia and in other early cretaceous basins at high paleolatitudes ikaite precipitation in the marine environment requires near freezing temperatures not higher than 4 c high alkalinity increased levels of orthophosphate and high pco2 the rapid and complete transformation of ikaite to calcite at temperatures between 5 and 8 c provides an upper limit on the oxygen isotopic composition of the pore waters 2 6 w 3 4 smow if it is assumed that these pore waters are representative of the shallow eromanga basin the calculated w can be used to reassess belemnite fossil oxygen isotopic paleotemperatures temperature recorded by fauna living in the basin at the time of ikaite precipitation data previously reported as 11 to 16 c assuming w 0 0 smow yield paleotemperatures ranging from 1 to 5 c squarely in the range of ikaite stability the low w indicates hyposaline conditions most likely caused by mixing high latitude meteoric waters with seawater the 18o depleted low temperature waters suggest that the region was at least seasonally colder than previously accepted

cross borehole resistivity tomography electrical resistivity tomography ert is a method for determining the electrical resistivity distribution in a volume from discrete measurements of current and voltage made within the volume or on its surface we have developed an ert algorithm that is an iterative modified least squares inversion based on a finite element forward solution of laplace s equation we report the results of tests on this algorithm designed to determine how resistance measurements made from two boreholes may be used to image the resistivity distribution between them a number of simple but geophysically significant structures are modeled these include a single isolated block anomaly two layers a thin isolated continuous layer and a vertical band the main features of most resistivity models were identifiable in the reconstructions limited data accuracy and noise were simulated and found to cause a deterioration of the image however even with measurements of only one significant figure accuracy the algorithm converg

2 d and 3 d resistivity image reconstruction using crosshole data theoretical changes in the distribution of electrical potential near subsurface resistivity anomalies have been studied using two resistivity models the results suggest that the greatest response from such anomalies can be observed with buried electrodes and that the resistivity model of a volume between boreholes can be accurately reconstructed by using crosshole data the distributive properties of crosshole electrical potential data obtained by the pole pole array method have also been examined using the calculated partial derivative of the observed apparent resistivity with respect to a small cell within a given volume the results show that for optimum two dimensional 2 d and three dimensional 3 d target imaging in line data and crossline data should be combined and an area outside the zone of exploration should be included in the analysis in this paper the 2 d and 3 d resistivity images presented are reconstructed from crosshole data by the combination of two inversion algorithms the first algorithm uses the alpha center method for forward modeling and reconstructs a resistivity model by a nonlinear least squares inversion alpha centers ex press a continuously varying resistivity model and the distribution of the electrical potential from the model can be calculated quickly an initial general model is determined by the resistivity backprojection technique rbpt prior to the first inversion step the second process uses finite elements and a linear inversion algorithm to improve the resolution of the resistivity model created by the first step simple 2 d and 3 d numerical models are discussed to illustrate the inversion method used in processing data from several field studies are also presented to demonstrate the capabilities of using crosshole resistivity exploration techniques the numerical experiments show that by using the combined reconstruction algorithm thin conductive layers can be imaged with good resolution for 2 d and 3 d cases the integration of finite element computations is shown to improve the image obtained by the alpha center inversion process for 3 d applications the first field test uses horizontal galleries to evaluate complex 2 d features of a zinc mine the second field test illustrates the use of three boreholes at a dam site to investigate base rock features and define the distribution of an altered zone in three dimensions

ikaite tufa towers in ikka fjord southwest greenland their formation by mixing of seawater and alkaline spring water abstract ikka fjord in southwest greenland is the type locality for ikaite a metastable hexahydrate of calcium carbonate here ikaite forms submarine tufa columns rising up to 18 m above the fjord bottom the columns are spectacular examples of abiogenic carbonate precipitation in a cold seawater environment and so far represent the only known formation of ikaite in seawater we have analyzed the 2h 13c 14c 18o and 87sr contents and major element and minor element compositions of ikaite and of the different water types in and around ikka fjord in order to understand the formation of the ikka columns water from inside the columns is fresh but alkaline rich in ions of sodium bicarbonate and carbonate and has a stable isotope composition identical to precipitation falling on the nearby gronnedal ika igneous complex and we conclude that the tufa columns form over submarine springs issuing from the bottom of ikka fjord dissolution of unidentified sodium carbonate minerals in carbonatites in the igneous complex probably accounts for the peculiar chemistry of the springs ikaite supersaturation and precipitation is controlled by mixing of spring water and seawater at the cold 6 c fjord bottom and precipitation is accelerated by the formation of hydrated caco3o aq ion pairs while phosphate ions in the spring water act as inhibitor for precipitation of anhydrous carbonates we propose that the spring water seeps in ikka fjord literally create their own conduits in the form of the vertical chimney like columns with ikaite forming continuously at the tops of the columns the only limits to upward growth are winter ice and the fresh water layer capping the fjord during summer

the variability of crater identification among expert and community crater analysts abstract the identification of impact craters on planetary surfaces provides important information about their geological history most studies have relied on individual analysts who map and identify craters and interpret crater statistics however little work has been done to determine how the counts vary as a function of technique terrain or between researchers furthermore several novel internet based projects ask volunteers with little to no training to identify craters and it was unclear how their results compare against the typical professional researcher to better understand the variation among experts and to compare with volunteers eight professional researchers have identified impact features in two separate regions of the moon small craters diameters ranging from 10 m to 500 m were measured on a lunar mare region and larger craters 100s m to a few km in diameter were measured on both lunar highlands and maria volunteer data were collected for the small craters on the mare our comparison shows that the level of agreement among experts depends on crater diameter number of craters per diameter bin and terrain type with differences of up to 45 we also found artifacts near the minimum crater diameter that was studied these results indicate that caution must be used in most cases when interpreting small variations in crater size frequency distributions and for craters 10 pixels across because of the natural variability found projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information

detection of seepage paths in earth dams using self potential and electrical resistivity methods abstract earth and rockfill dams are designed to operate under steady state seepage anomalous seepage may be a threat to the integrity of the structure in spite of advances made in the fields of geotechnical engineering it is not possible to have 100 leak proof structure any excessive and unplanned seepage may lead to the failure of the dam especially in unconsolidated or fractured terrains geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time enabling to plan technically and economically worthwhile remedial measures in the present paper utilisation of electrical methods for delineation of seepage zones at two of the four saddle dams of the som kamla amba project rajasthan state india which is founded on heterogeneous rock mass is discussed electrical resistivity method was used to delineate zones favourable for seepage whereas self potential sp method was used to delineate the seepage paths sp measurements have shown negative anomaly of the order of 10 20 mv in amplitude indicating low seepage coinciding with the seepage measurements made by the project authorities

assessing the potential of internal instability and suffusion in embankment dams and their foundations suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces soils susceptible to suffusion are described as internally unstable this technical note describes a method for assessing the potential of internal instability of silt sand gravel or clay silt sand gravel soils based on their particle size distribution based on laboratory tests carried out by the writers and results published by others it is shown that some commonly used methods are conservative for these soils

monitoring of internal erosion processes by time lapse electrical resistivity tomography abstract internal erosion phenomena are a major threat to all earthen structures such as river levees and dams studying these phenomena has been limited because they occur concealed inside the material which makes them difficult to observe and monitor non destructive geophysical monitoring techniques are powerful tools that can provide insight into the processes involved for this reason a test rig has been specifically designed to conduct three dimensional electrical resistivity tomography of soil specimens undergoing internal erosion due to seepage two suffusion tests were conducted where the erosion evolution has been monitored the time series of eroded mass weight were then used to correlate the changes in three dimensional resistivity distribution to the porosity change in media by means of archie s law the results from the first suffusion test were used to calibrate archie s model parameters it was found that the resistivity variations were able to predict changes in the porous matrix structure the data obtained from the second test were used to validate the model parameters and confirmed that the time lapse three dimensional inverted resistivity images were able to successfully quantify the global erosion rate

three dimensional geophysical anatomy of an active landslide in lias group mudrocks cleveland basin uk a geoelectrical investigation of a slow moving earth slide earth flow in lower jurassic lias group rocks of the cleveland basin uk is described these mudrock slopes are particularly prone to failure and are a major source of lowland landslides in the uk but few attempts have been made to spatially or volumetrically characterise the subsurface form of these slides the primary aim of this study was to consider the efficacy of fully three dimensional geoelectrical imaging for landslide investigation with reference to a geological setting typical of lias group escarpments the approach described here included a reconnaissance survey phase using two dimensional electrical resistivity tomography ert resistivity mapping self potential sp profiling and mapping followed by a detailed investigation of an area of the landslide using three dimensional 3d ert and self potential tomography spt interpretation of the geophysical data sets was supported by surface observations aerial lidar and differential gps geomorphological surveys and intrusive investigations boreholes and auger holes the initial phase of the study revealed the existence of a strong sp signature at the site consistent with a streaming potential source and established the relationships between the main geological units the geomorphologic expression of the landslide and the resistivity of the materials in and around the study area the 3d spt model generated during the second phase of the study indicated drainage patterns across the landslide and preferential flow from the low permeability mud rocks into the underlying more permeable sandstone formation because of favourable resistivity contrasts between the clay rich whitby mudstone formation landslide material and the underlying staithes sandstone formation the volumetric 3d ert image allowed a number of surface and subsurface landslide features to be identified and spatially located these included the lateral extent of slipped material and zones of depletion and accumulation the surface of separation and the thickness of individual earth flow lobes and the dipping in situ geological boundary between the whitby mudstone and staithes sandstone bedrock formations