electrical resistivity imaging of the architecture of substream sediments 1 the modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments there are few methods for noninvasive characterization of streambeds invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments and we have applied the use of one of those techniques to streambeds we demonstrate through two examples how electrical resistivity imaging can be utilized for characterization of subchannel architecture in the first example electrodes installed in riparian boreholes and on the streambed are used for imaging under the river bed the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk in the second example electrical resistivity images determined from data collected using electrodes installed on the river bed provide a constrained estimate of the sediment volume behind a log jam vital to modeling biogeochemical exchange which had eluded measurement using conventional drilling methods owing to the boulder content of the stream the two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

controls of tor formation cairngorm mountains scotland tors occur in many granitic landscapes and provide opportunities to better understand differential weathering we assess tor formation in the cairngorm mountains scotland by examining correlation

cyclic cold climate during the nantuo glaciation evidence from the cryogenian nantuo formation in the yangtze block south china abstract geological and paleomagnetic data indicate that the ice sheets might have extended to low latitude regions in the cryogenian 720 635 ma the snowball earth hypothesis proposed that the earth was completely ice covered during global glaciation however the glacial sedimentary record seems to contradict with the snowball earth hypothesis detailed sedimentological investigations of the glacial deposits would provide the first order constraint on the nature of global glaciation the nantuo formation 654 635 ma in the yangtze block of south china has been correlated with the marinoan snowball earth in this study we conducted systematic sedimentological analyses of six sections cores of the nantuo formation three facies associations were recognized the proximal glaciomarine distal glaciomarine and non glacial marine facies associations the vertical stacking pattern of facies associations can be correlated among the five slope and basin sections while their correlation with the shelf section remains obscure our data indicate two episodes of glaciation that are separated by an interglacial interval during the nantuo glaciation the first glacial episode is recorded by successions of coarse grained facies e g massive diamictite in the lower part of the nantuo formation the re appearance of massive diamictite in the middle to upper part of the nantuo formation indicates onset of the second glacial episode these two glacial episodes were separated by a siltstone shale sequence of several 10 s m thick suggesting an interglacial period with limited influence from glaciation the top of nantuo formation consists of alternative distal glaciomarine and non glacial marine facies associations representing the deglacial sequence of the nantuo glaciation the sedimentary facies analysis indicates that the cold climate during the nantuo glaciation may be cyclic finally our sedimentary analysis confirms a lag between the deglaciation and precipitation of cap carbonate

a relict landscape in the centre of fennoscandian glaciation geomorphological evidence of minimal quaternary glacial erosion abstract the parkajoki area in northeastern sweden is situated near the central area of fennoscandian glaciation despite its location the area is dominated by landforms induced by subaerial weathering and erosion processes such as well developed tors and associated saprolites boulder fields and boulder depressions the glacial geomorphology is dominated by lateral and proglacial meltwater channels subglacial imprints indicative of thawed bed conditions and reshaping by glacier sliding e g fluting drumlins striae are lacking hence most of the landscape still exhibits a preglacial appearance because of its location near the central area of glaciation we attribute preservation to frozen bed conditions of overriding ice sheets the widespread distribution of well developed tors and boulder fields and the degree of chemical weathering of the bedrock indicate that the area has been protected from glacial erosion during all glacial cycles since ice sheet initiation in the late cenozoic unlike most other areas with tors in glaciated regions the parkajoki area is uniquely situated in the lowlands at 150 400 m a s l moreover this relict landscape is surrounded by glacial landscapes including drumlins ribbed moraine and eskers of varying age and at similar elevation hence topographical reasons for this area being persistently cold based cannot be invoked by inference we conclude that strain heat release never managed to cancel the initial subglacial permafrost conditions we attribute this to divergent ice flow towards the convex outline of the ice sheet margin during deglaciations and to the relative roughness of the area compared to its surroundings the implication is that to explain preservation throughout the quaternary all large scale glaciations must have had a similar evolution concerning ice sheet configuration and internal dynamics as the last glaciation for which good constraints on evolution and outline are available

influence of rock mass strength on the erosion rate of alpine cliffs collapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first order control on the morphologic development of these landscapes in this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs to quantify rockwall competence we employed the slope mass rating smr geomechanical strength index a metric that combines numerous factors contributing to the strength of a rock mass the magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face while accounting for the loss of production area as talus buries the base of the wall selecting sites within basins swept clean by advancing last glacial maximum lgm glaciers allowed us to estimate the time period over which talus accumulation occurred i e the production time dividing the magnitude of normal cliff retreat by the production time we calculated recession rates for each site our study area included a portion of the sierra nevada between yosemite national park and lake tahoe rockwall recession rates determined for 40 alpine cliffs in this region range from 0 02 to 1 22 mm year with an average value of 0 28 mm year we found good correlation between rockwall recession rate and smr which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength analysis of the individual components of the smr reveals that joint orientation with respect to the cliff face is the most important parameter affecting the rockwall erosion rate the complete smr score however best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation aspect or slope angle copyright 2009 john wiley sons ltd

imaging the movement of toxic pollutants with 2d electrical resistivity tomography ert in the geological environment of the hoa khanh industrial park da nang vietnam this study presents the results of a geophysical survey undertaken by 2d electrical resistivity tomography ert along two traverses the study was conducted between an industrial park ip and a residential area bounding the hoa khanh industrial park da nang vietnam the first traverse 300 m long which is at the boundary between the industrial park and bau tram lake includes 504 measured data points the second traverse which includes 189 measured data points is 200 m in length and runs alongside the boundary between bau tram lake and the residential area bau tram lake is located between the ip and the residential area and acts as a natural boundary after discarding noisy data points the data were processed using the commercial software res2dinv which creates a 2d visual section of the resistivity distribution below surface using a finite difference algorithm and the method of least squares inversion the result of an inversion which is a simulated 2d resistivity image of the subsurface or electrical resistivity tomogram ert showed the formation characteristics and geological structure along the first traverse from surface to 39 4 m in depth including two overlapping geological layers with indistinctive local boundaries the resulting image illustrates the amalgamation of anthropometric transported soil and rocks with local lake material brought into the lake from other areas to fill up the lake with rock and improve the engineering foundation for the construction of the industrial park buildings the research results show that the main components of the second geological layer on both sides of the survey area have the same electrical signature associated with black mud and sand and represent the natural lake sediments the inferred groundwater level identified in the electrical imagery and two boreholes corresponds approximately to the water level in bau tram lake at a depth of approximately 10 m along both traverses the groundwater in bau tram lake and the surrounding residential areas is contaminated by electrolytes and heavy metals furthermore the groundwater inside the industrial park contains a significant amount of industrial electrolytes with a high probability of chemicals such as kcl nacl and heavy metal contamination with a high probability of elements such as pb hg zn at a greater density than measured in the residential areas this suggests that bau tram lake acts as a filter to strongly reduce the movement of these toxic substances from seeping into the groundwater below the residential area

an evaluation of the electrical resistivity method for water reservoir salinity studies an important potential application of the electrical resistivity method occurs in salinity studies of lakes and water reservoirs however uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle contrasts of a factor of two and changes over short intervals of time typically in hours or days we carry out numerical modeling and inversion of synthetic data and field resistivity data from lake whitney texas u s a to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical resistivity method our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs the simulated freshwater target in the synthetic data effectively is realized from the inversion with root mean square rms error less than 10 however the resolutionof the inverted sections decreases w

the occurrence and behavior of radium in saline formation water of the u s gulf coast region abstract radium has been measured in deep saline formation waters produced from a variety of u s gulf coast subsurface environments including oil reservoirs gas reservoirs and water producing geopressured aquifers a strong positive correlation has been found between formation water salinity and ra activity resulting from the interaction of formation water with aquifer matrix ra isotopes enter the fluid phase after being produced by the decay of parent elements u and th which are located at sites on and within the solid matrix processes that are belived to be primarily responsible for transferring ra from matrix to formation water are chemical leaching and alpha particle recoil factors controlling the observed salinity ra relationship may be one or a combination of the following factors a ion exchange b increased solubility of matrix silica surrounding ra atoms coupled with a salinity controlled rate of reequilibration of silica between solution and quartz grains and c the equilibration of ra in solution with detrial barite within the aquifer no difference was found in the brine ra relation in water produced from oil or gas wells and water produced from wells penetrating only water bearing aquifers although the relation was more highly correlated for water bearing aquifers than hydrocarbon containing reservoirs

estimation of submarine groundwater discharge from bulk ground electrical conductivity measurements the utility of bulk ground conductivity bgc measurements in the estimation of submarine groundwater discharge sgd was investigated at four sites covering a range of hydrogeological settings namely cockburn sound australia shelter island usa ubatuba bay brazil and flic en flac bay mauritius at each of the sites bgc was surveyed in the intertidal zone and seepage meters were used for direct measurements of sgd flow rates in the presence of detectable salinity gradients in the sediment a negative correlation between sgd and bgc was recorded the correlation is site specific and is dependent on both the type of sediment and the mixing processes for example at shelter island the maximum mean flow rates were 65 cm d 1 at a bgc of 0 ms cm 1 while at mauritius maximum mean flow rates were 364 cm d 1 at a bgc of 0 ms cm 1 bgc measurements are used to estimate sgd over a large scale and to separate its fresh and saline components extrapolating bgc measurements throughout the study sites yields a total discharge of 2 91 1 59 7 16 and 25 4 103 m3 d 1 km 1 of shoreline with a freshwater fraction of 41 24 29 and 63 at cockburn sound shelter island ubatuba bay and flic en flac bay respectively the results demonstrate that ground conductivity is a useful tracer to survey and separate freshwater and recirculated seawater component of sgd the presented investigation is a subset within a series of experiments designed to compare different methods to investigate sgd co organized and carried out by scor loicz ioc and iaea

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

relating estuarine geology to groundwater discharge at an oyster reef in copano bay tx abstract coastal bays with fresh submarine groundwater discharge sgd have been found to provide a favorable environment to shellfish e g oysters significant variability in the spatial distribution and magnitude of sgd may occur because of subsurface heterogeneity we investigated the relationship between stratigraphic controls i e paleovalley systems and the spatial distribution of sgd in relation to oyster reefs in copano bay south texas major oyster reefs have been shown to be oriented perpendicular to shore along interfluves and near paleovalley margins a novel combination approach of radioactive geochemical tracers stable isotopes geophysical and petrophysical techniques were used to identify estuarine depositional environments for individual hydrogeologic characterization and evaluation of sgd distribution with implications to ecological features such as oyster reefs a 1 km2 area within a paleovalley system in copano bay yielded discernible differences in sediment type apparent resistivity and sgd rates among four different depositional environments paleovalley paleovalley margin oyster reef and interfluve electrical resistivity tomography revealed a direct connection between the oyster reef and the underlying more permeable interfluve and the presence of a fresher sgd component in the subsurface measurements of sgd from stationary and mobile continuous radon 222 surveys across each depositional environment showed that by and large areas in proximity to reefs have larger sgd rates 62 6 11 3 cm d in january and 28 7 10 8 cm d in july when compared to paleovalleys 31 9 8 9 cm d in january and 19 5 7 2 cm d in july the role of depositional environments as hydrologic controls on sgd to oyster reefs revealed in this study is further confirmed by significant differences in stable and radioactive isotopes observed over small spatial scales offshore when compared to the entire estuary although constant mixing and radon 222 degassing of bay waters are likely altering the relationships between the different depositional environments and magnitude of sgd this study provides an improved understanding of possible pathways of freshwater and solute inputs to oyster reefs for more informed decisions on reef restoration efforts

tidally regulated chemical fluxes across the sediment water interface in elkhorn slough california evidence from a coupled geochemical and hydrodynamic approach measurements of four ra isotopes ba mn u and dissolved nutrients were used in concert with hydrodynamic modeling to reveal a large tidally regulated sediment surface water exchange within elkhorn slough an estuary in monterey bay california hydrologic and oceanographic data from in situ sensors and geophysical surveys of estuarine bottom sediments were integrated with the chemical measurements to develop ra flux boundary conditions for a three dimensional hydrodynamic transport model of the estuary sediment and surface water exchange is the dominant source of ra isotopes within this system this process occurs without significant fresh terrestrial groundwater discharge a number of known solute transport and pore water flushing mechanisms can explain the 224ra input including diffusion evaporative transport bioirrigation and inundation and drainage of borrows and macropores the 226ra results suggest that some of these mechanisms or others are capable of mobilizing ra from deeper sediments the sediments supplying this flux may cover an area as large as the entire intertidal zone primarily salt marsh to a depth of 1 2 cm in addition the ra delivery to the estuary appears to be temporally regulated by the tidal inundation of the salt marsh and subsequent drainage through tidal creek channels these results illustrate the importance of the intertidal zone as a flowpath in the estuarine water cycle and the tidal phase lag that results when solute from this zone is transported into the estuary this process is essential to understanding estuarine biogeochemical budgets of elements with significant sedimentary sources among marine environments estuaries stand out for their high biologic productivity numerous societal functions and hydrologic and chemical complexity because of their complexity and variability estuaries are also challenging environments to study and even more so to predict large tidal excursions temporally variable freshwater inputs and stratification can confound efforts to relate water chemistry to anything but the largest features e g riverine inputs mixing processes and thus net tidal exchange are spatially and temporally variable in many estuaries uncles 2002 making it difficult to predict chemical exchange with the sea the complex morphology of intertidal salt marshes and mudflats results in irregularly flushed areas where evaporation and stagnation can alter the salinity trace element and nutrient chemistry of intertidal water such water is ultimately remixed back into the main estuary influencing surface water chemistry sediment pore waters also possess distinct chemical characteristics and can influence surface water chemistry through a variety of exchange processes huettel et al 1998 charette and sholkovitz 2006 in shelf sands intertidal sand flats and other permeable sediments the dominant solute exchange mechanism is pressure induced advection created by the interaction of currents waves

linking regional sources and pathways for submarine groundwater discharge at a reef by electrical resistivity tomography 222rn and salinity measurements 1 submarine groundwater discharge sgd is an important component of the hydrologic cycle connecting terrestrial to marine environments sgd in fringing reefs and its consequences on biogeochemistry and ecology remain mostly unexplored the 222rn activity and salinity of seawater indicate a substantial groundwater contribution throughout most of the 20 km2 studied tropical reef in pangasinan philippines over 30 km of electrical resistivity profiles with a penetration depth of 12 5 m shows widespread zones within the reef that are much more resistive than porous reef rocks or sediment saturated with typical seawater some discrete resistive areas are located close to where seawater has 222rn peaks and where geologic lineaments are likely located suggesting that these are preferential pathways for fresher groundwater discharging to the reef sgd at the site could be a major ecological factor connecting the reef to the subsurface environment which in turn may lead to connections to land

submarine groundwater discharge in tidal flats revealed by space borne synthetic aperture radar most space borne sensors cannot detect subsurface features groundwater is a typical subsurface feature and its discharge to coastal ocean waters plays an important role in transporting terrestrial chemical constituents and providing habitats for various species of fauna and flora this is the first paper to report observational evidence for submarine groundwater discharge sgd in tidal flats using space borne synthetic aperture radar sar tidal flats are composed of high moisture saturated sediments and water puddles these shallow water puddles were imaged effectively by using sar systems the presence of water puddles is usually indicated by low radar backscatter in sar images due to specular reflections on the water surface this effect was proved by comparing radar backscattering coefficients obtained from two space borne sar systems terrasar x and radarsat 2 with those obtained from two theoretical scattering models iem and oh model we observed relatively large widely distributed water puddles in belt shape along the upper parts of the tidal flat which were confirmed to be related to the discharge of groundwater the results of this research suggest that sar can be a powerful tool for observing and determining the areal distributions of possible groundwater discharge in large tidal flats which is normally difficult to detect with traditional measurement tools or survey techniques for groundwater discharge we firmly believe that this technique can reduce significantly the efforts of field work to confirm sgd in tidal flats

understanding the hydrogeology of the venice lagoon subsurface with airborne electromagnetics abstract the occurrence of alternating dry wet conditions in transitional environments such as wetlands deltas and lagoons usually challenges the use of traditional direct and geophysical surveys for comprehensive hydrogeologic investigations moreover significant mixing between continental fresh groundwater and marine salty surface waters generally takes place in these flat coastal areas airborne electromagnetics aem is a promising tool in this respect as it provides in a fast and cost effective manner large scale distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models the results of a skytem aem survey in the venice lagoon italy show the capability of this technique to significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland subsurface irrespective of the different features characterizing the area the environment consists of salt marshes mud flats shallows tidal channels islands together with reclaimed farmlands crossed by natural watercourses and drainage channel networks in particular the aem shows i the presence of fresh water with resistivity larger than 20 m underneath the central part of the lagoon at depths from 10 to 25 m below m s l ii the interface between different relevant stratigraphic units e g the clayey layer bounding the holocene pleistocene sedimentation and iii the occurrence of areas with possible submarine fresh groundwater discharge moreover the source and inland extent of the saltwater contamination in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed aem data were complemented with very high resolution seismic vhrs acquisitions the integrated analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability of the subsurface fluids

temporal variability of freshwater and pore water recirculation components of submarine groundwater discharges at baffin bay texas submarine groundwater discharges sgds are an important source of freshwater as well as nutrients and other chemicals to bays and estuaries sgds are particularly important for coastal bodies in arid and semi arid regions that are not fed by perennial streams the baffin bay tx is a shallow coastal water body that is weakly connected to the gulf of mexico and has no major rivers or streams draining into it a year long submarine groundwater discharge measurement study was carried out at the loyola beach of the baffin bay during the months of july 2005 june 2006 a total of 23 synoptic sgd sampling events were carried out with most events collecting sgd data continuously over a period of 24 h at a 1 min temporal resolution using an ultrasonic seepage meter the median sgd was noted to be 3 83 cm d with an inter quartile range iqr of 11 36 cm d four sampling events had anomalously high sgd values 27 48 cm d which are hypothesized to be due to the geologic heterogeneity of the sea bed and meteorological effects eight of the 23 sampling events had a negative average sgd flux indicating landward flow the short term diurnal variability of sgd was comparable or sometimes higher than the longer term and between events variability no long term trend could be inferred in the short term sgd measurements showed considerable persistence and the effective sample size analysis indicated each sampling event consisting of over 1 000 samples yielded only a handful of statistically independent measurements of sgd the measured sgd values exhibited both negative hydraulically controlled and positive wave set up controlled correlations with the bay water levels marine controls appeared to be the most significant sgd drivers and are in turn controlled by prevailing aeolian forcings the salinity of the sgds were estimated from measured sonic velocities and used in conjunction with the end member mixing models to estimate fresh meteoric and re circulated pore water fractions the freshwater fraction of the sgd was estimated to vary between nearly 4 and 89 with a median value of 9 96 and an iqr of 7 16 three events were noted to have abnormally high freshwater fractions 28 50 and 84 which are likely artifacts caused by bay water freshening from rainfall and plausible thermal expansion the meteoric and pore water partitioning was sensitive to the assumed end member concentrations this study provides preliminary estimates for sgds along the south texas coast line and is useful for calibrating groundwater flow models and understanding the relative importance of terrestrial and marine controls on sgd however the heterogeneous nature of the sedimentary geology of the texas gulf coast implies the sgd fluxes are likely to exhibit considerable spatial variation that has not been characterized yet therefore the study provides useful insights for such future data collection and monitoring activities the measured sgd values at baffin bay tx are comparable to those reported at other parts of the gulf of mexico

stress and fracture evolution in a cooling pluton an example from the diamond joe stock western arizona u s a abstract an analytical model of fracturing in a crystallizing cylindrical pluton is applied to the natural fracture distribution in the diamond joe stock western arizona u s a the model accounts for three inputs to the stress during cooling thermal contraction magma pressure and regional tectonics fracture type shear or tensile orientation and density were determined at over 300 locations throughout the 8 km diameter stock a distinct pattern of fractures radiates outward from the center of the stock a deflection of these fracture trends toward the regional maximum principal stress direction provides a constraint on the magnitude and orientation of regional stress at the time of crystallization and cooling a calculated model of the fracture pattern suggests that regional maximum and minimum principal stress were 75 and 15 mpa with the orientation controlled by local tectonism the distribution of fractures appears to be insensitive to variations in magma pressure except near the wall of the chamber hence little constraint on magma pressure could be derived from the model thermal gradients during cooling and regional stress appeared to have a greater effect than magma pressure on the overall fracture distribution larger thermal gradients during the early stages of crystallization led to abundant early tensile fractures assuming that the crystalline portions of the pluton behaved elastically during cooling and that all strain was accommodated by fractures the variation of theoretical strain is similar to the distribution of fracture densities within the stock

surface water groundwater exchange in transitional coastal environments by airborne electromagnetics the venice lagoon example 1 a comprehensive investigation of the mixing between salt fresh surficial water and groundwater in transitional environments is an issue of paramount importance considering the ecological cultural and socio economic relevance of coastal zones acquiring information which can improve the process understanding is often logistically challenging and generally expensive and slow in these areas here we investigate the capability of airborne electromagnetics aem at the margin of the venice lagoon italy the quasi 3d interpretation of the aem outcome by the spatially constrained inversion sci methodology allows us to accurately distinguish several hydrogeological features down to a depth of about 200 m for example the extent of the saltwater intrusion in coastal aquifers and the transition between the upper salt saturated and the underlying fresher sediments below the lagoon bottom are detected the research highlights the aem capability to improve the hydrogeological characterization of subsurface processes in worldwide lagoons wetlands deltas

weathering mantles and their significance for geomorphological evolution of central and northern europe since the mesozoic abstract weathering mantles saprolites are very widespread in central western and northern europe where they form thick near surface residual deposits often in excess of 50 m they vary in the type of weathering the bedrock lithology involved the topographic setting and the age and stratigraphic context this review paper provides information about the distribution and major characteristics of weathering mantles from a number of key areas including the british isles the central european belt of mid mountains and uplands the scandinavian mountains and the fennoscandian shield it also examines the evidence for weathering etched origin of various landforms including boulders tors inselbergs basins and some regional landforms assemblages major types of regionally important weathering mantles include ferrallitic lateritic saprolites kaolinite rich saprolites sandy to grus mantles and various residuals left after partial dissolution of carbonate rocks although dating of weathering mantles is often circumstantial it appears sufficiently precise to argue for various ages of deep weathering mesozoic pre late cretaceous mantles are particularly widespread but there are also early tertiary and miocene saprolites widely present whilst most grus weathering is likely to be of miocene to pleistocene age individual upland areas have been subjected to multiple episodes of weathering whose legacy is the present day co existence of different weathering products continental and shallow marine deposits around the uplands particularly in the north sea and intra continental graben structures are often dominated by quartz and kaolinite pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale they demonstrate that weathering mantles repeatedly formed and were subjected to erosion and new cycles of weathering were initiated we suggest that deep unroofing of basement structures in many parts of europe has been mainly accomplished by deep weathering and stripping of pre weathered rock the phenomenon of deep weathering has been very important for geomorphology etched landforms vary in size from small residual boulders up to regional characteristic landscapes etchsurfaces such as joint valley landscapes of southern sweden or undulating multi convex and multi concave landscapes of many uplands in central europe deep weathering has played a major part in the geomorphological evolution of europe since at least the late triassic and the concept involving long term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features

mineralogical and textural controls on the weathering of granitoid rocks summary the results obtained in several recent studies provide convincing evidence that potassium rich granitoid rocks are relatively more resistant to weathering than their less potassic counterparts this reflects the fact that microcline and orthoclase are more stable in most weathering environments than calcic plagioclase and biotite relatively slight differences in bulk rock chemical composition can lead to differential rates of weathering in areas of inhomogeneous granitoid terrain thereby leading to the development of topographic features such as inselbergs a second major control on the rate of weathering is rock permeability this is largely a function of degree of microfracturing and jointing in most circumstances grain size and other textural differences probably exert a minor influence on rates of chemical weathering although laboratory tests have shown they may profoundly affect physical strength parameters

the granite tors of dartmoor southwest england rapid and recent emergence revealed by late pleistocene cosmogenic apparent exposure ages dartmoor in sw england is a classic periglaciated granite upland adorned with a population of over 150 tors the origin of the tors has been controversial but their emergence by differentiation after stripping of regolith during pleistocene cold phases is accepted however their actual age has been unknown with possible scenarios ranging from preservation since the early middle pleistocene to relatively short lived landforms in a maritime climate with high denudation rates the latter is now supported by 32 cosmogenic surface exposure dates from 28 tors across the whole upland the distribution of apparent 10be ages peaks strongly in the middle devensian 36 50 ka which with corrections for weathering and limited ice shielding could be interpreted as early devensian these ages are much younger than those found for three glacially unmodified cairngorms tors and somewhat younger even than glacially modified cairngorms tors the dates show little spatial variation although an ice cap has now been modelled in the heart of northern dartmoor tors here are of median age suggesting that ice cover sufficient to shield tors from incoming radiation was of short duration the few younger tor ages support the idea of continuing landform instability across the landscape with weathering flakes redeveloping soon after inferred loss of top pillows by gelifraction or gravitational toppling the few older tor ages have no systematic explanation and may indicate inheritance from an earlier cycle of bedrock near exposure since most tors are modest in height typically 2 5 m volumetrically insignificant and often in advanced stages of disintegration the general impression is that they are evanescent features which emerge and quickly disappear during every pleistocene climatic downturn tor populations may thus flicker across the landscape rather randomly over the quaternary the remarkably consistent age of the present tor population could be associated with a stripping event at the start of the devensian but fuller analysis must await closer controls on tor denudation rates in different climatic phases and on ice cover extent and duration these results only date extant tor surfaces not the landscape but as the best available erosion pins they have evident value in exploring theories of the evolution of dartmoor during the quaternary

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

detecting submarine groundwater discharge with synoptic surveys of sediment resistivity radium and salinity 1 a synoptic geophysical and geochemical survey was used to investigate the occurrence and spatial distribution of submarine discharges of water to upper nueces bay texas the 17 km survey incorporated continuous resistivity profiling measurements of surface water salinity temperature and dissolved oxygen and point measurements of dissolved ra isotopes the survey revealed areas of interleaving vertical fingers of high and low conductivity extending up through 7 m of bay bottom sediments into the surface water located within 100 m of surface salinity and dissolved ra maxima along with peaks in water temperature and lows in dissolved oxygen these results indicate either brackish submarine groundwater discharge or the leakage of oil field brine from submerged petroleum pipelines

geoelectrical signals of geologic and hydrologic processes in a fringing reef lagoon setting summary coastal groundwater may discharge into nearshore and offshore waters forced by terrestrial fluxes controlled by local geology and modulated by the hydrodynamics of littoral water we investigated the electrical signature of these features with a dense multiscale network of electrical resistivity tomography ert surveys in the muri lagoon of rarotonga cook islands the ert surveys spanned from onshore to 400 m into the lagoon and used standard electrodes on land and across the foreshore submerged electrodes in the shallow subtidal zone and floating electrodes towed throughout the reef lagoon by a boat ert surveys on land mapped a typical freshwater lens underlain by a saltwater wedge but with possible deviations from the classical model due to an adjacent tidal creek further inland ert surveys imaged a layer of lava flow deposits that is potentially a confining hydrogeologic unit this unit was used to constrain the expected electrical resistivity of these deposits below the lagoon ert surveys across the intertidal zone and into the lagoon indicated fresh groundwater and porewater salinity patterns consistent with previous small scale studies including the seaward extension of fresh groundwater pathways to the lagoon electrical resistivity er variations in the lagoon subsurface highlighted heterogeneities in the lagoon structure that may focus submarine groundwater discharge sgd through previously unknown buried lava flow deposits in the lagoon a transition to higher er values near the reef crest is consistent with the er signature of porosity reduction due to ongoing differential cementation of reef deposits across the lagoon the imaged coastal hydrostratigraphic heterogeneity may thus control terrestrial and marine porewater mixing support sgd and provide the pathways for groundwater and the materials it transports into the lagoon this hydrogeophysical investigation highlighted the spatial heterogeneity of submarine coastal geology and its hydrogeologic control in a reef lagoon setting but is likely to occur in many similar coastal settings ignoring geologic complexity can result in mischaracterization of sgd and other coastal groundwater processes at many spatial scales