a field based classification scheme for gravel beaches a tripartite classification of gravel beaches based upon morphodynamic properties is proposed and demonstrated for 42 new zealand beaches the main advantage of this scheme is that it is based on simple visual classification that can be applied globally in the field and is underpinned by morphodynamic differences between the beach types the three types identified from the results are 1 pure gravel beach 2 mixed sand and gravel beach 3 composite gravel beach pure gravel beaches have steep slopes tan 0 08 0 24 and gravels extending from the storm berm to below mean low water spring tide level mixed sand and gravel beaches have moderate slopes tan 0 04 0 13 with sand and gravel entirely mixed both cross shore and at depth composite gravel beaches have a steep gravel berm fronted by a low angle intertidal terrace with overall beach slopes of tan 0 05 0 14 on composite beaches there is distinct hydrodynamic cross shore sorting of the sand and gravel component these broad types are tested using discriminant analysis and the three classes are shown to be highly significant f 16 24 df 8 p 0 00005 the key discriminating variables are iribarren number beach width average grain size and storm berm height

mechanism of rifting considerations based on results of physical modelling and on geological and geophysical data abstract on the basis of results of physical modelling and an analysis of the relevant geological and geophysical data the mechanism and regularity of rifting are studied as a rule rifting develops in extensive and long living hot regions characterized by a reduced thickness of lithosphere rifts develop due to regional extension of the lithosphere in the hot regions and are zones of localization of deformation neckings the style of deformation and faulting in a necking are studied experimentally the plastic layers of low strength in the continental crust play an essential role in rifting those places favourable for the localization of plastic deformation are related to the parameters expressiveness of these layers in various parts of a hot region the development of a necking rifting is accompanied by replacement of the lower crust by high strength mantle ultrabasic material when there is an interruption of the extension this might cause an effective strengthening of the lithosphere in the rift zones and results in jumps when tension is renewed modelling has indicated that rifts can form angular junctions and branching in hot spots and older faulting zones various generations of rifts can converge and intersect in a hot spot in contrast to this cold lithospheric zones of higher strength are detoured by rifts basic magmatism including plateau basalts is often present in such zones

coastal embayment rotation response to extreme events and climate control using full embayment surveys abstract barrier beach change in directionally bi modal wave climates presents an increasing challenge for coastal communities both in the short term storm events and decadal to centurial time scales long term evolution predicting and planning for subsequent variations requires understanding of the morphological response to changes in wave energy along with the atmospheric forces driving the wave climate in this paper multi method topo bathymetric surveys are used to assess the morphological change of a semi sheltered gravel barrier start bay devon uk total sediment budgets supra to sub tidal with spatially varying uncertainty levels indicate the embayment is closed one third of total sediment flux occurred in the sub tidal establishing the importance of sub tidal transport for this type of coastline our results demonstrate that under the predominance of a given wave direction rotation first occurs within sub embayments additional sustained and extreme energy levels are then required for full embayment rotation to occur with significant headland bypassing in this instance 6 105 m3 of gravel was transported alongshore during a 3 year sustained period of dominant southerly waves including a 1 50 year storm season full embayment rotation whilst 3 105 m3 was returned during a 2 year period of dominant easterly waves sub embayment rotation only a novel parameter is introduced that predicts beach rotation based on the directional wave balance in turn winter wave direction is shown to correlate with a combination of two climate indices given adequate predictions of relevant climate indices these findings constitute the basis of a generalisable method to predict and plan for future beach rotation on similar beaches globally

fabric related seismic anisotropy in upper mantle xenoliths evidence from measurements and calculations the seismic properties and their directional dependence have been measured in four mantle peridotites from picritic tuffs vitim baikal region russia geothermobarometric data suggest a source depth for the xenoliths corresponding to the spinel garnet transition zone 40 90km the experimental data include the measurement of p and s wave velocities and densities at confining pressures to 600 mpa and temperatures to 600 c and the determination of velocity anisotropy and shear wave splitting the measured velocities are compared with velocity calculations based on lattice preferred orientation lpo of olivine orthopyroxene the modal composition of the rocks and the single crystal stiffness coefficients macroscopic velocity anisotropy is strongly controlled by the lpo of olivine measured 600 mpa room temperature and calculated p wave anisotropies compare fairly well although the experimentally determined velocities are markedly lower than the calculated velocities the correspondence between measured and calculated shear wave splitting data is less pronounced this is attributed to grain boundary effects retrogressive reactions interstitial glass incomplete crack closure and to the fact that the lpo of the cpx fraction has not been included in the calculation the magnitude of p wave anisotropy corresponds to that observed in mantle peridotites exposed at the surface ivrea zone northern italy ronda southern spain

flow system controls of the chemical evolution of groundwater abstract isotopic and major ion analyses of 130 fresh and brackish groundwater samples reveal a strikingly consistent pattern of variation over 28 000 km 2 of the western canada sedimentary basin hydrodynamic interpretations based on drill stem tests and piezometric data reveal a pattern of broad regional flow from south to north however there is some evidence to suggest that patterns of groundwater flow have been influenced in the past by wisconsin glaciation all the permeable units appear to be recharged by meteoric water in the south where they outcrop or come close to the surface samples of groundwater collected down dip in each of six major sandstone units are progressively enriched in d 18 o na and cl for example the deepest waters of the artesian milk river aquifer are enriched by up to 70 and 15 with respect to the d and 18 o of the modern recharge waters the pattern of chemical evolution is strongly related to the hydraulic characteristics of individual units the isotopic composition is determined by the extent to which hydraulic conductivity has facilitated meteoric water flushing of connate water thus more permeable units and permeable zones within a unit tend to be isotopically lighter because of a more complete and more rapid invasion of meteoric water interestingly the largest conductivity values are found in some of the deepest units 1500 m consequently water in these deeper units have d and 18 o values which approach that of the recharge the major ion chemistry is controlled both by this process and a complex set of rock water interactions in addition to providing information about the chemical evolution of groundwater this study can begin to quantify the complex pattern of flushing in a large sedimentary basin

determination of crustal fluid residence times using nucleogenic 39ar abstract argon 39 is a radioactive isotope of ar with a half life of 269 years there are two natural sources of 39 ar on earth cosmogenic production in the upper atmosphere and nucleogenic production in rocks cosmogenic 39 ar has been recognized as an ideal tracer for groundwater residence times and oceanic circulation nucleogenic 39 ar has generally been considered problematic for groundwater studies in this work we developed simple models for the evolution of 39 ar 40 ar ratios where 40 ar denotes radiogenic 40 ar produced in the model system in rocks and fluids in rocks both 39 ar and 40 ar are produced and a fraction of the 39 ar and 40 ar is released into the mobile fluid phase in both reservoirs 39 ar reaches production or supply decay equilibrium whereas 40 ar accumulates with time thereby the 39 ar 40 ar ratio in rocks and fluids generally decreases with time our models suggest that the co evolution of these two isotopes in rocks and fluids provides a new chronometer of fluid migration and reaction in the crust this chronometer is relevant to a much wider time range than that limited by radioactive decay of cosmogenic 39 ar i e 1400 years at the current detection limit of 3 modern atmospheric value the 39 ar 40 ar chronometer is applicable to estimating residence times of very old groundwater as well as for studying fluid rock interactions and fluid migration rates such as those occurring during co 2 sequestration and the formation of hydrocarbon reservoirs

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

geological control of beach morphodynamic state the concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid 1980s and expansion in the 1990s much of the pioneering work was undertaken in australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3 dimensional morphology and the dean s parameter h b wst was established subsequently the relative tidal range parameter h b tr was extended to beaches of all tidal ranges in this paper observations are presented from 25 beaches around the north coast of ireland these beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability micro to macrotidal and low to high wave energy each beach was visually categorised into one of several established beach states described in the literature on the basis of field observations for each beach the rtr and dean s parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships observed and predicted beach states were then compared comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria most other beach states did not lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the rtr and dean s parameter in addition this study identifies geological factors as important constraints on actual beach state in the majority of beaches studied inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics c 2005 elsevier b v all rights reserved

a review and assessment of longshore sediment transport equations for coarse grained beaches previous assessments of analytical longshore sediment transport formulae have been heavily biased towards sand sized sediment all have noted the shortage of high quality field data from coarse grained beaches against which to test predictions of longshore transport rates in this paper 12 existing formulae were identified as being potentially applicable for coarse grained sediments and predictions from these formulae are compared using a measured annual transport rate from a shingle beach and a concurrent hindcast wave climate two new empirical equations are also derived one from a numerical model calibrated against the same data set the other derived from field experiments on coarse grained beaches energetics based equations are found to give reasonable predictions of the shingle transport despite being derived for sand beaches in contrast those dimensional analysis type equations which had been validated using laboratory data grossly over predicted the measured transport rates the most accurate predictions were from formulae previously validated at sites similar to that used for this comparison and therefore require further testing against field data from dissimilar sites

rift flank segmentation basin initiation and propagation a neotectonic example from lake baikal new surficial data field landsat tm and topography define morpho tectonic domains and rift flank segmentation in the ol9khon region of the central baikal rift deformation drainage and depositional patterns indicate a change in the locus of active extension that may relate to a recent

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

sea ripple formation the heterogeneous sediment case abstract ripple formation beneath sea waves is analyzed both by experimental and analytical means when the bottom is made up of a mixture of sands an oscillatory flow is obtained in a closed duct by the oscillations of two rigidly connected pistons located at the ends of the duct the amplitude and period of the oscillations can be continuously varied a fixed tray located at the bottom of the duct and filled with different types of sediments allows ripple formation to be observed the presence of graded sediments is found to have a stabilizing effect and causes longer ripples to appear moreover a selective sediment transport is observed and quantified which tends to pile up the coarse grains at ripple crests leaving the fine ones in the troughs as in the companion paper the theory is based on a linear stability analysis of a flat sandy bottom subject to an oscillatory flow because of the presence of a mixture a modified version of exner equation is used and an hiding factor should be inserted in the sediment transport rate formula the flow regime in the bottom boundary layer is assumed to be turbulent the conditions for ripple appearance are determined along with their wavelengths as they form good agreement is found between experimental data and theoretical findings

evidence for small scale mantle convection in the upper mantle beneath the baikal rift zone 1 inversion of teleseismic p wave travel time residuals collected along a 1280 km long profile traversing the baikal rift zone brz reveals the existence of an upwarped lithosphere asthenosphere interface which causes a travel time delay of about 1 s at the rift axis central high an area with early arrivals relative to the stable siberian platform of up to 0 5 s is observed on each side of the rift about 200 km from the rift axis flank lows while the location of the central high is approximately fixed in the vicinity of the rift axis those of the flank lows vary as much as 200 km with the azimuth of the arriving rays we use three techniques to invert the travel time residuals for velocity anomalies beneath the profile two of the techniques assume an isotropic velocity structure and one of them considers a transversely isotropic velocity model with a vertical axis of symmetry we use independent geophysical observations such as gravity active source seismic exploration and crustal thickness measurements to compare the applicability of the models other types of geophysical measurements suggest that the model involving transverse isotropy is a plausible one which suggests that the central high and flank lows are caused by the combined effects of an upwarped asthenosphere with a 2 5 lateral velocity reduction and a velocity increase due to transverse isotropy with a vertical axis of symmetry we consider the anisotropy to be the result of the vertical component of a lithosphere asthenosphere small scale mantle convection system that is associated with the rifting

morpho sedimentary dynamics of a micro tidal mixed sand and gravel beach playa granada southern spain abstract this paper addresses the changes in the morphology and sedimentology of a micro tidal mixed sand and gravel beach playa granada southern spain forced by wave and water level variations and human intervention through nourishment monthly and storm event driven beach surveys consisting of topographical measurements and sediment sampling in two selected areas were carried out over a one year period three prevailing sediment fractions sand fine gravel and coarse gravel and two end member morphological states of the upper beach profile convex with multiple berms and concave with a single storm berm were identified between them several transitional profiles were formed characterized by developing berms that progressively overlapped generating sediment variability both across the beach profile and with depth the results indicate that the total run up including water level reached during an event represents a more accurate threshold for differentiating between erosional and depositional conditions than wave height they also suggest that mixed sand and gravel beaches recover faster from storm erosion than sandy beaches the long term benefit of the artificial nourishment that took place at the end of the survey period was very limited and this is attributed to the too fine sediment used for the nourishment and its placement too high on the beach clearly nourishment interventions must take into account the natural sediment distribution and the profile shape to avoid rapid losses of the nourished sediment

observations of morphological change and sediment transport on a steep gravel beach abstract observations of morphological change and swash sediment loads concurrent with measurements of water level waves and currents were obtained during a spring to spring tidal cycle on a steep macrotidal gravel beach in southwest england the wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0 4 m and 6 s respectively incident frequency water motions dominated the hydrodynamics and the phasing between water surface elevation and cross shore and alongshore currents was inconsistent with standing edge wave motion morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified regression and rollover in response to falling and rising water levels respectively and removal and reformation during and after storms respectively swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1 kg per swash onshore per unit metre beach width steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches

hydrodynamics and morphological adjustment of a mixed sand and gravel beach torere bay of plenty new zealand detailed measurements of cross shore wave energy transformation swash sediment transport and beach profile change under low energy conditions are reported from a mixed sand and gravel beach at torere bay bay of plenty new zealand measurements were undertaken during a 10 day period following a storm event and document post storm recovery of the beach nearshore wave spectra identify periods in which incident wave energy is dominated by swell and wind wave energy results show that wind wave energy observed in the nearshore is effectively removed from beachface spectra at the break point step under lower tidal stages swash is driven by longer period swell energy although dissipation of short period wave energy is critical in entraining sediments on the lower beach at higher tidal stages wind wave energy is able to propagate across the break point step shoal and break on the lower beachface tidal modulation of wave processes across the lower beachface under low incident wave conditions is found to stimulate active sediment reworking migration of the break point step and shoreward sediment flux to promote beach accretion

no moho uplift below the baikal rift zone evidence from a seismic refraction profile across southern lake baikal 1 the late cenozoic baikal rift zone brz in southern siberia is composed of several individual topographic depressions and half grabens with the deep lake baikal at its center we have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the baikal explosion seismic transects best project across the rift zone in the southern part of lake baikal the seismic velocity structure along the profile is determined by tomographic inversion of first arrival times and 2 d ray tracing of first arrivals and reflections the velocity model shows a gently deepening moho from the siberian platform 41 km depth into the sayan baikal fold belt 46 km depth we can exclude the presence of any moho uplift around the 10 km deep sedimentary graben structure of southern lake baikal the lower crust includes a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s slightly offset to the northeast from the rift axis we interpret this feature as resulting from mafic intrusions their presence may explain the flat moho by compensation of lower crustal thinning by intrusion of mafic melts the pn wave velocities 8 15 8 2 km s are normal for the area and do not show any sign of decompression melting in the sub moho mantle such that possible lithosphere thinning has not reached the base of the crust on the basis of the results of the best project we suggest that the brz is formed by passive rifting in the rheologically weak suture between the siberian platform and the amurian plate

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

morphological changes in a cuspate sandy beach under persistent high energy swells renaca beach chile abstract the present work proposes a morphological evolution model for sandy cuspate beaches which depends on two parameters swash excursion s and offshore wave steepness h0 l0 the model was derived from observations of morphology and wave climate at renaca beach in central chile comprising in situ instrumentation topographic surveys wave modeling and optical imagery it was found that wave steepness alone was unable to explain the morphological changes observed on the beach rather results indicate that swash excursion is better to distinguish between erosive and accretionary events with swash excursion exceeding 29 5 m for more than 12 h being indicative of erosive events while morphological changes are led by s wave steepness correlates with the erosive potential of waves especially when h0 l0 is greater than 0 017 although derived for a specific beach under a limited range of conditions this work adds to the understanding of the dynamic behavior of beaches exposed to persistent high energy swells

atmospheric hydrodynamic coupling in the nearshore 1 natural beach shorelines commonly present morphological rhythmic or non rhythmic features of varying geometrical characteristics traditionally their formation is believed to be due to wave induced processes a line thoroughly investigated during the last few decades however these natural beach formations are frequently bounded by coastal cliffs or capes and are affected by intense winds a fact not previously considered this paper presents the results of a field survey demonstrating the existence of atmospheric hydrodynamic coupling in the nearshore region outside of the breaking zone at carchuna beach motril spain where the atmospheric conditions are influenced by a lateral geographic obstacle cape sacratif

measurements of morphodynamic and hydrodynamic overwash processes in a large scale wave flume overwash is an important process that controls short term barrier dynamics as well as long term barrier migration but this process is difficult to study in the field due to its rare occurrence and the challenging conditions under which it occurs this paper uses data collected during the bardex ii experiment in the delta flume the netherlands where a proto type barrier was subjected to a range of wave and water level conditions the objectives of this research are to 1 compare the morphologic response to overwash on a gravel barrier bardex 2008 experiment with that on a sandy barrier bardex ii 2 understand the influence of wave period on overwash characteristics and sediment transport and 3 improve current knowledge of overwash hydrodynamics the comparative analysis shows that barrier overwash can be affected by negative feedback that stabilises the barrier through barrier crest accretion on gravel barriers and by submerged bar development on sandy barriers an increase in the wave period induced a reduction in overwash frequency over the crest but no significant relation was found between wave peak period and overwash discharge nevertheless overall water discharge during an overwash episode significantly correlates with overall overwash sediment transport rate overwash flow depths during the experiment were relatively shallow and velocities were similar compared to those measured during previous studies and reported in the literature despite the controlled laboratory conditions collection of reliable and accurate measurements of overwash velocities remains challenging

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

the influence of shelf indenting canyons and infralittoral prograding wedges on coastal morphology the carchuna system in southern spain abstract submarine canyons and progradational sedimentary bodies are common features of continental margins worldwide few studies have analyzed the relationship between the coastal morphology and the morphology and sedimentary characteristics of the adjacent shelf in wave dominated coasts or the potential role played by shelf indenting canyons as inducers of sediment deposition in shallow waters this work presents a study that correlates the coastal morphology with the characteristics of the adjacent offshore shallow shelf in an area with a complex inner bathymetry the carchuna system spain the study area is characterized by large scale non rhythmic cuspate features in the coastline whereas the inner bathymetry exhibits a shallow water infralittoral prograding wedge ipw and a shelf indenting canyon that has tributaries located a short distance from the coastline using detailed bathymetric measurements observational data and wave propagation modeling the influence of the different bathymetric elements was quantified and a mechanism proposed for the generation of the carchuna ipw the wave propagation results show that the canyon is the main source of the alongshore modulation of nearshore waves and that it plays a major role in the generation of the large scale cuspate features in the shoreline additionally these results suggest that the long term coastal erosion associated with extreme storms yielded sufficient sediment which when subsequently transported eastward the dominant littoral drift direction formed the ipw once formed the ipw modified the wave propagation patterns and contributed to the development and reinforcement of the shoreline features

reply to comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz

radiocarbon and stable isotopes in water and dissolved constituents milk river aquifer alberta canada abstract origin and age of groundwater in the milk river aquifer alberta canada was the focal point of the present study to answer related questions wells in this aquifer were sampled and 2 h and 18 o in water 13 c and 2 h in methane 34 s and 18 o in so 4 13 c and 14 c in dissolved inorganic carbon dic and dissolved organic carbon doc and tritium contents determined stable isotope analyses on ground water permitted the recognition of at least three different zones within the aquifer starting at the recharge zone modern type groundwaters are encountered for the first few kilometers these are followed by groundwater with slightly higher 18 o and 2 h contents i e waters which do not show a glacial signature and were probably recharged under warmer climatic conditions groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift they show the gradual admixture of far more saline formation waters from the alberta basin sulphate s and sulphate o isotope values indicate a till source for the so 4 however so 4 in wells close to the area where so 4 virtually disappears show isotopic values which suggest that so 4 reduction is occurring although other studies could not find bacterial populations of so 4 reducers methane is present in most wells and based on c and h isotope data has a biogenic origin methane production occurs close to some wells and or it diffuses from the confining shales into the aquifer radiocarbon is measurable only in the first 20 km from the recharge zone however transformation of measured concentrations to water ages is very difficult because of the complexity of the geochemical system comparison with 14 c data on doc was therefore very interesting and this new technique may complement the dic radiocarbon dating two wells near the recharge zone yielded dic doc high molecular weight hmw and doc low molecular weight lmw results the dic dates were much older than doc dates but the differenve in years between the wells for all three types of c were within 1000 a of each other the doc dates led to the conclusion that the initial dic radiocarbon content was as low as 30 modern when the water entered the aquifer the age of the water 20 km from the recharge zone was assessed at 20 000 a resulting in a velocity of 1 m a this result is much higher than estimates by other techniques

spatial and temporal variations of sediment size on a mixed sand and gravel beach abstract mixed sand and gravel beaches have been the subject of comparatively few studies in the uk this paper describes the sediment distribution before during and after a programme of beach nourishment along a section of mixed sand and gravel beach forming part of the pevensey bay coastal defences in east sussex uk the beach was recharged in september 2002 and beach profiles were measured along three cross shore transects from august 2002 to february 2003 sediment samples were taken along the transects between august and november 2002 and a total of 147 sediment samples were analysed 40 before nourishment and 107 after nourishment the majority of the sediment samples were strongly bimodal with mean sizes varying between a minimum of 0 18 mm 2 48 for the sand fraction and a maximum of 27 mm 4 74 for the gravel the recharge material was also bimodal but contained more fine sediment than the natural beach material particularly on the upper beach the recharge sediment had grain sizes and sorting similar to some of the natural material but lower bimodality parameters than any of the natural sediment the sediment distributions after recharge contained significantly more fine sediment particularly on the upper beach over time the beach profile lowered and fine sediment appeared to be selectively transported seawards from the beachface

implications of delta retreat on wave propagation and longshore sediment transport guadalfeo case study southern spain abstract the influence of both natural and human induced changes on the evolution of worldwide deltas has been widely addressed however the variations of the submerged morphology of the delta and their implications on coastal dynamics have received limited attention this work details the spatial and temporal variability of the mouth of the guadalfeo river southern spain and focuses on the influence of submerged morphological changes partly due to watershed regulation in 2004 on wave propagation and longshore sediment transport bathymetric measurements were carried out over a 15 year period 1999 2014 a wave propagation model was calibrated and applied and an updated expression for longshore sediment transport was applied using downscaling techniques to obtain the complete littoral drift time series the results show that the river damming led to coastline retreat and bed level erosion up to 3 m along a 1 km section around the river mouth with maximum erosion rates in excess of 760 m 3 m these subtidal morphological changes reduced wave refraction and led to higher breaking wave energy variations in wave climate during the study period have also played a role in influencing the coastline dynamics although the erosion around the river mouth has decreased since 2008 partly due to a sediment pulse in 2010 eastward longshore sediment transport rates under westerly storm wave conditions have significantly increased since then this has led to the propagation of the sediment deficit towards the east of the mouth endangering urban developments at this location this paper provides insights into the shift from wave river dominated deltas towards deltaic coasts increasingly controlled by wave directionality and longshore sediment transport and represents an advance on the understanding of the dynamics of many worldwide deltas where the river sediment supply has decreased due to human activities

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

influence of till provenance on regional groundwater geochemistry abstract a regional groundwater geochemistry study was conducted in the paskapoo formation of southern alberta canada our study area focused on a region where two continental ice sheets the cordilleran and laurentide met the glacial deposits transported by these ice sheets have different bulk characteristics reflective of the bedrock of the source region of the ice recharge through these two different glacial deposits generates distinctly different water geochemistry within the underlying paskapoo formation such that bedrock aquifer acquires a geochemical signature of the immediately overlying glacial deposits through which recharge occurs oxidation of pyrite in laurentide till generates high sulphate groundwater and associated acid generation leads to enhanced mineral weathering this generates high tds high na so4 groundwater in underlying bedrock aquifers this process appears transitory where thin laurentide drift deposits are completely oxidized and have reduced capacity to generate high sulphate water the same bedrock underlying carbonate dominated cordilleran drift deposits have low tds ca hco3 groundwater

beach face and berm morphodynamics fronting a coastal lagoon this study documents two different modes of berm development i vertical growth at spring tides or following significant beach cut due to substantial swash overtopping and 2 horizontal progradation at neap tides through the formation of a proto berm located lower and further seaward of the principal berm concurrent high frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes in mode i sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent the net transport of this sediment is landward only resulting in accretion onto the upper beach face and over the berm crest the final outcome is a steepening of the beach face gradient a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm in mode 2 sediment is eroded from the lower two thirds of the active swash zone during the rising tide and is transported both landward and seaward on the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide the net result is relatively slow steepening of the beach face a change of the profile shape towards convex and horizontal progradation through the formation of a neap berm the primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face this depends on the current phase of the spring neap tide cycle the wave runup height and indirectly offshore wave conditions and the height of the pre existing berm a conceptual model for berm morphodynamics is presented based on sediment transport shape functions measured during the two modes of berm growth c 2006 elsevier b v all rights reserved

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

style of active intraplate deformation from gravity and seismicity data the baikal rift asia to better understand how active deformation localizes within a continental plate in response to extensional and transtensional tectonics a combined analysis of high quality gravity bouguer anomaly and seismicity data is presented consisting of about 35000 earthquakes recorded in the baikal rift zone this approach allows imaging of deformation patterns from the surface down to the moho a comparison is made with heat flow variations in order to assess the importance of lithospheric rheology in the style of extensional deformation three different rift sectors can be identified the southwestern rift sector is characterized by strong gravity and topography contrasts marked by two major crustal faults and diffuse seismicity heat flow shows locally elevated values correlated with recent volcanism and negative seismic p velocity anomalies based on earthquake fault plane solutions and on previous stress field inversions it is proposed that strain decoupling may occur in this area in response to wrench compressional stress regime imposed by the india asia collision the central sector is characterized by two major seismic belts the southernmost one corresponds to a single steeply dipping fault accommodating oblique extension in the centre of lake baikal a second seismic belt is associated with several dip slip faults and subcrustal thinning at the rift axis in response to orthogonal extension the northern rift sector is characterized by a wide low bouguer anomaly which corresponds to a broad high topographic dome and seismic belts and swarms this topography can be explained by lithospheric buoyancy forces possibly linked to anomalous upper mantle at a more detailed scale no clear correlation appears between the surficial fault pattern and the gravity signal as in other continental rifts it appears that the lithospheric rheology influences extensional basins morphology however in the baikal rift the inherited structural fabric combined with stress field variations results in oblique rifting tectonics which seem to control the geometry of southern and northeastern rift basins

six thousand years of coastline evolution in the guadalfeo deltaic system southern iberian peninsula abstract the 4000 bc to present day coastal and shallow marine changes of the guadalfeo river deltaic system southeast spain are studied using historic maps aerial photographs diverse submarine data and hydrodynamic models the deltaic system evolved with little anthropic influence until the 1940s when the river mouth was diverted to the west during the pre diversion stage the system evolved from an estuary to a delta due to the enormous sediment yield in the catchment induced both by anomalously wet climate conditions and by deforestation practices accordingly the coastline advanced significantly up to 3 3 m year 1 during this period particularly during the 1500 to 1873 interval the estimate for volumetric changes in the deltaic system shows very high specific sediment yield values around 60 65 t ha 1 year 1 in the catchment the deltaic system mainly evolved by cannibalization of the older lobate outlet depocentre after the river diversion and the generation of a more elongated depocentre coincident with the current outlet due to enhanced lateral redistribution of sediments from east to west the construction of two major dams in the trunk river in the last 30 years has severely blocked sediment supply to the system although expected coastline erosion has been partially mitigated by longshore sediment redistribution

storm flood impacts along the shores of micro tidal inland seas a morphological and sedimentological study of the vesterlyng beach the belt sea denmark abstract the morphological and sedimentological impacts of an extreme storm event bodil in december 2013 were investigated at a mixed sand and gravel beach vesterlyng in a micro tidal environment along the belt sea denmark the storm response was characteristic for mixed sand and gravel beaches gravelly storm berms with sandy to gravelly washover fans were formed at the upper beach where swash processes dominated during extreme water levels in combination with overtopping and overwash in addition storm scarps and gravel flats were formed the elevation of the storm berm crest was identical to a summation of the still water level 1 60 m in the belt sea during the storm flood and the wave run up 0 75 m at the shore the crest of 2 35 m is therefore a precise measure of the storm flood level this storm flood was classified as a large scale extreme event in a holocene perspective it is suggested that storm berm beach ridge heights above contemporaneous sea level can be used as a proxy of past flood events along micro tidal shores

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

sedinet a configurable deep learning model for mixed qualitative and quantitative optical granulometry i describe a configurable machine learning framework to estimate a suite of continuous and categorical sedimentological properties from photographic imagery of sediment and to exemplify how machine learning can be a powerful and flexible tool for automated quantitative and qualitative measurements from remotely sensed imagery the model is tested on a large dataset consisting of 400 images and associated detailed label data the data are from a much wider sedimentological spectrum than previous optical granulometry studies consisting of both well and poorly sorted sediment terrigenous carbonate and volcaniclastic sands and gravels and their mixtures and grain sizes spanning over two orders of magnitude i demonstrate the model framework by configuring it in several ways to estimate two categories describing grain shape and population respectively and nine numeric grain size percentiles in pixels from a single input image grain size is then recovered using the physical size of a pixel finally i demonstrate that the model can be configured and trained to estimate equivalent sieve diameters directly from image features without the need for area to mass conversion formulas and without even knowing the scale of one pixel thus it is the only optical granulometry method proposed to date that does not necessarily require image scaling the flexibility of the model framework should facilitate numerous application in the spatio temporal monitoring of the grain size distribution shape mineralogy and other quantities of interest of sedimentary deposits as they evolve as well as other texture based proxies extracted from remotely sensed imagery

three dimensional unified geological model of the milk river transboundary aquifer alberta canada montana usa the milk river transboundary aquifer canada usa has been so intensively used over the 20th century that concerns have risen about the durability of this resource since the mid 1950s this aquifer actually corresponds to the middle virgelle member of the upper cretaceous milk river formation called eagle formation in montana to assess the conditions needed for a sustainable use of the aquifer a comprehensive and unified portrait of the aquifer is needed across its international boundary the stratigraphic framework and geometry of geological units on both sides of the international border were thus unified in a 50 000 km2 three dimensional 3d geological model the virgelle member is 0 60 m thick and it subcrops near the border and along both sides of the sweetgrass arch it dips away from the subcrop areas in a semi radial pattern the medicine hat gas field hosted by the alderson member alberta which is separated from the other members by a regional unconformity and the tiger ridge gas field n

bedload dynamics and associated snowmelt influence in mountainous and semiarid alluvial rivers abstract the influence of snowmelt in semiarid alluvial rivers is determined by the river bed configuration and erosion processes moreover the large amount of available sediment in the floodplains of these rivers limits traditional bedload sampling methodologies and suggests the use of large control volumes and long term studies to understand erosive dynamics in this study bedload monitoring in a large control volume 0 2 hm3 from 2004 to 2010 was used to study erosive processes of the guadalfeo river a semiarid alluvial river in southeastern spain with high mountain influences and a hydrological regime conditioned by snow dynamics the methodological approach to testing the performance of different transport models included characterization of the forcing agents precipitation and snowmelt events hydraulic configuration of the river determination of the river bed material surface and substrate and one off measurements for particular events the results indicate a sediment volume effective runoff relationship that is consistent with the existence of steep channels with a flashy runoff regime although the existence of an armored layer derived from snowmelt events greatly controls the transport dynamics with equivalent fractions of cobble gravel and sand in the measured bedload this apparent predominance of near equal mobility was confirmed by the calibrated hiding function exponent x 0 94 0 97 the thresholds for entrainment and transport efficiency are similar to those observed for mountain rivers that exhibit torrential flow although notable differences can be observed in the dynamics of the processes the strong performance of the original meyer peter and muller model with c 8 is shown to estimate the total transported volume associated with intense events when the variability of d50 is included in the analysis however this model does not sufficiently capture transport because of moderate events rain or snowmelt and thus underestimates bedload on medium and long timescales the calibrated model of parker klingeman adequately represents erosive dynamics with r50 values between 0 03 and 0 041 for moderate and intense events respectively and a flow threshold of 14 2 m3 s 1 that separates these two situations nevertheless these models based on hiding functions present greater dispersion if the variability of diameters related to cobbles and pebbles is considered for such cases the wilcock and crowe model performed better for both intense and moderate events the latter is important in the study area where snowmelt pulses occasionally exceed the critical flow and break the surface layer with significant sediment contributions these processes differentiate the transport dynamics from other studies and are distinctive characteristics that are more closely related to mountainous influences in semiarid environments where pulses of intense snowmelt are common despite its limitations the proposed methodology based on a large check dam has proven to be adequate and representative for assessment of erosion processes

swash zone sediment transport step dynamics and morphological response on a gravel beach abstract state of the art morphodynamic field data were collected from slapton sands uk a fine gravel beach d50 2 10 mm over a 10 day period under a range of wave tide conditions comprising a mixture of southerly swell and easterly wind waves hs 0 5 1 m ts 4 8 s tide range 3 4 m over the field period the upper beach experienced accretion and berm formation during tides with low steepness swell dominated wave conditions h l 0 01 surprisingly the intertidal beach showed an opposite trend with sediment losses under swell conditions and an increase in sediment volume due to wind waves and suggests that upper beach morphological change can be decoupled from the overall sediment budget a submerged accretionary feature the beach step grew and migrated onshore on the rising tide typically reaching a maximum relief of around 0 5 m then gradually decreased in prominence while migrating offshore as the tide fell resulting in little net morphological change the step was better developed during the falling tide than the rising tide and through its control on the swash hydro and sediment dynamics the step had a significant effect on the development of the berm swash flow velocities under the conditions measured were often in excess of 2 m s 1 for both the uprush and the backwash onshore mean flows occurred in the upper swash region 40 inundation was characterised by offshore mean flows swash infiltration losses in the swash zone increased from 40 in the lower swash region to 100 in the upper swash region the most energetic swash flows and the strongest offshore mean flows occurred at the transition between swash zone and surf zone 90 100 inundation

field observations of sediment transport across the rocky coast of east taiwan impacts of extreme waves on the coastal morphology by typhoon soudelor abstract after the 2015 typhoon soudelor large boulders and mixed sediments deposited extensively across the beach along the east coast of taiwan field measurements of these storm related sediments provide the first hand evidence to document the impacts of extreme waves induced by typhoon soudelor although the maximum inundation distance is only 170 m due to the lack of beach buffer zone the weight of the largest boulder was estimated over 1 t and the maximum run up was estimated up to 11 9 m the clast distribution of the washover and the beach face sediments exhibited reverse directions of coarsening reflecting different stages of wave propagation our field records show that a super typhoon like soudelor can potentially leave footprints of extreme values in the geologic records therefore a comprehensive understanding on the occurrence of the sediments and the depositional environment should be carefully considered to pin down the origin of the archived extreme events in addition the formation of the higher extreme wave berm and the destruction of the lower swell berm at the yen liao beach displayed the power of the storm surges suggesting the important role of the run up on the evolution of the berm

multigrain sedimentation erosion model based on cross shore equilibrium sediment distribution application to nourishment design abstract in the light of global warming and sea level rise there are many coastal beaches that suffer from erosion beach nourishment has become a common practice to maintain the sediment balance on a shore face in this paper a three dimensional numerical model for evaluating long term impact of beach nourishment projects has been developed the model addresses the longstanding complex issue of coastal morphology and sediment grain size distribution from an unconventional angle which exploits the strong links between grain size distribution and the prevailing transport direction of each sediment constituent under average wave and storm action the present model predicts the redistribution of nourished sediment according to the subtle clues implied by equilibrium distribution curves and latest coastal wave transformation theories after verification against recent field observations in terschelling the netherlands the model was used to predict long term effects of different beach nourishment strategies it was found that a given the source sediment available in terschelling the tactics of large volume and less frequent implementation are better than otherwise and b from a pure engineering point of view waterline nourishment outperforms offshore trough nourishment the model offers an additional tool for coastal engineers to evaluate the feasibility effectiveness and the optimization of dumping locations for beach nourishment projects it is also a useful tool for stratigraphic modelling of shallow marine sedimentation in conjunction with sea level changes

origin and distribution of sulfate in a fractured till in southern alberta canada glacial till in a 22 km sup 2 area of the interior plains region of southern alberta canada consists of an upper brown gypsiferous weathered zone up to 20 m thick and a lower discontinuous grey nonweathered zone up to 25 m thick although the total sulfur content of the two till zones is the same 0 34 the mean total sulfate content of the weathered till 4 0 mg g sup 1 exceeds that the nonweathered till 0 8 mg g sup 1 similarities suggest that all so sub 4 sup 2 in the nonweathered till and 20 of the sulfate in the weathered till was derived from sulfate rich bedrock fragments incorporated in the till during deposition laboratory experiments and delta sup 18 o and delta sup 34 s analyses of total so sub 4 sup 2 and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic s at some time after the till was deposited mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier altithermal period 11 000more to 3000 years b p the following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed the oxidation of reduced s produced so sub 4 sup 2 and h sup the h sup reacted with carbonate minerals under elevated p sub co2 with ca sup 2 loss by exchange for na sup and gypsum precipitation volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity less

detailed investigation of overwash on a gravel barrier abstract this paper uses results obtained from a prototype scale experiment barrier dynamics experiment bardex undertaken in the delta flume the netherlands to investigate overwash hydraulics and morphodynamics of a prototype gravel barrier gravel barrier behaviour depends upon a number of factors including sediment properties porosity permeability grain size and wave climate since overwash processes are known to control short term gravel barrier dynamics and long term barrier migration a detailed quantification of overwash flow properties and induced bed changes is crucial overwash hydrodynamics of the prototype gravel barrier focused on the flow velocity depth and discharge over the barrier crest and the overwash flow progression across and the infiltration through the barrier during the bardex experiment overwash peak depth 0 77 m velocity 5 m s 1 and discharge max 6 m 3 m 1 were high especially considering the relatively modest wave energy significant wave height 0 8 m conversely to schemes found in the literature average flow depth did not linearly decrease across the barrier rather it was characterised by a sudden decrease at the crest a milder decrease at the barrier top and then propagation as a shallow water lens over the backbarrier the barrier morphological evolution was analysed over a series of 15 min experimental runs and at the timescale of individual overwash events overall the morphological variation did not result from an accumulation of many small consistently erosive or accretionary events but rather the mean bed elevation change per event was quite large 10 mm and the overall morphology change occurred due to a small imbalance in the number of erosive and accretionary events at each location two relationships between overwash hydrodynamic variables were deduced from results 1 between overwash flow depth and velocity a power type relation was obtained and 2 a linear relation was observed between overwash flow depth and maximum overwash intrusion distance across the barrier top i e overwash intrusion findings from this study are useful to enhance the knowledge of overwash processes and also have practical applications on the one hand results shown here can be use for the validation of overwash predictive models and additionally the simple empirical relations deduced from the dataset can be used by coastal managers to estimate overwash intrusion distance which in turn can assist in the location of areas under risk of overwash and breaching

lower crustal intrusions beneath the southern baikal rift zone evidence from full waveform modelling of wide angle seismic data abstract the cenozoic baikal rift zone brz is situated in south central siberia in the suture between the precambrian siberian platform and the amurian plate this more than 2000 km long rift zone is composed of several individual basement depressions and half grabens with the deep lake baikal at its centre the best baikal explosion seismic transect project acquired a 360 km long deep seismic refraction wide angle reflection profile in 2002 across southern lake baikal the data from this project is used for identification of large scale crustal structures and modelling of the seismic velocities of the crust and uppermost mantle previous interpretation and velocity modelling of p wave arrivals in the best data has revealed a multi layered crust with smooth variation in moho depth between the siberian platform 41 km and the sayan baikal fold belt 46 km the lower crust exhibits normal seismic velocities around the rift structure except for beneath the rift axis where a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s is observed reverberant or ringing reflections with strong amplitude and low frequency originate from this zone whereas the lower crust is non reflective outside the rift zone synthetic full waveform reflectivity modelling of the high velocity anomaly suggests the presence of a layered sequence with a typical layer thickness of 300 500 m coinciding with the velocity anomaly the p wave velocity of the individual layers is modelled to range between 7 4 km s and 7 9 km s we interpret this feature as resulting from mafic to ultra mafic intrusions in the form of sills petrological interpretation of the velocity values suggests that the intrusions are sorted by fractional crystallization into plagioclase rich low velocity layers and pyroxene and olivine rich high velocity layers the mafic intrusions were probably intruded into the ductile lower crust during the main rift phase in the late pliocene as such the intrusive material has thickened the lower crust during rifting which may explain the lack of moho uplift across southern brz

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

on the relation between the direction of the wave energy flux and the orientation of equilibrium beaches abstract the equilibrium beach planform concept has been widely used in recent years as an engineering tool for modeling shoreline changes designing new beaches and for stability studies of existing ones it defines the final shape of a beach on a scale of years which is important for solving erosion problems and for the design of nourishment projects throughout the literature the planform final shape hereinafter denoted as the static equilibrium beach orientation sebo is obtained based on the direction of the mean wave energy flux of whole waves impinging on the coast this paper investigates the effect of beach sediment size and the shape of the directional distribution sdd of the energy flux of the wave climate on the direction that dictates the sebo the study employs field data from 32 beaches along the spanish coast and available long term databases of directional wave climates initiation of sediment motion due to wave action is taken into account in order to filter the directional wave climate to consider only waves that are capable of moving the sediment the results indicate that the direction of the mean energy flux of filtered waves is more appropriate for the determination of the sebo than that of whole waves additionally the results confirm the importance of both the filtration process of the local directional wave climate and the usage of the whole directional spectra in stability studies and coastal engineering practice

decoupling of solutes and water in regional groundwater systems the murray basin australia documenting the origins residence times and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems this study uses cl mass balance to determine the cl accession time i e the time required for cl to accumulate and cl to estimate the residence times of cl in the victorian portion of the murray basin southeast australia much of the murray basin contains saline groundwater with total dissolved solids tds concentrations commonly 14 000 mg l and locally up to 300 000 mg l the total mass of cl stored in the victorian portion of the basin is estimated as between 12 400 and 47 100 mt using present day rainfall totals and cl concentrations in rainfall the cl accession time is 170 to 650 ka aquifer thicknesses and groundwater salinity both increase westwards in this part of the murray basin consequently the cl accession times increase westward from 0 1 0 6 ka to 286 1080 ka by contrast c activities of the majority of the groundwater are 2 pmc and commonly much higher notwithstanding the difficulty in correcting c residence times the widespread occurrence of groundwater with above background c activities implies that groundwater residence times are generally 30 ka which is substantially shorter than the cl accession times rcl the ratio of cl to total cl 10 values of the groundwater are between 20 and 230 and are uncorrelated with cl concentrations while it is difficult to determine precise cl residence times the observation that the rcl values are significantly higher than those that represent secular equilibrium with the aquifer matrix rcl of 5 to 10 indicates that they are up to a few hundred thousand years and similar to the cl accession times the rcl values together with the geology of the aquifers stable isotope ratios and major ion geochemistry precludes halite dissolution incorporation of connate water or the long term diffusion of cl from clays as mechanisms of producing the elevated cl concentrations rather it is most likely that the high cl concentrations result from recycling of solutes in saline lakes and playas or repeated cycles of evapotranspiration in the unsaturated zone

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

storm response of a mixed sand gravel beach ridge plain under falling relative sea levels a stratigraphic investigation using ground penetrating radar beach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms as well as evidence of earthquake induced sediment pulses this study is a stratigraphic investigation of the late holocene mixed sand gravel msg beach ridge plain on the canterbury coast new zealand the subsurface was imaged along a 370 m shore normal transect using 100 and 200 mhz ground penetrating radar gpr antennae and cored to sample sediment textures results show that seaward of a back barrier lagoon the pegasus bay beach ridge plain prograded almost uniformly under conditions of relatively stable sea level nearshore sediment supply appears to have created a sustained sediment surplus perhaps as a result of post seismic sediment pulses resulting in a flat morphologically featureless beach ridge plain evidence of a high magnitude storm provides an exception with an estimated event return period in excess of 100 years evidence from the gpr sequence combined with modern process observations from msg beaches indicates that a palaeo storm initially created a washover fan into the back barrier lagoon with a large amount of sediment simultaneously moved off the beach face into the nearshore this erosion event resulted in a topographic depression still evident today in the subsequent recovery period sediment was reworked by swash onto the beach as a sequence of berm deposit laminations creating an elevated beach ridge that also has a modern day topographic signature as sediment supply returned to normal and under conditions of falling sea level a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern day beach as a large flat uniform progradation plain this study highlights the importance of extreme storm events and earthquake pulses on msg coastlines in triggering high volume beach ridge formation during the subsequent recovery period

the geochemistry and mixing of leakage in a semi confined aquifer at a municipal well field memphis tennessee usa abstract the memphis aquifer in southwestern tennessee is confined to a semi confined unconsolidated sand aquifer and is the primary municipal water source in the memphis metropolitan area past studies have identified regions in the metropolitan area in which the overlying upper claiborne confining unit lacks significant clay and provides a hydraulic connection between the shallow aquifer and the memphis aquifer in this study major solute chemistry 3h and 3h 3he groundwater dating are used to investigate the extent and chemical effects of leakage through the confining unit to the memphis aquifer in the vicinity of a municipal well field the 3h 3he dates and geochemical modeling of the chemical data are used to constrain mixing fractions and the timing of modern recharge tritium activities of as much as 2 8 tu are observed in shallow production wells but deeper production wells have 3h activities that approach the detection limit trends in water chemistry indicate vertical mixing in the aquifer of shallow na so4 cl rich water and deeper ca mg hco3 rich water water chemistry does not vary consistently with seasonal pumping but 3h activity generally decreases during low use periods stable o and h isotopes show little variation and are not useful groundwater tracers for this study the 3h bearing na so4 cl rich water is interpreted to reflect recharge of modern water through the upper claiborne confining unit the 3h 3he dates from 5 production wells indicate modern recharge that infiltrated 15 20 a ago is present in the shallow production wells geologic data and hydrologic boundary conditions suggest that the most likely source for continued leakage is a nearby stream nonconnah creek geochemical reaction modeling using the netpath computer code suggests that proportions of shallow aquifer water leaking into the memphis aquifer range from 6 to 32 the 3h 3he dating and netpath modeling results correlate well suggesting that these complementary analytical tools provide an effective means to evaluate proportions of modern water leaking into semi confined aquifers these results also indicate a need to carefully consider connections between surface water and semi confined groundwater resources in wellhead protection programs

an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada the milk river artesian aquifer underlies 15 000 km2 of southern alberta canada it consists of thin 30 75 m thick sandstone and is confined above by the pakowki shale typically 120 m thick and below by the colorado shale the aquifer subcrops in southern alberta and northern montana groundwater movement is to the north west and east from the outcrop area dominant recharge area cl and i concentrations increase in the direction of flow from less than 0 05 and 0 001 mmol l respectively near the recharge area to more than 140 and 0 15 mmol l at the northern edge of the aquifer similarly waters become more enriched in oxygen 18 and deuterium from less than 21 0 and 167 near the recharge area to values approaching 8 0 and 70 0 in the north isotope values in the recharge area plot on the global meteoric water line and indicate that the recharge waters are isotopically unaltered meteoric waters downgradient from the recharge area the data deviate from the meteoric water line slope of 6 3 instead of 8 0 three mechanisms have been advanced to explain the origin of the chemical and isotopic patterns the introduction of connate formation water through the colorado shale and subsequent mixing with infiltrating meteoric water a finite source of meteoric recharge mixing with more saline water in the aquifer and chemical and isotopic enrichment due to ion filtration hydraulic conductivity and hydraulic head data cl concentrations of drill cuttings and isotopic values from groundwater from the colorado shale provide arguments for reevaluating these ideas an alternative mechanism based on diffusion between saline isotopically enriched water in the colorado shale and fresher isotopically depleted water in the aquifer is tested using an analytical mass transport model although uncertainty exists in the model parameters results showed that the patterns in cl i 18o and 2h in the aquifer can be explained by aquitard diffusion further aquitard diffusion must be considered when using chlorine 36 dating methods in aquifer aquitard systems such as the milk river aquifer

storm driven variability of the beach nearshore profile at duck north carolina usa 1981 1991 the us army corps of engineers field research facility frf at duck north carolina has collected approximately biweekly beach nearshore profile data to 8 m depth and associated wave data since 1981 sediment budget analysis was used to examine the medium scale years to a decade variability of the beach nearshore profile from 1981 to 1991 significant changes occurred during four groups of energetic storm events during february march of 1983 1987 1989 and december 1989 each group was comprised of at least two storms within a period of less than 39 days both with hmo 4 m during each storm group offshore sediment movement caused a distinct outer bar to migrate offshore and grow in size resulting in an abrupt increase in the volume of sediment on the upper shoreface the net profile changes were much larger than the changes due to single storms and the cumulative effect of the storms can be considered as one event during these events the first storm appears to have a destabilizing effect on the profile which has insufficient time to recover before the second and subsequent storm s as a result several storms in quick succession are able to have a large impact on the morphology the intervening periods between the groups of storm events termed fairweather conditions lasted up to 4 years they are characterized by slow but steady sediment redistribution averaging 33 m3 m 1 year 1 from the upper shoreface 5 m depth toward the shore while the total sediment volume was effectively constant the onshore feed of sediment was not significantly affected by individual storms during the fairweather conditions these two processes of 1 morphologic change during groups of storm events and 2 the steady onshore feed of sediments from the shoreface during fairweather conditions appear to play an important role on medium and long term profile evolution at least at duck

uranium series radionuclides in fluids and solids milk river aquifer alberta canada abstract samples from 21 wells completed in the milk river aquifer were sampled and analysed for u isotopes in general u concentrations decrease with distance from the recharge area groundwater samples can be delineated into a small oxic group u content 101t 5 mmol 1 and a more predominant anoxic group u content of 10 7 mmol 1 all groundwater samples were undersaturated with respect to the common u minerals such as uraninite coffinite and rutherfordine the dominant u complexes were uranyl carbonates the234u 238u activity ratios increased from 2 to 11 with distance downflow of the outcrop the highest activity ratio of 11 8 was measured at a well defined redox front whereupon a steady decrease downdip to 4 was observed this decrease was interpreted to be due to the decay of234u excess with age of the groundwater and due to u loss by sorption precipitation processes from solution to solid surfaces two u isotope dating models were used to estimate the age of the groundwater in the milk river aquifer model 1 is a simple model of downdip decay of234u excess in solution under steady state conditions model 2 is a phenomenological model for the evolution of u isotope groundwater composition downdip based on a transport dispersion equation incorporating radioactive decay and assuming that sorption processes are of first order kinetics both models were applied to the u isotope data collected along the same flow path in the aquifer they yielded flowrates of 0 1 0 2 m a and 0 2 0 6 m a respectively the latter range is in good agreement with flowrates of 0 3 m a obtained from hydraulic considerations the lower value derived from model 1 is interpreted in terms of u migration velocity rather than as groundwater flowrate model 2 was also applied to an additional flowpath the calculated flowrate range of 0 1 0 4 m a is in excellent agreement with the hydraulic model flowrate of 0 2 m a the main conclusion of this work is that u isotopes can be used for dating very old groundwaters provided the local hydrogeology and u geochemistry are understood well

large scale experiments on gravel and mixed beaches experimental procedure data documentation and initial results abstract this paper provides information on the experimental set up data collection methods and results to date for the project large scale modelling of coarse grained beaches undertaken at the large wave channel gwk of fzk in hannover by an international group of researchers in spring 2002 the main objective of the experiments was to provide full scale measurements of cross shore processes on gravel and mixed beaches for the verification and further development of cross shore numerical models of gravel and mixed sediment beaches identical random and regular wave tests were undertaken for a gravel beach and a mixed sand gravel beach set up in the flume measurements included profile development water surface elevation along the flume internal pressures in the swash zone piezometric head levels within the beach run up flow velocities in the surf zone and sediment size distributions the purpose of the paper is to present to the scientific community the experimental procedure a summary of the data collected some initial results as well as a brief outline of the on going research being carried out with the data by different research groups the experimental data is available to all the scientific community following submission of a statement of objectives specification of data requirements and an agreement to abide with the gwk and eu protocols

modelling gravel barrier response to storms and sudden relative sea level change using xbeach g abstract this paper investigates the response of a mixed sand and gravel msg barrier coastline to storms and sudden relative sea level change using the numerical model xbeach g the barrier beaches of southern hawke s bay new zealand provide a natural laboratory for the work owing to spatial variability in instantaneous land deformation that occurred during the 1931 hawke s bay earthquake historic 1931 and contemporary 2017 morphodynamics of one tectonically uplifted 1 5 m and one subsided 0 78 m barrier were modelled under energetic waves hs 1 6 m xbeach g was designed to simulate pure gravel beach morphodynamics but despite this the model demonstrated high quantitative skill when calibrated for the msg coast results reveal the storm impact regimes of each profile and potential linkages to decadal scale barrier development observed in historical beach profile data storm swash processes at the uplifted profile indicate long term barrier stability due to a lack of change at the barrier crest and ridge building observed in model simulations provides a potential formative mechanism for decadal scale beach progradation at the subsided barrier modelled historic crest build up up to 0 3 m and narrowing over 5 m indicate an overtopping mode of response to sudden relative sea level rise simulation results are consistent with historical beach profile observations that also show chronic narrowing of the subsided barrier through time simulations of the modern barrier draw attention to the possibility that it may be on a trajectory toward catastrophic breakdown under extreme conditions but further work is needed to distinguish the relative importance of historical sudden sea level rise versus deficits in sediment supply to this shoreline

crustal structure of central lake baikal insights into intracontinental rifting this is the published version copyright 1976 american geophysical union all rights reserved

high frequency in situ field measurements of morphological response on a fine gravel beach during energetic wave conditions this paper presents novel data collected over four weeks at loe bar a fine gravel barrier d50 3 5 mm exposed to energetic wave conditions hs10 2 4 m combined remote and in situ measurements were used to identify 3d morphological response profile change and runup behaviour during successive energetic periods hs 2 5 m small intertidal beach volume losses occurred under high steepness waves h0 l0 0 01 but in general the overall beach volume was remarkably stable in fact the greatest morphological response was evident not in cross shore sediment exchanges but due to the alongshore redistribution related to the three dimensional beach cusp system specifically during energetic wave conditions the cusp morphology underwent horn growth and embayment deepening leading to increased cusp definition an additional explanation for the stability of the cross shore beach profile is related to the development of the beach step during energetic conditions and long period waves significant deposition c 1 m occurred at the top of the beach step above the still water line the enhanced step provided a focal point for wave breaking considerably curtailing the swash motion and reducing the runup limit thereby providing protection to the upper beach this study provides much needed insight into complex morphological response and runup characteristics on gravel beaches fundamental for improved model development and leading towards better predictive tools

coupling cross shore and longshore sediment transport to model storm response along a mixed sand gravel coast under varying wave directions abstract this paper investigates the profile response of a mixed sand gravel deltaic beach playa granada southern spain forced by storm waves from varying directions beach morphology was monitored over a 36 day period with variable wave conditions and profile response was compared to model predictions using the xbeach g model and a longshore sediment transport lst formulation xbeach g was applied over 2 day periods of low energy south westerly sw storm and south easterly se storm conditions and was coupled to lst using a parametric approach which distributes the lst across the swash surf and nearshore zones a calibrated wave propagation model delft3d was used to obtain the inshore conditions required to drive the xbeach g model and the lst formulation the storm response is clearly influenced by the free board difference between the height of the berm and the total run up and is also strongly dependent on storm wave direction with the sw storm eroding the surveyed area while the se storm induced beach accretion model results indicate that xbeach g on its own is capable of adequately reproducing the response of the beach under sw storm conditions b s s 0 95 but not under se storms due to the higher lst gradients at the study location the combination of xbeach g and lst fits the measured profiles reasonably well under both sw b s s 0 96 and se b s s 0 88 storms inspiring confidence in the coupled model to predict the storm response under varying wave conditions the combined xbeach g lst model was applied to the entire 6 8 km deltaic coastline to investigate the impact of extreme sw and se storm events and the model results reiterate the importance of cross shore and longshore sediment transport in driving coastal storm response at this location the approach proposed in this work can be extended to other worldwide coasts highly influenced by both cross shore and longshore sediment transport such as beaches with different coastline orientations and or forced by varying wave directions

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

deep structure and mechanical behavior of the lithosphere in the hangai hovsgol region mongolia new constraints from gravity modeling we investigate the deep structure and mechanical behavior of the lithosphere beneath the hangai ho vsgo l region central mongolia asia in order to explain the origin and support of large scale doming in this deforming area we propose a gravity and topography based model which accounts for constraints provided by other independent results from xenolith and tomography studies deviations of the measured gravity from the theoretical airy compensation model are examined a long wavelength low gravity anomaly is spatially correlated with low pressure and shear velocity anomalies in the mantle and with the extent of cenozoic volcanic outcrops we interpret it as a deep seated low density asthenosphere and model its effect on the bouguer gravity signal using a 600 km wide light asthenospheric body density reduction 310 kg m 33 located between 100 and 200 km north and south of the hangai ho vsgo l dome short wavelength highs and lows in the bouguer gravity field are clearly correlated with fault activity they seem to reflect opposite senses of flexure of a rigid lithosphere across two major active faults the sayan and bogd transpressional systems and are modeled by moho deflections of 10 and 5 km respectively finally a shortwavelength 200 km high amplitude 350 mgal gravity residual remains beneath the highest part of the mountain bulge namely the hangai dome based on previously published xenolith analyses we interpret it as an anomalous low density body which may represent underplated cumulates or mafic granulites at the uppermost mantle we conclude that upper mantle dynamics necessarily play an important role in the origin and evolution of the hangai ho vsgo l dome but without requiring significant thinning of the lithosphere fl 2002 elsevier science b v all rights reserved

baikal rift active or passive comparison of the baikal and kenya rift zones abstract the comparison of geological and geophysical data from the kenya and baikal rift zones permits us to consider the formation of these zones to be associated with the development of wide asthenospheric upwellings beneath them in this sense both rifts are active differences between them in amounts of volcanics and geological features may be explained by a higher degree of partial melting of asthenospheric material beneath the kenya rift

asthenospheric flow and origin of volcanism in the baikal rift area the origin of low volume hotspot like volcanism often observed in continental rift areas is debated as is the nature of the flow in the mantle beneath in this paper we assemble seismic constraints on the mantle flow below the baikal rift zone we combine new evidence from upper mantle tomography and from a radially anisotropic shear velocity profile measured beneath and se of the rift with published shear wave splitting constraints on azimuthal anisotropy fast directions of azimuthal anisotropy are perpendicular to the rift on both of its sides stable siberian platform lithosphere on the northern side extends down to 200 km on the southern side the lithosphere is only 60 70 km thick this asymmetry with the thick cratonic root forming a barrier to convective flow inhibits a mid ocean ridge like flow pattern the radially anisotropic profile yields evidence for horizontal flow in the upper asthenosphere 60 100 km se of the rift but no evidence for vertical flow these results are consistent with horizontal asthenospheric flow nw to se perpendicular to the rift from beneath the thick siberian towards the thin baikal mongolian lithosphere when asthenosphere ascends from the 200 km depth beneath the craton to shallower depths beneath the rift decompression melting of embedded veins of enriched rock can produce the hotspot like basaltic volcanism observed the occurrence of such veins of enriched mantle in sub cratonic asthenosphere has been predicted by geochemical mantle models we propose that sub horizontal asthenospheric flow from beneath cratons is a common cause for hotspot like volcanism in continental rift zones

volcanism of the baikal rift zone abstract the volcanism of the baikal rift zone is a specific case of intraplate volcanism where the tensional stress field in the lithosphere under the rift zone does not greatly exceed local tension in other volcanic regions of central asia in which rifting was not morphologically expressed the main phase of volcanism miocene pliocene preceded active extension and rift formation migration of volcanism from the periphery to the axial part of the rift as well as subsequent variation of the composition of volcanics from alkaline to tholeiitic are not specific to the baikal rift zone the volcanism of this zone and other interior regions of asia is considered to be a consequence not only of deep regional processes under volcanic areas connected to the formation and rise of a highly anomalous mantle but also of global processes caused by the indo eurasian collision which was responsible for the large scale deformations within the asiatic continent including tensional stress fields

comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz the milk river aquifer in southern alberta combines apparently simple classical confined aquifer hydrodynamics with somewhat enigmatic groundwater geochemistry of conservative solutes over the past 10 years five major papers have focused on the geochemistry of milk river aquifer groundwater most recently hendry and schwartz 1988 have proposed a different mechanism aquitard diffusion to explain the milk river geochemistry they described and evaluated previously proposed geochemical processes especially ion filtration hendry and schwartz 1988 concluded that ion filtration and the other proposed mechanisms were not supported by the data they then described the aquitard diffusion mechanism and used a simple analytical model to simulate observed aquifer trends in cl sup minus and sup 18 o from the results of this exercise they concluded that diffusion from the aquitards was controlling the solute distributions in the aquifer finally they interpreted previously published sup 36 cl data and new profiles of cl sup minus in the aquitards in terms of the diffusion model upon review the authors do not find the arguments against ion filtration to be as damaging as hendry and schwartz indicate nor do they find the evidence for aquitard diffusion to be as persuasive in this study they will first evaluate hendry andmore schwartz s arguments against ion filtration then they will review the arguments in favor of aquitard diffusion and finally the authors will address the implications for the interpretation of the vertical cl sup minus profiles and the sup 36 cl data less

off rift volcanism in rift zones determined by crustal unloading when continents are stretched over a long period of time deep elongated rift valleys form at earth s surface and zones of ponded magma centred beneath the rift form at the crust mantle boundary1 2 ascending magma sometimes erupts within the rift valley3 4 or counterintuitively at volcanic fields away from the rift valley that are offset by tens of kilometres from the source of magma at depth5 6 7 8 the controls on the distribution of this off rift volcanism are unclear here we use a numerical model of magmatic dyke propagation during rifting to investigate why some dykes reach the surface outside the rift valley whereas others are confined to the valley we find that the location of magmatism is governed by the competition between tectonic stretching and gravitational unloading pressure caused by crustal thinning and faulting along the rift borders when gravitational unloading dominates over tectonic stretching forces dykes ascending from the ponded magma are steered towards the rift sides eventually causing off rift eruptions our model also predicts the formation of stacked magma sills in the lower crust above the magma ponding zone as well as the along rift propagation of shallow dykes during rifting events consistent with observations of magmatism and volcanism in rift zones globally we conclude that rift topography induced stress changes provide a fundamental control on the transfer of magma from depth to the surface

landward migration of inner bars abstract a field investigation was carried out to collect data of inner bar migration profiles were measured once or twice a week for a two year period at naka beach ibaraki prefecture japan it was found that the onshore migration of inner bars could be described by two dimensionless quantities as 5d h b max h b max gt 2 max 20d h b max where h b max is the maximum value of daily average breaker height during one interval between surveys t max is the average wave period of the day giving h b max d is the mean size of the beach sediment and g is the acceleration due to gravity analyses based on surfzone sediment dynamics yields v wd b 2 10 11 h b d 3 where v is the average speed of onshore bar migration b is the bar height h b is the average breaker height and w is the fall velocity of the beach sediment nomographs for the speed of landward migrating bars are also presented

short and medium term response to storms on three mediterranean coarse grained beaches abstract the storm response of three italian coarse grained beaches was investigated to better understand the morphodynamics of coarse clastic beaches in a microtidal context two of the studied sites are located on the eastern side of the country portonovo and sirolo and the third one marina di pisa is on the western side portonovo and sirolo are mixed sand and gravel beaches where the storms approach from two main directions se and ne marina di pisa is a coarse grained gravel dominated beach exposed to storms driven by sw winds gravel nourishments were undertaken in recent years on the three sites beach topography was monitored measuring the same network of cross sections at a monthly i e short term to seasonal frequency i e medium term geomorphic changes were examined before and after storm occurrences by means of profile analyses and shoreline position evaluations the beach orientation and the influence of hard structures are the main factors controlling the transport and accumulation of significant amount of sediments and the consequent high variability of beach morphology over the medium term for marina di pisa storms tend to accumulate material towards the upper part of the beach with no shoreline rotation and no chance to recover the initial configuration sirolo and portonovo showed a similar behaviour that is more typical of pocket beaches both beaches show shoreline rotation after storms in a clockwise or counter clockwise direction according to the incoming wave direction the wider and longer beach at sirolo allows the accumulation of a thin layer of sediment during storms rather than at portonovo where given its longshore and landward boundaries the beach material tends to accumulate in greater thickness after storms sirolo and especially portonovo can quickly recover the initial beach configuration as soon as another storm of comparable energy approaches from the opposite direction of the previous one large morphological variations after the storm on mixed sand and gravel beaches do not necessarily mean a slower recovery of surface topography and shoreline position considering that all the three beaches were recently nourished with gravel it emerged that the differences between the nourishment and the native material in terms of size and composition seem to have an important influence on the dynamics of the sediment stock considering that recent studies have remarked the high abrasion rate of gravel further understanding of the evolution of nourishment material with time is needed the peculiar behaviour of gravel material artificially added to an originally sandy beach suggests the need to modify the widely used classification of jennings and shulmeister 2002 adding a fourth additional beach typology which could represent human altered beaches

behaviour of beach profiles during accretion and erosion dominated periods beach profiles have been surveyed at monthly intervals between 1972 and 1988 at moruya on the south coast of new south wales australia four profile sites have been used as a data set to provide an understanding of changes to beach volume width and shape moruya beach represents a moderately high energy microtidal environment which responds in a dramatic way to major storm events such as those experienced in the mid 1970s this study distinguishes between profile characteristics associated with such a period erosion dominated or edp compared with periods when accretion dominated adp accompanied by foredune expansion in both height and width