a lagrangian model for boundary layer growth and bed shear stress in the swash zone abstract a new model for the boundary layer development and associated skin friction coefficients and shear stress within the swash zone is presented the model is developed within a lagrangian reference frame following fluid trajectories and can be applied to both laminar flow and smooth turbulent flow the model is based on the momentum integral approach for steady flat plate boundary layers with appropriate modifications to account for the unsteady flow regime and flow history the model results are consistent with previous measurements of bed shear stress and skin friction coefficients within the swash zone these indicate strong temporal and spatial variation throughout the swash cycle and a clear distinction between the uprush and backwash phase this variation has been previously attributed the unsteady flow regime and flow history effects both of which are accounted for in the new model fluid particle trajectories and velocity are computed using the non linear shallow water wave equations and the boundary layer growth across the entire swash zone is estimated predictions of the bed shear stress and skin friction coefficients agree reasonably well with direct bed shear stress measurements reported by barnes et al barnes m p o donaghue t alsina j m baldock t e 2009 direct bed shear stress measurements in bore driven swash coastal engineering 56 8 853 867 and for a given flow velocity give stresses which are consistent with the bias toward uprush sediment transport which has consistently been observed in measurements the data and modelling suggest that the backwash boundary layer is initially laminar which results in the late development of significant bed shear during the backwash with a transition to a turbulent boundary layer later in the backwash a new conceptual model for the boundary layer structure at the leading edge of the swash is proposed which accounts for both the no slip condition at the bed and the moving wet dry interface however further development of the lagrangian boundary layer model is required in order to include bore generated turbulence and to account for variable roughness and mobile beds

hindered settling of sand grains the sedimentation rate of sand grains in the hindered settling regime has been considered to assess particle shape effects the behaviour of various particulate systems involving sand has been compared with the widely used richardson zaki expression the general form of the expression is found to hold in as much as remaining as a suitable means to describe the hindered settling of irregular particles the sedimentation exponent n in the richardson zaki expression is found to be significantly larger for natural sand grains than for regular particles the hindered settling effect is therefore greater leading to lower concentration gradients than expected the effect becomes more pronounced with increasing particle irregularity at concentrations around 0 4 the hindered settling velocity of fine and medium natural sands reduces to about 70 of the value predicted using existing empirical expressions for n using appropriate expressions for the fluidization velocity and the clear water settling velocity a simple method is discussed to evaluate the sedimentation exponent and to determine the hindered settling effect for sands of various shapes

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

settling and compaction of chromite cumulates employing a centrifuging piston cylinder and application to layered mafic intrusions the time scales and mechanics of gravitationally driven crystal settling and compaction is investigated through high temperature 1 280 1 500 c centrifuge assisted experiments on a chromite basalt melt system at 100 1 500g 0 5 gpa subsequently the feasibility of this process for the formation of dense chromite cumulate layers in large layered mafic intrusions lmis is assessed centrifugation leads to a single cumulate layer formed at the gravitational bottom of the capsule the experimentally observed mechanical settling velocity of a suspension of 24 vol chromite is calculated to be about half 0 53 of the stokes settling velocity with a sedimentation exponent n of 2 35 3 gravitational settling leads to an orthocumulate layer with a porosity of 0 52 all porosities as fraction formation times for such a layer from a magma with initial chromite contents of 0 1 1 vol are 140 3 5 days equal to a growth rate of 0 007 0 3 m day for grain sizes of 1 2 mm more compacted chromite layers form with increasing centrifugation time and acceleration through chemical compaction an increase of grain contact areas and grain sizes together with a decrease in porosity is best explained by pressure dissolution at grain contacts reprecipitation and grain growth into the intergranular space and a concomitant expulsion of intergranular melt the relation between the porosity in the cumulate pile and effective pressure integrated over time h a t is best fit with a logarithmic function in fact confirming that a pressure dissolution reprecipitation process is the dominant mechanism of compaction the experimentally derived equation allows calculating compaction times 70 80 chromite at the bottom of a 1 m thick chromite layer are reached after 9 250 years whereas equivalent compaction times are 0 2 0 9 years for olivine both for 2 mm grain size the experiments allow to determine the bulk viscosities of chromite and olivine cumulates to be of magnitude 109 pa s much lower than previously reported as long as melt escape from the compacting cumulate remains homogeneous fluidization does not play any role however channelized melt flow may lead to suspension and upward movement of cumulate crystals in lmis chromitite layers are typically part of a sequence with layers of mafic minerals compaction occurs under the additional weight of the overlying layers and can be achieved in a few years to decades

reservoir quality and rock properties modeling triassic and jurassic sandstones greater shearwater area uk central north sea abstract the complex burial and diagenetic histories of the jurassic fulmar and triassic skagerrak sandstones in the uk central north sea present significant challenges with regard to reservoir quality and rock property prediction commercial reservoir quality is retained despite deep burial and associated high temperatures and pressures shallow marine fulmar sands are normally compacted mean igv 26 3 yet have porosities of 21 33 porosity was preserved through inhibition of quartz cementation by clay and microquartz coatings and enhanced by dissolution of framework grains 5 skagerrak fluvial sands are more compacted mean igv 23 2 exhibit minor feldspar dissolution we modeled reservoir quality evolution using the forward diagenetic model touchstone which simulates porosity loss due to compaction and quartz cementation quantitative petrographic analyses and burial history data were used to calibrate touchstone model parameters the results were applied to deeper prospects for pre drill prediction of porosity and permeability in parallel petrophysical data were used to characterize the elastic properties of the sandstones to provide a basis for quantitative seismic forward modeling experimental data and core calibrated petrophysical results reflecting variable in situ fluids and saturations were used to build an elastic properties model the model is robust and was used to generate fluid filled sandstone properties incorporating touchstone results for prospect specific seismic attribute modeling well results from exploration wells are in good agreement with pre drill touchstone and elastic properties model predictions

hindered settling of silt abstractsediment particles smaller than 64 m with a noncohesive base mineral are referred to as silt the settling velocity of suspended sediment decreases with increasing concentration due to hindered settling effects compared with clay and sand hindered settling of silt is poorly documented and understood a formulation is proposed for the hindered settling of silt water mixtures derived from physical reasoning the effect of silt on the mixture s viscosity is addressed in particular the formulation compares favorably with laboratory experiments on the settling of silt sized sediment this study shows that effective settling velocities can be derived from a single concentration time series measured within the settling mixture provided that the sediment is initially homogeneously distributed

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

thickness of the martian crust improved constraints from geoid to topography ratios 1 the average crustal thickness of the southern highlands of mars was investigated by calculating geoid to topography ratios gtrs and interpreting these in terms of an airy compensation model appropriate for a spherical planet we show that 1 if gtrs were interpreted in terms of a cartesian model the recovered crustal thickness would be underestimated by a few tens of kilometers and 2 the global geoid and topography signals associated with the loading and flexure of the tharsis province must be removed before undertaking such a spatial analysis assuming a conservative range of crustal densities 2700 3100 kg m 3 we constrain the average thickness of the martian crust to lie between 33 and 81 km or 57 24 km when combined with complementary estimates based on crustal thickness modeling gravity topography admittance modeling viscous relaxation considerations and geochemical mass balance modeling we find that a crustal thickness between 38 and 62 km or 50 12 km is consistent with all studies isotopic investigations based on hf w and sm nd systematics suggest that mars underwent a major silicate differentiation event early in its evolution within the first 30 ma that gave rise to an enriched crust that has since remained isotopically isolated from the depleted mantle in comparing estimates of the thickness of this primordial crust with those obtained in this study we find that at least one third of the martian crust has an origin dating from the time of accretion and primary differentiation subsequent partial melting of the depleted mantle would have given rise to the remaining portion of the crust while we predict that a large portion of the crust should be composed of ancient enriched materials a representative sample of this primordial crust does not currently exist among the known martian meteorites index terms 6225 planetology solar system objects mars 5417 planetology solid surface planets gravitational fields 1227 5430 planetology solid surface planets interiors 8147 1227 geodesy and gravity planetary geodesy and gravity 5420 5714 6019 keywords mars crustal thickness crustal evolution geoid topography

late cretaceous cenozoic evolution of the north german basin results from 3 d geodynamic modelling abstract the late cretaceous cenozoic evolution of the north german basin has been investigated by 3 d thermomechanical finite element modelling the model solves the equations of motion of an elasto visco plastic continuum representing the continental lithosphere it includes the variations of stress in time and space the thermal evolution surface processes and variations in global sea level the north german basin became inverted in the late cretaceous early cenozoic the inversion was most intense in the southern part of the basin i e in the lower saxony basin the flechtingen high and the harz the lower crustal properties vary across the north german basin north of the elbe line the lower crust is dense and has high seismic velocity compared to the lower crust south of the elbe line the lower crust with high density and high velocity is assumed to be strong lateral variations in lithospheric strength also arise from lateral variations in moho depth in areas where the moho is deep the upper mantle is warm and the lithosphere is thereby relatively weak compression of the lithosphere causes shortening thickening and surface uplift of relatively weak areas tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression contemporaneously the margins of the weak zone subside cenozoic subsidence of the northern part of the north german basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north the modelled deformation patterns and resulting sediment isopachs correlate with observations from the area this verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

martian surface heat production and crustal heat flow from mars odyssey gamma ray spectrometry 1 martian thermal state and evolution depend principally on the radiogenic heat producing element hpe distributions in the planet s crust and mantle the gamma ray spectrometer grs on the 2001 mars odyssey spacecraft has mapped the surface abundances of hpes across mars from these data we produce the first models of global and regional surface heat production and crustal heat flow as previous studies have suggested that the crust is a repository for approximately 50 of the radiogenic elements on mars these models provide important directly measurable constraints on martian heat generation our calculations show considerable geographic and temporal variations in crustal heat flow and demonstrate the existence of anomalous heat flow provinces we calculate a present day average surface heat production of 4 9 0 3 10 11 w kg 1 we also calculate the average crustal component of heat flow of 6 4 0 4 mw m 2 the crustal component of radiogenically produced heat flow ranges from 1 mw m 2 in the hellas basin and utopia planitia regions to 13 mw m 2 in the sirenum fossae region these heat production and crustal heat flow values from geochemical measurements support previous heat flow estimates produced by different methodologies

small scale diagenetic facies heterogeneity controls porosity and permeability pattern in reservoir sandstones the fluvial aeolian upper rotliegend sandstones from the bebertal outcrop flechtingen high germany are the famous reservoir analog for the deeply buried upper rotliegend gas reservoirs of the southern permian basin while most diagenetic and reservoir quality investigations are conducted on a meter scale there is an emerging consensus that significant reservoir heterogeneity is inherited from diagenetic complexity at smaller scales in this study we utilize information about diagenetic products and processes at the pore and plug scale and analyze their impact on the heterogeneity of porosity permeability and cement patterns eodiagenetic poikilitic calcite cements illite iron oxide grain coatings and the amount of infiltrated clay are responsible for mm to cm scale reservoir heterogeneities in the parchim formation of the upper rotliegend sandstones using the petrel e p software platform spatial fluctuations and spatial variations of permeability porosity and calcite cements are modeled and compared offering opportunities for predicting small scale reservoir rock properties based on diagenetic constraints

mantle convection controls the observed lateral variations in lithospheric thickness on present day mars 1 sounding radar observations of the north polar layered deposits on mars suggest an elastic lithosphere thickness of at least 300 km in that region significantly larger than any prior estimate of lithospheric thickness on mars previous studies interpreted this result as requiring either that mars is significantly sub chondritic in its abundance of radioactive elements or alternatively that there are large lateral variations in lithospheric thickness we find that the required depletion of radioactivity is geochemically unlikely on the other hand stagnant lid convection naturally produces factor of two or more lateral variations in both mantle heat flux and lithospheric thickness and is the preferred explanation for the polar elastic thickness measurement our mantle plume models which have previously been shown to explain observations of present day magma production on mars can also explain the new elastic thickness observations

assessment of dispersive pressure as a beach placer mechanism the concept of sediment sorting extending from the bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation the traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments a binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear this observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation consequently the shear sorting process as currently formulated may not be an appropriate means to describe beach placer formation kinetic sieving appears to be a more likely mechanism in this context enhanced by the shearing and dilation of the granular fluid flow 2009 the authors journal compilation 2009 international association of sedimentologists

what classic greywacke litharenite can reveal about feldspar diagenesis an example from permian rotliegend sandstone in hessen germany abstract rotliegend siliciclastic sediments in southern hessen germany are a good example of dissolution of detrital feldspars which is a common feature in many sandstones dissolution occurred after mechanical compaction of the lithic rich sandstone which experienced framework collapse with pores and pore connections filled and obstructed by deformed ductile lithic grains pseudomatrix thereby reducing pore space to microporosity the advanced degree of compaction and reduced porosity caused low permeability and low hydraulic conductivity of the rock mass this is further reduced by the presence of wackes and shales that occur intercalated with the sandstones feldspar dissolution thus took place in low permeable sediments when large scale flow of meteoric or acidic fluids is ruled out as a cause of feldspar dissolution mineral precipitation illite kaolinite and albite took place within pseudomatrix and detrital matrix as well as in secondary pores created by feldspar dissolution feldspar was the source for the authigenesis the system was thus closed during burial after framework collapse and diagenetic reactants in the form of detrital components were already present within the system the original mass was preserved but redistributed and diagenetic minerals were the local sinks for the dissolved reactants precipitating within the system this also suggests that burial diagenesis in general might be more mass conservative than usually assumed rotliegend sandstones thus form a case where despite of the lack of external exchange of mass by fluid flow major diagenetic processes did take place and significantly modified the original mineralogy and texture feldspar diagenesis can take place from other processes than mere large scale flushing of open systems as often supposed it implies that the volumes of rock affected by feldspar diagenesis may be much larger than anticipated based upon the common hold believe that feldspar diagenesis is linked to unconformities and surface weathering or dissolution in near surface aquifers

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

lagrangian measurements and modelling of fluid advection in the inner surf and swash zones new laboratory and field data are presented on fluid advection into the swash zone the data illustrate the region of the inner surf zone from which sediment can be directly advected into the swash zone during a single uprush which is termed the advection length experiments were conducted by particle tracking in a lagrangian reference frame and were performed for monochromatic breaking waves solitary bores non breaking solitary waves and field conditions the advection length is normalised by the run up length to give an advection ratio a and different advection ratios are identified on the basis of the experimental data the data show that fluid enters the swash zone from a region of the inner surf zone that can extend a distance seaward of the bore collapse location that is approximately equal to half of the run up length this region is about eight times wider than the region predicted by the classical swash solution of shen and meyer shen m c meyer r e 1963 climb of a bore on a beach part 3 runup journal of fluid mechanics 16 113 125 as illustrated by pritchard and hogg pritchard d hogg a j 2005 on the transport of suspended sediment by a swash event on a plane beach coastal engineering 52 1 23 measured advection ratios for periodic waves show no significant trend with iribarren number consistent with self similarity in typical swash flows the data are compared to recent characteristic solutions of the non linear shallow water wave nlsw equations and both finite difference and finite volume solutions of the nlsw equations the model results are transformed into a lagrangian reference frame to illustrate particle trajectories from which advection lengths and particle excursions into and across the swash zone are determined the particle excursions represent a horizontal mixing length for fluid and sediment and define length scales over which boundary layer growth occurs during run up the model results are in excellent overall agreement with the means of the data series the region defined by the advection length represents the potential effective pickup zone for pre suspended sediment and therefore represents an important but diffuse boundary for sediment transport modelling in the inner surf and swash zone

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

estimates of martian crustal thickness from viscous relaxation of topography isostatically compensated crustal thickness variations and associated topographic contrasts at the surface of a planet result in lateral pressure gradients which may cause the lower crust to flow and reduce the relief areas of thicker crust are generally associated with more rapid relaxation of topography on mars topographic features such as impact basins and the hemispheric dichotomy have survived for 4 gyr we use a finite difference representation of depth dependent non newtonian lower crustal flow to investigate how topography decays with time for a dry diabase rheology total radiogenic concentrations 80 of terrestrial values and crustal radiogenic concentrations similar to terrestrial basalts we find that an upper bound on the mean planetary crustal thickness is 100 km in the probably unrealistic case where all the radiogenic elements are in the crust this maximum crustal thickness can be increased to 115 km the main uncertainty in these results is the total radiogenic abundances on mars comparing our results with the observed shape of the crustal dichotomy provides no evidence that this slope is primarily the result of lower crustal flow both hellas and the dichotomy are isostatically compensated if the mechanism is airy isostasy then the lower bound on mean crustal thickness is 30 km crustal thicknesses of 30 100 km on mars can be produced by mid ocean ridge spreading at potential temperatures of 1350 1600 c however for such crustal thicknesses the lithosphere is likely to be positively buoyant making subduction difficult

settling velocity of sediments at high concentrations new data on the settling velocity of artificial sediments and natural sands at high concentrations are presented the data are compared with a widely used semiempirical richardson and zaki equation trans inst chem eng 32 1954 35 which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n here a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds the resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands for sands the appropriate values of n are found to differ significantly from those suggested by richardson and zaki for spheres and are typically larger corresponding to a greater reduction in settling velocity at high concentrations for fine and medium sands at concentrations of order 0 4 the hindered settling velocity reduces to about 70 of that expected using values of n derived for spheres at concentrations of order 0 15 the hindered settling velocity reduces to less than half of the settling velocity in clear water these reduced settling velocities have important implications for sediment transport modelling close to and within sheet flow layers and in the swash zone

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

influence of sediment settling velocity on mechanistic soil erosion modeling we report on a series of soil erosion experiments performed on the 2 m x 6 m epfl erosion flume total sediment concentrations and the concentrations of seven size fractions 1000 mm were measured during 14 high intensity 47 5 52 5 mm h rainfall experiments on three different slopes 2 2 12 4 the short time and long time analytical solutions for the hairsine rose erosion model were rewritten to account for infiltration the newly collected data were used to test the model under conditions that had not been explored before steeper slopes infiltration more realistic soil composition the analytical solutions could predict the observed total sediment concentration well however the observed sediment concentrations for the individual size classes could be predicted only when adjusted settling velocities were used the adjusted settling velocities were estimated through manual optimization the optimized settling velocities for the smallest and midsize particles 315 mm were smaller than measured the effective settling velocities could also be calculated from the calculated amount of material in the shield of each size class at the end of the experiments this calculated settling velocity distribution agreed very well with the optimized settling velocities this study moves the hairsine rose model another step closer to an operational soil erosion model for field applications

sedimentary cycles and facies architecture of aeolian fluvial strata of the upper jurassic guara formation southern brazil the upper jurassic guara formation comprises an 80 200 m thick continental succession exposed in the western portion of the rio grande do sul state brazil it comprises four distinct facies associations i simple to locally composite crescentic aeolian dune sets ii aeolian sand sheets iii distal floodflows and iv fluvial channels the vertical stacking of the facies associations defines several 5 14 m thick wetting upward cycles each cycle starts with aeolian dune sets followed by aeolian sand sheets deposits and culminating in either fluvial channels or distal flood strata within some cycles aeolian sand sheets are absent and fluvial deposits rest directly above aeolian dune facies the transitions from one facies association to another are abrupt and marked by erosive surfaces that delineate distinct episodes of sediment accumulation the origin of both the wetting upward cycles and the erosive surfaces was controlled by the ground water table level dry sand availability and aeolian and fluvial sediment transport capacity variations related to climatic fluctuations between relatively arid and humid conditions preservation of the fluvial aeolian deposits reflects an overall relative water table rise driven by subsidence

process based modeling of tsunami inundation and sediment transport 1 the infrequent and unpredictable nature of tsunamis precludes the use of field experiments to measure the hydrodynamic and sediment transport processes that occur instead these processes are often approximated from laboratory numerical and theoretical studies or inferred from observations of the resultant sediment deposits here delft3d a three dimensional numerical model is used to simulate the inundation and sediment transport of a tsunami similar in magnitude to the 26 december 2004 indian ocean tsunami over one measured and three idealized morphologies the model is first shown to match well the observations taken at kuala meurisi sumatra and then used to examine in detail the processes that occur during the tsunami the model predicts that at a given cross shore location the onshore flow accelerates rapidly to a maximum as the wavefront passes and then gradually decelerates before reversing direction and flowing offshore the onshore flow does not tend to zero everywhere at maximum inundation but instead flow reversal occurs near the shoreline even as the wavefront continues to inundate landward while some sediment is eroded by the passing wavefront the suspension of sandy sediment is dominated by the long duration high velocity backwash that occurs along the beach face and offshore of the shoreline some of the sediment suspended during backwash is advected shoreward by the subsequent wave creating large spatial gradients in the suspended sediment concentrations which may not be in equilibrium with the local hydrodynamics the inundation and transport of sediment during a tsunami can be affected by complexities in the morphological profile and interactions between multiple waves and many of the hydrodynamic and sediment transport processes predicted here are similar to analogous processes previously observed in the swash zone

large ion lithophile element fractionation during the early differentiation of mars and the composition of the martian primitive mantle basaltic shergottites display a systematic decrease in k th k u and k la ratios with increasing k content these trends are interpreted as mixing lines between relatively young martian magmas derived from highly depleted mantle sources and an ancient large ion lithophile lil element enriched crustal component one implication of this is that a substantial fractionation of these ratios occurs during the early crustal differentiation on mars isotopic evidence from snc meteorites and compositional data from pathfinder and orbital gamma ray spectroscopy suggest that in excess of 50 of the lil element complement of mars resides in the crustal reservoir if so the primitive mantle of mars is significantly more volatile depleted i e lower k th k u k la than previously thought but probably though not necessarily still less volatile depleted than the primitive mantle of the earth the la th ratios of virtually all snc meteorites are subchondritic including those with the most severe lree depletion extrapolation of the basaltic shergottite trend suggests that both the depleted mantle end member and the enriched crustal end member have subchondritic la th ratios this is in contrast with the earth where basalts from lil element depleted sources such as morb have superchondritic la th ratios complementary to the subchondritic ratios of the continental crust accordingly assuming that the refractory elements are in chondritic proportions for the mars primitive mantle an additional major geochemical reservoir must exist on mars that may not yet have been sampled

two dimensional two phase depth integrated model for transients over mobile bed abstractfast geomorphic transients may involve complex scenarios of sediment transport occurring near the bottom as bed load i e saltating sliding and rolling or as suspended load in the upper portion of the flow the two sediment transport modalities may even coexist or alternate each other during the same event especially when the shear stress varies considerably modeling these processes is therefore a challenging task for which the usual representation of the flow as a mixture may result in being unsatisfactory in the present paper a new two phase depth averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads distinct phase velocities are considered for bed load whereas the slip velocity between the two phases is neglected in the suspended load it is shown that the resulting two phase model is hyperbolic and the analytical expression of the eigenvalues is provided the entrainment deposition of sediment between the bottom and the bed

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

stratigraphic evolution of an aeolian erg margin system the permian cedar mesa sandstone se utah usa the permian cedar mesa sandstone of south east utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which in terms of palaeogeographic setting reflects a transition from a dry erg centre through a water table controlled aeolian dominated erg margin to an outer erg margin subject to periodic fluvial incursion the erg margin succession represents a wet aeolian system accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes and a range of dry damp and wet flooded interdune elements is recognized variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre locally interconnected damp and or wet interdune ponds in the aeolian dominated erg margin and fully interconnected fluvially flooded interdune corridors in the outer erg margin relationships between aeolian dune and interdune units indicate that dry damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration temporal variation in the rates of water table rise and bedform migration determined the angle of climb of the erg margin succession such that accumulation rates increased during periods of rapidly rising water table whereas sediment bypassing zero angle of climb occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table during these periods in the outer erg margin the expansion of fluvially flooded interdunes in front of non climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass flood supersurfaces a spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the cedar mesa erg margin succession

suspended sediment transport around a large scale laboratory breaker bar this paper presents novel insights into suspended sediment concentrations and fluxes under a large scale laboratory plunging wave measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar covering the complete breaking region from shoaling to inner surf zone with particular high resolution near the bed using an acoustic concentration and velocity profiler wave breaking evidently affects sediment pick up rates which increase by an order of magnitude from shoaling to breaking zone time averaged reference concentrations correlate poorly with periodic and time averaged near bed velocities but correlate significantly with near bed time averaged turbulent kinetic energy the net depth integrated suspended transport is offshore directed and primarily attributed to current related fluxes undertow at outer flow elevations i e above the wave bottom boundary layer the wave related suspended transport is onshore directed and is generally confined to the wave bottom boundary layer cross shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick up and deposition and of cross shore sediment advection suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion leading to local intra wave concentration changes at locations between the breaker bar crest and bar trough intra wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer sediment is entrained in the bar trough during the wave trough phase almost instantly advected offshore and deposited near the bar crest during the wave crest phase finally these results are used to suggest improvements for suspended sediment transport models

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

the influence of crustal radioactivity on mantle convection and lithospheric thickness on mars orbital measurements of gravity and topography demonstrate that the crust of mars varies in thickness by about 100 km across the surface as a result the heat flux due to crustal radioactivity varies laterally by nearly 15 mw m 2 in an important new paper plesa et al 2016 doi 10 1002 2016je005126 have assessed how these variations in crustal thickness and heat flow affect the spatial pattern of convection in the martian mantle their results have important implications for the interpretation of the martian heat flux that will be measured by the upcoming insight mission to mars

sediment suspension and turbulence in the swash zone of dissipative beaches abstract this paper investigates mechanisms for stirring and transport of suspended sediment by infragravity scale swash using high frequency field measurements of horizontal and vertical flow velocities water depths and sediment concentration profiles the field data suggest that vertical velocity fluctuations generated by coherent eddies can be important to the process of sediment suspension and can contribute to asymmetrically distributed sediment transport rates between the uprush and backwash phases of the swash cycle this result indicates that the traditional and often used proxy for bed shear stress based solely on measurements of the horizontal component of flow u i e b fu 2 where is the water density and f is a friction factor may be inadequate when used in energetics type sediment transport models applied to the swash which is indeed the case we demonstrate that a bed shear stress formulation which is more consistent with the physics leads to improved predictive capability for energetics type transport models this formulation is based on the correlation between the horizontal and turbulent vertical components of the flow i e b uw despite the improvement it is evident that considerable amounts of calibration data are still required before each application of this model type moreover our data shows that the issue of calibration coefficients is more problematic than generally appreciated the calibration coefficients for energetics type models on a given beach not only differ between uprush and backwash but also vary with position within the swash zone particularly on the uprush phase

sediment transport under a swash event the effect of boundary conditions abstract using a lagrangian framework we obtain predictions for suspended sediment transport under a swash event described by a recently proposed shallow water model in which the swash is driven by a sustained off shore bore and the sediment supply from the bore may vary with time although the hydrodynamics of the modified swash flows differ somewhat from the classic shen meyer description the overall patterns of sediment transport are shown to be rather robust to this difference in particular it appears that in order to determine whether the swash zone imports or exports sediment it is still crucial to determine accurately how much sediment is suspended by the incoming bore and advected into the swash zone by the flow following bore collapse both the total amount of this pre suspended sediment and its phasing relative to the swash inflow are important if net deposition patterns are to be predicted accurately

the usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity quantifying outcrop hydraulic conductivity and its spatial variability saturated hydraulic conductivity k is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media although several well established laboratory methods exist for determining k in situ measurements of this parameter remain very complex and scale dependent often the limited accessibility of subsurface sediments for sampling means an additional impediment to our ability to quantify subsurface k heterogeneity one potential solution is the use of outcrops as analogues for subsurface sediments this paper investigates the use of air permeameter measurements on outcrops of unconsolidated sediments to quantify k and its spatial heterogeneity on a broad range of sediment types the neogene aquifer in northern belgium is used as a case study for this purpose to characterize the variability in k 511 small scale air permeability measurements were performed on outcrop sediments representative over five of the aquifer s lithostratigraphic units from these measurements outcrop scale equivalent k tensors were calculated using numerical upscaling techniques validation of the air permeameter based k values by comparison with laboratory constant head k measurements reveals a correlation of 0 93 overall the results indicate that hand held air permeameters are very efficient and accurate tools to characterize saturated k as well as its small scale variability and anisotropy on a broad range of unconsolidated sediments the studied outcrops further provided a qualitative understanding of aquifer hydrostratigraphy and quantitative estimates about k variability at the centimetre scale to metre scale copyright 2013 john wiley sons ltd

on the spatial variability of the martian elastic lithosphere thickness evidence for mantle plumes 1 the present day elastic lithosphere thickness at the martian north pole has recently been constrained to de 300 km and this is a factor of 3 4 larger than elastic thickness estimates for other amazonian surface features like the tharsis volcanoes here we present a model for the martian elastic lithosphere thickness which takes the locally varying crustal thickness the local concentration of heat producing elements as well as variations of strain rate into account the model predicts de 196 km at the north pole today whereas elastic thicknesses at the tharsis volcanoes are best compatible with middle to late amazonian loading ages therefore although a large degree of spatial heterogeneity can be explained by the presented model large elastic thicknesses in excess of 300 km cannot be reproduced in order to fit all elastic thickness estimates derived from observations mantle heat flux at the north pole needs to be reduced by 35 however this can only be reconciled with a bulk chondritic concentration of heat producing elements in the martian interior if the excess heat is deposited elsewhere therefore this argues for the presence of recently active mantle plumes possibly underneath tharsis the size and strength of such a plume can be constrained by the elastic thickness at the tharsis montes and maximum average heat flux between 8 and 24 mw m 2 corresponding to a central peak heat flux of 40 to 120 mw m 2 is consistent with the observations such a plume would leave a clear signature in the surface heat flux and should be readily detectable by in situ heat flux measurements