constitution of the moon 2 composition and seismic properties of the lower mantle abstract to constrain the composition of the moon we have calculated the stable phase assemblages and their seismic properties by the method of minimization of gibbs free energy to determine whether various compositional models are consistent with the seismic observations for the lunar lower mantle at depths between 500 and 1000 km p wave and s wave velocities have been calculated for a series of proposed bulk composition models compositional models for the moon impactor composition orgueil composition etc and earth like compositions lherzolite and pyrolite have been considered it is found that impactor and orgueil models are unlikely for the lower mantle within reasonable temperature adjustment in the temperature profile all of the terrestrial compositional models come close to the seismic data below the 500 km discontinuity it is found that a composition enriched in al 2 o 3 up to about 6 wt and having pyrolite content of the other major oxides lunar pyrolite is adequate to describe the seismic properties of the lunar lower mantle within the uncertainty of calculations and resolution of seismic data an al rich model with a terrestrial ol px ratio and unusually enriched in garnet gives the best fit to the lunar lower mantle seismic properties despite the uncertainty of the seismic data it is shown that none of the analysed compositional models satisfies the seismic constraints simultaneously in the middle and lower mantle phase changes in any model considered are not able to explain the nature of the 500 km discontinuity it is concluded that the lunar mantle is chemically stratified

chemical studies of h chondrites i mobile trace elements and gas retention ages abstract trends for 16 trace elements ag as au bi cd co cs ga in k rb sb se te tl and zn chosen to span a broad geochemical and thermal response range in 44 h4 6 chondrites differ widely from those in l4 6 chondrites in particular h chondrites classified as heavily shocked petrologically do not necessarily exhibit 40 ar loss and vice versa the clear cut causal relationship between siderophile and mobile element loss with increasing late shock seen in l chondrites is not generally evident in the h group h chondrite parent material experienced an early high temperature genetic episode that mobilized a substantial proportion of these trace elements so that later thermal episodes resulted in more subtle collateral fraction ations mildly shocked l chondrites escaped this early high temperature event indicating that the two most numerous meteorite groups differ fundamentally in genetic history

on mantle chemical and thermal heterogeneities and anisotropy as mapped by inversion of global surface wave data 1 we invert global observations of fundamental and higher order love and rayleigh surface wave dispersion data jointly at selected locations for 1 d radial profiles of earth s mantle composition thermal state and anisotropic structure using a stochastic sampling algorithm considering mantle compositions as equilibrium assemblages of basalt and harzburgite we employ a self consistent thermodynamic method to compute their phase equilibria and bulk physical properties p s wave velocity and density combining these with locally varying anisotropy profiles we determine anisotropic p and s wave velocities to calculate dispersion curves for comparison with observations models fitting data within uncertainties provide us with a range of profiles of composition temperature and anisotropy this methodology presents an important complement to conventional seismic tomography methods our results indicate radial and lateral gradients in basalt fraction with basalt depletion in the upper and enrichment of the upper part of the lower mantle in agreement with results from geodynamical calculations melting processes at mid ocean ridges and subduction of chemically stratified lithosphere compared with preliminary reference earth model prem and seismic tomography models our velocity models are generally faster in the upper transition zone tz and slower in the lower tz implying a steeper velocity gradient while less dense than prem density gradients in the tz are also steeper mantle geotherms are generally adiabatic in the tz whereas in the upper part of the lower mantle stronger lateral variations are observed the retrieved anisotropy structure agrees with previous studies indicating positive as well as laterally varying upper mantle anisotropy while there is little evidence for anisotropy in and below the tz

an igneous textured clast in the peace river meteorite insights into accretion and metamorphism of asteroids in the early solar system the mineralogy petrology and geochemistry of an igneous textured clast in the peace river l6 chondrite meteorite was examined to determine the roles of nebular processes accretion and parent body metamorphism in its origin the centimetre scale clast is grey and fine grained and is in sharp contact with the host chondrite two sub millimetre veins cut across both the clast and host indicating that the clast formed prior to the impact shock event s that produced the numerous veins present in the peace river meteorite the clast and host are indistinguishable in terms of mineral compositions in contrast there are differences in modal mineralogy texture as well as trace element and oxygen isotope composition between the clast and host these differences strongly suggest that the clast was formed by impact melting of ll group chondritic material involving loss of fe fes and phosphate components followed by relatively rapid cooling and incorporation into the peace river host meteorite subsequent metamorphism on the peace river parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host shock metamorphism including formation of shock melt veins occurred post metamorphism during fragmentation of the l chondrite parent body the results suggest that the formation of the peace river parent asteroid included the incorporation of material from other asteroids and that the pre metamorphic protolith was a breccia accordingly we propose that the peace river meteorite be reclassified as a polymict breccia

extensive impact melting on the h chondrite parent asteroid during the cataclysmic bombardment of the early solar system evidence from the achondritic meteorite dar al gani 896 dag 896 is an olivine rich microporphyritic rock of komatiitic composition both the olivine composition fa 17 5 2 1 mn mg 0 0061 and the bulk oxygen isotopic composition delta 17 o 2 55 delta 18 o 3 50 indicate that dag 896 is a sample of the h chondrite parent body the bulk chemistry shows an h chondritic distribution of lithophile elements whereas chalcophile and siderophile elements are strongly depleted indicating formation through whole rock melting or nearly so of h chondrite material nearly complete loss of the metal plus sulfide component and crystallization without significant igneous fractionation superheated severely shocked chondritic relics similar to10 vol typically in the form of corroded lithic fragments 100 mum in size intimately distributed within the igneous lithology indicate that melting was triggered by a highly energetic impact which possibly induced shock pressures of similar to80 100 gpa the relatively young 3 704 0 035 ga ar 40 ar 39 crystallization age is consistent with the impact melting origin as magmatism in the asteroid belt was active only in the first hundred million years of solar system history 1ased on textural data and thermodynamic crystallization modelling we infer that dag 896 crystallized from a liquidus temperature of similar to1630degreesc under relatively slow cooling rates similar to10degreesc h 1 to 1300degreesc before quenching the two stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor metal silicate fractionation may have been accomplished at least at the centimeter scale of the studied meteorite sample through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism alternatively dag 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid for metal particles 1 to 10 mm in size typically observed in partially differentiated impact melt rocks stokes law indicates a settling velocity 1 in h 1 during the first few hours of crystallization on asteroidal bodies of 25 kin radius the similar to3 7 ga age of dag 896 nearly overlaps with the slightly older resetting ages of h chondrites all impact melts available from the literature indicating that the h chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system such an age overlap may also indicate early disruption of the initial h chondrite parent asteroid the close similarity between the bulk composition and degassing age of dag 896 and silicate inclusions in he iron meteorites is further evidence in support of a common origin by impact melting and metal silicate segregation on the h chondrite parent asteroid our new high precision oxygen isotopic measurements of h chondrites delta 17 o 0 77 0 04 should be extended to iies to verify this possible petrogenetic link

meteomod a numerical model for the calculation of melting crystallization relationships in meteoritic igneous systems the meteomod model is a computer program designed to calculate melting crystallization relationships in igneous systems compositionally similar to ordinary chondrites and basaltic achondrites the core of meteomod is a set of empirically calibrated equations called geothermometers which describe equilibria between silicate melt and minerals such as olivine orthopyroxene pigeonite augite plagioclase and metallic fe in terms of pressure temperature and liquid compositions the silicate mineral geothermometers are calibrated from a database containing the compositions of melts and minerals produced in melting experiments on 113 meteoritic and 141 synthetic systems the metallic iron silicate melt geothermometer is calibrated from a database of 396 melting experiments the meteorite melting model or meteomod calculates crystallization temperatures and contents of major end members in mineral solid solutions with accuracies of 10 15 c and 1 2 mol respectively input parameters for the program are 1 increment in crystallization degree 2 one of 12fo2 buffers routinely used in petrology 3 shift from the buffer in log units if any 4 a choice of equilibrium or fractional crystallization trajectory 5 terminal crystallization degree 6 contents of ten major elements in wt 7 a set of minor and trace elements in parts per million 8 the number of initial compositions to be modeled in a single computation run the output consists of a series of tables that list equilibrium temperatures o fugacities and proportions of melt and minerals and their compositions as a function of the degree of crystallization the results of application of meteomod to modeling of melting crystallization of the st severin ll chondrite are compared with the experimental data of jurewicz et al 1995

a survey of clasts and large chondrules in ordinary chondrites we report the results of a survey of clasts and large 5 mm chondrules macrochondrules within the 833 ordinary chondrites of the natural history museum collection thirty six macrochondrules and 24 clasts were identified and studied macrochondrules have textures and mineral assemblages like normal chondrules and so share a common origin clasts show evidence for fracturing from larger bodies and can be classified as either 1 chemically fractionated if they have major and trace element compositions differing substantially from most chondrules and clasts 2 impact melt clasts if they have microporphyritic textures and signs that indicate they are derived from shock melted chondritic material 3 microporhyritic clasts if they are similar to the last category but lack evidence for derivation through shock melting or 4 indeterminate clasts forming a diverse class that includes all those clasts that do not fit into the other categories

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

on the role of infiltration and exfiltration in swash zone boundary layer dynamics boundary layer dynamics are investigated using a 2 d numerical model that solves the volume averaged reynolds averaged navier stokes equations with a vof tracking scheme and a k turbulence closure the model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds the spatial gradients of the velocity bed shear stress and turbulence intensity terms are investigated with reference to bottom boundary layer bl dynamics numerical results show that the mean vorticity responds to flow divergence convergence at the surface that result from accelerating decelerating portions of the flow bed shear stress and sinking injection of turbulence due to infiltration exfiltration hence the zero up crossing of the vorticity is employed as a proxy of the bl thickness inside the shallow swash zone flows during the uprush phase the bl develops almost instantaneously with bore arrival and fluctuates below the surface due to flow instabilities and related horizontal straining in contrast during the backwash phase the bl grows quasi linearly with less influence of surface induced forces however the infiltration produces a reduction of the maximum excursion and duration of the swash event these effects have important implications for the bl development the numerical results suggest that the bl growth rate deviates rapidly from a quasi linear trend if the infiltration is dominant during the initial backwash phase and the flat plate boundary layer theory may no longer be applicable under these conditions

the influence of beach porosity on wave uprush and backwash abstract packwood a r 1983 the influence of beach porosity on wave uprush and backwash coastal eng 7 29 40 a numerical model is described to calculate the influence of a porous bed on the run up of a bore on a gently sloping sandy beach it is shown that fine medium grade sands have very little effect in the run up phase significant differences between impermeable and porous bed solutions are found in the backwash which might explain certain sand erosion and deposition phenomena

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

a mineralogical model for density and elasticity of the earth s mantle 1 we present a thermodynamic model of high pressure mineralogy that allows the evaluation of phase stability and physical properties for the earth s mantle the thermodynamic model is built from previous assessments and experiments in the five component cfmas system cao feo mgo al2o3 sio2 including mineral phases that occur close to typical chemical models of the mantle and reasonable mantle temperatures in this system we have performed a system gibbs free energy minimization including pure end member phases and a nonideal formulation for solid solutions solid solutions were subdivided into discrete pseudocompounds and treated as stoichiometric phases during computation of chemical equilibrium by the simplex method we have complemented the thermodynamic model with a model of shear wave properties to obtain a full description of aggregate elastic properties density bulk and shear moduli that provide a useful basis for the consideration of seismic and geodynamic models of the earth s mantle the thermodynamic model described here is made available for research and training purposes through a web interface http www earthmodel org we examine its validity in light of experiments from mineral physics and briefly discuss inferences for mantle structure

chemical studies of l chondrites iii mobile trace elements and ar 40 ar 39 ages abstract we report data for trace elements ag au bi cd co cs ga in rb se te tl and zn determined by radiochemical neutron activation analysis in l4 6 chondrites with undisturbed 40 ar release patterns or with patterns showing some disturbance in the 4 4 4 6 gyr plateau indicating shock induced loss mean concentrations are lower many significantly so in 16 chondrites with disturbed patterns than in 4 with undisturbed ones consistent with shock induced mobilization similar trends were noted earlier in l4 6 chondrites having mineralogically observable shock indicators mean concentrations are lower in strongly shocked i e 22 gpa than in mildly shocked 40 ar release patterns are mildly shocked but chondrites with disturbed patterns are more strongly heated on average than those of shock facies d f i e 22 to 57 gpa pooling these populations significantly lower mean concentrations of nearly all trace elements in 26 strongly shocked l4 6 chondrites than in 14 mildly shocked ones indicate loss in shock formed fes fe eutectic and or by vaporization during cooling of shock heated collisional debris two element correlations and the pattern of them i e correlation profiles are also consistent with this picture trace elements can act as thermometers for collisional episodes in l4 6 chondrites but not for earlier thermal fractionations unless compensation can be made for late shock heating

water table outcropping on macro tidal beaches a simulation model abstract during the fall of the tide the coastal water table within a beach may become decoupled from the ocean resulting in the formation of a seepage face where water outcrops on the inter tidal profile a simulation model called seep is developed to simulate the point of decoupling and the subsequent motion of the seepage face as it continues to fall across the inter tidal profile the model is based entirely on the dynamics of an isolated water particle on the seepage face i e the pressure distribution within the beach is ignored sensitivity analysis of the seep model to beach face slope and permeability characteristics suggests that small variations to these parameters can result in significantly differing rates of exit point motion and hence seepage face extent to test the predictive capability of the seep model results are presented from a field investigation of exit point dynamics on a macro tidal beach north queensland australia the simulation model is found to accurately reproduce the observed seepage face motion at this field site in addition a re analysis of seepage face extent reported in nielsen 1990 from a protected micro tidal environment shows similarly strong agreement between the reported and modelled exit point elevation

numerical modelling of the flow and bed evolution of a single bore driven swash event on a coarse sand beach abstract this paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach in these conditions bed load is the dominant mode of sediment transport laboratory experiments of a single bore driven swash event are simulated numerically using a fully coupled model that solves the system of non linear shallow water equations and the exner sediment conservation formula the analysis focuses on two aspects the optimal choice of parameters for the meyer peter and muller sediment transport formula and the model used for computing the shear stress the methods tested for the bed shear stress are the momentum integral method and the chezy formulation in which the friction factor is computed using two different formulae infiltration into the beach and its effects on the shear stress and sediment transport are also modelled results show that the basic meyer peter and muller sediment transport formula provides good results in the run up on the other hand the sediment transport in the early stage of the backwash is overestimated a reduction of the sediment mobility constant in the formula in the backwash marginally improves the results however the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress while at later stages there are several contributions that are identified i e modelling of the sediment transport and infiltration it is also suggested that the meyer peter and muller sediment transport formula might not capture the complexity of the processes involved during the backwash the comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the chezy formulation with time and space varying friction factor the resulting bed evolution is also described in the predicted final profile deposition is found in the upper part of the beach and erosion in the lower part a bed step is formed just below the position of the initial shoreline this feature is determined by the onset of a hydraulic jump during the backwash

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

free energy minimization by simulated annealing with applications to lithospheric slabs and mantle plumes an optimization algorithm based upon the method of simulated annealing is of utility in calculating equilibrium phase assemblages as functions of pressure temperature and chemical composition operating by analogy to the statistical mechanics of the chemical system it is applicable both to problems of strict chemical equilibrium and to problems involving metastability the method reproduces known phase diagrams and illustrates the expected thermal deflection of phase transitions in thermal models of subducting lithospheric slabs and buoyant mantle plumes it reveals temperature induced changes in phase transition sharpness and the stability of fe rich phase within an field in cold slab thermal models and it suggests that transitions such as the possible breakdown of silicate perovskite to mixed oxides can amplify velocity anomalies

inferring the thermochemical structure of the upper mantle from seismic data summary we test a mineral physics model of the upper mantle against seismic observations the model is based on current knowledge of material properties at high temperatures and pressures in particular elastic properties are computed with a recent self consistent thermodynamic model based on a six oxides ncfmas system we focus on average structure between 250 and 800 km we invert normal modes eigenfrequencies and traveltimes to obtain best fitting average thermal structures for various compositional profiles the thermochemical structures are then used to predict long period waveforms ss precursors waveforms and radial profiles of attenuation these examples show the potential of our procedure to refine the interpretation combining different data sets we found that a mixture of morb and harzburgite with the morb component increasing with depth is able to reproduce well all the seismic data for realistic thermal structures if the proportions of morb with depth do not change unrealistic negative thermal gradients below 250 km would be necessary to explain the data equilibrium assemblages such as pyrolite cannot fit the seismic data the elastic velocities predicted by the reference mineral physics model tested are too low at the top of the lower mantle even for the fastest and most depleted composition that is harzburgite an increase in v p of 1 per cent and in vs of 2 per cent improves the data fit significantly and is required to find models that fit both traveltimes and normal modes indicating the need for further experimental measurements of these properties at the simultaneously elevated pressure temperature conditions of the lower mantle extending our procedure to other seismic and density data and interpreting the 3 d structure holds promise to further improve our knowledge of the thermochemical structure of the upper mantle in addition the same database of material properties can be used in dynamic models to test whether the thermochemical structure inferred from geophysical observations is consistent with the earth s evolution

rapid water table fluctuations within the beach face implications for swash zone sediment mobility abstract to incorporate groundwater infiltration exfiltration in the description of swash zone sediment transport it is required that the details of groundwater dynamics within the beach face be clarified field measurements of the vertical pore pressure structure within the bed identify capillarity effects as the primary mechanism driving rapid and relatively large magnitude water table fluctuations within the swash zone when the upper extent of the fully saturated capillary fringe coincides with the beach face surface wave runup produces near instantaneous increase in pore pressures across the capillary fringe corresponding to a rapid rise of the phreatic surface i e the surface where pore pressure atmospheric pressure to the sand surface therefore counter to previous conclusions in the literature the rapid rise and fall of the water table under the swash zone do not equate to regions of the beach face alternating between states that favor sediment deposition unsaturated and erosion saturated similar reports that rapid fluctuations of the water table within the beach face correspond to rapid rates of vertical flow and hence bed fluidization are also a misinterpretation field measurements and a careful consideration of saturation and pore pressure characteristics within the beach face demonstrate that rapid water table rise is associated with minute downwards swash infiltration rather than rapid upwards groundwater exfiltration the cause of the pressure fluctuations and phreatic surface oscillations is the alternating appearance and disappearance of meniscuses at the sand surface which generate pressure head fluctuations of decimeters due to the addition of millimeters of water

core formation in asteroids chemical arguments based on the s concentrations in the metallic magmas that formed magmatic iron meteorites and on the lack of pyroxene in pallasites suggest that core formation in asteroids was accompanied by 40 melting of the associated silicates the existence of plagioclase free residues from partial melting such as lodranite meteorites indicates that metal did not segregate from silicates when the amount of partial melting was only 15 thus core formation in asteroids requires substantial melting of an asteroid high interfacial energies between metallic melts and silicates require that metallic spherules sink through partially molten silicates to form cores in asteroids and planetesimals the globule sinking mechanism is not very efficient because silicate crystal liquid mixtures have high yield strengths making it difficult for the globules to sink calculations suggest that the melt fraction must reach 50 before globules can sink alternatively porous flow of molten metal is possible when the amount of metal is high enough to form an interconnected network about 50 this can be achieved by high initial abundances of metal or by gradual removal of silicate melt thereby enriching the residue in the metal sulfide assemblage this also requires removal of 50 silicate partial melt though not necessarily all at once such high amounts of melting were not always attained in asteroids so many asteroids probably consist of partially differentiated silicates and metallic masses that did not segregate to a core s asteroids might represent such partially differentiated bodies

constraining the composition and thermal state of the mantle beneath europe from inversion of long period electromagnetic sounding data 1 we reexamine the problem of inverting c responses covering periods between 1 month and 1 year collected from 42 european observatories to constrain the internal structure of the earth earlier studies used the c responses which connect the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations to obtain the conductivity profile of the earth s mantle here we go beyond this approach by inverting directly for chemical composition and thermal state of the earth rather than subsurface electrical conductivity structure the primary inversion parameters are the composition of the earth s mantle within the system cao feo mgo al2o3 sio2 and geotherm given these parameters we calculate mineral modes at the prevailing physical conditions and combine these with laboratory based models for the conductivity of individual minerals to estimate the bulk earth electrical conductivity structure from which c responses are calculated to further constrain the radial density profile we also invert for mass and moment of inertia the results agree with earlier geophysically derived conductivity and seismic velocity models and confirm that inversion of geophysical data for compositional parameters planetary composition and thermal state is feasible the inversion indicates most probable lower mantle geothermal gradients of 0 58 k km core mantle boundary temperatures of 2900 c bulk earth molar mg si ratios of 1 1 intermediate between the chondrite and pyrolite models and no significant change in mantle composition across the 670 km seismic discontinuity

chemical studies of l chondrites ii shock induced trace element mobilization abstract previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock heated collisional debris indicate that au co se ga rb cs te bi in ag zn tl and cd progress in mobility we report data for these 13 trace elements in 14 l4 6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier trace element contents vary with petrologic type s fe sub group and shock history the last dominating strongly absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock loading i e residual temperatures established from mineralogic petrologic study a tertiary process shock heating previously known to have affected radiogenic 40 ar and or 4 he in meteorites but not other elements apparently was at least as effective as other open system processes secondary parent body and primary nebular and or accretionary episodes in establishing mobile trace element contents of l chondrites and probably others if conditions during early genetic episodes are to be deduced from compositional information shocked meteorites should be avoided or effects of later processes should be compensated for

uncertainty of mantle geophysical properties computed from phase equilibrium models phase equilibrium models are used routinely to predict geophysically relevant mantle properties a limitation of this approach is that nonlinearity of the phase equilibrium problem precludes direct assessment of the resultant uncertainties to overcome this obstacle we stochastically assess uncertainties along self consistent mantle adiabats for pyrolitic and basaltic bulk compositions to 2000 km depth the dominant components of the uncertainty are the identity composition and elastic properties of the minerals for p wave speed and density the latter components vary little whereas the first is confined to the upper mantle consequently p wave speeds densities and adiabatic temperatures and pressures predicted by phase equilibrium models are more uncertain in the upper mantle than in the lower mantle in contrast uncertainties in s wave speeds are dominated by the uncertainty in shear moduli and are approximately constant throughout the model depth range

igneous inclusions from ordinary chondrites high temperature cumulates and a shock melt we report microprobe instrumental neutron activation analysis and radiochemical neutron activation analysis data for three large igneous inclusions in the yamato y 75097 y 793241 and y 794046 ordinary chondrites the inclusions in the first two chondrites are troctolitic cumulates that have undergone appreciable reactions with their hosts either during emplacement and or cooling olivine spinel fe mg exchange pairs in these two inclusions record equilibration temperatures of about 710 c and these temperatures are similar to those exhibited by mineral pairs in the y 75097 and y 793241 hosts the inclusion in y 794046 is texturally unique consisting of fine grained randomly distributed olivines coarse 2 mm fascicular pyroxene laths and angular pockets of maskelynite plagioclase feldspar the phase compositions are readily interpreted as having resulted from extremely rapid essentially isochemical cooling to temperatures 1670 c we suggest that this igneous inclusion formed in situ by shock

quantifying the relationship between short wavelength dynamic topography and thermomechanical structure of the upper mantle using calibrated parameterization of anelasticity oceanic residual depth varies on 5000 km wavelengths with amplitudes of 1 km a component of this short wavelength signal is dynamic topography caused by convective flow in the upper 300 km of the mantle it exerts a significant influence on landscape evolution and sea level change but its contribution is often excluded in geodynamic models of whole mantle flow using seismic tomography to resolve buoyancy anomalies in the oceanic upper mantle is complicated by the dominant influence of lithospheric cooling on velocity structure here we remove this cooling signal from global surface wave tomographic models revealing a correlation between positive residual depth and slow residual velocity anomalies at depths 300 km to investigate whether these anomalies are of sufficient amplitude to account for short wavelength residual depth variations we calibrate an experimentally derived parameterization of anelastic deformation at seismic frequencies to convert shear wave velocity into temperature density and diffusion creep viscosity asthenospheric temperature anomalies reach 150 c in the vicinity of major magmatic hotspots and correlate with geochemical and geophysical proxies for potential temperature along mid ocean ridges locally we find evidence for a 150 km thick low viscosity asthenospheric channel incorporating our revised density structure into models of whole mantle flow yields reasonable agreement with residual depth observations and suggests that 30 km deviations in local lithospheric thickness account for a quarter of total amplitudes these predictions remain compatible with geoid constraints and substantially improve the fit between power spectra of observed and predicted dynamic topography this improvement should enable more accurate reconstruction of the spatio temporal evolution of cenozoic dynamic topography

megacusps on rip channel bathymetry observations and modeling abstract the formation of beach megacusps along the shoreline of southern monterey bay ca is investigated using time averaged video and simulated with xbeach a recently developed coastal sediment transport model investigations focus on the hydrodynamic role played by the bay s ever present rip channels a review of four years of video and wave data from sand city ca indicates that megacusps most often form shoreward of rip channels under larger waves significant wave height hs 1 5 2 0 m however they also occasionally appear shoreward of shoals when waves are smaller hs 1 m and the mean water level is higher on the beach after calibration to the sand city site xbeach is shown to hindcast measured shoreline change moderately well skill 0 41 but to overpredict the erosion of the swash region and beach face simulations with small to moderate waves hs 0 5 1 2 m suggest similar to field data that megacusps will form shoreward of either rip channels or shoals depending on mean daily water level and pre existing beach shape a frequency based analysis of sediment transport forcing is performed decomposing transport processes to the mean infragravity and very low frequency vlf contributions for two highlighted cases results indicate that the mean flow plays the dominant role in both types of megacusp formation but that vlf oscillations in sediment concentration and advective flow are also significant

modelling gravel beach dynamics with xbeach abstract numerical cross shore profile evolution models have been good at predicting beach erosion during storm conditions but have difficulty in predicting the accretion of the beach during calm periods this paper describes the progress made in modifying and applying the public domain xbeach code to the prediction and explanation of the observed behaviour of coarse grained beaches in the laboratory and the field under accretive conditions the paper outlines in details the changes made to the original code version 12 including the introduction of a new morphological module based upon soulsby s sediment transport equation for waves and currents and the incorporation of packwood s infiltration approach in the unsaturated area of the swash region the competence of this modified model during calm conditions for describing the steepening of the profile and the growth of the beach berm is demonstrated preliminary results on the behaviour of the beach subject to both waves and tides are presented good agreement is found between the model simulations and large scale laboratory measurements as well as field observations from a composite beach in the uk the reasons for the model s capabilities are discussed

observations of wave run up and groundwater seepage line motions on a reflective to intermediate meso tidal beach abstract swash sw and ground water seepage line gwsl motions have been recorded at an exposed meso tidal reflective to intermediate beach using a coastal video monitoring system during a 15 month period the monitoring period allowed the collection of imagery under a wide variety of wave and beach morphological conditions and sw and gwsl velocities were extracted on a wave by wave basis the continuous double bounded kumaraswamy kw probability distribution is proposed to parameterize the sw and gwsl height distributions and since the distribution shape of the latter was shown to be influenced by the tidal elevation generic tidal elevation dependent kw pdfs are proposed the beach face slope more than any other factor tested was found to apply certain control to the mean uprush backwash and gwsl velocities the results also indicate that in reflective to intermediate beaches the gwsl lies between the mean and 2 exceedance swash elevation with the occurrence of swash running above a saturated beach face being controlled by the tidal gradient and the significant wave height

density profiles of oceanic slabs and surrounding mantle integrated thermodynamic and thermal modeling and implications for the fate of slabs at the 660 km discontinuity abstract we have calculated the mineralogical properties of the earth s mantle and the lithological units constituting the subducting oceanic slabs within a wide range of p t conditions within the cao feo mgo al2o3 sio2 system except for the basalt top layer of a slab for which the system is extended to include na2o the mineralogical data are then converted using the appropriate p v t relations to bulk densities the calculated adiabatic density vs depth profile of the mantle between 200 and 725 km depths is in good agreement with geophysical and experimental data the density data of the different compositional units are combined with calculated thermal structures for a variety of slab mantle systems to construct equilibrium density profiles as a function of depth the mean equilibrium densities of the slabs within the transition zone 400 660 km depth are found to be 0 04 0 05 g cm3 greater than those of the ambient mantle within the same depth interval for the entire upper mantle density differences between slabs and ambient mantle are slightly less but the slabs still remain denser than the latter at 670 km depth slabs have lower density than the ambient lower mantle because of the commencement of perovskite forming reactions within the mantle and displacements of these reaction boundaries to higher pressures within the slabs as a consequence of their negative p t slopes if perovskite forming reactions within slabs are hindered for kinetic sluggishness then neutral buoyancy would be achieved when the slabs have penetrated 100 km into the lower mantle however using the available data on the kinetics of spinel to perovskite plus periclase reaction we conclude that the reaction would go to completion in a peru type young slab 41 myr and very likely also in a tonga type old slab 110 myr before these penetrated 100 km into the lower mantle thus slabs should always remain negatively buoyant and therefore continue to subduct through the lower mantle once it penetrates through the 660 km discontinuity despite a negative buoyancy force a slab could deflect at the top of the lower mantle 660 km because of factors resisting subduction namely viscosity jump low dip angle slab roll back and metastable persistence of olivine in cold slabs if published scale model experiments represent realistic approximations of the factors affecting plate subduction then according to our density data any slab with a dip angle of 40 50 would bend at the 660 km discontinuity if there is a viscosity jump of at least by a factor of 10 and trench migration the basalt top layer of a slab is denser than other slab components and the ambient mantle at all depths to 660 km and therefore should continue to sink into the lower mantle especially if a slab directly penetrates the 660 km barrier instead of peeling off in the transition zone to form a perched eclogite or piclogite layer as previously proposed the harzburgite layer which is sandwiched between denser basalt and lherzolite layers faces greater resistance to subduction especially in a young slab and thus could significantly contribute to the deformation of a slab near the 660 km discontinuity

efficacy of beach dewatering alassio italy abstract the goal of this study is to estimate the efficiency of dewatering operations in alassio beach north italy by following an integrated approach which included beach volume calculations daily mapping of the shoreline position examination of specific beach widening events and daily comparisons of morphodynamic characteristics of the drained beach versus a control section which included wave run up bar patterns rip migration evolution of the berm and cusp morphology alassio beach was documented by a daily time lapse photography by repeated dgps profile measurements and by an hourly wave and sea level monitoring following one year of draining the shoreline position and the beach volume of the drained beach and the control section showed little differences i e accumulation of 0 28 m 3 m 2 and a shoreline advance of 1 1 m on the drained beach whereas on the control beach the volume change was 0 03 m 3 m 2 and the shoreline retreated 1 2 m short episodes of beach widening 1 7 days long which coincided with onshore bar movement and a relative low sea level occurred simultaneously on the drained and the control sector this data indicated the inefficiency of the draining operation an improved resolution for determining the draining effect was attained by the sequential snap shot photography which showed many systematic morphological differences between the drained beach and the reference segment the drained beach developed a berm crest and a linear often scarped foreshore with a narrow swash zone no such cumulative morphologies were observed on the non drained control beach which commonly displayed cusps that were usually absent on the drained foreshore the wave data showed recurrent medium wave events of hs 1 2 m which repeatedly interrupted the calms thus cutting off the beach evolution the draining in alassio was unable to promote beach accumulation by counteracting the erosive effect of the medium interrupting storms

seismic signature of a hydrous mantle transition zone abstract although water has a major influence on tectonic and other geodynamic processes little is known about its quantity and distribution within the deep earth in the last few decades laboratory experiments on nominally anhydrous minerals nams of the transition zone have shown that these minerals can contain significant amounts of water up to 3 3 wt in this study we investigate if it is possible to use seismic observations to distinguish between a hydrous and anhydrous transition zone we perform an extensive literature search of mineral experimental data to generate a compilation of the water storage capacities elastic parameters and phase boundary data for potentially hydrous minerals in the transition zone and use thermodynamic modelling to compute synthetic seismic profiles of density v p and v s at transition zone temperatures and pressures we find that large uncertainties on the mineral phase equilibria ca 2 gpa and elastic properties produce a wide range of seismic profiles in particular there is a lack of data at temperatures corresponding to those along a 1300 c adiabat or hotter which may be expected at transition zone pressures comparing our hydrous transition zone models with equivalent profiles at anhydrous conditions we see that the depths of the 410 and 660 discontinuities cannot at present be used to map the water content of the transition zone due to these uncertainties further while average velocities and densities inside the transition zone clearly decrease with increasing water content there is a near perfect trade off with increases in temperature it is therefore difficult to distinguish thermal from water effects and the conventional view of a slow and thick transition zone for water and slow and thin transition zone for high temperature should be regarded with caution a better diagnostic for water may be given by the average velocity gradients of the transition zone which increase with increasing water content but decrease for increasing temperature however the significance of this effect depends on the degree of water saturation and partitioning between the nams since seismology is better able to constrain the thickness of the transition zone than velocity gradients our study indicates that the most useful input from future mineral physics experiments would be to better constrain the phase relations between hydrous olivine and its high pressure polymorphs especially at high temperatures additionally the uncertainties on the mineral seismic properties could be reduced significantly if the experimentally observable correlations between bulk and shear moduli and their corresponding pressure derivatives would be published

a perovskitic lower mantle inferred from high pressure high temperature sound velocity data determination of the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle indicates that perovskite constitutes much more of the lower mantle than predicted by the conventional mantle model and is consistent with the chondritic earth model earth s upper mantle is apparently depleted of silicon when compared with meteorites which are thought to represent the material from which the earth formed this missing silicon problem has provoked intense debate it suggests that the deficit might be balanced by silicon in the core or that the upper mantle is not representative of the entire mantle and that the lower mantle is enriched in silicon murakami et al provide evidence to support the latter case they made laboratory measurements of sound wave transmission through silicate perovskite and ferropericlase minerals at pressures and temperatures matching those of the lower mantle and compared the resulting shear wave values with seismic data that sample the lower mantle they conclude that the mineralogical model that provides the best fit is one in which perovskite constitutes greater than 93 of the lower mantle this suggests that the lower mantle is enriched in silicon in comparison with the upper mantle consistent with the chondritic earth model and that there is limited mass transport between the upper and lower mantle the determination of the chemical composition of earth s lower mantle is a long standing challenge in earth science accurate knowledge of sound velocities in the lower mantle minerals under relevant high pressure high temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations1 but previous acoustic measurements were limited to a range of low pressures and temperatures here we determine the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using brillouin scattering spectroscopy2 the mineralogical model that provides the best fit to a global seismic velocity profile1 indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle which is a much higher proportion than that predicted by the conventional peridotitic mantle model it suggests that the lower mantle is enriched in silicon relative to the upper mantle which is consistent with the chondritic earth model such chemical stratification implies layered mantle convection with limited mass transport between the upper and the lower mantle

seismological evidence for thermo chemical heterogeneity in earth s continental mantle abstract earth s thermo chemical structure exerts a fundamental control on mantle convection plate tectonics and surface volcanism there are indications that mantle convection occurs as an intermittent stage process between layered and whole mantle convection in interaction with a compositional stratification at 660 km depth however the presence and possible role of any compositional layering in the mantle remains to be ascertained and understood by interfacing inversion of a novel global seismic data set with petrologic phase equilibrium calculations we show that a compositional boundary is not required to explain short and long period seismic data sensitive to the upper mantle and transition zone beneath stable continental regions yet radial enrichment in basaltic material reproduces part of the complexity present in the data recorded near subduction zones and volcanically active regions our findings further indicate that 1 cratonic regions are characterized by low mantle potential temperatures and significant lateral variability in mantle composition and 2 chemical equilibration seems more difficult to achieve beneath stable cratonic regions these findings suggest that the lithologic integrity of the subducted basalt and harzburgite may be better preserved for geologically significant times underneath cratonic regions

a calibration of the bagnold beach equation abstract a simple sand trap is used to measure swash and backwash bedload transport rates on intertidal profiles data from sixty eight beach experiments are used to calculate a mean value of 12 78 kg m 4 s 2 for the calibration coefficient in the bagnold beach equation

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

large scale laboratory investigation into the effect of varying back barrier lagoon water levels on gravel beach morphology and swash zone sediment transport abstract it is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea specifically a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion while the reverse is thought to hold for a high beach groundwater table here we use the results of a carefully designed series of tests conducted in the delta flume the netherlands as part of the barrier dynamics experiment bardex to unequivocally demonstrate the validity of this assertion during the experiment a 4 m high and 50 m long gravel barrier d 50 11 mm was constructed within the central region of the 250 m long and 7 m deep wave flume enabling a back barrier lagoon to be located at its landward side the groundwater table in the beach was manipulated by lowering and raising the lagoon level and the gravel beach was subjected to variable wave conditions and sea lagoon levels using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion the divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the bulk swash hydrodynamics i e based on single point velocity measurements arising from a difference in the amount of swash infiltration into the unsaturated beach instead application of a sediment transport model that accounts for the effects of in exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface due to the large hydraulic conductivity of gravel k o 0 1 m s 1 the effect of altered shear stresses due to in exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches

a thermodynamic model for subsolidus equilibria in the system caomgoal2o3sio2 this study integrates phase equilibrium and calorimetric data for the following phases in the cao mgo al2o3 sio2 system clinopyroxene orthopyroxene garnet fomente anorthite spinel kyanite sillimanite corundum and quartz the internally consistent data set includes mixing properties for clinopyroxene orthopyroxene and garnet solid solutions and enables calculation of any equilibrium involving the components of the above 10 phases under any desired p t conditions major conclusions of the study apart from the data set are 1 1 spinel appears to have an enthalpy of mg al exchange on the order of 20 kcal or more substantially above the calorimetrically measured value 2 2 caal2sio6 pyroxene has virtually complete al si disorder 3 3 enstatite has an enthalpy of formation from oxides at 1000 k of about 16840 cal mole substantially greater than the calorimetric value of 17620 340 cal 4 4 anorthite has about 0 6 cal k entropy of al si disorder 5 5 cmas garnets of between pyrope100 and pyrope80grossular20 composition have almost zero excess entropy 6 6 nonstoichiometry in clinopyroxene has a moderate but predictable influence on reaction boundaries in sio2 saturated compositions

retrodictions of mid paleogene mantle flow and dynamic topography in the atlantic region from compressible high resolution adjoint mantle convection models sensitivity to deep mantle viscosity and tomographic input model abstract although mantle convection at earth like vigor is a chaotic process it has been shown by conceptual studies that one can constrain its flow history back in time for periods comparable to a mantle overturn 100 million years if knowledge of the tangential surface velocity field and estimates on the present day heterogeneity state are available such retrodictions enabled through computationally demanding adjoint methods are a promising tool to improve our understanding of deep earth processes and to link uncertain geodynamic modeling parameters to geologic observables here we present the first mantle flow retrodictions for geodynamically plausible compressible high resolution earth models with 670 million finite elements going back in time to the mid paleogene our retrodictions involve the dynamic effects from a low viscosity zone lvz in the upper mantle assimilate a past plate motion model for the tangential surface velocity field and probe the influence from uncertain modeling parameters by using two different estimates for the present day heterogeneity state of the mantle as imaged by two recent seismic tomographic studies and two different values for deep mantle viscosity focusing on the african hemisphere we find that our retrodictions produce a spatially and temporally highly variable asthenosphere flow with faster than plate velocities and a history of dynamic topography characterized by local doming events in agreement with considerations on plate driving forces and regional scale uplifts reported in the geologic literature our results suggest that improved constraints on non isostatic vertical motion of earth s surface provided for instance by basin analysis seismic stratigraphy landform studies or the sedimentation record will play an important role in our understanding of the recent mantle flow history

infiltration effects on sediment mobility under waves sediment mobility measurements with a horizontal sand bed under non breaking waves are reported conditions include no seepage and steady downward seepage corresponding to head gradients up to 2 5 the results indicate that infiltration tends to inhibit sediment mobility for a horizontal bcd of 0 2 mm quartz sand exposed to moderated wave induced bed shear stresses the effect is weak for the parameter range of the present study the two opposing effects of shear stress increase due to boundary layer thinning and the stabilizing downward drag are successfully accounted for through the modified shields parameter of nielsen nielsen p 1997 coastal groundwater dynamics proc coastal dynamics 97 plymouth asce dp 546 555 using coefficients derived from independent studies that is from the shear stress experiments of conley conley d c 1993 ventilated oscillatory boundary layers phd thesis university of california san diego 74 pp and the slope stability experiments of martin and aral martin c s and m m aral 1971 seepage force on interfacial bed particles j hydraulics div proc asce vol 97 no hy7 pp 1081 1100 c 2001 elsevier science b v all rights reserved

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

a geophysical perspective on the bulk composition of mars we invert the martian tidal response and mean mass and moment of inertia for chemical composition thermal state and interior structure the inversion combines phase equilibrium computations with a laboratory based viscoelastic dissipation model the rheological model which is based on measurements of anhydrous and melt free olivine is both temperature and grain size sensitive and imposes strong constraints on interior structure the bottom of the lithosphere defined as the location where the conductive geotherm meets the mantle adiabat occurs deep within the upper mantle 250 500 km depth resulting in apparent upper mantle low velocity zones assuming an fe fes core our results indicate 1 a mantle with a mg molar mg mg fe of 0 75 in agreement with earlier geochemical estimates based on analysis of martian meteorites 2 absence of bridgmanite and ferropericlase dominated basal layer 3 core compositions 13 5 16 wt s core radii 1640 1740 km and core mantle boundary temperatures 1560 1660 c that together with the eutectic like core compositions suggest the core is liquid and 4 bulk martian compositions that are overall chondritic with a fe si wt ratio of 1 63 1 68 we show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters specifically we find that the inversion results are reproduced by stagnant lid convection models for a range of initial viscosities 1019 1020 pa s and radioactive element partitioning between crust and mantle around 0 001 the geodynamic models predict a mean surface heat flow between 15 25 mw m2

chemical studies of h chondrites ii weathering effects in the victoria land antarctic population and comparison of two antarctic populations with non antarctic falls abstract we report rnaa data for 14 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in sb se te tl u zn in interior portions of 45 different h4 6 chondrites 49 samples from victoria land antarctica and 5 h5 chondrites from the yamato mts antarctica relative to h5 chondrites of weathering types a and b all elements are depleted 10 at statistically significant levels in extensively weathered types b c and c samples probably by leaching on the ice sheet surface contents of 8 elements in extensively weathered samples may provide a qualitative ranking for terrestrial surface residence chondrites of weathering types a and b seem compositionally uncompromised and as useful as contemporary falls for trace element studies when data distributions for these 14 trace elements in non antarctic h chondrite falls and unpaired samples from victoria land and from the yamato mts queen maud land are compared statistically numerous significant differences are apparent concentrations of 8 elements differ significantly in the victoria land and non antarctic h5 chondrite populations essentially the same compositional differences and 53 mn content and shock history differences appear when h4 6 populations are compared contents of 8 elements differ when queen maud land and victoria land populations are compared and 5 for the queen maud land non antarctic comparison these and other differences give ample cause to doubt that the various sample populations derive from the same parent population the observed differences do not reflect weathering chance or other trivial causes a preterrestrial source must be responsible the least unlikely of these involves a temporal variation in the source regions from which meteoroids derive

sedimentology and morphodynamics of a macrotidal beach pendine sands sw wales abstract the foreshore of pendine sands forms the seaward part of an extensive sandy coastal barrier in a shallow carmarthen bay sw wales the sedimentological features of the macrotidal foreshore reflect a tide induced modification of nearshore wave characteristics as the tide ebbs the breaker height may decrease the surf zone widens and becomes increasingly dissipative and swash backwash velocities diminish a concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient a zero net transport model demonstrates that the beach profile is self stabilising in the short term and periodic levelling has shown that the beach is in long term equilibrium with prevailing conditions though this does not preclude a significant dynamic response to changing tides and waves the flow regimes of wave generated currents decline as the tide ebbs and normal beach processes do not usually affect the lower foreshore accordingly there is an overall seaward fining of the primary framework component of the sands in more detail this framework component displays a slight seaward coarsening across an upper foreshore dominated by high water swash and surf a rapid seaward fining across the mid foreshore in response to the ebb attenuating swash zone flow velocities and a slight seaward fining across the lower foreshore under the action of nearshore shoaling waves bedforms vary from a swash backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore the surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions partly to storms the upper foreshore is characterised by swash backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities the mid foreshore is composed of coarser grained shelly traction clogs arranged as landward and seaward dipping large scale cross bedding and or plane bedding these are probably storm breaker surf deposits the lower foreshore though partially and sometimes totally bioturbated shows landward dipping small scale cross bedding in very fine sands sorted by nearshore shoaling waves tide and storm induced modification of the nearshore flow regimes therefore produces a distinctive shore normal array of sedimentary facies each facies is characterised by diagnostic textural and structural signatures a prograding sequence of such macrotidal deposits would be similar to but more extensive than a comparable microtidal sequence

influence of infiltration on suspended sediment under waves the effect of percolation through a permeable bed on sediment suspension under regular waves was examined in a laboratory wave tank 28 in x i in x 1 in using acoustic backscatter sensors to make rapid 3 hz suspended sand profile measurements 0 005 m vertical resolution waves of 1 7 s period and heights ranging from 0 14 to 0 185 m were used over sand with a d 50 of 255 mum infiltration velocities of 0 5 0 x 10 4 m s 1 were used with percolation through an initially flat bed ripple development was suppressed particularly at lower wave heights ripples took longer to form and were more three dimensional suspension was also suppressed the total suspended load was correlated with shields number at the 1 significance level when the shields number was modified to take account of both the infiltration nielsen p 1997 coastal groundwater dynamics proceedings of coastal dynamics american society of civil engineers pp 546 555 and ripple steepness coastal eng 1986 23 the ripple steepness was found to be the most important factor relating to the reduction in the total suspended loads the influence of infiltration on time averaged concentration profiles over equilibrium ripples was investigated by switching the percolation on and off for 5 min periods the total suspended loads were reduced by up to 50 with percolation on these results suggest that fluctuation of the water table and drainage within a beach will affect sediment transport and ripple dynamics and that for sand of 0 25 mm percolation will tend to reduce suspension and transport c 2002 elsevier science b v all rights reserved

elasticity composition and temperature of the earth s lower mantle a reappraisal the interpretation of seismological models for the earth s lower mantle in terms of chemical composition and temperature is sensitive both to the details of the methodology employed and also to uncertainties in key thermoelastic parameters especially for the dominant mg fe sio3 perovskite phase here the alternative approaches adiabatic decompression of the lower mantle for comparison at zero pressure with laboratory data and the projection of laboratory data to lower mantle p t conditions for direct comparison with seismological observations are assessed along with the equations of state on which they are based it is argued that adiabatic decompression of the lower mantle is best effected by a strategy in which consistent third order finite strain expressions are required simultaneously to fit the strain dependence of both the seismic parameter and the density this procedure accords due weight to the most robust seismological observations namely the wave speeds and reduces to an acceptable level the otherwise very strong covariance among the fitted coefficients it is demonstrated that this approach can readily be adapted to include the effects of relaxation from the hill average to the reuss lower bound of the aggregate bulk modulus which governs the radial variation of density for the projection of laboratory thermoelastic data to lower mantle p t conditions the preferred equation of state is of the mie gruneisen type involving the addition at constant volume of the pressure along a finite strain principal 300 k isotherm and the thermal pressure calculated from the debye approximation to the lattice vibrational energy a high degree of consistency is demonstrated between these alternative equations of state possible departures of the lower mantle from conditions of adiabaticity and large scale homogeneity are assessed these are negligible for the prem model bullen parameter b 0 99 0 01 but significant for ak135 b 0 94 0 02 reviving the possibility of a substantially superadiabatic temperature gradient experimentally determined thermoelastic properties of the major mg fe sio3 perovskite and mg fe o magnesiowustite phases are used to constrain the equation of state parameters employed in the analysis of seismological information although the scarcity of information concerning the pressure and temperature dependence of the elastic moduli for the perovskite phase remains a serious impediment nevertheless it is demonstrated that the combination of a pyrolite composition simplified to the three component system sio2 mgo feo with molar xpv 0 67 and xmg 0 89 and a lower mantle adiabat with a potential temperature of 1600 k consistent with the preferred geotherm for the upper mantle and transition zone is compatible with the prem seismological model within the residual uncertainties of the thermoelastic parameters for the perovskite phase in particular such consistency requires values for the perovskite phase of ks ks p t and q ln ln v t of approximately 3 8 and 2 and g t near 0 022 gpa k 1 for the lower mantle assemblage more silicic models which have sometimes been advocated can also be reconciled with the seismological data but require lower mantle temperatures which are much higher by about 700 k for pyroxene stoichiometry however the absence of seismological and rheological evidence for the pair of thermal boundary layers separating convection above and below which is implied by such models remains a formidable difficulty under these circumstances the simplest possible model that of grossly uniform chemical composition throughout the mantle is preferred

onshore offshore sediment transport on beaches abstract the onshore offshore transport of sediment on beaches in analyzed by considering the time averaged behaviour of a control volume bounded by the wave breaking zone and by the beach face interactions are determined between the wave radiation stress the wave set up the shear stress on the beach face and the beach permeability simple theoretical relationships are derived which specify beach slope in terms of incident wave attack and beach material properties these relationships indicate that coarser sediment beaches are steeper because of the higher beach permeability it is also shown that any particular beach will decrease its slope as the wave attack increases according to an inverse function of the wave height not only the beach permeability but also the sediment grading curve is shown to be a key factor in determining beach slope the theory is used to discuss and explain some observed behaviour on real beaches and the possible implications for beach failure under storm attack

surface groundwater flow numerical model for barrier beach with exfiltration incorporated bottom boundary layer model abstract a surface groundwater flow model is developed for the swash flow on a barrier beach the non linear shallow water equations are used to simulate the surface flow laplace s equation is used to describe the groundwater flow and is solved using the boundary integral equation method to provide potential heads and normal potential derivatives at and within the boundaries of the barrier an exfiltration incorporated bottom boundary layer sub model is used to obtain bed shear stress the groundwater model is verified against the numerical test results in kazemzadeh parsi and daneshmand 2012 for the groundwater flow through a rectangular dam the coupled surface groundwater model is validated against the prototype scale bardex ii experimental results turner et al 2016 the steady state groundwater flow comparisons show excellent agreement in phreatic surfaces the comparisons of groundwater flow under the action of waves show reasonably good agreement with experimental results in phreatic surfaces the simulated time averaged pore velocities for the runs with and without waves are in satisfactory agreement with experimental results in general and certain discrepancies are observed near the beach side the bed shear stress variation due to exfiltration is investigated by incorporating the modified logarithmic bottom boundary layer model of cheng and chiew 1998 in the coupled surface groundwater flow model the results confirm that as exfiltration increases bed shear stress decreases as a result of thickening of the bottom boundary layer

a planetary h group pebble in the barwell l6 unshocked chondritic meteorite abstract one stone of the barwell l6 shower contains an igneous inclusion with the oxygen isotopic signature of h group chondrites the inclusion is composed dominantly of olivine with a composition fo 75 5 identical with that of its host other phases are only partially equilibrated with the host the inclusion has a fractionated rare earth element pattern showing depletion in the heavy rare earth elements and a positive eu anomaly it is depleted in siderophile elements inclusion and host have ar ar ages 4 44 and 4 51 ga respectively and 129 xe r i ratios identical within experimental error we conclude that melting occurred very early on an h group chondritic body two objects from a single meteorite have different oxygen isotopic ratios but identical 129 xe r 127 i ratios which may indicate that the i xe systematics reflect chronological differences in closure to xe rather than isotopically heterogeneous iodine the inclusion and its host cooled to xe closure temperature contemporaneously with chondrules from unequilibrated ordinary chondrites

flow velocity and sediment transport in the swash zone of a steep beach detailed measurements of flow velocity and total sediment load were obtained in the swash zone on a steep beach swash motion was measured using ducted impeller flow meters and capacitance water level probes during wave uprush the onshore flow increased almost instantaneously from zero to its maximum velocity after the arrival of the leading edge of the swash lens and subsequently decreased gradually to zero for the remainder of the uprush during backwash the offshore flow increased steadily from zero to its maximum towards the end of the backwash and dropped rapidly to zero as the beach fell dry the duration of backwash was typically longer than that of uprush and maximum water depth on the beach was attained just prior to the end of the uprush the total sediment load was measured for 35 individual wave uprush events using a sediment trap the amount of sediment transported by a single uprush was typically two to three orders of magnitude greater than the net transport per swash cycle difference between uprush and backwash inferred from surveys of beach profile change the measured immersed weight total load transport rate displayed a strong relationship with the time averaged velocity cubed which is consistent with equations for both bedload transport and total load transport under sheet flow conditions the bagnold 1963 1966 bedload transport model was tested against our field data and yielded ib ku3tu tan tan where ib is the immersed weight of bedload transported during the entire uprush kg m 1 k is a coefficient kg m 4 s2 u is the time averaged flow velocity for the uprush m s 1 tu is the uprush duration s is the friction angle of the sediment and is the beach slope the empirically determined value for the coefficient k was 1 37 0 17

suction effects on bridge pier scour under clear water conditions abstractthe experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear water conditions the results show that suction has a profound effect on pier scour development and the extent of the influence is related to the location of the suction source when the suction source is located at or upstream of the pier the equilibrium scour depth is reduced by up to 50 with qs qo 2 where qs and qo suction flow rate and undisturbed approach flow rate respectively the data also show that for the suction source that is located downstream of the pier the equilibrium scour depth is reduced by up to 30 with the same suction flow rate the extent of pier scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity results of this study show that bed suction may be used as an effective pier scour countermeasure

a transmission electron microscopy tem investigation of opaque phases in shocked chondrites shock defects in the most common silicate minerals of chondrites olivine pyroxenes and feldspars have been investigated in detail but there have been almost no studies of the shock defects in other components like metal and sulfide this probably stems from the fact that these latter phases are opaque in the optical microscope the same reason explains why veins and melt pockets which are constituted of microcrystalline or glassy phases i e isotropic are also poorly documented we have investigated such phases by analytical transmission electron microscopy atem in two shocked chondrites tenham l6 and gaines county h5 we have characterized shock defects in troilite very similar to those occurring in silicates i e a mosaic texture and sets of straight and very narrow 10 nm lamellae of amorphized fes there are many small regions in shocked chondrites that are composed of very fine grained 1 m mixtures of metal and sulfide or of various silicates they must result from local melting followed by a rapid cooling that prevented grain growth we have determined the chemical compositions and the volume proportions of the tiny grains in these veins and melt pockets which has allowed their temperature and pressure t p history to be partially deciphered finally we have observed a dense network of very narrow fractures down to 10 nm in the olivine and enstatite grains these fractures are systematically filled with an amorphous or cryptocrystalline material that stems from the melt pockets and was injected when the fractures were opened by the rarefaction wave this material was then quenched at the contact with the colder crystalline rims

impact cratering on the h chondrite parent asteroid 1 this paper reports petrological data for lapaz icefield 02240 03922 031125 031173 031308 04462 and 04751 which are meteoritic samples of clast rich impact melt rocks from the h chondrite parent asteroid the size distribution and metallographic characteristics of fe ni metal in the melts indicate very rapid 1 to 40 c s cooling in the temperature range between 1500 and 950 c when the clast melt mixtures were thermally equilibrating cooling slowed to values between 10 3 and 10 2 c s in the temperature range between 700 and 400 c when the melt rocks were cooling to their surroundings these data suggest that the rocks cooled near the surface of the h chondrite asteroid within suevitic impact deposits integrating these data with the petrologic characteristics of other h chondrite melt rocks and their radioisotopic ages indicates that the h chondrite asteroid suffered at least one large impact event while still cooling from endogenous metamorphism at 4500 ma this impact must have degraded the asteroid s integrity but did not cause shattering impact events in the era between 4100 and 3600 ma produced melt volumes large enough to allow segregation of metal and troilite from silicate melts possibly within continuous impact melt sheets contained in craters the impact record after 3600 ma does not display such assemblages which suggests a decrease in the rate of large impact events or a catastrophic size reduction of the h chondrite parent asteroid at around this time

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

swash infiltration exfiltration and sediment transport field measurements of vertical pore pressure gradients within the bed are used to quantify instantaneous 8 hz rates of swash infiltration exfiltration across the beach face cyclic infiltration exfiltration is associated with individual swash events with observed vertical flow rates o 10 3 m s rates of net swash groundwater exchange i e through bed flow integrated over several swash cycles are two orders of magnitude smaller at the timescale of individual swashes vertical pore pressure gradients within the beach face are much greater than horizontal pore pressure gradients this permits application of the numerical solution of darcy s law for one dimensional vertical flow to model fluctuating pore pressures and hence vertical through bed flow vertical flow through a porous bed modifies sediment mobility in at least two ways 1 seepage forces change the effective weight of surficial sediments and 2 boundary layer thickening or thinning result in altered bed shear stresses by considering these two opposing effects separately a new shields parameter is derived that incorporates terms for through bed flow simulation of time varying seepage force and bed stress effects over an uprush backwash cycle suggests that the effect of altered bed stresses dominates over the change in effective weight and that infiltration exfiltration effects are most important during uprush simulated transport rates are increased by up to 40 of the peak transport rate during uprush and reduced by 10 during backrush in summary swash infiltration exfiltration across a saturated beach face enhances the net upslope transport of sediment

chemical studies of l chondrites iv antarctic non antarctic comparisons abstract we report shock facies and rnaa data for 13 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in rb se te tl zn in interior portions of 19 different l3 6 chondrites from victoria land antartica comparison of these data for essentially unweathered antarctic samples with those previously published for 39 l4 6 chondrite falls indicate substantial differences the victoria land population lacks the most heavily shocked 35 gpa representatives found in the non antarctic population while contents of nearly all trace elements studied are lower at statistically significant levels in strongly shocked 22 gpa falls than in mildly shocked 22 gpa ones this is not true for the victoria land population contents of most trace elements vary with petrologic type of heavily shocked facies d 22 35 gpa l chondrites from victoria land such a variation is not observed for non antarctic falls or mildly shocked samples of either population l4 6 chondrites from victoria land contain significantly lesser amounts of nearly every trace element than do falls these differences are reflected in correlations between elements including the putative cosmothermometric trace elements bi in and tl while antarctic weathering could account for the compositional differences between antarctic and non antarctic l chondrites such processes cannot be responsible for the shock differences observed physical and chemical differences between other sorts of antarctic and non antarctic meteorites suggest rather that the l chondrite differences are preterrestrial in origin if so the parent region s for the victoria land samples that fell to earth 0 1 to 1 myr ago generally formed and or evolved under higher temperature conditions than those regions yielding contemporary falls the dominant influence of late shock that altered mobile trace element contents of l chondrites falls is not evident in samples from victoria land

hydro and morpho dynamic modeling of breaking solitary waves over a fine sand beach part ii numerical simulation abstract a comprehensive numerical model is developed to predict the transient wave propagation sediment transport morphological change and the elastodynamic responses of seabed due to breaking solitary waves runup and drawdown over a sloping beach the individual components of the numerical model are first validated against previous analytical numerical and experimental results the validated numerical model is then used to simulate breaking solitary wave runup and drawdown over a fine sand beach where the experimental results are presented in young et al 2010b hydro and morpho dynamic modeling of breaking solitary waves over a fine sand beach part i experimental study the strengths and weaknesses of the model are assessed through comparisons with the experimental data based on the results sediment transport mechanisms and wave seabed interactions in the nearshore region are discussed

asteroid 6 hebe the probable parent body of the h type ordinary chondrites and the iie iron meteorites the s iv type asteroid 6 hebe is identified as the probable parent body of the h type ordinary chondrites and of the iie iron meteorites the ordinary chondrites are the most common type of meteorites falling to earth but prior to the present study no large mainbelt source bodies have been confirmed hebe is located adjacent to both the v6 and 3 1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface the silicate portion of the surface assemblage of hebe is consistent both in overall average and in its range of variation with the silicate components in the suite of h type chondrites the high albedo of hebe rules out a lunar style space weathering process to produce the weakened absorption features and reddish spectral slope in the s type spectrum of hebe linear unmixing models show that a typical ni fe metal spectrum is consistent with the component that modifies an h chondrite spectrum to produce the s type spectrum of hebe on the basis of the association between the h chondrites and the he iron meteorites our model suggests that large impacts onto the relatively metal rich h chondrite target produced melt bodies sheets or pods that differentiated to form thin laterally extensive near surface layers of ni fe metal fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in h chondrite breccias alternately masses of metal could have been deposited on the surface of hebe by the impact of a core or core fragment from a differentiated parent body of h chondrite composition subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of hebe in this interpretation the nonmagmatic iie iron meteorites are samples of the ni fe metal masses on the surface of hebe whereas the h chondrites are samples from between and or beneath the metal masses

petrology and geochemistry of patuxent range 91501 a clast poor impact melt from the l chondrite parent body and lewis cliff 88663 an l7 chondrite we have performed petrologic and geochemical studies of patuxent range pat 91501 and lewis cliff lew 88663 pat 91501 originally classified as an l7 chondrite is rather a unique near total impact melt from the l chondrite parent body lewis cliff 88663 was originally classified as an achondrite but we find that it is a very weakly shocked l7 chondrite pat 91501 is an unshocked homogeneous igneous textured ultramafic rock composed of euhedral to subhedral olivine low ca pyroxene augite and chrome rich spinels with interstitial albitic plagioclase and minor silica alumina alkali rich glass only 10 relic chondritic material is present olivine grains are homogeneous fa25 2 26 8 low ca pyroxene wo1 9 7 2en71 9 78 2fs19 9 20 9 and augite wo29 8 39 0en49 2 55 3fs11 8 14 9 display a strong linear tio2 al2o3 correlation resulting from igneous fractionation plagioclase is variable in composition or3 0 7 7ab79 8 84 1an8 2 17 2 chrome rich spinels are variable in composition and zoned from cr rich cores to ti al rich rims some have evolved compositions with up to 7 9 wt tio2 pat 91501 bulk silicate has an l chondrite lithophile element composition except for depletions in zn and br siderophile and chalcophile elements are highly depleted due to sequestration in centimeter size metal troilite nodules the minerals in lew 88663 are more uniform in composition than those in pat 91501 olivine grains have low cao and cr2o3 contents similar to those in l5 6 chondrites pyroxenes have high tio2 contents with only a diffuse tio2 al2o3 correlation low ca pyroxenes are less calcic wo1 6 3 1en76 5 77 0fs20 4 21 4 while augites wo39 5 45 6en46 8 51 1fs7 6 9 4 and plagioclases or2 6 5 7ab74 1 83 1an11 2 23 3 are more calcic spinels are homogeneous and compositionally similar to those in l6 chondrites lew 88663 has an l chondrite bulk composition for lithophile elements and only slight depletions in siderophile and chalcophile elements that are plausibly due to weathering and or sample heterogeneity

formation conditions of igneous regions in ordinary chondrites chico rose city and other heavily shocked h and l chondrites we report microprobe and radiochemical neutron activation analysis rnaa data for hosts and igneous inclusions in the heavily shocked ordinary chondrites rose city h5 yanzhuang h6 farmington l5 malakal l5 chantonnay l6 chico l6 and tuan tuc l6 based on these analytical results equilibrium crystallization calculations ghiorso and sack 1995 phase equilibrium analysis e g sack and ghiorso 1994a b sack et al 1994 and experimental cooling rate studies e g walker et al 1976 we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites we infer that 1 unfractionated chondritic liquids were intruded to depths 0 1 km in the parent asteroid of rose city 2 early chondritic liquids experiencing 5 10 olivine fractionation were erupted onto the surface of the parent asteroid s of yanzhuang and chantonnay and 3 near surface crystallization is also indicated for the liquids in tuan tue and farmington with chico and malakal crystallizing at slightly greater depths in all but chantonnay liquids appear to have derived from melting of chondrite types corresponding to their hosts in the l chondrite chantonnay the intrusive liquids derive from melting an h chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts heating effects are also reflected in the trace element contents of the chondrites our rnaa data for rose city seem to reflect only the siderophile lithophile fractionation evident in the metal distribution the yanzhuang rnaa data are generally similar to those of other h chondrites severe shock not involving phase transport seems to leave h chondrites unaffected compositionally contents of the four most mobile elements cd bi t1 in and cs in chico indicate loss so that this assemblage experienced extended low temperature cooling after injection of dike material into the chico host rnaa data for the other four l chondrites examined indicate more rapid cooling