lithospheric structure and tectonics at isidis planitia mars abstract we characterize the lithospheric structure of isidis planitia on mars by analyzing mars global surveyor and mars odyssey gravity and topography data using a flexural model of a thin elastic shell including bending and membrane stresses isidis planitia is a circular relatively flat plain formed near the end of the early noachian at the edge of the highlands lowlands boundary and the site of a large free air gravity anomaly features consistent with modification and filling of an impact basin our results suggest that the bulk density of the fill material inside isidis must be more than 2600 kg m 3 and higher densities are probable a comparison of the faulting observed at nili fossae to the predicted zone of extensional strain northwest of isidis constrains the thickness of the elastic lithosphere to be 100 180 km thick beneath the basin at the time of loading we also find that loads outside of the basin play a significant role in the interpretation of the tectonics simplified models tend to overestimate the lithospheric thickness we place relatively narrow bounds on the thermal gradient 3 4 6 5 k km 1 and heat flux 13 6 26 mw m 2 at isidis at the time of loading

tectonics of planetary loading a general model and results the tectonic response of a planet s lithosphere to an imposed load contains information on the mechanical properties of the lithosphere particularly its thickness from which more general planetary properties such as heat flow and rheology may be inferred traditionally mathematical models of the lithosphere s response to loads were constructed using either a flat plate or thin shell approximation and tectonic patterns were predicted as a function of the lithospheric thickness such predictions were then compared with the observed tectonics to determine the thickness of the lithosphere at the time of loading many of these models however are restricted in the size of features that can be treated by assumptions on load width and or lithospheric thickness additionally since membrane stresses dominate over bending stresses for broad laods many of these models consider only the membrane stresses we here develop a general model for planetary tectonics due to an axisymmetric load that is valid for arbitrary shell thicknesses and load widths the model predicts two distinct tectonic styles the first which results from narrow loads on thick lithospheres is the style familiar to terrestrial geologists successive regions of radial thrust strike slip and concentric normal faulting with increasing radial distance from the load we call this pattern the plate response the second style is the result of wide loads on thin lithospheres successive regions of disorganized thrust concentric thrust and strike slip faulting we call this pattern the membrane response while this second style of faulting may not be as familiar it agrees with the predictions of membrane theory the transition between these two styles is not abrupt but occurs over a range of lithospheric thicknesses it is marked by the development of bands of radial thrust and radial normal faults on mars if the tharsis rise is treated strictly as a load only this transitional regime can produce the observed radial normal faulting for reasonable lithospheric thicknesses since it occurs in the transitional regime it is not predicted by either the traditional flat plate or membrane approximations we use the model to determine the limits of shell thickness and load width where the use of the end member approximations is appropriate the overall style of tectonic response turns out to be a function of the interplay between shell thickness load width and the ratio of buoyancy to flexural support and cannot be predicted on the basis of any one of these for example some authors extend membrane theory to an arbitrarily chosen lithospheric thickness of 10 of the planetary radius our results show that such an extension is valid only for very broad loads on small icy moons for terrestrial planets the tectonic response predicted by membrane theory is realized only when the lithospheric thickness is less than 5 of planetary radius depending on the load width tectonic analysis on a planetary scale must take account of these different response styles and the limited range of load widths and lithospheric thicknesses for which they occur

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

transport of gravel and cobble on a mixed sediment inner bank shoreline of a large inlet grays harbor washington gravel and cobble transport measurements were obtained by particle tracing experiments from a mixed sand gravel and cobble beach at the head of a crenulate shaped shoreline half moon bay in grays harbor washington the direct measurements and results provide insight regarding the differential transport of gravel and cobble sized material on mixed sediment beaches the results are of relevance to the development of both predictive formulae for coarse grained sediment transport and guidance for practical gravel and cobble beach design net alongshore transport of gravel and cobble is generally several times greater than the net cross shore transport at half moon bay larger and smaller particles both move preferentially alongshore however smaller particles tend to move across shore more than larger particles particle transport distance during a tidal cycle increases with particle size or mass up to a point beyond which the particle transport rate begins to decrease with increasing size the direct relationship between transport rate and particle size may reflect the selective entrainment and the rejection or overpassing of larger particles which are more exposed to fluid forces on the beach surface than smaller particles which are sheltered within the matrix of larger particles as well as the higher susceptibility to burial of smaller particles the decrease in transport rate for the largest sizes may reflect the limited competency of the fluid forces to transport larger and heavier particles under the observed conditions the direct transport measurements are consistent with the overall particle size and shape distributions observed on this crenulate shaped inner bank beach whereby the larger and flatter particles have tended to outrun the smaller and more spherical particles in the downdrift direction

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

morphodynamic evolution self organisation and instability of coarse clastic barriers on paraglacial coasts abstract beaches and barriers on many mid to high latitude coasts comprise mixtures of fine and coarse clastic materials forming a distinctive morphodynamic environment in many cases the sediments are derived primarily from limited glacigenic deposits and the coasts are considered paraglacial over relatively long time scales decades to centuries coarse clastic barriers on such coasts show evidence of self organisation through large scale morphological evolution and facies differentiation this process involves gradual reworking partitioning and textural sorting of material toward transport minima long intervals of slow evolution are punctuated by episodes of rapid reorganisation involving breakdown of stable barrier structures and facies patterns remixing of sediment and accelerated migration of transgressive systems drift aligned systems develop longshore cell structure sometimes leading to breaching and segmentation and may evolve toward progressively greater swash alignment under appropriate circumstances swash aligned systems may experience catastrophic transformation when appropriate environmental triggers lead to threshold exceedance in the morphodynamics of the shore system adjacent barriers may show quite different behaviour depending on the antecedent states of individual coastal cells while appropriate parameterisations and sediment budget formulations allow us to model the long term evolution of some barrier structures the non linear dynamics that appear to dominate large scale behaviour may limit predictability the identification of stability threshold criteria remains an important research priority

southern california coastal response to the 2015 2016 el nino author s young adam p flick reinhard e gallien timu w giddings sarah n guza r t harvey m lenain luc ludka b c melville w kendall o reilly w c

gravity inferred crustal attributes of visible and buried impact basins on mars 1 the impact basins of mars reveal important insights on martian tectonic evolution they involve strongly disrupted depressed regions of crust with likely enhanced porosity and permeability that may locally concentrate water and other crustal fluids hence the crustal properties of impact basins can also be important in the hunt for water and related clues for life on mars we assess the crustal details of impact basins by separating the mars global surveyor free air anomalies into terrain correlated and terrain decorrelated components the separation is based on the correlation spectrum between the free air anomalies and the gravity effects evaluated from the topography mapped by the mars orbital laser altimeter mola for topographically visible multiring basins like isidis striking circular patterns of alternating terrain correlated free air maxima and minima mark the uncompensated components of the central mantle plug and surrounding rings the first vertical derivatives of these anomalies effectively estimate the basin ring locations and a transient cavity depth to diameter ratio of 0 09 that is consistent with the ratio observed for lunar nearside multiring basins for the isidis basin we obtain an excavation depth of roughly 66 km that reflects considerably disrupted crust for concentrating local fluids since the noachian impact furthermore the related crustal terrain decorrelated free air anomalies suggest up to 2 km of high density basin fill may cap the central basin subtle quasi circular depressions in the relatively featureless mola terrain of the northern hemisphere have identified potentially buried impact basins frey et al 2002 an altimetry depression in acidalia planitia and another in utopia are also associated with ringed patterns of terrain decorrelated free air anomalies that may mark the uncompensated mass effects of buried impact basins the gravity derived transient excavation depths for these inferred basins are roughly 41 and 20 km respectively while the related ring diameters d follow the ubiquitous d rule of planetary impact basins the crust of these buried basins is likely to contain water at higher levels than the crust of the equatorial basins that was substantially dewatered with the development of the great northern basin hence analyzing surface fractures faults and other crustal discontinuities that can tap the more saturated crust of these inferred buried basins may facilitate the hunt for water on mars

longshore transport of cobbles on a mixed sand and gravel beach southern hawke bay new zealand abstract few large scale field measurements of longshore sediment transport have been undertaken on beaches composed of coarse sediments in part owing to difficulties associated with measurement in energetic swash zones in which large clasts are moving here we present results from a field experiment in which passive integrated transponder tags were used to investigate patterns of cobble transport over 8 months on a mixed sand and gravel beach on the east coast of new zealand the study objectives were to document rates of alongshore transport and measure rates of cobble abrasion under field conditions cobble recovery rates were highly variable over the study period with 30 60 recovery at site 1 compared to much lower 0 20 recovery rates at sites 2 and 3 consistent uni directional patterns of net alongshore sediment transport were observed the median cobble transport rate was approximately 500 m over 207 days indicating long term net northward transport rates on the order of 2 2 5 m day results highlight a number of factors in addition to longshore energy flux that are important for understanding the observed patterns in particular across shore sediment transport during storms may have been smaller at site 1 than the other sites owing to lesser wave exposure this is partly responsible for higher cobble recovery rates at this site and also an increased amount of time during which cobbles were able to be transported alongshore on the lower beachface unique to this study results demonstrate the use of pit tags to provide direct measurement of cobble abrasion under natural processes repeat weight measurement on individually tracked cobbles show that after 207 days the median loss was 11 3 g or 1 8 of total weight there was a general trend of abrasion increasing with net transport distance but longshore cobble movement was highly variable ranging from 130 to 2500 m

syrtis major and isidis basin contact morphological and topographic characteristics of syrtis major lava flows and material of the vastitas borealis formation received 18 october 2002 revised 10 march 2003 accepted 14 april 2003 published 28 june 2003 1 the floor of isidis basin is covered by materials of the vastitas borealis formation vbf that appear to be emplaced essentially as a single unit along its western boundary isidis basin is in contact with volcanic flows from syrtis major planum the contact between the isidis unit and volcanic flows from syrtis major is sharp to gradational and in places is characterized by a high 500 m scarp or by a network of faults that separate pieces of lava plains off the main plateau of syrtis clusters of knobs and mesas sometimes arranged in flow like features are also typical features of the transition zone several important characteristics of the transition from syrtis major to isidis basin are documented 1 the small scale surface texture seen in moc images appears to be the same for both the syrtis lava plateau and the knobs and mesas that characterize the transition 2 there is strong evidence for the breakup of the coherent surface of syrtis major where it is in contact with materials in isidis basin 3 the plateau breakup the knobby terrain occurs basinward after the major break of slope of syrtis major where it enters the isidis basin 4 there is no evidence for plateau breakup anywhere up on the slopes of syrtis major planum 5 the lavas of syrtis remain morphologically intact where they are in contact with other units such as the noachian cratered terrain or where lava flows are stacked within syrtis major itself these characteristic features of the transition zone from syrtis to isidis are readily explained if the zone of plateau breakup consists of relatively young lava flows that have been superimposed onto the surface of a volatile rich substratum such as the interior unit of isidis basin the vastitas borealis formation thus simple superposition of volcanic materials on top of volatile bearing sediments can explain the key geological and topographic aspects of the transition zone from syrtis major to isidis basin on the basis of our findings we outline the following scenario for the evolution of this region in the early hesperian volcanic plains are emplaced in syrtis major the lower part of the syrtis major formation and wrinkle ridges deform their surfaces soon thereafter concurrently volcanic plains are emplaced on the floor of the isidis basin and wrinkle ridges deform their surfaces soon thereafter the apparent simultaneity of these units may mean that syrtis major was the source of many of the flows in the isidis basin in the early part of the upper hesperian subsequent to the formation of most of the wrinkle ridges the vastitas borealis formation was emplaced in the isidis basin and elsewhere in the northern lowlands following the emplacement of the vastitas borealis formation the upper part of the syrtis major formation was emplaced erupting from the eastern margins of syrtis major planum and flowing down into the westernmost part of the isidis basin on top of the recently emplaced vastitas borealis formation modification of the superposed lavas by degradation and evolution of the vbf formed the scarps and unusual morphology of the marginal areas we found no compelling evidence for massive or sudden erosion from syrtis major to produce the plains currently on the surface of the floor of the isidis basin the vastitas borealis

an improved solution of the gravity field of mars gmm 2b from mars global surveyor a spherical harmonic solution of the mars gravity field to degree and order 80 goddard mars model 2b gmm 2b has been developed using x band tracking data of mars global surveyor mgs from october 1997 to february 2000 and altimeter crossovers formed from the mars orbiter laser altimeter mola data between march and december 1999 during the mapping mission mgs was located in a near polar 92 9 inclination and near circular orbit at a mean altitude of 400 km the tracking data from this orbit provide a detailed global and high resolution view of the gravity field of mars mars gravity solutions are stable to 60 60 even without application of a kaula power law constraint the valles marineris is resolved distinctly with lows reaching 450 mgals olympus mons and its aureole are both separately resolved and the volcano has a peak anomaly of 2950 mgals the global correlation of the gmm 2b gravity coefficients with mola derived topography is 0 78 through degree 60 and the correlation remains above 0 6 through degree 62 the global gravity anomaly error predicted from the gmm 2b error covariance through 60 60 is 11 mgal the global geoid error from gmm 2b through 60 60 is 1 8 m mgs orbit quality using gmm 2b as measured by overlapping orbital arcs is 1 m in the radial direction and 10 m in total position

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

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

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

strength of faults on mars from mola topography the stresses which must be maintained on faults bounding the rift topography at tempe fossae the north tempe rift ntr and valles marineris vm on mars are estimated using a simple elastic model and topographic data from the mars orbiter laser altimeter mola the absence of rift flank uplift at the ntr is consistent with an elastic thickness te of 20 km or greater at the time of rift formation the maximum resolved shear stresses on bounding faults due to this topography do not therefore exceed 20 mpa similar to the inferred strength of terrestrial faults elastic thickness estimates at vm are mostly around 50 km or greater therefore for canyon widths of 400 km the bounding faults of vm if present must be able to withstand stresses of up to approximately 100 mpa however if the fault controlled sections of the canyons do not exceed 150 km in width as suggested by geomorphological analysis the fault strength required is only 20 mpa although the maximum resolved shear stresses required to support the topography at vm may need to be greater than the stresses which terrestrial faults can support at least some faults on mars are no stronger than similar features on earth this observation is consistent with the existence of liquid water in the shallow subsurface of mars at the time the faults were active on venus plate tectonics is probably prevented by the frictional resistance to motion across strong faults on mars it is more likely that the large thickness of the elastic layer of the lithosphere and the possible positive buoyancy of the crust are responsible for the observed lack of plate tectonics c 2002 elsevier science usa

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

gravity field of mars a 75th degree and order model radiometric tracking data collected by nasa s deep space network dsn for mariner 9 viking 1 and 2 orbiters and mars global surveyor mgs have been analyzed to determine the gravity field of mars the gravity solution mgs75d is a complete spherical harmonics model to degree and order 75 also parts of the solution are the gravitational constants of mars phobos and deimos the significant improvement in the mgs75d mars gravity model is mainly a consequence of globally distributed data set collected from the mgs mapping orbits the use of optimal weighting and constrained least squares solution techniques and improved force and measurement models in the orbit determination process the gravity anomaly map reveals significantly more detail and larger amplitudes than any previous mars gravity map over the major impact and volcanic areas on mars olympus mons remains the largest known gravity anomaly in our solar system and isidis planitia the highest amplitude mascon there are mascons in the hellas argyre and utopia basins valles marineris has distinctive negative anomalies and all volcanic features are positive gravity anomalies over several craters have also been resolved the overall correlation of the mgs75d gravity anomaly map with topography derived from the mars orbiter laser altimeter mola is very high while the polar regions display relatively poor correlation

surface and crater exposed lithologic units of the isidis basin as mapped by coanalysis of themis and tes derived data products 1 the stratigraphy and mineral heterogeneity of surface and crater exposed deposits in the southwestern portion of the isidis basin were investigated using spatial spectral visible and thermophysical data sets from both the mars global surveyor and odyssey missions four themis spectral surface units were identified progressing from the libya montes highlands to the inner lowland plains of isidis planitia lithologic determinations of these spectral units were made by linear deconvolution analysis of tes data olivine rich surface materials correlate with a well documented high thermal inertia unit based on spatial and stratigraphic relationships interpreted from both crater exposed and surface exposures the olivine rich unit was determined to have formed subsequent to the isidis basin forming event morphology occurrence and linear deconvolution of this unit suggests that it may represent noachian age to hesperian age picritic lavas that erupted as early stage lavas originating from sources such as syrtis major beneath isidis and as far as tyrrhena patera these lavas are suggested to have partially filled the basin based on crater exposed occurrences and were subsequently buried by further evolved olivine poor lavas later these lavas were exposed by erosion and subsequent impacts into the basin crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d d ratios and the well developed positive mass anomaly associated with the basin this study also demonstrates that the remote sensing of impact craters in conjunction with surface mapping is a potent mapping tool for understanding stratigraphy and the petrogenesis of the martian crust

observations of surface cobbles at two southern california beaches abstract southern california beaches are often sandy but with largely undocumented cobble patches and berms we describe the first multi year spatially extensive observations of surface cobbles at southern california beaches the variation spatial and temporal of surface cobble distribution and backshore e g upper foreshore cobble morphology slope vertical extent and elevation are characterized using 11 years 2008 2018 of observations spanning 4 8 km of shoreline at cardiff and torrey pines state beaches quarterly global positioning system surveys of beach elevation and visually identified sediment type either sand or cobble are used to create 1076 cross shore profiles cobbles were not exposed continuously at either of these predominantly sandy beaches the 202 cross shore profiles with backshore cobbles and sandy foreshores are used for morphology analysis consistent with previous studies cobble and sandy morphologies varied seasonally and cobbles were most exposed during winter when wave energy increased extensive vertical extent 2 m backshore cobbles were usually fronted by low elevation low slope sandy foreshores at torrey pines cobble patches were occasionally exposed mid profile on primarily sandy summer beaches persistent 2008 2015 backshore cobbles at cardiff were apparently buried in 2016 by effects of a 2012 sand nourishment formation of year round cobble piles on these seasonally sandy beaches may result from chronically reduced sand input owing to anthropogenic controls on river flooding and coastal cliff erosion e g dams and seawalls

localization of gravity and topography constraints on the tectonics and mantle dynamics of venus summary we develop a method for spatio spectral localization of harmonic data on a sphere and use it to interpret recent high resolution global estimates of the gravity and topography of venus in the context of geodynamical models our approach applies equally to the simple spatial windowing of harmonic data and to variable length scale analyses which are analogous to a wavelet transform in the cartesian domain using the variable length scale approach we calculate the localized rms amplitudes of gravity and topography as well as the spectral admittance between the two fields as functions of position and wavelength the observed admittances over 10 per cent of the surface of venus highland plateaus and tessera regions are consistent with isostatic compensation of topography by variations in crustal thickness while admittances over the remaining 90 per cent of the surface rises plains and lowlands indicate that longwavelength topography is dominantly the result of vertical convective tractions at the base of the lithosphere the global average crustal thickness is less than 30 km but can reach values as large as 40 km beneath tesserae and highland plateaus we also note that an earth like radial viscosity structure cannot be rejected by the gravity and topography data and that without a mechanical model of the lithosphere admittance values cannot constrain the thickness of the thermal boundary layer of venus modelling the lithosphere as a thin elastic plate indicates that at the time of formation of relief in highland plateaus and tesserae the effective elastic plate thickness k was less than 20 km estimates of t at highland rises are consistently less than 30 km our inability to find regions with t 30 km is inconsistent with predictions made by a class of catastrophic resurfacing models

coarse clastic barrier beaches a discussion of the distinctive dynamic and morphosedimentary characteristics abstract coarse clastic barriers are common on mid and high latitude coasts they possess a morphosedimentary and dynamic distinctiveness which sets them apart from sandy fineclastic barrier forms the reflective nature of the seaward barrier favors the development of zero mode sub harmonic edge waves particularly during long period swells 10 20 s manifest in the formation of high level cusps in some circumstances the pattern of recent overwashing of the barrier is related to cusps lack of distinct tidal passes due partly to the high seepage potential of coarse barriers means that very little sediment is transported seaward thus the barriers roll steadily onshore and sections show a variety of washover facies related to the volume of overwash surges

mid el nino erosion at nourished and unnourished southern california beaches wave conditions in southern california during the 2015 2016 el nino were similar to the 2009 2010 el nino previously the most erosive minimum beach widths and subaerial sand levels in a 7 year record as of february 2016 torrey pines beach had eroded slightly below 2009 2010 levels threatening the shoulder of a major highway however cardiff solana and imperial beaches nourished with imported sand in 2012 were on average 1 2 m more elevated and more than 10 m wider than in 2009 2010 monthly subaerial sand elevation observations showed that the nourished beaches remained consistently wider than unnourished beaches under similar wave conditions in contrast to a 2001 nourishment at torrey pines built with native sized sand that was removed from the beach face during a single storm these relatively coarse grained nourishments protected shorelines for several years and during the significant wave attack of the 2015 2016 el nino as of february 2016

imaging ionospheric inhomogeneities using spaceborne synthetic aperture radar 1 we present a technique and results of 2 d imaging of faraday rotation and total electron content using spaceborne l band polarimetric synthetic aperture radar polsar the results are obtained by processing polsar data collected using the phased array type l band synthetic aperture radar palsar on board the advanced land observation satellite distinguished ionospheric inhomogeneities are captured in 2 d images from space with relatively high resolutions of hundreds of meters to a couple of kilometers in auroral middle and low latitude regions the observed phenomena include aurora associated ionospheric enhancement arcs the middle latitude trough traveling ionospheric disturbances and plasma bubbles as well as ionospheric irregularities these demonstrate a new capability of spaceborne synthetic aperture radar that will not only provide measurements to correction of ionospheric effects in earth science imagery but also significantly benefit ionospheric studies

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

seasonal patterns of coarse sediment transport on a mixed sand and gravel beach due to vessel wakes wind waves and tidal currents direct measurements of coarse sediment gravel transport are presented and analyzed from a mixed sand and gravel beach on bainbridge island puget sound wa that is exposed to wind waves vessel wakes and tidal currents in order to quantify the relative role of different forcing mechanisms and the corresponding time scales of morphological response radio frequency identification rfid passive integrated transponder pit technology is implemented in two coincident yearlong tracking studies of sediment particles and complemented with beach profile surveys and meteorological and hydrodynamic measurements the sampling of the gravel tracers provides sufficient resolution to reveal the dominant seasonal transport patterns which include a range of wave climates during winter storms the predominant transport is due to wind waves in an alongshore uni directional process whereas tides and wakes play a relatively minor role in non storm intervals transport is brought about by the combination of vessel wakes and tidal currents although tidal currents are not sufficient to initiate sediment movement alone the combination of tidal currents and vessel wakes generate significant transport and provide a mechanism for post storm recovery re distributing sediment onshore morphologic response occurs as a seasonal fluctuation of the upper beach profile from steep to flat and in sediment composition from gravel to coarse sand between non storm and storm conditions respectively these results which are unique in their duration suggest that mixed sand and gravel beaches experience different modes of behavior over the range of forcing conditions observed during a typical year they point to the need for including grain composition in modeling mixed sand and gravel beach response and the need for long term observations of both forcing and response

support of long wavelength loads on venus and implications for internal structure a thin shell formulation for computing stress distributions on the surfaces of one plate planets is developed the lithospheric model includes laterally varying density anomalies at two depths corresponding to undulations on a crust mantle boundary and variations in upper mantle density for a given set of model parameters values for the vertical displacement crustal thickness anomaly and mantle density anomaly required to satisfy the topographic and gravitational boundary conditions are computed along with the resulting stress field the computed stresses can then be compared to stress directions inferred from observed tectonic features this formulation is used to study loads on venus s lithosphere and it is found that most highland areas appear to have been formed in a state of isostasy or by uplift with a significant portion of their support probably derived from dynamic processes in the mantle a possible exception is ishtar terra whose circumferential mountain belts are most consistent with a radially compressive stress regime generated by flexural loading reasonable lithospheric models predict low density mantle beneath atla beta eisila thetis and tethus regiones and thick crust accompanied by higher density mantle under ishtar terra and ovda regio thus western aphrodite terra appears to be more closely related to ishtar than to the rest of the equatorial highlands these results favor a hot spot model of venus tectonics in which beta eastern aphrodite eisila and tethus are expected to be relatively young and thermally active while ovda and ishtar should be older and less active

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

pebble and cobble transport on a steep mega tidal mixed sand and gravel beach abstract natural tracer pebbles and cobbles were deployed on a steep slope 0 1 mixed sand and gravel mega tidal beach located at the head of the bay of fundy two experiments were carried out to investigate the response of natural pebble and cobble sized material both to energetic wave conditions during individual storm events and to tidal only forcing conditions between storms net displacement of different tracer sizes was the focus of the first experiment while the effect of different shapes was tested in the second the pebbles and cobbles were painted in fluorescent colors labeled and their positions measured at low tide over periods of 10 12 days the tracers were emplaced at mid tide level on the beach face at low water and later recovered and re deployed on successive low tides net travel distance and direction were measured upon recovery hydrodynamic forcing conditions and local morphology at mid tide level on the beach face were monitored continuously during the experiments in the first experiment recovery rates were 100 during calm and moderate wave conditions hs 0 5 m but decreased significantly in more energetic wave forcing hs up to 1 m recovery rates were lower for smaller tracers during a three day wind wave event net displacements of up to 48 m were measured comparable net displacements were observed for all tracers maximum displacements were 39 m onshore 42 m offshore and 46 m alongshore in calm conditions maximum displacements were less than 1 m indicating that the bottom stresses due to tidal currents alone are too low to cause significant tracer displacement on time scales of weeks despite the high tidal range in the second experiment recovery rates were lower due to more energetic wave forcing significant wave heights reached hs 0 5 m on 80 of the particle tracking days and hs 1 m on 30 of the days flat pebbles and cobbles reached the longest transport distances with a maximum net displacement of 98 m the flat tracers were observed to be flipped by the shore break and to ride the swash bore and were in this manner transported long distances shoreward up to 66 m in both experiments the directions of alongshore displacements were consistent with deviations of the angle of wave incidence from the shorenormal tracer burial and re exposure was observed via rotary imaging sonar with the evolution and migration of m wavelength ripples the study allowed a direct correlation of pebble and cobble tracer displacements to hydrodynamic forcing during individual storm events with consideration of tracer particle size and shape

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

tectonics of mascon loading resolution of the strike slip faulting paradox subsidence of lunar mascon maria impact basins partly filled with mare basalt and sites of prominent positive gravity anomalies typically led to the formation of concentric graben arcuate rilles around the flanks of the basin while compressive features mare ridges formed in interior regions although previous numerical models of the response of the lunar lithosphere to mascon loading predict that an annulus of strike slip faulting should also have formed around mascon maria no such faults have been observed this strike slip faulting paradox however arises from an oversimplification of the earlier models viscoelastic finite element models of lunar mascon basins that include the effects of lunar curvature heterogeneous crustal strength initial stress conditions and multistage load histories show that the width of a predicted annulus of strike slip faulting may be small the use of anderson s criterion for predicting fault styles may also overpredict the width of strike slip faulting a faulting style criterion that takes into account transitional faulting in which both strike slip and dip slip components are present predicts zones of pure strike slip faulting that are about half of the width predicted by the anderson criterion furthermore strike slip faulting should be observed only in regions in which flexural stresses are sufficient to induce rock failure however since stress patterns consistent with strike slip faulting around mascon loads represent a transition between compressional and extensional provinces differential stresses tend to be low in these regions and for at least part of this region are not sufficient to induce rock failure a mix of concentric and radial thrust faulting is observed in some mascon maria at odds with previous models that predict only radial orientations away from the basin center this apparent discrepancy may be partly explained by the multistage emplacement of mare basalt units a scenario that leads to a stress pattern where concentric and radial orientations of thrust faults are equally preferred detailed models of the serenitatis basin indicate a 25 km thick lunar lithosphere at the time of rille formation and a 75 km thick lithosphere at the time of late stage mare ridge formation the extent of observed mare ridges and the inferred cessation of rille formation around serenitatis prior to the time of emplacement of the youngest mare basalt units is consistent with the superposition of a global horizontal compressive stress field generated by the cooling and contraction of the lunar interior with the local stresses associated with lithospheric loading

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

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

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

admittance estimates of mean crustal thickness and density at the martian hemispheric dichotomy 1 admittance estimates from line of sight los acceleration profiles of the mars global surveyor spacecraft are used to constrain the mean crustal thickness and surface density centered on the hemispheric dichotomy from 110 e to 220 e 40 s to 20 n models with uniform crustal properties predict lower than expected bulk crustal densities two layer models with loading only at the surface and the moho produce satisfactory fits to the data the best fit surface density crustal thickness tc and elastic thickness te are 2 5 mg m 3 27 km and 61 km respectively higher elastic thicknesses require lower crustal thicknesses and vice versa the best fit ratio of moho to surface loading f is close to 1 models with no bottom loading f 0 provide a poor fit to the data underestimates in f result in underestimates of both tc and te the surface density is lower than that measured from martian meteorites and by admittance analyses of young volcanoes but is well constrained by the short wavelength admittance values for misfits up to 1 5 times the minimum value and a fixed surface density of 2 5 mg m 3 the ranges of tc te and f are 1 75 km 37 89 km and 0 4 2 6 respectively the apparently compensated nature of the large impact basins has been used to infer a lower bound on southern hemisphere crustal thickness of 45 km if this estimate is correct the likely mean crustal thickness in the area considered is 55 20 km

short term displacements of marked pebbles in the swash zone focus on particle shape and size abstract in this paper two short term experiments with tracers on a mixed beach are presented the aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions sediment transport was studied by means of rfid technology to univocally monitor every single marked pebble a size subdivision of injected pebbles was conducted based on three classes big from 5 5 to 6 5 phi medium from 5 to 5 5 phi and small from 4 5 to 5 phi two recoveries were realised 6 and 24 h after the injection during a single day the wave motion was very low in the first experiment and low to moderate in the second never exceeding 0 4 m the results showed that discs are less dynamic than spheres but can cover greater distances regarding the sediment size big pebbles are less dynamic if compared to finer classes and they move preferentially down the swash zone towards the step or do not move up slope if already at the step very low and steady energy conditions facilitate cross shore and offshore movement of pebbles rather than a slight raise in wave height producing predominant longshore transport even with non marginal displacements low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though t tests showed that shape was not statistically significant for pebble displacement the displacements of medium and small sized pebbles show a statistical dissimilarity compared to the big ones to refine the velocity estimation necessary to initiate pebble movement the threshold velocity formulas known up to now should involve the shape parameter especially for the short term better knowledge of the relationship between the sediment s characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material hence a better understanding of the role of particle characteristics is necessary

reductions in fluvial sediment discharge by coastal dams in california and implications for beach sustainability abstract the long term sustainability of california s beaches depends on periodic deliveries of sand and gravel from coastal rivers and streams to assess the long term health of california s beaches this study characterized the current state of fluvial sediment delivery and quantified on a littoral cell basis the cumulative impacts of dams in decreasing annual discharge presently more than 500 dams impound more than 42 000 km2 or 38 of california s coastal watershed area flow modeling suggests that by diminishing flood hydrographs these dams have reduced the average annual sand and gravel flux to 20 major littoral cells by 2 8 million m3 yr or 25 in 70 of the streams considered in this study suspended sediment loads during equivalent discharge events have declined over the past three decades which indicates that dams have also significantly reduced downstream sediment supplies approximately 23 or 274 km of the 1193 km of beaches in california are downcoast from rivers that have had s

organisational controls typologies and time scales of paraglacial gravel dominated coastal systems abstract the fundamental controls on the initiation and development of gravel dominated deposits beaches and barriers on paraglacial coasts are particle size and shape sediment supply storm wave activity primarily runup relative sea level rsl change and terrestrial basement structure primarily as it affects accommodation space this paper examines the stochastic basis for barrier organisation as shown by variation in gravel barrier architecture we recognise punctuated self organisation of barrier development that is disrupted by short phases of barrier instability the latter results from positive feedback causing barrier breakdown when sediment supply is exhausted we examine published typologies for gravel barriers and advocate a consolidated perspective using rate of rsl change and sediment supply we also consider the temporal variation in controls on barrier development these are examined in terms of a simple behavioural model barch for prograding gravel barrier architecture and its sensitivity to such controls the nature of macroscale 10 2 10 3 years gravel barrier development including inherited characteristics that influence barrier genesis as well as forcing from changing rsl sediment supply headland control and barrier inertia is examined in the context of long surviving barriers along the southern england coastline

the use of passive integrated transponder pit tags to trace cobble transport in a mixed sand and gravel beach on the high energy oregon coast usa abstract cobble transport is investigated on a mixed sand and gravel beach on the high energy oregon coast using radio frequency identification technology rfid to detect passive integrated transponder pit tags inserted in the gravels pit tags are glass encapsulated transponders that are activated when an antenna passes near them with each tag characterized by its own unique identification number the tags are sealed within the cobbles minimizing any effect on the hydrodynamic character of the particles the tags draw power from the antenna itself and have a potential lifespan of up to 50 years pit tags are simple to use and inexpensive permitting the release and tracking of large numbers of gravel particles as a result pit tags have tremendous potential for examining the complexities of particle movement and the parameters that control their distribution on the beach our experiments have been conducted at cape lookout state park on the northern oregon coast on a composite beach where a seasonally variable sand beach fronts a mixed sand and gravel beach with the latter impacted by waves only during the winter when the sand beach is cut back a total of 400 cobble tracers have been released at five different locations subsequent monitoring of the gravel tracers revealed that they can be detected up to 1 m below the surface of the beach using a 1 0 m diameter antenna and up to 0 5 m below the surface using a smaller 0 3 m diameter antenna while their positions were determined using a trimble 5700 5800 rtk dgps survey system gravel tracer recovery rates were found to vary significantly between the different release points from as high as 90 recovery after 8 months to a low of 18 after 17 months the lowest recovery rates are thought to be due to the extent of aggradation of the sandy beach during the summer partially covering the gravel berm and burying the tracer particles to depths where they could not be detected by the antennas used with our rfid system relocation of the gravel tracers has revealed a predominant northward migration of the cobbles and locally demonstrate a strong cross shore transport both upslope and downslope movements initial attempts to examine the relationship between the transport distances and particle sizes and shapes have thus far revealed that the larger gravels are tending to outrun the smaller particles this is despite the fact that both small and large particles were found to be capable of being transported both short and long distances in contrast our results revealed no relationships between particle shape and distance moved in time it is expected that the pit tag tracers may begin to yield more definitive patterns of sorting the results did highlight that the gravel movement occurs predominantly near the sand gravel beach junction on the profiles a region dominated by a higher incidence of wave breaking and strong swash activity finally our analyses revealed the potential for using pit tags to provide field assessments of the abrasion rates of gravel particles having already found measurable degrees of weight loss to abrasion in our experiments

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

utopia and hellas basins mars twins separated at birth 1 using topography and gravity data as constraints we formulate spherical harmonic thin elastic shell models to determine the subsurface structure of the hellas and utopia basins for hellas we show that our model is consistent with the elastic thickness results of mcgovern et al 2002 2004 the thin elastic lithosphere at the time of formation implies that hellas is close to isostatic since utopia formed earlier we argue that an isostatic assumption is justified for the utopia basin before it was filled from this supposition we derive a system of equations that allows us to solve for the amount of fill the prefill topography and the amount of flexure due to the fill within the utopia basin an analysis of the parameter space shows that the fill density and the amount of fill is strongly dependent on the elastic thickness at the time of infilling a thinner elastic lithosphere favors a denser fill while a thicker lithosphere will allow for less dense material likewise larger crustal thickness values lead to smaller fill density values the presence of quasi circular depressions interpreted as impact craters within the utopia basin indicates that the majority of the material within utopia was deposited prior to 4 04 4 11 ga the early timing for the deposition combined with the heat imparted by the basin forming event argues for a thinner lithosphere which could in turn suggest fill densities that are more consistent with a volcanic load than with pure sediment or ice rich material these results are supported using an alternative method of determining the amount of fill and flexure within utopia this model assumes that hellas and utopia were initially identical and that the only difference in their subsequent evolution was the addition of material in the utopia basin the volume of material needed to fill utopia is immense on the order of 50 million km3 or more the high density obtained for the fill requires that it contain a large igneous component the source of which is problematic relaxing the isostatic assumption to a reasonable degree perturbs the density bound only slightly

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

stealth quasi circular depressions sqcds in the northern lowlands of mars 1 while qcds are quasi circular depressions revealed in the mars orbiter laser altimeter mola gridded data set stealth qcds sqcds are those qcds that have no obvious structural representation in visible images of mars it has been suggested that sqcds are surface representations of buried impact craters and on the basis of this assumption size frequency distributions of all qcds in the northern lowlands have been constructed to date the buried lowland floor expanding upon previous studies of stealth qcds around the utopia basin 446 sqcds with diameters ranging from 7 to 115 km have been identified in the northern lowlands of mars the direct relationship of sqcd surface relief to diameter indicates that stealth qcds form due to differential compaction of a cover material over buried impact craters a comparison of sqcd location to the geologic map of the northern lowlands reveals that stealth qcds are only located in geologic units predicted to be capable of differential compaction consistent with models of their formation the slope of the trend of the sqcds surface relief versus diameter has a coefficient of determination r2 approaching 1 when sqcds are evaluated by geologic unit and by regions of inferred comparable cover thickness trend slope analysis also indicates that the lowland cover material is thickest in the scandia region and the center of the borealis and utopia basins and thinnest in isidis planitia and north of arabia terra

the california coastal wave monitoring and prediction system abstract a decade long effort to estimate nearshore 20 m depth wave conditions based on offshore buoy observations along the california coast is described offshore deep water directional wave buoys are used to initialize a non stationary linear spectral refraction wave model model hindcasts of spectral parameters commonly used in nearshore process studies and engineering design are validated against nearshore buoy observations seaward of the surfzone the buoy driven wave model shows significant skill at most validation sites but prediction errors for individual swell or sea events can be large model skill is high in north san diego county and low in the santa barbara channel and along the southern monterey bay coast overall the buoy driven model hindcasts have relatively low bias and therefore are best suited for quantifying mean e g monthly or annual nearshore wave climate conditions rather than extreme or individual wave events model error correlation with the incident offshore wave energy and between neighboring validation sites may be useful in identifying sources of regional modeling errors

field evidence of beach profile evolution toward equilibrium an equilibrium framework is used to describe the evolution of the cross shore profile of five beaches medium grain size sand in southern california elevations were observed quarterly on cross shore transects extending from the back beach to 8 m depth for 3 10 years transects spaced 100 m in the alongshore direction are alongshore averaged into nineteen 700 900 m long sections consistent with previous observations changes about the time average profile in many sections are captured by the first mode empirical orthogonal function eof the first eof poorly describes sections with hard substrate less than roughly 80 sandy bottom and also fails near the head of a submarine canyon and adjacent to an inlet at the 12 well described sections the time varying amplitude of the first eof the beach state a describes the well known seasonal sand exchange between the shoreline and offshore roughly between 4 and 7 m depth we show that the beach state change rate da dt depends on the disequilibrium between the present state a and wave conditions consistent with the equilibrium concepts of wright and short 1984 and wright et al 1985 empirically determined optimal model coefficients using the framework of yates et al 2009a 2011 vary between sections but a single set of globally optimized values performs almost as well the model implements equilibrium concepts using ad hoc assumptions and empirical parameter values the similarity with observed profile change at five southern california beaches supports the underlying model equilibrium hypotheses but for unknown reasons the model fails at duck nc