calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

the effects of soluble salts on the threshold shear velocity of fine sand wind tunnel tests were carried out to investigate the effects of two soluble salts nacl and kci on the threshold shear velocity of a well sorted fine sand a sensitive laser monitoring system was used to detect initial grain motion during the tests results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement like bonds formed between grains that tend to hold individual particles in place however with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity this is indicated by increased scatter of data on the threshold shear velocity surface salt concentration plots for both nacl and kcl although data scatter is evident significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case

amphibole as an archivist of magmatic crystallization conditions problems potential and implications for inferring magma storage prior to the paroxysmal 2010 eruption of mount merapi indonesia amphibole is widely employed to calculate crystallization temperature and pressure although its potential as a geobarometer has always been debated recently ridolfi et al contrib mineral petrol 160 45 66 2010 and ridolfi and renzulli contrib mineral petrol 163 877 895 2012 have presented calibrations for calculating temperature pressure fo2 melt h2o and melt major and minor oxide composition from amphibole with a large compositional range using their calibrations we have i calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations and ii calculated crystallization conditions for amphibole from basaltic andesitic pyroclasts erupted during the paroxysmal 2010 eruption of mount merapi in java indonesia to infer pre eruptive conditions our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates calculated fo2 and melt sio2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions however calculated crystallization pressure and melt h2o content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters amphibole from merapi s pyroclasts yields calculated conditions of 200 800 mpa 900 1 050 c nno 0 3 nno 1 1 3 7 7 2 wt melt h2o and 58 71 wt melt sio2 we interpret the variations in calculated temperature fo2 and melt sio2 content as reasonable estimates but conclude that the large calculated pressure variation for amphibole from merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range in contrast bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas respectively and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth

geology and geochemistry of archaean granites in the kalgoorlie region of the eastern goldfields western australia a syn collisional tectonic setting abstract granites in the kalgoorlie region of the archaean yilgarn craton are predominantly biotite granodiorite and monzogranite with some hornblende bearing varieties granites are divided on the basis of field relationships petrography and chemical composition into five supersuites an older supersuite containing four suites pre dates regional folding and four supersuites post date regional folding the potassic composition of the mainly silica rich granites 68 sio2 suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite most supersuites evolved by fractional crystallization mainly of biotite and plagioclase some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched mantle derived magmas there was only limited and local chemical interaction between granite and mantle derived magmas geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event however s type granites which are widespread in some modern syn collision settings are absent in the kalgoorlie region the predominance of high fo2 i type granites in the study area probably reflects the absence of large graphite bearing metasedimentary accumulations in the lower crustal source regions the distribution of suites and supersuites implies a common source region beneath the kalgoorlie and gindalbie granite greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition

relative array analysis of upper mantle lateral velocity variations in southern california spatial averaging of short period teleseismic p wave arrivals across scarlet constrains upper mantle lateral velocity variations beneath southern california we compare dt d back azimuth and averaged arrival time estimates determined from the entire network for 154 events to the same parameters derived from small subsets of scarlet the resulting relative array diagrams and plots of net subarray delays computed for 171 overlapping subarrays exhibit large anomalies that vary smoothly as a function of subarray position implying substantial lateral heterogeneity under the network patterns of mislocation vectors for more than 100 subarrays permit identification of an east west striking high velocity antiform beneath the transverse ranges further constraints on both the lateral configuration and depth of the anomaly are obtained through thin lens analysis of the net delay data where all the time perturbations are assumed to originate at a single depth projection of 2798 net delays requires a lens deeper than 100 km a representative lens at 150 km depth features low velocities beneath the salton trough as well as a concentrated high velocity zone between 116 3 118 3 w and 33 7 34 8 n consistent with the relative array diagrams and the pkp delay contours of hadley and kanamori 1977 therefore the bulk of the high velocity material observed by hadley and kanamori may in fact lie at or deeper than 150 km rather than 40 100 km this possibility prompts renewed speculation regarding the relationship of this body to the plate tectonic history of the region

determining soil moisture and sediment availability at white sands dune field new mexico from apparent thermal inertia data 1 determinations of soil moisture and sediment availability in arid regions are important indicators of local climate variability and the potential for future dust storm events data from the advanced spaceborne thermal emission and reflection aster radiometer were used to derive the relationships among potential soil erosion soil moisture and thermal inertia ti at the spatial scale of aeolian landforms for the white sands dune field between may 2000 and march 2008 land surface apparent thermal inertia ati data were used to derive an approximation of actual ti in order to estimate the wind threshold velocity ratio wtr the wtr is a ratio of the wind velocity thresholds at which soil erosion occurs for wet soil versus dry soil the aster derived soil moisture retrievals and the changes through time at white sands were interpreted to be driven primarily by precipitation but the presence of a perched groundwater table may also influence certain areas the sediment availability of dunes active playa surfaces and the margin of the alluvial fans to the west were determined to be consistently higher than the surrounding area the sediment availability can be primarily explained by precipitation events and the number of dry days prior to the data acquisition other factors such as vegetation and the amount of surface crusting may also influence soil mobility but these were not measured in the field this approach showed the highest modeled sediment availability values just days prior to the largest dust emission event at white sands in decades such an approach could be extended to a global monitoring technique for arid land systems that are prone to dust storms and for other regional land surface studies in the sahara

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

assessing aeolian beach surface dynamics using a remote sensing approach a remote sensing technique for assessing beach surface moisture was used to provide insight into beach surface evolution during an aeolian event an experiment was carried out on october 21 2007 at greenwich dunes prince edward island national park canada during which cameras were mounted on a mast on the foredune crest at a height of about 14 m above the beach maps of beach surface moisture were created based on a calibrated relationship between surface brightness from the photographs and surface moisture content measured in situ at points spaced every 2 5 metres along a transect using a delta t moisture probe a time sequence of maps of surface moisture content captured beach surface evolution through the transport event at a spatial and temporal resolution that would be difficult to achieve with other sampling techniques such as impedance probes erosion of the foreshore and berm crest resulted in an increase in surface moisture content in these areas as the wetter underlying sediments were exposed flow expansion downwind of the berm crest led to sand deposition and a consequent decrease in surface moisture content remote sensing systems such as the one presented here allow observations of the combined evolution of beach surface moisture shoreline position and fetch distances during short term experiments and hence provide a comprehensive rendering of sediment erosion and transport processes

sensitivity of post hurricane beach and dune recovery to event frequency the recovery of santa rosa island in northwest florida is characterized following hurricane katrina september 2005 which was preceded by hurricanes ivan 2004 and dennis 2005 beach and dune recovery were quantified to the east and west of pensacola beach through a comparison of lidar data collected immediately following hurricane katrina and in july 2006 after almost a year of recovery east of pensacola beach the santa rosa unit the shoreline retreated by an average of 64 m during the 2004 2005 hurricane season and recovered by an average of 19 m to the west of pensacola beach the fort pickens unit the shoreline retreated by an average of 30 m and while no significant shoreface recovery was observed the presence of vegetation on low profile dunes promoted backshore accretion it is found that beachface recovery in the santa rosa unit and backshore accretion in the fort pickens unit occurred at the widest sections of the island where the pre storm profile volume had been relatively large and overwash penetration was at a minimum the narrow sections of the island between cuspate headlands had a smaller profile volume before the storms leading to greater overwash penetration and in some cases island breaching in both sections which limited the volume of sediment available for shoreface recovery the alongshore variation in recovery is not only related to the island width but also the offshore bathymetry height of the pre storm dunes and the overwash penetration if sufficient time is allowed for the return of vegetation and the recovery of the dunes the variations in storm impact observed during hurricane ivan will be reinforced during subsequent storms in this respect the level of impact during subsequent storms and the ability of the island to recover will depend on the frequency of storm events copyright 2009 john wiley sons ltd

aeolian sediment transport on a beach surface moisture wind fetch and mean transport abstract temporal and spatial changes in wind speed wind direction and moisture content are ubiquitous across sandy coastal beaches often these factors interact in unknown ways to create complexity that confounds our ability to model sediment transport at any point across the beach as well as our capacity to predict sediment delivery into the adjacent foredunes this study was designed to measure wind flow and sediment transport over a beach and foredune at greenwich dunes prince edward island national park with the express purpose of addressing these complex interactions detailed measurements are reported for one stormy day october 11 2004 during which meteorological conditions were highly variable wind speed ranged from 4 ms 1 to over 20 ms 1 wind direction was highly oblique varying between 60 and 85 from shore perpendicular and moisture content of the sand surface ranged from a minimum of about 3 by mass to complete saturation depending on precipitation tidal excursion and storm surge that progressively inundated the beach the data indicate that short term variations i e minutes to hours in sediment transport across this beach arise predominantly because of short term changes in wind speed as is expected but also because of variations in wind direction precipitation intensity and tide level even slight increases in wind speed are capable of driving more intense saltation events but this relationship is mediated by other factors on this characteristically narrow beach as the angle of wind approach becomes more oblique the fetch distance increases and allows greater opportunity for the saltation system to evolve toward an equilibrium transport state before reaching the foredunes whether the theoretically predicted maximum rate of transport is ever achieved depends on the character of the sand surface e g grain size slope roughness vegetation moisture content and on various attributes of the wind field e g average wind speed unsteadiness approach angle flow compression boundary layer development moisture content is widely acknowledged as an important factor in controlling release of sediment from the beach surface all other things being equal the rate of sediment transport over a wet surface is lesser than over a dry surface on this beach the moisture effect has two important influences a in a temporal sense the rate of sediment transport typically decreases in association with rainfall and increases when surface drying takes place and b in a spatio temporal sense shoreline excursions associated with nearshore processes such as wave run up storm surge and tidal excursions have the effect of constraining the fetch geometry of the beach i e narrowing the width of the beach because saturated sand surfaces such as found in the swash zone will only reluctantly yield sediments to aeolian entrainment the available beach surface across which aeolian transport can occur becomes narrower as the sea progressively inundates the beach under these constrained conditions the transport system begins to shut down unless wind angle becomes highly oblique thereby increasing fetch distance in this study maximum sediment transport was usually measured on the mid beach rather than the upper beach i e closer to the foredunes this unusual finding is likely because of internal boundary layer development across the beach which yields a decrease in near surface wind speed and hence transport capacity in the landward direction although widely recognized in the fluid mechanics literature this decrease in near surface shear stress as a by product of a developing boundary layer in the downwind direction has not been adequately investigated in the context of coastal aeolian geomorphology

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

problems of scale in the modeling and interpretation of coastal dunes abstract coastal dune systems are studied at time scales from seconds to millennia and space scales from millimeters to kilometers present approaches to the study of coastal dunes make it difficult to integrate models and interpretations of these systems over these scale ranges and arrive at reasonable conclusions it is argued that identification of key controls on dune development measurement of those controls and synthesis of data describing past and present conditions and used as calibration points will improve the viability of coastal dune models theoretical and empirical advances are necessary to improve the reliability of predictions across a range of geomorphological scales attempts at linking theoretical systematic models process synoptic measurement and historical or paleoenvironmental synthetic approaches make explicit the recognition that at time scales of more than a few hours and space scales greater than a few hundred meters deterministic models become unstable vis a vis prototype environments process climatologies provide one means to link process based work with broader scaled analysis as scales increase such climatologies will become less appropriate as the data become less reliable or as the systems change or as the scales become too large relative to the process record lengths in these conditions specific data i e samples representing points in time and space become check points for calibrating models it should be possible ideally to integrate both up and down time and space scales this is not yet possible

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

aeolian sand strip mobility and protodune development on a drying beach examining surface moisture and surface roughness patterns measured by terrestrial laser scanning ephemeral aeolian sand strips are commonplace on beaches their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns however due to their temporary nature little is known of their formation mobility or the specifics of their interaction with beach surface characteristics similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well their resolution over mainly dry sand close to the aeolian transport threshold is not ideal particularly where moisture gradients close to the surface are large in this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development surface roughness and surface moisture our results demonstrate that as the beach surface dries sand transport increases with sediment erosion occurring at the wet dry surface boundary and deposition further downwind this dynamic structure dependent upon changing surface moisture characteristics results in the formation of a rippled sand strip and ultimately a protodune our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings the terrestrial laser scanner provides a suitable apparatus with which to accomplish this

erosion by rivers and transport pathways in the ocean a provenance tool using 40ar 39ar incremental heating on fine grained sediment measured from 39 ar and 37 ar respectively are consistent with typical values for k and ca bearing minerals calculations show that the bulk mineralogy is reflected in the outgassing k ca spectra and identify plagioclase as the dominant mineral contributing to the plateau defining portion of the age spectra a second model predicts bulk sediment ages from integrated bedrock cooling age area estimates in order to examine whether bulk sediment plateau ages are representative of the average cooling age of rocks from a given river basin calculated and observed ages are notably similar in three river basins when topographic and lithologic effects are accounted for overall this technique shows considerable promise not only in tracking individual terrigenous sources in the marine realm but also for understanding processes such as erosion and sediment transport in terrestrial systems

temporal and spatial variabilities in the surface moisture content of a fine grained beach abstract this study examined spatial and temporal variations in the surface moisture content of a fine grained beach at padre island texas usa surface moisture measurements were collected on a 27 24 m grid that extended from the dune toe to the upper foreshore the grid was surveyed at 2 to 4 h intervals for two tidal cycles generating 17 maps of the spatial distribution of surface moisture simultaneous measurements of air temperature and humidity wind speed and direction tidal elevation and water table elevation were used to interpret observed changes in surface moisture it was found that the spatial distribution of surface moisture was broadly characterized by a cross shore gradient of high to low content moving landward from the swash zone the distribution of surface moisture was conceptualized in terms of three zones saturated 25 intermediate or transitional 5 25 and dry

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

a simple method to estimate threshold friction velocity of wind erosion in the field 1 this study provides a fast and easy to apply method to estimate threshold friction velocity tfv of wind erosion in the field wind tunnel experiments and a variety of ground measurements including air gun pocket penetrometer torvane and roughness chain were conducted in moab utah and cross validated in the mojave desert california patterns between tfv and ground measurements were examined to identify the optimum method for estimating tfv the results show that tfvs were best predicted using the air gun and penetrometer measurements in the moab sites this empirical method however systematically underestimated tfvs in the mojave desert sites further analysis showed that tfvs in the mojave sites can be satisfactorily estimated with a correction for rock cover which is presumably the main cause of the underestimation of tfvs the proposed method may be also applied to estimate tfvs in environments where other non erodible elements such as postharvest residuals are found

characterization of alluvial formation by stochastic modelling of paleo fluvial processes the concept and method summary modelling fluvial processes is an effective way to reproduce basin evolution and to recreate riverbed morphology however due to the complexity of alluvial environments deterministic modelling of fluvial processes is often impossible to address the related uncertainties we derive a stochastic fluvial process model on the basis of the convective exner equation that uses the statistics mean and variance of river velocity as input parameters these statistics allow for quantifying the uncertainty in riverbed topography river discharge and position of the river channel in order to couple the velocity statistics and the fluvial process model the perturbation method is employed with a non stationary spectral approach to develop the exner equation as two separate equations the first one is the mean equation which yields the mean sediment thickness and the second one is the perturbation equation which yields the variance of sediment thickness the resulting solutions offer an effective tool to characterize alluvial aquifers resulting from fluvial processes which allows incorporating the stochasticity of the paleoflow velocity

controls on coastal dune morphology shoreline erosion and barrier island response to extreme storms abstract the response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore while it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge the underlying causes of the alongshore variation remain poorly understood this study examines the alongshore variation in dune morphology along a 11 km stretch of santa rosa island in northwest florida and relates the variation in morphology to the response of the island during hurricane ivan and historic and storm related rates of shoreline erosion the morphology of the foredune and backbarrier dunes was characterized before and after hurricane ivan using empirical orthogonal function eof analysis and related through canonical correlation analysis cca the height and extent of the foredune and the presence and relative location of the backbarrier dunes varied alongshore at discrete length scales of 750 1450 and 4550 m that are statistically significant at the 95 confidence level cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner shelf the backbarrier cuspate headlands and the historical and storm related trends in shoreline change sections of the coast with little to no dune development before hurricane ivan were observed in the narrowest portions of the island between headlands west of the transverse ridges overwash penetration tended to be larger in these areas and island breaching was common leaving the surface close to the watertable and covered by a lag of shell and gravel in contrast large foredunes and the backbarrier dunes were observed at the widest sections of the island the cuspate headlands and at crest of the transverse ridges due to the large dunes and the presence of the backbarrier dunes these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper shoreface it is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively these findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during hurricane ivan

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

wind tunnel experimental investigation of sand velocity in aeolian sand transport sand velocity in aeolian sand transport was measured using the laser doppler technique of pdpa phase doppler particle analyzer in a wind tunnel the sand velocity profile probability distribution of particle velocity particle velocity fluctuation and particle turbulence were analyzed in detail the experimental results verified that the sand horizontal velocity profile can be expressed by a logarithmic function above 0 01 in while a deviation occurs below 0 01 m the mean vertical velocity of grains generally ranges from 0 2 m s to 0 2 m s and is downward at the lower height upward at the higher height the probability distributions of the horizontal velocity of ascending and descending particles have a typical peak and are right skewed at a height of 4 turn in the lower part of saltation layer the vertical profile of the horizontal rms velocity fluctuation of particles shows a single peak the horizontal rms velocity fluctuation of sand particles is generally larger than the vertical rms velocity fluctuation the rms velocity fluctuations of grains in both horizontal and vertical directions increase with wind velocity the particle turbulence intensity decreases with height the present investigation is helpful in understanding the sand movement mechanism in windblown sand transport and also provides a reference for the study of blowing sand velocity c 2007 elsevier b v all rights reserved

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

a simple model for the prediction of the deflation threshold shear velocity of dry loose particles abstract a very important parameter in aeolian equations is the de ation thresholdshear velocity which quanti es the instant of particle motion in this paper asimple model is presented for the prediction of the threshold shear velocity ofdry loose particles it has the same functional form as the widely used modelsof bagnold 1941 and greeley iversen 1985 but differs in its treatment ofthe so called threshold parameter as the new expression was based on themoment balance equation used by greeley iversen it includes a function forthe aerodynamic forces including the drag force the lift force and theaerodynamic moment force and a function for the interparticle forces theeffect of gravitation is incorporated in both functions however rather thanusing an implicit function for the effect of the aerodynamic forces as in thegreeley iversen model a constant aerodynamic coef cient was introduced from consideration of the van der waals force between two particles it wasalso shown that the function for the interparticle cohesion force is inverselyproportional to the particle diameter squared the model was calibrated ondata reported by iversen white 1982 the new expression compared atleast for terrestrial conditions very well with the greeley iversen model although it is much simpler it was nally validated with data from wind tunnel experiments on different fractions of dune sand and sandy loam soilaggregates the soil aggregates were treated as individual particles with adensity equal to their bulk density the good agreement between observationsand predictions means that when predicting mass transport of particles abovea given soil minimally dispersed particle size distributions should beconsidered rather than the granulometric composition of the soil keywords de ation threshold wind erosion wind tunnel introductionde ation is the blowing away of soil particles bywind particles start to move only if the aerody namic destabilizing forces exceed the stabilizingforces that keep the particles together once thewind erosion process has started particles willalso be detached as a result of impact forcescaused by the collisions that occur when settlingparticles hit the surface the initiation of particlemovement is generally quanti ed by means of thethreshold shear velocity u

a fully predictive model for aeolian sand transport abstract this paper presents the development calibration and verification of a fully predictive model for wind blown dry sand the model is based on the modification of the well known bagnold equation by including the threshold shear velocity which is also slightly modified to ensure a smoother transition from the non transport regime to the transport regime the sand transport rate is related to the static and dynamic grain roughness by using a semi empirical roughness predictor which is calibrated based on sand transport data from wind tunnel experiments with a flat mobile sand surface the model input for dry sand is the wind velocity at one height above the surface and the sand characteristics d50 d90 the effects of moisture vegetation and shells on the sand transport process are included by fairly simple expressions which are acting on the shear velocity the threshold value and the transport rate in all 105 high quality data sets have been used for verification of the proposed predictive model about 72 of the predicted values are within a factor of 2 of measured values of the transport rate

using a structure correction method to improve the location accuracy of the hotan seismic array a structure correction method is investigated and used to improve the location results of the wenchuan pishan and 171 other earthquakes using the hotan seismic array data systematic slowness anomalies are found between frequency wavenumber analysis and the location results from the china earthquake network center and all slowness error vectors point to about 300 it is found that the back azimuth and slowness errors change from positive to negative as the back azimuth of different ray paths turns from north to south and from east to west respectively this phenomenon can be attributed to a dipping layer beneath the array with strike dip and velocity contrast of 210 45 and 0 78 respectively after correction for this dipping structure the location results of the two main sequences are improved by 25 5 and 70 8 in terms of back azimuth and slowness respectively moreover the location results of the other 171 earthquakes are improved by 28 5 and 7 1 in terms of back azimuth and slowness respectively

modelling the formation of residual dune ridges behind barchan dunes in north east brazil residual dune ridges are often formed by vegetation growing along a line some distance upwind of the lower stoss slope of migrating dunes this process is common in areas where vegetation germinates along the edge of the water during the rainy period when the water level is higher and interdune areas are flooded the phenomenon occurs on a large scale in north east brazil because of the rise and fall in groundwater level at the end of the rainy season each residual dune ridge corresponds to the position of the dune during the wet period in each year therefore variations in the distance between these residual dune ridges could be used potentially to monitor climatic fluctuations in rainfall and wind to examine the potential use of these residual dune ridges for the reconstruction of past climatic fluctuations a model that simulates them under varying conditions of wind rainfall and evaporation rates was formulated the model was tested for sensitivity to climatic variability in north east brazil and validated against residual dune ridge displacements as measured in the field and from high spatial resolution satellite images based on the results it is concluded that residual dune ridges may not form in north east brazil in years which are exceptionally

alpine turf exfoliation pans in lesotho southern africa climate process morphological linkages abstract although alpine pans have been reported from a variety of mountain regions these have received limited research attention and are thus amongst the least known of closed basins this study investigates macro and fine scale morphological attributes and the process dynamics of alpine turf exfoliation pans in the high drakensberg of lesotho southern africa climate data temperature precipitation and wind are used to better ascertain climate surface process linkages and how these may be associated with the observed morphological phenomena thirty pans were assessed for both macro and fine scale aspect controlled morphological attributes during 2005 tinytag temperature loggers recorded ground temperatures on various pan riser aspects to establish the potential for cryogenic activity similarly wind speed and direction data from 2001 were used to identify the potential role of wind as an erosion and transportation mechanism the number and total weight of detached turf clumps accumulated at the base of various pan riser aspects were determined in july 1999 september 2001 and september 2004 it is suggested that the pans originated through initial turf disruption by animal trampling and turf burning followed by the cryogenic up heave of sediments the pans typically elongate towards the southeast as they enlarge demonstrate most active erosion on eastern and southeastern riser aspects and host seasonal micro echo and micro climbing dunes along such riser aspects it is concluded that an annual cyclic seasonal pattern of contemporary climate driven geomorphic processes dominated by strong northwesterly winds control the fine scale morphological evolution of alpine turf exfoliation pans in the lesotho highlands

biotite oxidation processes in ash flow tuffs mendoza argentina a mossbauer spectroscopy and chemical study abstract biotites and their alteration products muscovites and chlorites from six different cooling units of a dacitic to rhyodacitic ash flow tuff of early permian age yacimiento los reyunos formation mendoza argentina have been examined by means of mossbauer spectroscopy xrd and electron microprobe techniques four different types of layer silicate minerals were identified normal biotites oxybiotites muscovites and biotite chlorite oxybiotites were distinguished by means of mossbauer spectroscopy based on the presence of a fe3 doublet called des which is characteristic of biotites that were dehydroxilated under heat treatment in laboratory experiments and also on the very low fe 2 fe 3 ratios obtained fe3 is present only at the octahedral sites mossbauer spectroscopy data suggested that some of the muscovites originated from oxybiotites whereas biotite chlorite seem to have been altered from normal biotites the chemistry of layer silicate minerals showed that both the octahedral sites and the interlayer occupancy are deficient with respect to normal biotites oxybiotites are enriched in mg and k muscovites in si al and k and biotite chlorite in mg and al the fe fe mg ratio decreases in oxybiotites the rocks from which biotites and muscovites were extracted show oxidation ratios that correlate with those of the layer silicate minerals this trend was not observed for the biotite chlorite samples the presence of muscovites and biotite chlorite intergrowths are readily explained as due to hydrothermal alteration processes the fact that oxybiotites plot well above the haematite magnetite buffer curve in the fe2 fe3 mg diagram indicates a high fo2 value suggesting that they were formed during postmagmatic processes related to eruptive conditions rather than in the magma chamber the possible mechanisms for oxidizing biotites are discussed considering three different stages the presence of normal biotites only at the lowermost unit would indicate different eruptive conditions for this unit

backshore coarsening processes triggered by wave induced sand transport the critical role of storm events spatial backshore processes were investigated through field observations of topography and median sand grain size at a sandy beach facing the pacific ocean in japan a comparison of the backshore profile and cross shore distribution of the median sand grain size in 1999 and 2004 revealed an unusual sedimentary process in which sand was coarsened in a depositional area in the 5 year period although sediment is generally coarsened in erosional areas in support of these observations monthly spatial field analyses carried out in 2004 demonstrated a remarkable backshore coarsening process triggered by sedimentation in the seaward part of the backshore during a storm event in order to elucidate mechanisms involved in the backshore coarsening process thresholds of movable sand grain size under wave and wind actions a uniform parameter for both these cases in the onshore and offshore directions were estimated using wave tide and wind data the cross shore distributions of the estimated thresholds provided reasonable values and demonstrated a coarsening mechanism involving the intermediate zone around the shoreline under alternating wave and wind actions as a result of which coarse sand was transported toward the seaward part of the backshore by large waves during storms and then toward the landward part by strong onshore winds the 5 year backshore coarsening is most certainly explained by repetition of short term coarsening mechanisms caused by wave induced sand transport occurring from the nearshore to the intermediate zone copyright 2010 john wiley sons ltd

the stabilizing role of bonding agents on the entrainment of sediment by wind well sorted fine sand pretreated with varying concentrations of two soluble salts mgcl2 and cacl2 was tested for threshold shear velocity in a recirculating wind tunnel these tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity however the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different which is similar to the results for monovalent chlorides presented by nickling ecclestone a general relationship between threshold shear velocity and total surface soluble salt content is presented

a parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment abstract a new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented it is based on the balance of moments acting on particles at the instant of particle motion the model hence includes a term for the aerodynamic forces including the drag force the lift force and the aerodynamic moment force and a term for the interparticle forces the effect of gravitation is incorporated in both terms rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature a constant aerodynamic coefficient was introduced from consideration of the van der waals force between two particles it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared the interparticle force was further extended to include wet bonding forces the latter were considered as the sum of capillary forces and adhesive forces a model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well known model of fisher and the young laplace equation the adhesive force was assumed to be equal to tensile strength and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived by combining the capillary force model and the adhesive force model the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential the latter was loglinearly related to the gravimetric moisture content a relationship that is valid in the low moisture content range that is important in the light of deflation of sediment by wind by introducing a correction to force the relationship to converge to zero moisture content at oven dryness the matric potential moisture content relationship contained only one unknown model parameter viz moisture content at 1 5 mpa working out the model led to a rather simple parameterisation containing only three coefficients two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by iversen and white sedimentology 29 1982 111 the third parameter for the wet sediment part of the model was determined from wind tunnel experiments on prewetted sand and sandy loam aggregates the model was validated using data from wind tunnel experiments on the same but dry sediment and on data obtained from simulations with the model of chepil soil sci soc am proc 20 1956 288 the experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density furthermore it was shown that the surface had to dry to a moisture content of about 75 of the moisture content at 1 5 mpa before deflation became sustained the threshold shear velocities simulated with our model were found to be in good agreement with own observations and with simulations using chepil s model

wind tunnel investigation of the influence of surface moisture content on the entrainment and erosion of beach sand by wind using sands from tropical humid coastal southern china abstract wind erosion has major impacts on dune growth desertification and architecture on sea coasts the deflation threshold shear velocity is a crucial parameter in predicting erosion and surface moisture greatly affects this threshold and thus sand stability wind tunnel studies have shown that reduced moisture contents decrease entrainment thresholds and increase wind erosion but field and wind tunnel test data is lacking for tropical humid coastal areas in this study we investigated the influence of surface moisture contents at 1 mm depth on sand entrainment and erosion using tropical humid coastal sands from southern china shear velocities were deduced from velocity profiles above the sand the threshold shear velocity increased linearly with increasing ln100 m m gravimetric moisture content the increase was steepest below a moisture content of 0 0124 i e at m 1 5 the moisture content in the sand at a matric potential of 1 5 mpa we compared several popular models that predict threshold shear velocity of moisture sediment and found substantial differences between their predicted results at a surface moisture content of 0 0124 the predicted increase in the wet threshold shear velocity compared with the dry threshold shear velocity ranged from 34 to 195 the empirical model of chepil and selah simulated the data well for m m 1 5 whereas belly s empirical model simulated the data best for m 0 0062 wind erosion modulus increased with increasing effective wind velocity following a power function with a positive exponent at all moisture contents but decreased with increasing surface moisture content following a power function with a negative exponent when wind speed and moisture content varied simultaneously wind erosion modulus was proportional to the 0 73 power of effective wind velocity but inversely proportional to the 1 48 power of m the increase in resistance to erosion at low moisture contents probably results from cohesive forces in the water films surrounding the sand particles at a moisture content near m 1 5 wind erosion ceases nearly for all wind velocities that we tested

deciphering magmatic processes in calc alkaline plutons using trace element zoning in hornblende hornblende in the kuna crest lobe kcl of the tuolumne intrusive complex tic and the upper zone of the wooley creek batholith wcb precipitated over a temperature range of 835 to 700 c and thus has the potential to record magmatic processes we measured trace element concentrations in hornblende from the wcb from the kcl of the tic and from one sample from an adjacent interior unit of the tic to compare and contrast magmatic processes in these two mid crustal intrusions in both systems the magmatic amphibole is magnesiohornblende in which ti zr hf nb sr ba and rare earth elements ree typically decrease from crystal interiors to rims an indication of compatible behavior of these elements and the size of the negative eu anomaly decreases in the kuna crest lobe hornblende from individual mapped units differs in trace element abundances and zoning trends some samples contain at least two distinct hornblende populations which is particularly evident in the shapes of ree patterns in contrast compositions of hornblende from all structural levels of the upper wcb and related dacitic roof zone dikes form a single broad array and the ree patterns are essentially indistinguishable regardless of rock type from quartz diorite to granite in the wcb zr hf ratios in hornblende are consistent with crystallization from a melt with chondritic zr hf values in contrast most hornblende in the kcl has zr hf values lower than expected from crystallization from a melt with chondritic values suggesting that zircon fractionation occurred before and during crystallization of the hornblende simple fractional crystallization models indicate that ree high field strength elements sr and ba were compatible in kcl and wcb magmas as hornblende grew these trends require removal of hornblende plagioclase zircon ilmenite biotite the uniform variations of trace element concentrations and patterns in the upper wcb and roof zone dikes indicates crystallization from a large magma body that was compositionally uniform probably stirred by convection caused by influx of mafic magmas at the base of the zone coint et al 2013a 2013b cf burgisser and bergantz 2011 in contrast in the kcl each analyzed sample displays distinct hornblende compositions and zoning patterns some of which are bimodal these features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes and thereby relating plutonic rocks to hypabyssal and volcanic equivalents

complex systems in aeolian geomorphology aeolian geomorphology provides a rich ground for investigating earth surface processes and landforms as complex systems sand transport by wind is a classic dissipative process withnon linear dynamics while dunefield evolution is a prototypical self organisation phenomenon bothofthesebroadareasofaeoliangeomorphologyarediscussedandanalysedinthecontextofcomplexityandasystems approach afeedbackloopanalysisoftheaeolianboundary layer flow sediment transport bedforminteractions basedoncontemporary physicalmodels revealsthatthesystemisfundamentallyunstable oratmostmeta stable andlikelytoexhibitchaoticbehaviour recent field experimental research on aeolian streamers and spatio temporal transport patterns however indicates that sand transport by wind may be wholly controlled by a self similar turbulence cascade in the boundary layer flow and that key aspects of transport event timeseriescanbefullyreproducedfromacombinationof self organised 1 fforcing motionthreshold andsaltationinertia theevolutionof various types of bare sand dunes and dune field patterns have been simulated successfully with self organising cellular automata that incorporateonlysimplifiedphysically basedinteractions rules becauseoftheirundefinedphysicalscale however itnotclearwhether they in fact simulate ripples bedforms or dunes landforms raising fundamental cross cutting questions regarding the difference between aeolian dunes impact ripples and subaqueous current ripples and dunes an extended cellular automaton ca model currently under development incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas blow outs and parabolic coastal dunes preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes progress is limited however by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale state variables currently used in the bare sand models are far from capturing the rich 3d topography and patterns and are not sufficiently discriminative to distinguish different attractors the vegetationcomponentintheextendedmodel andindeedecogeomorphicsystemsingeneral poseevengraverchallengestoestablishing

aeolian sand transport an optimized model consideration of the available equations for prediction of aeolian sand transport led to the development of a model which relies on optimization techniques for the production of improved performance the model has been applied to the characterization of dunesand movement in coastal environments in eastern australia

submarine and superimposed contact metamorphic oxygen isotopic exchange in an oceanic arc sawyers bar area central klamath mountains california usa new bulk rock oxygen isotope data indicate a complicated history of fluid rock interactions in the upper few kilometers of a basaltic arc attending its mesozoic accretion to the western margin of north america folded multiply recrystallized weakly metasomatized mafic volcanics and interstratified sediments of the sawyers bar terrane an eastern segment of the western triassic and paleozoic belt were investigated the following scenario can now be reconstructed 1 island arc tholeiites iats ocean island basalts oibs and distal turbidites were deposited in a subsea environment during permian and early mesozoic time 170 245 ma basaltic rocks underwent low temperature alteration by seawater recrystallization occurred at 100 200 c and 1 kbar alkali exchange and variable mg enrichment were accompanied by increases in bulk rock 18o values of the greenstones from 6 to approximately 10 o preceeding initial stages of island arc formation 2 middle jurassic 165 170 ma suturing of the seaward oceanic arc structurally beneath a landward 227 ma blueschist terrane resulted in regional deformation and greenschist facies metamorphism pervasive overprinting took place without important chemical or isotopic exchange under conditions of 300 425 c 3 1 kbar 3 granitoid plutons emplaced during late middle jurassic time 160 165 ma heated adjacent wallrocks to 500 600 c at pressures of approximately 2 3 kbar thermal upgrading resulted in devolatilization of isotopically heavy metasediments and in the exchange of high 18o fluids with intercalated greenstones 18o values in iat and oib metavolcanics increased from 9 to 10 along axial portions of ns trending folds to more than 15 o where metabasalts are intimately interlayered with the metasediments construction of this sector of the continental margin through the assembly of a weakly deformed and polymetamorphosed oceanic arc was attended by a sequence of aqueous fluid rock isotopic exchanges reflecting the p t time evolution of the complex

erodibility of some crust forming soils sediments from the southern aral sea basin as determined in a wind tunnel severe dust storms in the southern aral sea basin have become common with the desiccation of the sea the high incidence of dust in the area has had severe ecological consequences within the framework of efforts to reduce this phenomenon deflatability as well as deflatability related characteristics of some prominent soils sediment surfaces in the southern aral sea basin were examined the materials included a salt crust from a developed solonchak a takyr crust and a takyr like soil and salt crusts from undeveloped solonchaks formed on the exposed bottom of the aral sea characteristics determined were particle size distribution dry aggregate size distribution and salt carbonate and organic carbon contents deflatability was examined using a suction type wind tunnel with a sensit type sensor to detect airborne unconsolidated material on materials treated to different moisture levels and with a chemical stabilizer and on restored crusts created from the unconsolidated materials fine sand dominates in the materials and in the takyr crust and takyr like soils is accompanied by significant amounts of silt and clay all materials contain moderate amounts of carbonate and are low in organic matter all soils sediments contain salts but in the salt crusts of the solonchaks the salt fraction dominates they all have more than 50 per cent pm850 particles with diameter 850 m indicating a relatively high deflatability potential the materials from the takyr crusts and takyr like soil with a high proportion of fine aggregates had the lowest threshold friction velocities while the salt crusts of the solonchaks with a high proportion of coarse aggregates had the highest this suggests that takyrs and takyr like soils are the most deflatable and solonchak soils the least deflatable these differences are attributed to the presence of salts that create stable large aggregates in the solonchak crusts wetting of the materials to three moisture levels considerably increased threshold friction velocity the increase was most prominent in the salt rich materials and was attributed to the rapid formation of surface films by drying in the course of the wind tunnel determinations applications of chemical stabilizers at two levels also considerably increased threshold friction velocity on the restored crusts threshold friction velocity dramatically increased occasionally to non recordable values this increase was monitored with both the salt crusts characteristic for the solonchak soils and the fine grained crusts characteristic for the takyr soils the stability was attributed to the tightly packed salt particles in the salt crusts and to the cohesive properties of the fine grained materials in the takyr crusts once the crusts were ruptured however strong deflation commenced these results suggest that by maintaining moisture in the soils sediments for example by maintaining a high water table in the amu darya river flood plain deflation can be reduced by the same means deflation can be reduced by creating new crusts or by preserving existing crusts copyright 2005 john wiley sons ltd

soil moisture and dry bulk density patterns in bare dune sands abstract recent research has shown that irregular wetting and preferential flow may occur in heterogeneous field soils bare dune sands which at first sight show the greatest homogeneity were sampled volumetrically at nine locations in temperate and arid areas to determine the spatial distribution of soil moisture content and dry bulk density soil moisture patterns were irregular even in extremely dry situations as functions for dune sands are very steep in the dry range small differences in water content result in huge differences in hydraulic conductivity these differences induced by soil moisture variability may result in anisotropy of the system and hysteresis tends to magnify this phenomenon so if soil moisture differences exist they will be consolidated and even amplified during new rain events at one site on a recently deposited dune sand infiltrating water was able to transform a one layer soil system into a two layer soil system inducing preferential flow at the layer interface at another site preferential flow paths appeared at the soil surface as sand columns as a result of the displacement of the dry sand between the flow paths caused by wind erosion in all the dunes studied dry bulk density patterns were irregular and tended to be slightly vertically orientated spatial distributions of volumetric and gravimetric soil water content showed great similarity

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v

the effect of wind gusts moisture content and fetch length on sand transport on a beach this paper reports on an analysis of instantaneous sediment transport in relation to wind gusts moisture content and fetch length from a field study carried out at skallingen denmark wind speeds were measured with cup anemometers and instantaneous sediment transport with vertical traps coupled to electronic balances moisture content was measured gravimetrically using samples taken along a beach profile at intervals of 1 to 2 h sediment transport and wind speeds were sampled at 1 hz and a 5 s running mean was used to smooth the data from the trap because of limitations of the balance resolution three measures of the threshold of sediment motion the intermittency threshold minimum threshold and maximum threshold were explored using data from five runs carried out on october 26 2000 the intermittency threshold and maximum threshold were largely insensitive to wind speed but varied spatially along the fetch distance the minimum threshold increased significantly with increasing mean wind speed as a result of reduced time for drying of the surface layer examination of time series for instantaneous wind speed and sediment transport for a number of runs on october 26 and november 6 2000 showed close agreement between fluctuations in wind speed and fluctuations in sediment transport cross spectral analysis of instantaneous wind speed and sediment transport for one run on each day where there was continuous transport showed high coherence between the two variables over a range of frequencies from 0 2 hz to 0 01 hz plots of all non zero instantaneous sediment transport values versus wind speed show considerable scatter in general transport rates are highest for traps located further from the upwind non erodible boundary i e along the fetch best fit power relationships show r2 values generally ranging from 0 4 to 0 6 and exponents ranging from 4 5 to 6 94 i e much higher than the traditional value of 3 found in most transport equations traps located close to the upwind boundary had lower r2 values and exponents 2 5

evaluation of aeolian sand transport equations using intertidal zone measurements saunton sands england sand transport rates were measured using a vertical sand trap along the intertidal zone of a beach in north devon england together with simultaneous monitoring of the wind speed on the beach and moisture levels in the surface layers of sand the results of 88 sand trap samples in a wide range of wind speeds showed that moisture levels up to 14 in the top 1 2 mm of the beach sand have no discernible effect on the transport rates transport rates measured from areas of the beach where the moisture was below this level are compared with the rates predicted by seven expressions based on theoretical and wind tunnel research together with the empirical results of other published research measured transport rates range from 0 0001 to 0 22 kg m 1 s 1 the results indicate that expressions based on a power relation between the wind speed and the transport rate and which include a threshold velocity term provide the best estimates of the observed transport rates

aeolus ii an interactive program for the simulation of aeolian sedimentation abstract a computer program has been developed to simulate two or three dimensional topographic change associated with aeolian sediment transport because predictions generated by available models of aeolian transport can vary by about an order of magnitude for a given set of environmental conditions selection of an appropriate model is problematic this program includes a number of models and provides for interactive selection of a desired model combination s to allow for comparison between model predictions topography represented by a set of coordinates in two or three dimensions is defined by bins of sediment differential rates of transport between adjacent bins resulting from variations in grain size slope and surface moisture content are used to determine mass flux and to adjust the topography in an iterative fashion sub routines allow the simulation of temporally varying levels of surface moisture resulting from evaporation and periodic restoration of upwind boundary conditions the wind field can be represented by a constant shear velocity by a spatial cross shore distribution of shear velocities or by a time series of values representing multiple wind events output is in the form of a graphic display or tabulated results written to disk example results are presented which qualitatively suggest that simulated topographic changes are reasonable areas where further refinement is needed to improve correspondence with reality are identified and discussed

climate driven changes in tropical cyclone intensity shape dune activity on earth s largest sand island abstract in this study historical aerial photos and detailed climatic time series are used to show the geomorphological consequences of a significant decrease in tropical cyclone frequency and intensity in eastern australia since the early 1980s leading to rapid dune stabilization on earth s largest sand island and a world heritage site fraser island australia it is shown that cyclone frequency and intensity significantly declined in eastern australia south of 20 s since the early 1980s corresponding with the shift to a positive phase of the interdecadal pacific oscillation in 1977 and an increased frequency of enso events since 1982 83 using historical aerial photos and remote sensing techniques it is shown that most of fraser island s transgressive dune fields were advancing inland during the period between 1948 and 1982 and that tropical cyclones in that period were strong enough to initiate small blow outs

p wave backazimuth anomalies observed by a small aperture seismic array at pinyon flat southern california implications for structure and source location abstract seismograms of earthquakes and explosions recorded at local regional and teleseismic distances by a small aperture dense seismic array located on pinyon flat in southern california reveal large 15 backazimuth anomalies we investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques the broadband frequency wavenumber bbfk technique the polarization technique and the beamforming technique while each technique provided nearly the same direction as a most likely estimate the beamforming estimate was associated with the smallest uncertainties backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the anza and caltech seismic networks and the preliminary determination of epicenters pde bulletin these backazimuth anomalies have a simple sinelike dependence on azimuth with the largest anomalies observed from the southeast and northwest directions such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array a best fit model of a single interface has a dip and strike of 20 and 315 respectively and a velocity contrast of 0 82 km sec application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions suggesting that this is an upper crustal feature we confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

on the effect of moisture bonding forces in air dry soils on threshold friction velocity of wind erosion wind erosion is a dominant geomorphological process in arid and semi arid regions with major impacts on regional climate and desertification the erosion process occurs when the wind speed exceeds a certain threshold value which depends on a number of factors including surface soil moisture the understanding and modelling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions in arid regions during the dry season the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity by a series of wind tunnel tests and theoretical analyses this dependence of threshold velocity on near surface air humidity is shown for three soils of different textures sand sandy loam and clay loam the results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40 and 65 while above and below this range the threshold shear velocity increases with air humidity a theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the humidity of the overlying atmosphere the conditions under which soil atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions

the influence of rainfall on transport of beach sand by wind this paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments although sediment transport by splash is of secondary importance on coastal dunes splash saltation processes can move sediments in conditions where no motion is predicted by aeolian processes the effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler in general an increase of particle movement by wind at the sensor heights was observed during rainfall rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface the influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles

structural corrections for slowness and azimuth of seismic signals arriving at gauribidanur array abstract slowness and azimuth anomalies directly measured from the data recorded at seismic arrays have been used for observing deviations from spherical symmetric earth interpretation of such observations for reliable refinement of earth models requires correction for the effect of irregularities in the crust and upper mantle structure beneath the recording sites because it introduces large systematic errors in slowness and ray direction observations of large systematic errors in slowness and azimuth for teleseismic events approaching gauribidanur gba seismic array from the east were compensated by introducing a number of dipping moho beneath recording sites it was found that a dipping interface having a dip of 6 and a strike of n13 e explains observations of ray direction anomalies in a satisfactory manner this can deviate seismic rays up to 11 5 per cent in slowness and 6 5 in azimuth the quantum of errors seems quite significant as far as refinement of earth models is concerned a correction table has been prepared which would be useful in the analysis of slowness and azimuth of earthquakes recorded at gba from the eastern direction we have applied these structural corrections successfully to the observed slowness and azimuth of earthquakes from this direction this is illustrated in the form of array diagrams

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

optimal backazimuth estimation for three component recordings of regional seismic events augmenting travel time data with backazimuth information can improve regional seismic event locations for which only a few recording stations are available this study examines the achievable accuracy of backazimuths derived from 164 regional short period p waves recorded at regional seismic test network rstn stations the data represent 62 events with a good distribution of distance azimuth and signal to noise ratio snr at each of four rstn stations using preliminary determination of epicenter locations to generate reference backazimuths we examine the effects of computational method signal window length frequency content and snr on rstn backazimuth estimates the variety of geologic environments at the receivers also allows assessment of the effect of receiver structure on backazimuth estimation our results indicate that regional three component recordings can produce useful backazimuths more than 75 per cent of the records yield backazimuths within 20 of the correct value when reasonable parameters are used the accuracy of the calculated backazimuths does vary with the receiver however rstn stations in new york and ontario located in precambrian terranes produce very accurate backazimuths for snrs greater than 5 db at the south dakota and tennessee stations located in sedimentary rocks complicated receiver structure is the controlling factor in backazimuth estimation propagational complexities at the south dakota site preclude recovery of reasonable backazimuth values poor statistics are obtained for all parameter combinations at the tennessee site backazimuth accuracy depends strongly on the computational method used in general the choice of frequency band is important and varies by stations while the length of the signal window is less critical if the problematic south dakota records are excluded we achieve an rms backazimuth error of about 6 for recordings with snr above 10 db while a single optimized choice of parameters produces good results for the 164 record data set a further 5 to 10 per cent improvement can be achieved if the parameters are customized on a station by station basis

effect of source width and tidal elevation changes on aeolian transport on an estuarine beach data from a moderate energy meso tidal beach on the east side of delaware bay new jersey usa revealed the significance of both beach width as a source for aeolian transport and the effect of tidal rise on source width wind speeds averaged over 17 1 min recorded 6 m above the crest of a 0 5 m high dune ranged from 11 6 to 12 7 m s 1 during the experiment the highest observed rate of transport on the beach was 0 0085 kg m 1 s 1 monitored at rising low tide when the average wind speed was 11 6 m s 1 across 0 35 mm diameter surface sediments the wind direction was oblique to the shoreline creating a source width of 34 m the reduction in the width of the beach as a source for aeolian transport during rising tide was approximately arithmetic whereas the reduction in volume of sediment trapped was exponential aeolian transport effectively ceased when source width was less than 8 m wind conditions moisture content of the surface sediments and presence of binding salts did not appear to vary dramatically and no coarse grained lag deposit formed on the surface of the beach the decrease in rate of sediment trapped through time in the tidal cycle is attributed to differences in source width sediment deposited in the litter behind the active beach by strong winds during the rising tide was eroded during the high water period by the high waves and storm surge generated by these winds and net losses of sediment were observed despite initial aeolian accretion

seismic image of the tarim basin and its collision with tibet a broadband seismic deployment in 1998 1999 in southwestern tarim provided data for imaging the crust and upper mantle across the contact between the tarim block and the tibetan plateau a profile composed of migrated teleseismic receiver functions clearly shows lateral structural changes the crust under the tarim basin is relatively simple the moho discontinuity is mapped at a depth of 42 km near the northern end of the array and dips gently toward the south to 50 km under the kunlun foreland the tarim basin appears to be rigid with little shortening farther to the south the imaging reveals a complex of reflectors in the lower crust and the upper mantle there are both north and south dipping upper mantle structures under the kunlun foreland and kunlun shan region we found the observations to be more consistent with a model of lithospheric collision in which the crust and the upper mantle on both sides interpenetrate and deform

investigation of azimuth residuals observed at stations of the gsett 3 alpha network the gsett 3 experiment was conducted for more than two years and the international data center idc reported more than 20 000 events for 1995 in the reviewed event bulletins reb we have used this data base to investigate the location bias of arrays and selected three component stations in the alpha network for which the recorded data is automatically processed to determine earthquake locations in near real time the alpha network which consists of 14 arrays provides estimates of event azimuths determined by f k processing we selected 19 three component stations that were operated all or most of 1995 and for which event azimuth was estimated by polarization analysis only events with epicentral distances of less than 100 were considered in order to exclude phases with steep incidence angles associated with unreliable azimuth estimates teleseismic p phases and the major regional and local phases were examined only data for which a signal to noise ratio was given were included in this analysis the signal to noise ratios were used as a weighting factor for the statistical parameters and the graphical representation of the azimuth residuals the preliminary analysis of azimuth residuals identified some arrays that give significantly erroneous azimuths in some cases the error is systematic in other cases it is random one array with systematic azimuthal bias is cmar this array shows positive residuals for event paths from the south while phases for events with paths from the north show negative residuals similar patterns which strongly suggest azimuthal bias are observed for pdar txar and spits in the case of mjar the large azimuthal errors observed particularly for regional and local distances are not a function of direction the scatter in the azimuth residuals is much larger for 3 c stations than for the arrays clear systematic errors were identified for schq and cpup which show constant offsets and at vnda which has negative residuals for events to the north and positive residuals for events from the south the most significant azimuth bias was observed for pdy where the azimuth residuals change from about 90 to more than 90 at backazimuths near 120 meaning that all rays appear from the northwest

a wind tunnel study of aeolian sand transport on a wetted sand surface using sands from tropical humid coastal southern china this article reported a wind tunnel test of sediment transport related to surface moisture content and wind velocity using sands from tropical humid coastal area a 1 mm thick portion of surface sand was scraped using a self made sediment sampler and the gravimetric moisture content was determined sand transport was measured via a standard vertical sand trap with a 60 cm height the result shows that the sand transport profile above the wet surface can be expressed with an exponential equation in general the influence of moisture content on sand transport profile mainly focuses on the bottom of the blowing sand cloud meanwhile with moisture content increased total sand transport dropped and a relatively larger proportion is transported at greater heights the vertical movement of particles on higher moisture surface 0 587 1 448 the total sand transport rate varying with moisture content is divided into three regions of differing gradient at the moisture contents of 0 587 and 1 448 the gradient of the curve reflected the different influences of the various water forms in surface sediments the higher moisture surface m 1 448 merely functions as a transport plain for the saltation material surface moisture content was the dominant control factor for saltation activity between the moisture contents of 0 587 and 1 448 wind velocity could resume control saltation after the surface dried to the extent m 0 587

a teleseismic study of the west african craton margin in senegal p wave slowness and azimuth anomalies summary slowness azimuth anomalies for p arrivals at the kedougou temporary teleseismic array on the west african craton near its western margin are small except for westerly azimuths implying uniform structure beneath the array itself and the existence of a steeply dipping refracting interface in the mantle to the west at the missira array located on the mauritanide orogenic belt west of the craton margin the pattern of slowness anomalies can be explained by north dipping upper crustal structure plus a single transition east of this array across which the velocity contrast reverses with depth a single transition could explain the data from both arrays and could be the downward extension of the craton margin into the upper mantle that boundary demarcates lower velocity sub orogenic structure from higher velocity 8 per cent sub cratonic structure between 80 and 220 km while at greater depths the sub cratonic structure has 3 per cent lower velocity this model agrees with models previously derived from p wave delay time anomalies and is qualitatively consistent with the pattern of late p arrivals which are interpreted as multipathed refractions across the boundary

winter variability of aeolian sediment transport threshold on a cold climate dune abstract changes in surface conditions on cold climate aeolian dunes are pronounced during winter dunes are wet snow covered and or frozen for extended periods of time it is unknown how the critical wind speed for sediment transport threshold varies and how threshold may influence sediment transport predictions although the impact of surface conditions on threshold has been examined in synthetic experiments wind tunnels complicated feedbacks between threshold sand transport and surface conditions that occur in natural environments suggest that a ground based empirical approach may provide enhanced insight in this study we investigate threshold variability for 73 days during fall winter spring surface conditions from 18 november 2008 to 30 may 2009 in the bigstick sand hills of saskatchewan canada simultaneous measurements of threshold and atmospheric variables air temperature relative humidity solar radiation wind speed and direction were used to examine the extent to which surface erodibility was regulated by meteorology time lapse images of the surface from a co located camera were used for quality control and interpreting changes in the surface affecting threshold results reveal that threshold varied throughout the deployment 25 75 quartiles 6 92 8 28 m s 1 mean 7 79 m s 1 threshold variability was especially evident at two scales i event timescale and ii seasonal timescale event scale variability peaked during mid winter in one event the threshold varied by 6 m s 1 in 2 h with freezing and re freezing of the surface and relatively constant atmospheric conditions the causes of event scale variability are complex though qualitatively related to changes of wind direction antecedent meteorological conditions and vertical variations of grain scale bonding agents such as pore ice and moisture seasonal scale changes manifested as an increase in threshold during fall peaking in mid winter and decreasing in spring increased threshold in mid winter was linked to lower insolation and air temperature suggesting low erodibility due to the presence of pore ice correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations air temperature r 0 322 relative humidity r 0 388 solar radiation r 0 309 that also varied according to wind direction suggesting that the link between atmospheric conditions and surface erodibility on cold climate dunes is complex this contrasts with results from field based studies in warmer climates and controlled wind tunnel experiments which show a more direct link between atmospheric variables temperature and humidity and surface erodibility nevertheless our results do show a seasonal pattern of threshold that could be important for modeling cold climate aeolian sediment transport

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

recalibrating aeolian sand transport models a quality controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models those of bagnold kawamura zingg owen hsu and lettau and lettau and to recalibrate the empirical constants in those models shear velocity estimates were obtained using the von karman constant and an apparent von karman parameter models were recalibrated using non linear regression and non linear regression with least squares lines forced through axes origins recalibration using the apparent von karman parameter and forced regression reduced the empirical constants for all models the disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude the recalibrated lettau and lettau model provided the greatest statistical agreement between observed and predicted transport rates with a coefficient of determination of 0 77 evaluation of the results suggests that our estimations of threshold shear velocity may be too slow causing errors in predicted transport rates copyright 2012 john wiley sons ltd

the effect of surface moisture on the entrainment of dune sand by wind an evaluation of selected models reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not among the several factors that govern the initiation of soil movement by wind surface moisture is one of the most significant some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated wind tunnel experiments were conducted on pre wetted dune sand with moisture contents ranging from 0 00 to 0 04 kg kg 1 sand samples were exposed to different wind speeds for 2 min moisture content was determined gravimetrically before and after each experiment and the saltation of sand particles was recorded electronically with a saltiphone shear velocities were deduced from the wind speed profiles for each moisture content the experiments were repeated at different shear velocities with the threshold shear velocity being determined by least squares analysis of the relationships between particle number rates and shear velocity within the 2 min test runs temporal changes in particle number rates and moisture contents were detected a steep increase in the threshold shear velocity with moisture content was observed when comparing the models large differences between the predicted results became apparent at a moisture content of 0 007 kg kg 1 which is half the moisture content retained to the soil matrix at a water tension or matric potential of 1 5 mpa the increase in wet threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117 to 171 the highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment nevertheless the models of chepil 1956 proc soil sci soc am 20 288 292 and saleh fryrear 1995 soil sci 160 304 309 are the best alternatives available

the effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach this paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement intensity of sand transport by wind and mass flux the experiment was carried out over a period of five weeks at greenwich dunes prince edward island canada in may and june 2002 moisture content was measured with a delta t moisture probe over a 50 m by 25 m grid established on the beach measurements of wind speed and direction were made with arrays of cup anemometers and a two dimensional sonic anemometer transport intensity was measured at a height of 2 4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal anemometers and saltation probes were sampled at 1 hz sand transport was measured with vertical integrating sand traps over periods of 10 20 minutes results show that where there is a considerable supply of dry sand the saltation system responds very rapidly 1 2 s to fluctuations in wind speed i e to wind gusts where sand supply from the surface is limited by moisture mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind mass flux increases with increasing fetch length and the relationship is described best by a power function further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance copyright 2007 john wiley sons ltd

the role of maximum wind speed in sand transporting events abstract a sand transporting event is the minimum unit of aeolian sand transport process to understand the role of maximum wind speed in such sand transporting events wind speeds were measured at a height of 2 m above the ground in the arid menggen and semi arid taibus banner regions in north china during 2009 and 2011 the sand transport flux of each sand transporting event was calculated based on theoretical equations then the relationships between the maximum wind speed and the average wind speed the duration and sand transport flux of sand transporting events were analyzed it was found that the maximum wind speed was proportional to the average wind speed of sand transporting events with a linear model fit and was also significantly correlated with the duration of sand transporting events with a power model fit the maximum wind speed was also positively correlated with sand transport flux of sand transporting events according to a power model the maximum wind speed could therefore represent both wind speed and the duration of sand transporting events and play a decisive role in the sand transport process of these events the sand transport flux of sand transporting events can be predicted rapidly and conveniently by monitoring maximum wind speed

contact erosion at the interface between granular coarse soil and various base soils under tangential flow condition under embankment dams and dykes horizontal groundwater seepage prevails if the subsoil is layered and if some coarse layers are not appropriate filters for finer layers there can be contact erosion at the interface between fine and coarse soils in order to study contact erosion threshold some base soil and coarse soil combinations were submitted to a flow parallel to the interface between the coarse soil and the base soil critical velocities and critical hydraulic gradients were measured for various base soils using effective base soil grain diameter an empirical expression for critical velocity was proposed that is well adapted for silts or sand clay mixtures as well as for sands the mass of eroded soil was measured relative to the flow velocity for each base soil coarse soil setup the shear stress applied to the interface between base soil and coarse soil was derived from the hydraulic gradient using an empirical relationship between applied shear stress and measured eroded mass erosion rate was estimated for each base soil coarse soil setup