numerical modelling of downstream migrating antidunes a numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes the model solves the navier stokes equations together with the k epsilon turbulence model to find the water flow field over the bedforms a two dimensional width averaged grid is used the bed elevation changes are computed by solving the convection diffusion equation for suspended sediments and bed load together with the engelund hansen sediment transport formula the free surface is computed with an algorithm based on water continuity in the surface cells non orthogonal adaptive grids were used moving vertically with the computed location of the bed and the free water surface the numerical model was tested on data from a physical model study where regular downstream migrating antidunes had been observed the numerical model started out with a flat bed and the trains of antidunes formed over time many of the physical processes observed in earlier studies were replicated by the numerical model four dune parameters were computed in the current tests the antidune wavelength height and celerity together with the average water depth the antidune wavelengths were best predicted with an accuracy of 3 8 compared with the measurements the antidune heights were computed with a deviation of 11 25 compared with an empirical formula the water depths over the antidunes were predicted with an accuracy of 3 9 related to the measured values the average antidune celerity was the parameter with largest deviation for the coarsest grid it was overpredicted with 37

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

barchan dune mobility in mauritania related to dune and interdune sand fluxes 1 we present a 1 year study of 50 dunes in a small field of barchan dunes in mauritania we documented the morphological evolution of the dunes and their migration rates and measured at 10 min intervals the interdune sand transport the wind strength and its direction for the same interval of time the dune heights h 0 range between 2 and 5 m and their celerity c is found to be well approximated by the standard migration law c q 0 h 0 with q 0 50 m 3 m yr from both the interdune sand flux and the migration rate of the dunes we were able to estimate the spatially averaged sand flux at the dune crest as well as the bulk sand flux associated with the mass of sand transported by the dune we found that the sand flux at the crest was about 3 times greater than the interdune mass transport rate whereas the bulk sand flux was surprisingly of the same order as the interdune flux moreover we analyzed carefully the interdune sand transport data which can be well described by the sorensen law the cumulative mass of sand transported during moderate wind events within 1 year was much greater than that transported during strong wind events

flow deflection over a foredune flow deflection of surface winds is common across coastal foredunes and blowouts incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest normal orientation across the stoss slope of the foredune this paper examines field measurements for obliquely incident winds and compares them to computational fluid dynamics cfd modelling of flow deflection in 10 increments from onshore 0 to alongshore 90 wind approach angles the mechanics of flow deflection are discussed followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement cfd modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0 and gradually increases as the incident wind turns towards 30 to the dune crest the greatest deflection occurs between 30 and 70 incident to the dune crest the degree of flow deflection depends secondarily on height above the dune surface with the greatest effect near the surface and toward the dune crest topographically forced flow acceleration speed up across the stoss slope of the foredune is greatest for winds less than 30 i e roughly perpendicular and declines significantly for winds with more oblique approach angles there is less lateral uniformity in the wind field when the incident wind approaches from 60 because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced

secondary flow deflection in the lee of transverse dunes with implications for dune morphodynamics and migration measurements of lee side airflow response from an extensive array of meteorological instruments combined with smoke and flow streamer visualization is used to examine the development and morphodynamic significance of the lee side separation vortex over closely spaced transverse dune ridges a differential deflection mechanism is presented that explains the three dimensional pattern of lee side airflow structure for a variety of incident flow angles these flow patterns produce reversed along dune and deflected surface flow vectors in the lee that are inferred to result in net lateral diversion of sand transport over one dune wavelength for incident angles as small as 10 from crest transverse i e 80 from the crest line this lateral displacement increases markedly with incident flow angle when expressed as the absolute value of the total deflection in degrees reversed and multi directional flow occurs for incident angles between 90 and 50 these results document the three dimensional nature of flow and sand transport over transverse dunes and provide empirical evidence for an oblique migration model copyright 2013 john wiley sons ltd

coastal foredune topography as a control on secondary airflow regimes under offshore winds aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes results presented here indicate however that depending on wind orientation and foredune morphology positive contributions to the sediment budget can arise from offshore winds lee side airflow patterns seaward of the foredune crest under offshore winds were studied at three sites of varying foredune geometry along magilligan strand northern ireland ultrasonic anemometers recorded 1 hz wind velocity data at 1 intervals descriptive statistics and wind rose diagrams were used in the analysis of these data under perpendicularly offshore winds each site exhibited a different type of lee side airflow pattern a tall 11 4 m sharp crested foredune produced flow separation with a recirculation cell a lower 6 6 m more rounded foredune crest exhibited lee side flow that remained attached but was deflected parallel to the crest while flow over a low incipient foredune crest resulted in attached flow with no deflection in the lee the morphology of the lee slopes best explained these airflow adjustments more obliquely offshore winds were also found to affect the secondary airflow patterns with a smooth transition from flow separation to flow attachment as the incident angle decreased at higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airflow types this threshold was located at similar approach angles to those recorded for desert dunes 90 20 these findings have significant implications for the post storm recovery and long term evolution of beach dune systems where the predominant winds are offshore and offer an explanation for the presence of many beach dune systems in lee coast locations copyright 2010 john wiley sons ltd

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

the formation of shadow dunes abstract an investigation of the modification of airflow by a discrete semi circular roughness element in this case vegetation the resulting flow structure and the formation of pyramidal shaped shadow dunes is presented two erect pioneer sand dune grasses festuca littoralis and ammophila arenaria were used in the experiments which were conducted in both the field and a wind tunnel for a range of wind velocities 4 20 m sec 1 the three dimensional flow structure about the vegetation is dominated by horizontal separation characterized by symmetrically opposed reversing vortices which form within a triangular wake a vertical separation envelope is also formed over the vegetation pyramidal shadow dunes are formed within this flow structure when aeolian sand transport occurs shadow dune height is dependent on element basal width and repose angle of the sand shadow dune length is dependent on element basal width and wind velocity the results are extrapolated to include all semi porous to non porous semicircular discrete roughness elements the role of shadow dune formation in the development of foredunes and related environments is examined

description of a contourite depositional system on the demerara plateau results from geophysical data and sediment cores the demerara plateau belonging to the passive transform margin of french guiana was investigated during the iguanes cruise in 2013 the objectives of the cruise were to explore the poorly known surficial sedimentary column overlying thick mass transport deposits as well as to understand the factors controlling recent sedimentation the presence of numerous bedforms at the seafloor was observed thanks to newly acquired iguanes bathymetric high resolution seismic and chirp data while sediment cores allowed the characterization of the deposits covering the mass transport deposits modern oceanographic conditions were determined in situ using mooring monitoring over a 10 month period our data indicate the presence of a contourite depositional system along the demerara plateau most likely related to bottom current activity of the north atlantic deep water nadw however at the regional scale large longitudinal waves parallel the nadw flow their shape and orientation seem to be inherited from interactions between bottom currents and paleomorphologies expressed at the top of mass transport deposits their evolution is possibly driven by the intensity of bottom current activity that might have changed over time overall this work presents an integrated approach combining seismic and sedimentological evidence to study the processes at the origin of contourite formation in the demerara plateau other regional factors such as local slope values and slope instability also control sedimentation

the pattern of grainfall deposition in the lee of aeolian dunes a simple model for the deposition pattern in the lee of aeolian dunes is presented that relies heavily upon a recently developed understanding of aeolian saltation grainfall deposition at any position on the lee face is the result of all saltation trajectories that leave any point on the surface of the dune upwind of the brink with sufficient initial velocity to travel the intervening distance the deposition rate at any position on the lee slope is obtained by integrating over all combinations of initial position and required velocity the velocity being weighted by its probability density the resulting calculated total deposition rate patterns show distinct maxima on the order of one to a few decimetres from the brink beyond which deposition rates fall off roughly exponentially an important length scale emerges that characterizes this decay with distance from the brink the length increasing with wind velocity and decreasing with grain diameter it is shown that this length scale is on the order of one metre for typical grain size and wind conditions that this is typically smaller than the length of the lee slope is what gives rise to the oversteepening and eventual avalanching of the lee sides of aeolian dunes the position of a pivot point on the lee slope may be predicted separating source regions from accumulation regions for grainflow avalanche deposits the calculated patterns provide not only a means for quantitative interpretation of active and fossil dune grainfall deposits but they provide the initial geometry for grainflow avalanches the initial failures should coincide with the steepest gradient in grainfall deposition slightly downslope from the grainfall maximum

storm controlled oblique dunes of the oregon coast discussion and reply no abstract available the article discussed appeared in the bulletin v 94 p 1450 1465

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

bedform spurs a result of a trailing helical vortex wake the formative conditions for bedform spurs and their roles in bedform dynamics and associated sediment transport are described herein bedform spurs are formed by helical vortices that trail from the lee surface of oblique segments of bedform crestlines trailing helical vortices quickly route sediment away from the lee surface of their parent bedform scouring troughs and placing this bed material into the body of the spur the geometric configuration of bedform spurs to their parent bedform crests is predicted by a cross stream strouhal number when present spur bearing bedforms and their associated trailing helical wakes exert tremendous control on bedform morphology by routing enhanced sediment transport between adjacent bedforms field measurements collected at the north loup river nebraska and flume experiments described by venditti et al 2005a 2005b 2005c demonstrate that this trailing helical vortex mediated sediment transport is a mechanism for bedform deformation interactions and transitions between two dimensional and three dimensional bedforms this article is protected by copyright all rights reserved

a field study of mean and turbulent flow characteristics upwind over and downwind of barchan dunes field measured patterns of mean velocity and turbulent airflow are reported for isolated barchan dunes turbulence was sampled using a high frequency sonic anemometer deriving near surface reynolds shear and normal stresses measurements upwind of and over a crest brink separated barchan indicated that shear stress was sustained despite a velocity reduction at the dune toe the mapped streamline angles and enhanced turbulent intensities suggest the effects of positive streamline curvature are responsible for this maintenance of shear stress this field evidence supports an existing model for dune morphodynamics based on wind tunnel turbulence measurements downwind the effect of different dune profiles on flow re attachment and recovery was apparent with transverse incident flow a re attachment length between 2 3 and 5 0h h is dune brink height existed for a crest brink separated dune and 6 5 to 8 6h for a crest brink coincident dune the lee side shear layer produced elevated turbulent stresses immediately downwind of both dunes and a decrease in turbulence with distance characterized flow recovery recovery of mean velocity for the crest brink separated dune occurred over a distance 6 5h shorter than the crest brink coincident form as the application of sonic anemometers in aeolian geomorphology is relatively new there is debate concerning the suitability of processing their data in relation to dune surface and streamline angle this paper demonstrates the effect on reynolds stresses of mathematically correcting data to the local streamline over varying dune slope where the streamline angle was closely related to the surface windward slope time averaged shear stress agreed best with previous wind tunnel findings when data were rotated along streamlines in the close lee however the angle of downwardly projected separated flow was not aligned with the flat ground surface here shear stress appeared to be underestimated by streamline correction and corrected shear stress values were less than half of those uncorrected

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

sediment transport dis continuity across a beach dune profile during an offshore wind event abstract flow dynamics and sediment transport responses over a large vegetated foredune at prince edward island canada during an offshore wind event are examined data were collected along an instrumented transect that extended from the dune crest down the lee side seaward slope of the dune across a wave cut scarp and on to the back beach when the wind direction at the dune crest was approximately crest normal less than about 15 deviation the mean near surface flow directions along the dune slope and on the back beach were generally onshore indicating reversed onshore flow relative to the regional offshore wind direction although flow patterns were consistent with a lee side recirculation eddy large excursions in flow direction were also prevalent suggesting that the eddy was unstable and alternated with highly turbulent wake flow as wind direction at the crest veered to greater than 20 from crest normal lee side winds shifted toward strongly alongshore flow with minimal directionally variability on the dune slope the wind vectors were slightly offshore whereas on the back beach they were slightly onshore wind speeds and sediment transport were greatest at the foredune crest and declined rapidly downslope due to flow expansion and deceleration in the wake zone as well as to the influence of a sparse vegetation layer mean particle counts averaged over a 15 min interval derived from laser sensors positioned at the crest were large 7 76 per second in comparison to those measured in the immediate lee of the crest 0 52 per second and farther down the dune slope these results demonstrate that sediment transport across the beach dune system was spatially discontinuous during this offshore wind event rebuilding of the dune ramp at the toe of the scarp occurred quite independently of and with a different sediment source than the broadening of the dune crest which was fed with sediment from the landward side of the foredune such process decoupling is an example of the complexity by which foredunes evolve or are maintained and as with previous research reinforces the importance of offshore and alongshore wind events to beach dune morphodynamics

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

reevaluation of the aeolian sand flux from the ulan buh desert into the upper yellow river based on in situ monitoring abstract aeolian sand transport into rivers is a crucial factor influencing channel sediment dynamics and fluvial processes in rivers that flow through desert areas few studies have examined the dynamic processes controlling factors and the amount of aeolian sand transported into river channels here we report a case study of aeolian sand transport into in the upper reaches of the yellow river as it flows along the eastern margin of the ulan buh desert which is a major desert in northern china the present study is based on systematic monitoring of wind flow characteristics aeolian sediment dynamics saltation creep and suspension and the migration of typical sand dunes mobile semi anchored and anchored from 2013 to 2016 the relationship between wind speed and wind blown sand transport in the study area was determined the relationship between the rate of aeolian sand transport saltation and creep and the wind speed 2 m above the ground surface can be depicted with a polynomial relation when the wind speed is 5 7 m s and with a power function when the wind speed is

grainfall processes in the lee of transverse dunes silver peak nevada grainfall deposition and associated grainflows in the lee of aeolian dunes are important in that they are preserved as cross beds in the geological record and provide a key to the interpretation of the aeolian rock record despite their recognized importance there have been very few field laboratory or numerical simulation studies of leeside depositional processes on aeolian dunes as part of an ongoing study the relationships among grainfall wind speed and direction stoss sand transport rates and dune morphometry height and aspect ratio were investigated on four relatively small straightcrested transverse dunes at silver peak nevada between 55 and 95 of the total grainfall was found to be deposited within 1 m of the crest and 84 99 within 2 m depending primarily on dune size and shape grainfall decay rates on high dunes of large aspect ratio were observed to be very consistent with a weak positive dependence on wind speed for small dunes with low aspect ratios grainfall deposition was more varied and decreased rapidly within 1 m of the dune crest whereas at increased distance from the dune crest it eventually approached the smaller decay rates observed on the large dunes no dependence of grainfall on wind speed was observed for these small dunes comparison of field data with predictions from anderson s 1988 saltation model of grainfall based on the computation of saltation path lengths indicates lack of agreement in the following areas 1 deposition rate magnitude 2 variation in decay rate with wind speed and 3 the magnitude and location of the localized lee slope depositional maxima the silver peak field results demonstrate the importance of dune aspect ratio and related wake effects in determining the rate and pattern of grainfall this work confirms earlier speculation by mcdonald anderson 1995 that temporary turbulent suspension or modified saltation of relatively large grains does occur within the dune wake so that transport distances generally are larger than predicted by numerical simulations of true saltation

the geomorphological significance of airflow patterns in transverse dune interdunes abstract the interdunes between aeolian dunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves this neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole especially with regard to dune spacing this paper considers the mean airflow within four relatively simple transverse dune interdunes the study locations were chosen in order to sample interdunes with different size and surface characteristics the dynamics of which were investigated for when incident flow was normal to the upwind crest the findings confirm existing models of flow reattachment length and recovery for aeolian dune lee side flow and show a consistent pattern of increasing near surface velocity downwind of reattachment that supports a mechanism for interdunes as sand free features flow dynamics are characterised for the different types of interdune observed where two groups are recognised the flow patterns in relatively short interdunes where dunes are closely spaced with a sandy surface were accordant with those of the flow response model in extended interdunes where bounding dunes were spaced with a length well over that for flow separation evidence at the downwind edge of the interdunes suggested that flow reacted to the subsequent dune for the case of these extended interdunes a new descriptive model is presented to characterise their dynamics in this model the variation in near surface flow allowed process zones to be identified through the interdune the geomorphological significance of the processes dominating each zone is discussed and comparisons are made between the flow response case and the new interdune model from this study in a discussion on the controls of spacing between dunes where reattachment length exerts a fundamental control the role of sediment availability is also highlighted as a significant factor the presence of a sandy bed can in some circumstances determine whether dune development and therefore spacing is controlled primarily by elements of flow response

petrology and potential tectonic significance of a k bentonite in a taconian shale basin eastern ontario canada northern appalachians a 6 cm thick k bentonite herein defined as the russell bed occurs in an upper ordovician deep basin shale succession in eastern ontario canada forming part of the distal taconic foreland in eastern north america the bed lies within the pygmaeus graptolite biozone which is about 451 to 452 ma in age although some bentonites are reported from this interval in eastern north america we are reporting the first set of compositional data for a bentonite of this age gamma log correlation identifies a potential minimum distribution area of 5 km 2 for the k bentonite covering part of southern quebec new york state and eastern ontario the deposit coincides with the first influx of distal turbdites into this shale basin associated with taconic flysch and simultaneous abrupt ventilation of the once anoxic deep water basin which had formed initially after foundering of the upper ordovician carbonate platform concurrent intrabasinal extinction of several graptolite species suggests that change in sedimentation palaeoceanography and volcanism were linked to a regional external process compositionally the bentonite is distinct from the older ordovician platform deposits in eastern north america the deposit contains abundant titaniferous phlogopite with 1 6 bao fluoroapatite with 2 5 f and dynamically shaped glass spherules now altered to clay the spherules and clay matrix constitute 45 of the bed and compositionally define an illite 90 smectite i s structure with about 7 5 k 2 o age dating by ar ar analysis of the phlogopite crystals yielded a younger than expected 440 445 ma age this difference along with evidence of localized chloritization of phlogopite likely reflects known post ordovician hydrothermal activity within the basin on the basis of several geochemical proxies the magmatic source of the russell k bentonite falls within the trachyandesite field and was ba enriched comparison of geochemistry and mineralogy with older middle to late ordovician and younger early silurian k bentonites within the taconic orogen along eastern laurentia and baltica reveals that the potential source magma for the russell bed was more mafic more alkaline and less fractionated than sources typical of older platform bentonites instead it is more similar to the younger llandovery bentonites of scandinavia and scotland it remains uncertain if it signals local or regional compositional change in volcanic source in the northern appalachians

foredune accretion under offshore winds experiments carried out at magilligan strand on the north coast of ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location a five day study 18 22 june 2005 investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux a simple instrument setup was used to characterise the airflow a sonic anemometer was placed at the dune crest with another on the mid beach horizontal traps electronic and integrating measured sediment flux on the supra tidal beach results show that offshore wind flow deviated from its original direction in the lee of the dune seaward of foredune the change in direction was not a simple steering of flow to a singular new direction but rather flow separation resulting in turbulent multidirectional flow including reversal traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds data from sediment traps wind and observational evidence have been used to argue that sedimentation was occurring in this zone when budgeting for sediment movement within beach dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation particularly in post storm recovery c 2008 elsevier b v all rights reserved

dune and dune field development on padre island texas with implications for interdune deposition and water table controlled accumulation abstract portions of the back island dune fields on padre island texas undergo seasonal destructive and constructive phases in which they are reduced to a nearly planar surface during the winter and then reform during the spring and summer initial depositional sites for dry sand that we observed were associated with roughness elements that caused a lowering of the transport capacity of the flow bedforms develop through a series of morphologic and dynamic stages 1 irregular patches of dry sand 2 wind ripple protodunes with leeward flow expansion 3 grainfall protodunes with a range from leeward flow expansion to flow separation 4 barchan dunes with grainflow and 5 crescentic ridges that characterize the mature field the survival and further development of protodunes and dunes is f vored by increased size a more advanced stage of development unidirectional and moderate wind and a plentiful sand supply these factors can be viewed as the result of the interrelationship of aspects of eolian transport the nature of leeward secondary airflow patterns and sand supply dune field ordering occurs by repeated merging splitting cannibalization and lateral linking of dunes on padre island and other areas of dunes that we studied flow conditions across portions of interdune flats favor the transport of dry loose sand from interdune flats onto the dunes so that dunes grow at the expense of interdune flats dry surface deposits are therefore unlikely to accumulate on interdune flats but rather to characterize interdune depressions that may represent the minimum d stance to which an interdune flat can be closed otherwise accumulations on interdune flats most commonly should be formed on wet or damp surfaces or occur associated with some mechanism that protects the deposits from deflation padre island dune fields represent a type of eolian system where accumulations of dunes and interdune flats occur during periods of a water table rise with bypassing and deflation occurring as the water table becomes static or falls respectively

three years of morphologic changes at a bowl blowout cape cod usa this study presents measurements of blowout topography obtained with annual terrestrial laser surveys carried out over a three year period at a single large bowl blowout located in the provincelands dunes section of cape cod national seashore in massachusetts the study blowout was selected because its axis is aligned with northwest winds that dominate the region and because it was seemingly interacting with a smaller saucer blowout that had recently formed on the southern rim of the primary feature assuming that blowouts enlarge both horizontally and vertically in response to the wind regime the objectives of the study were to determine both the amount of horizontal growth that the blowout experiences annually and the spatial patterns of vertical change that occur within the blowout changes to the blowout lobe surrounding the feature were also determined for areas with sparse enough vegetation cover to allow laser returns from the sand surface the results show that the blowout consistently expanded outward during the three years with the greatest expansion occurring at its southeast corner opposite the prevailing winds the most significant occurrence was the removal in the first year of the ridge that separated the two blowouts resulting in a major horizontal shift of the southern rim of the new combined blowout this displacement then continued at a lesser rate in subsequent years the rim also shifted horizontally along the northwest to northeast sections of the blowout significant vertical loss occurred along the main axis of the blowout with the greatest loss concentrated along the southeast rim on the lobe there were large areas of deposition immediately downwind of the high erosion zones inside the blowout however there were also small erosion areas on the lobe extending downwind from eroding sections of the rim this study shows that 1 blowouts can experience significant areal and volumetric changes in short periods of time 2 significant changes may occur relatively suddenly when adjacent blowouts combine into a single feature and 3 the sediment transport paths are highly controlled by the topography the joining of two blowouts not only creates a new larger feature but it also releases large amounts of sediment that are then distributed across the landscape downwind creating a potential for major changes to a landscape over the longer term

lateral migration of linear dunes in the strzelecki desert australia linear dunes in the strzelecki desert trend roughly south north sand transport which is toward the nne has caused the dunes to migrate eastward while they extend or migrate northward eastward lateral migration is evidenced by 1 asymmetrical shape of the dunes east facing slopes are several times as steep as west facing slopes 2 asymmetrical accumulation of loose recently transported sand relatively abundant on east facing slopes 3 asymmetrical outcropping of older semiconsolidated aeolian sand on the dune surface more abundant on west facing slopes and 4 east dipping foreset beds that underly the west facing flanks of some dunes dunes in the strzelecki desert are still active in the sense that sand is transported along and across many dune crests however the dunes are composed primarily of pleistocene strata indicating that the trend of the dunes was established before the holocene the obliquity of the dunes to the transport direction is not merely an aberration of the wind regime of the last few decades preferential accumulation of sand on east facing flanks indicates that the dunes migrated eastward several metres during the holocene moreover the west facing flanks of some dunes have experienced a minimum of tens of metres of erosion this asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the pleistocene dunes in the strzelecki desert and in the adjacent simpson desert display a variety of grossly different internal structures computer graphics experiments demonstrate that many of these differences in structure can be explained by different angles of climb of the dunes

longitudinal dunes can move sideways longitudinal dunes occur in all major sand areas in the world their dominant mode of migration or extension is considered to be either prevailing or resultant wind parallel the dunes extending downwind via accretion of the terminal nose in the qaidam pendi in northwest china a series of active longitudinal dunes extend downwind at 5 10 m yr 1 internal sedimentary structures examined in the dunes however display beds dipping in one direction rather than two opposed directions as is expected analysis of aerial photographs confirms that these dunes migrate laterally up to three metres per year whilst maintaining a symmetrical longitudinal dune morphology

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

kinoshitalite ba mg 3 al2si2 o10 oh f 2 a brittle mica from a manganese deposit in oman paragenesis and crystal chemistry kinoshitalite ideally ba mg 3 al 2 si 2 o 10 oh f 2 was studied in a granulite facies manganese ore associated with calcium bearing magnesian tephroite hausmannite calcite and manganoan clinochlore and in a second assemblage together with hausmannite altered tephroite manganoan diopside and calcite the metamorphic rocks occur enclosed in peridotites of the semail ophiolite sultanate of oman and were metamorphosed during ophiolite obduction single crystal x ray data collected on an inclusion free kinoshitalite of ba 0 99 k 0 06 na 0 01 mg 2 64 mn 0 31 al 2 01 si 2 03 o 10 oh 1 61 f 0 37 cl 0 02 composition yielded a c centered lattice of monoclinic symmetry with a 5 316 1 b 9 230 2 c 10 197 2 a 100 06 1 v 492 6 a 3 and z 1 characteristic of the 1 m polytype the structure was refined in two models assuming complete si al ordering in the space groups c 2 and c 1 allowing for additional twinning the data clearly suggest that in spite of the si al ratio of 1 assumption of complete si al ordering can be rejected two models both in agreement with space group c 2 m causing si al disorder are discussed three dimensional si al disorder would lead to violation of the al avoidance rule and substantial ba displacement the rather well defined ba position capped by two six membered rings of si 3 al 3 o 18 composition suggests one dimensional disorder where completely si al ordered layers exist parallel to 001 the disorder occurs perpendicular to 001 and may be interpreted as random stacking faults

aeolian dynamics of beach scraped ridge and dyke structures abstract where urban areas are situated close to a beach sand dunes act as protection from flooding and erosion when a dune has been removed or damaged by erosion dune ridge or dyke re building using heavy machinery a process known as beach scraping is a common method of restoration following construction natural accretion of sediment on the backshore is preferable as it facilitates sustained natural dune building growth of vegetation and habitat creation and reduces the need for further beach scraping this study investigates the near surface flow and transport potential for three artificial structure designs a single ridge a double ridge and a dyke the three shapes contained an identical volume of sand and were preceded by 50 m of beach at an angle of 3 a computational fluid dynamic model cfd was created for each scenario to calculate wind flow and shear velocity from 4 different wind directions at 22 5 intervals from 0 onshore to 67 5 from this data sediment flux was predicted along a two dimensional transect for each of the scenarios for all structures shear velocity on the beach and stoss slope decreased as incident wind direction became more oblique conversely shear velocity in the lee of the crest increased a reduction in shear velocity at the foot of each structure also occurred and appears related to stoss slope with the greatest reduction at the toe of the dyke structure stoss slope 34 and the least before the single ridge stoss slope 17 specifically the results suggest that the double ridge structure is the most resilient to aeolian erosion shear velocity reduction on the back beach is comparable to the dyke and sediment flux from the stoss slope of the double ridge structure may become trapped in the swale between the two ridges encouraging sediment deposition thus reducing sediment transport beyond the dunes and backshore although the dyke structure underwent the greatest reduction in shear velocity on the back beach it experienced substantial sediment flux at the crest and along the top of the structure making it susceptible to erosion during a strong wind event the highest sediment transport rate was calculated at the crest of the single ridge and the single ridge structure also created the smallest reduction of shear velocity on the back beach thus making it less desirable than the double ridge

suspended sediment transport and deposition over a dune rio parana argentina field data from the rio parana argentina are used to examine patterns of suspended sediment transport over a sand dune measurements of three dimensional velocity are made with an acoustic doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed with an upward vertical flux over the stoss side of the dune and downward flux over the lee side suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed about 17 of the suspended load transported over the crest is deposited in the lee side before it reaches the trough most of this deposited sand is coarser sediment that originates close to the bed over the crest a result consistent with simulations based on the model of mohrig and smith water resources research 1996 32 3207 3217 for the excursion lengths of sediment dispersed in the lee side of a dune copyright 2009 john wiley sons ltd

aerodynamic roughness height for gravel mantled megaripples with implications for wind profiles near tars on mars abstract aerodynamic roughness heights of 1 3 cm were obtained from measured wind profiles collected among fields of gravel mantled megaripples in the high desert of the puna region of northwestern argentina roughness height appears to be relatively insensitive to the angle at which the wind was incident upon the bedforms throughout the study sites the results represent the first wind profiling measurements for large megaripples but they also demonstrate the importance of a careful evaluation of many potential effects that can influence the utility of wind profiling data the same effects that influence collection of fieldwork data must also be considered in any prediction of wind profiles anticipated to occur near transverse aeolian ridges and other aeolian features on mars that are intermediate in scale between wind ripples and small sand dunes

toward a model for airflow on the lee side of aeolian dunes the interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes from 15 dunes studied during transverse flow conditions at padre island in texas white sands in new mexico and the algodones in california distinct flow regions can generally be recognized with the overall flow structure comparing favourably to that proposed for subaqueous bedforms downwind of dunes with flow separation is a back flow eddy that extends about four dune brink heights downwind from the brink of the dune beyond the separation cell the velocity profiles can be divided into regions based upon segments separated by kinks in the velocity profiles the interior is an area above the dunes of relative high wind speed but low velocity gradient beneath the interior is the wake which consists of two layers the upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow so that the overall velocity gradient decreases downwind the lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights but primarily near the top of the layer thereby causing the velocity gradient to increase downwind at about eight dune heights downwind the upper and lower wakes equilibrate to a single profile with the kink between them no longer apparent the lowest recognizable region is the internal boundary layer it is recognized by a relatively steep velocity gradient below the wake and never exceeds a few tens of centimetres in height for our data set because of acceleration and increasing shear stress within this layer interdune flats are at least potentially erosional overall the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers where flow separation does not occur simple flow expansion down the lee face causes flow deceleration

coseismic slip distribution for the mw 9 2011 tohoku oki earthquake derived from 3 d fe modeling 1 the coseismic slip distribution of the mw 9 0 2011 tohoku oki earthquake has been estimated by inverting near field onshore and offshore geodetic data using green s function calculated with a 3 d finite element fe model the fe model simulates several geophysical features of the subduction zone that hosted the rupture surface of the event these features include a 3 d geometric configuration and distribution of material properties of the tectonic system a precise geometric configuration of the irregular rupture surface and an irregular free surface according to the topography and bathymetry a model that simulates rupture along the interface between the relatively weak overriding okhotsk plate and stiff subducting slab of the pacific plate requires less slip to produce the observed surface deformation compared to a model having uniform material properties across the rupture interface furthermore the estimated slip of the heterogeneous model is more widely distributed over the shallow portion of the plate boundary whereas the estimated slip of the homogeneous model is more focused updip of the epicenter this demonstrates the sensitivity of inverse analyses of geodetic data for the 2011 tohoku oki earthquake to the simulated domain geometry and configuration of material properties

flow dynamics and geomorphology of a trough blowout the dynamics and geomorphological development of a trough blowout located at fiona beach in the myall lakes national park in nsw australia are examined wind speeds velocities and flow structure were measured utilizing an array of miniature rimco cup anemometers gill bivane and uvw instruments and wind vanes flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation jets occur both in the deflation basin and along the erosional walls relative flow deceleration and expansion occurs up the depositional lobe jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls maximum erosion and transport occurs up the deflation basin and onto the depositional lobe trough blowout morphologies are explained as a function of these flow patterns when the wind approaches the blowout obliquely the flow is steered considerably within the blowout and the degree and complexity of topographic steering is dependent on the blowout topography the flow is usually extremely turbulent and large corkscrew vortices are common the local topography of a blowout can be very important in determining overall sand transport and blowout evolutionary conditions and paths estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used

a wind tunnel study of flow structure adjustment on deformable sand beds containing a surface mounted obstacle roughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments they perturb the local fluid flow so that the entrainment transport and deposition of particles surrounding each element is fundamentally altered fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed planar walls however self regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport until it reaches a stable form that enhances the net physical roughness the present wind tunnel study examines how the flow pattern surrounding an isolated cylinder a problem extensively studied in classical fluid mechanics is altered through morphodynamic development of a deep well that envelopes the windward face and side walls of the roughness element spatial patterns in the fluid velocity turbulence intensity and reynolds stress obtained from laser doppler anemometer lda measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self regulation of the bed topography as it reaches steady state for example flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and side walls of the cylinder respectively along the center line of the wake flow to the rear of the cylinder several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well feedback plays a complex time dependent role in this system

flow dynamics and sediment transport over a reversing barchan changli china abstract the flow and sediment transport over a reversing 6 9 m high barchan dune is examined on the changli gold coast in hebei province china wind velocity profiles are non logarithmic exhibit rapid accelerations up slope and display near surface jets at the dune crest and downwind lee slope from the windward lower slope to dune crest the wind speed at 5 cm height increased by 55 the windward slope is a slipface and therefore has a significantly greater gradient than most normal windward slopes and the magnitude of speed up is significantly greater speed up ratio of 5 25 the majority of sediment was transported in the 0 4 cm height above the bed range maximum total sediment flux occurred at the dune crest and was greater than the total flux from three other sites combined the leeward mid slope sedimentation rate is strongly influenced by the sediment plume streaming upwards and downwind from the actively reversing dune crest dunes in the process of reversing display quite different wind flow and sedimentation patterns than when the dune is in normal flow conditions

tsunami forecast by joint inversion of real time tsunami waveforms and seismic or gps data application to the tohoku 2011 tsunami correctly characterizing tsunami source generation is the most critical component of modern tsunami forecasting although difficult to quantify directly a tsunami source can be modeled via different methods using a variety of measurements from deep ocean tsunameters seismometers gps and other advanced instruments some of which in or near real time here we assess the performance of different source models for the destructive 11 march 2011 japan tsunami using model data comparison for the generation propagation and inundation in the near field of japan this comparative study of tsunami source models addresses the advantages and limitations of different real time measurements with potential use in early tsunami warning in the near and far field the study highlights the critical role of deep ocean tsunami measurements and rapid validation of the approximate tsunami source for high quality forecasting we show that these tsunami measurements are compatible with other real time geodetic data and may provide more insightful understanding of tsunami generation from earthquakes as well as from nonseismic processes such as submarine landslide failures

sedimentary underplating at the cascadia mantle wedge corner revealed by seismic imaging earth s largest earthquakes occur at the boundary between subducting oceanic crust and the overriding plate yet the position of the plate boundaries remains uncertain analysis of zones of low seismic wave velocities beneath the northern cascadia subduction zone implies that the plate boundary here may be deeper than previously thought

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

an empirical model of aeolian dune lee face airflow airflow data gathered over dunes ranging from 60 m tall complex crescentic dunes to 2 m tall simplecrescentic dunes were used to develop an empirical model of dune lee face airflow for straight crested dunes the nature of lee face flow varies and was found to be controlled by the interaction of at least three factors dune shape the incidence angle between the primary wind direction and the dune brinkline and atmospheric thermal stability three types of lee face flow separated attached and deflected along slope or attached and undeflected were found to occur separated flows characterized by a zone of low speed 0 3o of crestal speed back eddy flow typically occur leeward of steep sided dunes in transverse flow conditions unstable atmospheric thermal stability also favours flow separation attached flows characterized by higher flow speeds up to 84 of crestal speed that are a cosine function of the incidence angle typically occur leeward of dunes that have a lower average lee slope and are subject to oblique flow conditions depending on the slope of the lee face attached flow may be either deflected along slope lee slopes greater than about 20 or have the same direction as the primary flow lee slopes less than about 20 neutral atmospheric thermal stability also favours flow attachment as each of the three types of lee face flow is defined by a range of wind speeds and directions the nature of lee face flow is intimately tied to the type of aeolian depositional process i e wind ripple or superimposed dune migration grainflow or grainfall that occurs on the lee slope and the resulting pattern of dune deposits therefore the model presented in this paper can be used to enhance the interpretation of palaeowind regime and dune type from aeolian cross strata

field measurements of mean and turbulent airflow over a barchan sand dune advances in our knowledge of the aeolian processes governing sand dune dynamics have been restricted by a reliance on measures of time averaged airflow such as shear velocity u it has become clear that such measures are incapable of explaining the complete dynamics of sediment transport across dune surfaces past evidence from wind tunnel and modelling studies has suggested that in some regions on a dune s surface the sediment transport might be better explained through investigations of the turbulent nature of the airflow however to date there have been no field studies providing data on the turbulent characteristics of the airflow around dunes with which to support or refute such hypotheses the field investigation presented here provides mean and turbulent airflow measurements across the centre line of a barchan sand dune in namibia data were collected using arrays of sonic anemometers and were compared with sand flux data measured using wedge shaped traps results support previously published data derived from wind tunnels and numerical models the decline in mean wind velocity at the upwind toe of the dune is shown to coincide with a rise in turbulence whilst mean velocity acceleration on the upper slope corresponds with a general decline in measured turbulence analysis of the components of reynold shear stress u w and normal stresses u 2 and w 2 supports the notion that the development of flow turbulence along the dune centre line is likely to be associated with the interplay between streamline curvature and mean flow deceleration acceleration it is suggested that due to the nature of its calculation turbulence intensity is a measure of less practical use than direct assessments of the individual components of reynolds stress particularly the instantaneous horizontal streamwise component u 2 and shear stress u w whilst increases in reynolds shear stress and the horizontal streamwise component of stress in the toe region of the dune may effectively explain the maintenance of sand flux in a region of declining mean velocity they have much less explanatory power for sand flux on the upper windward slope and in the crestal region of the dune here it is suggested that mean flow acceleration is likely to provide the most significant driving force on sand flux possibly augmented by a rise in the horizontal streamwise component of reynolds stress u 2 in the crest brink region therefore although wind turbulence is considered to be of fundamental importance in explaining the sediment transport dynamics across the dune s surface it is recognised that the interaction between mean flow deceleration acceleration streamline curvature and individual components of reynolds stress is complex and the identification of a single element of flow that offers a panacea for accounting for sand flux and dune dynamics is difficult to find

investigation of three dimensional wind flow behaviour over coastal dune morphology under offshore winds using computational fluid dynamics cfd and ultrasonic anemometry the behaviour of offshore directed winds over coastal dune and beach morphology was examined using a combination of modelling 3 d computational fluid dynamics cfd and field measurement both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential the influence of flow reversals on the beach dune transport system and foredune growth patterns has previously received little attention detailed wind flow measurements were made using an extensive array of mast mounted 3 d ultrasonic anemometers 50 hz arranged parallel to the dominant incident wind direction large eddy simulation les of the offshore wind flow over the dune was conducted using the open source cfd tool openfoam the computational domain included a terrain model obtained by airborne lidar and detailed ground dgps measurements the computational grid 22 million cells included localized mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach measured and simulated wind flow are presented and discussed the cfd simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system simulation of 3 d wind flows over complex terrain such as dune systems presents a valuable new tool for geomorphological research as it enables new insights into the relationship between the wind field and the underlying topography the results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20m from the embryo dune toe the potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13m s 1 and 7m s 1 respectively have the potential to create onshore directed winds at the back beach with mean velocities above 3 3m s 1 these are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations

airflow and roughness characteristics over partially vegetated linear dunes in the southwest kalahari desert there is little understanding of the flow field surrounding semi vegetated linear dunes and predictions of dune mobility are hampered by a lack of empirical data concerning windflow in an attempt to characterize the near surface airflow upwind of and over partially vegetated linear dunes in the southwest kalahari desert this study presents measurements of vertical and horizontal wind velocity profiles across cross sectional transects of seven partially vegetated linear dunes vegetation surveys combined with velocity measurements from vertical arrays of cup anemometers placed up to 2 3 m above the ground surface were used to gain information concerning the modification of airflow structure caused by the intrusion of the dunes into the atmospheric boundary layer and to predict the variability of aerodynamic roughness z0 from interdune to crest the results suggest an acceleration of flow up the windward slopes of the dunes and as such the data correspond to classical theory concerning flow over low hills essentially jackson and hunt 1975 principles where the theory is incapable of explaining the airflow structure and acceleration characteristics this is explained in part by the presence of a spatially variable vegetation cover over the dunes the vegetation is important both in terms of the varying aerodynamic roughness z0 and problems concerning the definition of a zero plane displacement d it is considered that any attempts to characterize surface shear stress over the kalahari linear dunes in order to predict sand transport and dune mobility will be hampered by two problems these are the progressively non log linear nature of the velocity profiles over the dunes caused by flow acceleration and the production of thin near surface boundary layers caused by areally variable aerodynamic roughness as a result of the partially vegetated nature of the dunes

secondary airflow and sediment transport in the lee of a reversing dune lee side windspeed and sediment transport were measured over a small 1 2 m transverse ridge in the silver peak dunefield west central nevada usa using an intensive array of 25 cup anemometers and seven total flux traps during crest transverse and transporting flow conditions u0 3crest 8 4 m s 1 windspeed near the surface of the lee slope averaged half 48 per cent that of crest speeds dimensionless speeds in the separation zone ranged from 0 2 to 0 8 that of the outer flow u12 along the boundary of the separation cell windspeed increased by 10 per cent of the crest speed before separation equilibrium of upper and lower wake regions was not observed by the documented eight dune heights suggesting that wake recovery may not occur over closely spaced dunes sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs this suggests that a significant amount c 70 95 per cent of sediment transported over the crest moved as fallout for this data set flux was approximately proportional to the cube of the near surface windspeed u0 3 and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection beyond the interdune transport direction progressed from oblique to crest transverse this indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest transverse flows regarding the grain size and sorting properties of transported sediment there was no significant difference in mean grain size over the dune although in general particles were finer and more poorly sorted in the lee copyright 1999 john wiley sons ltd

enhanced gps inversion technique applied to the 2004 sumatra earthquake and tsunami 1 since the devastating earthquake and tsunami in 2004 offshore sumatra many source models have been put forward recent studies clearly show that modern gps processing could achieve high resolving power for slip in near real time which is crucial for determining tsunami initial conditions provided accurate gps processing and inversion here we propose an inversion technique with improved representation of the subduction zone geometry and physically justified boundary conditions we show that the discrepancy between the inversion of near and far field gps data for the 2004 event which is often explained by postseismic slip can be eliminated by using our inversion method and iasp91 earth model inverted source models including versions with splay faulting are shown to be consistent with satellite altimetry data of offshore tsunami wave height suggesting that displacement at the splay fault might have been present but was likely a second order process

jet flow over foredunes jet flows which are localized flows exhibiting a high speed maxima are relatively common in nature and in many devices they have only been occasionally observed on dunes and their dynamics are poorly known this paper examines computational fluid dynamic cfd two dimensional 2d modelling of jet flow over a foredune topography flow was simulated in 10 increments from onshore 0 to highly oblique alongshore 70 incident wind approach angles cfd modelling reveals that the formation of a jet is not dependent on a critical wind speed and an increase in incident wind velocity does not affect the magnitude of jet flow a jet is first formed at 1 0m seawards of the foredune crest on the prince edward island foredune morphology example examined here a jet is not developed when the incident wind is from an oblique approach angle greater than 50 because there is significantly less flow acceleration across a much lower slope at this incident angle the presence of a scarp does influence the structure of the crest jet in that the jet is more pronounced where a scarp is present surface roughness affects the magnitude of jet expansion and jets are better developed on bare surfaces compared to vegetated ones

did a submarine landslide contribute to the 2011 tohoku tsunami many studies have modeled the tohoku tsunami of march 11 2011 as being due entirely to slip on an earthquake fault but the following discrepancies suggest that further research is warranted 1 published models of tsunami propagation and coastal impact underpredict the observed runup heights of up to 40 m measured along the coast of the sanriku district in the northeast part of honshu island 2 published models cannot reproduce the timing and high frequency content of tsunami waves recorded at three nearshore buoys off sanriku nor the timing and dispersion properties of the waveforms at offshore dart buoy 21418 3 the rupture centroids obtained by tsunami inversions are biased about 60 km nne of that obtained by the global cmt project based on an analysis of seismic and geodetic data together with recorded tsunami waveforms we propose that while the primary source of the tsunami was the vertical displacement of the seafloor due to the earthquake an additional tsunami source is also required we infer the location of the proposed additional source based on an analysis of the travel times of higher frequency tsunami waves observed at nearshore buoys we further propose that the most likely additional tsunami source was a submarine mass failure smf i e a submarine landslide a comparison of pre and post tsunami bathymetric surveys reveals tens of meters of vertical seafloor movement at the proposed smf location and a slope stability analysis confirms that the horizontal acceleration from the earthquake was sufficient to trigger an smf forward modeling of the tsunami generated by a combination of the earthquake and the smf reproduces the recorded on near and offshore tsunami observations well particularly the high frequency component of the tsunami waves off sanriku which were not well simulated by previous models the conclusion that a significant part of the 2011 tohoku tsunami was generated by an smf source has important implications for estimates of tsunami hazard in the tohoku region as well as in other tectonically similar regions

an aeolian grainflow model for martian recurring slope lineae abstract recurring slope lineae rsl on mars have been enigmatic since their discovery their behavior resembles a seeping liquid but sources of water remain puzzling this work demonstrates that the properties of rsl are consistent with observed behaviors of martian and terrestrial aeolian processes specifically rsl are well explained as flows of sand that remove a thin coating of dust observed rsl properties are supportive of or consistent with this model which requires no liquid water or other exotic processes but rather indicates seasonal aeolian behavior these settings and behaviors resemble features observed by rovers and also explain the occurrence of many slope lineae on mars that do not meet the strict definition of rsl this indicates that rsl can be explained simply as aeolian features other processes may add complexities just as they could modify the behavior of any sand dune

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

the 25 october 2010 mentawai tsunami earthquake from real time discriminants finite fault rupture and tsunami excitation 1 the moment magnitude 7 8 earthquake that struck offshore the mentawai islands in western indonesia on 25 october 2010 created a locally large tsunami that caused more than 400 human causalities we identify this earthquake as a rare slow source tsunami earthquake based on 1 disproportionately large tsunami waves 2 excessive rupture duration near 125 s 3 predominantly shallow near trench slip determined through finite fault modeling and 4 deficiencies in energy to moment and energy to duration cubed ratios the latter in near real time we detail the real time solutions that identified the slow nature of this event and evaluate how regional reductions in crustal rigidity along the shallow trench as determined by reduced rupture velocity contributed to increased slip causing the 5 9 m local tsunami runup and observed transoceanic wave heights observed 1600 km to the southeast

an experimental study of turbulent flow over a low angle dune 1 many large sand bed alluvial channels are dominated by dunes that possess low angle lee sides often 10 which play a critical role in the transportation of sediment and generation of significant bed form roughness despite the fact that these low angle dunes are very common in such channels many current models of dune flow dynamics are based on bed forms with an angle of repose slip face that generates a zone of permanent separated flow in the dune lee study of flow associated with low angle dunes in the field is inherently difficult since it is usually both hard to measure very near the bed and hard to quantify the nature of turbulence over these bed forms results from a detailed scale model experimental study of flow over a low angle dune which is based on a prototype dune from the fraser river canada present a necessary link between flume and field studies and document the origins of macroturbulence associated with these bed forms two dimensional laser doppler anemometer measurements over a low angle dune maximum lower lee side slope 14 show that dune morphology exerts a dominant control on the turbulent flow causing flow deceleration in the lower lee and development of an intermittent layer of shear at the interface with the higher velocity flow above the scale model confirms that permanent flow separation does not occur over low angle dunes but instead is replaced by a small region here 7 of the dune wavelength in length of intermittent flow reversal which may be present for up to 4 of the time shear layers generated along this small zone of decelerated and or separated flow in the lower lee have a much smaller velocity differential than is characteristic of shear layers generated by flow separation in the lee of angle of repose dunes turbulence production associated with low angle dunes is dominated by eddies generated along this shear layer which produce highly variable horizontal and vertical velocities and large reynolds stresses in this region these results show that macroturbulence associated with low angle dunes is generated by intermittent separation or shear layer generation due to velocity gradients established in the zone of lee side flow expansion velocity profiles and maps of turbulence structure from the scale model are in reasonable agreement with field measurements from low angle dunes in natural sand bed rivers these results highlight the need to consider the temporal evolution and intermittency of shear layer behavior often very near the bed when interpreting the generation of macroturbulence and dispersal of sediment associated with low angle dunes

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

probabilistic tsunami hazard assessment at seaside oregon for near and far field seismic sources 1 the first probabilistic tsunami flooding maps have been developed the methodology called probabilistic tsunami hazard assessment ptha integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment psha application of the methodology to seaside oregon has yielded estimates of the spatial distribution of 100 and 500 year maximum tsunami amplitudes i e amplitudes with 1 and 0 2 annual probability of exceedance the 100 year tsunami is generated most frequently by far field sources in the alaska aleutian subduction zone and is characterized by maximum amplitudes that do not exceed 4 m with an inland extent of less than 500 m in contrast the 500 year tsunami is dominated by local sources in the cascadia subduction zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km the primary sources of uncertainty in these results include those associated with interevent time estimates modeling of background sea level and accounting for temporal changes in bathymetry and topography nonetheless ptha represents an important contribution to tsunami hazard assessment techniques viewed in the broader context of risk analysis ptha provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard which can then be combined with vulnerability and exposure to yield estimates of tsunami risk

geomorphology of desert sand dunes a review of recent progress through the 1980s and 1990s studies of the geomorphology of desert sand dunes were dominated by field studies of wind flow and sand flow over individual dunes alongside these there were some attempts numerically to model dune development as well as some wind tunnel studies that investigated wind flow over dunes as developments with equipment allowed field measurements became more sophisticated however by the mid 1990s it was clear that even these more complex measurements were still unable to explain the mechanisms by which sand is entrained and transported most importantly the attempt to measure the stresses imposed by the wind on the sand surface proved impossible and the use of shear or friction velocity as a surrogate for shear stress also failed to deliver at the same time it has become apparent that turbulent structures in the flow may be as or more important in explaining sand flux in a development paralleled in fluvial geomorphology aeolian geomorphologists have attempted to measure and model turbulent structures over dunes progress has recently been made through the use of more complex numerical models based on computational fluid dynamics cfd some of the modelling work has also suggested that notions of dune equilibrium form may not be particularly helpful this range of recent developments has not meant that field studies are now redundant for linear dunes careful observations of individual dunes have provided important data about how the dunes develop but in this particular field some progress has been made through ground penetrating radar images of the internal structure of the dunes the paradigm for studies of desert dune geomorphology for several decades has been that good quality empirical data about wind flow and sand flux will enable us to understand how dunes are created and maintain their form at least some of the difficulty in the past arose from the plethora of undirected data generated by largely inductive field studies more recently attention has shifted although not completely to modelling approaches and very considerable progress has been made in developing models of dune development it is clear however that the models will continue to require accurate field observations in order for us to be able to develop a clear understanding of desert sand dune geomorphology

composition of barian mica in multiphase solid inclusions from orogenic garnet peridotites as evidence of mantle metasomatism in a subduction zone setting multiphase solid inclusions in minerals formed at ultra high pressure uhp provide evidence for the presence of fluids during deep subduction this study focuses on barian mica which is a common phase in multiphase solid inclusions enclosed in garnet from mantle derived uhp garnet peridotites in the saxothuringian basement of the northern bohemian massif the documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite kmg3 si3al o10 oh 2 kinoshitalite bamg3 al2si2 o10 oh 2 and ferrokinoshitalite bafe3 al2si2 o10 oh 2 in addition to ba 0 24 0 67 apfu mica is significantly enriched in mg xmg 0 85 to 0 95 cr 0 03 0 43 apfu and cl 0 04 0 34 apfu the substitution vector involving ba in the i site which describes the observed chemical variability can be expressed as bafeivalclk 1mg 1si 1 oh 1 a minor amount of cr and vial enters octahedral sites following a substitution vector vi cr al 2 vi mg fe 3 towards chromphyllite and muscovite as demonstrated by variable ba and cl contents positively correlating with fe barian mica composition is partly controlled by its crystal structure textural evidence shows that barian mica together with other minerals in multiphase solid inclusions crystallized from fluids trapped during garnet growth the unusual chemical composition of mica reflects the mixing of two distinct sources 1 an internal source i e the host peridotite and its garnet providing mg fe al cr and 2 an external source represented by crustal derived subduction zone fluids supplying ba k and cl at uhp uht conditions recorded by the associated diamond bearing metasediments c 1100 c and 4 5 gpa located above the second critical point in the pelitic system the produced subduction zone fluids transporting the elements into the overlying mantle wedge had a solute rich composition with properties of a hydrous melt the occurrence of barian mica with a specific chemistry in barium poor mantle rocks demonstrates the importance of its thorough chemical characterization

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

f phlogopites in the alban hills volcanic district central italy indications regarding the role of volatiles in magmatic crystallisation abstract a systematic analysis of micas contained in effusive pyroclastic and hypabyssal rocks of the alban hills volcanic district ahvd central italy was made in order to characterise minerals of pyroclastic units for tephrostratigraphy and to obtain as much information as possible on the activity of volatiles in this magmatic system the phlogopite shows a large range of f contents between 0 50 and 7 50 wt that make it possible to discriminate different ahvd lithologies in particular micas of lava groundmass are characterised by extremely high f up to 7 50 wt and ba up to 9 70 wt contents seldom or never found in other magmatic ultrapotassic rocks moreover the micas of pyroclastics ultramafic cumulates and holocrystalline inclusions made up of leucite clinopyroxene and phlogopite hereafter italites show mg mg fe values between 0 65 and 0 90 that are not correlated with f contents the variations in f contents observed in the ahvd micas do not appear to be due to a temperature effect or pressure changes but they may be due to variations in the h 2 o and co 2 activities in the magma chamber they make it possible to differentiate three crystallisation environments in the ahvd magmatic system the first one had elevated co 2 activity and formed the italites near the carbonate contact these rocks represent at least those enriched in clinopyroxene without skarn minerals the hypabyssal crystallisation of the ahvd magmas at the periphery of magma chamber the second one characterised by a higher water activity is represented by the micas of the ultramafic cumulates and pyroclastic scorias and is located in the inner part of magma chamber the third environment the groundmass of the lavas it is not related with the previous ones and is characterised by the absence of water and by a high f activity in general our results suggest that the compositional variations observed in the micas al si ti ba reflect different h 2 o activities inversely correlated with f activity in the magma chamber

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

airflow and sand transport variations within a backshore parabolic dune plain complex ne graham island british columbia canada onshore aeolian sand transport beyond the beach and foredune is often overlooked in the morphodynamics and sediment budgets of sandy coastal systems this study provides detailed measurements of airflow sand transport via saltation and modified suspension vegetation density and surface elevation changes over an extensive 325 30 m swath of a backshore foredune parabolic dune plain complex near surface 30 cm wind speeds on the backshore ranged from 4 3 to 7 3 m s 1 gusting to 14 0 m s 1 oblique onshore flow is steered alongshore near the incipient foredune then landward into a trough blowout where streamline compression flow acceleration to 1 8 times the incident speed and increasing steadiness occur highest saltation rates occur in steady topographically accelerated flow within the blowout as such the blowout acts as a conduit to channel flow and sand through the foredune into the foredune plain beyond the blowout flow expands vegetation roughness increases and flow decelerates over the foredune plain localized flow steering and acceleration to 1 6 times the incident speed occurs followed by a drop to 40 of incident flow speed in a densely vegetated zone upwind of an active parabolic dune at 250 m from the foredune sediment properties reflect variations in near surface flow and transport processes well sorted fine skewed backshore sands become more poorly sorted and coarse skewed in the blowout due to winnowing of fines sorting improves and sands become fine skewed over the foredune plain toward the parabolic dune due to grainfall of finer sands winnowed from the beach and foredune during the fall winter season significant amounts of sand up to 110 kg m 2 are transported via modified suspension and deposited as grainfall up to 300 m landward of the foredune no distinct trend in grainfall was found although most fell on the depositional lobe of the blowout and at 200 m near an isolated active parabolic dune grainfall amounts may reflect several transporting events over the measurement period and the transport process is likely via localized modified suspension from the crest of the foredune and other compound dune features in the foredune plain this evidence suggests that the process of grainfall delivery though often overlooked in coastal research may be a key process in maintaining active dunes hundreds of metres from the shoreline in a densely vegetated foredune plain the effectiveness of this process is controlled by seasonal changes in vegetation cover and wind strength as well as shorter term e g tidally controlled variations in sand availability from the beach

development of hybrid aeolian dunes the william river dune field northwest saskatchewan canada observations have been made on the structure morphology and pattern of sand movement on large scale roughly elongate northwest southeast aligned aeolian sand dunes in a desert area of northern saskatchewan canada transverse profiles show steeper northeast flanks the lower parts of which are covered with psammophilous grasses dune structure is dominated by northeast dipping accretion laminae and 14c dates of organic material trapped between such exposed laminae on the southwest flank indicate migration to the northeast at about 0 5 m year in the last few centuries on the other hand there is a progressive increase in height bulk symmetry and peakedness of the dunes from northwest to southeast suggestive of substantial along dune sand movement the present day wind regime shows a potential resultant sand transport vector to the southeast virtually parallel to the dune axis winds from the north northeast and northeast dominate the first 6 months of the year followed by winds from the west so

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

alaska megathrust 2 imaging the megathrust zone and yakutat pacific plate interface in the alaska subduction zone we image the slab underneath a 450 km long transect of the alaska subduction zone to investigate 1 the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and 2 the interplate coupled zone where the great 1964 earthquake mw 9 2 exhibited the largest amount of rupture the joint teleseismic migration of two array data sets based on receiver functions rfs reveals a prominent shallow dipping low velocity layer at 25 30 km depth in southern alaska modeling of rf amplitudes suggests the existence of a thin layer vs of 2 1 2 6 km s that is 20 40 slower than underlying oceanic crustal velocities and is sandwiched between the subducted slab and the overriding plate the observed megathrust layer with vp vs of 1 9 2 3 may be due to a thick sediment input from the trench in combination with elevated pore fluid pressure in the channel our image also includes an unusually thick low velocity crust subducting with a 20 dip down to 130 km depth at 200 km inland beneath central alaska the unusual nature of this subducted segment results from the subduction of the yakutat terrane crust our imaged western edge of the yakutat terrane aligns with the western end of a geodetically locked patch with high slip deficit and coincides with the boundary of aftershock events from the 1964 earthquake it appears that this sharp change in the nature of the downgoing plate could control the slip distribution of great earthquakes on this plate interface

responses of three dimensional flow to variations in the angle of incident wind and profile form of dunes greenwich dunes prince edward island canada abstract this study reports the responses of three dimensional near surface airflow over a vegetated foredune to variations in the conditions of incident flow during an 8 h experiment two parallel measurement transects were established on morphologically different dune profiles i a taller concave convex west foredune transect with 0 5 m high densely vegetated 45 seaward incipient foredune and ii a shorter concave straight east foredune transect with lower sparsely vegetated 14 seaward incipient foredune five stations on each transect from the incipient dune to the crest were equipped with ultrasonic anemometers at 0 6 and 1 65 m height and logged at 1 hz incident conditions were recorded from a 4 m tower over a flat beach winds increased from 6 m s 1 to 20 m s 1 and were generally obliquely onshore ene 73 three sub events and the population of 10 minute averages of key properties of flow u w s cvu from all sample locations on the east transect n 235 are examined to identify location and profile specific responses over 52 of the incident direction of flow from 11 to 63 onshore topographic steering and forcing cause major deviations in the properties and vectors of near surface flow from the regional wind topographic forcing on the concave straight dune profile increases wind speed and steadiness toward the crest with speed up values to 65 in the backshore wind speed and steadiness of flow are least responsive to changes in incident angle in the backshore because of stagnation of flow and are most responsive at the lower stoss under pronounced streamline compression on the steeper concave convex profile speed and steadiness decrease toward the crest because of stagnation of flow at the toe and flow expansion at the slope inflection point on the lower stoss net downward vertical velocity occurs over both profiles increases toward the crest and reflects enhanced turbulent momentum conveyance toward the surface all of these flow responses are enhanced with faster speeds of incident flow and or more onshore winds significant onshore steering of near surface vectors of flow to 37 occurs and is greatest closer to the surface and during highly oblique winds 15 onshore therefore even subtle effects of streamline compression and amplification of flow under alongshore conditions effectively steer flow and sand transport toward the dune as topographic forcing and steering cause significant three dimensional deviations in near surface properties of flow most regional scale and or two dimensional models of dune process response dynamics are insufficient for characterizing coastal and desert dune sediment budgets and morphodynamics in particular deflection of sand transport vectors with greater fetch distances than those derived from regional winds may occur coincident flow transport and morphological response data are required to better quantitatively model these processes

wind energy variations in the southwestern kalahari desert and implications for linear dunefield activity the southwestern kalahari linear dunefield which displays marked morphological variability possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield palaeo status has been ascribed on the basis of several criteria including the presence of vegetation but also because dunes are thought to be out of alignment with modern resultant potential sand moving wind directions and because present day wind energy is regarded as low for the period 1960 1992 wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions potential sand transport directions including spatial and temporal variations and potential drift directions for the windiest three month periods are calculated and explained it is concluded that the present day potential sand transport environment is markedly variable from year to year and from place to place while periods of low sand transport energy do occur it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield directional variability is also relatively high perhaps exceeding that under which linear dunes can be expected to form because linear dune aeolian activity has a number of states however the present day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

finite element inversion of dinsar data from the mw 6 3 l aquila earthquake 2009 italy 1 fault slip distribution is usually retrieved from geodetic data assuming that the local crust is an elastic homogeneous and isotropic half space in the last decades spatially dense geodetic data e g dinsar maps have highlighted complex patterns of coseismic deformation that require new modeling tools such as numerical methods able to represent rheological and geometrical complexities of the earth s crust in this work we develop a procedure to perform inversion of geodetic data based on the finite element method accounting for a more realistic description of the local crust the method is applied to the 2009 l aquila earthquake mw 6 3 using dinsar images of the coseismic displacement results highlight the non negligible influence of the medium structure homogeneous and heterogeneous models show discrepancies up to 20 in the fault slip distribution values furthermore in the heterogeneous models a new area of slip appears above the hypocenter we also perform a resolution study showing that the information about fault slip distributions retrieved from geodetic data should be considered as averaged on surrounding patches