recent climatic significance of chemical signals in a shallow firn core from an alpine glacier in the south asia monsoon region abstract there are 19 sub tropical temperate glaciers on mount yulong the southernmost currently glacier covered area in eurasia controlled by the south western monsoon climate in the summer of 1999 a firn core 10 10 m long extending down to glacier ice was recovered in the accumulation area of the largest glacier baishui no 1 periodic variations of climatic signals above 7 8 m depth were apparent and net accumulation of four years was identified by the annual oscillations of isotopic and ionic composition the boundaries of annual accumulation were confirmed by higher values of electrical conductivity and ph and by dirty refreezing ice layers at the levels of summer surfaces calculated mean annual net accumulation from 1994 95 to 1997 98 was about 900 mm water equivalent the amplitude of isotopic variations in the profile decreased with increasing depth and isotopic homogenization occurred below 7 8 m as a result of meltwater percolation variations of 18 o above 7 8 m showed an approximate correlation with the winter climatic trend at lijiang station 25 km away concentrations of ca 2 and mg 2 were much higher than those of na and k indicating that the air masses for precipitation were mainly from a continental source and that the core material accumulated during the winter period the close correspondence of cl and na indicated their common origin the decreasing trend of na cl ratios with increasing depth further reflects a progressive homogenization process caused by meltwater percolation concentrations of so 4 2 and no 3 in the core are quite low the mean annual net accumulation in the core and the estimated ablation indicate that the average annual precipitation above the glacier s equilibrium line is 2400 3100 mm but this needs to be confirmed by long term observation of mass balance

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

variation in grain size and morphology of an inland parabolic dune during the incipient phase of stabilization in the hobq desert china abstract a significant increase in rainfall in the summer of 2012 on the southern fringe of the hobq desert inner mongolia resulted in the vegetation and thus stability of dunes in this area our research focuses on a typical parabolic dune which was active in 2011 and became stabilized after vegetation colonization topographic surveys and surface sediment analysis of the morphology and surface sands of the parabolic dune indicate that decreasing mean grain size and sorting values better sorting slightly more positive skewness and increasing kurtosis occurred over the dune surface during the incipient phase of stabilization there was a strong relationship between grain size sorting and dune mobility surface sand from the stabilized dune was generally finer and better sorted than at the same location when the dune was active during 2011 2012 the dune head had moved eastwards by approximately 2 3 m while its two arms expanded outward by approximately 3 2 m the height of the dune decreased and the dune became larger with a decreasing volume once anchored 2013 2014 the overall morphology and the grain size and sorting characteristics of the dune became more constant and quite different than when the dune was active

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

environmental controls morphodynamic processes and ecogeomorphic interactions of barchan to parabolic dune transformations the transformation of barchans into parabolic dunes has been observed in various dune systems around the world precise details of how environmental controls influence the dune transformation and stabilisation mechanism however remain poorly understood a horns anchoring mechanism and a nebkhas initiation mechanism have previously been proposed and selected environmental controls on the transformation have been explored by some modelling efforts but the morphodynamic processes and eco geomorphic interactions involved are unclear and comparison between different dune systems is challenging this study extends a cellular automaton model informed by empirical data from fieldwork and remote sensing to fully explore how vegetation characteristics boundary conditions and wind regime influence the transformation process and the resulting dune morphologies a dynamic growth function is introduced for clump like perennials to differentiate between growing and non growing seasons and to simulate the development of young plants into mature plants over multiple years modelling results show that environmental parameters interact with each other in a complex manner to impact the transformation process the study finds a fundamental power law relation between a non dimensional parameter group so called the dune stabilising index s and the normalised migration distance of the transforming dune which can be used to reconstruct paleo environmental conditions and monitor the impacts of changes in climate or land use on a dune system four basic eco geomorphic interaction zones are identified which bear different functionality in the barchan to parabolic dune transformation the roles of different environmental controls in changing the eco geomorphic interaction zones transforming processes and resulting dune morphologies are also clarified

parabolic dune development modes according to shape at the southern fringes of the hobq desert inner mongolia china since the 1970s parabolic dunes at the southern fringe of the hobq desert inner mongolia china have exhibited many different shapes v shaped u shaped and palmate each with a unique mode of development in the study area parabolic dunes are mainly distributed in regions a b and c with an intermittent river running from the south to the north we used high resolution remote sensing images from 1970 to 2014 and rtk gps measurements to study the development modes of different dune shapes the modes are characterized by the relationship between the intermittent river and dunes formation of the incipient dune patterns the predominant source supply of dunes and the primary formation of different shapes v shaped u shaped and palmate most parabolic dunes in region a are v shaped and closer to the bank of the river the original barchans in this region exhibit disconnected arms behavior with the sand blown out of the riverbed through gullies the nebkhas on the disconnected arms acquire the external sand source through the fertile island effect thereby developing into triangular sand patches and further developing into v shaped parabolic dunes most parabolic dunes in regions b and c are palmate the residual dunes cut by the re channelization of river from transverse dune fields on the west bank are the main sand source of region b the parabolic dunes in region c are the original barchans having then been transformed the stoss slopes of v shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape the dune crest of v shaped parabolic dune is the deposition area which forms the arc shaped sand ridge their two arms are non parallel the lateral airflow of the arms jointly transport sand to the middle part of dunes resulting in a narrower triangle that gradually becomes v shaped palmate parabolic dunes have a steeper stoss slope and height the dune crest of the palmate parabolic dune is the erosion area which forms a long and narrow trough between nebkhas by the funnelling effect this process forces sand towards lee slopes which transform from concave original barchans into convex ultimately resulting in the formation of palmate parabolic dunes

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

relations between dune morphology air flow and sediment flux on reversing dunes silver peak nevada relations between wind speed sediment flux and dune morphology were measured for two reversing dunes situated in the south western part of the silver peak dunefield in clayton valley west central nevada the larger dune was 120 m in length with a height of 12ae5 m and the smaller dune 80 m long and 6 m high both dunes were sharp crested aligned approximately e w perpendicular to the dominant wind direction and had slightly concave stoss profiles twenty seven rotating cup anemometers were placed 0ae3 m elevation along n s transects on each of the dunes at each anemometer site a passive wedge shaped sediment trap was used to measure sediment flux amplification of wind speed was observed towards the crest on the stoss side of both dunes with speed up factors ucrest ubase ranging from 1ae50 3ae19 with a corresponding increase in sediment flux by 1 2 orders of magnitude in general the ratio of crest flux to base flux qc qb increased with increasing incident basal wind speed on both dunes direct measurements of the stoss slope variation in sediment flux relative to the dune crest are in good agreement with owen s transport model friction speed u was approximated from near surface 0ae3 m point wind speed although not all assumptions of the owen model are upheld the modified model performance is sufficiently robust to predict short term variation in stoss sediment flux on the study dunes improved models that adequately account for variation in sediment flux under changing air flow and transport conditions are necessary for the prediction of longterm evolution of dunes in this regard further progress in model development will require increased understanding of the spatial and temporal variability of airflow and the short term response of sediment flux to these flow conditions

barchan parabolic dune pattern transition from vegetation stability threshold 1 many dune fields exhibit a downwind transition from forward pointing barchan dunes to stabilized backward pointing parabolic dunes accompanied by an increase in vegetation a recent model predicts this pattern transition occurs when dune surface erosion deposition rates decrease below a threshold of half the vegetation growth rate we provide a direct test using a unique data set of repeat topographic surveys across white sands dune field and find strong quantitative support for the model threshold we also show the threshold hypothesis applied to a barchan dune results naturally in its curvature inversion as the point of threshold crossing progresses from the horns to the crest this simple general threshold framework can be an extremely useful tool for predicting the response of dune landscapes to changes in wind speed sediment supply or vegetation growth rate near the threshold a small environmental change could result in a drastic change in dune pattern and activity

modeling grain size variations of aeolian gypsum deposits at white sands new mexico using aviris imagery abstract visible and near infrared vnir through short wavelength infrared swir 0 4 2 5 m aviris data along with laboratory spectral measurements and analyses of field samples were used to characterize grain size variations in aeolian gypsum deposits across barchan transverse parabolic and barchan dunes at white sands new mexico usa all field samples contained a mineralogy of 100 gypsum in order to document grain size variations at white sands surficial gypsum samples were collected along three transects parallel to the prevailing downwind direction grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621 m which were subjected to spectral measurements absorption band depths of the size fractions were determined after applying an automated continuum removal procedure to each spectrum then the relationship between absorption band depth and gypsum size fraction was established using a linear regression three software processing steps were carried out to measure the grain size variations of gypsum in the dune area using aviris data aviris mapping results field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits in contrast the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits based on laboratory estimates a representative barchan transverse dune transect 1 has a mean grain size of 1 16 449 m the error bar results show that the error ranges from 50 to 50 m mean grain size for a representative parabolic dune transect 2 is 1 51 352 m and 1 52 347 m for a representative barchan dune transect 3 t test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas the t test results also show that there are no significant differences between modeled and laboratory measured grain size values hyperspectral grain size modeling can help to determine dynamic processes shaping the formation of the dunes such as wind directions and the relative strengths of winds through time this has implications for studying such processes on other planetary landforms that have mineralogy with unique absorption bands in vnir swir hyperspectral data

vegetated dune morphodynamics during recent stabilization of the mu us dune field north central china the response of dune fields to changing environmental conditions can be better understood by investigating how changing vegetation cover affects dune morphodynamics significant increases in vegetation and widespread dune stabilization over the years 2000 2012 are evident in high resolution satellite imagery of the mu us dune field in north central china possibly a lagged response to changing wind strength and temperature since the 1970s these trends provide an opportunity to study how dune morphology changes with increasing vegetation stabilization vegetation expansion occurs mainly by expansion of pre existing patches in interdunes as vegetation spreads from interdunes onto surrounding dunes it modifies their shapes in competition with wind driven sand movement primarily in three ways 1 vegetation anchoring horns of barchans transforms them to parabolic dunes 2 vegetation colonizes stoss faces of barchan and transverse dunes resulting in lower dune height and an elongated stoss face with shortening of barchan horns and 3 on transverse dunes the lee face is fixed by plants that survive sand burial along each of these pathways of stabilization dune morphology tends to change from more barchanoid to more parabolic forms but that transformation is not always completed before full stabilization artificial stabilization leads to an extreme case of frozen barchans or transverse dunes with original shapes preserved by rapid establishment of vegetation observations in the mu us dune field emphasize the point that vegetation growth and aeolian sand transport not only respond to external factors such as climate but also interact with each other for example some barchans lose sand mass during vegetation fixation and actually migrate faster as they become smaller and vegetation growth on a barchan s lower stoss face may alter sand transport over the dune in a way that favors more rapid stabilization conceptual models were generalized for the development of vegetation stabilized dunes which should be helpful in better understanding of vegetated dune morphology model verification and prediction and guiding practical dune stabilization efforts

linkage between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary abstract knowledge of the role of c4 vegetation expansion in regulating dune stabilization during the late quaternary is important for understanding the evolution of the environment and climate in the climatically sensitive margin of the east asian summer monsoon however due to the lack of both reliable vegetation records and chronological control during episodes of dune activity the relationship between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary remains unclear here we present a new regional compilation of late quaternary stable carbon isotopic data from organic matter together with dated records from sub aerial sedimentary deposits in the region our compilation of vegetation development and dune activity in these deserts suggests that c4 vegetation expansion with a main contribution from chenopodiaceae and a secondary contribution from poaceae and cyperaceae may have played a critical role in dune semi stabilization with a northwestward trend from 13 to 9 ka and dune stabilization throughout the entire study region from 9 to 5 ka in addition during the late holocene intensified millet cultivation or overgrazing and or climatic deterioration at 1 5 ka likely caused an increase in c4 vegetation abundance in the deserts of ne china which is associated with a dune mobilization episode in contrast after 2 5 ka decreased vegetation cover and dune mobilization in the mu us and hobq deserts were likely caused by poor land use practices and historically documented droughts overall c4 vegetation expansion was the main cause of dune stabilization in these deserts during the late quaternary

nearest neighbor methods applied to dune field organization the coral pink sand dunes kane county utah usa dune fields have recently come to be recognized as self organizing systems that can be seen progressing from states of disorganization or randomness to uniformity dune systems can be highly sensitive to changes in factors such as climate and sediment transport that determine system state changes in climate and sediment state can take time to work their way through a dune system this in turn leads to spatial heterogeneity in dune field organization using the coral pink sand dunes in southern utah as a model this study tests nearest neighbor analysis adapted as a method to objectively identify and characterize differences in two dimensional dune patterns within a dune field and to identify changes in dune patterns over time reducing transverse and barchanoid dunes from linear to three point features in planar space emphasizes the clustering that occurs when dune lengths and wavelengths are more disorganized or random this clustering may be in response to a system perturbation such as an influx of sediment and is reflected in lower nearest neighbor index r values as the system adjusts to the perturbation and moves towards steady state dune length and spacing increase through migration and coalescing of smaller dunes the resulting higher r values reflect this move towards greater uniformity in dune pattern with the organizational states of dune systems recording feedback to changes in extrinsic climate and sediment factors nearest neighbor analysis provides a proxy measure of system stability

barchan dunes stabilized under recent climate warming on the northern great plains we use light detection and ranging lidar imagery and optical stimulation luminescence dating to show that stable parabolic dunes on the canadian prairies originated from active barchan dunes 200 years ago residual dune ridges marking former lower stoss slope positions of migrating dunes record the transformation of barchan dunes to parabolic dunes between a d 1810 and 1880 parabolic dunes stabilized by ca a d 1910 with a few larger dunes and blowouts still active today a dry cool climate permitted sand transport to out compete vegetation stabilization and with lowered water tables maintain desert like barchan dunes with bare interdune sand sheets these findings explain why dune fields of the southern canadian prairies are currently more active than those of the united states great plains and the observation that dunes have stabilized under twentieth century warming our results emphasize the importance of viewing dune field responses to short term disturbances in the context of longer term system response particularly when relatively modest climatic changes can cause major shifts in dune activity

ecogeomorphic state variables and phase space construction for quantifying the evolution of vegetated aeolian landscapes cellular automaton modelling for the simulation of dune field formation and evolution has developed progressively in aeolian geomorphology in the last decade or so a model that incorporates the effects of vegetation and its interactions with geomorphic landscape development the discrete ecogeomorphic aeolian landscapes decal model can replicate a number of important visual and qualitative aspects of the complex evolution of aeolian dune landscapes under the influence of vegetation dynamics in coastal environments a key challenge in this research area is the analysis and comparison of both simulated and real world vegetated dune landscapes using objective and quantifiable principles this study presents a methodological framework or protocol for numerically quantifying various ecogeomorphic attributes using a suite of mathematically defined landscape metrics to provide a rigorous and statistical evaluation of vegetated dune field evolution within this framework the model parameter space can be systematically explored and simulation outcomes can be methodically compared against real world landscapes based on a simplified scenario of parabolic dunes developing out of blow outs the resulting dune field realizations are investigated as a function of variable growth vigour of two simulated vegetation types pioneer grass and successional woody shrub by establishing a typological phase diagram of different landscape classes the set of simulation outcomes furthermore defines a higher dimensional phase space whose axes or dimensions can be interpreted by analysing how individual ecogeomorphic landscape metrics or state variables contribute to the data distribution principal component analysis can reduce this to a visual three dimensional 3d phase space where landscape evolution can be plotted as time trajectories and where we can investigate the effects of changing environmental conditions partway through a simulation scenario the use of landscape state variables and the construction of a 3d phase space presented here may provide a general template for quantifying many other eco geomorphic systems on the earth s surface

inland aeolian deposits of the iberian peninsula sand dunes and clay dunes of the duero basin and the manchega plain palaeoclimatic considerations abstract this paper describes the latest research on the geomorphological characteristics formation environment and chronology of the main inland aeolian deposits from the south eastern duero basin db and the manchega plain mp of the iberian peninsula similarities and differences between the aeolian deposits of these two locations are summarised wind deflation from the guadiana and jucar alluvial systems created the aeolian deposits of the mp these deposits are mainly composed of quartz sands however in the san juan alluvial plain mp there is a large extent of clay dunes formed by exposure to prevalent winds of seasonal playa lakes with salt and clay sediments in the db wind remobilisation of the small particles from quaternary terraces and tertiary arkosic sediments left aeolian deposits of quartz feldspar sands textural parameters of the aeolian deposits show large variations depending on the location and the original deposit thus in the db the aeolian sands derived from the deflation of fluvial sediments are better sorted and smaller in grain size than those created by the deflation of arkosic sediments morphologically simple and compound parabolic dunes u v forms hemicyclic lobate and elongate crescentic and linear dunes climbing dunes and blowout dunes have been recognized at both sites barchan and dome dunes are present only in the db while lunette lunette clay dunes are found only in the mp in both locations the large extent of aeolian sand sheets and the predominance of simple and compound parabolic dunes indicates the active role of sparse vegetation cover in the formation of this aeolian system in the db dunes were formed by southwest and west winds while in the mp the aeolian morphologies indicate that the prevalent winds were west and northwest the chronology of the dune deposits is being determined with luminescence tl osl dating and mass spectrometry analysis 14 c ams in this way the aeolian activity and stabilisation stages can be established the latter well marked in the db through soil a horizon development thus the main sand dune formation in the db and the eastern regions of the mp occurred between 13 5 and 7 ka bp during the cold and arid younger dryas episode and the early holocene the clay dunes of the mp accumulated mainly from 29 to 19 ka bp that corresponds with heinrich events he 3 and he 2 and the last glacial maximum however clay dunes were also formed between 13 5 and 7 ka bp in both locations there have been reactivations of some sand deposits in the recent holocene with maximum activity around 5 2 ka bp and 0 5 0 2 ka bp on the other hand three marked stages of stabilisation of the db aeolian system have been established with 14 c ams around 10 2 6 2 and 1 2 ka bp finally the main winds contributing to dune construction were also responsible for the deflation processes with the formation of erosional depressions

sediment flux and airflow on the stoss slope of a barchan dune abstract measurements of sediment flux on the windward slope of an isolated barchan using an array of 30 sand traps provide new data that can constrain models of dune dynamics the data show that at low wind incident speeds flux increases up the dune exponentially whereas at higher wind speeds the increase with distance approaches linearity wind profile measurements conducted at the same time as the flux measurements indicate that although wind speed at a given height increases by 1 2 times from dune toe to brinkline wind shear velocity derived from the profile data decreases up the dune and is in many cases below transport threshold values this demonstrates that conventional wind profiles derived from anemometry on dunes do not measure the part of the boundary layer that is significant for sediment transport

stabilized dune ridges in northern saskatchewan stabilized dune ridges occurring in northern saskatchewan have previously been identified as variedly as ice crack moraines and longitudinal dunes investigations of their morphological structural and sedimentary attributes reveal that they are indeed of eolian origin but they form a particular group within the parabolic dune association namely the cree lake type dune ridges the ridges occur in association with other types of parabolic dunes and other eolian features such as loess and wind abraded glacial blocks and bedrock outcrops the dunes and the associated eolian features were all formed by southeasterly paleowinds of uniform direction the dune ridges developed from primary parabolic dunes of simple and composite types through the process of dune elongation at the same time exposed rock surfaces were abraded by the wind and loess was deposited downwind from the developing dune fields the southeasterly direction of the paleowinds which is almost directly opposite to the direction of

dune phases as time transgressive phenomena manawatu new zealand abstract new zealand s most extensive holocene dunefield is situated in the manawatu and adjoining regions evidence collected from the area including 25 radiocarbon dates suggests that the dunefield developed in phases with the first probably initiated at the coast earlier than 6000 years ago the first phase may have ceased near the coastline around 4500 years ago but dunes continued to migrate until they reached 16 km inland ca 1600 years ago about 3500 years ago dunes again began migrating inland from the coast with some still active 400 years ago the time transgressive nature of transgressive dune deposits and the possible causes of the dune phases are discussed

investigating parabolic and nebkha dune formation using a cellular automaton modelling approach vegetation plays an important role in shaping the morphology of aeolian dune landscapes in coastal and semi arid environments where ecogeomorphic interactions are complex and not well quantified we present a discrete ecogeomorphic aeolian landscape model decal capable of simulating realistic looking vegetated dune forms permitting exploration of relationships between ecological and morphological processes at different temporal and spatial scales the cellular automaton algorithm applies three simple rules that lead to self organization of complex dune environments including nebkhas with distinctive deposition tails that form in association with mesquite type shrubs and hairpin long walled parabolic dunes with trailing ridges that evolve from blowouts in association with vegetation succession changing the conditions of simulations produces differing landscapes that conform qualitatively to observations of real world dunes the model mimics the response of the morphology to changes in sediment supply vegetation distribution density and growth characteristics as well as initial disturbances the introduction of vegetation into the model links spatial and temporal scales previously dimensionless in bare sand cellular automata grid resolutions coarser than the representative size of the modelled vegetation elements yield similar morphologies but when cell size is reduced to much smaller dimensions the resultant landscape evolution is dramatically different the model furthermore demonstrates that the relative response characteristics of the multiple vegetation types and their mutual feedback with geomorphological processes impart a significant influence on landscape equilibria suggesting that vegetation induces a characteristic length scale in aeolian environments this simple vegetated dune model illustrates the power and versatility of a cellular automaton approach for exploring the effects of interactions between ecology and geomorphology in complex earth surface systems

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

velocity profiles measured on the windward slope of a transverse dune velocity gradients measured on the windward slope of a transverse dune show that flow acceleration strongly affects the turbulence structure of wind wind profiles measured below a height of 1 6m are nonlogarithmic and the altered nature of velocity profiles varies over the windward slope of a dune these findings suggest that calculated values of shear velocity are largely dependent upon the height and location of wind speed measurements as well as the strength of the prevailing wind moreover if bagnold type transport equations are used to calculate rates of sand transport on a dune wind speeds must be measured within 0 2 m of the dune surface if wind speeds are measured above this height the resulting errors in calculated shear velocity will manifest themselves as errors in calculated rates of sand transport if rates of sand transport are derived from wind speeds measured above 0 2 m the calculated rates may underestimate sand transport on the windward face of a dune as a result of flow acceleration in contrast if a dune has a separate crest upwind of the brink the expansion and subsequent deceleration of flow downwind from the crest may result in an overestimation of sand transport

barriers barrier platforms and spillover deposits in st george s bay newfoundland paraglacial sedimentation on the flanks of a deep coastal basin abstract st george s bay and adjacent coastal areas of southwest newfoundland contain thick sequences of late quaternary glaciogenic sediments and have been subject to relative sea level fluctuations over a rang of 70 m during the past 13 5 ka glaciogenic sediments have been mobilized by littoral processes to form two types of deposits these are 1 the prograded barrier beach and spit at stephenville and flat island respectively which are associated with large subaqueous sandy platforms and 2 a wedge of well stratified sand and gravel on the landward flank of the shallow sill which extends across st george s bay at an average depth of about 25 m the subaerial barriers and spits are composed of gravel beach ridges overlain locally by thin aeolian deposits with freshwater and salt marsh peats in swales these barriers developed during the last several thousand years as relative sea level approached its present position from an early postglacial minimum of approximately 25 m the prerequisite for beach ridge formation was the deposition of large sandy subaqueous platforms which appear on shallow seismic reflection records as clinoform wedges prograded into the deep basin of inner st george s bay the barrier platform at stephenville is constructed across a deep submarine valley the flat island barrier platform sits on the flank of a glacially overdeepened trough partly filled by glacial and postglacial sediments and envelops a delta formed during the early postglacial low stand of relative sea level the platform and barrier together constitute a thick coastal sequence coarsening up from sandy mud at the base to gravel at the top the wedge of well stratified coarse sediment up to 50 m thick situated on the landward flank of the shallow sill overlies older glaciogenic sediments and passes laterally into postglacial basin muds steep foreset reflections dipping 10 20 are evident on shallow seismic reflection records suggesting that the wedge was formed by spillover of sediment entrained by wave and current action into the relatively deep basins of the inner bay active gravel ripples testify to the continued mobility of coarse sediment on the sill the formation of the spillover deposits barriers and platforms demonstrates the potential for glacially overdeepened basins to host thick heterogeneous coarse grained coastal and inner shelf deposits

deflection of sand movement on a sinuous longitudinal seif dune use of fluorescent dye as tracer abstract sand was marked by fluorescent dye in order to trace sand movement and deposition on a longitudinal seif sand dune in the sinai desert the wind regime was monitored simultaneously tracing the dyed sand was possible after light to moderate sand storms and was graphically represented on maps the dune was subjected to a seasonally bidirectional wind regime with the wind hitting the dune obliquely on either side on the windward flank the sand was transported parallel to the wind direction on the lee flank sand movement was deflected towards parallelism with the crest line sand movement was deflected if the dune had a sharp profile which favored separation of wind flow on the lee flank the deflection depended on the angle of incidence between the wind and the crest line when the angle of incidence was

sediment accumulation in low sedimentation wave dominated glaciated inlets abstract many fjords situated in lowland areas of resistant bedrock are characterized by a comparatively low fluvial sediment flux and are often dominated by wave processes several such fjords in eastern canada are used as examples to develop a generalized sediment distribution model physiographically the fjords can be subdivided into nearshore platforms basin slopes and basin floors where there has been marine transgression the principal sediment source is shoreline erosion of glacial till in areas of crustal rebound late glacial and early holocene muds deposited on highs are eroded as they come within the zone of wave erosion with the falling sea level storm waves resuspend fine grained sediment in water depths of many tens of metres and produce near bottom turbid water zones within basins fine sand and silt settle out rapidly leading to the deposition of graded beds on the basin floors residual sand and gravel accumulate on the near shore platforms while silt and mud prograde over or are advected beyond basin slopes burying older basin fill sediment

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

evaluating eolian climatic interactions using a regional climate model from hanford washington usa abstract a regional climate model rcm developed for the hanford site washington illustrates a potentially useful method for assessing eolian responses to regional climate change the rcm is based on long term relations between fundamental climatic variables of precipitation temperature and wind speed modelled data are integrated into eolian climatic scenarios through maps of eolian susceptibility plots of sand dune mobility and calculated trends of unvegetated dune sand volumes results demonstrate the sensitivity of eolian climatic interactions to small changes in precipitation analyses suggest that continuation of the 1977 1987 trend toward a cooler 0 16 c and wetter 1 8 cm yr 1 climate over the next 10 15 years will result in a decrease of 18 in the volume of unvegetated dune sand further temperature reductions totaling 0 7 c would promote precipitation increases of 30 leading to an additional reduction of 98 in the volume of unvegetated dune sand modelling scenarios for a possible global warming of 4 c indicate that annual precipitation at hanford would be negligible and vegetation would be eliminated from dune surfaces sand dune mobility would increase by over 400

patterns of wind flow and aeolian deposition on a parabolic dune on the southeastern shore of lake michigan abstract sand deposition and patterns of wind flow were studied on green mountain beach gmb dune a large lake michigan coastal dune that is transitional between a trough blowout and a fully developed parabolic dune deposition pins were used to study the amount and pattern of aeolian sand deposition on the lee slopes of gmb dune over 20 months in the late fall and winter sand supported by ice between the grains accumulated on the upper to mid slopes and became over steepened 38 during measurement periods containing two major storms with wind gusts up to 25 m s a total of 44 of the deposition on the lee slope occurred compared to an average of 9 for comparable time periods between storms sand was delivered by mass movement to the lower slopes during the spring thaw very little sand was deposited on lee slopes during the summer maximum sand deposition occurred near the dune axis oriented southwest northeast and then decreased rapidly along the limbs maximum sand transport and dune migration were oriented towards the northeast despite the dominant regional winds during the fall and winter being from the west and northwest arrays of anemometers and wind vanes were used to study airflow patterns within gmb dune on five different days these studies indicate that steering of winds in the deflation area of the dune may be responsible for the northeasterly sediment transport they also suggest however that the ability of the dune to steer winds and thus control the direction of sand transport and deposition decreases when the angle between the oncoming winds and the dune axis is too great

the effect of unsteady winds on sediment transport on the stoss slope of a transverse dune silver peak nv usa rapid 10 s measurements of sediment transport and wind speed on the stoss slope of a transverse dune indicate that the majority of sand transported is associated with fluctuations in wind speed with a periodicity of 5 20 min duration increases in the sediment transport rate towards the dune crest are associated with a small degree of flow acceleration the increase in wind speed is sufficient however to greatly increase values of the intermittency index so that the duration of saltation is extended in crestal regions of the dune the pattern of sediment transport on the stoss slope and therefore the locus of areas of erosion and deposition change with the regional wind speed erosion of the crest occurs during wind speed events just above transport threshold whereas periods of higher magnitude winds result in deposition of sand upwind of the crest thereby increasing dune height although short term temporal and spatial relations between sand transport and wind speed on the stoss slope are well understood it is not clear how these relations affect dune morphology over longer periods of time

dynamic processes of a simple linear dune a study in the taklimakan sand sea china samples of dune sands surveys of the morphology and field measurements of wind velocity and direction of a simple linear dune in taklimakan sand sea show that the airflow and sand flux vary with the change of wind direction on the dune surface decrease of the airflow stress on the lee flank does not result in much decrease of the sand flux because of the low threshold shear velocities and the airflow conditions there are no significant relations between the sand flux on the lee flank and the angle of incidence of the airflow the low threshold shear velocities and the maintenance of the sand flux at the lee flank are the main mechanisms keeping the linear shape of the dunes measurements of the sand flux shows that it reaches a maximum on the crest of the dune the grain size of the transported sands has some differences compared to that of the dune surface the sands transported are finer than that on the dune surface but better sorted under the influence of the medium to low wind activity the field experiment results exhibit that it is possible for the dunes to be shaped as linear dunes during the processes of accumulation and elongation

a late pleistocene coarse grained spit platform sequence in northern jylland denmark several well preserved late pleistocene spit systems occur uplifted in northern jylland denmark their present day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits two characteristic vertical sequences are recognized in the systems the first sequence i consists of a giant scale cross bedded foreset unit overlain by topset and beach units while the second sequence ii consists of the foreset unit overlain by bar trough and beach units the two sequence types pass laterally into each other with a short overlap zone they can be interpreted in terms of meistrell s 1966 1972 model for spit platform growth based on scaled wave tank experiments the giant scale cross bedded unit corresponds to prograding of a coarse grained subaqueous spit platform while the topset bar trough and beach units reflect the growth of the subaerial spit the alternation between sequence i and ii reflects the inversely related growth of the spit and platform structures when the rate of subaqueous platform progradation declines the subaerial spit grows uniformly and when the platform progrades uniformly spit growth declines the model is probably only valid for relatively coarse grained systems because only these deposits would have a relatively steep front the water depth in which the spit system progrades and thus bottom topography determines the thickness of the giant scale cross bedded foreset unit because the water depth over the top of the platform is relatively constant if the water is less than a few metres deep the spit platform is not developed as seen where the late pleistocene spit systems prograded over elevations of the sea bottom conversely the correct recognition of spit platform sequences allows precise determination of sea level and water depth at the time of formation finally the model adds one further mode of formation of giant scale cross bedding to those already known from fluvial transverse lateral and point bars subtidal sand waves and gilbert deltas

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

aeolian dune field pattern boundary conditions aeolian dune field patterns reflect the complex external environment within which the pattern evolves these external environmental controls are the boundary conditions on aeolian dune field pattern formation the influences of boundary conditions such as wind regime and sediment supply are well known however boundary conditions represent a relatively unexplored area of dune field pattern formation source area geometry and areal limits are two newly recognized boundary conditions measurements of crest spacing and crest length from satellite images of dune field patterns with point and line source area geometries show an increase in spacing and crest length over distance whereas spacing and crest length in plane sourced patterns emerge equally across the dune field the impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area and that dune fields that are five times longer in the direction of dune migration than in the crest parallel direction can achieve the greatest spacing within a given area empirical measurements of spacing defect density and dune field area from ten different dune fields ranging over four orders of magnitude in size show that spacing increases and defect density decreases as dune field area increases because the formation of all dune fields involves a wind regime and sediment supply there must be interplay of boundary conditions within the same dune field at different stages of pattern development one boundary condition may dominate over others and with changing climatic eustatic or tectonic parameters boundary conditions may change to modify an existing pattern recognizing boundary condition controls on aeolian dune field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change

measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north eastern brazil in this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north eastern brazilian coast we extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index c of high resolution quickbird panchromatic satellite images of the dune field we then introduce the vegetation data into a continuous model for vegetated dunes coupling sand erosion and vegetation growth and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes finally from the comparison of both the measurements and the simulation results we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow out