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Gary Kocurek - One of the best experts on this subject based on the ideXlab platform.
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aeolian Dune accommodation space for holocene wadi channel avulsion strata wahiba Dune Field oman
Sedimentary Geology, 2020Co-Authors: Gary Kocurek, Robin Westerman, Caroline Hern, Dominic Tatum, H M Rajapara, A K SinghviAbstract:Abstract Geomorphic evolution of the Wahiba Dune Field, Oman, during the Quaternary has occurred within a set of boundary conditions that include climatic forcing of fluvial, aeolian and eustatic cycles within an active tectonic basin. Because of basin down-warping and sediment transport into the basin, evolution of the geomorphic surface has been accompanied by the generation of a distinctive stratigraphic record. The coupled geomorphic and stratigraphic record of the northeastern portion of the Dune Field illustrates wadi-aeolian interactions, in which a channel avulsion, likely initiated during a flood, scoured through the interDune corridor between linear Dunes. InterDune outcrops (7 m thick) consist of a lower interval interpreted as deposited by ephemeral fluvial flow, but an upper interval consists of six fining-upward units, each of which is interpreted to represent a flood event that culminated in ponding followed by desiccation. Luminescence dating indicates that the channel remained open for 2–3 ka during the Holocene, but ground-penetrating radar imaging shows that Dunes encroached into the channel between floods and suggests that the transition from ephemeral flow to ponding resulted from Dune damming. Maximum channel width and length are unknown, but width was greater than the current interDune area, and a speculative extended channel course is identified. Subsequently, interDune strata and linear Dunes were buried by crescentic Dunes sourced by an influx of sand with wadi affinity. The resultant complex stratigraphic architecture illustrates the role of existing surface topography in providing local geomorphic accommodation space for short-lived, concentrated patterns of sedimentation.
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Dune deformation in a multi directional wind regime white sands Dune Field new mexico
Earth Surface Processes and Landforms, 2015Co-Authors: Anine Pedersen, Gary Kocurek, David Mohrig, Virginia SmithAbstract:As with most Dune Fields, the White Sands Dune Field in New Mexico forms in a wind regime that is not unimodal. In this study, crescentic Dune shape change (deformation) with migration at White Sands was explored in a time series of five LiDAR-derived digital elevation models (DEMs) and compared to a record of wind direction and speed during the same period. For the study period of June 2007 to June 2010, 244 sand-transporting wind events occurred and define a dominant wind mode from the SW and lesser modes from the NNW and SSE. Based upon difference maps and tracing of Dune brinklines, overall Dune behavior consists of crest-normal migration to the NE, but also along-crest migration of Dune sinuosity and stoss superimposed Dunes to the SE. The SW winds are transverse to Dune orientations and cause most forward migration. The NNW winds cause along-crest migration of Dune sinuosity and stoss bedforms, as well as SE migration of NE-trending Dune terminations. The SSE winds cause ephemeral Dune deformation, especially crestal slipface reversals. The Dunes deform with migration because of differences in Dune-segment size, and differences in the lee-face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation. Each wind event deforms Dune shape, this new shape then serves as the boundary condition for the next wind event. Shared incidence-angle control on Dune deformation and lee-face stratification types allows for an idealized model for White Sands Dunes. Copyright © 2015 John Wiley & Sons, Ltd.
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Dune deformation in a multi‐directional wind regime: White Sands Dune Field, New Mexico
Earth Surface Processes and Landforms, 2015Co-Authors: Anine Pedersen, Gary Kocurek, David Mohrig, Virginia SmithAbstract:As with most Dune Fields, the White Sands Dune Field in New Mexico forms in a wind regime that is not unimodal. In this study, crescentic Dune shape change (deformation) with migration at White Sands was explored in a time series of five LiDAR-derived digital elevation models (DEMs) and compared to a record of wind direction and speed during the same period. For the study period of June 2007 to June 2010, 244 sand-transporting wind events occurred and define a dominant wind mode from the SW and lesser modes from the NNW and SSE. Based upon difference maps and tracing of Dune brinklines, overall Dune behavior consists of crest-normal migration to the NE, but also along-crest migration of Dune sinuosity and stoss superimposed Dunes to the SE. The SW winds are transverse to Dune orientations and cause most forward migration. The NNW winds cause along-crest migration of Dune sinuosity and stoss bedforms, as well as SE migration of NE-trending Dune terminations. The SSE winds cause ephemeral Dune deformation, especially crestal slipface reversals. The Dunes deform with migration because of differences in Dune-segment size, and differences in the lee-face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation. Each wind event deforms Dune shape, this new shape then serves as the boundary condition for the next wind event. Shared incidence-angle control on Dune deformation and lee-face stratification types allows for an idealized model for White Sands Dunes. Copyright © 2015 John Wiley & Sons, Ltd.
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definition and origin of the Dune Field pattern at white sands new mexico
Aeolian Research, 2014Co-Authors: Gary Kocurek, R C Ewing, Elke Baitis, Virginia Smith, David Mohrig, Aymeric Pierre B PeyretAbstract:Abstract A LiDAR-derived digital elevation model (DEM) of a representative portion of the White Sands Dune Field, New Mexico, allows for characterization of an unprecedented range of Dune-Field parameters and serves as a basis for pattern analysis. Dune-Field parameters were measured and statistically analyzed for populations of Dunes selected at random and occurring along transects. Populations sampled by these two different methods are comparable, but highlight the sensitivity of transect placement in a Dune Field that has pattern heterogeneity. Based upon coefficients of variation, pattern emerges at White Sands primarily because of a strong fabric of crestline orientation, and secondarily because of the regularity of spacing between Dunes of similar shape as defined by sinuosity, height and length. Linear regression of Dune parameters shows that Dune geometric relationships vary primarily with crestline length, but there is little correlation between other parameters, including Dune spacing and height. This result highlights the sensitivity of identifying topographic heterogeneity in a LiDAR-derived DEM, given that mean ratios conform to global averages. Stripping off the Dunes in Matlab shows a terraced surface, which is interpreted to represent paleo-shorelines formed during relative still stands in the overall retreat of Lake Otero. Elevated bands of higher, more closely spaced Dunes occur just leeward of the paleo-shorelines. A revised model for the White Sands Dune Field consists of the basinward progradation of successive Dune-Field segments. Each segment is associated with a paleo-shoreline, and consists of an upwind Dune ridge, represented by the elevated bands, and a leeward Dune Field.
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Modelling controls on aeolian Dune-Field pattern evolution
Sedimentology, 2011Co-Authors: Erin N. Eastwood, Joanna M. Nield, Andreas Baas, Gary KocurekAbstract:A second-generation, source-to-sink cellular automaton-based model presented here captures and quantifies many of the factors controlling the evolution of aeolian Dune-Field patterns by varying only a small number of parameters. The role of sediment supply, sediment availability and transport capacity (together defined as sediment state) in the development and evolution of an aeolian Dune-Field pattern over long time scales is quantified from model simulations. Seven Dune-Field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of Dune interactions, the sediment availability of the system and, ultimately, the development of Dune-Field patterns. This model allows predictions to be made about the range of sediment supply and wind strengths required to produce the Dune-Field patterns seen in the real world. A new clustered Dune-Field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed Dunes. Bedforms are hypothesized to cluster together, simultaneously forming two spatial scales of bedforms without first developing a large basal Dune with small superimposed Dunes. Manipulation of boundary conditions produces evolving Dune Fields with different spatial configurations of sediment supply. Trends of spacing and crest length increase with decreasing variability as the Dune Field matures. This simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian Dune-Field patterns.
Ryan C. Ewing - One of the best experts on this subject based on the ideXlab platform.
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low angle eolian deposits formed by protoDune migration and insights into slipface development at white sands Dune Field new mexico
Aeolian Research, 2019Co-Authors: John D Phillips, Ryan C. Ewing, Roy Bowling, Bradley A Weymer, Patrick Barrineau, Jeffrey A Nittrouer, Mark E EverettAbstract:Abstract ProtoDunes emerge from a flat sand bed at the upwind margin of White Sands Dune Field, and, over several hundred meters, transition into fully developed Dunes. Here, we investigate spatial and temporal changes in topography across this transition from 2007 to 2016 using lidar-derived topography, structure-from-motion-derived topography, and RTK GPS. We characterize the deposits present in 2015 using ground penetrating radar. Symmetric protoDunes give way downwind to an asymmetric protoDune at the transition to slipface development. Between 2007 and 2016, protoDune amplitude increased from 0.2 m to 4.0 m, migration rate increased from 3.2 m/yr to 6.1 m/yr, and wavelength increased from 76 m to 122 m. Ground-penetrating radar surveys show strata between flat and 15° make up the stratigraphic architecture of the protoDunes. Strata increase in steepness commensurate with an increase in amplitude. Decimeter accumulations of low-angle strata associated with initial protoDune stages give way to 4 m of accumulation composed of sets up to 1 m thick prior to slipface development. Topsets present in the thickest sets indicate near critical angles of bedform climb. Growth and slipface development occur by aerodynamic sand trapping and protoDune merging. Changes in asymmetry erase initial slipfaces prior to permanent slipface development, after which efficient sand trapping and scour promotes the transition to a Dune across 20 m in 5 years. ProtoDune stratification has hallmarks of sandsheet stratification and can be appreciated within the greater suite of processes that create low-angle eolian stratification found in modern and ancient environments.
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Multi-spatial analysis of aeolian Dune-Field patterns
Geomorphology, 2015Co-Authors: Ryan C. Ewing, George D. Mcdonald, Alexander G. HayesAbstract:Abstract Aeolian Dune-Fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales. This study examines how variations in spatial scales of Dune and ripple patterns found within Dune Fields are used in environmental reconstructions on Earth, Mars and Titan. Within a single bedform type, different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well-organized pattern, such as with the transition from protoDunes to Dunes. Additionally, different types of bedforms, such as ripples, coarse-grained ripples and Dunes, coexist at different spatial scales within a Dune-Field. Analysis of Dune-Field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform. Interpretations of environmental conditions from any scale of bedform, however, are limited to environmental signals associated with the response time of that bedform. Large-scale Dune-Field patterns integrate signals over long-term climate cycles and reveal little about short-term variations in wind or sediment supply. Wind ripples respond instantly to changing conditions, but reveal little about longer-term variations in wind or sediment supply. Recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from Dune-Field patterns.
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Aeolian Dune-Field pattern boundary conditions
Geomorphology, 2010Co-Authors: Ryan C. Ewing, Gary KocurekAbstract: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.
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Aeolian Dune interactions and Dune‐Field pattern formation: White Sands Dune Field, New Mexico
Sedimentology, 2010Co-Authors: Ryan C. Ewing, Gary KocurekAbstract:Pattern formation is a fundamental aspect of self-organization in Fields of bedforms. Time-series aerial photographs and airborne light detection and ranging show that fully developed, crescentic aeolian Dunes at White Sands, New Mexico, interact and the Dune pattern organizes in systematically similar ways as wind ripples and subaqueous Dunes and ripples. Documented interactions include: (i) merging; (ii) lateral linking; (iii) defect repulsion; (iv) bedform repulsion; (v) off-centre collision; (vi) defect creation; and (vii) Dune splitting. Merging and lateral linking are constructive interactions that give rise to a more organized pattern. Defect creation and bedform splitting are regenerative interactions that push the system to a more disorganized state. Defect/bedform repulsion and off-centre collision cause significant pattern change, but appear to be neutral in overall pattern development. Measurements of pattern parameters (number of Dunes, crest length, defect density, crest spacing and Dune height), Dune migration rates, and the type and frequency of Dune interactions within a 3500 m box transect from the upwind margin to the core of the Dune Field show that most pattern organization occurs within the upwind Field. Upwind dominance by constructive interactions yields to neutral and regenerative interactions in the Field centre. This spatial change reflects upwind line source and sediment availability boundary conditions arising from antecedent palaeo-lake topography. Pattern evolution is most strongly coupled to the pattern parameters of Dune spacing and defect density, such that spatially or temporally the frequency of bedform interactions decreases as the Dunes become further apart and have fewer defects.
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Origin of a complex and spatially diverse Dune-Field pattern, Algodones, southeastern California
Geomorphology, 2008Co-Authors: Dana Derickson, Gary Kocurek, Ryan C. Ewing, Charlie BristowAbstract: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
R C Ewing - One of the best experts on this subject based on the ideXlab platform.
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definition and origin of the Dune Field pattern at white sands new mexico
Aeolian Research, 2014Co-Authors: Gary Kocurek, R C Ewing, Elke Baitis, Virginia Smith, David Mohrig, Aymeric Pierre B PeyretAbstract:Abstract A LiDAR-derived digital elevation model (DEM) of a representative portion of the White Sands Dune Field, New Mexico, allows for characterization of an unprecedented range of Dune-Field parameters and serves as a basis for pattern analysis. Dune-Field parameters were measured and statistically analyzed for populations of Dunes selected at random and occurring along transects. Populations sampled by these two different methods are comparable, but highlight the sensitivity of transect placement in a Dune Field that has pattern heterogeneity. Based upon coefficients of variation, pattern emerges at White Sands primarily because of a strong fabric of crestline orientation, and secondarily because of the regularity of spacing between Dunes of similar shape as defined by sinuosity, height and length. Linear regression of Dune parameters shows that Dune geometric relationships vary primarily with crestline length, but there is little correlation between other parameters, including Dune spacing and height. This result highlights the sensitivity of identifying topographic heterogeneity in a LiDAR-derived DEM, given that mean ratios conform to global averages. Stripping off the Dunes in Matlab shows a terraced surface, which is interpreted to represent paleo-shorelines formed during relative still stands in the overall retreat of Lake Otero. Elevated bands of higher, more closely spaced Dunes occur just leeward of the paleo-shorelines. A revised model for the White Sands Dune Field consists of the basinward progradation of successive Dune-Field segments. Each segment is associated with a paleo-shoreline, and consists of an upwind Dune ridge, represented by the elevated bands, and a leeward Dune Field.
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Dune Field pattern formation and recent transporting winds in the olympia undae Dune Field north polar region of mars
Journal of Geophysical Research, 2010Co-Authors: Gary Kocurek, R C Ewing, Aymeric Pierre B Peyret, M C BourkeAbstract:High-Resolution Imaging Science Experiment (HiRISE) imagery of the central Olympia Undae Dune Field in the north polar region of Mars shows a reticulate Dune pattern consisting of two sets of nearly orthogonal Dune crestlines, with apparent slipfaces on the primary crests, ubiquitous wind ripples, areas of coarse-grained wind ripples, and deflated interDune areas. Geomorphic evidence and Dune Field pattern analysis of Dune crest length, spacing, defect density, and orientation indicates that the pattern is complex, representing two constructional generations of Dunes. The oldest and best-organized generation forms the primary crestlines and is transverse to circumpolar easterly winds. Gross bed form-normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and NE winds and is reworking the older pattern. Mapping of secondary flow Fields over the Dunes indicates that the most recent transporting winds were from the NE. The younger pattern appears to represent an influx of sediment to the Dune Field associated with the development of the Olympia Cavi reentrant, with NE katabatic winds channeling through the reentrant. A model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow Fields shows that the development of the secondary pattern is controlled by the boundary condition of the older Dune topography.
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aeolian Dune interactions and Dune Field pattern formation white sands Dune Field new mexico
Sedimentology, 2010Co-Authors: R C Ewing, Gary KocurekAbstract:Pattern formation is a fundamental aspect of self-organization in Fields of bedforms. Time-series aerial photographs and airborne light detection and ranging show that fully developed, crescentic aeolian Dunes at White Sands, New Mexico, interact and the Dune pattern organizes in systematically similar ways as wind ripples and subaqueous Dunes and ripples. Documented interactions include: (i) merging; (ii) lateral linking; (iii) defect repulsion; (iv) bedform repulsion; (v) off-centre collision; (vi) defect creation; and (vii) Dune splitting. Merging and lateral linking are constructive interactions that give rise to a more organized pattern. Defect creation and bedform splitting are regenerative interactions that push the system to a more disorganized state. Defect/bedform repulsion and off-centre collision cause significant pattern change, but appear to be neutral in overall pattern development. Measurements of pattern parameters (number of Dunes, crest length, defect density, crest spacing and Dune height), Dune migration rates, and the type and frequency of Dune interactions within a 3500 m box transect from the upwind margin to the core of the Dune Field show that most pattern organization occurs within the upwind Field. Upwind dominance by constructive interactions yields to neutral and regenerative interactions in the Field centre. This spatial change reflects upwind line source and sediment availability boundary conditions arising from antecedent palaeo-lake topography. Pattern evolution is most strongly coupled to the pattern parameters of Dune spacing and defect density, such that spatially or temporally the frequency of bedform interactions decreases as the Dunes become further apart and have fewer defects.
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aeolian Dune Field self organization implications for the formation of simple versus complex Dune Field patterns
Geomorphology, 2005Co-Authors: Gary Kocurek, R C EwingAbstract:Abstract The interpretation of aeolian Dune-Field patterns as self-organizing complex systems is a new paradigm in which pattern evolution may be addressed. Computer simulations, supported by Field and experimental data, indicate that a given wind regime produces a simple Dune-Field pattern. Dune type and crest orientation are determined by wind regime and pattern ordering occurs through Dune–Dune interactions over time. Because Dunes reorient only at their crest terminations with a change in wind regime, the rate of formation of a new pattern of small Dunes is typically faster than the rate of reorientation of the existing pattern, resulting in the superposition of simple patterns to give rise to complex patterns. Complex patterns are distinct from spatial changes in a simple pattern, and from the type of superposition that characterizes compound/complex Dunes. Complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface.
Jon D Pelletier - One of the best experts on this subject based on the ideXlab platform.
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Controls on the large‐scale spatial variations of Dune Field properties in the barchanoid portion of White Sands Dune Field, New Mexico
Journal of Geophysical Research: Earth Surface, 2015Co-Authors: Jon D PelletierAbstract:Previous studies have shown that sediment fluxes and Dune sizes are a maximum near the upwind margin of the White Sands Dune Field and decrease, to first order, with increasing distance downwind. These patterns have alternatively been attributed to a shear-stress overshoot associated with a roughness transition localized at the upwind margin and to the influence of long-wavelength topography on the hydrology and hence erodibility of Dune Field sediments. I point out an issue that compromises the shear-stress overshoot model and further test the hypothesis that long-wavelength topographic variations, acting in concert with feedbacks among aerodynamic, granulometric, and geomorphic variables, control Dune Field properties at White Sands. Building upon the existing literature, I document that the mean and variability of grain sizes, sand dryness, aerodynamic roughness lengths, bed shear stresses, sediment fluxes, and ripple and Dune heights all achieve local maxima at the crests of the two most prominent scarps in the Dune Field, one coincident with the upwind margin and the other located 6–7 km downwind. Computational fluid dynamics (CFD) modeling predicts that bed shear stresses, erosion rates, and the supply of relatively coarse, poorly sorted sediments are localized at the two scarps due to flow line convergence, hydrology, and the spatially distributed adjustment of the boundary layer to variations in Dune size. As a result, the crests of the scarps have larger ripples due to the granulometric control of ripple size. Larger grain sizes and/or larger ripples lead to larger Dunes and hence larger values of bed shear stress in a positive feedback.
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controls on the large scale spatial variations of Dune Field properties in the barchanoid portion of white sands Dune Field new mexico
Journal of Geophysical Research, 2015Co-Authors: Jon D PelletierAbstract:Previous studies have shown that sediment fluxes and Dune sizes are a maximum near the upwind margin of the White Sands Dune Field and decrease, to first order, with increasing distance downwind. These patterns have alternatively been attributed to a shear-stress overshoot associated with a roughness transition localized at the upwind margin and to the influence of long-wavelength topography on the hydrology and hence erodibility of Dune Field sediments. I point out an issue that compromises the shear-stress overshoot model and further test the hypothesis that long-wavelength topographic variations, acting in concert with feedbacks among aerodynamic, granulometric, and geomorphic variables, control Dune Field properties at White Sands. Building upon the existing literature, I document that the mean and variability of grain sizes, sand dryness, aerodynamic roughness lengths, bed shear stresses, sediment fluxes, and ripple and Dune heights all achieve local maxima at the crests of the two most prominent scarps in the Dune Field, one coincident with the upwind margin and the other located 6–7 km downwind. Computational fluid dynamics (CFD) modeling predicts that bed shear stresses, erosion rates, and the supply of relatively coarse, poorly sorted sediments are localized at the two scarps due to flow line convergence, hydrology, and the spatially distributed adjustment of the boundary layer to variations in Dune size. As a result, the crests of the scarps have larger ripples due to the granulometric control of ripple size. Larger grain sizes and/or larger ripples lead to larger Dunes and hence larger values of bed shear stress in a positive feedback.
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multiscale bed form interactions and their implications for the abruptness and stability of the downwind Dune Field margin at white sands new mexico usa
Journal of Geophysical Research, 2014Co-Authors: Jon D Pelletier, Douglas J JerolmackAbstract:The downwind margin of White Sands Dune Field is an abrupt transition from mobile aeolian Dunes to a Dune-free vegetated surface. This margin is also relatively stable; over the past 60 years it has migrated several times more slowly than the slowest Dunes within the Dune Field, resulting in a zone of Dune coalescence, aggradation, and, along most of the margin, development of a Dune complex (i.e., Dunes superimposed on draas). Repeat terrestrial laser scanning surveys conducted over a 3 month period demonstrate that sediment fluxes within the Dune complex decrease on approach to the margin. Computational fluid dynamics modeling indicates that this decrease is due, in part, to a decrease in mean turbulent bed shear stress on the lee side of the Dune complex as a result of flow line divergence or sheltering of the lee-side Dunes by the stoss side of the Dune complex. Conservation of mass demands that this decrease in bed shear stress causes aggradation. We speculate that aggradation on the lee side of the Dune complex further enhances the sheltering effect in a positive feedback, contributing to the growth and/or maintenance of the Dune complex and a relatively abrupt and stable Dune Field margin. Our model and data add to a growing body of evidence that aeolian Dune Field patterns are influenced by feedbacks that occur at scales larger than individual Dunes.
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the effects of interDune vegetation changes on eolian Dune Field evolution a numerical modeling case study at jockey s ridge north carolina usa
Earth Surface Processes and Landforms, 2009Co-Authors: Jon D Pelletier, Helena Mitasova, Russell S Harmon, Margery F OvertonAbstract:Changes in vegetation cover within Dune Fields can play a major role in how Dune Fields evolve. To better understand the linkage between Dune Field evolution and interDune vegetation changes, we modified Werner's (Geology, 23, 1995: 1107–1110) Dune Field evolution model to account for the stabilizing effects of vegetation. Model results indicate that changes in the density of interDune vegetation strongly influence subsequent trends in the height and area of eolian Dunes. We applied the model to interpreting the recent evolution of Jockey's Ridge, North Carolina, where repeat LiDAR surveys and historical aerial photographs and maps provide an unusually detailed record of recent Dune Field evolution. In the absence of interDune vegetation, the model predicts that Dunes at Jockey's Ridge evolve towards taller, more closely-spaced, barchanoid Dunes, with smaller Dunes generally migrating faster than larger Dunes. Conversely, the establishment of interDune vegetation causes Dunes to evolve towards shorter, more widely-spaced, parabolic forms. These results provide a basis for understanding the increase in Dune height at Jockey's Ridge during the early part of the twentieth century, when interDune vegetation was sparse, followed by the decrease in Dune height and establishment of parabolic forms from 1953-present when interDune vegetation density increased. These results provide a conceptual model that may be applicable at other sites with increasing interDune vegetation cover, and they illustrate the power of using numerical modeling to model decadal variations in eolian Dune Field evolution. We also describe model results designed to test the relative efficacy of alternative strategies for mitigating Dune migration and deflation. Installing sand-trapping fences and/or promoting vegetation growth on the stoss sides of Dunes are found to be the most effective strategies for limiting Dune advance, but these strategies must be weighed against the desire of many park visitors to maintain the natural state of the Dunes. Copyright © 2009 John Wiley & Sons, Ltd.
Nicholas Lancaster - One of the best experts on this subject based on the ideXlab platform.
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decadal scale evolution of a small Dune Field keeler Dunes california 1944 2010
Geomorphology, 2013Co-Authors: Nicholas Lancaster, Grace MccarleyholderAbstract:Abstract Aerial photographs and satellite images have been used to document the evolution of a small ( 2 ) DuneField over the past 60–70 years. Over this period, the DuneField has undergone significant changes, including development of well defined linear and crescentic Dunes from an initial small area of partially vegetated Dunes, resulting in an increase in the area of the Dunes by a factor of 3 since 1944. The Dune Field continues to expand toward the southeast but its upwind margins are now experiencing significant erosion because the sand supply is now cut off by dust control measures in the source area and transport pathway. This study provides some information on the timescales of Dune development in a high-energy aeolian environment, which formerly experienced an abundant supply of sand, with rapid development of crescentic Dunes over a period of 20 years. The complexity of DuneField development is also highlighted, even on decadal timescales, and the important role of episodic sediment supply in forming new generations of Dunes. Periods of rapid DuneField change involving lagged input of additional sand from external sources appear to be linked to episodes of high flows in the Owens River, which is the main sediment source for the Keeler Dunes.
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determining soil moisture and sediment availability at white sands Dune Field new mexico from apparent thermal inertia data
Journal of Geophysical Research, 2010Co-Authors: S P Scheidt, Michael S Ramsey, Nicholas LancasterAbstract:[1] Determinations of soil moisture and sediment availability in arid regions are important indicators of local climate variability and the potential for future dust storm events. Data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer were used to derive the relationships among potential soil erosion, soil moisture, and thermal inertia (TI) at the spatial scale of aeolian landforms for the White Sands Dune Field between May 2000 and March 2008. Land surface apparent thermal inertia (ATI) data were used to derive an approximation of actual TI in order to estimate the wind threshold velocity ratio (WTR). The WTR is a ratio of the wind velocity thresholds at which soil erosion occurs for wet soil versus dry soil. The ASTER‐derived soil moisture retrievals and the changes through time at White Sands were interpreted to be driven primarily by precipitation, but the presence of a perched groundwater table may also influence certain areas. The sediment availability of Dunes, active playa surfaces and the margin of the alluvial fans to the west were determined to be consistently higher than the surrounding area. The sediment availability can be primarily explained by precipitation events and the number of dry days prior to the data acquisition. Other factors such as vegetation and the amount of surface crusting may also influence soil mobility, but these were not measured in the Field. This approach showed the highest modeled sediment availability values just days prior to the largest dust emission event at White Sands in decades. Such an approach could be extended to a global monitoring technique for arid land systems that are prone to dust storms and for other regional land surface studies in the Sahara.
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aeolian system sediment state theory and mojave desert kelso Dune Field example
Sedimentology, 1999Co-Authors: Gary Kocurek, Nicholas LancasterAbstract: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.
