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Sample records for aeolian dune sands

  1. Numerical study of turbulent flow over complex aeolian dune fields: the White Sands National Monument.

    PubMed

    Anderson, William; Chamecki, Marcelo

    2014-01-01

    The structure and dynamics of fully developed turbulent flows responding to aeolian dune fields are studied using large-eddy simulation with an immersed boundary method. An aspect of particular importance in these flows is the downwind migration of coherent motions associated with Kelvin-Helmholtz instabilities that originate at the dune crests. These instabilities are responsible for enhanced downward transport of high-momentum fluid via the so-called turbulent sweep mechanism. However, the presence of such structures and their role in determining the bulk characteristics of fully developed dune field sublayer aerodynamics have received relatively limited attention. Moreover, many existing studies address mostly symmetric or mildly asymmetric dune forms. The White Sands National Monument is a field of aeolian gypsum sand dunes located in the Tularosa Basin in southern New Mexico. Aeolian processes at the site result in a complex, anisotropic dune field. In the dune field sublayer, the flow statistics resemble a mixing layer: At approximately the dune crest height, vertical profiles of streamwise velocity exhibit an inflection and turbulent Reynolds stresses are maximum; below this, the streamwise and vertical velocity fluctuations are positively and negatively skewed, respectively. We evaluate the spatial structure of Kelvin-Helmholtz instabilities present in the dune field sublayer (shear length L(s) and vortex spacing Λ(x)) and show that Λ(x)=m(dune)L(s), where m(dune)≈7.2 in the different sections considered (for turbulent mixing layers, 7

  2. Optically stimulated luminescence dating of aeolian sand in the otindag dune field and holocene climate change

    USGS Publications Warehouse

    Zhou, Y.L.; Lu, H.Y.; Mason, J.; Miao, X.D.; Swinehart, J.; Goble, R.

    2008-01-01

    The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are obtained, and these ages provide a relatively complete and well-dated chronology for wet and dry variations in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ???2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world. ?? Science in China Press and Springer-Verlag GmbH 2008.

  3. A numerical study of turbulent flow over complex aeolian dune fields: the White Sands National Monument

    NASA Astrophysics Data System (ADS)

    Anderson, W. W.; Chamecki, M.; Kocurek, G.; Mohrig, D. C.

    2013-12-01

    The structure and dynamics of fully-developed turbulent flows responding to aeolian dune fields are studied using large-eddy simulation with an immersed boundary method. An aspect of particular importance in these flows is the downwind migration of coherent motions associated with Kelvin-Helmholtz instabilities which originate at the dune crests. These instabilities are responsible for enhanced downward transport of high momentum fluid via the so-called turbulent sweep mechanism. However, the presence of such structures and their role in determining the bulk characteristics of fully developed dune field sublayer aerodynamics has received relatively limited attention. Moreover, many existing studies address mostly symmetric or mildly asymmetric dune forms. The White Sands National Monument is a field of aeolian gypsum sand dunes located in the Tularosa Basin in southern New Mexico. Aeolian processes at the site result in a complex, anisotropic dune field. In the dune field sublayer, the flow statistics resemble a mixing layer: at approximately the dune crest height, vertical profiles of streamwise velocity exhibit an inflection and turbulent Reynolds stresses are maximum; below this, the streamwise and vertical velocity fluctuations are positively and negatively skewed, respectively. We evaluate the spatial structure of Kelvin-Helmholtz instabilities present in the dune field sublayer -- shear length, Ls, and vortex spacing, Lambda_x -- and show that Ls = m Lambda_x, where m is approximately 8 in the different sections considered (for turbulent mixing layers, 7 < m < 10, Rogers and Moser, 1994: Phys. Fluids A, 6, 903-922). These results guide discussion on the statistics of aerodynamic drag across the dunes; probability density functions of time-series of aerodynamic drag for the dunes are shown to exhibit skewness and variance much greater than values reported for turbulent boundary layer flow over an homogeneous roughness distribution. Thus, we propose that

  4. Temperature and humidity measurements within desert barchan sand dunes, relation to dune aeolian mobility and microbial growth

    NASA Astrophysics Data System (ADS)

    Louge, Michel; Hay, Anthony; Richer, Renee; Valance, Alexandre; Ould el Moctar, Ahmed; Xu, Jin; Abdul-Majid, Sara

    2013-04-01

    We present diurnal variations of temperature and humidity profiles below the surface of hyper-arid aeolian crescent-shaped "barchan" dunes in Qatar and Mauritania, measured using a thermal probe and a new ultra-sensitive capacitance instrument that we developed for this purpose. We also report long-term measurements from a probe sunk on the downwind avalanche face of a mobile Qatar barchan, recording temperature and humidity until it emerged on the upwind slope 15 months later. We interpret the data by modeling heat and moisture transfer at the surface in terms of measured net surface radiation, wind, and atmospheric conditions. We demonstrate the presence of microbes on sand grains within these mobile dunes using microscopic observations, fluorescence counts, metagenomic sequencing, and C12/C13 isotope analysis of carbon dioxide sampled below the surface. By determining how water activity grows with moisture adsorbed on these sands, we delimit regions within the dune where our instruments recorded humidity conducive to microbial growth. Finally, we compare the mobility of two adjacent Mauritania barchans having distinct surface grain size, shape, and depth humidity profiles. Armored by large grains on its surface, the smaller dune was more oblong. As a result, it lacked flow recirculation in its wake, trapped less aeolian sand downwind, and was much less mobile than its smaller size would suggest. This slower mobility led to greater humidity and cohesion at depth than the larger dune exposed to the same atmospheric and wind conditions.

  5. Turbulent Flow and Sand Dune Dynamics: Identifying Controls on Aeolian Sediment Transport

    NASA Astrophysics Data System (ADS)

    Weaver, C. M.; Wiggs, G.

    2007-12-01

    Sediment transport models are founded on cubic power relationships between the transport rate and time averaged flow parameters. These models have achieved limited success and recent aeolian and fluvial research has focused on the modelling and measurement of sediment transport by temporally varying flow conditions. Studies have recognised turbulence as a driving force in sediment transport and have highlighted the importance of coherent flow structures in sediment transport systems. However, the exact mechanisms are still unclear. Furthermore, research in the fluvial environment has identified the significance of turbulent structures for bedform morphology and spacing. However, equivalent research in the aeolian domain is absent. This paper reports the findings of research carried out to characterise the importance of turbulent flow parameters in aeolian sediment transport and determine how turbulent energy and turbulent structures change in response to dune morphology. The relative importance of mean and turbulent wind parameters on aeolian sediment flux was examined in the Skeleton Coast, Namibia. Measurements of wind velocity (using sonic anemometers) and sand transport (using grain impact sensors) at a sampling frequency of 10 Hz were made across a flat surface and along transects on a 9 m high barchan dune. Mean wind parameters and mass sand flux were measured using cup anemometers and wedge-shaped sand traps respectively. Vertical profile data from the sonic anemometers were used to compute turbulence and turbulent stress (Reynolds stress; instantaneous horizontal and vertical fluctuations; coherent flow structures) and their relationship with respect to sand transport and evolving dune morphology. On the flat surface time-averaged parameters generally fail to characterise sand transport dynamics, particularly as the averaging interval is reduced. However, horizontal wind speed correlates well with sand transport even with short averaging times. Quadrant

  6. Surface moisture feedback in modelled aeolian rippled sand strip and dune field patterns

    NASA Astrophysics Data System (ADS)

    Nield, J. M.

    2010-12-01

    Surface moisture plays a key role in controlling sediment availability and transport in aeolian systems which leads to the development of a diverse range of spatial patterns including transient sand strips on beaches with small temporal and spatial scales, and large-scale dune patterns dominated by wet interdune areas. By altering feedback response times between surface moisture and transport dynamics, these different patterns can be explored and modelled using a cellular automaton-based algorithm. This algorithm includes stochastic transport and mimics real-world behaviour, where surface moisture limits aeolian erosion, but a modest amount of moisture hardens the surface, increasing the elasticity of rebounding grains. Simulations allow for examination of different sediment availability scenarios which can be related to the developed internal stratigraphy of the modeled landscape. Results elucidate the controlling mechanism of surface moisture in sediment availability and highlight the importance of mutual feedback for developing diverse aeolian landscape patterns at different spatial and temporal scales.

  7. Inland aeolian deposits of the Iberian Peninsula: Sand dunes and clay dunes of the Duero Basin and the Manchega Plain. Palaeoclimatic considerations

    NASA Astrophysics Data System (ADS)

    Bernat Rebollal, M.; Pérez-González, A.

    2008-12-01

    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 Júcar 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 ( 14C-AMS). In this way, the aeolian activity and stabilisation

  8. Sand Flux Results for Aeolian Dunes at Current and Candidate Landing Sites on Mars

    NASA Astrophysics Data System (ADS)

    Chojnacki, M.; Urso, A.; Yingling, W.

    2015-12-01

    It is now known unambiguously that wind-driven bedform activity is occurring on Mars today. It has also been demonstrated the rapid aeolian abrasion of sedimentary deposits that potentially host ancient habitable environments may provide the best mechanism for exposing samples containing relatively undegraded organics (Farley et al. 2014). Thus, current processes operating on the surface of Mars are highly relevant to our understanding of the past. Here, we discuss new sand flux results of active dune across Mars, including several current and candidate landing sites with Meridiani Planum, Gale crater, Valles Marineris, and Mawrth Vallis. For this task, we have utilized multi-temporal images acquired annually by the HiRISE camera (25 cm/pixel) along with co-located HiRISE Digital Terrain Models. Falling dunes in Coprates Chasma (Mars 2020 candidate landing site) measuring 6-10 meters in height were detected migrating on average 0.5 m per Earth year, yielding crest fluxes of 3.1 m3 m-1 yr-1 (units hereafter assumed). Barchans near the MSL rover at Gale crater have slightly lower fluxes of 1.2, while earlier work in Endeavour crater, the current site of the Opportunity Rover, showed dome dunes with fluxes as high as 13 (average of 6.8; Chojnacki et al. 2015). New results of Mawrth Vallis (Mars 2020 candidate) dunes suggest these high rates are not uncommon, as barchans there possess average fluxes of 11.5. Assuming ripple reptation rates are 1/10th that of crest fluxes, total flux (saltation plus reptation) would range 3.2 to 12.7 m3 m-1 yr-1 for all sites studied herein. Active dunes and the abrasion susceptibility (Sa) of local rocks are relevant to assess how sand fluxes modify the landscape. Using the methodology and assumptions (Sa for basalt, mean trajectory height etc.) described in Bridges et al. (2012), we estimated abrasion rates of local basaltic bedrock. For example, sand blasting at Mawrth Vallis is estimated to produce 2-8 μm/yr for flat ground and 15

  9. Natural and human controls of the Holocene evolution of the beach, aeolian sand and dunes of Caesarea (Israel)

    NASA Astrophysics Data System (ADS)

    Roskin, J.; Sivan, D.; Shtienberg, G.; Roskin, E.; Porat, N.; Bookman, R.

    2015-12-01

    The study focuses on the Holocene appearance, chronology and drivers of beach sand deposition and inland aeolian sand transport around the Roman-Byzantine ruins of Caesarea, Israel. Beach sand, sand sheets, nebkha, linear and transverse dunes as well as parabolic and transverse interdunes along two transects were sampled in the current study down to their substrate. Sixteen new optically stimulated luminescence ages cluster at ∼5.9-3.3 ka, ∼1.2-1.1 ka (800-900 AD) and ∼190-120 years ago (1825-1895 AD) indicating times of middle and late Holocene sand sheet depositions and historical dune stabilization. The first age cluster indicates that beach sand accumulated when rates of global sea level rise declined around 6-5 ka. Until ∼4 ka sand sheets encroached up to 2.5 km inland. Historical and archaeological evidence points to sand mobilization since the first century AD. Sand sheets dating to 1.2-1.1 ka, coevally found throughout the dunefield represent sand stabilization due to vegetation reestablishment attributed to gradual and fluctuating decline in human activity from the middle Early Islamic period until the 10th century. Historical and chronological evidence of the existence of transverse and coppice dunes from the 19th century suggest that dunes only formed in the last few centuries. The study illustrates the initial role of natural processes, in this case decline in global sea level rise and the primary and later role of fluctuating human activity upon coastal sand mobility. The study distinguishes between sand sheets and dunes and portrays them as sensors of environmental changes.

  10. Recent Aeolian Dune Change on Mars

    NASA Technical Reports Server (NTRS)

    Bourke, M. C.; Edgett, K. S.; Cantor, B. A.

    2007-01-01

    Previous comparisons of Martian aeolian dunes in satellite images have not detected any change in dune form or position. Here, we show dome dunes in the north polar region that shrank and then disappeared over a period of 3.04 Mars years (5.7 Earth years), while larger, neighboring dunes showed no erosion or movement. The removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on Mars, but that any sand that is available for transport is likely to be moved. Dunes that show no evidence of change could be crusted, indurated. or subject to infrequent episodes of movement.

  11. Aeolian sand as a tool for understanding Mars: Thermal infrared remote sensing of volcaniclastic Mars-analog sand dunes in Christmas Lake Valley, Oregon, U.S.A.

    NASA Astrophysics Data System (ADS)

    Edgett, Kenneth S.

    1996-10-01

    INTRODUCTION: On Earth, aeolian sand dunes are used as tools of scientific inquiry. Holocene and Pleistocene dunes preserve clues about Quaternary climate variations and human activities ranging from Ice Age hunting practices to Twentieth Century warfare. Modern dunes contain the sedimentary textures and structures necessary for interpreting ancient sandstones, and they provide natural laboratories for investigation of aeolian physics and desertification processes. The dunes of Mars can likewise be used as scientific tools. Dunes provide relatively dust-free surfaces. From a remote sensing perspective, martian dunes have much potential for providing clues about surface mineralogy and the interaction between the surface and atmosphere. Such information can in turn provide insights regarding crust composition, volcanic evolution, present and past climate events, and perhaps weathering rates. The Mars Global Surveyor Thermal Emission Spectrometer (TES) is expected to reach the planet in September 1997. TES will provide 6 to 50 micrometer spectra of the martian surface at ground resolutions of 3 to 9 km. Sandy aeolian environments on Mars might provide key information about bedrock composition. To prepare for the TES investigation, I have been examining a thermal infrared image of a Mars-composition analog dune field in Christmas Lake Valley, Oregon. COMPOSITION AND GEOLOGIC SETTING: The "Shifting Sand Dunes" dune field is located at the eastern end of Christmas Lake Valley, in what was once the Pleistocene Fort Rock Lake [1]. Much of the sand that makes up the Shifting Sand Dunes dune field is reworked Mt. Mazama airfall from its terminal eruption 6,800 years ago, plus material deflated from the lake bed [1, 2]. The main constituents of the dunes are volcanic glass and devitrified glass fragments, plagioclase crystals, basalt lithic fragments, aggregates of silt and clay-size volcanic ash, pyroxenes, opaque oxide minerals (mostly magnetite), and trace occurrences of

  12. Avalanche grainflow on a simulated aeolian dune

    NASA Astrophysics Data System (ADS)

    Sutton, S. L. F.; McKenna Neuman, C.; Nickling, W.

    2013-09-01

    Avalanches maintain the slipface of aeolian dunes, which alters their airflow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel under wind velocities of 8-11 m s-1. Changes in slipface topography were observed photographically and measured utilizing a 3-D laser scanner with 1 mm2 spatial resolution. Avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32°) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed. This independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport.

  13. Aeolian sedimentary processes at the Bagnold Dunes, Mars: Implications for modern dune dynamics and sedimentary structures in the aeolian stratigraphic record of Mars

    NASA Astrophysics Data System (ADS)

    Ewing, Ryan C.; Bridges, Nathan T.; Sullivan, Rob; Lapotre, Mathieu G. A.; Fischer, Woodward W.; Lamb, Mike P.; Rubin, David M.; Lewis, Kevin W.; Gupta, Sanjeev

    2016-04-01

    Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under Martian conditions. In-situ observations of sand dunes (informally called the Bagnold Dunes) by Curiosity Rover in Gale Crater, Mars provide the first opportunity to make observations of dunes from the grain-to-dune scale thereby filling the gap in knowledge between theory and orbital observations and refining our understanding of the martian aeolian stratigraphic record. We use the suite of cameras on Curiosity, including Navigation Camera (Navcam), Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI), to make observations of the Bagnold Dunes. Measurements of sedimentary structures are made where stereo images are available. Observations indicate that structures generated by gravity-driven processes on the dune lee slopes, such as grainflow and grainfall, are similar to the suite of aeolian sedimentary structures observed on Earth and should be present and recognizable in Mars' aeolian stratigraphic record. Structures formed by traction-driven processes deviate significantly from those found on Earth. The dune hosts centimeter-scale wind ripples and large, meter-scale ripples, which are not found on Earth. The large ripples migrate across the depositional, lee slopes of the dune, which implies that these structures should be present in Mars' stratigraphic record and may appear similar to compound-dune stratification.The Mars Science Laboratory Curiosity Rover Team is acknowledged for their support of this work.

  14. Understanding early-stage dune development: morphodynamics of aeolian protodunes

    NASA Astrophysics Data System (ADS)

    Baddock, Matthew; Wiggs, Giles; Nield, Joanna

    2016-04-01

    For such a fundamental aspect of bedform development, the initiation and early-stage growth of sand dunes remain poorly understood. Protodunes are bedforms within the continuum of early-stage depositional aeolian features that exist between flat sand patches and small dunes. As transitory bedforms with the potential to develop into dunes, the detailed study of protodune morphodynamics can provide significant insights into nascent dune development. As part of a multi-annual study investigating bedform change through repeat morphological surveys of bedforms with differing maturity, measurements of near-surface airflow and sand transport were conducted over a protodune in a small Namibian barchan dune field. The protodune was approximately 85 m in length and 1 m high, and was without a slipface. Data show that over the course of a week, patterns of airflow and transport flux variation were linked with accretion at the crest, and erosion of the leeside edge showing an increase in protodune height, and providing evidence of the dune's vertical development. Surveys reveal the longer term evolution of the protodune, in the context of changes exhibited by nearby, fully developed barchan dunes, and long term monitoring of wind regime at the site.

  15. Booming Sand Dunes

    NASA Astrophysics Data System (ADS)

    Vriend, Nathalie

    "Booming" sand dunes are able to produce low-frequency sound that resembles a pure note from a music instrument. The sound has a dominant audible frequency (70-105 Hz) and several higher harmonics and may be heard from far distances away. A natural or induced avalanche from a slip face of the booming dune triggers the emission that may last for several minutes. There are various references in travel literature to the phenomenon, but to date no scientific explanation covered all field observations. This thesis introduces a new physical model that describes the phenomenon of booming dunes. The waveguide model explains the selection of the booming frequency and the amplification of the sound in terms of constructive interference in a confined geometry. The frequency of the booming is a direct function of the dimensions and velocities in the waveguide. The higher harmonics are related to the higher modes of propagation in the waveguide. The experimental validation includes quantitative field research at the booming dunes of the Mojave Desert and Death Valley National Park. Microphone and geophone recordings of the acoustic and seismic emission show a variation of booming frequency in space and time. The analysis of the sensor data quantifies wave propagation characteristics such as speed, dispersion, and nonlinear effects and allows the distinction between the source mechanism of the booming and the booming itself. The migration of sand dunes results from a complicated interplay between dune building, wind regime, and precipitation. The morphological and morphodynamical characteristics of two field locations are analyzed with various geophysical techniques. Ground-penetrating radar images the subsurface structure of the dunes and reveal a natural, internal layering that is directly related to the history of dune migration. The seismic velocity increases abruptly with depth and gradually increases with downhill position due to compaction. Sand sampling shows local

  16. Fortune Cookie Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-432, 25 July 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a field of small barchan sand dunes in the north polar region near 71.7oN, 51.3oW. Some of them are shaped like fortune cookies. The message these dunes provide: winds blow through this region from the lower right toward the upper left. The steep slip face slopes of these dunes, which point toward the upper left, indicate the wind direction. The scene is illuminated by sunlight from the upper right. The image is 3 km (1.9 mi) wide.

  17. Sand Dunes with Frost

    NASA Technical Reports Server (NTRS)

    2004-01-01

    9 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a suite of frost-covered sand dunes in the north polar region of Mars in early spring, 2004. The dunes indicate wind transport of sand from left to right (west to east). These landforms are located near 78.1oN, 220.8oW. This picture is illuminated by sunlight from the lower left and covers an area about 3 km (1.9 mi) across.

  18. Stratigraphic Architecture of Aeolian Dune Interactions

    NASA Astrophysics Data System (ADS)

    Brothers, S. C.; Kocurek, G.

    2015-12-01

    Dune interactions, which consist of collisions and detachments, are a known driver of changing dune morphology and provide the dynamics for field-scale patterning. Although interactions are ubiquitous in modern dune fields, the stratigraphic record of interactions has not been explored. This raises the possibility that an entire class of signature architectures of bounding surfaces and cross-strata has gone misidentified or unrecognized. A unique data set for the crescentic dunes of the White Sands Dune Field, New Mexico, allows for the coupling of dune interactions with their resultant stratigraphic architecture. Dune interactions are documented by a decadal time-series of aerial photos and LiDAR-derived digital elevation models. Plan-view cross-strata in interdune areas provide a record tying past dune positions and morphologies to the current dunes. Three-dimensional stratigraphic architecture is revealed by imaging of dune interiors with ground-penetrating radar. The architecture of a dune defect merging with a target dune downwind consists of lateral truncation of the target dune set by an interaction bounding surface. Defect cross-strata tangentially approach and downlap onto the surface. Downwind, the interaction surface curves, and defect and adjacent target dune sets merge into a continuous set. Predictable angular relationships reflect field-scale patterns of dune migration direction and approach angle of migrating defects. The discovery of interaction architectures emphasizes that although dunes appear as continuous forms on the surface, they consist of discrete segments, each with a distinct morphodynamic history. Bedform interactions result in the morphologic recombination of dune bodies, which is manifested stratigraphically within the sets of cross-strata.

  19. Sand Dunes in Hellas

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-537, 7 November 2003

    The smooth, rounded mounds in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture are sand dunes. The scene is located in southern Hellas Planitia and was acquired in mid-southern autumn, the ideal time of year for Hellas imaging. Sunlight illuminates the scene from the upper left. These dunes are located near 49.1oS, 292.6oW. The picture covers an area 3 km (1.9 mi) wide.

  20. Sand Dunes, Afghanistan

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This ASTER image covers an area of 10.5 x 15 km in southern Afghanistan and was acquired on August 20, 2000. The band 3-2-1 composite shows part of an extensive field of barchan sand dunes south of Kandahar. The shape of the dunes indicates that the prevailing wind direction is from the west. The image is located at 30.7 degrees north latitude and 65.7 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  1. Giant aeolian dune size determined by the average depth of the atmospheric boundary layer.

    PubMed

    Andreotti, Bruno; Fourrière, Antoine; Ould-Kaddour, Fouzia; Murray, Brad; Claudin, Philippe

    2009-02-26

    Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.

  2. Giant aeolian dune size determined by the average depth of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Claudin, P.; Fourrière, A.; Andreotti, B.; Murray, A. B.

    2009-12-01

    Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.

  3. Vegetation and substrate properties of aeolian dune fields in the Colorado River corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Draut, Amy E.

    2011-01-01

    This report summarizes vegetation and substrate properties of aeolian landscapes in the Colorado River corridor through Grand Canyon, Arizona, in Grand Canyon National Park. Characterizing these parameters provides a basis from which to assess future changes in this ecosystem, including the spread of nonnative plant species. Differences are apparent between aeolian dune fields that are downwind of where modern controlled flooding deposits new sandbars (modern-fluvial-sourced dune fields) and those that have received little or no new windblown sand since river regulation began in the 1960s (relict-fluvial-sourced dune fields). The most substantial difference between modern- and relict-fluvial-sourced aeolian dune fields is the greater abundance of biologic soil crust in relict dune fields. These findings can be used with similar investigations in other geomorphic settings in Grand Canyon and elsewhere in the Colorado River corridor to evaluate the health of the Colorado River ecosystem over time.

  4. Alluvial Fans on Dunes in Kaiser Crater Suggest Niveo-Aeolian and Denivation Processes on Mars

    NASA Technical Reports Server (NTRS)

    Bourke, M. C.

    2005-01-01

    On Earth, cold region sand dunes often contain inter-bedded sand, snow, and ice. These mixed deposits of wind-driven snow, sand, silt, vegetal debris, or other detritus have been termed Niveo-aeolian deposits. These deposits are often coupled with features that are due to melting or sublimation of snow, called denivation features. Snow and ice may be incorporated into dunes on Mars in three ways. Diffusion of water vapour into pore spaces is the widely accepted mechanism for the accretion of premafrost ice. Additional mechanisms may include the burial by sand of snow that has fallen on the dune surface or the synchronous transportation and deposition of snow, sand and ice. Both of these mechanisms have been reported for polar dunes on Earth. Niveo-aeolian deposits in polar deserts on Earth have unique morphologies and sedimentary structures that are generally not found in warm desert dunes. Recent analysis of MOC-scale data have found evidence for potential niveo-aeolian and denivation deposits in sand dunes on Mars.

  5. Aeolian Sand Transport with Collisional Suspension

    NASA Technical Reports Server (NTRS)

    Jenkins, James T.; Pasini, Jose Miguel; Valance, Alexandre

    2004-01-01

    Aeolian transport is an important mechanism for the transport of sand on Earth and on Mars. Dust and sand storms are common occurrences on Mars and windblown sand is responsible for many of the observed surface features, such as dune fields. A better understanding of Aeolian transport could also lead to improvements in pneumatic conveying of materials to be mined for life support on the surface of the Moon and Mars. The usual view of aeolian sand transport is that for mild winds, saltation is the dominant mechanism, with particles in the bed being dislodged by the impact of other saltating particles, but without in-flight collisions. As the wind becomes stronger, turbulent suspension keeps the particles in the air, allowing much longer trajectories, with the corresponding increase in transport rate. We show here that an important regime exists between these two extremes: for strong winds, but before turbulent suspension becomes dominant, there is a regime in which in-flight collisions dominate over turbulence as a suspension mechanism, yielding transport rates much higher than those for saltation. The theory presented is based on granular kinetic theory, and includes both turbulent suspension and particle-particle collisions. The wind strengths for which the calculated transport rates are relevant are beyond the published strengths of current wind tunnel experiments, so these theoretical results are an invitation to do experiments in the strong-wind regime. In order to make a connection between the regime of saltation and the regime of collisional suspension, it is necessary to better understand the interaction between the bed and the particles that collide with it. This interaction depends on the agitation of the particles of the bed. In mild winds, collisions with the bed are relatively infrequent and the local disturbance associated with a collision can relax before the next nearby collision. However, as the wind speed increases, collision become more frequent

  6. Sand dunes as migrating strings

    NASA Astrophysics Data System (ADS)

    Guignier, L.; Niiya, H.; Nishimori, H.; Lague, D.; Valance, A.

    2013-05-01

    We develop a reduced complexity model for three-dimensional sand dunes, based on a simplified description of the longitudinal and lateral sand transport. The spatiotemporal evolution of a dune migrating over a nonerodible bed under unidirectional wind is reduced to the dynamics of its crest line, providing a simple framework for the investigation of three-dimensional dunes, such as barchan and transverse dunes. Within this model, we derive analytical solutions for barchan dunes and investigate the stability of a rectilinear transverse dune against lateral fluctuations. We show, in particular, that the latter is unstable only if the lateral transport on the dune slip face prevails over that on the upwind face. We also predict the wavelength and the characteristic time that control the subsequent evolution of an unstable transverse dune into a wavy ridge and the ultimate fragmentation into barchan dunes.

  7. Sand dunes as migrating strings.

    PubMed

    Guignier, L; Niiya, H; Nishimori, H; Lague, D; Valance, A

    2013-05-01

    We develop a reduced complexity model for three-dimensional sand dunes, based on a simplified description of the longitudinal and lateral sand transport. The spatiotemporal evolution of a dune migrating over a nonerodible bed under unidirectional wind is reduced to the dynamics of its crest line, providing a simple framework for the investigation of three-dimensional dunes, such as barchan and transverse dunes. Within this model, we derive analytical solutions for barchan dunes and investigate the stability of a rectilinear transverse dune against lateral fluctuations. We show, in particular, that the latter is unstable only if the lateral transport on the dune slip face prevails over that on the upwind face. We also predict the wavelength and the characteristic time that control the subsequent evolution of an unstable transverse dune into a wavy ridge and the ultimate fragmentation into barchan dunes.

  8. Dune-like dynamic of Martian Aeolian large ripples

    NASA Astrophysics Data System (ADS)

    Silvestro, S.; Vaz, D. A.; Yizhaq, H.; Esposito, F.

    2016-08-01

    Martian dunes are sculpted by meter-scale bed forms, which have been interpreted as wind ripples based on orbital data. Because aeolian ripples tend to orient and migrate transversely to the last sand-moving wind, they have been widely used as wind vanes on Earth and Mars. In this report we show that Martian large ripples are dynamically different from Earth's ripples. By remotely monitoring their evolution within the Mars Science Laboratory landing site, we show that these bed forms evolve longitudinally with minimal lateral migration in a time-span of ~ six terrestrial years. Our observations suggest that the large Martian ripples can record more than one wind direction and that in certain cases they are more similar to linear dunes from a dynamic point of view. Consequently, the assumption of the transverse nature of the large Martian ripples must be used with caution when using these features to derive wind directions.

  9. Investigation of Reversing Sand Dunes at the Bruneau Dunes, Idaho, as Analogs for Features on Mars

    NASA Astrophysics Data System (ADS)

    Zimbelman, J. R.; Scheidt, S. P.

    2012-12-01

    The Bruneau Dunes in south-central Idaho include several large reversing sand dunes located within a cut-off meander of the Snake River. These dunes include the largest single-structured sand dune present in North America. Wind records from the Remote Automated Weather Station (RAWS) installation at the Mountain Home Air Force Base, which is ~21 km NW of the Bruneau Dunes, have proved to be very helpful in assessing the regional wind patterns at this section of the western Snake River Plains province; a bimodal wind regime is present, with seasonal changes of strong (sand-moving) winds blowing from either the northwest or the southeast. During April of 2011, we obtained ten precision topographic surveys across the southernmost reversing dune using a Differential Global Positioning System (DGPS). The DGPS data document the shape of the dune going from a low, broad sand ridge at the southern distal end of the dune to the symmetrically shaped 112-m-high central portion of the dune, where both flanks of the dune consist of active slopes near the angle of repose. These data will be useful in evaluating the reversing dune hypothesis proposed for enigmatic features on Mars called Transverse Aeolian Ridges (TARs), which could have formed either as large mega-ripples or small sand dunes. The symmetric profiles across TARs with heights greater than 1 m are more consistent with measured profiles of reversing sand dunes than with measured profiles of mega-ripples (whose surfaces are coated by large particles ranging from coarse sand to gravel, moved by saltation-induced creep). Using DGPS to monitor changes in the three-dimensional location of the crests of the reversing dunes at the Bruneau Dunes should provide a means for estimating the likely timescale for changes of TAR crests if the Martian features are indeed formed in the same manner as reversing sand dunes on Earth.

  10. Southern high latitude dune fields on Mars: Morphology, aeolian inactivity, and climate change

    USGS Publications Warehouse

    Fenton, L.K.; Hayward, R.K.

    2010-01-01

    In a study area spanning the martian surface poleward of 50?? S., 1190 dune fields have been identified, mapped, and categorized based on dune field morphology. Dune fields in the study area span ??? 116400km2, leading to a global dune field coverage estimate of ???904000km2, far less than that found on Earth. Based on distinct morphological features, the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding. The six dune field classes occur in specific latitude zones, with a sequence of reduced activity and degradation progressing poleward. In particular, the first signs of stabilization appear at ???60?? S., which broadly corresponds to the edge of high concentrations of water-equivalent hydrogen content (observed by the Neutron Spectrometer) that have been interpreted as ground ice. This near-surface ground ice likely acts to reduce sand availability in the present climate state on Mars, stabilizing high latitude dunes and allowing erosional processes to change their morphology. As a result, climatic changes in the content of near-surface ground ice are likely to influence the level of dune activity. Spatial variation of dune field classes with longitude is significant, suggesting that local conditions play a major role in determining dune field activity level. Dune fields on the south polar layered terrain, for example, appear either potentially active or inactive, indicating that at least two generations of dune building have occurred on this surface. Many dune fields show signs of degradation mixed with crisp-brinked dunes, also suggesting that more than one generation of dune building has occurred since they originally formed. Dune fields superposed on early and late Amazonian surfaces provide potential upper age limits of ???100My on the south polar layered deposits and ???3Ga elsewhere at high latitudes. No craters are present on any identifiable dune

  11. 3D numerical simulation of the evolutionary process of aeolian downsized crescent-shaped dunes

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaosi; Zhang, Yang; Wang, Yuan; Li, Min

    2016-06-01

    A dune constitutive model was coupled with a large eddy simulation (LES) with the Smagorinsky subgrid-scale (SGS) model to accurately describe the evolutionary process of dunes from the macroscopic perspective of morphological dynamics. A 3D numerical simulation of the evolution of aeolian downsized crescent-shaped dunes was then performed. The evolution of the 3D structure of Gaussian-shaped dunes was simulated under the influence of gravity modulation, which was the same with the vertical oscillation of the sand bed to adjust the threshold of sand grain liftoff in wind tunnel experiments under the same wind speed. The influence of gravity modulation intensity on the characteristic scale parameter of the dune was discussed. Results indicated that the crescent shape of the dune was reproduced with the action of gravity during regulation of the saturation of wind-sand flow at specific times. The crescent shape was not dynamically maintained as time passed, and the dunes dwindled until they reached final decomposition because of wind erosion. The height of the dunes decreased over time, and the height-time curve converged as the intensity of modulation increased linearly. The results qualitatively agreed with those obtained from wind tunnel experiments.

  12. Element geochemical analysis of the contribution of aeolian sand to suspended sediment in desert stream flash floods.

    PubMed

    Jia, Xiaopeng; Wang, Haibing

    2014-01-01

    The interaction of wind and water in semiarid and arid areas usually leads to low-frequency flash flood events in desert rivers, which have adverse effects on river systems and ecology. In arid zones, many aeolian dune-fields terminate in stream channels and deliver aeolian sand to the channels. Although aeolian processes are common to many desert rivers, whether the aeolian processes contribute to fluvial sediment loss is still unknown. Here, we identified the aeolian-fluvial cycling process responsible for the high rate of suspended sediment transport in the Sudalaer desert stream in the Ordos plateau of China. On the basis of element geochemistry data analysis, we found that aeolian sand was similar to suspended sediment in element composition, which suggests that aeolian sand contributes to suspended sediment in flash floods. Scatter plots of some elements further confirm that aeolian sand is the major source of the suspended sediment. Factor analysis and the relation between some elements and suspended sediment concentration prove that the greater the aeolian process, the higher the suspended sediment concentration and the greater the contribution of aeolian sand to suspended sediment yield. We conclude that aeolian sand is the greatest contributor to flash floods in the Sudalaer desert stream.

  13. Element Geochemical Analysis of the Contribution of Aeolian Sand to Suspended Sediment in Desert Stream Flash Floods

    PubMed Central

    Wang, Haibing

    2014-01-01

    The interaction of wind and water in semiarid and arid areas usually leads to low-frequency flash flood events in desert rivers, which have adverse effects on river systems and ecology. In arid zones, many aeolian dune-fields terminate in stream channels and deliver aeolian sand to the channels. Although aeolian processes are common to many desert rivers, whether the aeolian processes contribute to fluvial sediment loss is still unknown. Here, we identified the aeolian-fluvial cycling process responsible for the high rate of suspended sediment transport in the Sudalaer desert stream in the Ordos plateau of China. On the basis of element geochemistry data analysis, we found that aeolian sand was similar to suspended sediment in element composition, which suggests that aeolian sand contributes to suspended sediment in flash floods. Scatter plots of some elements further confirm that aeolian sand is the major source of the suspended sediment. Factor analysis and the relation between some elements and suspended sediment concentration prove that the greater the aeolian process, the higher the suspended sediment concentration and the greater the contribution of aeolian sand to suspended sediment yield. We conclude that aeolian sand is the greatest contributor to flash floods in the Sudalaer desert stream. PMID:25089295

  14. Armoring and vertical sorting in aeolian dune fields

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Narteau, Clément; Rozier, Olivier

    2016-04-01

    Unlike ripples, there are only few numerical studies on grain-size segregation at the scale of dunes in aeolian environments. Here we use a cellular automaton model to analyze vertical sorting in granular mixtures under steady unidirectional flow conditions. We investigate the feedbacks between dune growth and the segregation mechanisms by varying the size of coarse grains and their proportion within the bed. We systematically observe the development of a horizontal layer of coarse grains at the top of which sorted bed forms may grow by amalgamation. The formation of such an armor layer controls the overall sediment transport and availability. The emergence of dunes and the transition from barchan to transverse dune fields depend only on the grain size distribution of the initial sediment layer. As confirmed by observation, this result indicates that armor layers should be present in most arid deserts, where they are likely to control dune morphodynamics.

  15. Facies architecture and stratigraphic evolution of aeolian dune and interdune deposits, Permian Caldeirão Member (Santa Brígida Formation), Brazil

    NASA Astrophysics Data System (ADS)

    Jones, Fábio Herbert; Scherer, Claiton Marlon dos Santos; Kuchle, Juliano

    2016-05-01

    The Permian Caldeirão Member (Santa Brígida Formation), located in the Tucano Central Basin, northeast region of Brazil, is characterized by a sandstone succession of aeolian origin that comprises the preserved deposits of dunes and interdunes. Grainflow and translatent wind-ripple strata, and frequent presence of reactivation surface, compose the cross-bedding of crescent aeolian dune deposits. The aeolian cross-strata show a mean dip toward the ENE. In places, interlayered with dune cross-beds, occur interdune units composed of facies indicative of dry, damp and wet condition of the substrate, suggesting spatial and/or temporal variations in the moisture content of the interdune accumulation surface. The presence of NNW current ripple cross-lamination in wet interdune areas indicates streamflows confined to interdune corridors and oriented perpendicular to aeolian transport direction. Lenses of damp and wet interdune strata exhibit mainly interdigitated and transitional relationships with the toe-sets of overlying aeolian dune units in sections parallel to aeolian transport, indicating that dune migration was contemporaneous with accumulation in adjacent interdunes. Lateral variations in the preserved thickness of the interdune units and the associated rare occurrence of abrupt and erosive contacts between interdune and overlying dune sets, suggest temporal variations in the angle of dune and interdune climb that may be related to high-frequency changes in water table position. Four stratigraphic intervals in the Caldeirão Member can be identified, two intervals showing cross-bedding of aeolian dunes without wet interdune areas and two intervals exhibiting aeolian dunes separated by wet interdune areas, marking the transition between dry aeolian systems (Intervals I and III) and wet aeolian systems (Intervals II and IV). The temporal alternations between dry and wet aeolian systems reflect changes in the availability of dry sand and/or the rate in the water

  16. 2008 Weather and Aeolian Sand-Transport Data from the Colorado River Corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Draut, Amy E.; Sondossi, Hoda A.; Hazel, Joseph E.; Andrews, Timothy; Fairley, Helen C.; Brown, Christopher R.; Vanaman, Karen M.

    2009-01-01

    This report presents measurements of weather parameters and aeolian (windblown) sand transport made in 2008 near selected archaeological sites in the Colorado River corridor through Grand Canyon, Ariz. The quantitative methods and data discussed here form a basis for monitoring ecosystem processes that affect archeological-site stability. Combined with forthcoming work to evaluate landscape evolution at nearby archaeological sites, these data can be used to document the relationship between physical processes, including weather and aeolian sand transport, and their effects on the physical integrity of archaeological sites. Data collected in 2008 reveal event- and seasonal-scale variations in rainfall, wind, temperature, humidity, and barometric pressure. Broad seasonal changes in aeolian sediment flux are also apparent at most study sites. The continuation of monitoring that began in 2007, and installation of equipment at several new sites in early 2008, allowed evaluation of the effects of the March 2008 high-flow experiment (HFE) on aeolian sand transport. At two of the nine sites studied, spring and summer winds reworked 2008 HFE sandbars to form new aeolian dunes, at which sand moved inland toward larger, well-established dune fields. At the other seven study sites, neither dune formation nor enhanced sand transport after the HFE were observed. At several of those sites, dominant wind directions in spring 2008 were not oriented such that much HFE sand would have moved inland; at other sites, lack of increased inland sand flux is attributable to lack of sandbar enlargement near the study sites or to inhibition of sand movement by vegetation or local topography.

  17. A bedload trap for aeolian sand transport

    NASA Astrophysics Data System (ADS)

    Swann, C.; Sherman, D. J.

    2013-12-01

    This paper describes a bedload trap designed to separate bedload from saltation load in aeolian environments. The trap is installed below the sand surface and features a chimney that can be adjusted to the height of the surface. The chimney houses an internal wall to separate saltation load from bedload. Bedload particles are funneled to a piezo-electric sensor that converts grain impacts to voltages that can be sampled at very high frequencies (44,000 Hz in this example). Grains are then collected in a container that is easily retrieved so that sand samples can be obtained for weighing and subsequent grain size analysis. An algorithm to isolate single grain impacts is described. The version of the trap presented here is intended for the study of the initiation of grain motion.

  18. Aeolian Sand Transport by Boundary Layer Turbulence

    NASA Astrophysics Data System (ADS)

    Baas, A. C.

    2007-12-01

    The erratic and intermittent nature of wind-driven sand transport challenges our current transport models, which lack physical mechanisms for explaining and taking into account this spatio-temporal variability. This paper presents a collective overview of results from investigations into the nature of spatio-temporal variability in sand transport generally, and the formation and behaviour of aeolian streamers specifically. This includes three principal studies. First, the results of field investigations into the formation and behaviour of aeolian streamers in coastal and desert environments, where spatio-temporal transport variability and associated turbulence characteristics were assessed with an extensive instrument array. Streamers were measured with a transverse array of Safires, while the wind field and associated turbulent structures were monitored with cup-anemometry and a rake of hot-film probes. Second, these field data were used to assess the statistical trends in transport variability as a function of spanwise scale of measurement and the temporal scale of time-averaging transport rates. Third, spectral wavelet analysis of high-frequency collocated wind speed (hot- film probes) and transport flux (Safires) time-series revealed distinct forcing-response regimes at different temporal scales. The transitions between these regimes and their ranges compare favourably with physically meaningful scales, such as the minimum temporal scale of saltation response to wind speed fluctuations, and the integral time-scale of the observed internal boundary layer turbulence dynamics. The paper concludes with a tentative conceptual framework that attempts to integrate the results and insights from these studies towards an improved understanding of aeolian sediment transport processes.

  19. Crest line minimal model for sand dune

    NASA Astrophysics Data System (ADS)

    Guignier, Lucie; Valance, Alexandre; Lague, Dimitri

    2013-04-01

    In desert, complex patterns of dunes form. Under unidirectional wind, transverse rectilinear dunes or crescent shaped dunes called barchan dunes can appear, depending on the amount of sediment available. Most rectilinear transverse sand dunes are observed to fragment, for example at White Sands (New Mexico, United States of America) or Walvis Bay (Namibia). We develop a reduced complexity model to investigate the morphodynamics of sand dunes migrating over a non-erodible bed under unidirectional wind. The model is simply based on two physical ingredients, namely, the sand capture process at the slip face and the cross-wind sand transport. The efficiency of the sand capture process is taken to be dependent of the dune height and lateral diffusion is considered on both the windward and lee sides of the dune. In addition, the dune cross section is assumed to be scale invariant and is approximated by a triangular shape. In this framework, the dune dynamics is reduced to the motion of a string representing the dune crest line and is expressed as a set of two coupled nonlinear differential equations. This simple model reveals its ability to reproduce basic features of barchan and transverse dunes. Analytical predictions are drawn concerning dune equilibrium shape, stability and long-term dynamics. We derive, in particular, analytical solutions for barchan dunes, yielding explicit relationships between their shape and the lateral sand diffusion; and analytical predictions for the migration speed and equilibrium sand flux. A stability analysis of a rectilinear transverse dune allows us to predict analytically the wavelength emerging from fluctuations of the dune crest. We also determine the characteristic time needed for the rectilinear dune to fragment into a multitude of barchan dunes. These outcomes show that extremely simple ingredients can generate complex patterns for migrating dunes. From several dune field data, we are able to determine values of the model

  20. The sedimentary structure of linear sand dunes

    PubMed

    Bristow; Bailey; Lancaster

    2000-07-06

    Linear sand dunes--dunes that extend parallel to each other rather than in star-like or crescentic forms--are the most abundant type of desert sand dune. But because their development and their internal structure are poorly understood, they are rarely recognized in the rock record. Models of linear dune development have not been able to take into account the sub-surface structure of existing dunes, but have relied instead either on the extrapolation of short-term measurements of winds and sediment transport or on observations of near-surface internal sedimentary structures. From such studies, it has not been clear if linear dunes can migrate laterally. Here we present images produced by ground penetrating radar showing the three-dimensional sedimentary structure of a linear dune in the Namib sand sea, where some of the world's largest linear dunes are situated. These profiles show clear evidence for lateral migration in a linear dune. Moreover, the migration of a sinuous crest-line along the dune produces divergent sets of cross-stratification, which can become stacked as the dune height increases, and large linear dunes can support superimposed dunes that produce stacked sets of trough cross-stratification. These clear structural signatures of linear dunes should facilitate their recognition in geological records.

  1. Sedimentological, Mineralogical and Geochemical Characterization of Sand Dunes in Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Benaafi, Mohammed; Abdullatif, Osman

    2014-05-01

    Sedimentological, mineralogical, morphological and geochemical studies of sand dunes from ten locations in Saudi Arabia were conducted in order to determine the differences between them and to find out the provenance and tectonic setting of these sand dunes. Sixty seven samples were collected from different sand dunes types ranging in morphology from linear, barchans, parabolic to stars dunes. In overall, the sand dunes are fine to coarse grained mean grain size, moderately sorted, near symmetrical skewness with mesokurtic distribution characterized sand dunes in most locations. The sand dunes grains are subrounded in all locations except in the Red sea, Qassim, central Arabia and the eastern province which showed sub-angular grains. The main mineral compositions of studied aeolian sand dunes are quartz, feldspar, calcite, and mica. Quartz is the dominant mineral in locations with significant amount of feldspars and mica in Najran, Red sea and Central Arabia locations. Moreover, calcite is present in Sakaka and NW Empty Quarter (Jafurah). Basement related sand dunes in Najran, Central Arabia and Red sea locations are sub-mature in terms of their mineralogical maturity. Whereas, sand dunes in other locations are texturally mature except those from the Red sea which showed sub-mature sand. The sands are classified as quartz arenite, except in the basement related sand dunes in Najran, central Arabia and the Red sea are ranging from sub-arkose, sub-litharenite and lithraenite. Morphologically, parallel to sub-parallel sand ridges with NE-SW orientation occurred in east and north parts of Empty Quarter (Najran and Jafurah) and NW-SE orientation in Dahna and Nafud deserts in central and north regions of Saudi Arabia. Parabolic sand dunes characterized the Nafud desert (Hail, Sakaka, Tayma locations). Barchans and star sand dunes characterize the Empty Quarter (Jafurah). Major, trace, and rare earth elements studies were carried out to determine the composition

  2. A Comparative Analysis of Barchan Dunes in the Intra-Crater Dune Fields and the North Polar Sand Sea

    NASA Technical Reports Server (NTRS)

    Bourke, M. C.; Balme, M.; Zimbelman, J.

    2004-01-01

    Martian sand dunes have the potential to contribute data on geological history through a study of their form. Recognition of the characteristics of both recent and ancient dunes is the first step towards understanding the present as well as past aeolian systems, and by proxy, climatic conditions on Mars. Dunes studied in detail in Viking 1 and 2 Orbiter images have been classified as barchan, barchanoid, transverse, and complex. Regionally, they are concentrated in four locations: The North and South Polar regions, in intra crater dune fields and in troughs and valleys. Here we present the results of a morphometric analysis of barchan dunes in two of these locations: the North Polar Sand Sea (NPSS) and intra-crater dunes.

  3. Meso-scale modelling of aeolian sediment input to coastal dunes

    NASA Astrophysics Data System (ADS)

    Delgado-Fernandez, Irene

    2011-07-01

    The collection of a time series coupling hourly wind data (speed and direction) with sand transport over months has provided new insights into the dynamics of transport events that input sediment to the foredune at Greenwich Dunes, Prince Edward Island National Park, Canada. This paper summarises the key aspects of aeolian sediment movement for a period of 9 months and presents a modelling approach for resolving aeolian transport to coastal dunes at the meso-scale. The main hypothesis of the modelling approach is that a small number of key factors control both the occurrence and the magnitude of transport events. Thresholds associated with these factors may be used to filter the time series and isolate potential transport periods over the year. The impacts of nearshore processes are included in the approach as part of the dynamics of coastal dunes, as are supply-limiting factors and trade-offs between fetch distances, angle of wind approach, and beach dimensions. A simple analytical procedure, based on previously published equations, is carried out to assess the general viability of the conceptual approach. Results show that the incorporation of moisture and fetch effects in the calculation of transport for isolated potential transport periods result in improved predictions of sediment input to the dune. Net changes, measured with three different techniques, suggest that survey data with coarse temporal resolution underestimates the amount of sand input to the dune, because sediment is often removed from the embryo dune and foredune by other processes such as wave scarping. Predictions obtained by the proposed modelling approach are of the same order of magnitude as measured deposition and much less than predicted by models based solely on wind speed and direction. Areas for improvement and alternative modelling approaches, such as probabilistic approaches similar to weather forecasting, are covered in the discussion.

  4. Hematite Outlier and Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 4 December 2003

    This image shows a crater just south of the edge of the famous hematite-bearing surface, which is visible in the context image as a smooth area to the north. The crater has two features of immediate note. The first is a layered mound in the north part of the crater floor. This mound contains hematite, and it is an outlying remnant of the greater deposits to the north that have otherwise completely disappeared in this crater. The second feature is a dune field in the center of the crater floor, with dark dunes indicating winds from the northwest. The dunes grade into a dark sand sheet with no coherent structure, indicating that the sand layer thins out to the south and east.

    Image information: VIS instrument. Latitude -4.4, Longitude 357.3 East (2.7 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  5. Debris Flow Gullies at the Great Kobuk Sand Dunes, Alaska: Implications for Analogous Features on Mars

    NASA Astrophysics Data System (ADS)

    Hooper, D. M.; Dinwiddie, C. L.; Mcginnis, R. N.; Smart, K. J.; Roberts, M.

    2011-12-01

    Debris flows with fresh-appearing gullies or erosion tracks occur on the slopes of several mid- to high-latitude dune fields in both Martian hemispheres. These features originate in alcoves near dune crests, become channelized down lee faces, and terminate with depositional fans. They bear a striking resemblance to small meltwater-induced debris flows observed on the lee slopes of large dunes at the 67 degrees N latitude Great Kobuk Sand Dunes (GKSD), Kobuk Valley National Park, Alaska. The high-latitude, cold-climate GKSD are an optimal terrestrial system within which to conduct a Mars analog study focused on understanding the integrated factors that cause alluvial debris flows to initiate on the lee slopes of aeolian dunes. Debris flow processes in the GKSD are activated by seasonal thawing and consist of a mixture of sand and liquid water cascading down the dune slipface. A distinguishing environmental attribute that separates cold-climate dune fields from temperate and warm-climate dune fields is the seasonal and prolonged occurrence of snow and ice. Cold region dunes often include niveo-aeolian deposits composed of interbedded sand, snow, and ice. The GKSD are variably affected by snowcover for ~70% of each year, which likely has direct analogy to hydrocryospheric factors that influence debris flow development on Mars. Melting and/or sublimation of snow and ice during warm periods cause distinctive morphologic and sedimentologic phenomena ascribed as denivation features or forms, including spongy and hummocky surfaces, tensional cracks, deformed strata, slumping, and compressional structures. We observed small debris flows, niveo-aeolian deposits, and denivation features in the GKSD during fieldwork in March 2010. Wind-transported sand and snow accumulated on the lee slopes of large transverse, longitudinal, and barchanoid dunes. Snow banks with intercalated sand layers are especially prominent and thickest near the top of westward-facing lee slopes at the

  6. Sand dune tracking from satellite laser altimetry

    NASA Astrophysics Data System (ADS)

    Dabboor, Mohammed

    Substantial problems arise from sand movement in arid and semi-arid countries. Sand poses a threat to infrastructure, agricultural and urban areas. These issues are caused by the encroachment of sand on roads and railway tracks, farmland, towns and villages, and airports, to name a few. Sand movement highly depends on geomorphology including vegetation cover, shape and height of the terrain, and grain size of the sand. However, wind direction and speed are the most important factors that affect efficient sand movement. The direction of the movement depends on the main direction of the wind, but it has been shown that a minimum wind speed is required, e.g. wind gusts, to initiate sand transport. This fact prevents a simple calculation of sand transport from conventional wind data as wind records rarely contain sub-minute intervals masking out any wind gusts. An alternative of predicting sand transport is the direct observation of sand advance by in situ measurements or via satellite. Until recently, satellite imagery was the only means to compare dune shape and position for predicting dune migration over several years. In 2003, the NASA laser altimetry mission ICESat became operational and monitors elevations over all surface types including sand dunes with an accuracy of about 10-20 cm. In this study, ICESat observations from repeat tracks (tracks overlapping eachother within 50 m) are used to derive sand dune advance and direction. The method employs a correlation of the elevation profiles over several dunes and was sucessfully validated with synthetic data. The accuracy of this method is 5 meters of dune advance. One of the most active areas exhibiting sand and dune movement is the area of the Arabian Peninsula. Approximately one-third of the Arabian Peninsula is covered by sand dunes. Different wind regimes (Shamal, Kaus) cause sand dune movement in the selected study area in the eastern part of the Arabian Peninsula between 20-25 degrees North and 45-55 degrees

  7. Great Kobuk Sand Dunes, Alaska: A Terrestrial Analog Site for Polar, Topographically Confined Martian Dune Fields

    NASA Astrophysics Data System (ADS)

    Dinwiddie, C. L.; Hooper, D. M.; Michaels, T. I.; McGinnis, R. N.; Stillman, D.; Bjella, K.; Stothoff, S.; Walter, G. R.; Necsoiu, M.; Grimm, R. E.

    2010-12-01

    Martian dune systems belong to two broad categories: (i) the sprawling north polar erg, rich in and immobilized by seasonal and perennial volatiles; and (ii) isolated low- to high-latitude dune fields confined by topography. While modern dune migration on Mars is nearly imperceptibly slow, recent studies are producing robust evidence for aeolian activity, including bedform modification. Cold-climate terrestrial dunes containing volatile reservoirs provide an important analog to Martian polar dunes because permafrost and seasonal cycles of CO2 and H2O frost mantling are thought to partially decouple Martian polar dunes from atmospheric forcing. The 67°N latitude, 62 km2 Great Kobuk Sand Dunes (GKSD) are a terrestrial analog for polar, intercrater dune fields on Mars. Formative winds affected by complex topography and the presence of volatiles and intercalated snow within the GKSD have direct analogy to factors that impede migration of Martian polar dunes. This system offers the opportunity to study cold-climate, noncoastal, topographically constrained, climbing and reversing barchanoid, transverse, longitudinal, and star dunes. The Kobuk Valley climate is subarctic and semiarid with long, cold winters and brief, warm summers. Niveoaeolian sedimentation occurs within west-facing lee slope catchments. In March 2010, we found the seasonally frozen layer to range in thickness from 1.5 to 4.0 m, and no evidence for shallow permafrost. Instead, using GPR and boreholes, we found a system-wide groundwater aquifer that nearly parallels topography and cuts across steeply dipping bedforms. GPR cannot uniquely detect ice and water; however, a similar analysis of rover-based GPR might be used to detect volatiles in Martian dunes. The perennial volatile reservoir is liquid because of mean annual air temperature, intense solar heating before, during, and after 38 days of continuous summer daylight, high dry sand thermal conductivity, higher wet sand thermal conductivity

  8. Morphological characteristics and sand volumes of different coastal dune types in Essaouira Province, Atlantic Morocco

    NASA Astrophysics Data System (ADS)

    Flor-Blanco, Germán; Flor, Germán; Lharti, Saadia; Pando, Luis

    2013-04-01

    Altogether three coastal dune fields, one located north and two south of the city of Essaouira, Atlantic Morocco, have been investigated to establish the distribution and overall sand volumes of various dune types. The purpose of the study was to characterize and classify the aeolian landforms of the coastal dune belt, to estimate their sand volumes and to assess the effectiveness of coastal dune stabilization measures. The northern dune field is 9 km long and lined by a wide artificial foredune complex fixed by vegetation, fences and branches forming a rectangular grid. Active and ephemeral aklé dunes border the inner backshore, while some intrusive dunes have crossed the foredune belt and are migrating farther inland. The total sand volume of the northern dune belt amounts 13,910,255 m3. The central coastal sector comprises a much smaller dune field located just south of the city. It is only 1.2 km long and, with the exception of intrusive dunes, shows all other dune types. The overall sand volume of the central dune field amounts to about 172,463 m3. The southern dune field is characterized by a narrower foredune belt and overall lower dunes that, in addition, become progressively smaller towards the south. In this sector, embryonic dunes (coppice, shadow dunes), tongue-like and tabular dunes, and sand sheets intrude from the beach, the profile of which has a stepped appearance controlled by irregular outcrops of old aeolianite and beach rock. The total volume of the southern dune field amounts 1,446,389 m3. For the whole study area, i.e. for all three dune fields combined, a sand volume of about 15,529,389 m3 has been estimated. The sand of the dune fields is derived from coastal erosion and especially the Tensift River, which enters the sea at Souira Qedima some 70 km north of Essaouira. After entering the sea, the sand is transported southwards by littoral drift driven by the mainly north-westerly swell climate and the Trade Winds blowing from the NNE. This

  9. Mars aeolian sand: Regional variations among dark-hued crater floor features

    NASA Astrophysics Data System (ADS)

    Edgett, K. S.; Christensen, P. R.

    1994-01-01

    Different regions on Mars appear to have low-albedo intracrater deposits that have distinct regional thermophysical and/or aeolian dune characteristics. Thermal inertia derived from a carefully selected set of Viking infrared thermal mapper observations of the dark features obtained in 1977-1978 supports this conclusion. The observed similarities and differences among dark intracrater features on Mars is probably a function of the combined influences of sand availability and regional wind conditions.

  10. 2009 weather and aeolian sand-transport data from the Colorado River corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Draut, Amy E.; Sondossi, Hoda A.; Dealy, Timothy P.; Hazel, Joseph E.; Fairley, Helen C.; Brown, Christopher R.

    2010-01-01

    This report presents measurements of weather parameters and aeolian sand transport made in 2009 near selected archeological sites in the Colorado River corridor through Grand Canyon, Ariz. The quantitative methods and data discussed here form a basis for monitoring ecosystem processes that affect archeological-site stability. Combined with forthcoming work to evaluate landscape evolution at nearby archeological sites, these data can be used to document the relation between physical processes, including weather and aeolian sand transport, and their effects on the physical integrity of archeological sites. Data collected in 2009 reveal event- and seasonal-scale variations in rainfall, wind, temperature, humidity, and barometric pressure. Broad seasonal changes in aeolian sediment flux are also apparent at most study sites. Differences in weather patterns between 2008 and 2009 included an earlier spring windy season, greater spring precipitation even though 2009 annual rainfall totals were in general substantially lower than in 2008, and earlier onset of the reduced diurnal barometric-pressure fluctuations commonly associated with summer monsoon conditions. Weather patterns in middle to late 2009 were apparently affected by a transition of the ENSO cycle from a neutral phase to the El Ni?o phase. The continuation of monitoring that began in 2007, and installation of additional equipment at several new sites in early 2008, allowed evaluation of the effects of the March 2008 high-flow experiment (HFE) on aeolian sand transport. As reported earlier, at 2 of the 9 sites studied, spring and summer winds in 2008 reworked the HFE sandbars to form new aeolian dunes, where sand moved inland toward larger, well-established dune fields. Observations in 2009 showed that farther inland migration of the dune at one of those two sites is likely inhibited by vegetation. At the other location, the new aeolian dune form was found to have moved 10 m inland toward older, well

  11. Aeolian processes in Proctor Crater on Mars: Mesoscale modeling of dune-forming winds

    NASA Astrophysics Data System (ADS)

    Fenton, Lori K.; Toigo, Anthony D.; Richardson, Mark I.

    2005-06-01

    Both atmospheric modeling and spacecraft imagery of Mars are now of sufficient quality that the two can be used in conjunction to acquire an understanding of regional- and local-scale aeolian processes on Mars. We apply a mesoscale atmospheric model adapted for use on Mars (the Mars MM5) to Proctor Crater, a 150 km diameter crater in the southern highlands. Proctor Crater contains numerous aeolian features that indicate wind direction, including a large dark dune field with reversing transverse and star dunes containing three different slipface orientations, small and older bright bedforms that are most likely transverse granule ripples, and seasonally erased dust devil tracks. Results from model runs spanning a Martian year, with a horizontal grid spacing of 10 km, predict winds aligned with two of the three dune slipfaces as well as spring and summer winds matching the dust devil track orientations. The primary (most prevalent) dune slipface orientation corresponds to a fall and winter westerly wind created by geostrophic forces. The tertiary dune slipface orientation is caused by spring and summer evening katabatic flows down the eastern rim of the crater, influencing only the eastern portion of the crater floor. The dunes are trapped in the crater because the tertiary winds, enhanced by topography, counter transport from the oppositely oriented primary winds, which may have originally carried sand into the crater. The dust devil tracks are caused by light spring and summer westerly winds during the early afternoon caused by planetary rotation. The secondary dune slipface orientation is not predicted by model results from either the Mars MM5 or the Geophysical Fluid Dynamics Laboratory Mars general circulation model. The reason for this is not clear, and the wind circulation pattern that creates this dune slipface is not well constrained. The Mars MM5 model runs do not predict stresses above the saltation threshold for dune sand of the appropriate size and

  12. Singing-sand avalanches without dunes

    NASA Astrophysics Data System (ADS)

    Dagois-Bohy, S.; Courrech du Pont, S.; Douady, S.

    2012-10-01

    Singing-sand dunes have attracted curiosity for centuries and are now the subject of controversy. We address here two aspects of this controversy: first the possible link between the frequency heard and the shear rate (for a gravity avalanche on a dune slip-face, scaling as 0.4g/d, with d the ‘mean’ grain diameter), and second, the assumed necessity of a layered dune structure under the avalanche that acts as a resonator. Field recordings of singing dunes over the world reveal that they can present very different spectral characteristics: a dune with polydisperse grains produces a very broad and noisy spectrum, while a dune with sorted grains produces a well-defined frequency. Performing laboratory avalanches on a hard plate with singing-dune sand shows that there is no need for a dune below the sand avalanche to produce the singing sound, and a fortiori neither for the dune's layered structure nor for its particular sound transmission. By sieving the polydisperse grains, the same well-defined frequency is obtained to that of the dune with sorted grains, with the same diameter-frequency relation. The various frequencies heard in the field avalanches match the shear rates not calculated from the average size, but from the various peaks of the grain size distributions.

  13. Aerolian erosion, transport, and deposition of volcaniclastic sands among the shifting sand dunes, Christmas Lake Valley, Oregon: TIMS image analysis

    NASA Technical Reports Server (NTRS)

    Edgett, Kenneth S.; Ramsey, Michael S.; Christensen, Philip R.

    1995-01-01

    Remote sensing is a tool that, in the context of aeolian studies, offers a synoptic view of a dune field, sand sea, or entire desert region. Blount et al. (1990) presented one of the first studies demonstrating the power of multispectral images for interpreting the dynamic history of an aeolian sand sea. Blount's work on the Gran Desierto of Mexico used a Landsat TM scene and a linear spectral mixing model to show where different sand populations occur and along what paths these sands may have traveled before becoming incorporated into dunes. Interpretation of sand transport paths and sources in the Gran Desierto led to an improved understanding of the origin and Holocene history of the dunes. With the anticipated advent of the EOS-A platform and ASTER thermal infrared capability in 1998, it will become possible to look at continental sand seas and map sand transport paths using 8-12 mu m bands that are well-suited to tracking silicate sediments. A logical extension of Blount's work is to attempt a similar study using thermal infrared images. One such study has already begun by looking at feldspar, quartz, magnetite, and clay distributions in the Kelso Dunes of southern California. This paper describes the geology and application of TIMS image analysis of a less-well known Holocene dune field in south central Oregon using TIMS data obtained in 1991.

  14. Invasive plants on disturbed Korean sand dunes

    NASA Astrophysics Data System (ADS)

    Kim, Kee Dae

    2005-01-01

    The sand dunes in coastal regions of South Korea are important ecosystems because of their small size, the rare species found in this habitat, and the beautiful landscapes they create. This study investigated the current vegetative status of sand dunes on three representative coasts of the Korean peninsula, and on the coasts of Cheju Island, and assessed the conditions caused by invasive plants. The relationships between the degree of invasion and 14 environmental variables were studied. Plots of sand dunes along line transects perpendicular to the coastal lines were established to estimate vegetative species coverage. TWINSPAN (Two-Way Indicator Species Analysis), CCA (Canonical Correspondence Analysis), and DCCA (Detrended Canonical Correspondence Analysis) were performed to classify communities on sand dunes and assess species composition variation. Carex kobomugi, Elymus mollis, and Vitex rotundifolia were found to be the dominant species plotted on the east, the west, and the peripheral coasts of Cheju Island, respectively. Vegetation on the south coast was totally extinct. The 19 communities, including representative C. kobomugi, C. kobomugi- Ixeris repens, C. kobomugi- Oenothera biennis, E. mollis, Lolium multiflorum- Calystegia soldanella, and V. rotundifolia- C. kobomugi, were all classified according to TWINSPAN. Oenothera biennis and L. multiflorum were exotics observed within these native communities. CCA showed that invasive native and exotic species distribution was segregated significantly, according to disturbance level, exotic species number, gravel, sand and silt contents, as well as vegetation size. It further revealed that human disturbance can strongly favor the settlement of invasive and exotic species. Restoration options to reduce exotic plants in the South Korean sand dune areas were found to be the introduction of native plant species from one sand dune into other sand dune areas, prohibition of building and the introduction of exotic

  15. Aeolian dunes as ground truth for atmospheric modeling on Mars

    USGS Publications Warehouse

    Hayward, R.K.; Titus, T.N.; Michaels, T.I.; Fenton, L.K.; Colaprete, A.; Christensen, P.R.

    2009-01-01

    Martian aeolian dunes preserve a record of atmosphere/surface interaction on a variety of scales, serving as ground truth for both Global Climate Models (GCMs) and mesoscale climate models, such as the Mars Regional Atmospheric Modeling System (MRAMS). We hypothesize that the location of dune fields, expressed globally by geographic distribution and locally by dune centroid azimuth (DCA), may record the long-term integration of atmospheric activity across a broad area, preserving GCM-scale atmospheric trends. In contrast, individual dune morphology, as expressed in slipface orientation (SF), may be more sensitive to localized variations in circulation, preserving topographically controlled mesoscale trends. We test this hypothesis by comparing the geographic distribution, DCA, and SF of dunes with output from the Ames Mars GCM and, at a local study site, with output from MRAMS. When compared to the GCM: 1) dunes generally lie adjacent to areas with strongest winds, 2) DCA agrees fairly well with GCM modeled wind directions in smooth-floored craters, and 3) SF does not agree well with GCM modeled wind directions. When compared to MRAMS modeled winds at our study site: 1) DCA generally coincides with the part of the crater where modeled mean winds are weak, and 2) SFs are consistent with some weak, topographically influenced modeled winds. We conclude that: 1) geographic distribution may be valuable as ground truth for GCMs, 2) DCA may be useful as ground truth for both GCM and mesoscale models, and 3) SF may be useful as ground truth for mesoscale models. Copyright 2009 by the American Geophysical Union.

  16. Debris flows on the Great Kobuk Sand Dunes, Alaska: Implications for analogous processes on Mars

    NASA Astrophysics Data System (ADS)

    Hooper, Donald M.; Dinwiddie, Cynthia L.

    2014-02-01

    We observed niveo-aeolian deposits, denivation features, and small meltwater-induced debris flows that had formed at the Great Kobuk Sand Dunes, northwestern interior Alaska in late March 2010. This high-latitude, cold-climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes. Debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing. We hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow, enabling meltwater to form and sand to be mobilized. This investigation provides insights into the interactions between niveo-aeolian deposition, slope aspect and insolation, thawing, and initiation of alluvial processes. These debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid- to high-latitude dune fields in both martian hemispheres. Localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions.

  17. Particle-size fractionation of aeolian sand along a climatic and geomorphic gradient of the Sinai-Negev erg

    NASA Astrophysics Data System (ADS)

    Roskin, Joel; Katra, Itzhak; Blumberg, Dan G.

    2015-04-01

    This study examines changes in the aeolian sand fractions along the west-east aeolian transport path of the northern Sinai Peninsula - northwestern (NW) Negev erg of Egypt and Israel. This erg originates from the Nile Delta and is composed of currently active linear (seif) dunes in northern Sinai (its western part), and currently stabilized vegetated linear dunes (VLDs) in the NW Negev dunefield (its eastern part). Sand samples from the Nile Delta, northern Sinai and NW Negev were analyzed for particle-size distribution and sand grain morphology in accordance to their Eastern Mediterranean INQUA Dunes Atlas luminescence and radiocarbon chronologies. Linear seif dunes differ from VLDs in their vegetation cover, linearity, and dynamics. Although both are continuous landforms with similar orientations and sand-grain roundness values, the linear dunes of Sinai are coarser-grained than the Negev VLDs. The VLDs have a significantly higher proportion of very fine sand (125-50 μm) content and a varying but lower sand fining ratio defined as the ratio of fine sand percentage to very fine sand percentage. Very fine sands are suggested to have been winnowed by saltation and low suspension from source deposits and sand sheets. Detailed semi-quantitative examinations of sand grains by a SEM of a Negev VLD shows that most grains do not exhibit features that can be attributed to aeolian abrasion by sand grain-grain collisions. From these observations we infer that fractionation of sand was a major process leading to downwind fining along the studied aeolian transport path. We suggest that the very fine sand fraction of Nile Delta and Sinai sands has been transported downwind since the late middle Pleistocene. In the late Pleistocene, sand reached the NW Negev in the form of VLDs due to last-glacial period windiness of intensities unprecedented today and probably larger sediment supply. Generally current and inferred past decreasing wind velocities and increasing precipitation

  18. Compressive strength of dune sand reinforced concrete

    NASA Astrophysics Data System (ADS)

    Mohammed, Mani; Abdelouahed, Kriker; Allaoua, Belferrag

    2017-02-01

    Many areas of south Algeria suffer from the problem of accumulation of sand on constructions. In fact, the phenomenon of sand silting causes technical and economical problems. Besides, these areas and other regions in Algeria suffer from the problem of unavailability of suitable sand for building. The use of dune sand offers an alternative solution for construction. In the same context, many researches confirm the possibility of using dune sand in the composition of concrete. In this paper, concrete made with dune sand was studied. For correction of the granulometry of dune sand by river sand, the rates of 50% DS+50% RS and 40% DS+60% RS were used. Also, two types of fibers were used, with 45 and 30 mm lengths, and diameters of 1 and 0.5 mm respectively. The percentage of the used fibers in the sand concrete was 1% and 1.5%. In this work an improvement of the compressive strength for the metal fibers reinforced sand concrete compared to plain concrete was obtained.

  19. Aeolian processes and dune morphology in the Gobi and Badain Jaran Desert using LandSat Imagery.

    NASA Astrophysics Data System (ADS)

    Cardinale, Marco; Cannito, Arturo; Marinangeli, Lucia

    2014-05-01

    The Gobi and Badain Jaran Deserts are parts of the vast sand sea of the Alashan Region, one of the greatest dunefield in China [1]. They lie between the southern Mongolia and the northern China (latitude 37° 06'N - 41°50'N; longitude 99°10'E - 107°09'E) [2]. The studied area is characterized by an arid climate with low average annual rainfall between 50-60mm, extreme fluctuation in temperature, very strong winds and by the occurrence of mega dunes and permanent lakes within the dunefield [3]. According to our morphological analysis, wind action has been one of the main factors that have shaped the surface features inside the investigated area. We produce a detailed geomorphological map of the desertic zone, highlighting the aeolian morphologies, in order to characterize aeolian deposits and processes. The LandSat ETM+ data [4], providing a continuous coverage of the dune fields with no gaps, were processed using ENVI software and then ingested in a GIS project. We also used DTMs (30m / pixel) from Aster data [5]. The dune morphology was classified using McKee criteria [6] and we interpreted the pattern of the complex ergs as the result of self - organization within complex systems [7]. Compound transverse mega dunes and barchanoid dunes developed under a variable wind regime, star dunes in the northern area near the mountain have been formed under a multi directional wind regime. The area covered by mega dunes suggests a complex evolution of these features dominated by the wind activity. Different episodes of deposition, erosion and motion, could explain the height of these dunes measured by the DTMs. The diverse aeolian features identified in the investigated area suggest that aeolian activity play a key role for the evolution of the surface morphologies of the Gobi Desert. To understand the local dynamics of aeolian processes, we are currently comparing these features with meteorological data from mesoscale wind models. References: [1] E. D.McKee. A Study of

  20. Microbial Characterization of Qatari Barchan Sand Dunes

    PubMed Central

    Chatziefthimiou, Aspassia D.; Nguyen, Hanh; Richer, Renee; Louge, Michel; Sultan, Ali A.; Schloss, Patrick; Hay, Anthony G.

    2016-01-01

    This study represents the first characterization of sand microbiota in migrating barchan sand dunes. Bacterial communities were studied through direct counts and cultivation, as well as 16S rRNA gene and metagenomic sequence analysis to gain an understanding of microbial abundance, diversity, and potential metabolic capabilities. Direct on-grain cell counts gave an average of 5.3 ± 0.4 x 105 cells g-1 of sand. Cultured isolates (N = 64) selected for 16S rRNA gene sequencing belonged to the phyla Actinobacteria (58%), Firmicutes (27%) and Proteobacteria (15%). Deep-sequencing of 16S rRNA gene amplicons from 18 dunes demonstrated a high relative abundance of Proteobacteria, particularly enteric bacteria, and a dune-specific-pattern of bacterial community composition that correlated with dune size. Shotgun metagenome sequences of two representative dunes were analyzed and found to have similar relative bacterial abundance, though the relative abundances of eukaryotic, viral and enterobacterial sequences were greater in sand from the dune closer to a camel-pen. Functional analysis revealed patterns similar to those observed in desert soils; however, the increased relative abundance of genes encoding sporulation and dormancy are consistent with the dune microbiome being well-adapted to the exceptionally hyper-arid Qatari desert. PMID:27655399

  1. Microbial Characterization of Qatari Barchan Sand Dunes.

    PubMed

    Abdul Majid, Sara; Graw, Michael F; Chatziefthimiou, Aspassia D; Nguyen, Hanh; Richer, Renee; Louge, Michel; Sultan, Ali A; Schloss, Patrick; Hay, Anthony G

    This study represents the first characterization of sand microbiota in migrating barchan sand dunes. Bacterial communities were studied through direct counts and cultivation, as well as 16S rRNA gene and metagenomic sequence analysis to gain an understanding of microbial abundance, diversity, and potential metabolic capabilities. Direct on-grain cell counts gave an average of 5.3 ± 0.4 x 105 cells g-1 of sand. Cultured isolates (N = 64) selected for 16S rRNA gene sequencing belonged to the phyla Actinobacteria (58%), Firmicutes (27%) and Proteobacteria (15%). Deep-sequencing of 16S rRNA gene amplicons from 18 dunes demonstrated a high relative abundance of Proteobacteria, particularly enteric bacteria, and a dune-specific-pattern of bacterial community composition that correlated with dune size. Shotgun metagenome sequences of two representative dunes were analyzed and found to have similar relative bacterial abundance, though the relative abundances of eukaryotic, viral and enterobacterial sequences were greater in sand from the dune closer to a camel-pen. Functional analysis revealed patterns similar to those observed in desert soils; however, the increased relative abundance of genes encoding sporulation and dormancy are consistent with the dune microbiome being well-adapted to the exceptionally hyper-arid Qatari desert.

  2. Recent advances in research on the aeolian geomorphology of China's Kumtagh Sand Sea

    NASA Astrophysics Data System (ADS)

    Dong, Z.; Lv, P.

    2014-02-01

    The Kumtagh Sand Sea in the hyper-arid region of northwestern China remained largely unexplored until the last decade. It deserves study due to its significance in understanding the evolution of the arid environments in northwestern China, and even central Asia. Aeolian geomorphology in the sand sea has received unprecedented study in the last decade. Encouraging advances have been made in types of aeolian landforms, geological outlines, wind systems, the formation of aeolian landforms, several unique aeolian landforms, aeolian geomorphic regionalization, aeolian geomorphological heritages and tourism development, and aeolian sand hazards and their control. These advances expand our knowledge of aeolian geomorphology.

  3. Meso-scale aeolian sediment input to coastal dunes: The nature of aeolian transport events

    NASA Astrophysics Data System (ADS)

    Delgado-Fernandez, Irene; Davidson-Arnott, Robin

    2011-03-01

    Observations of aeolian transport in coastal areas have focused on short-term experiments because of limitations imposed by instrumentation. This paper uses a case study at Greenwich Dunes, Prince Edward Island National Park, Canada, to analyze how sediment transport takes place at the beach over periods of weeks to months. A monitoring station provided hourly time series of vegetation cover, shoreline position, fetch distances, surficial moisture content, presence of ice and snow, wind speed and direction and transport processes over nine months. Analysis shows that high wind speeds may not generate any net transport into the dunes because of the limitations imposed by snow/ice cover, moisture, and short fetch distances. Despite extreme winds during intense storms, such events often lead to wave scarping rather than aeolian sediment input to the foredunes. When sediment was transported on the beach, the magnitude was regulated by a combination of factors including: angle of wind approach, fetch distance, moisture content, and duration of the wind event. In particular, angle of wind approach (and therefore fetch distance) may demote a high magnitude wind event with strong transport potential to one with no transport at all, which poses challenges for predicting the effects of individual storms over the course of several months. A significant proportion of sediment delivery to the foredunes was associated with wind events of low to medium magnitude. It is suggested here that large magnitude wind events have low probabilities of resulting in transport towards the foredune because factors such as wave inundation play an increasing role in preventing sediment movement across the beach. This has implications for modelling and management, and highlights differences between the magnitude and frequency of aeolian transport events in the coastal environment compared to those in deserts and to fluvial sediment transport.

  4. Do dune sands redden with age? The case of the northwestern Negev dunefield, Israel

    NASA Astrophysics Data System (ADS)

    Roskin, Joel; Blumberg, Dan G.; Porat, Naomi; Tsoar, Haim; Rozenstein, Offer

    2012-08-01

    The redness index of aeolian sand has been shown to be a promising qualitative spectroscopic method to define sand grain redness intensity, which reflects the extent of iron-oxide quartz grain coatings. This study investigates the relationship between redness intensity and optically stimulated luminescence (OSL) based depositional ages of sand samples taken from exposed and fully-drilled vegetated linear dunes in the northwestern Negev dunefield, Israel. Sand redness intensity did not vary greatly along the Negev sand transport paths and dune sections dated to be active during the Late Pleistocene (˜18-11.5 ka), Late Holocene, and modern times. No correlation was found between RI intensity (i.e., redness) and the depositional age of the sand. The relatively uniform RI values and sedimentological properties along most of the dunes suggest that sand grain coating development, and consequent rubification, have probably been minimal since the Late Pleistocene. Although it is possible that RI developed rapidly following deposition in a wetter Late Pleistocene climate, the drier and less stormy Holocene does not seem conducive to sand-grain rubification. Based on analyses of northern Sinai sand samples, remote sensing, and previous studies, we suggest that the attributes of the sand grain RI have been inherited from upwind sources. We propose that the sand grain coatings are early diagenetic features that have been similarly red since their suggested aeolian departure from the middle and upper Nile Delta.

  5. Layers, Landslides, and Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 27 October 2003

    This image shows the northern rim of one of the Valles Marineris canyons. Careful inspection shows many interesting features here. Note that the spurs and gullies in the canyon wall disappear some distance below the top of the canyon wall, indicating the presence of some smooth material here that weathers differently from the underlying rocks. On the floor of the canyon, there are remains from a landslide that came hurtling down the canyon wall between two spurs. Riding over the topography of the canyon floor are many large sand dunes, migrating generally from the lower right to upper left.

    Image information: VIS instrument. Latitude -14.1, Longitude 306.7 East (53.3 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  6. A simple cellular model to quantify controls on aeolian dune-field pattern development

    NASA Astrophysics Data System (ADS)

    Eastwood, E. N.; Nield, J. M.; Baas, A. C.; Kocurek, G.

    2009-12-01

    A second-generation, source-to-sink cellular automaton model captures and quantifies many of the factors controlling the evolution of aeolian dune-field patterns by varying only a small number of parameters. Our model quantifies the role of sediment supply, sediment availability, and transport capacity in the development and evolution of an aeolian dune-field pattern over long time scales. Simulation results produced by varying the sediment supply and transport capacity identified seven dune-field patterns. A new clustered dune-field pattern is identified 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 and small superimposed dunes. Sediment supply and transport capacity control the type and frequency of dune interactions, the sediment availability of the system, and ultimately the development of dune-field patterns. Our model allows predictions about the range of sediment supply and wind strengths required to produce many of the dune-field patterns seen in the real world. This simple model demonstrates the dominant control of aeolian sediment state on the construction and evolution of aeolian dune-field patterns.

  7. Dynamics of sediment storage and release on aeolian dune slip faces: A field study in Jericoacoara, Brazil

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.; Sherman, Douglas J.; Ellis, Jean T.; Farrell, Eugene J.; Jackson, Nancy L.; Li, Bailiang; Nordstrom, Karl F.; Maia, Luis Parente; Omidyeganeh, Mohammad

    2015-09-01

    Sediment transport on the lee sides of aeolian dunes involves a combination of grain-fall deposition on the upper portion of the slip face until a critical angle is exceeded, transport of a portion of those sediments down the slip face by grain flows and, finally, deposition at an angle of repose. We measured the mean critical and repose angles and the rate of slip-face avalanching using terrestrial laser scanning (TLS) on two barchans of different size in Jericoacoara, Brazil. Wind speeds and sand fluxes were measured simultaneously at the dune crests. We found that the mean critical decreased with increasing wind speed. We attribute this effect to turbulent shear stresses, the magnitude of which we quantified using 3-D large eddy simulation modeling, that randomly act down the slip face (i.e., in the direction of gravity) to trigger grain flows at lower angles than would be possible with gravity stresses alone. We developed and tested a new predictive model for the frequency of avalanching that depends on both the sediment flux delivered to the slip face and changes in the critical angle with time. In this model, increasing turbulent shear stresses drive avalanching even in the absence of sand flux delivered to the slip face if the critical angle decreases below the slope angle. We also document that the mean critical angle decreases slightly with increasing slip-face height. These results have important implications for aeolian dune evolution, interpretations of aeolian stratigraphy, and granular mechanics.

  8. Explaining the surprisingly poor correlation between turbulent surface wind and aeolian sand flux

    NASA Astrophysics Data System (ADS)

    Martin, R. L.; Barchyn, T. E.; Hugenholtz, C.; Jerolmack, D. J.; Kok, J. F.

    2012-12-01

    Existing models of aeolian sand transport, derived theoretically and from wind-tunnel experiments, often disagree substantially with field observations. Despite advancements in anemometry and sediment flux detection technologies, even very high-resolution observations of aeolian sand transport show only weak correlation with concurrent surface wind speeds and model predictions. Unlike in experiments and numerical models, winds in natural environments exhibit turbulent fluctuations over a broad range of length scales extending from individual grains to the top of the atmospheric boundary layer and over a similarly large range of time scales. Here, we present simultaneous high-resolution (10 Hz) measurements of surface wind and saltation sand transport over a ~5 m tall barchan dune (median grain diameter = 0.35 mm) collected at White Sands Dune Field, New Mexico, USA. Studying aeolian transport in the field offered a natural experiment for understanding how the rate of aeolian saltation responds to turbulent changes in wind and frequent crossings of the threshold for particle motion. In agreement with past observations, our data indicate that: (1) saltation flux lags wind fluctuations by about 1 second, (2) the threshold for initiation of particle motion ("entrainment") exceeds the threshold for cessation ("distrainment") by about 20%, (3) concurrent instantaneous wind and sediment flux measurements are poorly correlated. Based on our data, we show how lagged transport and threshold hysteresis are related to inertia in the transport system arising from ballistic particle trajectories and non-instantaneous momentum transfers among grains and wind. We argue that this nonlinear and lagged response of saltation to turbulent wind fluctuations accounts for the poor correlation between wind and transport as well as the poor performance of existing saltation models.

  9. Dune ages in the sand deserts of the southern Sahara and Sahel

    NASA Astrophysics Data System (ADS)

    Bristow, Charlie; Armitage, Simon

    2015-04-01

    In this paper we aim to document the history of aeolian processes within the southern Sahara as part of the INQUA Dune Atlas. We review available luminescence ages for sand dunes across the southern Sahara and attempt to correlate periods of sand accumulation and to develop an improved understanding of the dune chronology on a regional basis. This was achieved by analysing dune age by country, as well as by latitude and longitude. The results show a very patchy spatial distribution of dune ages with large gaps that encompass some of the largest sand seas. Despite these gaps, some related patterns in dune morphology and stratigraphy appear to be consistent between northern Nigeria and southern Mali where older linear dunes are distinct from younger Late Holocene transverse and barchanoid dunes. Elsewhere in Mauretania linear dunes with different orientations appear to have accumulated at different times, most likely in response to changes in atmospheric circulation. Regional climatic changes are identified where dunes are transgressed by lake deposits within endorehic basins. We identify four locations where dune accumulation is terminated by lacustrine transgressions, two of which, in Lake Chad and the Bodélé Depression, occur shortly after the last glacial maximum (LGM). The third example at Gobiero in Niger occurred later, in the early Holocene, around 8.4 ka and a fourth marks a later transgression of Palaeolake MegaChad after 4.7 ka. Larger-scale latitudinal and longitudinal distributions in dune ages across the southern Sahara do not show any consistent patterns, though this may due to the small sample size relative to the study area. In addition, local variations in external controls such as wind regime, rainfall, vegetation and sand supply need to be considered, sometimes on a site by site basis. Limiting the analysis to dune ages determined using the single-aliquot regenerative-dose (SAR) protocol indicates a lack of dune preservation during the LGM and

  10. Autumn Frost, North Polar Sand Dunes

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Autumn in the martian northern hemisphere began around August 1, 1999. Almost as soon as northern fall began, the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) started documenting the arrival of autumn frost--a precursor to the cold winter that will arrive in late December 1999. The first features to become covered by frost were the sand dunes that surround the north polar ice cap. The dunes seen here would normally appear very dark--almost black--except when covered by frost. Why the dunes begin to frost sooner than the surrounding surfaces is a mystery: perhaps the dunes contain water vapor that emerges from the sand during the day and condenses again at night. This picture shows dunes near 74.7oN, 61.4oW at a resolution of about 7.3 meters (24 feet) per pixel. The area covered is about 3 km (1.9 mi) across and is illuminated from the upper right. The picture appears to be somewhat fuzzy and grainy because the dunes here are seen through the thin haze of the gathering north polar winter hood (i.e., clouds).

  11. Measuring aeolian sand transport using acoustic sensors

    NASA Astrophysics Data System (ADS)

    Poortinga, Ate; van Rheenen, Hans; Ellis, Jean T.; Sherman, Douglas J.

    2015-03-01

    Acoustic sensors are frequently used to measure aeolian saltation. Different approaches are used to process the signals from these instruments. The goal of this paper is to describe and discuss a method to measure aeolian saltation with acoustic sensors. In a laboratory experiment, we measured the output from an advanced signal processing scheme on the circuit board of the saltiphone. We use a software implementation of this processing scheme to re-analyse data from four miniphones obtained during a field experiment. It is shown that a set of filters remove background noise outside the frequency spectrum of aeolian saltation (at 8 kHz), whereas signals within this frequency spectrum are amplified. The resulting analogue signal is a proxy of the energy. Using an AC pulse convertor, this signal can be converted into a digital and analogue count signal or an analogue energy signal, using a rectifier and integrator. Spatio-temporal correlation between field deployed miniphones increases by using longer integration times for signal processing. To quantify aeolian grain impact, it is suggested to use the analogue energy output, as this mode is able to detect changes in frequency and amplitude. The analogue and digital count signals are able to detect an increase in frequency, but are not able to detect an increase in signal amplitude. We propose a two-stage calibration scheme consisting of (1) a factory calibration, to set the frequency spectrum of the sensor and (2) a standardized drop-test conducted before and after the experiment to evaluate the response of the sensor.

  12. 'Sharks Teeth' -- Sand Dunes in Proctor Crater

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Sometimes, pictures received from Mars Global Surveyor's Mars Orbiter Camera (MOC) are 'just plain pretty.' This image, taken in early September 2000, shows a group of sand dunes at the edge of a much larger field of dark-toned dunes in Proctor Crater. Located at 47.9oS, 330.4oW, in the 170 km (106 mile) diameter crater named for 19th Century British astronomer Richard A. Proctor (1837-1888), the dunes shown here are created by winds blowing largely from the east/northeast. A plethora of smaller, brighter ripples covers the substrate between the dunes. Sunlight illuminates them from the upper left.

  13. Interplay between seasonal frost and aeolian processes on Matara crater dunes (Mars)

    NASA Astrophysics Data System (ADS)

    Diniega, S.

    2012-12-01

    Matara crater dune field exhibits a complex and fascinating geologic history. It first gained scientific attention when dune gullies (of alcove-channel-apron morphology, a few hundred meters to 3 km in length) were observed in MOC and HiRISE images to be actively evolving during the last Mars decade. These gullies are located on the slopes of both types of dunes found here: the field is predominantly composed of long-wavelength transverse dunes with slipfaces to the east, and small barchans dunes originating along the eastern boundary of the field clamber over these dunes, towards the north-west. Although these dunes have not been observed to migrate (yet), aeolian processes are clearly active as the dune brinks are quite crisp in appearance, ripples on the surfaces of these dunes have been observed to migrate, and ripples have formed within sediment recently remobilized by dune-gully activity. This study seeks to understand how sediment has been redistributed/mobilized through both aeolian processes and seasonal processes leading to gully formation/evolution, and possible influences these processes have on each other. The aim is to connect the field's present-day morphology with the field's formation history and thus identify and quantify relevant processes (and process-interactions) and environmental/atmospheric conditions. Beatiful large (3km long) dune gully on eastern margin of Matara crater dune field. It originates along the crest of a large transverse dune; also visible are the smaller barchans that march up and over the field.

  14. Mapping the Stratigraphy of Booming Sand Dunes

    NASA Astrophysics Data System (ADS)

    Vriend, N. M.; Hunt, M. L.; Clayton, R. W.

    2008-12-01

    Booming dunes emit a loud rumbling sound after a man-made or natural sand avalanche is generated on the slip face of a large desert dune. The sound consist of one dominant frequency (70 - 105 Hz) with several higher harmonics. A recent publication (Vriend et al., 2007) presented a model of an internal, natural waveguide that propagates the booming emission, amplifies the sound, and sets the booming frequency. The mapping of the subsurface layering, which is necessary for the existence of a waveguide, prompted additional work on the dune structure and stratigraphy. The current work highlights geophysical measurements at Eureka Dunes in Death Valley National Park, CA and Dumont Dunes in the Mojave Desert, CA. Seismic refraction studies indicate strong layering with large velocity jumps across the interfaces. Ground Penetrating Radar (GPR) profiles, at frequencies of 100 MHz and 200 MHz, map out the stratigraphic structure of the dunes. Variations in the near surface layering are able to predict the seasonal variability in booming frequency both quantitatively and qualitatively. The Kirchhoff migrated GPR profiles are superimposed on the local topography obtained with a laser rangefinder. The complex dune structure is resolved to a depth of over 30 meters for the 100 MHz antenna. The GPR profiles of the longitudinal Eureka dune display complex internal structures from old dune crests. Both slopes have slip faces at 30 degrees with parallel layering (< 2m) at the near surface. At the transverse Dumont dune the GPR profile exhibits strong parallel layering on the booming leeward slipface only. The shallower windward face features a remarkable tilted repetitive layering that cuts through the surface. At Dumont Dunes the layering on the leeward face explains the change in booming frequency between 70 - 95 Hertz in the period 2005 - 2008. The tilted layering structure of the shallow windward face prevents the formation of a waveguide and is never able to sustain the

  15. A linear dune dam - a unique late Pleistocene aeolian-fluvial archive bordering the northwestern Negev Desert dunefield, Israel

    NASA Astrophysics Data System (ADS)

    Roskin, Joel; Bookman, Revital; Friesem, David; Vardi, Jacob

    2016-04-01

    Interactions between aeolian and fluvial processes, known as aeolian-fluvial (A-F) interactions, play a fundamental role in shaping the surface of the Earth especially in arid zones. The blocking of wadis by dunes (dune-damming) is an A-F interaction that is perceived to be an archive of periods of aeolian 'superiority' on fluvial transport power and has had a strong impact on arid landscapes and prehistoric man since the late Quaternary. The southern fringes of the northwestern Negev dunefield are lined with discontinuous surfaces of light-colored, playa-like, low-energy, fine-grained fluvial deposits (LFFDs). Abundant Epipalaeolithic camp sites mainly border the LFFDs. The LFFDs are understood to be reworked loess-like sediment deposited in short-lived shallow water bodies during the late Pleistocene. These developed adjacently upstream of hypothesized dune dams of wadis that drain the Negev highlands. However, no dune dam structures by the LFFDs have been explicitly identified or analyzed. This paper presents for the first time the morphology, stratigraphy and sedimentology of a hypothesized dune dam. The studied linear-like dune dam structure extends west-east for several hundred meters, has an asymmetric cross-section and is comprised of two segments. In the west, the structure is 3-5 m high, 80 m wide, with a steep southern slope, and is covered by pebbles. Here, its morphology and orientation resembles the prevailing vegetated linear dunes (VLDs) of the adjacent dunefield though its slope angles differ from VLDs. To the south of the structure extends a thick LFFD sequence. In the east the structure flattens and is covered by nebkhas with its southern edge overlapped by LFFD units. The structures' stratigraphy is found to be comprised of a thick LFFD base, overlaid by aeolian and fluvially reworked sand, a thin middle LFFD unit, and a crest comprised of LFFDs, fluvial sand and pebbles. Carbonate contents and particle size distributions of the sediments easily

  16. Aeolian sands and buried soils in the Mecklenburg Lake District, NE Germany: Holocene land-use history and pedo-geomorphic response

    NASA Astrophysics Data System (ADS)

    Küster, Mathias; Fülling, Alexander; Kaiser, Knut; Ulrich, Jens

    2014-04-01

    The present study is a pedo-geomorphic approach to reconstructing Holocene aeolian sand dynamics in the Mecklenburg Lake District (NE Germany). Stratigraphical, sedimentological and soil research supplemented by morphogenetic interpretations of the genesis of dunes and aeolian sands are discussed. A complex Late Holocene aeolian stratigraphy within a drift sand area was developed at the shore of Lake Müritz. The results were confirmed using palynological records, archaeological data and regional history. Accelerated aeolian activity was triggered by the intensification of settlement and land-use activities during the 13th and in the 15th to 16th century AD. After a period of stability beginning with population decline during the ‘Thirty Years War' and continuing through the 18th century, a final aeolian phase due to the establishment of glassworks was identified during the 19th century AD. We assume a direct link between Holocene aeolian dynamics and human activities. Prehistoric Holocene drift sands on terrestrial sites have not been documented in the Mecklenburg Lake District so far. This might be explained either by erosion and incorporation of older aeolian sediments during younger aeolian phases and/or a lower regional land-use intensity in older periods of the Holocene. The investigated drift sands are stratigraphically and sedimentologically characterised by a high degree of heterogeneity, reflecting the spatial and temporal variability of Holocene human impact.

  17. Regional aeolian dynamics and sand mixing in the Gran Desierto: Evidence from Landsat thematic mapper images

    SciTech Connect

    Blount, G.; Greeley, R.; Christensen, P.R. ); Smith, M.O.; Adams, J.B. )

    1990-09-10

    Spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea, the Gran Desierto of Sonora, Mexico. Mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes. The results were used to interpret the Quaternary geologic history of the tectonically active region at the mouth of the Colorado River. Landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain. A spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types. Compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper. A simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low-albedo accessory grains occurring on dormant aeolian surfaces. A technique for discriminating between low-albedo materials and macroscopic shade is implemented by combing thermal images with the results of the spectral mixing model. The image analysis revealed important compositional variations over large areas that were not readily apparent in the field.

  18. Regional aeolian dynamics and sand mixing in the Gran Desierto: Evidence from Landsat thematic mapper images

    NASA Astrophysics Data System (ADS)

    Blount, Grady; Smith, Milton O.; Adams, John B.; Greeley, Ronald; Christensen, Phillip R.

    1990-09-01

    Spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea, the Gran Desierto of Sonora, Mexico. Mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes. The results were used to interpret the Quaternary geologic history of the tectonically active region at the mouth of the Colorado River. Landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain. A spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types. Compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper. A simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low-albedo accessory grains occurring on dormant aeolian surfaces. A technique for discriminating between low-albedo materials and macroscopic shade is implemented by combining thermal images with the results of the spectral mixing model. The image analysis revealed important compositional variations over large areas that were not readily apparent in the field.

  19. Aeolian sedimentation in the middle buntsandstein in the eifel north-south depression zone: Summary of the variability of sedimentary processes in a buntsandstein erg as a base for evaluation of the mutual relationships between aeolian sand seas and fluvial river systems in the mid-european buntsandstein

    NASA Astrophysics Data System (ADS)

    Mader, Detlef

    The spectrum of aeolian depositional subenvironments in the upper Middle Buntsandstein Karlstal-Schichten sequence in the Eifel North-South-zone at the western margin of the Mid-European Triassic Basin comprises trains of larger and higher narrowly-spaced dunes in sand seas, isolated smaller and lower widely-spaced dunes in floodplains and interdune playas, dry interdune sheet sands, damp interdune adhesive sandflats, wet interdune playa lakes, rainfall runoff watercourses and ephemeral channels cutting through the dune belt, and deflation gravel lag veneers. Distinction of aeolian and fluvial sediments within the succession of closely intertonguing wind- and water-laid deposits is possible by independent analysis of the conventional criteria and the more modern stratification styles. Thick cross-bedded aeolian sand sequences originate as barchanoid-type dunes which accumulate and migrate in the regime of narrow to wide unimodal southeasterly to southwesterly trade winds in low northern palaeolatitude in summer when the intertropical convergence zone is shifted to the north. The predominantly transverse-ridge dunes accrete mainly by grainfall and subcritical climbing of wind ripples, subordinately also by grainflow interfingering with grainfall. Horizontal-laminated aeolian sands form as sand sheets in dry interdune playas by subcritical migration of wind ripple trains, rarely also by plane bed accretion. Thin cross-bedded dune sands or horizontal-laminated aeolian sands capping fluvial cyclothems originate by deflation of emerged alluvial bar sands during low-water stages and subsequent accumulation of the winnowed sand as widely-spaced dunelets or chains of wind ripples in desiccated parts of the adjoining floodplain. The aeolian sand layers at the base of lacustrine cyclothems record migration of isolated little dunes across the dry playa floor at the beginning of a wetting-upwards cyclothem, with the sand deriving from deflation of fluvial incursions or

  20. Winter variability of aeolian sediment transport threshold on a cold-climate dune

    NASA Astrophysics Data System (ADS)

    Barchyn, Thomas E.; Hugenholtz, Chris H.

    2012-12-01

    Changes in surface conditions on cold-climate aeolian dunes are pronounced; during winter dunes are wet, snow covered, and/or frozen for extended periods of time. It is unknown how the critical wind speed for sediment transport (“threshold”) varies and how threshold may influence sediment transport predictions. Although the impact of surface conditions on threshold has been examined in synthetic experiments (wind tunnels), complicated feedbacks between threshold, sand transport, and surface conditions that occur in natural environments suggest that a ground-based empirical approach may provide enhanced insight. In this study we investigate threshold variability for 73 days during fall-winter-spring surface conditions from 18 November 2008 to 30 May 2009 in the Bigstick Sand Hills of Saskatchewan, Canada. Simultaneous measurements of threshold and atmospheric variables (air temperature, relative humidity, solar radiation, wind speed and direction) were used to examine the extent to which surface erodibility was regulated by meteorology. Time-lapse images of the surface from a co-located camera were used for quality control and interpreting changes in the surface affecting threshold. Results reveal that threshold varied throughout the deployment (25-75% quartiles: 6.92-8.28 m s- 1; mean: 7.79 m s- 1). Threshold variability was especially evident at two scales: (i) event timescale and (ii) seasonal timescale. Event-scale variability peaked during mid-winter; in one event the threshold varied by 6 m s- 1 in 2 h with freezing and re-freezing of the surface and relatively constant atmospheric conditions. The causes of event-scale variability are complex though qualitatively related to changes of wind direction, antecedent meteorological conditions, and vertical variations of grain-scale bonding agents such as pore ice and moisture. Seasonal-scale changes manifested as an increase in threshold during fall, peaking in mid-winter, and decreasing in spring. Increased

  1. Trickle-down boundary conditions in aeolian dune-field pattern formation

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.; Kocurek, G.

    2015-12-01

    One the one hand, wind-blown dune-field patterns emerge within the overarching boundary conditions of climate, tectonics and eustasy implying the presence of these signals in the aeolian geomorphic and stratigraphic record. On the other hand, dune-field patterns are a poster-child of self-organization, in which autogenic processes give rise to patterned landscapes despite remarkable differences in the geologic setting (i.e., Earth, Mars and Titan). How important are climate, tectonics and eustasy in aeolian dune field pattern formation? Here we develop the hypothesis that, in terms of pattern development, dune fields evolve largely independent of the direct influence of 'system-scale' boundary conditions, such as climate, tectonics and eustasy. Rather, these boundary conditions set the stage for smaller-scale, faster-evolving 'event-scale' boundary conditions. This 'trickle-down' effect, in which system-scale boundary conditions indirectly influence the event scale boundary conditions provides the uniqueness and richness of dune-field patterned landscapes. The trickle-down effect means that the architecture of the stratigraphic record of dune-field pattern formation archives boundary conditions, which are spatially and temporally removed from the overarching geologic setting. In contrast, the presence of an aeolian stratigraphic record itself, reflects changes in system-scale boundary conditions that drive accumulation and preservation of aeolian strata.

  2. Hierarchical organization of a Sardinian sand dune plant community

    PubMed Central

    Ceccherelli, Giulia; Bertness, Mark

    2016-01-01

    Coastal sand dunes have attracted the attention of plant ecologists for over a century, but they have largely relied on correlations to explain dune plant community organization. We examined long-standing hypotheses experimentally that sand binding, inter-specific interactions, abiotic factors and seedling recruitment are drivers of sand dune plant community structure in Sardinia, Italy. Removing foundation species from the fore-, middle- and back-dune habitats over three years led to erosion and habitat loss on the fore-dune and limited plant recovery that increased with dune elevation. Reciprocal species removals in all zones suggested that inter-specific competition is common, but that dominance is transient, particularly due to sand burial disturbance in the middle-dune. A fully factorial 2-year manipulation of water, nutrient availability and substrate stability revealed no significant proximate response to these physical factors in any dune zone. In the fore- and middle-dune, plant seeds are trapped under adult plants during seed germination, and seedling survivorship and growth generally increase with dune height in spite of increased herbivory in the back-dune. Sand and seed erosion leads to limited seed recruitment on the fore-dune while high summer temperatures and preemption of space lead to competitive dominance of woody plants in the back-dune. Our results suggest that Sardinian sand dune plant communities are organized hierarchically, structured by sand binding foundation species on the fore-dune, sand burial in the middle-dune and increasingly successful seedling recruitment, growth and competitive dominance in the back-dune. PMID:27478701

  3. Hierarchical organization of a Sardinian sand dune plant community.

    PubMed

    Cusseddu, Valentina; Ceccherelli, Giulia; Bertness, Mark

    2016-01-01

    Coastal sand dunes have attracted the attention of plant ecologists for over a century, but they have largely relied on correlations to explain dune plant community organization. We examined long-standing hypotheses experimentally that sand binding, inter-specific interactions, abiotic factors and seedling recruitment are drivers of sand dune plant community structure in Sardinia, Italy. Removing foundation species from the fore-, middle- and back-dune habitats over three years led to erosion and habitat loss on the fore-dune and limited plant recovery that increased with dune elevation. Reciprocal species removals in all zones suggested that inter-specific competition is common, but that dominance is transient, particularly due to sand burial disturbance in the middle-dune. A fully factorial 2-year manipulation of water, nutrient availability and substrate stability revealed no significant proximate response to these physical factors in any dune zone. In the fore- and middle-dune, plant seeds are trapped under adult plants during seed germination, and seedling survivorship and growth generally increase with dune height in spite of increased herbivory in the back-dune. Sand and seed erosion leads to limited seed recruitment on the fore-dune while high summer temperatures and preemption of space lead to competitive dominance of woody plants in the back-dune. Our results suggest that Sardinian sand dune plant communities are organized hierarchically, structured by sand binding foundation species on the fore-dune, sand burial in the middle-dune and increasingly successful seedling recruitment, growth and competitive dominance in the back-dune.

  4. Discrimination of active and inactive sand from remote sensing - Kelso dunes, Mojave Desert, California

    NASA Technical Reports Server (NTRS)

    Paisley, Elizabeth C. I.; Lancaster, Nicholas; Gaddis, Lisa R.; Greeley, Ronald

    1991-01-01

    Landsat TM images, field data, and laboratoray reflectance spectra were examined for the Kelso dunes, Mojave Desert, California to assess the use of visible and near-infrared (VNIR) remote sensing data to discriminate aeolian sand populations on the basis of spectral brightness. Results show that areas of inactive sand have a larger percentage of dark, fine-grained materials compared to those composed of active sand, which contain less dark fines and a higher percentage of quartz sand-size grains. Both areas are spectrally distinct in the VNIR, suggesting that VNIR spectral data can be used to discriminate active and inactive sand populations in the Mojave Desert. Analysis of laboratory spectra was complicated by the presence of magnetite in the active sands, which decreases their laboratory reflectance values to those of inactive sands. For this application, comparison of TM and laboratory spectra suggests that less than 35 percent vegetation cover does not influence the TM spectra.

  5. Late Quaternary aeolian and fluvial interactions on the Cooper Creek Fan and the association between linear and source-bordering dunes, Strzelecki Desert, Australia

    NASA Astrophysics Data System (ADS)

    Cohen, T. J.; Nanson, G. C.; Larsen, J. R.; Jones, B. G.; Price, D. M.; Coleman, M.; Pietsch, T. J.

    2010-02-01

    The Innamincka Dome and associated low-gradient fan in the Strzelecki Desert is the product of Cenozoic crustal warping that has aided formation of an extensive array of palaeochannels, source-bordering transverse dunes and superimposed linear dunes. These dunes have impeded the course of Cooper Creek and provided a repository of evidence for Quaternary climate change as well as the interactive processes between transverse and linear dune formation. At Turra, Gidgealpa and sites nearby are extensive fluvial and aeolian sand bodies that date from marine isotope stages (MIS) 8-3 and the Last Glacial Maximum (LGM) and are now surrounded or buried by overbank mud. The sandy alluvium was deposited on the downstream slope of the dome by large channels transporting abundant bedload, subsequently blown northward to form transverse dunes from what were probably seasonally-exposed bars in a palaeo-Cooper system. Thermoluminescence (TL) and optically stimulated luminescence (OSL) ages demonstrate that the base of the dune complex is at least MIS 7 in age (˜250 ka) but that it has been subsequently reworked by wind with additional sand blown from the river. Source-bordering dunes formed during a period of enhanced river flow and sand supply from ˜120 to 100 ka, with another short episode of the same at ˜85-80 ka and from ˜68 to 53. The LGM was associated with enhanced flows and the supply of dune sediment, from 28 to 18 ka. Pronounced river flow and dune activity occurred in the early to mid Holocene, but there is no evidence of dunes being supplied from Cooper Creek since the LGM. The dunes forming the oldest basal sand units appear to be largely transverse in form and are aligned roughly parallel to adjacent east-west trending palaeochannels. Linear dunes have formed from and over these, and yield basal ages ranging from MIS 5 or MIS 4 but continuing to accrete and rework through to the Holocene. The study results in one of the few detailed chronological investigations

  6. Recent seasonal variations in arid landscape cover and aeolian sand mobility, Navajo Nation, southwestern U.S.

    USGS Publications Warehouse

    Draut, Amy E.; Redsteer, Margaret Hiza; Amoroso, Lee; Giosan, Liviu; Fuller, Dorian Q.; Nicoll, Kathleen; Flad, Rowan K.; Clift, Peter D.

    2013-01-01

    The socioeconomic impacts of climate change pose problems not only in devel- oping countries but also to residents of arid lands in the United States among marginalized societies with limited economic means. In the Navajo Nation, warming temperatures and recent drought have increased aeolian sediment mobility such that large, migrating sand dunes affect grazing lands, housing, and road access. Dust derived from this region also affects albedo and longevity of the Rocky Mountains snowpack, located downwind. We present initial results from a study that monitors sand transport and vegetation within a 0.2 km2 site in the Navajo lands, measuring the effects of drought on landscape stability since 2009. Sand mobility decreased substantially as 1 year with near-normal monsoon rainfall (2010) somewhat abated a decade-long drought, temporarily doubling vegetation cover. Vegetation that grew during 2010, with adequate rain, died off rapidly during dry conditions in 2011. Short-term increases in rainfall that promote annual, but not perennial, plant growth will not improve landscape stability in the long term. Climate projections suggest that a warmer, drier climate and potentially enhanced sediment supply from ephem- eral washes will further increase aeolian sand transport and dune activity, worsening the present challenges to people living in this region. Connections among climate, vegetation, and aeolian sediment erodibility in this region are highly relevant to other areas of the world with similar environmental problems.

  7. Impacts of Vegetation and Development on the Morphology of Coastal Sand Dunes Using Modern Geospatial Techniques: Jockey's Ridge Case Study

    NASA Astrophysics Data System (ADS)

    Weaver, K.; Mitasova, H.; Overton, M.

    2011-12-01

    area of sand that once fed the dunes, limiting aeolian sand transport and migration of the dune system. Not only are vegetation and development increasing around the Jockey's Ridge State Park, but vegetation is increasing inside the park boundaries with the majority of growth along the windward side of the dune system, blocking sand from feeding the dunes. Vegetation growth is also found to increase in front of the dune field, recently causing the migration of the dune to slow down.

  8. Behavior and identification of ephemeral sand dunes at the backshore zone using video images.

    PubMed

    Guimarães, Pedro V; Pereira, Pedro S; Calliari, Lauro J; Ellis, Jean T

    2016-09-01

    The backshore zone is transitional environment strongly affected by ocean, air and sand movements. On dissipative beaches, the formation of ephemeral dunes over the backshore zone plays significant contribution in the beach morphodynamics and sediment budget. The aim of this work is to describe a novel method to identify ephemeral dunes in the backshore region and to discuss their morphodynamic behavior. The beach morphology is identified using Argus video imagery, which reveals the behavior of morphologies at Cassino Beach, Rio Grande do Sul, Brasil. Daily images from 2005 to 2007, topographic profiles, meteorological data, and sedimentological parameters were used to determine the frequency and pervasiveness of these features on the backshore. Results indicated that coastline orientation relative to the dominant NE and E winds and the dissipative morphological beach state favored aeolian sand transport towards the backshore. Prevailing NE winds increase sand transportation to the backshore, resulting in the formation of barchans, transverse, and barchanoid-linguiod dunes. Precipitation inhibits aeolian transport and ephemeral dune formation and maintains the existing morphologies during strong SE and SW winds, provided the storm surge is not too high.

  9. Space Radar Image of Namibia Sand Dunes

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This spaceborne radar image shows part of the vast Namib Sand Sea on the west coast of southern Africa, just northeast of the city of Luderitz, Namibia. The magenta areas in the image are fields of sand dunes, and the orange area along the bottom of the image is the surface of the South Atlantic Ocean. The region receives only a few centimeters (inches) of rain per year. In most radar images, sandy areas appear dark due to their smooth texture, but in this area the sand is organized into steep dunes, causing bright radar reflections off the dune 'faces.' This effect is especially pronounced in the lower center of the image, where many glints of bright radar reflections are seen. Radar images of this hyper-arid region have been used to image sub-surface features, such as abandoned stream courses. The bright green features in the upper right are rocky hills poking through the sand sea. The peninsula in the lower center, near Hottentott Bay, is Diaz Point; Elizabeth Point is south of Diaz Point. This image was acquired by Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) onboard the space shuttle Endeavour on April 11, 1994. The image is 54.2 kilometers by 82.2 kilometers (33.6 miles by 51.0 miles) and is centered at 26.2 degrees South latitude, 15.1 degrees East longitude. North is toward the upper left. The colors are assigned to different radar frequencies and polarizations of the radar as follows: red is L-band, horizontally transmitted and received; green is L-band, horizontally transmitted, vertically received; and blue is C-band, horizontally transmitted, horizontally received. SIR-C/X-SAR, a joint mission of the German, Italian, and United States space agencies, is part of NASA's Mission to Planet Earth.

  10. The north-eastern aeolian 'European Sand Belt' as potential record of environmental changes: A case study from Eastern Latvia and Southern Estonia

    NASA Astrophysics Data System (ADS)

    Kalińska-Nartiša, Edyta; Thiel, Christine; Nartišs, Māris; Buylaert, Jan-Pieter; Murray, Andrew S.

    2016-09-01

    The Latvian and Estonian inland dunes belong to the north-eastern part of the 'European Sand Belt' (ESB). These dunes are widely distributed over broad glaciolacustrine plains and Late Glacial alluvial deltas, considered to be potential sources for the aeolian material. Little is known about these aeolian sediments and their substratum; here we present a detailed sedimentary structural and textural characterisation together with a luminescence-based chronology. Through a comparison between grain-size, rounding of quartz grains and surface characteristics in medium/coarse (0.5-0.8 mm) sand, and the light mineral content, we found an alternation of aeolian and periglacial components. Further, short-lasting aeolian abrasion and/or transportation periods, and a significant contribution of a nearby sediment source are suggested. Luminescence dating points to aeolian sand accumulation and dune formation between ∼16 ka and ∼9 ka. However, we also observed some presumably watertable controlled environmental conditions at ∼13 ka; this corresponds with the occurrence of an ice-dammed/proglacial lake.

  11. Controls on Dune Deformation Patterns in White Sands, New Mexico

    NASA Astrophysics Data System (ADS)

    Lee, D. B.; Ferdowsi, B.; Jerolmack, D. J.

    2015-12-01

    Eolian dune fields exhibit a variety of pattern transitions, including: the ab initio appearance of dunes from no dunes; transverse to barchan and unvegetated barchan to vegetated parabolic. Recent model predictions offer some insight into the mechanisms underlying some of these transitions. However, there are few direct observations, and tests providing empirical verification are sparse. The White Sands dune field exhibits all three of the aforementioned transitions in sequence, from the upwind to downwind margin, and has the potential to be a testing ground for these predictions. Repeat LiDAR data at White Sands provide an excellent opportunity to study not only dune structure, but also dune dynamics, which can provide insight into how dunes destabilize from one dune morphology into another. We employ a recently developed method for decomposing dune migration into two components: "translation" of a dune, and changes in dune shape referred to as "deformation". We find that the fastest moving dunes (i.e. the dunes translating most quickly) have the largest amount of deformation. Patterns of deformation also vary depending on dune type: transverse dunes experience coherent deformation, while parabolic dunes exhibit highly localized and apparently random deformation. Only a fraction of the deformation can be explained by the migration rate. A significant amount of deformation appears to be attributable to dune-dune interactions, which destabilize dune patterns in locations where dune density is high. At the interface between the transverse to barchan dune patterns, we describe how transverse dunes break up into barchans and compare it to published model results. Regarding the barchan to parabolic transition, we find that the onset of vegetation drives a gradual slowdown in migration rates, while the magnitude of deformation drops and becomes localized to dune crests as the arms are stabilized by plants.

  12. Modeling grain size variations of aeolian gypsum deposits at White Sands, New Mexico, using AVIRIS imagery

    USGS Publications Warehouse

    Ghrefat, H.A.; Goodell, P.C.; Hubbard, B.E.; Langford, R.P.; Aldouri, R.E.

    2007-01-01

    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 ??{symbol} (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 ??{symbol} (352????m), and 1.52 ??{symbol} (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

  13. Field measurements on spatial variations in aeolian sediment availability at the Sand Motor mega nourishment

    NASA Astrophysics Data System (ADS)

    Hoonhout, Bas; de Vries, Sierd

    2017-02-01

    Spatial variations in aeolian sediment transport were measured at the Sand Motor mega nourishment in The Netherlands during a six week field campaign in the fall of 2014. A consistent significant increase in sediment transport in downwind direction (positive gradient) was measured over the intertidal beach area, indicating that the intertidal beach is a primary source of aeolian sediment, despite the high soil moisture contents. A small positive increase in transport in downwind direction was measured over the dry beach, indicating that local aeolian sediment supply was hampered. A consistent decrease in sediment transport in downwind direction (negative gradient) was measured at the transition between intertidal and dry beach, indicating local deposition of sediment. The negative gradients coincide with the berm edge and the onset of a shell pavement. Therefore deposition might be promoted by morphological feedback between a berm and the wind and the entrapment of sediment in the beach armor layer. The local sediment deposits cause the sediment supply to the dunes to be continued even during high water, resulting in a phased process. The influence of the beach armor layer reduces during storm events as the armor layer itself is being mobilized.

  14. Sand availability control on dune shape and orientation

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Narteau, Clement; Rozier, Olivier; Courrech Du Pont, Sylvain

    2015-04-01

    An increasing body of evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism. Consequently, the same wind regime can produce different bedform orientations. Here, we use numerical simulations with different conditions of sand availability to predict dune shape and alignment in asymmetric bimodal wind regimes. In zones of abundant sand supply, linear dunes grow in height and propagate selecting the orientation for which the normal to crest components of transport reaches a maximum. In zones of limited sand supply, linear dunes grow by extension in the direction of the resultant sand flux. Considering these two independent dune growth mechanisms, we find good agreement between numerical and analytical models, and estimate the magnitude of wind velocity acceleration up the dune stoss slopes. In the extensional mode of linear dune formation, there is no abrupt change in dune trend when the divergence angle between the two winds crosses 90°. Instead, there are systematic transitions in dune type from linear to barchan for critical values of the divergence angle that depend on the transport ratio. We show how the growth rates of the two dune growth mechanisms may be used to infer the dune field morphology in zones of low sediment availability.

  15. Vulnerability and fate of a coastal sand dune complex, Rosetta-Idku, northwestern Nile Delta, Egypt

    NASA Astrophysics Data System (ADS)

    El Banna, Mahmoud M.

    2008-05-01

    Types, distribution, and origin of recent sand dunes between Rosetta and Idku, in the western sector of the Nile Delta, Egypt were investigated. Sand samples from the dunes, beach, and seafloor were studied for grain size distribution and mineralogical composition. It has been found that most of the dunes in the study area have been subjected to deterioration and removal due to the construction of buildings and the International Coastal Highway. The remnant constitutes a damaged belt of foredunes that extends from El Bouseily village to the west of Idku town. The dune’s origin is interpreted to be the result of coastal drifting and the subsequent transport of sediments of the former Canopic Nile branch eastward by the predominant longshore current and by aeolian processes. The blown sand grains accumulated to form a belt of coastal sand dunes of original longitudinal and crescentic forms. Urbanization of the coast has severely altered the landscape. The study area is considered vulnerable to the impacts of climate change and the expected rise in sea level. The outcome of potential sea level rise is serious; erosion problems are expected to be exacerbated and vast areas from land and property would be lost. Thus, protection and preservation the remaining dunes in the study area are vital requirements for shore protection.

  16. Heterogeneous Wireless Sensor Network for Real Time Remote Monitoring of Sand Dynamics on Coastal Dunes

    NASA Astrophysics Data System (ADS)

    Pozzebon, Alessandro; Bove, Carmine; Cappelli, Irene; Alquini, Fernanda; Bertoni, Duccio; Sarti, Giovanni

    2016-10-01

    In this paper, the architecture of a heterogeneous Wireless Sensor Network (WSN) to be deployed on coastal sand dunes is described, the aim of which is to provide real time measurements of physical parameters to better define the sediment transport in connection with Aeolian processes. The WSN integrates different typologies of sensors and is provided with both local and remote connection. In particular, three different typologies of sensors are integrated in the network: a multilayer anemometric station, a sensor developed ad-hoc to measure the sand dune level and a sand collector capable of measuring the weight of trapped sand and its quantity. Each sensor node is made up at least of a ZigBee radio module that is able to transmit the data collected by the sensor at a distance of about 100 meters. While the sand level sensor and the sand collector are provided only with this transmission module, the anemometric station also integrates a microprocessor board in charge of data processing. A Gateway node provided with a GSM connection for remote data transmission and a Zigbee radio module for Local Area communication has also been developed. This node is in charge of collecting all the data packets sent by the Sensor Nodes and transmit them to a remote server through GPRS connection. A Web server has been set up to collect these packets and store them in a database. The proposed WSN can provide both a static and a dynamic framework of sand transport processes acting on coastal dunes.

  17. Coastal Sand Dune Plant Ecology: Field Phenomena and Interpretation

    ERIC Educational Resources Information Center

    McDonald, K.

    1973-01-01

    Discusses the advantages and disadvantages of selecting coastal sand dunes as the location for field ecology studies. Presents a descriptive zonal model for seaboard sand dune plant communities, suggestions concerning possible observations and activities relevant to interpreting phenomena associated with these forms of vegetation, and additional…

  18. Variation of bee communities on a sand dune complex in the Great Basin: Implications for sand dune conservation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sand dunes across the Mojave and Great Basin Deserts house rich bee communities. The pollination services these bees provide can be vital in maintaining the diverse, and often endemic, dune flora. These dune environments, however, are threatened by intense off-highway vehicle (OHV) use. Conservati...

  19. The effects of psammophilous plants on sand dune dynamics

    NASA Astrophysics Data System (ADS)

    Bel, Golan; Ashkenazy, Yosef

    2014-07-01

    Mathematical models of sand dune dynamics have considered different types of sand dune cover. However, despite the important role of psammophilous plants (plants that flourish in moving-sand environments) in dune dynamics, the incorporation of their effects into mathematical models of sand dunes remains a challenging task. Here we propose a nonlinear physical model for the role of psammophilous plants in the stabilization and destabilization of sand dunes. There are two main mechanisms by which the wind affects these plants: (i) sand drift results in the burial and exposure of plants, a process that is known to result in an enhanced growth rate, and (ii) strong winds remove shoots and rhizomes and seed them in nearby locations, enhancing their growth rate. Our model describes the temporal evolution of the fractions of surface cover of regular vegetation, biogenic soil crust, and psammophilous plants. The latter reach their optimal growth under either (i) specific sand drift or (ii) specific wind power. The model exhibits complex bifurcation diagrams and dynamics, which explain observed phenomena, and it predicts new dune stabilization scenarios. Depending on the climatological conditions, it is possible to obtain one, two, or, predicted here for the first time, three stable dune states. Our model shows that the development of the different cover types depends on the precipitation rate and the wind power and that the psammophilous plants are not always the first to grow and stabilize the dunes.

  20. Geomorphology of coastal sand dunes, Baldwin County, Alabama

    USGS Publications Warehouse

    Bearden, Bennett L.; Hummell, Richard L.; Mink, Robert M.

    1989-01-01

    Alabama's coastal eolian deposits are primarily vegetated dunes that are exemplified by sand ridges with flat to undulating upper surfaces and continuous irregular crests. Dune fields occur along Morgan peninsula between the foredune line and Little Lagoon and the Mobile Bay area. These dune fields consist primarily of one or more continuous ridges that parallel the coast and are generally vegetaed to grassy. Washover of the beach and backshore during Hurricane Frederic (1979) and subsequent smaller scale storms resulted in significant erosion of many of Alabama's dune fields. The primary dunes or foredunes are beginning to recover from the effects of these storms; however, numerous breaks in the primary dune line are present. Sand dunes in coastal Alabama provide protection against storm-generated waves and washover. The foredunes are protected by adherence to a Coastal Construction Control Line (CCCL) or construction setback line identified by markers along coastal Baldwin County.

  1. Seasonal geomorphic processes and rates of sand movement at Mount Baldy dune in Indiana, USA

    NASA Astrophysics Data System (ADS)

    Kilibarda, Zoran; Kilibarda, Vesna

    2016-12-01

    Winds are very strong, frequent, and have high energy (annual DP ∼800 VU) along the southern shores of Lake Michigan, allowing the coexistence of fixed and active dunes. Six years (2007-13) of monitoring Mount Baldy in the Indiana Dunes National Lakeshore reveals that this is the most active coastal dune in the Great Lakes region. This paper documents aeolian processes and changes in the dune's morphology that occur temporarily, following storms, or seasonally, due to weather (climate) variations. Most of the sand transport in this area takes place during strong storms with gale force (>17.5 m/s) winds, which occur in the autumn and winter months. A single storm, such as the October 28-31, 2013 event, can contribute 25% of the annual sand transport and dune movement inland. In its most active year (June 1, 2011 through May 31, 2012), Mount Baldy moved inland on average 4.34 m, with a maximum of 6.52 m along the blowout's axis (155° azimuth). During this particularly active season, there were six storms with sustained gale force winds, winter air temperatures were warmer than average, and shelf ice on Lake Michigan lasted only one day. The dune is least active during the summer season, when the winds are weakest. The late fall and winter winds are the strongest. But in a typical year, most of the dune's advance inland takes place during the spring thaw when sand is released from over-steepened and lumpy slip face, allowing it to avalanche to the toe of the slip face. However, with a warming air temperatures, a reduction in the duration of winter shelf ice, and rising Lake Michigan levels, the annual rates of sand transport and dune movement may increase. The recent Mount Baldy management strategy, which includes planting vegetation and installing wind barriers on the dune's stoss side in an effort to fix the dune and stop its further movement inland, may potentially cause the destruction of the mobile sand, open dune habitat, resulting in the extinction of rare

  2. Quantifying wind blown landscapes using time-series airborne LiDAR at White Sands Dune Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.

    2011-12-01

    Wind blown landscapes are a default geomorphic and sedimentary environment in our solar system. Wind sand dunes are ubiquitous features on the surfaces of Earth, Mars and Titan and prevalent within the aeolian rock records of Earth and Mars. Dunes are sensitive to environmental and climatic changes and a complete understanding of this system promises a unique, robust and quantitative record of paleoclimate extending to the early histories of these worlds. However, our understanding of how aeolian dune landscapes evolve and how the details of the wind are recorded in cross-strata is limited by our lack of understanding of three-dimensional dune morphodynamics related to changing boundary conditions such as wind direction and magnitude and sediment source area. We use airborne LiDAR datasets over 40 km2 of White Sands Dune Field collected from June 2007, June 2008, January 2009, September 2009 and June 2010 to quantify 1) three-dimensional dune geometries, 2) annual and seasonal patterns of erosion and deposition across dune topography, 3) spatial changes in sediment flux related to position within the field, 4) spatial changes in sediment flux across sinuous crestlines and 5) morphologic changes through dune-dune interactions. In addition to measurements, we use the LiDAR data along with wind data from two near-by weather stations to develop a simple model that predicts depositional and stratigraphic patterns on dune lee slopes. Several challenges emerged using time series LiDAR data sets at White Sands Dune Field. The topography upon which the dunes sit is variable and rises by 16 meters over the length of the dune field. In order to compare individual dune geometries across the field and between data sets a base surface was interpolated from local minima and subtracted from the dune topography. Co-registration and error calculation between datasets was done manually using permanent vegetated features within the active dune field and structures built by the

  3. Mulitple Origins of Sand Dune-Topography Interactions on Titan

    NASA Astrophysics Data System (ADS)

    Goggin, H.; Ewing, R. C.; Hayes, A.; Cisneros, J.; Epps, J. C.

    2015-12-01

    The interaction between sand dune patterns and topographic obstacles is a primary signal of sand transport direction in the equatorial region of Saturn's moon, Titan. The streamlined, tear drop appearance of the sand-dune patterns as they wrap around obstacles and a dune-free zone on the east side of many obstacles gives the impression that sand transport is from the west to east at equatorial latitudes. However, the physical mechanism behind the dune-obstacle interaction is not well explained, leaving a gap in our understanding of the equatorial sand transport and implied wind directions and magnitudes on Titan. In order to better understand this interaction and evaluate wind and sand transport direction, we use morphometric analysis of optical images on Earth and Cassini SAR images on Titan combined with analog wind tunnel experiments to study dune-topography interactions. Image analysis is performed in a GIS environment to map spatial variations in dune crestline orientations proximal to obstacles. We also use digital elevation models to and analyze the three-dimensional geometry - height, length, width and slope of the dune-topography relationships on Earth. Preliminary results show that dune patterns are deflected similarly around positive, neutral, or negative topography, where positive topography is greater than the surrounding dune height, neutral topography is at dune height and negative topography is lower than dune heights. In the latter case these are typically intra-dune field playas. The obstacle height, width, slope and wind variability appear to play a primary role in determining if a lee-dune, rather than a dune-free lee-zone, develops. In many cases a dune-free playa with evaporite and mud desiccation polygons forms lee-ward of the obstacle. To support and elaborate on the mapping and spatial characterization of dune-topography interactions, a series of experiments using a wind tunnel were conducted. Wind tunnel experiments examine the formation

  4. A high-efficiency, low-cost aeolian sand trap

    NASA Astrophysics Data System (ADS)

    Sherman, D. J.; Swann, C.; Barron, J. D.

    2014-06-01

    We present a design for an aeolian sand trap that is based on the streamer trap concept used in sediment transport studies. The trap is inexpensive, has excellent trapping efficiency, is durable, and easy to use. It is fabricated from stainless steel that is cut and bent to form a frame to support a fine nylon mesh. Typical trap openings are 100 mm wide and 25, 50, or 100 mm high. Traps are 250 mm long, and are stackable to measure vertical characteristics of saltation. The nylon mesh has 64 μm openings that comprise 47% of the area of the material. Aerodynamic efficiency was tested in a wind tunnel, and sediment trapping efficiency evaluated in field deployments. Both evaluations support the use of this trap for short-term measurements.

  5. A Global Digital Database and Atlas of Quaternary Dune Fields and Sand Seas

    NASA Astrophysics Data System (ADS)

    Lancaster, N.; Halfen, A. F.

    2012-12-01

    Sand seas and dune fields are globally significant sedimentary deposits, which archive the effects of climate and sea level change on a variety of temporal and spatial scales. Dune systems provide a valuable source of information on past climate conditions, including evidence for periods of aridity and unique data on past wind regimes. Researchers have compiled vast quantities of geomorphic and chronological data from these dune systems for nearly half a century, however, these data remain disconnected, making comparisons of dune systems challenging at global and regional scales. The primary goal of this project is to develop a global digital database of chronologic information for periods of desert sand dune accumulation and stabilization, as well as, pertinent stratigraphic and geomorphic information. This database can then be used by scientists to 1) document the history of aeolian processes in arid regions with emphasis on dune systems in low and mid latitude deserts, 2) correlate periods of sand accumulation and stability with other terrestrial and marine paleoclimatic proxies and records, and 3) develop an improved understanding of the response of dune systems to climate change. The database currently resides in Microsoft Access format, which allows searching and filtering of data. The database includes 4 linked tables containing information on the site, chronological control (radiocarbon or luminescence), and the pertinent literature citations. Thus far the database contains information for 838 sites world wide, comprising 2598 luminescence and radiocarbon ages, though these numbers increase regularly as new data is added. The database is only available on request at this time, however, an online, GIS database is being developed and will be available in the near future. Data outputs from the online database will include PDF reports and Google Earth formatted data sets for quick viewing of data. Additionally, data will be available in a gridded format for

  6. Sand dunes on the central Delmarva Peninsula, Maryland and Delaware

    USGS Publications Warehouse

    Denny, Charles Storrow; Owens, James Patrick

    1979-01-01

    Inconspicuous ancient sand dunes are present in parts of the central Delmarva Peninsula, Maryland and Delaware. Many dunes are roughly V-shaped, built by northwest winds, especially on the east sides of some of the large rivers. On the uplands, the form and spacing of the dunes are variable. A surficial blanket composed mainly of medium and fine-grained sand-the Parsonsburg Sand-forms both the ancient dunes and the broad plains between the dunes. The sand that forms the dunes is massive and intensely burrowed in the upper part; traces of horizontal or slightly inclined bedding appear near the base. Quartz is the dominant mineral constituent of the sand. Microline is abundant in the very fine to fine sand fraction. The heavy-mineral assemblages (high zircon, tourmaline, rutile) are more mature than in most of the possible source rocks. The most abundant minerals in the clay-sized fraction are dioctahedral vermiculite, kaolinite, illite, montmorillonite, and gibbsite. The first four minerals are common in deposits of late Wisconsin and Holocene age. The gibbsite may be detrital, coming from weathered rocks of Tertiary age. The soil profile in the dune sand is weakly to moderately developed. At or near the base of the Parsonsburg Sand are peaty beds that range in age from about 30,000 to about 13,000 radiocarbon years B.P. Microfloral assemblages in the peaty beds suggest that the dunes on the uplands formed in a spruce parkland during the late Wisconsin glacial maximum. The river dunes may also be of late Wisconsin age, but could be Holocene.

  7. Modelling aeolian sand transport using a dynamic mass balancing approach

    NASA Astrophysics Data System (ADS)

    Mayaud, Jerome R.; Bailey, Richard M.; Wiggs, Giles F. S.; Weaver, Corinne M.

    2017-03-01

    Knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes. Whilst many aeolian studies have relied on time-averaged parameters such as wind velocity (U) and wind shear velocity (u*) to determine sediment flux, there is increasing field evidence that high-frequency turbulence is an important driving force behind the entrainment and transport of sand. At this scale of analysis, inertia in the saltation system causes changes in sediment transport to lag behind de/accelerations in flow. However, saltation inertia has yet to be incorporated into a functional sand transport model that can be used for predictive purposes. In this study, we present a new transport model that dynamically balances the sand mass being transported in the wind flow. The 'dynamic mass balance' (DMB) model we present accounts for high-frequency variations in the horizontal (u) component of wind flow, as saltation is most strongly associated with the positive u component of the wind. The performance of the DMB model is tested by fitting it to two field-derived (Namibia's Skeleton Coast) datasets of wind velocity and sediment transport: (i) a 10-min (10 Hz measurement resolution) dataset; (ii) a 2-h (1 Hz measurement resolution) dataset. The DMB model is shown to outperform two existing models that rely on time-averaged wind velocity data (e.g. Radok, 1977; Dong et al., 2003), when predicting sand transport over the two experiments. For all measurement averaging intervals presented in this study (10 Hz-10 min), the DMB model predicted total saltation count to within at least 0.48%, whereas the Radok and Dong models over- or underestimated total count by up to 5.50% and 20.53% respectively. The DMB model also produced more realistic (less 'peaky') time series of sand flux than the other two models, and a more accurate distribution of sand flux data. The best predictions of total sand transport are achieved using

  8. Relating climate and sand transport to incipient dune development.

    NASA Astrophysics Data System (ADS)

    van Puijenbroek, Marinka; Limpens, Juul; Gleichman, Maurits; Berendse, Frank

    2014-05-01

    Sea levels are continuously rising, increasing the risk of flooding and coastal erosion in low-elevation countries, such as the Netherlands. Coastal dunes are seen as a flexible and natural type of coastal defence, that is able to keep pace with rising water levels. Until now most research has focussed on dynamics and maintenance of established dunes, largely ignoring two critical transitions in early dune development: the transition from bare beach to vegetated incipient dune and that from incipient dune to established foredune. This knowledge is essential to enable more accurate prediction and even stimulation of new dune formation through sand nourishment. We explored the relative contributions of climate and sand transport to incipient dune development combining a 30 year time-series of aerial photographs (1979 - 2010) of the natural Wadden Island coast with high-resolution monitoring data of sand volume changes and climatic parameters. We selected 20 strips of 2.5 km in length along the coast of the Wadden Islands, with a 2 km buffer between them to avoid autocorrelation. For each of these strips of coast we assessed the changes in presence and area of incipient dunes over periods of 5-6 years. Change in fore dune volume and beach width were derived from high resolution beach elevation data. Seawater level and climate data were derived from a nearby meteorological station Preliminary analysis of the first half of the dataset showed that incipient dune area was positively related to beach width, but negatively to storm intensity. In our poster we will present the whole dataset and discuss the implications of our results for future dune development and anthropogenic sand nourishment schemes.

  9. Measurements of wind, aeolian sand transport, and precipitation in the Colorado River corridor, Grand Canyon, Arizona; January 2005 to January 2006

    USGS Publications Warehouse

    Draut, Amy E.; Rubin, David M.

    2006-01-01

    evaluate the potential for aeolian reworking of new fluvial sand deposits, and restoration of higher-elevation aeolian deposits, following the 60-hour controlled flood release from Glen Canyon Dam in November 2004. Substantial deposition of new sand occurred at all study sites during this high-flow experiment, but most of the new sediment was eroded by high flow fluctuations between January and March 2005. Comparison of aeolian sand transport in the spring windy seasons of the preand post-flood years indicates that, where some of the flood-deposited sand remained by spring, aeolian sand transport was significantly higher than during the pre-flood spring. Gully incision in an aeolian dune field was observed to be partially ameliorated by deposition of wind-blown sand derived from a nearby 2004 flood deposit. These results imply that sediment-rich controlled floods can renew sand deposition in aeolian dune fields above the flood-stage elevation. The potential for restoration of archaeological sites in aeolian deposits can be maximized by using dam operations that maximize the open sand area on fluvial sandbars during spring, when aeolian sediment transport is greatest.

  10. Effects of beach raking and sand fences on dune dimensions and morphology

    NASA Astrophysics Data System (ADS)

    Nordstrom, Karl F.; Jackson, Nancy L.; Freestone, Amy L.; Korotky, Katherine H.; Puleo, Jack A.

    2012-12-01

    Raking beaches to remove wrack (natural and human litter) to enhance recreational use, and using sand fences to build and stabilize dunes are common practices on developed shores, but their effects on the landscape are not well understood. Managers in Avalon, NJ ceased using sand fences and raking in a portion of beach in 1991, providing the opportunity to evaluate evolution of natural and managed dune systems over a 19-year period. Topographic and vegetation characteristics were evaluated on 15 transects within 5 sites in a managed area, where raking and sand fences are still used, and at 15 transects within 5 sites in a naturally evolving (unmanaged) area. Raking and deploying fences in the managed area restricted the size of the cross-shore zone in which aeolian accretion occurred but resulted in greater dune crest heights than in the unmanaged area. Crest heights of the foredune in the managed area ranged from 4.45 m to 5.27 m. Crest heights in the unmanaged area ranged from 3.02 m to 4.27 m. Dune volume and beach volume were greater on average in the unmanaged area, and the dune was wider (mean of 72 m versus 40 m) and had an additional ridge. The unmanaged area had 35% more species and contained a greater percentage of all species encountered in the study area than the managed area (88% compared to 65%). More species occurred in the swales than any other of the cross-shore habitats, and most of these species were observed in the deeper, wider swales in the unmanaged area. Removing wrack from the beach prevents incipient dunes from forming, thus reducing the number of dune crests and size of swales that create topographic variability and increase the number and types of habitats for flora and fauna. Suspension of raking can allow the dunes to build seaward while producing a greater variety and number of habitats, but seaward growth does not mean that the height of the dune will increase substantially, and fences may be needed to build an initial dune ridge for

  11. Evidence of active dune sand on the Great Plains in the 19th century from accounts of early explorers

    USGS Publications Warehouse

    Muhs, D.R.; Holliday, V.T.

    1995-01-01

    Dune fields are found in several areas of the Great Plains, and though mostly stabilised today, the accounts of early explorers show that they were more mobile in the last century. Using an index of dune mobility and tree ring data, it is found that these periods of mobility were related to temperature-induced drought, the high temperatures increasing evapotranspiration. Explorers also record that rivers upwind of these dune fields had shallow braided channels in the 19th century, and these would have supplied further aeolian sand. It is concluded that these dunes are extremely susceptible to climate change and that it may not need global warming to increase their mobility again. -K.Clayton

  12. The influence of different environmental and climatic conditions on vegetated aeolian dune landscape development and response

    NASA Astrophysics Data System (ADS)

    Nield, Joanna M.; Baas, Andreas C. W.

    2008-11-01

    Aeolian dune field development in coastal and semi-arid environments is a function of complex ecogeomorphic interactions which are sensitive to fluctuations in climatic and environmental conditions. We explore the relationships between ecological and geomorphic processes in the development of these landscape patterns and speculate on their response to variations in vegetation vitality and sediment transport capacity, indicating possible consequences of climate and land use change, using the Discrete ECogeomorphic Aeolian Landscape (DECAL) cellular automaton algorithm. This algorithm models dune field behaviour that reflects long-term trends prevalent in palaeo-records, but also elucidates possible evolutionary progressions, relaxation period sequences and threshold sensitivities. The landscape response is sensitive both to the perturbation itself and the state of the system when the disturbance occurs. Response amplitude decreases in simulated systems with reduced mobility unless an external disturbance mimicking fire or land clearance is applied concurrently with a reduction in growth vigour triggering a threshold type response when sufficient vegetation is removed. The model demonstrates that the relative response characteristics of the multiple vegetation types and their mutual feedback with geomorphic processes impart a significant influence on landscape equilibrium or attractor states. Fast growing vegetation enables the formation of hairpin (long-walled) parabolic dune systems, which eventually become sediment starved and stabilise, whereas inhospitable conditions inhibiting vegetation growth contribute to the development of active transgressive transverse dune fields. This simple vegetated dune model illustrates the power and versatility of a cellular automaton approach for exploring thresholds, sensitivities and possible evolutionary trajectories associated with the interactions between ecology, geomorphology and climatic conditions in complex earth surface

  13. Documentation of Recent Surface Winds on Martian Sand Dunes

    NASA Astrophysics Data System (ADS)

    Zimbelman, J. R.; Johnson, M. B.

    2013-12-01

    Images from the High Resolution Imaging Science Experiment (HiRISE) are of sufficient resolution to record wind ripple patterns on the surfaces of sand dunes present across the surface of Mars. We are in the early stages of an investigation to map the ripple orientations preserved on Martian sand dunes, in order to evaluate the recent wind flow over the dunes, and compare that wind flow pattern to the winds documented over terrestrial sand dunes. HiRISE image ESP_025645_1455 covers a sand dune field on the floor of a 20-km-diameter unnamed impact crater in the Terra Cimmeria region of the southern highlands, east of the Hellas impact basin. This image is centered at 34.23 S latitude, 138.437 E longitude with 25 cm/pixel resolution, and was taken on Jan 25 of 2012 during northern spring (Ls = 57.4). Using ArcGIS, lines were drawn across three ripples perpendicular to the ripple crests, avoiding places where complex ripple patterns suggest more than one recent wind direction. The length of the lines provides a measure of ripple wavelength, and the line orientation gives azimuth (with a 180 degree absolute ambiguity). The barchan-like shape of some dunes, including occasional slip faces, suggest sand driving winds were from the southwest, although dune asymmetries indicate the wind regime likely was much more complex than a unimodal wind. Measurements of ripple orientations are being collected from dune locations across the planet, which should provide new constraints for the modeling of recent Martian winds. This work was supported by NASA MDAP grant NNX12AJ38G.

  14. How High is that Dune? A Comparison of Methods Used to Constrain the Morphometry of Aeolian Bedforms on Mars

    NASA Technical Reports Server (NTRS)

    Bourke, M.; Balme, M.; Beyer, R. A.; Williams, K. K.

    2004-01-01

    Methods traditionally used to estimate the relative height of surface features on Mars include: photoclinometry, shadow length and stereography. The MOLA data set enables a more accurate assessment of the surface topography of Mars. However, many small-scale aeolian bedforms remain below the sample resolution of the MOLA data set. In response to this a number of research teams have adopted and refined existing methods and applied them to high resolution (2-6 m/pixel) narrow angle MOC satellite images. Collectively, the methods provide data on a range of morphometric parameters (many not previously available for dunes on Mars). These include dune height, width, length, surface area, volume, longitudinal and cross profiles). This data will facilitate a more accurate analysis of aeolian bedforms on Mars. In this paper we undertake a comparative analysis of methods used to determine the height of aeolian dunes and ripples.

  15. Sand transportation and reverse patterns over leeward face of sand dune

    NASA Astrophysics Data System (ADS)

    Jiang, Hong; Dun, Hongchao; Tong, Ding; Huang, Ning

    2017-04-01

    Sand saltation has complex interactions with turbulent flow and dune form. Most models of wind-blown sand consider ideal circumstances such as steady wind velocity and a flat surface, and the bulk of data on wind flow and sand transport over an individual dune has focused mostly on the influence of dune shape or inter-dune space on the wind flow, neglecting the effect of morphology on sand saltation, particularly airflow and sand transportation over the leeward slope. Wind flow structures over the leeward slope of sand dunes have a fundamental influence on the organization of sand dunes. In order to understand sand dune dynamics, lee face airflow and sediment transportation should be paid more attention. Previous field observations could not measure turbulent flow structure well because of the limited observation points and the influence of experiment structure on wind field. In addition, the reverse sand particles over leeward face could not be collected by sand trap in field. Numerous field observations could not measure turbulent flow structure because of the limited observation points and the influence of experimental structures on the wind field. In addition, the reverse transport of sand particles over leeward face could not be collected by sand traps in field. Therefore, this paper aims to investigate the turbulent flow structure and sand transport pattern over the leeward slope. A numerical model of sand saltation over slope terrain is constructed, which also considers the coupling effects between air flow and sand particles. The large eddy simulation method is used to model turbulent flow. Sand transport is simulated by tracking the trajectory of each sand particle. The results show that terrain significantly alters the turbulent air flow structure and wind-blown sand movement, especially over the leeward slope. Here, mass flux increases initially and then decreases with height in the reversed flow region in the direction of wind flow, and the mass flux

  16. Late Quaternary aeolian sand deposition sustained by fluvial reworking and sediment supply in the Hexi Corridor - An example from northern Chinese drylands

    NASA Astrophysics Data System (ADS)

    Nottebaum, Veit; Lehmkuhl, Frank; Stauch, Georg; Lu, Huayu; Yi, Shuangwen

    2015-12-01

    Aeolian deposits are frequently used for palaeoenvironmental change studies. Their formation depends on an array of requirements: the supply of material suitable for aeolian transport and favorable conditions of sediment availability and wind strength. In order to infer palaeoenvironmental information from aeolian sand deposits these factors need to be carefully evaluated. We present a study from northern Chinese Hexi Corridor, based on 11 optically stimulated luminescence (OSL) dated sediment sections. These represent interchanging aeolian and alluvial deposits under gravel surfaces and aeolian sand in dune fields interrupted by interdunal flood deposits. Investigations in two subareas reveal contrasting geomorphologic and sedimentary histories: (1) sediment deposition during the Pleistocene-Holocene transition (~ 12 ka) followed by deflation during the Holocene and (2) frequent sediment recycling revealed by a wide spectrum of ages throughout the Holocene. The late glacial sediment pulse recorded in the western Hexi Corridor is attributed to high sediment supply, generated by efficient (peri-)glacial sediment production during glacial times in the adjacent Qilian Shan (< 5700 m asl) and a moisture increase inducing the reworking of those (glacio-)fluvial deposits during the Pleistocene-Holocene transition. The absence of a powerful reworking agent preserved these late glacial deposits in the western Hexi Corridor in contrast to moister eastern parts where Holocene sediment reworking prevailed. Geomorphological and hydrological preconditions of the subareas are discussed and reveal the controlling influence of fluvial processes on sand supply for the aeolian system. While a perennial drainage is missing in the drier western part, the Hei River drainage is fed by higher monsoonal precipitation in the central Hexi Corridor. It maintains a sediment recycling system and has ensured a sufficient sediment supply throughout the Holocene. The study promotes closer

  17. The dune effect on sand-transporting winds on Mars

    PubMed Central

    Jackson, Derek W. T.; Bourke, Mary C; Smyth, Thomas A. G.

    2015-01-01

    Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface–atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern ‘wind vanes' on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today. PMID:26537669

  18. The dune effect on sand-transporting winds on Mars.

    PubMed

    Jackson, Derek W T; Bourke, Mary C; Smyth, Thomas A G

    2015-11-05

    Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface-atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern 'wind vanes' on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today.

  19. Quantifying the effects of European beach grass on aeolian sand transport over the last century: Bodega Marine Reserve, California

    NASA Astrophysics Data System (ADS)

    Cesmat, R.; Werner, S.; Smith, M. E.; Riedel, T.; Best, R.; Olyarnik, S.

    2012-12-01

    Introduction of European beach grass (Ammophila arenaria) to coastal dune systems of western North America induced significant changes to the transport and storage of sediment, and consequently the nesting habitat of the western snowy plover (Charadrius alexandrinus nivosus). At the Bodega Marine Reserve and Sonoma Coast State Park, Ammophila was introduced within the ~0.5 km2 dune area in the 1920's to limit the flux of sand through Bodega Harbor and agricultural land. To assess the potential impact of restoration efforts (Ammophila removal) on aeolian sediment flux, we measured sediment flux as a function of wind speeds and ground cover, and used these measurements to parameterize a spatial model for historical sand deposition Fine- to coarse-grained lithic to sub-lithic sand is delivered to the Bodega dune system from Salmon Creek beach, the down-shore terminus of a littoral system fed by the 3846 km2 Russian River catchment, several small (<100 km2) coastal catchments, and seacliff erosion. Littoral sediment traverses the 1.8 km wide dune system from NW to SE via aeolian transport. Ammophila colonization occurred initially adjacent to the shoreface, inducing deposition of a ~10 meter-high foredune and has subsequently encroached the ~0.5 km2 region between the foredune and Bodega Harbor. Comparison of historical topographic maps via raster subtraction indicates rapid construction of both the foredune and a ~15 meter-high transverse dune (Gaffney ridge) at the edge of the planted region. An average accumulation rate of ~4,000 m3/yr is indicated within the study swath by the preserved sediment volumes. Within the modern dune system, unvegetated areas exhibit 2-3 meter wavelength, ~1/2 meter amplitude mega-ripples, and the uppermost 2-10 cm consists of coarse-sand to granule-sized armor layer. In contrast, grain-sizes in vegetated areas are largely vertically homogenous. Open areas are typically 2-8 meters lower than adjacent vegetated areas, and show evidence for

  20. Use of coal ash for enhancing biocrust development in stabilizing sand dunes

    NASA Astrophysics Data System (ADS)

    Zaady, Eli; Katra, Itzhak; Sarig, Shlomo

    2015-04-01

    In dryland environments, biocrusts are considered ecosystem engineers since they play significant roles in ecosystem processes. In the successional pathway of crust communities, the new areas are colonized after disturbance by pioneers such as filamentous cyanobacteria - Microcoleus spp. This stage is followed by colonization of green algae, mosses, and lichens. Aggregation of soil granules is caused by metabolic polysaccharides secreted by cyanobacteria and green algae, gluing the soil particles to form the crust layer. It was suggested that incorporating dust into the biocrusts encourages the growth of cyanobacteria, leading to a strengthening of the biocrusts' cohesion. Moreover, biocrusts cover a larger portion of the surface when the soil contains finer particles, and it was observed that at least 4-5% of clay and silt is required to support a measurable biocrust. While natural and undisturbed sand dunes are generally stabilized by biocrusts in the north-western Negev desert, stabilization of disturbed and movable sand dunes is one of the main problems in this desertified land, as in vast areas in the world. Daily breezes and seasonal wind storms transport sand particles to populated and agricultural areas causing damages to field crops and livelihood. Moving sand dunes consist of relatively coarse grains (250-2000 μm) with a low percent of clay and silt. This phenomenon negatively affects cyanobacterial colonization rate, even in relatively wet desert areas (100-250 mm rainfalls). In order to face the problem it was suggested to enrich the dune surface by using coal fly-ash. The research was conducted in two stages: first, examining the feasibility in Petri-dishes in laboratory conditions and in Experimental Aeolian Greenhouse conditions. The results showed that adding coal fly-ash and biocrust inoculum increased aggregate stability, penetration resistance and shear strength, as opposed to the control-sand plot. Using mobile wind-tunnel simulations, sand

  1. [Research progress on plant diversity conservation in sand dune areas].

    PubMed

    Liu, Zhi-min; Ma, Jun-ling

    2008-01-01

    The landscape in sand dune areas is characterized by the alternate distribution of sand dune and interdune lowland, and the unique floras in these areas are some endemic or rare plant species. In recent years, the decrease in plant species richness and the disappearance of some endemic or rare plant species in these areas have been received special attention, which were listed in the Program of International Biodiversity Conservation, and studied in many countries and districts. In this paper, the research progress in these fields was summarized from the aspects of significance of plant diversity conservation, formation mechanisms of plant diversity, ways of plant diversity conservation, roles of plant diversity research in the development of ecological theories, and important issues in operating plant diversity conservation project. To conserve plant diversity in sand dune areas, attentions should be paid to the differences in conservation goals (to maintain high species richness or to conserve endemic or rare species) among different regions, and the balances between the stabilization of active sand and the conservation of endemic or rare species, and the maintenance of high species richness and the conservation of endemic or rare species. It needed also to consider the sand dune and the interdune lowland as a unified landscape unit to explore the impacts of disturbances and habitat fragment on plant diversity.

  2. 76 FR 57074 - Transfer of Administrative Jurisdiction at or Near Great Sand Dunes National Park

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-15

    ... National Park Service Transfer of Administrative Jurisdiction at or Near Great Sand Dunes National Park... benefit of Great Sand Dunes National Park, Baca National Wildlife Refuge, and the Rio Grande National... (Secretary) acquired certain lands and interests in land for the benefit of Great Sand Dunes National...

  3. 76 FR 68503 - Ungulate Management Plan/Environmental Impact Statement, Great Sand Dunes National Park and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-04

    ... National Park Service Ungulate Management Plan/Environmental Impact Statement, Great Sand Dunes National... Intent to prepare an Environmental Impact Statement for the Ungulate Management Plan, Great Sand Dunes... Ungulate Management Plan, Great Sand Dunes National Park and Preserve, Colorado. The purpose of this...

  4. Aeolian Sand Transport in the Planetary Context: Respective Roles of Aerodynamic and Bed-Dilatancy Thresholds

    NASA Technical Reports Server (NTRS)

    Marshall, J. R.; Borucki, J.; Bratton, C.

    1999-01-01

    The traditional view of aeolian sand transport generally estimates flux from the perspective of aerodynamic forces creating the airborne grain population, although it has been recognized that "reptation" causes a significant part of the total airborne flux; reptation involves both ballistic injection of grains into the air stream by the impact of saltating grains as well as the "nudging" of surface grains into a creeping motion. Whilst aerodynamic forces may initiate sand motion, it is proposed here that within a fully-matured grain cloud, flux is actually governed by two thresholds: an aerodynamic threshold, and a bed-dilatancy threshold. It is the latter which controls the reptation population, and its significance increases proportionally with transport energy. Because we only have experience with terrestrial sand transport, extrapolations of aeolian theory to Mars and Venus have adjusted only the aerodynamic factor, taking gravitational forces and atmospheric density as the prime variables in the aerodynamic equations, but neglecting reptation. The basis for our perspective on the importance of reptation and bed dilatancy is a set of experiments that were designed to simulate sand transport across the surface of a martian dune. Using a modified sporting crossbow in which a sand-impelling sabot replaced the bolt-firing mechanism, individual grains of sand were fired at loose sand targets with glancing angles typical of saltation impact; grains were projected at about 80 m/s to simulate velocities commensurate with those predicted for extreme martian aeolian conditions. The sabot impelling method permitted study of individual impacts without the masking effect of bed mobilization encountered in wind-tunnel studies. At these martian impact velocities, grains produced small craters formed by the ejection of several hundred grains from the bed. Unexpectedly, the craters were not elongated, despite glancing impact; the craters were very close to circular in planform

  5. Aeolian Sand Transport in the Planetary Context: Respective Roles of Aerodynamic and Bed-Dilatancy Thresholds

    NASA Astrophysics Data System (ADS)

    Marshall, J. R.; Borucki, J.; Bratton, C.

    1999-09-01

    The traditional view of aeolian sand transport generally estimates flux from the perspective of aerodynamic forces creating the airborne grain population, although it has been recognized that "reptation" causes a significant part of the total airborne flux; reptation involves both ballistic injection of grains into the air stream by the impact of saltating grains as well as the "nudging" of surface grains into a creeping motion. Whilst aerodynamic forces may initiate sand motion, it is proposed here that within a fully-matured grain cloud, flux is actually governed by two thresholds: an aerodynamic threshold, and a bed-dilatancy threshold. It is the latter which controls the reptation population, and its significance increases proportionally with transport energy. Because we only have experience with terrestrial sand transport, extrapolations of aeolian theory to Mars and Venus have adjusted only the aerodynamic factor, taking gravitational forces and atmospheric density as the prime variables in the aerodynamic equations, but neglecting reptation. The basis for our perspective on the importance of reptation and bed dilatancy is a set of experiments that were designed to simulate sand transport across the surface of a martian dune. Using a modified sporting crossbow in which a sand-impelling sabot replaced the bolt-firing mechanism, individual grains of sand were fired at loose sand targets with glancing angles typical of saltation impact; grains were projected at about 80 m/s to simulate velocities commensurate with those predicted for extreme martian aeolian conditions. The sabot impelling method permitted study of individual impacts without the masking effect of bed mobilization encountered in wind-tunnel studies. At these martian impact velocities, grains produced small craters formed by the ejection of several hundred grains from the bed. Unexpectedly, the craters were not elongated, despite glancing impact; the craters were very close to circular in planform

  6. Analysis of Wind-blown Sand Movement over Transverse Dunes

    PubMed Central

    Jiang, Hong; Huang, Ning; Zhu, Yuanjian

    2014-01-01

    Wind-blown sand movement often occurs in a very complicated desert environment where sand dunes and ripples are the basic forms. However, most current studies on the theoretic and numerical models of wind-blown sand movement only consider ideal conditions such as steady wind velocity, flat sand surface, etc. In fact, the windward slope gradient plays a great role in the lift-off and sand particle saltation. In this paper, we propose a numerical model for the coupling effect between wind flow and saltating sand particles to simulate wind-blown sand movement over the slope surface and use the SIMPLE algorithm to calculate wind flow and simulate sands transport by tracking sand particle trajectories. We furthermore compare the result of numerical simulation with wind tunnel experiments. These results prove that sand particles have obvious effect on wind flow, especially that over the leeward slope. This study is a preliminary study on windblown sand movement in a complex terrain, and is of significance in the control of dust storms and land desertification. PMID:25434372

  7. Geologic map of Great Sand Dunes National Park, Colorado

    USGS Publications Warehouse

    Madole, Richard F.; VanSistine, D. Paco; Romig, Joseph H.

    2016-10-20

    Geologic mapping was begun after a range fire swept the area of what is now the Great Sand Dunes National Park in April 2000. The park spans an area of 437 square kilometers (or about 169 square miles), of which 98 percent is blanketed by sediment of Quaternary age, the Holocene and Pleistocene Epochs; hence, this geologic map of the Great Sand Dunes National Park is essentially a surficial geologic map. These surficial deposits are diverse and include sediment of eolian (windblown), alluvial (stream and sheetwash), palustrine (wetlands and marshes), lacustrine (lake), and mass-wasting (landslides) origin. Sediment of middle and late Holocene age, from about 8,000 years ago to the present, covers about 80 percent of the park.Fluctuations in groundwater level during Holocene time caused wetlands on the nearby lowland that bounds the park on the west to alternately expand and contract. These fluctuations controlled the stability or instability of eolian sand deposits on the downwind (eastern) side of the lowland. When groundwater level rose, playas became lakes, and wet or marshy areas formed in many places. When the water table rose, spring-fed streams filled their channels and valley floors with sediment. Conversely, when groundwater level fell, spring-fed streams incised their valley floors, and lakes, ponds, and marshes dried up and became sources of windblown sand.Discharge in streams draining the west flank of the Sangre de Cristo Range is controlled primarily by snowmelt and flow is perennial until it reaches the mountain front, beyond which streams begin losing water at a high rate as the water soaks into the creek beds. Even streams originating in the larger drainage basins, such as Sand and Medano Creeks, generally do not extend much more than 4 km (about 2.5 miles) beyond where they exit the mountains.The Great Sand Dunes contain the tallest dunes (maximum height about 750 feet, or 230 m) in North America. These dunes cover an area of 72 square kilometers

  8. Early diagenesis of eolian dune and interdune sands at White Sands, New Mexico

    USGS Publications Warehouse

    Schenk, C.J.; Fryberger, S.G.

    1988-01-01

    The degree of early diagenesis in eolian dune and interdune sands at White Sands, New Mexico, is largely a function of the relationship between sand location and the water table. Most active and vegetation-stabilized dune sands are in the vadose zone, whereas interdune sands are in the capillary fringe and phreatic zones. Crystallographically controlled dissolution of the framework gypsum grains results in elongate, prismatic etch pits on sand grains from the capillary fringe and phreatic zones, whereas dissolution of sand grains in the vadose zone is slight, causing minute irregularities on grain surfaces. Vadose water percolating through the sand is manifest as meniscus layers. Consequently, dune sands in the vadose zone are cemented mainly by meniscus-shaped gypsum at grain contacts. Pendant cements formed on the lower margins of some sand grains. Cementation in the capillary fringe and the phreatic zone is more extensive than the vadose regardless of strata type. Typically, well-developed gypsum overgrowths form along the entire edge of a grain, or may encompass the entire grain. Complex diagenetic histories are suggested by multiple overgrowths and several episodes of dissolution on single grains, attesting to changing saturation levels with respect to gypsum in the shallow ground water. These changes in saturation are possibly due to periods of dilution by meteoric recharge, alternating with periods of concentration of ions and the formation of cement due to evaporation through the capillary fringe. ?? 1988.

  9. Controls on and effects of armoring and vertical sorting in aeolian dune fields: A numerical simulation study

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Narteau, Clément; Rozier, Olivier

    2016-03-01

    Unlike ripples, there are only few numerical studies on grain size segregation at the scale of dunes in aeolian environments. Here we use a cellular automaton model to analyze vertical sorting in granular mixtures under steady unidirectional flow conditions. We investigate the feedbacks between dune growth and the segregation mechanisms by varying the size of coarse grains and their proportion within the bed. We systematically observe the development of a horizontal layer of coarse grains at the top of which sorted bed forms may grow by amalgamation. The formation of such an armor layer controls the overall sediment transport and availability. The emergence of dunes and the transition from barchan to transverse dune fields depend only on the grain size distribution of the initial sediment layer. As confirmed by observation, this result indicates that armor layers should be present in most arid deserts, where they are likely to control dune morphodynamics.

  10. Comparison of two Satellite Imaging Platforms for Evaluating Sand Dune Migration in the Ubari Sand Sea (Libyan Fazzan)

    NASA Astrophysics Data System (ADS)

    Els, A.; Merlo, S.; Knight, J.

    2015-04-01

    Sand dunes can change location, form or dimensions depending on wind direction and strength. Sand dune movements can be effectively monitored through the comparison of multi-temporal satellite images. However, not all remote sensing platforms are suitable to study sand dunes. This study compares coarse (Landsat) and fine (Worldview) resolution platforms, specifically focussing on sand dunes within the Ubari Sand Sea (Libya). Sand dune features (crest line, dune ridge basal outlines) were extracted from Landsat and Worldview 2 imagery in order to construct geomorphic maps. These geomorphic maps were then compared using image overlay and differencing, and the Root Mean Squared Error (RMSE) was used to determine if the mapped dune patterns were significantly different. It was found that Landsat is a sufficient data source when studying dune patterns within a regional sand sea, but smaller dunes identified from Worldview data were not capable of being extracted in the data sourced from Landsat. This means that for studies concerned with the dune patterns and movements within sand seas, Landsat is sufficient. But in studies where the specific dynamics of specific dunes are required, a finer resolution is required; platforms such as Worldview are needed in order to gain more detailed insight and to link the past and present day climate and environmental change.

  11. Sand ripple dynamics in the case of out-of-equilibrium aeolian regimes.

    PubMed

    Misbah, C; Valance, A

    2003-12-01

    From a phenomenological hydrodynamical model, we analyze the aeolian sand ripple evolution in an out-of-equilibrium aeolian regime where erosion exceeds accretion (and vice versa). We find, in particular, that the ripple structure can be destroyed in favor of a flat sand bed. In the ripple regime we report on a new class of generic dynamics described by the Benney equation. This equation reveals either order or disorder depending on whether wave dispersion is strong or weak. In both cases, the average wavelength of the pattern is fixed in time. This markedly contrasts with the regime of equilibrium aeolian regime -reached when erosion balances deposition- where ripples undergo a coarsening process at long time (i.e., the wavelength increases indefinitely with time).

  12. Preliminary study of Kelso Dunes using AVIRIS, TM, and AIRSAR

    NASA Technical Reports Server (NTRS)

    Xu, Pung; Blumberg, Dan G.; Greeley, Ronald

    1995-01-01

    Remote sensing of sand dunes helps in the understanding of aeolian process and provides important information about the regional geologic history, environmental change, and desertification. Remotely sensed data combined with field studies are valuable in studying dune morphology, regional aeolian dynamics, and aeolian depositional history. In particular, active and inactive sands of the Kelso Dunes have been studied using landsat TM and AIRSAR. In this report, we describe the use of AVIRIS data to study the Kelso dunes and to compare the AVIRIS information with that from TM and AIRSAR.

  13. Diurnal emissivity dynamics in bare versus biocrusted sand dunes.

    PubMed

    Rozenstein, Offer; Agam, Nurit; Serio, Carmine; Masiello, Guido; Venafra, Sara; Achal, Stephen; Puckrin, Eldon; Karnieli, Arnon

    2015-02-15

    Land surface emissivity (LSE) in the thermal infrared depends mainly on the ground cover and on changes in soil moisture. The LSE is a critical variable that affects the prediction accuracy of geophysical models requiring land surface temperature as an input, highlighting the need for an accurate derivation of LSE. The primary aim of this study was to test the hypothesis that diurnal changes in emissivity, as detected from space, are larger for areas mostly covered by biocrusts (composed mainly of cyanobacteria) than for bare sand areas. The LSE dynamics were monitored from geostationary orbit by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) over a sand dune field in a coastal desert region extending across both sides of the Israel-Egypt political borderline. Different land-use practices by the two countries have resulted in exposed, active sand dunes on the Egyptian side (Sinai), and dunes stabilized by biocrusts on the Israeli side (Negev). Since biocrusts adsorb more moisture from the atmosphere than bare sand does, and LSE is affected by the soil moisture, diurnal fluctuations in LSE were larger for the crusted dunes in the 8.7 μm channel. This phenomenon is attributed to water vapor adsorption by the sand/biocrust particles. The results indicate that LSE is sensitive to minor changes in soil water content caused by water vapor adsorption and can, therefore, serve as a tool for quantifying this effect, which has a large spatial impact. As biocrusts cover vast regions in deserts worldwide, this discovery has repercussions for LSE estimations in deserts around the globe, and these LSE variations can potentially have considerable effects on geophysical models from local to regional scales.

  14. Simulation of aeolian sand saltation with rotational motion

    NASA Astrophysics Data System (ADS)

    Huang, Ning; Wang, Cong; Pan, Xiying

    2010-11-01

    In this work, we propose a theoretical model based on the distribution functions of initial liftoff velocity and angular velocity of sand grains to describe a sand saltation process in which both wind field-sand grain coupling and the Magnus force experienced by saltating sand grains have been incorporated. The computation results showed that the Magnus force had significant effects on sand grain saltation. In particular, when the Magnus force was incorporated, the calculated sand transport fluxes and sand transport rate per unit width were closer to the experimental value than when this force was excluded. The sand transport flux is enhanced because the Magnus force owing to particle rotation causes the particles to have higher and longer trajectories, so the particles can get more speed and energy from the wind, which leads to a larger sand transport flux. In addition, it was found that when taking the Magnus force into account, the probability density of the impact velocity and angular velocity of saltating sand grains followed an exponential distribution and a unimodal asymmetric distribution, respectively. Moreover, the sand energy flux increased with the height above the sand surface until the energy flux reached its maximum and then decreased. Furthermore, the energy flux near the ground surface decreased as the grain diameter increased, but beyond a specific height the energy flux increased with the grain diameter. Finally, for the same sand grain diameter, the energy flux increased with the friction velocity.

  15. 2007 Weather and Aeolian Sand-Transport Data from the Colorado River Corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Draut, Amy E.; Andrews, Timothy; Fairley, Helen C.; Brown, Christopher R.

    2009-01-01

    Weather data constitute an integral part of ecosystem monitoring in the Colorado River corridor and are particularly valuable for understanding processes of landscape change that contribute to the stability of archeological sites. Data collected in 2007 are reported from nine weather stations in the Colorado River corridor through Grand Canyon, Ariz. The stations were deployed in February and March 2007 to measure wind speed and direction, rainfall, air temperature, relative humidity, and barometric pressure. Sand traps near each weather station collect windblown sand, from which daily aeolian sand-transport rates are calculated. The data reported here were collected as part of an ongoing study to test and evaluate methods for quantifying processes that affect the physical integrity of archeological sites along the river corridor; as such, these data can be used to identify rainfall events capable of causing gully incision and to predict likely transport pathways for aeolian sand, two landscape processes integral to the preservation of archeological sites. Weather data also have widespread applications to other studies of physical, cultural, and biological resources in Grand Canyon. Aeolian sand-transport data reported here, collected in the year before the March 2008 High-Flow Experiment (HFE) at Glen Canyon Dam, represent baseline data against which the effects of the 2008 HFE on windblown sand will be compared in future reports.

  16. Seismic Evidence for a Resonance Layer in Booming Sand Dunes

    NASA Astrophysics Data System (ADS)

    Vriend, N. M.; Hunt, M. L.; Clayton, R. W.

    2006-12-01

    "Booming sand dunes" are large desert dunes that emit a loud droning, low-frequency sound during an avalanche of sand on the leeward face of a dune. The monotone sound (70-105 Hz) may continue for up to a minute after initiation, even after all visible motion has ceased. The source of the booming sound has long been a mystery and no accepted scientific explanation has been proposed yet. Seismic refraction experiments conducted with a closely-spaced 48 channel system show a shallow (< 10 m) subsurface layering inside the dune with significant velocity contrasts between the individual layers. The seismic body wave velocities in the top three layers of sand (240 m/s, 360 m/s and 460 m/s) are very close to the acoustic velocity in air (355 m/s) while at the same time the surface waves are highly attenuated. The seismic velocity changes cannot be explained by increasing confined pressure but must be provided by a seasonally changing physical structure. From the seismic survey it is further noted that the layering narrows towards the foothill. During the sustained boom, the frequency rises slightly (from 85 Hertz to 95 Hertz) as the source due to the avalanche proceeds downwards. This observation was deduced from analyzing the booming emission on all 48 geophones in conjunction with a high-quality air microphone. The multi-layer internal structure of the dune provides a resonance cavity that amplifies particular frequencies and creates the loud booming sound. The resonance and its interaction with the air is modeled with finite- difference simulations.

  17. Hydrologic Modeling of the White Sands Dune Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Bourret, S. M.; Newton, B. T.; Person, M. A.

    2013-12-01

    The shallow groundwater flow system of White Sands dune field, located within the Tularosa Basin of Southern New Mexico, likely stabilizes the base of the largest gypsum dunefield in the world. Water table geometry and elevation play a critical role in controlling dune thickness, spatial extent, and migration rates. The White Sands National Monument (WHSA) is concerned that lowering the water table may lead to increased scour and migration of the dune field, which could be unfavorable to the preservation of the flora and fauna that have adapted to survive there. In response to projected increases in groundwater pumping in the regional Tularosa Basin groundwater system, changes in surface water use, and the threat of climate change, the WHSA is interested in understanding how these changes on a regional scale may impact the shallow dune aquifer. We have collected hydrological, geochemical, and geophysical data in order to identify the sources of recharge that contribute to the shallow dune aquifer and to assess interactions between this water table aquifer and the basin-scale, regional system. Vertical head gradients, temperature, and water quality data strongly suggest that local precipitation is the primary source of recharge to the dune aquifer today. This suggests that the modern dune system is relatively isolated from the deeper regional system. However, geochemical and electrical resistivity data indicates that the deeper basin groundwater system does contribute to the shallow system and suggests that hydrologic conditions have changed on geologic time scales. We have constructed a preliminary cross-sectional hydrologic model to attempt to characterize the interaction of the shallow dune aquifer with the deeper basin groundwater. The model cross-section extends about 80 km across the Tularosa Basin in a NW-SE direction parallel to the primary flow path. We represented 6 km of Precambrian crystalline basement, Paleozoic sedimentary rocks as well as Pleistocene

  18. Phase diagrams of dune shape and orientation depending on sand availability.

    PubMed

    Gao, Xin; Narteau, Clément; Rozier, Olivier; Courrech du Pont, Sylvain

    2015-09-30

    New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation.

  19. Phase diagrams of dune shape and orientation depending on sand availability

    PubMed Central

    Gao, Xin; Narteau, Clément; Rozier, Olivier; du Pont, Sylvain Courrech

    2015-01-01

    New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation. PMID:26419614

  20. Fire scars and ancient sand dunes in southern Australia

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The rectangular green areas in this view of southern Australia are protected areas of natural forest (national parks and biospheric reserves), and the lighter surrounding colors (tan-brown) are agricultural croplands occupying land which once must have looked as green as the nature reserves but are now cleared of forest. The major green patch has been recently burned, as shown by the irregular pattern of a large, multiple burn scar. The pattern of the fire scar indicates that the fires were driven by winds blowing from left to right. Close examination of the view shows that the forests are rooted in a soil made up of a widespread sheet of ancient dune sand. The dunes can be seen best within the area of the large fire scar where the characteristic wavy, scalloped pattern of crescent dunes can be detected. The crescents indicate that the sand was heaped up by winds blowing from right to left in this view, in the opposite direction to the winds which fanned the fires. A few straight dunes

  1. The Role of Reproductive Phenology, Seedling Emergence and Establishment of Perennial Salix gordejevii in Active Sand Dune Fields

    PubMed Central

    Yan, Qiaoling; Liu, Zhimin; Ma, Junling; Jiang, Deming

    2007-01-01

    Background and Aims The function of sexual reproduction of perennials in restoration of vegetation of active dune fields frequently has been underestimated. The objective of this study was to evaluate the role of sexual reproduction of the perennial Salix gordejevii in the revegetation of active dunes. Methods Seedling emergence and establishment of S. gordejevii were examined both in controlled experiments (germination at different burial depths with different watering regimes) and in field observations in three dune slacks. The reproductive phenology and soil seed bank of S. gordejevii, the dynamics of soil moisture, the groundwater table and the landform level of three dune slacks were monitored. Key Results Seeds of S. gordejevii began maturation on 1 May, and seed dispersal lasted from 8 May to 20 May. Seeds on the soil surface germinated significantly faster than those buried in soil (P<0·05). Seedling emergence was negatively correlated with landform level. When most seedlings emerged, there was a significantly positive correlation between soil moisture and seedling emergence (P<0·01). Rainfall was negatively correlated with seedling emergence. Seedling establishment was significantly and positively correlated with seedling emergence (P<0·05), and 72·3 % of the emergent seedlings were established at the end of the growing season. These results indicated that (a) seeds matured and dispersed before the rainy season; (b) seeds germinated as soon as they contacted a moist surface and relied more on soil moisture than on rainfall; and (c) more seedlings emerged at lower sampling points in dune slacks. Conclusions In natural conditions, restoration of active sand dune fields generally commences with revegetation of dune slacks where sexual reproduction of perennials contributes greatly to species encroachment and colonization and hence plays an important role in restoration of active dune fields. Furthermore, aeolian erosion in dune slacks, leading to good

  2. Circular feature among dunes of the Great Sand Sea, Egypt

    NASA Technical Reports Server (NTRS)

    El-Baz, F.

    1981-01-01

    A circular crater, about 4 kilometers in diameter and located at 24.2 deg N, 26.4 deg E, was discovered in Landsat images among the linear dunes of the Great Sand Sea, Egypt. The crater has a sharp and crenulated rim crest, a terraced wall, a discontinuous inner structure (approximately 1.6 kilometers in diameter), and a few rim blocks. Its morphological and morphometric characteristics are similar to those of meteorite impact craters and other circular structures on the moon and the terrestrial planets. Because of its interaction with windblown sand, it is particularly comparable with craters on Mars.

  3. Spring Time View of North Polar Sand Dunes

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Spring has come to the martian northern hemisphere. The northern spring season began in mid-July 1998. With the arrival of spring comes the annual shrinkage of the north polar frost cap. Sunlight is now falling on the north polar cap, and all of the carbon dioxide frost and snow that accumulated during winter has been sublimating--going directly from solid to gas--and the surface beneath the frost is being revealed.

    The MOC image shown above, 45205, was obtained during the 452nd orbit of Mars Global Surveyor at 3:10 p.m. PDT on July 26, 1998. The image is located near latitude 76.87oN, longitude 253.81oW, and it shows a close-up view of martian sand dunes. These dunes were not visible to MOC until the last week of July. Just a few months earlier, the dunes were likely covered with frost, obscured by thick clouds, and cloaked by the darkness of the martian polar winter. Indeed, small patches of bright frost were still present when the picture was taken (e.g., the bright patches on the west (left) side of each crescentic dune in (left image).

    As the above picture illustrates, the camera on board Mars Global Surveyor (MOC) continued to take exciting new views of the martian surface throughout July 1998. As the month progressed, the ground track-- the area visible to the camera--migrated farther north. Simultaneously, sunlight began falling on the north polar regions, making it possible to take some pictures at far northern latitudes. However, these regions have been tricky to photograph because of thick clouds and hazes. The image shown here, for example, is relatively bland gray (has relatively low contrast) because of clouds.

    As first seen by the Viking 2 Orbiter in 1976, a vast 'sea' of sand dunes surrounds the north polar cap. The dunes imaged by MOC (above) are classic forms known as barchan dunes--the small, crescent-shaped hills (see left image above)-- and transverse dunes--ridges that resemble coalesced barchans (shown in right image above). These

  4. Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA

    NASA Astrophysics Data System (ADS)

    Draut, Amy E.

    2012-06-01

    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.

  5. Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA

    USGS Publications Warehouse

    Draut, Amy E.

    2012-01-01

    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.

  6. Giant calcite concretions in aeolian dune sandstones; sedimentological and architectural controls on diagenetic heterogeneity, mid-Cretaceous Iberian Desert System, Spain

    NASA Astrophysics Data System (ADS)

    Arribas, Maria Eugenia; Rodríguez-López, Juan Pedro; Meléndez, Nieves; Soria, Ana Rosa; de Boer, Poppe L.

    2012-01-01

    Aeolian dune sandstones of the Iberian erg system (Cretaceous, Spain) host giant calcite concretions that constitute heterogeneities of diagenetic origin within a potential aeolian reservoir. The giant calcite concretions developed in large-scale aeolian dune foresets, at the transition between aeolian dune toeset and damp interdune elements, and in medium-scale superimposed aeolian dune sets. The chemical composition of the giant concretions is very homogeneous. They formed during early burial by low Mg-calcite precipitation from meteoric pore waters. Carbonate components with yellow/orange luminescence form the nuclei of the poikilotopic calcite cement. These cements postdate earlier diagenetic features, characterized by early mechanical compaction, Fe-oxide cements and clay rims around windblown quartz grains resulting from the redistribution of aeolian dust over the grain surfaces. The intergranular volume (IGV) in friable aeolian sandstone ranges from 7.3 to 15.3%, whereas in cemented aeolian sandstone it is 18.6 to 25.3%. The giant-calcite concretions developed during early diagenesis under the influence of meteoric waters associated with the groundwater flow of the desert basin, although local (e.g. activity of fluid flow through extensional faults) and/or other regional controls (e.g. variations of the phreatic level associated with a variable water influx to the erg system and varying sea level) could have favoured the local development of giant-calcite concretions. The spatial distribution pattern of carbonate grains and the main bounding surfaces determined the spatial distribution of the concretions. In particular, the geometry of the giant calcite concretions is closely associated with main bounding aeolian surfaces. Thus, interdune, superimposition and reactivation surfaces exerted a control on the concretion geometries ranging from flat and tabular ones (e.g. bounded by interdunes) to wedge-shaped concretions at the dune foresets (e.g. bounded by

  7. Airflow and sand transport variations within a backshore parabolic dune plain complex: NE Graham Island, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Anderson, Jeffrey L.; Walker, Ian J.

    2006-07-01

    Onshore aeolian sand transport beyond the beach and foredune is often overlooked in the morphodynamics and sediment budgets of sandy coastal systems. This study provides detailed measurements of airflow, sand transport (via saltation and modified suspension), vegetation density, and surface elevation changes over an extensive (325 × 30 m) "swath" of a backshore foredune-parabolic dune plain complex. Near-surface (30 cm) wind speeds on the backshore ranged from 4.3 to 7.3 m s - 1 , gusting to 14.0 m s - 1 . Oblique onshore flow is steered alongshore near the incipient foredune then landward into a trough blowout where streamline compression, flow acceleration to 1.8 times the incident speed, and increasing steadiness occur. Highest saltation rates occur in steady, topographically accelerated flow within the blowout. As such, the blowout acts as a conduit to channel flow and sand through the foredune into the foredune plain. Beyond the blowout, flow expands, vegetation roughness increases, and flow decelerates. Over the foredune plain, localized flow steering and acceleration to 1.6 times the incident speed occurs followed by a drop to 40% of incident flow speed in a densely vegetated zone upwind of an active parabolic dune at 250 m from the foredune. Sediment properties reflect variations in near-surface flow and transport processes. Well-sorted, fine skewed backshore sands become more poorly sorted and coarse skewed in the blowout due to winnowing of fines. Sorting improves and sands become fine skewed over the foredune plain toward the parabolic dune due to grainfall of finer sands winnowed from the beach and foredune. During the fall-winter season, significant amounts of sand (up to 110 kg m - 2 ) are transported via modified suspension and deposited as grainfall up to 300 m landward of the foredune. No distinct trend in grainfall was found, although most fell on the depositional lobe of the blowout and at 200 m near an isolated, active parabolic dune. Grainfall

  8. Sand Dunes of Nili Patera in 3-D

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The most exciting new aspect of the Mars Global Surveyor (MGS) Extended Mission is the opportunity to turn the spacecraft and point the Mars Orbiter Camera (MOC) at specific features of interest. Opportunities to point the spacecraft come about ten times a week. Throughout the Primary Mission (March 1999 - January 2001), nearly all MGS operations were conducted with the spacecraft pointing 'nadir'--that is, straight down. A search for the missing Mars Polar Lander in late 1999 and early 2000 demonstrated that pointing the spacecraft could allow opportunities for MOC to see things that simply had not entered its field of view during typical nadir-looking operations, and to target areas previously seen in a nadir view so that stereo ('3-D') pictures could be derived.

    One of the very first places photographed by the MOC at the start of the Mapping Mission in March 1999 was a field of dunes located in Nili Patera, a volcanic depression in central Syrtis Major. A portion of this dune field was shown in a media release on March 11, 1999, 'Sand Dunes of Nili Patera, Syrtis Major'. Subsequently, the image was archived with the NASA Planetary Data System, as shown in the Malin Space Science Systems MOC Gallery. On April 24, 2001, an opportunity arose in which the MGS could be pointed off-nadir to take a new picture of the same dune field. By combining the nadir view from March 1999 and the off-nadir view from April 2001, a stereoscopic image was created. The anaglyph shown here must be viewed with red (left-eye) and blue (right-eye) '3-D' glasses. The dunes and the local topography of the volcanic crater's floor stand out in sharp relief. The images, taken more than one Mars year apart, show no change in the shape or location of the dunes--that is, they do not seem to have moved at all since March 1999.

  9. Aeolian environments and sand damage along the Qinghai-Tibet Railway, China

    NASA Astrophysics Data System (ADS)

    Zhang, Kecun; Qu, Jiaunjun; Han, Qingjie; An, Zhishan

    2016-04-01

    The Qinghai-Tibet Railway (QTR), with a total length of 1956 km, is the word's longest high-altitude railway. Located in the Tibet Plateau, the QTR is frequently damaged by windblown sand because of strong winds and abundant sand. Based on the detailed wind data, in situ observation of wind blown sand and field wind tunnel simulations along the QTR, the aeolian sand environment, involving sand-laden wind, drift potential, sand transport and their spatial variation were investigated. Sand-laden wind presents unidirectional characteristics along the QTR and its prevailing direction is westerly. The annual drift potential along the QTR reaches 970.54 Vector Units (VU), which belongs to a high-energy wind environment. In cold-high environments, sand transport rate increases with increasing wind velocity, but decreases exponentially with increasing height in the wind stream. As the altitude increases, the threshold velocity for sand movement linearly increases with altitude, and the sand transport per unit width decreases gradually. The results can be used to guide the design of sand-control structures both in the study area and in other areas that experience threats from windblown sand.

  10. A Comparison of Methods Used to Estimate the Height of Sand Dunes on Mars

    NASA Technical Reports Server (NTRS)

    Bourke, M. C.; Balme, M.; Beyer, R. A.; Williams, K. K.; Zimbelman, J.

    2006-01-01

    The collection of morphometric data on small-scale landforms from other planetary bodies is difficult. We assess four methods that can be used to estimate the height of aeolian dunes on Mars. These are (1) stereography, (2) slip face length, (3) profiling photoclinometry, and (4) Mars Orbiter Laser Altimeter (MOLA). Results show that there is good agreement among the methods when conditions are ideal. However, limitations inherent to each method inhibited their accurate application to all sites. Collectively, these techniques provide data on a range of morphometric parameters, some of which were not previously available for dunes on Mars. They include dune height, width, length, surface area, volume, and longitudinal and transverse profiles. Thc utilization of these methods will facilitate a more accurate analysis of aeolian dunes on Mars and enable comparison with dunes on other planetary surfaces.

  11. Laboratory studies of dune sand for the use of construction industry in Sri Lanka

    NASA Astrophysics Data System (ADS)

    de Silva Jayawardena, Upali; Wijesuriya, Roshan; Abayaweera, Gayan; Viduranga, Tharaka

    2015-04-01

    With the increase of the annual sand demand for the construction industry the excessive excavation of river sand is becoming a serious environmental problem in Sri Lanka. Therefore, it is necessary to explore the possibility for an alternative to stop or at least to minimize river sand mining activities. Dune sand is one of the available alternative materials to be considered instead of river sand in the country. Large quantities of sand dunes occur mainly along the NW and SE coastal belt which belong to very low rainfall Dry Zone coasts. The height of dune deposits, vary from 1m to about 30 meters above sea level. The objective of this paper is to indicate some studies and facts on the dune sand deposits of Sri Lanka. Laboratory studies were carried out for visual observations and physical properties at the initial stage and then a number of tests were carried out according to ASTM standards to obtain the compressive strength of concrete cylinders and mortar cubes mixing dune sand and river sand in different percentages keeping a constant water cement ratio. Next the water cement ratio was changed for constant dune sand and river sand proportion. Microscopic analysis shows that the dune sand consist of 95 % of quartz and 5 % of garnet, feldspar, illmenite and other heavy minerals with clay, fine dust, fine shell fragments and organic matters. Grains are sub-rounded to angular and tabular shapes. The grain sizes vary from fine to medium size of sand with silt. The degree of sorting and particle size observed with dune sands are more suited with the requirement of fine aggregates in the construction industry. The test result indicates that dune sand could be effectively used in construction work without sieving and it is ideal for wall plastering due to its'-uniformity. It could also be effectively used in concrete and in mortars mixing with river sand. The best mixing ratio is 75% dune sand and 25% river sand as the fine aggregate of concrete. For mortar the mixing

  12. Cruise Report: South China Sea Upper Slope Sand Dunes Project, May 8-14, 2013

    DTIC Science & Technology

    2013-06-01

    NPS-OC-14-003 NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA CRUISE REPORT: SOUTH CHINA SEA UPPER SLOPE SAND DUNES PROJECT...Report 3. DATES COVERED (From-To) May 8-14, 2013 4. TITLE AND SUBTITLE Cruise Report: South China Sea Upper Slope Sand Dunes Project, May 8-14, 2013...in partnership with Taiwan, a field project to investigate the effects of the large amplitude sand dunes , discovered on the upper slope of the

  13. Normal incidence measurement in a subaqueous sand dune field in the South China Sea.

    PubMed

    Chiu, Linus Y S; Chang, Andrea Y Y

    2014-11-01

    Regions with subaqueous sand dunes have been discovered on the upper continental slope of the northern South China Sea. These large subaqueous sand dunes are expected to cause errors in the measurement of normal incidence reflection. This letter presents experiment results of two normal incidence survey tracks conducted in 2013, and the errors in reflection coefficient estimation and the resulting sediment properties induced by sand dune bedforms. The results demonstrate that the reflected energy is focused and scattered by different parts of sand dune bedforms and that they produce significant variation in the estimated reflection coefficients and the inverted geoacoustic properties.

  14. Dynamics of Unusual Debris Flows on Martian Sand Dunes

    NASA Technical Reports Server (NTRS)

    Miyamoto, Hideaki; Dohm, James M.; Baker, Victor R.; Beyer, Ross A.; Bourke, Mary

    2004-01-01

    Gullies that dissect sand dunes in Russell impact crater often display debris flow-like deposits in their distal reaches. The possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a Bingham plastic flow to help explain the formation of these features. Our simulated results are best explained by a rapid debris flow. For example, a debris flow with the viscosity of 10(exp 2) Pa s and the yield strength of 10(exp 2) Pa can form the observed deposits with a flow rate of 0.5 cu m/s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters, which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth.

  15. Dynamics of unusual debris flows on Martian sand dunes

    NASA Astrophysics Data System (ADS)

    Miyamoto, Hideaki; Dohm, James M.; Baker, Victor R.; Beyer, Ross A.; Bourke, Mary

    2004-07-01

    Gullies that dissect sand dunes in Russell impact crater often display debris flow-like deposits in their distal reaches. The possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a Bingham plastic flow to help explain the formation of these features. Our simulated results are best explained by a rapid debris flow. For example, a debris flow with the viscosity of 102 Pa s and the yield strength of 102 Pa can form the observed deposits with a flow rate of 0.5 m3/s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters, which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth.

  16. A preliminary source-to-sink sediment budget for aeolian sands

    NASA Astrophysics Data System (ADS)

    Sebe, Krisztina; Csillag, Gábor; Timár, Gábor; Jámbor, Áron

    2015-04-01

    Source-to-sink sediment budgets are being intensively studied in fluvial systems. In contrast, sediment budget calculations are very rare for wind-transported material. This may be attributed to the fact that the exact delineation of both source and sink areas in aeolian systems can pose difficulties. In the Pannonian Basin, aeolian action by northwesterly to northerly winds exerted a thorough impact on landscape evolution during the Quaternary, testified among others by yardangs, wind corridors and numerous ventifacts as well as extensive blown sand fields. Wind erosion has been dated to be important since at least 1.5 Ma ago. Considering the sand fraction, the Pleistocene Pannonian Basin seems to be a nearly complete aeolian sedimentary system from source to sink, thus it provides a good opportunity to carry out sediment budget calculations. The largest blown sand accumulation occupies ~10 000 km2 in the central part of the Pannonian Basin, in the area called Kiskunság, and contains considerable volumes of aeolian sands extending down to the Lower Pleistocene. Its material is traditionally considered to originate from fluvial sediments of the Danube floodplain. However, recent studies on wind erosion and wind direction reconstructions have indicated that a considerable portion of the sand can have had a provenance in the extensive unconsolidated sediments of the Late Miocene Lake Pannon, which cover the uplifting Transdanubian Range and its surroundings. To gain data on this question, we carried out sediment budget calculations to assess if material volumes of the supposed source and sink areas are comparable. In the source area we reconstructed a paleotopography, practically a bounding envelope surface for the Pliocene/Pleistocene boundary using existing knowledge e.g. on the typical succession of Lake Pannon sediments and the evolution history of the area. The missing volume down to the present-day surface was then calculated, where the removed material was

  17. Storms, shoreface morphodynamics, sand supply, and the accretion and erosion of coastal dune barriers in the southern North Sea

    NASA Astrophysics Data System (ADS)

    Anthony, Edward J.

    2013-10-01

    The coast of the southern North Sea is bound by dune barriers that have developed adjacent to a shallow storm- and tide-dominated shoreface comprising numerous shore-parallel to sub-shore-parallel tidal sand banks. The banks evolve under the joint control of tide-, wave- and wind-induced shore-parallel currents, which tend to ‘stretch' them, eventually leading to bank division, and to shoaling and breaking storm waves, which tend to drive them ashore. The banks, thus, modulate the delivery of storm wave energy to the coast, redirect currents alongshore and are the sand sources for the accretion of coastal dunes. Foredune accretion occurs where major sand banks have migrated shoreward over the last centuries to be finally driven ashore and weld under the impact of storm waves. Morphological changes in the bank field can impact on shoreline stability through dissipation or enhanced shoreward transmission of storm wave energy and effects on radiation stress, particularly when waves are breaking over the banks. Where banks are close to the shore, mitigation of offshore sediment transport, especially during storms, can occur because of gradients in radiation stress generated by the complex 3D bank structure. These macro-scale mechanisms involve embedded meso-scale interactions that revolve around the mobility of sand waves, mobility of beach bars and troughs and foredune mobility, and micro-scale processes of bedform mobility in the subaqueous and intertidal domains, and of swash and aeolian beach-dune sand transport. These embedded interactions and the morphodynamic feedback loops illustrate the importance of synchroneity of sand transport from shoreface to dune on this coast. Large stretches of the foredunes show either signs of stability, or mild but chronic erosion. Furthermore, a demonstrated lack of a clear relationship occurs between storminess and coastal response over the second half of the 20th century. The present situation may be indicative of conditions

  18. The composition of Martian aeolian sands: Thermal emissivity from Viking IRTM observations

    NASA Technical Reports Server (NTRS)

    Edgett, Kenneth S.; Christensen, Philip R.

    1992-01-01

    Aeolian sands provide excellent surfaces for the remote determination of the mineralogic composition of Martian materials, because such deposits consist of relatively well-sorted, uniform particle sizes and might consist of chemically unaltered, primary mineral grains derived from bedrock. Dark features on the floors of Martian craters are controlled by aeolian processes and many consist largely of unconsolidated, windblown sand. Measurement of the thermal emissivity of geologic materials provides a way to identify mid-infrared absorption bands, the strength and positions of which vary with mineral structure and composition. The Viking Infrared Thermal Mapper (IRTM) had four surface-sensing mid-IR bands, three of which, the 7, 9, and 11 micron channels, correspond to absorption features characteristic of carbonates, sialic, and mafic minerals, respectively. In this study, the highest quality IRTM data were constrained so as to avoid the effects of atmospheric dust, clouds, surface frosts, and particle size variations (the latter using data obtained between 7 and 9 H, and they were selected for dark intracrater features such that only data taken directly from the dark feature were used, so as to avoid thermal contributions from adjacent but unrelated materials. Three-point emissivity spectra of Martian dart intracrater features were compared with laboratory emission spectra of minerals and terrestrial aeolian sands convolved using the IRTM response function to the four IRTM spectral channels.

  19. Complex systems in aeolian geomorphology

    NASA Astrophysics Data System (ADS)

    Baas, Andreas C. W.

    2007-11-01

    Aeolian geomorphology provides a rich ground for investigating Earth surface processes and landforms as complex systems. Sand transport by wind is a classic dissipative process with non-linear dynamics, while dune field evolution is a prototypical self-organisation phenomenon. Both of these broad areas of aeolian geomorphology are discussed and analysed in the context of complexity and a systems approach. A feedback loop analysis of the aeolian boundary-layer-flow/sediment-transport/bedform interactions, based on contemporary physical models, reveals that the system is fundamentally unstable (or at most meta-stable) and likely to exhibit chaotic behaviour. Recent field-experimental research on aeolian streamers and spatio-temporal transport patterns, however, indicates that sand transport by wind may be wholly controlled by a self-similar turbulence cascade in the boundary layer flow, and that key aspects of transport event time-series can be fully reproduced from a combination of (self-organised) 1/ f forcing, motion threshold, and saltation inertia. The evolution of various types of bare-sand dunes and dune field patterns have been simulated successfully with self-organising cellular automata that incorporate only simplified physically-based interactions (rules). Because of their undefined physical scale, however, it not clear whether they in fact simulate ripples (bedforms) or dunes (landforms), raising fundamental cross-cutting questions regarding the difference between aeolian dunes, impact ripples, and subaqueous (current) ripples and dunes. An extended cellular automaton (CA) model, currently under development, incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas, blow-outs, and parabolic coastal dunes. Preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes. Progress is limited, however, by a serious lack of

  20. Vegetation against dune mobility.

    PubMed

    Durán, Orencio; Herrmann, Hans J

    2006-11-03

    Vegetation is the most common and most reliable stabilizer of loose soil or sand. This ancient technique is for the first time cast into a set of equations of motion describing the competition between aeolian sand transport and vegetation growth. Our set of equations is then applied to study quantitatively the transition between barchans and parabolic dunes driven by the dimensionless fixation index theta which is the ratio between the dune characteristic erosion rate and vegetation growth velocity. We find a fixation index theta(c) below which the dunes are stabilized, characterized by scaling laws.

  1. Lee slope sediment processes leading to avalanche initiation on an aeolian dune

    NASA Astrophysics Data System (ADS)

    Sutton, S. L. F.; McKenna Neuman, C.; Nickling, W.

    2013-09-01

    In order to detail the governing conditions through which a slipface matures to the point of failure, dry sand avalanches were observed in the Dune Simulation Wind Tunnel on a 1:1 replica transverse dune with a crest height of approximately 1.2 m. Areal distributions of grainfall and reptation were measured using traps. Changes in the slipface elevation were observed using 3-D laser scanning with a vertical accuracy of 0.096 mm for approximately every 1 mm2 of surface area. Grainfall decayed exponentially from the brink with a constant rate across all wind velocities. Reptation removed sediment from areas close to the brink and deposited it downslope, creating low amplitude, cross-slope ripples on the slipface. A critical length scale separating grainscale and bulk sediment behavior is identified, and it defines the lower limit to the validity of angle of repose measurements. Avalanche initiation occurred in an area of steep surface slope below a sediment bulge, with distance from the brink independent of wind velocity. The time between avalanches was found to be constant for constant wind velocity.

  2. Turbulence and sediment transport over sand dunes and ripples

    NASA Astrophysics Data System (ADS)

    Bennis, A.; Le Bot, S.; lafite, R.; Bonneton, P.; Ardhuin, F.

    2013-12-01

    Several bedforms are present near to the surfzone of natural beaches. Dunes and ripples are frequently observed. Understanding the turbulence over these forms is essential for the sediment transport. The turbulent flow and the suspended sand particles interact with each other. At the moment, the modelling strategy for turbulence is still a challenge. According to the spatial scales, some different methods to model the turbulence are employed, in particular the RANS (Reynolds Averaged Navier-Stokes) and the LES (Large Eddy Simulation). A hybrid method combining both RANS and LES is set up here. We have adapted this method, initially developed for atmospheric flow, to the oceanic flow. This new method is implemented inside the 3D hydrodynamic model, MARS 3D, which is forced by waves. LES is currently the best way to simulate turbulent flow but its higher cost prevents it from being used for large scale applications. So, here we use RANS near the bottom while LES is set elsewhere. It allows us minimize the computational cost and ensure a better accuracy of the results than with a fully RANS model. In the case of megaripples, the validation step was performed with two sets of field data (Sandy Duck'97 and Forsoms'13) but also with the data from Dune2D model which uses only RANS for turbulence. The main findings are: a) the vertical profiles of the velocity are similar throughout the data b) the turbulent kinetic energy, which was underestimated by Dune2D, is in line with the observations c) the concentration of the suspended sediment is simulated with a better accuracy than with Dune2D but this remains lower than the observations.

  3. Twentieth century dune migration at the Great Sand Dunes National Park and Preserve, Colorado, relation to drought variability

    NASA Astrophysics Data System (ADS)

    Marín, L.; Forman, S. L.; Valdez, A.; Bunch, F.

    2005-08-01

    The Great Sand Dunes National Park and Preserve in southern Colorado contains a large dune mass banked against the Sangre de Cristo Mountains. The dune mass is bounded for hundreds of kilometers by a vegetated low-relief sand sheet with abundant active parabolic and barchanoid dunes. The clear morphology of these dunes, formed by winds mostly from the southwest, and the unambiguous identification of these forms in remotely sensed images provide straightforward targets to assess temporal changes in dune position. A digital database of georeferenced remote sensing images from 1936 to 1999 is used to quantify parabolic and barchan dune migration rates and surface reflectance, an indicator of vegetation cover, with evolving drought conditions in the twentieth century. The total net migration of 13 parabolic dunes in 63 years is 0.31 to 0.66 km, whereas 11 barchan dunes moved an average of 0.12 to 0.47 km. Compared to intervening wet year, there is at least a three-fold increase in average parabolic dune migration, during well-documented droughts in the 1930s, 1950s, and 1990s with a concomitant reduction in vegetation cover and surface water resources. The landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m/year, which is a six-fold acceleration over prior wet years, and similar to dune response during the 1930s. A nonlinear threshold for parabolic dune migration is indicated with lower quartile Palmer Drought Severity Index values of < - 2, which corresponds to at least a 25% reduction in summer and autumn precipitation.

  4. Regional aeolian dynamics and sand mixing in the Gran Desierto - Evidence from Landsat Thematic Mapper images

    NASA Technical Reports Server (NTRS)

    Blount, Grady; Greeley, Ronald; Christensen, Phillip R.; Smith, Milton O.; Adams, John B.

    1990-01-01

    Mesoscale mapping of spatial variations in sand composition of the Gran Desierto (Sonora, Mexico) was carried out on multispectral Landsat TM images of this region, making it possible to examine the dynamic development of sand sheets and dunes. Compositions determined from remote imagery were found to agree well with samples from selected areas. The sand populations delineated were used to describe the sediment source areas, transport paths, and deposition sites. The image analysis revealed important compositional variations aver large areas that were not readily apparent in the field data.

  5. Challenges in Measuring and Predicting Medium Term (Weeks to Annual) Aeolian Sediment Transport in Beach-Dune Systems

    NASA Astrophysics Data System (ADS)

    Delgado-Fernandez, I.

    2009-05-01

    Coastal dune budgets depend on sediment input by wind from the beach. Calculation of aeolian transport is thus a primary factor to understand coastal dune evolution and beach-dune coupled dynamics. However, measuring aeolian sediment transport in coastal areas presents fundamental technical and conceptual limitations that make numerical modeling difficult. Wind tunnel experiments isolate and reduce the number of variables to study, which is a necessary procedure to clearly manifest mechanistic relationships between cause and effect. But even with refinement and inclusion of new variables, traditional sediment transport formulas derived from wind tunnel experiments do not usually work well in natural areas. Short-term experiments may include precise instrumentation to obtain high frequency, detail time series of variables involved in aeolian transport, but inferring information at larger scales is problematic without knowledge of the timing and magnitude of particular transport events. There are two primary problems in attempting to predict sediment inputs to coastal dunes over periods of weeks, months or years: 1) to determine an appropriate set of predictive equations that incorporate complexities such as surface moisture content, beach width and the presence of vegetation; and 2) to provide quantitative data on these variables for input into the model at this time scale. Remote sensing techniques and the use of GIS software open the possibility to monitor key parameters regulating sediment transport dynamics at high spatial and temporal resolution over time scales beyond short-term experiments. These were applied at Greenwich Dunes, Prince Edward Island National Park (Canada), in an attempt to measure factors affecting aeolian sediment input to the foredune at a medium scale. Three digital cameras covering different sections of the beach and foredune provide time series on shoreline position, fetch distances, vegetation cover, ice/snow presence, or superficial

  6. 77 FR 55224 - Notice of Availability of the Proposed Imperial Sand Dunes Recreation Area Management Plan and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-07

    ... Bureau of Land Management Notice of Availability of the Proposed Imperial Sand Dunes Recreation Area... Impact Statement (EIS), for the Imperial Sand Dunes Recreation Area (ISDRA), and by this notice is... Register. ADDRESSES: Copies of the Proposed Imperial Sand Dunes RAMP and CDCA Plan Amendment/Final EIS...

  7. 75 FR 45653 - Notice of Re-Opening of Comment Period for the Draft Imperial Sand Dunes Recreation Area...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-03

    ... Bureau of Land Management Notice of Re-Opening of Comment Period for the Draft Imperial Sand Dunes... of the comment period on the Draft Imperial Sand Dunes Recreation Area Management Plan (RAMP) and... So. 4th St., El Centro, California 92243. Copies of the Draft Imperial Sand Dunes RAMP/EIS...

  8. 75 FR 14623 - Notice of Availability of the Draft Imperial Sand Dunes Recreation Area Management Plan and Draft...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-26

    ... Bureau of Land Management Notice of Availability of the Draft Imperial Sand Dunes Recreation Area... Plan (RAMP)/Draft Environmental Impact Statement (EIS) for the Imperial Sand Dunes Recreation Area... Sand Dunes RAMP/EIS are available in the El ] Centro Field Office at the above address and at the...

  9. Episodic Late Holocene dune movements on the sand-sheet area, Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Forman, S. L.; Spaeth, M.; Marín, L.; Pierson, J.; Gómez, J.; Bunch, F.; Valdez, A.

    2006-07-01

    The Great Sand Dunes National Park and Preserve (GSDNPP) in the San Luis Valley, Colorado, contains a variety of eolian landforms that reflect Holocene drought variability. The most spectacular is a dune mass banked against the Sangre de Cristo Mountains, which is fronted by an extensive sand sheet with stabilized parabolic dunes. Stratigraphic exposures of parabolic dunes and associated luminescence dating of quartz grains by single-aliquot regeneration (SAR) protocols indicate eolian deposition of unknown magnitude occurred ca. 1290-940, 715 ± 80, 320 ± 30, and 200-120 yr ago and in the 20th century. There are 11 drought intervals inferred from the tree-ring record in the past 1300 yr at GSDNPP potentially associated with dune movement, though only five eolian depositional events are currently recognized in the stratigraphic record. There is evidence for eolian transport associated with dune movement in the 13th century, which may coincide with the "Great Drought", a 26-yr-long dry interval identified in the tree ring record, and associated with migration of Anasazi people from the Four Corners areas to wetter areas in southern New Mexico. This nascent chronology indicates that the transport of eolian sand across San Luis Valley was episodic in the late Holocene with appreciable dune migration in the 8th, 10-13th, and 19th centuries, which ultimately nourished the dune mass against the Sangre de Cristo Mountains.

  10. Australian Red Dune Sand: A Potential Martian Regolith Analog

    NASA Technical Reports Server (NTRS)

    Kuhlman, K. R.; Marshall, J.; Evans, N. D.; Luttge, A.

    2001-01-01

    To demonstrate the potential scientific and technical merits of in situ microscopy on Mars, we analyzed a possible Martian regolith analog - an acolian red dune sand from the central Australian desert (near Mt. Olga). This sand was chosen for its ubiquitous red coating and the desert environment in which is it found. Grains of this sand were analyzed using a variety of microanalytical techniques. A database of detailed studies of such terrestrial analogs would assist the study of geological and astrobiological specimens in future missions to Mars. Potential instrument concepts for in situ deployment on Mars include local electrode atom probe nanoanalysis (LEAP), vertical scanning white light interferometry (VSWLI), scanning electron microscopies, energy dispersive x-ray microanalysis (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD). While in situ deployment of these techniques is many years away, ground-based studies using these analytical techniques extend our understanding of the data obtained from instruments to be flown in the near future.

  11. Climate-driven changes to dune activity during the Last Glacial Maximum and deglaciation in the Mu Us dune field, north-central China

    NASA Astrophysics Data System (ADS)

    Xu, Zhiwei; Lu, Huayu; Yi, Shuangwen; Vandenberghe, Jef; Mason, Joseph A.; Zhou, Yali; Wang, Xianyan

    2015-10-01

    One significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind-blown sand dunes. The relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood, however. Evidence of aeolian sand deposition during the Last Glacial Maximum (LGM) is scarce in many mid-latitude dune fields, whereas abundant evidence exists for aeolian sand accumulation during the deglaciation, i.e. after about 15 ka. Whether this contrast actually reflects changes in dune activity is still unclear, making paleoclimatic interpretation uncertain. Comprehensive field investigation and luminescence dating in the Mu Us dune field, north-central China, demonstrates that aeolian sands deposited during the LGM are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin. The scarcity of LGM dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation. Increasing sand accumulation after 15 ka, reflected by much more extensive preservation, signals a change in sand supply relative to sand transportation through the dune field. Reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation; the dunes, however, remained largely mobile as they were in the LGM. Similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid-latitude dune fields imply broad climatic controls linked to the changes in high-northern-latitude forcing.

  12. Laboratory simulations of Martian gullies on sand dunes

    NASA Astrophysics Data System (ADS)

    Védie, E.; Costard, F.; Font, M.; Lagarde, J. L.

    2008-11-01

    Small gullies, observed on Mars, could be formed by groundwater seepage from an underground aquifer or may result from the melting of near-surface ground ice at high obliquity. To test these different hypotheses, a cold room-based laboratory simulation has been performed. The experimental slope was designed to simulate debris flows on sand dune slopes at a range of angles, different granulometry and permafrost characteristics. Preliminary results suggest that the typical morphology of gullies observed on Mars can best be reproduced by the formation of linear debris flows related to the melting of a near-surface ground ice with silty materials. This physical modelling highlights the role of the periglacial conditions, especially the active-layer thickness during debris-flow formation.

  13. Analysis of an optical gate device for measuring aeolian sand movement

    NASA Astrophysics Data System (ADS)

    Etyemezian, V.; Nikolich, G.; Nickling, W.; King, J. S.; Gillies, J. A.

    2017-02-01

    Movement of sand in response to wind is the most important feature of aeolian sediment transport on Earth and other planets. Through sand blasting during saltation, large amounts of dust are ejected into the atmosphere and transported long distances, impacting climate and human health. Despite continuing improvements, currently available devices for field measurement of sand movement have limitations. An optical gate device (OGD) for detecting the movement, size, and possibly speed of individual sand grains during aeolian sediment transport was analyzed. The approach uses the highly time resolved signal from these sensors, which consist of a light emitter and a photosensitive sensor. A specific OGD that is manufactured by Optek (Carrollton, Texas, USA) was tested in a sediment transport wind tunnel alongside trap-style devices. The OGD device provided particle counts and total signal response that were well correlated with sand trap data (R2 between 0.66 and 0.88). Inter-comparison among eight identical units of the OGD showed excellent repeatability (R2 > 0.98 for 7 of 8 units). Subsequent tests revealed that the response of the phototransistor (light sensor) can be linear when operated within certain workable limits. Practical implications of this are that there is potential for extracting size distribution information. Limits imposed by noise levels in the signal and interferences from extraneous light sources were also identified. Despite the results presented being specific to the OGD model tested, much of the approach outlined is applicable to any OGD-type device (including Wenglor®) if the signal of the photo detector can be accessed directly.

  14. Definition and origin of the dune-field pattern at White Sands, New Mexico

    NASA Astrophysics Data System (ADS)

    Baitis, Elke; Kocurek, Gary; Smith, Virginia; Mohrig, David; Ewing, Ryan C.; Peyret, A.-P. B.

    2014-12-01

    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.

  15. An integrated model for dune morphology and sand fluxes on Mars

    NASA Astrophysics Data System (ADS)

    Runyon, K. D.; Bridges, N. T.; Ayoub, F.; Newman, C. E.; Quade, J. J.

    2017-01-01

    The transport and deposition of sand is the most prevalent agent of landscape modification on Mars today, with fluxes comparable to some sand dunes on Earth. Until now, the relationship between sand flux and dune field morphology has been poorly constrained. By tracking dune movement over ∼10 km-long dune fields in Herschel Crater and Nili Patera, representative of many dune fields on Mars, we find a downwind flux decrease that correlates with a sequence of changing morphology from barchans to barchanoids and seifs (longitudinal dunes) to isolated dome dunes and ending with sand sheets. We show empirical consistency with atmospheric Internal Boundary Layer (IBL) theory which can describe these broad flux and morphology changes in Martian dune fields. Deviations from IBL flux predictions are from wind streamline compressions up slopes, leading to a speedup effect. By establishing a dune field morphology type example and correlating it with measured and predicted flux changes, we provide an integrated morphology and flux model that can be applied to other areas of Mars and be used to infer paleo-environmental conditions from preserved sandstone.

  16. On the origin and age of the Great Sand Dunes, Colorado

    NASA Astrophysics Data System (ADS)

    Madole, Richard F.; Romig, Joe H.; Aleinikoff, John N.; VanSistine, D. Paco; Yacob, Ezra Y.

    2008-07-01

    Over the past 100 yr, several hypotheses have been proposed for the origin and age of the Great Sand Dunes. These hypotheses differ widely in the descriptions of dune morphometry, the immediate source of eolian sand, and when sand transport occurred. The primary purpose of this paper is to evaluate these hypotheses and, where warranted, to present new ideas about the origin and age of the Great Sand Dunes. To evaluate the previous hypotheses, we had to develop more detailed information about the surficial geology of the northern San Luis Valley. Thus, we mapped the surficial geology of an area extending several tens of kilometers north, south, and west of the Great Sand Dunes and examined subsurface stratigraphy in more than 200 wells and borings. In addition, we used relative-dating criteria and several radiocarbon and OSL ages to establish the chronology of surficial deposits, and we determined the U-Pb ages of detrital zircons to obtain information about the sources of the sand in the Great Sand Dunes. The first principal finding of this study is that the lower part of the closed basin north of the Rio Grande, referred to here as the sump, is the immediate source of the sand in the Great Sand Dunes, rather than the late Pleistocene flood plain of the Rio Grande (the most widely accepted hypothesis). A second principal finding is that the Great Sand Dunes are older than late Pleistocene. They postdate the draining of Lake Alamosa, which began ˜ 440 ka, and predate the time when streams draining the west flank of the Sangre de Cristo Mountains were deflected by incipient dunes that formed near the mountain front. Geomorphic and stratigraphic evidence indicate that this deflection occurred prior to the end of the next to last glaciation (Bull Lake), i.e., prior to ˜ 130 ka.

  17. On the origin and age of the Great Sand Dunes, Colorado

    USGS Publications Warehouse

    Madole, R.F.; Romig, J.H.; Aleinikoff, J.N.; VanSistine, D.P.; Yacob, E.Y.

    2008-01-01

    Over the past 100??yr, several hypotheses have been proposed for the origin and age of the Great Sand Dunes. These hypotheses differ widely in the descriptions of dune morphometry, the immediate source of eolian sand, and when sand transport occurred. The primary purpose of this paper is to evaluate these hypotheses and, where warranted, to present new ideas about the origin and age of the Great Sand Dunes. To evaluate the previous hypotheses, we had to develop more detailed information about the surficial geology of the northern San Luis Valley. Thus, we mapped the surficial geology of an area extending several tens of kilometers north, south, and west of the Great Sand Dunes and examined subsurface stratigraphy in more than 200 wells and borings. In addition, we used relative-dating criteria and several radiocarbon and OSL ages to establish the chronology of surficial deposits, and we determined the U-Pb ages of detrital zircons to obtain information about the sources of the sand in the Great Sand Dunes. The first principal finding of this study is that the lower part of the closed basin north of the Rio Grande, referred to here as the sump, is the immediate source of the sand in the Great Sand Dunes, rather than the late Pleistocene flood plain of the Rio Grande (the most widely accepted hypothesis). A second principal finding is that the Great Sand Dunes are older than late Pleistocene. They postdate the draining of Lake Alamosa, which began ??? 440??ka, and predate the time when streams draining the west flank of the Sangre de Cristo Mountains were deflected by incipient dunes that formed near the mountain front. Geomorphic and stratigraphic evidence indicate that this deflection occurred prior to the end of the next to last glaciation (Bull Lake), i.e., prior to ??? 130??ka.

  18. Temporal observations of a linear sand dune in the Simpson Desert, central Australia: Testing models for dune formation on planetary surfaces

    NASA Astrophysics Data System (ADS)

    Craddock, Robert A.; Tooth, Stephen; Zimbelman, James R.; Wilson, Sharon A.; Maxwell, Ted A.; Kling, Corbin

    2015-10-01

    Linear dunes are the most common dune form found on planetary surfaces, yet questions remain about their formation. Temporal observations of a linear dune located in the Simpson Desert of central Australia were made to monitor dune movement and to test competing hypotheses regarding linear dune formation. Our observations were collected on three separate occasions from 2006 to 2014. Rebar stakes were placed in a gridded pattern so that multiple measurements of sand thickness, GPS surveys, and photographs could be taken at the same locations over time. We observed widespread reworking of sand on and around the dune crest, with sand accumulation locally exceeding a meter between surveys. Overall, the height of the dune crest increased by several centimeters. We also observed fluctuations in the sand cover in the adjacent swales that often exceeded 2-3 cm between surveys, yet we did not observe any appreciable changes in the position of the dune's downwind terminus. Weather data indicate that the effective sand-transporting winds in the Simpson are widely unimodal. Net sediment flux (resultant drift direction) is toward the north-northwest, locally at an oblique angle to dune orientation. Collectively, our results suggest that the linear dune is actively maintained by vertical accretion. The implications from our observations are that linear dunes on other planetary surfaces could form in wind regimes that are widely unimodal, even where the resultant drift direction is locally oblique to dune orientation. In particular, such findings may provide support for global circulation models of Titan.

  19. Monitoring and analysis of sand dune movement and growth on the Navajo Nation, southwestern United States

    USGS Publications Warehouse

    Redsteer, Margaret Hiza; Bogle, Rian C.; Vogel, John M.

    2011-01-01

    Recurring drought and rising temperatures have caused reactivation and renewed growth of sand dunes on the lands of the Navajo Nation on the Colorado Plateau. Migrating dunes threaten health, housing, and transportation pathways. U.S. Geological Survey (USGS) scientists are conducting research to better understand the processes of dune growth and movement. This research will provide critical data to the Native peoples of the region in their response to the changing environment.

  20. The geomorphology and evolution of aeolian landforms within a river valley in a semi-humid environment: A case study from Mainling Valley, Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    Zhou, Na; Zhang, Chun-Lai; Wu, Xiao-Xu; Wang, Xun-ming; Kang, Li-qiang

    2014-11-01

    This paper systematically analyzes a valley's aeolian landforms in a semi-humid region and presents a model of its contemporary evolution. Mainling Valley of the Yarlung Zangbo River on the Qinghai-Tibet Plateau was chosen as the case study for the analysis of morphometric characteristics and the evolution sequence of aeolian landforms via field data and remote sensing images. The aeolian landforms were primarily composed of aeolian sand belts on river terraces and dunes (sheets) on hillside slopes. Three types of aeolian sand belts were identified based on their dune types. In type I belts, an erosive air stream combined with relatively high vegetation cover (10%) produced sparsely distributed parabolic dunes with a high variability of dune heights; in type II belts, the continual reworking by the erosive air stream in combination with low vegetation cover (3%) formed more densely distributed barchans and transitional dunes with a moderate variability of dune heights; and in type III belts, the gradual evolution from an erosive sand-laden air stream to a saturated sand-laden air stream in combination with low vegetation cover (2%) produced the densest crescentic dunefields but with the least variability in dune heights. Dune sizes increase, dune shapes become uniform, and dune distribution becomes close from type I to III belts. Lateral linking and merging of the dunes were also observed within the belts. Together this evidence indicates that an evolution sequence may exist. Aeolian dunefields in the belt appear to evolve from embryonic parabolic dunefields to adolescent barchan dunefields and, subsequently, to mature compound crescentic dunefields. As the aeolian sand belt evolves into the mature stage, sand accumulations at the foot of the mountain valley can be steps for sand accumulation on valley-side slopes.

  1. Complexity confers stability: Climate variability, vegetation response and sand transport on longitudinal sand dunes in Australia's deserts

    NASA Astrophysics Data System (ADS)

    Hesse, Paul P.; Telfer, Matt W.; Farebrother, Will

    2017-04-01

    The relationship between antecedent precipitation, vegetation cover and sand movement on sand dunes in the Simpson and Strzelecki Deserts was investigated by repeated (up to four) surveys of dune crest plots (≈25 × 25 m) over a drought cycle (2002-2012) in both winter (low wind) and spring (high wind). Vegetation varied dramatically between surveys on vegetated and active dune crests. Indices of sand movement had significant correlations with vegetation cover: the depth of loose sand has a strong inverse relationship with crust (cyanobacterial and/or physical) while the area covered by ripples has a strong inverse relationship with the areal cover of vascular plants. However, the relationship between antecedent rainfall and vegetation cover was found to be complex. We tentatively identify two thresholds; (1) >10 mm of rainfall in the preceding 90 days leads to rapid and near total cover of crust and/or small plants <50 cm tall, and (2) >400 mm of rainfall in the preceding three years leads to higher cover of persistent and longer-lived plants >50 cm tall. These thresholds were used to predict days of low vegetation cover on dune crests. The combination of seasonality of predicted bare-crest days, potential sand drift and resultant sand drift direction explains observed patterns of sand drift on these dunes. The complex vegetation and highly variable rainfall regime confer meta-stability on the dunes through the range of responses to different intervals of antecedent rainfall and non-linear growth responses. This suggests that the geomorphic response of dunes to climate variation is complex and non-linear.

  2. 76 FR 47123 - Endangered and Threatened Wildlife and Plants; 90-Day Finding on a Petition To List Six Sand Dune...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-04

    ...- southeast of Fallon, Churchill County, Nevada. Sand Mountain is a star dune (roughly star-shaped) and ranges... Heritage Program 2006, p. 43). Blowsand Mountains is a complex of star and linear dunes occurring partially... 2010, p. 15). Big Dune is a complex star dune that reaches 2,731 ft (832.4 m) in elevation and...

  3. Meso-scale aeolian transport of beach sediment via dune blowout pathways within a linear foredune

    NASA Astrophysics Data System (ADS)

    O'Keeffe, Nicholas; Delgado-Fernandez, Irene; Jackson, Derek; Aplin, Paul; Marston, Christopher

    2016-04-01

    The evolution of coastal foredunes is largely controlled by sediment exchanges between the geomorphic sub-units of the nearshore, beach, foredune and dune field. Although blowouts are widely recognised as efficient sediment transport pathways, both event-scale and meso-scale quantification of their utility in transferring beach sediments landwards is limited. Foredunes characterised by multiple blowouts may be more susceptible to coastline retreat through the enhanced landwards transport of beach or foredune sediments. To date, a key constraint for investigations of such scenarios has been the absence of accurate blowout sediment transport records. Here we use the Sefton coast in north-west England as a study area where an unprecedented temporal coverage of LIDAR data is available between 1999 and 2015. Additionally, an extensive set of aerial photography also exists, dating back to 1945 allowing comparison of blowout frequency and magnitude together with the alongshore limits of coastline retreat. Digital terrain models are derived for each year that LIDAR data is available. Informed by LIDAR based topography and areas of bare sand (aerial photos) terrain models have been created containing individual blowouts. Differentials in 'z' values between each terrain model of each available year has identified topographic change and total levels of transport. Preliminary results have confirmed the importance of blowouts in transporting beach or foredune sediment landwards and thus potentially promoting coastline retreat. Repetition of processes across a larger number of blowout topographies will allow better identification of individual blowouts for 'event' scale field investigations to examine spatial and temporal variability of beach sediment transport via blowouts routes.

  4. Plant functional traits and diversity in sand dune ecosystems across different biogeographic regions

    NASA Astrophysics Data System (ADS)

    Mahdavi, P.; Bergmeier, E.

    2016-07-01

    Plant species of a functional group respond similarly to environmental pressures and may be expected to act similarly on ecosystem processes and habitat properties. However, feasibility and applicability of functional groups in ecosystems across very different climatic regions have not yet been studied. In our approach we specified the functional groups in sand dune ecosystems of the Mediterranean, Hyrcanian and Irano-Turanian phytogeographic regions. We examined whether functional groups are more influenced by region or rather by habitat characteristics, and identified trait syndromes associated with common habitat types in sand dunes (mobile dunes, stabilized dunes, salt marshes, semi-wet sands, disturbed habitats). A database of 14 traits, 309 species and 314 relevés was examined and trait-species, trait-plot and species-plot matrices were built. Cluster analysis revealed similar plant functional groups in sand dune ecosystems across regions of very different species composition and climate. Specifically, our study showed that plant traits in sand dune ecosystems are grouped reflecting habitat affiliation rather than region and species pool. Environmental factors and constraints such as sand mobility, soil salinity, water availability, nutrient status and disturbance are more important for the occurrence and distribution of plant functional groups than regional belonging. Each habitat is shown to be equipped with specific functional groups and can be described by specific sets of traits. In restoration ecology the completeness of functional groups and traits in a site may serve as a guideline for maintaining or restoring the habitat.

  5. Adaptation to life in aeolian sand: how the sandfish lizard, Scincus scincus, prevents sand particles from entering its lungs

    PubMed Central

    Vihar, Boštjan; Günther, Mathias; Huemer, Michaela; Riedl, Martin; Shamiyeh, Stephanie; Mayrhofer, Bernhard; Böhme, Wolfgang; Baumgartner, Werner

    2016-01-01

    ABSTRACT The sandfish lizard, Scincus scincus (Squamata: Scincidae), spends nearly its whole life in aeolian sand and only comes to the surface for foraging, defecating and mating. It is not yet understood how the animal can respire without sand particles entering its respiratory organs when buried under thick layers of sand. In this work, we integrated biological studies, computational calculations and physical experiments to understand this phenomenon. We present a 3D model of the upper respiratory system based on a detailed histological analysis. A 3D-printed version of this model was used in combination with characteristic ventilation patterns for computational calculations and fluid mechanics experiments. By calculating the velocity field, we identified a sharp decrease in velocity in the anterior part of the nasal cavity where mucus and cilia are present. The experiments with the 3D-printed model validate the calculations: particles, if present, were found only in the same area as suggested by the calculations. We postulate that the sandfish has an aerodynamic filtering system; more specifically, that the characteristic morphology of the respiratory channel coupled with specific ventilation patterns prevent particles from entering the lungs. PMID:27852763

  6. Solitary wave behavior in sand dunes observed from space

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2011-11-01

    Although the dynamics of individual barchan dunes are well understood, their interactions are the subject of ongoing scientific interest and debate. Numerical and analog model predictions of shape-preserving binary dune collisions have been hard to test due to the long timescales over which such processes typically occur. This paper documents ten binary dune collisions in a 45-year time sequence of satellite images from the Bodélé Depression in Chad. The observations confirm that when two barchan dunes collide, a transfer of mass occurs so that one dune appears to travel through the other unscathed, like a solitary wave.

  7. The interaction of unidirectional winds with an isolated barchan sand dune

    NASA Technical Reports Server (NTRS)

    Gad-El-hak, M.; Pierce, D.; Howard, A.; Morton, J. B.

    1976-01-01

    Velocity profile measurements are determined on and around a barchan dune model inserted in the roughness layer on the tunnel floor. A theoretical investigation is made into the factors influencing the rate of sand flow around the dune. Flow visualization techniques are employed in the mapping of streamlines of flow on the dune's surface. Maps of erosion and deposition of sand are constructed for the barchan model, utilizing both flow visualization techniques and friction velocities calculated from the measured velocity profiles. The sediment budget found experimentally for the model is compared to predicted and observed results reported. The comparison shows fairly good agreement between the experimentally determined and predicted sediment budgets.

  8. Aeolian Sediment Transport Pathways and Aerodynamics at Troughs on Mars

    NASA Technical Reports Server (NTRS)

    Bourke, Mary C.; Bullard, Joanna E.; Barnouin-Jha, Olivier S.

    2004-01-01

    Interaction between wind regimes and topography can give rise to complex suites of aeolian landforms. This paper considers aeolian sediment associated wit11 troughs on Mars and identifies a wider range of deposit types than has previously been documented. These include wind streaks, falling dunes, "lateral" dunes, barchan dunes, linear dunes, transverse ridges, sand ramps, climbing dunes, sand streamers, and sand patches. The sediment incorporated into these deposits is supplied by wind streaks and ambient Planitia sources as well as originating within the trough itself, notably from the trough walls and floor. There is also transmission of sediment between dneTsh. e flow dynamics which account for the distribution of aeolian sediment have been modeled using two-dimensional computational fluid dynamics. The model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin. The inferred patterns of sediment transport compare well with the distribution of aeolian forms. Model data indicate an increase of wind velocity by approx. 30 % at the downwind trough margin. This suggests that the threshold wind speed necessary for sand mobilization on Mars will be more freqentmlye t in these inclined locations.

  9. 2010 weather and aeolian sand-transport data from the Colorado River corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Dealy, Timothy P.; East, Amy E.; Fairley, Helen C.

    2014-01-01

    Measurements of weather parameters and aeolian sand transport were made in 2010 near selected archeological sites in the Colorado River corridor through Grand Canyon, Arizona. Data collected in 2010 indicate event- and seasonal-scale variations in rainfall, wind, temperature, humidity, and barometric pressure. Differences in weather patterns between 2009 and 2010 included a slightly later spring windy season, greater spring precipitation and annual rainfall totals, and a later onset and length of the reduced diurnal barometric-pressure fluctuations commonly associated with summer monsoon conditions. The increase in spring precipitation was consistent with the 2010 spring El Niño conditions compared to the 2009 spring La Niña conditions, whereas the subsequent transition to an El Niño-Southern Oscillation neutral phase appeared to delay the reduction in diurnal barometric fluctuations.

  10. Laser particle counter validation for aeolian sand transport measurements using a highspeed camera

    NASA Astrophysics Data System (ADS)

    Duarte-Campos, Leonardo; Wijnberg, Kathelijne M.; Oyarte-Gálvez, Loreto; Hulscher, Suzanne J. M. H.

    2017-04-01

    Measuring aeolian sand transport rates in the field has been a long-standing challenge. In this paper, we present the results of a laboratory experiment to test the ability of a laser particle counter sensor (Wenglor) to accurately count sand grains of various grain size classes and stainless steel beads. We compared the count data collected by the Wenglor with images from a Highspeed camera which revealed the actual number of grains passing the laser beam. A Silicon photodiode was used to record the laser intensity reduction induced by the sand grain passage through the laser beam to derive the minimal necessary reduction for the Wenglor to count grains. For the two possible settings of the Wenglor, i.e., Minimal Teach-in or Normal Teach-in, a minimum of 18% and 78% blocking of the laser beam was required for recording a count. This implies that the minimum grain size that can be observed by the Wenglor is 210 ± 3 μm and 495 ± 10 μm for the two settings respectively, which is considerably coarser than previously assumed. Due to the non-uniform power distribution of the laser sensor intensity, at the detection limit of 210 μm, only grains passing through the centre of the beam will be counted.

  11. A comparison of seed banks across a sand dune successional gradient at Lake Michigan dunes (Indiana, USA)

    USGS Publications Warehouse

    Leicht-Young, S. A.; Pavlovic, N.B.; Grundel, R.; Frohnapple, K.J.

    2009-01-01

    In habitats where disturbance is frequent, seed banks are important for the regeneration of vegetation. Sand dune systems are dynamic habitats in which sand movement provides intermittent disturbance. As succession proceeds from bare sand to forest, the disturbance decreases. At Indiana Dunes National Lakeshore, we examined the seed banks of three habitat types across a successional gradient: foredunes, secondary dunes, and oak savanna. There were differences among the types of species that germinated from each of the habitats. The mean seed bank density increased across the successional gradient by habitat, from 376 to 433 to 968 seeds m-2, but with foredune and secondary dune seed bank densities being significantly lower than the savanna seed bank density. The number of seeds germinated was significantly correlated with soil organic carbon, demonstrating for this primary successional sequence that seed density increases with stage and age. The seed bank had much lower species richness than that of the aboveground vegetation across all habitats. Among sites within a habitat type, the similarity of species germinated from the seed banks was very low, illustrating the variability of the seed bank even in similar habitat types. These results suggest that restoration of these habitats cannot rely on seed banks alone. ?? 2008 Springer Science+Business Media B.V.

  12. Morphology and formation of the upwind margin at White Sands Dune Field

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.; Jerolmack, D. J.; Martin, R. L.; Reitz, M. D.; Phillips, C. B.; Falcini, F.; Masteller, C.

    2012-12-01

    A remarkable transitional landscape occurs at the upwind margin of White Sands Dune Field. Over the course a few hundred meters the landscape changes from an flat, sand availability-limited playa, to a sand sheet with strong spatial grain-size sorting, to meter high slipfaceless proto-dunes and finally to several meter high dunes with angle-of-repose slip faces. Within one wavelength of the first dune, dunes rise to nearly 10 meters in height above Alkali Flat, the upwind playa that extends for 13 km westward from the dune field. This abrupt rise in topography may perturb the dominant southwesterly wind flow and trigger an internal boundary layer, which causes a spatial decrease in surface wind stress and decline sediment flux, thereby altering the dune dynamics and dune field morphology downwind. Though the emergence of this upwind transition may play a key role in the morphodynamics of the dune field, what are the morphodynamics of the transition? What are the feedbacks between the emerging topography and the wind within the transition? This presentation uses high-resolution aerial photos, time-series airborne LiDAR and terrestrial laser scanning to characterize the transitional morphology the upwind margin of White Sands and discusses these morphologies in the context of the interplay between wind flow and dune field topography. Alkali Flat playa is sparsely sand covered, the amount of which varies temporally. The sparse sand cover occurs as sand patches that form in the lee of bushes or within topographic lows generated by deflated gypsum crust. Adjacent and downwind of the playa is a sand sheet composed of variable wavelength, coarse grained ripples. Ten to thirty meter wide ripple patches organized into a repeating sequence of coarse-grained, > 15 cm wavelength ripples to fine-grained, < 15 cm wavelength ripples occur across the sand sheet. Downwind the ripple patches organize into low-relief protodune hummocks. The protodunes are covered by a range of ripple

  13. Multi-scale Hydrologic Modeling of the White Sands Dune Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Bourret, S. M.; Newton, B. T.

    2014-12-01

    The shallow groundwater flow system of White Sands dune field, located within the arid to semi-arid Tularosa Basin of Southern New Mexico, likely stabilizes the base of the largest gypsum dune field in the world. The dune is saturated throughout nearly its entire accumulation thickness, resulting in a shallow water table (< 3 ft bgs) in the inter-dunal areas. Water table elevation influences the spatial extent of the dune field and accumulation thickness. The White Sands National Monument (WHSA) is concerned that lowering the water table may lead to increased scour and migration of the dune field, which could be unfavorable to the preservation of the flora and fauna that have adapted to survive there. In response to projected increases in groundwater pumping in the regional Tularosa Basin groundwater system, changes in surface water use, and the threat of climate change, the WHSA is interested in understanding how these changes on a regional scale may impact the shallow dune field aquifer. Mathematical modeling techniques on varying spatial and temporal scales are used to characterize the relative importance of the sources of water (local vs. regional) to the dune aquifer, and to quantify the timescales on which changes may affect the water table in the dune field. A 2-dimensional, dune-scale heat and fluid flow model uses the seasonal temperature fluctuations to estimate the vertical and horizontal flow of water from the regional system to the dune field aquifer. We have also constructed a 2-dimensional, hydrologic model to characterize the regional groundwater flow regime near to the dune aquifer system, as well as across the Tularosa Basin to a depth of 6 km. Additionally, a 3-dimensional, hydrologic model of the Tularosa Basin and the White Sands dune field quantifies hydrologic characteristics, sources and sinks of groundwater in the basin and at the dune field. Computed and observed salinity, groundwater residence times, and water level data are the primary

  14. Oceanobacillus chungangensis sp. nov., isolated from a sand dune.

    PubMed

    Lee, Dong Chae; Kang, Hyeonji; Weerawongwiwat, Veeraya; Kim, Beomjoon; Choi, Young-Wan; Kim, Wonyong

    2013-10-01

    A Gram-stain-positive, spore-forming, rod-shaped, motile, strictly aerobic bacterial strain, designated CAU 1051(T), was isolated from a sand dune and its taxonomic position was investigated using a polyphasic approach. Strain CAU 1051(T) grew optimally at pH 5.0 and 30 °C. NaCl was not required for growth but up to 10.0 % (w/v) NaCl was tolerated. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CAU 1051(T) formed a distinct lineage within the genus Oceanobacillus and was most closely related to Oceanobacillus profundus CL-MP28(T), Oceanobacillus caeni S-11(T), and Oceanobacillus picturae LMG 19492(T) (96.8 %, 95.6 % and 95.3 % similarity, respectively). DNA-DNA reassociation analysis showed that strain CAU 1051(T) displayed 28.2±0.7 % relatedness to O. profundus KCTC 13625(T). Strain CAU 1051(T) contained MK-7 as the only isoprenoid quinone and anteiso-C15 : 0 as the major fatty acid. The cell wall peptidoglycan of strain CAU 1051(T) contained meso-diaminopimelic acid. The polar lipids were composed of diphosphatidylglycerol, phosphatidylglycerol, six unidentified phospholipids, an unidentified glycolipid, and six unidentified polar lipids. The major whole-cell sugars were glucose and ribose. The DNA G+C content was 36.3 mol%. On the basis of phenotypic data and phylogenetic inference, strain CAU 1051(T) represents a novel species of the genus Oceanobacillus for which the name Oceanobacillus chungangensis sp. nov. is proposed. The type strain is CAU 1051(T) ( = KCTC 33035(T) = CCUG 63270(T)).

  15. Postdam evolution of aeolian landscapes in the Colorado River corridor through Grand Canyon National Park, Arizona, USA

    NASA Astrophysics Data System (ADS)

    Draut, A. E.; Collins, B. D.; Fairley, H. C.; Rubin, D. M.

    2009-12-01

    Sediment deposits within the Colorado River corridor in Grand Canyon, USA, include fluvial sandbars and aeolian dune fields; fluvial deposits are the primary sediment source for the dune fields. We present a conceptual model describing evolution of aeolian landscapes in Grand Canyon, based upon field measurements of wind and sand transport and on surveys of vegetation and substrate properties. The data indicate that Glen Canyon Dam operations can affect geomorphic evolution above the elevation reached by river flows because of the link between fluvial deposition and aeolian transport of sediment. Evolution of aeolian landscapes, in turn, can affect the stability and preservation of archaeological material that occurs in numerous dune fields. Before closure of Glen Canyon Dam on the Colorado River in 1963, sediment-rich floods (mean annual flood 2400 m3/s) formed sandbars from which wind moved sand inland to form aeolian dunes. After dam operations reduced the amplitude and frequency of high flows, and eliminated the mainstream fluvial sediment supply, fluvial sandbars lost open sand area owing to erosion by river flows and the spread of riparian vegetation. Two types of aeolian landscapes now occur: (1) modern fluvial sourced, those downwind of postdam sandbars; and (2) relict fluvial sourced, which are not downwind of postdam sandbars and whose primary sediment source was deposits from predam floods that were larger than any postdam flows have been. Sediment supply has been reduced to type (1) dune fields because postdam sandbars are smaller than in the predam era; new sediment supply to type (2) dune fields has been essentially eliminated. Decreased aeolian sediment supply leads to increased vegetation and biologic soil crust in dune fields, and can result in greater susceptibility to gully formation during rainfall due to lack of infilling aeolian sand. Modern-fluvial-sourced dunes can receive new windblown sand from sandbars formed by controlled

  16. Multifrequency and multipolarization radar scatterometry of sand dunes and comparison with spaceborne and airborne radar images

    NASA Technical Reports Server (NTRS)

    Blom, Ronald; Elachi, Charles

    1987-01-01

    Airborne radar scatterometer data on sand dunes, acquired at multiple frequencies and polarizations, are reported. Radar backscatter from sand dunes is very sensitive to the imaging geometry. At small incidence angles the radar return is mainly due to quasi-specular reflection from dune slopes favorably oriented toward the radar. A peak return usually occurs at the incidence angle equal to the angle of repose for the dunes. The peak angle is the same at all frequencies as computed from specular reflection theory. At larger angles the return is significantly weaker. The scatterometer measurements verified observations made with airborne and spaceborne radar images acquired over a number of dune fields in the U.S., central Africa, and the Arabian peninsula. The imaging geometry constraints indicate that possible dunes on other planets, such as Venus, will probably not be detected in radar images unless the incidence angle is less than the angles of repose of such dunes and the radar look direction is approximately orthogonal to the dune trends.

  17. Radionuclide transfer to invertebrates and small mammals in a coastal sand dune ecosystem.

    PubMed

    Wood, M D; Leah, R T; Jones, S R; Copplestone, D

    2009-06-15

    International intercomparisons of models to assess the impact of ionising radiation on wildlife have identified radionuclide transfer assumptions as a significant source of uncertainty in the modelling process. There is a need to improve the underpinning data sets on radionuclide transfer to reduce this uncertainty, especially for poorly-studied ecosystems such as coastal sand dunes. This paper presents the results of the first published study of radionuclide transfer to invertebrates and small mammals in a coastal sand dune ecosystem. Activity concentrations of (137)Cs, (238)Pu, (239+240)Pu and (241)Am are reported for detritivorous, herbivorous, carnivorous and omnivorous biota. Differences in activity concentrations measured in the sand dune biota are related to the trophic level of the organisms and the influence of sea-to-land transfer is apparent in the food chain transfer observed at the site. There are notable differences in the concentration ratios (CRs) calculated for the sand dune biota compared to other terrestrial ecosystems, especially for the small mammals which have CRs that are two orders of magnitude lower than the generic terrestrial ecosystem CRs published by the recent EC EURATOM ERICA project. The lower CRs at the sand dunes may be due to the influence of other cations from the marine environment (e.g. K and Na) on the net radionuclide transfer observed, but further research is required to test this hypothesis.

  18. Sand dune patterns on Titan controlled by long-term climate cycles

    NASA Astrophysics Data System (ADS)

    Ewing, Ryan C.; Hayes, Alex G.; Lucas, Antoine

    2015-01-01

    Linear sand dunes cover the equatorial latitudes of Saturn's moon Titan and are shaped by global wind patterns. These dunes are thought to reflect present-day diurnal, tidal and seasonal winds, but climate models have failed to reproduce observed dune morphologies with these wind patterns. Dunes diagnostic of a specific wind or formative timescale have remained elusive. Here we analyse radar imagery from NASA's Cassini spacecraft and identify barchan, star and reoriented dunes in sediment-limited regions of Titan's equatorial dune fields that diverge by 23° on average from the orientation of linear dunes. These morphologies imply shifts in wind direction and sediment availability. Using a numerical model, we estimate that the observed reorientation of dune crests to a change in wind direction would have taken around 3,000 Saturn years (1 Saturn year ~ 29.4 Earth years) or longer--a timescale that exceeds diurnal, seasonal or tidal cycles. We propose that shifts in winds and sediment availability are the product of long-term climate cycles associated with variations in Saturn's orbit. Orbitally controlled landscape evolution--also proposed to explain the distribution of Titan's polar lakes--implies a dune-forming climate on equatorial Titan that is analogous to Earth.

  19. Effects of Sand Dune Stabilization on the Spatial Pattern of Artemisia ordosica Population in Mu Us Desert, Northwest China

    PubMed Central

    Zhang, Jiachen; Zhang, Yuqing; Fan, Dongqing; Qin, Shugao; Jia, Xin; Wu, Bin; Chen, Dong; Gao, Hao; Zhu, Linfeng

    2015-01-01

    Vegetation patterns are strongly influenced by sand mobility in desert ecosystems. However, little is known about the spatial patterns of Artemisia ordosica, a dominant shrub in the Mu Us desert of Northwest China, in relation to sand fixation. The aim of this study was to investigate and contrast the effects of sand dune stabilization on the population and spatial distribution of this desert shrub. Spatial autocorrelation, semi-variance analysis, and point-pattern analysis were used jointly in this study to investigate the spatial patterns of A. ordosica populations on dunes in Yanchi County of Ningxia, China. The results showed that the spatial autocorrelation and spatial heterogeneity declined gradually, and the distance between the clustered individuals shortened following sand dune fixation. Seedlings were more aggregated than adults in all stage of dune stabilization, and both were more aggregated on shifting sand dunes separately. Spatial associations of the seedlings with the adults were mostly positive at distances of 0–5 m in shifting sand dunes, and the spatial association changed from positive to neutral in semi-fixed sand dunes. The seedlings were spaced in an almost random pattern around the adults, and their distances from the adults did not seem to affect their locations in semi-fixed sand dunes. Furthermore, spatial associations of the seedlings with the adults were negative in the fixed sand dune. These findings demonstrate that sand stabilization is an important factor affecting the spatial patterns of A. ordosica populations in the Mu Us desert. These findings suggest that, strong association between individuals may be the mechanism to explain the spatial pattern formation at preliminary stage of dune fixation. Sand dune stabilization can change the spatial pattern of shrub population by weakening the spatial association between native shrub individuals, which may affect the development direction of desert shrubs. PMID:26102584

  20. Effects of Sand Dune Stabilization on the Spatial Pattern of Artemisia ordosica Population in Mu Us Desert, Northwest China.

    PubMed

    Zhang, Jiachen; Zhang, Yuqing; Fan, Dongqing; Qin, Shugao; Jia, Xin; Wu, Bin; Chen, Dong; Gao, Hao; Zhu, Linfeng

    2015-01-01

    Vegetation patterns are strongly influenced by sand mobility in desert ecosystems. However, little is known about the spatial patterns of Artemisia ordosica, a dominant shrub in the Mu Us desert of Northwest China, in relation to sand fixation. The aim of this study was to investigate and contrast the effects of sand dune stabilization on the population and spatial distribution of this desert shrub. Spatial autocorrelation, semi-variance analysis, and point-pattern analysis were used jointly in this study to investigate the spatial patterns of A. ordosica populations on dunes in Yanchi County of Ningxia, China. The results showed that the spatial autocorrelation and spatial heterogeneity declined gradually, and the distance between the clustered individuals shortened following sand dune fixation. Seedlings were more aggregated than adults in all stage of dune stabilization, and both were more aggregated on shifting sand dunes separately. Spatial associations of the seedlings with the adults were mostly positive at distances of 0-5 m in shifting sand dunes, and the spatial association changed from positive to neutral in semi-fixed sand dunes. The seedlings were spaced in an almost random pattern around the adults, and their distances from the adults did not seem to affect their locations in semi-fixed sand dunes. Furthermore, spatial associations of the seedlings with the adults were negative in the fixed sand dune. These findings demonstrate that sand stabilization is an important factor affecting the spatial patterns of A. ordosica populations in the Mu Us desert. These findings suggest that, strong association between individuals may be the mechanism to explain the spatial pattern formation at preliminary stage of dune fixation. Sand dune stabilization can change the spatial pattern of shrub population by weakening the spatial association between native shrub individuals, which may affect the development direction of desert shrubs.

  1. Nourishment of perched sand dunes and the issue of erosion control in the Great Lakes

    NASA Astrophysics Data System (ADS)

    Marsh, William M.

    1990-09-01

    Although limited in coverage, perched sand dunes situated on high coastal bluffs are considered the most prized of Great Lakes dunes. Grand Sable Dunes on Lake Superior and Sleeping Bear Dunes on Lake Michigan are featured attractions of national lakeshores under National Park Service management. The source of sand for perched dunes is the high bluff along their lakeward edge. As onshore wind crosses the bluff, flow is accelerated upslope, resulting in greatly elevated levels of wind stress over the slope brow. On barren, sandy bluffs, wind erosion is concentrated in the brow zone, and for the Grand Sable Bluff, it averaged 1 m3/yr per linear meter along the highest sections for the period 1973 1983. This mechanism accounts for about 6,500 m3 of sand nourishment to the dunefield annually and clearly has been the predominant mechanism for the long-term development of the dunefield. However, wind erosion and dune nourishment are possible only where the bluff is denuded of plant cover by mass movements and related processes induced by wave erosion. In the Great Lakes, wave erosion and bluff retreat vary with lake levels; the nourishment of perched dunes is favored by high levels. Lake levels have been relatively high for the past 50 years, and shore erosion has become a major environmental issue leading property owners and politicians to support lake-level regulation. Trimming high water levels could reduce geomorphic activity on high bluffs and affect dune nourishment rates. Locally, nourishment also may be influenced by sediment accumulation associated with harbor protection facilities and by planting programs aimed at stabilizing dunes.

  2. Digital data from the Great Sand Dunes airborne gravity gradient survey, south-central Colorado

    USGS Publications Warehouse

    Drenth, B.J.; Abraham, J.D.; Grauch, V.J.S.; Labson, V.F.; Hodges, G.

    2013-01-01

    This report contains digital data and supporting explanatory files describing data types, data formats, and survey procedures for a high-resolution airborne gravity gradient (AGG) survey at Great Sand Dunes National Park, Alamosa and Saguache Counties, south-central Colorado. In the San Luis Valley, the Great Sand Dunes survey covers a large part of Great Sand Dunes National Park and Preserve. The data described were collected from a high-resolution AGG survey flown in February 2012, by Fugro Airborne Surveys Corp., on contract to the U.S. Geological Survey. Scientific objectives of the AGG survey are to investigate the subsurface structural framework that may influence groundwater hydrology and seismic hazards, and to investigate AGG methods and resolution using different flight specifications. Funding was provided by an airborne geophysics training program of the U.S. Department of Defense's Task Force for Business & Stability Operations.

  3. 78 FR 37845 - Meeting of the Imperial Sand Dunes Recreation Area (ISDRA) Subgroup of the California Desert...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-24

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Land Management Meeting of the Imperial Sand Dunes Recreation Area (ISDRA) Subgroup of the... 92-463 and 94-579, that the Imperial Sand Dunes Recreation Area Subgroup of the California...

  4. Titan's sand seas of longitudinal dunes as indicators of winds and sediment transport

    NASA Astrophysics Data System (ADS)

    Radebaugh, J.; Lorenz, R. D.; Lunine, J. I.; Wall, S. D.; Spencer, C.; Kirk, R. L.; Lopes, R. M.; Stofan, E. R.; Allison, M.; Callahan, P.; Cassini RADAR Team

    2007-12-01

    The Cassini Titan Radar Mapper has revealed nearly ten thousand longitudinal dunes on the surface of Titan, mainly within +-30 deg latitude [1,2,3]. Based on dune orientations, divergence around topography, similarity to dune fields on Earth, and other features such as bright streaks, the prevailing wind hypothesis model for longitudinal dune formation is favored, in which winds blow generally parallel to the dune long axis [e.g.5,6,7]. On Titan, these winds are dominantly Eastward [2,3], but as observed in more recent Radar swaths (2,4,5/2007) there is Northeastward deviation from this direction at higher latitudes. Vast fields of longitudinal dunes at Titan's equatorial regions are described as sand seas [2,3]. On Earth, these regions are typified not so much by the transport as by the accumulation of sand. This may occur when there is a large nearby source of sand or when there is reduced sand removal due to decreased winds or topographic obstacles [7,8,9]. Sand transport could be inhibited both upwind and downwind of the topographically complex region Xanadu, for example. Seasonally reversing wind regimes could also lead to the stagnation of sand transportation and net accumulation within sand sea regions [7,8,9]. This scenario may help reconcile global wind model predictions with directionality opposed to that predicted from observation. Sand seas on Earth are formed in arid regions and in some places cover 30-40 percent of the surface [8], a percent coverage similar to that in the equatorial regions on Titan [2,3]. Sand seas on Earth are long-lived, having taken up to tens of thousands of years to accumulate; whether the Titan dunes are more or less stable is an outstanding question. [1] Elachi et al. 2006. [2] Lorenz et al. 2006. [3] Radebaugh et al. in rev. [4] Stofan et al. 2007. [5] Fryberger and Dean 1979. [6] Tsoar 1983. [7] Lancaster 1982. [8] Lancaster 1995. [9] Fryberger and Ahlbrandt 1979.

  5. Mega-ripples in Iran: A new analog for transverse aeolian ridges on Mars

    NASA Astrophysics Data System (ADS)

    Foroutan, M.; Zimbelman, J. R.

    2016-08-01

    A new terrestrial analog site for transverse aeolian ridges (TARs) is described in this study. The Lut desert of Iran hosts large ripple-like aeolian bedforms, with the same horizontal length scales and patterns of TARs on Mars. Different classes of TARs and different types of other aeolian features such as sand dunes, zibars, dust devil tracks and yardangs can be found in this area, which signify an active aeolian region. This area represents a unique site to study the formation and evolution of these enigmatic features, with potential relevance toward a better understanding of TARs on Mars.

  6. Constraints on the age of the Great Sand Dunes, Colorado, from subsurface stratigraphy and OSL dates

    USGS Publications Warehouse

    Madole, Richard F.; Mahan, Shannon; Romig, Joseph H.; Havens, Jeremy C.

    2013-01-01

    The age of the Great Sand Dunes has been debated for nearly 150 yr. Seven ages ranging from Miocene to late Holocene have been proposed for them. This paper presents new information—chiefly subsurface stratigraphic data, OSL dates, and geomorphic evidence—that indicates that the Great Sand Dunes began to form in the latter part of the middle Pleistocene. The dunes overlie a thick wedge of piedmont-slope deposits, which in turn overlies sediment of Lake Alamosa, a paleolake that began to drain about 440 ka. The wedge of piedmont-slope deposits extends westward for at least 23 km and is as much as 60 m thick at a distance of 10 km from the Sangre de Cristo Range. Ostracodes from one well indicate that the eastern shoreline of Lake Alamosa extended to within 4.3 km of where the Great Sand Dunes eventually formed. The time represented by the wedge of piedmont-slope deposits is not known exactly, but the wedge post-dates 440 ka and was in place prior to 130 ka because by then the dunes overlying it were sufficiently close and tall enough to obstruct streams draining from the Sangre de Cristo Range.

  7. The influence of barchan shape on the moisture and temperature of the dune sand and the diversity of local climate

    NASA Astrophysics Data System (ADS)

    Dluzewski, M.; Zmudzka, E.; Woronko, D.; Biejat, K.

    2012-04-01

    The aim of the research was to determine the impact of the barchan shape on moisture and temperature of dune sand in near surface layer. The study was carried out in the spring 2010 on the dune field located 20 km to the north of Laâyoune (Western Sahara). This region is one of the most humid, located in tropical, desert areas, which is associated with the influx of air masses from the Atlantic. Moisture and temperature of the dune sand in near surface layer was analysed on the basis of measurements in different parts of barchans. The studies included also analysis of the physical condition of the atmosphere, meteorological elements within the analyzed dune fields, the grain size distribution and mineral composition of dune sand. Shape of barchans and their orientations were determined on the basis of the detailed topographic survey. The results show important spatial variation in moisture and temperature of dune sand in near surface layer, characterized by very small differences on grain size distribution and mineral composition. It was found that variations in moisture and temperature of dune material were mainly related to the inflow of solar energy. The advection played a lesser role. The main factors affecting the distribution of moisture and temperature of dune sand as well the air surface layer were the aspect and the slope angle of the dunes. Eastern and southern (lee side) parts of the dunes were characterized by several times less moisture than their western and northern parts (stoss side). With the direction of advection from the north-west which occurred during the field studies, there was no evidence of less moisture in the sand of the stoss sides of dunes (despite the greater wind speed intensifying the process of evaporation). It can therefore be assumed that the intensity of sand transport within a dune located in the region with the impact of oceanic air masses depends mainly on the shape and spatial orientation of barchans.

  8. The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

    PubMed

    Lorenz, R D; Wall, S; Radebaugh, J; Boubin, G; Reffet, E; Janssen, M; Stofan, E; Lopes, R; Kirk, R; Elachi, C; Lunine, J; Mitchell, K; Paganelli, F; Soderblom, L; Wood, C; Wye, L; Zebker, H; Anderson, Y; Ostro, S; Allison, M; Boehmer, R; Callahan, P; Encrenaz, P; Ori, G G; Francescetti, G; Gim, Y; Hamilton, G; Hensley, S; Johnson, W; Kelleher, K; Muhleman, D; Picardi, G; Posa, F; Roth, L; Seu, R; Shaffer, S; Stiles, B; Vetrella, S; Flamini, E; West, R

    2006-05-05

    The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

  9. The sand seas of titan: Cassini RADAR observations of longitudinal dunes

    USGS Publications Warehouse

    Lorenz, R.D.; Wall, S.; Radebaugh, J.; Boubin, G.; Reffet, E.; Janssen, M.; Stofan, E.; Lopes, R.; Kirk, R.; Elachi, C.; Lunine, J.; Mitchell, Ken; Paganelli, F.; Soderblom, L.; Wood, C.; Wye, L.; Zebker, H.; Anderson, Y.; Ostro, S.; Allison, M.; Boehmer, R.; Callahan, P.; Encrenaz, P.; Ori, G.G.; Francescetti, G.; Gim, Y.; Hamilton, G.; Hensley, S.; Johnson, W.; Kelleher, K.; Muhleman, D.; Picardi, G.; Posa, F.; Roth, L.; Seu, R.; Shaffer, S.; Stiles, B.; Vetrella, S.; Flamini, E.; West, R.

    2006-01-01

    The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show ???100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of ???0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

  10. Sand mining impacts on long-term dune erosion in southern Monterey Bay

    USGS Publications Warehouse

    Thornton, E.B.; Sallenger, Abby; Sesto, Juan Conforto; Egley, L.; McGee, Timothy; Parsons, Rost

    2006-01-01

    Southern Monterey Bay was the most intensively mined shoreline (with sand removed directly from the surf zone) in the U.S. during the period from 1906 until 1990, when the mines were closed following hypotheses that the mining caused coastal erosion. It is estimated that the yearly averaged amount of mined sand between 1940 and 1984 was 128,000 m3/yr, which is approximately 50% of the yearly average dune volume loss during this period. To assess the impact of sand mining, erosion rates along an 18 km range of shoreline during the times of intensive sand mining (1940–1990) are compared with the rates after sand mining ceased (1990–2004). Most of the shoreline is composed of unconsolidated sand with extensive sand dunes rising up to a height of 46 m, vulnerable to the erosive forces of storm waves. Erosion is defined here as a recession of the top edge of the dune. Recession was determined using stereo-photogrammetry, and LIDAR and GPS surveys. Long-term erosion rates vary from about 0.5 m/yr at Monterey to 1.5 m/yr in the middle of the range, and then decrease northward. Erosion events are episodic and occur when storm waves and high tides coincide, allowing swash to undercut the dune and resulting in permanent recession. Erosion appears to be correlated with the occurrence of El Niños. The calculated volume loss of the dune in southern Monterey Bay during the 1997–98 El Niño winter was 1,820,000 m3, which is almost seven times the historical annual mean dune erosion of 270,000 m3/yr. The alongshore variation in recession rates appears to be a function of the alongshore gradient in mean wave energy and depletions by sand mining. After cessation of sand mining in 1990, the erosion rates decreased at locations in the southern end of the bay but have not significantly changed at other locations.

  11. Measurements of Coupled Fluid and Sediment Motion Over Mobile Sand Dunes in a Laboratory Flume

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The relation between turbulent fluid motions and sediment particles over mobile sand dunes may be better understood by examining the time scales over which the quantities fluctuate. In laboratory experiments performed at the USDA-ARS-National Sedimentation Laboratory, profiles of acoustic backscatt...

  12. Time Scales in Turbulence and Sediment Concentration Over Mobile Sand Dunes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The relationship between turbulent fluid motions and sediment particles over mobile sand dunes may be better understood by examining the time scales over which the quantities fluctuate. In laboratory experiments performed at the USDA-ARS-National Sedimentation Laboratory, profiles of acoustic backs...

  13. Soil water and temperature patterns in an arid desert dune sand

    NASA Astrophysics Data System (ADS)

    Berndtsson, Ronny; Nodomi, Kanichi; Yasuda, Hiroshi; Persson, Thomas; Chen, Heshen; Jinno, Kenji

    1996-11-01

    Under arid natural conditions, soil water content governs and limits the number and size of perennial plant species. Thus, plant-available soil water is the main constraint for sustainable control of desert encroachment. To evaluate possibilities for re-vegetation of bare sand surfaces, soil water and temperature patterns for typical sand dunes in a desert climate were investigated. Bare and vegetated soil transects were selected for observation of soil water content and temperature. The investigated soil transects covered crest-to-crest spacings (about 60 m horizontally and 15 m vertically) in a shifting sand dune area. Observations were made at Shapotou field research station bordering the Tengger Desert in Northwestern China. The paper presents two-dimensional properties of soil water content (0.1-3.0 m depth) and temperature (0-1.0 m depth) before and after rainfall. Rainfall (15-22 mm) affected soil water distribution down to 1.5-2.0 m and temperature distribution down to 1.0 m. Soil water appeared to be transported through the apparently highly pervious and homogeneous sand along the dune slopes. High water contents and, thus, infiltration occurred mainly at the non-sloping parts, i.e. the dune crests and bottoms. Rainfall changed the temperature patterns from a mainly horizontally layered appearance before the rainfall to increasingly vertically shaped patterns.

  14. Solitary Dunes under Bimodal Winds

    NASA Astrophysics Data System (ADS)

    Reffet, Erwan; Courrech du Pont, S.; Hersen, P.; Fulchignoni, M.; Douady, S.

    2009-01-01

    The high resolution and coverage achieved on Mars' surface have detailed lots of sand dunes of various types [1]. Many are reported as barchan or barchanoid dunes and present a diversity of shape ascribed to compound wind regimes, collisions or cementation. This diversity reminds us that aeolian structures are fairly complex. Although dunes have been extensively observed and documented, the conditions of their formation and evolution are still difficult to study because of the long time required for their development and their large length-scale. We developed a laboratory approach using underwater experiments to study the morphology of dunes. This method has been used successfully to reproduce various types of dunes downsized to a few centimeters. Barchan dunes are formed using a unidirectional wind-equivalent regime on a pile of ceramic sand-sized grains [2]. Changing the wind regime to a more complex one reveals other structures. In the case of multiple wind directions star dunes can be observed. A bimodal wind regime, e.g. switching between two distinct directions, over an homogeneous layer of sand leads to transverse, longitudinal or complex compound sandbeds depending on the angle between these wind directions [3]. Here, we apply bimodal wind regimes to isolated patches of sand in order to observe the variation of morphology of the resulting dunes. We present the barchanoid dunes obtained for various angles of bimodal wind and show the transition to the "chestnut” dunes type. We also investigate sudden variations in wind direction over a barchan dune. Therefore, we illustrate how the (not so) simple barchan shape can be affected by a more complex wind regime and give a new insight in understanding dunes on Mars. [1] http://www.mars-dunes.org/ . [2] Hersen et al. PRL, 2003. [3] Reffet et al. pldu.work 2008.

  15. Vegetated dune morphodynamics during recent stabilization of the Mu Us dune field, north-central China

    NASA Astrophysics Data System (ADS)

    Xu, Zhiwei; Mason, Joseph A.; Lu, Huayu

    2015-01-01

    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

  16. Clear cutting (10-13th century) and deep stable economy (18-19th century) as responsible interventions for sand drifting and plaggic deposition in cultural landscapes on aeolian sands (SE-Netherlands).

    NASA Astrophysics Data System (ADS)

    van Mourik, Jan; Vera, Hein; Wallinga, Jakob

    2013-04-01

    landscapes, characterized by deflation plains (gleyic arenosols) and complexes of inland dunes (haplic arenosols). Clear cutting was responsible for the mediaeval first large scale expansion of drift sand landscapes. In such driftsand landscapes, the majority of the podzolic soils in coversand has been truncated by aeolian erosion. Only on scattered sheltered sites in the landscape, palaeopodzols were buried under mono or polycyclic driftsand deposits. They are now the valuable soil archives for palaeoecological research. During the 18th century, the population growth and regional economic activity stimulated the agricultural productivity. Farmers introduced the innovative 'deep stable' technique to increase the production of fertilizers. Farmers started sod digging, including the top of the Ah horizon of the humus forms. This consequently promoted heath degradation and sand drifting, resulting in the extension of driftsand landscapes. Deep stable economy and sod digging was responsible for the 18th century second large scale expansion of drift sand landscapes. During the 19th century, farmers tried to find alternative fertilizers and authorities initiated reforestation projects. The invention of chemical fertilizers at the end of the 19th century marked the end of the period of heath management and plaggic agriculture. The heath was no longer used for the harvesting of plaggic matter and new land management practices were introduced. Heath was reclaimed to new arable land or reforested with Scotch pine. Geomorphological features as inland dunes and plaggic covers survived in the landscape and are now included in the geological inheritance.

  17. The contribution of aeolian sand and dust to iron fertilization of phytoplankton blooms in southwestern Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Winton, V. H. L.; Dunbar, G. B.; Bertler, N. A. N.; Millet, M.-A.; Delmonte, B.; Atkins, C. B.; Chewings, J. M.; Andersson, P.

    2014-04-01

    Iron is a limiting micronutrient for primary production in the Ross Sea, Antarctica. Recent observations reveal low dissolved Fe (dFe) concentrations in the Ross Sea polynya following high initial rates of primary production in summer, after the dFe winter reserve has been consumed. Significant new sources of dFe are therefore required to further sustain phytoplankton blooms. Iron from aeolian sand and dust (ASD) released from melting sea ice is one potential source. To constrain aeolian Fe inputs, we determined ASD mass accumulation rates and the total and soluble Fe content of ASD on sea ice in McMurdo Sound, southwestern (SW) Ross Sea. The mean mass accumulation rate was ~1.5 g m-2 yr-1, total Fe content of this ASD was 4 ± 1 wt %, and the percentage of soluble Fe was 11 ± 1%. Our mean estimate of the bulk aeolian dFe flux of 122.1 µmol m-2 yr-1 for the McMurdo Sound region suggests that aeolian Fe can support between 9.0 × 109 and 4.1 × 1011 mol C yr-1 (0.1-4.9 Tg C yr-1) of new primary production. This equates to only ~15% of new primary production in the SW Ross Sea, suggesting that aeolian dFe is a minor component of seasonal Fe supply. The very high ASD accumulation on sea ice in McMurdo Sound compared to other regions of Antarctica suggests that our results represent the upper limit of dFe supply to the ocean from this source in the Ross Sea.

  18. The physics of wind-blown sand and dust.

    PubMed

    Kok, Jasper F; Parteli, Eric J R; Michaels, Timothy I; Karam, Diana Bou

    2012-10-01

    The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

  19. Breeding and solitary wave behavior of dunes.

    PubMed

    Durán, O; Schwämmle, V; Herrmann, H

    2005-08-01

    Beautiful dune patterns can be found in deserts and along coasts due to the instability of a plain sheet of sand under the action of the wind. Barchan dunes are highly mobile aeolian dunes found in areas of low sand availability and unidirectional wind fields. Up to now modelization mainly focused on single dunes or dune patterns without regarding the mechanisms of dune interactions. We study the case when a small dune bumps into a bigger one. Recently Schwämmle and Herrmann [Nature (London) 426, 610 (2003)] and Katsuki [(e-print cond-mat 0403312)] have shown that under certain circumstances dunes can behave like solitary waves. This means that they can "cross" each other which has been questioned by many researchers before. In other cases we observe coalescence--i.e., both dunes merge into one--breeding--i.e., the creation of three baby dunes at the center and horns of a Barchan dune--or budding--i.e., the small dune, after "crossing" the big one, is unstable and splits into two new dunes.

  20. Environmental dynamics of a star dune

    NASA Astrophysics Data System (ADS)

    Zhang, Weimin; Qu, Jianjun; Tan, Lihai; Jing, Zhefan; Bian, Kai; Niu, Qinghe

    2016-11-01

    Star dunes, the largest aeolian bedforms in the sand seas of the world, are usually distributed within specific geographical areas that have multi-directional wind regimes. However, relatively few studies have focused on the environmental factors that impart such great volumes of sand to these dunes. Specifically, verification of the developmental processes of star dunes through long-term monitoring is scarce. In this study, by observing 3-D airflow fields and long-term dune dynamics, we demonstrate how topographic barriers, which generate vertical airflow and local air circulation, control the development of a star dune on Mingsha Mountain in Dunhuang, China. Results show that airflow stagnation and deflection caused by topography is one of the major mechanisms for the formation of star dunes. In our study, topographic barriers contribute to the development of intensive vertical airflow dominated by easterly winds. This intensive vertical airflow is one of the main driving mechanisms of the upward growth of mega-dunes. Vertical airflow is the strongest developed airflow reported in available data on aeolian geomorphology. In addition, star dunes are usually distributed in areas where the local air circulation is strong. The results of long-term dune dynamics verify that local air circulation, which forms three wind directions with the regional wind regime, contributes to the maintenance and development of star dunes. Our study indicates that complex mega-dunes are products of topographic barriers, which facilitate their recognition in aeolian geomorphology. We introduce a new evolution pattern of star dunes under the influence of local environment and topographic barriers.

  1. 78 FR 36568 - Notice of Availability of the Record of Decision for the Approved Imperial Sand Dunes Recreation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-18

    ... Bureau of Land Management Notice of Availability of the Record of Decision for the Approved Imperial Sand... Management (BLM) announces the availability of the Imperial Sand Dunes Recreation Area Record of Decision... receive a reply during normal business hours. SUPPLEMENTARY INFORMATION: The Imperial Sand...

  2. Sand Dune Ridge Alignment Effects on Surface BRF over Libya-4 Calibration Site

    NASA Astrophysics Data System (ADS)

    Govaerts, Yves

    2015-12-01

    The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm..

  3. Sand dune ridge alignment effects on surface BRF over the Libya-4 CEOS calibration site.

    PubMed

    Govaerts, Yves M

    2015-02-03

    The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm.

  4. Sand Dune Ridge Alignment Effects on Surface BRF over the Libya-4 CEOS Calibration Site

    PubMed Central

    Govaerts, Yves M.

    2015-01-01

    The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm. PMID:25654721

  5. Ground-water resources of the Clatsop Plains sand-dune area, Clatsop County, Oregon

    USGS Publications Warehouse

    Frank, F.J.

    1970-01-01

    Although the average annual precipitation of the Clatsop Plains is 78.5 inches, the area is not without problems of water supply. The Clatsop Plains area ix underlain by Tertiary bedrock of low permeability that stores and yields small quantities of ground water, which may be of poor chemical quality. This Tertiary bedrock furnishes only minor ground-water discharge to maintain the base flow of streams. The flow of rivers and creeks, normally abundant during the wet season, decreases greatly during the dry summer months. The lowlands are overlain by extensive deposits of dune and beach sand. The dune sand is permeable and can absorb and store, as fresh water, a large percentage of the annual precipitation. In the central part of the dune area, the saturated thickness of the sand ranges from 95 to more than 150 feet. Most of the ground water in the sand discharges to the ocean through beach-line seeps and underflow. Much of the water now being discharged to the ocean could be recovered by pumping from properly located, designed, and constructed wells. Three test wells drilled as part of this study are capable of yielding 100 gallons per minute although they are equipped with only short lengths of well screen. It is estimated that 2,500 acre-feet of ground water per year per square mile of area may be available for withdrawal in the 10 square mile area that is most favorable for development. The water from the dune sand is soft to moderately hard, has a low chloride concentration, and is of generally good chemical quality; however, at places it is weakly acidic and contains sufficient dissolved iron to make iron removal necessary for some uses. Ground water from shallow depths beneath a few swampy low-lying areas is brown and contains excessive concentrations of iron.

  6. Parameterization of Finite-Element Cryo-Hydrologic Sand Dune Model to Constrain Debris-Flow-Initiating Subsurface Temperatures and Pore-Water Pressures, Great Kobuk Sand Dunes, Alaska

    NASA Astrophysics Data System (ADS)

    Dinwiddie, C. L.; Hooper, D. M.

    2015-05-01

    To explain how debris flows form at subfreezing air temperatures, we present meteorology-driven, numerical simulation-derived subsurface temperature and pore-water pressure profiles in the Great Kobuk Sand Dunes of Alaska, for incipient flow events.

  7. Observations regarding the movement of barchan sand dunes in the Nazca to Tanaca area of southern Peru

    NASA Astrophysics Data System (ADS)

    Parker Gay, S.

    1999-03-01

    Significant studies of sand dunes and sand movement made in coastal southern Peru in 1959-1961 [Gay, S.P., 1962. Origen, distribución y movimiento de las arenas eólicas en el área de Yauca a Palpa. Boletin de la Sociedad Geologica del Perú 37, 37-58] have never been published in the English language and consequently have never been referred to in the standard literature. These studies contain valuable information, not developed by later workers in this field, that may be of broad general interest. For example, using airphotos of barchan dunes and plotting the rates of movement vs. dune widths, the author quantified the deduction of Bagnold [Bagnold, R.A., 1941. The Physics of Blown Sand and Desert Dunes. Methuen, London.] that the speed of barchan movement is inversely proportional to barchan size (as characterized by height or width). This led to the conclusion that all barchans in a given dune field, regardless of size, sweep out approximately equal areas in equal times. Another conclusion was that collisions between smaller, overtaking dunes and larger dunes in front of them do not result in destruction or absorption of the smaller dunes if the collision is a `sideswipe'. The dunes simply merge into a compound dune for a time, and the smaller dune then moves on intact, i.e., passes, the larger dune, whilst retaining its approximate original size and shape. Another result of the 1959-1961 studies was a map that documents the Pacific coast beaches as the source of the sand ( Fig. 1), which is then blown inland through extensive dune fields of barchans and other dune forms in great clockwise-sweeping paths, to its final resting place in huge sand masses, sometimes called `sand seas' [Lancaster, N., 1995. Geomorphology of Desert Dunes. Routledge, London], at higher elevations 20 to 60 km from the coast. A minor, but nevertheless interesting, discovery was a small heavy mineral dune located directly in the lee of a large barchan, evidently formed by the winnowing

  8. Spatial differences of aeolian desertification responses to climate in arid Asia

    NASA Astrophysics Data System (ADS)

    Wang, Xunming; Hua, Ting; Lang, Lili; Ma, Wenyong

    2017-01-01

    Most areas of arid Asia are covered by aeolian dunes, sand sheets, gravels, and desert steppes, and may jeopardize nearly 350 million people if climate change increases aeolian desertification. Although the aeolian desertification is mainly triggered by climate changes are extensively acknowledged, the responses of aeolian desertification to various climate scenarios are poorly understood. Based on the tight combinations of dune activity index (DAI) trends and of aeolian desertification, here the spatial differences of aeolian desertification responses on various climate scenarios were reported. The analyzed results show that the variations in temperature, precipitation and wind regime have no significant contributions on aeolian desertification in the extremely arid Asia. From the early to blooming periods of vegetation growth, although temperature rise may benefit vegetation growths in some high latitudes and altitudes, the temperature rise may increase aeolian desertification in most arid Asia regions such as Mongolia, West and Central Asia. In arid Asia, although precipitation increases may benefit the rehabilitation, decreases in precipitation is not the key role on aeolian desertification occurrences in extremely arid regions. From the early to blooming periods of vegetation growths, spatial trends of the sensitivity of aeolian desertification to wind regime varied. Generally, at the regional scales there are relative high sensitivities for aeolian desertification to climate changes in the eastern and western regions of arid Asia, and the climate changes may not play important roles on aeolian desertification occurrence in the central regions. The spatial differences of aeolian desertification responses to climate changes indicate various strategies for aeolian desertification combating are needed in different regions of arid Asia.

  9. Vertical structure of aeolian turbulence in a boundary layer with sand transport

    NASA Astrophysics Data System (ADS)

    Lee, Zoe S.; Baas, Andreas C. W.

    2016-04-01

    originating from the top of the boundary layer, indicating a downwards direction of eddy motion. While directionality of turbulence cannot be definitively determined, our results indicate that the top-down turbulence model is a suitable explanation, further supported by the presence of 'incomplete' eddies which originate at higher elevations but fail to extend to the surface. This provides the first evidence in support of a top down turbulence model as observed in aeolian geomorphology, and we present preliminary findings on its relationship to sand transport activity. Lee, Z.S., Baas, A.C.W. (2016) Variable and conflicting shear stress estimates inside a boundary layer with sediment transport. Earth Surface Processes and Landforms; DOI: 10.1002/esp.3829

  10. Oscillation-induced sand dunes in a liquid-filled rotating cylinder

    NASA Astrophysics Data System (ADS)

    Dyakova, Veronika; Kozlov, Victor; Polezhaev, Denis

    2016-12-01

    The dynamics of granular medium in a liquid-filled horizontal cylinder with a time-varying rotation rate is experimentally studied. When the cylinder is purely rotated, the granular medium develops an annular layer near the cylindrical wall. The interface between fluid and sand is smooth and axisymmetric. The time variation of the rotation rate initiates the azimuthal oscillation of the liquid in the cylinder's frame of reference and provokes the onset of quasisteady relief in the form of regular dunes. The stability of the axisymmetric sand surface and dynamics of regular dunes are examined. It is found that the ripple formation is provoked by the quasisteady instability of the Stokes boundary layer. In the range of high Reynolds numbers, the ripple formation occurs at a constant critical Shields number θc≃0.05 . The spatial period of the relief is not sensitive to the fluid viscosity and granule diameter; it is determined by the amplitude of oscillation and ratio between the oscillation frequency and mean rotation rate. Long-term experiments show that there are forward and backward azimuthal drifts of dunes. An initial analysis of the issues related to the dune migration is provided.

  11. Investigating Effects of the November 2004 High-Flow Release From Glen Canyon Dam on Aeolian Sand-Transport Rates in the Colorado River Corridor, Grand Canyon, Arizona

    NASA Astrophysics Data System (ADS)

    Draut, A. E.; Rubin, D. M.

    2005-12-01

    In November, 2004, a 60-hour experimental flood release from Glen Canyon Dam held the Colorado River flow through Grand Canyon, Arizona, above 1,160 m3 s-1 (41,000 ft3 s-1). This high-flow experiment was designed to rebuild fluvial sand deposits, restoring a component of the ecosystem that had declined since closure of the dam in 1963. Transport and deposition of aeolian sand has important implications for archaeological resources in the river corridor, many of which are located in and covered by aeolian deposits. This study presents aeolian sediment-transport data collected in the river corridor during the year before and in the months after the flood experiment. At each of the six study locations, substantial new deposition of fluvial sand occurred as a result of the 2004 flood, which temporarily increased the amount of sand available for aeolian entrainment. However, high daily fluctuations (142 to 566 m3 s-1; 5,000 to 20,000 ft3 s-1) of the river flow from January to March 2005 removed much of the new sand before the start of the 2005 windy season. The greatest potential for aeolian re-distribution of flood-deposited sand occurred during the April-May windy season, during which the highest measured winds can locally exceed 25 m s-1, with sand-transport rates ~5 kg cm-1 day-1. These data may be used to guide decisions regarding future experimental floods and subsequent flow schedules, if maximizing sand redistribution by wind is a management objective.

  12. Development of a grazing monitoring program for Great Sand Dunes National Park, Colorado

    USGS Publications Warehouse

    Zeigenfuss, Linda C.; Schoenecker, Kathryn A.

    2015-08-07

    National parks in the United States face the difficult task of managing natural resources within park boundaries that are influenced to a large degree by historical land uses or by forces outside of the park’s protection and mandate. Among the many challenges faced by parks is management of wildlife populations that occupy larger landscapes than individual park units but that concentrate within park lands both seasonally and opportunistically. Great Sand Dunes National Park and Preserve in south-central Colorado is currently developing an Ungulate Management Plan to address management of elk and bison populations within the park. Execution of the Ungulate Management Plan will require monitoring and assessment of habitat conditions in areas that appear sensitive to ungulate use or heavily used by elk and bison. Several sources of information on the various habitats within the park and their use and response to foraging elk and bison exist from recent and on-going research in Great Sand Dunes National Park and Preserve as well as from studies in other regions of the Intermountain West. All of this data can be used to inform the planning process. This report provides background on vegetation types that make up the primary bison and elk ranges in Great Sand Dunes National Park and Preserve and on the potential effects of ungulate grazing and browsing in these specific vegetation communities (both locally and regionally). The report also provides a review of the elements necessary to develop a long-term monitoring program for Great Sand Dunes National Park and Preserve that addresses both the responses to ungulate herbivory seen in important habitats in the park and the amount and patterns of ungulate habitat use.

  13. Spatial-temporal evolution of aeolian blowout dunes at Cape Cod

    NASA Astrophysics Data System (ADS)

    Abhar, Kimia C.; Walker, Ian J.; Hesp, Patrick A.; Gares, Paul A.

    2015-05-01

    This paper explores historical evolution of blowouts at Cape Cod National Seashore (CCNS), USA - a site that hosts one of the world's highest densities of active and stabilized blowouts. The Spatial-Temporal Analysis of Moving Polygons (STAMP) method is applied to a multi-decadal dataset of aerial photography and LiDAR to extract patterns of two-dimensional movement and morphometric changes in erosional deflation basins and depositional lobes. Blowout development in CCNS is characterized by several geometric (overlap) and movement (proximity) responses, including: i) generation and disappearance, ii) extension and contraction, iii) union or division, iv) clustering and v) divergence by stabilization. Other possible movement events include migration, amalgamation and proximal stabilization, but they were not observed in this study. Generation events were more frequent than disappearance events; the former were highest between 1985 and 1994, while the latter were highest between 2000 and 2005. High rates of areal change in erosional basins occurred between 1998 and 2000 (+ 3932 m2 a-1), the lowest rate (+ 333 m2 a-1) between 2005 and 2009, and the maximum rate (+ 4589 m2 a-1) between 2009 and 2011. Union events occurred mostly in recent years (2000-2012), while only one division was observed earlier (1985-1994). Net areal changes of lobes showed gradual growth from a period of contraction (- 1119 m2 a-1) between 1998 and 2000 to rapid extension (+ 2030 m2 a-1) by 2010, which is roughly concurrent with rapid growth of erosional basins between 2005 and 2009. Blowouts extended radially in this multi-modal wind regime and, despite odd shapes initially, they became simpler in form (more circular) and larger over time. Net extension of erosional basins was toward ESE (109°) while depositional lobes extended SSE (147°). Lobes were aligned with the strongest (winter) sand drift vector although their magnitude of areal extension was only 33% that of the basins. These

  14. Occurrence and scale of compositional heterogeneity in Martian dune fields: Toward understanding the effects of aeolian sorting on Martian sediment compositions

    NASA Astrophysics Data System (ADS)

    Pan, Cong; Rogers, A. Deanne

    2017-01-01

    Aeolian transport and hydrodynamic sorting have been proposed to be a significant influence on Martian sediment bulk compositions, through laboratory experiments, modeling and terrestrial analogies. But to date, few studies have directly examined compositional-grain size relationships within sediment fields on Mars; thus the prevalence of hydrodynamic sorting as well as the scales at which sorting is important remain poorly understood. To that end, we assessed the degree and occurrence of thermophysical and compositional heterogeneity for 25 dune fields within a ∼42,000,000 km2 area on Mars. Among these, only four exhibit spatial heterogeneity in spectral properties and composition. Two of these four sites show a strong positive relationship between particle size and olivine abundance. The rarity of compositional heterogeneity within dune fields in our study region (5-185°E, 45°N-20°S) may indicate phenocryst-poor source rocks; alternatively, sorting within individual bedforms may be present but not at the scale of the full dune field (∼10-20 km). Compositional segregation correlated with grain size due to hydrodynamic sorting has been observed by rovers at scales much smaller than THEMIS ground resolution (100 m/pixel); thus these small scales might be the operable, relevant ones of hydrodynamic compositional sorting prevailing most commonly in Martian dune fields.

  15. Microbial Diversity in Soil, Sand Dune and Rock Substrates of the Thar Monsoon Desert, India.

    PubMed

    Rao, Subramanya; Chan, Yuki; Bugler-Lacap, Donnabella C; Bhatnagar, Ashish; Bhatnagar, Monica; Pointing, Stephen B

    2016-03-01

    A culture-independent diversity assessment of archaea, bacteria and fungi in the Thar Desert in India was made. Six locations in Ajmer, Jaisalmer, Jaipur and Jodhupur included semi-arid soils, arid soils, arid sand dunes, plus arid cryptoendolithic substrates. A real-time quantitative PCR approach revealed that bacteria dominated soils and cryptoendoliths, whilst fungi dominated sand dunes. The archaea formed a minor component of all communities. Comparison of rRNA-defined community structure revealed that substrate and climate rather than location were the most parsimonious predictors. Sequence-based identification of 1240 phylotypes revealed that most taxa were common desert microorganisms. Semi-arid soils were dominated by actinobacteria and alpha proteobacteria, arid soils by chloroflexi and alpha proteobacteria, sand dunes by ascomycete fungi and cryptoendoliths by cyanobacteria. Climatic variables that best explained this distribution were mean annual rainfall and maximum annual temperature. Substrate variables that contributed most to observed diversity patterns were conductivity, soluble salts, Ca(2+) and pH. This represents an important addition to the inventory of desert microbiota, novel insight into the abiotic drivers of community assembly, and the first report of biodiversity in a monsoon desert system.

  16. Detecting changes on coastal primary sand dunes using multi-temporal Landsat imagery

    NASA Astrophysics Data System (ADS)

    Gonçalves, Gil; Duro, Nuno; Sousa, Ercilia; Pinto, Luís.; Figueiredo, Isabel

    2014-10-01

    Due to both natural and anthropogenic causes the coastal primary sand dunes, keeps changing dynamically and continuously their shape, position and extend over time. In this paper we use a case study to show how we monitor the Portuguese coast, between the period 2000 to 2014, using free available multi-temporal Landsat imagery (ETM+ and OLI sensors). First, all the multispectral images are panshaperned to meet the 15 meters spatial resolution of the panchromatic images. Second, using the Modification of Normalized Difference Water Index (MNDWI) and kmeans clustering method we extract the raster shoreline for each image acquisition time. Third, each raster shoreline is smoothed and vectorized using a penalized least square method. Fourth, using an image composed by five synthetic bands and an unsupervised classification method we extract the primary sand dunes. Finally, the visual comparison of the thematic primary sand dunes maps shows that an effective monitoring system can be implemented easily using free available remote sensing imagery data and open source software (QGIS and Orfeo toolbox).

  17. Source-to-sink cycling of aeolian sediment in the north polar region of Mars

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.; Kocurek, G.

    2012-12-01

    Aeolian sand dunes are prominent features on the landscapes of Earth, Mars, Venus and Titan and sedimentary deposits interpreted as aeolian in origin are found in the rock records of Earth and Mars. The widespread occurrence of aeolian dunes on the surface of these worlds and within their deep-time depositional records suggests that aeolian systems are and likely have been a default depositional environment for the Solar System. Within an aeolian source-to-sink context, we hypothesize that planet-specific boundary conditions strongly impact production, transport, accumulation and preservation of aeolian sediment, whereas dunes and dune-field patterns remain largely similar. This hypothesis is explored within the north polar region of Mars, which hosts the most extensive aeolian dune fields and aeolian sedimentary deposits yet recognized on Mars and appears to be a region of dynamic source-to-sink cycling of aeolian sediments. The Planum Boreum Cavi Unit rests beneath north polar ice cap of Mars and is composed of several hundred meters of niveo-aeolian dune cross-stratification. The overall architecture of the unit consists of sets of preserved dune topography with an upward increase in the abundance of ice. Dune sets are defined by stabilized, polygonally fractured bounding surfaces, erosional bounding surfaces and typical internal lee foresets made of sediment and ice. The accumulation of the Cavi Unit is interpreted as occurring through freezing and serves as an example of a cold temperature boundary condition on aeolian sediment accumulation. Preservation of the Cavi Unit arises because of deposition of the overlying ice cap and contrasts with preservation of aeolian sediment on Earth, which is largely driven by eustasy and tectonics. The Cavi Unit is thought to be one source of sediment for the north polar Olympia Undae Dune Field. The region of Olympia Undae near the Cavi Unit shows a reticulate dune field pattern composed of two sets of nearly orthogonal

  18. Effects of River Regulation on Aeolian Landscapes, Grand Canyon National Park, USA

    NASA Astrophysics Data System (ADS)

    Draut, A. E.

    2010-12-01

    Sediment deposits in the Colorado River corridor include fluvial sandbars and aeolian dune fields, and the fluvial deposits are the primary sediment source for sand in the aeolian dunes. This 7-year study examined the effects of river regulation at Glen Canyon Dam (alteration of flow regime, sediment-supply reduction, and consequent loss of fluvial sandbars) on aeolian landscapes downstream in Grand Canyon National Park. A comparative study was developed between aeolian landscapes in Grand Canyon, Arizona, and Cataract Canyon, Utah, upstream of Glen Canyon Dam and its reservoir (Lake Powell), where hydrology and sediment supply of the Colorado River are affected substantially less by artificial river regulation than occurs in Grand Canyon. Before closure of Glen Canyon Dam in 1963, sediment-rich floods (mean annual peak 2400 m3/s) formed sandbars from which wind moved sand inland to form aeolian dunes. After dam operations reduced the amplitude and frequency of high flows, and eliminated the mainstream fluvial sediment supply, Grand Canyon’s fluvial sandbars lost open sand area owing to erosion by river flows and the spread of riparian vegetation. Two types of aeolian landscapes now occur in Grand Canyon: (1) modern fluvial sourced, those downwind of post-dam sandbars; and (2) relict fluvial sourced, whose primary sediment source was deposits from pre-dam floods that were larger than any post-dam flows have been. Sediment supply has been reduced to type (1) dune fields because post-dam sandbars are smaller than in the pre-dam era; new sediment supply to type (2) dune fields essentially has been eliminated. Type 1 aeolian landscapes can receive new windblown sand from sandbars formed by controlled floods (1160 m3/s), which occurred in 1996, 2004, and 2008. Type 1 dune fields, being downwind and within 100 m of controlled-flood sandbars, have significantly higher aeolian sand-transport rates, more open sand, and less biologic soil crust than relict type 2 dune

  19. The importance of dunes on a variety of planetary surfaces

    USGS Publications Warehouse

    Titus, Timothy N.; Zimbelman, James R.; Radebaugh, Jani

    2015-01-01

    Scientists observe aeolian bed forms, or dune-like structures, throughout the solar system in a range of locations, from bodies with only transient atmospheres, such as comets, to places with thick atmospheres, such as Venus and the Earth’s ocean floor. Determining the source of sand and the different dune formations that result are thus important to understanding solar system and planetary evolution.

  20. Heavy metal levels in dune sands from Matanzas urban resorts and Varadero beach (Cuba): Assessment of contamination and ecological risks.

    PubMed

    Díaz Rizo, Oscar; Buzón González, Fran; Arado López, Juana O; Denis Alpízar, Otoniel

    2015-12-30

    Concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in dune sands from six urban and suburban Matanzas (Cuba) resorts and Varadero beach were estimated by X-ray fluorescence analysis. Ranges of metal contents in dune sands show a strong variation across the studied locations (in mg/kg(-1)): 20-2964 for Cr, 17-183 for Ni, 17-51 for Cu, 18-88 for Zn and 5-29 for Pb. The values of contamination factors and contamination degrees how that two of the studied Matanzas's resorts (Judio and Chirry) are strongly polluted. The comparison with Sediment Quality Guidelines shows that dune sands from Judio resort represent a serious risk for humans, due to polluted Cr and Ni levels, while sands from the rest of the studied resorts, including Varadero beach, do not represent any risk for public use.

  1. Erosion of North Polar Layers and Genesis of nearby Sand Dunes

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) is used by the MOC science team as a tool to test hypotheses about the geology, geomorphology, and meteorology of Mars. In 1999, MOC images revealed that the layers of the martian north polar cap are divided into two distinct units: an upper, light-toned sequence of layers, and a lower, darker-toned suite of layers. The team suspected that the lower unit, because of its dark tone and apparent association with nearby dune fields, might be a source of windblown sand. However, most of the 1999 images were of very low contrast because the frequent dust storms in the region made the atmosphere extremely hazy. Very few images of the north polar cap were obtained in 2000 because it was first hidden during the long winter's night, then coated by springtime frost. By early 2001, the north polar cap was in summer and the MOC team set out to test the idea that sand is eroding out of the lower unit. This picture, obtained in February 2001, shows streamers of dark sand coming from outcrops of the lower, dark-toned unit. The streamers join a nearby dune field less than a few kilometers (less than a mile) away. Erosion of the lower layered unit liberates sand that was long ago deposited in these layers. The upper unit, by contrast, contains almost no sand. Wind erosion of the lower unit leads to creation of steep scarps as the sand is removed and the upper unit is undermined. The sand moves downwind (in this case, toward the bottom left of the image) and creates dunes. The new views of the martian north polar cap obtained in 1999 and 2001 suggest that it may not contain as much water ice as previously believed. Indeed, the amount of ice may be as little as half of what was once thought. The picture shown here is 3 km (1.9 mi) wide and illuminated from the lower left.

  2. Using Ground Penetrating Radar to Image Paleotopography and Structural Controls at Coral Pink Sand Dunes, Kane County, Utah

    NASA Astrophysics Data System (ADS)

    Rozar, E. J.; Bradford, J. H.; Ford, R. L.; Wilkins, D. E.

    2014-12-01

    The Coral Pink Sand Dunes (CPSD) are one of the largest dune fields in the Great Basin-Colorado Plateau Transition Zone. The dune field rests on Navajo Sandstone, and is bisected by the Sevier Normal Fault, which also forms the bedrock escarpment along the eastern boundary of the lower dune field (LDF). Limited ground penetrating radar (GPR) collected previously, as well as recent ground-based LiDAR data and geomorphic observations, suggest that underlying bedrock is topographically lower in the center of the LDF than on its margins. In order to image the dune-bedrock interface and any structures contained within the bedrock, including buried faults, 50-MHz and 100-MHz GPR antennae with 400-V transmitters were used to conduct over 25 transects, totaling several kilometers, across the LDF. We recorded radar reflections at depths of up to 30 m within the bedrock beneath the modern dunes. Outcrops and/or shallow boreholes along some transects provide ground truth for dune-bedrock contacts. The resulting radar profiles suggest at least two antithetic fault zones within the LDF that, in places, appear to control the location of smaller dunes. Further examination of the relationship between these fault zones and dune forms, as imaged with LiDAR, will help inform whether or not these structural controls affect variation in dune type and patterning across the LDF, and may also explain why the CPSD exist in this location.

  3. Namibian Analogs To Titan Dunes

    NASA Astrophysics Data System (ADS)

    Wall, Stephen D.; Lopes, R.; Kirk, R.; Stofan, E.; Farr, T.; Van der Ploeg, P.; Lorenz, R.; Radebaugh, J.

    2009-09-01

    Titan's equatorial dunes, observed in Cassini SAR, have been described as longitudinal, similar to longitudinal dunes in the Namib sand sea in southern Africa. Their "Y” junctions and the way they divert around topography are used as evidence of equatorial wind flow direction. In two instances of such diversion they exhibit overlying or crosshatched patterns in two distinct directions that have been interpreted as a transition to transverse dunes. Here we describe field observations of the Namibian dunes and these comparisons, we present images of the dunes from terrestrial SAR missions, and we discuss implications to both the Titan dunes and the wind regime that created them. Selected portions of the Namibian dunes resemble Titan's dunes in peak-to-peak distance and length. They are morphologically similar to Titan, and specific superficial analogs are common, but they also differ. For example, when Titan dunes encounter topography they either terminate abruptly, "climb” the upslope, or divert around; only the latter behavior is seen in remote sensing images of Namibia. Namib linear dunes do transition to transverse as they divert, but at considerably smaller wavelength, while at Titan the wavelengths are of the same scale. Crosshatching of similar-wavelength dunes does occur in Namibia, but not near obstacles. Many additional aeolian features that are seen at Namibia such as star dunes, serpentine ridges and scours have not been detected on Titan, although they might be below the Cassini SAR's 300-m resolution. These similarities and differences allow us to explore mechanisms of Titan dune formation, in some cases giving us clues as to what larger scale evidence to look for in SAR images. Viewed at similar resolution, they provide interesting comparisons with the Titan dunes, both in likeness and differences. A part of this work was carried out at JPL under contract with NASA.

  4. Anatomy and controlling factors of a Late Cretaceous Aeolian sand sheet: The Marília and the Adamantina formations, NW Bauru Basin, Brazil

    NASA Astrophysics Data System (ADS)

    Basilici, Giorgio; Führ Dal'Bó, Patrick Francisco

    2010-04-01

    Few previous studies have given significant consideration to the palaeosols in aeolian sand sheet sedimentary successions and, mainly, to their palaeoenvironmental and stratigraphic meaning in interaction with the deposits. These themes are considered in this study that deals with the depositional architecture and the factors controlling the construction, accumulation and preservation of an ancient aeolian sand sheet, that forms part of the Adamantina and Marília formations, in the Bauru Basin (Late Cretaceous, Brazil). In the NW portion of the Bauru Basin, these two units, ca 220 m thick, consist of sandstone, and secondarily of sandy conglomerate and mudstone, and are characterised by vertically alternated palaeosols and deposits. Facies analyses of the deposits and macroscopic characterisation of the palaeosols in 45 outcrops were integrated with laboratory analyses that consisted in descriptions of slabs of rock samples, petrographic analyses, clay mineralogy determination, geochemical analyses of the major oxides, and micromorphological characterisation of the palaeosols. Three architectural elements were recognised: palaeosols, wind-ripple-dominated aeolian sand sheet deposits, and ephemeral river deposits. The palaeosols constitute 66% of the entire sedimentary succession, and consist principally of Aridisols and, subordinately, of Alfisols, Vertisols, and Entisols. The wind-ripple-dominated aeolian sand sheet deposits (25%) are composed of sandstone, organised in translatent climbing wind-ripple strata, and secondarily of sandstone and mudstone deposited by infrequent floods. The ephemeral river deposits (9%) consist of sandy conglomerates 4 m thick and ca 2 km wide. Wind-ripple-dominated aeolian sand sheet deposits formed during relatively dry climate period on an unstable topographic surface of an aeolian sand sheet, where aeolian deposition or erosion prevailed. Palaeosols and ephemeral river deposits formed in a more humid climate period on a stable

  5. Acoustic observations of near-bed sediment concentration and flux statistics above migrating sand dunes

    NASA Astrophysics Data System (ADS)

    Wilson, G. W.; Hay, A. E.

    2016-06-01

    A coherent Doppler profiler was used to measure coincident time series of velocity (u,w), sediment mass concentration (c), and sediment grain size (d), above mobile sand dunes in unidirectional flow (˜1 m/s, ˜1 m water depth). The measurements are used to extract statistical distributions of sediment concentration and flux just above the bed. Observed mass fluxes (uc,wc) were well fit by quasi-exponential distributions, at all positions along the dune profile, similar to previous observations of single-particle momenta for bed load over flat beds. Observed concentrations of moving particles were well fit by negative-binomial distributions, also similar to previous observations over flat beds. These probability distributions relate to two recent stochastic theories, previously derived and verified for uniform flow over flat beds. It is hypothesized that these theories may also be used as a local approximation in natural-scale flows with bed forms.

  6. Optical and radiocarbon ages of stacked paleosols and dune sands in the Nebraska Sand Hills, USA

    NASA Astrophysics Data System (ADS)

    Goble, R. J.; Mason, Joseph A.; Loope, David B.; Swinehart, James B.

    2004-05-01

    Optical ages for eolian sands from the Nebraska Sand Hills indicate periods of extensive eolian activity at ca 115±25, 840±70, 2300±240, and 3560±340 a. Activity was also noted at single sampling locations at ca 6180±370, 8430±510 and 13110±800 a. Many of these ages are similar to those noted by earlier authors. Optical ages from samples collected within paleosols indicate shorter and possibly less extensive periods of eolian activity at approximately 1220±150, 1590±110, and possibly 1950±150 a, during which the paleosol sands accumulated. What was originally interpreted as a single 1.2 m thick paleosol is shown by optical dating to consist of three or more welded soils developed within eolian sands with optical ages of ca 3800±240, 2740±240, 1560±110, and possibly 1930±140 a, each of which match eolian pulses recognized elsewhere. Scatter in some optical ages is attributable to intersection of sand-filled rodent burrows extending in outcrop 1.5 m below the contact between paleosol and overlying topset beds. A 5310±360 a optical age for one probable intersected burrow provides evidence for upward or lateral transport of older sands.

  7. Lizard assemblage from a sand dune habitat from southeastern Brazil: a niche overlap analysis.

    PubMed

    Winck, Gisele R; Hatano, Fabio; Vrcibradic, Davor; VAN Sluys, Monique; Rocha, Carlos F D

    2016-01-01

    Communities are structured by interactions of historical and ecological factors, which influence the use of different resources in time and space. We acquired data on time of activity, microhabitat use and diet of a lizard assemblage from a sand dune habitat in a coastal area, southeastern Brazil (Restinga de Jurubatiba). We analyzed the data of niche overlap among species in these three axes (temporal, spatial and trophic) using null models. We found a significant overlap within the trophic niche, whereas the overlap for the other axes did not differ from the expected. Based on this result, we discuss the factors acting on the structure of the local lizard community.

  8. Resonant interaction of acoustic waves with subaqueous bedforms: Sand dunes in the South China Sea.

    PubMed

    Chiu, Linus Y S; Chang, Andrea Y Y; Reeder, D Benjamin

    2015-12-01

    The large subaqueous sand dunes in the South China Sea are expected to produce the coupling of energy between acoustic normal modes. In this letter, resonant interaction between acoustic propagating modes and subaqueous bedforms are numerically investigated as a function of bedform wavelength, acoustic frequency and bedform packet length. The results demonstrate that bedform wavelength impacts acoustic mode coupling behavior, with the principal transfer of energy occurring between acoustic modes whose eigenvalue difference is equal to the peak value in the bedform wavenumber spectrum. The observed effect of wavelength is greater than that of acoustic frequency and bedform packet length.

  9. Sedimentary cycles in a Mesoproterozoic aeolian erg-margin succession: Mangabeira Formation, Espinhaço Supergroup, Brazil

    NASA Astrophysics Data System (ADS)

    Bállico, M. B.; Scherer, C. M. S.; Mountney, N. P.; Souza, E. G.; Reis, A. D.; Raja Gabaglia, G. P.; Magalhães, A. J. C.

    2017-03-01

    Aeolian systems were abundant and widespread in the early Proterozoic, post-2.2 Ga. However, the majority of aeolian successions of such great age are intensely deformed and are preserved only in a fragmentary state meaning that, hitherto, few attempts have been made to apply a sequence stratigraphic approach to determine mechanisms of aeolian construction, accumulation and preservation in such systems. The Mangabeira Formation is a well preserved Mesoproterozoic erg successions covering part of the São Francisco Craton, northeastern Brazil. The lower unit of the Mangabeira Formation ( 500 m thick) comprises aeolian deposits of dune, interdune, and sand-sheet origin, as well as some of waterlain origin. These deposits are organized into vertically stacked depositional cycles, each 6 to 20 m thick, and characterized by aeolian sandsheet and waterlain deposits succeeded by aeolian dune and interdune deposits indicative of a drying-upward trend. Aeolian cross-strata exhibit a mean dip direction to the north. Each of these cycles likely arose in response to climatic oscillation from relatively humid to arid conditions, possibly related to orbital forcing. The lower unit of the Mangabeira Formation comprises up to 14 erg sequences. The accumulation and preservation of each was determined by the relative rate of water-table rise and the availability of sand for aeolian transport, both of which changed through time, resulting in the preservation of a succession of repeated drying-upward cycles.

  10. Early Successional Microhabitats Allow the Persistence of Endangered Plants in Coastal Sand Dunes

    PubMed Central

    2015-01-01

    Many species are adapted to disturbance and occur within dynamic, mosaic landscapes that contain early and late successional microhabitats. Human modification of disturbance regimes alters the availability of microhabitats and may affect the viability of species in these ecosystems. Because restoring historical disturbance regimes is typically expensive and requires action at large spatial scales, such restoration projects must be justified by linking the persistence of species with successional microhabitats. Coastal sand dune ecosystems worldwide are characterized by their endemic biodiversity and frequent disturbance. Dune-stabilizing invasive plants alter successional dynamics and may threaten species in these ecosystems. We examined the distribution and population dynamics of two federally endangered plant species, the annual Layia carnosa and the perennial Lupinus tidestromii, within a dune ecosystem in northern California, USA. We parameterized a matrix population model for L. tidestromii and examined the magnitude by which the successional stage of the habitat (early or late) influenced population dynamics. Both species had higher frequencies and L. tidestromii had higher frequency of seedlings in early successional habitats. Lupinus tidestromii plants in early successional microhabitats had higher projected rates of population growth than those associated with stabilized, late successional habitats, due primarily to higher rates of recruitment in early successional microhabitats. These results support the idea that restoration of disturbance is critical in historically dynamic landscapes. Our results suggest that large-scale restorations are necessary to allow persistence of the endemic plant species that characterize these ecosystems. PMID:25835390

  11. Early successional microhabitats allow the persistence of endangered plants in coastal sand dunes.

    PubMed

    Pardini, Eleanor A; Vickstrom, Kyle E; Knight, Tiffany M

    2015-01-01

    Many species are adapted to disturbance and occur within dynamic, mosaic landscapes that contain early and late successional microhabitats. Human modification of disturbance regimes alters the availability of microhabitats and may affect the viability of species in these ecosystems. Because restoring historical disturbance regimes is typically expensive and requires action at large spatial scales, such restoration projects must be justified by linking the persistence of species with successional microhabitats. Coastal sand dune ecosystems worldwide are characterized by their endemic biodiversity and frequent disturbance. Dune-stabilizing invasive plants alter successional dynamics and may threaten species in these ecosystems. We examined the distribution and population dynamics of two federally endangered plant species, the annual Layia carnosa and the perennial Lupinus tidestromii, within a dune ecosystem in northern California, USA. We parameterized a matrix population model for L. tidestromii and examined the magnitude by which the successional stage of the habitat (early or late) influenced population dynamics. Both species had higher frequencies and L. tidestromii had higher frequency of seedlings in early successional habitats. Lupinus tidestromii plants in early successional microhabitats had higher projected rates of population growth than those associated with stabilized, late successional habitats, due primarily to higher rates of recruitment in early successional microhabitats. These results support the idea that restoration of disturbance is critical in historically dynamic landscapes. Our results suggest that large-scale restorations are necessary to allow persistence of the endemic plant species that characterize these ecosystems.

  12. Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems

    NASA Astrophysics Data System (ADS)

    Máguas, C.; Rascher, K. G.; Martins-Loução, A.; Carvalho, P.; Pinho, P.; Ramos, M.; Correia, O.; Werner, C.

    2011-12-01

    In spite of the relative importance of groundwater in costal dune systems, studies concerning the responses of vegetation to ground water (GW) availability variations, particularly in Mediterranean regions, are scarce. Thus, the main purpose of this study is to compare the responses of co-occurring species possessing different functional traits, to changes in GW levels (i.e. the lowering of GW levels) in a sand dune ecosystem. For that, five sites were established within a 1 km2 area in a meso-mediterranean sand dune ecosystem dominated by a Pinus pinaster forest. Due to natural topographic variability and anthropogenic GW exploitation, substantial variability in depth to GW between sites was found. Under these conditions it was possible to identify the degree of usage and dependence on GW of different plant species (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous sites. Results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). Species comparison revealed that variability in pre-dawn water potential (Ψpre) and bulk leaf δ13C was related to site differences in GW use in the deep-rooted (Pinus pinaster, Myrica faya) and phreatophyte (Salix repens) species. However, such variation was more evident during spring than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in Ψpre and bulk leaf δ13C. In contrast, the response of Corema album, an endemic understory drought-adapted shrub, seemed to be independent of water availability across seasons and sites. Thus, the susceptibility to lowering of GW due to anthropogenic exploitation, in plant species from sand dunes, is variable, being particularly relevant for deep

  13. Laboratory simulation of debris flows over sand dunes: Insights into gully-formation (Mars)

    NASA Astrophysics Data System (ADS)

    Jouannic, Gwenaël; Gargani, Julien; Conway, Susan J.; Costard, François; Balme, Matthew R.; Patel, Manish R.; Massé, Marion; Marmo, Chiara; Jomelli, Vincent; Ori, Gian G.

    2015-02-01

    Gully morphology (often summarized as comprising an alcove, channel and debris apron) is one of the key elements used to support the argument for liquid water in the recent past on Mars. Nevertheless, the processes that create different gully morphologies, on both Mars and Earth, are not fully understood. One of the puzzling morphologic attributes of Martian dune gullies is their apparent lack of an apron, or terminal deposit, which has caused debate about their formation process. Several physical processes such as runoff, debris flows, granular flows, and sliding blocks falling downslope could explain the formation of these gullies. In this work, we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis. We performed a series of analogue experiments to investigate the formation of gullies on sand dune-like substrates. We used controlled flows of water over an inclined sand-box to produce gully-like forms. Ice-rich sedimentary substrates were used, including substrates that included a thin liquid water-saturated thawed layer (an 'active layer') above the ice-saturated zone to give an analogue for a 'periglacial' environment. We quantitatively demonstrate that debris flow processes in 'periglacial' experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels. By re-analysis of Martian elevation data for dune-gullies on Mars, we have found good evidence that such terminal deposits could exist. Our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow-length due to the subsequent reduction in infiltration capacity. Water is incorporated into the flow by erosion of the wet thawed layer (sand plus water) and by drainage of the thawed layer. Using a Mars environment simulation chamber, we found that atmospheric pressure conditions seem to have a limited influence on the

  14. Digital Data from the Great Sand Dunes and Poncha Springs Aeromagnetic Surveys, South-Central Colorado

    USGS Publications Warehouse

    Drenth, B.J.; Grauch, V.J.S.; Bankey, Viki; New Sense Geophysics, Ltd.

    2009-01-01

    This report contains digital data, image files, and text files describing data formats and survey procedures for two high-resolution aeromagnetic surveys in south-central Colorado: one in the eastern San Luis Valley, Alamosa and Saguache Counties, and the other in the southern Upper Arkansas Valley, Chaffee County. In the San Luis Valley, the Great Sand Dunes survey covers a large part of Great Sand Dunes National Park and Preserve and extends south along the mountain front to the foot of Mount Blanca. In the Upper Arkansas Valley, the Poncha Springs survey covers the town of Poncha Springs and vicinity. The digital files include grids, images, and flight-line data. Several derivative products from these data are also presented as grids and images, including two grids of reduced-to-pole aeromagnetic data and data continued to a reference surface. Images are presented in various formats and are intended to be used as input to geographic information systems, standard graphics software, or map plotting packages.

  15. Parabolic dunes and their transformations under environmental and climatic changes: Towards a conceptual framework for understanding and prediction

    NASA Astrophysics Data System (ADS)

    Yan, Na; Baas, Andreas C. W.

    2015-01-01

    The formation and evolution of parabolic aeolian dunes depend on vegetation, and as such are particularly sensitive to changes in environmental controls (e.g., temperature, precipitation, and wind regime) as well as to human disturbances (e.g., grazing, agriculture, and recreation). Parabolic dunes can develop from the stabilisation of highly mobile barchan dunes and transverse dunes as well as from blowouts, as a consequence of colonisation and establishment of vegetation when aeolian sand transport is reduced and/or when water stress is relieved (by increasing precipitation, for instance). Conversely, existing parabolic dunes can be activated and may be transformed into barchan dunes and/or transverse dunes when vegetation suffers environmental or anthropogenic stresses. Predicted increases in temperature and drought severity in various regions raise concerns that dune activation and transformations may intensify, and this intensification would have far-reaching implications for environmental, social, and economic sustainability. To date, a broad examination of the development of parabolic dunes and their related transformations across a variety of climate gradients has been absent. This paper reviews existing literature, compares data on the morphology and development of parabolic dunes in a comprehensive global inventory, and scrutinises the mechanisms of different dune transformations and the eco-geomorphic interactions involved. This knowledge is then integrated into a conceptual framework to facilitate understanding and prediction of potential aeolian dune transformations induced by changes in environmental controls and human activities. This conceptual framework can aid judicious land management policies for better adaptations to climatic changes.

  16. Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems

    NASA Astrophysics Data System (ADS)

    Máguas, C.; Rascher, K. G.; Martins-Loução, A.; Carvalho, P.; Pinho, P.; Ramos, M.; Correia, O.; Werner, C.

    2011-02-01

    In spite of the relative importance of groundwater in coastal dune systems, the number of studies concerning the responsiveness of vegetation to ground water (GW) variability, in particularly in Mediterranean regions, is scarce. In this study, we established 5 study sites within a meso-mediterranean sand dune Pinus pinaster forest on the Atlantic coast of Portugal, taking advantage of natural topographic variability and artificial GW exploitation, which resulted in substantial variability in depth to GW between microsites. Here we identify the degree of usage and dependence on GW of different plant functional groups (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous microsites. Our results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). The species comparison revealed that variability in pre-dawn water potential (Ψpre) and bulk leaf δ13C was related to microsite differences in GW use in deep-rooted (Pinus pinaster, Myrica faya) and phreatophyte (Salix repens) species. However, such variation was more evident during spring rather than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in Ψpre and bulk leaf δ13C. In contrast, the response of Corema album, an endemic understorey drought adapted shrub, across seasons and microsites seemed to be independent of water availability. Thus, the susceptibility to changing GW availability in sand dune plant species is variable, being particularly relevant for deep rooted species and phreatophytes, which have typically been less exposed to GW fluctuations.

  17. New Ways to Continuous Measurements of Soil Moisture in a Hyper-arid Dune Sand Environment

    NASA Astrophysics Data System (ADS)

    Rödiger, T.; Königer, F.; Bonitz, F.; Siebert, C.

    2014-12-01

    Particularly in arid regions, a profound knowledge about infiltration rates eventually leading to groundwater recharge is the major parameter for any resources management. Unfortunately, in arid areas, the rate of infiltration is one of the most difficult values to derive with sufficient accuracy. In 2010 a 3D monitoring site was developed within a sand-dune belt SW of Riyadh (KSA). At the site, one 45°-sloped and 6 vertical drillings were deepened down to max. 13 m below ground and each is equipped with (i) continuous TDR sensors: Taupe- (sloped drilling) and tube- (vertical drilling) sensors as well as (ii) discrete temperature sensors to allow continuous moisture and temperature monitoring within the upper 13 m. The combination of the chosen sensors and the application of direct push by using a Geoprobe 7730DT guaranteed two major advantages: minimal invasiveness and continuous measurements of the relative dielectric permittivity along the borehole walls. Topp equation (Topp et al. 1980) was used to convert the raw signals from sensor into volumetric water content. To calibrate TDR data, the actual soil-moisture contents in the upper 8 m of the dune were derived from drilling core samples. Within the dune, the moisture fluctuates between 0-10.3 vol.-% and quickly reacts on seasonal climatic impacts in the uppermost 2 m, while moisture below persists at around 1.5 vol.-%. Only precipitation events with exceeding 6 mm/d induce increasing moisture in the uppermost 1.5 m of minimum 1.5 vol.-%. That indicates a threshold for effective precipitation of 6 mm/d below of which no remarkable infiltration occurs. During the observation, we derived from the observed precipitation events and the depth of the resulting infiltration fronts, that the infiltration process is driven by the amount of a singular precipitation event. As a consequence, recharge estimations for the so-called sand seas based on annual or monthly precipitation data are not applicable for the region.

  18. Aeolian sediment transport and landforms in managed coastal systems: A review

    NASA Astrophysics Data System (ADS)

    Jackson, Nancy L.; Nordstrom, Karl F.

    2011-11-01

    Humans modify beaches and dunes and aeolian transport potential by building structures, walking or driving, extracting resources, accommodating recreation, increasing levels of protection, removing storm deposits, or restoring landforms and habitats. The effects of human adjustments are reviewed here in terms of cross-shore zones because humans tend to compartmentalize landforms and habitats through their actions and regulations. Common human modifications in the beach zone include nourishing beaches, constructing shore protection structures and raking to remove litter. Modifications affecting the dune zone include altering the location, size and stability of dunes using sand-trapping fences, vegetation plantings and bulldozers or replacing dunes with shore-parallel structures. Modifications affecting the landward zone include buildings, roads, and parking lots. Landform and habitat resilience requires levels of dynamism and geomorphic complexity not often found in managed systems. Preserving or enhancing dynamism and complexity requires emphasis on innovative designs rooted in geomorphological and aeolian research. Future studies are suggested for: (1) quantifying the effect of small and large scale beach nourishment designs and sediment characteristics on dune initiation, development, and evolution; (2) quantifying the extent to which size and spacing of human structures and landform alterations inhibit sediment transfers alongshore or onshore; (3) identifying the advantages or disadvantages of "niche" dunes formed by structures; (4) providing quantitative data on the effects of raking or driving on the beach; (5) identifying the role of aeolian landforms on private properties; and (6) identifying alternative ways of employing sand fences and vegetation plantings to increase topographic and habitat diversity.

  19. Macroinvertebrate community sample collection methods and data collected from Sand Creek and Medano Creek, Great Sand Dunes National Park and Preserve, Colorado, 2005–07

    USGS Publications Warehouse

    Ford, Morgan A.; Zuellig, Robert E.; Walters, David M.; Bruce, James F.

    2016-08-11

    This report provides a table of site descriptions, sample information, and semiquantitative aquatic macroinvertebrate data from 105 samples collected between 2005 and 2007 from 7 stream sites within the Sand Creek and Medano Creek watersheds in Great Sand Dunes National Park and Preserve, Saguache County, Colorado. Additionally, a short description of sample collection methods and laboratory sample processing procedures is presented. These data were collected in anticipation of assessing the potential effects of fish toxicants on macroinvertebrates.

  20. An integrated coastal model for aeolian and hydrodynamic sediment transport

    NASA Astrophysics Data System (ADS)

    Baart, F.; den Bieman, J.; van Koningsveld, M.; Luijendijk, A. P.; Parteli, E. J. R.; Plant, N. G.; Roelvink, J. A.; Storms, J. E. A.; de Vries, S.; van Thiel de Vries, J. S. M.; Ye, Q.

    2012-04-01

    Dunes are formed by aeolian and hydrodynamic processes. Over the last decades numerical models were developed that capture our knowledge of the hydrodynamic transport of sediment near the coast. At the same time others have worked on creating numerical models for aeolian-based transport. Here we show a coastal model that integrates three existing numerical models into one online-coupled system. The XBeach model simulates storm-induced erosion (Roelvink et al., 2009). The Delft3D model (Lesser et al., 2004) is used for long term morphology and the Dune model (Durán et al., 2010) is used to simulate the aeolian transport. These three models were adapted to be able to exchange bed updates in real time. The updated models were integrated using the ESMF framework (Hill et al., 2004), a system for composing coupled modeling systems. The goal of this integrated model is to capture the relevant coastal processes at different time and spatial scales. Aeolian transport can be relevant during storms when the strong winds are generating new dunes, but also under relative mild conditions when the dunes are strengthened by transporting sand from the intertidal area to the dunes. Hydrodynamic transport is also relevant during storms, when high water in combination with waves can cause dunes to avalanche and erode. While under normal conditions the hydrodynamic transport can result in an onshore transport of sediment up to the intertidal area. The exchange of sediment in the intertidal area is a dynamic interaction between the hydrodynamic transport and the aeolian transport. This dynamic interaction is particularly important for simulating dune evolution at timescales longer than individual storm events. The main contribution of the integrated model is that it simulates the dynamic exchange of sediment between aeolian and hydrodynamic models in the intertidal area. By integrating the numerical models, we hope to develop a model that has a broader scope and applicability than

  1. An annotated list of the mayflies, stoneflies, and caddisflies of the Sand Creek basin, Great Sand Dunes National Park and Preserve, Colorado, 2004 and 2005

    USGS Publications Warehouse

    Zuellig, Robert E.; Kondratieff, Boris C.; Ruiter, David E.; Thorp, Richard A.

    2006-01-01

    The U.S. Geological Survey, in conjunction with the Great Sand Dunes National Park and Preserve and its cooperators, did an extensive inventory of certain targeted aquatic-insect groups in the Sand Creek Basin, Great Sand Dunes National Park and Preserve, to establish a species list for future monitoring efforts. Study sites were established to monitor these groups following disturbance events. Such potential disturbances may include, but are not limited to, chemical treatment of perennial stream reaches to remove nonnative fishes and the subsequent reintroduction of native fish species, increased public use of backcountry habitat (such as hiking and fishing), and natural disturbances such as fire. This report is an annotated list of the mayflies, stoneflies, and caddisflies found in the Sand Creek Basin, Great Sand Dunes National Park and Preserve, 2004 and 2005. The primary objective of the study was to qualitatively inventory target aquatic-insect groups in perennial streams, and selected unique standing-water habitats, such as springs, and wetlands associated with the Sand Creek Basin. Efforts focused on documenting the presence of aquatic-insect species within the following taxonomic groups: Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies). These insect orders were chosen because published species accounts, geographic distribution, and identification keys exist for many Colorado species. Given the extent of available information for these groups, there existed a potential for identifying new species and documenting range extensions of known species.

  2. Interactions between nematodes and their microbial enemies in coastal sand dunes.

    PubMed

    Costa, Sofia R; Kerry, Brian R; Bardgett, Richard D; Davies, Keith G

    2012-12-01

    European foredunes are almost exclusively colonised by Ammophila arenaria, and both the natural succession and the die-out of this plant have been linked to populations of plant-parasitic nematodes (PPN). The overarching aim of this study was to investigate top-down control processes of PPN in these natural ecosystems through comparative analyses of the diversity and dynamics of PPN and their microbial enemies. Our specific aims were, first, to identify and quantify PPN microbial enemies in European sand dunes; second, to assess their life history traits, their spatial and temporal variation in these ecosystems, and third, to evaluate their control potential of PPN populations. This was done by seasonal sampling of a range of sites and making observations on both the nematode and the microbial enemy communities in rhizosphere sand. Nine different nematode microbial enemies belonging to different functional groups were detected in European sand dunes. Their high diversity in these low productivity ecosystems could both result from or lead to the lack of dominance of a particular nematode genus. The distribution of microbial enemies was spatially and temporally variable, both among and within sampling sites. Obligate parasites, either with low host-specificity or having the ability to form an environmentally resistant propagule, are favoured in these ecosystems and are more frequent and abundant than facultative parasites. Three microbial enemies correlated, either positively or negatively, with PPN population size: Catenaria spp., Hirsutella rhossiliensis and Pasteuria penetrans. Microbial-enemy supported links in the food-web may be involved in the control of PPN populations through indirect effects. The endospore-forming P. penetrans was the most successful top-down control agent, and was implicated in the direct control of Meloidogyne spp. and indirect facilitation of Pratylenchus spp. Overall, our findings suggest strong and diverse top-down control effects on

  3. Stars and linear dunes on Mars

    NASA Technical Reports Server (NTRS)

    Edgett, Kenneth S.; Blumberg, Dan G.

    1994-01-01

    A field containing 11 star and incipient star dunes occurs on Mars at 8.8 deg S, 270.9 deg W. Examples of linear dunes are found in a crater at 59.4 deg S, 343 deg W. While rare, dune varieties that form in bi- and multidirectional wind regimes are not absent from the surface of Mars. The occurence of both of these dune fields offers new insight into the nature of martian wind conditions and sand supply. The linear dunes appears to have formed through modification of a formerly transverse aeolian deposit, suggesting a relatively recent change in local wind direction. The 11 dunes in the star dune locality show a progressive change from barchan to star form as each successive dune has traveled up into a valley, into a more complex wind regime. The star dunes corroborate the model of N. Lancaster (1989), for the formation of star dunes by projection of transverse dunes into a complex, topographically influenced wind regime. The star dunes have dark streaks emanating from them, providing evidence that the dunes were active at or near the time the relevant image was obtained by the Viking 1 orbiter in 1978. The star and linear dunes described here are located in different regions on the martian surface. Unlike most star and linear dunes on Earth, both martian examples are isolated occurrences; neither is part of a major sand sea. Previously published Mars general circulation model results suggest that the region in which the linear dune field occurs should be a bimodal wind regime, while the region in which the star dunes occur should be unimodal. The star dunes are probably the result of localized complication of the wind regime owing to topographic confinement of the dunes. Local topographic influence on wind regime is also evident in the linear dune field, as there are transverse dunes in close proximity to the linear dunes, and their occurrence is best explained by funneling of wind through a topographic gap in the upwind crater wall.

  4. Camera Monitoring of Coastal Dune Erosion in a Macrotidal Environment

    NASA Astrophysics Data System (ADS)

    Kim, Taerim; Kim, Dongsoo

    2015-04-01

    The recent dune erosion in the west coast of Korea is serious in terms of its speed and harmful influence on the adjacent coastal waters as well as dune forest. The west coast of Korea is in the macro-intertidal environment and aeolian sediment transport on the intertidal flat is very active during an ebb tide, especially in winter. There is strong interaction between sand beach and dune by supplying or depositing sand. Coastal dune, as one part of beach system, contributes for beach recovery as well as preventing beach erosion by exchanging sands between beach and dune. Due to high tidal range, the boundary of sand dunes is outside the high water line during spring tide and it makes people think coastal dune is safe from wave forces causing beach erosion. However it seems that high waves during spring high tide cause serious erosion in a relatively short period. This paper investigates the erosion status of the dunes located in the JangHang beach in the southwest coast of Korean Peninsula, by analyzing images from camera monitoring system, and tide and wave data observed adjacent to the study site during the passage of 4 typhoons in 2012. It shows the importance of the timing of wave and tide condition in coastal dune erosion in macrotidal environment.

  5. Hydrological behaviour of microbiotic crusts on sand dunes of NW China: Experimental evidences and numerical simulations

    NASA Astrophysics Data System (ADS)

    Wang, Xin Ping; Tedeschi, Anna; Orefice, Nadia; de Mascellis, Roberto; Menenti, Massimo

    2010-05-01

    Large ecological engineering projects were established to reduce and combat the hazards of sandstorms and desertification in northern China. An experiment to evaluate the effects of dunes stabilization by vegetation was carried out at Shapotou in Ningxia Hui Autonomous Region at the southeast edge of the Tengger Desert using xerophyte shrubs (Caragana korshinskii, Hedysarum scoparium and Artemisia ordosica) planted in straw checkerboard plots in 1956, 1964, 1981, 1987, 1998, and 2002. The fixed sand surface led to the formation of biotic soil crusts. Biotic crusts formed at the soil surface in the interspaces between shrubs and contribute to stabilization of soil surfaces. Previous results on the area have showed that: i) straw checkerboards enhance the capacity of the dune system to trap dust, leading to the accumulation of soil organic matter and nutrients; ii) the longer the period of dune stabilization, the greater the soil clay content in the shallow soil profile (0-5 cm), and greater the fractal dimension of soil particle size distribution. Benefit apart, one should be aware that the formation of a crusted layer at the soil surface is generally characterized by an altered pore-size distribution, with a frequent decrease of hydraulic conductivity which can induce changes of the water regime of the whole soil profile. Accordingly, the main objective of the paper is to evaluate the equivalent (from a hydraulic point of view) geometry of the crusted layer and to verify if the specific characteristics of the crusted soil layer, although local by nature, affect the hydrological behaviour of the whole soil profile. In fact, it is expected that, due to the formation of an upper, impeding soil layer, the lower soil layers do not reach saturation. Such behaviour has important consequences on both water flow and storages in soils. The final aim will be to understand how the crust at the surface of the artificially stabilized sand dune affects the infiltration capacity

  6. A new modelling concept for aeolian sediment transport on beaches

    NASA Astrophysics Data System (ADS)

    de Vries, S.; Arens, S. M.; Stive, M. J. F.; Ranasinghe, R.

    2012-04-01

    This paper presents a new modelling concept for aeolian transport on beaches. Many research is invested in describing aeolian sediment transport for desert situations. Some of the principles of aeolian sediment transport in deserts are valid for application at the coastal zone but, where in deserts abundant sand is available for transport, in coastal situations sediment availability is limited. Sediment availability (or supply) is limited due to supply limiting factors such as moisture content of the bed, fetch effects and armouring of the surface. We propose a new sediment transport concept where we quantify aeolian sediment transport while quantifying the sediment availability rather than the more conventional (Bagnold, 1954) wind driven transport capacity. The concept is illustrated using field data. The field data is collected during a measurement campaign which has been designed to measure aeolian transport with special focus on sediment availability. Wind and sediment transport rates are measured on a beach for a period of 1 week. During this week onshore wind occurred allowing the analysis of aeolian transport across the beach towards the dunes. A total of 5 sediment transport gauges are dynamically placed over the cross section of the beach from locations in the intertidal zone (at low tide) until the dunefoot. The observations show that the amount of aeolian transport is very much dependent on the tidal phase. Low tides correspond to large aeolian transport and high tides to significantly lower aeolian transport across the beach. Wind conditions during the experiment were relatively constant implying that the specific variability in time of the measured aeolian transport is caused by variability with respect to the source rather than variability in wind conditions. Additional to this specific case, existing data of similar experiments (Arens, 1996) are analysed. Re-analysing this data, from experiments covering larger timespans, more evidence is found for

  7. Aeolian Morphodynamics of Loess Landscapes

    NASA Astrophysics Data System (ADS)

    Mason, J. A.; Hanson, P. R.; Sweeney, M.; Loope, H. M.; Miao, X.; Lu, H.

    2012-12-01

    Striking aeolian landforms characterize loess landscapes of the Great Plains and Upper Mississippi Valley, USA, shaped in Late Pleistocene environments with many characteristics of modern deserts including large active dunefields. Similar aeolian morphodynamics are evident in northern China and the Columbia Basin, USA, and are clearly important for interpreting the paleoenvironmental record of loess. Four zones spanning the upwind margin of thick loess can be defined from landforms and surficial deposits. From upwind to downwind, they are: A) A largely loess-free landscape, with patchy to continuous aeolian sand mantling bedrock. B) Patchy loess deposits, often streamlined and potentially wind-aligned, intermingled with dunes and sand sheets; interbedding of loess and sand may be common. C) Thick, coarse loess with an abrupt upwind edge, with troughs, yardang-like ridges, and/or wind-aligned scarps recording large-scale wind erosion. D) Thinner, finer loess with little evidence of post-depositional wind erosion. The degree of development and spatial scale of these zones varies among the loess regions we studied. To explain this zonation we emphasize controls on re-entrainment of loess by the wind after initial deposition, across gradients of climate and vegetation. The role of saltating sand in dust entrainment through abrasion of fine materials is well known. Using the Portable In situ Wind Erosion Laboratory (PI-SWERL), we recently demonstrated that unvegetated Great Plains loess can also be directly entrained under wind conditions common in the region today (Sweeney et al., 2011, GSA Abstracts with Programs, Vol. 43, No. 5, p. 251). Rainfall-induced crusts largely prevent direct entrainment in fine loess, but appear less effective in coarse loess. We propose that in zone A, any loess deposited was both abraded by saltating sand and directly re-entrained, so none accumulated. Sparse vegetation in this zone was primarily an effect of climate, but the resulting

  8. Robotic Measurement of Aeolian Processes

    NASA Astrophysics Data System (ADS)

    Roberts, S.; Duperret, J. M.; Jerolmack, D. J.; Lancaster, N.; Nikolich, G.; Shipley, T. F.; Van Pelt, R. S.; Zobeck, T. M.; Koditschek, D. E.

    2015-12-01

    Local and regional measurements of sand transport and dust emission in complex natural settings presently lack spatiotemporal resolution adequate to inform models relevant for land management, climate policy, and the basic science of geomorphology. Deployments of wind, sand and dust sensors sophisticated enough to begin unpacking the complex relations among wind turbulence, surface roughness, sand flux and dust emission remain largely stationary. Aerial observations from satellites, planes and even UAVs help fill in, but none of these modalities offer the hope of "capturing the action" by being at the right place at the right time relative to the highly localized nature of sediment transport during wind storms. We have been developing a legged robot capable of rapidly traversing desert terrain, and are now adapting it to serve as a platform for scientific instrumentation. We aim to field a semi-autonomous, reactive mobile sensory package suited to the needs of aeolian science that can address the limitations of existing alternatives. This presentation reports on early trials in the Jornada LTER and White Sands National Monument aimed at gathering measurements of airflow and rates of sand transport on a dune face, assessing the role of roughness elements such as vegetation in modifying the wind shear stresses incident on the surface, and estimating erosion susceptibility in a natural arid soil. We will solicit ideas from the audience about other potentially interesting and viable measurement targets. Future close collaboration between aeolian, cognitive and robotics scientists such as we hope to promote through this presentation may yield machines with scientifically relevant sensory suites possessing sufficient autonomy to operate in-situ at the most intense episodes of wind and sediment movement under conditions far too uncomfortable and hazardous for human presence.

  9. Variable wind ripple migration at Great Sand Dunes National Park and Preserve, observed by timelapse imaging

    NASA Astrophysics Data System (ADS)

    Lorenz, Ralph D.; Valdez, Andrew

    2011-10-01

    Granule ripples at Great Sand Dunes National Park and Preserve (GSDNPP) were observed using inexpensive digital timelapse cameras over a 70-day period in winter 2010-2011. The ripples migrated during a handful of discrete events — visible ripple movement occurred on only 11 days during the observation period. The movement conditions are documented with hourly and 15-minute records from two nearby weather stations, and by a cup anemometer at the site itself. During the most prominent movement episode, when local winds averaged ~ 10 m/s, ripples of several sizes were observed simultaneously and a reciprocal relationship of ripple size and propagation speed was seen, with small (~ 10 cm) ripples moving at ~ 1.4 cm/min, and larger (~ 80 cm) ripples at ~ 0.15 cm/min. Ripple sizes and morphologies evolve throughout the observation period.

  10. Active sand dunes are largest dust source in the Sahara Desert

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Atreyee

    2012-09-01

    Dried up lakebeds and playas in the Sahara Desert of North Africa are large sources of dust in the atmosphere. The Bodélé Depression at the southern edge of the Sahara Desert, for example, is the single largest source of dust in the world; on average, 100 dust storms a year originate from the Bodélé Depression. A new study by Crouvi et al., however, finds that active sand dunes could be even bigger sources of desert dust in the atmosphere. Atmospheric dust plays active roles in climate and biological processes in the ocean: It regulates heating at the surface of the Earth; modifies cloud properties that affect rainfall; and acts as the only source of iron, a critical nutrient for microorganisms in the ocean. Little is known about types of dust sources in the Sahara Desert, which alone accounts for more than 50% of the dust in the atmosphere.

  11. Mediterranean Coastal Sand Dune Vegetation: Influence of Natural and Anthropogenic Factors

    NASA Astrophysics Data System (ADS)

    Ciccarelli, Daniela

    2014-08-01

    The aim of the present work was to assess the conservation status of coastal dune systems in Tuscany (Italy). Emphasis was given to the presence and abundance of plant communities identified as habitat in accordance with the Directive 92/43/EEC. Twenty transects perpendicular to the shoreline were randomly positioned on the whole coastal area (30 km in length) in order to sample the full spectrum of plant communities. Vegetation zonation and relationships with the most frequent disturbance factors in the study area—beach cleaning, coastline erosion, presence of paths and roads, bathing settlements and trampling—were investigated through principal coordinate analysis and canonical correspondence analysis. Natural factors, such as distance from the sea and total length, were also considered. Differences in the conservation status of the sites were found, ranging from the total disappearance of the foredune habitats to the presence of the complete psammophilous (sand-loving) plant communities. Erosion, trampling, and paths were found to be closely correlated with degradation and habitat loss. Furthermore, the overall plant species diversity of dunes was measured with NHDune, a modified version of the Shannon index; while the incidence of invasive taxa was calculated using N, a naturalness index. However, these diversity indices proved to be a weaker bioindicator of ecosystem integrity than habitat composition along transects. A possible strategy for the conservation and management of these coastal areas could be to protect the foredunes from erosion and limit trampling through the installation of footbridges or the use of appropriate fences.

  12. Mediterranean coastal sand dune vegetation: influence of natural and anthropogenic factors.

    PubMed

    Ciccarelli, Daniela

    2014-08-01

    The aim of the present work was to assess the conservation status of coastal dune systems in Tuscany (Italy). Emphasis was given to the presence and abundance of plant communities identified as habitat in accordance with the Directive 92/43/EEC. Twenty transects perpendicular to the shoreline were randomly positioned on the whole coastal area (30 km in length) in order to sample the full spectrum of plant communities. Vegetation zonation and relationships with the most frequent disturbance factors in the study area-beach cleaning, coastline erosion, presence of paths and roads, bathing settlements and trampling-were investigated through principal coordinate analysis and canonical correspondence analysis. Natural factors, such as distance from the sea and total length, were also considered. Differences in the conservation status of the sites were found, ranging from the total disappearance of the foredune habitats to the presence of the complete psammophilous (sand-loving) plant communities. Erosion, trampling, and paths were found to be closely correlated with degradation and habitat loss. Furthermore, the overall plant species diversity of dunes was measured with NHDune, a modified version of the Shannon index; while the incidence of invasive taxa was calculated using N, a naturalness index. However, these diversity indices proved to be a weaker bioindicator of ecosystem integrity than habitat composition along transects. A possible strategy for the conservation and management of these coastal areas could be to protect the foredunes from erosion and limit trampling through the installation of footbridges or the use of appropriate fences.

  13. Field observations of wind profiles and sand fluxes above the windward slope of a sand dune before and after the establishment of semi-buried straw checkerboard barriers

    NASA Astrophysics Data System (ADS)

    Zhang, Chunlai; Li, Qing; Zhou, Na; Zhang, Jiaqiong; Kang, Liqiang; Shen, Yaping; Jia, Wenru

    2016-03-01

    Straw checkerboard barriers are effective and widely used measures to control near-surface sand flow. The present study measured the wind profiles and sand mass flux above the windward slope of a transverse dune before and after the establishment of semi-buried straw checkerboards. The 0.2 m high checkerboards enhanced the aerodynamic roughness length to larger than 0.02 m, which was two to three orders of magnitude higher than that of the bare sand. The modified Charnock model predicted the roughness length of the sand bed during saltation well, with Cm = 0.138 ± 0.003. For the checkerboards, z0 increased slowly to a level around 0.037 m with increasing wind velocity and the rate of increase tended to slow down in strong wind. The barriers reduced sand flux and altered its vertical distribution. The total height-integrated dimensionless mass flux of saltating particles (q0) above bare sand followed the relationship ln q0 = a + b(u∗t/u∗) + c(u∗t/u∗)2, with a peak at u∗/u∗t ≈ 2, whereas a possible peak appeared at u∗/u∗t ≈ 1.5 above 1 m × 1 m straw checkerboards. The vertical distribution of mass flux above these barriers resembled an "elephant trunk", with maximum mass flux at 0.05-0.2 m above the bed, in contrast with the continuously and rapidly decreasing mass flux with increasing height above the bare sand. The influences of the barriers on the wind and sand flow prevent dune movement and alter the evolution of dune morphology.

  14. Optical dating of tufa via in situ aeolian sand grains: A case example from the Southern High Plains, USA

    USGS Publications Warehouse

    Rich, J.; Stokes, S.; Wood, W.; Bailey, R.

    2003-01-01

    Precipitated carbonates (commonly termed tufas or travertines) maybe of considerable utility for palaeoenvironmental reconstruction. Their potential, however, for such reconstruction is commonly limited by difficulties associated with their absolute age control. Attempts to date such deposits via uranium series techniques have been complicated by their chemically open behaviour. Here we describe an alternative approach to date tufa deposits associated with ephemeral saline lake basins from the Southern High Plains, USA. We have optically dated sand grains of a mixed aeolian/fluvial (spring fed) origin as the integrating dosimeter. We assume that the grains are fully resetting prior to their incorporation into the tufa deposits and employ a time-dependent disequilibrium dosimetric model to account for the build-up of uranium series daughter products. The approach was applied to a set of four samples with known stratigraphic association. We obtained stratigraphically sensible optical ages ranging from 78??8 to 56??4ka. These data are consistent with existing palaeoenvironmental models of regional recharge. ?? 2003 Elsevier Science Ltd. All rights reserved.

  15. Observations of Sand Dune Migration on the Colorado River in Grand Canyon using High-Resolution Multibeam Bathymetry

    NASA Astrophysics Data System (ADS)

    Kaplinski, M. A.; Buscmobe, D.; Ashley, T.; Tusso, R.; Grams, P. E.; McElroy, B. J.; Mueller, E. R.; Hamill, D.

    2015-12-01

    Repeat, high-resolution multibeam bathymetric surveys were conducted in March and July 2015 along a reach of the Colorado River in Grand Canyon near the Diamond Creek gage (362 km downstream of Lees Ferry, AZ) to characterize the migration of sand dunes. The surveys were collected as part of a study designed to quantify the relative importance of bedload and suspended sediment transport and develop a predictive relationship for bedload transport. Concurrent measurements of suspended-sediment concentrations, bed-sediment grain size, and water velocity were also collected. The study site is approximately 350 m long and 50 m wide; water depths are 7 to 10 m during normal flows; and a field of sand dunes form along its entire length with negligible coarse material at the bed surface. Full swath coverage of the site required about 6 to 10 minutes to complete with two passes of the survey vessel. Mapping occurred continuously during several survey periods. For each survey period, time-series of bathymetric maps were constructed from each pair of survey lines. In March, surveys were collected over durations of 2, 3, 9, and 11 hours, at discharges of 339 to 382 m3/s. In July, surveys were collected over durations of 4, 4, and 13 hours, at discharges ranging from 481 to 595 ft3/s. These surveys capture the migration of sand dunes over a wide range of discharge with an unprecedented temporal resolution. The dunes in March were between 30 and 50 cm in height, 5 m in length, and migrating downstream at about 1 m per hour. In July, dunes were between 75 and 130 cm in height and 10-15 m in length, and were migrating downstream at rates of 5 to 2 m per hour. The surveys also reveal that the dune migration is spatially and temporally variable, with fast-migrating small dunes variably superimposed on slower-moving larger dunes. The dunes also refract around shoreline talus piles and other flow constrictions collectively causing a large degree of dune deformation as they migrate.

  16. Aeolian Processes and Features on Venus

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Bender, Kelly C.; Saunders, Stephen; Schubert, Gerald; Weitz, Catherine M.

    1997-01-01

    Aeolian features on Venus include dune fields, eroded hills (yardangs), wind streaks, (miniature dunes of 10 to 30 cm wavelength). Although and possibly microdunes (in repetitive imaging by Magellan did show changes in the appearance of the surface, these changes are attributed to radar artifacts as a consequence of look direction rather than to physical changes of the surface. Nonetheless, measurements of wind speeds near the surface of Venus and wind tunnel simulations suggest that aeolian processes could be currently active on Venus. Study of radar images of terrestrial analogs shows that radar wavelength, polarization, and viewing geometry, including look direction and incidence angle, all influence the detection of dunes, yardangs, and wind streaks. For best detection, dune crests and yardangs should be oriented perpendicular to look direction. Longer wavelength systems can penetrate sand sheets a meter or more thick, rendering them invisible, especially in arid regions. For wind streaks to be visible, there must be a contrast in surface properties between the streak and the background on which it occurs. Nonetheless, more than 6000 aeolian features have been found on Magellan images of Venus, the most common of which are various wind streaks. Mapping wind streak orientations enables near-surface wind patterns to be inferred for the time of their formation. Type P streaks are associated with parabolic ejecta crater deposits and are considered to have formed in association with the impact event. Most Type P streaks are oriented westward, indicative of the upper altitude superrotation winds of Venus. Non Type P streaks have occurrences and orientations consistent with Hadley circulation. Some streaks in the southern hemisphere are oriented to the northeast, suggesting a Coriolis effect.

  17. Insights from a Geophysical and Geomorphological Mars Analog Field Study at the Great Kobuk Sand Dunes, Northwestern Alaska

    NASA Astrophysics Data System (ADS)

    McGinnis, R. N.; Dinwiddie, C. L.; Stillman, D.; Bjella, K.; Hooper, D. M.; Grimm, R. E.

    2010-12-01

    Terrestrial dune systems are used as natural analogs to improve understanding of the processes by which planetary dunes form and evolve. Selected terrestrial analogs are often warm-climate dune fields devoid of frozen volatiles, but cold-climate dunes offer a better analog for polar dunes on Mars. The cold-climate Great Kobuk Sand Dunes (GKSD) of Kobuk Valley National Park, Alaska, are a high-latitude, slowly migrating analog for polar, inter- and intracrater dune fields on Mars. The 67°N latitude, 62 km2 GKSD consist of moderately well sorted, fine-grained sands deposited within the Kobuk River valley ~50 km north of the Arctic Circle and ~160 km inland from Kotzebue Sound. Winds at the GKSD are influenced significantly by complex surrounding topography, an influence that is similar to many high-latitude inter- and intracrater dune fields on Mars. Average annual temperature and precipitation at the GKSD are -5°C and 430 mm. The dune field is generally resistant to atmospheric forcing (wind) for a significant portion of the year because of snowcover, similar to the effect that seasonal CO2 and H2O frost mantling have on Martian polar dunes. The dune field, which ranges in elevation from 33 to 170 m above mean sea level, consists of sand sheets as well as climbing and reversing barchanoid, transverse, longitudinal, and star dunes. Several tributaries to the Kobuk River bound and dissect the GKSD, producing cutbank exposures and alcoves that reveal internal structure. We report results from our detailed geophysical and geomorphological site characterization field study, which was conducted near peak freeze conditions from March 15 through April 2, 2010. We used multifrequency ground-penetrating radar (25, 50, 100, 250, 500, 1000 MHz) and capacitively coupled resistivity methods to image the internal structure of representative dunes, and performed ground truthing using a sampling auger, natural exposures, and Real-Time Kinematic Differential GPS. Data from twenty

  18. Possible seasonal activity of gullies on an sand dune (Russell crater, Mars)

    NASA Astrophysics Data System (ADS)

    Jouannic, Gwénaël.; Gargani, Julien; Costard, François

    2010-05-01

    . Geophysical Research Letters, 30, doi:10.1029/2002GL016704. Vedie, E., Costard, F., Font, M. and Lagarde, J.L., 2008. Laboratory simulations of Martian gullies on sand dunes. Geophysical Research Letters, 35, doi:10.1029/2008GL035638.

  19. The potential scale of aeolian structures on Venus

    NASA Technical Reports Server (NTRS)

    Marshall, J. R.; Greeley, Ronald

    1991-01-01

    Simulations of the Venusian aeolian environment with the Venus Wind Tunnel have shown that microdunes are formed during the entrainment of sand-sized material. These structures are several tens of centimeters long (2-3 cm high) and combine the morphological and behavioral characteristics of both full-scale terrestrial dunes and current ripples formed in subaqueous environments. Their similarity to both reflects the fact that the Venusian atmosphere has a density intermediate between air and water. Although the development of microdunes in the wind tunnel experiments was limited by tunnel dimensions, it is possible to make some predictions about their potential size on Venus, and the potential size of related aeolian structures. Microdunes are fluid-filled structures (as are dunes and current ripples) and as such have no theoretical upper limit to their size from a fluid dynamics viewpoint. Limitations to size observed in subaqueous structures are set by, for example, water depth; limitations to the size of dunes are set by, for example, sand supply. It is therefore reasonable to suppose that the microdunes on Venus could evolve into much larger features than those observed in experiments. In addition, the researchers note that current ripples (which are closely related to microdunes) are often found in association with giant ripples that have dimensions similar to aeolian dunes. Thus, it may be reasonable to assume that analogous large scale structures occur on Venus. Both (terrestrial) aeolian and subaqueous environments generate structures in excess of one hundred meters in wavelength. Such dimensions may therefore be applicable to Venusian bedforms. Analysis of Magellan data may resolve the issue.

  20. Timing and origin for sand dunes in the Green River Lowland of Illinois, upper Mississippi River Valley, USA

    USGS Publications Warehouse

    Miao, X.; Hanson, P.R.; Wang, Hongfang; Young, A.R.

    2010-01-01

    The recent increase in dune studies in North America has been heavily focused in the Great Plains, while less attention has historically been given to the dune fields east of the Mississippi River. Here we report ages and suggest a potential sediment source for sand dunes in the Green River Lowland, Illinois, which may provide a better understanding of the dynamic interactions between eolian, glacial, lacustrine and fluvial processes that shaped the landscapes of the upper Midwest. Seven coherent optically stimulated luminescence ages (OSL, or optical ages) obtained from four sites suggest that major dune construction in the Green River Lowland occurred within a narrow time window around 17,500 ago. This implies either an enhanced aridity or an episodic increase of sediment supply at 17,500 years ago, or combination of the both. Contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the Lake Michigan Lobe retreated from the area, we propose that Green River Lowland dunes sand originated from the Green Bay Lobe through the Rock River. Specifically, sediment supply increased in the Rock River valley during drainage of Glacial Lake Scuppernong, which formed between ???18,000 and 17,000 years ago, when the Green Bay Lobe retreated from its terminal moraine. The lake drained catastrophically through the Rock River valley, providing glacial sediment and water to erode the preexisting sandy sediments. Throughout the remainder of the late Pleistocene, the Laurentide Ice Sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys. Therefore, the dunes in the Green River Lowland formed only during the catastrophic drainage of Glacial Lake Scuppernong, but were stabilized through the remainder of the Pleistocene. This scenario explains the abrupt dune construction around 17,500 years ago, and explains the lack of later dune activity up to the Pleistocene

  1. The Signature of Life in Stabilized Dune Topography

    NASA Astrophysics Data System (ADS)

    Barchyn, T. E.; Hugenholtz, C.

    2012-12-01

    Life dramatically affects aeolian dunes on Earth by modifying dune morphology and immobilizing sediment. Complete immobilization (stabilization) occurs when vegetation growth shelters the surface and eliminates sediment transport (and the capacity of the dune to clear vegetation). In unidirectional dune forms stabilization is usually preceded by a period of transition dominated by pronounced morphological change (e.g., parabolic dunes). Here, we hypothesize that stabilized topography holds previously unidentified clues detailing the kinematics and behavior of vegetation during stabilization (a 'signature'). During stabilization dune ridges advance downwind and 'bulldoze' vegetation in their path. We split dune ridges into a series of wind-parallel 'dune slices' and outline how slipface vegetation could prove to be a 'tipping point' in stabilization for each dune slice. Slipface vegetation sets off a self-reinforcing stabilization feedback, simplifying our treatment and yielding two predictable behaviors: slipfaces either clear vegetation (deposition rate > vegetation deposition tolerance), or succumb to vegetation and become immobilized (deposition rate < vegetation deposition tolerance). We model slipface deposition rates through slipface geometry and show how predictable variations in classical dune forms (i) could be responsible for incipient transformation of barchan to parabolic dunes, (ii) result in a progressive stabilization feedback fundamentally inconsistent with widely used dune activity indices, and (iii) record a quantitative signature of the relative kinematics of sediment flux and vegetation growth in stabilized slipface geometries. To explore the idea in real dune fields, we extract slipface deposition rates through slipface geometry recorded in digital terrain data for three dune fields: (i) Bigstick Sand Hills, SK, Canada, (ii) White Sands, NM, USA, and (iii) Cape Cod, MA, USA. With independent estimates of sediment flux and vegetation deposition

  2. Efficiency of plant growth promoting rhizobacteria isolated from sand dunes of Chennai coastal area.

    PubMed

    Muthezhilan, R; Sindhuja, B S; Hussain, A Jaffar; Jayaprakashvel, M

    2012-08-15

    Plant Growth Promoting Rhizobacteria (PGPR) are beneficial bacteria that colonize the plant root and enhance the plant growth. The use of PGPR is steadily increasing in agriculture and offers an attractive way to replace chemical fertilizers, pesticides and supplements. In the present study, PGPR were isolated from 18 different rhizosphere soil samples of coastal sand dune plants, belonging to the genus Ipomoea sp. collected from the Chennai coastal area. For isolation of bacteria from soil samples, pour plate technique was followed. The rhizobacterial population was ranged from 4.4 x 10(6)-7.5 x 10(7) CFU g(-1). From that, 46 morphologically different bacterial strains were isolated. Among 46, 18 strains exhibited the production of Indole Acetic Acid. (IAA). When screened for phosphate solubilzing activity, six strains showed maximum activity. All these selected six strains were screened for seed germination among which these two strains (AMET1136 and AMET 1148) showed remarkable increase in the seed germination of black gram and green gram. For plant growth promotion, three types of treatments namely, seed bacterization, soil drenching and mixed (seed+soil) were carried out to check the potential of these two strains. Among that one strain which was identified as Pseudomonas sp. AMET1148 showed remarkable and significant increase in shoot length and root length of the tested plants. The study concluded that PGPR from coastal sand dund plants can be developed as plant growth promoters in agricultural crops.

  3. [Crust development and subsurface soil properties under dominant shrubs in the process of dune restoration, Horqin Sand Land].

    PubMed

    Guo, Yi-rui; Zhao, Ha-lin; Zuo, Xiao-an; Li, Yu-Lin; Huang, Yin-xin; Wang, Shao-kun

    2008-04-01

    Soil crust is a common and widespread phenomenon in desert areas all over the world due to its extraordinary ability to survive desiccation and extreme temperatures, high pH and salinity. Despite its unassuming appearance, biological soil crusts play a significant role in desert ecosystems, including involvement in the process of formation, stability and fertility of soil, preventing soil erosion by water or wind, increasing the possibility of vascular plant colonization, and being responsible for the stabilization of sand dunes. This study taking Horqin Sand Land as research region, by field sampling, crust and topsoil (0-2.5 cm and 2.5-5 cm under crust) samples in different dune habitats and shrub communities were collected, and their physicochemical properties were analyzed, including particle size distribution, bulk density, total nutrients and available nutrients, pH, EC and CaCO3 content. The result revealed that Artemisia halodendron in semi-mobile dune, Caragana microphylla in semi-fix dune, Artemisia frigida in fix dune and Salix microstachya in interdunal lowland were respectively developed physical soil crust, algae crust, lichen crust and moss crust. Crust thickness, hardness, water content, fine fraction, total and available nutrients gradually increased by semi-mobile dune < semi-fix dune < fix dune < interdunal lowland in terms of different dune habitats, and by physical soil crust < algae crust < lichen crust < moss crust in terms of different crust types. There were significant differences among crust types on nutrient content and particle size distribution (p < 0.01). Meanwhile, crust enhanced the < 0.05 mm content and nutrient content of topsoil, following an increasing trend from semi-mobile dune to interdunal lowland. As to each crust, the parameters of 0-2.5 cm subsurface soil layer were higher than that in 2.5-5 cm soil layer. The result also showed that the fine fraction and nutrient content of moss crust under Salix microstachya in

  4. Assessment of Ni, Cu, Zn and Pb levels in beach and dune sands from Havana resorts, Cuba.

    PubMed

    Díaz Rizo, Oscar; Buzón González, Fran; Arado López, Juana O

    2015-11-15

    Concentrations of nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in beach and dune sands from thirteen Havana (Cuba) resorts were estimated by X-ray fluorescence analysis. Determined mean metal contents (in mg·kg(-1)) in beach sand samples were 28±12 for Ni, 35±12 for Cu, 31±11 for Zn and 6.0±1.8 for Pb, while for dune sands were 30±15, 38±22, 37±15 and 6.8±2.9, respectively. Metal-to-iron normalization shows moderately severe and severe enrichment by Cu. The comparison with sediment quality guidelines shows that dune sands from various resorts must be considered as heavily polluted by Cu and Ni. Almost in every resort, the Ni and Cu contents exceed their corresponding TEL values and, in some resorts, the Ni PEL value. The comparison with a Havana topsoil study indicates the possible Ni and Cu natural origin.

  5. First Report of Longidorus kuiperi and Rotylenchus eximius from Coastal Sand Dunes in Crete, Greece

    PubMed Central

    Tzortzakakis, Emmanuel A.; Cantalapiedra-Navarrete, Carolina; Archidona-Yuste, Antonio; Palomares-Rius, Juan E.; Castillo, Pablo

    2016-01-01

    Plant-parasitic nematode species have been reported on several occasions from coastal sand dunes, including Longidorus and Rotylenchus species (Vovlas et al., 2008; De Luca et al., 2009; Mateille et al., 2014). In April 2016, 10 soil samples of 3 to 4 kg from the rhizosphere of Tamarix smyrnensis with different vegetation around (viz. Elymus farctus, Lycium schweinfurthii, Crithmum maritimum, and Arthrocnemum sp.) were collected for diagnosis of plant-parasitic nematodes. The area of sampling was a coastal sand dune near the archeological site of Komos, southwest of Crete, Greece. Low soil populations of a needle and a spiral nematode were detected (3 and 8 individuals/1,000 cm3 of soil, respectively), which prompted us to undertake a detailed morphological and molecular comparative study with previous reported data. Nematodes were extracted from soil with the wet sieving and decanting method (Cobb, 1918). Morphological and molecular analyses of females identified these species as Longidorus kuiperi Brinkman, Loof and Barbez, 1987, and Rotylenchus eximius Siddiqi, 1964. The morphology of L. kuiperi females (six specimens studied) was characterized by having a slender body; very broad lip region (27 ± 1.5 [25 to 30] μm in width); short, hemispherical tail; body length of (7.1 ± 0.8 [6.5 to 8.5] mm); vulva position at 47% to 55% of body length; odontostyle length of (105 ± 6.5 [90 to 115] μm); males very common (but less frequent than females [45% vs 55%]); tail region with 15 to 20 supplements and bulged terminal cuticle. The morphology of R. eximius females (four specimens studied) was characterized by having a hemispherical lip region clearly set off; with four annuli; body without longitudinal striations; lateral fields areolated in the pharyngeal region only; stylet 36 to 38 μm; and broadly rounded tail. The morphology of the isolated nematodes agreed with previous descriptions of L. kuiperi (Brinkman et al., 1987; De Luca et al., 2009), and R. eximius

  6. First Report of Longidorus kuiperi and Rotylenchus eximius from Coastal Sand Dunes in Crete, Greece.

    PubMed

    Tzortzakakis, Emmanuel A; Cantalapiedra-Navarrete, Carolina; Archidona-Yuste, Antonio; Palomares-Rius, Juan E; Castillo, Pablo

    2016-09-01

    Plant-parasitic nematode species have been reported on several occasions from coastal sand dunes, including Longidorus and Rotylenchus species (Vovlas et al., 2008; De Luca et al., 2009; Mateille et al., 2014). In April 2016, 10 soil samples of 3 to 4 kg from the rhizosphere of Tamarix smyrnensis with different vegetation around (viz. Elymus farctus, Lycium schweinfurthii, Crithmum maritimum, and Arthrocnemum sp.) were collected for diagnosis of plant-parasitic nematodes. The area of sampling was a coastal sand dune near the archeological site of Komos, southwest of Crete, Greece. Low soil populations of a needle and a spiral nematode were detected (3 and 8 individuals/1,000 cm(3) of soil, respectively), which prompted us to undertake a detailed morphological and molecular comparative study with previous reported data. Nematodes were extracted from soil with the wet sieving and decanting method (Cobb, 1918). Morphological and molecular analyses of females identified these species as Longidorus kuiperi Brinkman, Loof and Barbez, 1987, and Rotylenchus eximius Siddiqi, 1964. The morphology of L. kuiperi females (six specimens studied) was characterized by having a slender body; very broad lip region (27 ± 1.5 [25 to 30] μm in width); short, hemispherical tail; body length of (7.1 ± 0.8 [6.5 to 8.5] mm); vulva position at 47% to 55% of body length; odontostyle length of (105 ± 6.5 [90 to 115] μm); males very common (but less frequent than females [45% vs 55%]); tail region with 15 to 20 supplements and bulged terminal cuticle. The morphology of R. eximius females (four specimens studied) was characterized by having a hemispherical lip region clearly set off; with four annuli; body without longitudinal striations; lateral fields areolated in the pharyngeal region only; stylet 36 to 38 μm; and broadly rounded tail. The morphology of the isolated nematodes agreed with previous descriptions of L. kuiperi (Brinkman et al., 1987; De Luca et al., 2009), and R. eximius

  7. Aeolian processes in Proctor Crater on Mars: Sedimentary history as analyzed from multiple data sets

    USGS Publications Warehouse

    Fenton, L.K.; Bandfield, J.L.; Ward, A.W.

    2003-01-01

    Proctor Crater is a 150 km diameter crater in Noachis Terra, within the southern highlands of Mars. The analysis leading to the sedimentary history incorporates several data sets including imagery, elevation, composition, and thermal inertia, mostly from the Mars Global Surveyor mission. The resulting stratigraphy reveals that the sedimentary history of Proctor Crater has involved a complex interaction of accumulating and eroding sedimentation. Aeolian features spanning much of the history of the crater interior dominate its surface, including large erosional pits, stratified beds of aeolian sediment, sand dunes, erosional and depositional streaks, dust devil tracks, and small bright bed forms that are probably granule ripples. Long ago, up to 450 m of layered sediment filled the crater basin, now exposed in eroded pits on the crater floor. These sediments are probably part of an ancient deposit of aeolian volcaniclastic material. Since then, some quantity of this material has been eroded from the top layers of the strata. Small, bright dune forms lie stratigraphically beneath the large dark dune field. Relative to the large dark dunes, the bright bed forms are immobile, although in places, their orientations are clearly influenced by the presence of the larger dunes. Their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill. Dust devil tracks form during the spring and summer, following a west-southwesterly wind. Early in the spring the dust devils are largely restricted to dark patches of sand. As the summer approaches, dust devil tracks become more plentiful and spread to the rest of the crater floor, indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils. The dark dunes contain few dust devil tracks, suggesting that accumulated dust is swept away directly by saltation

  8. Aeolian processes in Proctor Crater on Mars: Sedimentary history as analyzed from multiple data sets

    NASA Astrophysics Data System (ADS)

    Fenton, Lori K.; Bandfield, Joshua L.; Ward, A. Wesley

    2003-12-01

    Proctor Crater is a 150 km diameter crater in Noachis Terra, within the southern highlands of Mars. The analysis leading to the sedimentary history incorporates several data sets including imagery, elevation, composition, and thermal inertia, mostly from the Mars Global Surveyor mission. The resulting stratigraphy reveals that the sedimentary history of Proctor Crater has involved a complex interaction of accumulating and eroding sedimentation. Aeolian features spanning much of the history of the crater interior dominate its surface, including large erosional pits, stratified beds of aeolian sediment, sand dunes, erosional and depositional streaks, dust devil tracks, and small bright bed forms that are probably granule ripples. Long ago, up to 450 m of layered sediment filled the crater basin, now exposed in eroded pits on the crater floor. These sediments are probably part of an ancient deposit of aeolian volcaniclastic material. Since then, some quantity of this material has been eroded from the top layers of the strata. Small, bright dune forms lie stratigraphically beneath the large dark dune field. Relative to the large dark dunes, the bright bed forms are immobile, although in places, their orientations are clearly influenced by the presence of the larger dunes. Their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill. Dust devil tracks form during the spring and summer, following a west-southwesterly wind. Early in the spring the dust devils are largely restricted to dark patches of sand. As the summer approaches, dust devil tracks become more plentiful and spread to the rest of the crater floor, indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils. The dark dunes contain few dust devil tracks, suggesting that accumulated dust is swept away directly by saltation

  9. Terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest Ohio, USA

    USGS Publications Warehouse

    Campbell, M.C.; Fisher, T.G.; Goble, R.J.

    2011-01-01

    Optically stimulated luminescence dated sand dunes and Pleistocene beach ridges in northwest Ohio are used to reconstruct landscape modification more than 5000. yr after deglaciation. Four of the OSL ages (13.3-11.1. ka) cluster around the Younger Dryas cold event, five ages (10.8-8.2. ka) cluster around the Preboreal, one young age (0.9-0.7. ka) records more recent aeolian activity, and one age of 15.1-13.1. ka dates a barrier spit in Lake Warren. In northwest Ohio, both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the Younger Dryas. However, the climate conditions during the Preboreal resulting in aeolian activity are not recorded in the available pollen records. From this, we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler, drier episodes of climate and can complement pollen data. Younger Dryas and Preboreal aged aeolian activity in northwestern Ohio coincides with aeolian records elsewhere in the Great Lakes region east of the prairie-forest ecotone. ?? 2011 University of Washington.

  10. Transient Electromagnetic Soundings Near Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado (2006 Field Season)

    USGS Publications Warehouse

    Fitterman, David V.; de Sozua Filho, Oderson A.

    2009-01-01

    Time-domain electromagnetic (TEM) soundings were made near Great Sand Dunes National Park and Preserve in the San Luis Valley of southern Colorado to obtain subsurface information of use to hydrologic modeling. Seventeen soundings were made to the east and north of the sand dunes. Using a small loop TEM system, maximum exploration depths of about 75 to 150 m were obtained. In general, layered earth interpretations of the data found that resistivity decreases with depth. Comparison of soundings with geologic logs from nearby wells found that zones logged as having increased clay content usually corresponded with a significant resistivity decrease in the TEM determined model. This result supports the use of TEM soundings to map the location of the top of the clay unit deposited at the bottom of the ancient Lake Alamosa that filled the San Luis Valley from Pliocene to middle Pleistocene time.

  11. Behaviour and transport of radionuclides in soil and vegetation of a sand dune ecosystem.

    PubMed

    Copplestone, D; Johnson, M S; Jones, S R

    2001-01-01

    A sand dune ecosystem in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK was used to examine the spatial, temporal and depth distributions of 134Cs, 137Cs, 238Pu, 239 + 240Pu and 241Am in soil and in two species of vegetation (Festuca rubra, Ammophila arenaria). Core samples showed evidence of the accumulation of radionuclides derived mainly from sea-to-land transfer. Accumulated deposits of radioactivity (0-0.1 m) lie within the range: 1.1-3.4 Bq kg-1 (134Cs), 260-440 Bq kg-1 (137Cs), 31-40 Bq kg-1 (238Pu), 150-215 Bq kg-1 (239 + 240Pu) and 190-240 Bq kg-1 (241Am). Soil profiles showed greater activity concentrations in their deeper regions and this is attributed to leaching of radionuclides in percolating drainage water accentuated by the coarse texture, low organic matter and clay mineral content of coastal sands. Radionuclide activity concentrations in F. rubra and A. arenaria were similar, in the ranges 20-70 Bq kg-1 (137Cs), 1-5 Bq kg-1 (238Pu), 10-30 Bq kg-1 (239 + 240Pu) and 10-65 Bq kg-1 (241Am). Clear temporal and spatial variations were observed in both species of vegetation, reflecting the weather conditions antecedent to the sampling period and the influence of sea-to-land transfer. Concentration ratios (vegetation:soil) for activity concentrations in the two species were similar, in the ranges: 0.05-0.14 (137Cs), 0.025-0.097 (238Pu), 0.022-0.057 (239 + 240Pu) and 0.025-0.212 (241Am).

  12. Possible Aeolian megaripples on Mars

    NASA Technical Reports Server (NTRS)

    Williams, S. H.

    1990-01-01

    Viking orbiter image frames 442B01-10, at 8 m/pxl resolution show that valley floors are not smooth at all, but rather are covered with mounds of material interpreted as dunes. Striations oriented perpendicular to the valley axis can be seen in several locations. The striations are here interpreted to be aeolian megaripples formed from debris weathered from the yardangs. Terrestrial aeolian megaripples have wavelengths up to 25 m; it is not unreasonable that larger megaripples might form under favorable Martian conditions, given the wind speeds available and the lower Martian gravity. If the megaripple interpretation is correct, then by terrestrial analog the deposit in which they occur has a bimodal particle size distribution. One size will undergo saltation; the other, concentrated at the crests of the megaripples, is too large/and or too dense to be put into saltation. For Mars the former is sand-sized, the latter gravel-sized, provided the materials have typical densities.

  13. Deviations from self-similarity in barchan form and flux: The case of the Salton Sea dunes, California

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.

    2013-12-01

    are the type of aeolian dune associated with a relatively uniform wind direction, incomplete sand coverage of the substrate, and low vegetation cover. Here I present an analysis of the morphology and migration rates of 40 dunes in the Salton Sea dune field using historical aerial orthophotographs, airborne laser swath mapping, terrestrial laser scanning, and measurements of the aerodynamic roughness length derived from wind velocity profiles. The data demonstrate that the Salton Sea dunes deviate from self-similarity such that smaller dunes have a lower ratio of slip face height to crest height and a lower slope, on average, compared with larger dunes and that smaller dunes migrate more slowly than would be predicted based on an inverse relationship between migration rate and dune height. The lack of self-similarity in barchans has been attributed to the dependence of speed-up ratios on dune size and the presence of a finite saturation length in the physics of aeolian transport. Here I argue that deviations from self-similarity at this study site are more likely due to the systematic decrease in aerodynamic roughness length with increasing elevation on stoss slopes. The data set I developed should prove useful to the aeolian geomorphic community for the further testing of models for barchan evolution.

  14. Immunotoxicological and neurotoxicological profile of health effects following subacute exposure to geogenic dust from sand dunes at the Nellis Dunes Recreation Area, Las Vegas, NV.

    PubMed

    Keil, Deborah; Buck, Brenda; Goossens, Dirk; Teng, Yuanxin; Leetham, Mallory; Murphy, Lacey; Pollard, James; Eggers, Margaret; McLaurin, Brett; Gerads, Russell; DeWitt, Jamie

    2016-01-15

    Exposure to geogenic particulate matter (PM) comprised of mineral particles has been linked to human health effects. However, very little data exist on health effects associated with geogenic dust exposure in natural settings. Therefore, we characterized particulate matter size, metal chemistry, and health effects of dust collected from the Nellis Dunes Recreation Area (NDRA), a popular off-road vehicle area located near Las Vegas, NV. Adult female B6C3F1 mice were exposed to several concentrations of mineral dust collected from active and vegetated sand dunes in NDRA. Dust samples (median diameter: 4.4 μm) were suspended in phosphate-buffered saline and delivered at concentrations ranging from 0.01 to 100 mg dust/kg body weight by oropharyngeal aspiration. ICP-MS analyses of total dissolution of the dust resulted in aluminum (55,090 μg/g), vanadium (70 μg/g), chromium (33 μg/g), manganese (511 μg/g), iron (21,600 μg/g), cobalt (9.4 μg/g), copper (69 μg/g), zinc (79 μg/g), arsenic (62 μg/g), strontium (620 μg/g), cesium (13 μg/g), lead 25 μg/g) and uranium (4.7 μg/g). Arsenic was present only as As(V). Mice received four exposures, once/week over 28-days to mimic a month of weekend exposures. Descriptive and functional assays to assess immunotoxicity and neurotoxicity were performed 24 h after the final exposure. The primary observation was that 0.1 to 100 mg/kg of this sand dune derived dust dose-responsively reduced antigen-specific IgM antibody responses, suggesting that dust from this area of NDRA may present a potential health risk.

  15. Effects of sedimentation on soil physical and chemical properties and vegetation characteristics in sand dunes at the Southern Dongting Lake region, China

    PubMed Central

    Pan, Ying; Zhang, Hao; Li, Xu; Xie, Yonghong

    2016-01-01

    Sedimentation is recognized as a major factor determining the ecosystem processes of lake beaches; however, the underlying mechanisms, especially in freshwater sand dunes, have been insufficiently studied. To this end, nine belt transects from nine freshwater sand dunes, classified into low (<23.7 m), medium (25.4–26.0 m), and high-elevation groups (>28.1 m) based on their elevations in 1972, were sampled to investigate differences in sedimentation rate and soil and vegetation characteristics in Southern Dongting Lake, China. Sedimentation rate, soil sand content, and soil pH increased, whereas soil clay, fine silt, moisture (MC), organic matter (OM), total N, and total K content, in addition to the growth and biodiversity of sand dune plants generally decreased with decreasing belt transect elevation. Regression analyses revealed that the negative effects of sedimentation on the ecosystem functions of sand dunes could be attributed to higher fine sand content in deposited sediments and stronger inhibition of plant growth. These results are consistent with previous studies performed in coastal sand dunes, which highlights the importance of sedimentation in determining ecological processes. PMID:27808154

  16. Effects of sedimentation on soil physical and chemical properties and vegetation characteristics in sand dunes at the Southern Dongting Lake region, China

    NASA Astrophysics Data System (ADS)

    Pan, Ying; Zhang, Hao; Li, Xu; Xie, Yonghong

    2016-11-01

    Sedimentation is recognized as a major factor determining the ecosystem processes of lake beaches; however, the underlying mechanisms, especially in freshwater sand dunes, have been insufficiently studied. To this end, nine belt transects from nine freshwater sand dunes, classified into low (<23.7 m), medium (25.4–26.0 m), and high-elevation groups (>28.1 m) based on their elevations in 1972, were sampled to investigate differences in sedimentation rate and soil and vegetation characteristics in Southern Dongting Lake, China. Sedimentation rate, soil sand content, and soil pH increased, whereas soil clay, fine silt, moisture (MC), organic matter (OM), total N, and total K content, in addition to the growth and biodiversity of sand dune plants generally decreased with decreasing belt transect elevation. Regression analyses revealed that the negative effects of sedimentation on the ecosystem functions of sand dunes could be attributed to higher fine sand content in deposited sediments and stronger inhibition of plant growth. These results are consistent with previous studies performed in coastal sand dunes, which highlights the importance of sedimentation in determining ecological processes.

  17. Mars global digital dune database: MC-30

    USGS Publications Warehouse

    Hayward, R.K.; Fenton, L.K.; Titus, T.N.; Colaprete, A.; Christensen, P.R.

    2012-01-01

    The Mars Global Digital Dune Database (MGD3) provides data and describes the methodology used in creating the global database of moderate- to large-size dune fields on Mars. The database is being released in a series of U.S. Geological Survey Open-File Reports. The first report (Hayward and others, 2007) included dune fields from lat 65° N. to 65° S. (http://pubs.usgs.gov/of/2007/1158/). The second report (Hayward and others, 2010) included dune fields from lat 60° N. to 90° N. (http://pubs.usgs.gov/of/2010/1170/). This report encompasses ~75,000 km2 of mapped dune fields from lat 60° to 90° S. The dune fields included in this global database were initially located using Mars Odyssey Thermal Emission Imaging System (THEMIS) Infrared (IR) images. In the previous two reports, some dune fields may have been unintentionally excluded for two reasons: (1) incomplete THEMIS IR (daytime) coverage may have caused us to exclude some moderate- to large-size dune fields or (2) resolution of THEMIS IR coverage (100 m/pixel) certainly caused us to exclude smaller dune fields. In this report, mapping is more complete. The Arizona State University THEMIS daytime IR mosaic provided complete IR coverage, and it is unlikely that we missed any large dune fields in the South Pole (SP) region. In addition, the increased availability of higher resolution images resulted in the inclusion of more small (~1 km2) sand dune fields and sand patches. To maintain consistency with the previous releases, we have identified the sand features that would not have been included in earlier releases. While the moderate to large dune fields in MGD3 are likely to constitute the largest compilation of sediment on the planet, we acknowledge that our database excludes numerous small dune fields and some moderate to large dune fields as well. Please note that the absence of mapped dune fields does not mean that dune fields do not exist and is not intended to imply a lack of saltating sand in other areas

  18. A review of the chronologies and geomorphology of the aeolian landforms in the northwestern Negev dunefield (Israel)

    NASA Astrophysics Data System (ADS)

    Roskin, Joel

    2015-04-01

    The northwestern (NW) Negev Desert dunefield covering an area of only 1,300 km2, comprises the eastern end of the northern Sinai Peninsula - NW Negev erg and is probably the most densely dated dune body in the INQUA Dunes Atlas chronologic database. Over 230 luminescence ages (TL, IRSL, and mainly OSL) and radiocarbon dates have been retrieved over the past course of 20 years from calcic and sandy palaeosols serving as dune substrates, sand sheets, vegetated linear dunes (VLDs), fluvial deposits, and archaeological sites. Despite being from different deposit types and aeolian morphologies, and based on different methodologies, the chronologies usually show good compatibility. By reviewing and reassessing the significance of the Eastern Mediterranean INQUA Dunes Atlas chronologies, along with detailed stratigraphic, structural and geomorphologic data and understandings, the major, and possibly extreme, episodes of aeolian activity and stability are outlined. Repetitive chronostratigraphic sequences in VLDs indicate that this dune type, at least in the Negev, comprises a reliable recorder of main dune mobilization periods. This presentation demonstrates that certain combinations of research finds, using different OSL dating strategies and other regional and local late Quaternary records and in particular aeolian ones, are required assets for providing for acceptable local and regional palaeoclimatic interpretations. The distribution of the VLD chronologies points to rapid mobilization during the Heinrich 1 and Younger Dryas, characterized by powerful winds, though VLDs also form in late Holocene palaeoenvironments. Time slices illustrate the different sensitivities of the studied aeolian landforms to the source, availability, and supply of sediment; long- and short-term climate change, local human-induced environmental changes and also their joint effects, that enable evaluation of aeolian responses to future environmental and climate changes.

  19. Global Change and Response of Coastal Dune Plants to the Combined Effects of Increased Sand Accretion (Burial) and Nutrient Availability

    PubMed Central

    Frosini, Silvia; Lardicci, Claudio; Balestri, Elena

    2012-01-01

    Coastal dune plants are subjected to natural multiple stresses and vulnerable to global change. Some changes associated with global change could interact in their effects on vegetation. As vegetation plays a fundamental role in building and stabilizing dune systems, effective coastal habitat management requires a better understanding of the combined effects of such changes on plant populations. A manipulative experiment was conducted along a Mediterranean dune system to examine the individual and combined effects of increased sediment accretion (burial) and nitrogen enrichment associated with predicted global change on the performance of young clones of Sporobolus virginicus, a widespread dune stabilizing species. Increased burial severity resulted in the production of taller but thinner shoots, while nutrient enrichment stimulated rhizome production. Nutrient enrichment increased total plant biomass up to moderate burial levels (50% of plant height), but it had not effect at the highest burial level (100% of plant height). The effects of such factors on total biomass, shoot biomass and branching were influenced by spatial variation in natural factors at the scale of hundreds of metres. These results indicate that the effects of burial and nutrient enrichment on plant performance were not independent. Their combined effects may not be predicted by knowing the individual effects, at least under the study conditions. Under global change scenarios, increased nutrient input could alleviate nutrient stress in S. virginicus, enhancing clonal expansion and productivity, but this benefit could be offset by increased sand accretion levels equal or exceeding 100% of plant height. Depletion of stored reserves for emerging from sand could increase plant vulnerability to other stresses in the long-term. The results emphasize the need to incorporate statistical designs for detecting non-independent effects of multiple changes and adequate spatial replication in future works to

  20. Global change and response of coastal dune plants to the combined effects of increased sand accretion (burial) and nutrient availability.

    PubMed

    Frosini, Silvia; Lardicci, Claudio; Balestri, Elena

    2012-01-01

    Coastal dune plants are subjected to natural multiple stresses and vulnerable to global change. Some changes associated with global change could interact in their effects on vegetation. As vegetation plays a fundamental role in building and stabilizing dune systems, effective coastal habitat management requires a better understanding of the combined effects of such changes on plant populations. A manipulative experiment was conducted along a Mediterranean dune system to examine the individual and combined effects of increased sediment accretion (burial) and nitrogen enrichment associated with predicted global change on the performance of young clones of Sporobolus virginicus, a widespread dune stabilizing species. Increased burial severity resulted in the production of taller but thinner shoots, while nutrient enrichment stimulated rhizome production. Nutrient enrichment increased total plant biomass up to moderate burial levels (50% of plant height), but it had not effect at the highest burial level (100% of plant height). The effects of such factors on total biomass, shoot biomass and branching were influenced by spatial variation in natural factors at the scale of hundreds of metres. These results indicate that the effects of burial and nutrient enrichment on plant performance were not independent. Their combined effects may not be predicted by knowing the individual effects, at least under the study conditions. Under global change scenarios, increased nutrient input could alleviate nutrient stress in S. virginicus, enhancing clonal expansion and productivity, but this benefit could be offset by increased sand accretion levels equal or exceeding 100% of plant height. Depletion of stored reserves for emerging from sand could increase plant vulnerability to other stresses in the long-term. The results emphasize the need to incorporate statistical designs for detecting non-independent effects of multiple changes and adequate spatial replication in future works to

  1. The opposition effect and its relationship to sediment density in BRDF measurements from the Algodones Sand Dunes System

    NASA Astrophysics Data System (ADS)

    Ambeau, Brittany; Bachmann, Charles M.; Griffo, Carrie; Harms, Justin; Myers, Emily; Badura, Gregory

    2016-09-01

    Density, particle size distribution, surface moisture, and mineral content are some important geophysical properties that affect the bi-directional reflectance factor (BRF) of particulate media such as sand. According to radiative transfer theory, several of these geophysical properties are known to directly affect the overall level of reflectance, as well as the functional form of the opposition effect, for homogeneous, particulate media.1 Most sands are composite, i.e. non-homogeneous, and do not follow the standard distributions (with approximate analytical solutions) for particle size. Therefore, conventional radiative transfer models need to be modified to account for the complex nature of sand. In this work, we examine the impact of density on the functional form of the opposition effect, and we show that differences in density are expressed in a characteristic way. The measurements are collected using the laboratory and field-deployable Goniometer of the Rochester Institute of Technology-Two (GRIT-T). And, the results are based on sediment samples collected from the Algodones Sand Dunes System in southeastern California during the NASA Algodones Dunes Field Experiment conducted in March 2015.

  2. Effects of disturbance on vegetation by sand accretion and erosion across coastal dune habitats on a barrier island.

    PubMed

    Miller, Thomas E

    2015-01-12

    Coastal geomorphology and vegetation are expected to be particularly sensitive to climate change, because of disturbances caused by sea-level rise and increased storm frequency. Dunes have critical reciprocal interactions with vegetation; dunes create habitats for plants, while plants help to build dunes and promote geomorphological stability. These interactions are also greatly affected by disturbances associated with sand movement, either in accretion (dune building) or in erosion. The magnitude and intensity of disturbances are expected to vary with habitat, from the more exposed and less stable foredunes, to low-lying and flood-prone interdunes, to the protected and older backdunes. Permanent plots were established at three different spatial scales on St George Island, FL, USA, where the vegetation and dune elevation were quantified annually from 2011 to 2013. Change in elevation, either through accretion or erosion, was used as a measure of year-to-year disturbance over the 2 years of the study. At the scale of different dune habitats, foredunes were found to have the greatest disturbance, while interdunes had the least. Elevation and habitat (i.e. foredune, interdune, backdune) were significantly correlated with plant community composition. Generalized linear models conducted within each habitat show that the change in elevation (disturbance) is also significantly correlated with the plant community, but only within foredunes and interdunes. The importance of disturbance in exposed foredunes was expected and was found to be related to an increasing abundance of a dominant species (Uniola paniculata) in eroding areas. The significant effect of disturbance in the relatively stable interdunes was surprising, and may be due to the importance of flooding associated with small changes in elevation in these low-lying areas. Overall, this study documents changes in the plant community associated with elevation, and demonstrates that the foredune and interdune

  3. Using Large-Scale Roughness Elements to Control Sand and Dust Flux at the Keeler Dunes, Keeler, CA

    NASA Astrophysics Data System (ADS)

    Gillies, John; McCarley-Holder, Grace

    2014-05-01

    Controlling dust emission from areas that subsequently degrade air quality and threaten human and animal health and reduce the quality of life for people residing in proximity to such sources is necessary, but also challenging. Recent research has indicated that arrays of large roughness elements (height >0.3 m) can be used effectively to modulate sand transport and the associated dust emissions. Prediction of the rate of sand flux reduction as a function of downwind distance upon entering an array of roughness elements, and the equilibrium flux reduction in the interior of the array is possible using the known geometric properties of the roughness elements, their number, and published relationships. Air quality in the town of Keeler, CA (36 deg 29' 17.92" N, 117 deg 52' 24.62" W) is degraded by levels of particulate matter <10 µm aerodynamic diameter (PM10) during periods of elevated wind speeds due to sand transport and dust emissions in the nearby Keeler Dunes. A demonstration project was designed to evaluate the effectiveness of an array of roughness elements composed of solid elements and managed vegetation to meet sand and dust flux reduction criteria. This project has two major goals: 1) to demonstrate that solid roughness elements placed on areas of the Keeler Dunes immediately arrest sand movement to specified levels (target of 85% reduction), and 2) to assess whether native plant species, planted in the sheltered area of the solid roughness elements can effectively thrive and subsequently replace the solid roughness to achieve the desired sand flux reduction control efficiency. This poster describes the results related mostly to objective one, as considerable time has to pass before sufficient data will be obtained to evaluate the success of the planted and managed vegetation to achieve a control level provided by the solid element roughness array.

  4. Mechanism of early meteoric diagenesis in carbonate dune sands, Tarama Island, Ryukyu Islands, southwestern Japan

    NASA Astrophysics Data System (ADS)

    Kumai, N.; Matsuda, H.

    2012-12-01

    Carbonate sediments are useful for the interpretation of depositional environments and environmental changes because their components and chemistry reflect depositional environments sensitively. However, primary records on their depositional environments are often modified by various types of early carbonate diagenesis immediately after their deposition. Longman (1980) pointed out that sedimentary textures and mineral compositions of carbonate sediments near a subaerial exposure surface are easily changed by dissolution and cementation associated with early meteoric diagenesis. Hudson (1977) also suggested that their primary stable carbon and oxygen isotopic compositions are altered by early meteoric diagenesis. In this way, the qualitative changes of carbonate sediments with early meteoric diagenesis are well known. On the other hand, the quantitative changes, time scale and detailed mechanisms of early meteoric diagenesis are not fully understood at present. To clarify the detailed mechanism of early meteoric diagenesis, the Upper Pleistocene carbonate dune sands in Tarama Island, the Ryukyu Islands, southwestern Japan, were analyzed. These sediments consist mainly of unconsolidated to weakly-consolidated carbonate sands, composed mainly of a variety of shallow marine bioclasts. Detailed petrographical observation and XRD and isotopic analyses were carried out. As a result of examinations of these carbonate sediments, low-Mg calcite (LMC), high-Mg calcite (HMC) and aragonite (ARG) contents of unconsolidated carbonate sands (UCS) are 20 to 47%, 0 to 44% and 33 to 54%, respectively. On the other hand, LMC, HMC and ARG contents of weakly-consolidated carbonate sands (WCS) are 64 to 95%, 0 to 18% and 5 to 18%, respectively. δ13C and δ18O values of UCS have narrow ranges of 0.51 to 1.70‰ and -1.87 to -1.46‰, respectively. On the other hand, δ13C and δ18O values of WCS have wide ranges of -4.67 to 0.62‰ and -4.82 to 2.92‰, respectively. The mineral and

  5. Two-site kinetic modeling of bacteriophages transport through columns of saturated dune sand.

    PubMed

    Schijven, Jack F; Hassanizadeh, S Majid; de Bruin, Ria H A M

    2002-08-01

    Breakthrough curves, on a semi-log scale, from tests in porous media with block-input of viruses, bacteria, protozoa and colloidal particles often exhibit a typical skewness: a rather slowly rising limb and a smooth transition of a declining limb to a very long tail. One-site kinetic models fail to fit the rising and declining limbs together with the tail satisfactorily. Inclusion of an equilibrium adsorption site does not seem to improve simulation results. This was encountered in the simulation of breakthrough curves from a recent field study on the removal of bacteriophages MS2 and PRD1 by passage through dune sand. In the present study, results of laboratory experiments for the study of this issue are presented. Breakthrough curves of salt and bacteriophages MS2, PRDI, and phiX174 in 1 D column experiments have been measured. One- and two-site kinetic models have been applied to fit and predict breakthrough curves from column experiments. The two-site model fitted all breakthrough curves very satisfactorily, accounting for the skewness of the rising limb as well as for the smooth transition of the declining limb to the tail of the breakthrough curve. The one-site model does not follow the curvature of the breakthrough tail, leading to an overestimation of the inactivation rate coefficient for attached viruses. Interaction with kinetic site 1 is characterized by relatively fast attachment and slow detachment, whereas attachment to and detachment from kinetic site 2 is fast. Inactivation of viruses and interaction with kinetic site 2 provide only a minor contribution to removal. Virus removal is mainly determined by the attachment to site 1. Bacteriophage phiX174 attached more than MS2 and PRD1, which can be explained by the greater electrostatic repulsion that MS2 and PRD1 experience compared to the less negatively charged phiX174.

  6. Comparison of stemflow for two xerophytic shrubs in re-vegetated sand dunes in N. China

    NASA Astrophysics Data System (ADS)

    Wang, X.

    2012-04-01

    Precipitation, as the sole source of water replenishment in the semiarid area, plays a key role in sustaining the desert ecosystem. Stemflow, a spatially localized point input of precipitation at the plant stem, of two xerophytic shrubs (Caragana korshinskii Kom. and Artemisia ordosica Krasch.) was quantified at the re-vegetated sand dunes of Shapotou Desert Experimental Research Station near Lanzhou. The results indicated that stemflow, expressed as an equivalent depth based on the canopy area of the sampled shrubs, averaged 3.3% and 7.9% of the bulk precipitation for C. korshinskii and A. ordosica, respectively. This is not a high value but important to be taken into account in the determination of the water balance of the desert ecosystem. An antecedent precipitation of 2.2 and 1.3 mm was necessary for the initiation of the stemflow for C. korshinskii and A. ordosica, respectively. The relationship between funnelling ratios and rainfall suggested that there existed a rainfall depth threshold of 7 mm for the two shrubs; while large variability in funnelling ratio were found for rainfall intensity less than 4 mm h-1, but it tended to decease with increasing rain intensity when rainfall intensity was greater than 4 mm h-1. Significant positive linear relationships were found between stemflow production (l) and rainfall depth (mm) for the two shrubs. Statistical analysis showed that the volume of precipitation channelized as stemflow varies as a function of canopy area and canopy volume characteristics. There was a positive effect on redistribution of rainwater and funnelling ratio as shrub size increases for C. korshinskii , while, for A. ordosica, a negative effect on funnelling ratio was found. This study was supported by the 100-talents Program of the Chinese Academy of Sciences, and the National Natural Science Foundation of China (grant no. 31070415) and the Joint Scholar Project of Western (China) Lightening Talent Program of the Chinese Academy of Sciences.

  7. Late Pleistocene and Holocene aeolian sedimentation in Gonghe Basin, northeastern Qinghai-Tibetan Plateau: Variability, processes, and climatic implications

    NASA Astrophysics Data System (ADS)

    Qiang, Mingrui; Jin, Yanxiang; Liu, Xingxing; Song, Lei; Li, Hao; Li, Fengshan; Chen, Fahu

    2016-01-01

    Although stratigraphic sequences of aeolian deposits in dryland areas have long been recognized as providing information about past environments, the exact nature of the environmental processes they reflect remains unclear. Here, we report the results of a detailed investigation of eight outcrop sections in the Gonghe Basin, northeastern Qinghai-Tibetan Plateau. Measurements of sediment grain-size and chemical composition indicate that the deposits are primarily of aeolian origin, consisting of interbedded, well-sorted sand, silty sand, loess and/or palaeosol; however, their occurrence varies from site to site. Fossil dune sands mainly occur in or close to the currently stabilized or semi-stabilized dune fields, whereas loess is distributed along the downwind marginal areas. This pattern of basin-scale differentiation was controlled mainly by spatial variability of sediment supply due to the antecedent sedimentary patterns within the basin. Together with previously-published optically stimulated luminescence (OSL) ages, 24 new OSL dates are used to elucidate the history of aeolian activity and its relationship to climatic changes. There is no apparent relationship between past dune activity and downwind loess deposits. Deposition of silty sand probably occurred during past phases of windy, dry and cold climate in the Late Pleistocene. However, climatic factors alone cannot explain the occurrence of silty sand deposition. This is because the deposition of silty sand was always preceded by episodes of fluvial deposition prior to river incision, thereby indicating the importance of an 'activated' sediment supply associated with fluvial processes. Deposition of well-sorted sand occurred episodically, not only during the Late Pleistocene, but also during the early- to mid-Holocene. Vegetation conditions, controlled either by the occurrence of intervals of moisture deficit during the Late Pleistocene or by changes in the balance between precipitation and

  8. Modeling the biogeomorphic evolution of coastal dunes in response to climate change

    NASA Astrophysics Data System (ADS)

    Keijsers, J. G. S.; De Groot, A. V.; Riksen, M. J. P. M.

    2016-06-01

    Coastal dunes form in many parts of the world the first flood defense line against the sea. To study effects of climate change on coastal dune evolution, we used a cellular model of dune, beach, and vegetation development. The model was calibrated and validated against field measurements of the Dutch coast, showing good performance for 10 year simulations. A sensitivity analysis showed that dune size and morphology are most sensitive to the rate of aeolian input and wave dissipation. Finally, 100 year climate change scenarios were run to establish the impacts of sea level rise and changes in vegetation growth rate on dune evolution. The results are in good agreement with conceptual models of dune evolution. Sea level rise largely determines the direction of dune evolution: the rate of rising controls whether dunes are able to preserve their height or sand volume while migrating landward. The effect of changing vegetation growth rates, resulting from climate change, is most manifest in dune response to large disturbances. If vegetation is removed halfway into the simulation, vegetation growth rate determines whether a foredune will revegetate and recover its height. Low vegetation growth rates result in mobile dunes that lose sand. The good agreement between observations and predictions indicates that the model successfully incorporates the suite of biogeomorphic and marine processes involved in dune building.

  9. Quantification of Barchan Dune Evolution over Monthly to Interannual Time Scales Using Airborne LIDAR and Terrestrial Laser Scanning

    NASA Astrophysics Data System (ADS)

    Hoose, M.; Pelletier, J. D.

    2013-12-01

    Barchan dunes are among the most rapidly evolving landforms on Earth, with migration rates of up to 100 m/yr. Despite the central importance of barchan dunes in aeolian geomorphology and the relative ease of quantifying changes in their shape and position, basic questions remain about barchan dune evolution. For example, how does the position of a dune relative to its neighbors affect the evolution of a dune? The presence of a dune influences the air flow around the dune, potentially modifying the evolution of neighboring dunes. Also, a dune may grow in size more rapidly if neighboring dunes are located immediately upwind of the dune, thus providing additional sources of sand for the dune relative to the case of an isolated dune. To address these questions, we quantified the change in the position of 14 dunes, and the sand flux among them, in the Salton Sea dune field over two time scales: 1 month and 3 years. The 1-month change map was created using two TLS surveys completed in the summer of 2013, and the 3-year change map was created using the results of a TLS survey in 2013 and an airborne LIDAR survey from 2010. The PHOENICS Computational Fluid Dynamics solver was used to predict the change in the positions of the dunes and the flux of sand among them. PHOENICS was used to model the shear stress over the dune field using DEM data from the beginning of each interval of study, together with data on the wind profile collected at the study site using a wind tower. The output of PHOENICS was used as input to a shear-stress-dependent aeolian transport formula with the effect of slope on the threshold of entrainment included. Preliminary analyses of the ALSM- and TLS-derived change maps indicate that clustered dunes interact via boundary layer effects to alter the migration and growth rates of their downwind neighbors. Additionally, the effects of subdominant, southeasterly winds were observed in the 1-month change map in the form of sand wedges deposited along the

  10. Speculation on martian north polar wind circulation and the resultant orientations of polar sand dunes

    USGS Publications Warehouse

    Ward, A.W.; Doyle, K.B.

    1983-01-01

    Dunes in the Martian north polar erg show two dominant orientations. When seen at frost cap minimum, dunes north of 80??N record east winds, dunes south of 80??N record west winds. Many of the transverse dunes are considered to be reversing dunes. Dunes in two fields may have reversed at least once during the lifetime of the Viking Orbiters. Poor agreement exists among published predictive models of north polar winds and the interpretations derived from the major published map of the north polar dunes. We propose that the average polar winds are: (1) strong, off-pole northwest winds in fall; (2) moderate west winds in winter; (3) latitude-dependent weak to strong off-pole northeast winds in spring; and (4) weak west winds in summer. Viking images of near-polar clouds confirm much of the hypothesis. Images discussed in other studies can be given alternative interpretations that support this hypothesis also. Over millenia, the combination of reversing west and east winds could produce the binodal distributions of dune orientations observed at the north pole. ?? 1983.

  11. An environmental perspective of the post-tsunami scenario along the coast of Tamil Nadu, India: role of sand dunes and forests.

    PubMed

    Mascarenhas, Antonio; Jayakumar, Seelam

    2008-10-01

    An endeavor to feel the pulse of a coast devastated by a powerful oceanographic event is made. Results of field investigations along Tamil Nadu seaside revealed that the tsunami of December 2004 demolished dwellings within strips ranging from 6 to 132 m (average width, 41 m) from the dune, and flooded up to 862 m (average, 247 m) from the shore. The event damaged sand dunes, ripped dune vegetation, created new water bodies and shattered high value assets. Comparatively, casuarina forests performed remarkably. Uprooting of trees was exclusively restricted to a frontal strip ranging from 5 to 25 m (average width, 14 m) nearest to the shore where the maximum wave run-up was 6.5m above sea level. Sand dunes in general, and casuarina forests in particular, possess an innate capacity to dissipate powerful waves. This inference is supported by (a) negligible over wash along belts characterized by high dune complexes, (b) intact villages shielded by dense forests as well as sand dunes, and (c) maximum destruction of open beach front influenced by intense human activity. In this context, the coastal regulation zone (CRZ) Notification of 1991 offers sufficient scientific validity to be endorsed. However, post-tsunami ecosystem management initiatives lack a scientific basis. Therefore, a coastal hazards policy, that considers adaptation, dune restoration and forested buffer zones, is a sustainable long-term option for Indian coasts.

  12. Understanding the role of Aeolian Processes and Physical Sorting on Martian Surface Compositions Through Analysis of Spectrally and Thermophysically Heterogeneous Dune Fields

    NASA Astrophysics Data System (ADS)

    Pan, C.; Rogers, A. D.

    2014-07-01

    We analyzed composition, thermal inertia (TI) and morphology of heterogeneous dune fields. A cubic polynomial fit is used to quantitatively map compositional variations of THEMIS spectra. Compositional difference within a dune exhibit TI difference.

  13. Impacts of simulated climate change and fungal symbionts on survival and growth of a foundation species in sand dunes.

    PubMed

    Emery, Sarah M; Rudgers, Jennifer A

    2013-12-01

    For many ecosystems, one of the primary avenues of climate impact may be through changes to foundation species, which create habitats and sustain ecosystem services. For plants, microbial symbionts can often act as mutualists under abiotic stress and may mediate foundational plant responses to climate change. We manipulated the presence of endophytes in Ammophila breviligulata, a foundational sand dune species, to evaluate their potential to influence plant responses to climate change. We simulated projected climate change scenarios for temperature and precipitation using a growth chamber experiment. A 5 °C increase in temperature relative to current climate in northern Michigan reduced A. breviligulata survival by 45 %. Root biomass of A. breviligulata, which is critical to dune stabilization, was also strongly reduced by temperature. Plants inoculated with the endophyte had 14 % higher survival than endophyte-free plants. Contrary to our prediction, endophyte symbiosis did not alter the magnitude or direction of the effects of climate manipulations on A. breviligulata survival. However, in the absence of the endophyte, an increase in temperature increased the number of sand grains bound by roots by 80 %, while in symbiotic plants sand adherence did not significantly respond to temperature. Thus, plant-endophyte symbiosis actually negated the benefits in ecosystem function gained under a warmer climate. This study suggests that heat stress related to climate change in the Great Lakes may compromise the ability of A. breviligulata to stabilize dune ecosystems and reduce carbon storage and organic matter build-up in these early-successional systems due to reduced plant survival and root growth.

  14. Studies of the terrestrial O2 and carbon cycles in sand dune gases and in biosphere 2

    SciTech Connect

    Severinghaus, Jeffrey Peck

    1995-01-01

    Molecular oxygen in the atmosphere is coupled tightly to the terrestrial carbon cycle by the processes of photosynthesis, respiration, and burning. This dissertation examines different aspects of this coupling in four chapters. Chapter 1 explores the feasibility of using air from sand dunes to reconstruct atmospheric O2 composition centuries ago. Such a record would reveal changes in the mass of the terrestrial biosphere, after correction for known fossil fuel combustion, and constrain the fate of anthropogenic CO2.

  15. Global Distribution of Dunes on Titan With VIMS

    NASA Astrophysics Data System (ADS)

    Le Corre, L.; Le Mouelic, S.; Sotin, C.; Barnes, J.; Brown, R. H.; Buratti, B. J.; Jaumann, R.; Soderblom, J.; Soderblom, L. A.; Clark, R.; Baines, K. H.; Nicholson, P. D.

    2008-12-01

    The carbon cycle on Titan involves several processes in the deep interior, in the sub-surface and in the atmosphere. The dunes, which were first seen by the Cassini/SAR (Synthetic Aperture Radar) [Lorenz et al., 2006], are thought to be composed of hydrocarbon grains deposited onto the surface after they formed in the atmosphere. Although their composition has not been determined during the nominal mission, pure water ice grains can be ruled out by the IR spectra obtained by the VIMS (Visual and Infrared Mapping Spectrometer). This study compares RADAR and VIMS images of dune fields to determine the spectral characteristics of these areas and uses the global VIMS spectral maps in order to provide a global map of the dune fields on Titan. Most of the Aeolian sand deposits are found in sand seas. In addition, isolated groups of "cat scratches", very sinuous short dunes [Radebaugh et al., 2008] and sand sheets [Lunine et al., 2008] are recognized. Their emplacement is most probably related to the available sand supply. In VIMS infrared dataset, the detailed study of dune fields by Barnes et al. [2008] shows that dune patterns are found mainly in brown units, which cover 18% of the whole Titan's surface and are found in equatorial regions. Dark blue units cover roughly 2% of Titan's surface. They are systematically associated with bright terrains and are never found isolated within brown units. The dune fields in SAR images generally end at the limit between infrared brown and bright units. Dunes can also be found on dark blue terrains as seen by Barnes et al. [2007] and Soderblom et al. [2007]. 82% of SAR dunes are located in brown units and 4.5% in dark blue units. The remnant dunes, corresponding to "cat scratches" or not well defined dune fields, appear in infrared bright units as isolated patches. These dunes may form with a low sand supply. They account for about 13.5% RADAR dunes. From the global mapping, we inferred that dunes in the RADAR data are highly

  16. Tracking aeolian transport patterns across a mega-nourishment using video imagery

    NASA Astrophysics Data System (ADS)

    Wijnberg, Kathelijne; van der Weerd, Lianne; Hulscher, Suzanne

    2014-05-01

    Coastal dune areas protect the hinterland from flooding. In order to maintain the safety level provided by the dunes, it may be necessary to artificially supply the beach-dune system with sand. How to best design these shore nourishments, amongst others with respect to optimal dune growth on the long-term (decadal scale), is not yet clear. One reason for this is that current models for aeolian transport on beaches appear to have limited predictive capabilities regarding annual onshore sediment supply. These limited capabilities may be attributed to the lack of appropriate input data, for instance on moisture content of the beach surface, or shortcomings in process understanding. However, it may also be argued that for the long-term prediction of onshore aeolian sand supply from the beach to the dunes, we may need to develop some aggregated-scale transport equations, because the detailed input data required for the application of process-scale transport equations may never be available in reality. A first step towards the development of such new concepts for aggregated-scale transport equations is to increase phenomenological insight into the characteristics and number of aeolian transport events that account for the annual volume changes of the foredunes. This requires high-frequency, long-term data sets to capture the only intermittently occurring aeolian transport events. Automated video image collection seems a promising way to collect such data. In the present study we describe the movement (direction and speed) of sand patches and aeolian bed forms across a nourished site, using video imagery, to characterize aeolian transport pathways and their variability in time. The study site is a mega-nourishment (21 Mm3 of sand) that was recently constructed at the Dutch coast. This mega-nourishment, also referred to as the Sand Motor, is a pilot project that may potentially replace current practice of more frequently applying small scale nourishments. The mega

  17. Geology along Mosca Pass Trail, Great Sand Dunes National Park and Preserve, Colorado

    USGS Publications Warehouse

    Lindsey, David A.; Klein, Terry L.; Valdez, Andrew; Webster, Robert J.

    2012-01-01

    Mosca Pass Trail takes the hiker on a journey into the Earth's crust. Here you can see the results of tremendous tectonic forces that bend and tear rocks apart and raise mountain ranges. The trail begins near the Sangre de Cristo fault, which separates the Sangre de Cristo Range from the San Luis Valley. The valley is part of the Rio Grande rift, a series of fault basins extending from southern New Mexico to central Colorado, wherein the Earth's crust has been pulled apart during the last 30 million years. Thousands of feet of sediment, brought by streams mostly from the Sangre de Cristo Range, fill the San Luis Valley beneath the Great Sand Dunes. The trail ends at Mosca Pass overlooking Huerfano Park. The park is part of the larger Raton Basin, formed by compression of the Earth's crust during the Laramide orogeny, which occurred 70–40 million years ago. Massive highlands, the remnants of which are preserved in the Sangre de Cristo Range, were uplifted and pushed over the western side of the Raton Basin. Streams eroded the highland as it rose and filled the Raton Basin with sediment. After the sediment was compacted and cemented to form sedimentary rock, the Huerfano River and other streams began to excavate the basin. Over an unknown but long timespan that probably lasted millions of years, relatively soft sedimentary rocks were removed by the river to form the valley we call "Huerfano Park." Between the ends of the trail, the hiker walks through an erosional "window," or opening, into red sedimentary rocks overridden by gneiss, a metamorphic rock, during the Laramide orogeny. This window gives the hiker a glimpse into the Laramide highland of 70–40 million years ago that preceded the present-day Sangre de Cristo Range. The window is the focus of this trail guide. At the east end of the trail, near Mosca Pass, another trail follows the ridgeline south to Carbonate Mountain. Immediately after reaching the first summit above tree line, this trail crosses a

  18. Temperature and humidity within a mobile barchan sand dune, implications for microbial survival

    NASA Astrophysics Data System (ADS)

    Louge, M. Y.; Valance, A.; el-Moctar, A. Ould; Xu, J.; Hay, A. G.; Richer, R.

    2013-12-01

    Although microorganisms play an important role in biological soil crusts and plant rhizospheres in deserts, it is unclear whether temperature and moisture deep within relatively fast moving hyperarid mobile dunes present a suitable habitat for microbes. To inform this question, we report measurements of temperature and humidity from probes initially sunk below the leeward avalanche face of a mobile barchan dune in the Qatar desert, emerging windward after 15 months of deep burial. Despite large diurnal variations on the surface, temperature within this dune of 5.6 m height is predictable, as long as dune advection is properly considered. It evolves on smaller amplitude and longer timescale than the surface, lagging average seasonal atmospheric conditions by about 2 months. We contrast these deep thermal records with measurements of diurnal variations of the temperature profile just below the surface, which we calculate with a thermal model predicting the relative roles of wind‒driven convective heat transfer and net radiation flux on the dune. Observations and analyses also suggest why random precipitation on the leeward face produces a more unpredictable moisture patchwork on the windward slope. By rapidly reaching sheltered depths, small quantities of rain falling on that face escape evaporation and endure within the dune until resurfacing upwind. At depths below 10 cm, we show that moisture, rather than temperature, determines the viability of microbes and we provide initial microscopic and respiration‒based evidence of their presence below the windward slope.

  19. The growth responses of coastal dune species are determined by nutrient limitation and sand burial.

    PubMed

    Gilbert, Matthew; Pammenter, Norman; Ripley, Brad

    2008-05-01

    Past work suggests that burial and low nutrient availability limit the growth and zonal distribution of coastal dune plants. Given the importance of these two factors, there is a surprising lack of field investigations of the interactions between burial and nutrient availability. This study aims to address this issue by measuring the growth responses of four coastal dune plant species to these two factors and their interaction. Species that naturally experience either high or low rates of burial were selected and a factorial burial by nutrient addition experiment was conducted. Growth characteristics were measured in order to determine which characteristics allow a species to respond to burial. Species that naturally experience high rates of burial (Arctotheca populifolia and Scaevola plumieri) displayed increased growth when buried, and this response was nutrient-limited. Stable-dune species had either small (Myrica cordifolia, N-fixer) or negligible responses to burial (Metalasia muricata), and were not nutrient-limited. This interspecific difference in response to burial and/or fertiliser is consistent with the idea that burial maintains the observed zonation of species on coastal dunes. Species that are unable to respond to burial are prevented from occupying the mobile dunes. Species able to cope with high rates of burial had high nitrogen-use efficiencies and low dry mass costs of production, explaining their ability to respond to burial under nutrient limitation. The interaction between burial and nutrient limitation is understudied but vital to understanding the zonation of coastal dune plant species.

  20. 10 years of aeolian geomorphology at the EGU: past achievements and future challenges

    NASA Astrophysics Data System (ADS)

    Baas, Andreas C. W.; Wiggs, Giles F. S.; Claudin, Philippe

    2016-04-01

    On this tenth anniversary of the Aeolian Processes & Landforms session at the EGU the original conveners review and reflect on the recent achievements and expansion in aeolian geomorphological research, focussing on advances in our understanding of sand transport processes, dune development and dynamics, and the mechanisms and scalings involved. This talk will highlight the variety and impact of the dramatic increase in the extent and interest of research on aeolian processes and landforms in the last ten years, including the increasingly strong community presence at international meetings, the diversity and extent of collaborations across subject boundaries, and the application of new measurement technologies and mathematical approaches. We conclude with a forward-looking prospectus of exciting future challenges and open research questions.

  1. Sand rubification with time? The case of the Sinai - Negev erg

    NASA Astrophysics Data System (ADS)

    Roskin, J.; Rozenstein, O.; Tsoar, H.; Blumberg, D. G.; Porat, N.

    2012-04-01

    The redness index (RI) (RI = R2/(B*G3) of aeolian sand has been shown to be a promising qualitative spectroscopic method to define sand grain redness intensity, which reflects the extent of iron-oxide quartz grain coatings(1,2). Using the RI, this study investigates the relationship between redness intensity and optically stimulated luminescence (OSL) based depositional ages of sand samples taken from exposed and fully-drilled vegetated linear dunes in the northwestern Negev dunefield, Israel at the downwind end of the Sinai Negev erg. Sand redness intensity did not vary greatly along the Negev sand transport paths and dune sections dated to be active during the Late Pleistocene, late Holocene, and modern times. No correlation was found between RI intensity (i.e., redness) and the depositional age of the sand. The relatively uniform RI values and sedimentological properties along most of the dunes suggest that sand grain coating development, and consequent rubification, have probably been minimal since the Late Pleistocene. Although it is possible that RI developed rapidly following deposition in a wetter Late Pleistocene climate, the drier and less stormy Holocene does not seem conducive to sand-grain rubification. Based on analyses of northern Sinai sand samples, remote sensing, and previous studies, we suggest that the attributes of the sand grain RI have been inherited from upwind sources. We propose that the sand grain coatings are early diagenetic features that have been similarly red since their suggested aeolian departure from the middle and upper Nile Delta.

  2. Development of cliff-top dunes in the Hengchun Peninsula of the southern Taiwan

    NASA Astrophysics Data System (ADS)

    Ho, Lih-Der; Wong, Yi-Chia; Lüthgens, Christopher; Chyi, Shyhjeng; Yen, Jiun-Yee

    2016-04-01

    Fung-Chuei-Sha cliff-top dune is located on a 60-meter-high cliff surface in the Hengchun Peninsula of Taiwan. It is still unclear that the history of the aeolian sediment deposition on the top of the cliff, and what factors may influence the evolution of the cliff-top dune. This study aims to investigate the evolutionary history of the Fung-Chuei-Sha cliff-top dune by analyzing the grain size, CaCO3 concentration and absolute dates of the dune sediment, and the land snail species found in the deposit.The results show three phases of aeolian sand accumulation in the Fung-Chuei-Sha cliff-top dune. 1. Phase I: aeolian sediment may accumulate in the bottom of the cliff between 2800 yr BP and 2100 yr BP. 2. Phase II: the cliff-top dune accumulated a 3.1-meter-thick sediment layer from 1500 yr BP to 1300 yr BP. In this phase, dune sediment deposited in a rate of 1.55 cm/yr. The paleoclimate proxy data from the nearby area indicate that the environment was cool and dry, and the Asian winter monsoon was strong during 1500-1300 yr BP. It blew the old coastal dune deposit at the bottom of the cliff up to the cliff top, and induced the C14 age reverse phenomenon. The aeolian deposition began to stabilize because of the wetter environment in the end of the Phase II. At the same time, the stable dune formed the silt and clay layer on the surface of the dune. A layer cemented by CaCO3 may indicate the position of the palaeo-groundwater table. 3. Phase III: the phase stared from 1500-1300 yr BP to the present. A 2.4-meter-thick eolian deposit was accumulated in a rate of 0.18 cm/yr during this phase. Four kinds of land snail shells, Cyclophorus formosensis, Hemiphaedusa similaris, Platyrhaphe swinhoei, Odontartemon heudei, which prefer to live in a relatively humid environment, were commonly observed in the dune deposit, indicating the environment was wet and consequently caused a slower aeolian deposition rate at this phase. Between 1000 yr BP and 500 yr BP, there was a

  3. Antioxidant activity of raw, cooked and Rhizopus oligosporus fermented beans of Canavalia of coastal sand dunes of Southwest India.

    PubMed

    Niveditha, Vedavyas R; Sridhar, Kandikere R

    2014-11-01

    The raw and processed (cooked and cooked + solid-state fermented with Rhizopus oligosporus) split beans of two landraces of coastal sand dune wild legumes (Canavalia cathartica and Canavalia maritima) of the southwest coast of India were examined for bioactive compounds (total phenolics, tannins and vitamin C) and antioxidant potential (total antioxidant activity, ferrous-ion chelating capacity, DPPH free radical-scavenging activity and reducing activity). One-way ANOVA revealed significant elevation of bioactive compounds as well as antioxidant activities in fermented beans compared to raw and cooked beans in both legumes (p < 0.001). The EC50 values in fermented beans of both legumes were significantly lowest compared to raw and cooked beans (p < 0.001). In principal component analysis, total phenolics along with antioxidant activities (total antioxidant, ferrous-ion chelating and free radical-scavenging activities) of fermented beans of C. cathartica, while total antioxidant and free radical-scavenging activities of fermented beans of C. maritima were clustered. The present study demonstrated that split beans of coastal sand dune Canavalia fermented by R. oligosporus endowed with high bioactive principles as well as antioxidant potential and thus serve as future nutraceutical source.

  4. GPR imaging of a sand dune aquifer: A case study in the niayes ecoregion of Tanma, Senegal

    NASA Astrophysics Data System (ADS)

    Rejiba, F.; Bobée, C.; Maugis, P.; Camerlynck, C.

    2012-06-01

    Local agriculture in Senegal is dependent on truck farming, which is concentrated in the narrow interdunal zone of peat deposits, called "niayes". The viability of the niayes significantly depends on the sand dune aquifer, as a consequence of recent over-pumping. In the present paper, we discuss the ability of GPR to locate the water table, in a highly vegetated interdunal area which includes peat fields, as well as internal dips, which were shown to be complex. Three profiles determined in the interdunal zone have been associated with several boreholes. Analysis of the radargrams clearly shows that 1) the presence of dense vegetation is not a penalising factor; 2) phase inversion in the measured signal could be useful in distinguishing between the presence of a significant water contrast, and that of a strong stratigraphic reflector; 3) in sand dunes, the electromagnetic contrast resulting from a wetting front is likely to be of the same order as that of the water table. The outcome of this study may provide clues to the characterisation and management of water resources in niayes area.

  5. Contribution to the physical-mechanical study of cement CRS basis of dune-sand powder and other minerals

    NASA Astrophysics Data System (ADS)

    Dahmani, Saci; Kriker, Abdelouahed

    2016-07-01

    The Portland cements are increasingly used for the manufacture of cement materials (mortar or concrete). Sighting the increasing demand of the cement in the field of construction, and the wealth of our country of minerals. It is time to value these local materials in construction materials and in the manufacture of cement for the manufacture of a new type of cement or for the improvement of the cement of characteristics for several reasons either technical, or ecological or economic or to improve certain properties to the State fees or hardened. The uses of mineral additions remain associated to disadvantages on the time of solidification and the development of the mechanical resistance at the young age [8]. The objective of our work is to study the effects of the incorporation of additions minerals such the pozzolan (active addition) [3], slag of blast furnace (active addition) [4] and the sand dune powder (inert addition) on the physico-mechanical properties of compositions of mortar collaborated compositions according to different binary combinations basis of these additions. This will allow selecting of optimal dosages of these combinations the more efficient, from the point of view of mechanical resistanceas well. The results of this research work confirm that the rate of 10% of pozzolan, slag or powder of dune sand contributes positively on the development of resistance in the long term, at of this proportion time,there is a decrease in the latter except for the slag (20 - 40%) [4]Seems the more effective resistors and physical properties.

  6. Holocene formation and evolution of coastal dunes ridges, Brittany (France)

    NASA Astrophysics Data System (ADS)

    Van Vliet-Lanoë, Brigitte; Goslin, Jérôme; Hénaff, Alain; Hallégouët, Bernard; Delacourt, Christophe; Le Cornec, Erwan; Meurisse-Fort, Murielle

    2016-07-01

    Holocene coastal dune formation under a continuously rising sea level (SL) is an abnormal response to increasing storm frequency. The aim of this work is to understand the coastal sedimentary budget and the present-day sand starvation, controlled by climate and man. Dating in Brittany shows that Aeolian deposition initiated from ca. 4000 cal BP, with the slowing down of the SL rise. Pre-historical dunes appeared here from ca. 3000 cal BP, without SL regression. After, further building phases recycled the same stock of sands. Historical dunes I developed from ca. 350 AD. Major storms between 900 and 1200 AD resulted in the construction of washover coastal ridges, the Historical dunes II. A part of the sand was evacuated offshore. From ca. 1350 AD, the pre-existing ridges are reworked forming the Historical dunes III, leading to rapid coastal erosion and inland drift. Holocene dunes with a rising SL constitute a temporary anomaly, mostly forced by man, soon erased by storms in Brittany.

  7. Vegetation controls on the maximum size of coastal dunes

    PubMed Central

    Durán, Orencio; Moore, Laura J.

    2013-01-01

    Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand “dune-building” species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought. PMID:24101481

  8. Vegetation controls on the maximum size of coastal dunes

    NASA Astrophysics Data System (ADS)

    Durán, Orencio; Moore, Laura J.

    2013-10-01

    Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand "dune-building" species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought.

  9. Vegetation controls on the maximum size of coastal dunes.

    PubMed

    Durán, Orencio; Moore, Laura J

    2013-10-22

    Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand "dune-building" species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought.

  10. Holocene aeolian sediments on the NE Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Stauch, G.; Lehmkuhl, F.; Hilgers, A.; Zhao, H.

    2012-04-01

    The semiarid climate of the northeastern Tibetan Plateau supports the formation of different types of aeolian sediments and landforms during the Holocene. Aeolians silts and sands in the catchment of the Donggi Cona in an elevation above 4000m to 4800 m asl reflect variable climate conditions during that time as well as different sediment sources. Based on 51 OSL datings and catchment wide geomorphological mapping a complex pattern of long and short distance sediment transport has been reconstructed. Only few aeolian archives are preserved from the late Pleistocene in this mountain environment indicating cold and dry climate conditions which prevented a continuous accumulation. During the early Holocene a phase of increased aeolian sedimentation of sand at the slopes of the mountains has been reconstructed. The sand originated from a large alluvial fan which was highly active during the Pleistocene. In addition, a thin loess cover is preserved at a few sites in the neighboring mountains ranges. The sedimentation of the loess started around 2000 years later than the sedimentation of the sand at the foot slope. Both archives are related to an increase in precipitation at the northern margin of the Tibetan Plateau which was related to a strengthening of the Asian Monsoon during that time. The wetter climate conditions favored the development of a vegetation cover which leads to the trapping and fixation of the aeolian sediments. However, with a further strengthening of the Monsoon systems these archives subsequently eroded due to higher run off and accumulated as colluvial and fluvial deposits in the basins. These phase lasted until 6 ka. A second aeolian period started at around 3 ka with the formation new dunes in the basins. This period can be associated with dry and cold climate of the late Holocene supporting the reactivation of the sand in the area. This might be further enhanced by an increased human impact by grazing during the late Holocene and resulting

  11. Characterizing subsurface complexity of aeolian morphotypes with georadar

    NASA Astrophysics Data System (ADS)

    Bentley, Andrew Phillip Keller

    Aeolian landforms are classified based on their plan morphology, which is a function of sediment transport volume, wind direction, and vegetation. In the case of compound landforms or two-dimensional exposures (outcrops), there is insufficient information for discriminating between 3D morphotypes (e.g., barchans vs. parabolic dunes). To characterize the dip-section architecture of near end-member morphologies (interacting barchans and sparsely vegetated parabolics), a series of axial transects were selected from >25 km of high-resolution (500 MHz) ground-penetrating radar (GPR) data from the gypsum dune field of White Sands National Monument, New Mexico. For dunes of comparable size (6-7 m high), a series of attributes were analyzed for unsaturated portions along the thickest (axial) radargram sections. Given the limitations in vertical resolution (7 cm in dry sand), the average measureable slipface thickness in barchans ranged between 10-22 cm, whereas parabolic slipfaces were thinner at 10-14 cm. High-amplitude diffractions produced by buried vegetation, semi-lithified pedestals, and bioturbation structures were rare within barchans (point-source diffraction density = 0.03/m2; hyperbolics per 1-m-wide cross-sectional area of the image), in contrast to a point-source density of 0.07/m2 in parabolics. An aeolian internal complexity threshold (pi) is proposed, which incorporates standardized scores of slipface thickness, point-source diffraction density, and continuity of major bounding surfaces at mesoscale range determined through semivariogram analysis. For the study region, these variables were sufficient for discriminating barchans (pi = -2.39 to -0.25; pib= -1.65) from parabolic (pi = 0.13 to 2.87; pip= 1.65) dunes. This threshold has the potential for differentiating dune morphotypes in areas where surface morphology is masked and for identifying compound landforms (e.g., a re-activated parabolic dune converted into a barchan in situ ). Ultimately

  12. Aeolian Processes at Meridiani Planum

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Fike, D. A.; Greeley, R.; Grotzinger, J. P.; Jerolmack, D. J.; Malin, M. C.; Soderblom, L.; Squyres, S.; Sullivan, R.; Thompson, S.

    2004-12-01

    The Opportunity Rover has observed a variety of aeolian features at Meridiani Planum. These features imply wind-related processes that operate on a range of time-scales, so that at least a relative time-scale of formation and modification can be assigned to many. (a) Features forming and changing in the shortest time include probable impact ripples (cm-scale) that occur in dark basalt sand on the floors of local depressions throughout the plains. Also in this category are deposits of bright airfall dust (in the form of streaks) that are not removed downwind of topographic features such as crater rims. Analysis of MOC imagery indicates that streaks change orientation after intense dust storms. The similar orientations of impact ripples and bright streaks are thought to indicate the prevailing direction of the most-recent vigorous wind regime. (b) Forming and changing on a longer, intermediate time-scale (and hence older) are deflationary ripples armored with well-sorted mm-sized hematitic grains that likely propagate by creep (i.e., pushed by the impacts of smaller saltating grains). The removal of dust from the plains during storms implies saltation of sand ( ˜ 100 μ m) which indicates shear velocities approaching what is required to roll the ˜ 1 mm hematitic grains. The ``plains ripples'' rarely occupy local depressions and cover the plains at Meridiani Planum ( ˜ 1 cm tall, ˜ 10 cm wide, up to ˜ 1 m long). Plains ripples indicate two prominent orientations: the orientation of individual bedforms as well as that of en-echelon ripple trains. As deflationary structures that form by the winnowing of small grains, these features require relatively long periods to form. The presence of multiple orientations indicates that, once formed, multiple episodes of vigorous winds may be required to change markedly the orientations of these features. (c) Requiring probably the longest formation times are tails of protected rock downwind of hematite spherules embedded in

  13. Have the northwest Negev dunefield sands reddened since their deposition?

    NASA Astrophysics Data System (ADS)

    Roskin, Joel; Tsoar, Haim; Blumberg, Dan G.; Porat, Naomi; Rozensten, Ofer

    2010-05-01

    Sand grain coating redness has been extensively both in coastal and inland desert dunes. In Israel, sand redness has been quantified by calculating a spectral redness index (RI) using single RGB bands (RI= R2/(B*G3)) from reflectance spectroscopy. The RI values have been correlated to ferric oxide mass that was dissolved from sand grain coatings (Ben Dor et al., 2006; Tsoar et al., 2008). Five main requirements have been proposed to enhance sand grain reddening: iron source from the weathering of iron-bearing minerals originating from parent rock or aeolian dust, minimum moisture content, oxidizing interstitial conditions, sediment stability and time. Thus, as many researches have suggested, when the source factors and climatic conditions are homogenous, redder sands indicate increased maturity. The northwest Negev dunefield has been classified by Tsoar et al. (2008) into 3 incursion units based upon contouring a grid of RI values for surface sand samples. The central incursion unit has been suggested to be younger due to relatively lower RI values that decrease to the east. This work tests the relationship between RI values and optically stimulated luminescence (OSL) ages of aeolian sand sampled from the near surface down to dune substrate throughout the NW Negev dunefield. Room-dried sand samples were measured in the laboratory with an ASD FieldSpec spectrometer and RI was calculated. Dune sections have been found to usually have similar RI values throughout their vertical profile despite OSL ages ranging between recent and Late Pleistocene. Along a W-E transect, RI values also tend to be similar. The central (Haluzza) part of the dunefield exhibits significantly lower RI values than RI of sands south of the Qeren Ridge. Dune base OSL ages possibly representing burial/stabilization of an initial incursion are slightly more mature in the south and may be evidence of the earliest dune incursion into the Negev. Thus the increased redness may be attributed to an

  14. Effects of biological soil crust development on the hydrological behavior of vegetation-stabilized sand dunes in arid desert ecosystems of NW China

    NASA Astrophysics Data System (ADS)

    Coppola, Antonio; Wang, Xinping; Pan, Yan-xia; Basile, Angelo; Comegna, Alessandro

    2014-05-01

    Approximately 24.5% of the Chinese area locates in arid and semi-arid area in northwest China, which has been severely affected by desertification. An experiment to evaluate the effects of dunes fixation by vegetation was carried out at Shapotou in Ningxia Hui Autonomous Region at the southeast edge of the Tengger Desert using xerophyte shrubs (Caragana korshinskii, Hedysarum scoparium and Artemisia ordosica) planted in straw checkerboard plots initiated in 1956. The artificially stabilized shrub-covered dunes have strongly enhanced the formation of biotic crusts. Knowing if and how local hydrological processes are altered by desert ecosystems restoration is basic to create vegetation-protective systems that control or cease migration of sand dunes. Accordingly, the main objective of this work was to evaluate the time dynamics of the hydraulic properties and surface infiltration behavior with the general soil formation processes. We compared the soil physical and hydraulic properties, along with infiltration characteristics of soils of vegetated and un-vegetated sand dunes. Finally, by numerically simulating water flow processes naturally occurring in the area, we investigated if the changes in the surface infiltration behavior, local by nature, have consequences on the fluxes deeper in the soil profile Key words: Microbiotic crusts, Hydraulic properties, Sand dune migration, Tension infiltrometer method, Numerical simulations

  15. Computational modeling of dissipation and regeneration of fluvial sand dunes under variable discharges

    NASA Astrophysics Data System (ADS)

    Nabi, M.; Kimura, I.; Hsu, S. M.; Giri, S.; Shimizu, Y.

    2015-07-01

    It is observed, during flood events, that bed forms initially grow in height and make the riverbed rougher. But later, under high discharge, the bed forms grow longer with the opposite effect of making the riverbed smoother. After the discharge drops to a lower value, new bed forms regenerate on top of the elongated bed forms. This mechanism leads to a significant variation in the bed roughness and the water stage and hence determines the behavior of floods and the risk of flood disasters. This work presents detailed modeling of bed forms under discharge hydrographs and simulates the conditions under which the bed is flattened out in the upper plane bed regime. The flow was simulated by large-eddy simulation, and the sediments were considered as rigid spheres and modeled in a Lagrangian framework. The bed morphodynamics were the result of entrainment and deposition of sediment particles. We examined several discharge hydrographs. In the first case, we increased the discharge linearly and then kept it constant after reaching the upper plane bed condition. The dunes were generated and grew during the rising stage of discharge. When the flow conditions reached the upper plane bed regime, high-frequency ripples were generated and helped to flatten the bed. The results also showed that in contrast with mechanisms in the dune regime, the flattening of the bed was associated with a distinct pattern of sediment transport which deposited sediment mainly in the lee side of the dunes and led to flattening of the bed. After flattening, the sediments were mainly transported in suspension mode. As long as flow conditions stayed in the upper plane bed regime, the bed remained flat with small high-frequency ripples. We also examined two other scenarios: one with an immediate falling stage of discharge after the rising stage and the other with a period of constant discharge between the rising and falling stages. Dunes were regenerated during the falling stage of discharge for both

  16. Reestablishing Naturally Functioning Dunes on Developed Coasts.

    PubMed

    Nordstrom; Lampe; Vandemark

    2000-01-01

    / The potential for reestablishing dune habitat is investigated in municipalities in New Jersey, USA, where natural coastal landforms and biota have been eliminated or reduced in extent. Dunes are classified using width, relationship to natural and cultural features, and changes through time, and they are assessed for their value as naturally functioning landforms in developed municipalities. The relationship between size and longevity that exists under natural conditions is altered by human activity. Small dunes on privately owned lots can survive as long as larger dunes in natural areas that are located farther inland, and foredunes repaired using sand fences and earth-moving equipment can survive where they could not under natural conditions.Common beach management practices reduce the ecological values of coastal dunes. Mechanical beach cleaning eliminates incipient dunes, habitat for nesting birds, seed sources for pioneer dune colonizers and food for fauna, and artificially small, stabilized foredunes reduce the variability in microenvironments necessary for biodiversity. Recent initiatives for reducing coastal hazards, protecting nesting birds, and encouraging nature-based tourism provide incentive for the development of a restoration program for beaches and dunes that is compatible with human use. Suggested changes in management practice include restricting or rerouting pedestrian traffic, altering beach-cleaning procedures, using symbolic fences to allow for aeolian transport while preventing trampling of dunes, and eliminating or severely restricting exotic species. Landforms will be more natural in function and appearance but will be more dynamic, smaller and in a different position from those in natural areas. Research needs are specified for ecological, geomorphological, and attitudinal studies to support and inform restoration planning.

  17. Dynamics of soil organic carbon and its fractions after revegetation on sand dunes in the Tengger Desert, Northern China

    NASA Astrophysics Data System (ADS)

    Li, X.; Liu, Y.; Li, X.

    2015-12-01

    Revegetation has become increasingly important for desertified land restoration in arid and semiarid regions. Little is known about the dynamics of soil organic carbon (SOC) after the establishment of shrubland on shifting sand dunes; especially the changes in SOC fractions following planting were poorly understood. 0-10 cm soil samples were collected along chronosequence plots were to: (1) quantitatively analyze the changes of SOC and its fractions over time following the establishment of shrublands on shifting sand dunes; (2) precisely assess the relative contribution of different components to total organic carbon at different times. The results showed that revegetation can promote SOC accumulation in desert regions. SOC increased from 0.33±0.11 g kg-1 in mobile sand dunes to 5.08±0.11 g kg-1 in 57-year shrublands, while the light fraction of organic C (LF-OC) ranged from 0.05±0.02 g kg-1 to 2.96±0.24 g kg-1, the dissolved organic C (DOC) increased from 5.95±0.42 mg kg-1 to 23.63±2.79 mg kg-1 and microbial biomass C (MBC) from 6.54±1.64 mg kg-1 to 135.35±19.49 mg kg-1. Their dynamics patterns can be divided into three stages, i.e. slow increase, fast increase and slow increase stages; especially, both SOC and its fractions showed no significant changes in the first 14 years, which suggested that soil restoration is a slow process in dry environments, and therefore the maintenance of soil habitat is a crucial for land management. Our results also demonstrated that revegetation can increase the ratio of labile to stable pools in desert regions. Although, the content of HF-OC significantly increased after afforestation, but its contribution to SOC decreased from 85.15% to 41.52%, implied that more SOC stocks were stabilized in labile pools with the elapse of time, this would give rise to the risk of significant SOC losses caused by potential global warming and human-induced disturbances.

  18. Concentration and grain-size distribution of aeolian sands in peat bogs as an indicator of past storminess in coastal areas of Estonia

    NASA Astrophysics Data System (ADS)

    Vandel, Egert; Vaasma, Tiit; Tõnisson, Hannes; Sugita, Shinya; Vilumaa, Kadri; Anderson, Agnes; Terasmaa, Jaanus; Kangur, Mihkel; Pensa, Margus; Küttim, Martin; Umbleja, Liisa; Puusepp, Liisa

    2016-04-01

    Storminess in the Baltic Sea region has significantly increased over the last 50 years. As we do not have meteorological data beyond 20th century, therefore the long-term changes in storminess (e.g., frequency and magnitude of the storms) and its impact on the coastal evolution are mostly unknown. This study aims to reconstruct the extreme storm events along the coast of Estonia in late Holocene, inferred from changes in grain-size distribution and concentration of aeolian sands preserved in peat deposits. Four cores in total were collected from bogs of coastal Estonia; three from west Estonian archipelago (Hiiumaa Island and Saaremaa Island); one from the northern coast of the mainland (Juminda Peninsula). Core from Saaremaa (166 cm) covers the last 2700 years, cores from Hiiumaa (171 cm and 330 cm) cover ca 4000 years, and core from Juminda (465 cm) covers ca 8500 years. All AMS dates (77) are converted to cal yrs BP. Analyses of LOI and grain size are carried out at every centimetre in order to obtain data for mineral matter content and concentration of sand particles. The Juminda core shows a consistently low content of mineral matter (LOI < 2%) without clear peaks over the last 8000 years. The LOI results at both Hiiumaa sites show that mineral matter content gradually decreases from 4000 to 1500 cal yrs BP and then becomes the lowest in the period of 1500-1000 cal yrs BP; since then, it becomes higher (up to 10%) with fluctuations and has a clear peak around 700 cal yrs BP. At Saaremaa, the overall trend of mineral matter content is similar to that at the Hiiumaa sites: gradual decline from 2700 to 1500 cal yrs BP, lowest in 1500-1000 cal yrs BP, and relatively high over the last millennium. Concentration of mineral particles reveal clear peaks of aeolian sands at each site. At northern Hiiumaa, concentration has peaks around 3500, 3000 and 2500 cal yrs BP and is relatively high over the last 700 years. At Saaremaa, concentration has peaked at 2100, 1600 and

  19. ESTIMATING THE ECONOMIC VALUE OF NATIONAL PARKS WITH COUNT DATA MODELS USING ON-SITE, SECONDARY DATA: THE CASE OF THE GREAT SAND DUNES NATIONAL PARK AND PRESERVE

    EPA Science Inventory

    We estimate an individual travel cost model for Great Sand Dunes National Park and Preserve (GSD) in Colorado using on-site, secondary data. The purpose of the on-site survey was to help the National Park Service better understand the visitors of GSD; it was not intended for a t...

  20. Breeding system and its consequence on fruit set of a rare sand dune shrub Eremosparton songoricum (Fabaceae: Papilionoideae): implications for conservation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The breeding system and its consequence on fruit set of Eremosparton songoricum (Litv.) Vass., a rare shrubby legume occurring in moving or semi-fixed sand dunes of Central Asian deserts, were examined by manipulative experiments and observational studies in natural populations during the period of ...

  1. Possibility of star (pyramid) dune development in the area of bimodal wind regime

    NASA Astrophysics Data System (ADS)

    Biejat, K.

    2012-04-01

    Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star

  2. Deflated rims along the Xiangshui River on the Xiliaohe Plain, Northeast China: A case of active fluvial-aeolian interactions

    NASA Astrophysics Data System (ADS)

    Han, Guang; Zhang, Guifang; You, Li; Wang, Yong; Yang, Lin; Yang, Ji; Zhou, Liang; Yuan, Minghuan; Zou, Xueyong; Cheng, Hong

    2016-03-01

    Riverine source-bordering sand dunes, as a result of active fluvial-aeolian interactions, are a pronounced feature on the semiarid Xiliaohe Plain, Northeast China. By means of satellite imagery analysis, and both field survey and observation, this paper presents a new type of riverine source-bordering sand dunes - deflated rims, on the downwind margins of the Xiangshui River. They largely result from the deflation of escarpments on the downwind side of valley by local prevailing winds of NW direction, not from the reworking of point bars on floodplain by wind. In general, a rim is primarily composed of three distinct zones: 1) the upwind frontal escarpment zone with variable plan-form shape, gradient and relief, which is formed by either active lateral erosion by river or significant erosion by wind and transient slope runoff; 2) the deflation zone with gentle slopes of 8-18° and small-scale aeolian bedforms, i.e. ripples of fine sand, ridges of coarse sand; and 3) the downwind dynamic deposition zone with distinctive bedforms with variable superficial texture and slip faces. The sand mass on rims derives overwhelmingly from underlying loose late Quaternary sediments, is sufficient and sustainable by successive retreats of the escarpment, and is gradually transported downwind by pulse motions of bedforms, coupled with high wind events. Essentially, deflated rims are a starting point and the incipient phase of mature riverine dunefields. The superimposed bedforms on rims are fundamentally governed by windflow dynamics, sand sediments and antecedent bedform, exhibiting in turn the manner and intensity of rim development. Consequently, the upwind river valley and downwind deflated rim can jointly stimulate marked wave-like motion of both windflow and aeolian bedforms at different scales, especially when high wind events occur. This study sheds some light on the understanding of the origin and development of riverine source-bordering dunefields, and offers new

  3. Ground-Water Flow Direction, Water Quality, Recharge Sources, and Age, Great Sand Dunes National Monument, South-Central Colorado, 2000-2001

    USGS Publications Warehouse

    Rupert, Michael G.; Plummer, L. Niel

    2004-01-01

    Great Sand Dunes National Monument is located in south-central Colorado along the eastern edge of the San Luis Valley. The Great Sand Dunes National Monument contains the tallest sand dunes in North America; some rise up to750 feet. Important ecological features of the Great Sand Dunes National Monument are palustrine wetlands associated with interdunal ponds and depressions along the western edge of the dune field. The existence and natural maintenance of the dune field and the interdunal ponds are dependent on maintaining ground-water levels at historic elevations. To address these concerns, the U.S. Geological Survey conducted a study, in collaboration with the National Park Service, of ground-water flow direction, water quality, recharge sources, and age at the Great Sand Dunes National Monument. A shallow unconfined aquifer and a deeper confined aquifer are the two principal aquifers at the Great Sand Dunes National Monument. Ground water in the unconfined aquifer is recharged from Medano and Sand Creeks near the Sangre de Cristo Mountain front, flows underneath the main dune field, and discharges to Big and Little Spring Creeks. The percentage of calcium in ground water in the unconfined aquifer decreases and the percentage of sodium increases because of ionic exchange with clay minerals as the ground water flows underneath the dune field. It takes more than 60 years for the ground water to flow from Medano and Sand Creeks to Big and Little Spring Creeks. During this time, ground water in the upper part of the unconfined aquifer is recharged by numerous precipitation events. Evaporation of precipitation during recharge prior to reaching the water table causes enrichment in deuterium (2H) and oxygen-18 (18O) relative to waters that are not evaporated. This recharge from precipitation events causes the apparent ages determined using chlorofluorocarbons and tritium to become younger, because relatively young precipitation water is mixing with older waters

  4. Barchan Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    28 April 2004 One of the simplest forms a sand dune can take is the barchan. The term, apparently, comes from the Arabic word for crescent-shaped dunes. They form in areas with a single dominant wind direction that are also not overly-abundant in sand. The barchan dunes shown here were imaged in March 2004 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) as it passed over a crater in western Arabia Terra near 21.1oN, 17.6oW. The horns and steep slope on each dune, known as the slip face, point toward the south, indicating prevailing winds from the north (top). The picture covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.

  5. Aeolian features and processes at the Mars Pathfinder landing site

    USGS Publications Warehouse

    Greeley, Ronald; Kraft, Michael; Sullivan, Robert; Wilson, Gregory; Bridges, Nathan; Herkenhoff, Ken; Kuzmin, Ruslan O.; Malin, Michael; Ward, Wes

    1999-01-01

    The Mars Pathfinder landing site contains abundant features attributed to aeolian, or wind, processes. These include wind tails, drift deposits, duneforms of various types, ripplelike features, and ventifacts (the first clearly seen on Mars). Many of these features are consistant with formation involving sand-size particles. Although some features, such as dunes, could develop from saltating sand-size aggregates of finer grains, the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline, rather than aggregates. Excluding the ventifacts, the orientations of the wind-related features correlate well with the orientations of bright wind steaks seen on Viking Orbiter images in the general area. They also correlate with wind direction predictions from the NASA-Ames General Circulation Model (GCM) which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209°. Copyright 1999 by the American Geophysical Union.

  6. Russell Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    26 March 2004 Dark streaks made by dozens of spring and summer dust devils created a form of martian graffiti on the sand dunes of Russell Crater near 54.5oS, 347.4oW. Gullies have developed on some of the dune slopes, as well. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

  7. Dominance of an ~150-year cycle of sand-supply change in late Holocene dune-building along the eastern shore of Lake Michigan

    USGS Publications Warehouse

    Loope, W.L.; Arbogast, A.F.

    2000-01-01

    Outcrops of buried soils on lake-plains and glacial headlands along Lake Michigan's eastern shore suggest that periodic dune-building has occurred there after relatively long (≥100 yr) periods of low sand supply. We located, described, and radiocarbon dated 75 such buried soils that crop out in 32 coastal dune fields beside the lake. We assume that peaks in probability distributions of calibrated 14C ages obtained from wood, charcoal, and other organic matter from buried A horizons approximate the time of soil burial by dunes. Plotted against a late Holocene lake-level curve for Lake Michigan, these peaks are closely associated with many ∼150-yr lake highstands previously inferred from beach ridge studies. Intervening periods of lower lake levels and relative sand starvation apparently permitted forestation and soil development at the sites we studied. While late Holocene lake-level change led to development and preservation of prominent foredunes along the southern and southwestern shores of Lake Michigan, the modern dune landscape of the eastern shore is dominated by perched dunes formed during ∼150-yr lake highstands over the past 1500 yr.

  8. Laboratory Analyses Of Basaltic Dunes In The Ka'u Desert Of Hawaii And Implications For Understanding Dark Dunes On Mars

    NASA Astrophysics Data System (ADS)

    Tirsch, D.; Craddock, R. A.; Nanson, G.; Tooth, S.; Langhans, M.

    2010-12-01

    Dark dunes are the dominant aeolian bedforms on Mars and consist of ancient volcanic ashes and reworked basaltic lavas. Basaltic dunes are rare on Earth and only occur in limited areas, such Hawaii. Because the Hawaiian dunes are composed of reworked basaltic sediments transported by eolian processes, they are a promising subject matter of analogy studies. Samples of dark dune sands, ash, and tephra collected in Hawaii's Ka'u Desert were collected during field trips in summer 2009 and 2010. They were analyzed by a variety of laboratory methods, including spectral, microscope, and microprobe investigations, in order examine their detailed mineralogical composition and constitution. We then compared the results to the eolian dunes on Mars. Sand samples were collected from three different dark dunes in Ka'u Desert: a large, vegetated, parabolic dune, a falling dune, and a large climbing dune. Tephra from the phreatic eruption that began in March 2008 was collected over a two year period using sample collectors placed at different locations downwind of Kilauea caldera. Analyses of these samples allow us to determining the initial composition, grain shape, and grain size of probable source materials. The visible and near-infrared reflectance spectra of the samples were acquired for the 0.5 to 2.5µm range. The overall spectral shape of the dune sand samples indicates a mineralogical correlation between Martian and terrestrial dune sands indicating a similar volcanic origin of the sediments. The spectra of the Hawaiian samples reveal some aqueous alteration, which is probably related to hydrated amorphous silica. Initial microscope and microprobe analyses reveal a high amount of volcanic glass and rock fragments in the samples, followed by olivine, feldspars, and pyroxene. Vitric particles that dominate the majority of the dune samples indicate in situ material accumulation following larger phreatic eruptions. The top coarse-grained layer of the climbing dune comprises a

  9. Dune morphodynamics

    NASA Astrophysics Data System (ADS)

    Courrech du Pont, Sylvain

    2015-01-01

    The physics of dunes relies on the interaction between a wind flow and an erodible topography. Thus, if strong enough to transport grains, the wind shapes sandy areas into dune fields. These dunes are reminiscent of a wavy sea so that sandy deserts are called sand seas. However, the comparison stops there. Contrary to water waves, dunes propagate only under wind action and when the wind stops, they do not vanish but stand. Consequently, dunes are not only the result of the present winds, but can integrate the wind regimes over long periods. Thus, they exhibit a range of shapes and sizes with superimposed patterns. They are witnesses of past wind regimes and their shape and orientation are used to constraint climatic models on other planetary bodies where they are observed as well (e.g., Mars, Titan and Venus). Here, we discuss the morphodynamics of dunes and endeavor to identify and to explain the physical mechanisms at play in the selection of their shape, size and orientation, whilst focusing on Earth desert sand dunes.

  10. Temporal characteristics of coherent flow structures generated over alluvial sand dunes, Mississippi River, revealed by acoustic doppler current profiling and multibeam echo sounding

    USGS Publications Warehouse

    Czuba, John A.; Oberg, Kevin A.; Best, Jim L.; Parsons, Daniel R.; Simmons, S. M.; Johnson, K.K.; Malzone, C.

    2009-01-01

    This paper investigates the flow in the lee of a large sand dune located at the confluence of the Mississippi and Missouri Rivers, USA. Stationary profiles collected from an anchored boat using an acoustic Doppler current profiler (ADCP) were georeferenced with data from a real-time kinematic differential global positioning system. A multibeam echo sounder was used to map the bathymetry of the confluence and provided a morphological context for the ADCP measurements. The flow in the lee of a low-angle dune shows good correspondence with current conceptual models of flow over dunes. As expected, quadrant 2 events (upwellings of low-momentum fluid) are associated with high backscatter intensity. Turbulent events generated in the lower lee of a dune near the bed are associated with periods of vortex shedding and wake flapping. Remnant coherent structures that advect over the lower lee of the dune in the upper portion of the water column, have mostly dissipated and contribute little to turbulence intensities. The turbulent events that occupy most of the water column in the upper lee of the dune are associated with periods of wake flapping.

  11. The developmental trend and influencing factors of aeolian desertification in the Zoige Basin, eastern Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    Hu, Guangyin; Dong, Zhibao; Lu, Junfeng; Yan, Changzhen

    2015-12-01

    The Zoige Basin is located in the northeastern region of the Qinghai-Tibet Plateau and covers an area of 19,400 km2. At a mean altitude of 3500 m, the basin is highly sensitive to global environmental change and human disturbance due to its high elevation and fragile cold environment. The process of aeolian desertification in the basin can be clearly recognized in Landsat images that show the development of sand sheets and dunes over time. To monitor the spatial and temporal changes of aeolian desertification in the Zoige Basin, we analyzed Landsat images recorded in 1975, 1990, 2000, 2005, and 2010. Results showed that aeolian desertification increased rapidly from 1975 to 1990, was stable from 1990 to 2000, decreased slightly from 2000 to 2005, and decreased sharply from 2005 to 2010. Increasing temperature, overgrazing, rodent damage, and drainage of wetlands were considered the key driving factors of the expansion of aeolian desertification. A number of political measures were initiated in the 1990s to slow desertification, but the countermeasures of grazing prohibition, enclosures, and paving straw checkerboard barriers were not implemented until around 2005. These measures resulted in a dramatic recovery of aeolian desertified land between 2005 and 2010. Based on the cause analysis, anthropogenic factors were identified as the dominant driving force for both development and recovery of aeolian desertified land.

  12. Caterpillar Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    28 June 2004 Looking somewhat like caterpillars, this April 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows some of the rounded, wind-eroded sand dune features in a crater in the southern hemisphere near 61.7oS, 160.3oW. For such rounding to occur, the dune sand might need to be somewhat cemented. The picture covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  13. Initial insights into the age and origin of the Kubuqi sand sea of northern China

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoping; Forman, Steven; Hu, Fangen; Zhang, Deguo; Liu, Ziting; Li, Hongwei

    2016-04-01

    The Kubuqi Desert is the only active sand sea in the semiarid regions of northern China and occurs along the southern margin of the Yellow River. Little is known about the age and origin of this large (17,000 km2) sand sea with a present annual precipitation of 200-480 mm. Sand drift potentials indicated net capable winds for aeolian transport are from the northwest, though winds are stronger to north beyond the dune field than within the sand sea. Geomorphic and stratigraphic observations indicate that Holocene aeolian sand often drapes over bedrock and river terraces as a palimpsest landscape. Field investigations identified four stratigraphic sections with multiple aeolian sand units and palaeosols, with age control by optically stimulated luminescence (OSL) dating of quartz grains. Palaeosols are weakly developed, mostly accumulative A horizon with organic carbon content < 1% and reflect sand sheet deposition possibly in a steppe environment. Although sediments near river channels or former lakes might give old ages, the initial formation and age of the Kubuqi sand sea should be judged from the occurrence of the sandy palimpsest of the landscape that is OSL dated to the Holocene in general. The latest period of aeolian reactivation may be related to human activity associated with grazing and farming from lost cities in the Kubuqi Desert during the Han (206 B.C. - A.D. 220) and the Tang (A.D. 608 - 907) Dynasties. Also, variable discharge of the Yellow River with local diversions for irrigation and throughout the catchment resulted in possibly an increased supply of aeolian particles for dune field expansion in the past 2 ka.

  14. Diagnosis of the heating effect on the electrical resistivity of Ouargla (Algeria) dunes sand using XRD patterns and FTIR spectra

    NASA Astrophysics Data System (ADS)

    Mechri, Mohammed Laïd; Chihi, Smaïl; Mahdadi, Naouia; Beddiaf, Samiha

    2017-01-01

    XRD patterns and FTIR spectra have shown that dunes sand of Ouargla's region, in its natural state, is formed of a high percentage of quartz, gypsum and very low percentage of kaolinite and hematite, in addition to some organic compounds. The electrical resistivity of the natural sand has been measured, it was 6 × 1014 Ω cm. Six samples of the sand were heated separately at 200, 400, 600, 800, 1000 and 1200 °C. The XRD patterns and FTIR spectra of these samples were carried out. On the other hand, the electrical resistivities of these samples have been measured. The change of the electrical resistivity with heat shows a nonlinear behavior. The heated sample of sand at 200 °C has lost some water. Most of the gypsum in the 200 °C heated sample has transformed into anhydrite, and the rest has transformed into bassanite, and its electrical resistivity has fallen down to 3.5 × 1014 Ω cm. By heating at 400 °C, the gypsum has lost all its water and it has transformed entirely to anhydrite, and its electrical resistivity became 6.75 × 1012 Ω cm, it has the lowest measured resistivity. At 600 °C and 800 °C, in addition to anhydrite, the kaolinite transformed to meta-kaolin due to the continuous breaking of OH bond and formation of water vapor, and the electrical resistivity increased to (1.5-1.9) × 1014 Ω cm. Heating at 1000 °C leads to the initiation of the interaction between anhydrite and quartz, the wollastonite appears, and the meta-kaolin transforms to aluminum-silicon and cristobalite. The wollastonite is a good electrical insulator. It raises the electrical resistivity of sand to 2.6 × 1014 Ω cm. The heating at 1200 °C makes all anhydrite to interact with quartz due to the increasing of volume of wollastonite, the anhydrite disappears completely, the quartz transforms into cristobalite. The cristobalite increases due to the dissociation of aluminium-silicon into mullite and cristobalite, as well as the transformation of quartz into cristobalite at

  15. The characteristic of aeolian environment and its impact on engineering construction in the Gurbantonggut Desert, China

    NASA Astrophysics Data System (ADS)

    Lei, Jiaqiang; Zhao, Congju

    2003-07-01

    Gurbantonggut Desert, located at the center of Jungar Basin, has an area of 48,800km2, which is the biggest immovable and semi-immovable desert in China. There is profuse oil-gas resource. Along with the oil-gas resource exploiting, more and more engineering has been built in the center of the desert, such as the desert highway and the oil fields and so on. However, aeolian environment in the Gurbantonggut Desert has a great impact on the engineering building and engineering safety. There are more than 20 gale-days per year in the center of the desert, and the main directions of the effective sand-moving winds are NE and NW, and sometimes the strong SE winds occur in the east part of the desert. The effective sand-moving winds appear mainly between April and September, which occupies 80% of whole year. It is obvious that the huge transport potential formed by the strong wind force badly endangers the engineering construction. Primary shapes of sand dunes in the desert are longitudinal and dendritic dunes, which occupy 80% of total area of the immovable and semi-immovable desert. The sand grains of the desert are coarser, and the average grain size is 0.2~0.22mm and 0.15~0.17mm in the southern and the northern part of the desert respectively. The vegetation coverage is 15~50%, and also there is about 85% of the total sand surface to be covered by the microbial crust. In this case, most dunes are fixed or semi-fixed, only on the top of the dunes existing about 30m mobile or semi-mobile sand belts. That indicates that the fixed or semi-fixed sand surfaces are dominant in desert, which prevents blown sand from doing harm to the engineering construction. Meanwhile, with the engineering construction, the fixed or semi-fixed sand surfaces are easy to be destroyed in the desert, which threatens the engineering construction and safety greatly. In general, there are about 1m thick moist sand layers in the desert and the moisture content has great changes in time and space

  16. Mineralogical and gemorphological characterization of sand dunes in the eastern part of United Arab Emirates using orbital remote sensing integrated with field investigations

    NASA Astrophysics Data System (ADS)

    Howari, F. M.; Baghdady, A.; Goodell, P. C.

    2007-01-01

    In this study, Landsat 7 ETM+ data sets were used to study the geomorphology and mineralogy of different dune types in the eastern part of Abu Dhabi in United Arab Emirates. The extraction and mapping of the dominant mineral phase of the investigated sand dunes were carried out using image processing integrated with field techniques. Band ratios 6/4 and 5/7 were very useful for mineralogical distinction of (i) high mafic content areas (ratio 5/7), and (ii) carbonate and quartz content (ratio 6/4). The results of the present study show that these dunes are classified into several main classes based on composition. The first class is low dunes composed of a mixture of quartz and carbonate, the second class is carbonate-rich, the third quartz-rich and the fourth mafic mineral-rich. Morphologically, the dunes in the investigated area belong to two main types. The first is linear and is trending NE-SW. This type shows transitional change in mineralogy from carbonate-rich components to iron oxide-rich components. This mineral gradient was observed on Landsat images as spectral variations and color tones, and was confirmed from ground truth data. The second type is star dunes and appears in images as radially symmetrical to mound shape that characterize multidirectional wind systems. The results of this study show that multispectral data can be used to differentiate between different dune types and their associated mineralogy, and to reveal information on the dynamic processes shaping dunes, such as prevailing wind directions.

  17. A complex origin for the Kelso Dunes, Mojave National Preserve, California, USA: A case study using a simple geochemical method with global applications

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Lancaster, Nicholas; Skipp, Gary L.

    2017-01-01

    The Kelso Dune field in southern California is intriguing because although it is of limited areal extent ( 100 km2), it has a wide variety of dune forms and contains many active dunes ( 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

  18. Dune Variety

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

    Our final look at the north polar erg was taken at 80 degrees North latitude during Northern summer. This image is of lower resolution than the previous images, but covers a much larger area. The dunes have very little remaining frost cover. Note the large extent of coverage, and the different dune forms.

    Image information: VIS instrument. Latitude 80.8, Longitude 184.6 East (175.4 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  19. Field Measurement of Sand Dune Bidirectional Reflectance Characteristics for Absolute Radiometric Calibration of Optical Remote Sensing Data.

    NASA Astrophysics Data System (ADS)

    Coburn, C. A.; Logie, G.; Beaver, J.; Helder, D.

    2015-12-01

    The use of Pseudo Invariant Calibration Sites (PICS) for establishing the radiometric trending of optical remote sensing systems has a long history of successful implementation. Past studies have shown that the PICS method is useful for evaluating the trend of sensors over time or cross-calibration of sensors but was not considered until recently for deriving absolute calibration. Current interest in using this approach to establish absolute radiometric calibration stems from recent research that indicates that with empirically derived models of the surface properties and careful atmospheric characterisation Top of Atmosphere (TOA) reflectance values can be predicted and used for absolute sensor radiometric calibration. Critical to the continued development of this approach is the accurate characterization of the Bidirectional Reflectance Distribution Function (BRDF) of PICS sites. This paper presents the field data collected by a high-performance portable goniometer system in order to develop a BRDF model for the Algodones Dunes in California. These BRDF data are part of a larger study that is seeking to evaluate and quantify all aspects of this dune system (from regional effects to the micro scale optical properties of the sand) in order to provide an absolute radiometric calibration PICS. This paper presents the results of a dense temporal measurement sequence (several measurements per hour with high angular resolution), to yield detailed information on the nature of the surface reflectance properties. The BRDF data were collected covering typical view geometry of space borne sensors and will be used to close the loop on the calibration to create an absolute calibration target for optical satellite absolute radiometric calibration.

  20. Observed particle sizes and fluxes of Aeolian sediment in the near surface layer during sand-dust storms in the Taklamakan Desert

    NASA Astrophysics Data System (ADS)

    Huo, Wen; He, Qing; Yang, Fan; Yang, Xinghua; Yang, Qing; Zhang, Fuyin; Mamtimin, Ali; Liu, Xinchun; Wang, Mingzhong; Zhao, Yong; Zhi, Xiefei

    2016-08-01

    Monitoring, modeling and predicting the formation and movement of dust storms across the global deserts has drawn great attention in recent decades. Nevertheless, the scarcity of real-time observations of the wind-driven emission, transport and deposition of dusts has severely impeded progress in this area. In this study, we report an observational analysis of sand-dust storm samples collected at seven vertical levels from an 80-m-high flux tower located in the hinterland of the great Taklamakan Desert for ten sand-dust storm events that occurred during 2008-2010. We analyzed the vertical distribution of sandstorm particle grain sizes and horizontal sand-dust sediment fluxes from the near surface up to 80 m high in this extremely harsh but highly representative environment. The results showed that the average sandstorm grain size was in the range of 70 to 85 μm. With the natural presence of sand dunes and valleys, the horizontal dust flux appeared to increase with height within the lower surface layer, but was almost invariant above 32 m. The average flux values varied within the range of 8 to 14 kg m-2 and the vertical distribution was dominated by the wind speed in the boundary layer. The dominant dust particle size was PM100 and below, which on average accounted for 60-80 % of the samples collected, with 0.9-2.5 % for PM0-2.5, 3.5-7.0 % for PM0-10, 5.0-14.0 % for PM0-20 and 20.0-40.0 % for PM0-50. The observations suggested that on average the sand-dust vertical flux potential is about 0.29 kg m-2 from the top of the 80 m tower to the upper planetary boundary layer and free atmosphere through the transport of particles smaller than PM20. Some of our results differed from previous measurements from other desert surfaces and laboratory wind-dust experiments, and therefore provide valuable observations to support further improvement of modeling of sandstorms across different natural environmental conditions.

  1. Carbon sequestration capacity of shifting sand dune after establishing new vegetation in the Tengger Desert, northern China.

    PubMed

    Yang, Haotian; Li, Xinrong; Wang, Zengru; Jia, Rongliang; Liu, Lichao; Chen, Yongle; Wei, Yongping; Gao, Yanhong; Li, Gang

    2014-04-15

    Reconstructing vegetation in arid and semiarid areas has become an increasingly important management strategy to realize habitat recovery, mitigate desertification and global climate change. To assess the carbon sequestration potential in areas where sand-binding vegetation has been established on shifting sand dunes by planting xeric shrubs located near the southeastern edge of the Tengger Desert in northern China, we conducted a field investigation of restored dune regions that were established at different times (20, 30, 47, and 55 years ago) in the same area. We quantified the total organic carbon (TOC) in each ecosystem by summing the individual carbon contributions from the soil (soil organic carbon; SOC), shrubs, and grasses in each system. We found that the TOC, as well as the amount of organic carbon in the soil, shrubs, and grasses, significantly increased over time in the restored areas. The average annual rate of carbon sequestration was highest in the first 20 years after restoration (3.26 × 10(-2)kg·m(-2) ·year(-1)), and reached a stable rate (2.14 × 10(-2) kg·m(-2) ·year(-1)) after 47 years. Organic carbon storage in soil represented the largest carbon pool for both restored systems and a system containing native vegetation, accounting for 67.6%-85.0% of the TOC. Carbon in grass root biomass, aboveground grass biomass, litter, aboveground shrub biomass, and shrub root biomass account for 10.0%-21.0%, 0.2%-0.6%, 0.1%-0.2%, 1.7%-12.1% and 0.9%-6.2% of the TOC, respectively. Furthermore, we found that the 55-year-old restored system has the capacity to accumulate more TOC (1.02 kg·m(-2) more) to reach the TOC level found in the natural vegetation system. These results suggest that restoring desert ecosystems may be a cost-effective and environmentally friendly way to sequester CO2 from the atmosphere and mitigate the effects of global climate change.

  2. They're Alive! Present-Day Evolution of Martian Dunes

    NASA Technical Reports Server (NTRS)

    Diniega, S.; Bridges, N.; Hansen, C.

    2011-01-01

    The sharp brinks and margins, smooth and steep lee slopes, and lack of superimposed landforms (such as small impact craters) on many Martian sand dunes suggests that these features are geologically young clean brinks and smooth/steep lee slopes (HiRISE image PSP_010413_1920; 20 deg N,79 deg E; image widthis about 500m).Within the last decade, and often primarily through the detailed inspection of high-resolution (HiRISE) images, we have finally found clear evidence that many dunes of Mars are active -- through both aeolian and seasonal (frost) processes. However, it is yet unclear if active dune formation does occur or if we are observing surficial modification of dunes which formed under different climate conditions.

  3. The contribution of micrometeorites to the iron stocks of buried podzols, developed in Late-glacial aeolian sand deposits (Brabant, The Netherlands)

    NASA Astrophysics Data System (ADS)

    van Mourik, Jan; de Vet, Sebastiaan

    2015-04-01

    The surface geology of an extensive part of NW-Europe is dominated by coversands (Late-glacial chemical poor aeolian sand deposits). The geomorphology of coversand landscapes is dominated by ridges and planes. Podzolation is the dominant soil forming process in coversands under moderate humid climatic conditions. Umbric Podzols developed on the ridges under Quercetum-mixtum, Gleyic and Histic Podzols developed in the planes under Alnetum. Even in chemical poor coversands, iron will be released by hydrolysis from iron containing silicate minerals (such as feldspars). It is well known that the vertical iron distribution in Podzols is effected by translocation of active iron from eluvial to illuvial horizons and that iron is leaching to the aquifer. Iron stocks of Podzols, in contrasts, have not been widely studied for comparison purposes of individual soil horizons or between soils. We determined the stocks of active and immobile iron in the horizons of buried xeromorphic Podzols (soils that developed without any contact with groundwater). The results show that the total amount of iron exceeds the potential amount which can be released by hydrolysis from the parent material. Furthermore, to amount of iron that leached to the groundwater is unknown. It is evident that we must find an additional source to explain the total iron stocks in buried Podzols. It is known from analysis of ice cores that the earth atmosphere is subjected to a continuous influx of (iron rich) micrometeorites. The precipitation of micrometeorites (and other aerosols) on the earth surface is concentrated in humid climatic zones with (intensive) rain fall. We analyzed minerals, extracted from the ectorganic horizon of the Initial Podzols, developed in driftsand that stabilized around 1900 AD, overlying Palaeopodzols, buried around 1200 AD. Among blown in quartz grains, we could determine also micrometeorites, embedded in the organic skeleton of the fermentation horizon of the Initial Podzol

  4. Sand dunes development of Vistula River mouth during May 2014 flood

    NASA Astrophysics Data System (ADS)

    Lisimenka, Aliaksandr; Rudowski, Stanisław; Kałas, Maciej; Szefler, Kazimierz

    2015-04-01

    The Vistula, Poland's primary river, is the largest river of the southern Baltic Sea and is one of the least regulated amongst large rivers in Europe. The Vistula has a vast delta with the main mouth in the form of an artificial cross-cut channel of about 3000 m length, 400 m width and up to 10 m depth. The comprehensive riverbed morphology in the area is characterized by the set of both 2D and 3D sandy bedforms of various orientations (Lisimenka et al., 2013). About 95% of total Vistula water, with the long-term average annual water discharge of 1081 m3/s, outflows into the Baltic Sea through this channel, which also plays a crucial role in sediment delivery processes into the Vistula External Delta, coast and neighbouring marine waters. Results of bathymetry measurements which were carried out in the main Vistula river mouth during the 23-26 May 2014 flood are presented. Echosounding records were made using boat mounted high-resolution Reson Seabat 7101 multibeam echosounder system (MBES) operating at 240 kHz. The measurements set includes data from: (1) the central part of the river channel with a wide band width for the first and last days of the experiment; (2) the riverbed elevation along axis longitudinal profile obtained on a daily basis with a twice per day registration at the final stage of the rising limb of a flood wave. During the considered period of time, extremely high magnitudes of water level and water discharge values changed from 2590 m3/s up to 4110 m3/s were observed. Estimated based on positioning system data, water flow velocity amounted to about 2 m/s and exceeded a long-term average conditions in more than two times. Based on bedform tracking tool proposed by Van der Mark and Blom (2007), the geometric variables of individual bedforms for each elevation profiles were extracted and histograms of the dune height and length were obtained. The results revealed significant changes in bedform geometry with a counterclockwise hysteresis effect as

  5. Submarine Sand Dunes on the Continental Slope in the South China Sea and Their Impact on Internal Wave Transformation and Acoustic Propagation

    DTIC Science & Technology

    2014-09-30

    South China Sea and Their Impact on Internal Wave Transformation and Acoustic Propagation Steven R. Ramp Soliton Ocean Services, Inc. 691 Country...sea floor to form and maintain the large (>16 m) sand dunes over the Chinese continental slope NE of Dongsha Island • Study how enhanced bottom...ES) Soliton Ocean Services, Inc,691 Country Club Drive,Monterey,CA,93924 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY

  6. Monte Carlo path sampling approach to modeling aeolian sediment transport

    NASA Astrophysics Data System (ADS)

    Hardin, E. J.; Mitasova, H.; Mitas, L.

    2011-12-01

    Coastal communities and vital infrastructure are subject to coastal hazards including storm surge and hurricanes. Coastal dunes offer protection by acting as natural barriers from waves and storm surge. During storms, these landforms and their protective function can erode; however, they can also erode even in the absence of storms due to daily wind and waves. Costly and often controversial beach nourishment and coastal construction projects are common erosion mitigation practices. With a more complete understanding of coastal morphology, the efficacy and consequences of anthropogenic activities could be better predicted. Currently, the research on coastal landscape evolution is focused on waves and storm surge, while only limited effort is devoted to understanding aeolian forces. Aeolian transport occurs when the wind supplies a shear stress that exceeds a critical value, consequently ejecting sand grains into the air. If the grains are too heavy to be suspended, they fall back to the grain bed where the collision ejects more grains. This is called saltation and is the salient process by which sand mass is transported. The shear stress required to dislodge grains is related to turbulent air speed. Subsequently, as sand mass is injected into the air, the wind loses speed along with its ability to eject more grains. In this way, the flux of saltating grains is itself influenced by the flux of saltating grains and aeolian transport becomes nonlinear. Aeolian sediment transport is difficult to study experimentally for reasons arising from the orders of magnitude difference between grain size and dune size. It is difficult to study theoretically because aeolian transport is highly nonlinear especially over complex landscapes. Current computational approaches have limitations as well; single grain models are mathematically simple but are computationally intractable even with modern computing power whereas cellular automota-based approaches are computationally efficient

  7. The Carolina Sandhills: Quaternary eolian sand sheets and dunes along the updip margin of the Atlantic Coastal Plain province, southeastern United States

    USGS Publications Warehouse

    Swezey, Christopher; Fitzwater, Bradley A.; Whittecar, G. Richard; Mahan, Shannon; Garrity, Christopher P.; Aleman Gonzalez, Wilma B.; Dobbs, Kerby M.

    2016-01-01

    The Carolina Sandhills is a physiographic region of the Atlantic Coastal Plain province in the southeastern United States. In Chesterfield County (South Carolina), the surficial sand of this region is the Pinehurst Formation, which is interpreted as eolian sand derived from the underlying Cretaceous Middendorf Formation. This sand has yielded three clusters of optically stimulated luminescence ages: (1) 75 to 37 thousand years ago (ka), coincident with growth of the Laurentide Ice Sheet; (2) 28 to 18 ka, coincident with the last glacial maximum (LGM); and (3) 12 to 6 ka, mostly coincident with the Younger Dryas through final collapse of the Laurentide Ice Sheet. Relict dune morphologies are consistent with winds from the west or northwest, coincident with modern and inferred LGM January wind directions. Sand sheets are more common than dunes because of effects of coarse grain size (mean range: 0.35–0.59 mm) and vegetation. The coarse grain size would have required LGM wind velocities of at least 4–6 m/sec, accounting for effects of colder air temperatures on eolian sand transport. The eolian interpretation of the Carolina Sandhills is consistent with other evidence for eolian activity in the southeastern United States during the last glaciation.

  8. Investigation of water quality in the Great Sand Dunes National Monument and Preserve, Saguache County, Colorado, February 1999 through September 2000: Qualifying for outstanding waters designation

    USGS Publications Warehouse

    Ferguson, Sheryl A.

    2003-01-01

    Great Sand Dunes National Monument and Preserve is located on the eastern side of the San Luis Valley in south-central Colorado. The monument covers 60.4 square miles in Saguache and Alamosa Counties and lies at the base of the Sangre de Cristo Mountains, where a unique combination of climate, topography, and hydrology has created and maintained the Nation?s tallest inland sand dunes. The Sangre de Cristo Mountains, which rise to more than 14,000 feet to the north and east of the dunes, are the source of several streams that flow around the dunes and eventually recharge the aquifer beneath the valley. Sand Creek and Medano Creeks are the largest of the streams in the monument that originate in the Sangre de Cristo Mountains; several ephemeral streams flow into Sand Creek and Medano Creek. Maintaining the high surface-water quality in the Great Sand Dunes National Monument and Preserve is identified as a critical issue by the National Park Service. Additionally, the National Park Service has indicated a desire to pursue an Outstanding Waters Designation, which offers the highest level of water-quality protection available under the Clean Water Act and Colorado regulations. This designation is designed to prevent any degradation from existing conditions (Chatman and others, 1997). Assessment is needed to evaluate whether the water quality of the streams in the monument meets the requirements for an Outstanding Waters Designation. Historically, prospecting and mining activities have occurred in the watersheds of Sand and Medano Creeks; currently, however, there is no mining activity in those watersheds. In addition, the camping and recreation that occur upstream from the monument on national preserve lands and water activities that occur in Medano Creek during the summer are a potential source of human-waste contamination. Figure 1. Location of study area, sampling sites, and indication of sites that meet or exceed instream standards. The U.S. Geological Survey (USGS

  9. Downslope coarsening in aeolian grainflows of the Navajo Sandstone

    NASA Astrophysics Data System (ADS)

    Loope, David B.; Elder, James F.; Sweeney, Mark R.

    2012-07-01

    Downslope coarsening in grainflows has been observed on present-day dunes and generated in labs, but few previous studies have examined vertical sorting in ancient aeolian grainflows. We studied the grainflow strata of the Jurassic Navajo Sandstone in the southern Utah portion of its outcrop belt from Zion National Park (west) to Coyote Buttes and The Dive (east). At each study site, thick sets of grainflow-dominated cross-strata that were deposited by large transverse dunes comprise the bulk of the Navajo Sandstone. We studied three stratigraphic columns, one per site, composed almost exclusively of aeolian cross-strata. For each column, samples were obtained from one grainflow stratum in each consecutive set of the column, for a total of 139 samples from thirty-two sets of cross-strata. To investigate grading perpendicular to bedding within individual grainflows, we collected fourteen samples from four superimposed grainflow strata at The Dive. Samples were analyzed with a Malvern Mastersizer 2000 laser diffraction particle analyser. The median grain size of grainflow samples ranges from fine sand (164 μm) to coarse sand (617 μm). Using Folk and Ward criteria, samples are well-sorted to moderately-well-sorted. All but one of the twenty-eight sets showed at least slight downslope coarsening, but in general, downslope coarsening was not as well-developed or as consistent as that reported in laboratory subaqueous grainflows. Because coarse sand should be quickly sequestered within preserved cross-strata when bedforms climb, grain-size studies may help to test hypotheses for the stacking of sets of cross-strata.

  10. Examining the Relationship Between Suspended Sand Load and Bedload on the Colorado River Using Concurrent Measurements of Suspended Sand and Observations of Sand Dune Migration.

    NASA Astrophysics Data System (ADS)

    Ashley, T.; McElroy, B. J.; Buscombe, D.; Grams, P. E.; Kaplinski, M. A.

    2015-12-01

    Spatial variability in sediment flux is directly related to geomorphic change. Along the Colorado River, measurements of sediment flux are used to track changes in sediment storage and time the release of controlled floods aimed at building eroded sandbars. The very high uncertainty typical of measurements of sediment flux has been reduced by a program of continuous measurement of suspended-sediment concentration by acoustic surrogates. However, there is still significant uncertainty in calculations of total flux. A large fraction of that uncertainty may be caused by overly simplified treatment of bedload flux, which is currently estimated as a constant 5% of the suspended sand flux. That constant is based on estimates of bedform migration rate made with side-scan sonar. Here, we apply theory which relates bedform migration and streamwise sediment flux, to bathymetric data collected at unprecedented temporal and spatial resolution adjacent to the USGS sediment monitoring station above Diamond Creek (362 km downstream from Lees Ferry, AZ). Quantitative time series measurements of reach averaged bedform transport are calculated and compared to fluxes estimated by expressing bedload as a constant fraction of suspended load. Over the range of discharges expected during normal dam operations, bedload transport estimated from the migration of bedforms in the study reach is at least 20% of instantaneous suspended sand load measured at the gage. While bedload appears to be controlled primarily by discharge (and therefore transport capacity of the flow), suspended sand load varies inversely with the grain size of suspended material, suggesting dependence on sediment supply. Sediment transport capacity can vary significantly at a given discharge depending on local hydraulic geometry, so it is likely that there is more spatial variability in bedload transport than suspended sand transport.

  11. Global map of Titan's dune fields

    NASA Astrophysics Data System (ADS)

    Le Corre, L.; Le Mouélic, S.; Sotin, C.; Barnes, J. W.; Brown, R. H.; Baines, K.; Buratti, B.; Clark, R.; Nicholson, P.

    2008-09-01

    small dunes in low sand supply zones. Most of the aeolian sand deposits are found in sand seas. In addition, isolated groups of "cat scratches", very sinuous short dunes [9] and sand sheets [10] (visible as dark uniform terrains) are recognized. Their emplacement is most probably related to the available sand supply. Comparison of infrared and SAR units Sand seas and small dunes match different kind of terrains in the infrared. Radar dune fields boundaries in the infrared. The dune fields in SAR images generally end at the limit between infrared brown and bright units (Fig. 1b and 1c). Dunes can also be found on dark blue terrains as seen by [7] and [11]. 82% of SAR dunes are located in brown units and 4.5% in dark blue units. The remnant dunes corresponding to "cat scratches" or not well defined dune fields appear in infrared bright units as isolated patches. These dunes may form with a low sand supply, thus VIMS detects a bright terrain because of the lower resolution than SAR. It could account for some of the 13.5% radar dunes found on bright areas. It should be noted that the limit between SAR dunes and brown units is sometimes shifted by about 20 km. This could be due to the obliquity and spin rate of Titan, which are not taken into account in our georeferenced images [12]. An accurate model of Titan obliquity and spin rate would be needed to correct this effect. But yet, there is a significant overlapping between VIMS brown units and dunes seen with the RADAR at global scale. The relationship seems to be more complex for the dark blue terrains, since dunes overlap this unit or are stopped at the border. Dark blue units may correspond to an aeolian deposit younger than the dunes [6]. By using a mean height of 150 m for the dunes [3, 10] and an average thickness of 20 m [3], we find a total amount of dune material in the brown units of 3.01 105 km3. This is consistent with the estimation from [3]. Conclusion From the global mapping, we inferred that dunes in the

  12. Abrupt sand-dune accumulation at the northeastern margin of the Tibetan Plateau challenges the wet MIS3a inferred from numerous lake-highstands.

    PubMed

    Long, Hao; Fuchs, Markus; Yang, Linhai; Cheng, Hongyi

    2016-05-13

    Over the Tibetan Plateau and adjacent regions, numerous (14)C-based lake records revealed a ubiquitous wet climatic period during 40-25 ka (late MIS 3), which is in contradiction with the global pattern of generally cold and dry climates. This paper focuses on OSL dating results of a large set of sand dunes and alluvial sediments (50 OSL ages) from the Qinwangchuan (QWC) Basin at the northeast edge of the Tibetan Plateau, with the aim to test the validity of the anomalous wet condition for the late MIS 3 interval, evidenced by numerous lake highstands. The abrupt sand dune accumulation as indication of increased aridity in the study area was OSL dated to ~40-13 ka. This dry climatic inference of the sand dune system from QWC apparently shows no wet MIS 3a event. Thus, the anomalous wet conditions revealed by high lake levels for the late MIS 3 phase may not be a universal phenomena across entire western China.

  13. Abrupt sand-dune accumulation at the northeastern margin of the Tibetan Plateau challenges the wet MIS3a inferred from numerous lake-highstands

    PubMed Central

    Long, Hao; Fuchs, Markus; Yang, Linhai; Cheng, Hongyi

    2016-01-01

    Over the Tibetan Plateau and adjacent regions, numerous 14C-based lake records revealed a ubiquitous wet climatic period during 40–25 ka (late MIS 3), which is in contradiction with the global pattern of generally cold and dry climates. This paper focuses on OSL dating results of a large set of sand dunes and alluvial sediments (50 OSL ages) from the Qinwangchuan (QWC) Basin at the northeast edge of the Tibetan Plateau, with the aim to test the validity of the anomalous wet condition for the late MIS 3 interval, evidenced by numerous lake highstands. The abrupt sand dune accumulation as indication of increased aridity in the study area was OSL dated to ~40–13 ka. This dry climatic inference of the sand dune system from QWC apparently shows no wet MIS 3a event. Thus, the anomalous wet conditions revealed by high lake levels for the late MIS 3 phase may not be a universal phenomena across entire western China. PMID:27172907

  14. Bunge Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    21 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows low albedo (dark), windblown sand dunes on the floor of Bunge Crater, located near 33.8oS, 48.9oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

  15. Spring Dunes

    NASA Technical Reports Server (NTRS)

    2006-01-01

    22 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dunes in the north polar region of Mars. In this scene, the dunes, and the plain on which the dunes reside, are at least in part covered by a bright carbon dioxide frost. Dark spots indicate areas where the frost has begun to change, either by subliming away to expose dark sand, changing to a coarser particle size, or both. The winds responsible for the formation of these dunes blew from the lower left (southwest) toward the upper right (northeast).

    Location near: 76.3oN, 261.2oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Spring

  16. Arkhangelsky Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    29 April 2004 These dark-toned barchan sand dunes in Arkhangelsky Crater were viewed by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in late southern summer on 17 February 2004. Hundreds of narrow, dark streaks crisscross the dunes and the interdune terrain; these were most likely formed by the disruption of fine sediment by passing dust devils. The dune field is located near 41.2oS, 25.0oW, and is illuminated by sunlight from the upper left. Dune horns and slip faces indicate that the dominant winds blow from the southwest (lower left). The picture covers an area about 3 km (1.9 mi) across.

  17. Population dynamics of Agriophyllum squarrosum, a pioneer annual plant endemic to mobile sand dunes, in response to global climate change.

    PubMed

    Qian, Chaoju; Yin, Hengxia; Shi, Yong; Zhao, Jiecai; Yin, Chengliang; Luo, Wanyin; Dong, Zhibao; Chen, Guoxiong; Yan, Xia; Wang, Xiao-Ru; Ma, Xiao-Fei

    2016-05-23

    Climate change plays an important role in the transition of ecosystems. Stratigraphic investigations have suggested that the Asian interior experienced frequent transitions between grassland and desert ecosystems as a consequence of global climate change. Using maternally and bi-parentally inherited markers, we investigated the population dynamics of Agriophyllum squarrosum (Chenopodiaceae), an annual pioneer plant endemic to mobile sand dunes. Phylogeographic analysis revealed that A. squarrosum could originate from Gurbantunggut desert since ~1.6 Ma, and subsequently underwent three waves of colonisation into other deserts and sandy lands corresponding to several glaciations. The rapid population expansion and distribution range shifts of A. squarrosum from monsoonal climate zones suggested that the development of the monsoonal climate significantly enhanced the population growth and gene flow of A. squarrosum. These data also suggested that desertification of the fragile grassland ecosystems in the Qinghai-Tibetan Plateau was more ancient than previously suggested and will be aggravated under global warming in the future. This study provides new molecular phylogeographic insights into how pioneer annual plant species in desert ecosystems respond to global climate change, and facilitates evaluation of the ecological potential and genetic resources of future crops for non-arable dry lands to mitigate climate change.

  18. Diet of the lizard Liolaemus occipitalis in the coastal sand dunes of southern Brazil (Squamata-Liolaemidae).

    PubMed

    Verrastro, L; Ely, I

    2015-05-01

    Knowledge of a species' diet provides important information on adaptation and the relationship between the organism and its environment. The genus Liolaemus occurs in the southern region of South America and is an excellent model to investigate the adaptive processes of vertebrate ecology in ecosystems of this region of the world. Liolaemus occipitalis is an endangered species that inhabits the coastal sand dunes of southern Brazil. This species is the most abundant vertebrate in this environment, and it presents unique adaptation characteristics to the restinga environment. The present study analyzed this lizard's diet to verify similarities or differences between this species and other species of the same genus. Specimens were collected monthly from January 1996 to December 1997. The number of items, frequency of occurrence and volume of each prey taxon were determined. Arthropods were identified to the order level, and plant material was identified as flower, fruit, seed and leaves. Variations in the diet of males and females, adults and juveniles and seasons were also analyzed. The data indicate that Liolaemus occipitalis is a generalist, "sit-and-wait" or ambush predator as well as omnivorous, feeding on both arthropods and plant material. Significant ontogenetic differences were verified. Juveniles are more carnivorous, and the intake of plant material increases with size and age. Seasonal differences in diet composition were also observed. In the spring, arthropod and plant materials were more diversified and, therefore, consumed more often.

  19. Temporal dynamics of sand dune bidirectional reflectance characteristics for absolute radiometric calibration of optical remote sensing data

    NASA Astrophysics Data System (ADS)

    Coburn, Craig A.; Logie, Gordon; Beaver, Jason

    2016-09-01

    The use of Pseudo Invariant Calibration Sites (PICS) for establishing the radiometric trending of optical remote sensing systems has a long history of successful implementation. Past studies have shown that the PICS method is useful for evaluating the trend of sensors over time or cross-calibration of sensors but was not considered until recently for deriving absolute calibration. Current interest in using this approach to establish absolute radiometric calibration stems from recent research that indicates that with empirically derived models of the surface properties and careful atmospheric characterisation Top of Atmosphere (TOA) reflectance values can be predicted and used for absolute sensor radiometric calibration. Critical to the continued development of this approach is the accurate characterization of the Bidirectional Reflectance Distribution Function (BRDF) of PICS sites. This paper presents BRDF data collected by a high-performance portable goniometer system in order to develop a temporal BRDF model for the Algodones Dunes in California. The results demonstrated that the BRDF of a reasonably simple sand surface was complex with changes in anisotropy taking place in response to changing solar zenith angles. The nature of these complex interactions would present challenges to future model development.

  20. Yeasts and coliform bacteria of water accumulated in bromeliads of mangrove and sand dune ecosystems of southeast Brazil.

    PubMed

    Hagler, A N; Rosa, C A; Morais, P B; Mendonça-Hagler, L C; Franco, G M; Araujo, F V; Soares, C A

    1993-10-01

    Yeasts and coliform bacteria were isolated from water that accumulated in the central cups and adjacent leaf axilae of two bromeliads, Neoregelia cruenta of a coastal sand dune and Quesnelia quesneliana of a mangrove ecosystem near the city of Rio de Janeiro, Brazil. The mean total coliform counts were above 10,000 per 100 mL for waters of both plants, but the mean fecal coliform counts were only 74 per 100 mL for Q. quesneliana and mostly undetected in water from N. cruenta. Of 90 fecal coliform isolates, 51 were typical of Escherichia coli in colony morphology and indol, methyl red, Volges-Proskauer, and citrate (IMViC) tests. Seven representatives of the typical E. coli cultures were identified as this species, but the identifications of nine other coliform bacteria were mostly dubious. The yeast community of N. cruenta was typical of plant surfaces with basidiomycetous yeasts anamorphs, and the black yeast Aureobasidium pullulans was prevalent. Quesnelia quesneliana had a substantial proportion of ascomycetous yeasts and their anamorphs, including a probable new biotype of Saccharomyces unisporus. Our results suggested that the microbial communities in bromeliad waters are typically autochtonous and not contaminants.

  1. Degradation of seed mucilage by soil microflora promotes early seedling growth of a desert sand dune plant.

    PubMed

    Yang, Xuejun; Baskin, Carol C; Baskin, Jerry M; Zhang, Wenhao; Huang, Zhenying

    2012-05-01

    In contrast to the extensive understanding of seed mucilage biosynthesis, much less is known about how mucilage is biodegraded and what role it plays in the soil where seeds germinate. We studied seed mucilage biodegradation by a natural microbial community. High-performance anion-exchange chromatography (HPAEC) was used to determine monosaccharide composition in achene mucilage of Artemisia sphaerocephala. Mucilage degradation by the soil microbial community from natural habitats was examined by monosaccharide utilization tests using Biolog plates, chemical assays and phospholipid fatty acid (PLFA) analysis. Glucose (29.4%), mannose (20.3%) and arabinose (19.5%) were found to be the main components of achene mucilage. The mucilage was biodegraded to CO(2) and soluble sugars, and an increase in soil microbial biomass was observed during biodegradation. Fluorescence microscopy showed the presence of mucilage (or its derivatives) in seedling tissues after growth with fluorescein isothiocyanate (FITC)-labelled mucilage. The biodegradation also promoted early seedling growth in barren sand dunes, which was associated with a large soil microbial community that supplies substances promoting seedling establishment. We conclude that biodegradation of seed mucilage can play an ecologically important role in the life cycles of plants especially in harsh desert environments to which A. sphaerocephala is well-adapted.

  2. Population dynamics of Agriophyllum squarrosum, a pioneer annual plant endemic to mobile sand dunes, in response to global climate change

    PubMed Central

    Qian, Chaoju; Yin, Hengxia; Shi, Yong; Zhao, Jiecai; Yin, Chengliang; Luo, Wanyin; Dong, Zhibao; Chen, Guoxiong; Yan, Xia; Wang, Xiao-Ru; Ma, Xiao-Fei

    2016-01-01

    Climate change plays an important role in the transition of ecosystems. Stratigraphic investigations have suggested that the Asian interior experienced frequent transitions between grassland and desert ecosystems as a consequence of global climate change. Using maternally and bi-parentally inherited markers, we investigated the population dynamics of Agriophyllum squarrosum (Chenopodiaceae), an annual pioneer plant endemic to mobile sand dunes. Phylogeographic analysis revealed that A. squarrosum could originate from Gurbantunggut desert since ~1.6 Ma, and subsequently underwent three waves of colonisation into other deserts and sandy lands corresponding to several glaciations. The rapid population expansion and distribution range shifts of A. squarrosum from monsoonal climate zones suggested that the development of the monsoonal climate significantly enhanced the population growth and gene flow of A. squarrosum. These data also suggested that desertification of the fragile grassland ecosystems in the Qinghai-Tibetan Plateau was more ancient than previously suggested and will be aggravated under global warming in the future. This study provides new molecular phylogeographic insights into how pioneer annual plant species in desert ecosystems respond to global climate change, and facilitates evaluation of the ecological potential and genetic resources of future crops for non-arable dry lands to mitigate climate change. PMID:27210568

  3. An Assessment of Spontaneous Vegetation Recovery in Aggregate Quarries in Coastal Sand Dunes in Buenos Aires Province, Argentina

    NASA Astrophysics Data System (ADS)

    Fernández Montoni, María Victoria; Fernández Honaine, Mariana; del Río, Julio Luis

    2014-08-01

    Sand dune quarries are a location of common aggregate mining activity developed in coastal areas, especially in the southeast Buenos Aires province, Argentina. In this article, spontaneous plant development after extraction activity ceased was evaluated. Five areas (three quarried and two natural/conservation areas) were sampled for plant cover and composition as well as sediment characterization. Different indexes, principal component analysis, and cluster analyses were applied to compare the areas. The dominant families observed in four of the five areas were Asteraceae, Poaceae, and Cyperaceae, and most of the species are commonly found in sandy and humid soils and/or modified/anthropized ones. Percentages of plant cover increased with time because of the cessation of active aggregate extraction. Indexes and multivariate analyses showed that it was possible to distinguish quarried and natural areas based on composition and vegetation cover. The distribution of plant species among the four areas responded to the presence of mining activity, but it also responded to the topographical position and consequently the depth of the groundwater level. Besides these differences, the four areas shared many native species. The results might indicate that once the activity has ceased, quarried areas may spontaneously and quickly develop a plant community with some similarities to those present in the nonquarried areas. However, given that the extracting activity involves the removal of the soil, revegetation of this type of environment depends on the presence of natural areas in the surroundings, which can serve as a source of seeds and propagules for plant regeneration.

  4. Sand transport on Mars: Preliminary results from models

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Anderson, F. S.; Blumberg, D.; Lo, E.; Xu, P.; Pollack, J.

    1993-01-01

    Most studies of active aeolian processes on Mars have focused on dust, i.e., particles approximately 1 micron in diameter that are transported in suspension by wind. The presence of sand dunes on Mars indicates that larger grains (approximately greater than 60 microns, transported primarily in saltation) are also present. Although indirect evidence suggests that some dunes may be active, definitive evidence is lacking. Nonetheless, numerous studies demonstrate that sand is substantially easier to transport by wind than dust, and it is reasonable to infer that sand transportation in saltation occurs under present Martian conditions. In order to assess potential source regions, transportation pathways, and sites of deposition for sand on Mars, an iterative sand transport algorithm was developed that is based on the Mars General Circulation Model of Pollack et al. The results of the dust transport model are then compared with observed surface features, such as dune field locations observed on images, and surficial deposits as inferred from Viking IRTM observations. Preliminary results suggest that the north polar dune fields in the vicinity of 270 degrees W, 70 degrees N originated from weathered polar layered plains centered at 280 degrees W, 85 degrees N, and that Thaumasia Fossae, southern Hellas Planitia, and the area west of Hellespontus Montes are sand depositional sites. Examples of transportation 'corridors' include a westward pathway in the latitudinal band 35 degrees N to 45 degrees N, and a pathway southward from Solis Planum to Thaumasia Fossae, among others.

  5. XRD and mineralogical analysis of gypsum dunes at White Sands National Monument, New Mexico and applications to gypsum detection on Mars

    NASA Astrophysics Data System (ADS)

    Lafuente, B.; Bishop, J. L.; Fenton, L. K.; King, S. J.; Blake, D.; Sarrazin, P.; Downs, R.; Horgan, B. H.

    2013-12-01

    A field portable X-ray Diffraction (XRD) instrument was used at White Sands National Monument to perform in-situ measurements followed by laboratory analyses of the gypsum-rich dunes and to determine its modal mineralogy. The field instrument is a Terra XRD (Olympus NDT) based on the technology of the CheMin (Chemistry and Mineralogy) instrument onboard the Mars Science Laboratory (MSL) rover Curiosity which is providing the mineralogical and chemical composition of scooped soil samples and drilled rock powders collected at Gale Crater [1]. Using Terra at White Sands will contribute to 'ground truth' for gypsum-bearing environments on Mars. Together with data provided by VNIR spectra [2], this study clarifies our understanding of the origin and history of gypsum-rich sand dunes discovered near the northern polar region of Mars [3]. The results obtained from the field analyses performed by XRD and VNIR spectroscopy in four dunes at White Sands revealed the presence of quartz and dolomite. Their relative abundance has been estimated using the Reference Intensity Ratio (RIR) method. For this study, particulate samples of pure natural gypsum, quartz and dolomite were used to prepare calibration mixtures of gypsum-quartz and gypsum-dolomite with the 90-150μm size fractions. All single phases and mixtures were analyzed by XRD and RIR factors were calculated. Using this method, the relative abundance of quartz and dolomite has been estimated from the data collected in the field. Quartz appears to be present in low amounts (2-5 wt.%) while dolomite is present at percentages up to 80 wt.%. Samples from four dunes were collected and prepared for subsequent XRD analysis in the lab to estimate their composition and illustrate the changes in mineralogy with respect to location and grain size. Gypsum-dolomite mixtures: The dolomite XRD pattern is dominated by an intense diffraction peak at 2θ≈36 deg. which overlaps a peak of gypsum, This makes low concentrations of dolomite

  6. Constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast

    NASA Astrophysics Data System (ADS)

    Kaplan, Kayla L.; Nordstrom, Karl F.; Jackson, Nancy L.

    2016-10-01

    Landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them. This field study evaluates how buildings and sand-trapping fences change the direction of wind approach, reduce wind speed, and restrict fetch distances for sediment entrainment, thereby reducing the potential for aeolian transport and development of dunes in enclaves. Field data were gathered in an 80 m long, 44 m deep beach enclave on the ocean shoreline of New Jersey, USA. Comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses, increasing the relative importance of longshore winds. Vertical arrays of anemometers on the foredune crest, foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore, with strongest winds on the berm crest. Vertical cylindrical traps on the foredune crest, foredune toe, mid-backshore, berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest. Sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes. Strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes. The length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth. The landward edge of the enclave (defined by a sand fence near the dune toe) is sheltered along its entire length from winds blowing at an angle to the shoreline of 25° or less. A foredune set back this distance in an enclave the length of an individual lot (about 20 m) would be sheltered at an angle of 57° or less, reducing the opportunity for dune building by onshore winds

  7. Environmental Controls and Eco-geomorphic Interactions of the Barchan-to-parabolic Dune Stabilisation and the Parabolic-to-barchan Dune Reactivation

    NASA Astrophysics Data System (ADS)

    Yan, Na; Baas, Andreas

    2015-04-01

    Parabolic dunes are one of a few common aeolian landforms which are highly controlled by eco-geomorphic interactions. Parabolic dunes, on the one hand, can be developed from highly mobile dune landforms, barchans for instance, in an ameliorated vegetation condition; or on the other hand, they can be reactivated and transformed back into mobile dunes due to vegetation deterioration. The fundamental mechanisms and eco-geomorphic interactions controlling both dune transformations remain poorly understood. To bridge the gap between complex processes involved in dune transformations on a relatively long temporal scale and real world monitoring records on a very limited temporal scale, this research has extended the DECAL model to incorporate 'dynamic' growth functions and the different 'growth' of perennial shrubs between growing and non-growing seasons, informed by field measurements and remote sensing analysis, to explore environmental controls and eco-geomorphic interactions of both types of dune transformation. A non-dimensional 'dune stabilising index' is proposed to capture the interactions between environmental controls (i.e. the capabilities of vegetation to withstand wind erosion and sand burial, the sandy substratum thickness, the height of the initial dune, and the sand transport potential), and establish the linkage between these controls and the geometry of a stabilising dune. An example demonstrates how to use the power-law relationship between the dune stabilising index and the normalised migration distance to assist in extrapolating the historical trajectories of transforming dunes. The modelling results also show that a slight increase in vegetation cover of an initial parabolic dune can significantly increase the reactivation threshold of climatic impact (both drought stress and wind strength) required to reactivate a stabilising parabolic dune into a barchan. Four eco-geomorphic interaction zones that govern a barchan-to-parabolic dune transformation

  8. Landscape and soil development in Lower Lusatia - results from archaeological and soil-geomorphological investigations on a small dune field nearby Jänschwalde (Brandenburg, Germany)

    NASA Astrophysics Data System (ADS)

    Nicolay, Alexander; Schulz, Deborah; Raab, Thomas; Raab, Alexandra

    2014-05-01

    Within the apron of the opencast mine Jänschwalde (SE Brandenburg, Germany) archaeological excavations on a multiple populated small dune were complemented with soil-geomorphological investigations in the vicinity. Archaeological findings in the dune stratigraphy (especially cremation graves) are intercalated within aeolian sediments and/or buried soils and thus give a record of the Late Quaternary geomorphodynamic and soil development. The archaeological results confirm the presence of Mesolithic and Neolithic populations at the study site. The Mesolithic to Neolithic factory sites are preferably located on slightly elevated places like the remnants of late glacial dunes. On these late glacial aeolian sediments subsequently a podzol formation took place, indicating stable environmental conditions. At the excavation site, this soil was buried by aeolian drift sands in which a cemetery was found. According to grave goods and grave type the excavated bi-ritual cemetery was created at the end of the 3rd and used until the early 5th century AD (Late Roman Iron Age to Migration Period). Within this period the aeolian activity, proven by about 1 m deep drift sands, increased and a small dune was formed wherein 4 inhumation and approx. 26 cremation graves (Schichtgräberfeld) were documented. The cremation graves were mainly recorded as small reddish/gray 5-20 cm thick sandy layers which were separated by the drift sand layers. Soil-geomorphological investigations, two kilometers north of the excavated cremation and settle-ment site corroborate the detected phases of morphological stability and aeolian activity in this time period. Our complementing investigations indicate that the Late Roman Iron Age to Migration Period population had affected the landscape due to deforestation and agricultural land use.

  9. Dune Avalanche Scars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    05 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, low albedo (dark) sand dunes in Kaiser Crater near 47.2oS, 340.4oW. The dunes are--ever so slowly--moving east to west (right to left) as sand avalanches down the steeper, slip face slopes of each. Avalanching sand in the Kaiser dune field has left deep scars on these slopes, suggesting that the sand is not loose but is instead weakly cemented. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  10. Aeolian processes on Venus

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1989-01-01

    This review assesses the potential aeolian regime on Venus as derived from spacecraft observations, laboratory simulations, and theoretical considerations. The two requirements for aeolian processes (a supply of small, loose particles and winds of sufficient strength to move them) appear to be met on Venus. Venera 9, 10, 13, and 14 images show particles considered to be sand and silt size on the surface. In addition, dust spurts (grains 5 to 50 microns in diameter) observed via lander images and inferred from the Pioneer-Venus nephalometer experiments suggest that the particles are loose and subject to movement. Although data on near surface winds are limited, measurements of 0.3 to 1.2 m/sec from the Venera lander and Pioneer-Venus probes appear to be well within the range required for sand and dust entrainment. Aeolian activity involves the interaction of the atmosphere, lithosphere, and loose particles. Thus, there is the potential for various physical and chemical weathering processes that can effect not only rates of erosion, but changes in the composition of all three components. The Venus Simulator is an apparatus used to simulate weathering under venusian conditions at full pressure (to 112 bars) and temperature (to 800 K). In one series of tests, the physical modifications of windblown particles and rock targets were assessed and it was shown that particles become abraded even when moved by gentle winds. However, little abrasion occurs on the target faces. Thus, compositional signatures for target rocks may be more indicative of the windblown particles than of the bedrock. From these and other considerations, aeolian modifications of the venusian surface may be expected to occur as weathering, erosion, transportation, and deposition of surficial materials. Depending upon global and local wind regimes, there may be distinctive sources and sinks of windblown materials. Radar imaging, especially as potentially supplied via the Magellan mission, may enable the

  11. Aeolian beach ridges and their significance for climate and sea level: Concept and insight from the Levant coast (East Mediterranean)

    NASA Astrophysics Data System (ADS)

    Mauz, B.; Hijma, M. P.; Amorosi, A.; Porat, N.; Galili, E.; Bloemendal, J.

    2013-06-01

    preservation potential due to the small sediment budget of the complex. The falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold. On the Levant coast, sand delivery to the backshore continued during relative sea-level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues. The significance of the dune-soil succession for climate is limited because the dunes are governed by relative sea-level change; the vegetation response to changes in precipitation is non-linear and the dune dynamics are characterised by low resilience and hysteresis.

  12. Field measurement and analysis of climatic factors affecting dune mobility near Grand Falls on the Navajo Nation, southwestern United States

    NASA Astrophysics Data System (ADS)

    Bogle, Rian; Redsteer, Margaret Hiza; Vogel, John

    2015-01-01

    Aeolian sand covers extensive areas of the Navajo Nation in the southwestern United States. Much of this sand is currently stabilized by vegetation, although many drier parts of these Native lands also have active and partly active dunes. Current prolonged drought conditions that started in the mid-1990s are producing significant changes in dune mobility. Reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations, agriculture, grazing, and infrastructure. To understand and document the current and future potential for mobility, seasonally repeated surveys were used to track the location of multiple active barchan dunes. By utilizing Real-Time Kinematic GPS field surveys and simultaneously collecting in-situ meteorological data, it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences. Through analysis of the recorded data, we examined the fit of various climate parameters, and demonstrate that under the current prolonged drought, wind power is the dominant factor controlling dune mobility.

  13. Morphology and Sediment Transport Dynamics of a Trough-Blowout Dune, Bodega Marine Reserve, Northern California

    NASA Astrophysics Data System (ADS)

    Jorgenson, D.; Dunleavy, C. J.; Smith, M. E.

    2014-12-01

    Blowout dunes are a primary mechanism for transporting sand within vegetated coastal dune systems. Understanding the fine-scale variation in sediment transport within these systems is critical to predicting their formation and migration. Previous investigations of a coastal dune system located at the Bodega Marine Reserve, on the Sonoma Coast of Northern California have indicated that aeolian sand flux in unvegetated sand is ~450x greater than in vegetated areas. To better understand sand flux and its relationship with wind speed, direction and precipitation, we deployed an array of 12 sand traps within a single blowout area adjacent to the BOON marine climatology station. The blowout is trough- shaped, approximately 50 meters long and 15 meters wide. Its main 'fairway' is 5-10 meters below the surrounding beach grass (Ammophila)-covered land surface. Surface sediment within the blowout is fine-grained to granule-sized lithic to sub-lithic sand, and is coarsest in the center. Dune sediment in the Bodega Marine Reserve has been transported by aeolian processes from Salmon Creek Beach to the NW. Within the blowout, typical bedforms include 15-25 cm-wavelength, ~10 cm high sinuous to lingoid ripples arranged perpendicularly to the dominant wind direction (~280 degrees). An 8-10 meter-high mound at the downwind end has accumulated due to the trapping of sand flux by vegetation. Sediment flux across the studied blowout was sampled monthly over a 10-month period of 2013-2014. Sand traps were constructed using modified PVC cylinders, and are 0.5 meter high and 0.3 meter in diameter, with a 0.74-micron mesh screen. Based on measured sand flux, the sites can be categorized into three groups-axial, medial, and peripheral. Rates increase downwind within the blowout. Inter-site sand flux variability within unvegetated locations of the blowout is greater than two orders of magnitude. Axial sites, which experience the greatest sand flux, occur on the edge of the blowout adjacent

  14. A test of a climatic index of dune mobility using measurements from the southwestern United States

    USGS Publications Warehouse

    Lancaster, N.; Helm, P.

    2000-01-01

    The climatic index of dune mobility developed by Lancaster (1988) has been applied to a variety of different environments. The index is, however, untested and unverified. We tested the index by comparison of values of the dune mobility index calculated from climate data with rates of sand transport measured at three stations in Arizona and New Mexico over the period 1985 to 1997. Our results show that changes in measured rates of sand transport closely parallel temporal changes in the dune mobility index. The mobility index is, however, a relatively poor predictor of the magnitude of actual sand transport on a year-to-year basis. This discrepancy is probably due to the fact that sand transport rates at these sites are strongly influenced by vegetation cover, the state of which may lag changes in annual precipitation. There is, however, a good relation between the mean annual mobility index and mean annual rates of sand transport. This indicates that the dune mobility index is a valid predictor of the long-term state of the aeolian system and can be used confidently for the purposes for which it was originally intended. Copyright (C) 2000 John Wiley and Sons, Ltd.

  15. Dune and ripple migration along Curiosity's traverse in Gale Crater on Mars

    NASA Astrophysics Data System (ADS)

    Silvestro, S.; Vaz, D.; Ewing, R. C.; Fenton, L. K.; Michaels, T. I.; Ayoub, F.; Bridges, N. T.

    2013-12-01

    The NASA Mars Science Laboratory (MSL) rover, Curiosity, has safely landed near a 35-km-long dark dune field in Gale Crater on Mars. This dune field lies along Curiosity's traverse to Aeolis Mons (Mt. Sharp). Here we present new evidence of aeolian activity and further estimate wind directions within the dune field through analysis of ripple migration with the COSI-Corr technique, which provides precise measurements of ripple displacement at the sub-pixel scale.The area analyzed is located ~10 km southwest of rover Curiosity's current position and ~4 km SW of its selected path through Aeolis Mons (Mt. Sharp) (Fig. 1a). Here barchan dunes with elongated horns and seif dunes coexist with more typical barchan and dome dunes (Fig. 1a, b), with slopes sculpted by two intersecting ripple crestline orientations trending at 45° and 330°. The range of dune types and ripple orientations indicate the dune field morphology is influenced by at least two winds from the NW and the NE. The direction of migration is toward the SW, suggesting the most recent sand transporting winds were from the NE (Fig. 1c). These results match previous predictions and can be used to forecast the wind conditions close to the entry point to Mt. Sharp. Fig. 1: a-b) Study area c) Ripple migration direction computed using the COSI-Corr technique

  16. Poster 17: Methane storms as a driver of Titan's dune orientation.

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clement; Lebonnois, Sebastien; Rodriguez, Sebastien; Courech Du Pont, Sylvain; Lucas, Antoine

    2016-06-01

    Titan's equatorial regions are covered by eastward oriented linear dunes [1,2]. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds on Earth. We propose that Titan's dune orientation is actually determined by equinoctial tropical methane storms producing a coupling with superrotation and dune formation [3]. Using meso-scale simulations of convective methane clouds [4] with a GCM wind profile featuring the superrotation [5,6], we show that Titan's storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind calculations and analogies with terrestrial dune fields [7], we show that Titan's dune propagation occurs eastward under these conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major features of Titan's dunes as the divergence from the equator or the dune size and spacing. It also implies an equatorial origin of Titan's dune sand and a possible occurence of dust storms.

  17. Is Titan's Dune Orientation Controlled by Tropical Methane Storms?

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clément; Lebonnois, Sébastien; Rodriguez, Sébastien; Courrech du Pont, Sylvain; Lucas, Antoine

    2014-11-01

    Titan’s equatorial regions are covered by eastward oriented linear dunes. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds on Earth [1, 2].Here, we propose that Titan’s dune orientation is actually determined by equinoctial tropical methane storms producing a coupling with superrotation and dune formation. Using meso-scale simulations of convective methane clouds [3, 4] with a GCM wind profile featuring the superrotation [5, 6], we show that Titan’s storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind roses and analogies with terrestrial dune fields [7], we show that Titan's dune growth occurs eastward under these conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major features of Titan's dunes (i.e. divergence from the equator, size and spacing).References:[1] Lorenz et al.: The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes, Science (2006)[2] Lorenz & Radebaugh: Global pattern of Titan’s dunes: Radar survey from the Cassini prime mission, Geophysical Research Letter (2009)[3] Barth & Rafkin.: TRAMS: A new dynamic cloud model for Titan’s methane clouds, Geophysical Research Letter (2007)[4] Barth & Rafkin.: Convective cloud heights as a diagnostic for methane environment on Titan, Icarus (2010)[5] Charnay & Lebonnois: Two boundary layers in Titan's lower troposphere inferred from a climate model, Nature Geoscience (2012)[6] Lebonnois et al.: Titan global climate model: A new 3-dimensional version of the IPSL Titan GCM, Icarus (2012)[7] Courrech du Pont, Narteau & Gao: Two modes for dune orientation, Geology (2014)

  18. Vegetation of semi-stable rangeland dunes of the Navajo Nation, Southwestern USA

    USGS Publications Warehouse

    Thomas, Kathryn A.; Redsteer, Margaret H.

    2016-01-01

    Dune destabilization and increased mobility is a worldwide issue causing ecological, economic, and health problems for the inhabitants of areas with extensive dune fields. Dunes cover nearly a third of the Navajo Nation within the Colorado Plateau of southwestern USA. There, higher temperatures and prolonged drought beginning in 1996 have produced significant increases in dune mobility. Vegetation plays an important role in dune stabilization, but there are few studies of the plants of the aeolian surfaces of this region. We examined plant species and their attributes within a moderately vegetated dune field of the Navajo Nation to understand the types and characteristics of plants that stabilize rangeland dunes. These dunes supported a low cover of mixed grass-scrubland with fifty-two perennial and annual species including extensive occurrence of non-native annual Salsola spp. Perennial grass richness and shrub cover were positively associated with increased soil sand composition. Taprooted shrubs were more common on sandier substrates. Most dominant grasses had C4 photosynthesis, suggestive of higher water-use efficiencies and growth advantage in warm arid environments. Plant cover was commonly below the threshold of dune stabilization. Increasing sand movement with continued aridity will select for plants adapted to burial, deflation, and abrasion. The study indicates plants tolerant of increased sand mobility and burial but more investigation is needed to identify the plants adapted to establish and regenerate under these conditions. In addition, the role of Salsola spp. in promoting decline of perennial grasses and shrubs needs clarification.

  19. Temporal and spatial variation of groundwater in quantity and quality in sand dune at coastal region, Kamisu city, central Japan.

    NASA Astrophysics Data System (ADS)

    Umei, Yohei; Tsujimura, Maki; Sakakibara, Koichi; Watanabe, Yasuto; Minema, Motomitsu

    2016-04-01

    The role of groundwater in integrated water management has become important in recent 10 years, though the surface water is the major source of drinking water in Japan. Especially, it is remarked that groundwater recharge changed due to land cover change under the anthropogenic and climatic condition factors. Therefore, we need to investigate temporal and spatial variation of groundwater in quantity and quality focusing on the change during recent 10-20 years in specific region. We performed research on groundwater level and quality in sand dune at coastal region facing Pacific Ocean, Kamisu city, Ibaraki Prefecture, which have been facing environmental issues, such as land cover change due to soil mining for construction and urbanization. We compared the present situation of groundwater with that in 2000 using existed data to clarify the change of groundwater from 2000 to 2015. The quality of water is dominantly characterized by Ca2+-HCO3- in both 2000 and 2015, and nitrate was not observed in 2015, though it was detected in some locations in 2000. This may be caused by improvement of the domestic wastewater treatment. The topography of groundwater table was in parallel with that of ground surface in 2015, same as that in 2000. However, a depletion of groundwater table was observed in higher elevation area in 2015 as compared with that in 2000, and this area corresponds to the locations where the land cover has changed due to soil mining and urbanization between 2015 and 2000. In the region of soil mining, the original soil is generally replaced by impermeable soil after mining, and this may cause a decrease of percolation and net groundwater recharge, thus the depletion of groundwater table occurred after the soil mining.

  20. Morphologic characteristics and migration rate assessment of barchan dunes in the Southeastern Western Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Hamdan, M. A.; Refaat, A. A.; Abdel Wahed, M.

    2016-03-01

    This work explores the morphologic characteristics of aeolian dune sand in the southeastern part of Western Desert of Egypt. It aims to assess the movement of barchan dunes and evaluate their environmental influence on the Toshka Project. Morphometric investigation of barchan dunes in the Toshka area revealed that most barchans have high length/width (a/c) ratios (fat to pudgy), while one-fifth of the studied barchans have lower a/c ratios and so appear normal in their morphologic forms. Statistical analysis of the main parameters of barchan dunes in Toshka and other desert regions in the Kharga (Egypt), Kuwait, Southern Morocco, California and Southern Peru demonstrates that barchans of the Toshka area are distinctive in their appearance. They are characterized by distinct aspect with higher values of length and width and greater growth in height. The high-energy wind environment in addition to the large amount of drifting sand are principal factors responsible for the unique shape of Toshka barchans. The migration rate of barchan dunes in four chosen test locations, within the central and western Toshka area, ranges from about 3 to 10.82 m/year. The calculated average migration rate of these dunes is about 6 m/year in a SSW direction. Sand encroachment is more extensive in the central and western parts of the investigated Toshka area. Risk evaluation of sand dune movements in the southeastern part of the Western Desert points to medium to high sand encroachment risk values. These may represent serious hazards to the newly-established Toshka Project, threatening roads, as well as cultivated lands in the area.

  1. Municipal initiatives for managing dunes in coastal residential areas: a case study of Avalon, New Jersey, USA

    NASA Astrophysics Data System (ADS)

    Nordstrom, Karl F.; Jackson, Nancy L.; Bruno, Michael S.; de Butts, Harry A.

    2002-10-01

    The characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values. Shoreline management zones include a naturally evolving, undeveloped segment; a noneroding, developed segment; eroding and noneroding segments of an "improved beach" where dunes have been built by artificial nourishment; and a privately built, artificially nourished dune on the shoreline of an inlet. A disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences, vegetation plantings, purchase of undeveloped lots, and sediment backpassing to maintain beach widths and dune elevations. The present nourished and shaped foredune in the improved beach is higher, wider, and closer to the berm crest than the natural dune. Restricted inputs of aeolian sand keep the surface flat and poorly vegetated. A stable section of this engineered shore has a wider beach, and sand fences have created a higher foredune with greater topographic diversity. The cross shore zonation of vegetation here is more typical of natural dunes, but the environmental gradient is much narrower. The privately built dune is low, narrow, and located where it could not be created naturally. Foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size (0.16-0.21 mm) and sorting (0.31-0.39 φ), but sediment on the surface of the nourished dune is coarser (28.1% gravel) with a more poorly sorted sand fraction (1.30 φ) representing lag elements on the deflation surface. Willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the Federal Emergency Management Agency (FEMA) to replace lost sediment, thus placing an economic value on dunes. Success of the management program is attributed to: (i

  2. Aeolian cliff-top deposits and buried soils in the White River Badlands, South Dakota, USA

    USGS Publications Warehouse

    Rawling, J. E.; Fredlund, G.G.; Mahan, S.

    2003-01-01

    Aeolian deposits in the North American Great Plains are important sources of Holocene palaeo-environmental records. Although there are extensive studies on loess and dune records in the region, little is known about records in aeolian cliff-top deposits. These are common on table (mesa) edges in the White River Badlands. These sediments typically have loam and sandy-loam textures with dominantly very fine sand, 0.5-1% organic carbon and 0.5-5% CaCO3. Some of these aeolian deposits are atypically coarse and contain granules and fine pebbles. Buried soils within these deposits are weakly developed with A-C and A-AC-C profiles. Beneath these are buried soils with varying degrees of pedogenic development formed in fluvial, aeolian or colluvial deposits. Thickness and number of buried soils vary. However, late-Holocene soils from several localities have ages of approximately 1300, 2500 and 3700 14C yrs BP. The 1300 14C yr BP soil is cumulic, with a thicker and lighter A horizon. Soils beneath the cliff-top deposits are early-Holocene (typically 7900 but as old as 10000 14C yrs BP) at higher elevation (???950 m) tables, and late-Holocene (2900 14C yrs BP) at lower (???830 m) tables. These age estimates are based on total organic matter 14C ages from the top 5 cm of buried soils, and agreement is good between an infrared stimulated luminescence age and bracketing 14C ages. Our studies show that cliff-top aeolian deposits have a history similar to that of other aeolian deposits on the Great Plains, and they are another source of palaeoenvironmental data.

  3. Lunar and Planetary Science XXXV: Martian Aeolian and Mass Wasting Processes: Blowing and Flowing

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The session Martian Aeolian and Mass Wasting Processes: BLowing and Flowing included the following topics: 1) Three Decades of Martian Surface Changes; 2) Thermophysical Properties of Isidis Basin, Mars; 3) Intracrater Material in Eastern Arabia Terra: THEMIS, MOC, and MOLA Analysis of Wind-blown Deposits and Possible High-Inertia Source Material; 4) Thermal Properties of Sand from TES and THEMIS: Do Martian Dunes Make a Good Control for Thermal Inertia Calculations? 5) A Comparative Analysis of Barchan Dunes in the Intra-Crater Dune Fields and the North Polar Sand Sea; 6) Diluvial Dunes in Athabasca Valles, Mars: Morphology, Modeling and Implications; 7) Surface Profiling of Natural Dust Devils; 8) Martian Dust Devil Tracks: Inferred Directions of Movement; 9) Numerical Simulations of Anastomosing Slope Streaks on Mars; 10) Young Fans in an Equatorial Crater in Xanthe Terra, Mars; 11) Large Well-exposed Alluvual Fans in Deep Late-Noachian Craters; 12) New Evidence for the Formation of Large Landslides on Mars; and 13) What Can We Learn from the Ages of Valles Marineris Landslides on Martian Impact History?

  4. Morphodynamics of star dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Narteau, C.; Rozier, O.; Courrech du Pont, S.

    2012-04-01

    Star dunes are among the biggest and the most impressive dunes in Earth sand seas. Nonetheless, they remain poorly studied, probably because of their apparent complexity. They are massive pyramidal dunes with interlaced arms whose slip faces are oriented in various directions. Being large, they can integrate wind properties over a wide range of time scales. Thus, they are observed for wind regimes with multiple directions, and may result from the amalgamation of dunes or from the development of arms on a well-established dune pattern. In both cases, the roles of wind directional variability and secondary flow have been emphasized but not precisely quantified. Here, we report simulations where the star dune shape results from a a combination of longitudinal dunes, which form the star dune arms. These arms may radiate and so interact with the other dunes in the field. This mass exchange, controlled by the morphodynamics of star dunes arms, must play an important role in the large-scale arrangement of star dunes networks. We first demonstrate that star dune arms orientation maximizes the flux in the direction of crests. This is opposed to the usually admit dunes orientation, which maximizes the sediment transport perpendicular to the crest. Indeed, depending on sand availability, dunes development results from the growth of a wave on a sand bed or from a net transport of sediment, which grows and extends an isolated longitudinal dune over a non-erodible soil. These two different mechanisms lead to two different modes of crests orientation. Then, we show that the propagating arms reach a stationary state characterized by constant width, height and growth rate. These are controlled by the frequency at which the wind changes direction. Arm width and height increase, whereas the propagation speed decreases with a decreasing frequency. These morphodynamics properties are helpful to assess from pattern observation the variability of wind directionality over several time

  5. Quaternary palaeoenvironments in Namibia: new records from optically stimulated dating of Kalahari linear dune accumulation and northern Namib Sand Sea interdune deposits.

    NASA Astrophysics Data System (ADS)

    Stone, Abigail; Thomas, David; Viles, Heather; Bailey, Richard

    2010-05-01

    In this study we consider new linear dune accumulation records from the west of the southern Kalahari linear dunefield (~24o S 18oE) and a new chronology for three sites along the former course of the Tsondab River in the northern Namib Sand Sea (23o49'15'S, 14o57'30'E, 23o48'39'S, 15o02'21'E and 23o56'11'S, 15o17'89'E) from Namibia, southern Africa. Optically stimulated luminescence dating (OSL) has been applied to both sites in order to: (i) provide a chronology for linear dune accumulation in a previously unstudied region of the southern Kalahari linear dunefield and (ii) to provide a chronological reassessment for water-lain units from the Namib Sand Sea, previously dated using radiocarbon applied to inorganic carbonate sediments. The 48 OSL ages from the linear dunes include the oldest linear dune sediment ages recorded in the southern Kalahari and also reveal that the dunefield has been partially active throughout much of the past 120 ka. These ages are considered alongside the net accumulation record for the entire southern Kalahari linear dunefield (141 optical ages) and we make some important observations about the influence of sampling strategy. We attempt to isolate a rigorous signal that does not depend on sampling strategy by removing cores and comparing the net accumulation record from different parts of the dataset. We consider the young bias resulting from the predominance of shallow sampling in the total dataset. The bracketing OSL ages (from sand units that inter-bed water-lain calcareous rich sediments) in the northern Namib Sand Sea suggest that the series of seven mud units at Narabeb (23o49'15'S, 14o57'30'E) are substantially older than the existing radiocarbon chronology from the mud units themselves. Twelve of the thirteen OSL ages fall within MIS 5. By contrast, at Ancient Tracks (23o56'11'S, 15o17'89'E) the OSL-based chronological reassessment suggests the water-lain units were 1 to 2 ka younger than the existing radiocarbon ages, with

  6. Expression of terrain and surface geology in high-resolution helicopter-borne gravity gradient (AGG) data: examples from Great Sand Dunes National Park, Rio Grande Rift, Colorado

    USGS Publications Warehouse

    Drenth, Benjamin J.

    2013-01-01

    Airborne gravity gradient (AGG) data are rapidly becoming standard components of geophysical mapping programs, due to their advantages in cost, access, and resolution advantages over measurements of the gravity field on the ground. Unlike conventional techniques that measure the gravity field, AGG methods measure derivatives of the gravity field. This means that effects of terrain and near-surface geology are amplified in AGG data, and that proper terrain corrections are critically important for AGG data processing. However, terrain corrections require reasonable estimates of density for the rocks and sediments that make up the terrain. A recommended philosophical approach is to use the terrain and surface geology, with their strong expression in AGG data, to the interpreter’s advantage. An example of such an approach is presented here for an area with very difficult ground access and little ground gravity data. Nettleton-style profiling is used with AGG data to estimate the densities of the sand dunefield and adjacent Precambrian rocks from the area of Great Sand Dunes National Park in southern Colorado. Processing of the AGG data using the density estimate for the dunefield allows buried structures, including a hypothesized buried basement bench, to be mapped beneath the sand dunes.

  7. Geochemical evidence for a complex origin for the Kelso dunes, Mojave National Preserve, California USA

    USGS Publications Warehouse

    Muhs, Daniel; Lancaster, Nicholas; Skipp, Gary L.

    2017-01-01

    The Kelso Dune field in southern California is intriguing because although it is of limited areal extent (~ 100 km2), it has a wide variety of dune forms and contains many active dunes (~ 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

  8. Arabian Dunes

    NASA Technical Reports Server (NTRS)

    2005-01-01

    11 June 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a field of low-albedo (dark) barchan sand dunes in a crater located in western Arabia Terra. Small dunes like these are common in the craters of western Arabia Terra and they are often the source of finer, dark sediment that forms windstreaks further downwind. The steepest slopes on the dunes, their slipfaces, are pointed toward the southeast (lower right), indicating that the dominant winds in this location come from the opposite direction.

    Location near: 6.4oN, 346.2oW Image width: 3 km (1.9 mi Illumination from: lower left Season: Northern Autumn

  9. Mid-latitude Dunes

    NASA Technical Reports Server (NTRS)

    2005-01-01

    7 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark sand dunes on the floor of a southern mid-latitude impact crater. Craters are commonly the site of sand dunes, as sand may become trapped in these topographic depressions. In this case, the winds responsible for the dunes generally blew from the south/southeast (bottom/lower right),

    Location near: 51.8oS, 105.5oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  10. Quantifying spatiotemporal dynamics of root-zone soil water in a mixed forest on subtropical coastal sand dune using surface ERT and spatial TDR

    NASA Astrophysics Data System (ADS)

    Fan, Junliang; Scheuermann, Alexander; Guyot, Adrien; Baumgartl, Thomas; Lockington, David A.

    2015-04-01

    We jointly used surface electrical resistivity tomography (surface ERT) and spatial time domain reflectometry (spatial TDR) to quantify spatial patterns and seasonal dynamics of root-zone soil water under three contrasting vegetation covers in a sand dune forest of subtropical coastal Australia. We wanted to obtain a better understanding of the applicability of both techniques in these environments as well as investigate vegetation-soil water interactions. Soil temperature and topographic changes were taken into account in soil resistivity interpretation. The results demonstrated the capability of both surface ERT and spatial TDR to spatially monitor root-zone soil water dynamics, with root mean square error (RMSE) <0.018 cm3 cm-3 and absolute deviation <0.034 cm3 cm-3 between gravimetrically derived water content and those derived by the two geophysical techniques. Soil water was depleted to low levels during the dry season but quickly replenished with onset of the wet season. Soil water content profiles revealed obvious differences in water dynamics of the dune sands under different vegetation covers, with highest infiltration and deep drainage under the grassland compared with tree cover. The spatial variation in soil water content due to rainfall interception by trees, root water uptake and preferential infiltration associated with stemflow could be detected by the joint use of surface ERT and spatial TDR. We conclude that surface ERT can be an effective method for quantifying two-dimensional root-zone soil water dynamics and understanding the hydrological processes in these sand dune environments, if complemented by the one-dimensional high-resolution soil water measurements from spatial TDR.

  11. A 45-year time series of Saharan dune mobility from remote sensing

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2012-04-01

    Decadal trends in the aeolian dust record of the Sahara affect the global climate system and the nutrient budget of the Atlantic Ocean. One proposed cause of these trends are changes in the frequency and intensity of dust storms, which have hitherto been hard to quantify. Because sand flux scales with the cube of wind speed, dune migration rates can be used as a proxy for storminess. Relative changes in the storminess of the Sahara can thus be monitored by tracking the migration rates of individual sand dunes over time. The Bodélé Depression of northern Chad was selected as a target area for this method, because it is the most important point-source of aeolian dust on the planet and features the largest and fastest dunes on Earth. A collection of co-registered Landsat, SPOT, and ASTER scenes, combined with declassified American spy satellite images was used to construct a 45 year record of dune migration in the Bodélé Depression. One unexpected outcome of the study was the observation of binary dune interactions in the imagery sequence, which reveals that when two barchan dunes collide, a transfer of mass occurs so that one dune appears to travel through the other unscathed, like a solitary wave. This confirms a controversial numerical model prediction and settles a decade-old debate in aeolian geomorphology. The COSI-Corr change detection method was used to measure the dune migration rates from 1984 until 1987, 1990, 1996, 2000, 2003, 2005, 2007, 2008, 2009, and 2010. An algorithm was developed to automatically warp the resulting displacement fields back to a common point in time. Thus, individual image pixels of a dune field were tracked over time, allowing the extraction of a time series from the co-registered satellite images without further human intervention. The automated analysis was extended further back into the past by comparison of the 1984 image with declassified American spy satellite (Corona) images from 1965 and 1970. Due to the presence of

  12. Effect of vegetation on the temporal stability of soil moisture in grass-stabilized semi-arid sand dunes

    NASA Astrophysics Data System (ADS)

    Wang, Tiejun; Wedin, David A.; Franz, Trenton E.; Hiller, Jeremy

    2015-02-01

    Soil moisture is a critical state variable affecting a va