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Sample records for aeolian sand ripples

  1. Aeolian sand ripples around plants.

    PubMed

    Zhang, Qian-Hua; Miao, Tian-De

    2003-05-01

    Plants in the desert may locally change the aeolian process, and hence the pattern of sand ripples traveling nearby. The effect of plants on ripples is investigated using a coupled map lattice model with nonuniform coupling coefficients. PMID:12786143

  2. Formation of aeolian ripples and sand sorting.

    PubMed

    Manukyan, Edgar; Prigozhin, Leonid

    2009-03-01

    We present a continuous model capable of demonstrating some salient features of aeolian sand ripples: the realistic asymmetric ripple shape, coarsening of the ripple field at the nonlinear stage of ripple growth, saturation of ripple growth for homogeneous sand, typical size segregation of sand, and formation of armoring layers of coarse particles on ripple crests and windward slopes if the sand is inhomogeneous. PMID:19391931

  3. Nonlinear dynamics of Aeolian sand ripples.

    PubMed

    Prigozhin, L

    1999-07-01

    We study the initial instability of flat sand surface and further nonlinear dynamics of wind ripples. The proposed continuous model of ripple formation allowed us to simulate the development of a typical asymmetric ripple shape and the evolution of a sand ripple pattern. We suggest that this evolution occurs via ripple merger preceded by several soliton-like interaction of ripples. PMID:11969814

  4. Direct numerical simulations of aeolian sand ripples

    PubMed Central

    Durán, Orencio; Claudin, Philippe; Andreotti, Bruno

    2014-01-01

    Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873

  5. Direct numerical simulations of aeolian sand ripples.

    PubMed

    Durán, Orencio; Claudin, Philippe; Andreotti, Bruno

    2014-11-01

    Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873

  6. Aeolian sand ripples: experimental study of fully developed states.

    PubMed

    Andreotti, Bruno; Claudin, Philippe; Pouliquen, Olivier

    2006-01-20

    We report an experimental investigation of aeolian sand ripples, performed both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed, we can identify three regimes: appearance of an initial wavelength, coarsening of the pattern, and finally saturation of the ripples. We show that both initial and final wavelengths, as well as the propagative speed of the ripples, are linear functions of the wind velocity. Investigating the evolution of an initially corrugated bed, we exhibit nonlinear stable solutions for a finite range of wavelengths, which demonstrates the existence of a saturation in amplitude. These results contradict most of the models. PMID:16486644

  7. 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). PMID:15007749

  8. Mean flow and Reynolds stress structure over aeolian ripples

    NASA Astrophysics Data System (ADS)

    Li, Bailiang; McKenna Neuman, Cheryl; Bédard, Otto; O'Brien, Patrick

    2015-04-01

    Mean flow and turbulence structure on transverse ripples have been well documented in hydrodynamic literature. However, very few studies have described the flow characteristics over aeolian ripples. This study adopted laser Doppler anemometry (LDA) to measure the wind field above granular ripples with different bimodal particle size distributions in a wind tunnel. Multiple runs were conducted to examine the vertical profiles of time-averaged horizontal and vertical velocities and Reynolds stress above four different locations: crest, lee slope, trough, and stoss slope. The rippled sand bed has a fine beige fraction with grain size smaller than 0.542 mm concentrated in the troughs and a coarse fraction dyed in red with grain size greater than 0.542 mm concentrated in the crests. The magnitude of the ripples at equilibrium is controlled by both wind velocity and the ratio of beige sand to red sand. Freestream velocity has a range between 8-11 m/s (above the saltation threshold of beige sand and below the threshold of red sand) and the percentage coarse by mass varies from 5.2% to 27.5% with median grain size from 0.289 mm to 0.399 mm. Experimental results indicate that the ripples have the wave length ranged between 20 mm and 140 mm with a characteristic ripple index (wave length/wave height) of 15. Flow streamlines are generally parallel to the bed surface, which is inconsistent with previous hydrodynamic observations that a return flow is usually found at the lee side of the ripples. Reynolds stress has demonstrated a strong spatial differentiation near the sand surface: greatest at crests and smallest at the troughs, however, this difference diminishes with elevation. This is an exploratory study on the turbulence characteristics of air flow above aeolian ripples, and we believe the finding of this research will enhance the understanding the interaction mechanisms between the air and bed morphology.

  9. Mars Rover Curiosity Traverses of Sand Ripples

    NASA Astrophysics Data System (ADS)

    Stein, N.; Arvidson, R. E.; Zhou, F.; Heverly, M.; Maimone, M.; Hartman, F.; Bellutta, P.; Iagnemma, K.; Senatore, C.

    2014-12-01

    Martian sand ripples present a challenge for rover mobility, with drives over ripples often characterized by high wheel sinkage and slippage that can lead to incipient embedding. Since landing in Gale Crater, Curiosity has traversed multiple sand ripples, including the transverse aeolian ridge (TAR) straddling Dingo Gap on sols 533 and 535. On sol 672, Curiosity crossed backward over a series of sand ripples before ending its drive after high motor currents initiated visual odometry (VO) processing, which detected 77% slip, well in excess of the imposed 60% slip limit. At the end of the drive, the right front wheel was deeply embedded at the base of a ripple flank with >20 cm sinkage and the rear wheels were near a ripple crest. As Curiosity continues its approach to Mount Sharp it will have to cross multiple ripples, and thus it is important to understand Curiosity's performance on sol 672 and over similar ripples. To this end the sol 672 drive was simulated in ARTEMIS (Adams-Based Rover Terramechanics Interaction Simulator), a software tool consisting of realistic rover mechanical models, a wheel-terrain interaction module for deformable and non-deformable surfaces, and realistic terrain models. ARTEMIS results, Dumont Dunes tests performed in the Mojave Desert using the Scarecrow test rover, and single wheel tests performed at MIT indicate that the high slip encountered on sol 672 likely occurred due to a combination of rover attack angle, ripple geometry, and soil properties. When ripple wavelength approaches vehicle length, the rover can reach orientations in which the leading wheels carry minimal normal loads and the trailing wheels sink deeply, resulting in high slippage and insufficient thrust to propel the rover over ripples. Even on relatively benign (i.e. low tilt) terrains, local morphology can impose high sinkage, thus impeding rover motion. Work is underway to quantify Curiosity's drive performance over various ripple geometries to retrieve soil

  10. Intricately Rippled Sand Deposits

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Click on the image for Intricately Rippled Sand Deposits (QTVR)

    NASA's Mars Exploration Rover Spirit welcomed the beginning of 2006 on Earth by taking this striking panorama of intricately rippled sand deposits in Gusev Crater on Mars. This is an approximate true-color rendering of the 'El Dorado' ripple field provided by Spirit over the New Year's holiday weekend. The view spans about 160 degrees in azimuth from left to right and consists of images acquired by Spirit's panoramic camera on Spirit's 708th and 710th Martian days, or sols, (Dec. 30, 2005 and Jan. 1, 2006). Spirit used the Pancam's 750-nanometer, 530-nanometer and 430-nanometer filters to capture the colors on Mars. Scientists have eliminated seams between individual frames in the sky portion of the mosaic to better simulate the vista a person standing on Mars would see. Spirit spent several days acquiring images, spectral data, and compositional and mineralogical information about these large sand deposits before continuing downhill toward 'Home Plate.'

  11. 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.

  12. Dynamical evolution of sand ripples under water.

    PubMed

    Stegner, A; Wesfreid, J E

    1999-10-01

    We have performed an experimental study on the evolution of sand ripples formed under the action of an oscillatory flow. An annular sand-water cell was used in order to investigate a wide range of parameters. The sand ripples follow an irreversible condensation mechanism from small to large wavelength until a final state is reached. The wavelength and the shape of these stable sand patterns are mainly governed by the fluid displacement and the static angle of the granular media. A strong hysteresis affects the evolution of steep ripples. When the acceleration of the sand bed reaches a critical value, the final pattern is modified by the superficial fluidization of the sand layer. PMID:11970264

  13. Formational Mechanisms and Morphology of Windblown Coarse-Grained Sand Ripples at White Sands, New Mexico

    NASA Astrophysics Data System (ADS)

    Glade, R.; Jerolmack, D. J.; Pelletier, J. D.

    2014-12-01

    Coarse-grained ripples, also known as "megaripples," are large sand ripples found in both aeolian and aquatic environments on Earth, and are common on Mars. The formation and morphology of coarse-grained ripples are not as well understood as more common splash ripples. Current understanding suggests that formative wind speeds are above the saltation threshold for the fine grains, but below this threshold for coarse grains found on the crests, such that they creep. Based on this idea, we hypothesize that wind speeds above this coarse-grain saltation threshold will destroy the ripples. We further hypothesize that these ripples do not have an equilibrium size; rather, their size is related to the persistence of formative winds in a given direction. To test this model, we studied windblown coarse-grained ripples in White Sands, New Mexico. Terrestrial LiDAR was used to obtain high resolution ripple morphology and migration over a three month period. Wind velocity profiles and concurrent saltating grain size data were collected during a wind storm to directly relate modes of transport to particle size and wind stress. These local data were used to calibrate wind records from a nearby meteorological station to estimate local fluid stress using a long-term record. LiDAR data indicate that these ripples were destroyed and reoriented between March and June 2013, while the wind record shows that the coarse-grain saltation threshold was indeed exceeded during this time. Morphological analysis indicates that the lee slope of these ripples is set by saltation impact - similar to splash ripples - but that height, wavelength and stoss slope are not related to instantaneous transport conditions. The historical wind record also shows that the range of wind directions decreases rapidly with increasing speed, restricting strong winds to a narrow range of direction. From these results we explore the idea that coarse-grained ripples are typically larger and less frequently destroyed

  14. A Threshold Continuum for Aeolian Sand Transport

    NASA Astrophysics Data System (ADS)

    Swann, C.; Ewing, R. C.; Sherman, D. J.

    2015-12-01

    The threshold of motion for aeolian sand transport marks the initial entrainment of sand particles by the force of the wind. This is typically defined and modeled as a singular wind speed for a given grain size and is based on field and laboratory experimental data. However, the definition of threshold varies significantly between these empirical models, largely because the definition is based on visual-observations of initial grain movement. For example, in his seminal experiments, Bagnold defined threshold of motion when he observed that 100% of the bed was in motion. Others have used 50% and lesser values. Differences in threshold models, in turn, result is large errors in predicting the fluxes associated with sand and dust transport. Here we use a wind tunnel and novel sediment trap to capture the fractions of sand in creep, reptation and saltation at Earth and Mars pressures and show that the threshold of motion for aeolian sand transport is best defined as a continuum in which grains progress through stages defined by the proportion of grains in creep and saltation. We propose the use of scale dependent thresholds modeled by distinct probability distribution functions that differentiate the threshold based on micro to macro scale applications. For example, a geologic timescale application corresponds to a threshold when 100% of the bed in motion whereas a sub-second application corresponds to a threshold when a single particle is set in motion. We provide quantitative measurements (number and mode of particle movement) corresponding to visual observations, percent of bed in motion and degrees of transport intermittency for Earth and Mars. Understanding transport as a continuum provides a basis for revaluating sand transport thresholds on Earth, Mars and Titan.

  15. 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

  16. Sand transport by wind, erosion and deposition and the origin of aeolian bedforms

    NASA Astrophysics Data System (ADS)

    Duran Vinent, Orencio

    2014-05-01

    Aeolian processes involve the wind action on a sedimentary substrate, namely erosion, sand transport and deposition. They are responsible for the emergence of aeolian dunes and ripples. Here, we discuss the physics of aeolian sediment transport from a physical point of view. Relevant time and length scales associated to turbulent wind fluctuations are summarized using aerodynamic theory. At the microscopic scale, the main forces acting on the grains are detailed. Sand transport is then studied using two phase numerical simulations based on a discrete element method for particles coupled to a continuum Reynolds averaged description of hydrodynamics. We then introduce the concepts - e.g. saturated flux, saturation length - and the relevant framework for the development of a continuum (macroscopic) quantitative description of transport at the core of our current understanding of aeolian dunes formation. At smaller scales, aeolian ripples arise from the interaction of sediment transport and topography. At larger scales, the nonlinear nature of the interaction between dunes leads to the formation of dune fields.

  17. Granular size segregation in underwater sand ripples.

    PubMed

    Rousseaux, G; Caps, H; Wesfreid, J-E

    2004-02-01

    We report an experimental study of a binary sand bed under an oscillating water flow. The formation and evolution of ripples is observed. The appearance of a granular segregation is shown to strongly depend on the sand bed preparation. The initial wavelength of the mixture is measured. In the final steady state, a segregation in volume is observed instead of a segregation at the surface as reported before. The correlation between this phenomenon and the fluid flow is emphasised. Finally, different "exotic" patterns and their geophysical implications are presented. PMID:15052430

  18. Video-based observations of nearshore sand ripples and ripple migration

    NASA Astrophysics Data System (ADS)

    Becker, J. M.; Firing, Y. L.; Aucan, J.; Holman, R.; Merrifield, M.; Pawlak, G.

    2007-01-01

    Observations of O(1 m) length and O(0.1 m) height sand ripples at Waimea Bay, a steep (slope ˜ 0.05) pocket beach on the north shore of Oahu, Hawaii, are presented. Time series of ripple patterns over a 900 m2 section of the nearshore in depths of 1-2 m are obtained using time-averaged video images from an Argus station overlooking the bay. Ripples are detected during weak wave conditions in the summer or between winter swell events. The ripple field exhibits narrow-band wave number structure, with ripple crests oriented parallel to the shoreline. The ripple wavelengths vary with wave orbital displacements, but they are shorter than predicted by orbital vortex ripple scaling relationships. A new suspension-limited model (Smith and Wiberg, 2006; Traykovski, 2006) in which the suborbital ripple wavelengths vary with wave period appears to describe well the observed ripple wavelength scaling. Lagged correlations between sequential Argus images reveal area-average ripple migration rates ranging from -3.3 m day-1 (offshore) to 4.5 m day-1. The corresponding estimated sediment transport ranges from -0.3 m3 m-1 day-1 to 0.5 m3 m-1 day-1, similar to previous estimates of cross-shore transport based on observed volume changes at the subaerial beach. This suggests that the recovery of beach sand following major swell-driven erosion events may be accomplished in part by the shoreward migration of seabed ripples.

  19. 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.

  20. Dynamical models for sand ripples beneath surface waves.

    PubMed

    Andersen, K H; Chabanol, M L; van Hecke, M

    2001-06-01

    We introduce order parameter models for describing the dynamics of sand ripple patterns under oscillatory flow. A crucial ingredient of these models is the mass transport between adjacent ripples, which we obtain from detailed numerical simulations for a range of ripple sizes. Using this mass transport function, our models predict the existence of a stable band of wave numbers limited by secondary instabilities. Small ripples coarsen in our models and this process leads to a sharply selected final wave number, in agreement with experimental observations. PMID:11415228

  1. Coarsening of sand ripples in mass transfer models.

    PubMed

    Hellén, E K O; Krug, J

    2002-07-01

    Coarsening of sand ripples is studied in a one-dimensional stochastic model, where neighboring ripples exchange mass with algebraic rates, Gamma(m) approximately m(gamma), and ripples of zero mass are removed from the system. For gamma<0, ripples vanish through rare fluctuations and the average ripple mass grows as (t) approximately -gamma(-1)ln(t). Temporal correlations decay as t(-1/2) or t(-2/3) depending on the symmetry of the mass transfer, and asymptotically the system is characterized by a product measure. The stationary ripple mass distribution is obtained exactly. For gamma>0, ripple evolution is linearly unstable, and the noise in the dynamics is irrelevant. For gamma=1, the problem is solved on the mean-field level, but the mean-field theory does not adequately describe the full behavior of the coarsening. In particular, it fails to account for the numerically observed universality with respect to the initial ripple size distribution. The results are not restricted to sand ripple evolution since the model can be mapped to zero range processes, urn models, exclusion processes, and cluster-cluster aggregation. PMID:12241351

  2. Recent near-surface wind directions inferred from mapping sand ripples on Martian dunes

    NASA Astrophysics Data System (ADS)

    Liu, Zac Yung-Chun; Zimbelman, James R.

    2015-11-01

    The High Resolution Imaging Science Experiment (HiRISE) provides the capability to obtain orbital images of Mars that are of sufficient resolution to record wind ripple patterns on the surfaces of sand dunes. Ripple patterns provide valuable insights into aeolian erosion and deposition on Earth and Mars. In this study, we develop a systematic mapping procedure to examine sand ripple orientations and create surface process maps to evaluate the recent wind flow over the dunes, as well as the interplay of wind and dune shape. By carefully examining the morphology of the dunes and the location of grainflow and grainfall on dune slipfaces, the recent near-surface wind direction (short-term wind) can be identified. Results from the analysis of three dune fields on the floors of craters west of Hellas Basin show regional N, NW, SE, and ESE wind directions. In the three adjacent dune fields, surface process and flow maps suggest a complex wind pattern. The comparison of short-term wind with dune-constructing wind (long-term wind) shows NE and ESE winds may be persistent at least for the past thousands of years. The results also show that the orientation of inferred wind direction on linear dunes is correlated with the crestlines, which suggest that form-flow interaction may take place. The results of local wind flow documentation should improve Martian surface wind modeling and advance our understanding of sand transport, as well as the rates of sand mobility on both Mars and Earth.

  3. Aeolian sand transport: a wind tunnel model

    NASA Astrophysics Data System (ADS)

    Dong, Zhibao; Liu, Xiaoping; Wang, Hongtao; Wang, Xunming

    2003-09-01

    Wind sand transport is an important geological process on earth and some other planets. Formulating the wind sand transport model has been of continuing significance. Majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis. However, the wind shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs, especially at high wind velocity. Moreover, the effect of grain size on sand transport is open to argument. Detailed wind tunnel tests were carried out with respect to the threshold velocity, threshold shear velocity, and transport rate of differently sized, loose dry sand at different wind velocities to reformulate the transport model. The results suggest that the relationship between threshold shear velocity and grain size basically follow the Bagnold-type equation for the grain size d>0.1 mm. However, the threshold coefficient A in the equation is not constant as suggested by Bagnold, but decreases with the particle Reynolds number. The threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter. Attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement. The reformulated transport model for loose dry sand follows the modified O'Brien-Rindlaub-type equation: Q= f1( d)(1- Ru) 2( ρ/ g) V3, or the modified Bagnold-type equation: Q= f2( d)(1- Rt) 0.25( ρ/ g) U*3. Where Q is the sand transport rate, the sand flux per unit time and per unit width, in kg m -1 s -1; ρ is the air density, 1.25 kg m -3; g is the acceleration due to gravity, 9.81 m s -2; Ru= Vt/ V; Rt= U*t/ U*; V is the wind velocity at the centerline of the wind tunnel, in m s -1; Vt is the threshold velocity measured at the same height as V, in m s -1; U* is the shear velocity with saltating flux, in m s -1; U*t is threshold shear

  4. Pattern formation of underwater sand ripples with a skewed drive.

    PubMed

    Bundgaard, F; Ellegaard, C; Scheibye-Knudsen, K; Bohr, T; Sams, T

    2004-12-01

    In this paper we present an experimental study of the dynamics of underwater sand ripples when a regular pattern of ripples is subjected to a skewed oscillatory flow, i.e., one not perpendicular to the direction of the ripple crests. Striking patterns with new, superposed ripples on top of the original ones occur very quickly with a characteristic angle, which is, in general, not perpendicular to the flow. A slower, more complex transition then follows, leading to the final state where the ripples are again perpendicular to the flow. We investigate the variation of the superposed pattern as a function of the direction, amplitude, and frequency of the drive, and as a function of the viscosity (by changing the temperature). We quantify the dynamics of the entire transition process and finally study the grain motion around idealized (solid) skewed ripples. This leads to a characteristic mean path of a single particle. The path has a shape close to a parallelogram, with no apparent connection to the pattern of real, superposed ripples. On the other hand, a thin layer of sand sprinkled on the solid ripples leads to qualitatively similar patterns. PMID:15697484

  5. New Method for Estimation of Aeolian Sand Transport Rate Using Ceramic Sand Flux Sensor (UD-101)

    PubMed Central

    Udo, Keiko

    2009-01-01

    In this study, a new method for the estimation of aeolian sand transport rate was developed; the method employs a ceramic sand flux sensor (UD-101). UD-101 detects wind-blown sand impacting on its surface. The method was devised by considering the results of wind tunnel experiments that were performed using a vertical sediment trap and the UD-101. Field measurements to evaluate the estimation accuracy during the prevalence of unsteady winds were performed on a flat backshore. The results showed that aeolian sand transport rates estimated using the developed method were of the same order as those estimated using the existing method for high transport rates, i.e., for transport rates greater than 0.01 kg m−1 s−1. PMID:22291553

  6. Oscillation-induced sand ripples in a circular geometry.

    PubMed

    Rousseaux, Germain; Kruithof, Joachim; Jenffer, Patrice; Wesfreid, José Eduardo

    2008-07-01

    This study deals with the observation of sand ripples in a circular geometry under oscillatory flow. We characterize the observed patterns as a function of the excitation parameters. We report the time evolution of the corrugated front invading the flat bed. These experiments reveal unambiguously, because of the gradient of shear stress, the existence of two separated thresholds: one for grain motion and the other for the appearance of ripples. In addition, we display the phase diagram of this instability as a function of the Froude number and a Reynolds number. PMID:18764045

  7. Dynamics of propagating front into sand ripples under regular waves.

    PubMed

    Lebunetel-Levaslot, J; Jarno-Druaux, A; Ezersky, A B; Marin, F

    2010-09-01

    The results of an experimental study of pattern formation on sandy bottom under the action of regular harmonic surface waves are reported. It is found that two modes of pattern formation occur: sand ripples form uniformly on the whole bottom or from localized nucleation sites. In the second regime, the ripples appear in isolated regions (patches) increasing in size, and front propagation speed is measured. A simple dynamical model based on the Ginzburg-Landau equation is proposed to explain the characteristics of patches. PMID:21230122

  8. 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

  9. Aeolian sand preserved in Silver Lake: a new signal of Holocene high stands of Lake Michigan

    USGS Publications Warehouse

    Fisher, Timothy G.; Loope, Walter L.

    2005-01-01

    Aeolian sand within lake sediment from Silver Lake, Michigan can be used as a proxy for the timing of high lake levels of Lake Michigan.We demonstrate that the sand record from Silver Lake plotted as percent weight is in-phase with the elevation curve of Lake Michigan since the mid-Holocene Nipissing Phase. Because fluctuations in Lake Michigan's lake level are recorded in beach ridges, and are a response to climate change, the aeolian sand record within Silver Lake is also a proxy for climate change. It appears that increases in dune activity and lake sand are controlled by similar climatic shifts that drive fluctuations in lake level of Lake Michigan. High lake levels destabilize coastal bluffs that drive dune sand instability, and along with greater wintertime storminess, increase niveo-aeolian transport of sand across lake ice. The sand is introduced into the lake each spring as the ice cover melts.

  10. Energy regimes for aeolian sand grain surface textures

    NASA Astrophysics Data System (ADS)

    Marshall, J. R.; Bull, P. A.; Morgan, R. M.

    2012-05-01

    An experimental study of aeolian sand grain surface texture development was undertaken with an air-driven grain-recirculating desktop apparatus. Scanning electron microscope analysis of resulting textures indicated that different texture types can be associated with distinct zones in a grain-shape/grain speed matrix. In particular, for subrounded and rounded grains, low and high energy transport can be unequivocally distinguished by the occurrence of upturned plates and Hertzian frustra respectively. Textural development does not have a simple relationship to grain velocity, but appears to relate to the energy expended per unit area within the contact zone generated by elastic deformation during impact. Hertzian theory was adapted to irregular sand grain shapes and close agreement was found between experimental results and theoretical predictions for textural development. Results of this study improve our ability to reconstruct palaeoaeolian environments and therefore our ability to determine grain provenance; in particular, the latter is shown to have direct relevance to forensic inquiries and terrorism investigations.

  11. Predicting aeolian sand transport rates: A reevaluation of models

    NASA Astrophysics Data System (ADS)

    Sherman, Douglas J.; Li, Bailiang

    2012-01-01

    Eight aeolian sand-transport models are evaluated using a field data set and a new approach to estimating shear velocity. The models are those of Bagnold (1937), Kawamura (1951), Zingg (1953), Owen (1964), Kadib (1965), Hsu (1971), Lettau and Lettau (1978) and Sørensen (2004). All of these models predict transport as a function of shear velocity to the third power. Shear velocities are estimated using wind profile data (log-linear slope) with the von Kármán constant and with the apparent von Kármán parameter and the results of the different approaches are evaluated based on comparison of regression statistics and RMS error. The models were not adjusted to account for sediment moisture content or local surface slope effects. All of the models have about the same statistical explanatory power, so evaluations were made by comparing slopes and intercepts of best fit (least-squares) lines and RMSE. From this basis, we conclude that predictions made with the Bagnold (1937) model best match our observations, with the models of Kadib (1965) and Hsu (1971) performing nearly as well. The Lettau and Lettau (1978) and Kawamura (1951) model predictions match observations least.

  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. PMID:25089295

  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. Tidal-cycle changes in oscillation ripples on the inner part of an estuarine sand flat

    USGS Publications Warehouse

    Dingler, J.R.; Clifton, H.E.

    1984-01-01

    Oscillation ripples form on subaqueous sand beds when wave-generated, near-bottom water motions are strong enough to move sand grains. The threshold of grain motion is the lower bound of the regime of oscillation ripples and the onset of sheet flow is the upper bound. Based on the relation between ripple spacing and orbital diameter, three types of symmetrical ripples occur within the ripple regime. In the lower part of the ripple regime (orbital ripples), spacing is proportional to orbital diameter; in the upper part (anorbital ripples) spacing is independent of orbital diameter. Between these regions occurs a transitional region (suborbital ripples). Oscillation ripples develop on a sandy tidal flat in Willapa Bay, Washington, as a result of waves traversing the area when it is submerged. Because wave energy is usually low within the bay, the ripples are primarily orbital in type. This means that their spacing should respond in a systematic way to changes in wave conditions. During the high-water parts of some tidal cycles, ripples near the beach decrease in spacing during the latter stage of the ebb tide while ripples farther offshore do not change. Observations made over several tidal cycles show that the zone of active ripples shifts on- or offshore in response to different wave conditions. Detailed bed profiles and current measurements taken during the high-water part of spring tides show the manner in which the oscillation ripples change with changes in orbital diameter. Changes in ripple spacing at the study site could be correlated with changes in orbital diameter in the manner suggested by the criterion for orbital ripples. However, there appeared to be a lag time between a decrease in orbital diameter and the corresponding decrease in ripple spacing. Absence of change during a tidal cycle could be attributed to orbital velocities below the threshold for grain motion that negated the effects of changes in orbital diameter. Because changes in sand

  15. 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., Jr.; 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.

  16. 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

  17. 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.

  18. 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.

  19. Precessive sand ripples in intense steady shear flows.

    PubMed

    Restrepo, Juan M; Moulton, Derek E; Uys, Hermann

    2011-03-01

    We describe experimental observations of fully developed, large-amplitude bars under the action of a shearing fluid. The experiments were performed in an annular tank filled with water and sheared above by a steady motor source. The same steady shearing flow can produce a variety of different erodible bed manifestations: advective or precessive bars, which refer to bar structures with global regularity and a near-steady precession velocity; interactive bars, the structure of which depends on local rearrangements, which are in turn a response to complex background topography; and dispersive bars, which are created when an initially isolated mound of sand evolves into a train of sand ripples. Of these, the most amenable to analysis are the precessive bars. For precession bars, we find that the skin depth, which is the nondimensionalized mean-field transport rate, grows exponentially as a function of the shear velocity. From this, we arrive at an analytical expression that approximates the precession speed of the bars as a function of shear velocity. We use this to obtain a formula for sediment transport rate. However, in intense flows, the bars can get large engendering boundary layer separation, leading to a different dynamic for bar formation and evolution. Numerical flow calculations over an experimentally obtained set of precessive bars are presented and show that classical parametrizations of mass flux in terms of bottom gradients have shortcomings. Within the range of shear rates considered, a quantity that does not change appreciably in time is the aspect ratio, which is defined as the ratio of the average bar amplitude, with respect to a mean depth, to the average bar length. PMID:21517492

  20. Precessive sand ripples in intense steady shear flows

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan M.; Moulton, Derek E.; Uys, Hermann

    2011-03-01

    We describe experimental observations of fully developed, large-amplitude bars under the action of a shearing fluid. The experiments were performed in an annular tank filled with water and sheared above by a steady motor source. The same steady shearing flow can produce a variety of different erodible bed manifestations: advective or precessive bars, which refer to bar structures with global regularity and a near-steady precession velocity; interactive bars, the structure of which depends on local rearrangements, which are in turn a response to complex background topography; and dispersive bars, which are created when an initially isolated mound of sand evolves into a train of sand ripples. Of these, the most amenable to analysis are the precessive bars. For precession bars, we find that the skin depth, which is the nondimensionalized mean-field transport rate, grows exponentially as a function of the shear velocity. From this, we arrive at an analytical expression that approximates the precession speed of the bars as a function of shear velocity. We use this to obtain a formula for sediment transport rate. However, in intense flows, the bars can get large engendering boundary layer separation, leading to a different dynamic for bar formation and evolution. Numerical flow calculations over an experimentally obtained set of precessive bars are presented and show that classical parametrizations of mass flux in terms of bottom gradients have shortcomings. Within the range of shear rates considered, a quantity that does not change appreciably in time is the aspect ratio, which is defined as the ratio of the average bar amplitude, with respect to a mean depth, to the average bar length.

  1. Wave-induced ripple development in mixed clay-sand substrates

    NASA Astrophysics Data System (ADS)

    Wu, Xuxu; Parsons, Daniel; Baas, Jaco H.; Mouazé, Dominique; McLelland, Stuart; Amoudry, Laurent; Eggenhuisen, Jorris; Cartigny, Matthieu; Ruessink, Gerben

    2016-04-01

    This paper reports on a series of experiments that aim to provide a fuller understanding of ripple development within clay-sand mixture substrates under oscillatory flow conditions. The work was conducted in the Total Environment Simulator at the University of Hull and constituted 6 separate runs, in which 5 runs were conducted under identical sets of regular waves (an additional run was conducted under irregular waves, but is not discussed in present paper). The bed content was systematically varied in its composition ranging from a pure sand bed through to a bed comprising 7.4% clay. A series of state-of-the-art measurements were employed to quantify interactions of near-bed hydrodynamics, sediment transport, and turbulence over rippled beds formed by wave action, during and after, each run. The experimental results demonstrate the significant influence of the amount of cohesive clay materials in the substrate on ripple evolution under waves. Most importantly, addition of clay in the bed dramatically slowed down the rate of ripple development and evolution. The equilibrium time of each run increased exponentially from 30 minutes under the control conditions of a pure sand bed, rising to ~350 minutes for the bed with the highest fraction of clay. The paper discusses the slower ripple growth rates with higher cohesive fractions, via an influence on critical shear, but highlights that the end equilibrium size of ripples is found to be independent of increasing substrate clay fraction. The suspended particles mass (SPM) concentration indicates that clay particles were suspended and winnowed by wave action. Additionally, laser granulometry of the final substrates verified that ripple crests were composed of pure sand layers that were absent at ripple troughs, reflecting a relatively higher winnowing efficiency at wave ripples crest. The winnowing process and its efficiency is inexorably linked to wave ripple development and evolution. The implications of the results

  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. 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.

  4. 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., Jr.; 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

  5. Numerical study of shear stress distribution at sand ripple surface in wind tunnel flow

    NASA Astrophysics Data System (ADS)

    Bar, Nitsan; Elperin, Tov; Katra, Itzhak; Yizhaq, Hezi

    2016-06-01

    The mechanism responsible for the formation and sustainability of sand ripples sheared by a uniform air flow is not well understood, despite the significant attention that has been given to it ever since the pioneering studies of Bagnold (1941). In this study we explore ANSYS Fluent simulations of fine-scale turbulent flow structure in the vicinity of 2D sand ripples with particular emphasis on shear stress distribution at the sand bed. The flow parameters in the simulations were pertinent to the wind tunnel experiments for studying sand ripples formation. The simulations show that the shear stress at the crest is about 2.5 times larger than the shear stress at the trough and that in most of the simulations a separation bubble has been developed at the lee slope. In contrast to wind tunnel experiments the simulations show that ripples will be flattened at wind speed of 9 m/s as shear stress at the ripples surface exceeds the fluid threshold. This discrepancy between the calculations and real wind tunnel measurements are due to the important role of the saltation layer on the decrease of the shear stress at the surface. Without this effect ripples cannot grow higher and will be diminished at quite moderate winds.

  6. Basaltic sand ripples at Eagle Crater as indirect evidence for the hysteresis effect in martian saltation

    NASA Astrophysics Data System (ADS)

    Yizhaq, H.; Kok, J. F.; Katra, I.

    2014-02-01

    The rover Opportunity documented small basaltic sand ripples at the bottom of Eagle Crater, Meridiani Planum on Mars. These ripples are composed of fine basaltic sand (˜100 μm diameter) and their average wavelength and height are 10 cm and 1 cm, respectively. Present theories on the transition between saltation and suspension predict that such light particles are suspended by turbulence at the fluid threshold, which is the minimum wind speed required to initiate saltation. Consequently, the existence of these ˜100 μm ripples on Mars indicates that either current suspension theories are incorrect, or that saltation can take place at wind speeds substantially below the fluid threshold. Indeed, recent studies point to the occurrence of hysteresis in martian saltation. That is, once initiated, hysteresis can be maintained at much lower wind speeds than the fluid threshold. We investigated the possible role of hysteresis in the formation of fine-grained ripples on Mars by coupling, for the first time, a detailed numerical saltation model (COMSALT) with a dynamic model for sand ripple formation. The results from the coupled model indicate that ripples with properties similar to those observed at Eagle Crater can be developed by the impact mechanism at shear velocities far below the fluid threshold. These findings are consistent with the occurrence of hysteresis in martian saltation, and support the hypothesis that hysteresis plays a role in the surprisingly large sand mobility observed at several locations on Mars.

  7. Discrete Element Method simulations of the saturation of aeolian sand transport

    NASA Astrophysics Data System (ADS)

    Pähtz, Thomas; Omeradžić, Amir; Carneiro, Marcus V.; Araújo, Nuno A. M.; Herrmann, Hans J.

    2015-03-01

    The saturation length of aeolian sand transport (Ls), characterizing the distance needed by wind-blown sand to adapt to changes in the wind shear, is essential for accurate modeling of the morphodynamics of Earth's sandy landscapes and for explaining the formation and shape of sand dunes. In the last decade, it has become a widely accepted hypothesis that Ls is proportional to the characteristic distance needed by transported particles to reach the wind speed (the "drag length"). Here we challenge this hypothesis. From extensive numerical Discrete Element Method simulations, we find that, for medium and strong winds, Ls∝Vs2/g, where Vs is the saturated value of the average speed of sand particles traveling above the surface and g is the gravitational constant. We show that this proportionality is consistent with a recent analytical model, in which the drag length is just one of four similarly important length scales relevant for sand transport saturation.

  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. 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. 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

  11. Sand ripples under water with complex wave motion.

    PubMed

    Scheibye-Knudsen, K; Ellegaard, C; Bundgaard, F; Sams, Thomas

    2005-07-01

    Experiments studying ripple formation under water have usually used sinusoidal driving force. Here an experiment is presented where the driving force can be an arbitrary wave form, thus trying to mimic the realistic wave motion in shallow water coastal zones. We study a simple modulated sine wave and more complicated wave forms with several superposed harmonics. In particular we demonstrate how a small higher order harmonic can have a dramatic effect on the wavelength of the ripple pattern. PMID:16090068

  12. 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.

  13. Morphology and stratigraphic evolution of aeolian protodunes at White Sands Dune Field

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.; Weymer, B. A.; Barrineaux, P.

    2014-12-01

    Protodunes are low-relief, slipfaceless migrating bed forms thought to represent fundamental emergent bed forms that develop from a flat bed of sand and evolve into dunes. Protodunes at White Sands Dune Field in New Mexico are found at the upwind margin of the field, on dune stoss slopes and in interdune areas. Here we used time-series aerial photos from 1996, 2003, 2005 and 2012 and digital elevation models from 2007, 2008, 2009 and 2010 in conjunction with ground penetrating radar (GPR) to characterize the morphodynamics of protodunes and the stratigraphy generated by protodune migration. Protodunes at the upwind margin of the dune field are larger in wavelength and amplitude and coarser grained than those in the interior of the field. Wind ripples cover protodunes in all areas of the field, but the protodunes at the upwind margin are covered by coarse grained ripples. A consistent progression of ripple patterns occurs over protodunes in which ripples coarsen in wavelength and grain size toward the protodune crest and then decrease in wavelength and grain size toward the troughs. Ripple migration across the protodunes appears to the primary mode by which the protodunes migrate. Trenching and GPR data show low-angle cross-stratification generated by wind ripples migrating down the protodune lee slope of the protodunes. Internal bounding surfaces within the protodunes likely arise from laterally migration and lee slope reactivation in response to the complex wind regime and dune-modified secondary flow within the dune field at White Sands. Understanding the morphology, distribution and genesis of protodunes in dune fields provides a basis to evaluate the significance of protodune strata in the rock record.

  14. Pattern dynamics of vortex ripples in sand: nonlinear modeling and experimental validation.

    PubMed

    Andersen, K H; Abel, M; Krug, J; Ellegaard, C; Søndergaard, L R; Udesen, J

    2002-06-10

    Vortex ripples in sand are studied experimentally in a one-dimensional setup with periodic boundary conditions. The nonlinear evolution, far from the onset of instability, is analyzed in the framework of a simple model developed for homogeneous patterns. The interaction function describing the mass transport between neighboring ripples is extracted from experimental runs using a recently proposed method for data analysis, and the predictions of the model are compared to the experiment. An analytic explanation of the wavelength selection mechanism in the model is provided, and the width of the stable band of ripples is measured. PMID:12059366

  15. 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.

  16. Measurements of subcritical grazing angle detection of targets buried under a rippled sand interface

    NASA Astrophysics Data System (ADS)

    Lopes, J. L.; Nesbitt, C. L.; Lim, R.; Tang, D.; Williams, K. L.; Thorsos, E. I.

    2003-04-01

    A series of controlled measurements were conducted to investigate shallow grazing angle acoustic detection of targets buried in sand having a rippled sediment-water interface. The measurements were performed in a 13.7-m deep, 110-m long, 80-m-wide test-pool with a 1.5-m layer of sand on the bottom. A silicone oil filled target sphere was buried under a rippled interface with contours formed by scraping the sand with a machined rake moved along a guide frame. Broadband, broad beam transducers were placed onto the shaft of a tilting motor. The transducers and tilting motor were attached to an elevated rail that enabled this assembly to be translated horizontally, permitting acquired data to be processed using synthetic aperture sonar techniques. Acoustic backscatter data were acquired at subcritical grazing angles in the frequency range of 10 to 50 kHz for various ripple wavelengths and heights. For each bottom configuration, the ripple profile over the buried target was measured using the In-situ Measurement of Porosity 2 (IMP2) system. Measurement results are presented that illustrate target detection via ripple scattering. The characteristics of the target return are found to depend sensitively on the ripple height and wavelength. [Work supported by ONR.

  17. Experimental and Numerical Study of Sharp's Shadow Zone Hypothesis on Sand Ripples Spacing and Implication for Martian Sand Ripples

    NASA Astrophysics Data System (ADS)

    Yizhaq, H.; Schmerler, E.; Katra, I.; Tsoar, H.; Kok, J.

    2015-05-01

    We show by wind tunnel experiments and numerical simulations that the impact angle of saltation grains decreases with wind velocity. This relationship can explain the increase in ripple wavelength with wind speed as was suggested by Sharp (1963).

  18. Amplitude equation for under water sand-ripples in one dimension.

    NASA Astrophysics Data System (ADS)

    Schnipper, Teis; Mertens, Keith; Ellegaard, Clive; Bohr, Tomas

    2007-11-01

    Sand-ripples under oscillatory water flow form periodic patterns with wave lengths primarily controlled by the amplitude d of the water motion. We present an amplitude equation for sand-ripples in one spatial dimension which captures the formation of the ripples as well as secondary bifurcations observed when the amplitude d is suddenly varied. The equation has the form [ ht=- ɛ(h-h)+((hx)^2-1)hxx- hxxxx+ δ((hx)^2)xx] which, due to the first term, is neither completely local (it has long-range coupling through the average height h) nor has local sand conservation. We discuss why this is reasonable and how this term (with ɛ˜d-2) stops the coarsening process at a finite wavelength proportional to d. We compare our numerical results with experimental observations in a narrow channel.

  19. Laboratory Observations of Sand Ripple Evolution in a Small Oscillatory Flow Tunnel

    NASA Astrophysics Data System (ADS)

    Calantoni, J.; Palmsten, M. L.; Chu, J.; Landry, B. J.; Penko, A.

    2014-12-01

    The dynamics of sand ripples are vital to understanding numerous coastal processes such as sediment transport, wave attenuation, boundary layer development, and seafloor acoustic properties. Experimental work was conducted in a small oscillatory flow tunnel at the Sediment Dynamics Laboratory at the Naval Research Laboratory, Stennis Space Center. Six different monochromatic oscillatory forcings, three with velocity asymmetry and three without, were used to investigate sand ripple dynamics using a unimodal grain size distribution with D50=0.65 mm. The experiments represent an extension of previous work using bimodal grain size distributions. A DSLR camera with a 180-degree fisheye lens collected images of the sediment bed profile every 2 seconds to resolve changes in ripple geometries and migration rates resulting from the different flow conditions for over 127 hours (229,388 images). Matlab © algorithms undistorted the fisheye images and quantified the ripple geometries, wavelengths, heights, and migration rates as a function of flow forcing. The mobility number was kept nearly constant by increasing and decreasing the semi-excursion amplitude and the wave frequency, respectively. We observed distinct changes in ripple geometry and migration rate for the pair of oscillatory forcings having nearly identical mobility numbers. The results suggested that the commonly used mobility number might not be appropriate to characterize ripple geometry or migration rates.

  20. Occurrence and orientation of anorbital ripples in near-shore sands

    NASA Astrophysics Data System (ADS)

    Maier, Irene; Hay, Alex E.

    2009-12-01

    The orientation of linear transition ripples (LTRs) relative to incident wave direction is studied using rotary fan beam sonar images and wave and current data from electromagnetic flowmeters in ˜3 m water during SandyDuck97. LTR occurrence is determined objectively with an automatic recognition algorithm. LTRs occurred for RMS wave orbital velocities between 0.15 and 0.35 m s-1. The ripples were highly two dimensional, and of the anorbital type (λ0/D50 = 524 to 535, d0/D50 = 4300 to 25,000) with 7.6 cm mean wavelength in 150 μm median diameter sand. The ripple crests were typically aligned perpendicular to the incident sea-and-swell direction: specifically, about 60% of the normals to the crests differ from wave direction by less than 5° and more than 90% by less than 10°. During rapid changes in wave direction, however, ripple orientation adjustment lagged the wave direction by O(1 h). Ripple reorientation occurred piecewise along the crests, with new crest segments sometimes bridging two or more old segments. The 1 h reorientation time scale is longer by several orders of magnitude than the adjustment time based on theoretical bed load transport rate and the ripple volume. As a possible explanation, we suggest that a significant fraction of the transport, more than 90%, bypasses the ripples during orientation adjustment through large angles.

  1. Mapping Winds over Martian Sand Dunes from Ripples and Digital Terrain Models

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Sand dunes preserve wind flow patterns in their ripple formations. DTMs can be used with wind modeling software to simulate wind speed and direction over these dunes. Results can be compared and together offer a more complete picture of recent wind.

  2. 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

  3. 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.

  4. Long-time behavior of sand ripples induced by water shear flow.

    PubMed

    Betat, A; Kruelle, C A; Frette, V; Rehberg, I

    2002-08-01

    The formation of sand ripples under water shear flow in a narrow annular channel and the approach of the ripple pattern towards a steady state were studied experimentally. Four results are obtained: i) The mean amplitude, the average drift velocity and the mean sediment transport rate of the evolving bed shape are strongly related. A quantitative characterization of this relation is given. ii) The ripple pattern reaches a stationary state with a finite ripple amplitude and wavelength. The time needed to reach the state depends on the shear stress and may be several days. iii) The onset of ripple formation is determined by the bed shear stress, but it seems neither to depend on the grain diameter nor on the depth of the water layer. iv) The ripple amplitude, drift velocity and sediment transport in this stationary state depend on the grain size. This dependency is neither captured by the particle Reynolds number nor by the Shields parameter: an empirical scaling law is presented instead. PMID:15015119

  5. Wave-induced ripples development in mixed clay-sand substrates

    NASA Astrophysics Data System (ADS)

    Wu, Xuxu; Parsons, Daniel; Baas, Jaco Hugo; McLelland, Stuart; Amoudry, Laurent; Mouazé, Dominique; Eggenhuisen, Jorris; Cartigny, Matthieu; Ruessink, Gerben

    2015-04-01

    Wave-induced ripples development in mixed clay-sand substrates A large-scale flume experiment (as part of EU HYDRALAB IV) was conducted in the Total Environment Simulator, University of Hull from 27th August to 25th September, 2013. The purpose of the experiments was to provide full quantification of near-bed turbulence and sediment transport interactions over rippled beds of clay-sand mixtures under oscillatory flow conditions. A series of state-of-the-art measurements were employed to quantify interactions of near-bed hydrodynamics, sediment transport, and turbulence over rippled beds formed by wave action. The experimental results demonstrate the significant influence of the amount of cohesive materials in the substrate on bedform evolution under regular surface waves. Most importantly, the time of initial ripples appearance is delayed around 30 minutes in substrates with higher percentages of cohesive clays (Run 5, 5.3%; Run 6, 5.5%) compared with experiments conducted with well-sorted sand (a median diameter of ~ 496

  6. 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

  7. 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

  8. Gully annealing by fluvially-sourced Aeolian sand: remote sensing investigations of connectivity along the Fluvial-Aeolian-hillslope continuum on the Colorado River

    USGS Publications Warehouse

    Sankey, Joel B.; East, Amy E.; Collins, Brian D.; Caster, Joshua

    2015-01-01

    Processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide, and particularly in dryland regions where soil loss and land degradation from gully erosion pose long-term, land-management problems. Whereas gully formation has been relatively well studied, much less is known of the processes that anneal gullies and impede their growth. This work investigates gully annealing by aeolian sediment, along the Colorado River downstream of Glen Canyon Dam in Glen, Marble, and Grand Canyons, Arizona, USA (Figure 1). In this segment of the Colorado River, gully erosion potentially affects the stability and preservation of archaeological sites that are located within valley margins. Gully erosion occurs as a function of ephemeral, rainfall-induced overland flow associated with intense episodes of seasonal precipitation. Measurements of sediment transport and topographic change have demonstrated that fluvial sand in some locations is transported inland and upslope by aeolian processes to areas affected by gully erosion, and aeolian sediment activity can be locally effective at counteracting gully erosion (Draut, 2012; Collins and others, 2009, 2012; Sankey and Draut, 2014). The degree to which specific locations are affected by upslope wind redistribution of sand from active channel sandbars to higher elevation valley margins is termed “connectivity”. Connectivity is controlled spatially throughout the river by (1) the presence of upwind sources of fluvial sand within the contemporary active river channel (e.g., sandbars), and (2) bio-physical barriers that include vegetation and topography that might impede aeolian sediment transport. The primary hypothesis of this work is that high degrees of connectivity lead to less gullying potential.

  9. Remote sensing and spatial analysis of aeolian sand dunes: A review and outlook

    NASA Astrophysics Data System (ADS)

    Hugenholtz, Chris H.; Levin, Noam; Barchyn, Thomas E.; Baddock, Matthew C.

    2012-03-01

    For more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes. Early studies focused on mapping and classifying dunes. Recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development. These advances have taken place alongside progress in numerical models, which are capable of simulating the multitude of dune patterns observed in nature. The potential to integrate remote sensing (RS), spatial analysis (SA), and modeling to predict the future changes of real-world dune systems is steadily becoming a reality. Here we present a comprehensive review of significant recent advances involving RS and SA. Our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains: (1) dune activity, (2) dune patterns and hierarchies, and (3) extra-terrestrial dunes. We outline how several recent advances have capitalized on the improved spatial and spectral resolution of RS data, the availability of topographic data, and new SA methods and software. We also discuss some of the key research challenges and opportunities in the application of RS and SA dune field, including: the integration of RS data with field-based measurements of vegetation cover, structure, and aeolian transport rate in order to develop predictive models of dune field activity; expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models; the development and application of objective and reproducible SA methods for characterizing dune field pattern; and, expanding efforts to quantify three-dimensional topographic changes of dune fields in order to develop improved understanding of spatio-temporal patterns of erosion and deposition. Overall, our review indicates a progressive evolution in the way sand dunes

  10. Amplitude equation and long-range interactions in underwater sand ripples in one dimension

    NASA Astrophysics Data System (ADS)

    Schnipper, Teis; Mertens, Keith; Ellegaard, Clive; Bohr, Tomas

    2008-10-01

    We present an amplitude equation for sand ripples under oscillatory flow in a situation where the sand is moving in a narrow channel and the height profile is practically one dimensional. The equation has the form ht=-γ(h- hmacr )+((hx)2-1)hxx-hxxxx+δ((hx)2)xx which, due to the first term, is neither completely local (it has long-range coupling through the average height hmacr ) nor has local sand conservation. We argue that this is reasonable and show that the equation compares well with experimental observations in narrow channels. We focus in particular on the so-called doubling transition, a secondary instability caused by the sudden decrease in the amplitude of the water motion, leading to the appearance of a new ripple in each trough. This transition is well reproduced for sufficiently large δ (asymmetry between trough and crest). We finally present surprising experimental results showing that long-range coupling is indeed seen in the initial details of the doubling transition, where in fact two small ripples are initially formed, followed by global symmetry breaking removing one of them.

  11. Amplitude equation and long-range interactions in underwater sand ripples in one dimension.

    PubMed

    Schnipper, Teis; Mertens, Keith; Ellegaard, Clive; Bohr, Tomas

    2008-10-01

    We present an amplitude equation for sand ripples under oscillatory flow in a situation where the sand is moving in a narrow channel and the height profile is practically one dimensional. The equation has the form ht = - epsilon(h-h)+((hx)2-1)hxx-hxxxx+delta((hx)2)xx which, due to the first term, is neither completely local (it has long-range coupling through the average height h) nor has local sand conservation. We argue that this is reasonable and show that the equation compares well with experimental observations in narrow channels. We focus in particular on the so-called doubling transition, a secondary instability caused by the sudden decrease in the amplitude of the water motion, leading to the appearance of a new ripple in each trough. This transition is well reproduced for sufficiently large delta (asymmetry between trough and crest). We finally present surprising experimental results showing that long-range coupling is indeed seen in the initial details of the doubling transition, where in fact two small ripples are initially formed, followed by global symmetry breaking removing one of them. PMID:18999572

  12. 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

  13. 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.

  14. 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.

  15. Evaluation of Surface Slope Effects on Ripple Orientations Observed on Sand Dunes in the Terra Tyrrhena Region of Mars

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The High Resolution Imaging Science Experiment (HiRISE) has revealed abundant wind ripples on sand dunes across Mars. Ripple orientations have been documented using HiRISE images of sand dunes at 24 widely distributed sites across Mars, in order to identify the last significant wind directions at these locations. Howard (GSAB, 1977) gives a mathematical expression for how surface slopes on a sand dune can affect the orientation of ripples with respect to the formative winds. In order to evaluate this mechanism for measured ripple orientations on Mars, quantitative data for surface slopes on the sand dunes is required. Stereo pairs of HiRISE images are used to generate Digital Terrain Models (DTMs) with postings of one meter. In June 2014 we produced a DTM of sand dunes in the Terra Tyrrhena region of Mars (14.55° S, 97.77° E) using SOCET SET at the Astrogeology Branch, USGS-Flagstaff. Typically it is difficult for feature matching software to work well on sand dunes, but our stereo images (ESP_022609_1655 and ESP_026675_1655) were obtained only six Earth days apart under excellent illumination conditions. The Terra Tyrrhena DTM had remarkably few artifacts on the sand dunes (except at slip faces, where the average slope between slip face crest and base was interpolated) and excellent control from irregular terrain exposed in interdune areas. Slopes on the stoss sides of sand dunes are generally <10°; the Howard equation indicates ripple deflection angles should be <17° with respect to the actual surface wind direction. We are adjusting documented ripple orientations to account for surface slopes utilizing the DTM data, and so far we do not see major changes to inferred surface wind directions that would be derived directly from the ripple orientations.

  16. 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

  17. 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

  18. Initiation and evolution of current ripples on a flat sand bed under turbulent water flow.

    PubMed

    Langlois, V; Valance, A

    2007-03-01

    We investigate the formation and dynamics of sand ripples under a turbulent water flow. Our experiments were conducted in an open flume with spherical glass beads between 100 and 500 microm in diameter. The flow Reynolds number is of the order of 10,000 and the particle Reynolds number of the order of 1 to 10. We study the development of ripples by measuring their wavelength and amplitude in course of time and investigate the influence of the grain size and the flow properties. In particular, we demonstrate two different regimes according to the grain size. For fine grains, a slow coarsening process (i.e., a logarithmic increase of the wavelength and amplitude) takes place, while for coarser grains, this process occurs at a much faster rate (i.e., with a linear growth) and stops after a finite time. In the later case, a stable pattern is eventually observed. Besides, we carefully analyze the wavelength of ripples in the first stages of the instability as a function of the grain size and the shear velocity of the flow, and compare our results with other available experimental data and with theoretical predictions based on linear stability analyses. PMID:17426938

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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. PMID:22982806

  4. On a new hydrid method to modelize the turbulence over marine sand ripples

    NASA Astrophysics Data System (ADS)

    Bennis, Anne-claire; Le Bot, Sophie; Lafite, Robert; Bonneton, Philippe; Ardhuin, Fabrice

    2015-04-01

    Marine sand ripples are frequently observed due to water motion. Modelling coastal sediment transport is a difficult task because of the turbulent small-scale processes. At regional scale, the accurate methods such as LES and DNS cannot be used due to limitations of computing ressources. Most of coastal models are based on the RANS method. A hybrid method combining RANS and LES is a relevant option. We implement a new hybrid method in our 3D hydrodynamic model forced by the waves. The first step was to test on cases where the intraripple dynamic is resolved. RANS and LES are employed near the bottom and elsewhere respectively, thus allowing us to ensure a better accuracy of the results than using a fully RANS model. This also reduces the computational cost compared to a fully LES model. The validation step was performed with two sets of field data and also with the data from Dune2D model which uses only RANS for turbulence. The main comparison results are: a) the vertical profiles of the velocity are similar to all the data b) the turbulent kinetic energy, underestimated by Dune2D, agrees with the observations c) the concentration of the suspended sediment is simulated with a better accuracy than using Dune2D, however it remains slightly lower than the observations. Secondly, the hybrid method is evaluated for coastal simulations in the Bay of Somme where the effects of ripples are parameterized. As expected, our method improves the results in comparison with the original fully RANS model.

  5. Sorting during Migration of Aeolian Megaripples

    NASA Astrophysics Data System (ADS)

    Sullivan, R. J., Jr.; Zimbelman, J. R.

    2014-12-01

    Aeolian sediments commonly are well sorted. However, aeolian megaripples (aka coarse-grained ripples or granule ripples) have bimodal grain size-frequencies. Distinguishing aeolian megaripple deposits from mixed grain size fluvial deposits is important, particularly for martian sedimentary rocks where implications for flowing water in the martian past (if revealed by legitimate fluvial deposits) are important mission drivers for rovers and landers. Aeolian megaripples are relatively minor components of terrestrial aeolian settings (e.g., as interdune features), but on Mars, megaripples have been encountered in many locations by landers and rovers, are durable due to indurated, armoring surface layers of very coarse sand, and therefore are likely candidates for preservation in the martian sedimentary rock record. Unfortunately, megaripple deposits preserved in martian sedimentary rocks must be recognized with much less data or context than obtained typically during terrestrial fieldwork. We have undertaken wind tunnel experiments and fieldwork to assist interpretations distinguishing aeolian megaripple deposits from mixed grain fluvial materials. Lags of coarse or very coarse sand from ancient aeolian environments within the White Rim Sandstone, Canyonlands NP, UT, and at some localities along the J2 Unconformity at Buckhorn Wash, UT, are well sorted, with a sharply defined maximum grain size in each case. We conducted wind tunnel experiments to explore whether the well-sorted, sharp cutoff in maximum grain size of the coarse fraction in these deposits could be diagnostic of aeolian megaripple formation and migration. Wind tunnel experiments involved 250 μm sand saltating against 600-2800 μm grains. For a given wind tunnel speed, only a narrow grain size range appeared on megaripple surfaces as these bedforms developed spontaneously from the bed; somewhat finer grains migrated rapidly downwind, while slightly coarser grains remained immobile. The physics of

  6. 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.

  7. 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

  8. Observations of plan-view sand ripple behavior and spectral wave climate on the inner shelf of San Pedro Bay, California

    USGS Publications Warehouse

    Xu, J. P.

    2005-01-01

    Concurrent video images of sand ripples and current meter measurements of directional wave spectra are analyzed to study the relations between waves and wave-generated sand ripples. The data were collected on the inner shelf off Huntington Beach, California, at 15 m water depth, where the sea floor is comprised of well-sorted very fine sands (D50=92 ??m), during the winter of 2002. The wave climate, which was controlled by southerly swells (12-18 s period) and westerly wind waves (5-10 s period), included three wave types: (A) uni-modal, swells only; (B) bi-modal, swells dominant; and (C) bi-modal, wind-wave dominant. Each wave type has distinct relations with the plan-view shapes of ripples that are classified into five types: (1) sharp-crested, two-dimensional (2-D) ripples; (2) sharp-crested, brick-pattern, 3-D ripples; (3) bifurcated, 3-D ripples; (4) round-crested, shallow, 3-D ripples; and (5) flat bed. The ripple spacing is very small and varies between 4.5 and 7.5 cm. These ripples are anorbital as ripples in many field studies. Ripple orientation is only correlated with wave directions during strong storms (wave type C). In a poly-modal, multi-directional spectral wave environment, the use of the peak parameters (frequency, direction), a common practice when spectral wave measurements are unavailable, may lead to significant errors in boundary layer and sediment transport calculations. ?? 2004 Elsevier Ltd. All rights reserved.

  9. On the modeling of the bottom particles segregation with non-linear diffusion equations: application to the marine sand ripples

    NASA Astrophysics Data System (ADS)

    Tiguercha, Djlalli; Bennis, Anne-claire; Ezersky, Alexander

    2015-04-01

    The elliptical motion in surface waves causes an oscillating motion of the sand grains leading to the formation of ripple patterns on the bottom. Investigation how the grains with different properties are distributed inside the ripples is a difficult task because of the segration of particle. The work of Fernandez et al. (2003) was extended from one-dimensional to two-dimensional case. A new numerical model, based on these non-linear diffusion equations, was developed to simulate the grain distribution inside the marine sand ripples. The one and two-dimensional models are validated on several test cases where segregation appears. Starting from an homogeneous mixture of grains, the two-dimensional simulations demonstrate different segregation patterns: a) formation of zones with high concentration of light and heavy particles, b) formation of «cat's eye» patterns, c) appearance of inverse Brazil nut effect. Comparisons of numerical results with the new set of field data and wave flume experiments show that the two-dimensional non-linear diffusion equations allow us to reproduce qualitatively experimental results on particles segregation.

  10. Assessing the Martian Surface Distribution of Aeolian Sand using a Mars General Circulation Model

    NASA Technical Reports Server (NTRS)

    Anderson, F. S.; Greeley, R.; Xu, P.; Lo, E.; Blumberg, D. G.; Haberle, R. M.; Murphy, J. R.

    1999-01-01

    A sand transport model using White's sand flux equation and the Mars beneral circulation model was developed to understand the erosional sources, transport pathways, and depositional sinks of windblown sand on Mars. An initially uniform distribution of sand (4 mm over the entire surface) is reeionally transported based on wind stress, saltation threshold, and percentage of topogaphic trapping. Results are consistsnt with the , observed polar and Hellespontus dunes and Christensen's madeled block size distribution, butonly for an extremely law saltation threshold (0.024 N/sq m): Low thresholds generally result in transport of sand-sized particles originating in the northern mid latitudes to the north pole, and transport from the northern lower latitudes to the southern hemisphere. Our results indicate that the polar dune fields could form in 50,000 years, consistent with the active polar dunes and lack of longitudinal dunes observed on the surface of Mars.

  11. Nonlinear ripple dynamics on amorphous surfaces patterned by ion beam sputtering.

    PubMed

    Muñoz-García, Javier; Castro, Mario; Cuerno, Rodolfo

    2006-03-01

    Erosion by ion-beam sputtering (IBS) of amorphous targets at off-normal incidence frequently produces a (nanometric) rippled surface pattern, strongly resembling macroscopic ripples on aeolian sand dunes. A suitable generalization of continuum descriptions of the latter allows us to describe theoretically for the first time the main nonlinear features of ripple dynamics by IBS, namely, wavelength coarsening and nonuniform translation velocity, that agree with similar results in experiments and discrete models. These properties are seen to be the anisotropic counterparts of in-plane ordering and (interrupted) pattern coarsening in IBS experiments on rotating substrates and at normal incidence. PMID:16606197

  12. 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.

  13. 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.

  14. 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.

  15. Rippled Dune

    NASA Technical Reports Server (NTRS)

    2004-01-01

    10 October 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows ripples on the surface of a dune in a crater west of Sinus Meridiani near 2.5oN, 9.3oW. Most martian dune surfaces do not show ripples at the scale of MOC images---a higher resolution (better than 15 cm/pixel) view would be needed. These ripples are probably not typical sand ripples; they may be coarser-grained granule ripples (usually made up, in part, of grains 1-4 millimeters in size). The light-toned features in the image are wind-eroded outcrops of sedimentary rock. The image covers an area about 1.5 km (0.9 mi) wide. Sunlight illuminates the scene from the upper left.

  16. Rolling Ripple

    NASA Technical Reports Server (NTRS)

    2006-01-01

    NASA's Mars Exploration Rover Opportunity continues to cut southward across a plain marked by large sand ripples and a pavement of outcrop rock. The ripple in the center of the image shows a distinct pattern of banding, which the science team hopes to investigate more closely during the trek through this terrain. The banding and other features have inspired a hypothesis that Meridiani ripples are old features that are currently being eroded, and not transported, by wind. This navigation camera image was taken on Opportunity's sol 795, April 19, 2006.

  17. 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

  18. 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.

  19. Arbuscular mycorrhizal fungal community divergence within a common host plant in two different soils in a subarctic Aeolian sand area.

    PubMed

    Francini, Gaia; Männistö, Minna; Alaoja, Vilhelmiina; Kytöviita, Minna-Maarit

    2014-10-01

    There is rising awareness that different arbuscular mycorrhizal (AM) fungi have different autoecology and occupy different soil niches and that the benefits they provide to the host plant are dependent on plant-AM fungus combination. However, the role and community composition of AM fungi in succession are not well known and the northern latitudes remain poorly investigated ecosystems. We studied AM fungal communities in the roots of the grass Deschampsia flexuosa in two different, closely located, successional stages in a northern Aeolian sand area. The AM fungal taxa richness in planta was estimated by cloning and sequencing small subunit ribosomal RNA genes. AM colonization, shoot δ (13)C signature, and %N and %C were measured. Soil microbial community structure and AM fungal mycelium abundance were estimated using phospholipid (PLFA) and neutral lipid (NLFA) analyses. The two successional stages were characterized by distinct plant, microbial, and fungal communities. AM fungal species richness was very low in both the early and late successional stages. AM frequency in D. flexuosa roots was higher in the early successional stage than in the late one. The AM fungal taxa retrieved belonged to the genera generally adapted to Arctic or extreme environments. AM fungi seemed to be important in the early stage of the succession, suggesting that AM fungi may help plants to better cope with the harsh environmental conditions, especially in an early successional stage with more extreme environmental fluctuations. PMID:24687606

  20. Turbulent flow structures and aeolian sediment transport over a barchan sand dune

    NASA Astrophysics Data System (ADS)

    Wiggs, G. F. S.; Weaver, C. M.

    2012-03-01

    The turbulent structure of airflow over a barchan sand dune is determined using quadrant analysis of wind velocity data derived from sonic anemometers. Results indicate an increased frequency of ejection and sweep events in the toe region of the dune, characteristic of the turbulent bursting process. In contrast, at the crest there was a significant increase in the occurrence of outward interactions. Combined with high frequency saltation data our analyses show that turbulent structures characterised by a positive streamwise fluctuating velocity (+u‧ sweeps at the toe and outward interactions at the crest) have a dominant influence on sand transport on the dune, together accounting for up to 83% and 95% of transporting events at the toe and crest respectively.

  1. Theoretical and measured aeolian sand transport on a barrier island, Louisiana, USA

    USGS Publications Warehouse

    Dingler, J.R.; Hsu, S.A.; Reiss, T.E.

    1992-01-01

    Over the past 100 yr, the Isles Dernieres, a low lying barrier island chain along the coast of central Louisiana, has undergone more than 1km of northward beach face retreat within the loss of 70% of its surface area. The erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition. The theoretical estimate of 1.28 m3 m-1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1.26m3 m-1, which was determined by comparing beach profiles from the start and end of the period of northerly winds. The theoretical estimate of 0.04m3 m-1 for the rate of sand transport by the southerly wind, however, is notably less than the measured rate of 0.45m3 m-1. -from Authors

  2. Effects of non-erodible particles on aeolian erosion: Wind-tunnel simulations of a sand oblong storage pile

    NASA Astrophysics Data System (ADS)

    Furieri, B.; Russeil, S.; Santos, J. M.; Harion, J. L.

    2013-11-01

    Non-erodible particles have strong influence on the aeolian erosion phenomena. An oblong stockpile model of sand (bimodal granulometry) was implemented to perform wind-tunnel experiments as similar literature works have only carried out experimental investigations on a flat bed of particles. Thus, the influence of the fluid flow structures around the complex obstacle will be analysed. The tested configurations consisted of two different values of non-erodible particles cover rate (10% and 20%), and three free stream velocities (6, 7 and 8 m s-1). Good repeatability was found. The results showed that the largest amount of particles emitted was for the highest wind velocity and the smallest cover rate. The temporal decreasing of emitted mass flux was found steeper for larger amount of non-erodible particles and higher velocity. The mass flux of particles decreases very strongly in the first four minutes of measurements and the cover rate influences this downward sloping. The same analysis applies for the effects of the free stream velocity. The qualitative analysis (high quality photographic system) of the stockpile surface gradual change has shown that non-erodible particles aggregation induces a pavement effect on some areas of the pile. This analysis indicated typical wind erosion zones: high wall friction on the crest line and lateral sides; low wall friction on the windward wall near the ground and on the recirculation downstream the leeward wall. The results and discussions presented here allows for the understanding of the impact of non-erodible particle on dust emissions.

  3. 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

  4. Sands at Gusev Crater, Mars

    USGS Publications Warehouse

    Cabrol, Nathalie A.; Herkenhoff, Kenneth E.; Knoll, Andrew H.; Farmer, Jack D.; Arvidson, Raymond E.; Grin, E.A.; Li, Ron; Fenton, Lori; Cohen, B.; Bell, J.F., III; Yingst, R. Aileen

    2014-01-01

    Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

  5. Sands at Gusev Crater, Mars

    NASA Astrophysics Data System (ADS)

    Cabrol, Nathalie A.; Herkenhoff, Kenneth; Knoll, Andrew H.; Farmer, Jack; Arvidson, Raymond; Grin, Edmond; Li, Ronxing; Fenton, Lori; Cohen, Barbara; Bell, James F.; Aileen Yingst, R.

    2014-05-01

    Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

  6. 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

  7. 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

  8. Persistent Aeolian Activity at Endeavour Crater, Mars

    NASA Astrophysics Data System (ADS)

    Chojnacki, M.; Michaels, T. I.; Fenton, L. K.

    2013-12-01

    Long-term monitoring of sites that are known to have active dunes and ripples is generally limited to 3 Mars-Years (MY). Here, we discuss new results of dune activity and albedo change in Endeavour crater (EC), Meridiani Planum (MP) that record eight MY of aeolian activity. MP dune fields often show large yearly variations in albedo; EC darkened by ~12% in TES albedo between MY 24 and 26 (from 0.14 to 0.12). THEMIS VIS albedo of dunes did not change significantly from MY 26 to 29, but did decrease notably (~15 %) in MY 30. These darkening events are most likely related to aeolian-driven dust cleaning (e.g., removal by saltating sand, dust devils). For example, the Opportunity rover (poised on the western rim of EC) observed evidence for a MY 31 dune field dust-clearing event. HiRISE monitoring of MP has shown it be one of the most active regions outside of north polar latitudes. Paired images of western EC taken 3 MY apart show clear evidence for dune modification that include: ripple migration, change in dune perimeters, exposure of previously buried light-toned rock, and/or burial of rock by sand (Fig. 1a-1b). Dune slip face movement is evident for most dunes, where crests and aprons advanced (2-7 m) in the downwind direction (to the SSE) at rates of 0.7-2.3 m per MY. Small dome dunes in the eastern EC were found to have a large degree of aeolian activity (e.g., deflation and/or translation) by an earlier study that used MGS-MRO images (MY 24-30). New MY 31 images validate earlier observations, showing clear evidence for bedform deflation where dunes often occupy less area (~50%) than in earlier MY 29 images (Fig. 1c-1d). Areal removal rates are on par with earlier estimates. Bedform modification and sand streamer orientation appear to be caused by a NNW wind regime, consistent with earlier observations, mesoscale modeling, and the transport direction of barchans to the west. Dunes in EC are now known to be periodically (consistently?) active from over a decade

  9. 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

    The landscape in extensive areas in SE-Netherlands is underlain by coversand, deposited during the Late Glacial of the Weichselian. In the Preboreal, aeolian processes reduced soil formation. From the Preboreal to the Atlantic a deciduous climax forest developed. The geomorphology was a coversand landscape, composed of ridges (umbric podzols), coversand plains (gleyic podzols), coversand depressions (histic podzols) and small valleys (gleysols). The area was used by hunting people during the Late Paleolithic and Mesolithic. During the Bronze and Iron Ages the area was populated by people, living from forest grazing, shifting cultivation and trade. The natural deciduous forest gradually degraded into Calluna heath. The deforestation accelerated the soil acidification and affected the hydrology, which is reflected in drying out of ridges and wetting of depressions, promoting the development of histic podzols and even histosols. Aeolian erosion was during this period restricted to local, small scale sand drifting, related to natural hazards as forest fires and hurricanes and shifting cultivation. Sustainable crop productivity on chemically poor sandy substrates required application of organic fertilizers, composed of a mixture of organic litter and animal manure with a very low mineral compound, produced in shallow stables. At least since 1000 AD, heath management was regulated by a series of rules that aimed to protect the valuable heat lands against degradation. During the 11th, 12th and 13th centuries there was an increasing demand for wood and clear cutting transformed the majority of the forests in driftsand landscapes. The most important market was formed by the very wealthy Flemish cities. The exposed soil surface was subjected to wind erosion and sand drifting which endangered the Calluna heath, arable land and even farmhouses. As a consequence, umbric podzols, the natural climax soil under deciduous forests on coversand, degraded into larger scale driftsand

  10. Measuring sand flux on Mars using HiRISE Images

    NASA Astrophysics Data System (ADS)

    Ayoub, F.; Bridges, N. T.; Avouac, J.; Leprince, S.; Lucas, A.; Mattson, S.

    2011-12-01

    As wind is the major agent of sediment transport on Mars, a quantitative estimate of aeolian processes is therefore essential to assess recent geological evolution and current climate. We adapted the Co-registration of Optically Sensed Image and Correlation (COSI-Corr) toolbox to the MRO HiRISE imager specifications to produce a dense map of the ripples migration on the surface of the Martian dunes on the Nili Patera area. The ripple migration rate, along with an estimate of the ripple height, were used to derive the sand flux, a key quantity that controls the style and rate of landscape evolution. Using the dunes shape, size, and height, which were extracted from a DEM of the dune field, we show that the dunes are near steady state, and we observe that dune migration rate varies inversely with size and position within the dune field. The time scale associated with the formation and evolution of the Nili Patera dune field, estimated from comparing the sand volume with the sand flux and the dunes migration rates with the length scale of the dune field, is on the order of 10s to 100s of thousands Earth years. However, sand fluxes at the dune crests are 0.7 - 4.8 m3 m-1 per Earth year, which is comparable to that of dunes in Victoria Valley, Antarctica. This implies that rates of landscape modification from aeolian abrasion on Mars may be comparable to that on Earth.

  11. Sands-on Learning.

    ERIC Educational Resources Information Center

    Vandervoort, Frances S.

    1989-01-01

    Provides information for the development of a lesson which teaches students about sand, discusses facts about sands, sand studies, life in the sands, and sand activities. Includes diagrams showing the range in sand grain shape, formation of sand ripples, and sand samples from around the world. (RT)

  12. Spatial and temporal patterns of aeolian sediment transport on an inland parabolic dune, Bigstick Sand Hills, Saskatchewan, Canada

    NASA Astrophysics Data System (ADS)

    Hugenholtz, C. H.; Wolfe, S. A.; Walker, I. J.; Moorman, B. J.

    2009-04-01

    Topographic changes from erosion pins and on-site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation-stabilized inland, prairie dune field. Over two years, the sediment budget, calculated from digital elevation models, shows that the total volume of erosion (9890 m 3) is greater than the amount of deposition (6990 m 3), indicating a net loss of 2900 m 3 of sediment (or ˜ 29% of eroded sediment) from the dune. Sediment erosion occurred mainly on the stoss slope (3600 m 3; ˜ 36% of eroded sediment), but also on the south (2100 m 3; ˜ 21%) and north sides of the dune head (1700 m 3; ˜ 17%), the blowouts along the arms (1740 m 3, ˜ 18%) and the crest (650 m 3; ˜ 7%). Erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit (100 m 3; ˜ 1%). Thus, the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind. Sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes (5500 m 3; ˜ 80%), coinciding with the southeasterly resultant transport direction for November 2004-05. The net loss of about 2900 m 3 (˜ 29%) may be attributed to sediment carried in suspension over and beyond the dune. Correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions (e.g., vegetation cover, ground freezing, moisture) buffer the relative importance of temperature and precipitation on rates of sediment transport. Conversely, wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions. Seasonal effects produce a complex interaction between wind, climate and surface conditions. This leads to a dynamic range of threshold velocities, which in turn causes spatial and

  13. 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

  14. Ripple Trap

    NASA Technical Reports Server (NTRS)

    2006-01-01

    3 April 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the margin of a lava flow on a cratered plain in the Athabasca Vallis region of Mars. Remarkably, the cratered plain in this scene is essentially free of bright, windblown ripples. Conversely, the lava flow apparently acted as a trap for windblown materials, illustrated by the presence of the light-toned, wave-like texture over much of the flow. That the lava flow surface trapped windblown sand and granules better than the cratered plain indicates that the flow surface has a rougher texture at a scale too small to resolve in this image.

    Location near: 10.7oN, 204.5oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

  15. 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

  16. 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

  17. 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

  18. Persistent aeolian activity at Endeavour crater, Meridiani Planum, Mars; new observations from orbit and the surface

    NASA Astrophysics Data System (ADS)

    Chojnacki, Matthew; Johnson, Jeffrey R.; Moersch, Jeffrey E.; Fenton, Lori K.; Michaels, Timothy I.; Bell, James F., III

    2015-05-01

    Aeolian-driven bedform activity is now known to occur in many regions of Mars, based on surface and orbital observation of contemporary martian ripple and dune mobility events. Many of these sites have only been monitored with sufficient resolution data for the last few Mars years, when the High Resolution Imaging Science Experiment (HiRISE) began acquiring images of Mars. One exception is the well-monitored Endeavour crater in Meridiani Planum, which was one of the first known sites of unambiguous dune activity (migration and deflation). However, those early detections used lower resolution images over longer temporal baselines (versus the HIRISE data now available), leaving some measurements poorly constrained. New orbital and surface observations of Endeavour show multiple spatial (cm, m, km) and temporal (seasons, Mars year) scales of aeolian-driven surface change, which confirms earlier reports. Dome dunes in the eastern portion of the crater persistently deflate, disseminating dark sand across lighter-toned regolith and/or eroded bright dust, and likely contribute to the crater interior's episodic decreases in orbital albedo measurements. Other dome dunes are detected with the highest migration rates (4-12 m per Mars year) and volumetric sand fluxes reported yet for Mars. Estimated dune construction times or "turnover times" here and elsewhere on Mars are significantly shorter than martian obliquity cycles, implying that it is not necessary to invoke paleoclimate wind regimes to explain current dune morphologies. Located on the crater rim, the Opportunity rover detected evidence for near- and far-field aeolian-driven activity, with observations of spherules/sand movement in the rover workspace, bedform albedo alteration, and dust-lifting events. Observations of intracrater dunes show periodic shifting dark streaks that significantly constrain local wind regimes (directionality and seasonality). Constraints on wind directions from surface and orbital images

  19. Aeolian Transport of Invertebrates

    NASA Astrophysics Data System (ADS)

    Gill, T. E.; Walsh, E. J.; Wallace, R. L.; Rojo, L.; Rivas, J. A.

    2012-12-01

    Playas and other ephemeral desert wetlands are preferential terrestrial landforms for dust emission. These sites also are habitat for a diverse assemblage of minute invertebrates. When wetlands desiccate, these invertebrates survive as resting stages (propagules). Thus, playas serve as isolated, ephemeral, biogeographical islands for aquatic invertebrates, but it is unclear how propagules disperse across distances as far as hundreds of kilometers to colonize hydrologically disconnected basins. Aeolian transport (anemochory) may provide the mechanism, especially since many invertebrate propagules are long-lived, aerodynamically shaped, possess low-density, and their size (30-600 μm) falls within the same texture as aeolian dust and sand grains. We are collecting and culturing wind-transported sediment to document its ability to serve in the dispersal of aridland invertebrate propagules. Deposited aeolian sediment was collected from marble-type traps placed on the roof of the Biological Sciences Building at the University of Texas, El Paso, during 19 individual regional-scale Chihuahuan Desert blowing dust/sand events between April 2010 and May 2012. Known source areas for these dust events include playas and ephemeral streams ~40- 150 km upwind. The mean dry grain size of the deposited sediment for each event ranged from 66 to 141 μm. Clean-water rinses of material from each event or standard rehydrations for culturing invertebrates were monitored microscopically for the appearance of organisms. Invertebrates hatched from the sediment of 13 events. Ciliates were detected in each of those samples: gastrotrichs appeared in three samples, nematodes and bdelloid rotifers in two samples, and clam shrimp in one. We have also rehydrated aeolian sediments, collected in standard dust traps, from many dust-emitting playas in Southwest North America and hatched viable organisms including all those previously mentioned as well as branchiopods, fairy shrimp, copepods

  20. Ripples or Dunes?

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This approximate true-color image taken by the Mars Exploration Rover Spirit's panoramic camera shows the windblown waves of soil that characterize the rocky surface of Gusev Crater, Mars. Scientists were puzzled about whether these geologic features were 'ripples' or 'dunes.' Ripples are shaped by gentle winds that deposit coarse grains on the tops or crests of the waves. Dunes are carved by faster winds and contain a more uniform distribution of material. Images taken of these features by the rover's microscopic imager on the 41st martian sol, or day, of the rover's mission revealed their identity to be ripples. This information helps scientists better understand the winds that shape the landscape of Mars. This image was taken early in Spirit's mission.

    [figure removed for brevity, see original site] Click on image for larger view [Image credit: NASA/JPL/ASU]

    This diagram illustrates how windblown sediments travel. There are three basic types of particles that undergo different motions depending on their size. These particles are dust, sand and coarse sand, and their sizes approximate flour, sugar, and ball bearings, respectively. Sand particles move along the 'saltation' path, hitting the surface downwind. When the sand hits the surface, it sends dust into the atmosphere and gives coarse sand a little shove. Mars Exploration Rover scientists are studying the distribution of material on the surface of Mars to better understand how winds shaped the landscape.

  1. Late Amazonian aeolian features, gradation, wind regimes, and Sediment State in the Vicinity of the Mars Exploration Rover Opportunity, Meridiani Planum, Mars

    NASA Astrophysics Data System (ADS)

    Fenton, Lori K.; Michaels, Timothy I.; Chojnacki, Matthew

    2015-03-01

    The 2° × 2° region surrounding the landing site and traverse of Mars Exploration Rover (MER) Opportunity is richly blanketed with several generations and classes of aeolian features, including coarse-grained ripples, large dark dunes (LDDs), transverse aeolian ridges (TARs), erosional scars, depositional wind streaks of two types, and a new class of wind streak comprised entirely of coarse-grained ripples. The extensive observation campaigns from orbiting spacecraft in support of the MER and 2016 ExoMars missions, as well as in situ data from Opportunity, have provided unprecedented coverage of the region, permitting further interpretation of the local aeolian history than is typically possible on Mars. We present an analysis of bedform construction, sediment-transporting wind patterns, crater gradation and resulting erosion rate, sand provenance, and sediment state resulting from surficial mapping and geomorphic backstripping of aeolian features. Coarse-grained ripples on the intercrater plains formed from local sediments, with induration and low wind speeds preventing them from migrating more than roughly one bedform wavelength from their source region. Limited migration and a likely local, planar sand source of plains bedforms suggests their provenance is previously-eroded layers within the underlying Burns Formation. Although the bedform stabilization process is different from that of Earth, these ripples appear to be analogous to coarse-grained ripples that form and quickly stabilize on the Argentinean Puna. Some small craters (<100 m) exhibit inverted topography as high as ∼1 m, produced by an armoring effect of the indurated coarse-grained ripples. The erosion rate leading to this relief is ∼0.014 m/Myr over the past 71 ± 2 Ma, falling between values estimated for younger and older surfaces. Present-day winds are not represented uniformly in the region, with most active sandy wind streaks on the plains formed by a southeasterly wind and intracrater

  2. Evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 ExoMars landing ellipse in Meridiani Planum, Mars

    NASA Astrophysics Data System (ADS)

    Silvestro, S.; Vaz, D. A.; Di Achille, G.; Popa, I. C.; Esposito, F.

    2015-04-01

    We present evidence for a complex, multigenerational bed form pattern and a new type of wind streak (the ripple streak) in the landing site ellipse of the 2016 ExoMars Entry descent and landing Demonstrator Module (EDM) in Meridiani Planum (Mars). We identified three main groups of bright-toned bed forms. Population 3, represented by NE-SW trending bed forms located inside craters, was emplaced by winds coming from the NW or the SE. Population 2, emplaced by strong easterlies, formed by intracrater transverse aeolian ridges (TARs) and N-S trending megaripples (plains ripples). Population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south. Alternatively, population 1 can represent a sand ribbon pattern that formed together with the plain ripples. We also report the presence of a new type of wind streak, the ripple streak, which is formed by the population 2 bed forms clustered in the wake zone of impact craters. Based on the results of this work, we now know the EDM module is set to land in a complex aeolian environment. Data from the Dust Characterization, Risk Assessment, and Environment Analyser on the Martian Surface onboard the EDM can help to better decipher the wind regime in Meridiani Planum.

  3. Laboratory studies of aeolian sediment transport processes on planetary surfaces

    NASA Astrophysics Data System (ADS)

    Rasmussen, Keld R.; Valance, Alexandre; Merrison, Jonathan

    2015-09-01

    , but not all, older or recent wind tunnel observations. Similarly some measurements performed with uniform sand samples having grain diameters of the order of 0.25-0.40 mm indicate that ripple spacing depends on friction velocity in a similar way as particle jump length. The observations are thus in agreement with a recent ripple model that link the typical jump length to ripple spacing. A possible explanation for contradictory observations in some experiments may be that long observation sequences are required in order to assure that equilibrium exists between ripple geometry and wind flow. Quantitative understanding of saltation characteristics on Mars still lacks important elements. Based upon image analysis and numerical predictions, aeolian ripples have been thought to consist of relatively large grains (diameter > 0.6 mm) and that saltation occurs at high wind speeds (> 26 m/s) involving trajectories that are significantly longer than those on Earth (by a factor of 10-100). However, this is not supported by recent observations from the surface of Mars, which shows that active ripples in their geometry and composition have characteristics compatible with those of terrestrial ripples (Sullivan et al., 2008). Also the highest average wind speeds on Mars have been measured to be < 20 m/s, with even turbulent gusts not exceeding 25 m/s. Electrification is seen as a dominant factor in the transport dynamics of dust on Mars, affecting the structure, adhesive properties and detachment/entrainment mechanisms specifically through the formation of aggregates (Merrison et al., 2012). Conversely for terrestrial conditions electric fields typically observed are not intense enough to significantly affect sand transport rates while little is known in the case of extra-terrestrial environments.

  4. Aeolian Sediments on the northeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Stauch, G.; Lehmkuhl, F.

    2013-12-01

    The timing and spatial distribution of aeolian sediments on the northeastern Tibetan Plateau have gained increasing interest during the last decades. The formation of the aeolian deposits is often related to cold and dry climate conditions. However, further important parameters are the local geomorphological setting and sediment availability in the source areas of the sediments. Aeolian sediments including loess, sandy loess and sands are widespread in the catchment of the Donggi Cona on the northeastern Tibetan Plateau at around 4000 m asl. Detailed geomorphological mapping of the deposits and geochemical analyses of the sediments revealed varying sources throughout the Holocene. The timing of the sediment deposition is based on 43 OSL (optical stimulated luminescence) ages. Several phases of enhanced aeolian deposition took place during the Holocene. The accumulation of aeolian sands lasted from 10.5 until 7 ka. The main source area of these sands was a large alluvial fan. Parallel to the formation of the dunes loess was deposited on the adjacent slopes from 10.5 until 7.5 ka. These sediments most probably originate in the nearby Qaidam Basin. In contrast to the general linkage of aeolian sediments to dryer climate conditions formation of these aeolian deposits is related to wetter conditions due to a strengthening of the Asian Summer Monsoons. The wetter climate enhanced the trapping and continuous fixation of the aeolian sediments by vegetation. With the further strengthening of the Monsoon fluvial processes eroded the aeolian deposits at least until 6 ka. From about 3 ka to the present a reactivation of aeolian sands and the formation of new dunes took place. This reactivation is related to drier conditions on the north-eastern Tibetan Plateau. Additionally, an increased human influence might have enhanced the aeolian activity. Similar phases of enhanced aeolian activity have been documented in more than 170 available OSL ages from loess and aeolian sands in

  5. On the formation of current ripples.

    PubMed

    Bartholdy, J; Ernstsen, V B; Flemming, B W; Winter, C; Bartholomä, A; Kroon, A

    2015-01-01

    For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples. Although numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The model contradicts the conventional view of current ripples as bedforms not scaling with flow depth. Furthermore, it confirms the dependence of ripple dimensions on grain size, and their relative insensitivity to flow strength. PMID:26065918

  6. On the formation of current ripples

    PubMed Central

    Bartholdy, J.; Ernstsen, V. B.; Flemming, B. W.; Winter, C.; Bartholomä, A.; Kroon, A.

    2015-01-01

    For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples. Although numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The model contradicts the conventional view of current ripples as bedforms not scaling with flow depth. Furthermore, it confirms the dependence of ripple dimensions on grain size, and their relative insensitivity to flow strength. PMID:26065918

  7. On the formation of current ripples

    NASA Astrophysics Data System (ADS)

    Bartholdy, J.; Ernstsen, V. B.; Flemming, B. W.; Winter, C.; Bartholomä, A.; Kroon, A.

    2015-06-01

    For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples. Although numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The model contradicts the conventional view of current ripples as bedforms not scaling with flow depth. Furthermore, it confirms the dependence of ripple dimensions on grain size, and their relative insensitivity to flow strength.

  8. Ripples and Dunes

    NASA Technical Reports Server (NTRS)

    2006-01-01

    27 May 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark sand dunes on the floor of an impact crater west of Hellas Planitia. Portions of the crater floor are exposed near the center and lower right corner of the image but, in general, the floor is covered by large, windblown ripples. The dark dune sand typically covers ripples, indicating that the dunes are younger and made of a more mobile material.

    Location near: 43.7oS, 320.4oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

  9. Numerical modeling of wind-blown sand on Mars.

    PubMed

    Huang, HaoJie; Bo, TianLi; Zheng, XiaoJing

    2014-09-01

    Recent observation results show that sand ripples and dunes are movable like those on Earth under current Martian climate. And the aeolian process on Mars therefore is re-attracting the eyes of scientific researchers in different fields. In this paper, the spatial and temporal evolution of wind-blown sand on Mars is simulated by the large-eddy simulation method. The simulations are conducted under the conditions of both friction wind speed higher and lower than the "fluid threshold", respectively. The fluid entrainment of the sand particles, the processes among saltation sand particles and sand bed, and the negative feedback of sand movement to flow field are considered. Our results show that the "overshoot" phenomenon also exists in the evolution of wind-blown sand on Mars both temporally and spatially; impact entrainment affects the sand transport rate on Mars when the wind speed is smaller or larger than the fluid threshold; and both the average saltation length and height are one order of magnitudes larger than those on Earth. Eventually, the formulas describing the sand transport rate, average saltation length and height on Mars are given, respectively. PMID:25236498

  10. 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

  11. Introducing a New International Society of Aeolian Research

    NASA Astrophysics Data System (ADS)

    Zobeck, T. M.; Lee, J.; Lancaster, N.; Bullard, J. E.

    2008-12-01

    Aeolian research is a long-standing and rapidly growing area of geological study where scientists of many disciplines meet to investigate the effects of wind on the surface of the Earth and other planetary bodies such as Mars and Titan. Fields of study in aeolian research cover a broad spectrum ranging from developing a basic scientific understanding of the fundamental physical processes of grain motion to the effects of soil erosion on landscape health and environmental sustainability. Aeolian research also includes studies of the effects of aeolian particles on global climate, air quality, and human health, coastal sand transport processes, land degradation, dune migration, the formation of sand seas, and much more. A growing number of international conferences have been organized to focus specifically on aeolian phenomena and a vast number of scholarly publications have been produced to support the science. One popular bibliography includes over 30,000 citations and hundreds of peer-reviewed papers are published each year. Until very recently, no scientific society specifically dealing with aeolian research has been available. The new International Society of Aeolian Research (ISAR) that has been organized to bring together aeolian scientists from around the world. The new society was created to promote contacts among researchers in aeolian processes and related subjects for discussion and comparison of research, to initiate conferences (such as the International Conference on Aeolian Research), to organize excursions, and support the publication of a peer-reviewed scientific journal. The International Society of Aeolian Research sponsors the new Elsevier journal Aeolian Research in support of these activities. This paper will provide further details about the new society and the journal. Please see www.aeolianresearch.org for details.

  12. Wind ripples in low density atmospheres

    NASA Technical Reports Server (NTRS)

    Miller, J. S.; Marshall, J. R.; Greeley, R.

    1987-01-01

    The effect of varying fluid density (rho) on particle transport was examined by conducting tests at atmospheric pressures between 1 and 0.004 bar in the Martian Surface Wind Tunnel (MARSWIT). This study specifically concerns the effect of varying rho on the character of wind ripples, and elicits information concerning generalized ripple models as well as specific geological circumstances for ripple formation such as those prevailing on Mars. Tests were conducted primarily with 95 micron quartz sand, and for each atmospheric pressure chosen, tests were conducted at two freestream wind speeds: 1.1 U*(t) and 1.5 U*(t), where U*(t) is saltation threshold. Preliminary analysis of the data suggests: (1) ballistic ripple wavelength is not at variance with model predictions; (2) an atmospheric pressure of approximately 0.2 bar could represent a discontinuity in ripple behavior; and (4) ripple formation on Mars may not be readily predicted by extrapolation of terrestrial observations.

  13. 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.

  14. 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.

  15. Large Windblown Ripples

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-519, 20 October 2003

    This April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) high resolution image shows a depression in the martian southern cratered highlands near 1.3oS, 244.3oW. The floor of the depression and some nearby craters are covered by large windblown ripples or small sand dunes. This image of ancient martian terrain covers an area 3 km (1.9 mi) across and is illuminated by sunlight from the upper left.

  16. Large Bright Ripples

    NASA Technical Reports Server (NTRS)

    2004-01-01

    3 February 2004 Wind is the chief agent of change on Mars today. Wind blows dust and it can move coarser sediment such as sand and silt. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows bright ripples or small dunes on the floors of troughs northeast of Isidis Planitia near 31.1oN, 244.6oW. The picture covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  17. 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.

  18. Are They Telltale Ripples?

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This false-color image from the Mars Exploration Rover Spirit's panoramic camera shows peak-like formations on the martian terrain at Gusev Crater. Scientists have been analyzing these formations, which have coarse particles accumulating on their tops, or crests. This characteristic classifies them as ripples instead of dunes, which have a more uniform distribution of particle sizes. Scientists are looking further into such formations, which can give insight to the wind direction and velocity on Mars, as well as the material that is being moved by the wind. This image was taken on the 40th martian day, or sol, of Spirit's mission.

    [figure removed for brevity, see original site] Click on image for larger view [Image credit: NASA/JPL/ASU]

    This diagram illustrates how windblown sediments travel. There are three basic types of particles that undergo different motions depending on their size. These particles are dust, sand and coarse sand, and their sizes approximate flour, sugar, and ball bearings, respectively. Sand particles move along the 'saltation' path, hitting the surface downwind. When the sand hits the surface, it sends dust into the atmosphere and gives coarse sand a little shove. Mars Exploration Rover scientists are studying the distribution of material on the surface of Mars to better understand how winds shaped the landscape.

  19. 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

  20. Building of tropical beach ridges, northeastern Queensland, Australia: Cyclone inundation and aeolian decoration

    NASA Astrophysics Data System (ADS)

    Tamura, Toru; Nicholas, William; Brooke, Brendan; Oliver, Thomas

    2016-04-01

    Processes associated with tropical cyclones are thought responsible for building coarse sand beach ridges along the northeastern Queensland coast, Australia. While these ridges are expected to be geological records of the past cyclone, they question the general consensus of the aeolian genesis of sandy beach ridges. To explore the ridge-forming process, we carried out the GPR survey, auger drilling, pit excavation, grain-size analysis, and OSL dating for coarse sand beach ridges at the Cowley Beach, northeastern Queensland. The Cowley Beach is a mesotidal beach characterized by a low-tide terrace and steep beach face. Ten beach ridges are recognized along the survey transect that extends 700 m inland from the shore. 37 OSL ages are younger seawards, indicating the seaward accretion of the ridge sequence over the last 2700 years. The highest ridge is +5.1 m high above AHD (Australian Height Datum). Two GPR units are bounded by a groundwater surface at c. +1.5 m AHD. The upper unit is characterized by horizontal to hummocky reflectors punctuated by seaward dipping truncation surfaces. These reflectors in places form dome-like structure that appears to be the nucleus of a beach ridge. The shape and level (+2.5 m AHD) of the dome are similar to those of the present swash berm. The lower unit shows a sequence of reflectors that dip at an angle of present beach face. The sequence is dissected by truncation surfaces, some of which are continuous to those in the upper unit. Coarse sand mainly forms beach ridge deposits below +4.0 m AHD, while a few higher ridges have an upward fining layer composed of medium sand above +4.0 m, which is finer than aeolian ripples found on the backshore during the survey. In addition, pumice gravel horizons underlie the examined ridge crests. The sequence of seaward dipping reflectors indicates that the Cowley Beach, like other many sandy beaches, has prograded during onshore sand accretion by fairweather waves and has been eroded by storms

  1. Rippled Mars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    29 July 2004 Hundreds of large ripples or small dunes cover the landscape in the Terra Tyrrhena region of Mars in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. The winds responsible for these dunes blew from the north-northwest (top/upper left). This scene is located near 8.8oS, 252.8oW, and covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the terrain from the left.

  2. Ripple Belt

    NASA Technical Reports Server (NTRS)

    2006-01-01

    16 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows windblown materials that have collected and been shaped into large ripples in a valley in the Auqakuh Vallis system in northeastern Arabia Terra, Mars.

    Location near: 29.1oN, 299.6oW Image width: 2 km (1.2 mi) Illumination from: lower left Season: Northern Winter

  3. Automated Detection of Transverse Aeolian Ridges on Mars Using Convolutional Neural Networks and a Field-Based Terrestrial Orthoimage Training Set

    NASA Astrophysics Data System (ADS)

    Scheidt, S. P.; Palafox, L. F.; Hamilton, C. W.; Zimbelman, J. R.

    2015-05-01

    This work uses field-based photogrammetric data of ripple bedform topography and orthoimages to train a machine learning algorithm to map transverse aeolian ridges (TARs) in planetary remote sensing data of Mars.

  4. Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

    NASA Astrophysics Data System (ADS)

    Arvidson, R. E.; Ashley, J. W.; Bell, J. F.; Chojnacki, M.; Cohen, J.; Economou, T. E.; Farrand, W. H.; Fergason, R.; Fleischer, I.; Geissler, P.; Gellert, R.; Golombek, M. P.; Grotzinger, J. P.; Guinness, E. A.; Haberle, R. M.; Herkenhoff, K. E.; Herman, J. A.; Iagnemma, K. D.; Jolliff, B. L.; Johnson, J. R.; Klingelhöfer, G.; Knoll, A. H.; Knudson, A. T.; Li, R.; McLennan, S. M.; Mittlefehldt, D. W.; Morris, R. V.; Parker, T. J.; Rice, M. S.; Schröder, C.; Soderblom, L. A.; Squyres, S. W.; Sullivan, R. J.; Wolff, M. J.

    2011-02-01

    Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date.

  5. Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

    USGS Publications Warehouse

    Arvidson, R. E.; Ashley, James W.; Bell, J.F., III; Chojnacki, M.; Cohen, J.; Economou, T.E.; Farrand, W. H.; Fergason, R.; Fleischer, I.; Geissler, P.; Gellert, Ralf; Golombek, M.P.; Grotzinger, J.P.; Guinness, E.A.; Haberle, R.M.; Herkenhoff, K. E.; Herman, J.A.; Iagnemma, K.D.; Jolliff, B.L.; Johnson, J. R.; Klingelhofer, G.; Knoll, A.H.; Knudson, A.T.; Li, R.; McLennan, S.M.; Mittlefehldt, D. W.; Morris, R.V.; Parker, T.J.; Rice, M.S.; Schroder, C.; Soderblom, L.A.; Squyres, S. W.; Sullivan, R.J.; Wolff, M.J.

    2011-01-01

    Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date.

  6. Active aeolian processes on Mars: A regional study in Arabia and Meridiani Terrae

    USGS Publications Warehouse

    Silvestro, S.; Vaz, D.A.; Fenton, L.K.; Geissler, P.E.

    2011-01-01

    We present evidence of widespread aeolian activity in the Arabia Terra/Meridiani region (Mars), where different kinds of aeolian modifications have been detected and classified. Passing from the regional to the local scale, we describe one particular dune field in Meridiani Planum, where two ripple populations are distinguished by means of different migration rates. Moreover, a consistent change in the ripple pattern is accompanied by significant dune advancement (between 0.4-1 meter in one Martian year) that is locally triggered by large avalanche features. This suggests that dune advancement may be common throughout the Martian tropics. ?? 2011 by the American Geophysical Union.

  7. Ripples and Dunes

    NASA Technical Reports Server (NTRS)

    2006-01-01

    21 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small portion of the floor of Kaiser Crater in the Noachis Terra region, Mars. The terrain in the upper (northern) half of the image is covered by large windblown ripples and a few smoother-surfaced sand dunes. The dominant winds responsible for these features blew from the west/southwest (left/lower left).

    Location near: 47.2oS, 341.3oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Winter

  8. 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.

  9. Studies in Aeolian geology

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1988-01-01

    The objective of the research was to assess the significance of aeolian (windblown) processes in the evolution of planetary surfaces. The approach was to use wind tunnel simulations, field studies of possible analogs, and analyses of spacecraft data.

  10. Publication trends in aeolian research: An analysis of the Bibliography of Aeolian Research

    NASA Astrophysics Data System (ADS)

    Stout, John E.; Warren, Andrew; Gill, Thomas E.

    2009-04-01

    An analysis of the Bibliography of Aeolian Research has provided information regarding publication trends in aeolian research. Results suggest that there has been a significant increase in the number of publications per year since the first aeolian-research publication appeared in 1646. Rates of publication have increased from only three publications in the 17th Century to nearly three publications per day in the 21st Century. The temporal distribution of publications follows a complex pattern that is influenced by many factors. In the 17th and 18th Centuries, publications appear as isolated clusters indicating limited interest in aeolian research and limited opportunities for individuals to contribute to scientific literature. With time, many new scientific societies are formed and many new scientific journals are established, opening new opportunities for scientists to contribute to scientific discourse. Landmark publications open up new research areas and define new directions for aeolian research. General advances in science and technology provide new techniques for sampling blowing sand and dust. In addition, clear signs exist that publication rates respond to major environmental and climatic events, especially large-scale disasters that focus attention on wind erosion and blowing dust. The Sirocco dust events of 1901-1903, the North American Dust Bowl of the1930s, and the recent sand and dust storm problems in China have all led to significant increases in the number of publications in aeolian research. Rates of publication are negatively influenced by major political and social upheavals, especially global conflicts such as World Wars I and II. Sudden shifts in government structure and support can also influence publication rates. A good example is the increased publication rates in China following the end of the Cultural Revolution, a trend that continues today.

  11. Bursts in discontinuous Aeolian saltation.

    PubMed

    Carneiro, M V; Rasmussen, K R; Herrmann, H J

    2015-01-01

    Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number θc. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold. PMID:26073305

  12. Bursts in discontinuous Aeolian saltation

    PubMed Central

    Carneiro, M. V.; Rasmussen, K. R.; Herrmann, H. J.

    2015-01-01

    Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number θc. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold. PMID:26073305

  13. Video monitoring of meso-scale aeolian activity on a narrow beach

    NASA Astrophysics Data System (ADS)

    Hage, Pam; Ruessink, Gerben

    2014-05-01

    The morphologic evolution of coastal dunes is inextricably linked to the neighbouring beach through the incessant exchange of sand. Intense storm-wave processes erode the foredune within a few hours and transport its sand sand seaward, while aeolian processes return the eroded sand from the beach into the dune system, although at a much lower pace (months to years, or meso scale). Here we use an 8-year long data set of half-hourly snapshot video images, collected from an ≡ 50 m high tower on Egmond Beach (The Netherlands), and a concurrent meteorological and water level data set, to examine which factors affect aeolian sand delivery into the dunes. Egmond is a north-south oriented, micro- to meso-tidal, wave-dominated site that faces the North Sea. Its beach is relatively narrow ( ~ 100 m at spring low tide) and mildly sloping (~ 1 : 30), and consists of quartz sand with a median diameter of about 300 μm. Aeolian activity is clearly visible on the images as sand streamers and, in particular, sand strips, defined as low-amplitude, large-wavelength and slipfaceless deposits that migrate slowly in the wind direction and, depending on wind direction, can have orientations from almost shore-parallel to shore-normal. Beach width in combination with wind direction appeared to be the dominant factors in controlling aeolian activity. Many high wind (>≡ 13 m/s) events, especially from the west and northwest, were associated with a storm surge that inundated almost the entire beach with, accordingly, no possibility for aeolian transport. In contrast, sand-strip fields covered the entire beach during medium wind (≡ 12 - 13 m/s) events, especially when the wind was nearly shore-parallel. Many sand-strip events were observed to be regulated by the tide. Prominent sand-strip fields on the intertidal and upper beach were largely limited to low-tide situations with a wide beach, with a rising tide obviously destroying the intertidal sand strips and sometimes also negatively

  14. Windblown Dunes and Ripples

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-411, 4 July 2003

    July 4, 2003, is the 6th anniversary of the Mars Pathfinder landing. One of the elements carried to the red planet by Pathfinder was the Wind Sock Experiment. This project was designed to measure wind activity by taking pictures of three aluminum 'wind socks.' While the winds at the Mars Pathfinder site did not blow particularly strong during the course of that mission, dust storms seen from orbit and Earth-based telescopes attest to the fact that wind is a major force of change on the dry, desert surface of Mars today. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle image shows dark sand dunes and lighter-toned ripples trapped among the mountainous central peak of an old impact crater in Terra Tyrrhena near 13.9oS, 246.7oW. The dune slip faces--the steepest slope on the larger dunes--indicate sand transport is from the top/upper left toward the bottom/lower right. North is toward the top/upper right; the picture is 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left. This picture was obtained in April 2003.

  15. Braidplain, floodplain and playa lake, alluvial-fan, aeolian and palaeosol facies composing a diversified lithogenetical sequence in the permian and triassic of South Devon (England)

    NASA Astrophysics Data System (ADS)

    Mader, Detlef

    flat seaming the toes of the fan chain. Sedimentation is characterized by flashy discharge with many episodic flood pulses of short periodicity and mainly rapid waning of high-water phases with quick underrunning of the threshold velocity for keeping the large clasts rolling. Pronounced slack water episodes allow occasionally the draping of gravel sheets with thin veneers of waning-flow and stagnant-water fines. Spectacular invertebrate burrows in finer breccias underline the flashy nature of most of the flood and flow events, allowing the colonization of the sediments with ground-living invertebrates during interruptions of transport and accumulation. Some peculiar dewatering structures being infilling of crack systems in breccias with wash-load sand are probably induced by earthquake shocks thus pointing to the active tectonic setting of the depositional area. Aeolian sands originate as transverse dune ridges in restricted dune fields and extensive sand seas and as sheet sands in interdune playa depressions. Associated mudstones and ventifact gravel form in wet interdunes or in playa lakes and in deflationary interdunes, respectively. Accumulation of aeolian dunes and interdune sheet sands takes place by both spreading out of drapes on flats and infilling of abandoned fluvial channels which enhance the trapping of sand by topographical effects. The dunes and wind ripple trains migrate across dry interdune floors under predominantly unidirectional winds. Sedimentary processes are grainfall and grainflow on the lee slope of dunes and subcritical climbing of wind ripples. Episodical wetting and dampening of dry interdune flats by intermittent rainfall, periodical dew and even ephemeral fluvial or alluvial-fan incursions allow formation of adhesion-rippled sands on damp surfaces and origin of sandy and silty-clayey lacustrine sediments in shallow water veneers of the flooded playa. Aquatic modification of aeolian sands by invading flood surges of atmospheric or alluvial

  16. Holocene aeolian activities in the southeastern Mu Us Desert, China

    NASA Astrophysics Data System (ADS)

    Jia, Feifei; Lu, Ruijie; Gao, Shangyu; Li, Jinfeng; Liu, Xiaokang

    2015-12-01

    Aeolian deposits from three sites in the Mu Us Desert were used to reconstruct the history of aeolian activities during the Holocene. The results of the lithologies, chronologies and proxy indicators showed that aeolian activities occurred at ∼9.96 cal ka BP, 7.9-6.9 ka BP, 6.4 ka BP and 3.8 cal ka BP∼. The cold event that occurred around 6.4 ka BP interrupted the Holocene Optimum period, which is largely consistent with the findings from sediments in adjacent regions and the monsoon areas of China. Combined with punished OSL and 14C ages of aeolian deposits samples in this region, the environmental changes in the Mu Us Desert were divided into four stages. Active sand dunes dominated before 11 ka BP. Aeolian activities occurred regionally from 11 to 8.5 ka BP and typical sandy paleosol widely developed with episodic aeolian activities between 8.5 and 4 ka BP. Dunes have reactivated and active sand dunes have gradually increased since 4 ka BP. Comparisons with the other paleoclimatic records indicated that the evolution of the Mu Us Desert was closely related to the East Asian monsoon. Paleosol development depended more on the precipitation brought by the East Asian summer monsoon (EASM). The stronger East Asian winter monsoon (EAMW) and higher isolation resulted in the aeolian activities in the early Holocene, while during the mid-Holocene the fluctuating EAWM played a more important role in inducing episodic aeolian activities. The environmental deterioration during the late Holocene can be related to weakened EASM or to increased anthropogenic influence.

  17. The aeolian wind tunnel

    NASA Technical Reports Server (NTRS)

    Iversen, J. D.

    1991-01-01

    The aeolian wind tunnel is a special case of a larger subset of the wind tunnel family which is designed to simulate the atmospheric surface layer winds to small scale (a member of this larger subset is usually called an atmospheric boundary layer wind tunnel or environmental wind tunnel). The atmospheric boundary layer wind tunnel is designed to simulate, as closely as possible, the mean velocity and turbulence that occur naturally in the atmospheric boundary layer (defined as the lowest portion of the atmosphere, of the order of 500 m, in which the winds are most greatly affected by surface roughness and topography). The aeolian wind tunnel is used for two purposes: to simulate the physics of the saltation process and to model at small scale the erosional and depositional processes associated with topographic surface features. For purposes of studying aeolian effects on the surface of Mars and Venus as well as on Earth, the aeolian wind tunnel continues to prove to be a useful tool for estimating wind speeds necessary to move small particles on the three planets as well as to determine the effects of topography on the evolution of aeolian features such as wind streaks and dune patterns.

  18. Aeolian vertical mass flux profiles above a dry and moist sandy beach

    NASA Astrophysics Data System (ADS)

    Rotnicka, Joanna

    2013-04-01

    The vertical distribution of aeolian mass flux was investigated in a natural beach environment. Field experiments conducted on the beach of the Łeba Barrier, southern Baltic coast, Poland, measured the sand transport rate and the vertical mass flux distribution above dry rippled sand and a moist flat sandy surface. The experiments were intended to show the changes in the vertical distribution of sand with changing wind speed. All the data represent maximum flux conditions achieved during alongshore winds. Sand transport was measured using 0.5 m-high vertically segmented sand traps, the wind speed and direction were monitored at 1 m elevation. The obtained dataset comprises 65 measurements on dry surfaces and 51 measurements on moist sandy surfaces. The sand transport rate above the moist surface was higher than above the dry surface, but higher velocities gave smaller differences between the surfaces. The saltation layer was thicker above the moist surface than above the dry surface. All the vertical sand flux profiles are best described by exponential decay functions. Analysis of the normalised flux profiles grouped by wind velocity shows that the fitted curves are less inclined for moist surfaces than dry surfaces.The regression coefficients depict a marked trend in which the intercept decreases and the slope increases with increasing wind speed; this indicates that more sand is transported at higher elevations above the bed and less at lower elevations. The proportion of total transport seems to be independent of wind speed at elevations of approximately 35 mm and 50 mm above the dry and moist surfaces, respectively. Differences between the measured- and exponential-fit values of mass flux are particularly distinct close to the bed, where the exponential fit either over- or under-predicts the measured values. Over-predictions occur in weaker winds, whereas under-predictions become more pronounced as the wind becomes stronger and when the layer in which the

  19. Dust and Sand Mixing

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 10 November 2003

    The bright and dark tones observed in this THEMIS image of part of an unnamed impact crater (85 km in diameter) near the larger impact crater Schiaparelli are due to variable amounts of bright dust and dark sand covering the surface. Wind Shadows observed around small impact craters at the top of the image and small grooves and ripple-like marks observed throughout the scene illustrate dynamic and continued aeolian processes on Mars.

    Image information: VIS instrument. Latitude -1.4, Longitude 10.9 East (349.1 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.

  20. 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.

  1. Abrasion by aeolian particles: Earth and Mars

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Marshall, J. R.; White, B. R.; Pollack, J. B.; Marshall, J.; Krinsley, D.

    1984-01-01

    Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates.

  2. Niveo-aeolian and Denivation Deposits on Mars

    NASA Astrophysics Data System (ADS)

    Bourke, M. C.

    2004-12-01

    Hydrogen abundance data from the Gamma Ray Spectrometer on board the Mars Odyssey platform indicate that large areas of the North Polar Sand Sea have high concentrations (40-60% weight) of hydrogen molecules in the surface deposits. On Earth, cold region sand dunes often contain inter-bedded sand, snow and ice. These niveo-aeolian deposits have unique morphologies and sedimentary structures that are generally not found in warm desert dunes. An atlas of dune niveo-aeolian and denivation features was compiled from published studies of polar deserts on Earth. Features occur at a range of scales and signatures are both morphologic and stratigraphic. The atlas is used to identify similar features on Mars. Examination of high resolution Mars Orbiter Camera images of the North Polar Sand Sea and Southern Crater dune fields have identified several potential signatures of niveo-aeolian and denivation processes on Mars. These include: over steepened lee slopes, cornices, rounded slipface and/or crest, protruding ice cemented beds, alluvial meltwater channels and fans and sublimation avalanches. Other smaller-scale forms probably occur but are not detectable with current resolution data. While these findings have implications for our understanding of martian dune geomorphology, mobility and the geological evolution of the sand seas, they also highlight the potential for a significant volatile reservoir and biological habitat in sand dunes on Mars.

  3. Assessment on TF ripple

    NASA Astrophysics Data System (ADS)

    Shinohara, Kouji

    2008-11-01

    The TF ripple can reduce fast ion confinement and reduce plasma performance. Additionally, recent experiment results from JT-60U and JET imply that ripple can affect bulk plasma confinement. Here, the characteristics of TF ripple and its effect on fast ion confinement is reported. The TF ripple amplitude in ITER is ˜1.2% in case of TF coil alone at the separatrix. This ripple will be compensated by ferritic inserts (FIs), placed between the vacuum vessel shells. In the current design, the ripple amplitude is 0.4% at the separatrix at full field. It should be noted that, in this case, the ripple is overcompensated at half field and that the ripple amplitude is -0.4%. A test blanket module (TBM), some of whose components are ferromagnetic, is another source of TF ripple. TBMs will be installed at three mid-plane ports. The TF ripple induced by TBMs is localized in the poloidal direction as well as in the toroidal direction. The ripple is ˜1% at the mid-plane. Fast ion confinement was evaluated. The fast ion loss was small <2.5% in the Scenario 2 and 4. However, at half field, the effectiveness of FI is reduced and the TBM enhances the loss; the loss is larger than half of that in case of TFC alone.

  4. The evolution of rippled seafloor topography with acoustic implications

    NASA Astrophysics Data System (ADS)

    Richardson, Michael D.; Traykovski, Peter

    2003-04-01

    Rippled seafloors are often responsible for anisotropic patterns of acoustic backscattering and allow penetration of high-frequency energy into the seafloor below the critical angle. Both natural and manipulative experiments conducted during the Sediment Acoustic Experiment (SAX99) demonstrate the importance of understanding the temporal evolution and characterizing the spatial statistics of naturally occurring ripple fields for prediction of sonar performance and the detection of buried targets. Current and wave-induced sand ripples evolve in a more or less predictable pattern. Numerous empirical and semi-empirical predictive models, based on well-established principles of sediment transport, allow prediction of ripple wavelength, height, and shape. Degradation of sand ripple fields, especially by biological processes such as feeding, burrowing, and emergence is less known and has not been modeled. The temporal evolution of rippled topography measured with sector scanning sonar in high-energy environments is presented. These high-fidelity and nearly continuous observations coupled with measurements of bottom currents and near-bottom wave-induced orbital motion provide improved insights and new models of the evolution of rippled seafloor topography. In low-energy environments (SAX99 and the proposed SAX04) the longer times between storms allow characterization of rates of biological processes which destroy ripple structure and create isotropic roughness. [Work supported by ONR.

  5. Gully annealing by aeolian sediment: field and remote-sensing investigation of aeolian-hillslope-fluvial interactions, Colorado River corridor, Arizona, USA

    NASA Astrophysics Data System (ADS)

    Sankey, Joel B.; Draut, Amy E.

    2014-09-01

    Processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide, and particularly in dryland regions where soil loss and land degradation from gully erosion pose long-term land-management problems. Whereas gully formation has been relatively well studied, much less is known of the processes that anneal gullies and impede their growth. This study of gully annealing by aeolian sediment, spanning 95 km along the Colorado River corridor in Glen, Marble, and Grand Canyon, Arizona, USA, employed field and remote sensing observations, including digital topographic modelling. Results indicate that aeolian sediment activity can be locally effective at counteracting gully erosion. Gullies are less prevalent in areas where surficial sediment undergoes active aeolian transport, and have a greater tendency to terminate in active aeolian sand. Although not common, examples exist in the record of historical imagery of gullies that underwent infilling by aeolian sediment in past decades and evidently were effectively annealed. We thus provide new evidence for a potentially important interaction of aeolian-hillslope-fluvial processes, which could affect dryland regions substantially in ways not widely recognized. Moreover, because the biologic soil crust plays an important role in determining aeolian sand activity, and so in turn the extent of gully development, this study highlights a critical role of geomorphic-ecologic interactions in determining arid-landscape evolution.

  6. Longevity of aeolian megaripples

    NASA Astrophysics Data System (ADS)

    Yizhaq, H.; Katra, I.

    2015-07-01

    Megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain-size distributions. The interplay between wind, grain size and ripple morphology (height and wavelength) controls their development. Two main mechanisms limit megaripple height. The first, megaripple flattening due to winds that are above the fluid threshold of the coarse grains, destroys the armoring layer of the megaripple. The second is megaripple erosion by the impacts of fast-moving, fine saltating grains that propel the coarse grains constituting the armoring layer. For any given wind regime and grain size distribution, the potential megaripple dimensions are limited by these two mechanisms. Here we study the first mechanism and estimate the duration of strong winds (sustained above the fluid threshold) needed to flatten megaripples. Strong gusts of wind, in contrast, cannot destroy the megaripples but can cause ripple migration. Based on data from previous works on megaripples, we find a scaling law between the ripple morphology and the coarse mode of grains at the crest. Using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening. In general, the coarser the particles at the megaripple crest, the stronger the wind needed to flatten the megaripples. Moreover, the greater the strength of the wind required to flatten the megaripples, the lower the recurrence probability. Taken together, these findings increase the longevity of megaripples. We apply the results for a megaripple field in the southern Arava valley (Israel).

  7. Ripples in disk galaxies

    SciTech Connect

    Schweizer, F.; Seitzer, P.

    1988-05-01

    Evidence is presented that ripples occur not only in ellipticals but also in disk galaxies of Hubble types S0, S0/Sa, and Sa, and probably even in the Sbc galaxy NGC 3310. It is argued that the ripples cannot usually have resulted from transient spiral waves or other forced vibrations in existing disks, but instead consist of extraneous sheetlike matter. The frequent presence of major disk-shaped companions suggests that ripple material may be acquired not only through wholesale mergers but also through mass transfer from neighbor galaxies. The implications of ripples in early-type disk galaxies are addressed. 40 references.

  8. Aeolian processes over gravel beds: Field wind tunnel simulation and its application atop the Mogao Grottoes, China

    NASA Astrophysics Data System (ADS)

    Zhang, Weimin; Tan, Lihai; Zhang, Guobin; Qiu, Fei; Zhan, Hongtao

    2014-12-01

    The aeolian processes of erosion, transport and deposition are threatening the Mogao Grottoes, a world culture heritage site. A field wind tunnel experiment was conducted atop the Mogao Grottoes using weighing sensors to quantify aeolian processes over protective gravel beds. Results reveal that aeolian erosion and deposition over gravel beds are basically influenced by gravel coverage and wind speed. Erosion is a main aeolian process over gravel beds and its strength level is mainly determined by gravel coverage: strong (<30%), medium (30-50%) and slight (>50%). Aeolian deposition only occurs when gravel coverage is equal to or greater than 30% and wind speeds are between 8 and 12 m s-1, and this process continues until the occurrence of the equilibrium coverage. In addition, the change in conditions of external sand supply affects the transition between aeolian deposition and erosion over gravel beds, and the quantity of sand transport at the height of 0-24 mm is an important indicator of aeolian deposition and erosion over gravel beds. Our results also demonstrate that making the best use of wind regime atop the Mogao Grottoes and constructing an artificial gobi surface in staggered arrays, with 30% coverage and 30-mm-high gravels and in 40 mm spacing can trap westerly invading sand flow and enable the stronger easterly wind to return the deposited sand on the gravel surface back to the Mingsha Mountain so as to minimize the damage of the blown sand flux to the Mogao Grottoes.

  9. Modeling aeolian erosion in presence of vegetation

    NASA Astrophysics Data System (ADS)

    Dupont, S.; Bergametti, G.; Simoëns, S.

    2014-02-01

    Semiarid landscapes are characterized by vegetated surfaces. Understanding the impact of vegetation on aeolian soil erosion is important for reducing soil erosion or limiting crop damage through abrasion or burial. In the present study, a saltation model fully coupled with a large-eddy simulation airflow model is extended to vegetated landscapes. From this model, the sensitivity of sand erosion to different arrangements and type of plants (shrub versus tree) representative of semiarid landscapes is investigated and the wind erosion reduction induced by plants is quantified. We show that saltation processes over vegetated surfaces have a limited impact on the mean wind statistics, the momentum extracted from the flow by saltating particles being negligible compared to that extracted by plants. Simulated sand erosion patterns resulting from plant distribution, i.e., accumulation and erosion areas, appear qualitatively consistent with previous observations. It is shown that sand erosion reduction depends not only on vegetation cover but also on plant morphology and plant distribution relative to the mean wind direction. A simple shear stress partitioning approach applied in shrub cases gives similar trends of sand erosion reduction as the present model following wind direction and vegetation cover. However, the magnitude of the reduction appears significantly different from one approach to another. Although shrubs trap saltating particles, trees appear more efficient than shrubs to reduce sand erosion. This is explained by the large-scale sheltering effect of trees compared to the local shrub one.

  10. Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

    USGS Publications Warehouse

    Arvidson, R. E.; Ashley, James W.; Bell, J.F., III; Chojnacki, M.; Cohen, J.; Economou, T.E.; Farrand, W. H.; Fergason, R.; Fleischer, I.; Geissler, P.; Gellert, Ralf; Golombek, M.P.; Grotzinger, J.P.; Guinness, E.A.; Haberle, R.M.; Herkenhoff, K. E.; Herman, J.A.; Iagnemma, K.D.; Jolliff, B.L.; Johnson, J. R.; Klingelhofer, G.; Knoll, A.H.; Knudson, A.T.; Li, R.; McLennan, S.M.; Mittlefehldt, D. W.; Morris, R.V.; Parker, T.J.; Rice, M.S.; Schroder, C.; Soderblom, L.A.; Squyres, S. W.; Sullivan, R.J.; Wolff, M.J.

    2011-01-01

    Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date. Copyright 2011 by the American Geophysical Union.

  11. Flood Induced Increases in Aeolian Transport Along the Missouri River

    NASA Astrophysics Data System (ADS)

    Benthem, A. J.; Strong, L.; Schenk, E.; Skalak, K.; Hupp, C. R.; Galloway, J.

    2014-12-01

    In 2011, heavy winter snow melt combined with extensive spring rains caused the Missouri River to experience the most extensive flooding since the river was dammed in the 1950s. Large sections of the river banks, islands, and floodplains experienced weeks of prolonged inundation, resulting in extensive sand deposition as up to1 km inland from the established channel. Though locally variable, deposits of up to 3m of loose sand were deposited on the floodplain and extensive areas of shrub, grasslands, and agricultural fields were completely buried or had vegetation washed away in the inundation zone. The flooding also created a number of new unvegetated islands which provide important habitat for endangered species including the Piping Plover (Charadrius melodus). These newly created sand surfaces are unconsolidated and have very little vegetation to prevent aeolian transport. Strong sustained regional winds of up to 20m/s (45mph) cause substantial sediment fluxes which modify landscape topography, shift river morphology, and increase regional dust levels. Our study monitors and quantifies the increase in aeolian transport that occurred following flooding along the Garrison Reach, a 110 km section of free flowing Missouri River in North Dakota. In 2012 and 2013 we measured sand transport and accumulation rates using Leatherman style sand traps and erosion pins to at 9 sites of varying vegetation densities. We apply these flux rates to a high resolution remote sensing vegetation map to estimate the total flux of sand for this segment of the river. We also quantify total available new sand for transport using repeat Light Detection and Ranging (LiDAR) coverage from before and after the flood and examine the relationship between sand deposition and the rate of reestablishment of vegetation. All of these results are used to estimate the scale of flood induced aeolian processes and predict where they may continue to influence the landscape.

  12. Large wind ripples on Mars: A record of atmospheric evolution.

    PubMed

    Lapotre, M G A; Ewing, R C; Lamb, M P; Fischer, W W; Grotzinger, J P; Rubin, D M; Lewis, K W; Ballard, M J; Day, M; Gupta, S; Banham, S G; Bridges, N T; Des Marais, D J; Fraeman, A A; Grant, J A; Herkenhoff, K E; Ming, D W; Mischna, M A; Rice, M S; Sumner, D A; Vasavada, A R; Yingst, R A

    2016-07-01

    Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere. PMID:27365444

  13. Large wind ripples on Mars: A record of atmospheric evolution

    NASA Astrophysics Data System (ADS)

    Lapotre, M. G. A.; Ewing, R. C.; Lamb, M. P.; Fischer, W. W.; Grotzinger, J. P.; Rubin, D. M.; Lewis, K. W.; Ballard, M. J.; Day, M.; Gupta, S.; Banham, S. G.; Bridges, N. T.; Des Marais, D. J.; Fraeman, A. A.; Grant, J. A.; Herkenhoff, K. E.; Ming, D. W.; Mischna, M. A.; Rice, M. S.; Sumner, D. A.; Vasavada, A. R.; Yingst, R. A.

    2016-07-01

    Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter– to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.

  14. Contemporary research in aeolian geomorphology

    NASA Astrophysics Data System (ADS)

    Bauer, B. O.

    2009-04-01

    The first International Conference on Aeolian Geomorphology (ICAR) was held in 1986, and every four years since then, aeolian geomorphologists from around the world have assembled to discuss their research and to showcase recent advancements in understanding and modeling of aeolian processes. A content analysis of the "Bibliography of Aeolian Research" [Stout, J.E., Warren, A., Gill, T.E., 2009. Publication trends in aeolian research: An analysis of the Bibliography of Aeolian Research. Geomorphology 105, 6-17 (this volume)] shows that the number of publications on aeolian topics has increased exponentially from the mid-20th Century with approximately 50 publications per year to about 500 publications per year when the first ICAR was held, to almost 1000 publications per year currently. Areas of focus have shifted historically from initial concerns with aeolian erosion and dust events as isolated phenomenon of localized curiosity or only regional importance, to comprehensive physically-based investigations and modeling of the mechanics of aeolian transport. Recently, more applied studies have been motivated by the recognition of the importance of aeolian processes to dust emissions into the atmosphere (with relevance for human health and for meteorological conditions and climate change) and within regional management contexts (especially on coasts where impending sea-level rise is of great concern and in arid and semi-arid environments given the dependence of sediment surface stability and remobilization on meteorological and ecological conditions). Aeolian geomorphology is a rapidly growing sub-discipline of Geomorphology that offers rich opportunities for interdisciplinary collaborations with colleagues from the Atmospheric Sciences, Climatology, Sedimentology, Quaternary Geology, Fluid Mechanics, Physics, Mathematics, Computer Science, Physical Geography, Ecology, and Agricultural Sciences, as well as our counterparts in fluvial, coastal, and arid

  15. Aeolian process-induced hyper-concentrated flow in a desert watershed

    NASA Astrophysics Data System (ADS)

    Ta, Wanquan; Wang, Haibin; Jia, Xiaopeng

    2014-04-01

    Ephemeral desert channels are characterized by very high rates of sediment transport during infrequent flood events. Here we show that aeolian process-induced hyper-concentrated (AHC) flows occur in the Sudalaer desert watershed in the Ordos Plateau of China, which primarily transport 0.08-0.25 mm non-cohesive aeolian sand and have a peak suspended sediment concentration of 1.1-1.4 × 106 mg l-3. Aeolian sand supply and storage in the channel play a crucial role in causing hyper-concentrated flow. Our results indicate that non-cohesive aeolian sand can be entrained from the bed and suspended in the turbulent flow when the channel bed slope exceeds a critical threshold (0.0003). We also show that if the frequency ratio of wind-blown sandstorms to rainstorms Tw/Tp exceeds β(γ - γ0)/α (P/V3) (A/L) (where α is the wind-blown sand transport coefficient, β is the runoff coefficient, γ - γ0 is the increase in suspension concentration caused by addition of aeolian sands, P is the density of rainstorms, V is the wind speed of sandstorms, A is the runoff-generating area, L is the aeolian sand-filled channel length), an AHC flow occurs during the passage of a flood in a desert channel. Since high-frequency aeolian processes provide an adequate quantity of transportable sediment and promote AHC flow, most of the infrequent rainfall-induced floods occurring in arid zones can develop as AHC flows.

  16. Synthesis on Quaternary aeolian research in the unglaciated eastern United States

    NASA Astrophysics Data System (ADS)

    Markewich, Helaine W.; Litwin, Ronald J.; Wysocki, Douglas A.; Pavich, Milan J.

    2015-06-01

    Late-middle and late Pleistocene, and Holocene, inland aeolian sand and loess blanket >90,000 km2 of the unglaciated eastern United States of America (USA). Deposits are most extensive in the Lower Mississippi Valley (LMV) and Atlantic Coastal Plain (ACP), areas presently lacking significant aeolian activity. They provide evidence of paleoclimate intervals when wind erosion and deposition were dominant land-altering processes. This study synthesizes available data for aeolian sand deposits in the LMV, the Eastern Gulf Coastal Plain (EGCP) and the ACP, and loess deposits in the Middle Atlantic Coastal Plain (MACP). Data indicate: (a) the most recent major aeolian activity occurred in response to and coincident with growth and decay of the Laurentide Ice Sheet (LIS); (b) by ∼40 ka, aeolian processes greatly influenced landscape evolution in all three regions; (c) aeolian activity peaked in OIS2; (d) OIS3 and OIS2 aeolian records are in regional agreement with paleoecological records; and (e) limited aeolian activity occurred in the Holocene (EGCP and ACP). Paleoclimate and atmospheric-circulation models (PCMs/ACMs) for the last glacial maximum (LGM) show westerly winter winds for the unglaciated eastern USA, but do not resolve documented W and SW winds in the SEACP and WNW and N winds in the MACP. The minimum areal extent of aeolian deposits in the EGCP and ACP is ∼10,000 km2. For the LMV, it is >80,000 km2. Based on these estimates, published PCMs/ACMs likely underrepresent the areal extent of LGM aeolian activity, as well as the extent and complexity of climatic changes during this interval.

  17. Stability balloon for two-dimensional vortex ripple patterns.

    PubMed

    Hansen, J L; van Hecke, M; Ellegaard, C; Andersen, K H; Bohr, T; Haaning, A; Sams, T

    2001-11-12

    Patterns of vortex ripples form when a sand bed is subjected to an oscillatory fluid flow. Here we describe experiments on the response of regular vortex ripple patterns to sudden changes of the driving amplitude a or frequency f. A sufficient decrease of f leads to a "freezing" of the pattern, while a sufficient increase of f leads to a supercritical secondary "pearling" instability. Sufficient changes in the amplitude a lead to subcritical secondary "doubling" and "bulging" instabilities. Our findings are summarized in a "stability balloon" for vortex ripple pattern formation. PMID:11690476

  18. Multi-spatial analysis of aeolian dune-field patterns

    NASA Astrophysics Data System (ADS)

    Ewing, Ryan C.; McDonald, George D.; Hayes, Alex G.

    2015-07-01

    Aeolian dune-fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales. This study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on Earth, Mars and Titan. Within a single bedform type, different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well-organized pattern, such as with the transition from protodunes to dunes. Additionally, different types of bedforms, such as ripples, coarse-grained ripples and dunes, coexist at different spatial scales within a dune-field. Analysis of dune-field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform. Interpretations of environmental conditions from any scale of bedform, however, are limited to environmental signals associated with the response time of that bedform. Large-scale dune-field patterns integrate signals over long-term climate cycles and reveal little about short-term variations in wind or sediment supply. Wind ripples respond instantly to changing conditions, but reveal little about longer-term variations in wind or sediment supply. Recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune-field patterns.

  19. 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

  20. Geochemical provenance of soils in Kerman urban areas, Iran: Implications for the influx of aeolian dust

    NASA Astrophysics Data System (ADS)

    Dehbandi, Reza; Aftabi, Alijan

    2016-06-01

    The investigation of the interaction of aeolian dust with residual soils has not been fully explored in the Kerman urban areas, Iran. To assess the geochemical influence of aeolian dust on the residual soils of the Kerman urban areas of Iran, 27 samples were studied petrogeochemically. The arid-semi-arid climate of the area together with the southwest-northeast prevailing wind, have deposited aeolian sands over the residual soils. Residual soils reflect similar mineral compositions to that of the underlying bedrock and include mostly calcite and quartz. However, the minor occurrences of pyroxene, amphibole, olivine, plagioclase and volcanic clasts in urban soils and aeolian dust are attributed to volcanogenic inputs transported by aeolian dust. Urban soils and aeolian dust show different geochemical signatures from the local carbonate rocks. All samples contain trace element concentrations that are higher than the carbonate bedrock. Discrimination diagrams indicate that immobile trace elements have geochemical affinity to the detrital ferromagnesian dust inputs and are different from the local carbonate bedrock. Based on the elemental bivariate and ternary diagrams, the soils and aeolian dust are derived from the interaction of carbonate and volcanic rocks. This highlights that the urban soils in the Kerman urban areas have been formed by interactions of the aeolian dust with the primitive residual soils.

  1. Gully annealing by aeolian sediment: field and remote-sensing investigation of aeolian-hillslope-fluvial interactions, Colorado River corridor, Arizona, USA

    USGS Publications Warehouse

    Sankey, Joel B.; Draut, Amy E.

    2014-01-01

    Processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide, and particularly in dryland regions where soil loss and land degradation from gully erosion pose long-term land-management problems. Whereas gully formation has been relatively well studied, much less is known of the processes that anneal gullies and impede their growth. This study of gully annealing by aeolian sediment, spanning 95 km along the Colorado River corridor in Glen, Marble, and Grand Canyon, Arizona, USA, employed field and remote sensing observations, including digital topographic modelling. Results indicate that aeolian sediment activity can be locally effective at counteracting gully erosion. Gullies are less prevalent in areas where surficial sediment undergoes active aeolian transport, and have a greater tendency to terminate in active aeolian sand. Although not common, examples exist in the record of historical imagery of gullies that underwent infilling by aeolian sediment in past decades and evidently were effectively annealed. We thus provide new evidence for a potentially important interaction of aeolian–hillslope–fluvial processes, which could affect dryland regions substantially in ways not widely recognized. Moreover, because the biologic soil crust plays an important role in determining aeolian sand activity, and so in turn the extent of gully development, this study highlights a critical role of geomorphic–ecologic interactions in determining arid-landscape evolution.

  2. Rippling of polymer nanofibers.

    PubMed

    Wu, Xiang-Fa; Kostogorova-Beller, Yulia Y; Goponenko, Alexander V; Hou, Haoqing; Dzenis, Yuris A

    2008-12-01

    This paper studies the evolution mechanism of surface rippling in polymer nanofibers under axial stretching. This rippling phenomenon has been detected in as-electrospun polyacrylonitrile in recent single-fiber tension tests, and in electrospun polyimide nanofibers after imidization. We herein propose a one-dimensional nonlinear elastic model that takes into account the combined effect of surface tension and nonlinear elasticity during the rippling initiation and its evolution in compliant polymer nanofibers. The polymer nanofiber is modeled as an incompressible, isotropically hyperelastic Mooney-Rivlin solid. The fiber geometry prior to rippling is considered as a long circular cylinder. The governing equation of surface rippling is established through linear perturbation of the static equilibrium state of the nanofiber subjected to finite axial prestretching. The critical stretch and ripple wavelength are determined in terms of surface tension, elastic property, and fiber radius. Numerical examples are demonstrated to examine these dependencies. In addition, a critical fiber radius is determined, below which the polymer nanofibers are intrinsically unstable. The present model, therefore, is capable of predicting the rippling condition in compliant nanofibers, and can be further used as a continuum mechanics approach for the study of surface instability and nonlinear wave propagation in compliant fibers and wires at the nanoscale. PMID:19256861

  3. Ripple depth and density resolution of rippled noise.

    PubMed

    Supin AYa; Popov, V V; Milekhina, O N; Tarakanov, M B

    1999-11-01

    Depth resolution of spectral ripples was measured in normal humans using a phase-reversal test. The principle of the test was to find the lowest ripple depth at which an interchange of peak and trough position (the phase reversal) in the rippled spectrum is detectable. Using this test, ripple-depth thresholds were measured as a function of ripple density of octave-band rippled noise at center frequencies from 0.5 to 8 kHz. The ripple-depth threshold in the power domain was around 0.2 at low ripple densities of 4-5 relative units (center-frequency-to-ripple-spacing ratio) or 3-3.5 ripples/oct. The threshold increased with the ripple density increase. It reached the highest possible level of 1.0 at ripple density from 7.5 relative units at 0.5 kHz center frequency to 14.3 relative units at 8 kHz (5.2 to 10.0 ripple/oct, respectively). The interrelation between the ripple depth threshold and ripple density can be satisfactorily described by transfer of the signal by frequency-tuned auditory filters. PMID:10573895

  4. 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

  5. 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.

  6. Martian Dune Ripples as Indicators of Recent Surface Wind Patterns

    NASA Astrophysics Data System (ADS)

    Johnson, M.; Zimbelman, J. R.

    2015-12-01

    Sand dunes have been shown to preserve the most recent wind patterns in their ripple formations. This investigation continues the manual documentation of ripples on Martian dunes in order to assess surface wind flow. Study sites investigated must have clear HiRISE frames and be able to represent diverse locations across the surface, decided primarily by their spread of latitude and longitude values. Additionally, frames with stereo pairs are preferred because of their ability to create digital terrain models. This will assist in efforts to relate dune slopes and obstacles to ripple patterns. The search and analysis period resulted in 40 study sites with mapped ripples. Lines were drawn perpendicular to ripple crests across three adjacent ripples in order to document both ripple wavelength from line length and inferred wind direction from azimuth. It is not possible to infer a unique wind direction from ripple orientation alone and therefore these inferred directions have a 180 degree ambiguity. Initial results from all study sites support previous observations that the Martian surface has many dune types in areas with adequate sand supply. The complexity of ripple patterns varies greatly across sites as well as within individual sites. Some areas of uniform directionality for hundreds of kilometers suggest a unimodal wind regime while overlapping patterns suggest multiple dominant winds or seasonally varying winds. In most areas, form flow related to dune shape seems to have a large effect on orientation and must be considered along with the dune type. As long as the few steep slip faces on these small dunes are avoided, form flow can be considered the dominant cause of deviation from the regional wind direction. Regional results, wind roses, and comparisons to previous work will be presented for individual sites.

  7. Transverse Aeolian Ridges on Mars: Sediment sources, volumes, and ages.

    NASA Astrophysics Data System (ADS)

    Berman, D. C.; Balme, M. R.

    2014-12-01

    Transverse Aeolian Ridges (TARs) are aeolian bedforms that are morphologically and dimensionally distinct from Large Dark Dune (LDD) fields, being generally brighter than, or of similar albedo to, the surrounding terrain. These features are significantly smaller than the LDDs, appear to form normal to local winds, and tend to have simple, transverse, ripple-like morphologies. Whether these small martian bedforms represent large granule ripples, small transverse dunes, or something else entirely is currently under debate. The spatial distribution of TARs provides important information about where on Mars aeolian sediments are concentrated, and determining their volume can help us constrain the sediment transport regime on Mars. Also, if we can determine if TARs were active only in the past, or whether TARs are mobile under today's wind conditions, then we can begin to assess when and where TARs are/were active over Mars' recent geological history. Thus TARs have the potential for being indicators/records of climate change on Mars. In this work we build on previous work [1,2] and focus on the local/regional scale. We have identified six regional study areas, each 5° by 5°, to investigate the behavior of TARs in detail; one in the northern hemisphere, three in the equatorial band, and two in the southern hemisphere. We have systematically mapped TAR and LDD deposits in each study area to constrain sediment transport pathways and identify sediment sources. In general, TAR sediments appear to be tied to local sources such as LDDs or layered terrains. HiRISE DTMs were utilized to measure TAR heights, widths, wavelengths, and lengths to calculate sediment volumes and estimate volumes over entire study areas based on mapping. Crater count analyses on contiguous TAR fields in the equatorial regions, where the bedforms appear more lithified, reveal ages of several million years. Mid-latitude TAR fields do not show any superposed craters, suggesting much younger deposits

  8. Use of radar to assess aeolian processes

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Lancaster, N.; Gaddis, L.; Blumberg, D.; Debrovolskis, A.; Saunders, R. S.; Wall, S.; Iversen, J. D.; White, B.; Rasmussen, K. R.

    1991-01-01

    The interaction between wind and desert surfaces has important implications for sediment transport on Earth, Mars, and Venus, and for understanding the relationship between radar backscatter and aerodynamic roughness. Here, researchers report results from measurements of atmospheric boundary layer profiles, assessment of radar backscatter at P, L, and C wavelengths, and surface roughness in Death Valley, the Mojave Desert, and Lunar Lake, NV, and discuss the implications for aeolian process. The sites include playas, gravel and sand regs, alluvial fans, and lava flows. Boundary layer wind profiles were measured using anemometers at heights of 0.75, 1.25, 2.07, 3.44, 5.72, and 9.5 m; temperature sensors at heights of 1.3 and 9.6 m; and wind vanes at 9.7 and 1.5 m. Microtopographic measurements were made using a template and a laser-photo device to obtain RMS height. This study demonstrates that radar backscatter coefficients obtained from airborne and perhaps orbiting instruments could permit the derivation of aerodynamic roughness values for large areas. Such values, when combined with wind frequency data, could enable assessment of aeolian processes on a regional scale.

  9. Radar-aeolian roughness project

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Dobrovolskis, A.; Gaddis, L.; Iversen, J. D.; Lancaster, N.; Leach, Rodman N.; Rasnussen, K.; Saunders, S.; Vanzyl, J.; Wall, S.

    1991-01-01

    The objective is to establish an empirical relationship between measurements of radar, aeolian, and surface roughness on a variety of natural surfaces and to understand the underlying physical causes. This relationship will form the basis for developing a predictive equation to derive aeolian roughness from radar backscatter. Results are given from investigations carried out in 1989 on the principal elements of the project, with separate sections on field studies, radar data analysis, laboratory simulations, and development of theory for planetary applications.

  10. Geochemical characterization of a Holocene aeolian profile in the Zhongba area (southern Tibet, China) and its paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Li, Tuoyu; Wu, Yongqiu; Du, Shisong; Huang, Wenmin; Hao, Chengzhi; Guo, Chao; Zhang, Mei; Fu, Tianyang

    2016-03-01

    The Zhongba area lies in the valley of the Maquan River in southern Tibet, where there are both strong modern aeolian activities and ancient aeolian sand sediments. A Holocene aeolian sand and paleosol profile in the Zhongba area was selected for study and termed (Zhuzhu (ZZ) profile). The chronology of the ZZ profile was established by optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating. Based on the grain size and geochemical elements of the ZZ profile, the geochemical characterization was analyzed, the Holocene aeolian activity processes were reconstructed in the study area, and the paleoclimatic implications were discussed. The major elements and the chemical indicators are highly correlated with different grain-sizes in the ZZ profile. The evolutionary sequence of the aeolian activities and the paleoclimate in Holocene reveal four stages: before 7.3 ka BP, the climate was warm and wet with weak winds when the sand paleosol developed; at 7.3-3.8 ka BP, the climate turned dry, with strong aeolian activities; at 3.8-0.7 ka BP, the climate became wetter and the winds weakened when the silt paleosol developed; and since 0.7 ka BP, it was cold and dry with strong aeolian activities.

  11. Wavelength selection of rolling-grain ripples in the laboratory.

    PubMed

    Rousseaux, Germain; Stegner, Alexandre; Wesfreid, José Eduardo

    2004-03-01

    We have performed an experimental study, at very high resolution, of the wavelength selection and the evolution of rolling-grain ripples. A clear distinction is made between the flat sand bed instability and the ripple coarsening. The observation of the initial wavelength for the rolling-grain ripples is only possible close to the threshold for movement which imposes a constraint on the parameters. Moreover, we have proposed a law for the selection of the unstable wavelength under the latter constraint. Our results suggest that the initial wavelength depends on the amplitude of oscillation, the grain diameter, and the Stokes layer. Besides, during the coarsening, we observe no self-similarity of the ripple shape and for few cases a logarithmic growth of the wavelength. PMID:15089286

  12. Surface instability in windblown sand.

    PubMed

    Kurtze, D A; Both, J A; Hong, D C

    2000-06-01

    We investigate the formation of ripples on the surface of windblown sand based on the one-dimensional model of Nishimori and Ouchi [Phys. Rev. Lett. 71, 197 (1993)], which contains the processes of saltation and grain relaxation. We carry out a nonlinear analysis to determine the propagation speed of the restabilized ripple patterns, and the amplitudes and phases of their first, second, and third harmonics. The agreement between the theory and our numerical simulations is excellent near the onset of the instability. We also determine the Eckhaus boundary, outside which the steady ripple patterns are unstable. PMID:11088369

  13. Microtopography-Induced Lag Formation on Bedforms and Biogenic Structures in Aeolian Settings

    NASA Astrophysics Data System (ADS)

    Buynevich, I. V.

    2010-12-01

    In a variety of sand-dominated depositional settings, high-energy events typically culminate with the formation of a lag deposit, expressed as an increase in coarse fraction, accumulation of shell fragments, or a concentration of heavy minerals (density >2.9) beyond their background values. In aeolian settings, grain impact plays a greater role in sediment transport than under subaqueous conditions, but there is a similar segregation of minerals by size and density due to different threshold entrainment and fall velocities of sand grains. For fine-to-medium sand transition, near-surface wind velocities increase from 4.5 m/s for quartz to 6.5 m/s for magnetite, which has twice the density. Most heavy minerals occur in a finer fraction of the surface sediment layer, which further increases their entrainment threshold due to high pivot angles and sheltering by the lighter minerals. Prolonged periods of increased wind activity generate heavy-mineral-enriched horizons ranging in thickness from a few grain diameters to more than 10-20 cm, producing distinct marker horizons and placers of economic importance. However, even under relatively low wind regime, localized density lag may form due to minor variations in topography and bed roughness. This process was exemplified along Revere Beach (Massachusetts, USA), where a series of 15-cm-high steps were installed at the base of a low seawall to prevent the formation of aeolian ramp that facilitated frequent overtopping. During the following months, a clear trend was established where the heavy-mineral fraction (primarily almandine garnet) progressively increased in a landward direction, toward higher substrate elevations. In natural settings with even a small background fraction of heavy minerals (2-5%), microtopographic highs of less than 1 cm are sufficient for the formation of a density lag. In a backshore area of Assateague Island (Maryland, USA), a clear increase in heavy-mineral content (mostly magnetite) was observed

  14. [Nutrient contents and microbial populations of aeolian sandy soil in Sanjiangyuan region of Qinghai Province].

    PubMed

    Lin, Chao-feng; Chen, Zhan-quan; Xue, Quan-hong; Lai, Hang-xian; Chen, Lai-sheng; Zhang, Deng-shan

    2007-01-01

    Sanjiangyuan region (the headstream of three rivers) in Qinghai Province of China is the highest and largest inland alpine wetland in the world. The study on the nutrient contents and microbial populations of aeolian sandy soils in this region showed that soil organic matter content increased with the evolution of aeolian sand dunes from un-stabilized to stabilized state, being 5.9 and 3.8 times higher in stabilized sand dune than in mobile and semi-stabilized sand dunes, respectively. Soil nitrogen and phosphorus contents increased in line with the amount of organic matter, while potassium content and pH value varied slightly. The microbial populations changed markedly with the development of vegetation, fixing of mobile sand, and increase of soil nutrients. The quantities of soil bacteria, fungi and actinomycetes were 4.0 and 2.8 times, 19.6 and 6.3 times, and 12.4 and 2.6 times higher in stabilized and semi-stabilized sand dunes than in mobile sand dune, respectively, indicating that soil microbial bio-diversity was increased with the evolution of aeolian sand dunes from mobile to stabilized state. In addition, the quantities of soil microbes were closely correlated with the contents of soil organic matter, total nitrogen, and available nitrogen and phosphorus, but not correlated with soil total phosphorus, total and available potassium, or pH value. PMID:17396507

  15. A field study of large-scale oscillation ripples in a very coarse-grained, high-energy marine environment

    USGS Publications Warehouse

    Hirschaut, D.W.; Dingler, J.R.

    1982-01-01

    Monastery Beach, Carmel, California is a pocket beach that sits within 200 m of the head of Carmel Submarine Canyon. Coarse to very coarse sand covers both the beach and adjacent shelf; in the latter area incoming waves have shaped the sand into large oscillation ripples. The accessibility of this area and a variable wave climate produce a unique opportunity to study large-scale coarse-grained ripples in a high-energy environment. These ripples, which only occur in very coarse sand, form under the intense, wave-generated currents that exist during storm conditions. Once formed, these ripples do not significantly change under lower energy waves. On three separate occasions scuba divers measured ripples and collected sand samples from ripple crests near fixed reference stakes along three transects. Ripple wavelength and grain size decreased with an increase in water depth. Sediment sorting was best closest to the surf zone and poorest at the rim of Carmel Canyon. Cobbles and gravel observed in ripple troughs represent lag deposits. Carmel Canyon refracts waves approaching Monastery Beach such that wave energy is focused towards the northern and southern portions of the beach, leaving the central part of the beach lower in energy. This energy distribution causes spatial variations in the ripples and grain sizes with the shortest wavelengths and smallest grain sizes being in the central part of the shelf.

  16. 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

  17. Effects of aeolian erosion on microbial release from solids.

    NASA Technical Reports Server (NTRS)

    Gustan, E. A.; Olson, R. L.; Taylor, D. M.; Green, R. H.

    1972-01-01

    This study was initiated to determine the percentage of spores that would be expected to be released from the interior of solid materials by aeolian erosion on a planetary surface. Methyl methacrylate and Eccobond disks were fabricated so that each disk contained approximately 40,000 Bacillus subtilis var. niger spores. The disks were placed in a specially designed sandblasting device and eroded. Exposure periods of 0.5, 2 and 24 hours were investigated using filtered air to accelerate the sand. A series of tests was also conducted for a 0.5 hour period using carbon dioxide. Examination of the erosion products showed that less than 1% of the spores originally contained in the solids was released by aeolian erosion.

  18. Character and provenance of aeolian sediments in northeast Thailand

    NASA Astrophysics Data System (ADS)

    Nichol, Janet E.; Nichol, Douglas W.

    2015-12-01

    Aeolian activity is not generally associated with the humid tropics, and although reports of loess-like soils in various locations in southeast Asia exist, these mainly lack the detailed analysis to set them in meaningful spatial or historical context. This paper examines the red and yellow sandy sediments of the Khorat Plateau in northeast Thailand which have been variously referred to as 'cover sands', 'loessial soils' or 'loess'. The sediments are referred to as having alluvial, biological as well as aeolian origin, and a date of 9-35 ka is reported. The study compares the Khorat sediments physically and geochemically with loess and aeolian sediments from other regions, as well as with other sites in southeast Asia which are reported here. The moderate degree of particle sorting and unimodal sizes of the sediments along with a sub-spherical sub-rounded form, supports previous diagnoses of an aeolian origin. Geochemical analysis of the Khorat sediments indicates severe depletion in both mobile and immobile elements, which are even more depleted than other southeast Asian loessic soils examined. This depletion, along with the only moderate particle sorting, suggests the source of the sediments to be the local weathered sandstones outcropping around the edge of the Khorat Plateau. The dissimilarity of the Khorat sediments from Upper Continental Crust (UCC) elemental values supports this, as homogenisation would occur if diverse source areas were involved. The study suggests that aeolian sediments of humid tropical regions warrant more attention as climate proxy markers, due to the dissimilarity between the present climate and conditions required for their formation.

  19. Detecting Patterns of Aeolian Transport Direction

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The magnitude and direction of aeolian transport are of direct interest to those engaged in the study of aeolian processes. Although the magnitude of sediment transport has been studied extensively, the study of aeolian transport direction has garnered less attention. This paper describes the deve...

  20. 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.

  1. Intermittency of aeolian saltation.

    PubMed

    Wang, Zhen-Ting; Zhang, Chun-Lai; Wang, Hong-Tao

    2014-12-01

    Saltation motion of sand grains in a steady wind was measured using a high-speed camera at very high frequency in a wind tunnel. A Heaviside-type function was defined to quantificationally describe an inherent property of saltation, i.e. intermittency. Kurtosis and periodicity of state function are statistical manifestations of intermittency. In addition, the strong autocorrelation of time series of volume concentration clearly confirms that saltation is not a completely random process at the timescale of subsecond. Formation mechanism, especially turbulent structures responsible for intermittent saltation, remains to be revealed from the viewpoint of classical mechanics. PMID:25528744

  2. Ripples in intertidal mud—a conceptual explanation

    NASA Astrophysics Data System (ADS)

    Chang, Tae Soo; Flemming, Burghard W.

    2013-12-01

    aggregates deposited from suspension around high-water slack tide under moderate weather conditions initially respond as single (non-cohesive) particles which are hydraulically equivalent to ambient very fine sands. During exposure at low tide, gradual loss of water transforms the rippled mud into increasingly more cohesive mud drapes which are more resistant to erosion. Unless destroyed during high-energy events, the mud ripples may remain intact long enough to become buried and thereby preserved. Indeed, occasional but persistent observations of ripples in sub-Recent to ancient mudrocks document their preservation potential.

  3. Ripple density resolution for various rippled-noise patterns.

    PubMed

    Supin AYa; Popov, V V; Milekhina, O N; Tarakanov, M B

    1998-04-01

    Ripple-density resolution was measured in normal humans using rippled noise with a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of spectral peak and trough positions (the phase reversal) is detectable. Different rippled noise patterns were used: (i) either frequency-proportional or constant ripple spacing; (ii) various bandwidth; and (iii) either steep or shallow slopes of the spectrum envelope. When tested with frequency-proportional rippled noise, ripple-density resolution as expressed in relative units (the center frequency to ripple spacing ratio) little depended on frequency within a range of 1 to 8 kHz: from 11.4 at 1 kHz to 14.9 at 8 kHz, mean 13.1. These values were virtually independent on noise bandwidth. When tested with constant ripple spacing, the resolution was of similar values taking the relative ripple density at the lower part of the passband. Being measured by noise with steep spectral edges, the resolution was five units higher than it was for shallow-enveloped spectra, thus suggesting some edge effects at the spectrum boundaries. The resolution values obtained were about twice higher than those predicted by peripheral auditory filter tuning. PMID:9566326

  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. Microdunes and other aeolian bedforms on Venus - Wind Tunnel simulations

    NASA Astrophysics Data System (ADS)

    Greeley, R.; Marshall, J. R.; Leach, R. N.

    1984-10-01

    The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind Tunnel. It is found that the development of specific bedforms, including ripples, dunes, and 'waves', as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.

  6. Microdunes and Other Aeolian Bedforms on Venus: Wind Tunnel Simulations

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Marshall, J. R.; Leach, R. N.

    1985-01-01

    The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind tunnel. It is found that the development of specific bedforms, including ripples, dunes, and waves, as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.

  7. Microdunes and other aeolian bedforms on Venus - Wind Tunnel simulations

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Marshall, J. R.; Leach, R. N.

    1984-01-01

    The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind Tunnel. It is found that the development of specific bedforms, including ripples, dunes, and 'waves', as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.

  8. Aeolian transport pathways along the transition from Tibetan highlands towards northwestern Chinese deserts

    NASA Astrophysics Data System (ADS)

    Nottebaum, Veit; Lehmkuhl, Frank; Stauch, Georg

    2014-05-01

    The identification and semi-quantification of aeolian transport pathways enhances the understanding of aeolian sediment archive formation and thus supports reliability and explanatory power concerning palaeoenvironmental reconstructions. Grain size analysis of 279 surface sediment samples from the transition of Tibetan highlands (Qilian Shan) towards northwestern Chinese deserts allows the differentiation of contributing pathways among three types of aeolian sediments: silty loess, sandy loess, and aeolian sands. The study area exhibits a high diversity of geomorphological surfaces due to varieties in relief, elevation and climatic conditions. Therefore, it provides the opportunity to investigate the characteristics of sediments in different geomorphological settings. Using the peaks of grain size frequency's standard deviation of primary loess allows identification of the most sensitive fractions to varying accumulation conditions. mU/fS-ratio (7 - 13 μm / 58 - 84 μm) of primary silty loess relates the far-travelled dust proportion to the locally transported fine sand component. In vicinity to fluvial channels in the foreland mU/fS-values are significantly decreased, whereas mU/fS-values increase with altitude (r2 = 0.74). This indicates higher contribution of long distance transport compared to lower regions. A prominent increase of mU/fS-values above 3000 m asl likely indicates an increasing contribution of fine and medium silt particles transported by Westerlies in higher altitudes. In contrast, lower areas seem to be more strongly influenced by low altitude monsoon currents (NW-Winter- / SE-summer monsoon). The difference in grain size properties is additionally enhanced by the contrasting geomorphologic settings along the mountain declivity: Plain foreland alluvial fans support fine sand supply and availability whereas steep high mountain topography provides only limited potential for fine sand deflation. Similarly, the relatively low relief in intramontane

  9. Opportunity Mars Rover Mission: Overview and Selected Results from Leaving Purgatory Ripple to Traverses Toward Endeavour Crater

    NASA Astrophysics Data System (ADS)

    Arvidson, R. E.; Athena Team

    2010-12-01

    Opportunity has been traversing the plains of Meridiani since January 25, 2004, acquiring remote sensing and in-situ observations of soils, cobbles, and bedrock, together with atmospheric observations. This paper provides an overview of discoveries between sols 511 (July 1, 2005) and 2300 (July 13, 2010), complementing a similar paper by Squyres et al., [2006] covering results from the initial phase of the mission. Use of the Alpha Particle X-Ray Spectrometer to measure atmospheric argon shows the importance of the southern seasonal ice cap in controlling atmospheric dynamics, with inter-annual variations evident over the three Mars years of observations. The plains are partially covered by aeolian ripples produced by easterly winds during a previous epoch with enhanced Hadley cell circulation. During the current climatic regime, fine-grained particles continue to be reworked locally and trapped. Ripple surfaces are composed of basaltic sand mixed with varying amounts of dust and hematitic concretions. Cobbles examined by Opportunity include iron and stony iron meteorites and both sedimentary and basaltic impact ejecta. Hematite-rich deposits in fractures within ejecta from Concepcion crater, together with iron oxide deposits on meteorites, imply on-going aqueous alteration at low rates. Measurements of sulfate-rich rock strata within the walls of Erebus and Victoria craters provide compelling evidence of sand deposition by wind, with local reworking within ephemeral lakes. We continue to search for the lacustrine facies that would confirm or refute the hypothesis that the sands were produced in an acid-sulfate evaporitic environment. Rocks examined in the upper walls of Victoria and Endurance craters also show enrichment of Cl and a decrease in Mg and S with increasing depth. This pattern implies that regional-scale aqueous alteration took place before formation of these craters. Opportunity has been traversing toward the rim of the 20 km wide Endeavour crater

  10. Identification of a late Quaternary alluvial-aeolian sedimentary sequence in the Sichuan Basin, China

    NASA Astrophysics Data System (ADS)

    Feng, Jin-Liang; Ju, Jian-Ting; Chen, Feng; Hu, Zhao-Guo; Zhao, Xiang; Gao, Shao-Peng

    2016-03-01

    The late Quaternary sedimentary sequence in the northwestern part of the Sichuan Basin consists of five lithological units and with increasing depth include the: Chengdu Clay; Brown Clay; Red Clay; Sandy Silt; and basal Muddy Gravel. The genesis, provenance and age of the sediments, as well as the possible presence of hiatuses within this sequence are debated. Measurements of grain-size, magnetic susceptibility, quartz content, quartz δ18O values, element composition, and Sr-Nd isotopic concentrations of samples from a typical sedimentary sequence in the area provides new insights into the genesis and history of the sequence. The new data confirm that the sediments in study site are alluvial-aeolian in origin, with basal alluvial deposits overlain by aeolian deposits. Like the uppermost Chengdu Clay, the underlying Brown Clay and Red Clay are aeolian in origin. In contrast, the Silty Sand, like the basal Muddy Gravel, is an alluvial deposit and not an aeolian deposit as previously thought. Moreover, the succession of the aeolian deposits very likely contains two significant sedimentary hiatuses. Sedimentological analysis demonstrates that the source materials for the aeolian deposits in the northwestern part of the Sichuan Basin and those on the eastern Tibetan Plateau are different. Furthermore, the loess deposits on the eastern Tibetan Plateau are derived from heterogeneous local sources.

  11. Containerless Ripple Turbulence

    NASA Technical Reports Server (NTRS)

    Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

    2002-01-01

    One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear

  12. Containerless Ripple Turbulence

    NASA Astrophysics Data System (ADS)

    Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

    2002-11-01

    One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear

  13. The effect of biological cohesion on current ripple development

    NASA Astrophysics Data System (ADS)

    Malarkey, Jonathan; Baas, Jaco H.; Hope, Julie

    2014-05-01

    Results are presented from laboratory experiments examining the role of biological cohesion, associated with Extra Polymeric Substances, on the development of current ripples. The results demonstrate the importance of biological cohesion compared to the effect of physical cohesion associated with clays in an otherwise sandy bed. FURTHER INFORMATION In fluvial and marine environments sediment transport is mainly dependent on the nature of the bed surface (rippled or flat) and the nature of cohesion in the bed. Cohesion can be either physical, as a result of the presence of clays, or biological as a result of the presence of organisms. In the case of the latter, biological cohesion occurs as a result of the presence of Extra Polymeric Substances (EPS) secreted by microorganisms. While it is known that EPS can dramatically increase the threshold of motion (Grant and Gust, 1987), comparatively little is known about the effect of EPS on ripple formation and development. The experiments described here seek to fill this gap. They also allow the effect of biological cohesion to be compared with that of physical cohesion from previous experiments (Baas et al., 2013). The experiments, which were conducted in a 10m flume at Bangor University, involved a current over a bed made of fine sand, with a median diameter of 0.148mm, and various amounts of xanthan gum, a proxy for naturally occurring EPS (Vardy et al., 2007). The hydrodynamic experimental conditions were matched very closely to those of Baas et al. (2013). The ripple dimensions were recorded through the glass side wall of the tank using time lapse photography. In the physical cohesion experiments of Baas et al. (2013) for clay contents up to 12%, the clay was very quickly winnowed out of the bed, leaving essentially clay-free ripples that developed at more or less the same rate as clean sand ripples. The resulting equilibrium ripples were essentially the same length as the clean sand ripples but reduced in height. By

  14. The Icelandic volcanic aeolian environment: Processes and impacts - A review

    NASA Astrophysics Data System (ADS)

    Arnalds, Olafur; Dagsson-Waldhauserova, Pavla; Olafsson, Haraldur

    2016-03-01

    Iceland has the largest area of volcaniclastic sandy desert on Earth or 22,000 km2. The sand has been mostly produced by glacio-fluvial processes, leaving behind fine-grained unstable sediments which are later re-distributed by repeated aeolian events. Volcanic eruptions add to this pool of unstable sediments, often from subglacial eruptions. Icelandic desert surfaces are divided into sand fields, sandy lavas and sandy lag gravel, each with separate aeolian surface characteristics such as threshold velocities. Storms are frequent due to Iceland's location on the North Atlantic Storm track. Dry winds occur on the leeward sides of mountains and glaciers, in spite of the high moisture content of the Atlantic cyclones. Surface winds often move hundreds to more than 1000 kg m-1 per annum, and more than 10,000 kg m-1 have been measured in a single storm. Desertification occurs when aeolian processes push sand fronts and have thus destroyed many previously fully vegetated ecosystems since the time of the settlement of Iceland in the late ninth century. There are about 135 dust events per annum, ranging from minor storms to >300,000 t of dust emitted in single storms. Dust production is on the order of 30-40 million tons annually, some traveling over 1000 km and deposited on land and sea. Dust deposited on deserts tends to be re-suspended during subsequent storms. High PM10 concentrations occur during major dust storms. They are more frequent in the wake of volcanic eruptions, such as after the Eyjafjallajökull 2010 eruption. Airborne dust affects human health, with negative effects enhanced by the tubular morphology of the grains, and the basaltic composition with its high metal content. Dust deposition on snow and glaciers intensifies melting. Moreover, the dust production probably also influences atmospheric conditions and parameters that affect climate change.

  15. Ripples and Rocks

    NASA Technical Reports Server (NTRS)

    2005-01-01

    26 February 2005 This Mars Global Surveyor (MGS) Orbiter Camera (MOC) image shows light-toned sedimentary rock outcrops and large dark-toned, windblown ripples in Aram Chaos.

    Location near: 3.0oN, 20.9oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Northern Summer

  16. Sand waves in environmental flows: Insights gained by coupling large-eddy simulation with morphodynamics

    NASA Astrophysics Data System (ADS)

    Sotiropoulos, Fotis; Khosronejad, Ali

    2016-02-01

    Sand waves arise in subaqueous and Aeolian environments as the result of the complex interaction between turbulent flows and mobile sand beds. They occur across a wide range of spatial scales, evolve at temporal scales much slower than the integral scale of the transporting turbulent flow, dominate river morphodynamics, undermine streambank stability and infrastructure during flooding, and sculpt terrestrial and extraterrestrial landscapes. In this paper, we present the vision for our work over the last ten years, which has sought to develop computational tools capable of simulating the coupled interactions of sand waves with turbulence across the broad range of relevant scales: from small-scale ripples in laboratory flumes to mega-dunes in large rivers. We review the computational advances that have enabled us to simulate the genesis and long-term evolution of arbitrarily large and complex sand dunes in turbulent flows using large-eddy simulation and summarize numerous novel physical insights derived from our simulations. Our findings explain the role of turbulent sweeps in the near-bed region as the primary mechanism for destabilizing the sand bed, show that the seeds of the emergent structure in dune fields lie in the heterogeneity of the turbulence and bed shear stress fluctuations over the initially flatbed, and elucidate how large dunes at equilibrium give rise to energetic coherent structures and modify the spectra of turbulence. We also discuss future challenges and our vision for advancing a data-driven simulation-based engineering science approach for site-specific simulations of river flooding.

  17. 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.

  18. Atlas of Dutch drift sands

    NASA Astrophysics Data System (ADS)

    Riksen, Michel; Jungerius, Pieter

    2013-04-01

    The Netherlands is well known for its aeolian landscapes. Frequent storms during the High Middle Ages (1000-1300 AD) reactivated Pleistocene coversands and river dunes and are responsible for the formation of the Holocene drift sands at a scale which is unique for Europe. A hypothesized relationship with farmer practices for making plaggensoils has recently been refuted, because drift sand formation began centuries earlier. The coastal dune belt with their parabolic dunes dates from the same period as the drift sand. An estimate of the extent of drift sands can be made from soil maps: drift sands are too young to show much profile development (Regosols). With this method Koster estimated the maximum extent of Holocene drift sands in the Netherlands to be about 800 km2 (Koster 2005). Laser altimetry allows a more precise estimate of the total surface affected by wind from the characteristic relief patterns produced by the Holocene wind, which is different from the smooth surface of cover sand deposits. Laser altimetry has been used before to investigate the mechanism of drift sand formation (Jungerius & Riksen 2010). Most of the surface affected by wind is not active anymore, but the tell-tale rough surface survived ages of different landuse. The total affected surface amounts to 825 km2. It is noteworthy that both methods give comparable results. We recorded a total number of 367 of affected areas of varying shapes, ranging in size from 1.6 ha to a large complex of drif sands of 7,119.5 ha. As is to be expected from their mode of origin, most occurrences are associated with cover sands, and with river dunes along the river Meuse and smaller rivers in other parts of the country. Particularly the final phases of cover sand and river dunes that show more relief as parabolic dunes were affected. There are also small aeolian deposits at the lee side blown from fallow agricultural fields but they are (sub)recent. Most of the relief is irregular, but the larger

  19. Quantifying the provenance of aeolian sediments using multiple composite fingerprints

    NASA Astrophysics Data System (ADS)

    Liu, Benli; Niu, Qinghe; Qu, Jianjun; Zu, Ruiping

    2016-09-01

    We introduce a new fingerprinting method that uses multiple composite fingerprints for studies of aeolian sediment provenance. We used this method to quantify the provenance of sediments on both sides of the Qinghai-Tibetan Railway (QTR) in the Cuona Lake section of the Tibetan Plateau (TP), in an environment characterized by aeolian and fluvial interactions. The method involves repeatedly solving a linear mixing model based on mass conservation; the model is not limited to spatial scale or transport types and uses all the tracer groups that passed the range check, Kruskal-Wallis H-test, and a strict analytical solution screening. The proportional estimates that result from using different composite fingerprints are highly variable; however, the average of these fingerprints has a greater accuracy and certainty than any single fingerprint. The results show that sand from the lake beach, hilly surface, and gullies contribute, respectively, 48%, 31% and 21% to the western railway sediments and 43%, 33% and 24% to the eastern railway sediments. The difference between contributions from various sources on either side of the railway, which may increase in the future, was clearly related to variations in local transport characteristics, a conclusion that is supported by grain size analysis. The construction of the QTR changed the local cycling of materials, and the difference in provenance between the sediments that are separated by the railway reflects the changed sedimentary conditions on either side of the railway. The effectiveness of this method suggests that it will be useful in other studies of aeolian sediments.

  20. Characterizing the instability of aeolian environments using analytical reasoning

    NASA Astrophysics Data System (ADS)

    Houser, C.; Bishop, M. P.; Dobreva, I. D.; Barrineau, C. P.; Weymer, B. A.

    2013-12-01

    Characterization of aeolian systems is complicated by rapidly changing surface-process regimes, spatio-temporal scale dependencies, and subjective interpretation of imagery and spatial data. Stability and instability of the South Texas sand sheet is addressed using an artificial intelligence approach that integrates spatial information and analytical reasoning. Specifically, the purpose of this study is to determine if landscape evolutionary sequences could be mapped and characterized based on simple conceptual relationships amongst biophysical variables including topography, vegetation, surface moisture, wind speed, and surface erosion and deposition. A digital elevation model was derived from airborne LiDAR data and combined with moisture and vegetation indices computed using Spectral feature extraction from Landsat Thematic Mapper data. Our analysis reveals unique scale dependent spatial patterns and the use of fuzzy cognitive maps provides an analytical reasoning approach to address the complexity of aeolian environments in response to changes in climate forcing. The application to other Holocene aeolian deposits and the potential for this approach to model landscape evolution are also discussed.

  1. Genetics Home Reference: rippling muscle disease

    MedlinePlus

    ... Genetics Home Health Conditions rippling muscle disease rippling muscle disease Enable Javascript to view the expand/collapse ... Download PDF Open All Close All Description Rippling muscle disease is a condition in which the muscles ...

  2. Studies in Martian Aeolian Geology

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    2001-01-01

    This report gives the results from the investigation through March 15, 1999 for the first two years of the three year investigation (year 3 runs from March 1, 1999 to February 27, 2000). The investigation included three tasks, all involving windblown dust (particles a few micrometers in diameter) to simulate the aeolian regime on Mars. Experiments were conducted primarily in the Mars Surface Wind Tunnel (MARSWIT) at NASA-Ames Research Center.

  3. 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.

  4. Large, Bright Wind Ripples

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-397, 20 June 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, relatively bright ripples of windblown sediment in the Sinus Sabaeus region south of Schiaparelli Basin. The surrounding substrate is thickly mantled by very dark material, possibly windblown silt that settled out of the atmosphere. The picture is located near 7.1oS, 343.7oW. Sunlight illuminates the scene from the left.

  5. Selective deposition response to aeolian-fluvial sediment supply in the desert braided channel of the upper Yellow River, China

    NASA Astrophysics Data System (ADS)

    Wang, H.; Jia, X.; Li, Y.; Peng, W.

    2015-09-01

    Rivers flow across aeolian dunes and develop braided stream channels. Both aeolian and fluvial sediment supplies regulate sediment transport and deposition in such cross-dune braided rivers. Here we show a significant selective deposition in response to both aeolian and fluvial sediment supplies in the Ulan Buh desert braided channel. The Ulan Buh desert is the main coarse sediment source for this desert braided channel, and the mean percentage of the coarser (> 0.08 mm) grains on the aeolian dunes surface is 95.34 %. The lateral selective deposition process is developed by the interaction between the flows and the aeolian-fluvial sediment supplies, causing the coarser sediments (> 0.08 mm) from aeolian sand supply and bank erosion to accumulate in the channel centre and the finer fluvial sediments (< 0.08 mm) to be deposited on the bar and floodplain surfaces, forming a coarser-grained thalweg bed bounded by finer-grained floodplain surfaces. This lateral selective deposition reduces the downstream sediment transport and is a primary reason for the formation of an "above-ground" river in the braided reach of the upper Yellow River in response to aeolian and fluvial sediment supplies.

  6. Wavelength selection and symmetry breaking in orbital wave ripples

    NASA Astrophysics Data System (ADS)

    Nienhuis, Jaap H.; Perron, J. Taylor; Kao, Justin C. T.; Myrow, Paul M.

    2014-10-01

    Sand ripples formed by waves have a uniform wavelength while at equilibrium and develop defects while adjusting to changes in the flow. These patterns arise from the interaction of the flow with the bed topography, but the specific mechanisms have not been fully explained. We use numerical flow models and laboratory wave tank experiments to explore the origins of these patterns. The wavelength of "orbital" wave ripples (λ) is directly proportional to the oscillating flow's orbital diameter (d), with many experimental and field studies finding λ/d ≈ 0.65. We demonstrate a coupling that selects this ratio: the maximum length of the flow separation zone downstream of a ripple crest equals λ when λ/d ≈ 0.65. We show that this condition maximizes the growth rate of ripples. Ripples adjusting to changed flow conditions develop defects that break the bed's symmetry. When d is shortened sufficiently, two new incipient crests appear in every trough, but only one grows into a full-sized crest. Experiments have shown that the same side (right or left) wins in every trough. We find that this occurs because incipient secondary crests slow the flow and encourage the growth of crests on the next flank. Experiments have also shown that when d is lengthened, ripple crests become increasingly sinuous and eventually break up. We find that this occurs because crests migrate preferentially toward the nearest adjacent crest, amplifying any initial sinuosity. Our results reveal the mechanisms that form common wave ripple patterns and highlight interactions among unsteady flows, sediment transport, and bed topography.

  7. Publication trends in Aeolian research: An analysis of the biblography of Aeolian research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An analysis of the Bibliography of Aeolian Research has provided information regarding publication trends in aeolian research. Overall, results suggest that there has been a significant increase in the number of publications per year since the first aeolian-research publication appeared in 1646. P...

  8. Martian aeolian processes, sediments, and features

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Lancaster, Nicholas; Lee, Steven; Thomas, Peter

    1992-01-01

    In this review of the aeolian regime on Mars, consideration is given to the sources and characteristics of the particles that are involved in aeolian processes and the winds that are required to set grains into motion. Dust storms are reviewed and previous observations and the mechanisms of dust-storm generation are assessed. Various aeolian features, including dunes and albedo features, as well as windblown mantle deposits are discussed. In planning for future missions to Mars, aeolian processes must be taken into account. Surface modifications by the wind and windblown deposits can influence remote-sensing observations, affect sampling strategies, and have detrimental effects on manned and unmanned spacecraft on the surface.

  9. 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.

  10. 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.

  11. 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.

  12. Rapid Coarsening of Ion Beam Ripple Patterns by Defect Annihilation

    SciTech Connect

    Hansen, Henri; Messlinger, Sebastian; Stoian, Georgiana; Redinger, Alex; Krug, Joachim; Michely, Thomas

    2009-04-10

    Ripple patterns formed on Pt(111) through grazing incidence ion beam erosion coarsen rapidly. At and below 450 K coarsening of the patterns is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation for sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monatomic steps illuminated by the ion beam.

  13. 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

  14. A Stellar Ripple

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This false-color composite image shows the Cartwheel galaxy as seen by the Galaxy Evolution Explorer's far ultraviolet detector (blue); the Hubble Space Telescope's wide field and planetary camera 2 in B-band visible light (green); the Spitzer Space Telescope's infrared array camera at 8 microns (red); and the Chandra X-ray Observatory's advanced CCD imaging spectrometer-S array instrument (purple).

    Approximately 100 million years ago, a smaller galaxy plunged through the heart of Cartwheel galaxy, creating ripples of brief star formation. In this image, the first ripple appears as an ultraviolet-bright blue outer ring. The blue outer ring is so powerful in the Galaxy Evolution Explorer observations that it indicates the Cartwheel is one of the most powerful UV-emitting galaxies in the nearby universe. The blue color reveals to astronomers that associations of stars 5 to 20 times as massive as our sun are forming in this region. The clumps of pink along the outer blue ring are regions where both X-rays and ultraviolet radiation are superimposed in the image. These X-ray point sources are very likely collections of binary star systems containing a blackhole (called massive X-ray binary systems). The X-ray sources seem to cluster around optical/ultraviolet-bright supermassive star clusters.

    The yellow-orange inner ring and nucleus at the center of the galaxy result from the combination of visible and infrared light, which is stronger towards the center. This region of the galaxy represents the second ripple, or ring wave, created in the collision, but has much less star formation activity than the first (outer) ring wave. The wisps of red spread throughout the interior of the galaxy are organic molecules that have been illuminated by nearby low-level star formation. Meanwhile, the tints of green are less massive, older visible-light stars.

    Although astronomers have not identified exactly which galaxy collided with the Cartwheel, two of three

  15. Observations Regarding Small Eolian Dunes and Large Ripples on Mars

    NASA Technical Reports Server (NTRS)

    Edgett, Kenneth S.

    2001-01-01

    Eolian bedforms occur at the interface between a planetary surface and its atmosphere; they present a proxy record of the influence of climate, expressed in sediment transport, over that surface. High resolution images (1.5 - 12 m/pixel) from the Mars Global Surveyor (MGS) Mars Orbiter Camera provide glimpses of the most recent events shaping the martian landscape. Thousands of images exhibit small transverse dunes or large eolian ripples that have crest-to-crest spacings of 10 to 60 m, heights of a few to 10 m. Bedforms of the size and patterns seen in the Mars photographs are rarely described among Earth's eolian landforms; in terms of size and morphology, most of these fall between traditional definitions of "ripples" and "dunes". Dunes are composed chiefly of materials transported by saltation, ripples are smaller forms moved along by the impact of saltating grains (traction). The largest reported eolian ripples on Earth (granule ripples, megaripples) are typically smaller than the bedforms observed on Mars; likewise, most dunes are typically larger. The small dunes and large ripples on Mars come in a variety of relative albedos, despite an early MGS impression that they are all of high albedo. Some ripples occur on the surfaces of sand dunes; these are most likely true granule ripples. However, most of these bedforms occur in troughs, pits, craters, and on deflated plains. Despite impressions early in the MGS mission, they do not occur everywhere (e.g., they are rare on the northern plains) but they do occur at a range of elevations from the highest volcanoes to the deepest basins. Where they occur on a hard substrate among larger sand dunes, the big dunes have over-ridden the smaller bedforms, indicating that the smaller features are older and perhaps indurated or very coarse-grained. At other locales, the small bedforms have been mantled by material settled from suspension, in other cases they are being exhumed and may be lithified. Still other examples are

  16. 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

  17. Planet-wide sand motion on mars

    USGS Publications Warehouse

    Bridges, N.T.; Bourke, M.C.; Geissler, P.E.; Banks, M.E.; Colon, C.; Diniega, S.; Golombek, M.P.; Hansen, C.J.; Mattson, S.; McEwen, A.S.; Mellon, M.T.; Stantzos, N.; Thomson, B.J.

    2012-01-01

    Prior to Mars Reconnaissance Orbiter data, images of Mars showed no direct evidence for dune and ripple motion. This was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low-density atmosphere. We show that many sand ripples and dunes across Mars exhibit movement of as much as a few meters per year, demonstrating that Martian sand migrates under current conditions in diverse areas of the planet. Most motion is probably driven by wind gusts that are not resolved in global circulation models. A past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains. ?? 2012 Geological Society of America.

  18. Aeolian Slipface Processes on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Cornwall, Carin; Jackson, Derek; Bourke, Mary; Cooper, Andrew

    2016-04-01

    The surface of Mars is dominated by aeolian features and many locations show ripple and dune migration over the past decade with some sediment fluxes comparable to terrestrial dunes. One of the leading goals in investigating aeolian processes on Mars is to explore the boundary conditions of sediment transport, accumulation, and dune mor-phology in relation to wind regime as well as to quantify migration rates and sediment flux. We combine terrestrial field observations, 3D computational fluid dynamics (CFD) modeling and remote sensing data to investigate com-plex, small scale wind patterns and grainflow processes on terrestrial and martian dunes. We aim to constrain grain flow magnitudes and frequencies that occur on slipface slopes of dunes in order to improve estimates of martian dune field migration and sediment flux related to wind velocity and flow patterns. A series of ground-based, high resolution laser scans have been collected in the Maspalomas dune field in Gran Canaria, Spain to investigate grainflow frequency, morphology and slipface advancement. Analysis of these laser scans and simultaneous video recordings have revealed a variety of slipface activity. We identify 6 different grain-flow morphologies including, hourglass shape (classic alcove formation with deposit fan below), superficial flow (thin lenses), narrow trough (vertical lines cm in width), sheet, column (vertical alcove walls), and complex (combi-nation of morphologies triggered simultaneously in the same location). Hourglass grainflow morphologies were the most common and occurred regularly. The superficial and narrow trough morphologies were the second most com-mon and frequently occurred in between large grain flows. Sheet grainflows were rare and unpredictable. These flows involved large portions of the slipface (metres across) and mobilized a substantial amount of sediment in one event. We have compared these grainflow morphologies from Maspalomas to those in martian dune fields and

  19. Coastal chevron deposits - sedimentology, methods and aeolian versus tsunamigenic origin

    NASA Astrophysics Data System (ADS)

    Spiske, Michaela; Garcia Garcia, Anna-Marietta; Tsukamoto, Sumiko; Schmidt, Volkmar

    2013-04-01

    The origin of v-shaped sediment bodies, so-called "chevrons", is currently controversially discussed. The term "chevron" is presently only defined in terms of the morphology of the sediment body, but not in terms of its genesis. Both an aeolian and an impact-tsunami origin are discussed. In this study, the sedimentology and origin of chevrons is investigated, examining deposits from the US west coast and the coast of Western Australia. We use internal structures obtained in trenches or by ground penetrating radar surveys, trenches, ages gained by radiocarbon and optically stimulated luminescence dating, grain size analysis and the general sediment composition. If the chevrons were deposited by a tsunami, all chevrons along one coastline should possess the same depositional ages, the grain-size distribution should be polymodal indicating various sediment sources and internal structures should be restricted mainly to normal grading. In case of an aeolian origin, the ages of the individual chevrons may vary and internal ages will reflect the migration of the sediment body. Furthermore, cross bedding should be present throughout the sediment body and soil horizons may represent inactive phases. Preliminary results indicate the presence of internal cross bedding and an unimodal grain-size distribution of the surveyed chevrons. Ages decrease in landward transport direction and to the top within vertical successions. At some locations soil layers intercalate between well sorted sands. The mean grain size of the chevron sands is 0.11-0.25 mm. A comparison of the chevron components with the mineral content of possible sediment sources (e.g., rivers, beaches, cliffs) shows that the chevrons are composed of the fine grain size fraction of the respective sources. Sediments of this grain size can easily be transported by aeolian forces under the local prevailing wind conditions. Terrestrial gastropods found within the chevrons give evidence of a long term development of these

  20. Why do sand furrow distributions vary in the North Polar latitudes on Mars?

    NASA Astrophysics Data System (ADS)

    Bourke, Mary; McGaley-Towle, Zoe

    2014-05-01

    Sand dunes on Mars display geomorphic evidence of an active and dynamic sediment flux. Barchan dunes migrate, ripples move and the slipface morphology changes annually. Aeolian sediment transport is seasonally constrained and linked to cryogenic processes. Sand furrows are geomorphic features that are eroded into the surface of dunes. They form during sublimation of the seasonal carbon dioxide deposit which moves gas and sand through vents in the ice (cryo-venting) (Bourke, 2013). They are visible on the surface of dunes using the highest resolution images available for Mars. Previous work has noted that the distribution of furrows varies spatially both on individual dunes and at different Polar locations. Here we report on the preliminary findings of a mapping project that seeks to confirm this previous qualitative observation. In addition, we aim to explain the observed spatial and temporal variation in sand furrows on North Polar dunes. Ten polar sites that reflect a latitudinal range of 9.5º are being analysed. The HiRISE images were acquired between 16/2/2012 and 31/05/2012, over a period of 105 Earth days or 102 Sols. We have completed mapping of 1711 sand furrows in an 84 km2 area of sand dunes, i.e. at four of the ten sites. The data confirm that there is variability in the distribution of sand furrows in the Polar Region. While data from all ten sites will be required to fully test the assertion of a latitudinal control, it is worth noting that the two most northerly sites have a significantly higher density of furrows compared to the two lower latitude sites. As the seasonal ice thickness is known to increases pole-ward on Mars, our data suggest that effective furrow formation may be linked to ice deposit thickness. In particular, it suggests that a threshold in ice thickness must be crossed in order for effective cryo-venting to occur. Bourke, M.C., 2013. Sand Furrows: A new surface feature on Martian dunes, EGU, EGU2013-11859, Vienna.

  1. Rippled scour depressions on continental shelf bank slopes off Nordland and Troms, Northern Norway

    NASA Astrophysics Data System (ADS)

    Bellec, Valérie K.; Bøe, Reidulv; Rise, Leif; Slagstad, Dag; Longva, Oddvar; Dolan, Margaret F. J.

    2010-05-01

    Multibeam bathymetry acquired under the MAREANO programme from the continental shelf off Nordland and Troms, northern Norway, show bedforms that we have interpreted as rippled scour depressions. They occur in three areas offshore on bank slopes facing southeast, more than 15 km from land. They are generally found where the slope gradient is low, in water depths of 70-160 m. Individual depressions are up to 3 km long, 1 m deep and up to 300 m wide. They occur in areas where sediments evolve quickly from glacial deposits on the banks to post-glacial muddy sediments on the glacial troughs. Multibeam backscatter and underwater video data show that depression floors are covered by rippled, gravelly, shelly sand. Ripple crests are parallel or slightly oblique to the depression axis orientation. Sand without bedforms is observed between the depressions. TOPAS seismic lines show that the uppermost seismic unit consists of the sand between the depressions. The base of this unit may be the last transgressive/tidal/wave ravinement surface. Physical oceanographic modelling indicates that maximum current velocities are up to 0.6 m/s in the rippled scour depression areas. Stronger currents appear to inhibit the building of these features. Tidal currents play an important role as they trend parallel to the southeast banks slopes and are likely responsible of the gravelly ripples formation inside the depressions as well as the persistence of these depressions which are not covered by finer sediments. On Malangsgrunnen bank, some of the rippled scour depressions are in the extension of NW-SE furrows located on the bank. Simulated bottom currents indicate currents mainly perpendicular to these furrows, as for the rippled scour depressions on the bank slopes. Nevertheless, these features could also highlight currents coming from the northwest which reach the bank margin and continue down to the areas of the rippled scour depressions. These currents could be responsible for the

  2. 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.

  3. Rippling muscle disease in childhood.

    PubMed

    Schara, Ulrike; Vorgerd, Matthias; Popovic, Nikola; Schoser, Benedikt G H; Ricker, Kenneth; Mortier, Wilhelm

    2002-07-01

    Rippling muscle disease is a rare autosomal dominant disorder first described in 1975. Recently, it could be classified as a caveolinopathy; in European families, mutations in the caveolin-3 gene were revealed as causing this disease. Although clinical symptoms were almost all described in adulthood, we are now reporting clinical data of seven children with rippling muscle disease owing to mutations in the caveolin-3 gene. Initial symptoms were frequent falls, inability to walk on heels, tiptoe walking with pain and a warm-up phenomenon, calf hypertrophy, and an elevated serum creatine kinase level. Percussion-/pressure-induced rapid contractions, painful muscle mounding, and rippling could be observed even in early childhood. The diagnosis can be confirmed by molecular genetic analysis. Muscle biopsy must be considered in patients without muscle weakness or mechanical hyperirritability to differentiate between rippling muscle disease and limb-girdle muscular dystrophy 1C. PMID:12269726

  4. Use of forecasting signatures to help distinguish periodicity, randomness, and chaos in ripples and other spatial patterns.

    PubMed

    Rubin, David M.

    1992-10-01

    Forecasting of one-dimensional time series previously has been used to help distinguish periodicity, chaos, and noise. This paper presents two-dimensional generalizations for making such distinctions for spatial patterns. The techniques are evaluated using synthetic spatial patterns and then are applied to a natural example: ripples formed in sand by blowing wind. Tests with the synthetic patterns demonstrate that the forecasting techniques can be applied to two-dimensional spatial patterns, with the same utility and limitations as when applied to one-dimensional time series. One limitation is that some combinations of periodicity and randomness exhibit forecasting signatures that mimic those of chaos. For example, sine waves distorted with correlated phase noise have forecasting errors that increase with forecasting distance, errors that are minimized using nonlinear models at moderate embedding dimensions, and forecasting properties that differ significantly between the original and surrogates. Ripples formed in sand by flowing air or water typically vary in geometry from one to another, even when formed in a flow that is uniform on a large scale; each ripple modifies the local flow or sand-transport field, thereby influencing the geometry of the next ripple downcurrent. Spatial forecasting was used to evaluate the hypothesis that such a deterministic process-rather than randomness or quasiperiodicity-is responsible for the variation between successive ripples. This hypothesis is supported by a forecasting error that increases with forecasting distance, a greater accuracy of nonlinear relative to linear models, and significant differences between forecasts made with the original ripples and those made with surrogate patterns. Forecasting signatures cannot be used to distinguish ripple geometry from sine waves with correlated phase noise, but this kind of structure can be ruled out by two geometric properties of the ripples: Successive ripples are highly

  5. Use of forecasting signatures to help distinguish periodicity, randomness, and chaos in ripples and other spatial patterns

    USGS Publications Warehouse

    Rubin, D.M.

    1992-01-01

    Forecasting of one-dimensional time series previously has been used to help distinguish periodicity, chaos, and noise. This paper presents two-dimensional generalizations for making such distinctions for spatial patterns. The techniques are evaluated using synthetic spatial patterns and then are applied to a natural example: ripples formed in sand by blowing wind. Tests with the synthetic patterns demonstrate that the forecasting techniques can be applied to two-dimensional spatial patterns, with the same utility and limitations as when applied to one-dimensional time series. One limitation is that some combinations of periodicity and randomness exhibit forecasting signatures that mimic those of chaos. For example, sine waves distorted with correlated phase noise have forecasting errors that increase with forecasting distance, errors that, are minimized using nonlinear models at moderate embedding dimensions, and forecasting properties that differ significantly between the original and surrogates. Ripples formed in sand by flowing air or water typically vary in geometry from one to another, even when formed in a flow that is uniform on a large scale; each ripple modifies the local flow or sand-transport field, thereby influencing the geometry of the next ripple downcurrent. Spatial forecasting was used to evaluate the hypothesis that such a deterministic process - rather than randomness or quasiperiodicity - is responsible for the variation between successive ripples. This hypothesis is supported by a forecasting error that increases with forecasting distance, a greater accuracy of nonlinear relative to linear models, and significant differences between forecasts made with the original ripples and those made with surrogate patterns. Forecasting signatures cannot be used to distinguish ripple geometry from sine waves with correlated phase noise, but this kind of structure can be ruled out by two geometric properties of the ripples: Successive ripples are highly

  6. 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.

  7. Defrosting Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-434, 27 July 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows retreating patches of frost on a field of large, dark sand dunes in the Noachis region of Mars. Large, windblown ripples of coarse sediment are also seen on some of the dunes. This dune field is located in a crater at 47.5oS, 326.3oW. The scene is illuminated by sunlight from the upper left.

  8. Sand Dunes in Kaiser Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Full size (780 KBytes) This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) high resolution image shows a field of dark sand dunes on the floor of Kaiser Crater in southeastern Noachis Terra. The steepest slopes on each dune, the slip faces, point toward the east, indicating that the strongest winds that blow across the floor of Kaiser move sand in this direction. Wind features of three different scales are visible in this image: the largest (the dunes) are moving across a hard surface (light tone) that is itself partially covered by large ripples. These large ripples appear not to be moving--the dunes are burying some and revealing others. Another type of ripple pattern is seen on the margins of the dunes and where dunes coalesce. They are smaller (both in their height and in their separation) than the large ripples. These are probably coarse sediments that are moving with the dunes. This picture covers an area approximately 3 km (1.9 mi) across and is illuminated from the upper left.

  9. Aeolian cliff-top deposits and buried soils in the White River Badlands, South Dakota, USA

    USGS Publications Warehouse

    Rawling, J. E., III; 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.

  10. Aeolian geomorphology from the global perspective

    NASA Technical Reports Server (NTRS)

    Greeley, R.

    1985-01-01

    Any planet or satellite having a dynamic atmosphere and a solid surface has the potential for experiencing aeolian (wind) processes. A survey of the Solar System shows at least four planetary objects which potentially meet these criteria: Earth, Mars, Venus, and possibly Titan, the largest satellite of Saturn. While the basic process is the same among these four objects, the movement of particles by the atmosphere, the aeolian environment is drastically different. It ranges from the hot (730 K), dense atmosphere of Venus to the extremely cold desert (218 K) environment of Mars where the atmospheric surface pressure is only approximately 7.5 mb. In considering aeolian processes in the planetary perspective, all three terrestrial planets share some common areas of attention for research, especially in regard to wind erosion and dust storms. Relevant properties of planetary objects potentially subject to aeolian processes are given in tabular form.

  11. Paleoclimatic implications of late Pleistocene and Holocene aeolian sediments in lake catchments on the northeastern part of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Lehmkuhl, F.; Stauch, G.; IJmker, J.; Poetsch, S.; Hilgers, A.; Hui, Z.; Diekmann, B.; Hartmann, K.; Wuennemann, B.

    2011-12-01

    On the northeastern part of the Tibetan Plateau aeolian sediments, such as loess, loess-like sediments, dunes and sand sheets, have been investigated. Such archives provide additional information for paleoclimate and environmental change in the catchments of lakes. We present a detailed analysis of aeolian sediments from the Donggi Cona catchment and a loess section from the Aynemachin Mts. on the north-eastern part of the Tibetan Plateau. In the Donggi Cona catchment long and short distance transport leads to a complex pattern in the aeolian sediments. Based on the largest dataset of luminescence dating (n = 51) from a single catchment so far different periods of enhanced sediment transport have been discriminated. Enhanced aeolian deposition in this environment in elevations of more than 4000m a.s.l. started in the early Holocene with the accumulation of sands from around 12 to 7.5ka. Loess have been preserved from a period from 10.5 to 7.5ka. However, further to the east on the southern slopes of the Aynemachin Mts. the sedimentation period of loess lasted longer and was interrupted by two paleosols around 10-9 and 5 ka. Both archives, sand and loess, are related to the strengthening of the East-Asian summer monsoon with wetter and warmer climate conditions. This climate leads to the trapping of aeolian sediments, in the moisture region of the Aynemachin including the development of initial paleosols. In addition, in some parts of the Donggi Cona catchment the enhanced summer monsoon from around 10 ka onwards lead to fluvial erosion of the aeolian archives and the formation of colluvial sediments until 6 ka. A reactivation of dune sands from 3 ka to the present can be associated to dryer and cooler climate conditions in combination with an enhanced human impact on the landscape. Aeolian sediments on the Tibetan Plateau therefore indicate two different climatic modes. During the early Holocene wetter conditions were favourable to retain aeolian sediments while

  12. Windblown Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-557, 27 November 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows sand dunes and large ripples in a crater in the Hellespontus region of Mars. The winds that formed these dunes generally blew from the left/lower-left (west/southwest). Unlike the majority of dunes on Earth, sand dunes on Mars are mostly made up of dark, rather than light, grains. This scene is located near 50.3oS, 327.5oW. The image covers an area 3 km (1.9 mi) wide, and is illuminated by sunlight from the upper left.

  13. The nature and formation of aeolian mineral dust material

    NASA Astrophysics Data System (ADS)

    Smalley, Ian; O'hara-Dhand, Ken; McLaren, Sue

    2013-04-01

    Aeolian dust affects climate and records past climates. It has become a much studied material but there has been a certain lack of emphasis on the actual nature of the dust, and an even greater neglect of actual production mechanisms for dust particles. Huge amounts of dust may be raised from the Bodele depression and other parts of North Africa, and much of it may be carried across the North Atlantic to aid in soil formation in Brazil. But what does it consist of? We know that much of the Bodele dust is diatoms from old Lake Chad, but what of the lithological inorganic mineral content? A very crude division of aeolian dust into large dust(say around 20-50um) and small dust (2-5um)has been proposed. Much of the study of loess has been confused by the failure to make this distinction, and similar problems may arise in the study of the finer fractions of aeolian dust. Much aeolian material is clay-mineral based- formed from clay mineral aggregates(CMA), from lake bottom sediments. This can form large dust particles, as in parna in Australia, but also contributes largely to small long travel aerosolic dust. Another major contributor is the quartz fragment. The large dust for classic loess deposits is mostly quartz silt- and there is considerable discussion about the controls that affect quartz silt. There are some interesting modalities in the world of quartz particle sedimentology which need to be examined. Quartz sand (say 200-500um) is the key initiating material and the formation processes for quartz sand have a down-the-line effect on the formation of smaller particles. The central observation is the action of two processes- a eutectic-like reaction in the proto-rock granite which defines the essential nature of sand particles, and the high-low displacive crystallographic transformation which introduces tensile stresses into the quartz particle systems. The limited range of eutectic particle size means a limited range of tensile stresses. A neat combination of

  14. Accretion of mudstone beds from migrating floccule ripples.

    PubMed

    Schieber, Juergen; Southard, John; Thaisen, Kevin

    2007-12-14

    Mudstones make up the majority of the geological record. However, it is difficult to reconstruct the complex processes of mud deposition in the laboratory, such as the clumping of particles into floccules. Using flume experiments, we have investigated the bedload transport and deposition of clay floccules and find that this occurs at flow velocities that transport and deposit sand. Deposition-prone floccules form over a wide range of experimental conditions, which suggests an underlying universal process. Floccule ripples develop into low-angle foresets and mud beds that appear laminated after postdepositional compaction, but the layers retain signs of floccule ripple bedding that would be detectable in the rock record. Because mudstones were long thought to record low-energy conditions of offshore and deeper water environments, our results call for reevaluation of published interpretations of ancient mudstone successions and derived paleoceanographic conditions. PMID:18079398

  15. 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.

  16. Aeolian Transport of Ferrous Minerals in the North Polar Region of Mars

    NASA Astrophysics Data System (ADS)

    Horgan, Briony H.; Bell, J. F., III; Noe Dobrea, E. Z.

    2008-09-01

    The north polar region of Mars contains two areally extensive, dark aeolian deposits: (1) the north polar sand seas that encircle the polar cap, and (2) the north polar veneers that drape over the polar cap itself. Both deposits have been previously identified as containing hydrated minerals, and exhibit spectral features consistent with gypsum, a hydrated calcium sulfate. However, it remains unclear whether or not the deposits have exchanged material in the past, and whether any portion of either deposit is active today. In this study, we are investigating the distribution of ferrous minerals in the north polar region using near-infrared spectral data from the Mars Express OMEGA imaging spectrometer. Ferrous minerals, such as olivine and pyroxene, are most readily identified by the presence of a wide absorption band around 1 micron. Observations of changes in the position, depth, and shape of the 1 micron absorption band may be used to track changes in composition. We have identified the presence of a strong 1 micron band in the veneers, the sand sea, and the surrounding plains. Initial results from study regions in Chasma Boreale and Olympia Planum suggest that the position, depth, and shape of the band do vary within the veneers and sand seas. These spectral differences may reflect: (1) compositional variations between the sources of the deposits, (2) the degree of modern activity of the deposits, or (3) changes in mineralogy due to breakdown of softer minerals during aeolian transport over long distances. By extending our observations of these spectral changes to the entire north polar region, we may be able to help identify sources of aeolian material, transport pathways, and the most active regions of modern aeolian activity.

  17. A unifying model for planform straightness of ripples and dunes in air and water

    USGS Publications Warehouse

    Rubin, David M.

    2012-01-01

    Geologists, physicists, and mathematicians have studied ripples and dunes for more than a century, but despite considerable effort, no general model has been proposed to explain perhaps the most fundamental property of their morphology: why are some bedforms straight, continuous, parallel, and uniform in planform geometry (i.e. two-dimensional) whereas others are irregular (three-dimensional)? Here we argue that physical coupling along the crest of a bedform is required to produce straight crests and that along-crest flow and sand transport provide effective physical mechanisms for that coupling. Ripples and dunes with the straightest and most continuous crests include longitudinal and oblique dunes in unidirectional flows, wave ripples, dunes in reversing flows, wind ripples, and ripples migrating along a slope. At first glance, these bedforms appear quite different (ripples and dunes; air and water; transverse, oblique, and longitudinal orientations relative to the net sand-transport direction), but they all have one property in common: a process that increases the amount of along-crest sand transport (that lengthens and straightens their crests) relative to the across-crest transport (that makes them migrate and take the more typical and more three-dimensional planform geometry). In unidirectional flows that produce straight bedforms, along-crest transport of sand is caused by along-crest flow (non-transverse bedform orientation), gravitational transport along an inclined crest, or ballistic splash in air. Bedforms in reversing flows tend to be straighter than their unidirectional counterparts, because reverse transport across the bedform crest reduces the net across-crest transport (that causes the more typical irregular geometry) relative to the along-crest transport (that smoothes and straightens planform geometry).

  18. Aeolian Processes at the Mars Exploration Rover Opportunity Landing Site

    NASA Technical Reports Server (NTRS)

    Sullivan, R.; Bell, J. F., III; Calvin, W.; Fike, D.; Golombek, M.; Greeley, R.; Grotzinger, J.; Herkenhoff, K.; Jerolmack, D.; Malin, M.

    2005-01-01

    The traverse of the Mars Exploration Rover Opportunity across its Meridiani Planum landing site has shown that wind has affected regolith by creating drifts, dunes, and ubiquitous ripples, by sorting grains during aeolian transport, by forming bright wind streaks downwind from craters seen from orbit, and by eroding rock with abrading, wind-blown material. Pre-landing orbiter observations showed bright and dark streaks tapering away from craters on the Meridiani plains. Further analysis of orbiter images shows that major dust storms can cause bright streak orientations in the area to alternate between NW and SE, implying bright wind streak materials encountered by Opportunity are transient, potentially mobilized deposits. Opportunity performed the first in situ investigation of a martian wind streak, focusing on a bright patch of material just outside the rim of Eagle crater. Data from Pancam, the Miniature Thermal Emission Spectrometer (Mini-TES), the Alpha-Particle X-Ray Spectrometer (APXS), and the Mossbauer spectrometer either are consistent with or permit an air fall dust interpretation. We conclude that air fall dust, deposited in the partial wind shadow of Eagle crater, is responsible for the bright streak seen from orbit, consistent with models involving patchy, discontinuous deposits of air fall dust distributed behind obstacles during periods of atmospheric thermal stability during major dust storms.

  19. The aeolian sedimentary system in the northern Qilian Shan and Hexi Corridor (N-China) - geomorphologic, sedimentologic and climatic drivers

    NASA Astrophysics Data System (ADS)

    Nottebaum, Veit; Lehmkuhl, Frank; Stauch, Georg

    2015-04-01

    The formation of aeolian deposits depends on the influence of climatic factors but also on non-climatic controls, such as local geomorphological setting and tectonic activity. Unravelling the environmental history needs a careful consideration of a set of sections to capture spatial variability and a detailed investigation of depositing processes and chronology. Along the northern margin of the Qilian Shan mountain range 22 OSL-dated loess and aeolian sand sections and additional surface samples reveal the interactions between climatic, geomorphologic and sedimentologic factors. Thin loess covers (~1-2 m) occur in elevations of 2000 to 3800 m asl, which were mainly accumulated during the Holocene. End-member modelling of loess grain size data exhibits three dominant aeolian transport pathways representing local transport from fluvial storages, dust storm contribution and background dust deposition. Their relative contributions show a clear dependence on geomorphological setting, and additionally, synchronous trends throughout the Holocene. Their relative changes allow conclusions about Holocene environmental conditions. Discontinuous archives (aeolian sand, lacustrine, and alluvial deposition) in the lower forelands of the Qilian Shan show a distinct spatial pattern contrasting western and eastern forelands. The comparison of OSL ages exhibits high sediment accumulation (~2 m/ka) in the drier western part during the Late Glacial, while the lack of Holocene ages indicates sediment discharge / deflation. In contrast, moister areas in the eastern foreland yield scattered Holocene ages. This indicates high sediment dynamics, benefiting from fluvial reworking and thus provided sediment availability. Fluvial sediment supply plays an important role in sediment recycling. Meanwhile, western forelands lack efficient sand sources and fluvial reworking agents. The study exemplifies the complex sedimentary systems acting along mountain to foreland transects which often host

  20. A Fuzzy Cognitive Model of aeolian instability across the South Texas Sandsheet

    NASA Astrophysics Data System (ADS)

    Houser, C.; Bishop, M. P.; Barrineau, C. P.

    2014-12-01

    Characterization of aeolian systems is complicated by rapidly changing surface-process regimes, spatio-temporal scale dependencies, and subjective interpretation of imagery and spatial data. This paper describes the development and application of analytical reasoning to quantify instability of an aeolian environment using scale-dependent information coupled with conceptual knowledge of process and feedback mechanisms. Specifically, a simple Fuzzy Cognitive Model (FCM) for aeolian landscape instability was developed that represents conceptual knowledge of key biophysical processes and feedbacks. Model inputs include satellite-derived surface biophysical and geomorphometric parameters. FCMs are a knowledge-based Artificial Intelligence (AI) technique that merges fuzzy logic and neural computing in which knowledge or concepts are structured as a web of relationships that is similar to both human reasoning and the human decision-making process. Given simple process-form relationships, the analytical reasoning model is able to map the influence of land management practices and the geomorphology of the inherited surface on aeolian instability within the South Texas Sandsheet. Results suggest that FCMs can be used to formalize process-form relationships and information integration analogous to human cognition with future iterations accounting for the spatial interactions and temporal lags across the sand sheets.

  1. Semiarid landscapes response to Aeolian processes during Holocene in Baikal Region

    NASA Astrophysics Data System (ADS)

    Dan'ko, Lidia; Opekunova, Marina

    2010-05-01

    Arid and semiarid landscapes play a significant role in global climate, biogeochemical, and hydrological processes. Regional analysis of the past aeolian processes is essential for improve our understanding of how various landscape and ecosystems responded to climate change in the past. Our investigation presents details on sand dunes and on loess-like sediments. The study areas are situated in the northern part of Baikal Region (Eastern Siberia). In its depressions, the so-called Barguzinskaya and Tunkinskaya Valley surrounded mountain ranges local dunefieds and loess-like sediments have developed. Present climate in the study areas is continental, characterized by low precipitation(mean annual 250-450 mm) and wide annual range of temperature. Field investigations indicate that the Holocene deposits of the Barguzinskaya and Tunkinskaya Valley are sealed the pedo-sedimentary interface. The analytical results suggest that one's represents a changeover from intensified soil formation to accelerated aeolian dust accumulation. The original content of calcium carbonate and gypsum at the base of some sections of loess-like sediments indicates the aeolian origin of these sediments. In whole, the soil horizons are a proof for humid phases. The change was forced by climatic aridity. Absolute dating of the organogenic components of soils (14C) indicate the age positions of the arid and humid climate phases. Our results indicate not only 1-4 long-time episodes of aeolian dust accumulation during the Holocene, but shot-time aeolian accumulation episodes, that were specific for Late Holocene. For example, in the Tunkinskaya Valley the Late Holocene soil formation replaced by aeolian deposit at 1700 - 1900, 800 and 200-250 years ago, in the Barguzinskaya Valley - about 3100 - 2900, 2300 and 600 years ago. It can be concluded that a periodical formation of the aeolian deposits in the semiarid landscapes during Holocene can be postulated. Aeolian and loess-like sediments of the

  2. Ripples in Tempe Mensa Region

    NASA Technical Reports Server (NTRS)

    2004-01-01

    1 February 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large windblown ripples (or, some might say, small dunes) in troughs between mesas of the Tempe Mensa region. The ripples are generally perpendicular to the trough walls, indicating that [missing text] the features blew through these canyons. The image is located near 33.5oN, 69.2oW. The picture covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  3. Geochemical and geomorphological evidence for the provenance of aeolian deposits in the Badain Jaran Desert, northwestern China

    NASA Astrophysics Data System (ADS)

    Hu, Fangen; Yang, Xiaoping

    2016-01-01

    Identifying provenance of aeolian deposits in the mid-latitude deserts of Asia is essential for understanding formation and changes of Earth surface processes due to palaeoclimatic fluctuations. While some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter-dune lacustrine sediments, research on provenance of desert sands in the vast Asian mid-latitude deserts is still rare. In this paper, we present new geochemical data which provide insight to the provenance of dune sands in the Badain Jaran Desert, northwestern China, an important part of this desert belt. We sampled aeolian and lacustrine sediments in various parts of the Badain Jaran Desert, and examined their major, trace and rare earth elements (REE) in bulk samples, coarse and fine fractions, respectively. In addition, we took and analyzed samples from a rarely known dune field with red sands, northeast of the Badain Jaran. Our results show that the sands from the Badain Jaran Desert are generally different from those in the red sand dune field in terms of REE pattern and geochemical characteristics, suggesting different sediment origins. Geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite, granitoids and granodiorite. Comparing the immobile trace elements and REE ratios of the samples from the Badain Jaran Desert, red sand dune field with rocks of granite, granitoids in their potential source areas, we conclude that: (1) The aeolian deposits in the Badain Jaran Desert are predominantly derived from the Qilian Mountains, northeastern Tibetan Plateau initially via fluvial processes; (2) The Altay Mountains and Mongolian Gobi are the ultimate source areas for the red sand dune field; (3) The Altai Mountains and Mongolian Gobi in the northwest, that could produce massive amounts of materials via intensive deflation and alluvial process

  4. 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

  5. Theoretical analysis of particle number density in steady aeolian saltation

    NASA Astrophysics Data System (ADS)

    Kang, Liqiang; Zou, Xueyong

    2014-01-01

    Particle number density or particle concentration in aeolian saltation is one important input parameter to calculate the sand flux, kinetic energy and mid-air collision probability in the aeolian saltation and particle concentration is also related to the wind erosion capacity, hence, in the present paper, the vertical distribution of particle number density in steady aeolian saltation is analyzed based on two different types of probability density functions of vertical lift-off velocity of saltating particles: one is the PDF (probability density function) of vertical velocity of lift-off particles in the three-dimensional space defined as a type-A PDF which considers the number of particles in various velocity bins per unit volume; and the other is the PDF of vertical velocity of lift-off particles ejected from the sand bed surface in a period of time as a type-B PDF which considers the number flux of particles in various velocity bins per unit surface area. These two types of PDFs are from two different perspectives (i.e., volume- and surface-based perspectives, respectively), and can be deduced from each other. The half-normal and exponential distributions are recommended for the type-A PDF, and the corresponding type-B PDF is expressed by Rayleigh and Gamma(2) distributions. The PDF distribution pattern of vertical velocity of lift-off particles has an important influence on the vertical profile of particle number density. If the type-A PDF of vertical velocity of ejected particles is a half-normal distribution, the particle number density decays exponentially with height. If the type-A PDF is an exponential distribution, the particle number density also decreases with height. If the type-A PDF is Gamma(3) and Rayleigh distributions, the particle number density first increases, then decreases with height. The type-A and type-B height parameters, which are calculated according to the mean vertical lift-off velocity from the type-A and type-B PDFs, respectively

  6. 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.

  7. 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

  8. Reconciling historical and contemporary evidence of aeolian-based, gully annealing processes in Glen, Marble, and Grand Canyon, USA

    NASA Astrophysics Data System (ADS)

    Sankey, J. B.; Draut, A. E.

    2013-12-01

    In the absence of large Colorado River floods in Glen, Marble, and Grand Canyons since the completion of Glen Canyon Dam, the geomorphic process most able to counteract the effects of gully incision on terraces and slopes above the contemporary active Colorado River channel is aeolian sand transport that can partially or entirely fill (anneal) small gullies. Whereas gully-formation processes have been much studied, relatively little is known about processes of gully annealing. Aeolian-based annealing has been observed in several instances in the modern Colorado River corridor operating on time scales of months. However, individual, short-term occurrences of aeolian deposition that counteract gully erosion have not yet been expanded into a landscape-scale evaluation of the prevalence of gully-annealing processes over longer time scales (years-decades) along the post-dam corridor. The extent that aeolian or other annealing processes might slow, or temporarily reverse, gully incision and erosion is important in this system because of the propensity for erosion damage to locations of cultural significance that are extensive on terraces and slopes above the contemporary active Colorado River channel. Moreover, the reduction of mainstem fluvial sediment inputs to the system since completion of Glen Canyon Dam might impact the potential of aeolian redistribution of Colorado River-derived sediment as an effective gully annealing mechanism on upper slopes and terraces. We present an investigation of the extent that observations of (i) historical annealing and (ii) contemporary annealing potential, reconcile with (iii) literature and/or model-based estimates of relative rates of gully formation and aeolian deposition in this system. The central question of this work is whether these complimentary lines of evidence support aeolian infilling as a viable mechanism for annealing gullies in Glen, Marble, and Grand Canyons, and analogous systems. We examine the evidence for

  9. Aeolian transport of biota with dust: A wind tunnel experiment

    NASA Astrophysics Data System (ADS)

    Rivas, J. A., Jr.; Gill, T. E.; Van Pelt, R. S.; Walsh, E.

    2015-12-01

    Ephemeral wetlands are ideal sources for dust emission, as well as repositories for dormant stages of aquatic invertebrates. An important component of invertebrate dispersal and colonization to new areas is the ability to be entrained into the atmosphere. Aquatic invertebrate eggs fall within the size of dust and sand grains (30-600μm), are less dense and aerodynamically shaped. We have shown previously that aquatic invertebrates can be dispersed long distances in dust storms but the extent of transport of taxa based on diapausing egg size/morphology has not been investigated. Here, we control the wind erosion process in a wind tunnel to test entrainment of diapausing stages of brine shrimp, clam shrimp, tadpole shrimp, fairy shrimp, Daphnia, and the rotifers Brachionus plicatilis and B. calyciflorus into the air by saltation. Diapausing eggs were mixed with sterilized wind-erodible soil. The soil/egg mixture was moistened with distilled water and air dried to form a crust. Dust was generated in a wind tunnel by releasing sand grains that act as saltator material similar to wind-entrained natural sands. Maximum wind velocity was 10m/s and entrained particles were sampled through an isokinetic horizontal intake opening. Aeolian sediment was collected from three points in the system; transfer section for coarse sediment, the pan subtending a settling chamber for finer saltation-sized sediment, and two paper filters for suspension-sized sediment. Samples were then passed through 250 and 350 μm sieves to remove abrader sand and rehydrated with various sterile media depending on the type of organism. We retrieved viable brine, fairy, and tadpole shrimp, ostracods, Daphnia, and diapausing eggs of the rotifers after hydration. This experiment demonstrates that resting stages of many invertebrates can be wind-eroded due to size and egg morphology and remain viable under controlled conditions mimicking dust emission.

  10. Frequency resolving power measured by rippled noise.

    PubMed

    Supin AYa; Popov, V V; Milekhina, O N; Tarakanov, M B

    1994-07-01

    Frequency resolving power (FRP) was measured in normal humans using rippled noise with a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and trough position (the phase reversal) in the rippled spectrum is detectable. In the frequency range below 0.5 kHz FRP was found to be about 21 ripples per kHz when tested by both broad-band and narrow-band rippled noise. In the frequency range above 2 kHz, FRP measured by the narrow-band rippled noise was 22 to 23 relative units (relation of the noise central frequency to the ripple frequency spacing). PMID:7961175

  11. Sandy inland braidplain deposition with local aeolian sedimentation in the lower and middle parts of the buntsandstein and sandy coastal braidplain deposition in the topmost zechstein in the sudetes (Lower Silesia, Poland)

    NASA Astrophysics Data System (ADS)

    Mroczkowski, Jerzy; Mader, Detlef

    The lower and middle parts of the Buntsandstein between Röt and Zechstein in the Sudetes (Lower Silesia, Poland) crop out in the marginal seams of the North Sudetic Trough and the Intra Sudetic Trough. The continental red beds originate in predominantly sandy braided river systems of an extensive inland alluvial plain in almost arid climate. The sediments are laid down in channels and floodplains of a moderately- to highly-braided, sandy to pebbly stream complex consisting of narrowly- to moderately-spaced low-sinuosity watercourses and narrow to wide overbank plains between the channels. Rapid aggradation and abandonment, quick lateral migration or high avulsion rates of the considerably mobile streams result in effective combing of the interchannel areas. Persistent high-energy overspilling of watercourse banks and invasion of bed-load-saturated flood surges into the overbank areas often lead to primary restriction or even suppression of formation of topstratum suspension fines. Secondarily, the silty-clayey and fine sandy overbank sediments which could occasionally originate in remote or sheltered lakes and ponds are frequently completely reworked by considerable lateral and vertical erosion during sidewards displacement of the rivers. As a result of both primary-depositional restriction and secondary-erosional removal of floodplain fines, the channel sediments are commonly stacked upon each other to multistorey stream sand complexes. Emergence and desiccation of parts of the alluvial plain sometimes give rise to aeolian deflation and accumulation of the winnowed sand to small dunelets and wind ripple trains. The aeolian depositional environment representing a more peripheral erg facies with sheet sand interdune milieu could not be fully ascertained due to poor outcrop conditions, but is likely to occur locally in view of comparative interpretation with other mixed dune and river sand sequences in the Mid-European Buntsandstein. Variations of fluvial style are

  12. Pore pressure in a wind-swept rippled bed below the suspension threshold

    NASA Astrophysics Data System (ADS)

    Musa, R. A.; Takarrouht, S.; Louge, M. Y.; Xu, J.; Berberich, M. E.

    2014-12-01

    Toward elucidating how a wavy porous sand bed perturbs a turbulent flow above its surface, we record pressure within a permeable material resembling the region just below desert ripples, contrasting these delicate measurements with earlier studies on similar impermeable surfaces. We run separate tests in a wind tunnel on two sinusoidal porous ripples with aspect ratio of half crest-to-trough amplitude to wavelength of 3% and 6%. For the smaller ratio, pore pressure is a function of streamwise distance with a single delayed harmonic decaying exponentially with depth and proportional to wind speed squared. The resulting pressure on the porous surface is nearly identical to that on a similar impermeable wave. Pore pressure variations at the larger aspect ratio are greater and more complicated. Consistent with the regime map of Kuzan et al., the flow separates, creating a depression at crests. Unlike flows on impermeable waves, the porous rippled bed diffuses the depression upstream, reduces surface pressure gradients, and gives rise to a slip velocity, thus affecting the turbulent boundary layer. Pressure gradients within the porous material also generate body forces rising with wind speed squared and ripple aspect ratio, partially counteracting gravity around crests, thereby facilitating the onset of erosion, particularly on ripples of high aspect ratio armored with large surface grains. By establishing how pore pressure gradients scale with ripple aspect ratio and wind speed, our measurements quantify the internal seepage flow that draws dust and humidity beneath the porous surface.

  13. Mid to late Holocene aeolian activity revealed by a multiproxy peat record in continental CE Europe (Northern Romania)

    NASA Astrophysics Data System (ADS)

    Panait, Andrei Marian; Feurdean, Angelica; Hutchinson, Simon Mark; Tanţǎu, Ioan

    2016-04-01

    Peat bogs, and especially ombrogenous mire, are increasingly used as continental archives of aeolian dust and sand deposition. Since ombrogenous peat is formed above ground water level all the inputs are atmospheric. Dust is more influenced by regional climatic patterns due to its small size, whereas sand tends to record local patterns in storm frequency and intensity reflecting its larger particle size. However, both size fractions are significantly underused proxies of past climate variability. Here, an ombrogenous peat profile from Tǎul Muced in the Rodnei Mountains (Northern Romanian Carpathians), located in a temperate continental climate, with Atlantic and Baltic influences, provides the very first record of mid to late Holocene aeolian activity from Romania highlighting the interplay between local and regional controls in a continental area of CE Europe. We use a multiproxy approach combining radiocarbon dating, the physical properties of the peat (loss-on-ignition, bulk density), mineral magnetic measurements (ARM, SIRM), geochemical (Ti and Zr) and particle size analysis (via both laser diffraction and the manual counting of sand particles under a steromicroscope) to determine changes in: i) atmospheric dust deposition and ii) wind velocities during the last 7800 years. We found that the aeolian particles are mainly silt (3.9-63 μm) (dust) and sand (63-1200 μm). The mineralogical composition of the aeolian sediment in peat is mainly quartz, more rarely calcite and very rarely other minerals such as feldspar, sulphur, mica (biotite and muscovite), magnetite and other melanocrate minerals. The roundness of the sand particles varies from well-rounded to sub-angular and angular, and suggests that the sand particles have different source areas. Results from this study show that over the last 7600 years the pattern of wind frequency changed several times: there are periods characterised by a low aeolian input around 6950-6550, 5000-3900, 3500-2900, 1650

  14. 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.

  15. Controls on the height and spacing of eolian ripples and transverse dunes: A numerical modeling investigation

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.

    2009-04-01

    Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner's [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929-955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth

  16. Boundary Conditions for Aeolian Activity in North American Dune Fields

    NASA Astrophysics Data System (ADS)

    Halfen, A. F.; Lancaster, N.; Wolfe, S.

    2014-12-01

    Geomorphic and chronological data for dune fields are evaluated for three contrasting areas of North America: 1) the Prairie-Parkland-Boreal ecozones of the northern Great Plains in Canada; 2) the Central Great Plains of the USA; and 3) the deserts of southwestern USA and northern Mexico. Luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply, availability, and mobility. Dune fields in the northern Great Plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16-11 ka. Subsequent aeolian deposition occurred in Parkland and Prairie dune fields as a result of mid-Holocene (8-5 ka) and late-Holocene (< 3.5 ka) activity related to drought conditions that reworked pre-existing aeolian sands. In the Central Great Plains, dune fields are closely linked to fluvial sediment sources. Sediment supply was high during deglaciation of the Rocky Mountains and resulted in widespread dune construction 16-10 ka. Multiple periods of Holocene reactivation are recorded and reflect increased sediment availability during drought episodes. Dune fields in the southwestern deserts experienced periods of construction as a result of enhanced supply of sediment from fluvial and lacustrine sources during the period 11.8-8 ka and at multiple intervals during the late Holocene. Despite spatial and temporal gaps in chronometric data as a result of sampling biases, the record from North American dune fields indicates the strong influence of sediment supply on dune construction, with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre-existing sediment.

  17. Abstracts for the Planetary Geology Field Conference on Aeolian Processes

    NASA Technical Reports Server (NTRS)

    Greeley, R. (Editor); Black, D. (Editor)

    1978-01-01

    The Planetary Geology Field Conference on Aeolian Processes was organized at the request of the Planetary Geology Program office of the National Aeronautics and Space Administration to bring together geologists working on aeolian problems on earth and planetologists concerned with similar problems on the planets. Abstracts of papers presented at the conference are arranged herein by alphabetical order of the senior author. Papers fall into three broad categories: (1) Viking Orbiter and Viking Lander results on aeolian processes and/or landforms on Mars, (2) laboratory results on studies of aeolian processes, and (3) photogeology and field studies of aeolian processes on Earth.

  18. Roughness configuration matters for aeolian sediment flux

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The parameterisation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Roughness effects are typically represented by bulk drag-partitioning schemes that scale the threshold friction velocity (u*t) for soil entrainment by the ratio of s...

  19. Incident velocity and incident angle of saltating sand grains on Mars

    NASA Astrophysics Data System (ADS)

    Zheng, Xiao-Jing; Fu, Lin-Tao; Bo, Tian-Li

    2013-04-01

    Incident velocity and incident angle are important parameters for Martian aeolian research. In this paper we have established a model for investigating the saltation of sand in steady state, mainly considering the hopping of sand in the air and sand-bed collision process. The model proves to be able to predict sand motion in steady-state saltation on Earth well both qualitatively and quantitatively. Thus, it was applied to the study of sand saltation on Mars. With the help of the model, we found incident velocities and incident angles of Martian grains in steady-state saltation in cases of various wind strengths. Then, these predicted velocities and angles were compared with previous studies. Besides, the model also can show information on lift-off parameters of saltating particles. Therefore, it allows us to study other features in aeolian processes such as the saltation length and sand transport rate.

  20. The Origin of Transverse Aeolian Ridges on Mars

    NASA Astrophysics Data System (ADS)

    Geissler, P.

    2015-12-01

    Transverse aeolian ridges, or TARs, are found throughout the tropics of Mars and typically appear as rows of bright ripples that are several meters tall and spaced semi-regularly several tens of meters apart. The origin of these features remained mysterious for decades after their discovery in Viking and Mars Global Surveyor images. A new hypothesis (Geissler, 2014, 10.1002-2014JE004633) suggests that TARs might be deposits left behind by dusty turbidity currents in the Martian atmosphere. The hypothesis assumes that the micron-sized dust particles are transported in suspension in turbulent flows, driven both by the winds and by gravity. The dust is concentrated near the surface, much like turbidity currents on Earth. Because of the difference in density, however, the dust clouds behave as a fluid distinct from the clear sky above. In particular, waves can appear at the surface of the dense "fluid" when the flows encounter topographic obstacles along their paths. Such gravity waves travel at speeds that are determined by gravity and the thickness of the flow, much like waves in shallow water on Earth. When the wave propagation speed matches the speed of the flow, stationary waves are produced that persist in fixed locations. The bedforms deposited by such stationary waves are called "antidunes" (Gilbert, 1914, USGS Prof. Paper 86) because, unlike dunes, they can migrate upstream in a supercritical flow. Antidunes are commonly seen in shallow, high energy fluvial deposits on Earth. They are usually destroyed as quickly as they form, and are rarely preserved. The Martian TARs survive because the dust is sticky; TARs are deposited by currents that are much slower than the wind speeds needed to lift the dust again. Subaerial antidunes are much rarer on Earth and less well studied, and so the giant subaerial stationary antidunes of Mars, if that is what the TARs turn out to be, may teach us much about a geological process that is poorly known on our planet.

  1. Earth-like sand fluxes on Mars.

    PubMed

    Bridges, N T; Ayoub, F; Avouac, J-P; Leprince, S; Lucas, A; Mattson, S

    2012-05-17

    Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving--implying large sand fluxes--or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar. PMID:22596156

  2. Seabed ripple morphology and surficial sediment size at the SAX04 experiments near Fort Walton Beach, Florida, fall 2004

    USGS Publications Warehouse

    Hanes, Daniel M.; Erikson, Li H.; Lescinski, Jamie M.R.; Harney, Jodi N.; Carter, Carissa L.; Hatcher, Gerry A.; Lacy, Jessica R.; Rubin, David M.

    2007-01-01

    Data presented in this report originates from measurements obtained off the Florida coast (fig. 1) as part of the Sediment Acoustics Experiment (SAX04) and Ripples Department Research Initiative (DRI) (Office of Naval Research (ONR), Critical Benthic Environmental Processes and Modeling, Long Range BAA 04-001, Sept. 10, 2003). The aim of this document is to present methods employed to extract data and the resulting measured ripple characteristics (ripple height, wavelength, and orientation) and seabed grain sizes. Application and analysis of the data with respect to hydro- and morphodynamics will be addressed in subsequent reports. Sediment transport in the coastal region is a complex process involving interactions between flow dynamics, sediments, and bedforms. Sediment type and bed geometry directly influence entrainment of sediments into suspension, and at sites where ripples occur (sand formations on the order of several cm high and less than two meter long wavelengths), the understanding of ripple dynamics is an essential component in improving sediment transport models. To gain a better understanding and ability to predict sediment transport, a field study was undertaken to investigate morphology, orientation, and dynamics of ripples on the seafloor. The data obtained from the field campaign also supports an on-going effort to study the effects of ripples on low grazing acoustic penetration into sandy marine sediments for the detection of objects, such as mines (Jackson and others, 2002).

  3. Spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces: Application to Meridiani Planum, Mars

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas J.; Mohrig, David; Grotzinger, John P.; Fike, David A.; Watters, Wesley A.

    2006-05-01

    The landscape seen by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum is dominated by eolian (wind-blown) ripples with concentrated surface lags of hematitic spherules and fragments. These ripples exhibit profound spatial grain size sorting, with well-sorted coarse-grained crests and poorly sorted, generally finer-grained troughs. These ripples were the most common bed form encountered by Opportunity in its traverse from Eagle Crater to Endurance Crater. Field measurements from White Sands National Monument, New Mexico, show that such coarse-grained ripples form by the different transport modes of coarse- and fine-grain fractions. On the basis of our field study, and simple theoretical and experimental considerations, we show how surface deposits of coarse-grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces. Activation of Meridiani Planum coarse-grained ripples requires a wind velocity of 70 m/s (at a reference elevation of 1 m above the bed). From images by the Mars Orbiter Camera (MOC) of reversing dust streaks, we estimate that modern surface winds reach a velocity of at least 40 m/s and hence may occasionally activate these ripples. The presence of hematite at Meridiani Planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments; however, the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site.

  4. Banana drift transport in tokamaks with ripple

    SciTech Connect

    Linsker, R.; Boozer, A.H.

    1982-01-01

    Ripple transport in tokamaks is discussed for the ''banana drift'' collisionality regime, which lies below the ripple plateau regime treated earlier. The physical mechanisms that dominate banana drift transport are found to differ from those considered in previous work on this regime, and consequently the resulting transport coefficients can differ by several orders of magnitude.

  5. Banana drift transport in tokamaks with ripple

    SciTech Connect

    Linsker, R.; Boozer, A.H.

    1981-04-01

    Ripple transport in tokamaks is discussed for the banana drift collisionality regime, which lies below the ripple plateau regime treated earlier. The physical mechanisms that dominate banana drift transport are found to differ from those considered in previous work on this regime, and the resulting transport coefficients can consequently differ by several orders of magnitude.

  6. Rippled-spectrum resolution dependence on level.

    PubMed

    Supin, Alexander Ya; Popov, Vladimir V; Milekhina, Olga N; Tarakanov, Mikhail B

    2003-11-01

    Rippled-density resolution of a rippled sound spectrum (probe band) in both the presence and absence of another band (masker) was studied as a function of sound level in normal listeners. The resolvable ripple density in the probe band was measured by finding the highest ripple density at which an interchange of ripple peak and valley positions was detectable (the phase-reversal test). Probe bands were 0.5 oct wide with center frequencies of 1, 2, and 4 kHz. In the control condition (no masker), the ripple-density resolution was almost independent of sound level within a range of 40-90 dB SPL. When an on-frequency masker coincided with the probe band (that resulted in reduced ripple depth), resolution decreased slightly relative to the control condition but remained little dependent on level. With an off-frequency low-side masker, the ripple-density resolution was a little less than in the control but almost independent of level within a range of 40-60 dB SPL and progressively decreased with level increase from 70 to 90 dB SPL. The dependence on level was qualitatively similar at all probe frequencies and at various widths and positions of the low-side off-frequency masker band. PMID:14599687

  7. Model of ripples in graphene

    NASA Astrophysics Data System (ADS)

    Bonilla, L. L.; Carpio, A.

    2012-11-01

    We propose a model of ripples in suspended graphene sheets based on plate equations that are made discrete with the periodicity of the honeycomb lattice and then periodized. In addition, the equation for the displacements with respect to the planar configuration contains a double-well site potential, a nonlinear friction, and a multiplicative white-noise term satisfying the fluctuation-dissipation theorem. The nonlinear friction terms agree with those proposed by Eichler [Nature Nanotech.1748-338710.1038/nnano.2011.71 6, 339 (2011)] to explain their experiments with a graphene resonator. The site double-well potential indicates that the carbon atoms at each lattice point have equal probability to move upward or downward off plane. For the considered parameter values, the relaxation time due to friction is much larger than the periods of membrane vibrations and the noise is quite small. Then ripples with no preferred orientation appear as long-lived metastable states for any temperature. Numerical solutions confirm this picture.

  8. 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.

  9. Ripple induced trapped particle loss in tokamaks

    SciTech Connect

    White, R.B.

    1996-05-01

    The threshold for stochastic transport of high energy trapped particles in a tokamak due to toroidal field ripple is calculated by explicit construction of primary resonances, and a numerical examination of the route to chaos. Critical field ripple amplitude is determined for loss. The expression is given in magnetic coordinates and makes no assumptions regarding shape or up-down symmetry. An algorithm is developed including the effects of prompt axisymmetric orbit loss, ripple trapping, convective banana flow, and stochastic ripple loss, which gives accurate ripple loss predictions for representative Tokamak Fusion Test Reactor and International Thermonuclear Experimental Reactor equilibria. The algorithm is extended to include the effects of collisions and drag, allowing rapid estimation of alpha particle loss in tokamaks.

  10. Aeolian particle flux profiles and transport unsteadiness

    NASA Astrophysics Data System (ADS)

    Bauer, Bernard O.; Davidson-Arnott, Robin G. D.

    2014-07-01

    Vertical profiles of aeolian sediment flux are commonly modeled as an exponential decay of particle (mass) transport with height above the surface. Data from field and wind-tunnel studies provide empirical support for this parameterization, although a large degree of variation in the precise shape of the vertical flux profile has been reported. This paper explores the potential influence of wind unsteadiness and time-varying intensity of transport on the geometry (slope, curvature) of aeolian particle flux profiles. Field evidence from a complex foredune environment demonstrates that (i) the time series of wind and sediment particle flux are often extremely variable with periods of intense transport (referred to herein as sediment "flurries") separated by periods of weak or no transport; (ii) sediment flurries contribute the majority of transport in a minority of the time; (iii) the structure of a flurry includes a "ramp-up" phase lasting a few seconds, a "core" phase lasting a few seconds to many tens of seconds, and a "ramp-down" phase lasting a few seconds during which the system relaxes to a background, low-intensity transport state; and (iv) conditional averaging of flux profiles for flurry and nonflurry periods reveals differences between the geometry of the mean profiles and hence the transport states that produce them. These results caution against the indiscriminate reliance on regression statistics derived from time-averaged sediment flux profiles, especially those with significant flurry and nonflurry periods, when calibrating or assessing the validity of steady state models of aeolian saltation.

  11. Biodiversity impact of the aeolian periglacial geomorphologic evolution of the Fontainebleau Massif (France)

    NASA Astrophysics Data System (ADS)

    Thiry, M.; Liron, M. N.

    2009-04-01

    Landscape features The geomorphology of the Fontainebleau Massif is noteworthy for its spectacular narrow ridges, up to 10 km long and 0.5 km wide, armored by tightly cemented sandstone lenses and which overhang sandy depressions of about 50m. Denudation of the sandstone pans lead to a highly contrasted landscape, with sandstone ridges ("platières") towering sandy depressions ("vallées") and limestone plateaus ("monts"). This forms the geological frame of the spectacular sceneries of the Fontainebleau Massif (Thiry & Liron, 2007). Nevertheless, there is little know about the erosive processes that have built-up these landscapes. Periglacial processes, and among them aeolian ones, appear significant in the development of the Fontainebleau Massif physiography. The periglacial aeolian geomorphology Dunes and dune fields are known since long and cover about 15% to 25% of the Fontainebleau Massif. The aeolian dunes developed as well on the higher parts of the landscape, as well as in the lower parts of the landscape. The dunes are especially well developed in the whole eastern part of the massif, whereas the western part of the massif is almost devoid of dunes. Nevertheless, detailed mapping shows that dunes can locally be found in the western district, they are of limited extension, restricted to the east facing backslope of outliers. Loamy-sand covers the limestone plateaus of the "monts". The loam cover is of variable thickness: schematically thicker in the central part of the plateaus, where it my reach 3 m; elsewhere it may thin down to 0,20-0,30 m, especially at the plateau edges. Blowout hollows are "negative" morphologies from where the sand has been withdrawed. Often these blowouts are decametric sized and well-delimited structures. Others, more complex structures, are made up of several elongated hectometric hollows relaying each other from and which outline deflation corridor more than 1 km long. A characteristic feature of these blowout hollows is the

  12. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  15. Origin of basaltic soils at Gusev crater, Mars, by aeolian modification of impact-generated sediment

    NASA Astrophysics Data System (ADS)

    McGlynn, Ian O.; Fedo, Christopher M.; McSween, Harry Y., Jr.

    2011-04-01

    Textural properties of soils including grain size, sorting, modality, skewness, shape (quantified as sphericity and qualified as form), roundness, and grain size distribution, have been measured and calculated from Microscopic Imager (MI) high-resolution images from the Mars Exploration Rover (MER) Spirit in Gusev crater. Soil targets were classified by grain size into five groups: fine to medium sand dark soil, medium sand to very fine pebble bed form armor, and very fine to medium pebble lithic fragments, a bimodal mixed soil, and an excavated soil trench. The abundance of submature, very poorly sorted, bimodal mixed soils indicates incomplete sorting by soil type. Probability distributions of excavated subsurface soil match crushed sediment analogs, indicating impact comminution, while all other soils show no direct evidence of an impact origin. If soils were produced primarily by impacts, then the evidence from probability distributions, angular shapes, and agglutinates have been reworked by postimpact surface activity. Soils in Gusev crater are continuously modified, reworked, and sandblasted. Textures of surface sediments are disconnected from subsurface textures and only reflect modern surficial aeolian processes. Models to reconstruct physical and chemical soil formation properties should not assume a static three-dimensional structure. A three-step model, initiated by the formation of basaltic crust and its alteration, followed by bolide impact, and finally modification by aeolian reworking is envisioned for the formation of soils. Such a scenario accounts for the potential that surface sediments may be compositionally and texturally distinct from the subsurface.

  16. 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.

  17. Holocene environment changes around the Sara Us River, northern China, revealed by optical dating of lacustrine-aeolian sediments

    NASA Astrophysics Data System (ADS)

    Zhao, Hui; Sheng, Yongwei; Li, Bo; Fan, Yuxin

    2016-04-01

    The Sara Us River is located along the boundary of the Mu Us Desert and the Chinese Loess Plateau in northern China. The river has cut down through Quaternary sediments creating 70-80 m deep valleys with thick lacustrine/aeolian sequences exposed. We applied optical stimulated luminescence on sediments from a Holocene section of aeolian sand/lacustrine deposits in the top of the river valley. The dating results show that a humid period existed from 7.1 to 2.0 ka ago as evidenced by two layers of peat and lacustrine sediments. However, compared to other published Holocene sections in the Sara Us River valleys close to the section under studying, the local environment experienced very complicated changes during the Holocene. All of the sections recorded a period with drought and/or cold before the Holocene at around 13 ka, and an episode of aridity after about 2 ka ago as evidenced by the layers of aeolian sand. However, the ages of the lacustrine and peat layers in these sections are substantially different. Geomorphological analysis by digital elevation models does not support the existence of a mega lake covering the study area at 2 ka. The intricate environmental changes may have been caused by the meandering of the Sara Us River. Environmental changes also strongly affected human migration in this area, which is documented by Chinese historical records.

  18. 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.

  19. Graphene cardboard: From ripples to tunable metamaterial

    NASA Astrophysics Data System (ADS)

    Koskinen, Pekka

    2014-03-01

    Recently, graphene was introduced with tunable ripple texturing, a nanofabric enabled by graphene's remarkable elastic properties. However, one can further envision sandwiching the ripples, thus constructing composite nanomaterial, graphene cardboard. Here, the basic mechanical properties of such structures are investigated computationally. It turns out that graphene cardboard is highly tunable material, for its elastic figures of merit vary orders of magnitude, with Poisson ratio tunable from 10 to -0.5 as one example. These trends set a foundation to guide the design and usage of metamaterials made of rippled van der Waals solids.

  20. Hearing sensitivity to shifts of rippled-spectrum patterns.

    PubMed

    Nechaev, Dmitry I; Supin, Alexander Ya

    2013-10-01

    The sensitivity of human hearing to shifts in rippled spectrum patterns of sound was investigated. The test signal was band-limited rippled noise with spectrum ripples of various frequency spacing and bandwidth; this type of sound may be considered as a quantitatively controlled imitation of complex natural sounds. The listener was required to detect a shift in the spectrum ripple phase while keeping the other parameters of the noise constant. For cosine-shaped ripples, the lowest threshold (1.1%) was found at a ripple frequency of 3.5 ripples per octave (rpo), which corresponds to a ripple spacing of 20% of the center frequency. The threshold increased for both lower and higher ripple densities. Qualitatively similar patterns of threshold dependence on ripple density were observed for center frequencies from 1 to 4 kHz. Making the ripples narrower than cosine decreased the thresholds to 0.7%-0.75% for ripple densities of 2-5 rpo. Keeping the ripple width constant at 3.5%-7.5% of the frequency resulted in a monotonic threshold dependence on ripple density: The threshold decreased with decreasing density (down to 0.7%). An excitation-pattern model explains qualitatively the observed dependence of the ripple-phase shift threshold on ripple pattern parameters. PMID:24116427

  1. Vortex dynamics around a solid ripple in an oscillatory flow

    NASA Astrophysics Data System (ADS)

    Sand Jespersen, T.; Thomassen, J. Q.; Andersen, A.; Bohr, T.

    2004-03-01

    We investigate the time-dependent flow of water around a solid triangular profile oscillating horizontally in a narrow rectangular container. The flow is quasi two-dimensional and using particle image velocimetry we measure 20 snapshots of the entire velocity field during a period of oscillation. From the velocity measurements we obtain the circulation of the vortices and study the vortex dynamics. The time-dependence of the flow gives rise to the formation of a jet-like flow structure which enhances the vorticity production compared to the time-independent case. We introduce a simple phenomenological model to describe the important dynamical parameters of the flow, i.e., the vortex circulation and the jet velocity. We solve the model analytically without viscous damping and find good agreement between the model predictions and our measurements. Our work adds to the recent effort to understand more complicated flows past sand-ripples and insect wings.

  2. Sand waves on an epicontinental shelf: Northern Bering Sea

    USGS Publications Warehouse

    Field, M.E.; Nelson, C.H.; Cacchione, D.A.; Drake, D.E.

    1981-01-01

    Sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges (20 km ?? 5 km ?? 10 m high) lying in an open-marine setting in the northern Bering Sea. The sand wave area, which lies west of Seward Peninsula and southeast of Bering Strait, is exposed to the strong continuous flow of coastal water northward toward Bering Strait. A hierarchy of three sizes of superimposed bedforms, all facing northward, was observed in successive cruises in 1976 and 1977. Large sand waves (height 2 m; spacing 200 m) have smaller sand waves (height 1 m; spacing 20 m) lying at a small oblique angle on their stoss slopes. The smaller sand waves in turn have linguoid ripples on their stoss slopes. Repeated studies of the sand wave fields were made both years with high-resolution seismic-reflection profiles, side-scan sonographs, underwater photographs, current-meter stations, vibracores, and suspended-sediment samplers. Comparison of seismic and side-scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year. Gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year, further documenting modification to the bottom by sediment transport. During calm sea conditions in 1977, underwater video and camera observations showed formation and active migration of linguoid and straight-crested current ripples. Current speeds 1 m above the bottom were between 20 and 30 cm/s. Maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water. Many cross-stratified sand bodies in the geologic record are interpreted as having formed in a tidal- or storm-dominated setting. This study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open-marine setting. ?? 1981.

  3. The provenance of Taklamakan desert sand

    NASA Astrophysics Data System (ADS)

    Rittner, Martin; Vermeesch, Pieter; Carter, Andrew; Bird, Anna; Stevens, Thomas; Garzanti, Eduardo; Andò, Sergio; Vezzoli, Giovanni; Dutt, Ripul; Xu, Zhiwei; Lu, Huayu

    2016-03-01

    Sand migration in the vast Taklamakan desert within the Tarim Basin (Xinjiang Uyghur Autonomous region, PR China) is governed by two competing transport agents: wind and water, which work in diametrically opposed directions. Net aeolian transport is from northeast to south, while fluvial transport occurs from the south to the north and then west to east at the northern rim, due to a gradual northward slope of the underlying topography. We here present the first comprehensive provenance study of Taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea, and to consider the potential of the Tarim Basin as a contributing source to the Chinese Loess Plateau (CLP). Our dataset comprises 39 aeolian and fluvial samples, which were characterised by detrital-zircon U-Pb geochronology, heavy-mineral, and bulk-petrography analyses. Although the inter-sample differences of all three datasets are subtle, a multivariate statistical analysis using multidimensional scaling (MDS) clearly shows that Tarim desert sand is most similar in composition to rivers draining the Kunlun Shan (south) and the Pamirs (west), and is distinctly different from sediment sources in the Tian Shan (north). A small set of samples from the Junggar Basin (north of the Tian Shan) yields different detrital compositions and age spectra than anywhere in the Tarim Basin, indicating that aeolian sediment exchange between the two basins is minimal. Although river transport dominates delivery of sand into the Tarim Basin, wind remobilises and reworks the sediment in the central sand sea. Characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the Tarim River, and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea. Smaller ephemeral rivers from the Kunlun Shan end in the desert and discharge their sediment there. Both river run

  4. High albedo dune features suggest past dune migration and possible geochemical cementation of aeolian sediments on Mars

    NASA Astrophysics Data System (ADS)

    Gardin, Emilie; Bourke, Mary C.; Allemand, Pascal; Quantin, Cathy

    2011-04-01

    High albedo features are identified in association with barchan dunes in an equatorial inter-crater dune field on Mars using images from the MRO mission. This paper describes the morphometric properties of these features and their association with the present barchan dune field. We propose that these features are cemented aeolian deposits that form at the foot of the dune avalanche face. A possible terrestrial analog exists at White Sands National Monument, in south-central New Mexico, USA. The presence of these features suggests past episodes of dune migration in inter-crater dunefields and liquid water in the near sub-surface in sufficient quantity to cause the cementation of aeolian dune sediment.

  5. Multi-Resolution Analysis of LiDAR data for Characterizing a Stabilized Aeolian Landscape in South Texas

    NASA Astrophysics Data System (ADS)

    Barrineau, C. P.; Dobreva, I. D.; Bishop, M. P.; Houser, C.

    2014-12-01

    Aeolian systems are ideal natural laboratories for examining self-organization in patterned landscapes, as certain wind regimes generate certain morphologies. Topographic information and scale dependent analysis offer the opportunity to study such systems and characterize process-form relationships. A statistically based methodology for differentiating aeolian features would enable the quantitative association of certain surface characteristics with certain morphodynamic regimes. We conducted a multi-resolution analysis of LiDAR elevation data to assess scale-dependent morphometric variations in an aeolian landscape in South Texas. For each pixel, mean elevation values are calculated along concentric circles moving outward at 100-meter intervals (i.e. 500 m, 600 m, 700 m from pixel). The calculated average elevation values plotted against distance from the pixel of interest as curves are used to differentiate multi-scalar variations in elevation across the landscape. In this case, it is hypothesized these curves may be used to quantitatively differentiate certain morphometries from others like a spectral signature may be used to classify paved surfaces from natural vegetation, for example. After generating multi-resolution curves for all the pixels in a selected area of interest (AOI), a Principal Components Analysis is used to highlight commonalities and singularities between generated curves from pixels across the AOI. Our findings suggest that the resulting components could be used for identification of discrete aeolian features like open sands, trailing ridges and active dune crests, and, in particular, zones of deflation. This new approach to landscape characterization not only works to mitigate bias introduced when researchers must select training pixels for morphometric investigations, but can also reveal patterning in aeolian landscapes that would not be as obvious without quantitative characterization.

  6. Aeolian processes and the bioshpere: Interactions and feedback loops

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aeolian processes affect landform evolution, biogeochemical cycles, regional climate, human health, and desertification. The entrainment, transport and deposition of aeolian sediments are recognized as major drivers in the dynamics of the earth system and there is a growing interest in the scientif...

  7. Introducing a New International Society of Aeolian Research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aeolian research is long-standing and rapidly growing area of study where scientists of many disciplines meet to investigate the effects of wind on the surface of the Earth and other planetary bodies, such as Mars and Titan. Fields of study in aeolian research cover a broad spectrum ranging from dev...

  8. Are Ripples a Sign of Water?

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Scientists are investigating the ripples and textures seen in this 4-panel mosaic image, taken by the microscopic imager on the instrument deployment device or 'robotic arm' of NASA's Mars Exploration Rover Opportunity. The images were taken from 'Panoramic Position 2' on the southeast side of the rim of 'Endurance' Crater. This small set of nearly 150 images was acquired to examine small-scale ripple patterns suggestive of past aqueous processes on Mars.

  9. 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

    Relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results. Most studies link the aeolian coastal deposits to regressive phases, some to high sea-level stands, and a few to intermediate relative sea-level positions. We interpret the apparent contradictions as indicating the lack of an over-arching concept and the inconsistent usage of sea level-related terms. In this paper we present an integrated morpho-sedimentological concept for a microtidal, mid-latitudinal coast and review existing data from the Levant (East Mediterranean) coast to evaluate the concept and to eliminate nomenclatural confusion. A coastal depositional environment in a semi-arid environment consists of shallow-marine, aeolian and alluvial facies which together form an aeolian beach-ridge complex as a package of strata which respond simultaneously to sea-level change. A transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping. Under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit. Under regression the complex represents the falling stage and the associated downdip surface marks the lowstand. On the Levant coast we find chronologically well-constrained, offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between ~ 200 ka and 10 ka. The complexes represent the falling stage systems tract (FSST) of a short-lived (5th-order) depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge. Three of these FSSTs and their up dip and down dip super bounding surface together form the 4th order (~ 100 ka) sequence of the last interglacial/glacial cycle. The absence of transgressive, highstand and lowstand systems tract is explained by the poor

  10. Hippocampal CA1 Ripples as Inhibitory Transients.

    PubMed

    Malerba, Paola; Krishnan, Giri P; Fellous, Jean-Marc; Bazhenov, Maxim

    2016-04-01

    Memories are stored and consolidated as a result of a dialogue between the hippocampus and cortex during sleep. Neurons active during behavior reactivate in both structures during sleep, in conjunction with characteristic brain oscillations that may form the neural substrate of memory consolidation. In the hippocampus, replay occurs within sharp wave-ripples: short bouts of high-frequency activity in area CA1 caused by excitatory activation from area CA3. In this work, we develop a computational model of ripple generation, motivated by in vivo rat data showing that ripples have a broad frequency distribution, exponential inter-arrival times and yet highly non-variable durations. Our study predicts that ripples are not persistent oscillations but result from a transient network behavior, induced by input from CA3, in which the high frequency synchronous firing of perisomatic interneurons does not depend on the time scale of synaptic inhibition. We found that noise-induced loss of synchrony among CA1 interneurons dynamically constrains individual ripple duration. Our study proposes a novel mechanism of hippocampal ripple generation consistent with a broad range of experimental data, and highlights the role of noise in regulating the duration of input-driven oscillatory spiking in an inhibitory network. PMID:27093059

  11. Electron ripple injection concept for transport control

    SciTech Connect

    Choe, W.; Ono, M.; Hwang, Y.S.

    1992-01-01

    Recent experiments in many devices have provided firm evidence that the edge radial electric field profile differs between L- and H-modes, and that these fields can greatly modify transport in tokamak plasmas. A nonintrusive method for inducing radial electric field based on electron ripple injection is being developed by the CDX-U group. This technique utilizes a pair of special coils to create a local magnetic field ripple to trap the electrons at the edge of the plasma. The trapped electrons then drift into the plasma due to the [del]B drift. An ECH power is applied to accelerate electrons to sufficient perpendicular energy to penetrate into the plasma. Application of ECH power to the trapped electrons should provide the desired 20 A of electron current with electrons of a few keV of energy and v[perpendicular]/v[parallel] [much gt] 1. A controlled experiment to investigate the physics of ECH aided ripple injection has been designed on CDX-U. With the set of ripple coils designed for CDX-U, a ripple fraction of [delta] ([double bond] [del]B/B[sub av]) [approximately] 5% is attainable. At this ripple fraction, electrons are trapped if v[perpendicular]/v[parallel] [much gt] 1> (2[delta])[sup [minus][1/2

  12. Hippocampal CA1 Ripples as Inhibitory Transients

    PubMed Central

    Krishnan, Giri P; Fellous, Jean-Marc; Bazhenov, Maxim

    2016-01-01

    Memories are stored and consolidated as a result of a dialogue between the hippocampus and cortex during sleep. Neurons active during behavior reactivate in both structures during sleep, in conjunction with characteristic brain oscillations that may form the neural substrate of memory consolidation. In the hippocampus, replay occurs within sharp wave-ripples: short bouts of high-frequency activity in area CA1 caused by excitatory activation from area CA3. In this work, we develop a computational model of ripple generation, motivated by in vivo rat data showing that ripples have a broad frequency distribution, exponential inter-arrival times and yet highly non-variable durations. Our study predicts that ripples are not persistent oscillations but result from a transient network behavior, induced by input from CA3, in which the high frequency synchronous firing of perisomatic interneurons does not depend on the time scale of synaptic inhibition. We found that noise-induced loss of synchrony among CA1 interneurons dynamically constrains individual ripple duration. Our study proposes a novel mechanism of hippocampal ripple generation consistent with a broad range of experimental data, and highlights the role of noise in regulating the duration of input-driven oscillatory spiking in an inhibitory network. PMID:27093059

  13. Mars sampling strategy and aeolian processes

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1988-01-01

    It is critical that the geological context of planetary samples (both in situ analyses and return samples) be well known and documented. Apollo experience showed that this goal is often difficult to achieve even for a planet on which surficial processes are relatively restricted. On Mars, the variety of present and past surface processes is much greater than on the Moon and establishing the geological context of samples will be much more difficult. In addition to impact hardening, Mars has been modified by running water, periglacial activity, wind, and other processes, all of which have the potential for profoundly affecting the geological integrity of potential samples. Aeolian, or wind, processes are ubiquitous on Mars. In the absence of liquid water on the surface, aeolian activity dominates the present surface as documented by frequent dust storms (both local and global), landforms such as dunes, and variable features, i.e., albedo patterns which change their size, shape, and position with time in response to the wind.

  14. 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.

  15. How common are aeolian processes on planetary bodies with very thin atmospheres?

    NASA Astrophysics Data System (ADS)

    Pähtz, Thomas; Duran, Orencio

    2016-04-01

    Observations from the Voyager 2, New Horizons, and Rosetta missions indicate that aeolian surface features, such as ripples and dunes, do not only occur on the surfaces of Earth, Mars, and Titan, but seemingly also on the surfaces of planetary bodies with extremely thin atmospheres, such as Triton, Pluto, and the comet 67P/Churyumov-Gerasimenko. This is highly intriguing since the saltation-threshold wind shear velocities predicted for these bodies from standard saltation-threshold models are so large that wind erosion actually should not occur. Here, guided by coupled DEM/RANS numerical simulations of sediment transport in Newtonian fluid using the numerical model by Duran et al. (POF 24, 103306, 2012), we propose an analytical model based entirely on physical princinples that predicts the minimal fluid speeds required to sustain sediment transport in Newtonian fluid. The analytical model is consistent with measurements of the transport threshold in water and Earth's air and with a recent observational estimate of the threshold on Mars. When applied to Triton and Pluto, it predicts threshold wind shear velocities (ut) of about 1-3m/s, which is comparable to wind shear occurring during storms on Earth and Mars, for particles with diameters (d) within the range d ∈ [200,3000]μm. The minimal values (≈ 1m/s) are thereby predicted for surprisingly large particles with d ≈ 2000μm. When applied to 67P/Churyumov-Gerasimenko, the analytical model predicts threshold wind shear velocities that are fairly extreme (e.g., ut = 45m/s for d = 1cm), but nonetheless consistent with wind shear velocities estimated to occur on this comet. From our results, we conclude that surface-shaping wind erosion and thus the occurrence of aeolian surface features might be much more common on low-air-density planetary bodies than previously thought.

  16. Electron ripple injection concept for transport control

    SciTech Connect

    Choe, W.; Ono, M.; Hwang, Y.S.

    1992-10-01

    Recent experiments in many devices have provided firm evidence that the edge radial electric field profile differs between L- and H-modes, and that these fields can greatly modify transport in tokamak plasmas. A nonintrusive method for inducing radial electric field based on electron ripple injection is being developed by the CDX-U group. This technique utilizes a pair of special coils to create a local magnetic field ripple to trap the electrons at the edge of the plasma. The trapped electrons then drift into the plasma due to the {del}B drift. An ECH power is applied to accelerate electrons to sufficient perpendicular energy to penetrate into the plasma. Application of ECH power to the trapped electrons should provide the desired 20 A of electron current with electrons of a few keV of energy and v{perpendicular}/v{parallel} {much_gt} 1. A controlled experiment to investigate the physics of ECH aided ripple injection has been designed on CDX-U. With the set of ripple coils designed for CDX-U, a ripple fraction of {delta} ({double_bond} {del}B/B{sub av}) {approximately} 5% is attainable. At this ripple fraction, electrons are trapped if v{perpendicular}/v{parallel} {much_gt} 1> (2{delta}){sup {minus}{1/2}} {approx}3. A resonant cavity box was fabricated for efficient heating of the trapped electrons. It is also capable of measuring the effect of the field ripple in conjunction with trapped electrons. Some preliminary results are given.

  17. Aeolian removal of dust from photovoltaic surfaces on Mars

    NASA Technical Reports Server (NTRS)

    Gaier, James R.; Perez-Davis, Marla E.; Marabito, Mark

    1990-01-01

    It is well documented that Mars is totally engulfed in huge dust storms nearly each Martian year. Dust elevated in these global dust storms, or in any of the numerous local dust storms could settle on photovoltaic surfaces and seriously hamper photovoltaic power system performance. Using a recently developed technique to uniformly dust simulated photovoltaic surfaces, samples were subjected to Martian-like winds in an attempt to determine whether natural aeolian processes on Mars would sweep off the settled dust. The effects of wind velocity, angle of attack, height off the Martian surface, and surface coating material were investigated. Principles which can help to guide the design of photovoltaic arrays bound for the Martian surface were uncovered. Most importantly, arrays mounted with an angle of attack approaching 45 deg show the most efficient clearing. Although the angular dependence is not sharp, horizontally mounted arrays required significantly higher wind velocities to clear off the dust. From the perspective of dust-clearing it appears that the arrays may be erected quite near the ground, but previous studies have suggested that saltation effects can be expected to cause such arrays to be covered by sand if they are set up less than about a meter from the ground. Providing that the surface chemistry of Martian dusts is comparable to our test dust, the materials used for protective coating may be optimized for other considerations such as transparency, and chemical or abrasion resistance. The static threshold velocity is low enough that there are regions on Mars which experience winds strong enough to clear off a photovoltaic array if it is properly oriented. Turbulence fences proved to be an ineffective strategy to keep dust cleared from the photovoltaic surfaces.

  18. Aeolian Abrasion, a Dominant Erosion Agent in the Martian Environment

    NASA Astrophysics Data System (ADS)

    Bridges, N.; Cooper, G.; Eddlemon, E.; Greeley, R.; Laity, J.; Phoreman, J.; Razdan, A.; van Note, S.; White, B.; Wilson, G.

    2004-12-01

    Aeolian abrasion is one of the predominant erosion mechanisms on Mars today. Martian ventifacts record the climate under which the rocks were modified (wind direction, wind speeds and particle flux) and therefore tie into the overall climatic regime of the planet. By better understanding the rates at which rocks abrade and the features diagnostic of specific climatic conditions, we can gain insight into past climates. Herein we report on numerical models, wind tunnel experiments, and field work to determine 1) Particle and kinetic fluxes on Earth and Mars, 2) the degree to which these parameters control abrasion, and 3) how, in detail, rocks of various shapes and compositions erode over time. Kinetic energy generally increases with height, whereas flux decreases, and impact angles, which affect energy transfer, and rebound effects are functions of the rock facet angle. This results in a non-linear relationship between abrasion potential and height that is a function of wind speed, planetary environment, and target geometry. We have computed the first three of these parameters numerically using a numerical saltation code, combined with published flux calculations These results have been compared to wind tunnel tests of flux vs. height, abrasion of erodible targets, and high speed video analysis under terrestrial and Martian pressures. We are also using high resolution laser scanning to characterize textures, shapes, and weathering changes for terrestrial and Martian rocks at the 100s of microns scale. We find that facet angle, texture, and rock heterogeneity are of critical importance in determining the rate and style of abrasion. Field and theoretical results demonstrate that high speed winds, not the integrated flux of lower speeds, and sand, not dust, produce most rock abrasion. On Mars, this requires sustained winds above 20-25 m/s at the near surface, a challenge in the current environment.

  19. Earth and planetary aeolian streaks: A review

    NASA Astrophysics Data System (ADS)

    Cohen-Zada, Aviv Lee; Blumberg, Dan Gabriel; Maman, Shimrit

    2016-03-01

    Wind streaks are abundant aeolian features that have been observed on planetary surfaces by remote sensing means. They have been widely studied, particularly on Mars and Venus and to a much lesser extent on Earth. In imagery, these streaks appear as elongated features that are easily distinguishable from their surroundings. Geomorphologically, these streaks have, thus far, been interpreted as the presence or absence of small loose particles on the surface, deposited or eroded, respectively, by wind. However, the use of different (optical and radar) remote-sensing tools to study wind streaks has led to uncertain interpretations of these features and has hindered their geomorphological definition. Since wind streaks indicate the prevailing wind direction at the time of their formation, they may be used to map near-surface winds and to estimate atmospheric circulation patterns. The aim of this article is to review the main studies focusing on wind streaks and to present the most up-to-date knowledge on this topic. Moreover, a new perspective for wind streak research is suggested: As 'wind streak' is a collective term for a variety of aeolian features that when viewed from above appear as distinctive albedo surface patterns, we suggest that the term should not be used to refer to a geomorphological feature. Since the definition of wind streaks is constrained to remote sensing rather than to geomorphology and is affected by the inherent biases of remote sensing methods, we suggest that 'wind streaks' should be used as a collective term for aeolian surfaces that are discernable from above as bright and dark patterns due to alterations in the characteristics of the surface or to the presence of bedforms. To better understand the mechanisms, time-frames, climate compatibility of wind streaks and the influences of remote sensing on their appearance, we have compiled a new database containing more than 2,900 Earth wind streaks. A comprehensive study of these Earth wind

  20. Incident Angle of Saltating Particles in Wind-Blown Sand

    PubMed Central

    Fu, Lin-Tao; Bo, Tian-Li; Gu, Hai-Hua; Zheng, Xiao-Jing

    2013-01-01

    Incident angle of saltating particles plays a very important role in aeolian events. In this paper, the incident angles of sand particles near the sand bed were measured in wind tunnel. It reveals that the incident angles range widely from 0° to 180° and thereby the means of angles are larger than published data. Surprisingly, it is found the proportion that angles of 5°–15° occupy is far below previous reports. The measuring height is probably the most important reason for the measurement differences between this study and previous investigations. PMID:23874470

  1. A theoretical model of asymmetric wave ripples

    PubMed Central

    Blondeaux, P.; Foti, E.; Vittori, G.

    2015-01-01

    The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19–39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285–301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive. PMID:25512587

  2. A theoretical model of asymmetric wave ripples.

    PubMed

    Blondeaux, P; Foti, E; Vittori, G

    2015-01-28

    The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19-39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285-301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive. PMID:25512587

  3. A comparison of general circulation model predictions to sand drift and dune orientations

    SciTech Connect

    Blumberg, D.G.; Greeley, R. |

    1996-12-01

    The growing concern over climate change and decertification stresses the importance of aeolian process prediction. In this paper the use of a general circulation model to predict current aeolian features is examined. A GCM developed at NASA/Goddard Space Flight Center was used in conjunction with White`s aeolian sand flux model to produce a global potential aeolian transport map. Surface wind shear stress predictions were used from the output of a GCM simulation that was performed as part of the Atmospheric Model Intercomparison Project on 1979 climate conditions. The spatial resolution of this study (as driven by the GCM) is 4{degrees} X 5{degrees}; instantaneous 6-hourly wind stress data were saved by the GCM and used in this report. A global map showing potential sand transport was compared to drift potential directions as inferred from Landsat images from the 1980s for several sand seas and a coastal dune field. Generally, results show a good correlation between the simulated sand drift direction and the drift direction inferred for dune forms. Discrepancies between the drift potential and the drift inferred from images were found in the North American deserts and the Arabian peninsula. An attempt to predict the type of dune that would be formed in specific regions was not successful. The model could probably be further improved by incorporating soil moisture, surface roughness, and vegetation information for a better assessment of sand threshold conditions. The correlation may permit use of a GCM to analyze {open_quotes}fossil{close_quotes} dunes or to forecast aeolian processes. 48 refs., 8 figs.

  4. Analysis of wind-blown sand movement over transverse dunes.

    PubMed

    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

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Jiang, Hong; Huang, Ning; Zhu, Yuanjian

    2014-12-01

    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.

  7. Tar sands

    SciTech Connect

    Wennekers, J.H.N.

    1981-10-01

    The four largest oil sand deposits contain over 90% of the world's known heavy oil. The total heavy oil and bitumen in place, estimated at nearly 6 trillion barrels is almost entirely concentrated in western Canada, principally Alberta, and eastern Venezuela. The known tar sand resource in the United States consists of about 550 occurrences located in 22 states. The total oil in place in 39 of these occurrences is estimated to be between 23.7 billion and 32.7 billion barrels. At least 90% of this resource is located in Utah. Other significant deposits are in Texas, New Mexico, California, and Kentucky. Bituminous sand deposits and petroleum-impregnated rocks are found in Malagasy, Albania, Rumania, the USSR, and Trinidad. 4 figures, 2 tables. (DP)

  8. Geographical Detector-Based Identification of the Impact of Major Determinants on Aeolian Desertification Risk.

    PubMed

    Du, Ziqiang; Xu, Xiaoming; Zhang, Hong; Wu, Zhitao; Liu, Yong

    2016-01-01

    Arid and semi-arid areas in North China are facing the challenge of a rising aeolian desertification risk (ADR) due to the intertwined effects of complex natural processes and intensified anthropogenic activities. An accurate quantitative assessment of the relationship between ADR and its determinants is beneficial for understanding the driving mechanisms of aeolian desertification and for controlling future desertification. Previous studies have failed to quantify the relative role of determinants driving ADR and have been limited in assessing their interactive impacts. In this study, a spatial variance analysis-based geographical detector methodology is used to quantify the effects of geological, physical, and human factors on the occurrence of ADR in an area characterized by mountains and hills in northern China. It is found that soil type, precipitation, and wind velocity are the major determinants of ADR, which implies that geological and physical elements (e.g., soil attribute) and climatic factors (e.g., precipitation and wind velocity) rather than human activities have played a greater role in the incidence of ADR. Particularly, the results show that the interaction of various determinants causes significant non-linearly enhanced impacts on the ADR. The findings of our study will assist local inhabitants and policy makers in developing measures for wind prevention and sand control to mitigate the effects of desertification in the region. PMID:26987114

  9. Measurement uncertainties in quantifying aeolian mass flux: evidence from wind tunnel and field site data.

    PubMed

    Poortinga, Ate; Keijsers, Joep G S; Maroulis, Jerry; Visser, Saskia M

    2014-01-01

    Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from such measurements are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative distribution and relative sediment flux derived from both wind tunnel and field studies. Vertical flux data was examined using existing data in combination with a newly acquired dataset; comprising meteorological data and sediment fluxes from six different events, using three customized catchers at Ameland beaches in northern Netherlands. Fast-temporal data collected in a wind tunnel shows that the median transport height has a scattered pattern between impact and fluid threshold, that increases linearly with shear velocities above the fluid threshold. For finer sediment, a larger proportion was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the distribution of sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced but localized effect than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface. PMID:25071984

  10. Geographical Detector-Based Identification of the Impact of Major Determinants on Aeolian Desertification Risk

    PubMed Central

    Du, Ziqiang; Xu, Xiaoming; Zhang, Hong; Wu, Zhitao; Liu, Yong

    2016-01-01

    Arid and semi-arid areas in North China are facing the challenge of a rising aeolian desertification risk (ADR) due to the intertwined effects of complex natural processes and intensified anthropogenic activities. An accurate quantitative assessment of the relationship between ADR and its determinants is beneficial for understanding the driving mechanisms of aeolian desertification and for controlling future desertification. Previous studies have failed to quantify the relative role of determinants driving ADR and have been limited in assessing their interactive impacts. In this study, a spatial variance analysis-based geographical detector methodology is used to quantify the effects of geological, physical, and human factors on the occurrence of ADR in an area characterized by mountains and hills in northern China. It is found that soil type, precipitation, and wind velocity are the major determinants of ADR, which implies that geological and physical elements (e.g., soil attribute) and climatic factors (e.g., precipitation and wind velocity) rather than human activities have played a greater role in the incidence of ADR. Particularly, the results show that the interaction of various determinants causes significant non-linearly enhanced impacts on the ADR. The findings of our study will assist local inhabitants and policy makers in developing measures for wind prevention and sand control to mitigate the effects of desertification in the region. PMID:26987114

  11. Measurement uncertainties in quantifying aeolian mass flux: evidence from wind tunnel and field site data

    PubMed Central

    Keijsers, Joep G.S.; Maroulis, Jerry; Visser, Saskia M.

    2014-01-01

    Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from such measurements are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative distribution and relative sediment flux derived from both wind tunnel and field studies. Vertical flux data was examined using existing data in combination with a newly acquired dataset; comprising meteorological data and sediment fluxes from six different events, using three customized catchers at Ameland beaches in northern Netherlands. Fast-temporal data collected in a wind tunnel shows that the median transport height has a scattered pattern between impact and fluid threshold, that increases linearly with shear velocities above the fluid threshold. For finer sediment, a larger proportion was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the distribution of sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced but localized effect than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface. PMID:25071984

  12. The ripple effect: patients influencing others.

    PubMed

    Paniagua, Cecilio

    2012-10-01

    This paper deals with what seems an insufficiently explored aspect of psychoanalytic practice: the ripple effect of a patient's evolution on the present and future of his or her significant others. Clinical vignettes are provided to illustrate patients' influence on relatives; patients acting as therapists; psychoanalysis by proxy; the ripple effect in psychotherapy; and some countertransference problems. The psychic lives of individuals not in treatment may be considerably affected by their interactions with our patients; seemingly, extraclinical character adjustments may ensue. Sociological findings and plausible psychodynamic explanations are discussed. A psychoanalytic perspective may not only help the analyst understand how therapeutic influence extends beyond the identified patient, but may also help guide interventions that are ripple-effective, even when they depart from classical analytic technique. PMID:23327000

  13. 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.

  14. Mixing efficiency of sediment and momentum above rippled beds under oscillatory flows

    NASA Astrophysics Data System (ADS)

    Malarkey, J.; Magar, V.; Davies, A. G.

    2015-10-01

    While the nature of the suspended load above steep, wave-induced, sand ripples is of practical importance, it also raises intriguing questions about the relative mixing efficiencies of sediment and momentum above the seabed. It has been widely accepted that the mixing efficiency of sediment is substantially greater than that of momentum. But, hitherto, this has not been explained clearly in terms of the underlying, detailed physical mechanisms which revolve around the generation and ejection of sediment-laden vortices at the ripple crest, and their subsequent advection by the flow. A two-dimensional discrete-vortex, particle-tracking research model, with the parameter settings corresponding to a well-documented laboratory experiment, is used here to represent these processes. Both the modelled and also experimental flow and concentration fields are described in detail, together with the horizontally (ripple-) averaged fields, and the cycle-mean, ripple-averaged fields. From these considerations, the ratio (β) of the sediment diffusivity to the eddy viscosity, or the inverse of the Schmidt number, is then determined. It is found that β is larger than unity, in fact between 1.3 and 3.1 for two different computational approaches (based on harmonics and exponential fitting) for the model and data. These values for β agree well with previous results reported in the literature. This research elucidates, from fundamental principles related to spatio-temporal correlations between concentration and velocity, the improved efficiency of sediment mixing compared with momentum mixing in the vortex layer above rippled beds and its key role in determining suspension profiles in such flows.

  15. Trajectories of saltating sand particles behind a porous fence

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Lee, Sang Joon; Chen, Ting-Guo

    2015-01-01

    Trajectories of aeolian sand particles behind a porous wind fence embedded in a simulated atmospheric boundary layer were visualized experimentally, to investigate the shelter effect of the fence on sand saltation. Two sand samples, one collected from a beach (d = 250 μm) and the other from a desert (d = 100 μm), were tested in comparison with the previous studies of a 'no-fence' case. A wind fence (ε = 38.5%) was installed on a flat sand bed filled with each sand sample. A high-speed photography technique and the particle tracking velocimetry (PTV) method were employed to reconstruct the trajectories of particles saltating behind the fence. The collision processes of these sand particles were analyzed, momentum and kinetic energy transfer between saltating particles and ground surface were also investigated. In the wake region, probability density distributions of the impact velocities agree well with the pattern of no-fence case, and can be explained by a log-normal law. The horizontal component of impact velocity for the beach sand is decreased by about 54%, and about 76% for the desert sand. Vertical restitution coefficients of bouncing particles are smaller than 1.0 due to the presence of the wind fence. The saltating particles lose a large proportion of their energy during the collision process. These results illustrate that the porous wind fence effectively abates the further evolution of saltating sand particles.

  16. Biodiversity impact of the aeolian periglacial geomorphologic evolution of the Fontainebleau Massif (France)

    NASA Astrophysics Data System (ADS)

    Thiry, M.; Liron, M. N.

    2009-04-01

    Landscape features The geomorphology of the Fontainebleau Massif is noteworthy for its spectacular narrow ridges, up to 10 km long and 0.5 km wide, armored by tightly cemented sandstone lenses and which overhang sandy depressions of about 50m. Denudation of the sandstone pans lead to a highly contrasted landscape, with sandstone ridges ("platières") towering sandy depressions ("vallées") and limestone plateaus ("monts"). This forms the geological frame of the spectacular sceneries of the Fontainebleau Massif (Thiry & Liron, 2007). Nevertheless, there is little know about the erosive processes that have built-up these landscapes. Periglacial processes, and among them aeolian ones, appear significant in the development of the Fontainebleau Massif physiography. The periglacial aeolian geomorphology Dunes and dune fields are known since long and cover about 15% to 25% of the Fontainebleau Massif. The aeolian dunes developed as well on the higher parts of the landscape, as well as in the lower parts of the landscape. The dunes are especially well developed in the whole eastern part of the massif, whereas the western part of the massif is almost devoid of dunes. Nevertheless, detailed mapping shows that dunes can locally be found in the western district, they are of limited extension, restricted to the east facing backslope of outliers. Loamy-sand covers the limestone plateaus of the "monts". The loam cover is of variable thickness: schematically thicker in the central part of the plateaus, where it my reach 3 m; elsewhere it may thin down to 0,20-0,30 m, especially at the plateau edges. Blowout hollows are "negative" morphologies from where the sand has been withdrawed. Often these blowouts are decametric sized and well-delimited structures. Others, more complex structures, are made up of several elongated hectometric hollows relaying each other from and which outline deflation corridor more than 1 km long. A characteristic feature of these blowout hollows is the

  17. Ripple Ring Basins on Ganymede and Callisto

    NASA Technical Reports Server (NTRS)

    Croft, S. K.

    1985-01-01

    The unusual morphology of the Valhalla multiple or ripple-ring basin in Callisto was totally unexpected in light of the morphologies of large impact structures on the terrestrial planets. Two other ripple-ring basins (RRB's), Asgard and a smaller structure near the crater Adlinda are also described. Several additional RRB's were found on Callisto, an example of which is shown. A previously unrecognized RRB on Ganymede was also found. An image and geologic sketch map of this RRB are shown. Morphometric and positional data for all known RRB's are given.

  18. 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

  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. 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.

  1. 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.

  2. 26Al/10Be dating of an aeolian dust mantle soil in western New South Wales, Australia

    NASA Astrophysics Data System (ADS)

    Fisher, Adrian; Fink, David; Chappell, John; Melville, Michael

    2014-08-01

    Aeolian dust mantle soils are an important element of many landscapes in south-eastern Australia, though the age of these aeolian deposits has not been radiometrically determined. At Fowlers Gap in western New South Wales, surface cobbles of silcrete and quartz overlie a stone-free, aeolian dust mantle soil, which has a thickness of about 1.6 m. The clay-rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer. Modelling in-situ cosmogenic 26Al and 10Be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks, reveals that each has experienced a complex exposure-burial history. Due to the absence of quartz stones or sand at intermediate depths, our cosmogenic 26Al and 10Be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial. Various scenarios of stone formation, transport, burial and exhumation were tested that constrain the age of the deposit to range from 0.9 ± 0.2 Ma to 1.8 ± 0.2 Ma, based largely on different assumptions taken for the time-dependency of the net sedimentation rate. This corresponds with the initiation of the Simpson Desert dune fields and the deflation of lakes in central Australia, which probably responded to the shift to longer-wavelength, larger-amplitude Quaternary glacial cycles at around 1 Ma. Sensitivity analyses were carried out to identify those parameters which better constrained model outputs. Within model errors, which largely are the result of analytical errors in measured 26Al and 10Be concentrations, all three competing theories of colluvial wash, upward displacement of stones, and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement.

  3. Dependence of ripple dimensions on cohesive and non-cohesive bed properties in the intertidal Dee Estuary

    NASA Astrophysics Data System (ADS)

    Lichtman, Ian; Thorne, Peter; Baas, Jacobus; O'Boyle, Louise; Cooke, Richard; Amoudry, Laurent; Bell, Paul; Aspden, Rebecca; Bass, Sarah; Davies, Alan; Hope, Julie; Malarkey, Jonathan; Manning, Andrew; Parsons, Daniel; Paterson, David; Peakall, Jeffrey; Schindler, Robert; Ye, Leiping

    2014-05-01

    There is a need to better understand the effects of cohesive and mixed sediments on coastal processes, to improve sediment transport models for the management of coastal erosion, siltation of navigation channels and habitat change. Although reasonable sediment transport predictors are available for pure sands, it still is not the case for mixed cohesive and non-cohesive sediments. Existing predictors mostly relate ripple dimensions to hydrodynamic conditions and median sediment grain diameter, assuming a narrow unimodal particle size distribution. Properties typical of mixed conditions, such as composition and cohesion for example, are not usually taken into account. This presents severe shortcomings to predictors' abilities. Indeed, laboratory experiments using mixed cohesive sediments have shown that bedform dimensions decrease with increasing bed mud content. In the field, one may expect current predictors to match data for well-sorted sands closely, but poorly for mixed sediments. Our work is part of the COHBED project and aims to: (1) examine, in field conditions, if ripple dimensions are significantly different for mixed cohesive sediment beds compared to beds with pure sand; (2) compare the field data with laboratory results that showed reduced ripple length due to cohesive mud content; and (3) assess the performance of a selection of ripple predictors for mixed sediment data. The COHBED project was set up to undertake laboratory experiments and fieldwork to study how physical and biological processes influence bedform development in a mixed cohesive-cohesionless sediment environment. As part of COHBED, a suite of instruments was deployed on tidal flats in the Dee Estuary (on the NW coast of England), collecting co-located measurements of the hydrodynamics, suspended sediment properties and bed morphology. The instruments occupied three sites collecting data over different bed compositions during a two week period (21 May to 4 June 2013). One site was

  4. Mechanisms limiting the growth of aeolian megaripples

    NASA Astrophysics Data System (ADS)

    Katra, I.; Yizhaq, Hezi; Kok, Jasper F.

    2014-02-01

    Megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution. The interplay between wind, grain size, and morphology controls their development, but the exact mechanisms that limit the size of megaripples have been unclear. Using wind tunnel experiments, we found two main mechanisms that limit the height of megaripples. The first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation; the second mechanism is megaripple deflation by impacts of faster saltation grains. In this latter mechanism, the coarse grains are propelled by the impacts of fine saltating grains. The occurrence of both these mechanisms depends on the grain size distribution and increases with both megaripple height and wind speed. Thus, for a given wind environment and grain size distribution, there exists a limit on the size of megaripples, which is determined by these two mechanisms.

  5. Eolian cover sands: a sedimentologic model and paleoenvironmental implications

    SciTech Connect

    Lea, P.D.

    1985-01-01

    In periglacial areas, accumulations of eolian sand commonly form low-relief blankets without well-developed dunes. Internally, these sandsheet deposits exhibit subhorizontal lamination rather than high-angle cross-bedding. Such cover sands of late-Pleistocene age mantle extensive areas in northern Europe, but have been reported more rarely from North America. The processes by which cover sands, as opposed to dunes, accumulate have not yet been determined conclusively. Wind ripples and sand dunes do not form a continuum; flow separation and avalanching and negligible in the former and vital in the latter. Accretion of a sand patch into a mound sufficient to cause flow separation and dune growth requires a consistently available supply of loose sand. In cover-sand areas, sand may be immobilized prior to dune development by several factors: (1) a sparse vegetation cover, (2) moist ground conditions, (3) snow cover, and (4) a shallow permafrost table and/or an ice-cemented active layer. Detailed sedimentologic studies may allow discrimination among these various controls. The importance of the individual controlling factors can vary seasonally in a given deposit, as well as between deposits in different paleogeographic settings. However, all factors imply more mesic conditions than those associated with many dune deposits. The association of cover sands with paraboloid dunes is also consistent with somewhat moist conditions. The relatively mesic nature of cover sands controls their Pleistocene distribution; they become decreasingly important relative to dunes in maritime-to-continental transects across Alaska and northern Europe.

  6. Cobbles in Troughs Between Meridiani Ripples

    NASA Technical Reports Server (NTRS)

    2006-01-01

    As NASA's Mars Exploration Rover Opportunity continues to traverse from 'Erebus Crater' toward 'Victoria Crater,' the rover navigates along exposures of bedrock between large, wind-blown ripples. Along the way, scientists have been studying fields of cobbles that sometimes appear on trough floors between ripples. They have also been studying the banding patterns seen in large ripples.

    This view, obtained by Opportunity's panoramic camera on the rover's 802nd Martian day (sol) of exploration (April 27, 2006), is a mosaic spanning about 30 degrees. It shows a field of cobbles nestled among wind-driven ripples that are about 20 centimeters (8 inches) high.

    The origin of cobble fields like this one is unknown. The cobbles may be a lag of coarser material left behind from one or more soil deposits whose finer particles have blown away. The cobbles may be eroded fragments of meteoritic material, secondary ejecta of Mars rock thrown here from craters elsewhere on the surface, weathering remnants of locally-derived bedrock, or a mixture of these. Scientists will use the panoramic camera's multiple filters to study the rock types, variability and origins of the cobbles.

    This is an approximately true-color rendering that combines separate images taken through the panoramic camera's 753-nanometer, 535-nanometer and 432-nanometer filters.

  7. Toroidal Alfven eigenmode-induced ripple trapping

    SciTech Connect

    White, R.B.; Fredrickson, E.; Darrow, D.; Zarnstorff, M.; Wilson, R.; Zweben, S.; Hill, K.; Chen, Y.; Fu, G.

    1995-08-01

    Toroidal Alfven eigenmodes are shown to be capable of inducing ripple trapping of high-energy particles in tokamaks, causing intense localized particle loss. The effect has been observed in TFTR [R. Hawryluk, Plasma Phys. Controlled Fusion {bold 33}, 1509 (1991)]. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  8. Constrained ripple optimization of Tokamak bundle divertors

    SciTech Connect

    Hively, L.M.; Rome, J.A.; Lynch, V.E.; Lyon, J.F.; Fowler, R.H.; Peng, Y-K.M.; Dory, R.A.

    1983-02-01

    Magnetic field ripple from a tokamak bundle divertor is localized to a small toroidal sector and must be treated differently from the usual (distributed) toroidal field (TF) coil ripple. Generally, in a tokamak with an unoptimized divertor design, all of the banana-trapped fast ions are quickly lost due to banana drift diffusion or to trapping between the 1/R variation in absolute value vector B ..xi.. B and local field maxima due to the divertor. A computer code has been written to optimize automatically on-axis ripple subject to these constraints, while varying up to nine design parameters. Optimum configurations have low on-axis ripple (<0.2%) so that, now, most banana-trapped fast ions are confined. Only those ions with banana tips near the outside region (absolute value theta < or equal to 45/sup 0/) are lost. However, because finite-sized TF coils have not been used in this study, the flux bundle is not expanded.

  9. Measuring Social Capital Change Using Ripple Mapping

    ERIC Educational Resources Information Center

    Baker, Barbara; Johannes, Elaine M.

    2013-01-01

    This article provides a detailed description of how to implement a ripple mapping activity to assess youth program effects on community capital and concludes with examples from Maine and Kansas. The maps lead to group reflection on project outcomes and further research and evaluation questions for group members. The results from five Maine…

  10. Unified theory of ripple transport in stellarators

    SciTech Connect

    Beidler, C.D.; Hitchon, W.N.G.; van Rij, W.I.; Hirshman, S.P.; Shohet, J.L.

    1987-04-27

    The distribution function for ripple-trapped particles has been found in a series form valid for all low collision frequencies, for standard and transport-optimized stellarators. The diffusion coefficient obtained with this distribution function shows excellent agreement with the results of Monte Carlo and Fokker-Planck computer codes, in the cases studied.

  11. 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

  12. A Japan-Sino joint project, ADEC - Aeolian Dust Experiment on Climate Impact

    NASA Astrophysics Data System (ADS)

    Mikami, M.

    2004-05-01

    In recent years, aeolian dust has been thought to be an important factor of the climate system on the earth by the radiative forcing effect in the atmosphere and by the influence on the carbon dioxide cycle because deposited dust supplies nutrient salts for the phytoplankton on the ocean surface. Among them, radiative forcing direct and/or indirect effects are important factors of the global warming. Nevertheless, the reliability of the evaluation regarding the radiative forcing impact of aeolian dust is very low. [IPCC, 2001]. This is because the understanding and the model representations of dust entrainment, spatial and temporal distribution of dust, and optical properties of dust particles are not so accurate. Based on this background, Aeolian Dust Experiment on Climate Impact (ADEC) was started in April 2000 as a Japan-Sino Joint Project. The goal of this project is to evaluate the global dust supply to the atmosphere and its radiative forcing direct effect. For this purpose, we have made: 1) in situ observations at desert areas in China for wind erosion processes, 2) network observations from China to Japan, ranging from 80 to 140 East, for understanding spatial-size distribution, chemical, and optical properties of dust particles, and 3) numerical simulation by GCM dust model for evaluation of dust impact on the global climate over the past 50 years. This was planned as a five-year project and two intensive observations, IOP-1, April 12-25 2002, and IOP-2, March 15-26 2003, were put into practice. Intensive observations were made at 6 sites in China (Qira, Aksu, Dunhuang, Shapotou, Beijing, and Qingdao) and 4 sites in Japan (Naha, Fukuoka, Nagoya, and Tsukuba). Preliminary results show that 1) saltation flux at a gobi desert monitored by a newly developed sand particle counter was around 10 times larger than that of a sand dune, which will be caused by the difference of the parent soil size distribution of each ground condition, 2) the background of KOSA

  13. Gap junction networks can generate both ripple-like and fast ripple-like oscillations

    PubMed Central

    Simon, Anna; Traub, Roger D.; Vladimirov, Nikita; Jenkins, Alistair; Nicholson, Claire; Whittaker, Roger G.; Schofield, Ian; Clowry, Gavin J.; Cunningham, Mark O.; Whittington, Miles A.

    2014-01-01

    Fast ripples (FRs) are network oscillations, defined variously as having frequencies of > 150 to > 250 Hz, with a controversial mechanism. FRs appear to indicate a propensity of cortical tissue to originate seizures. Here, we demonstrate field oscillations, at up to 400 Hz, in spontaneously epileptic human cortical tissue in vitro, and present a network model that could explain FRs themselves, and their relation to ‘ordinary’ (slower) ripples. We performed network simulations with model pyramidal neurons, having axons electrically coupled. Ripples (< 250 Hz) were favored when conduction of action potentials, axon to axon, was reliable. Whereas ripple population activity was periodic, firing of individual axons varied in relative phase. A switch from ripples to FRs took place when an ectopic spike occurred in a cell coupled to another cell, itself multiply coupled to others. Propagation could then start in one direction only, a condition suitable for re-entry. The resulting oscillations were > 250 Hz, were sustained or interrupted, and had little jitter in the firing of individual axons. The form of model FR was similar to spontaneously occurring FRs in excised human epileptic tissue. In vitro, FRs were suppressed by a gap junction blocker. Our data suggest that a given network can produce ripples, FRs, or both, via gap junctions, and that FRs are favored by clusters of axonal gap junctions. If axonal gap junctions indeed occur in epileptic tissue, and are mediated by connexin 26 (recently shown to mediate coupling between immature neocortical pyramidal cells), then this prediction is testable. PMID:24118191

  14. Defrosting Sand

    NASA Technical Reports Server (NTRS)

    2005-01-01

    19 June 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark spots formed in carbon dioxide frost that covers the surfaces of patches of sand in the south polar region. As spring arrived this year in the martian southern hemisphere, so began the annual defrosting process. The fact that sand dunes begin to defrost earlier than other surfaces, and that the defrosting process involves the formation of spots like these, has been known since the earliest days of the MGS mission.

    Location near: 66.8oS, 15.7oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  15. Basaltic lava flows covering active aeolian dunes in the Paraná Basin in southern Brazil: Features and emplacement aspects

    NASA Astrophysics Data System (ADS)

    Waichel, Breno L.; Scherer, Claiton M. S.; Frank, Heinrich T.

    2008-03-01

    Burial of active aeolian dunes by lava flows can preserve the morphology of the dunes and generate diverse features related to interaction between unconsolidated sediments and lavas. In the study area, located in southern Brazil, burial of aeolian deposits by Cretaceous basaltic lava flows completely preserved dunes, and generate sand-deformation features, sand diapirs and peperite-like breccia. The preserved dunes are crescentic and linear at the main contact with basalts, and smaller crescentic where interlayered with lavas. The various feature types formed on sediment surfaces by the advance of the flows reflect the emplacement style of the lavas which are compound pahoehoe type. Four feature types can be recognized: (a) type 1 features are related to the advance of sheet flows in dune-interdune areas with slopes > 5°, (b) type 2 is formed where the lava flows advance in lobes and climb the stoss slope of crescentic dunes (slopes 8-12°), (c) type 3 is generated by toes that descend the face of linear dunes (slopes 17-23°) and (d) type 4 occurs when lava lobes descend the stoss slope of crescentic dunes (slopes 10-15°). The direction of the flows, the disposition and morphology of the dunes and the ground slope are the main factors controlling formation of the features. The injection of unconsolidated sand in lava lobes forms diapirs and peperite-like breccias. Sand diapirs occur at the basal portion of lobes where the lava was more solidified. Peperite-like breccias occur in the inner portion where lava was more plastic, favoring the mingling of the components. The generation of both features is related to a mechanical process: the weight of the lava causes the injection of sand into the lava and the warming of the air in the pores of the sand facilitates this process. The lava-sediment interaction features presented here are consistent with previous reports of basalt lavas with unconsolidated arid sediments, and additional new sand-deformation features

  16. Effect of Holocene sea level change on aeolian activity in the coastal plain of Ras El Hekma area, NW coast of Egypt

    NASA Astrophysics Data System (ADS)

    Farghaly, Enas; Torab, Magdy

    2015-04-01

    Ras El Hekma area located in north western coast of Egypt, west of Alexandria city for about 220 km, in this area, environmental changes during the Holocene can be interpreted based on morphological and sedimentological similarities between Holocene geomorphic features such as cemented beaches and fossilized dunes with recent coastal features. Sand dunes and nebkhas are the most common aeolian landforms and they occur in semi-arid climatic conditions. The active separated coastal dunes and nebkhas dunes of Ras El-Hekma area are located between the swash zone and the coastal limestone ridges as well as in the coastal sabkhas. The effect of waves during storms reaches far beyond the actual beach and can cause great changes to sandy beaches at an exceptional speed. Sand accumulated by swash drifts with the wind on open beaches and bays. The aeolian sand, which originates from fluvial-marine sediments washed by sea waves. the available sediment depends on fluvial transport to the littoral zone and on biological activity in the carbonate environments as well as on longshore and cross-shore currents. This paper treats the coastal dunes in Ras El Hekma area in their entirety and defines the effects of sea level change on coastal sand dunes and sabkhas dunes, it depends upon field geomorphic surveying, sampling and mapping as well as satellite image interpretation using ENVI software and GIS techniques.

  17. Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow

    NASA Astrophysics Data System (ADS)

    Blake, D. F.; Morris, R. V.; Kocurek, G.; Morrison, S. M.; Downs, R. T.; Bish, D.; Ming, D. W.; Edgett, K. S.; Rubin, D.; Goetz, W.; Madsen, M. B.; Sullivan, R.; Gellert, R.; Campbell, I.; Treiman, A. H.; McLennan, S. M.; Yen, A. S.; Grotzinger, J.; Vaniman, D. T.; Chipera, S. J.; Achilles, C. N.; Rampe, E. B.; Sumner, D.; Meslin, P.-Y.; Maurice, S.; Forni, O.; Gasnault, O.; Fisk, M.; Schmidt, M.; Mahaffy, P.; Leshin, L. A.; Glavin, D.; Steele, A.; Freissinet, C.; Navarro-González, R.; Yingst, R. A.; Kah, L. C.; Bridges, N.; Lewis, K. W.; Bristow, T. F.; Farmer, J. D.; Crisp, J. A.; Stolper, E. M.; Des Marais, D. J.; Sarrazin, P.; Agard, Christophe; Alves Verdasca, José Alexandre; Anderson, Robert; Anderson, Ryan; Archer, Doug; Armiens-Aparicio, Carlos; Arvidson, Ray; Atlaskin, Evgeny; Atreya, Sushil; Aubrey, Andrew; Baker, Burt; Baker, Michael; Balic-Zunic, Tonci; Baratoux, David; Baroukh, Julien; Barraclough, Bruce; Bean, Keri; Beegle, Luther; Behar, Alberto; Bell, James; Bender, Steve; Benna, Mehdi; Bentz, Jennifer; Berger, Gilles; Berger, Jeff; Berman, Daniel; Blanco Avalos, Juan Jose; Blaney, Diana; Blank, Jen; Blau, Hannah; Bleacher, Lora; Boehm, Eckart; Botta, Oliver; Böttcher, Stephan; Boucher, Thomas; Bower, Hannah; Boyd, Nick; Boynton, Bill; Breves, Elly; Bridges, John; Brinckerhoff, William; Brinza, David; Brunet, Claude; Brunner, Anna; Brunner, Will; Buch, Arnaud; Bullock, Mark; Burmeister, Sönke; Cabane, Michel; Calef, Fred; Cameron, James; Cantor, Bruce; Caplinger, Michael; Rodríguez, Javier Caride; Carmosino, Marco; Blázquez, Isaías Carrasco; Charpentier, Antoine; Choi, David; Clark, Benton; Clegg, Sam; Cleghorn, Timothy; Cloutis, Ed; Cody, George; Coll, Patrice; Conrad, Pamela; Coscia, David; Cousin, Agnès; Cremers, David; Cros, Alain; Cucinotta, Frank; d'Uston, Claude; Davis, Scott; Day, Mackenzie; Juarez, Manuel de la Torre; DeFlores, Lauren; DeLapp, Dorothea; DeMarines, Julia; Dietrich, William; Dingler, Robert; Donny, Christophe; Drake, Darrell; Dromart, Gilles; Dupont, Audrey; Duston, Brian; Dworkin, Jason; Dyar, M. Darby; Edgar, Lauren; Edwards, Christopher; Edwards, Laurence; Ehlmann, Bethany; Ehresmann, Bent; Eigenbrode, Jen; Elliott, Beverley; Elliott, Harvey; Ewing, Ryan; Fabre, Cécile; Fairén, Alberto; Farley, Ken; Fassett, Caleb; Favot, Laurent; Fay, Donald; Fedosov, Fedor; Feldman, Jason; Feldman, Sabrina; Fitzgibbon, Mike; Flesch, Greg; Floyd, Melissa; Flückiger, Lorenzo; Fraeman, Abby; Francis, Raymond; François, Pascaline; Franz, Heather; French, Katherine Louise; Frydenvang, Jens; Gaboriaud, Alain; Gailhanou, Marc; Garvin, James; Geffroy, Claude; Genzer, Maria; Godber, Austin; Goesmann, Fred; Golovin, Dmitry; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Gondet, Brigitte; Gordon, Suzanne; Gorevan, Stephen; Grant, John; Griffes, Jennifer; Grinspoon, David; Guillemot, Philippe; Guo, Jingnan; Gupta, Sanjeev; Guzewich, Scott; Haberle, Robert; Halleaux, Douglas; Hallet, Bernard; Hamilton, Vicky; Hardgrove, Craig; Harker, David; Harpold, Daniel; Harri, Ari-Matti; Harshman, Karl; Hassler, Donald; Haukka, Harri; Hayes, Alex; Herkenhoff, Ken; Herrera, Paul; Hettrich, Sebastian; Heydari, Ezat; Hipkin, Victoria; Hoehler, Tori; Hollingsworth, Jeff; Hudgins, Judy; Huntress, Wesley; Hurowitz, Joel; Hviid, Stubbe; Iagnemma, Karl; Indyk, Steve; Israël, Guy; Jackson, Ryan; Jacob, Samantha; Jakosky, Bruce; Jensen, Elsa; Jensen, Jaqueline Kløvgaard; Johnson, Jeffrey; Johnson, Micah; Johnstone, Steve; Jones, Andrea; Jones, John; Joseph, Jonathan; Jun, Insoo; Kahanpää, Henrik; Kahre, Melinda; Karpushkina, Natalya; Kasprzak, Wayne; Kauhanen, Janne; Keely, Leslie; Kemppinen, Osku; Keymeulen, Didier; Kim, Myung-Hee; Kinch, Kjartan; King, Penny; Kirkland, Laurel; Koefoed, Asmus; Köhler, Jan; Kortmann, Onno; Kozyrev, Alexander; Krezoski, Jill; Krysak, Daniel; Kuzmin, Ruslan; Lacour, Jean Luc; Lafaille, Vivian; Langevin, Yves; Lanza, Nina; Lasue, Jeremie; Le Mouélic, Stéphane; Lee, Ella Mae; Lee, Qiu-Mei; Lees, David; Lefavor, Matthew; Lemmon, Mark; Lepinette Malvitte, Alain; Léveillé, Richard; Lewin-Carpintier, Éric; Li, Shuai; Lipkaman, Leslie; Little, Cynthia; Litvak, Maxim; Lorigny, Eric; Lugmair, Guenter; Lundberg, Angela; Lyness, Eric; Maki, Justin; Malakhov, Alexey; Malespin, Charles; Malin, Michael; Mangold, Nicolas; Manning, Heidi; Marchand, Geneviève; Marín Jiménez, Mercedes; Martín García, César; Martin, Dave; Martin, Mildred; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Mauchien, Patrick; McAdam, Amy; McCartney, Elaina; McConnochie, Timothy; McCullough, Emily; McEwan, Ian; McKay, Christopher; McNair, Sean; Melikechi, Noureddine; Meyer, Michael; Mezzacappa, Alissa; Miller, Hayden; Miller, Kristen; Milliken, Ralph; Minitti, Michelle; Mischna, Michael; Mitrofanov, Igor; Moersch, Jeff; Mokrousov, Maxim; Molina Jurado, Antonio; Moores, John; Mora-Sotomayor, Luis; Morookian, John Michael; Mueller-Mellin, Reinhold; Muller, Jan-Peter; Muñoz Caro, Guillermo; Nachon, Marion; Navarro López, Sara; Nealson, Kenneth; Nefian, Ara; Nelson, Tony; Newcombe, Megan; Newman, Claire; Newsom, Horton; Nikiforov, Sergey; Niles, Paul; Nixon, Brian; Dobrea, Eldar Noe; Nolan, Thomas; Oehler, Dorothy; Ollila, Ann; Olson, Timothy; Owen, Tobias; Pablo, Hernández; Paillet, Alexis; Pallier, Etienne; Palucis, Marisa; Parker, Timothy; Parot, Yann; Patel, Kiran; Paton, Mark; Paulsen, Gale; Pavlov, Alex; Pavri, Betina; Peinado-González, Verónica; Pepin, Robert; Peret, Laurent; Perez, Rene; Perrett, Glynis; Peterson, Joe; Pilorget, Cedric; Pinet, Patrick; Pla-García, Jorge; Plante, Ianik; Poitrasson, Franck; Polkko, Jouni; Popa, Radu; Posiolova, Liliya; Pradler, Irina; Prats, Benito; Prokhorov, Vasily; Purdy, Sharon Wilson; Raaen, Eric; Radziemski, Leon; Rafkin, Scot; Ramos, Miguel; Raulin, François; Ravine, Michael; Reitz, Günther; Rennó, Nilton; Rice, Melissa; Richardson, Mark; Robert, François; Rodriguez Manfredi, José Antonio; Romeral-Planelló, Julio J.; Rowland, Scott; Saccoccio, Muriel; Salamon, Andrew; Sandoval, Jennifer; Sanin, Anton; Sans Fuentes, Sara Alejandra; Saper, Lee; Sautter, Violaine; Savijärvi, Hannu; Schieber, Juergen; Schmidt, Walter; Scholes, Daniel; Schoppers, Marcel; Schröder, Susanne; Sebastian Martinez, Eduardo; Sengstacken, Aaron; Shterts, Ruslan; Siebach, Kirsten; Siili, Tero; Simmonds, Jeff; Sirven, Jean-Baptiste; Slavney, Susie; Sletten, Ronald; Smith, Michael; Sobrón Sánchez, Pablo; Spanovich, Nicole; Spray, John; Squyres, Steven; Stack, Katie; Stalport, Fabien; Stein, Thomas; Stern, Jennifer; Stewart, Noel; Stipp, Susan Louise Svane; Stoiber, Kevin; Sucharski, Bob; Summons, Roger; Sun, Vivian; Supulver, Kimberley; Sutter, Brad; Szopa, Cyril; Tate, Christopher; Teinturier, Samuel; ten Kate, Inge Loes; Thomas, Peter; Thompson, Lucy; Tokar, Robert; Toplis, Mike; Torres Redondo, Josefina; Trainer, Melissa; Tretyakov, Vladislav; Urqui-O'Callaghan, Roser; Van Beek, Jason; Van Beek, Tessa; VanBommel, Scott; Varenikov, Alexey; Vasavada, Ashwin; Vasconcelos, Paulo; Vicenzi, Edward; Vostrukhin, Andrey; Voytek, Mary; Wadhwa, Meenakshi; Ward, Jennifer; Webster, Chris; Weigle, Eddie; Wellington, Danika; Westall, Frances; Wiens, Roger Craig; Wilhelm, Mary Beth; Williams, Amy; Williams, Joshua; Williams, Rebecca; Williams, Richard B.; Wilson, Mike; Wimmer-Schweingruber, Robert; Wolff, Mike; Wong, Mike; Wray, James; Wu, Megan; Yana, Charles; Zeitlin, Cary; Zimdar, Robert; Zorzano Mier, María-Paz

    2013-09-01

    The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at Mars instrument and of the fine-grained nanophase oxide component first described from basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations.

  18. Curiosity at Gale crater, Mars: characterization and analysis of the Rocknest sand shadow.

    PubMed

    Blake, D F; Morris, R V; Kocurek, G; Morrison, S M; Downs, R T; Bish, D; Ming, D W; Edgett, K S; Rubin, D; Goetz, W; Madsen, M B; Sullivan, R; Gellert, R; Campbell, I; Treiman, A H; McLennan, S M; Yen, A S; Grotzinger, J; Vaniman, D T; Chipera, S J; Achilles, C N; Rampe, E B; Sumner, D; Meslin, P-Y; Maurice, S; Forni, O; Gasnault, O; Fisk, M; Schmidt, M; Mahaffy, P; Leshin, L A; Glavin, D; Steele, A; Freissinet, C; Navarro-González, R; Yingst, R A; Kah, L C; Bridges, N; Lewis, K W; Bristow, T F; Farmer, J D; Crisp, J A; Stolper, E M; Des Marais, D J; Sarrazin, P

    2013-09-27

    The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at Mars instrument and of the fine-grained nanophase oxide component first described from basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations. PMID:24072928

  19. Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow

    NASA Technical Reports Server (NTRS)

    Blake, David F.; Morris, Richard V.; Kocurek, G.; Morrison, S. M.; Downs, R. T.; Bish, D.; Ming, D. W.; Edgett, K. S.; Rubin, D.; Goetz, W.; Madsen, M. B.; Sullivan, R.; Gellert, R.; Campbell, I.; Treiman, A. H.; McLennan, S. M.; Yen, A. S.; Grotzinger, J.; Vaniman, D. T.; Chipera, S. J.; Achilles, C. N.; Rampe, E. B.; Sumner, D.; Meslin, P. -Y.; Maurice, S.; Forni, O.; Gasnault, O.; Fisk, M.; Schmidt, M.; Mahaffy, P.; Leshin, L. A.; Glavin, D.; Steele, A.; Freissinet, C.; Navarro-Gonzalez, R.; Yingst, R. A.; Kah, L. C.; Bridges, N.; Lewis, K. W.; Bristow, T. F.; Farmer, J. D.; Crisp, J. A.; Stolper, E. M.; DesMarais, D. J.; Sarrazin, P.

    2013-01-01

    The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MER) Spirit and Opportunity. The fraction of sand <150 micron in size contains approx. 55% crystalline material consistent with a basaltic heritage, and approx. 45% X-ray amorphous material. The amorphous component of Rocknest is Fe-rich and Si-poor, and is the host of the volatiles (H2O, O2, SO2, CO2, and Cl) detected by the Surface Analysis at Mars (SAM) instrument and of the fine-grained nanophase oxide (npOx) component first described from basaltic soils analyzed by MER. The similarity between soils and aeolian materials analyzed at Gusev crater, Meridiani Planum and Gale crater implies locally sourced, globally similar basaltic materials, or globally and regionally sourced basaltic components deposited locally at all three locations.

  20. Rippled scour depressions on the inner continental shelf off central California

    USGS Publications Warehouse

    Cacchione, David A.; Drake, David E.; Grant, William D.; Tate, George B.

    1984-01-01

    Side-scan sonar records taken during the recent Coastal Ocean Dynamics Experiment (CODE) show elongate, shore-normal tippled depressions of low relief on the inner continental shelf off central California between Bodega Bay and Point Arena. These features extend up to 2 kin from the coast into water depths of up to 65 m. The proposed mechanism for their generation is storm- generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine-sand sediment and expose the coarser-sand substrate in the depressions. The zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features. The large straight-crested ripples within the depres- sions (heights to 40 cm; wavelengths to 1.7 m) are probably formed by large-amplitude, long-period surface waves generated by winter storms.

  1. 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

  2. Aeolian dust as a transport hazard

    NASA Astrophysics Data System (ADS)

    Baddock, M. C.; Strong, C. L.; Murray, P. S.; McTainsh, G. H.

    2013-06-01

    The effects of blowing dust on transport operations are often mentioned as one of the significant impacts of aeolian processes on human welfare. However, few studies have been presented to demonstrate this impact. This research examined official air traffic incident reports in Australia for inclusively 1969-2010 to characterise the hazard of blowing dust to aviation in the country, the first such study of its kind. For the 42 year record, 61 incidents were identified (mean 1.4 per annum), with the large majority occurring in the first half of the 1970s. Only 20% of incidents occurred from 1984 onwards. Australian dust activity has not decreased over time, and the reduction in incidents is partly explained by improvements in aviation technology. The centralisation of Air Traffic Control operations to major coastal cities may however have reduced pilot reporting of dust-induced aviation incidents. By type of dust activity, dust storms were associated with nearly half of the reported incidents and dust hazes produced around a quarter. Only 5% of incidents resulted in any physical damage to aircraft and only one case involving personal injury was reported. The majority of the adverse effects on aviation due to dust (nearly 60% of reported incidents) were related to difficulties for navigation and completion of scheduled journey. Since aircraft damage and bodily harm were rare, the impact of dust in Australia is mostly that of inconvenience and associated raised economic costs. From 1990, the temporal pattern of incidents does not show any significant increase despite several intensely dusty years associated with recent droughts. This suggests that Australian aviation safety may be relatively resistant to the adverse effects of atmospheric dust as a hazard.

  3. Rippled beam free electron Laser Amplifier

    SciTech Connect

    Carlsten, Bruce E.

    1998-04-21

    A free electron laser amplifier provides a scalloping annular electron beam that interacts with the axial electric field of a T{sub 0n} mode. A waveguide defines an axial centerline and . A solenoid arranged about the waveguide produces an axial constant magnetic field within the waveguide. An electron beam source outputs a annular electron beam that interacts with the axial magnetic field to have an equilibrium radius and a ripple radius component having a variable radius with a ripple period along the axial centerline. An rf source outputs an axial electric field that propagates within the waveguide coaxial with the electron beam and has a radial mode that interacts at the electron beam at the equilibrium radius component of the electron beam.

  4. Ripples in Rocks Point to Water

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image taken by the Mars Exploration Rover Opportunity's panoramic camera shows the rock nicknamed 'Last Chance,' which lies within the outcrop near the rover's landing site at Meridiani Planum, Mars. The image provides evidence for a geologic feature known as ripple cross-stratification. At the base of the rock, layers can be seen dipping downward to the right. The bedding that contains these dipping layers is only one to two centimeters (0.4 to 0.8 inches) thick. In the upper right corner of the rock, layers also dip to the right, but exhibit a weak 'concave-up' geometry. These two features -- the thin, cross-stratified bedding combined with the possible concave geometry -- suggest small ripples with sinuous crest lines. Although wind can produce ripples, they rarely have sinuous crest lines and never form steep, dipping layers at this small scale. The most probable explanation for these ripples is that they were formed in the presence of moving water.

    Crossbedding Evidence for Underwater Origin Interpretations of cross-lamination patterns presented as clues to this martian rock's origin under flowing water are marked on images taken by the panoramic camera and microscopic imager on NASA's Opportunity.

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1Figure 2

    The red arrows (Figure 1) point to features suggesting cross-lamination within the rock called 'Last Chance' taken at a distance of 4.5 meters (15 feet) during Opportunity's 17th sol (February 10, 2004). The inferred sets of fine layers at angles to each other (cross-laminae) are up to 1.4 centimeters (half an inch) thick. For scale, the distance between two vertical cracks in the rock is about 7 centimeters (2.8 inches). The feature indicated by the middle red arrow suggests a pattern called trough cross-lamination, likely produced when flowing water shaped sinuous ripples in underwater sediment and pushed the ripples to migrate

  5. Rippled beam free electron laser amplifier

    DOEpatents

    Carlsten, Bruce E.

    1999-01-01

    A free electron laser amplifier provides a scalloping annular electron beam that interacts with the axial electric field of a TM.sub.0n mode. A waveguide defines an axial centerline and, a solenoid arranged about the waveguide produces an axial constant magnetic field within the waveguide. An electron beam source outputs a annular electron beam that interacts with the axial magnetic field to have an equilibrium radius and a ripple radius component having a variable radius with a ripple period along the axial centerline. An rf source outputs an axial electric field that propagates within the waveguide coaxial with the electron beam and has a radial mode that interacts at the electron beam at the equilibrium radius component of the electron beam.

  6. Parameterization of intrawave ripple-averaged sediment pickup above steep ripples

    NASA Astrophysics Data System (ADS)

    Amoudry, L. O.; Souza, A. J.; Thorne, P. D.; Liu, P. L.-F.

    2016-01-01

    Near-bed sediment pickup is critical for predictions of intrawave suspension and in turn net sediment transport in coastal models. In the present study, numerical results from a two-dimensional Reynolds-averaged Navier-Stokes model are used to assess the functional relationship of intrawave ripple-averaged sediment pickup above steep ripples. The numerical model provides intrawave time histories of ripple-averaged near-bed velocities and turbulence, which are qualitatively interrogated to determine pickup functional relationships. Several specific sediment pickup formulations are implemented within the numerical model: expressions relating pickup to near-bed velocity or near-bed turbulent kinetic energy via the bed shear stress; and expressions relating pickup to near-bed shear production of turbulent kinetic energy. These are then tested via model-data comparisons of near-bed suspended sediment concentration. The results show that the traditional functions relating sediment pickup to near-bed velocity cannot lead to reasonable intrawave suspension predictions above vortex ripples under a ripple-averaged framework. Instead, relating sediment pickup to near-bed turbulence quantities, such as turbulent kinetic energy or shear production of turbulent kinetic energy, significantly improves the numerical predictions for these conditions.

  7. Reduction of ripple voltage in a dynamitron

    SciTech Connect

    Langsdorf, A. Jr.

    1982-01-01

    We determined that a precise neutralization of the RF ripple voltage on the high-voltage terminal of a Dynamitron has previously been prevented by a nonegligible phase shift of RF currents in the two halves of the approx. 100-kHz class C oscillator tank circuit, which is actually constituted of two slightly unequal high-Q coupled circuits because it has two ground points: the inescapable center-tap-ground in the capacitive legs and a center-tap-ground lead to the induction coil. The latter is needed to prevent damage by flashover transients; equivalent to its removal was the adjusting of RF ground return current to a null by aid of a current transformer on this lead and the suitable adjusting of trimmer capacitance. While the phase shift was thus held to a null, the actual ripple amplitude on the hv terminal was minimized by adjusting additional trimmer capacitances installed in the terminal of the machine. Then p/p 100-kHz ripple at 2-MV dc output was reduced to about 50V and RMS resolution by (p,..gamma..) resonance threshold data near 1 MV was about 250 V. The limit to resolution has various causes including mechanical vibrations and unbalanced harmonics of the RF.

  8. Laboratory Simulations of Martian and Venusian Aeolian Processes

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1999-01-01

    With the flyby of the Neptune system by Voyager, the preliminary exploration of the Solar System was accomplished. Data have been returned for all major planets and satellites except the Pluto system. Results show that the surfaces of terrestrial planets and satellites have been subjected to a wide variety of geological processes. On solid- surface planetary objects having an atmosphere, aeolian processes are important in modifying their surfaces through the redistribution of fine-grained material by the wind. Bedrock may be eroded to produce particles and the particles transported by wind for deposition in other areas. This process operates on Earth today and is evident throughout the geological record. Aeolian processes also occur on Mars, Venus, and possibly Titan and Triton, both of which are outer planet satellites that have atmospheres. Mariner 9 and Viking results show abundant wind-related landforms on Mars, including dune fields and yardangs (wind-eroded hills). On Venus, measurements made by the Soviet Venera and Vega spacecraft and extrapolations from the Pioneer Venus atmospheric probes show that surface winds are capable of transporting particulate materials and suggest that aeolian processes may operate on that planet as well. Magellan radar images of Venus show abundant wind streaks in some areas, as well as dune fields and a zone of possible yardangs. The study of planetary aeolian processes must take into account diverse environments, from the cold, low-density atmosphere of Mars to the extremely hot, high- density Venusian atmosphere. Factors such as threshold wind speeds (minimum wind velocity needed to move particles), rates of erosion and deposition, trajectories of windblown particles, and aeolian flow fields over various landforms are all important aspects of the problem. In addition, study of aeolian terrains on Earth using data analogous to planetary data-collection systems is critical to the interpretation of spacecraft information and

  9. Records of human occupation from Pleistocene river terrace and aeolian sediments in the Arneiro depression (Lower Tejo River, central eastern Portugal)

    NASA Astrophysics Data System (ADS)

    Cunha, Pedro P.; Almeida, Nelson A. C.; Aubry, Thierry; Martins, António A.; Murray, Andrew S.; Buylaert, Jan-Pieter; Sohbati, Reza; Raposo, Luis; Rocha, Leonor

    2012-09-01

    In the uppermost reach of the Lower Tejo River (eastern central Portugal), where the river crosses two quartzite ridges that separate the Ródão (upstream) and Arneiro (downstream) depressions, Palaeolithic artefacts have been recovered from three lower river terrace levels and a cover unit of aeolian sands. This paper presents data on the discovery of archaeological artefacts from the terrace levels and the aeolian sands that can be linked to Middle and Upper Palaeolithic industries from new field sites at Tapada do Montinho and Castelejo. The archaeological data when placed in a geomorphological, sedimentary and chronological framework, contribute new information on the understanding of human occupation in western Iberia during cold-climate episodes of the last 62 to 12 ka; and especially during the cooler and driest conditions that occurred between 32 and 12 ka, when the climate favoured aeolian sediment transport. In the Lower Tejo River, the integration of absolute age datasets with archaeological, geomorphological and sedimentary data indicate that in westernmost Iberia the first appearance of artefacts in river terrace sediments suggests that the earliest marker for human occupation dates from the lower Acheulian (Lower Palaeolithic), probably corresponding to an age of ~ 340 ka. Data also suggest, for the first time, that Acheulian lithic industries were replaced by Middle Palaeolithic ones (namely the Levallois stone knapping technique) by ~ 160 ka (~ MIS6). Middle Palaeolithic industries were later replaced by Upper Palaeolithic industries at 32 ka. The post 32 ka period, dominated by aeolian sediment transport, is related to the onset of cold-dry climate conditions which resulted in low river flow discharges, floodplain exposure and reworking by NW winds. This cold-dry period is coeval with the disappearance of Megafauna and associated Neanderthal communities, and the replacement of the Middle Palaeolithic industries by Upper Palaeolithic ones in this

  10. Luminescence chronology of the inland sand dunes from SE India

    NASA Astrophysics Data System (ADS)

    Reddy, Dontireddy Venkat; Singaraju, Vuddaraju; Mishra, Rakesh; Kumar, Devender; Thomas, Puthusserry Joseph; Rao, Karra Kameshwa; Singhvi, Ashok Kumar

    2013-09-01

    Records of past climate changes have been preserved variously on the earth's surface. Sand dunes are one such prominent imprint, and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases. We report inland sand dunes from Andhra Pradesh (SE India) spread over an area of ~ 500 km2, ~ 75 km inland from the east coast. The dune sands are examined to understand their provenance, transportation, timing of sand aggradation and their relationship to past climates. The dune distribution, grain morphology and the grain-size studies on sands suggest an aeolian origin. Physiography of the study area, heavy mineral assemblage, and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first-order streams emanating from hills in the region and from weathering of the Nellore schist belt. It appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area. OSL dating of 47 dune samples ranged from the present to ~ 50 ka, thereby suggesting a long duration of sand-dune aggradation and/or reworking history.

  11. Ancient wet aeolian environments on Earth: Clues to presence of fossil/live microorganisms on Mars

    USGS Publications Warehouse

    Mahaney, W.C.; Milner, M.W.; Netoff, D.I.; Malloch, D.; Dohm, J.M.; Baker, V.R.; Miyamoto, H.; Hare, T.M.; Komatsu, G.

    2004-01-01

    Ancient wet aeolian (wet-sabkha) environments on Earth, represented in the Entrada and Navajo sandstones of Utah, contain pipe structures considered to be the product of gas/water release under pressure. The sediments originally had considerable porosity allowing the ingress of living plant structures, microorganisms, clay minerals, and fine-grained primary minerals of silt and sand size from the surface downward in the sedimentary column. Host rock material is of a similar size and porosity and presumably the downward migration of fine-grained material would have been possible prior to lithogenesis and final cementation. Recent field emission scanning electron microscopy (FESEM) and EDS (energy-dispersive spectrometry) examination of sands from fluidized pipes in the Early Jurassic Navajo Sandstone reveal the presence of fossil forms resembling fungal filaments, some bearing hyphopodium-like structures similar to those produced by modern tropical leaf parasites. The tropical origin of the fungi is consistent with the paleogeography of the sandstone, which was deposited in a tropical arid environment. These fossil fungi are silicized, with minor amounts of CaCO3 and Fe, and in some cases a Si/Al ratio similar to smectite. They exist as pseudomorphs, totally depleted in nitrogen, adhering to the surfaces of fine-grained sands, principally quartz and orthoclase. Similar wet aeolian paleoenvironments are suspected for Mars, especially following catastrophic sediment-charged floods of enormous magnitudes that are believed to have contributed to rapid formation of large water bodies in the northern plains, ranging from lakes to oceans. These events are suspected to have contributed to a high frequency of constructional landforms (also known as pseudocraters) related to trapped volatiles and water-enriched sediment underneath a thick blanket of materials that were subsequently released to the martian surface, forming piping structures at the near surface and

  12. 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?

  13. Mechanics of aeolian processes: Soil erosion and dust production

    NASA Technical Reports Server (NTRS)

    Mehrabadi, M. M.

    1989-01-01

    Aeolian (wind) processes occur as a result of atmosphere/land-surface system interactions. A thorough understanding of these processes and their physical/mechanical characterization on a global scale is essential to monitoring global change and, hence, is imperative to the fundamental goal of the Earth observing system (Eos) program. Soil erosion and dust production by wind are of consequence mainly in arid and semi arid regions which cover 36 percent of the Earth's land surface. Some recent models of dust production due to wind erosion of agricultural soils and the mechanics of wind erosion in deserts are reviewed and the difficulties of modeling the aeolian transport are discussed.

  14. Industrial sand and gravel

    USGS Publications Warehouse

    Dolley, T.P.

    2011-01-01

    Domestic production of industrial sand and gravel in 2010 was about 26.5 Mt (29.2 million st), a 6-percent increased from 2009. Certain end uses of industrial sand and gravel, such as sand for container glass, golf course sand, recreational sand, specialty glass and water filtration, showed increased demand in 2010.

  15. Present-day aeolian activity in Herschel Crater, Mars

    NASA Astrophysics Data System (ADS)

    Cardinale, Marco; Silvestro, Simone; Vaz, David A.; Michaels, Timothy; Bourke, Mary C.; Komatsu, Goro; Marinangeli, Lucia

    2016-02-01

    In this report, we show evidence for ripple and dune migration in Herschel Crater on Mars. We estimate an average dune migration of 0.8 m and a minimum ripple migration of 1.1 m in a time span of 3.7 Earth-years. These dunes and ripples are mainly shaped by prevailing winds coming from the north, however we also report the presence of secondary winds which elongate the barchans' horns. Such a complex wind scenario is likely caused by the influence of winds blowing off the western crater rim as suggested by the Mars Regional Atmospheric Modeling System (MRAMS), an atmospheric mesoscale model. A multi-directional wind regime at the local scale is also supported by the observed bimodal distribution of the ripple trends. For the first time, a survey integrating the assessment of dune and ripple migration is presented, showing how dune topography can influence the migration patterns of ripples and how underlying topography appears to control the rates of dune migration.

  16. TF ripple loss of alpha particles in TFTR DT experiments

    SciTech Connect

    Redi, M.H.; Budny, R.V.; Darrow, D.S.

    1995-08-01

    Quantitative evaluation of TF ripple loss of DT alpha particles is a central issue for reactor design because of potentially severe first wall heat load problems. DT experiments on TFTR allow experimental measurements to be compared to modeling of the underlying alpha physics, with code validation an important goal. Modeling of TF ripple loss of alphas in TFTR now includes neoclassical calculations of alpha losses arising from first orbit loss, stochastic ripple diffusion, ripple trapping and collisional effects. Recent Hamiltonian coordinate guiding center code (ORBIT) simulations for TFTR have shown that collisions enhance the stochastic TF ripple losses at TFTR. A faster way to simulate experiment has been developed and is discussed here which uses a simple stochastic domain model for TF ripple loss within the TRANSP analysis code.

  17. Sand Diver

    NASA Astrophysics Data System (ADS)

    Scott, Alan J.

    2005-01-01

    A few years ago, I was preparing to teach a summer enrichment program for middle school students at the University of Wisconsin-Stout. With swimming on the minds of most kids during the summer, I thought buoyancy would be a fun topic to discuss. An interesting way to introduce this concept is by discussing the beer-drinking balloonist who, in a lawn chair, floated to 11,000 feet above Los Angeles in 1997. However, I needed a hands-on project and was not about to go purchase some lawn chairs to duplicate this experiment. A simple submersible called the "Sand Diver" was designed and is now used as a hands-on activity for my introductory physics course.

  18. Aeolian sediment transport over gobi: Field studies atop the Mogao Grottoes, China

    NASA Astrophysics Data System (ADS)

    Tan, Lihai; Zhang, Weimin; Qu, Jianjun; Wang, Junzhan; An, Zhishan; Li, Fang

    2016-06-01

    This paper reports on field studies of aeolian sediment transport over a rough surface-gobi atop the Mogao Grottoes, China, in relation to sediment entrainment, saltation mass flux and transport rate prediction. Wind speeds were measured with five cup anemometers at different heights and sediment entrainment and transport measured with horizontal and vertical sediment traps coupled to weighing sensors, where sediment entrainment and transport were measured synchronously with wind speeds. Four sediment transport events, with a measurement duration ranging between 2.5 and 11 h, were studied. The entrainment threshold determined by the horizontal sediment trap varied between 0.28 and 0.33 m s-1, and the effect of non-erodible roughness elements-gravels increased the entrainment threshold approximately by 1.8 times compared to a uniform sand surface. Unlike the non-monotone curve shape of sediment flux density profile over gobi measured in wind tunnels, the flux density profile measured in the field showed an exponential form. Aeolian sediment transport over gobi could be predicted by an Owen-type saltation model: q = Aρ /gu∗ (u∗2 - u∗t2) , where q is sediment transport rate, A is a soil-related dimensionless factor, u∗ is the friction velocity, u∗t is the threshold friction velocity, g is the gravitational acceleration, ρ is the air density. This study indicates that the sediment flux sampling using horizontal and vertical sediment traps coupled to weighing sensors provides a practical method to determine values for A in this model that can provide good estimates of sediment transport rates in gobi areas.

  19. Geochemistry of metalliferous, hydrothermal deposits in the Aeolian arc (Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Savelli, C.; Marani, M.; Gamberi, F.

    1999-03-01

    In shallow-water areas of the submerged volcanic complex around the island of Panarea (Aeolian archipelago), hydrothermal precipitation of both low-temperature Fe-oxyhydroxide-rich red muds and crusts, and high-temperature, sediment-hosted massive sulfides was discovered during an integrated, high-resolution survey. Iron-rich crusts were also found on the bathymetric high of Secca del Capo, north of Salina island. The exhalative iron-rich sediments occur in small (closed) depressions or in proximity to faults and scarps at water depths ranging from 55 to 285 m. The principal chemical characteristics of these deposits are high, but variable, Fe content ranging from 12.2 to 45%, and low contents of the transition elements Mn, Cu, Zn, Ni and Co. The low contents of Cu, Ni and Co suggest a hydrothermal origin. The Fe-oxyhydroxide deposits are enriched in light rare earth element (REE) (35-110×chondrite) compared to heavy REE (10-25×chondrite). Their REE patterns are similar to those of associated calc-alkaline volcanics: negative slope of light REE and a horizontal distribution of the heavy ones. This contrasts with the pattern for iron and manganese oxides of hydrogenous origin, which have tilted trends of heavy REE paralleling that of seawater. The mineralogy of the polymetallic sulfide deposits consists of galena, sphalerite, pyrite and barite in the form of silt-sand grains and decimeter-sized fragments disseminated in clay, 30 cm below the seabed, at a waterdepth of 80 m. The chemistry of the Aeolian iron-rich, low-temperature deposits and of the high-temperature, Ba-rich Pb and Zn sulfides suggests that they are genetically analogous to, respectively, the kuroko-type iron formation (`tetsusekiei') and the black ore exposed in the Miocene Hokuroku district of Japan.

  20. HIGH-ANGLE AEOLIAN CROSSBEDDING AT TRAIL RIDGE, FLORIDA.

    USGS Publications Warehouse

    Force, Eric; Garnar, Tom

    1985-01-01

    This paper described new evidence concerning the origin of the Trail Ridge mineral sands deposit in Florida. Rarely exposed sections of the orebody exhibit structures indicative of sand dune formation rather than coastal beach sand accumulation. The implications for mineral sands exploration, and therefore resources, in the southeastern USA are highlighted.

  1. Torque ripple in a Darrieus, vertical axis wind turbine

    SciTech Connect

    Reuter, R.C. Jr.

    1980-01-01

    Interaction between a steady wind and a rotating, Darrieus, vertical axis wind turbine produces time periodic aerodynamic loads which cause time dependent torque variations, referred to as torque ripple, to occur in the mechanical link between the turbine and the electrical generator. There is concern for the effect of torque ripple upon fatigue life of drive train components and upon power quality. An analytical solution characterizing the phenomenon of torque ripple has been obtained which is based upon a Fourier expansion of the time dependent features of the problem. Numerical results for torque ripple, some experimental data, determination of acceptable levels and methods of controlling it, are presented and discussed.

  2. The effect of masking noise on rippled-spectrum resolution.

    PubMed

    Supin, A Y; Popov, V V; Milekhina, O N; Tarakanov, M B

    2001-01-01

    Ripple-density resolution in a rippled sound spectrum (probe band) under the effect of another band (masker) was studied in normal listeners. The resolvable ripple density in the probe band was measured using a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and valley position (the ripple phase reversal) was detectable. Probe bands were 0.5 octave (oct) wide with center frequencies of 1, 2, and 4 kHz. When a masker band was below the probe one (a low-frequency masker), it markedly reduced the ripple-density resolution. The effect of the low-frequency masker enhanced (ripple-density resolution decreased) with decreasing the stop-band (frequency spacing) between the probe and masker bands. The strongest masker effect was observed at zero spacing between the probe and masker bands. However, when the probe band overlapped the masker one so that no masker power was below the probe band, the masker effect diminished (ripple-density resolution partially released). Increase of the masker bandwidth above 0.5 oct by shifting its lower boundary downwards did not enhance the masker effect. Masker bands above the probe one (high-frequency maskers) did not influence the ripple-density resolution. PMID:11124463

  3. The development of a modified spectral ripple test.

    PubMed

    Aronoff, Justin M; Landsberger, David M

    2013-08-01

    Poor spectral resolution can be a limiting factor for hearing impaired listeners, particularly for complex listening tasks such as speech understanding in noise. Spectral ripple tests are commonly used to measure spectral resolution, but these tests contain a number of potential confounds that can make interpretation of the results difficult. To measure spectral resolution while avoiding those confounds, a modified spectral ripple test with dynamically changing ripples was created, referred to as the spectral-temporally modulated ripple test (SMRT). This paper describes the SMRT and provides evidence that it is sensitive to changes in spectral resolution. PMID:23927228

  4. The molecular dynamics simulation of ion-induced ripple growth

    SciTech Connect

    Suele, P.; Heinig, K.-H.

    2009-11-28

    The wavelength-dependence of ion-sputtering induced growth of repetitive nanostructures, such as ripples has been studied by molecular dynamics (MD) simulations in Si. The early stage of the ion erosion driven development of ripples has been simulated on prepatterned Si stripes with a wavy surface. The time evolution of the height function and amplitude of the sinusoidal surface profile has been followed by simulated ion-sputtering. According to Bradley-Harper (BH) theory, we expect correlation between the wavelength of ripples and the stability of them. However, we find that in the small ripple wavelength ({lambda}) regime BH theory fails to reproduce the results obtained by molecular dynamics. We find that at short wavelengths ({lambda}<35 nm) the adatom yield drops hence no surface diffusion takes place which is sufficient for ripple growth. The MD simulations predict that the growth of ripples with {lambda}>35 nm is stabilized in accordance with the available experimental results. According to the simulations, few hundreds of ion impacts in {lambda} long and few nanometers wide Si ripples are sufficient for reaching saturation in surface growth for for {lambda}>35 nm ripples. In another words, ripples in the long wavelength limit seems to be stable against ion-sputtering. A qualitative comparison of our simulation results with recent experimental data on nanopatterning under irradiation is attempted.

  5. Aeolian desertification from the mid-1970s to 2005 in Otindag Sandy Land, Northern China

    NASA Astrophysics Data System (ADS)

    Liu, Shulin; Wang, Tao

    2007-01-01

    Aeolian desertification in Otindag Sandy Land has expanded dramatically during the past 50 years. This research explored processes and causes of aeolian desertification in the study area. The results showed that aeolian desertification development in Zhenglan Qi of typical region located at the center in the study area can be divided into three stages including rapid occurrence before 1987, parts of rehabilitation and most of deterioration from 1987 to 2000 and little rapid rehabilitation occurrence from 2000 to 2005, according to remote sensing images and field investigations. Gradually declining MI indicated that climate change was not the major cause of aeolian desertification development during the last 40 years, while increasing population should be the underlying cause of local aeolian desertification. Irrational human activities mainly including unsuitable reclamation in the 1960s and lasting over-grazing after 1980 are direct causes contributing to local aeolian desertification, especially over-grazing, while climate change often played a revealer of irrational human activities mainly through drought events. Over-grazing and undesirable climate have different functions during the whole aeolian desertification process. Over-grazing gradually changed grasslands to slight aeolian desertified lands at the initial stage, while climate with windy days or droughts often accelerated formation of serious aeolian desertified lands. Aeolian desertification in the study area both possesses occurrence possibility and great rehabilitative potential. At present, more integrated countermeasures combating local aeolian desertification still are expected.

  6. Optical Properties of Aeolian Dusts Common to West Texas

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Both recent models and historical events such as the Dust Bowl and volcanic eruptions have illustrated aerosols can play a significant role in climate change through direct and indirect optical effects. Soil dust aerosols generated by Aeolian processes represent a significant fraction of the total ...

  7. Agriculture as a source of Aeolian sediment affecting air quality

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aeolian processes on agricultural lands have been examined for the past several decades on nearly every continent and has led to a better understanding of detachment, entrainment, transport, and deposition. Relatively little is known concerning the effect of these processes on air quality. In fact, ...

  8. Laboratory Simulations of Martian and Venusian Aeolian Processes

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1999-01-01

    The objective of this work was to conduct research in the Planetary Aeolian Facility (PAF) at NASA-Ames Research Center as a laboratory for the planetary science community and to carry-out experiments on the physics and geology of particles moved by winds, and for the development of instruments and spacecraft components for planetary missions.

  9. Sand resistance of sunscreens.

    PubMed

    Caswell, Michael; Wood, Caryl; Martinez, Alexa

    2012-01-01

    Like water resistance in sunscreens, sand resistance in sunscreens is the ability of the sunscreen to retain its effectiveness while undergoing sand treatment. The influence of the type of sand on the sand resistance of sunscreens has not been described. The sand resistance of a control standard sunscreen, P2, and data on three grades of Quickrete commercial grade sand, #1961, #1962, and #1152, are described. These sands represent a fine sand, a medium sand, and an all-purpose sand. Using the methodology described in the 2007 proposed amendment of the Final Monograph (1) with one exception, we obtained an SPF of 16.5 (1.6) for the control standard, compared to the expected SPF of 16.3 (3.4). After a five-minute treatment of sand #1961, #1962, or #1151, the SPF of the control standard was 18.3 (1.6), 18.4 (2.0), and 17.5 (2.2), respectively. Thus, all three sands exhibited a similar sand-resistance response. Thus, there was no significant difference in the average SPF with and without sand. The medium grade sand, Quickrete commercial grade #1962, was preferred for sand-resistance testing because the fine sand was difficult to remove from the subject's backs and the coarse sand was unpleasant to the subjects. PMID:23193889

  10. Multiple dust sources in the Sahara Desert: The importance of sand dunes

    NASA Astrophysics Data System (ADS)

    Crouvi, Onn; Schepanski, Kerstin; Amit, Rivka; Gillespie, Alan R.; Enzel, Yehouda

    2012-07-01

    We determine the current sources of dust in the Sahara Desert using quantitative correlation between the number of days with dust storms (NDS), derived from remote-sensing data of high temporal resolution, with the distribution of the soil types and geomorphic units. During 2006-8 the source of over 90% of the NDS was found to be sand dunes, leptosols, calcisols, arenosols, and rock debris. In contrast to previous studies, only few dust storms originated from playas and dry lake beds. Land erodibility was estimated by regressing the NDS to the number of days with high-speed wind events, and was found to be high for sand dunes. Clay and fine-silt grains and aggregates are scarce in sand dunes, which most likely produce dust particles through aeolian abrasion of sand grains. Thus, saltating sand grains impacting clay aggregates on playa surfaces cannot be the sole process for generating dust in the Sahara.

  11. Ripple-Triggered Stimulation of the Locus Coeruleus during Post-Learning Sleep Disrupts Ripple/Spindle Coupling and Impairs Memory Consolidation

    ERIC Educational Resources Information Center

    Novitskaya, Yulia; Sara, Susan J.; Logothetis, Nikos K.; Eschenko, Oxana

    2016-01-01

    Experience-induced replay of neuronal ensembles occurs during hippocampal high-frequency oscillations, or ripples. Post-learning increase in ripple rate is predictive of memory recall, while ripple disruption impairs learning. Ripples may thus present a fundamental component of a neurophysiological mechanism of memory consolidation. In addition to…

  12. Transverse Aeolian Ridges (TARs) on Mars II: Distributions, orientations, and ages

    NASA Astrophysics Data System (ADS)

    Berman, Daniel C.; Balme, Matthew R.; Rafkin, Scot C. R.; Zimbelman, James R.

    2011-05-01

    Transverse Aeolian Ridges (TARs), 10 m scale, ripple-like aeolian bedforms with simple morphology, are widespread on Mars but it is unknown what role they play in Mars' wider sediment cycle. We present the results of a survey of all Mars Global Surveyor Narrow angle images in a pole-to-pole study area, 45° longitude wide. Following on from the classification scheme and preliminary surveys of Balme et al. (Balme, M.R., Berman, D.C., Bourke, M.C., Zimbelman, J.R. [2008a]. Geomorphology 101, 703-720) and Wilson and Zimbelman (Wilson, S.A., Zimbelman, J.R. [2004]. J. Geophys. Res. 109 (E10). doi: 10.1029/2004JE002247) we searched more than 10,000 images, and found that over 2000 reveal at least 5% areal cover by TARs. The mean TAR areal cover in the study area is about 7% (3% in the northern hemisphere and 11% in the southern hemisphere) but TARs are not homogenously distributed - they are concentrated in the mid-low latitudes and almost absent poleward of 35°N and 55°S. We found no clear correlation between TAR distribution and any of thermal inertia, kilometer-scale roughness, or elevation. We did find that TARs are less common at extremes of elevation. We found that TARs are most common near the equator (especially in the vicinity of Meridiani Planum, in which area they have a distinctive "barchan-like" morphology) and in large southern-hemisphere impact craters. TARs in the equatorial band are usually associated with outcrops of layered terrain or steep slopes, hence their relative absence in the northern hemisphere. TARs in the southern hemisphere are most commonly associated with low albedo, intercrater dune fields. We speculate that the mid-latitude mantling terrain (e.g., Mustard, J.F., Cooper, C.D., Rifkin, M.K. [2001]. Nature 412, 411-414; Kreslavsky, M.A., Head, J.W. [2002]. J. Geophys. Res. 29 (15). doi: 10.1029/2002GL015392) could also play a role in covering TARs or inhibiting saltation. We compared TAR distribution with general circulation model (GCM

  13. Mineralogical and sedimentological study of gypsiferous sands from the Saharian Desert

    NASA Astrophysics Data System (ADS)

    Somma, Roberta; Bella, Francesca

    2016-04-01

    A mineralogical and sedimentological study was carried out in Quaternary aeolian sands from the Sahara Desert (Tunisia and Libya). Gypsum resulted to be the dominant mineral (65%), whereas quartz resulted to be in significant amount (25%) in all samples. Aragonite and calcite, related to marine organisms, was found especially in the Libyan sands. Gypsum grains appear in euhedral crystals or as polycrystalline twinned crystals. Crystal habitus is pseudo-octahedric or tabular. Due to the euhedral habitus, the forms of the grains is discoid or bladed but with a low roundness. Quartz grains are mostly ialin or orange as the grain surfaces are coated with thin hematite films. Quartz grains dominantly appear as subhedral crystals. Habitus is prismatic or hexagonal. Due to the subhedral habitus, quartz grain forms can be classified as bladed with a low roundness. A minor amount of quartz grains is formed by well rounded and spherical grains showing frosted and pitted surfaces. The particle size analysis indicated that the studied sediments consist of well sorted very fine sands. The studied Quaternary aeolian sands can be classified as gypsiferous sands. Notwithstanding sands are well sorted, they are immature under a mineralogical and textural point of view. Particularly, gypsum formed in present or past sabkha and the amount of marine bioclasts should suggest that the source area of the Lybian gypsum grains could be a sabkha near the sea.

  14. Rippled-beam free-electron laser

    SciTech Connect

    Carlsten, B.E.

    1997-10-01

    The authors describe a new microwave generation mechanism involving a scalloping annular electron beam. The beam interacts with the axial electric field of a TM{sub 0n} mode in a smooth circular waveguide through the axial free-electron laser interaction, in which the beam ripple period is synchronous with the phase slippage of the rf mode relative to the electron beam. Due to nonlinearities in the orbit equation, the interaction can be made autoresonant, where the phase and amplitude of the gain is independent of the beam energy.

  15. 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.

  16. Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple

    NASA Astrophysics Data System (ADS)

    Squyres, S. W.; Arvidson, R. E.; Bollen, D.; Bell, J. F.; Brückner, J.; Cabrol, N. A.; Calvin, W. M.; Carr, M. H.; Christensen, P. R.; Clark, B. C.; Crumpler, L.; Des Marais, D. J.; d'Uston, C.; Economou, T.; Farmer, J.; Farrand, W. H.; Folkner, W.; Gellert, R.; Glotch, T. D.; Golombek, M.; Gorevan, S.; Grant, J. A.; Greeley, R.; Grotzinger, J.; Herkenhoff, K. E.; Hviid, S.; Johnson, J. R.; Klingelhöfer, G.; Knoll, A. H.; Landis, G.; Lemmon, M.; Li, R.; Madsen, M. B.; Malin, M. C.; McLennan, S. M.; McSween, H. Y.; Ming, D. W.; Moersch, J.; Morris, R. V.; Parker, T.; Rice, J. W.; Richter, L.; Rieder, R.; Schröder, C.; Sims, M.; Smith, M.; Smith, P.; Soderblom, L. A.; Sullivan, R.; Tosca, N. J.; Wänke, H.; Wdowiak, T.; Wolff, M.; Yen, A.

    2006-12-01

    The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop-scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine-grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg-sulfates and also include Ca-sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite-rich concretions known as ``blueberries.'' The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind-transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life.

  17. Wind regime and sand transport in China's Badain Jaran Desert

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengcai; Dong, Zhibao; Li, Chunxiao

    2015-06-01

    Wind controls the formation and development of aeolian dunes, therefore understanding the wind environment is necessary in aeolian dune research. In recent years, climate has changed in and around the Badain Jaran Desert, and the factors that control aeolian dune development have changed with it. In this paper, we analyzed characteristics of the desert's wind regime based on data from seven weather stations in and around the desert. The temporal and spatial variation in the wind regime's characteristics have different effects on dune formation and development. The annual mean wind velocity, maximum wind velocity, and the proportion of the time the wind exceeded the sand-entrainment threshold are largest at the northern margin of the desert, and these values decrease from north to south and from east to west. The dominant winds are from the northwest, northeast, and southwest. The drift potential (DP) in the desert decreases from north to south, and can be divided into three regions: high in the north, intermediate in the central region, and low in the south. The effects of climate change on the calculated DP will be complex; although DP increased with increasing mean wind velocity and temperature, there was little or no relationship with precipitation and relative humidity.

  18. 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

  19. Influence of current ripple on the tungsten cathode erosion

    NASA Astrophysics Data System (ADS)

    Mitrofanov, N. K.; Zabello, K. K.; Nemchinsky, V. A.; Shkol'nik, S. M.

    2016-04-01

    The erosion of a thermionic tungsten cathode is studied. Arc burning conditions under which gas-vapor erosion causes cathode mass losses are determined. It is shown that erosion does not depend on the current ripple amplitude and is roughly equal to 2 ng/C. In experiments, the current ripple amplitude ranges from ±1% to ±50%.

  20. No-scale ripple inflation revisited

    SciTech Connect

    Li, Tianjun; Li, Zhijin; Nanopoulos, Dimitri V. E-mail: lizhijin@physics.tamu.edu

    2014-04-01

    We revisit the no-scale ripple inflation model, where no-scale supergravity is modified by an additional term for the inflaton field in the Kähler potential. This term not only breaks one SU(N,1) symmetry explicitly, but also plays an important role for inflation. We generalize the superpotential in the no-scale ripple inflation model slightly. There exists a discrete Z{sub 2} symmetry/parity in the scalar potential in general, which can be preserved or violated by the non-canonical nomalized inflaton kinetic term. Thus, there are three inflation paths: one parity invariant path, and the left and right paths for parity violating scenario. We show that the inflations along the parity invariant path and right path are consistent with the Planck results. However, the gavitino mass for the parity invariant path is so large that the inflation results will be invalid if we consider the inflaton supersymmetry breaking soft mass term. Thus, only the inflation along the right path gives the correct and consistent results. Notably, the tensor-to-scalar ratio in such case can be large, with a value around 0.05, which may be probed by the future Planck experiment.

  1. Spectral resolvability of iterated rippled noise

    NASA Astrophysics Data System (ADS)

    Yost, William A.

    2005-04-01

    A forward-masking experiment was used to estimate the spectral ripple of iterated rippled noise (IRN) that is possibly resolved by the auditory system. Tonal signals were placed at spectral peaks and valleys of IRN maskers for a wide variety of IRN conditions that included different delays, number of iterations, and stimulus durations. The differences in the forward-masked thresholds of tones at spectral peaks and valleys were used to estimate spectral resolvability, and these results were compared to estimates obtained from a gamma-tone filter bank. The IRN spectrum has spectral peaks that are harmonics of the reciprocal of the delay used to generate IRN stimuli. As the number of iterations in the generation of IRN stimuli increases so does the difference in the spectral peak-to-valley ratio. For high number of iterations, long delays, and long durations evidence for spectral resolvability existed up to the 6th harmonic. For all other conditions spectral resolvability appeared to disappear at harmonics lower than the 6th, or was not measurable at all. These data will be discussed in terms of the role spectral resolvability might play in processing the pitch, pitch strength, and timbre of IRN stimuli. [Work supported by a grant from NIDCD.

  2. Rippling Instability of a Collapsing Bubble

    NASA Technical Reports Server (NTRS)

    daSilveira, Rava; Chaieb, Sahraoui; Mahadevan, L.

    1999-01-01

    The rippling instability of a liquid sheet was first observed by Debregeas, de Gennes, an Brochard-Wyart [Science 279, 1704 (1998)] on a hemispherical bubble resting on a free surface. Unlike a soap bubble, it collapses under its own weight while bursting, and folds into a wavy structure which breaks the original axisymmetry. In fact, this effect occurs for both purely elastic and purely viscous (liquid) sheets, and an analogy can be made between the two mechanisms. We present a theory for the onset of the instability in both cases, in which the growth of the corrugation out of an inextensible initial condition is governed by the competition between gravitational and bending (shearing) forces. The instability occurs for a range of densities, stiffnesses (viscosities), and sizes, a result which arises less from dynamics than from geometry, suggesting a wide validity. We further obtain a quantitative expression for the number of ripples. Finally, we present the results of experiments, which are consistent with our predictions.

  3. Wavelength selection of rippling patterns in myxobacteria.

    PubMed

    Bonilla, L L; Glavan, A; Marquina, A

    2016-01-01

    Rippling patterns of myxobacteria appear in starving colonies before they aggregate to form fruiting bodies. These periodic traveling cell density waves arise from the coordination of individual cell reversals, resulting from an internal clock regulating them and from contact signaling during bacterial collisions. Here we revisit a mathematical model of rippling in myxobacteria due to Igoshin et al. [Proc. Natl. Acad. Sci. USA 98, 14913 (2001)PNASA60027-842410.1073/pnas.221579598 and Phys. Rev. E 70, 041911 (2004)PLEEE81539-375510.1103/PhysRevE.70.041911]. Bacteria in this model are phase oscillators with an extra internal phase through which they are coupled to a mean field of oppositely moving bacteria. Previously, patterns for this model were obtained only by numerical methods, and it was not possible to find their wave number analytically. We derive an evolution equation for the reversal point density that selects the pattern wave number in the weak signaling limit, shows the validity of the selection rule by solving numerically the model equations, and describes other stable patterns in the strong signaling limit. The nonlocal mean-field coupling tends to decohere and confine patterns. Under appropriate circumstances, it can annihilate the patterns leaving a constant density state via a nonequilibrium phase transition reminiscent of destruction of synchronization in the Kuramoto model. PMID:26871106

  4. Wavelength selection of rippling patterns in myxobacteria

    NASA Astrophysics Data System (ADS)

    Bonilla, L. L.; Glavan, A.; Marquina, A.

    2016-01-01

    Rippling patterns of myxobacteria appear in starving colonies before they aggregate to form fruiting bodies. These periodic traveling cell density waves arise from the coordination of individual cell reversals, resulting from an internal clock regulating them and from contact signaling during bacterial collisions. Here we revisit a mathematical model of rippling in myxobacteria due to Igoshin et al. [Proc. Natl. Acad. Sci. USA 98, 14913 (2001), 10.1073/pnas.221579598 and Phys. Rev. E 70, 041911 (2004), 10.1103/PhysRevE.70.041911]. Bacteria in this model are phase oscillators with an extra internal phase through which they are coupled to a mean field of oppositely moving bacteria. Previously, patterns for this model were obtained only by numerical methods, and it was not possible to find their wave number analytically. We derive an evolution equation for the reversal point density that selects the pattern wave number in the weak signaling limit, shows the validity of the selection rule by solving numerically the model equations, and describes other stable patterns in the strong signaling limit. The nonlocal mean-field coupling tends to decohere and confine patterns. Under appropriate circumstances, it can annihilate the patterns leaving a constant density state via a nonequilibrium phase transition reminiscent of destruction of synchronization in the Kuramoto model.

  5. Industrial sand and gravel

    USGS Publications Warehouse

    Dolley, T.P.

    2012-01-01

    Domestic production of industrial sand and gravel in 2011 was about 30 Mt (33 million st), increasing slightly compared with 2010. Some important end uses for industrial sand and gravel include abrasives, filtration, foundry, glassmaking, hydraulic fracturing sand (frac sand) and silicon metal applications.

  6. Industrial sand and gravel

    USGS Publications Warehouse

    Dolley, T.P.

    2013-01-01

    Domestic production of industrial sand and gravel in 2012 was about 49.5 Mt (55 million st), increasing 13 percent compared with that of 2011. Some important end uses for industrial sand and gravel include abrasives, filtration, foundry, glassmaking, hydraulic fracturing sand (frac sand) and silicon metal applications.

  7. Angular tuning of the magnetic birefringence in rippled cobalt films

    SciTech Connect

    Arranz, Miguel A.; Colino, José M.

    2015-06-22

    We report the measurement of magnetically induced birefringence in rippled Co films. For this purpose, the magneto-optical properties of ion beam eroded ferromagnetic films were studied using Kerr magnetometry and magnetic birefringence in the transmitted light intensity. Upon sufficient ion sculpting, these ripple surface nanostructures developed a defined uniaxial anisotropy in the in-plane magnetization, finely tuning the magnetic birefringence effect. We have studied its dependence on the relative orientation between the ripple direction and the magnetic field, and found this effect to be dramatically correlated with the capability to neatly distinguish the mechanisms for the in-plane magnetization reversal, i.e., rotation and nucleation. This double refraction corresponds univocally to the two magnetization axes, parallel and perpendicular to the ripples direction. We have also observed that tuned birefringence in stack assemblies of rippled Co films, which enables us to technically manipulate the number and direction of refraction axes.

  8. Ripples in a string coupled to Glauber spins

    NASA Astrophysics Data System (ADS)

    Bonilla, L. L.; Carpio, A.; Prados, A.; Rosales, R. R.

    2012-03-01

    Each oscillator in a linear chain (a string) interacts with a local Ising spin in contact with a thermal bath. These spins evolve according to Glauber dynamics. Below a critical temperature, there appears an equilibrium, time-independent, rippled state in the string that is accompanied by a nonzero spin polarization. On the other hand, the system is shown to form “metastable,” nonequilibrium long-lived ripples in the string for slow spin relaxation. The system vibrates rapidly about these quasistationary states, which can be described as snapshots of a coarse-grained stroboscopic map. For moderate observation times, ripples are observed irrespective of the final thermodynamically stable state (rippled or not). Interestingly, the system can be considered as a “minimal” model to understand rippling in clamped graphene sheets.

  9. Pyramidal Cell-Interneuron Interactions Underlie Hippocampal Ripple Oscillations

    PubMed Central

    Stark, Eran; Roux, Lisa; Eichler, Ronny; Senzai, Yuta; Royer, Sebastien; Buzsáki, György

    2015-01-01

    SUMMARY High-frequency ripple oscillations, observed most prominently in the hippocampal CA1 pyramidal layer, are associated with memory consolidation. The cellular and network mechanisms underlying the generation, frequency control, and spatial coherence of the rhythm are poorly understood. Using multisite optogenetic manipulations in freely behaving rodents, we found that depolarization of a small group of nearby pyramidal cells was sufficient to induce high-frequency oscillations, whereas closed-loop silencing of pyramidal cells or activation of parvalbumin-(PV) or somatostatin-immunoreactive interneurons aborted spontaneously occurring ripples. Focal pharmacological blockade of GABAA receptors abolished ripples. Localized PV inter-neuron activation paced ensemble spiking, and simultaneous induction of high-frequency oscillations at multiple locations resulted in a temporally coherent pattern mediated by phase-locked inter-neuron spiking. These results constrain competing models of ripple generation and indicate that temporally precise local interactions between excitatory and inhibitory neurons support ripple generation in the intact hippocampus. PMID:25033186

  10. Cooperative phenomenon in a rippled graphene: Chiral spin guide

    NASA Astrophysics Data System (ADS)

    Pudlak, M.; Pichugin, K. N.; Nazmitdinov, R. G.

    2015-11-01

    We analyze spin scattering in ballistic transport of electrons through a ripple at a normal incidence of an electron flow. The model of a ripple consists of a curved graphene surface in the form of an arc of a circle connected from the left-hand and right-hand sides to two flat graphene sheets. At certain conditions the curvature-induced spin-orbit coupling creates a transparent window for incoming electrons with one spin polarization simultaneously with a backscattering of those with opposite polarization. This window is equally likely transparent for electrons with spin up and spin down that move in opposite directions. The spin-filtering effect that is small in one ripple becomes prominent with the increase of N consequently connected ripples that create a graphene sheet of the sinusoidal type. We present the analytical expressions for spin-up and spin-down transmission probabilities as a function of N connected ripples.

  11. Angular tuning of the magnetic birefringence in rippled cobalt films

    NASA Astrophysics Data System (ADS)

    Arranz, Miguel A.; Colino, José M.

    2015-06-01

    We report the measurement of magnetically induced birefringence in rippled Co films. For this purpose, the magneto-optical properties of ion beam eroded ferromagnetic films were studied using Kerr magnetometry and magnetic birefringence in the transmitted light intensity. Upon sufficient ion sculpting, these ripple surface nanostructures developed a defined uniaxial anisotropy in the in-plane magnetization, finely tuning the magnetic birefringence effect. We have studied its dependence on the relative orientation between the ripple direction and the magnetic field, and found this effect to be dramatically correlated with the capability to neatly distinguish the mechanisms for the in-plane magnetization reversal, i.e., rotation and nucleation. This double refraction corresponds univocally to the two magnetization axes, parallel and perpendicular to the ripples direction. We have also observed that tuned birefringence in stack assemblies of rippled Co films, which enables us to technically manipulate the number and direction of refraction axes.

  12. Towards a phoenix phase in aeolian research: shifting geophysical perspectives from fluvial dominance

    SciTech Connect

    Whicker, Jeffrey J; Field, Jason P; Breshears, David D

    2008-01-01

    Aeolian processes are a fundamental driver of earth surface dynamics, yet the importance of aeolian processes in a broader geosciences context may be overshadowed by an unbalanced emphasis on fluvial processes. Here we wish to highlight that aeolian and fluvial processes need to be considered in concert relative to total erosion and to potential interactions, that relative dominance and sensitivity to disturbance vary with mean annual precipitation, and that there are important scale-dependencies associated with aeolian-fluvial interactions. We build on previous literature to present relevant conceptual syntheses highlighting these issues. We then highlight the relative investments that have been made in aeolian research on dust emission and management relative to that in fluvial research on sediment production. Literature searches highlight that aeolian processes are greatly understudied relative to fluvial processes when considering total erosion in different environmental settings. Notably, within the USA, aeolian research was triggered by the Dust Bowl catastrophe of the 1930s, but the resultant research agencies have shifted to almost completely focusing on fluvial processes, based on number of remaining research stations and on monetary investments in control measures. However, numerous research issues associated with intensification of land use and climate change impacts require a rapid ramping up in aeolian research that improves information about aeolian processes relative to fluvial processes, which could herald a post-Dust Bowl Phoenix phase in which aeolian processes are recognized as broadly critical to geo- and environmental sciences.

  13. Aeolian Coastal Landscapes in changes (a study from Tahkuna, Estonia)

    NASA Astrophysics Data System (ADS)

    Anderson, A.

    2012-04-01

    The openness of the coast to the winds and storm waves has an important part in changing aeolian coastal landscapes as well as anthropogenic factor. The aeolian coastal landscapes are probably the most dynamic areas. Occurrence of aeolian coastal landscapes in Estonia is limited. They consist of sandy beaches, sandy beach ridges and dunes. The coastal ecosystems are strongly affected by their topography, based on the character of deposits and moisture conditions. The majority of their ecosystems are quite close to the specific natural habitat. These ecosystems are represented in the list of the European Union Habitats (Natura 2000). In recent decades human influence has changed the landscape over time in different activities (recreation, trampling, off-road driving) and their intensities, which has led to destruction or degradation of various habitats. Previously coastal landscapes were used for forestry and pasture. Nowadays one of the most serious threats to open landscape is afforestation. This study examines the relationships between landscape components during last decades. Trying to find out how much aeolian coastal landscapes are influenced by natural processes or human activities. The results are based on cartographic analysis, fieldwork data. The method of landscape complex profile was used. The profiles show a cross-sections of landforms and interrelationships between landscape components, most frequently describing the relations between soils and vegetation. In each sample point the mechanical composition of sediments, vegetation cover and soil is determined. Results show that changes in landscapes are induced by their own development as well as changes in environmental factors and human activities. Larger changes are due to increase of coastal processes activity. These processes can be observed in sandy beaches, which are easily transformed by waves. Higher sea levels during storm surges are reaching older beach formation, causing erosion and creating

  14. Wet sand flows better than dry sand

    NASA Astrophysics Data System (ADS)

    Wagner, Christian

    2015-03-01

    Wet sand that does not contain too much water is known to be stiff enough to build sand castles or in physical words has a significant yield stress. However, we could recently show that there are quite a few conditions under which such wet sand opposes less resistant to flow than its dry counterpart. This effect might have been already known to the old Egyptians: The Ancient painting of El Bersheh at the tomb of Tehutihetep shows that there was liquid poured in front of the sledge that was used to transport heavy weight stones and statues. While archeologist have attributed this to a sacral ceremony, our data clearly show that wetting the sand ground drastically decreases the effective sliding friction coefficient. We first study the stress-strain behavior of sand with and without small amounts of liquid under steady and oscillatory shear. Using a technique to quasistatically push the sand through a tube with an enforced parabolic (Poiseuille-like) profile, we minimize the effect of avalanches and shear localization. We observe that the resistance against deformation of the wet (partially saturated) sand is much smaller than that of the dry sand, and that the latter dissipates more energy under flow. Second we show experimentally that the sliding friction on sand is greatly reduced by the addition of some--but not too much--water. The formation of capillary water bridges increases the shear modulus of the sand, which facilitates the sliding.

  15. Sand Bed Morphodynamics under Standing Waves and Vegetated Conditions

    NASA Astrophysics Data System (ADS)

    Landry, B. J.; Garcia, M. H.

    2010-12-01

    Littoral processes such as sediment transport, wave attenuation, and boundary layer development are governed by the presence of bathymetric features, which include large-scale sand bars upon which smaller-scale sand ripples are superimposed, as well as the presence of submarine vegetation. Numerous studies on sand ripples and bars have aided to elucidate the dynamics in oscillatory flows; however, the effect of vegetation on the system is less understood. Recent laboratory studies have focused on quantifying wave attenuation by emergent vegetation as a natural method to mitigate storm surges. The emergent vegetation, while promising for coastal protection, alters sediment transport rates directly by the physical presence of the plants near the bed and indirectly from reduction in near-bed shear stresses due to attenuated wave energy. The experimental work herein focuses on the area near the deeply submerged vegetated canopy limit (current work has a ratio of mean still water depth to plant height, H/h, = 7.9) to minimize the effect on the surface waves and discern the direct impact vegetation has on sand bed morphodynamics. Experiments were conducted in the large wave tank (49-m long by 1.83-m wide by 1.22-m deep) in the Ven Te Chow Hydrosystems Laboratory at the University of Illinois in which a high reflection wave forcing was used over a uniform sand bed with a 0.25-mm median sediment diameter in which staggered and uniform arrangements of idealized vegetation (i.e., 6.35-mm diameter rigid wooden cylinders) were positioned along the bed (e.g., at predetermined sand bar troughs and over an entire sand bar). The resulting bathymetric evolution from the vegetated case experiments were compared to the base case of no vegetation using two optical methods: a high-resolution laser displacement sensor for three-dimensional surveys and digitized profiles via high-definition panoramic images of the entire test section. The experimental findings illustrate the profound

  16. 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.

  17. Soil Response to Aeolian Disturbance in West Greenland

    NASA Astrophysics Data System (ADS)

    Heindel, R. C.; Culler, L. E.; Chipman, J. W.; Virginia, R. A.

    2015-12-01

    Arctic soils are a critical ecological resource, yet are increasingly vulnerable to global change. In the Kangerlussuaq region of West Greenland, aeolian disturbance is the greatest threat to soil stability, with strong katabatic winds eroding vegetation and soil down to the underlying glacial till or bedrock. Little is known about what controls the distribution and rate of the aeolian erosion, which initially results in a state change from tundra to a deflated and nearly unvegetated ground. It is unclear if vegetation can eventually reestablish after erosion occurs, potentially aided by the biological soil crust (BSC) that develops within the eroded areas, or if this soil loss is an irreversible change in vegetation and soil carbon (C) and nitrogen (N) cycling. Our analysis of high-resolution satellite imagery shows that across the entire study region, deflated ground covers 22% of the terrestrial landscape. Aeolian erosion occurs more frequently closer to the Greenland Ice Sheet and on S-facing slopes. Using lichenometry, we estimate that erosional fronts move across the landscape at rates of 2.5 cm yr-1, leaving unproductive ground in their wake. The onset of widespread aeolian erosion occurred roughly 700-1000 years ago, pointing toward regional cooling and aridity as the drivers behind erosion. Finally, we consider whether the BSCs can improve soil quality enough to allow for full vegetation regrowth. Preliminary results show that while the BSCs fix atmospheric N and increase C storage, the rate of soil quality recovery is extremely slow. Understanding the thresholds between vegetated tundra and eroded ground is critical for predicting how the Kangerlussuaq landscape will respond to anticipated changes in climate and ice sheet dynamics.

  18. Strategy of restraining ripple error on surface for optical fabrication.

    PubMed

    Wang, Tan; Cheng, Haobo; Feng, Yunpeng; Tam, Honyuen

    2014-09-10

    The influence from the ripple error to the high imaging quality is effectively reduced by restraining the ripple height. A method based on the process parameters and the surface error distribution is designed to suppress the ripple height in this paper. The generating mechanism of the ripple error is analyzed by polishing theory with uniform removal character. The relation between the processing parameters (removal functions, pitch of path, and dwell time) and the ripple error is discussed through simulations. With these, the strategy for diminishing the error is presented. A final process is designed and demonstrated on K9 work-pieces using the optimizing strategy with magnetorheological jet polishing. The form error on the surface is decreased from 0.216λ PV (λ=632.8  nm) and 0.039λ RMS to 0.03λ PV and 0.004λ RMS. And the ripple error is restrained well at the same time, because the ripple height is less than 6 nm on the final surface. Results indicate that these strategies are suitable for high-precision optical manufacturing. PMID:25321688

  19. Seasonal and directional variations of aeolian sediment transport on the coarse-grained zibar surface of the Kumtagh Desert, NW China

    NASA Astrophysics Data System (ADS)

    Qian, Guangqiang; Yang, Zhuanling; Dong, Zhibao; Luo, Wanyin; Zhang, Zhengcai; Lu, Junfeng

    2016-04-01

    The aeolian process over fine to medium sand beds has been thoroughly discussed based on short-term, in-situ observations and wind tunnel tests. However, little is known about the long period variation of aeolian sediment transport as well as the geomorphological significance of saltating process, in particular, on the coarse-grained surface. By means of a segmented, eight-directional sand trap (SEDST) designed by the authors, the aeolian sediment transport on zibar surface was measured in the Kumtagh Desert of NW China. The SEDST has eight sub-traps faced to eight directions, each sub-trap contains a vertical array of samplers with four openings at 0 - 0.1 m, 0.1 - 0.2 m, 0.2 - 0.4 m and 0.4 - 1.0 m, respectively. Each opening is connected with an underground sand chamber. During the 1-yr field observation since May 2014, sediments were collected for six times with an interval of 1 to 3 months depending on the wind strength. The total weight of the captured sediments is 314.76 kg and most of them (54%) were transported within 0.1 m above the ground. The sediment transport rate ranges from 0.43 to 64.47 g/m.min for the six runs, the maximum transport rate occurred during the period of Aug to Oct 2014 with sediments from the north direction. The annual mean transport rate changes between 11.81 and 28.49 g/m.min and the sediments are mainly blown from the N, NE and NW directions. The resultant sediment transport direction (net transport) is SSE (172.92°), which implies the major sediment source direction. The sediment flux profiles can be fitted with the exponential decay function for six runs and all directions. Three groups can be identified from the gradients of the fitting curves, i.e. the N, NE and NW cluster, the S and SE cluster, as well as the E, SE and W cluster. Each cluster represents a particular combination of sediment source features and geomorphological settings that may significantly affect the formation process of zibars. The sediment transport

  20. RIPPLE - A new model for incompressible flows with free surfaces

    NASA Technical Reports Server (NTRS)

    Kothe, D. B.; Mjolsness, R. C.

    1991-01-01

    A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the continuum surface force model which represents surface tension as a (strongly) localized volume force. Other features include a higher-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE's unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods.

  1. Methods of torque ripple reduction for flux reversal motor

    NASA Astrophysics Data System (ADS)

    Vakil, Gaurang; Sheth, N. K.; Miller, David

    2009-04-01

    This paper presents two-dimensional finite element based results for various methods of torque ripple reduction in flux-reversal motors. The effects of variation in magnet and rotor pole heights, rotor pole skewing, and multiple teeth per rotor pole on the cogging torque, developed torque, torque ripple, and phase inductance and also an optimum value of the magnet and rotor pole heights, skew angle, and choice of teeth per rotor pole with the teeth depth resulting in torque ripple reduction are presented.

  2. Atmospheric significance of aeolian salts in the sandy deserts of northwestern China

    NASA Astrophysics Data System (ADS)

    Zhu, B.-Q.

    2015-12-01

    Large sandy deserts in the middle latitudes of northwestern China were investigated for soluble salt variations in modern and ancient aeolian sediments, aiming to explore the environmental significance of "aeolian salts". Results revealed that aeolian salt variations have a clear relationship with the changing meridional and zonal gradients of the desert locations and the aeolian differentiation effect, but are weakly linked to local geological conditions. It suggests that the natural system of aeolian salts is hydrologically open and the chemistry of the parent brines are different from that predicted for hydrologically closed systems. Atmospheric depositions of water-soluble chemical species are an important process/source contributing to aeolian salt. Sequential variations of soluble salts in sedimentary profiles interbedded with aeolian and non-aeolian deposits and their palaeoenvironmental implications in the hinterland areas of these deserts were further evaluated, based on the constraints of OSL dating and radiocarbon dating data. The results indicate that the inorganic salts may be a latent geoproxy in revealing regional palaeoclimatic changes in desert areas for the sediments deposited under onefold depositional environment, but the interpretation should be more careful for the sediments deposited under diverse depositional conditions. This study presents the evidence of atmospheric origin of aeolian salt in sandy deserts, with limited climatic significance in palaeoenvironmental reconstruction.

  3. Numerical modeling of subaqueous sand dune morphodynamics

    NASA Astrophysics Data System (ADS)

    Doré, Arnaud; Bonneton, Philippe; Marieu, Vincent; Garlan, Thierry

    2016-03-01

    The morphodynamic evolution of subaqueous sand dunes is investigated, using a 2-D Reynolds-averaged Navier-Stokes numerical model. A laboratory experiment where dunes are generated under stationary unidirectional flow conditions is used as a reference case. The model reproduces the evolution of the erodible bed until a state of equilibrium is reached. In particular, the simulation exhibits the different stages of the bed evolution, e.g., the incipient ripple generation, the nonlinear bed form growing phase, and the dune field equilibrium phase. The results show good agreement in terms of dune geometrical dimensions and time to equilibrium. After the emergence of the first ripple field, the bed growth is driven by cascading merging sequences between bed forms of different heights. A sequence extracted from the simulation shows how the downstream bed form is first eroded before merging with the upstream bed form. Superimposed bed forms emerge on the dune stoss sides during the simulation. An analysis of the results shows that they emerge downstream of a slight deflection on the dune profile. The deflection arises due to a modification of the sediment flux gradient consecutive to a reduction in the turbulence relaxation length while the upstream bed form height decreases. As they migrate, superimposed bed forms grow on the dune stoss side and eventually provoke the degeneration of the dune crest. Cascading merging sequences and superimposed bed forms dynamics both influence the dune field evolution and size and therefore play a fundamental role in the dune field self-organization process.

  4. '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.

  5. Difference in the wind speeds required for initiation versus continuation of sand transport on mars: implications for dunes and dust storms.

    PubMed

    Kok, Jasper F

    2010-02-19

    Much of the surface of Mars is covered by dunes, ripples, and other features formed by the blowing of sand by wind, known as saltation. In addition, saltation loads the atmosphere with dust aerosols, which dominate the Martian climate. We show here that saltation can be maintained on Mars by wind speeds an order of magnitude less than required to initiate it. We further show that this hysteresis effect causes saltation to occur for much lower wind speeds than previously thought. These findings have important implications for the formation of dust storms, sand dunes, and ripples on Mars. PMID:20366891

  6. Holocene aeolian sedimentation and episodic mass-wasting events recorded in lacustrine sediments on Langøya in Vesterålen, northern Norway

    NASA Astrophysics Data System (ADS)

    Nielsen, Pål Ringkjøb; Dahl, Svein Olaf; Jansen, Henrik Løseth; Støren, Eivind N.

    2016-09-01

    In this study, the frequency of mass-wasting events and past storminess has been reconstructed throughout the Holocene (11,500 cal yr BP to present) from lacustrine sediments in lake Trehynnvatnet (33 m a.s.l.), which is located in a glacially carved valley at Nykvåg on the outmost coast of western Langøya, Vesterålen, northern Norway. Sediment cores (∼2-5 m long) have been examined by use of high-resolution magnetic susceptibility and XRF-scanning as well as grain size and loss-on-ignition analysis. In total 35 episodic event layers have been identified throughout the Holocene. The majority of these events are characterized as discrete coarse-grained sediment layers followed by normal grading, and are related to past mass-wasting activity within the catchment. Periods with high mass-wasting activity are dated to 11,000-10,500, 5500-4500, 4000-3500, 3000-2500, 2000-1000 and 500-0 cal yr BP. The continuous input of sand grains (>250 μm) has been systematically investigated throughout the sediment cores. The sand grains are related to catchment samples from the sandy beach deposits in Sandvikbukta c. 750 m away in SW direction, and are suggested to indicate (niveo-) aeolian influx to the lake. The content of sand grains varies greatly throughout the record, although there is a clear increase in influx of sand during the last 2800 years. Periods with high aeolian influx are proposed to indicate increased storminess, which occurred between 1600 and 1550 (350-400 CE), 1400-1300 (450-550 CE), 750-550 (1200-1400 CE) and 250-20 cal yr BP (1700-1930 CE), which to some degree coincides with periods of increased storminess and winter precipitation recorded in other studies around the North Eastern Atlantic region.

  7. Exploring rippled scour depressions offshore Huntington Beach, CA

    USGS Publications Warehouse

    Phillips, Eleyne L.; Storlazzi, Curt D.; Dartnell, Peter; Edwards, Brian D.

    2007-01-01

    U.S. Geological Survey (USGS) scientists used 1999 multibeam data, and 2002 lidar data collected on the inner shelf off southern California to investigate a field of (<1 m) features, termed "Rippled Scour Depressions" (RSDs). RSDs are elongate, shore-normal, and bathymetrically depressed features; their morphology was determined from multibeam and lidar bathymetry. Wavelengths of ripples seen within RSDs and on the surrounding seafloor were calculated from photography and video collected in 2004 and related to sediment samples collected in the same year. The RSDs were divided into two areas: Region I RSDs contained large (∼80 cm wavelength), straight-crested ripples with coarse-grained lag, and decreased in area between 1999 and 2002; Region II RSDs were smaller, in shallower water, closer to shore, and contained shorter (∼30 cm wavelength) ripples, and increased in area from 1999–2002. The RSDs did not display marked alongshore asymmetry.

  8. Ripple coarsening on ion beam-eroded surfaces

    NASA Astrophysics Data System (ADS)

    Teichmann, Marc; Lorbeer, Jan; Frost, Frank; Rauschenbach, Bernd

    2014-08-01

    The temporal evolution of ripple pattern on Ge, Si, A l 2 O 3, and Si O 2 by low-energy ion beam erosion with Xe + ions is studied. The experiments focus on the ripple dynamics in a fluence range from 1.1 × 1017 cm-2 to 1.3 × 1019 cm-2 at ion incidence angles of 65° and 75° and ion energies of 600 and 1,200 eV. At low fluences a short-wavelength ripple structure emerges on the surface that is superimposed and later on dominated by long wavelength structures for increasing fluences. The coarsening of short wavelength ripples depends on the material system and angle of incidence. These observations are associated with the influence of reflected primary ions and gradient-dependent sputtering. The investigations reveal that coarsening of the pattern is a universal behavior for all investigated materials, just at the earliest accessible stage of surface evolution.

  9. Analysis of ripple formation in single crystal spot welds

    NASA Technical Reports Server (NTRS)

    Rappaz, M.; Corrigan, D.; Boatner, L. A.

    1997-01-01

    Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

  10. Ripple-patterned substrates for light enhancement applications

    NASA Astrophysics Data System (ADS)

    Buividas, Ricardas; Kudrius, Tadas; Sliupas, Remigijus; Rosa, Lorenzo; Slekys, Gintas; Bagdonas, Saulius; Rotomskis, Ricardas; Juodkazis, Saulius

    2010-11-01

    We report on surface structuring of sapphire, silicon carbide, and silicon by femtosecond laser pulses in multipulse irradiation mode. The formed ripples on the flat surface or on the vertical walls with hierarchical structures whose feature sizes are ranging from the irradiation wavelength down to ~ 50 nm are prospective templates for surface enhanced Raman scattering after coating with plasmonic metals. We study complex patterns of fine ripples with periods Λr, as small as λ/Rp, where Rp (see manuscript) 3 - 5. The mechanisms suggested for such Rp values are discussed: temperature and density of breakdown plasma, angle of incidence, mechanism of second harmonic generation (SHG) and absorption. Predictions of the surface and bulk models of ripple formation are compared with experimental values of Rp-factor. We propose a model of ripple formation on the surface, which is based on the known in-bulk sphere-to-plane formation of breakdown plasma in the surface proximity. In semiconductor 4H:SiC normal ripples with periods 190 and 230 nm were recorded with 800 nm and 1030 nm fs-laser pulses respectively. We show that the period of ripples is defined by the dielectric properties of crystalline (solid) phase rather than the molten phase in the case of silicon. Generation of SHG on the surface of sample and plasma nano-bubbles are discussed: surface-SHG is found not important in ripples' formation as revealed by comparative study of periods on Al2O3 and TiO2 at 800 nm wavelength of irradiation. We propose that ripple periodicity is pinned to the smallest possible standing wave cavity (λ/n)/2 inside material of refractive index n.

  11. Aeolian Abrasion at the Curiosity Landing Site: Clues to the Role of Wind in Landscape Modification

    NASA Astrophysics Data System (ADS)

    Bridges, N. T.; Le Mouélic, S.; Hallet, B.; Newman, C. E.; Rice, M. S.; Blaney, D. L.; Calef, F. J.; Herkenhoff, K. E.; Langevin, Y.; Lewis, K. W.; Maurice, S.; Pinet, P. C.; Wiens, R. C.; de Pablo, M.; Renno, N. O.

    2013-12-01

    The broad scale geomorphology of Gale Crater reflects diverse aeolian processes, from airfall settling that likely deposited much of the upper and some of the lower units of Mt. Sharp, to evidence of extensive wind exhumation and removal of material exterior to the mound, to active dunes on the crater floor. The integrated effect of aeolian sand transport can also be examined on a much smaller scale by the study of ventifacts, rocks that have been abraded by windborne particles. A diversity of ventifacts are found along Curiosity's traverse through the upper 'hummocky' (HY) geomorphic unit and the lower Yellowknife Bay (YKB) sedimentary rocks. The textures are analogous to abrasion features found on Earth and include cm-scale facets, keels, elongated pits, grooves, flutes, and basal sills. High-resolution images from ChemCam's Remote Micro-Imager also show mm-scale lineations. Evidence of differential erosion is common, with HY conglomerates (e.g., Hottah, Link) and the YKB Sheepbed mudstone unit containing distinct wind tails in the lee of resistant pebbles, and bedding features within Rocknest 3, the YKB Shaler sandstone unit, and other layered rocks displaying prominent ridge-groove topography. ChemCam LIBS depth profile data so far show no strong evidence for chemical differences in the elemental composition between abraded and non-abraded surfaces (as determined from qualitative assessment), as might be expected if there were rock coatings or weathering rinds undergoing active abrasion. Preliminary measurements of ventifact texture and wind tail orientations indicate sandblasting in HY and YKB from predominantly southwesterly and northerly directions, respectively. Based on meso-scale models of current winds and REMS results, SW flow is uncommon whereas N winds are frequent. Compositional and textural information from the suite of MSL instruments indicate that HY rocks are dominated by various types of basalt (either as whole rocks or the resistant clasts in

  12. Molecular Dynamics Study of Ripples in Graphene and Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Singh, Arunima; Hennig, Richard G.

    2012-02-01

    Transmission electron microscopy experiments have shown that suspended graphene is not perfectly flat, but displays ripples such that the surface normal of graphene varies by several degrees [1,2]. For multi-layered graphene, the ripples are suppressed with increasing numbers of layers. Recent experiments demonstrated that ripples in suspended graphene can also be controlled by mechanical and thermally induced strain [3]. Knowledge of and control over the ripples in graphene is desirable for fabricating and designing of strain-based devices. We show using molecular dynamics simulation that thermally induced ripples in suspended single and multi-layer graphene at room temperature result in deviations of the local surface normal by ± 7 ^o and ± 4 ^o for single and bilayer graphene, respectively. These angular deviations are in excellent agreement with transmission electron microscopy results [2] and confirm that these ripples can be dynamic and thermally induced. We also study how these angles change as a function of applied tensile and shear strain. [1] Meyer J. C., Geim A. K., et al. Solid State Communications, 143, 101 (2007). [2] Meyer J.C., Geim A.K., et al. Nature, 446, 60 (2007). [3] Bao W., Miao F., et al. Nature Nanotechnology, 4 (9), 562 (2009).

  13. Controlled ripple texturing of suspended graphene and ultrathin graphite membranes.

    PubMed

    Bao, Wenzhong; Miao, Feng; Chen, Zhen; Zhang, Hang; Jang, Wanyoung; Dames, Chris; Lau, Chun Ning

    2009-09-01

    Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties. Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials. The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering. Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains. We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite. These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory. This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene. PMID:19734927

  14. Controlled ripple texturing of suspended graphene and ultrathin graphite membranes

    NASA Astrophysics Data System (ADS)

    Bao, Wenzhong; Miao, Feng; Chen, Zhen; Zhang, Hang; Jang, Wanyoung; Dames, Chris; Lau, Chun Ning

    2009-09-01

    Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties. Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials. The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering. Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains. We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite. These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory. This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene.

  15. Deterministic ripple-spreading model for complex networks.

    PubMed

    Hu, Xiao-Bing; Wang, Ming; Leeson, Mark S; Hines, Evor L; Di Paolo, Ezequiel

    2011-04-01

    This paper proposes a deterministic complex network model, which is inspired by the natural ripple-spreading phenomenon. The motivations and main advantages of the model are the following: (i) The establishment of many real-world networks is a dynamic process, where it is often observed that the influence of a few local events spreads out through nodes, and then largely determines the final network topology. Obviously, this dynamic process involves many spatial and temporal factors. By simulating the natural ripple-spreading process, this paper reports a very natural way to set up a spatial and temporal model for such complex networks. (ii) Existing relevant network models are all stochastic models, i.e., with a given input, they cannot output a unique topology. Differently, the proposed ripple-spreading model can uniquely determine the final network topology, and at the same time, the stochastic feature of complex networks is captured by randomly initializing ripple-spreading related parameters. (iii) The proposed model can use an easily manageable number of ripple-spreading related parameters to precisely describe a network topology, which is more memory efficient when compared with traditional adjacency matrix or similar memory-expensive data structures. (iv) The ripple-spreading model has a very good potential for both extensions and applications. PMID:21599256

  16. 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

  17. 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

  18. Evaluation of a new model of aeolian transport in the presence of vegetation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aeolian transport is an important characteristic of many arid and semiarid regions worldwide that affects dust emission and ecosystem processes. The purpose of this paper is to evaluate a recent model of aeolian transport in the presence of vegetation [Okin, 2008]. This approach differs from previou...

  19. Atmospheric significance of aeolian salts in the sandy deserts of northwestern China

    NASA Astrophysics Data System (ADS)

    Zhu, B.-Q.

    2016-02-01

    Large sandy deserts in the middle latitudes of northwestern China were investigated for soluble salt variations in modern and ancient aeolian sediments, aiming to explore the environmental significance of "aeolian salts". Results revealed that aeolian salt variations have a clear relationship with the changing meridional and zonal gradients of the desert locations and the aeolian differentiation effect, but are weakly linked to local geological conditions. Atmospheric depositions of water-soluble chemical species are an important process/source contributing to aeolian salt. Sequential variations of soluble salts in sedimentary profiles interbedded with aeolian and non-aeolian deposits and their palaeoenvironmental implications in the hinterland areas of these deserts were further evaluated, based on the constraints of OSL dating and radiocarbon dating data. The results indicate that inorganic salts may be a latent geoproxy in revealing regional palaeoclimatic changes in desert areas for sediments deposited under a single depositional environment, but the interpretation should be more cautious for sediments deposited under diverse depositional conditions. This study presents evidence of the atmospheric origin of aeolian salt in sandy deserts, with limited climatic significance in palaeoenvironmental reconstruction.

  20. Spontaneous ripple formation in phosphorene: electronic properties and possible applications

    NASA Astrophysics Data System (ADS)

    Zhou, Yungang; Yang, Li; Zu, Xiaotao; Gao, Fei

    2016-06-01

    According to the Mermin-Wagner theorem and theory of elasticity, long-range order in two-dimensional (2D) crystals will be inevitably destroyed due to a thermal fluctuation. Thus, a 2D lattice prefers a corrugation meaning that a 2D crystal is easy to present a ripple. In this work, we, via employing ab initio molecular dynamics (AIMD) simulations, for the first time evidenced that the inherent dynamics of phosphorene would lead to a spontaneous formation of ripples at room temperature. The height of a ripple closely associates with the temperature and the width. Via density functional theory (DFT) calculations, we further demonstrated that the emergence of ripples would remarkably reduce the bandgap of phosphorene. Via the construction of the unique phosphorene structure, we finally found that such a rippled structure is expected to be used in the light-emitting field. These results give us further knowledge of phosphorene, which goes beyond the current scope of phosphorene limited to the flat lattice.According to the Mermin-Wagner theorem and theory of elasticity, long-range order in two-dimensional (2D) crystals will be inevitably destroyed due to a thermal fluctuation. Thus, a 2D lattice prefers a corrugation meaning that a 2D crystal is easy to present a ripple. In this work, we, via employing ab initio molecular dynamics (AIMD) simulations, for the first time evidenced that the inherent dynamics of phosphorene would lead to a spontaneous formation of ripples at room temperature. The height of a ripple closely associates with the temperature and the width. Via density functional theory (DFT) calculations, we further demonstrated that the emergence of ripples would remarkably reduce the bandgap of phosphorene. Via the construction of the unique phosphorene structure, we finally found that such a rippled structure is expected to be used in the light-emitting field. These results give us further knowledge of phosphorene, which goes beyond the current scope of

  1. Responses of aeolian desertification to a range of climate scenarios in China

    NASA Astrophysics Data System (ADS)

    Wang, Xunming; Hua, Ting; Ma, Wenyong

    2016-06-01

    Aeolian desertification plays an important role in earth-system processes and ecosystems, and has the potential to greatly impact global food production. The occurrence of aeolian desertification has traditionally been attributed to increases in wind speed and temperature and decreases in rainfall. In this study, by integrating the aeolian desertification monitoring data and climate and vegetation indices, we found that although aeolian desertification is influenced by complex climate patterns and human activities, increases in rainfall and temperature and decreases in wind speed may not be the key factors of aeolian desertification controls in some regions of China. Our results show that, even when modern technical approaches are used, different approaches to desertification need to be applied to account for regional differences. These results have important implications for future policy decisions on how best to combat desertification.

  2. Windblown sand on Mars: The effect of saltation threshold on drift potentials derived from Mars GCM

    NASA Technical Reports Server (NTRS)

    Xu, P.; Greeley, R.; Williams, S.; Pollack, J. B.

    1994-01-01

    The rate at which the wind can redistribute sedimentary material is an important part of any planet's sedimentologic cycle, particularly for Mars, where the competing effects of other gradational processes are less than on Earth. The aeolian drift potential (DP) is a measure of the amount of material capable of being moved through a unit length by the wind for a given period of time. DP is a useful measure of the potential redistribution rate of windblown material on regional scales. The Martian aeolian DP was calculated from laboratory studies of sand movement conducted at Martian atmospheric densities and from surface stress, temperature, and pressure values for that region as determined from the Mars General (Atmospheric) Circulation Model (GCM) developed at the NASA/Ames Research Center. In our simulations for Mars, DP changes in both magnitude (as expected) and direction if the saltation threshold is altered.

  3. 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.

  4. Gravity Waves Ripple over Marine Stratocumulus Clouds

    NASA Technical Reports Server (NTRS)

    2004-01-01

    In this natural-color image from the Multi-angle Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar to the ripples that occur when a pebble is thrown into a still pond, such 'gravity waves' sometimes appear when the relatively stable and stratified air masses associated with stratocumulus cloud layers are disturbed by a vertical trigger from the underlying terrain, or by a thunderstorm updraft or some other vertical wind shear. The stratocumulus cellular clouds that underlie the wave feature are associated with sinking air that is strongly cooled at the level of the cloud-tops -- such clouds are common over mid-latitude oceans when the air is unperturbed by cyclonic or frontal activity. This image is centered over the Indian Ocean (at about 38.9o South, 80.6o East), and was acquired on October 29, 2003.

    The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously and every 9 days views the entire globe between 82o north and 82o south latitude. These data products were generated from a portion of the imagery acquired during Terra orbit 20545. The image covers an area of 245 kilometers x 378 kilometers, and uses data from blocks 121 to 122 within World Reference System-2 path 134.

    MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.

  5. Optical properties of Aeolian dusts common to West Texas

    NASA Astrophysics Data System (ADS)

    Ma, Lulu; Zobeck, Ted M.; Hsieh, Daniel H.; Holder, Dean; Morgan, Cristine L. S.; Thompson, Jonathan E.

    2011-11-01

    Both recent models and historical events such as the Dust Bowl and volcanic eruptions have illustrated aerosols can play a significant role in climate change through direct and indirect optical effects. Soil dust aerosols generated by Aeolian processes represent a significant fraction of the total mass burden of atmospheric particles. Central to a better understanding of the climate effects of dust aerosols is knowledge of their optical properties. This research study utilized a dust generator and several instruments to determine certain optical properties of Aeolian dust mimics created by the Amarillo and Pullman soil types native to the panhandle of Texas, USA. Values for the mass-extinction coefficient ranged between 1.74 and 2.97 m 2 g -1 at 522 nm depending on how mass concentration was determined. Single-scatter albedo (SSA) for both soil types ranged from 0.947 to 0.980 at visible wavelengths with SSA increasing at longer wavelengths. Angstrom absorption exponents were measured as 1.73 for Pullman and 2.17 for Amarillo soil. Observed Angstrom extinction exponents were 0.110 and 0.168 for the Pullman and Amarillo soil types. The optical properties reported may be of use for optical based estimates of soil erosion and aid in understanding how regional soil dusts may alter radiative transport presently and during historical events such as the Dust Bowl era.

  6. Modelling TF ripple loss of alpha particles in TFTR DT experiments

    SciTech Connect

    Redi, M.H.; Budny, R.V.; Darrow, D.S.

    1995-07-01

    Modelling of TF ripple loss of alphas in DT experiments on TFTR now includes neoclassical calculations of first orbit loss, stochastic ripple diffusion, ripple trapping and collisional effects. A rapid way to simulate experiment has been developed which uses a simple stochastic domain model for TF ripple loss within the TRANSP analysis code, with the ripple diffusion threshold evaluated by comparison with more accurate but computationally expensive Hamiltonian coordinate guiding center code simulations. Typical TF collisional ripple loss predictions are 6-10% loss of alphas for TFTR D-T experiments at I{sub p} = 1.0-2.0 MA and R = 2.52 m.

  7. Morphometrics of aeolian blowouts from high-resolution digital elevation data: methodological considerations, shape metrics, and scaling

    NASA Astrophysics Data System (ADS)

    Hamilton, T. K.; Duke, G.; Brown, O.; Koenig, D.; Barchyn, T. E.; Hugenholtz, C.

    2011-12-01

    Aeolian blowouts are wind erosion hollows that form in vegetated aeolian landscapes. They are especially pervasive in dunefields of the northern Great Plains, yielding highly pitted or hummocky terrain, and adding to the spatial variability of microenvironments. Their development is thought to be linked to feedbacks between morphology and airflow; however, few measurements are available to test this hypothesis. Currently, a dearth of morphology data is limiting modeling progress. From a systematic program of blowout mapping with high-resolution airborne LiDAR data, we used a GIS to calculate morphometrics for 1373 blowouts in Great Sand Hills, Saskatchewan, Canada. All of the blowouts selected for this investigation were covered by grassland vegetation and inactive; their morphology represents the final stage of evolution. We first outline methodological considerations for delineating blowouts and measuring their volume. In particular, we present an objective method to enhance edge and reduce operator error and bias. We show that blowouts are slightly elongate and 49% of the sample blowouts are oriented parallel to the prevailing westerly winds. We also show that their size distribution is heavy-tailed, meaning that most blowouts are relatively small and rarely increase in size beyond 400 m3. Given that blowout growth is dominated by a positive feedback between sediment transport and vegetation erosion, these results suggest several possible mechanisms: i) blowouts simultaneously evolved and stabilized as a result of external climate forcing, ii) blowouts are slaved to exogenous biogenic disturbance patterns (e.g., bison wallows), or iii) a morphodynamic limiting mechanism restricts blowout size. Overall, these data will serve as a foundation for future study, providing insight into an understudied landform that is common in many dunefields.

  8. Aeolian to shallow-marine shelf architecture off a major desert since the Late Pleistocene (northern Mauritania)

    NASA Astrophysics Data System (ADS)

    Hanebuth, T. J. J.; Mersmeyer, H.; Kudrass, H. R.; Westphal, H.

    2013-12-01

    Continental shelves off major desert regions are not expected to host substantial amounts of sediments due to long-lasting and unfocused material supply and a high re-mobilization potential of aeolian material. This study, in contrast, demonstrates that significant volumes of sediments have accumulated on the northern Mauritanian shelf under the arid climate conditions and prevail over consecutive climatic cycles. Eight late Pleistocene to Holocene depositional units, each formed under contrasting depositional conditions, are identified in high-resolution seismo-acoustic data and dated sediment cores. These are: (1) a highly differentiated Pleistocene paleo-landscape older than the past climatic cycle, (2) a continental dune complex (MIS-4), (3) a thick regressive shallow-water clinoform (late MIS-3), (4) a regressive to lowstand shore deposit (latest MIS-3), and (5) a local transgressive cover (LGM to deglacial). Additionally, (6) an open-shelf highstand cover, (7) an outer-shelf highstand wedge and (8) mid-shelf mud depocenters have formed during the Holocene sea-level highstand. The common local offshore formation and preservation of confined stratigraphic units, in particular from during MIS-3, mark the interplay of: a) episodes of pronounced arid climatic conditions resulting in enhanced aeolian and coastal sediment input, b) shelf current patterns focusing sediment deposition locally, and c) early post-depositional sediment stabilization providing protection against erosion. Prominent internal surfaces at 63 and 115 m modern water depths indicate widespread and intense erosional activity during late MIS-3 regression and MIS-2 lowstand to post-LGM transgression, hosting coarse shell sands and gravels from beach and shoreface paleo-environments. The reasons for the high preservation potential of confined stratigraphic units are: a) carbonaceous cementation, b) sediment composition (massive widespread shore-related gravel and shell beds with subtle minor

  9. Industrial sand and gravel

    USGS Publications Warehouse

    Dolley, T.P.

    2006-01-01

    In 2005, domestic production of industrial sand and gravel was about 31 Mt, a 5% increase from 2004. This increase was bouyed by robust construction and petroleum sectors of the US economy. Based on estimated world production figures, the United States was the world's leading producer and consumer of industrial sand and gravel. In the short term, local shortages of industrial sand and gravel will continue to increase.

  10. Spontaneous ripple formation in phosphorene: electronic properties and possible applications.

    PubMed

    Zhou, Yungang; Yang, Li; Zu, Xiaotao; Gao, Fei

    2016-06-01

    According to the Mermin-Wagner theorem and theory of elasticity, long-range order in two-dimensional (2D) crystals will be inevitably destroyed due to a thermal fluctuation. Thus, a 2D lattice prefers a corrugation meaning that a 2D crystal is easy to present a ripple. In this work, we, via employing ab initio molecular dynamics (AIMD) simulations, for the first time evidenced that the inherent dynamics of phosphorene would lead to a spontaneous formation of ripples at room temperature. The height of a ripple closely associates with the temperature and the width. Via density functional theory (DFT) calculations, we further demonstrated that the emergence of ripples would remarkably reduce the bandgap of phosphorene. Via the construction of the unique phosphorene structure, we finally found that such a rippled structure is expected to be used in the light-emitting field. These results give us further knowledge of phosphorene, which goes beyond the current scope of phosphorene limited to the flat lattice. PMID:27226229

  11. Ripple formation on silicon by medium energy ion bombardment.

    PubMed

    Chini, Tapas Kumar; Datta, Debi Prasad; Bhattacharyya, Satya Ranjan

    2009-06-01

    The formation of a self-organized nanoscale ripple pattern after off-normally incident ion bombardment on the surface of amorphous materials, or on semiconductors like silicon that are easily amorphized by ion bombardment, has attracted much attention in recent years from the point of view of both theory and applications. As the energy of the impinging ions increases from low to medium, i.e. several hundred eV to a few tens of keV, the ratio of amplitude to wavelength of the generated ripple pattern becomes so large that inter-peak shadowing of the incident ion flux takes place. Morphologically, the sinusoidal surface profile starts to become distorted after prolonged ion bombardment under such conditions. Structural and compositional modifications of the ripple morphology generated under shadowing conditions include the formation of a thicker amorphous layer with high incorporation of argon atoms in the form of nanometer sized bubbles around the middle part of the front slope of the ripple facing the ion beam, as compared to the rear slope. The present paper reviews recent developments in the experimental study of morphological, structural and compositional aspects of ripple patterns generated on a silicon surface after medium keV (30-120 keV) argon bombardment mainly at an angle of ion incidence of 60°. PMID:21715743

  12. Evaluation of aeolian emissions from gold mine tailings on the Witwatersrand

    NASA Astrophysics Data System (ADS)

    Ojelede, M. E.; Annegarn, H. J.; Kneen, M. A.

    2012-01-01

    The Witwatersrand is known for the high frequency of aeolian dust storm episodes arising from gold mine tailings storage facilities (TSFs). Source and ambient atmosphere are poorly characterized from the point of view of particle size distribution and human health risk assessment. For years, routine monitoring was limited to sampling of dust fallout ⩾30 μm. Sampling and analyses of source and receptor material was conducted. Thirty-two bulk soils were collected from TSF along the east-west mining corridor, and size distribution analysis was performed in the range 0.05-900 μm using a Malvern® MS-14 Particle Size Analyser. Ambient aerosols in the range 0.25-32 μm were monitored at two separate locations using a Grimm® aerosol monitor, in the vicinity of three large currently active and a dormant TSF. Statistical analyses indicate that TSFs are rich in fine erodible materials, particularly active TSFs. Concentration of ⩽PM5 and ⩽PM10 components in source material was: recent slimes (14-24 vol.%; 22-38 vol.%), older slimes (6-17 vol.%; 11-26 vol.%) and sand (1-8 vol.%; 2-12 vol.%). Concentrations of airborne aerosols were below the South African Department of Environmental Affairs 24-h limit value of 120 μg m -3. With wind speeds exceeding 7 ms -1, ambient concentration reached 2160 μg m -3. This maximum is several times higher than the limit value. Erosion of tailings storage facilities is a strong driver influencing ambient particulate matter loading with adverse health implications for nearby residents.

  13. Rippling modes in the edge of a Tokamak plasma

    NASA Astrophysics Data System (ADS)

    Carreras, B. A.; Callen, J. D.; Gaffney, P. W.; Hicks, H. R.

    1982-02-01

    A promising resistive magnetohydrodynamic candidate for the underlying cause of turbulence in the edge of a Tokamak plasma is the rippling instability. A computational model for these modes in the cylindrical Tokamak approximation was developed and the linear growth and single helicity quasilinear saturation phases of the rippling modes for parameters appropriate to the edge of a Tokamak plasma was explored. Large parallel heat conduction does not stabilize these mode. Nonlinearly, individual rippling modes are found to saturate by quasilinear flattening of the resistivity profile. The saturated amplitude of the modes scales as m/sup -1/, and the radial extent of these modes grows linearly with time due to radial Vector E x Vector B0 convection. It is found that this evolution is terminated by parallel heat conduction.

  14. Frequency-temporal resolution of hearing measured by rippled noise.

    PubMed

    Supin AYa; Popov, V V; Milekhina, O N; Tarakanov, M B

    1997-06-01

    Frequency-temporal resolution of hearing was measured in normal hearers using rippled noise stimulation in conjunction with a phase-reversal test. The principle of the test was to interchange peak and trough positions (the phase reversal) and to find the highest ripple density at which such interchange is detectable depending on reversal rate. The measurements were made using narrow-band noises with center frequencies of 0.5-4 kHz. The ripple-density resolution limits were constant at phase-reversal rates below 2-3/s and diminished at higher phase-reversal rates. A model is proposed to explain the data based on the envelope fluctuations inherent in noise; these fluctuations are supposed to limit detection of frequency-temporal sound patterns. PMID:9213118

  15. Steam sand dryer in northeast part of sand tower. View ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Steam sand dryer in northeast part of sand tower. View to northeast - Duluth & Iron Range Rail Road Company Shops, Sand Tower, Southwest of downtown Two Harbors, northwest of Agate Bay, Two Harbors, Lake County, MN

  16. Mechanisms of sharp wave initiation and ripple generation.

    PubMed

    Schlingloff, Dániel; Káli, Szabolcs; Freund, Tamás F; Hájos, Norbert; Gulyás, Attila I

    2014-08-20

    Replay of neuronal activity during hippocampal sharp wave-ripples (SWRs) is essential in memory formation. To understand the mechanisms underlying the initiation of irregularly occurring SWRs and the generation of periodic ripples, we selectively manipulated different components of the CA3 network in mouse hippocampal slices. We recorded EPSCs and IPSCs to examine the buildup of neuronal activity preceding SWRs and analyzed the distribution of time intervals between subsequent SWR events. Our results suggest that SWRs are initiated through a combined refractory and stochastic mechanism. SWRs initiate when firing in a set of spontaneously active pyramidal cells triggers a gradual, exponential buildup of activity in the recurrent CA3 network. We showed that this tonic excitatory envelope drives reciprocally connected parvalbumin-positive basket cells, which start ripple-frequency spiking that is phase-locked through reciprocal inhibition. The synchronized GABA(A) receptor-mediated currents give rise to a major component of the ripple-frequency oscillation in the local field potential and organize the phase-locked spiking of pyramidal cells. Optogenetic stimulation of parvalbumin-positive cells evoked full SWRs and EPSC sequences in pyramidal cells. Even with excitation blocked, tonic driving of parvalbumin-positive cells evoked ripple oscillations. Conversely, optogenetic silencing of parvalbumin-positive cells interrupted the SWRs or inhibited their occurrence. Local drug applications and modeling experiments confirmed that the activity of parvalbumin-positive perisomatic inhibitory neurons is both necessary and sufficient for ripple-frequency current and rhythm generation. These interneurons are thus essential in organizing pyramidal cell activity not only during gamma oscillation, but, in a different configuration, during SWRs. PMID:25143618

  17. Modelling ac ripple currents in HTS coated conductors

    NASA Astrophysics Data System (ADS)

    Xu, Zhihan; Grilli, Francesco

    2015-10-01

    Dc transmission using high temperature superconducting (HTS) coated conductors (CCs) offers a promising solution to the globally growing demand for effective, reliable and economic transmission of green energy up to the gigawatt level over very long distances. The credible estimation of the losses and thereby the heat dissipation involved, where ac ripples (introduced in rectification/ac-dc conversion) are viewed as a potential source of notable contribution, is highly essential for the rational design of practical HTS dc transmission cables and corresponding cryogenic systems to fulfil this demand. Here we report a targeted modelling study into the ac losses in a HTS CC subject to dc and ac ripple currents simultaneously, by solving Maxwell’s equations using the finite element method (FEM) in the commercial software package COMSOL. It is observed that the instantaneous loss exhibits only one peak per cycle in the HTS CC subject to sinusoidal ripples, given that the amplitude of the ac ripples is smaller than approximately 20% of that of the dc current. This is a distinct contrast to the usual observation of two peaks per cycle in a HTS CC subject to ac currents only. The unique mechanism is also revealed, which is directly associated with the finding that, around any local minima of the applied ac ripples, the critical state of -J c is never reached at the edges of the HTS CC, as it should be according to the Bean model. When running further into the longer term, it is discovered that the ac ripple loss of the HTS CC in full-wave rectification decays monotonically, at a speed which is found to be insensitive to the frequency of the applied ripples within our targeted situations, to a relatively low level of approximately 1.38 × 10-4 W m-1 in around 1.7 s. Comparison between this level and other typical loss contributions in a HTS dc cable implies that ac ripple currents in HTS CCs should only be considered as a minor source of dissipation in superconducting dc

  18. Hippocampal sharp-wave ripples in waking and sleeping states.

    PubMed

    Roumis, Demetris K; Frank, Loren M

    2015-12-01

    Waking and sleeping states are privileged periods for distinct mnemonic processes. In waking behavior, rapid retrieval of previous experience aids memory-guided decision making. In sleep, a gradual series of reactivated associations supports consolidation of episodes into memory networks. Synchronized bursts of hippocampal place cells during events called sharp-wave ripples communicate associated neural patterns across distributed circuits in both waking and sleeping states. Differences between sleep and awake sharp-wave ripples, and in particular the accuracy of recapitulated experience, highlight their state-dependent roles in memory processes. PMID:26011627

  19. PWM Switching Strategy for Torque Ripple Minimization in BLDC Motor

    NASA Astrophysics Data System (ADS)

    Salah, Wael A.; Ishak, Dahaman; Hammadi, Khaleel J.

    2011-05-01

    This paper describes a new PWM switching strategy to minimize the torque ripples in BLDC motor which is based on sensored rotor position control. The scheme has been implemented using a PIC microcontroller to generate a modified Pulse Width Modulation (PWM) signals for driving power inverter bridge. The modified PWM signals are successfully applied to the next up-coming phase current such that its current rise is slightly delayed during the commutation instant. Experimental results show that the current waveforms of the modified PWM are smoother than that in conventional PWM technique. Hence, the output torque exhibits lower ripple contents.

  20. Gravitational-Like Lens Based on Graphene Ripple.

    PubMed

    Liu, Daqing; Chen, Shuyue; Ma, Ning; Zhao, Xiang; Xu, Zhuo

    2015-10-01

    We conducted a semiclassical study on carrier movement in curved graphene. A previous attempt was made to show that curved graphene is a readily available and cheap laboratory material used to study general relativity effects, especially if the electron energies satisfy 4μeV ≪ |E| ≪ 3eV. Furthermore, a gravitational-like lens can be constructed based on a special graphene ripple; this lens has neither chromatic nor cometic aberration. One can design an ideal electron lens using a graphene ripple. PMID:26306607

  1. Parametrically excited water surface ripples as ensembles of oscillons.

    PubMed

    Shats, M; Xia, H; Punzmann, H

    2012-01-20

    We show that ripples on the surface of deep water which are driven parametrically by monochromatic vertical vibration represent ensembles of oscillating solitons, or quasiparticles, rather than waves. The horizontal mobility of oscillons determines the broadening of spectral lines and transitions from chaos to regular patterns. It is found that microscopic additions of proteins to water dramatically affect the oscillon mobility and drive transitions from chaos to order. The shape of the oscillons in physical space determines the shape of the frequency spectra of the surface ripple. PMID:22400746

  2. China Dust and Sand

    Atmospheric Science Data Center

    2013-04-16

    ... article title:  Dust and Sand Sweep Over Northeast China     View Larger Image ... these views of the dust and sand that swept over northeast China on March 10, 2004. Information on the height of the dust and an ...

  3. An Affair with Sand.

    ERIC Educational Resources Information Center

    Stroud, Sharon

    1980-01-01

    Described is a resource idea developed for the teaching of oceanography to junior high students. Sand is studied to help make the study of beaches more relevant to students who may have never seen an ocean. Sand samples are brought into the classroom from various coastal cities, then analyzed and compared. (Author/DS)

  4. Lidar measurements of Aeolian dust: Mars and Earth

    NASA Astrophysics Data System (ADS)

    Dickinson, C. S.; Davy, R.; Komguem, L.; Junkermann, W.; Whiteway, J. A.

    2009-12-01

    The Phoenix Lidar system was operated in 2008, beginning in Martian northern spring (L_s = 78) through mid summer (L_s = 147). During this period, nighttime observations of dust indicate both persistent background dust up to heights of approximately 15 km, and enhanced dust loading in the Boundary Layer up to heights of approximately 4 km. The magnitude of the optical extinction was observed to decrease within the Boundary Layer with time following summer solstice. This situation is similar to that observed in the Australian desert: a persistent dust layer up to heights of 6 km, with a daytime Convective Boundary Layer increasing up to heights of 4 km during local dust storm activity, and then decreasing during night. A comparative study was undertaken, with the results being augmented by both in situ measurements of the Australian desert dust, as made by over-flying aircraft, and modeled results of Aeolian dust in both environments.

  5. Optical dating of dune sand from Blombos Cave, South Africa: I--multiple grain data.

    PubMed

    Jacobs, Z; Wintle, A G; Duller, G A T

    2003-05-01

    An aeolian sand unit overlies the Middle Stone Age deposits at Blombos Cave on the southern Cape coast. These deposits contained culturally-important artefacts, including bone tools and pieces of engraved ochre, as well as a large number of worked lithics. The aeolian sand and two other remnants of the sand dune formed against the coastal cliff were dated using optical dating. To determine the dose received since deposition, measurements were made on 5mg aliquots of purified quartz grains using the single-aliquot regenerative-dose (SAR) protocol. The results of several internal check procedures are reported and at least 15 replicate dose determinations are presented for each sample. Combining these dose values with measurements of the radioactive content of each sample resulted in an age of 69.2+/-3.9 ka for the unit within the cave, and a mean age of 70.1+/-1.9 ka for all three dune samples. This provides a minimum age for the Middle Stone Age material at Blombos Cave. PMID:12765620

  6. Basaltic island sand provenance

    SciTech Connect

    Marsaglia, K.M. . Dept. of Geological Sciences)

    1992-01-01

    The Hawaiian Islands are an ideal location to study basaltic sand provenance in that they are a series of progressively older basaltic shield volcanoes with arid to humid microclimates. Sixty-two sand samples were collected from beaches on the islands of Hawaii, Maui, Oahu and Kauai and petrographically analyzed. The major sand components are calcareous bioclasts, volcanic lithic fragments, and monomineralic grains of dense minerals and plagioclase. Proportions of these components vary from island to island, with bioclastic end members being more prevalent on older islands exhibiting well-developed fringing reef systems and volcanic end members more prevalent on younger, volcanically active islands. Climatic variations across the island of Hawaii are reflected in the percentage of weathered detritus, which is greater on the wetter, northern side of the island. The groundmass of glassy, basaltic lithics is predominantly black tachylite, with lesser brown sideromelane; microlitic and lathwork textures are more common than holohyaline vitric textures. Other common basaltic volcanic lithic fragments are holocrystalline aggregates of silt-sized pyroxene or olivine, opaque minerals and plagioclase. Sands derived from alkalic lavas are texturally and compositionally indistinguishable from sands derived from tholeiitic lavas. Although Hawaiian basaltic sands overlap in composition with magmatic arc-derived sands in terms of their relative QFL, QmPK and LmLvLs percentages, they are dissimilar in that they lack felsic components and are more enriched in lathwork volcanic lithic fragments, holocrystalline volcanic lithic fragments, and dense minerals.

  7. Cobbles in Troughs Between Meridiani Ripples (False Color)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    As NASA's Mars Exploration Rover Opportunity continues to traverse from 'Erebus Crater' toward 'Victoria Crater,' the rover navigates along exposures of bedrock between large, wind-blown ripples. Along the way, scientists have been studying fields of cobbles that sometimes appear on trough floors between ripples. They have also been studying the banding patterns seen in large ripples.

    This view, obtained by Opportunity's panoramic camera on the rover's 802nd Martian day (sol) of exploration (April 27, 2006), is a mosaic spanning about 30 degrees. It shows a field of cobbles nestled among wind-driven ripples that are about 20 centimeters (8 inches) high.

    The origin of cobble fields like this one is unknown. The cobbles may be a lag of coarser material left behind from one or more soil deposits whose finer particles have blown away. The cobbles may be eroded fragments of meteoritic material, secondary ejecta of Mars rock thrown here from craters elsewhere on the surface, weathering remnants of locally-derived bedrock, or a mixture of these. Scientists will use the panoramic camera's multiple filters to study the rock types, variability and origins of the cobbles.

    This is a false-color rendering that combines separate images taken through the panoramic camera's 753-nanometer, 535-nanometer and 432-nanometer filters. The false color is used to enhance differences between types of materials in the rocks and soil.

  8. Ripple coarsening on ion beam-eroded surfaces

    PubMed Central

    2014-01-01

    The temporal evolution of ripple pattern on Ge, Si, Al2O3, and SiO2 by low-energy ion beam erosion with Xe + ions is studied. The experiments focus on the ripple dynamics in a fluence range from 1.1 × 1017 cm-2 to 1.3 × 1019 cm-2 at ion incidence angles of 65° and 75° and ion energies of 600 and 1,200 eV. At low fluences a short-wavelength ripple structure emerges on the surface that is superimposed and later on dominated by long wavelength structures for increasing fluences. The coarsening of short wavelength ripples depends on the material system and angle of incidence. These observations are associated with the influence of reflected primary ions and gradient-dependent sputtering. The investigations reveal that coarsening of the pattern is a universal behavior for all investigated materials, just at the earliest accessible stage of surface evolution. PMID:25302058

  9. Ripple Effect Mapping: A "Radiant" Way to Capture Program Impacts

    ERIC Educational Resources Information Center

    Kollock, Debra Hansen; Flage, Lynette; Chazdon, Scott; Paine, Nathan; Higgins, Lorie

    2012-01-01

    Learn more about a promising follow-up, participatory group process designed to document the results of Extension educational efforts within complex, real-life settings. The method, known as Ripple Effect Mapping, uses elements of Appreciative Inquiry, mind mapping, and qualitative data analysis to engage program participants and other community…

  10. View forward from stern showing skylight with rippled glass over ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View forward from stern showing skylight with rippled glass over compartment c-110, officer's quarters; note manually operated capstan at center, and simulated eight inch guns in sheet metal mock-up turret; also note five inch guns in sponsons port and starboard. (p37) - USS Olympia, Penn's Landing, 211 South Columbus Boulevard, Philadelphia, Philadelphia County, PA

  11. Analysis of ripple formation in single crystal spot welds

    SciTech Connect

    Rappaz, M.; Corrigan, D.; Boatner, L.A.

    1997-10-01

    Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 {micro}m) and spacing (typically {approximately} 60 {micro}m) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f{sub 0} given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v{sub s}/f{sub 0}, where v{sub s} is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

  12. Absence of rippling in graphene under biaxial tensile strain

    NASA Astrophysics Data System (ADS)

    Rakshit, Bipul; Mahadevan, Priya

    2010-10-01

    Recent experiments [C. H. Lui, L. Liu, K. F. Mak, G. W. Flynn, and T. F. Heinz, Nature (London) 462, 339 (2009)10.1038/nature08569] on graphene grown on ultraflat substrates have found no rippling in graphene when subject to temperature cycling. Unsupported/unstrained films of graphene as well as films grown on various substrates on the other hand have been found to show rippling effects. As graphene grown on a substrate is invariably strained, we examine the behavior of the out-of-plane acoustic-phonon mode with biaxial tensile strain. This mode is generally associated with the rippling of graphene. We find that it can be fit to a relation of the form w2=Ak4+Bk2 , where w and k are the frequency and wave vector, respectively. The coefficient A is found to show a weak dependence on strain while B is found to increase linearly with strain. The strain-induced hardening explains the absence of rippling in graphene subject to biaxial strain. In addition, we find that graphene when subject to a biaxial tensile strain is found to undergo a structural transition with the mode at K going soft at a strain percentage of 15%.

  13. Thermomechanics of monolayer graphene: Rippling, thermal expansion and elasticity

    NASA Astrophysics Data System (ADS)

    Gao, Wei; Huang, Rui

    2014-05-01

    Thermomechanical properties of monolayer graphene with thermal fluctuation are studied by both statistical mechanics analysis and molecular dynamics (MD) simulations. While the statistical mechanics analysis in the present study is limited by a harmonic approximation, significant anharmonic effects are revealed by MD simulations. The amplitude of out-of-plane thermal fluctuation is calculated for graphene membranes under both zero stress and zero strain conditions. It is found that the fluctuation amplitude follows a power-law scaling with respect to the linear dimension of the membrane, but the roughness exponents are different for the two conditions due to anharmonic interactions between bending and stretching modes. Such thermal fluctuation or rippling is found to be responsible for the effectively negative in-plane thermal expansion of graphene at relatively low temperatures, while a transition to positive thermal expansion is predicted as the anharmonic interactions suppress the rippling effect at high temperatures. Subject to equi-biaxial tension, the amplitude of thermal rippling decreases nonlinearly, and the in-plane stress-strain relation of graphene becomes nonlinear even at infinitesimal strain, in contrast with classical theory of linear elasticity. It is found that the tangent biaxial modulus of graphene depends on strain non-monotonically, decreases with increasing temperature, and depends on membrane size. Both statistical mechanics and MD simulations suggest considerable entropic contribution to the thermomechanical properties of graphene, and as a result thermal rippling is intricately coupled with thermal expansion and thermoelasticity for monolayer graphene membranes.

  14. Hydrological indications of aeolian salts in mid-latitude deserts of northwestern China

    NASA Astrophysics Data System (ADS)

    Zhu, Bing-Qi

    2016-06-01

    Large sandy deserts in middle latitude of northwestern China were studied on salt variations in modern and ancient aeolian sediments, aiming to explore their hydrological indications at the present and past. Globally, sulphate is rich in arid to semi-arid deserts, including the aeolian loess sediments in China and soils in low-latitude deserts, but is less common in the aeolian sediments from the mid-latitude deserts in this study. The compositional differences between aeolian salts and local natural waters is evident, indicating the chemistry of aeolian salts and the associated parent brines may be significantly different than that predicted for hydrologically closed systems. The formation of aeolian salts in the studied deserts is strongly controlled by earth surface processes in a large scale but not in a local scale. Vertical changes in facies and salinities are abrupt in the studied palaeo-aeolian sediment samples, which were interbedded by lacustrine/fluvial sediments with OSL and 14C ages ranging between 40 and 2 ka BP, reflecting rapid high-amplitude changes in hydrological settings during late Pleistocene to later Holocene in these ancient playa systems. A great difference in salt composition between aeolian and lacustrine sediments suggests that the inorganic salt is a latent geoproxy in revealing local hydrological variations and climate change in the desert areas. But the environmental indications could be amphibolous for the sedimentary sequences with dual/multiple depositional end-members; under this situation an increase in sequence salinity does not always represent an enhanced environmental aridity. Ancient playas are arid or humid at the same time based on several sporadic records is not a valid approach to correlation of salt deposits in adjacent saline playa basin in the studied areas. Effects of earth surface processes including erosion, deposition and other processes on sediment properties will bias the hydrological implications of sediment

  15. A new turbulence-based model for sand transport

    NASA Astrophysics Data System (ADS)

    Mayaud, Jerome; Wiggs, Giles; Bailey, Richard

    2016-04-01

    Knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes. While 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 evidence that high-frequency turbulence is an important driving force behind the entrainment and transport of sand. However, turbulence 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 (the 'turbulence model') that accounts for high-frequency variations in the horizontal (u) and vertical (w) components of wind flow. The turbulence model is fitted to wind velocity and sediment transport data from a field experiment undertaken in Namibia's Skeleton Coast National Park, and its performance at three temporal resolutions (10 Hz, 1 Hz, 1 min) is compared to two existing models that rely on time-averaged wind velocity data (Radok, 1977; Dong et al., 2003). The validity of the three models is analysed under a variety of saltation conditions, using a 2-hour (1 Hz measurement resolution) dataset from the Skeleton Coast and a 5-hour (1 min measurement resolution) dataset from the southwestern Kalahari Desert. The turbulence model is shown to outperform the Radok and Dong models when predicting total saltation count over the three experimental periods. For all temporal resolutions presented in this study (10 Hz-10 min), the turbulence model predicted total saltation count to within at least 0.34%, whereas the Radok and Dong models over- or underestimated total count by up to 5.50% and 20.53% respectively. The strong performance of the turbulence model can be attributed to a lag in mass flux response built into its formulation, which can be adapted depending on the temporal resolution of investigation. This accounts for the inherent lag within the physical

  16. Industrial sand and gravel

    USGS Publications Warehouse

    Dolley, T.P.

    2010-01-01

    Domestic production of industrial sand and gravel in 2009 was about 27 Mt (30 million st), declining by 10 percent compared with 2008. Certain end uses of industrial sand and gravel, such as foundry and glassmaking sand, may have declined by a factor greater than 10 percent in 2009. U.S. apparent consumption was 24.7 Mt (27.2 million st) in 2009, down by 10 percent from the previous year, and imports declined to 83 kt (91,000 st).

  17. Transport and mixing of eolian sand from local sources resulting in variations in grain size in a gypsum dune field, White Sands, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Langford, Richard P.; Gill, Thomas E.; Jones, Slade B.

    2016-03-01

    The White Sands Dune Field, New Mexico (USA), provides a unique opportunity to study sources and eolian transport of sand. End member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types. Textural differences between sources allow local transport paths to be deduced. In total, 1214 surface samples from 10 dunes and 2 downwind-oriented transects were collected. Neither elevation on the dune, lee or stoss location nor distance downwind correlated with mean grain size, coarsest 10% (D90), or sorting. Instead, grain size distributions are controlled by mixing of locally sourced sand populations. Adjacent dunes can have different mean grain sizes, resulting from different local source populations. Local within-dune and between-dune variability resulting from different sand sources dominates any larger-scale trends across and within dunes. Four sand populations are identified, based on microscopically observable differences in grain size, shape and angularity. Each correlates with high loading of a different statistical factor, derived from End Member Mixing Analysis. End Member 1 (EM1) correlates with well-sorted populations of finer-grained, equant, rounded sands. EM2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes. EM3 is associated with samples of moderately to poorly sorted fine-grained sand containing fine sand-sized gypsum needles collected from areas of vegetated interdunes, and EM4 is associated with moderately well sorted coarse- and very coarse-grained sands collected from granule ripples. These results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field, rather than by dune-scale or erg-scale transport and sorting.

  18. Changes in soil aggregation and dust emission potential in response to aeolian processes

    NASA Astrophysics Data System (ADS)

    swet, Nitzan; Katra, Itzhak

    2016-04-01

    Aeolian (wind) dust emission has high environmental and socioeconomic significances due to loss of natural soil and air pollution. Dust emission involves complex interactions between the airflow and the soil surface. The soil aggregates were dust particles are held determine the topsoil erodibility in aeolian erosion. Although the key role of soil aggregation in dust emission mechanisms, information on changes in soil aggregate size distribution (ASD) due to aeolian erosion is lucking. This study is focused on quantitative ASD analyses before and after aeolian processes (saltation). Aeolian experiments and soil analyses were conducted on semiarid loess topsoils with different initial conditions of aggregation. The results show that saltation rates and PM emissions depend on the initial ASD and shear velocity. In all initial soil conditions, the content of aggregates at saltator-sized 63-250 μm was increased by 10-34 % following erosion of macro-aggregates > 500 μm. It revealed that the aggregate-saltator production increases with the shear velocity (up to 0.61 m s-1) for soils with available macro-aggregates. The findings highlight the dynamics in soil aggregation in response to aeolian transport and therefore its significance for determining the mechanisms of dust emission from soil aggregates.

  19. Gravel and sand resources of the New England-New York region

    USGS Publications Warehouse

    Currier, Louis W.

    1955-01-01

    Deposits of sand and gravel are widespread in the New England-New York regions and constitute one of its principal mineral resources. Most of the pits are operated intermittently to supply local needs. Because of the great number and variety of known deposits, and because they have been worked at countless points it is impracticable to describe in detail either the deposits or the individual pits. On the other hand, a broad description of the geologic modes of occurrence with relation to the regional geology will serve adequately to indicate the importance of the resource in the regional economy and development. Except for some special sands, such as "glass sand", certain molding and foundry sands, et. al., for which restrictive textural, compositional and physical properties are required, sand and gravel are used chiefly for local construction and are not commonly transported for long distances. Sand and gravel deposits of the region fall into four principal genetic categories - e.g., glacial, alluvial, marine, and aeolian. Of these, deposits of glacial origin are by far the most widespread and important.

  20. Foundry sand reclamation

    SciTech Connect

    Filipovitch, A.J.; Bleuenstein, J.M.

    1984-05-22

    A dry method of conditioning spent foundry sand is disclosed. After having sized the sand and removal of tramp metallic elements, the sand is subjected to a sequence of squeezing under a high-stress low kinetic energy system for a period of 5-30 minutes, and then propelled against a target with high-kinetic energy in the presence of a suction for several minutes. This sequence can be preferably repeated to increase the quality of the resulting product which should have 0.1% or less of fine particles, a pH of 6-9, a clay content and organic combustible content of substantially zero. The reclaimed sand will exhibit a density of at least 100 grams/biscuit when compacted for core making or molding.