Science.gov

Sample records for crescent dunes solar

  1. 76 FR 60475 - Issuance of a Loan Guarantee to Tonopah Solar Energy, LLC, for the Crescent Dunes Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-29

    ...ENERGY Issuance of a Loan Guarantee to Tonopah Solar Energy, LLC, for the Crescent Dunes Solar Energy Project AGENCY: U.S. Department of Energy...Act of 2009 (Recovery Act), to Tonopah Solar Energy, LLC (TSE), for construction and...

  2. 75 FR 81307 - Notice of Availability of Record of Decision for the Tonopah Solar Energy, LLC, Crescent Dunes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-27

    ...of public lands with a nominal capacity of 110 megawatts. The Crescent Dunes Solar Energy Project is a solar facility using concentrated solar thermal power technology. The project facility footprint will disturb approximately 1,620 acres...

  3. 76 FR 60475 - Issuance of a Loan Guarantee to Tonopah Solar Energy, LLC, for the Crescent Dunes Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-29

    ... Tonopah Solar Energy, LLC, Crescent Dunes Solar Energy Project, Nye County, Nevada (75 FR 70917, November... covered by the DOE loan guarantee, and DOE adopted the FEIS (76 FR 7844; February 11, 2011). ADDRESSES... Register (74 FR 225). Both the Environmental Protection Agency (EPA) and BLM published Notices...

  4. 76 FR 60475 - Issuance of a Loan Guarantee to Tonopah Solar Energy, LLC, for the Crescent Dunes Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-29

    ...The U.S. Department of Energy (DOE) announces its decision to issue a Federal loan guarantee under Title XVII of the Energy Policy Act of 2005 (EPAct 05), as amended by Section 406 of the American Recovery and Reinvestment Act of 2009 (Recovery Act), to Tonopah Solar Energy, LLC (TSE), for construction and start-up of the Crescent Dunes Solar Energy Project (the Project). The Project is a......

  5. 75 FR 81307 - Notice of Availability of Record of Decision for the Tonopah Solar Energy, LLC, Crescent Dunes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-27

    ...The Bureau of Land Management (BLM) announces the availability of the Record of Decision (ROD) for the Tonopah Solar Energy Crescent Dunes Solar Energy Project Environmental Impact Statement (EIS). The Secretary of the Interior approved the ROD on December 20, 2010, which constitutes the final decision of the...

  6. On the crescentic shape of barchan dune

    E-print Network

    P. Hersen

    2004-01-26

    Aeolian sand dunes originate from wind flow and sand bed interactions. According to wind properties and sand availability, they can adopt different shapes, ranging from huge motion-less star dunes to small and mobile barchan dunes. The latter are crescentic and emerge under a unidirectional wind, with a low sand supply. Here, a 3d model for barchan based on existing 2d model is proposed. After describing the intrinsic issues of 3d modeling, we show that the deflection of reptating particules due to the shape of the dune leads to a lateral sand flux deflection, which takes the mathematical form of a non-linear diffusive process. This simple and physically meaningful coupling method is used to understand the shape of barchan dunes.

  7. 75 FR 81307 - Notice of Availability of Record of Decision for the Tonopah Solar Energy, LLC, Crescent Dunes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-27

    ... analyzing impacts of the proposed project was published in the Federal Register on September 3, 2010 (75 FR... November 19, 2010 (75 FR 70917) and the BLM on November 26, 2010 (75 FR 72836). Three action alternatives...: 14X5017] Notice of Availability of Record of Decision for the Tonopah Solar Energy, LLC, Crescent...

  8. 75 FR 72836 - Notice of Availability of Final Environmental Impact Statement for the Tonopah Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-26

    ...Environmental Impact Statement for the Tonopah Solar Energy Crescent Dunes Solar Energy Project, Nye County, NV AGENCY: Bureau of...Impact Statement (EIS) for the Crescent Dunes Solar Energy Project, Nye County, Nevada, and by this...

  9. 75 FR 54177 - Notice of Availability of Draft Environmental Impact Statement for the Tonopah Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-03

    ...Environmental Impact Statement for the Tonopah Solar Energy Crescent Dunes Solar Energy Project, Nye County, NV AGENCY: Bureau of...Impact Statement (EIS) for the Crescent Dunes Solar Energy Project, Nye County, Nevada, and by this...

  10. Solar Storms, Devils, Dunes, and Gullies

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 12 December 2003

    Man, there sure is a lot going on here! This image was acquired during the peak of the late October record breaking solar storm outbursts. The white dots in this image were in fact caused when the charged particles from the sun hit our camera. One can also see the enigmatic gullies, dark barchan sand dunes and numerous dust devil tracks. This image is in the Noachis region of the heavily cratered southern hemisphere.

    Image information: VIS instrument. Latitude -42.1, Longitude 328.2 East (31.8 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.

  11. 75 FR 54177 - Notice of Availability of Draft Environmental Impact Statement for the Tonopah Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-03

    ...: 14X5017] Notice of Availability of Draft Environmental Impact Statement for the Tonopah Solar Energy Crescent Dunes Solar Energy Project, Nye County, NV AGENCY: Bureau of Land Management, Interior. ACTION... (EIS) for the Crescent Dunes Solar Energy Project, Nye County, Nevada, and by this Notice is...

  12. Crescent Wars

    NASA Astrophysics Data System (ADS)

    Schaefer, B. E.

    1997-12-01

    Historically, many calendars are based on lunar months, where the start of the month is based on the sighting of the thin crescent Moon in the evening twilight. Yet the problem of predicting (or postdicting) crescent visibility is a difficult task. In modern times, the Islamic calendar is used by more than a billion people, while its utility is abridged by the ambiguities in knowing the dates. As such, I would claim that crescent visibility is the single (nontrivial) astronomical problem that affects the most people. LeRoy Doggett spearheaded an effort to place crescent visibility on a firm observational basis by organizing five Moonwatch campaigns involving thousands of observers spread out across North America. His idea was to collect large numbers of actual observations for direct confrontation with models, and to measure the error rates. This talk will report on his results. The application of the results are broad; frequently in areas of scholarly, historical, social, or military disputes. For example, lunar visibility is vital for dating the Crucifixion, a task contentious among Biblical scholars. Another example is in testing the historicity of the claimed lunar impact reported by Gervase of Canterbury. The meeting will be held in the middle of the Islamic holy month of Ramadan, while in the past two decades the majority of Ramadans have been started based on reported crescent sightings before the time of New Moon.

  13. Barchan Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    28 April 2004 One of the simplest forms a sand dune can take is the barchan. The term, apparently, comes from the Arabic word for crescent-shaped dunes. They form in areas with a single dominant wind direction that are also not overly-abundant in sand. The barchan dunes shown here were imaged in March 2004 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) as it passed over a crater in western Arabia Terra near 21.1oN, 17.6oW. The horns and steep slope on each dune, known as the slip face, point toward the south, indicating prevailing winds from the north (top). The picture covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.

  14. Global Sea Level Stabilization-Sand Dune Fixation: A Solar-powered Sahara Seawater Textile Pipeline

    E-print Network

    Badescu, Viorel; Bolonkin, Alexander A

    2007-01-01

    Could anthropogenic saturation with pumped seawater of the porous ground of active sand dune fields in major deserts (e.g., the westernmost Sahara) cause a beneficial reduction of global sea level? Seawater extraction from the ocean, and its deposition on deserted sand dune fields in Mauritania and elsewhere via a Solar-powered Seawater Textile Pipeline (SSTP) can thwart the postulated future global sea level. Thus, Macro-engineering offers an additional cure for anticipated coastal change, driven by global sea level rise, that could supplement, or substitute for (1) stabilizing the shoreline with costly defensive public works (armoring macroprojects) and (2) permanent retreat from the existing shoreline (real and capital property abandonment). We propose Macro-engineering use tactical technologies that sculpt and vegetate barren near-coast sand dune fields with seawater, seawater that would otherwise, as commonly postulated, enlarge Earth seascape area! Our Macro-engineering speculation blends eremology with...

  15. Global Sea Level Stabilization-Sand Dune Fixation: A Solar-powered Sahara Seawater Textile Pipeline

    E-print Network

    Viorel Badescu; Richard B. Cathcart; Alexander A. Bolonkin

    2007-07-21

    Could anthropogenic saturation with pumped seawater of the porous ground of active sand dune fields in major deserts (e.g., the westernmost Sahara) cause a beneficial reduction of global sea level? Seawater extraction from the ocean, and its deposition on deserted sand dune fields in Mauritania and elsewhere via a Solar-powered Seawater Textile Pipeline (SSTP) can thwart the postulated future global sea level. Thus, Macro-engineering offers an additional cure for anticipated coastal change, driven by global sea level rise, that could supplement, or substitute for (1) stabilizing the shoreline with costly defensive public works (armoring macroprojects) and (2) permanent retreat from the existing shoreline (real and capital property abandonment). We propose Macro-engineering use tactical technologies that sculpt and vegetate barren near-coast sand dune fields with seawater, seawater that would otherwise, as commonly postulated, enlarge Earth seascape area! Our Macro-engineering speculation blends eremology with hydrogeology and some hydromancy. We estimate its cost at 1 billion dollars - about 0.01 per sent of the USA 2007 Gross Domestic Product.

  16. Barchan dune asymmetry: Numerical investigation

    E-print Network

    Parteli, Eric J R; Bourke, Mary C; Tsoar, Haim; Poeschel, Thorsten; Herrmann, Hans J

    2013-01-01

    Barchan dunes --- crescent-shaped dunes that form in areas of unidirectional winds and low sand availability --- commonly display an asymmetric shape, with one limb extended downwind. Several factors have been identified as potential causes for barchan dune asymmetry on Earth and Mars: asymmetric bimodal wind regime, topography, influx asymmetry and dune collision. However, the dynamics and potential range of barchan morphologies emerging under each specific scenario that leads to dune asymmetry are far from being understood. In the present work, we use dune modeling in order to investigate the formation and evolution of asymmetric barchans. We find that a bimodal wind regime causes limb extension when the divergence angle between primary and secondary winds is larger than $90^{\\circ}$, whereas the extended limb evolves into a seif dune if the ratio between secondary and primary transport rates is larger than 25%. Calculations of dune formation on an inclined surface under constant wind direction also lead to...

  17. An agent-based model of dune interactions produces the emergence of patterns in deserts

    NASA Astrophysics Data System (ADS)

    Génois, M.; Courrech Du Pont, S.

    2013-12-01

    Crescent-shaped barchan dunes are highly mobile dunes which are ubiquitous on Earth and other solar system bodies. Although they are unstable when considered separately, they form large assemblies in deserts and spatially organize in narrow corridors that extend in the wind direction. Collision of barchans has been proposed as a mechanism to redistribute sand between dunes and prevent the formation of very large dunes. Here, we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan fields. We tune the dune field density by changing the sand load/lost ratio and follow the transition between dilute fields, where barchans barely interact, and dense fields, where dune collisions control and stabilize the dune field. In this dense regime, barchans have a small, well selected size and form flocks: the dune field self-organizes in narrow corridors of dunes, as it is observed in real dense barchan deserts. Simulated dense barchan field, with spatial structuring along the wind direction.

  18. An agent-based model of dune interactions produces the emergence of patterns in deserts

    NASA Astrophysics Data System (ADS)

    GéNois, Mathieu; Pont, Sylvain Courrech; Hersen, Pascal; GréGoire, Guillaume

    2013-08-01

    Crescent-shaped barchan dunes are highly mobile dunes which are ubiquitous on Earth and other solar system bodies. Although they are unstable when considered separately, they form large assemblies in deserts and spatially organize in narrow corridors that extend in the wind direction. Collision of barchans has been proposed as a mechanism to redistribute sand between dunes and prevent the formation of very large dunes. Here we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan fields. We tune the dune field density by changing the sand load/lost ratio and follow the transition between dilute fields, where barchans barely interact, and dense fields, where dune collisions control and stabilize the dune field. In this dense regime, barchans have a small, well-selected size and form flocks: the dune field self-organizes in narrow corridors of dunes, as it is observed in real dense barchan deserts.

  19. Modelling of dune patterns by short range interactions Clement Narteau, Eric Lajeunesse, Francois Metivier & Olivier Rozier

    E-print Network

    Narteau, Clément

    on crescentic barchan dunes that are used as a benchmark for our numerical model of bedforms. Length and time scales of isolated barchan dunes are studied in order to constrain the parameters of the model. Then we concentrate on the formation and the evolution of crescentic barchans dunes as a bench- mark for a new model

  20. 75 FR 72836 - Notice of Availability of Final Environmental Impact Statement for the Tonopah Solar Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-26

    ... Availability for the Draft EIS for this project in the Federal Register (75 FR 54177). The BLM held two public...: 14X5017] Notice of Availability of Final Environmental Impact Statement for the Tonopah Solar Energy Crescent Dunes Solar Energy Project, Nye County, NV AGENCY: Bureau of Land Management, Interior....

  1. The temporal crescent syndrome.

    PubMed

    Ali, Khalid

    2015-02-01

    Retro-chiasmal lesions almost always give rise to homonymous field defects with only one exception. The nasal visual field extends to 60% of the horizon, whereas the temporal field extends to a further 30°-40° beyond that; this part of the visual field is represented on the contralateral anterior parieto-occipital sulcus. A lesion in this area will give rise to monocular visual field defect affecting the contralateral eye. This is called the temporal crescent or the half moon syndrome. In this case report, a woman presented with seizures secondary to haemorrhagic infarction of the anterior part of the parieto-occipital sulcus. She later presented with right-sided visual disturbance; her examination confirmed temporal crescent syndrome. I explain the pathophysiology of this rare neurological syndrome in this report. PMID:25416654

  2. Marching Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 15 September 2003

    The Ruza impact crater observed in this THEMIS image taken north of Argyre Planitia shows very interesting gullies and migrating sand dunes. The gullies appear to be more mature and subdued than some previously described gullies and are possibly being covered by a mantle of material. The barchan sand dunes observed in the northern edge of the impact crater are likely migrating up the crater wall as indicated by the crescent shape that points in the wind direction.

    Image information: VIS instrument. Latitude -34.2, Longitude 307.2 East (52.8 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.

  3. Linear stability analysis of transverse dunes

    E-print Network

    Hygor P. M. Melo; Eric J. R. Parteli; José S. Andrade Jr; Hans J. Herrmann

    2012-02-16

    Sand-moving winds blowing from a constant direction in an area of high sand availability form transverse dunes, which have a fixed profile in the direction orthogonal to the wind. Here we show, by means of a linear stability analysis, that transverse dunes are intrinsically unstable. Any along-axis perturbation on a transverse dune amplify in the course of dune migration due to the combined effect of two main factors, namely: the lateral transport through avalanches along the dune's slip-face, and the scaling of dune migration velocity with the inverse of the dune height. Our calculations provide a quantitative explanation for recent observations from experiments and numerical simulations, which showed that transverse dunes moving on the bedrock cannot exist in a stable form and decay into a chain of crescent-shaped barchans.

  4. Linear stability analysis of transverse dunes

    E-print Network

    Melo, Hygor P M; Andrade, José S; Herrmann, Hans J

    2012-01-01

    Sand-moving winds blowing from a constant direction in an area of high sand availability form transverse dunes, which have a fixed profile in the direction orthogonal to the wind. Here we show, by means of a linear stability analysis, that transverse dunes are intrinsically unstable. Any along-axis perturbation on a transverse dune amplify in the course of dune migration due to the combined effect of two main factors, namely: the lateral transport through avalanches along the dune's slip-face, and the scaling of dune migration velocity with the inverse of the dune height. Our calculations provide a quantitative explanation for recent observations from experiments and numerical simulations, which showed that transverse dunes moving on the bedrock cannot exist in a stable form and decay into a chain of crescent-shaped barchans.

  5. Stability of isolated Barchan dunes

    NASA Astrophysics Data System (ADS)

    Fourrière, Antoine; Charru, François

    2010-11-01

    When sand grains are entrained by an air flow over a non-erodible ground, or with limited sediment supply from the bed, they form isolated dunes showing a remarkable crescentic shape with horns pointing downstream. These dunes, known as Barchan dunes, are commonly observed in deserts, with height of a few meters and velocity of a few meters per year (Bagnold 1941). These dunes also exist under water, at a much smaller, centimetric size (Franklin & Charru 2010). Their striking stability properties are not well understood yet. Two phenomena are likely to be involved in this stability: (i) relaxation effects of the sand flux which increases from the dune foot up to the crest, related to grain inertia or deposition, and (ii) a small transverse sand flux due to slope effects and the divergence of the streamlines of the fluid flow. We reproduced aqueous Barchan dunes in a channel, and studied their geometrical and dynamic properties (in particular their shape, velocity, minimum size, and rate of erosion). Using coloured glass beads (see the figure), we were then able to measure the particle flux over the whole dune surface. We will discuss the stability of these dunes in the light of our measurements.

  6. Springtime Dunes, 2004

    NASA Technical Reports Server (NTRS)

    2004-01-01

    12 April 2004 Today is April 12, 2004, the 43rd anniversary of the first human flight into space (Yuri Gagarin, 1961) and the 23rd anniversary of the first NASA Space Shuttle flight (Columbia, 1981). Meanwhile, on Mars, spring is in full swing in the martian northern hemisphere. With spring comes the annual defrosting of the north polar dunes. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, acquired on April 7, 2004, shows a field of small barchan (crescent-shaped) dunes covered with the remains of wintertime frost. The dark spots around the base of each dune mark the first signs of the spring thaw. The sand in these dunes is dark, like the black sand beaches of Hawaii or the dark, sandy soil of the rover, Opportunity, landing site, but in winter and spring their dark tone is obscured by bright carbon dioxide frost. This picture is located near 75.9oN, 45.3oW, and covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

  7. Corridors of barchan dunes: Stability and size selection P. Hersen,1

    E-print Network

    Corridors of barchan dunes: Stability and size selection P. Hersen,1 K. H. Andersen,2 H. Elbelrhiti 29 January 2004 Barchans are crescentic dunes propagating on a solid ground. They form dune fields instabilities take place. First, barchans receive a sand flux at their back proportional to their width while

  8. On the shape of barchan dunes

    E-print Network

    Klaus Kroy; Sebastian Fischer; Benedikt Obermayer

    2005-01-07

    Barchans are crescent-shaped sand dunes forming in aride regions with unidirectional wind and limited sand supply. We report analytical and numerical results for dune shapes under different environmental conditions as obtained from the so-called `minimal model' of aeolian sand dunes. The profiles of longitudinal vertical slices (i.e. along the wind direction) are analyzed as a function of wind speed and sand supply. Shape transitions can be induced by changes of mass, wind speed and sand supply. Within a minimal extension of the model to the transverse direction the scale-invariant profile of transverse vertical cuts can be derived analytically.

  9. Crest line minimal model for sand dune

    NASA Astrophysics Data System (ADS)

    Guignier, Lucie; Valance, Alexandre; Lague, Dimitri

    2013-04-01

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

  10. When dunes move together, structure of deserts emerges

    E-print Network

    Génois, Mathieu; Pont, Sylvain Courrech du; Grégoire, Guillaume

    2012-01-01

    Crescent shaped barchan dunes are highly mobile dunes that are usually presented as a prototypical model of sand dunes. Although they have been theoretically shown to be unstable when considered separately, it is well known that they form large assemblies in desert. Collisions of dunes have been proposed as a mechanism to redistribute sand between dunes and prevent the formation of heavily large dunes, resulting in a stabilizing effect in the context of a dense barchan field. Yet, no models are able to explain the spatial structures of dunes observed in deserts. Here, we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan dune fields. Consequently, stationnary, out of equilibrium states emerge. Trigging the dune field density by a sand load/lost ratio, we show that large dune fields exhibit two assymtotic regimes: a dilute regime, where sand dune nucleation is needed to maintain a dune field, and a dense regime, where dune c...

  11. Dune morphodynamics

    NASA Astrophysics Data System (ADS)

    Courrech du Pont, Sylvain

    2015-01-01

    The physics of dunes relies on the interaction between a wind flow and an erodible topography. Thus, if strong enough to transport grains, the wind shapes sandy areas into dune fields. These dunes are reminiscent of a wavy sea so that sandy deserts are called sand seas. However, the comparison stops there. Contrary to water waves, dunes propagate only under wind action and when the wind stops, they do not vanish but stand. Consequently, dunes are not only the result of the present winds, but can integrate the wind regimes over long periods. Thus, they exhibit a range of shapes and sizes with superimposed patterns. They are witnesses of past wind regimes and their shape and orientation are used to constraint climatic models on other planetary bodies where they are observed as well (e.g., Mars, Titan and Venus). Here, we discuss the morphodynamics of dunes and endeavor to identify and to explain the physical mechanisms at play in the selection of their shape, size and orientation, whilst focusing on Earth desert sand dunes.

  12. Development of spatially diverse and complex dune-field patterns: Gran Desierto Dune Field, Sonora, Mexico

    USGS Publications Warehouse

    Beveridge, C.; Kocurek, G.; Ewing, R.C.; Lancaster, N.; Morthekai, P.; Singhvi, A.K.; Mahan, S.A.

    2006-01-01

    The pattern of dunes within the Gran Desierto of Sonora, Mexico, is both spatially diverse and complex. Identification of the pattern components from remote-sensing images, combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns. Age-bracketing by optically stimulated luminescence (OSL) indicates that the simple patterns represent relatively short-lived aeolian constructional events since ???25 ka. The simple dune patterns consist of: (i) late Pleistocene relict linear dunes; (ii) degraded crescentic dunes formed at ???12 ka; (iii) early Holocene western crescentic dunes; (iv) eastern crescentic dunes emplaced at ???7 ka; and (v) star dunes formed during the last 3 ka. Recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern. Palaeowind reconstructions, based upon the rule of gross bedform-normal transport, are largely in agreement with regional proxy data. The sediment state over time for the Gran Desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment (Ancestral Colorado River sediment), and contemporaneous influx from the lower Colorado River valley and coastal influx from the Bahia del Adair inlet. Aeolian constructional events are triggered by climatic shifts to greater aridity, changes in the wind regime, and the development of a sediment supply. The rate of geomorphic change within the Gran Desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests. ?? 2006 The Authors. Journal compilation 2006 International Association of Sedimentologists.

  13. Arkhangelsky Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    29 April 2004 These dark-toned barchan sand dunes in Arkhangelsky Crater were viewed by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in late southern summer on 17 February 2004. Hundreds of narrow, dark streaks crisscross the dunes and the interdune terrain; these were most likely formed by the disruption of fine sediment by passing dust devils. The dune field is located near 41.2oS, 25.0oW, and is illuminated by sunlight from the upper left. Dune horns and slip faces indicate that the dominant winds blow from the southwest (lower left). The picture covers an area about 3 km (1.9 mi) across.

  14. Arabian Dunes

    NASA Technical Reports Server (NTRS)

    2005-01-01

    11 June 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a field of low-albedo (dark) barchan sand dunes in a crater located in western Arabia Terra. Small dunes like these are common in the craters of western Arabia Terra and they are often the source of finer, dark sediment that forms windstreaks further downwind. The steepest slopes on the dunes, their slipfaces, are pointed toward the southeast (lower right), indicating that the dominant winds in this location come from the opposite direction.

    Location near: 6.4oN, 346.2oW Image width: 3 km (1.9 mi Illumination from: lower left Season: Northern Autumn

  15. Minimal size of a barchan dune.

    PubMed

    Parteli, E J R; Durán, O; Herrmann, H J

    2007-01-01

    Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B 28, 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E 64, 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002)] that this flux fetch distance is itself constant. Indeed, this could not explain the protosize of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three-dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars. PMID:17358139

  16. Windblown Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    18 June 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows barchan and linear dunes that seem to have grown from the coalescence of barchans in a crater in the Noachis Terra region. The winds responsible for these dunes blow from the lower left (southwest). The image occurs near 46.0oS, 323.6oW, and covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the upper left.

  17. Dune Field in Nili Pateria

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this image of the southeastern edge of a large dune field within Nili Patera, an irregularly shaped volcanic caldera that is about 65 kilometers (40 miles) in diameter. The image was acquired at 1333 UTC (8:33 a.m. EST) on Feb. 1, 2007, near 8.8 degrees north latitude, 67.3 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 20 meters (66 feet) across. The region covered by the image is just over 10 kilometers (6 miles) wide at its narrowest point.

    The top image was constructed from three visible wavelengths that correspond to what our eyes would see; the colors are stretched to bring out subtle color contrast. The bottom image is a spectral map constructed using three infrared wavelengths that usually highlight compositional variations. Areas with high concentrations of iron- and magnesium-rich igneous minerals appear red.

    The entire dune field, covering about 500 square kilometers, resides mainly in the southwest quadrant of the caldera, occupying approximately 15% of its floor. Some of the dune forms seen here are 'barchans' -- individual, crescent shaped dunes that form when winds come primarily from one direction, resulting in one slipface. The orientation of the slipfaces indicates that primary winds were coming from the east-northeast. Using images from Mars Global Surveyor's narrow-angle camera, researchers measured approximately 400 slipfaces throughout the dune field and calculated an average azimuth of 245 degrees. Some of the barchans have elongated horns, suggesting that they experienced a slight secondary wind, or that the primary wind direction varied a little. When sufficient sand is available, barchans will coalesce, losing their individual crescentic shape. The resulting dune form, referred to as barchanoid, describes the vast majority of dunes in this image.

    In the lower left portion of the image, where the dune pattern is most regular, the distance from dune crest to dune crest is about 400 meters (437 yards). The relationship shown here, with barchans at the margin of a barchanoid dune field, is common on Mars.

    CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument will also watch the seasonal variations in Martian dust and ice aerosols, and water content in surface materials -- leading to new understanding of the climate.

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

  18. Dune Exploration: Mars Allegories

    NASA Astrophysics Data System (ADS)

    Zahnle, K.; Sleep, N. H.; Abe, Y.; Abe-Ouchi, A.

    2005-12-01

    We know of one factual habitable planet, although other factual planets can be imagined as habitable. Sometimes the allegory is obvious. E.g., H. G. Wells imagined Martians exterminating humans as an allegory to Englishmen exterminating the Tasmanian aborigines, whilst Percival Lowell saw the global network of Martian canals as a world civilization that had progressed beyond war. But most habitable planets are overtly fictional. The planet properly known as Arrakis and colloquially known as Dune (Herbert 1965) provides an exceptionally well-developed example of a fictional habitable planet. In its particulars Dune resembles a warmer Mars with a breathable oxygen atmosphere. Like Mars, Dune is now a parched desert planet but there are signs that water flowed in the prehistoric past. Dune has small water ice caps at the poles and more extensive deep polar aquifers. The tropics are exceedingly dry but the polar regions are cool and moist enough to have morning dew. Dune is sparsely inhabited by a mix of indigenous and terran flora and fauna. The fictional Dune asks us to consider how much water is enough, why does oxygen accumulate in an atmosphere, and what actually sets the inner edge to the habitable zone. The inner edge of the habitable zone is conventionally set by the onset of the runaway greenhouse effect. The runaway greenhouse occurs when there is enough water vapor in the atmosphere to lift the planet's thermal photosphere off the ground. For a wet planet the mapping between saturation, temperature and optical depth is unique; together these set an upper limit on the rate the amount of thermal radiation that the planet can emit and still maintain a humid atmosphere. A dry atmosphere has a lower opacity for a given temperature, other things equal. With its vast dry equatorial deserts, a habitable Dune can radiate at a significantly higher effective temperature than a wet planet, and so it can provide an abode for life significantly closer to its sun. We use GCM modeling to show that liquid water can exist at places on the surface of a Dune-like planet at insolation levels as much as 170% of the present solar flux of the Earth.

  19. Origins of barchan dune asymmetry: Insights from numerical simulations

    NASA Astrophysics Data System (ADS)

    Parteli, Eric J. R.; Durán, Orencio; Bourke, Mary C.; Tsoar, Haim; Pöschel, Thorsten; Herrmann, Hans

    2014-03-01

    Barchan dunescrescent-shaped dunes that form in areas of unidirectional winds and low sand availability — commonly display an asymmetric shape, with one limb extended downwind. Several factors have been identified as potential causes for barchan dune asymmetry on Earth and Mars: asymmetric bimodal wind regime, topography, influx asymmetry and dune collision. However, the dynamics and potential range of barchan morphologies emerging under each specific scenario that leads to dune asymmetry are far from being understood. In the present work, we use dune modeling in order to investigate the formation and evolution of asymmetric barchans. We find that a bimodal wind regime causes limb extension when the divergence angle between primary and secondary winds is larger than 90°, whereas the extended limb evolves into a seif dune if the ratio between secondary and primary transport rates is larger than 25%. Calculations of dune formation on an inclined surface under constant wind direction also lead to barchan asymmetry, however no seif dune is obtained from surface tilting alone. Asymmetric barchans migrating along a tilted surface move laterally, with transverse migration velocity proportional to the slope of the terrain. Limb elongation induced by topography can occur when a barchan crosses a topographic rise. Furthermore, transient asymmetric barchan shapes with extended limb also emerge during collisions between dunes or due to an asymmetric influx. Our findings can be useful for making quantitative inference on local wind regimes or spatial heterogeneities in transport conditions of planetary dune fields hosting asymmetric barchans.

  20. Origins of barchan dune asymmetry: insights from numerical simulations

    E-print Network

    Eric J. R. Parteli; Orencio Durán; Mary C. Bourke; Haim Tsoar; Thorsten Poeschel; Hans J. Herrmann

    2013-12-02

    Barchan dunes --- crescent-shaped dunes that form in areas of unidirectional winds and low sand availability --- commonly display an asymmetric shape, with one limb extended downwind. Several factors have been identified as potential causes for barchan dune asymmetry on Earth and Mars: asymmetric bimodal wind regime, topography, influx asymmetry and dune collision. However, the dynamics and potential range of barchan morphologies emerging under each specific scenario that leads to dune asymmetry are far from being understood. In the present work, we use dune modeling in order to investigate the formation and evolution of asymmetric barchans. We find that a bimodal wind regime causes limb extension when the divergence angle between primary and secondary winds is larger than $90^{\\circ}$, whereas the extended limb evolves into a seif dune if the ratio between secondary and primary transport rates is larger than 25%. Calculations of dune formation on an inclined surface under constant wind direction also lead to barchan asymmetry, however no seif dune is obtained from surface tilting alone. Asymmetric barchans migrating along a tilted surface move laterally, with transverse migration velocity proportional to the slope of the terrain. Limb elongation induced by topography can occur when a barchan crosses a topographic rise. Furthermore, transient asymmetric barchan shapes with extended limb also emerge during collisions between dunes or due to an asymmetric influx. Our findings can be useful for making quantitative inference on local wind regimes or spatial heterogeneities in transport conditions of planetary dune fields hosting asymmetric barchans.

  1. Jenkins Dune

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This image is of a landform informally called Jenkins Dune and is thought to be a small barchan dune. This feature is less than 1 foot (0.3 m) tall and perhaps 2-3 meters wide. Inferred wind direction is from the left to the right. Near the crest of the feature is a demarcation that may represent the exposure of a crust on the sediments; similar features were seen on sediments on the rock Big Joe at the Viking landing site.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech).

  2. Lowell's Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    9 December 2004 A century ago, the name Percival Lowell and the planet Mars were intimately linked through his popular writings about canals built by intelligent beings on the fourth planet. Today, a crater in the southern hemisphere of Mars is named for Lowell, who usually observed the planet from a hilltop in Flagstaff, Arizona. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, acquired in October 2004, shows a portion of a sand dune field in western Lowell Crater. The dunes are located near 51.3oS, 82.5oW. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  3. Corridors of barchan dunes: Stability and size selection.

    PubMed

    Hersen, P; Andersen, K H; Elbelrhiti, H; Andreotti, B; Claudin, P; Douady, S

    2004-01-01

    Barchans are crescentic dunes propagating on a solid ground. They form dune fields in the shape of elongated corridors in which the size and spacing between dunes are rather well selected. We show that even very realistic models for solitary dunes do not reproduce these corridors. Instead, two instabilities take place. First, barchans receive a sand flux at their back proportional to their width while the sand escapes only from their horns. Large dunes proportionally capture more sand than they lose, while the situation is reversed for small ones: therefore, solitary dunes cannot remain in a steady state. Second, the propagation speed of dunes decreases with the size of the dune: this leads, through the collision process, to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further, yet unknown, mechanisms regulating and selecting the size of dunes. PMID:14995611

  4. 77 FR 39413 - Safety Zone: Crescent City Fourth of July Fireworks Event, Crescent City, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-03

    ...: Table of Acronyms DHS Department of Homeland Security FR Federal Register NPRM Notice of Proposed... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone: Crescent City Fourth of July Fireworks Event, Crescent City, CA AGENCY: Coast Guard, DHS. ACTION: Temporary final rule. SUMMARY: The...

  5. 78 FR 23866 - Safety Zone; Crescent City 4th of July Fireworks; Crescent City Harbor, Crescent City, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-23

    .... SUPPLEMENTARY INFORMATION: Table of Acronyms DHS Department of Homeland Security FR Federal Register NPRM Notice... public dockets in the January 17, 2008, issue of the Federal Register (73 FR 3316). 4. Public Meeting We... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; Crescent City 4th of July...

  6. Equilibrium versus disequilibrium of barchan dunes

    NASA Astrophysics Data System (ADS)

    El belrhiti, Hicham; Douady, Stéphane

    2011-02-01

    Barchans are crescentic dunes which occur in mainly mono-directional winds. Shape, aspect ratios and velocities of these dunes have been studied as if they were in equilibrium. However, following a study of the shape and migration of 11 barchans of different sizes for 18 months in the field on Moroccan Atlantic Sahara, we show that they only appear to be in a stationary state if studied over a long timeframe (at the scale of the year or several years), but are never in equilibrium at the scale of weeks or months. Rather, they are always 'trying' to reach a possible equilibrium state but never have enough time to accomplish this. This may be the main reason for the large variation observed in previous measurements, and justifies some caution in what can be deduced from them.

  7. Morphodynamic implications of flow around interacting barchan dunes

    NASA Astrophysics Data System (ADS)

    Tang, Z.; Blois, G.; Best, J.; Jiang, N.; Christensen, K. T.

    2013-12-01

    Barchan dunes are three-dimensional topographic features characterized by a crescentic shape. These bedforms are ubiquitous on Earth's surface and are also observed on Mars. Barchan dunes are predominantly found in regions of sediment starvation and unidirectional flow. The barchans-dune migration rates for a given wind speed are a function of their respective volume. A barchan dune field is composed of a widely distributed dune size, which provides the potential for barchan dunes to approach and amalgamate. The mechanisms governing dune-dune interaction, collision and merging remain poorly understood for such complex three-dimensional bedforms due to the complexity of their shape and the high number of geometrical configurations that can occur. In order to quantify the flow structure produced by interacting barchan dunes, particle-image Velocimetry (PIV) is coupled with a refractive-index-matching (RIM) approach, facilitating full optical access to the obstructed regions of flow and eliminates reflections from the liquid-solid boundaries, allowing near-wall data to be collected. Transparent barchan dune models with different volumes are arranged in tandem, immersed in a turbulent flow and rendered invisible through accurate matching of the index of refraction of the solid and fluid phases. The approach applied herein facilitates flow-field measurements in both streamwise-wall-normal planes at varying spanwise positions and streamwise-spanwise planes at varying elevations. Ensemble-averaged flow fields and Reynolds stresses were obtained for different barchan dune spacings and compared to the reference case of an isolated barchan. Additionally, proper orthogonal decomposition (POD) analysis was employed to shed light as to the energetic attributes of the shear-layer interactions. The morphodynamic implications of these results are discussed. Shear-layer interactions between adjacent bedforms, stoss-side erosion and downstream separation of new bedforms from the upstream horn are found to be key aspects of the interaction process.

  8. Collision dynamics of two barchan dunes simulated by a simple model

    E-print Network

    Atsunari Katsuki; Hiraku Nishimori; Noritaka Endo; Keisuke Taniguchi

    2004-12-24

    The collision processes of two crescentic dunes called barchans are systematically studied using a simple computer simulation model. The simulated processes, coalescence, ejection and reorganization, qualitatively correspond to those observed in a water tank experiment. Moreover we found the realized types of collision depend both on the mass ratio and on the lateral distance between barchans under initial conditions. A simple set of differential equations to describe the collision of one-dimensional (1D) dunes is introduced.

  9. PEDESTRIAN UNDERPASS AT CRESCENT ROAD AND ROOSEVELT CENTER FROM NORTH. ...

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

    PEDESTRIAN UNDERPASS AT CRESCENT ROAD AND ROOSEVELT CENTER FROM NORTH. NOTE DALE WINLING, 2005 SALLY KRESS TOMPKINS FELLOW, WALKING THROUGH UNDERPASS. - Old Greenbelt, Crescent Road and Southway, Greenbelt, Prince George's County, MD

  10. Movement of Whole Martian Dunes Difficult to Detect or Confirm

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Dunes on Earth move downwind at different speeds depending upon the local wind conditions, the amount of loose sand available to be transported by wind, the shape and volume of the dunes, and overgrowths of vegetation. Typically, smaller dunes move faster than larger dunes. On Earth, some of the fastest-moving dunes that have been measured (e.g., in the deserts of Peru) move 10 to 30 meters (33 to 100 feet) per year. Small dunes usually have an almost crescent-shape to them, and are known to geologists as barchan dunes.

    To look for evidence of dune movement on Mars, the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) has been used to re-visit some areas of known barchan dunes--because these types move the fastest--that were observed by the Mariner 9 orbiter in 1972 and the Viking 1 and 2 orbiters between 1976 and 1980. The picture above, left, shows a MOC high-resolution image taken December 25, 1999. The classic, crescentic shape of the dark barchan dunes can be seen in this picture. The steep slopes, also known as the dune slip faces, on these dunes are facing toward the southwest (north is up in both pictures). Thus, the shape of the dunes indicates that they are moving toward the southwest.

    The picture above right shows the MOC image from December 1999 superimposed on a Viking 1 image taken May 27, 1978. During the 11 1/2 Mars years that passed between these two dates, it turns out that no difference can be detected in the position of the dunes seen in the MOC image and the Viking image. The earlier Viking image had a resolution of about 17 meters (56 ft) per pixel, while the MOC image had a resolution of about 3.8 meters (12 ft) per pixel. Although it looks like the dunes didn't move between the Viking and MOC images, this observation is limited by the resolution of the Viking image. It is entirely possible that the dunes have moved as much as 17-20 meters (16-66 ft) and one would not be able to tell by comparing the images. As it is, movement of less than 20 meters (66 ft) in 11 martian years (nearly 22 Earth years) is slower than some dunes of similar size and shape on Earth. Thus, it appears that martian dunes are not 'experiencing' the level of activity commonly reported for some of the modern desert dunes found on Earth. The dune field illustrated in these pictures is located in a western Arabia Terra crater at 1.6oN, 351.6oW. Both the Viking and MOC images are illuminated from the left.

  11. 'Endurance Crater's' Dazzling Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    As NASA's Mars Exploration Rover Opportunity creeps farther into 'Endurance Crater,' the dune field on the crater floor appears even more dramatic. This approximate true-color panoramic camera image highlights the reddish-colored dust present throughout the scene.

    Sinuous tendrils of sand less than 1 meter (3.3 feet) high extend from the main dune field toward the rover. Scientists hope to send the rover down to one of these tendrils in an effort to learn more about the characteristics of the dunes. Dunes are a common feature across the surface of Mars, and knowledge gleaned from investigating the Endurance dunes close-up may apply to similar dunes elsewhere.

    Before the rover heads down to the dunes, rover drivers must first establish whether the slippery slope that leads to them is firm enough to ensure a successful drive back out of the crater. Otherwise, such hazards might make the dune field a true sand trap.

  12. First Visibility of the Lunar Crescent

    NASA Astrophysics Data System (ADS)

    Caldwell, J. A. R.; Laney, C. D.

    2000-12-01

    Astronomical observatories are often asked to predict the visibility of the young crescent moon by communities (especially Islamic and Karaite) which use traditional lunar calendars. The SAAO has provided such information for many years, but the early 1990s were a watershed of sorts. Astronomical visibility factors in those years created an unusually severe bias against visibility of the Ramadaan and Shawwall crescents from the southern half of the continent, relative to North Africa and the Mideast (to an extent not seen since the 1860s!). The perplexity caused by the resulting delay in sightings ultimately led to a much greater level of communication between astronomers and the crescent-watching community. The SAAO began collecting, systematizing, and propagating the astronomical information available on the crescent visibility issue, the current results of which are summarized here. Les communauté (spécialement islamiques et karaïtes) qui utilisent les calendriers lunaires traditionnels, demandent souvent aux observatoires astronomiques de prédire le moment oú le croissant de lune naissant devient visible. Depuis de nombreuses années le SAAO fournit cette information, mais les années 1990 furent une sorte de tournant. Dans ces années-là les facteurs de visibilité astronomiques créèrent une déviation exceptionnellement grave par rapport à la visibilité des croissants du Ramadan et du Shawal sur la moitié sud du continent relative à l'Afrique du Nord et au Moyen-Orient (dans une mesure jamais atteinte depuis les années 1860!). La perplexité due au retard qui en résulta dans la vision du nouveau croissant, conduisit finalement à renforcer la communication entre les astronomes et la communauté des observateurs du croissant. Le SAAO commença à collecter, systématiser et diffuser l'information astronomique disponible sur la question de la visibilité du croissant dont nous résumons ici les résultats actuels.

  13. 33 CFR 80.1152 - Crescent City Harbor, CA.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Crescent City Harbor, CA. 80.1152... NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1152 Crescent City Harbor, CA. A line drawn from Crescent City Entrance Light to the southeasternmost extremity of Whaler Island....

  14. Transverse instability of dunes.

    PubMed

    Parteli, Eric J R; Andrade, José S; Herrmann, Hans J

    2011-10-28

    The simplest type of dune is the transverse one, which propagates with invariant profile orthogonally to a fixed wind direction. Here we show, by means of numerical simulations, that transverse dunes are unstable with respect to along-axis perturbations in their profile and decay on the bedrock into barchan dunes. Any forcing modulation amplifies exponentially with growth rate determined by the dune turnover time. We estimate the distance covered by a transverse dune before fully decaying into barchans and identify the patterns produced by different types of perturbation. PMID:22107675

  15. Transverse instability of dunes

    E-print Network

    Eric J. R. Parteli; José S. Andrade Jr.; Hans J. Herrmann

    2011-09-22

    The simplest type of dune is the transverse one, which propagates with invariant profile orthogonally to a fixed wind direction. Here we show numerically and with a linear stability analysis that transverse dunes are unstable with respect to along-axis perturbations in their profile and decay on the bedrock into barchan dunes. Any forcing modulation amplifies exponentially with growth rate determined by the dune turnover time. We estimate the distance covered by a transverse dune before fully decaying into barchans and identify the patterns produced by different types of perturbation.

  16. Transverse Instability of Dunes

    NASA Astrophysics Data System (ADS)

    Parteli, Eric J. R.; Andrade, José S., Jr.; Herrmann, Hans J.

    2011-10-01

    The simplest type of dune is the transverse one, which propagates with invariant profile orthogonally to a fixed wind direction. Here we show, by means of numerical simulations, that transverse dunes are unstable with respect to along-axis perturbations in their profile and decay on the bedrock into barchan dunes. Any forcing modulation amplifies exponentially with growth rate determined by the dune turnover time. We estimate the distance covered by a transverse dune before fully decaying into barchans and identify the patterns produced by different types of perturbation.

  17. Fire scars and ancient sand dunes in southern Australia

    NASA Technical Reports Server (NTRS)

    1994-01-01

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

  18. Modeling the Large-Scale Structure and Long-Term Evolution of a Barchan Dune Field

    NASA Astrophysics Data System (ADS)

    Worman, S.; Littlewood, R. C.; Murray, A.; Andreotti, B.; Claudin, P.

    2011-12-01

    Barchans are mobile, crescent-shaped dunes that form atop hard, flat surfaces in regions where sediment supply is limited and fluid flow is approximately unidirectional. At the dune-scale, coupled models of sand transport and fluid dynamics have successfully reproduced their characteristic behavior and morphology. However, in nature, dunes rarely exist as isolated individuals but are instead found in highly-structured fields: Within a dune field with a cross-wind dimension on the order of 10 kilometers, patches of dunes can alternate spatially with sparse or dune-free regions, and the patches may have different characteristic dune size and spacing. The origin of such enigmatic structures cannot seem to be explained by differences in external forcing and remains an open research question. We use a partly rule-based numerical model that treats single dunes as discrete entities, based on the results of a dune-scale fluid-dynamics/sediment transport model. Our model integrates all currently known processes through which dunes interact with one another (i.e. sand flux exchange, collision, and calving). A rich array of patterns similar to those observed in nature emerge from these relatively simple interactions, offering a potential explanation of field-scale phenomena. We also develop simple statistics to characterize these structures and furnish testable predictions for future empirical work.

  19. Defrosting of Russell Crater Dunes

    NASA Technical Reports Server (NTRS)

    2007-01-01

    These two images (at right) were acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) 39 days apart at 19:10 UTC (2:10 PM EST) on December 28, 2006 (upper right) and at 20:06 UTC (3:06 PM EST) on February 5, 2007 (lower right). These CRISM data were acquired in 544 colors covering the wavelength range from 0.36-3.92 micrometers, and show features as small as 20 meters (about 65 feet) across. Both images are false color composites of bands at 2.5, 1.5, and 1.25 micrometers, and are nearly centered at the same location, 54.875oS, 12.919oE (upper right) and 54.895oS, 12.943oE (lower right). Each image is approximately 11 kilometers (7 miles) across at its narrowest. These are part of a series of images capturing the evolution of carbon dioxide frost on the surface of the dunes in Russell Crater.

    Russell Crater is one of many craters in the southern highland region of Mars that contain large areas of sand dunes. The sand in these dunes has accumulated over a very long time period -- perhaps millions of years -- as wind blows over the highland terrain, picking up sand in some places and depositing in others. The topography of the craters forces the wind to blow up and over the crater rims, and the wind often isn't strong enough to keep the tiny grains suspended. This makes the sand fall to the ground and gradually pile up, and over time the surface breezes shape the sand into ripples and dunes. A similar process is at work at the Great Sand Dunes National Park and Preserve in Colorado, USA.

    The above left image shows a THEMIS daytime infrared mosaic of Russell Crater and the location of its (approximately) 30-kilometer wide dune field in the northeastern quadrant of the crater floor. Superposed on this view and shown enlarged at the upper right is CRISM image FRT000039DF. This CRISM image was acquired during the late Martian southern winter (solar longitude = 157.7o), and the bright blue in this false color composite indicates the presence of carbon dioxide frost (dry ice) on the dunes. Sunlight is coming from the northeast, and the sunlit faces of the dunes appear red because they show very little frost compared to the colder, more shadowed areas. Thirty-nine days later at the beginning of southern spring (solar longitude = 178.9o), CRISM image FRT000042AA (lower right) was acquired almost at the same location. Notably, the bright blue frost-rich areas are considerably smaller and subdued, with slim patches only observed on the shadowed sides of the dunes that are most protected from the warmth of the rising sun. As the southern season continues to march toward summer, all of the frost will soon be gone and won't return until the next Martian winter.

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

  20. Color Voyager 2 Image Showing Crescent Uranus

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This image shows a crescent Uranus, a view that Earthlings never witnessed until Voyager 2 flew near and then beyond Uranus on January 24, 1986. This planet's natural blue-green color is due to the absorption of redder wavelengths in the atmosphere by traces of methane gas. Uranus' diameter is 32,500 miles, a little over four times that of Earth. The hazy blue-green atmosphere probably extends to a depth of around 5,400 miles, where it rests above what is believed to be an icy or liquid mixture (an 'ocean') of water, ammonia, methane, and other volatiles, which in turn surrounds a rocky core perhaps a little smaller than Earth.

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

    USGS Publications Warehouse

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

    2015-01-01

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

  2. 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.

  3. Windblown Dunes on the Floor of Herschel Impact Basin

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Herschel Basin, one of many meteor impact craters on Mars, has some dark material on its floor that appeared from earlier spacecraft missions to have been blown and/or deposited by wind. Herschel Basin was imaged at low resolution by the Mariner 9 and Viking orbiters ((A) above) in the 1970s, and again by the Phobos 2 orbiter in 1989.

    On June 14, 1998, Mars Global Surveyor's Mars Orbiter Camera revealed that part of the dark surface on the floor of Herschel Basin consists of a field of sand dunes ((B) above). These dunes have a distinct crescent-like shape characteristic of dunes on Earth called barchan dunes. They result from winds that blow from a single dominant direction.

    In the case of Herschel Basin, the dunes indicate that the strongest winds blow approximately north-to-south. The crescent horns on the ends of some of the dunes in this image are elongated. This condition indicates that the dominant winds do not always blow in exactly the same direction-- sometimes the winds blow from the northeast, sometimes from the northwest, and sometimes from the north. The local topography probably influences the wind direction--and hence dune shape--because this dune field is located on a narrow, low plain between a high crater rim to the east, and a narrow mountain range-- the inner ring of the Herschel impact basin--to the west (see image (A)).

    MOC image 36507 was obtained on Mars Global Surveyor's 365th orbit around 10:51 a.m. PDT on June 14, 1998. This subframe is centered around 14.27oS, 231.68oW.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  4. Dune Avalanche Scars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    05 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, low albedo (dark) sand dunes in Kaiser Crater near 47.2oS, 340.4oW. The dunes are--ever so slowly--moving east to west (right to left) as sand avalanches down the steeper, slip face slopes of each. Avalanching sand in the Kaiser dune field has left deep scars on these slopes, suggesting that the sand is not loose but is instead weakly cemented. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  5. Fortune Cookie Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

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

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

  6. Frosty Dune Field

    NASA Technical Reports Server (NTRS)

    2004-01-01

    1 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows frost-covered sand dunes in the early northern spring of 2004 in the north polar region. Sunlight illuminates the dunes from the bottom/lower left, but frost on slopes facing the lower right create the illusion of sunlight from that direction. This dune field, which would appear quite dark in summertime, is located near 80.3oN, 148.7oW. The picture covers an area about 3 km (1.9 mi) across.

  7. Linking Atmospheric Models and Dune Morphology - Testing a Forward Modeling Approach

    NASA Astrophysics Data System (ADS)

    Lancaster, N.; Newman, C. E.

    2014-12-01

    Observations of dune orientation provide information on unknown wind regimes, e.g. on other planets or in past climates. While orientation can be used to infer e.g. dominant wind directions, a more comprehensive 'forward modeling' approach first predicts the long-term wind field, then combines it with theory to predict dune orientation. Theory includes the gross bedform normal transport model (GBNT), in which dunes in unlimited sand availability orient normal to the direction of maximum gross transport, or the 'fingering mode' of Courrech du Pont et al. (2014), in which dunes align with the direction of resultant transport, R, in limited sand availability. A good match between observed and predicted orientations suggests the theory is sound and the simulated wind field realistic. Conversely, a poor match suggests either the simulated wind field is unrealistic or the theory lacking, and that the assumptions and parameters contained in one or both must be modified. Aspects of the approach may be tested on Earth, where ground truth wind data are often available. We used (1) surface wind data to predict dune orientations in the Arabian Peninsula; and (2) uncalibrated surface winds predicted by a regional climate model (WRF) to predict dune orientations in the Namib Sand Sea. We then compared the observed orientations with those predicted using the forward modeling approach. (1) provides a direct test of dune formation theory, while (2) provides a test of the complete 'blind' forward modeling approach. For (1) we predicted dune characteristics using 2000-2009 wind data for 20 stations in or near dune fields to calculate potential sand flux and thereby GBNT dune orientation and R. GBNT theory was a good predictor of crescentic dune orientation, but performed poorly for small and large linear dunes, which were well-predicted by R. This suggests the crescentic dunes formed in unlimited sand, whereas the linear dunes may have formed in areas with limited sand. For (2) we used a year of WRF winds at 3km resolution. The match between observed and predicted orientations appears much better for GBNT theory, compared to R (though mismatches remain), which may reflect high sand availability. The next steps are to vary the assumed saltation threshold, and to use winds after calibrating WRF to match nearby observational wind data.

  8. Syrtis Major Dune Field

    NASA Technical Reports Server (NTRS)

    2004-01-01

    20 December 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows barchan sand dunes west of the Meroe Patera volcanic caldera in central Syrtis Major. The winds that shape these dunes blow from the right/upper right (northeast). The surface across which the dunes have traveled is probably composed of volcanic rocks; the dunes, too, may have volcanic materials, such as sand-sized grains of tephra-volcanic ash-in them. This October 2003 view is located near 7.4oN, 292.3oW, and covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  9. Lunar Crescent Detection Based on Image Processing Algorithms

    NASA Astrophysics Data System (ADS)

    Fakhar, Mostafa; Moalem, Peyman; Badri, Mohamad Ali

    2014-11-01

    For many years lunar crescent visibility has been studied by many astronomers. Different criteria have been used to predict and evaluate the visibility status of new Moon crescents. Powerful equipment such as telescopes and binoculars have changed capability of observations. Most of conventional statistical criteria made wrong predictions when new observations (based on modern equipment) were reported. In order to verify such reports and modify criteria, not only previous statistical parameters should be considered but also some new and effective parameters like high magnification, contour effect, low signal to noise, eyestrain and weather conditions should be viewed. In this paper a new method is presented for lunar crescent detection based on processing of lunar crescent images. The method includes two main steps, first, an image processing algorithm that improves signal to noise ratio and detects lunar crescents based on circular Hough transform (CHT). Second using an algorithm based on image histogram processing to detect the crescent visually. Final decision is made by comparing the results of visual and CHT algorithms. In order to evaluate the proposed method, a database, including 31 images are tested. The illustrated method can distinguish and extract the crescent that even the eye can't recognize. Proposed method significantly reduces artifacts, increases SNR and can be used easily by both groups astronomers and who want to develop a new criterion as a reliable method to verify empirical observation.

  10. Booming Sand Dunes

    NASA Astrophysics Data System (ADS)

    Vriend, Nathalie

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

  11. Dark Barchan Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    13 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows north polar sand dunes in the summertime. During winter and early spring, north polar dunes are covered with bright frost. When the frost sublimes away, the dunes appear darker than their surroundings. To a geologist, sand has a very specific meaning. A sand grain is defined independently of its composition; it is a particle with a size between 62.5 and 2000 microns. Two thousand microns equals 2 millimeters. The dunes are dark because they are composed of sand grains made of dark minerals and/or rock fragments. Usually, dark grains indicate the presence of unoxidized iron, for example, the dark volcanic rocks of Hawaii, Iceland, and elsewhere. This dune field is located near 71.7oN, 51.3oW. Dune slip faces indicate winds that blow from the upper left toward lower right. This picture covers an area approximately 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.

  12. Optical properties of the crescent and coherent applications.

    PubMed

    Wang, Yufei; Zhou, Wenjun; Liu, Anjin; Chen, Wei; Fu, Feiya; Yan, Xinyu; Jiang, Bin; Xue, Qikun; Zheng, Wanhua

    2011-04-25

    By out-of-particle surface plasmon (SP) excitation in the near infrared range, the influences of key parameters on the basic optical properties of the Au crescent are qualitatively studied from the mode dispersion. Based on the coherent control of SP wave, a crescent pair sensor with the intensified extracted signal and the controllability of sensing is proposed. In addition, the crescent half replaced by Ag functioning as a position detector is also proposed. The particular phase of the detecting light as a detection parameter is used to improve the accuracy of the position detection. PMID:21643081

  13. Particle-image velocimetry measurements of flow over interacting barchan dunes

    NASA Astrophysics Data System (ADS)

    Palmer, Jessica A.; Mejia-Alvarez, Ricardo; Best, James L.; Christensen, Kenneth T.

    2012-03-01

    Barchan dunes are crescentic planform-shaped dunes that are present in many natural environments, and may occur either in isolation or in groups. This study uses high-resolution particle-image velocimetry (PIV) experiments using fixed-bed models to examine the effects of barchan dune interaction upon the flow field structure. The barchan dune models were created from an idealized contour map, the shape and dimensions of which were based upon previous empirical studies of dune morphology. The experimental setup comprised two, co-axially aligned, barchan dune models that were spaced at different distances apart. In this paper, two volumetric ratios ( V r, upstream dune: downstream dune) of 1.0 and 0.175 were examined. Models were placed in a boundary-layer wind tunnel and flow quantification was achieved via PIV measurements of the mean and turbulent flow field in the streamwise-wall-normal plane, along the centerline of the barchan(s), at an average flow Reynolds number of 59,000. The presence of an upstream barchan dune induces a "sheltering effect" on the flow. Flow on the stoss side of the downstream dune is controlled by the developing internal boundary layer from the upstream dune, as well as by the turbulent flow structures shed from the free shear layer of the upstream dune leeside. At both volumetric ratios, enhanced turbulence is present over the downstream barchan dune leeside, which is proposed to be caused by the interaction of shear layers from the upstream and downstream dunes. Both the size and magnitude of the shear layer formed in the leeside of the upstream dune control this interaction, together with the proximity of this shear layer to the stoss side of the downstream dune. Proper orthogonal decomposition (POD) analysis shows that the distribution of turbulent kinetic energy is shifted to higher modes (i.e., smaller spatial scales) over interacting barchan dunes, which also reflects the role of the leeside free shear layer in dominating the flow field by generation, or redistribution, of TKE to smaller scales.

  14. Sand dunes as migrating strings.

    PubMed

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

    2013-05-01

    We develop a reduced complexity model for three-dimensional sand dunes, based on a simplified description of the longitudinal and lateral sand transport. The spatiotemporal evolution of a dune migrating over a nonerodible bed under unidirectional wind is reduced to the dynamics of its crest line, providing a simple framework for the investigation of three-dimensional dunes, such as barchan and transverse dunes. Within this model, we derive analytical solutions for barchan dunes and investigate the stability of a rectilinear transverse dune against lateral fluctuations. We show, in particular, that the latter is unstable only if the lateral transport on the dune slip face prevails over that on the upwind face. We also predict the wavelength and the characteristic time that control the subsequent evolution of an unstable transverse dune into a wavy ridge and the ultimate fragmentation into barchan dunes. PMID:23767529

  15. Sand dunes as migrating strings

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  16. Predicting the effect of changing vegetation conditions on aeolian dune landscapes

    NASA Astrophysics Data System (ADS)

    Reitz, M. D.; Jerolmack, D. J.; Ewing, R. C.; Martin, R. L.

    2010-12-01

    One system in which climate change can directly alter a landscape through the medium of plant life is that of aeolian dunes. Under the influence of vegetation, barchan dunes invert their crescents and turn into stabilized parabolic dunes. Whether local vegetation succeeds in effecting this transition depends on the relative strengths of dune surface erosion/deposition rates, which impede plant growth by burial or excavation, and the growth rates of large plants that inhibit erosion/deposition through shielding from wind and stabilization by roots. A recent model predicts that this transition will occur at a threshold erosion/deposition rate of half the representative vegetation growth rate. We test this prediction using a unique dataset of repeated, high-resolution topographic measurements (LiDAR) at White Sands National Monument. Measurements allow precise quantification of annual erosion/deposition rates over a dune field that undergoes a spatial transition from barchan to parabolic forms. We find that the threshold hypothesis not only explains the transition across the dune field, but when applied to spatial variations in erosion rate over a barchan dune can also explain the shape inversion of individual dunes. The transition in dune pattern exhibits properties of a phase transition: a gradual decrease in erosion/deposition produces an abrupt increase in vegetation density in the vicinity of the threshold. The confirmed threshold ratio of erosion/deposition rate to vegetation growth rate is a general result, and can be a useful tool in predicting landscape response to climate changes. We explore the applications of this ratio by applying it to the case of the Nebraska Sand Hills, where the dunes are currently stabilized by vegetation, but have been active at various times in the past under different climate/vegetation conditions. By determining how close the present-day landscape is to the transition threshold, we also project the amount of climate/vegetation change that would reactivate these dunes.

  17. Can a Crescent Mars Ever Be Seen from Earth?

    ERIC Educational Resources Information Center

    Lamb, John F., Jr.

    1990-01-01

    Described is an activity that incorporates a computer, geometry, algebra, trigonometry, and calculus to answer questions about the planet Mars. A possible crescent of Mars is compared to those of Venus and Mercury. (KR)

  18. Spring Time View of North Polar Sand Dunes

    NASA Technical Reports Server (NTRS)

    1998-01-01

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

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

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

    As first seen by the Viking 2 Orbiter in 1976, a vast 'sea' of sand dunes surrounds the north polar cap. The dunes imaged by MOC (above) are classic forms known as barchan dunes--the small, crescent-shaped hills (see left image above)-- and transverse dunes--ridges that resemble coalesced barchans (shown in right image above). These dunes are similar in size and shape to familiar sand dunes found in desert regions on Earth. These two varieties form from winds that persistently come from a single direction (in this case, from the southwest).

    Over the next several months, the sky above these dunes will clear. Northern Summer will arrive near the end of January 1999, and Mars Global Surveyor should have an excellent view of this region when it begins its mapping mission in late March 1999. Because it is in a polar orbit, Mars Global Surveyor will have many opportunities to revisit the north polar dunes in 1999. The images in 1999 will have resolutions around 1.5 meters (5 feet) per pixel--a substantial improvement even over the pictures shown here.

  19. Simulation of barchan dynamics with inter-dune sand streams

    NASA Astrophysics Data System (ADS)

    Katsuki, Atsunari; Kikuchi, Macoto

    2011-06-01

    A group of barchans, crescent sand dunes, exhibit a characteristic flying-geese pattern in deserts on Earth and Mars. This pattern implies that an indirect interaction between barchans, mediated by an inter-dune sand stream, which is released from one barchan's horns and caught by another barchan, plays an important role in the dynamics of barchan fields. We used numerical simulations of a recently proposed cell model to investigate the effects of inter-dune sand streams on barchan fields. We found that a sand stream from a point source moves a downstream barchan laterally until the head of the barchan is finally situated behind the stream. This final configuration was shown to be stable by a linear stability analysis. These results indicate that flying-geese patterns are formed by the lateral motion of barchans mediated by inter-dune sand streams. By using simulations we also found a barchan mono-corridor generation effect, which is another effect of sand streams from point sources.

  20. Aligned Defrosting Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    17 August 2004 This July 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a group of aligned barchan sand dunes in the martian north polar region. At the time, the dunes were covered with seasonal frost, but the frost had begun to sublime away, leaving dark spots and dark outlines around the dunes. The surrounding plains exhibit small, diffuse spots that are also the result of subliming seasonal frost. This northern spring image, acquired on a descending ground track (as MGS was moving north to south on the 'night' side of Mars) is located near 78.8oN, 34.8oW. The image covers an area about 3 km (1.9 mi) across and sunlight illuminates the scene from the upper left.

  1. Dunes of the North

    NASA Technical Reports Server (NTRS)

    2005-01-01

    30 March 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows linear and barchan sand dunes in Chasma Boreale, a broad erosional trough in the martian north polar region. Winds responsible for these dunes generally blow from upper right toward the lower left. Martian dunes tend to be darker than their counterparts on Earth because they are composed of darker, iron-bearing minerals and rock fragments.

    Location near: 84.2oN, 37.9oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Summer

  2. Bright dunes on mars

    USGS Publications Warehouse

    Thomas, P.C.; Malin, M.C.; Carr, M.H.; Danielson, G.E.; Davies, M.E.; Hartmann, W.K.; Ingersoll, A.P.; James, P.B.; McEwen, A.S.; Soderblom, L.A.; Veverka, J.

    1999-01-01

    Seasonal changes observed on the surface of Mars can in part be attributed to the transport of geological materials by wind. Images obtained by orbiting spacecraft in the 1970s showed large wind-formed features such as dunes, and revealed regional time-varying albedos that could be attributed to the effects of dust erosion and deposition. But the resolution of these images was insufficient to identify different types and sources of aeolian materials, nor could they reveal aeolian deposits other than large dunes or extensive surface coverings that were redistributed by dust storms. Here we present images of Mars with up to 50 times better resolution. These images show that martian dunes include at least two distinct components, the brighter of which we interpret to be composed of relatively soft minerals, possibly sulphates. We also find large areas of the martian surface that have several metres or more of aeolian mantle lacking obvious bedforms.

  3. Russell Dune Gullies

    NASA Technical Reports Server (NTRS)

    2005-01-01

    5 November 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows gullies and dust devil streaks on the slopes of a large dune in Russell Crater. Gullies on martian dunes typically occur only in the Noachis Terra region, and almost exclusively form on southward-facing slopes. They might be the result of downslope movement of sand mixed with a fluid such as carbon dioxide gas or water that had been trapped as ice in the dune.

    Location near: 54.6oS, 347.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  4. Sand Dunes, Afghanistan

    NASA Technical Reports Server (NTRS)

    2001-01-01

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

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

  5. Sand Dunes in Hellas

    NASA Technical Reports Server (NTRS)

    2003-01-01

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

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

  6. Russell Dune Gullies

    NASA Technical Reports Server (NTRS)

    2005-01-01

    8 May 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows gullies on a large slip face in the Russell Crater dune field. When the image was acquired, the dunes were still covered with seasonal frost.

    Location near: 54.7oS, 347.0oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Winter

  7. Large eddy simulation of interacting barchan dunes in a steady, unidirectional flow

    NASA Astrophysics Data System (ADS)

    Omidyeganeh, Mohammad; Piomelli, Ugo; Christensen, Kenneth T.; Best, James L.

    2013-12-01

    Barchan dunes are bed forms found in many sedimentary environments with a limited supply of sediment, and may occur in isolation or in more complex dune fields. Barchans have a crescentic planform morphology with horns elongated in the downflow direction. To study flow over barchan dunes, we performed large eddy simulations in a channel with different interdune spacings at a flow Reynolds number, Re??26,000 (based on the free stream velocity and channel height). The largest interdune spacing (2.38?, where ? is the wavelength of the barchan dune) presents similar characteristics to a solitary dune in isolation, indicating that, at this distance, the sheltering effect of the upstream dune is rather weak. Barchan dunes induce two counterrotating streamwise vortices, one along each of the horns, which direct high-momentum fluid toward the symmetry plane and low-momentum fluid near the bed away from the centerline. The flow close to the centerline plane separates at the crest, but away from the centerline plane, and along the horns, flow separation occurs intermittently. The flow in the separation bubble is directed toward the horns and leaves the dune at its tips. The internal boundary layer developing on the bed downstream of the reattachment region develops similarly for various interdune spacings; the development slows down 14.5 dune heights downstream. The turbulent kinetic energy budgets show the importance of pressure transport and mean flow advection in transferring energy from the overlying wake layer to the internal boundary layer over the stoss side. For closely spaced dunes, the bed shear stress is 30% larger than at the largest spacing, and instantaneous coherent high- and low-speed streaks are shorter but stronger. Coherent eddies in the separated shear layer are generated more frequently for smaller interdune spacing, where they move farther away from the bed, toward the free surface, and remain located between the horns.

  8. Dunes in Noachis Terra

    NASA Technical Reports Server (NTRS)

    2004-01-01

    5 September 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a field of dark, windblown sand dunes in the Noachis Terra region near 45.2oS, 321.4oW. The image covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates this scene from the upper left.

  9. Efficiency characteristics of crescent-shaped wings and caudal fins

    NASA Technical Reports Server (NTRS)

    Van Dam, C. P.

    1987-01-01

    Caudal (tail) fins of fish and aquatic mammals that cruise long distances, and wings of certain birds, often have the shape of a crescent moon. This study investigates how the crescent shape contributes to the traveling performance of these animals. A steady-flow theory (Maskew, 1982) that correctly models the trailing wake was used to analyze lifting surface efficiency, which is dependent on the level of induced (or vortex) drag for a given lift and span of the lifting surface. This analysis shows that backward curvature of a wing improves induced efficiency to a value greater than that of the flat untwisted wing of elliptical shape considered optimal in classical wing theory (Prandt, 1921 and Munk, 1921). This increase of induced efficiency results from the nonplanar trailing vortex sheet produced by the crescent-shaped wing at a given angle of attack.

  10. Crescentic glomerulonephritis in a polar bear (Ursus maritimus).

    PubMed

    Baba, Hiroshi; Kudo, Tomoo; Makino, Yoshinori; Mochizuki, Yasumasa; Takagi, Takayo; Une, Yumi

    2013-11-01

    Spontaneous crescentic glomerulonephritis (CrGN) in animals has only been reported in dog and sheep. We report the pathological features of CrGN in a 17-year-old male polar bear that died due to renal failure. Histologically, the lesions were characterized by fibrocellular crescents, adhesion between Bowman's capsule and the glomerular capillary tuft and an increase in the mesangial matrix in glomeruli. The proliferating cells in the crescent were partly immunopositive for cytokeratin and intensely positive for vimentin, WT-1 and ?-smooth muscle actin, suggesting they originated from parietal epithelial cells. Ultrastructually, thickening of the glomerular basement membrane and loss of epithelial cell foot processes were observed with electron-dense deposits. PMID:23856758

  11. Dune formation under bimodal winds

    PubMed Central

    Parteli, Eric J. R.; Durán, Orencio; Tsoar, Haim; Schwämmle, Veit; Herrmann, Hans J.

    2009-01-01

    The study of dune morphology represents a valuable tool in the investigation of planetary wind systems—the primary factor controlling the dune shape is the wind directionality. However, our understanding of dune formation is still limited to the simplest situation of unidirectional winds: There is no model that solves the equations of sand transport under the most common situation of seasonally varying wind directions. Here we present the calculation of sand transport under bimodal winds using a dune model that is extended to account for more than one wind direction. Our calculations show that dunes align longitudinally to the resultant wind trend if the angle ?w between the wind directions is larger than 90°. Under high sand availability, linear seif dunes are obtained, the intriguing meandering shape of which is found to be controlled by the dune height and by the time the wind lasts at each one of the two wind directions. Unusual dune shapes including the “wedge dunes” observed on Mars appear within a wide spectrum of bimodal dune morphologies under low sand availability. PMID:20018703

  12. Layer Outcrops and Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-561, 1 December 2003

    This October 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows dark, windblown sand dunes amid outcrops of light-toned, sedimentary rock in a crater in western Arabia Terra. The darkest material in the scene is windblown sand; the steep slopes--the slip faces--of the dunes face toward the southwest (lower left), indicating that wind transport of sand has been from the northeast (upper right). The layered mounds are the remains of sedimentary rock that were once more extensive across this crater floor. The image is located near 8.9oN, 1.2oW, and covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  13. Flow over interacting barchan dunes studied in a refractive-index-matched environment

    NASA Astrophysics Data System (ADS)

    Tang, Z.; Jiang, N.; Blois, G.; Barros, J. M.; Best, J. L.; Christensen, K. T.

    2013-11-01

    Barchan dunes are three-dimensional topographic features characterized by a crescentic shape. Very common on Earth's surface, barchans are produced by unidirectional flows in regions of sediment starvation and are characterized by migration rates that are a function of their volume. This results in complex dune-to-dune interaction mechanisms that are poorly understood. In order to quantify the flow structure produced by interacting barchans, PIV measurements were made wherein the dune models were immersed in a flowing fluid that was refractive-index-matched to the dune material. Doing so provided full optical access to the obstructed regions of flow and eliminated reflections from the liquid-solid boundaries, allowing near-wall data to be collected. Clear barchan models with different volumetric ratios were arranged in tandem, and flow-field measurements were made in multiple streamwise-wall-normal and streamwise-spanwise planes. Ensemble-averaged flow fields and Reynolds stresses were obtained for different barchan spacings and compared to the reference case of an isolated barchan. Proper orthogonal decomposition analysis was employed to study the spatial characteristics of the energy distribution both between and downstream of the aligned dunes.

  14. Virulence of Hessian Fly (Diptera: Cecidomyiidae) in the Fertile Crescent

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Hessian fly, Mayetiola destructor (Say), is an important insect pest of wheat (Triticum spp.) in North Africa, North America, South Europe and North Kazakhstan. Similarly to wheat this pest is believed to originate from West Asia in the Fertile Crescent. To determine the virulence of the Hessian...

  15. Tsunami Hazard in Crescent City, California from Kuril Islands earthquakes

    NASA Astrophysics Data System (ADS)

    Dengler, L.; Uslu, B.; Barberopoulou, A.

    2007-12-01

    On November 15, Crescent City in Del Norte County, California was hit by a series of tsunami surges generated by the M = 8.3 Kuril Islands earthquake causing an estimated 9.7 million (US dollars) in damages to the small boat basin. This was the first significant tsunami loss on US territory since the 1964 Alaska tsunami. The damage occurred nearly 8 hours after the official tsunami alert bulletins had been cancelled. The tsunami caused no flooding and did not exceed the ambient high tide level. All of the damage was caused by strong currents, estimated at 12 to 15 knots, causing the floating docks to be pinned against the pilings and water to flow over them. The event highlighted problems in warning criteria and communications for a marginal event with the potential for only localized impacts, the vulnerability of harbors from a relatively modest tsunami, and the particular exposure of the Crescent City harbor area to tsunamis. It also illustrated the poor understanding of local officials of the duration of tsunami hazard. As a result of the November tsunami, interim changes were made by WCATWC to address localized hazards in areas like Crescent City. On January 13, 2007 when a M = 8.1 earthquake occurred in the Kuril Islands, a formal procedure was in place for hourly conference calls between WCATWC, California State Office of Emergency Services officials, local weather Service Offices and local emergency officials, significantly improving the decision making process and the communication among the federal, state and local officials. Kuril Island tsunamis are relatively common at Crescent City. Since 1963, five tsunamis generated by Kuril Island earthquakes have been recorded on the Crescent City tide gauge, two with amplitudes greater than 0.5 m. We use the MOST model to simulate the 2006, 2007 and 1994 events and to examine the difference between damaging and non-damaging events at Crescent City. Small changes in the angle of the rupture zone results can result in a half meter difference in water heights. We also look at the contribution of fault segments along the Kuril subduction zone using the FACTS server to look at the potentially most damaging source regions for Crescent City. A similar-sized rupture as the November 15 event located further south along the Hokkaido - Honshu area of the subduction zone, is likely to produce a slightly larger amplitude signal with and even greater delay between the first wave arrivals and the largest waves.

  16. Sand Ripples and Dunes Francois Charru,1

    E-print Network

    Claudin, Philippe

    qsat f H p d BarchanTransverse Water Air Figure 1 Migration velocity c of dunes as a function of their height H for aeolian barchan dunes ( filled circles), dunes propagating on the back of large aeolian dunes (open circles), and subaqueous barchan dunes (squares). The solid line is Bagnold's prediction

  17. Mars Digital Dune Database

    NASA Astrophysics Data System (ADS)

    Hayward, R. K.; Titus, T. N.; Mullins, K. F.; Fenton, L. K.; Bourke, M.; Christensen, P. R.

    2004-12-01

    Currently, there is no comprehensive, global, digital database for dune deposits on Mars. The advent of a series of successful Mars missions, coupled with advances in technology enabling a significant increase in instrument resolution, have provided a large compilation of data covering a wide range of wavelengths for the Martian surface. Given the recent availability of high-resolution data and detailed surficial information returned from orbital and rover missions, it is critical that we update the Mars global information base by creating a digital database of dune deposits that includes this new influx of data. As of spring 2004, the Thermal Emission Imaging System (THEMIS) infrared (IR) coverage of the surface of Mars was 98% for nighttime and 75% for daytime acquired images, forming a data set of global coverage at a resolution not previously possible. The combination of high-resolution and global coverage makes the THEMIS IR data set the logical choice for a planet wide inventory of dune deposits. Data sets of a global scale like those of Mars Orbiter Laser Altimeter (MOLA) and Thermal Emission Spectrometer (TES) will enable rapid and contiguous comparisons with the dune database. Other imagery like that of Mars Orbiter Camera (MOC) will provide very high-resolution, localized visual data for accurate interpretations of morphological characterizations. The dune database will provide researchers with an extensive, comprehensive and stable database for use in a wide-array of global studies. The database will also offer researchers a centralized depository for updating physical parameters with newly validated findings. The initial construction of the database is based upon dune forms or deposits identified, classified and digitized using only THEMIS IR images. These digitized polygons are converted from THEMIS image coordinates to ARCMAP aerographical coordinates, allowing delineation of areal extent of the deposits and preserving relevant THEMIS image information such as Ls, local time, and sun azimuth/angle. The ARCMAP polygons will also retain reference to all THEMIS IR images used in their construction. Where available, THEMIS VIS and/or MOC images will be used to confirm, modify or refine original classifications. In addition to providing an improved resolution for features below the IR image threshold, this secondary examination will also provide a list of cross-referenced THEMIS VIS and MOC images for future investigations. Physical parameters such as wind direction based on slip-face geometry, dune wavelength, elevation, and volume of the deposits will be incorporated into the database on a priority-based schedule. In addition to THEMIS VIS and MOC images, supplemental data sets, such as TES and others, will be used where available to further refine and/or validate existing data on global wind patterns, sediment transport, sources and sinks, and stratigraphic units.

  18. Sedimentary Rocks and Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    25 November 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows buttes composed of light-toned, sedimentary rock exposed by erosion within a crater occurring immediately west of Schiaparelli Basin near 4.0oS, 347.9oW. Surrounding these buttes is a field of dark sand dunes and lighter-toned, very large windblown ripples. The sedimentary rocks might indicate that the crater interior was once the site of a lake. The image covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  19. Sand Furrows: A new surface feature on martian dunes

    NASA Astrophysics Data System (ADS)

    Bourke, Mary

    2013-04-01

    Planetary geomorphology is at the forefront of today's Geoscience endeavours. A characteristic of frontier science is the discovery of new landforms and processes. Sand furrows are a new geomorphic feature that has not been previously described. They are ubiquitous and occur on 95% of polar dune images. Furrows are shallow and narrow erosion forms which can extend up to 300 m along a dune surface. Patterns are reminiscent of fluid flow, perhaps even fluvial flow (e.g., sinuosity, braiding and anastomosing) and are often slope-normal. However, furrows also display attributes that defy gravity (e.g., upslope trending flow paths) and they are not associated with terminal deposits. This suggests that the formative fluid is likely to be a pressurised gas. Cryo-venting has been proposed to explain the formation of dark spots and fans in the seasonal ice cap. It has also been linked to the formation of araniform. Here it is proposed to be the process by which aeolian sediment is eroded to form sand furrows. During the Martian spring, basal sublimation of the seasonal CO2 ice cap occurs on dune surfaces. Weaknesses in the ice allow pressurised gas and some dune sediment to be transported through vents to the surface. Furrows are eroded along the gas flow paths as it moves towards the vent. Cryo-venting is therefore identified as a new style of sediment transport on aeolian dunes in our solar system, and one that is, so far, unique to Mars. An estimate of the sand volume eroded from a sample dune during one Mars' spring is geomorphologically significant and is equivalent to that of a small dome dune on Mars (500m^3). The deposits are diffuse and extend into the interdune as well as back onto the source dune. The geomorphic efficacy of cryo-venting as a mechanism of aeolian dune erosion is dependent on the magnitude and frequency of venting, the location of vents and the scale of the source dune. Small dunes may undergo accelerated erosion rates as the ability to intersect vented sediment is reduced by a small surface area.

  20. Historical Note/ David Deming, History Editor Crescent Moon Spring: A Disappearing Natural

    E-print Network

    Jiao, Jiu Jimmy

    Historical Note/ David Deming, History Editor Crescent Moon Spring: A Disappearing Natural Wonder in the Gobi Desert, China by Jiu J. Jiao Introduction Yueya Spring, or Crescent Moon Spring, is a geolog- ical to the shape of the spring, or more precisely, the pond fed by the spring water, which resembles a crescent

  1. Mining-related ground deformation in Crescent Valley, Nevada: Implications for sparse GPS networks

    E-print Network

    Amelung, Falk

    Mining-related ground deformation in Crescent Valley, Nevada: Implications for sparse GPS networks. The analysis reveals areas of rapid deformation caused by mining and agricultural activities in the Crescent), Mining-related ground deformation in Crescent Valley, Nevada: Implications for sparse GPS networks

  2. Predicting vegetation-stabilized dune field morphology

    NASA Astrophysics Data System (ADS)

    Barchyn, Thomas E.; Hugenholtz, Chris H.

    2012-09-01

    The morphology of vegetation-stabilized dune fields on the North American Great Plains (NAGP) mostly comprises parabolic dunes; stabilized barchan and transverse dunes are rare, with the exception of transverse and barchan mega-dunes in the Nebraska Sand Hills. We present a hypothesis from a numerical dune field model explaining the vegetation-stabilized morphology of dunes under unidirectional wind. Simulations with a range of initial dune morphologies (closely-spaced transverse to disperse barchans) indicate that stabilized morphology is determined by the ratio of slipface deposition rate to deposition tolerance of vegetation. Slipface deposition rate is related to dune height, flux, and celerity. With a fixed depositional tolerance, large, slow-moving dunes have low slipface deposition rates and ‘freeze’ in place once vegetation is introduced. Relatively small, fast dunes have high slipface deposition rates and evolve into parabolic dunes, often colliding during stabilization. Our hypothesis could explain differences in stabilized morphology across the NAGP and elsewhere.

  3. Gullies and Dunes

    NASA Technical Reports Server (NTRS)

    2006-01-01

    7 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows gullies overlain by seasonal frost in the north wall of an unnamed crater west of Hellas Planitia. The gullies likely formed by a combination of mass movement (i.e., landsliding) and fluid flow (i.e., water-rich debris flows). Below (south of) the gullies is a field of sand dunes; they, too, are covered by seasonal frost.

    Location near: 47.4oS, 322.8oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Winter

  4. Grain size dependence of barchan dune dynamics

    E-print Network

    C. Groh; N. Aksel; I. Rehberg; C. Kruelle

    2008-11-28

    The dependence of the barchan dune dynamics on the size of the grains involved is investigated experimentally. Downsized barchan dune slices are observed in a narrow water flow tube. The relaxation time from an initial symmetric triangular heap towards an asymmetric shape attractor increases with dune mass and decreases with grain size. The dune velocity increases with grain size. In contrast, the velocity scaling and the shape of the barchan dune is independent of the size of the grains.

  5. Numerical modeling of the wind flow over a transverse dune

    PubMed Central

    Araújo, Ascânio D.; Parteli, Eric J. R.; Pöschel, Thorsten; Andrade, José S.; Herrmann, Hans J.

    2013-01-01

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee — the separation bubble — displays a surprisingly strong dependence on the wind shear velocity, u*: it is nearly independent of u* for shear velocities within the range between 0.2?m/s and 0.8?m/s but increases linearly with u* for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u* is larger than approximately 0.39?m/s, whereas a larger value of u* (about 0.49?m/s) is required to initiate this reverse transport. PMID:24091456

  6. Numerical modeling of the wind flow over a transverse dune

    E-print Network

    Ascânio D. Araújo; Eric J. R. Parteli; Thorsten Poeschel; José S. Andrade Jr.; Hans J. Herrmann

    2013-09-30

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee --- the {\\em{separation bubble}} --- displays a surprisingly strong dependence on the wind shear velocity, $u_{\\ast}$: it is nearly independent of $u_{\\ast}$ for shear velocities within the range between $0.2\\,$m$$s and $0.8\\,$m$$s but increases linearly with $u_{\\ast}$ for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if $u_{\\ast}$ is larger than approximately $0.39\\,$m$$s, whereas a larger value of $u_{\\ast}$ (about $0.49\\,$m$$s) is required to initiate this reverse transport.

  7. Different appearance of Titan's dunes

    NASA Astrophysics Data System (ADS)

    Paganelli, F.; Callahan, P.; Hensley, S.; Lorenz, R.; Lunine, J.; Kirk, R.; Stiles, B.; Gim, Y.; West, R.; Janssen, M.; Lopes, R.; Stofan, E.; Wall, S.; Paillou, P.; Radebaugh, J.; Cassini RADAR Team

    2008-12-01

    In this paper we analyze Cassini's Titan Radar Mapper recent flybys and yet more evidence of dark linear dunes, in the latitude between 30° S and 30° N, whose orientations are somewhat comparable to previous dune observations but at closer study show morphological differences. The appearance of Titan's dunes depends on the projected look direction of the Cassini Radar antenna, incidence angle and resolution. Dune fields are generally oriented East/West on Titan, and for many radar observations the flyby is in the equatorial plane. At closest approach the imaging direction is most nearly normal to the dune direction such as in the central portion of the T8 swath. Away from that configuration, and especially past the -/+10 minutes from close approach, the relative azimuth angle that the projected look direction of the Cassini Radar antenna has with respect to the surface changes rapidly along with incidence angle and resolution resulting in signal attenuation of the imaged features. Observational biases in the SAR images are key for dunes comparison across Titan's equatorial belt. The results show that in some regions the projected look direction could be on the order of 60° and parallel to the long axis of the radar dark features direction (i.e. T16, T25, T28), therefore suggesting that the variation in backscatter must be a combination of compositional dunes dark material and bright interdune material, varying roughness and topography when present. This suggests that we cannot assume that all the dune fields currently imaged can be characterized simply on the bases of their orientation and therefore we suggest that the characterization of the imaged surface features should be divided into at least two categories: -1) topography driven (in which Radar-clinometry can be applied); -2) compositional or due to varying roughness.

  8. Gypsum Dunes from White Sands National Monument - Potential Analog to North Polar Dunes on Mars

    NASA Astrophysics Data System (ADS)

    Szynkiewicz, A.; Pratt, L. M.; Glamoclija, M.; Bustos, D.

    2008-03-01

    Three aspects of White Sands gypsum dunes evolution relating to climate variation are discussed in comparison to Olimpia Undae gypsum-rich dunes on Mars: gypsum source, groundwater discharge into interdunes areas, and desiccation of dunes.

  9. Sand Dunes in Noachis Terra

    NASA Technical Reports Server (NTRS)

    2004-01-01

    11 February 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark-toned sand dunes in a crater in eastern Noachis Terra. Most big martian dunes tend to be dark, as opposed to the more familiar light-toned dunes of Earth. This difference is a product of the composition of the dunes; on Earth, most dunes contain abundant quartz. Quartz is usually clear (transparent), though quartz sand grains that have been kicked around by wind usually develop a white, frosty surface. On Mars, the sand is mostly made up of the darker minerals that comprise iron- and magnesium-rich volcanic rocks--i.e., like the black sand beaches found on volcanic islands like Hawaii. Examples of dark sand dunes on Earth are found in central Washington state and Iceland, among other places. This picture is located near 49.0oS, 326.3oW. Sunlight illuminates this scene from the upper left; the image covers an area 3 km (1.9 mi) wide.

  10. Summary of the Third International Planetary Dunes Workshop: remote sensing and image analysis of planetary dunes

    USGS Publications Warehouse

    Fenton, Lori K.; Hayward, Rosalyn K.; Horgan, Briony H.N.; Rubin, David M.; Titus, Timothy N.; Bishop, Mark A.; Burr, Devon M.; Chojnacki, Matthew; Dinwiddie, Cynthia L.; Kerber, Laura; Gall, Alice Le; Michaels, Timothy I.; Neakrase, Lynn D.V.; Newman, Claire E.; Tirsch, Daniela; Yizhaq, Hezi; Zimbelman, James R.

    2013-01-01

    The Third International Planetary Dunes Workshop took place in Flagstaff, AZ, USA during June 12–15, 2012. This meeting brought together a diverse group of researchers to discuss recent advances in terrestrial and planetary research on aeolian bedforms. The workshop included two and a half days of oral and poster presentations, as well as one formal (and one informal) full-day field trip. Similar to its predecessors, the presented work provided new insight on the morphology, dynamics, composition, and origin of aeolian bedforms on Venus, Earth, Mars, and Titan, with some intriguing speculation about potential aeolian processes on Triton (a satellite of Neptune) and Pluto. Major advancements since the previous International Planetary Dunes Workshop include the introduction of several new data analysis and numerical tools and utilization of low-cost field instruments (most notably the time-lapse camera). Most presentations represented advancement towards research priorities identified in both of the prior two workshops, although some previously recommended research approaches were not discussed. In addition, this workshop provided a forum for participants to discuss the uncertain future of the Planetary Aeolian Laboratory; subsequent actions taken as a result of the decisions made during the workshop may lead to an expansion of funding opportunities to use the facilities, as well as other improvements. The interactions during this workshop contributed to the success of the Third International Planetary Dunes Workshop, further developing our understanding of aeolian processes on the aeolian worlds of the Solar System.

  11. Pauci-Immune Crescentic Glomerulonephritis: An ANCA-Associated Vasculitis

    PubMed Central

    Syed, Rafeel; Rehman, Amina; Valecha, Gautam; El-Sayegh, Suzanne

    2015-01-01

    Rapidly progressive glomerulonephritis (RPGN) is a syndrome signified by a precipitous loss of renal function, with features of glomerulonephritis including dysmorphic erythrocyturia and glomerular proteinuria. RPGN is associated with extensive crescent formation, and, thus, the clinical term RPGN is often used interchangeably with the pathologic term crescentic glomerulonephritis (CGN). From an immunopathologic standpoint, primary RPGN is divided into pauci-immune GN (PICG), anti-GBM GN, and immune complex GN. PICG, the most common etiology of primary RPGN, refers to a necrotizing glomerulonephritis with few or no immune deposits by immunofluorescence (IF) or electron microscopy (EM). In most patients, pauci-immune CGN is a component of a systemic small vessel vasculitis such as granulomatosis with polyangiitis (GPA). Approximately 90% of patients with PICG have circulating ANCA antibodies, leading to the nomenclature ANCA-associated vasculitis (AAV). Recent research has identified several other antibodies associated with PICG, which is now understood to be a complex spectrum of disease with considerable overlap in terms of clinical phenotype and outcomes. In addition, several genetic and environmental factors have recently been implicated in the pathogenesis of this disorder. With new prognostic classifications, enhanced understanding of immunopathologic mechanisms, and novel treatment paradigms, clinical and experimental interest in PICG remains high. PMID:26688808

  12. Gullies and Dunes

    NASA Technical Reports Server (NTRS)

    2004-01-01

    2 June 2004 This 1.5 meters (5 ft.) per pixel Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image of gullies and dunes in a crater near Gorgonum Chaos was acquired in late May 2004. The gullies may have formed by a combination of processes. Many middle- and polar-latitude gullies such as these are thought to form both by mass movement of dry materials and action of liquid water. Some investigators suggest alternative fluids such as carbon dioxide. Still others make a case that no fluid was involved at all. Some gullies on Mars show clear association with subsurface layering and undermining of those layers; they also show banked channels; these kinds of observations are usually taken in support of the water hypothesis. The crater in which the landforms shown here occur is located at 37.5oS, 169.3oW. This image covers an area about 1.5 km (0.9 mi) across. The scene is illuminated by sunlight from the upper left.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    This paper describes the latest research on the geomorphological characteristics, formation environment and chronology of the main inland aeolian deposits from the south-eastern Duero Basin (DB) and the Manchega Plain (MP) of the Iberian Peninsula. Similarities and differences between the aeolian deposits of these two locations are summarised. Wind deflation from the Guadiana and Júcar alluvial systems created the aeolian deposits of the MP. These deposits are mainly composed of quartz sands. However, in the San Juan alluvial plain (MP) there is a large extent of clay dunes formed by exposure to prevalent winds of seasonal playa-lakes with salt and clay sediments. In the DB, wind remobilisation of the small particles from Quaternary terraces and Tertiary arkosic sediments left aeolian deposits of quartz-feldspar sands. Textural parameters of the aeolian deposits show large variations depending on the location and the original deposit. Thus, in the DB the aeolian sands derived from the deflation of fluvial sediments are better sorted and smaller in grain size than those created by the deflation of arkosic sediments. Morphologically, simple and compound parabolic dunes (U-V forms, hemicyclic, lobate and elongate), crescentic and linear dunes, climbing dunes and blowout dunes have been recognized at both sites. Barchan and dome dunes are present only in the DB while "lunette lunette-clay dunes" are found only in the MP. In both locations, the large extent of aeolian sand sheets and the predominance of simple and compound parabolic dunes indicates the active role of sparse vegetation cover in the formation of this aeolian system. In the DB, dunes were formed by southwest and west winds, while in the MP the aeolian morphologies indicate that the prevalent winds were west and northwest. The chronology of the dune deposits is being determined with luminescence (TL-OSL) dating and Mass Spectrometry Analysis ( 14C-AMS). In this way, the aeolian activity and stabilisation stages can be established, the latter well marked in the DB through soil A horizon development. Thus, the main sand dune formation in the DB and the eastern regions of the MP occurred between 13.5 and 7 ka BP, during the cold and arid Younger Dryas episode and the Early Holocene. The clay dunes of the MP accumulated mainly from 29 to 19 ka BP that corresponds with Heinrich events HE-3 and HE-2 and the Last Glacial Maximum. However, clay dunes were also formed between 13.5 and 7 ka BP. In both locations, there have been reactivations of some sand deposits in the recent Holocene, with maximum activity around 5-2 ka BP and 0.5-0.2 ka BP. On the other hand, three marked stages of stabilisation of the DB aeolian system have been established with 14C-AMS, around 10.2, 6.2 and 1.2 ka BP. Finally, the main winds contributing to dune construction were also responsible for the deflation processes with the formation of erosional depressions.

  14. Predicting vegetation-stabilized dune morphology

    NASA Astrophysics Data System (ADS)

    Barchyn, T.; Hugenholtz, C.

    2012-04-01

    The morphology of vegetation-stabilized dune fields on the North American Great Plains mostly comprises parabolic dunes; stabilized barchan and transverse dunes are rare. One notable exception is the Nebraska Sand Hills (NSH), where massive grass-covered barchan and transverse dunes bear proof of former desert-like conditions. We present a hypothesis from a numerical dune field model to explain the vegetation-stabilized morphology of dunes. The model incorporates a growth curve that preferentially grows vegetation in regions of sediment deposition with a sharp drop in growth at the peak depositional tolerance of vegetation, qualitatively matching biological response to erosion and deposition. Simulations on a range of pre-stabilization dune morphologies, from large closely-spaced transverse dunes to small dispersed barchans, indicate that the stabilized morphology is largely determined by the ratio of slipface deposition rate to peak depositional tolerance of vegetation. Conceptually, slipface deposition rate is related to dune height and celerity. By keeping depositional tolerance constant (representing a constant vegetation type and climate) the model shows that large slow-moving dunes have low slipface deposition rates and essentially 'freeze' in place once vegetation is introduced, retaining their pre-vegetation morphology. Small fast-moving dunes have higher slipface deposition rates and evolve into parabolic dunes. We hypothesize that, when barchan and transverse dunes are subjected to a stabilizing climate shift that increases vegetation growth rate, they retain their pre-stabilization morphology if deposition rates are below the depositional tolerance of stabilizing vegetation, otherwise they become parabolic dunes. This could explain why NSH dunes are stabilized in barchan and transverse morphologies while elsewhere on the Great Plains dune fields are dominated by smaller parabolic dunes.

  15. Breeding and solitary wave behavior of dunes.

    PubMed

    Durán, O; Schwämmle, V; Herrmann, H

    2005-08-01

    Beautiful dune patterns can be found in deserts and along coasts due to the instability of a plain sheet of sand under the action of the wind. Barchan dunes are highly mobile aeolian dunes found in areas of low sand availability and unidirectional wind fields. Up to now modelization mainly focused on single dunes or dune patterns without regarding the mechanisms of dune interactions. We study the case when a small dune bumps into a bigger one. Recently Schwämmle and Herrmann [Nature (London) 426, 610 (2003)] and Katsuki [(e-print cond-mat 0403312)] have shown that under certain circumstances dunes can behave like solitary waves. This means that they can "cross" each other which has been questioned by many researchers before. In other cases we observe coalescence--i.e., both dunes merge into one--breeding--i.e., the creation of three baby dunes at the center and horns of a Barchan dune--or budding--i.e., the small dune, after "crossing" the big one, is unstable and splits into two new dunes. PMID:16196557

  16. Development and steady states of transverse dunes: A numerical analysis of dune pattern coarsening and giant dunes

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Narteau, Clément; Rozier, Olivier

    2015-10-01

    We investigate the development and steady states of transverse dunes for ranges of flow depths and velocities using a cellular automaton dune model. Subsequent to the initial bed instability, dune pattern coarsening is driven by bed form interactions. Collisions lead to two types of coalescence associated with upstream or downstream dominant dunes. In addition, a single collision-ejection mechanism enhances the exchange of mass between two adjacent bed forms (throughpassing dunes). The power law increases in wavelength and amplitude exhibit the same exponents, which are independent of flow properties. Contrary to the wavelength, dune height is limited not only by flow depth but also by the strength of the flow. Superimposed bed forms may propagate and continuously destabilize the largest dunes. We identify three classes of steady state transverse dune fields according to the periodicity in crest-to-crest spacing and the mechanism of size limitation. In all cases, the steady state is reached and maintained through the dynamic equilibrium between flow strength and dune aspect ratio. In the limit of low flow strength, where it becomes the primary factor of size limitation, the bed shear stress in the dune trough regions is close to its critical value for motion inception. Comparisons with natural dune fields suggest that many of them may have reached a steady state. Finally, we infer that the sedimentary patterns in the model may be used to bring new constraints on the development of modern and ancient dune fields.

  17. Stars and linear dunes on Mars

    NASA Technical Reports Server (NTRS)

    Edgett, Kenneth S.; Blumberg, Dan G.

    1994-01-01

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

  18. First Evidence of Dune Movement on Mars

    NASA Astrophysics Data System (ADS)

    Bourke, M. C.; Edgett, K. S.

    2006-12-01

    Many sand dunes on Mars have pristine morphology, fresh grain flows on avalanche faces and sand streamers extending from barchan horns. This suggests that the saltation threshold for sand is exceeded and dune migration is possible under the current Martian climate. However, sand dune movement has not been observed and there is evidence that many of the dunes may be stabilized or indurated. We report the first evidence for the movement of bodies of windblown sand under current climate conditions on Mars. Repeat images of three sand dunes using the Mars Orbiter Camera were acquired between March 1999 and December 2004. We detected the complete removal of sediment from two small dome dunes in a barchan dune field in the North Polar Sand Sea during this time. The third and largest dome dune (77 m wide) in the sample suite had a slight reduction in size, but dune form remained intact. On Earth, dome dunes are circular to oval low mounds of loose, well-sorted, very fine to medium sand. Slip faces are absent or ephemeral and stand only a meter or so high. That these dunes did not migrate, but were eroded, suggests that they were not in equilibrium. Dome dune morphology is not always as effective as e.g., barchan morphology, for trapping sediment, particularly in locations of high velocity winds. In these situations, the removal of sand downwind can lead to the depletion of the dune. Our data confirms that first; the threshold wind speed for saltation is exceeded under present Martian climate conditions. Second, not all dunes on Mars are stabilized or indurated. Third, dune migration is possible under current Martian conditions; however it is likely to be limited to the smallest barchan and dome dunes (i.e. < 20 m wide).

  19. Water Vapor Transport and the Production of Precipitation in the Eastern Fertile Crescent

    E-print Network

    Evans, Jason

    Water Vapor Transport and the Production of Precipitation in the Eastern Fertile Crescent J. P to quantify the significance of southerly water vapor fluxes on precipitation occurring in the eastern Fertile occurring in the Fertile Crescent involve significant water vapor advected from the west, those events

  20. Climate change in the Fertile Crescent and implications of the recent Syrian drought

    E-print Network

    Smerdon, Jason E.

    Climate change in the Fertile Crescent and implications of the recent Syrian drought Colin P Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and un- sustainable agricultural and environmental policies, the drought had

  1. 'Endurance Crater's' Dazzling Dunes (false-color)

    NASA Technical Reports Server (NTRS)

    2004-01-01

    As NASA's Mars Exploration Rover Opportunity creeps farther into 'Endurance Crater,' the dune field on the crater floor appears even more dramatic. This false-color image taken by the rover's panoramic camera shows that the dune crests have accumulated more dust than the flanks of the dunes and the flat surfaces between them. Also evident is a 'blue' tint on the flat surfaces as compared to the dune flanks. This results from the presence of the hematite-containing spherules ('blueberries') that accumulate on the flat surfaces.

    Sinuous tendrils of sand less than 1 meter (3.3 feet) high extend from the main dune field toward the rover. Scientists hope to send the rover down to one of these tendrils in an effort to learn more about the characteristics of the dunes. Dunes are a common feature across the surface of Mars, and knowledge gleaned from investigating the Endurance dunes close-up may apply to similar dunes elsewhere.

    Before the rover heads down to the dunes, rover drivers must first establish whether the slippery slope that leads to them is firm enough to ensure a successful drive back out of the crater. Otherwise, such hazards might make the dune field a true sand trap.

  2. Mean residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Yang, X.; Rozier, O.; Narteau, C.

    2013-12-01

    A barchan dune migrates when the sediment trapped on its lee side is remobilized by the flow. Then, sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady-state barchan dunes by tracking individual cells of a 3D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan dune shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchan dunes. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchan dunes is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan dune morphodynamics. Finally, we initiate a discussion about sediment transport and memory in presence of bed forms using the advantages of the particle tracking technique.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  4. The dune size distribution and scaling relations of barchan dune fields

    E-print Network

    Orencio Durán; Veit Schwämmle; Pedro G. Lind; Hans J. Herrmann

    2008-10-27

    Barchan dunes emerge as a collective phenomena involving the generation of thousands of them in so called barchan dune fields. By measuring the size and position of dunes in Moroccan barchan dune fields, we find that these dunes tend to distribute uniformly in space and follow an unique size distribution function. We introduce an analyticalmean-field approach to show that this empirical size distribution emerges from the interplay of dune collisions and sand flux balance, the two simplest mechanisms for size selection. The analytical model also predicts a scaling relation between the fundamental macroscopic properties characterizing a dune field, namely the inter-dune spacing and the first and second moments of the dune size distribution.

  5. Recent drying of the Fertile Crescent: natural or externally forced?

    NASA Astrophysics Data System (ADS)

    Kelley, Colin

    2014-05-01

    There has been a reduction in observed precipitation over the greater Mediterranean region since the middle of the 20th Century. Recent studies suggest that while anthropogenic forcing has already begun to assert itself in recent decades, the preponderance of the winter drying trend is attributable to the large natural multidecadal variability of the North Atlantic Oscillation (NAO), while over the eastern Mediterranean, the anthropogenic, or forced drying signal is more clearly evident. This forced drying is projected to increase during the 21st Century according to the newest global climate models and this aridification would present significant challenges for a region that is already water-stressed. Although the Fertile Crescent is historically known for its agricultural prosperity, the severity and persistence of the recent multiyear drought in Syria, directly prior to the 2011 uprising there, leads us to ask whether this is evidence of emerging global warming influence. This drought exacerbated existing water insecurity, resulting in an agricultural collapse and a mass migration of rural drought refugees to the urban areas in Syria's west. This migration followed the previous influx of Iragi refugees and combined with strong natural population growth to place a severe strain on resources. Here we examine observations of precipitation and temperature, both gridded and stations, along with simulations and projections from the newest global climate models, to estimate the forced contribution to the recent Syrian drought, and assess the uncertainty in future drying according to the models. We find that this region has experienced a long-term downward trend in precipitation, and a concomitant increase in temperature, serving to further dry the soil, and in surface pressure. We find that the shift in the distributions of three-year running means of surface pressure and precipitation due to the forcing make severe events such as the recent Syrian drought several times more likely. Next we examine the moisture budget in the models and compare with the ground truth of atmospheric reanalyses to determine the relative contributions from the mean flow and the transient eddies. We find that the mean and transient patterns of moisture budget change over the eastern Mediterranean under forcing resemble the patterns of the NAO-induced moisture budget anomaly, but that over the greater Mediterranean there are distinct differences. Under forced moisture budget change, as noted in a recent study, the mean flow serves to strongly dry the greater Mediterranean, with a smaller contribution from the transients. For the eastern Mediterranean however, the transients oppose the drying by the mean flow, under climate change and under a positive phase of the NAO. These results suggest that anthropogenically forced drying of the Fertile Crescent may already be underway, primarily through a poleward shift in the mean flow, and represent a step forward toward a better understanding of the mechanisms associated with eastern Mediterranean hydroclimate change and variability and how they compare.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  7. Daily cycles in coastal dunes

    USGS Publications Warehouse

    Hunter, R.E.; Richmond, B.M.

    1988-01-01

    Daily cycles of summer sea breezes produce distinctive cyclic foreset deposits in dune sands of the Texas and Oregon coasts. In both areas the winds are strong enough to transport sand only during part of the day, reach a peak during the afternoon, and vary little in direction during the period of sand transport. Cyclicity in the foreset deposits is made evident by variations in the type of sedimentary structure, the texture, and the heavy-mineral content of the sand. Some of the cyclic deposits are made up entirely of one basic type of structure, in which the character of the structure varies cyclically; for example, the angle of climb in a climbing-wind-ripple structure may vary cyclically. Other cyclic deposits are characterized by alternations of two or more structural types. Variations in the concentration of fine-grained heavy minerals, which account for the most striking cyclicity, arise mainly because of segregation on wind-rippled depositional surfaces: where the ripples climb at low angles, the coarsegrained light minerals, which accumulate preferentially on ripple crests, tend to be excluded from the local deposit. Daily cyclic deposits are thickest and best developed on small dunes and are least recognizable near the bases of large dunes. ?? 1988.

  8. Size distribution and structure of Barchan dune fields

    E-print Network

    Orencio Durán; Veit Schwämmle; Pedro G. Lind; Hans J. Herrmann

    2011-05-19

    Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a cooperative behavior based on dune interaction. In Duran et al. (2009), we propose that the redistribution of sand by collisions between dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields but fail to reproduce their homogeneity along the wind direction.

  9. Size distribution and structure of Barchan dune fields

    NASA Astrophysics Data System (ADS)

    Durán, O.; Schwämmle, V.; Lind, P. G.; Herrmann, H. J.

    2011-07-01

    Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a cooperative behavior based on dune interaction. In Duran et al. (2009), we propose that the redistribution of sand by collisions between dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields but fail to reproduce their homogeneity along the wind direction.

  10. Dune formation on the present Mars.

    PubMed

    Parteli, Eric J R; Herrmann, Hans J

    2007-10-01

    We apply a model for sand dunes to calculate formation of dunes on Mars under the present Martian atmospheric conditions. We find that different dune shapes as those imaged by Mars Global Surveyor could have been formed by the action of sand-moving winds occurring on today's Mars. Our calculations show, however, that Martian dunes could be only formed due to the higher efficiency of Martian winds in carrying grains into saltation. The model equations are solved to study saltation transport under different atmospheric conditions valid for Mars. We obtain an estimate for the wind speed and migration velocity of barchan dunes at different places on Mars. From comparison with the shape of bimodal sand dunes, we find an estimate for the time scale of the changes in Martian wind regimes. PMID:17994981

  11. Growth mechanisms and dune orientation on Titan

    NASA Astrophysics Data System (ADS)

    Lucas, Antoine; Rodriguez, Sebastien; Narteau, Clement; Cahrnay, Benjamin; Courrech du Pont, Sylvain; Tokano, Tetsuya; Garcia, Amandine; Thiriet, Melanie; Hayes, Alexander; Lorenz, Ralph; Aharonson, Oded

    2015-04-01

    Dune fields on Titan cover more than 17 % of the moon's surface, constituting the largest known surface reservoir of organics. Their confinement to the equatorial belt, shape, and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply. Herein, we present a comprehensive analysis of Titan's dune orientations using automated detection techniques on non-local denoised radar images. By coupling a new dune growth mechanism with actual wind fields generated by climate modelling, we find that Titan's dunes grow by elongation on a non-mobile substratum. To be fully consistent with both the local crestline orientations and the eastward propagation of Titan's dunes, the sediment should be predominantly transported by strong eastward winds, most likely generated by equinoctial storms or occasional fast westerly gusts. Additionally, convergence of the meridional transport predicted in models can explain why Titan's dunes are confined within plus or minus 30 deg. latitudes, where sediment fluxes converge.

  12. Growth mechanisms and dune orientation on Titan

    NASA Astrophysics Data System (ADS)

    Lucas, Antoine; Rodriguez, Sébastien; Narteau, Clément; Charnay, Benjamin; Pont, Sylvain Courrech; Tokano, Tetsuya; Garcia, Amandine; Thiriet, Mélanie; Hayes, Alexander G.; Lorenz, Ralph D.; Aharonson, Oded

    2014-09-01

    Dune fields on Titan cover more than 17% of the moon's surface, constituting the largest known surface reservoir of organics. Their confinement to the equatorial belt, shape, and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply. Herein, we present a comprehensive analysis of Titan's dune orientations using automated detection techniques on nonlocal denoised radar images. By coupling a new dune growth mechanism with wind fields generated by climate modeling, we find that Titan's dunes grow by sediment transport on a nonmobile substratum. To be fully consistent with both the local crestline orientations and the eastward propagation of Titan's dunes, the sediment should be predominantly transported by strong eastward winds, most likely generated by equinoctial storms or occasional fast westerly gusts. Additionally, convergence of the meridional transport predicted in models can explain why Titan's dunes are confined within ±30° latitudes, where sediment fluxes converge.

  13. Stability of transverse dunes against perturbations: A theoretical study using dune skeleton model

    NASA Astrophysics Data System (ADS)

    Niiya, Hirofumi; Awazu, Akinori; Nishimori, Hiraku

    2013-06-01

    The dune skeleton model is a reduced model to describe the formation process and dynamics of characteristic types of dunes emerging under unidirectional steady wind. Using this model, we study the dependency of the morphodynamics of transverse dunes on the initial random perturbations and the lateral field size. It was found that (i) an increase of the lateral field size destabilizes the transverse dune to cause deformation of a barchan, (ii) the initial random perturbations decay with time by the power function until a certain time; thereafter, the dune shapes change into three phases according to the amount of sand and sand diffusion coefficient, and (iii) the duration time, until the transverse dune is broken, increases exponentially with increasing the amount of sand and sand diffusion coefficient. Moreover, under the condition without the sand supply from windward ground, the destabilization of transverse dune in this model qualitatively corresponds to the subaqueous dunes in water tank experiments.

  14. Relevant length scale of barchan dunes.

    PubMed

    Hersen, Pascal; Douady, Stéphane; Andreotti, Bruno

    2002-12-23

    A new experiment can create small scale barchan dunes under water: some sand is put on a tray moving periodically and asymmetrically in a water tank, and barchans rapidly form. We measure basic morphological and dynamical properties of these dunes and compare them to field data. These favorable results demonstrate experimentally the relevance of the so-called "saturation length" for the control of the dunes physics. PMID:12484824

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  16. Hematite Outlier and Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 4 December 2003

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

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

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

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

  17. Interdisciplinary Research Produces Results in the Understanding of Planetary Dunes

    NASA Astrophysics Data System (ADS)

    Titus, Timothy N.; Hayward, Rosalyn Kay; Bourke, Mary C.

    2010-08-01

    Second International Planetary Dunes Workshop: Planetary Analogs—Integrating Models, Remote Sensing, and Field Data; Alamosa, Colorado, 18-21 May 2010; Dunes and other eolian bed forms are prominent on several planetary bodies in our solar system. Despite 4 decades of study, many questions remain regarding the composition, age, and origins of these features, as well as the climatic conditions under which they formed. Recently acquired data from orbiters and rovers, together with terrestrial analogs and numerical models, are providing new insights into Martian sand dunes, as well as eolian bed forms on other terrestrial planetary bodies (e.g., Titan). As a means of bringing together terrestrial and planetary researchers from diverse backgrounds with the goal of fostering collaborative interdisciplinary research, the U.S. Geological Survey (USGS), the Carl Sagan Center for the Study of Life in the Universe, the Desert Research Institute, and the U.S. National Park Service held a workshop in Colorado. The small group setting facilitated intensive discussion of problems and issues associated with eolian processes on Earth, Mars, and Titan.

  18. Three-Dimensional and Multi-Temporal Dune-Field Pattern Analysis in the Olympia Undae Dune Field, Mars 

    E-print Network

    Middlebrook, William David

    2015-07-14

    Fields of sand dunes are ubiquitous in the north polar region of Mars and provide a record of sand transport processes influenced by Mars’ polar climate. Spatial and temporal variations in dunes, ripples, coarse-grained ripples, and exposed dune...

  19. Size of Suspended Sediment over Dunes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Samples of suspended sediment were collected at four elevations simultaneously over two-dimensional mobile dunes in two mixtures of 0.5 mm sand in a laboratory flume channel. A constant sampling position relative to the dunes was maintained by adjusting the translation rate of the sampling carriage...

  20. Size of Suspended Sediment Over Dunes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Samples of suspended sediment were collected at four elevations simultaneously over two-dimensional mobile dunes in 0.5 mm sand in a laboratory flume channel. A constant sampling position relative to the dunes was maintained by adjusting the translation rate of the sampling carriage to be the same ...

  1. Bedform-field pattern formation through bedform interactions within a set of boundary conditions: Example from White Sands Dune Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Ewing, R. C.; Kocurek, G.; Mohrig, D.

    2009-12-01

    The emergence of bedform patterns is explored within the context of self-organizing systems and the imposition of boundary conditions that affect the types and frequency of bedform interactions. One explanation for bedform patterns is self-organization in which the pattern emerges because of interactions among the bedforms themselves. Models, remote images, field studies and lab experiments have identified bedform interactions that involve whole bedforms, only bedform defects, or that are remote interactions between bedforms. It is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development. Constructive interactions, including merging, lateral linking, cannibalization, and remote transfer of sediment, push the system toward fewer, larger, more widely spaced bedforms. Regenerative interactions, including bedform splitting, defect creation and calving, push the system back toward a more initial state. Other interactions, including off-center collision, defect migration, and bedform and defect repulsion, cause pattern change, but may not be strongly constructive or regenerative. We argue that the rich diversity of bedform-field patterns arises because of boundary conditions, which are the unique set of environmental variables within which each field evolves. Boundary conditions are broadly similar within system types, but are unique for each bedform field so that no two are ever exactly alike. Boundary conditions guide the uniqueness of each pattern by altering the type and frequency of interactions. These hypotheses are tested using time-series aerial photographs and airborne LiDAR at White Sands Dune Field, New Mexico. Time-series imagery shows that fully developed, crescentic aeolian dunes, interact and the dune pattern organizes in systematically similar ways as wind ripples and subaqueous dunes and ripples. Documented interactions include: (1) merging, (2) lateral linking, (3) defect repulsion, (4) bedform repulsion, (5) off-center collision, (6) defect creation, and (7) dune splitting. Measurements of pattern parameters (number of dunes, crest length, defect density, crest spacing, dune height), dune migration rates, and the type and frequency of dune interactions within a 3,500 m box transect from the upwind margin to the core of the dune field show that most pattern organization occurs within the upwind field. Upwind dominance by constructive interactions yields to neutral and regenerative interactions in the field center. This spatial change reflects upwind line-source and sediment-availability boundary conditions arising from antecedent paleo-lake topography. Pattern evolution is most strongly coupled to the pattern parameters of dune spacing and defect density, such that spatially or temporally the frequency of bedform interactions decreases as the dunes become farther apart and have fewer defects.

  2. Dunes on Titan: A major landform revealing atmospheric and surface processes

    NASA Astrophysics Data System (ADS)

    Radebaugh, Jani; Lorenz, Ralph; Arnold, Karl; Savage, Christopher; Williams, Brigitte

    The surface of Saturn’s moon Titan is covered in features that herald an active atmosphere and perhaps interior, such as dunes, rivers, lakes, mountain chains, and possible cryovolcanoes. Examining the geomorphology of these features helps us approach an understanding of the processes that are occurring or have occurred in the atmosphere and subsurface. A major landform on Titan is dunes, composed of organic sands ultimately derived from upper atmospheric processing of methane, subsequently perhaps eroded from organic sedimentary layers by methane rainfall and fluvial flow. Dunes fill vast fields, termed sand seas, similar to those observed in the Sahara, Namibia, and the Arabian peninsula. The equatorial region of Titan contains five separate sand seas as observed by the Cassini Synthetic Aperture Radar (SAR), Imaging Science Subsystem (ISS) and Visual and Infrared Mapping Spectrometer (VIMS) instruments. Together these sand seas cover 14 percent of the surface, totaling 12 million km2, and each have areas on the scale of the Saharan Great Sand Sea. They adjoin each other through sediment pathways around landmasses, and these large-scale connections as well as individual dune interactions with topography indicate a general transport of sediment from west to east. Measurements of dune height, width and spacing in Cassini SAR images reveal all of Titan’s thousands of linear dunes are of the same population. This indicates there was general uniformity in the wind and sediment supply conditions that led to the current dune forms. Variations in the parametric values result from deviations from these conditions, in some locations where elevated terrains have deflected winds. Dunes and sand seas are among the stratigraphically youngest features on Titan, showing little evidence of being affected by impact cratering or fluvial flow. However, individual dunes may be relatively stable, as the reorganization time scale for these features on Earth can be tens to hundreds of thousands of years. Recent field studies of large, linear dunes in Namibia reveal a complex reworking of the dune interior, overprinted on the main duneform, as a result of changing regional conditions. These field studies, which can be undertaken at a level of detail not yet possible to obtain on Titan, help us better understand the history of similar landforms on a distant solar system body.

  3. Sand dune dynamics and climate change: A modeling H. Yizhaq,1

    E-print Network

    Ashkenazy, Yossi "Yosef"

    pressure and prolonged droughts the fixed dunes may turn active. Moreover, the model shows that the dune the juxtaposition of fully active dunes and relict stable dunes in the Kelso dune field, California. Lancaster [1994

  4. Contrast Threshold of Lunar Crescents Visibility for Ramadan and Syawal 1431 H at Bosscha Observatory

    NASA Astrophysics Data System (ADS)

    Arumaningtyas, E. P.; Raharto, M.

    2010-12-01

    In this paper we present the prediction of the first lunar crescent visibility using contrast based on Schaefer's model and best time proposed by [12] for the beginning of Ramadhan and Syawal 1431 H at observing place in Bosscha Observatory, [E 107° 36.96', S 6° 49.55', with elevation of 1310 meters above sea level]. The geocentric altitude of the Moon at the sunset time on August 10 is 1° 58.98' and illuminated fraction of crescent (FI) = 0.20%. On August 11, 2010 the altitude of the Moon at the sunset time is 15° 42.71' and FI = 2.57%. The calculated contrast on August 10, 2010 is less than zero. It means that the brightness of the moon is smaller than brightness of the sky. Based on the contrast value, it is impossible to observe the lunar crescent by the naked eye at that time, even equipped by special design telescope for the crescent observation at Bosscha Observatory. Sultan [11] proposed a predicted model it is still possible to observe the very young lunar crescent even under circumstance before the time of sunset, if the contrast of sky is perfect. On August 11, 2010 contrast has its maximum at 50 minutes after sunset. The result of observation of the lunar crescent at Bosscha Observatory, the crescent could be seen before sunset at 17.15 local time (UT+7 hours) using special design telescope with additional nose of 1 meter length [6]. The model used here is tend to predict the brightness for naked eye observation, which less contrast compare to observation with the well design telescope.

  5. Dunes

    E-print Network

    Reed, Michelle

    2006-01-01

    behind her shows a group of people gathered around the casino's marquee. Thanks for the Memories, it reads. It's been nineteen years since I've seen my sister. I search the crowd for her face, almost sure that I won't see her but hoping anyway. Lizzy...'m not sure," she said. "But I'll be back. I'll come back for you." "Momma's gonna be sad," I said. Lizzy put her arms around my back and pulled me into her. She kissed my forehead and then Mary Ann's. "Don't stay up late," she said. She rolled back out...

  6. Clinical-pathologic significance of CD163 positive macrophage in IgA nephropathy patients with crescents

    PubMed Central

    Li, Jun; Liu, Chang-Hua; Gao, Bo; Xu, Dao-Liang

    2015-01-01

    Background: CD163, a marker of M2 macrophages, express anti-inflammatory properties. This study aims to investigate the difference of CD163 positive macrophages expression between IgA nephropathy patients with and without crescents. Methods: Renal tissues from IgAN patients (n = 24), including IgAN with crescents (n = 10), IgAN without crescents (n = 14), minimal change disease (MCD, as disease control, n = 8) and normal control kidneys (negative control, n = 3), were included in this study. Expressions of CD163 and CD68 in renal tissues were detected by immunohistochemistry or immunofluorescence. Results: Compared with IgAN without crescent, IgAN patients with crescents have lower serum albumin and poor renal function. CD163 was mainly expressed in acute tubulointerstitial lesions. CD163 positive cells accumulate in areas around tubules with RBC casts. CD163 positive cells can also be seen in tubular lumen. CD163 positive cells can be seen in glomerular lesions, including endocapillary hypercellularity, cellular crescent and fibrous-cellular crescent. There were more CD163 positive cells in tubulointerstitial and glomerular lesions in IgAN patients with crescents. CD163 positive cells number in tubulointerstitial tissue was positive correlated with percentage of crescents, proteinuria, and negative correlated with serum albumin, eGFR. CD163 positive cells number in glomeruli was positive correlated with percentage of crescents, and was negative correlated with eGFR. Percentage of crescents was negative correlated with serum albumin, eGFR, and positive correlated with proteinuria. Dual staining showed that CD163 positive cells also expressed CD68. Conclusions: CD163 positive macrophages were involved in active crescent disease, acute tubular injury and glomerular lesions of IgAN with crescents. PMID:26309588

  7. Non-standard Neutrino Interactions at DUNE

    E-print Network

    de Gouvêa, André

    2015-01-01

    We explore the effects of non-standard neutrino interactions (NSI) and how they modify neutrino propagation in the Deep Underground Neutrino Experiment (DUNE). We find that NSI can significantly modify the data to be collected by the DUNE experiment as long as the new physics parameters are large enough. For example, If the DUNE data are consistent with the standard three-massive-neutrinos paradigm, order 0.1 (in units of the Fermi constant) NSI effects will be ruled out. On the other hand, if large NSI effects are present, DUNE will be able to not only rule out the standard paradigm but also measure the new physics parameters, sometimes with good precision. We find that, in some cases, DUNE is sensitive to new sources of CP-invariance violation. We also explored whether DUNE data can be used to distinguish different types of new physics beyond nonzero neutrino masses. In more detail, we asked whether NSI can be mimicked, as far as the DUNE setup is concerned, by the hypothesis that there is a new light neutr...

  8. Non-standard Neutrino Interactions at DUNE

    E-print Network

    André de Gouvêa; Kevin J. Kelly

    2015-11-17

    We explore the effects of non-standard neutrino interactions (NSI) and how they modify neutrino propagation in the Deep Underground Neutrino Experiment (DUNE). We find that NSI can significantly modify the data to be collected by the DUNE experiment as long as the new physics parameters are large enough. For example, If the DUNE data are consistent with the standard three-massive-neutrinos paradigm, order 0.1 (in units of the Fermi constant) NSI effects will be ruled out. On the other hand, if large NSI effects are present, DUNE will be able to not only rule out the standard paradigm but also measure the new physics parameters, sometimes with good precision. We find that, in some cases, DUNE is sensitive to new sources of CP-invariance violation. We also explored whether DUNE data can be used to distinguish different types of new physics beyond nonzero neutrino masses. In more detail, we asked whether NSI can be mimicked, as far as the DUNE setup is concerned, by the hypothesis that there is a new light neutrino state.

  9. Conceptual models of the evolution of transgressive dune field systems

    NASA Astrophysics Data System (ADS)

    A. Hesp, Patrick

    2013-10-01

    This paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world, and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields. Various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world. On coasts with high sediment supply, dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid-hyper to arid climate regimes, and as multiple, active discrete phases of dune field and deflation plain couplets in temperate to tropical environments. Active dune fields tend to be singular entities on coasts with low to moderate sediment supply. Landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins, precipitation ridges, nebkha fields and a host of other dune types associated with vegetation (e.g. trailing ridges, slacks, remnant knobs, gegenwalle ridges and dune track ridges, ‘tree islands' and ‘bush pockets'). Three principal scenarios of transgressive dune sheet and dune field development are discussed, including dune sheets or dune fields evolving directly from the backshore, development following foredune and/or dune field erosion, and development from the breakdown or merging of parabolic dunes. Various stages of evolution are outlined for each scenario. Knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse, change and/or modify dune fields to ‘restore' some perceived loss of ecosystem or dune functioning.

  10. Conceptual models of the evolution of transgressive dune field systems

    NASA Astrophysics Data System (ADS)

    Hesp, Patrick A.

    2013-10-01

    This paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world, and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields. Various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world. On coasts with high sediment supply, dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid-hyper to arid climate regimes, and as multiple, active discrete phases of dune field and deflation plain couplets in temperate to tropical environments. Active dune fields tend to be singular entities on coasts with low to moderate sediment supply. Landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins, precipitation ridges, nebkha fields and a host of other dune types associated with vegetation (e.g. trailing ridges, slacks, remnant knobs, gegenwalle ridges and dune track ridges, 'tree islands' and 'bush pockets'). Three principal scenarios of transgressive dune sheet and dune field development are discussed, including dune sheets or dune fields evolving directly from the backshore, development following foredune and/or dune field erosion, and development from the breakdown or merging of parabolic dunes. Various stages of evolution are outlined for each scenario. Knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse, change and/or modify dune fields to 'restore' some perceived loss of ecosystem or dune functioning.

  11. Transformation of barchans into parabolic dunes under the

    E-print Network

    Harting, Jens

    Transformation of barchans into parabolic dunes under the influence of vegetation O.Duran, H.Tsoar, V.Schatz & H.Herrmann #12;Introduction Parabolic dunes: Barchan dunes: #12;Transformation of parabolic dunes into barchans and viceversa Introduction #12;Models vnvnv hthhth +=++ )()( 1 (1) t hhH dt dh

  12. Effect of harbor modifications on the tsunami vulnerability of Crescent City, California

    NASA Astrophysics Data System (ADS)

    Dengler, L.; Uslu, B.

    2008-12-01

    Crescent City, California has experienced more damaging tsunami events in historic times than any other location on the West Coast of the United States. Thirty-one tsunamis have been observed at Crescent City since a tide gauge was established in 1933, including eleven events with maximum peak to trough wave range exceeding one meter and four that caused damage. The most damaging event occurred in 1964 as a result of the great Alaska earthquake. The ensuing tsunami flooded 29 city blocks and killed 11 in the Crescent City area. As a result of the 1964 tsunami and redevelopment projects, the Crescent City harbor was significantly modified in the early 1970s. A 200 x 300 meter small boat basin was carved into the preexisting shore line, a 123 meter dog leg extension was added to the central breakwater and significant deepening occurred on the eastern side of the harbor. In 2006, a Mw 8.3 earthquake in the Kuril Islands generated a moderate Pacific-wide tsunami. The only location with significant damage was the Crescent City harbor where strong currents damaged docks and boats, causing an estimated 9.2 million (US dollars) in damages. Strong currents estimated by the Harbor Master at 12 knots were observed near the entrance to the small boat basin. Past earthquakes from the northwestern Pacific including the 1933 M 8.3 Sanriku Japan earthquake may have produced similar amplitudes at Crescent City to the 2006 event but caused no damage. We have obtained the pre-modification harbor bathymetry and use the MOST model to compare tsunami water heights and current velocities for the 1933 and 2006 sources using modern and pre- modification bathymetry. We also examine model the 1964 inundation using the actual bathymetry and compare the results to numerical simulations that have only used the modern data.

  13. Sixth International Conference on Aeolian Research, Guelph, Canada. 2006 Barchan dune morphodynamics and linear dune formation on Mars

    E-print Network

    Bourke, Mary C.

    Sixth International Conference on Aeolian Research, Guelph, Canada. 2006 Barchan dune. A range of morphological interactions have been observed between smaller barchan and dome dunes that collide with larger barchan and barchanoid dunes. On reaching another dune, they tend to `side

  14. Real barchan dune collisions and ejections

    NASA Astrophysics Data System (ADS)

    Hugenholtz, Chris H.; Barchyn, Thomas E.

    2012-01-01

    From high-resolution satellite imagery of barchan sand dunes, we provide geomorphological evidence of collisions that result in the ejection of a barchan from the wake of another barchan dune. Previous interpretations suggest this outcome is evidence of soliton or solitary wave behaviour; however, the physical mechanisms for mass exchange are not fully understood, resulting in debate. Our evidence and interpretation indicates that mass is transferred to the upwind barchan by shadowing a portion of downwind barchan's stoss slope. Turbulent, unsaturated airflow erodes the surface between the dunes, creating a smaller dune that ejects from the wake region. Previous observations lacked the spatial resolution required to document this process; therefore, our observations clarify the collision dynamics of barchans. A broader implication of our observations is the role of collisions in maintaining an “equilibrium” size distribution in barchan swarms.

  15. Summary of the DUNE Mission Concept

    E-print Network

    Alexandre Refregier; Marian Douspis; the DUNE collaboration

    2008-07-25

    The Dark UNiverse Explorer (DUNE) is a wide-field imaging mission concept whose primary goal is the study of dark energy and dark matter with unprecedented precision. To this end, DUNE is optimised for weak gravitational lensing, and also uses complementary cosmolo gical probes, such as baryonic oscillations, the integrated Sachs-Wolf effect, a nd cluster counts. Immediate additional goals concern the evolution of galaxies, to be studied with groundbreaking statistics, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planets. DUNE is a medium class mission consisting of a 1.2m telescope designed to carry out an all-sky survey in one visible and three NIR bands (1deg$^2$ field-of-view) which will form a unique legacy for astronomy. DUNE has been selected jointly with SPACE for an ESA Assessment phase which has led to the Euclid merged mission concept.

  16. '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.

  17. Invasive plants on disturbed Korean sand dunes

    NASA Astrophysics Data System (ADS)

    Kim, Kee Dae

    2005-01-01

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

  18. Mean sediment residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Yang, X.; Rozier, O.; Narteau, C.

    2014-03-01

    When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3-D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.

  19. A Different Look At Titans Dunes

    NASA Astrophysics Data System (ADS)

    Paganelli, Flora; Callahan, P.; Hensley, S.; Lorenz, R.; Lunine, J.; Kirk, R.; Stiles, B.; Janssen, M.; Lopes, R.; Stofan, E.; Wall, S.; Paillou, P.; Radar Team

    2006-09-01

    In its six Titan flybys (T16: July 2006) the Cassini's Titan Radar Mapper has imaged yet again more evidence of dark linear streaks and/or dunes. The latitude, between 14-25 N, and orientation of these features is comparable to the one seen in the T3 (February 2005) Titan flyby. The implications of these new observation stand on the particular geometry in which the dunes have been imaged in the radar swath and consequently on the effect that this has on their characterization. Previous flyby geometries had look direction perpendicular to the general azimuth of the dunes, thus allowing identification of dunes with generally observed E-W orientation (see also Radebaugh et al., this conference) and --because of the favorable geometry -- to identify their topographic expression. T16 has shown that the same dark linear streaks and/or dunes trend can be imaged with look direction quasi-parallel to them, very similar to the + 25 E-W azimuth in T3. This has the implication that these features might be superposed streaks with none or minimal topography, and that they are visible because of differential erosion between the radar bright rougher substrate and the radar dark of fine particle smooth surface deposits. This paper will asses the imaging geometry at which these dark linear streaks and/or dunes are seen in T16 and T3 flybys, and what the data are telling us in terms of their physical and morphological properties.

  20. Mars Global Digital Dune Database (MGD3): Global dune distribution and wind pattern observations

    USGS Publications Warehouse

    Hayward, Rosalyn K.; Fenton, Lori; Titus, Timothy N.

    2013-01-01

    The Mars Global Digital Dune Database (MGD3) is complete and now extends from 90°N to 90°S latitude. The recently released south pole (SP) portion (MC-30) of MGD3 adds ?60,000 km2 of medium to large-size dark dune fields and ?15,000 km2 of sand deposits and smaller dune fields to the previously released equatorial (EQ, ?70,000 km2), and north pole (NP, ?845,000 km2) portions of the database, bringing the global total to ?975,000 km2. Nearly all NP dunes are part of large sand seas, while the majority of EQ and SP dune fields are individual dune fields located in craters. Despite the differences between Mars and Earth, their dune and dune field morphologies are strikingly similar. Bullseye dune fields, named for their concentric ring pattern, are the exception, possibly owing their distinctive appearance to winds that are unique to the crater environment. Ground-based wind directions are derived from slipface (SF) orientation and dune centroid azimuth (DCA), a measure of the relative location of a dune field inside a crater. SF and DCA often preserve evidence of different wind directions, suggesting the importance of local, topographically influenced winds. In general however, ground-based wind directions are broadly consistent with expected global patterns, such as polar easterlies. Intriguingly, between 40°S and 80°S latitude both SF and DCA preserve their strongest, though different, dominant wind direction, with transport toward the west and east for SF-derived winds and toward the north and west for DCA-derived winds.

  1. Mars Global Digital Dune Database (MGD3): Global dune distribution and wind pattern observations

    NASA Astrophysics Data System (ADS)

    Hayward, R. K.; Fenton, L. K.; Titus, T. N.

    2014-02-01

    The Mars Global Digital Dune Database (MGD3) is complete and now extends from 90°N to 90°S latitude. The recently released south pole (SP) portion (MC-30) of MGD3 adds ˜60,000 km2 of medium to large-size dark dune fields and ˜15,000 km2 of sand deposits and smaller dune fields to the previously released equatorial (EQ, ˜70,000 km2), and north pole (NP, ˜845,000 km2) portions of the database, bringing the global total to ˜975,000 km2. Nearly all NP dunes are part of large sand seas, while the majority of EQ and SP dune fields are individual dune fields located in craters. Despite the differences between Mars and Earth, their dune and dune field morphologies are strikingly similar. Bullseye dune fields, named for their concentric ring pattern, are the exception, possibly owing their distinctive appearance to winds that are unique to the crater environment. Ground-based wind directions are derived from slipface (SF) orientation and dune centroid azimuth (DCA), a measure of the relative location of a dune field inside a crater. SF and DCA often preserve evidence of different wind directions, suggesting the importance of local, topographically influenced winds. In general however, ground-based wind directions are broadly consistent with expected global patterns, such as polar easterlies. Intriguingly, between 40°S and 80°S latitude both SF and DCA preserve their strongest, though different, dominant wind direction, with transport toward the west and east for SF-derived winds and toward the north and west for DCA-derived winds.

  2. Teaching 21st Century Competencies: Lessons from Crescent Girls' School in Singapore

    ERIC Educational Resources Information Center

    Trinidad, Gucci; Patel, Deepa; Shear, Linda; Goh, Peishi; Quek, Yin Kang; Tan, Chen Kee

    2013-01-01

    This paper presents case studies of two teachers at Crescent Girl's School (an all-girls high school in Singapore) who implemented strategies learned through a teacher professional development program called 21st Century Learning Design (21CLD). Policymakers often state requirements for teachers to focus on 21st century (21C) competencies without…

  3. Regime shift in Arabian dust activity, triggered by persistent Fertile Crescent drought

    NASA Astrophysics Data System (ADS)

    Notaro, Michael; Yu, Yan; Kalashnikova, Olga V.

    2015-10-01

    The Arabian Peninsula has experienced pronounced interannual to decadal variability in dust activity, including an abrupt regime shift around 2006 from an inactive dust period during 1998-2005 to an active period during 2007-2013. Corresponding in time to the onset of this regime shift, the climate state transitioned into a combined La Niña and negative phase of the Pacific Decadal Oscillation, which incited a hiatus in global warming in the 2000s. Superimposed upon a long-term regional drying trend, synergistic interactions between these teleconnection modes triggered the establishment of a devastating and prolonged drought, which engulfed the Fertile Crescent, namely, Iraq and Syria, and led to crop failure and civil unrest. Dried soils and diminished vegetation cover in the Fertile Crescent, as evident through remotely sensed enhanced vegetation indices, supported greater dust generation and transport to the Arabian Peninsula in 2007-2013, as identified both in increased dust days observed at weather stations and enhanced remotely sensed aerosol optical depth. According to backward trajectory analysis of dust days on the Arabian Peninsula, increased dust lifting and atmospheric dust concentration in the Fertile Crescent during this recent, prolonged drought episode supported a greater frequency of dust events across the peninsula with associated northerly trajectories and led to the dust regime shift. These findings are particularly concerning, considering projections of warming and drying for the eastern Mediterranean region and potential collapse of the Fertile Crescent during this century.

  4. Extraordinary Transmission of Three-Dimensional Crescent-like Holes Arrays

    E-print Network

    & Jensen Li & Xia Chen & Hai-Xia Xu & Qiangzhong Zhu & Xuehua Wang & Chongjun Jin Received: 5 June 2011 periodic arrays of three-dimensional crescent- like holes (3DCLH) as shown in Fig. 1a, by colloidal Y. Shen Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275

  5. Expression of Ser729 Phosphorylated PKC Epsilon in Experimental Crescentic Glomerulonephritis: An Immunohistochemical Study

    PubMed Central

    Karavana, V.N.; Gakiopoulou, H.; Lianos, E.A.

    2014-01-01

    PKC?, a DAG-dependent, Ca2+- independent kinase attenuates extent of fibrosis following tissue injury, suppresses apoptosis and promotes cell quiescence. In crescentic glomerulonephritis (CGN), glomerular epithelial cells (GEC) contribute to fibro-cellular crescent formation while they also transdifferentiate to a mesenchymal phenotype. The aim of this study was to assess PKC? expression in CGN. Using an antibody against PKC-? phosphorylated at Ser729, we assessed its localization in rat model of immune-mediated rapidly progressive CGN. In glomeruli of control animals, pPKC? was undetectable. In animals with CGN, pPKC? was expressed exclusively in glomerular epithelial cells (GEC) and in GEC comprising fibrocellular crescents that had acquired a myofibroblasttype phenotype. In non-immune GEC injury induced by puromycin aminonucleoside and resulting in proteinuria of similar magnitude as in CGN, pPKC? expression was absent. There was constitutive pPKC? expression in distal convoluted tubules, collecting ducts and thick segments of Henley’s loops in both control and experimental animals. We propose that pPKC? expression occurring in GEC and in fibrocellular crescentic lesions in CGN may facilitate PKC? dependent pathologic processes. PMID:24998921

  6. Strategies to restore fragmented meta-populations of Fertile Crescent wheat landraces

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Historically, farmers in the Fertile Crescent (FC) planted diverse assemblages of genotypes (i.e., landraces, LRs) to lower the risk of failure and increase food security because they had limited capacity to control the spatially heterogeneous and temporally unpredictable environment of the FC with ...

  7. A bibliography of dunes: Earth, Mars, and Venus

    NASA Technical Reports Server (NTRS)

    Lancaster, N.

    1988-01-01

    Dunes are important depositional landforms and sedimentary environments on Earth and Mars, and may be important on Venus. The similarity of dune forms on Earth and Mars, together with the dynamic similarity of aeolian processes on the terrestrial planets indicates that it is appropriate to interpret dune forms and processes on Mars and Venus by using analog studies. However, the literature on dune studies is large and scattered. The aim of this bibliography is to assist investigators by providing a literature resource on techniques which have proved successful in elucidating dune characteristics and processes on Earth, Mars, and Venus. This bibliography documents the many investigations of dunes undertaken in the last century. It concentrates on studies of inland dunes in both hot and cold desert regions on Earth and includes investigations of coastal dunes only if they discuss matters of general significance for dune sediments, processes, or morphology.

  8. Predictability of dune activity in real dune fields under unidirectional wind regimes

    NASA Astrophysics Data System (ADS)

    Barchyn, Thomas E.; Hugenholtz, Chris H.

    2015-02-01

    We present an analysis of 10 dune fields to test a model-derived hypothesis of dune field activity. The hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes: active dunes have slipface deposition rates that exceed the vegetation deposition tolerance, and stabilizing dunes have the opposite. We quantified aeolian sand flux, slipface geometry, and vegetation deposition tolerance to directly test the hypothesis at four dune fields (Bigstick, White Sands Stable, White Sands Active, and Cape Cod). We indirectly tested the hypothesis at six additional dune fields with limited vegetation data (Hanford, Año Nuevo, Skagen Odde, Salton Sea, Oceano Stable, and Oceano Active, "inverse calculation sites"). We used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization. Results revealed a distinct, quantifiable, and consistent pattern despite diverse environmental conditions: the modal peak of prestabilization slipface deposition rates was 80% of the vegetation deposition tolerance at stabilized or stabilizing dune fields. Results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance (1 m a-1), and active sites had slipface deposition rates much higher. Overall, these results confirm the hypothesis and provide evidence of a globally applicable, simple, and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes.

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

    E-print Network

    Stillman, David E.

    P13B-1369 Great Kobuk Sand Dunes, Alaska: A Terrestrial Analog Site for Polar, Topographically. The 67°N latitude, 62 km2 Great Kobuk Sand Dunes (GKSD) are a terrestrial analog for polar, intercrater sand thermal conductivity, higher wet sand thermal conductivity, infiltration of relatively warm summer

  10. Modeling emergent large-scale structures of barchan dune fields

    NASA Astrophysics Data System (ADS)

    Worman, S. L.; Murray, A.; Littlewood, R. C.; Andreotti, B.; Claudin, P.

    2013-12-01

    In nature, barchan dunes typically exist as members of larger fields that display striking, enigmatic structures that cannot be readily explained by examining the dynamics at the scale of single dunes, or by appealing to patterns in external forcing. To explore the possibility that observed structures emerge spontaneously as a collective result of many dunes interacting with each other, we built a numerical model that treats barchans as discrete entities that interact with one another according to simplified rules derived from theoretical and numerical work, and from field observations: Dunes exchange sand through the fluxes that leak from the downwind side of each dune and are captured on their upstream sides; when dunes become sufficiently large, small dunes are born on their downwind sides ('calving'); and when dunes collide directly enough, they merge. Results show that these relatively simple interactions provide potential explanations for a range of field-scale phenomena including isolated patches of dunes and heterogeneous arrangements of similarly sized dunes in denser fields. The results also suggest that (1) dune field characteristics depend on the sand flux fed into the upwind boundary, although (2) moving downwind, the system approaches a common attracting state in which the memory of the upwind conditions vanishes. This work supports the hypothesis that calving exerts a first order control on field-scale phenomena; it prevents individual dunes from growing without bound, as single-dune analyses suggest, and allows the formation of roughly realistic, persistent dune field patterns.

  11. Modeling emergent large-scale structures of barchan dune fields

    NASA Astrophysics Data System (ADS)

    Worman, S. L.; Murray, A. B.; Littlewood, R.; Andreotti, B.; Claudin, P.

    2013-10-01

    In nature, barchan dunes typically exist as members of larger fields that display striking, enigmatic structures that cannot be readily explained by examining the dynamics at the scale of single dunes, or by appealing to patterns in external forcing. To explore the possibility that observed structures emerge spontaneously as a collective result of many dunes interacting with each other, we built a numerical model that treats barchans as discrete entities that interact with one another according to simplified rules derived from theoretical and numerical work and from field observations: (1) Dunes exchange sand through the fluxes that leak from the downwind side of each dune and are captured on their upstream sides; (2) when dunes become sufficiently large, small dunes are born on their downwind sides (`calving'); and (3) when dunes collide directly enough, they merge. Results show that these relatively simple interactions provide potential explanations for a range of field-scale phenomena including isolated patches of dunes and heterogeneous arrangements of similarly sized dunes in denser fields. The results also suggest that (1) dune field characteristics depend on the sand flux fed into the upwind boundary, although (2) moving downwind, the system approaches a common attracting state in which the memory of the upwind conditions vanishes. This work supports the hypothesis that calving exerts a first-order control on field-scale phenomena; it prevents individual dunes from growing without bound, as single-dune analyses suggest, and allows the formation of roughly realistic, persistent dune field patterns.

  12. A method for building 3D models of barchan dunes

    NASA Astrophysics Data System (ADS)

    Nai, Yang; Li-lan, Su; Lin, Wan; Jie, Yang; Shi-yi, Chen; Wei-lu, Hu

    2016-01-01

    The distributions of barchan dunes are usually represented by digital terrain models (DTMs) overlaid with digital orthophoto maps. Given that most regions with barchan dues have low relief, a 3D map obtained from a DTM may ineffectively show the stereoscopic shape of each dune. The method of building 3D models of barchan dunes using existing modeling software seldom considers the geographical environment. As a result, barchan dune models are often inconsistent with actual DTMs and incompletely express the morphological characteristics of dunes. Manual construction of barchan dune models is also costly and time consuming. Considering these problems, the morphological characteristics of barchan dunes and the mathematical relationships between the morphological parameters of the dunes, such as length, height, and width, are analyzed in this study. The methods of extracting the morphological feature points of barchan dunes, calculating their morphological parameters and building dune outlines and skeleton lines based on the medial axes, are also presented. The dune outlines, skeleton lines, and part of the medial axes of dunes are used to construct a constrained triangulated irregular network. C# and ArcEngine are employed to build 3D models of barchan dunes automatically. Experimental results of a study conducted in Tengger Desert show that the method can be used to approximate the morphological characteristics of barchan dunes and is less time consuming than manual methods.

  13. Layers, Landslides, and Sand Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 27 October 2003

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

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

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

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

  14. Dark Streaks Over-riding Inactive Dunes

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Not all sand dunes on Mars are active in the modern martian environment. This example from the Lycus Sulci (Olympus Mons'aureole') region shows a case where small windblown dunes at the base of a slope have been over-ridden by more recent dark streaks (arrows). The dark streaks are most likely caused by what geologists call mass wasting or mass movement (landslides and avalanches are mass movements). Dark slope streaks such as these are common in dustier regions of Mars, and they appear to result from movement of extremely dry dust or sand in an almost fluidlike manner down a slope. This movement disrupts the bright dust coating on the surface and thus appears darker than the surrounding terrain.

    In this case, the dark slope streaks have moved up and over the dunes at the bottom of the slope, indicating that the process that moves sediment down the slope is more active (that is, it has occurred more recently and hence is more likely to occur) in the modern environment than is the movement of dunes and ripples at this location on Mars. The dunes, in fact, are probably mantled by dust. This October 1997 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture is illuminated from the left and located near 31.6oN, 134.0oW.

  15. Dunes on Titan observed by Cassini Radar

    USGS Publications Warehouse

    Radebaugh, J.; Lorenz, R.D.; Lunine, J.I.; Wall, S.D.; Boubin, G.; Reffet, E.; Kirk, R.L.; Lopes, R.M.; Stofan, E.R.; Soderblom, L.; Allison, M.; Janssen, M.; Paillou, P.; Callahan, P.; Spencer, C.; The Cassini Radar Team

    2008-01-01

    Thousands of longitudinal dunes have recently been discovered by the Titan Radar Mapper on the surface of Titan. These are found mainly within ??30?? of the equator in optically-, near-infrared-, and radar-dark regions, indicating a strong proportion of organics, and cover well over 5% of Titan's surface. Their longitudinal duneform, interactions with topography, and correlation with other aeolian forms indicate a single, dominant wind direction aligned with the dune axis plus lesser, off-axis or seasonally alternating winds. Global compilations of dune orientations reveal the mean wind direction is dominantly eastwards, with regional and local variations where winds are diverted around topographically high features, such as mountain blocks or broad landforms. Global winds may carry sediments from high latitude regions to equatorial regions, where relatively drier conditions prevail, and the particles are reworked into dunes, perhaps on timescales of thousands to tens of thousands of years. On Titan, adequate sediment supply, sufficient wind, and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes. ?? 2007 Elsevier Inc. All rights reserved.

  16. The role of dune interactions and wind fluctuations in the selection of dune sizes within barchan fields

    NASA Astrophysics Data System (ADS)

    Duran Vinent, O.; Parteli, E. J.; Herrmann, H. J.

    2012-12-01

    Sand dunes dominate desert morphology. They naturally emerge under strong winds and sufficient sand supply from the interaction between sand transport, topography and hydrodynamics. The fact that dunes are mobile landforms gives a dynamical character to desert geomorphology with potential implications for the surrounding ecosystems. As dune mobility is closely related to dune morphology, in particular its size, the study of the long-term evolution of desert areas requires a better understanding of (1) the factors behind dune size selection and (2) the multi-scale nature of dune morphology. Recently it has been shown that dune size is bounded both at small and large scales by sand transport and hydrodynamics, respectively. The smallest dune size is limited to several meters in length by the existence of the so called "saturation length", i.e. the characteristic length of transport transients. The maximum dune size, in the order of hundreds of meters, is in turn limited by the stabilizing effect of the upper limit of the atmospheric boundary layer. Dune dynamics at both scales is also qualitatively different as elementary dunes emerge from a linear instability, and are thus ubiquitous, while giant dunes seem to result from the coalescence of smaller ones. In consequence, a typical dune field should consist in a roughly continuous hierarchy of dune sizes, with many elementary dunes and very few giant dunes. However, in several cases this is not the correct picture as dune sizes are quite uniform and seems to cluster around an intermediate value that is well above the minimum but much smaller than the maximum one. This points to an alternative selection mechanism different from the simple dune merging. Here, we argue that the combination of dune collisions and wind fluctuations, at least within barchan fields, is able to stop the continuous merging process and select a characteristic dune size in function of local conditions. To that end we use a morphodynamic dune model capable of reproducing the evolution of dune fields for different wind regimes. We find that colliding dunes of very different sizes tend to merge and thus increase the average dune size within the field. In contrast, colliding dunes of comparable sizes tend to redistribute the volume such that both dunes become more equal afterwards, which limits dune growth. In accordance with previous results, we find that dune growth is also limited by wind fluctuations, both in intensity and direction, which lead to the formation of elementary barchans from dune calving. As a result, the balance between those processes contributing to dune growth and those limiting it is able to select a specific, non-trivial dune size. In addition, simulations also suggest that this balance can be unstable in certain conditions and start a positive feedback for dune growth. As collisions with very large dunes have a higher probability of leading to the merging of both dunes, dune growth may continue until it is eventually limited by the size of the atmospheric boundary layer.

  17. Implications of dune pattern analysis for Titan's surface history

    NASA Astrophysics Data System (ADS)

    Savage, Christopher J.; Radebaugh, Jani; Christiansen, Eric H.; Lorenz, Ralph D.

    2014-02-01

    Analysis of large-scale morphological parameters can reveal the reaction of dunes to changes in atmospheric and sedimentary conditions. Over 7000 dune width and 7000 dune spacing measurements were obtained for linear dunes in regions across Saturn's moon Titan from images T21, T23, T28, T44 and T48 collected by the Synthetic Aperture RADAR (SAR) aboard the Cassini spacecraft in order to reconstruct the aeolian surface history of Titan. Dunes in the five study areas are all linear in form, with a mean width of 1.3 km and mean crest spacing of 2.7 km, similar to dunes in the African Saharan and Namib deserts on Earth. At the resolution of Cassini SAR, the dunes have the morphology of large linear dunes, and they lack evidence for features of compound or complex dunes. The large size, spacing and uniform morphology are all indicators that Titan's dunes are mature features, in that they have grown toward a steady state for a long period of time. Dune width decreases to the north, perhaps from increased sediment stabilization caused by a net transport of moisture from south to north, or from increased maturity in dunes to the south. Cumulative probability plots of dune parameters measured at different locations across Titan indicate there is a single population of intermediate-to-large-sized dunes on Titan. This suggests that, unlike analogous dunes in the Namib and Agneitir Sand Seas, dune-forming conditions that generated the current set of dunes were stable and active long enough to erase any evidence of past conditions.

  18. Linking restoration ecology with coastal dune restoration

    NASA Astrophysics Data System (ADS)

    Lithgow, D.; Martínez, M. L.; Gallego-Fernández, J. B.; Hesp, P. A.; Flores, P.; Gachuz, S.; Rodríguez-Revelo, N.; Jiménez-Orocio, O.; Mendoza-González, G.; Álvarez-Molina, L. L.

    2013-10-01

    Restoration and preservation of coastal dunes is urgently needed because of the increasingly rapid loss and degradation of these ecosystems because of many human activities. These activities alter natural processes and coastal dynamics, eliminate topographic variability, fragment, degrade or eliminate habitats, reduce diversity and threaten endemic species. The actions of coastal dune restoration that are already taking place span contrasting activities that range from revegetating and stabilizing the mobile substrate, to removing plant cover and increasing substrate mobility. Our goal was to review how the relative progress of the actions of coastal dune restoration has been assessed, according to the ecosystem attributes outlined by the Society of Ecological Restoration: namely, integrity, health and sustainability and that are derived from the ecological theory of succession. We reviewed the peer reviewed literature published since 1988 that is listed in the ISI Web of Science journals as well as additional references, such as key books. We exclusively focused on large coastal dune systems (such as transgressive and parabolic dunefields) located on natural or seminatural coasts. We found 150 articles that included "coastal dune", "restoration" and "revegetation" in areas such as title, keywords and abstract. From these, 67 dealt specifically with coastal dune restoration. Most of the studies were performed in the USA, The Netherlands and South Africa, during the last two decades. Restoration success has been assessed directly and indirectly by measuring one or a few ecosystem variables. Some ecosystem attributes have been monitored more frequently (ecosystem integrity) than others (ecosystem health and sustainability). Finally, it is important to consider that ecological succession is a desirable approach in restoration actions. Natural dynamics and disturbances should be considered as part of the restored system, to improve ecosystem integrity, health and sustainability.

  19. Barchan dune corridors: Field characterization and investigation of control parameters

    E-print Network

    Barchan dune corridors: Field characterization and investigation of control parameters H November 2007; published 8 March 2008. [1] The structure of the barchan field located between Tarfaya, H., B. Andreotti, and P. Claudin (2008), Barchan dune corridors: Field characterization

  20. Barchan-parabolic dune pattern transition from vegetation stability threshold

    NASA Astrophysics Data System (ADS)

    Reitz, Meredith D.; Jerolmack, Douglas J.; Ewing, Ryan C.; Martin, Raleigh L.

    2010-10-01

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

  1. Broadband colored-crescent generation in a single ?-barium-borate crystal by intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Wang, L.; Fan, Y. X.; Zhu, H.; Yan, Z. D.; Zeng, H.; Wang, H.-T.; Zhu, S. N.; Wang, Z. L.

    2011-12-01

    A visible colored crescent with a bandwidth broader than 220 nm is observed experimentally by loosely focused femtosecond pulses in a bulk quadratic nonlinear crystal (?-BBO crystal) at certain incident angles. Through the analysis based on a simple collinear phase-matching model, we suggest that the colored crescent might be the coexistence of spontaneous parametric down-conversions (SPDCs) in the infrared range and the corresponding efficient second-order harmonic generations (SHGs) that occur in a wide spectrum. We further provide a possible mechanism for the SHG process in which the phase-mismatching angles of the frequency doubling of SPDCs in ?-BBO crystal are assumed to be compensated by the strong diffraction effect during the self-focusing process of the generated intense SPDC signals.

  2. Electrowetting on dielectric device with crescent electrodes for reliable and low-voltage droplet manipulation.

    PubMed

    Xu, Xiaowei; Sun, Lining; Chen, Liguo; Zhou, Zhaozhong; Xiao, Junjian; Zhang, Yuliang

    2014-11-01

    Digital microfluidics based on electrowetting on dielectric is an emerging popular technology that manipulates single droplets at the microliter or even the nanoliter level. It has the unique advantages of rapid response, low reagent consumption, and high integration and is mainly applied in the field of biochemical analysis. However, currently, this technology still has a few problems, such as high control voltage, low droplet velocity, and continuity in flow, limiting its application. In this paper, through theoretical analysis and numerical simulation, it is deduced that a drive electrode with a crescent configuration can reduce the driving voltage. The experimental results not only validate this deduction but also indicate that crescent electrode can improve the droplet motion continuity and the success in split rate. PMID:25553184

  3. Electrowetting on dielectric device with crescent electrodes for reliable and low-voltage droplet manipulation

    PubMed Central

    Xu, Xiaowei; Sun, Lining; Chen, Liguo; Zhou, Zhaozhong; Xiao, Junjian; Zhang, Yuliang

    2014-01-01

    Digital microfluidics based on electrowetting on dielectric is an emerging popular technology that manipulates single droplets at the microliter or even the nanoliter level. It has the unique advantages of rapid response, low reagent consumption, and high integration and is mainly applied in the field of biochemical analysis. However, currently, this technology still has a few problems, such as high control voltage, low droplet velocity, and continuity in flow, limiting its application. In this paper, through theoretical analysis and numerical simulation, it is deduced that a drive electrode with a crescent configuration can reduce the driving voltage. The experimental results not only validate this deduction but also indicate that crescent electrode can improve the droplet motion continuity and the success in split rate. PMID:25553184

  4. Participation of Vaccinia Virus L2 Protein in the Formation of Crescent Membranes and Immature Virions?

    PubMed Central

    Maruri-Avidal, Liliana; Domi, Arban; Weisberg, Andrea S.; Moss, Bernard

    2011-01-01

    Morphogenesis of vaccinia virus begins with the appearance of crescent-shaped membrane precursors of immature virions in cytoplasmic factories. During the initial characterization of the product of the L2R reading frame, we discovered that it plays an important role in crescent formation. The L2 protein was expressed early in infection and was associated with the detergent-soluble membrane fraction of mature virions, consistent with two potential membrane-spanning domains. All chordopoxviruses have L2 homologs, suggesting an important function. Indeed, we were unable to isolate an infectious L2R deletion mutant. Consequently, we constructed an inducible mutant with a conditional lethal phenotype. When L2 expression was repressed, proteolytic processing of the major core proteins and the A17 protein, which is an essential component of the immature virion membrane, failed to occur, suggesting an early block in viral morphogenesis. At 8 h after infection in the presence of inducer, immature and mature virions were abundantly seen by electron microscopy. In contrast, those structures were rare in the absence of inducer and were replaced by large, dense aggregates of viroplasm. A minority of these aggregates had short spicule-coated membranes, which resembled the beginnings of crescent formation, at their periphery. These short membrane segments at the edge of the dense viroplasm increased in number at later times, and some immature virions were seen. Although the L2 protein was not detected under nonpermissive conditions, minute amounts could account for stunted and delayed viral membrane formation. These findings suggested that L2 is required for the formation or elongation of crescent membranes. PMID:21228235

  5. A GIS Representation of 1964 Tsunami Damage in Crescent City, California

    NASA Astrophysics Data System (ADS)

    Velasco Campos, C. J.; Dengler, L. A.

    2013-12-01

    The March 1964 Alaska tsunami caused major damage in Alaska and also impacted the west coast of North America. Crescent City, California, 3000 km away from the source region, suffered the greatest damage outside Alaska. Twenty-nine blocks of the downtown and harbor areas were inundated and nearly 300 homes and businesses damaged or destroyed. In the aftermath of the tsunami, numerous maps, reports and photographs of the impacts in Crescent City were released, some by engineers and scientists, and much by individuals and the popular press. The Del Norte Historical Society has a large amount of archival material (photographs and eye witness accounts) from the tsunami, much of which has never been thoroughly examined or correlated with other reports. In this study, we assemble all of the available information from these disparate sources into a GIS framework in order to examine the 1964 Crescent City damage in a systematic way and provide a quantitative framework for others who are modeling tsunami impacts. Using ArcGIS 10, old aerial photos, tsunami inundation maps, and photographs were georeferenced to produce GIS layers of 'before and after' Crescent City. Hyperlinks were created to connect photos with their locations in present day. We reference damage to a layer showing Magoon's 1968 map of inundation depth and extent. Structural damage falls into four main groupings: structures floated off of foundations, damage by impact from debris, pressure differences from water infilling structures, and fire. 15 structures were moved off of foundations, all in the direction of the outgoing flow. We also create layers of the structures of the modern city and the predicted tsunami run-up from a Cascadia event. Magoon, Orville T., 1966, Structural Damage by Tsunamis, Proceedings, American Society Civil Engineers, Specialty Conference on Coastal Engineering, Santa Barbara (California), Oct. 1965, pp. 35-68

  6. The Signature of Life in Stabilized Dune Topography

    NASA Astrophysics Data System (ADS)

    Barchyn, T. E.; Hugenholtz, C.

    2012-12-01

    Life dramatically affects aeolian dunes on Earth by modifying dune morphology and immobilizing sediment. Complete immobilization (stabilization) occurs when vegetation growth shelters the surface and eliminates sediment transport (and the capacity of the dune to clear vegetation). In unidirectional dune forms stabilization is usually preceded by a period of transition dominated by pronounced morphological change (e.g., parabolic dunes). Here, we hypothesize that stabilized topography holds previously unidentified clues detailing the kinematics and behavior of vegetation during stabilization (a 'signature'). During stabilization dune ridges advance downwind and 'bulldoze' vegetation in their path. We split dune ridges into a series of wind-parallel 'dune slices' and outline how slipface vegetation could prove to be a 'tipping point' in stabilization for each dune slice. Slipface vegetation sets off a self-reinforcing stabilization feedback, simplifying our treatment and yielding two predictable behaviors: slipfaces either clear vegetation (deposition rate > vegetation deposition tolerance), or succumb to vegetation and become immobilized (deposition rate < vegetation deposition tolerance). We model slipface deposition rates through slipface geometry and show how predictable variations in classical dune forms (i) could be responsible for incipient transformation of barchan to parabolic dunes, (ii) result in a progressive stabilization feedback fundamentally inconsistent with widely used dune activity indices, and (iii) record a quantitative signature of the relative kinematics of sediment flux and vegetation growth in stabilized slipface geometries. To explore the idea in real dune fields, we extract slipface deposition rates through slipface geometry recorded in digital terrain data for three dune fields: (i) Bigstick Sand Hills, SK, Canada, (ii) White Sands, NM, USA, and (iii) Cape Cod, MA, USA. With independent estimates of sediment flux and vegetation deposition tolerance we show how all three dune fields show consistent results with characteristic deposition rates approximately 60% of vegetation deposition tolerance. These results open the possibility that a consistent and identifiable 'signature of life' could be coded into all stabilized dune topography worldwide.

  7. Mars Global Digital Dune Database and initial science results

    NASA Astrophysics Data System (ADS)

    Hayward, Rosalyn K.; Mullins, Kevin F.; Fenton, Lori K.; Hare, Trent M.; Titus, Timothy N.; Bourke, Mary C.; Colaprete, Anthony; Christensen, Philip R.

    2007-11-01

    A new Mars Global Digital Dune Database (MGD3) constructed using Thermal Emission Imaging System (THEMIS) infrared (IR) images provides a comprehensive and quantitative view of the geographic distribution of moderate- to large-size dune fields (area >1 km2) that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of Mars. MGD3 extends from 65°N to 65°S latitude and includes ~550 dune fields, covering ~70,000 km2, with an estimated total volume of ~3,600 km3. This area, when combined with polar dune estimates, suggests moderate- to large-size dune field coverage on Mars may total ~800,000 km2, ~6 times less than the total areal estimate of ~5,000,000 km2 for terrestrial dunes. Where availability and quality of THEMIS visible (VIS) or Mars Orbiter Camera narrow-angle (MOC NA) images allow, we classify dunes and include dune slipface measurements, which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. For dunes located within craters, the azimuth from crater centroid to dune field centroid (referred to as dune centroid azimuth) is calculated and can provide an accurate method for tracking dune migration within smooth-floored craters. These indicators of wind direction are compared to output from a general circulation model (GCM). Dune centroid azimuth values generally correlate to regional wind patterns. Slipface orientations are less well correlated, suggesting that local topographic effects may play a larger role in dune orientation than regional winds.

  8. Lateral migration of linear dunes in the Strzelecki Desert, Australia

    USGS Publications Warehouse

    Rubin, D.M.

    1990-01-01

    Preferential accumulation of sand on east-facing flanks indicates that the dunes migrated eastward several metres during the Holocene. Moreover, the west-facing flanks of some dunes have experienced a minimum of tens of metres of erosion. This asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the Pleistocene. Dunes in the Strzelecki Desert and in the adjacent Simpson Desert display a variety of grossly different internal structures. -from Author

  9. Mars global digital dune database and initial science results

    USGS Publications Warehouse

    Hayward, R.K.; Mullins, K.F.; Fenton, L.K.; Hare, T.M.; Titus, T.N.; Bourke, M.C.; Colaprete, A.; Christensen, P.R.

    2007-01-01

    A new Mars Global Digital Dune Database (MGD3) constructed using Thermal Emission Imaging System (THEMIS) infrared (IR) images provides a comprehensive and quantitative view of the geographic distribution of moderate- to large-size dune fields (area >1 kM2) that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of Mars. MGD3 extends from 65??N to 65??S latitude and includes ???550 dune fields, covering ???70,000 km2, with an estimated total volume of ???3,600 km3. This area, when combined with polar dune estimates, suggests moderate- to large-size dune field coverage on Mars may total ???800,000 km2, ???6 times less than the total areal estimate of ???5,000,000 km2 for terrestrial dunes. Where availability and quality of THEMIS visible (VIS) or Mars Orbiter Camera. narrow-angle (MOC NA) images allow, we classify dunes and include dune slipface measurements, which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. For dunes located within craters, the azimuth from crater centroid to dune field centroid (referred to as dune centroid azimuth) is calculated and can provide an accurate method for tracking dune migration within smooth-floored craters. These indicators of wind direction are compared to output from a general circulation model (GCM). Dune centroid azimuth values generally correlate to regional wind patterns. Slipface orientations are less well correlated, suggesting that local topographic effects may play a larger role in dune orientation than regional winds. Copyright 2007 by the American Geophysical Union.

  10. Self-organization mechanisms for the formation of nearshore crescentic and transverse sand bars

    NASA Astrophysics Data System (ADS)

    Caballeria, M.; Coco, G.; Falqués, A.; Huntley, D. A.

    2002-08-01

    The formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow-water equations and on a simplified sediment transport parameterization. By assuming normally approaching waves and a saturated surf zone, rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed. Two types of bedforms appear: one is a crescentic bar pattern centred around the breakpoint and the other, herein modelled for the first time, is a transverse bar pattern. The feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations. Basically, the waves stir up the sediment and keep it in suspension with a certain cross-shore distribution of depth-averaged concentration. Then, a current flowing with (against) the gradient of sediment concentration produces erosion (deposition). It is shown that inside the surf zone, these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms. Numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro-morphodynamic input conditions to which of the patterns develops. It is suggested that crescentic bar growth would be favoured by high-energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment. In intermediate conditions mixed patterns may occur.

  11. High angle-of-attack aerodynamic characteristics of crescent and elliptic wings

    NASA Technical Reports Server (NTRS)

    Vandam, C. P.

    1989-01-01

    Static longitudinal and lateral-directional forces and moments were measured for elliptic- and crescent-wing models at high angles-of-attack in the NASA Langley 14 by 22-Ft Subsonic Tunnel. The forces and moments were obtained for an angle-of-attack range including stall and post-stall conditions at a Reynolds number based on the average wing chord of about 1.8 million. Flow-visualization photographs using a mixture of oil and titanium-dioxide were also taken for several incidence angles. The force and moment data and the flow-visualization results indicated that the crescent wing model with its highly swept tips produced much better high angle-of-attack aerodynamic characteristics than the elliptic model. Leading-edge separation-induced vortex flow over the highly swept tips of the crescent wing is thought to produce this improved behavior at high angles-of-attack. The unique planform design could result in safer and more efficient low-speed airplanes.

  12. KoG132009 G. Glaeser, K.H. Schott: Geometric Considerations About Seemingly Wrong Tilt of Crescent Moon Original scientific paper

    E-print Network

    Nawratil, Georg

    of Crescent Moon Original scientific paper Accepted 20. 12. 2009 Georg Glaeser, Karlheinz Schott Geometric Considerations About Seemingly Wrong Tilt of Crescent Moon Geometric Considerations About Seemingly Wrong Tilt of Crescent Moon ABSTRACT The following phenomenon is well-known and again and again appears as an unanswered

  13. Sand availability control on dune shape and orientation

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  14. Modeling emergent large-scale structures of barchan dune fields

    E-print Network

    Claudin, Philippe

    Modeling emergent large-scale structures of barchan dune fields S. Worman , A.B. Murray , R, barchan dunes typically exist as members of larger fields that display strik- ing, enigmatic structures as a collective result of many dunes interacting with each other, we built a numerical model that treats barchans

  15. ``Raked'' linear dunes in the Kumtagh Desert, China

    NASA Astrophysics Data System (ADS)

    Dong, Zhibao; Wei, Zhenhai; Qian, Guangqiang; Zhang, Zhengcai; Luo, Wanyin; Hu, Guangyin

    2010-11-01

    Linear dunes are extensive in sand seas and dune fields around the world, but they take a range of forms due to the complex factors that control their development. "Raked" linear dunes, composed of primary ridges and subsidiary ridges that lie almost perpendicular to the primary ridges, were recently identified in the northern part of China's Kumtagh Desert. The primary ridges are typical linear dunes, but the subsidiary ridges display vestiges of barchan dunes. The subsidiary ridges are sufficiently short that they do not greatly affect the general appearance of the linear dunes. However, the raked linear dunes in the Kumtagh Desert have several unique characteristics that distinguish them from typical linear dunes. These dunes develop in an environment that is deficient in available sediment, and under a wind regime typical of linear dunes: an environment with a high wind energy and a directional variability index (RDP/DP) around 0.5. The raked linear dunes appear to have evolved from barchans following a modified form of Tsoar's (1984) model. Barchans formed under a northern wind regime were modified by an eastern wind regime oriented at an oblique angle to the barchans. The strengths of the two wind regimes are similar. Under these conditions, the barchans became reoriented, with the limbs farthest from the eastern winds extending to form subsidiary ridges and the limbs closest to the eastern winds forming the primary ridges, which appear to form mainly from dune collisions.

  16. Barchan dunes morphology dynamics under different environmental conditions

    NASA Astrophysics Data System (ADS)

    Dluzewski, M.

    2012-04-01

    The aim of this study was to emphasize significance of diversified dynamics of barchans dune morphology. We analyzed and compared barchans found in two dune fields: Kharga (S Egypt) and Tarfaya-Laâyoune (S-Morocco). These dune fields are characterized by significantly different factors responsible for dunes development e.g. textural and mineralogical composition of dune sand, dune sand moisture, air humidity, inter dune vegetation cover. For each investigated dune filed and study period (2008, 2010, 2012 for Kharga and 2007, 2011, 2012 for Tarfaya-Laâyoune dune fields) detailed shape measurement of 20 simple isolated barchans of different dune sizes was made. The ± 10-2 m horizontal and ± 1,5 10-2m vertical accuracy was obtained (1 measuring point per 1m2 on average).In order to compare barchan dunes morphology and to determine depositional and erosional patterns, the 3D models were created. For better understanding of this processes, sand bulk density of barchan surface was measured (1 measuring point per 2m2 on average). The velocity of dunes in relation to dune shape was also analyzed. The results show that the relationship between typically correlated parameters change during movement of the barchans. Most values change by a few percent per year (slip face height, dune base area and dune volume) or by a dozen or so percent per year (windward side length, horns length and width). We obtain good linear relationship (with 0,05 significant level) between slip face height and the dune base area (0,77 < R2 < 0,83), dune volume (0,66 < R2 < 0,72), windward side length (0,58 < R2 < 0,87), horns length (0,71 < R2 < 0,90) or horns width (0,79 < R2 < 0,93). The linear relationship between displacement rate and the morphological parameters is not strong (0,54< R2 < 0,81) for Kharga dune field and (0,41< R2 < 0,66) for Tarfaya-Laâyoune dune field. We noted also good linear relationship between displacement rate and the angle of span of the horns (R2=0,73 on Tarfaya-Laâyoune dune fields). Comparison of shape change of the same barchan made it possible to determine the depositional and erosional zones. The annual changes of surface altitude do not exceed a few percent of the total sand thickness in analyzed zones (more for small dunes). However, we noted important shape differences between barchans of the same slip face height in two investigated dune fields (up to 20% of sand thickness in the same point). We also found a good correlation between barchans shape and bulk density of dune sand. The highest bulk density of the dune sand is noted at the dune horns (up to 1767kg m-3 for Kharga dune field and up to 1644 kg m-3 for Tarfaya-Laâyoune dune field). On the windward (stoss) sides the bulk density of the dune sand depends on barchans shape (slope inclination). The lee sides have the value around 1400 kg m-3. Generally our result show relatively small differences in dune morphology dynamics within the same dune field but much greater between the two analyzed areas.

  17. Exploring inner structure of Titan's dunes from Cassini Radar observations

    NASA Astrophysics Data System (ADS)

    Sharma, P.; Heggy, E.; Farr, T. G.

    2013-12-01

    Linear dunes discovered in the equatorial regions of Titan by the Cassini-Huygens mission are morphologically very similar to many terrestrial linear dune fields. These features have been compared with terrestrial longitudinal dune fields like the ones in Namib desert in western Africa. This comparison is based on the overall parallel orientation of Titan's dunes to the predominant wind direction on Titan, their superposition on other geomorphological features and the way they wrap around topographic obstacles. Studying the internal layering of dunes has strong implications in understanding the hypothesis for their origin and evolution. In Titan's case, although the morphology of the dunes has been studied from Cassini Synthetic Aperture Radar (SAR) images, it has not been possible to investigate their internal structure in detail as of yet. Since no radar sounding data is available for studying Titan's subsurface yet, we have developed another technique to examine the inner layering of the dunes. In this study, we utilize multiple complementary radar datasets, including radar imaging data for Titan's and Earth's dunes and Ground Penetrating Radar (GPR)/radar sounding data for terrestrial dunes. Based on dielectric mixing models, we suggest that the Cassini Ku-band microwaves should be able to penetrate up to ~ 3 m through Titan's dunes, indicating that the returned radar backscatter signal would include contributions from both surface and shallow subsurface echoes. This implies that the shallow subsurface properties can be retrieved from the observed radar backscatter (?0). In our analysis, the variation of the radar backscatter as a function of dune height is used to provide an insight into the layering in Titan's dunes. We compare the variation of radar backscatter with elevation over individual dunes on Titan and analogous terrestrial dunes in three sites (Great Sand Sea, Siwa dunes and Qattaniya dunes) in the Egyptian Sahara. We observe a strong, positive correlation between the backscatter and elevation along dune profile for the larger, older dunes in the Great Sand Sea in south-western Egypt and Siwa dune field in north-western Egypt, as opposed to the weak negative correlation exhibited by the smaller, younger Qattaniya dunes in north-eastern Egypt. This result is reinforced by our GPR survey on a large dune in the Siwa dune field and a smaller dune in the Qattaniya dune field. Our GPR data suggest the internal structure of larger dunes to consist of greater number of layers/cross-strata than smaller ones in the first 8 meters of the subsurface, which corresponds to the radar penetration depth at (0.8-1.2) GHz. Dunes on Titan exhibit backscatter-height dependency similar to the smaller Qattaniya dunes. In particular, the Shangri-La and Belet dunes on Titan exhibit a significantly stronger, negative correlation for the backscatter-height dependency compared to the Fensal and Aztlan dunes, suggesting a difference in the internal layering, relative ages and formation history of these dunes on Titan.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  19. Probabilistic assessment of beach and dune changes

    USGS Publications Warehouse

    Sallenger, A.H., Jr.; Stockdon, H.; Haines, J.; Krabill, W.; Swift, R.; Brock, J.

    2004-01-01

    The recent availability of spatially-dense airborne lidar data makes assessment of the vulnerability of beaches and dunes to storm impacts practical over long reaches of coast. As an initial test, elevations of the tops (D high) and bases (Dlow) of foredune ridges along a 55-km reach on the northern Outer Banks, NC were found to have considerable spatial variability suggesting that different parts of the barrier island would respond differently to storms. Comparing statistics of storm wave runup to D high and Dlow, we found that net erosion due to overwash and dune retreat should be greatest at the northern and southern ends of the study area and least in the central section. This predicted spatial pattern of storm-induced erosion is similar to the spatial pattern of long-term erosion of the shoreline which may be controlled by additional processes (such as gradients in longshore transport) as well as the cross-shore processes considered here. However, consider feedback where at erosional hot spots there is a deficit of sand (caused by gradients in longshore transport) which lead to lower dunes and enhanced erosional cross-shore processes, such as overwash. Hence, the erosional hot spots would be exacerbated, further increasing the vulnerability of the beach and dunes to net erosion.

  20. Beaches, Dunes, and Barrier Islands. Habitat Pac.

    ERIC Educational Resources Information Center

    Fish and Wildlife Service (Dept. of Interior), Washington, DC.

    The materials in this educational packet are designed for use with students in grades 4 through 7. They consist of a leader overview, teaching guides and student data sheets for three activities, and a poster. The leader overview describes the nature of beaches, dunes, and barrier islands, tracing their development, settlement, and management and…

  1. Solitary wave behavior in sand dunes observed from space

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2011-11-01

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

  2. How Altitude and Latitude Control Dune Morphometry on Titan

    NASA Technical Reports Server (NTRS)

    Le Gall, A.; Hayes, A.; Ewing, R.; Janssen, M. A.; Radebaugh, J.; Savage, C.; Encrenaz, P.

    2011-01-01

    Dune fields are one of the dominant landforms and represent the largest known organic reservoir on Titan. SAR-derived topography show that Titan's dune terrains tend to occupy the lowest altitude areas in equatorial regions occurring at mean elevations between approx.-400 and 0 m. In elevated dune terrains, there is a definite trend towards a smaller dune to interdune ratio, interpreted as due to limited sediment availability. A similar linear correlation is observed with latitude, suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north. These findings place important constraints on Titan's geology and climate.

  3. Changes of Bulgarian Coastal Dune Landscape under Anthropogenic Impact

    NASA Astrophysics Data System (ADS)

    Palazov, A.; Young, R.; Stancheva, M.; Stanchev, H.

    2012-04-01

    At one time large sand dune formations were widely distributed along the Bulgarian coast. However, due to increased urbanization in the coastal zone, the areas of total dune landscape has been constantly reduced. Dunes presently comprise only 10% of the entire 412 km long coastline of Bulgaria: they embrace a total length of 38.57 km and a total area of 8.78 km2 Important tasks in dune protection are identification of landscape changes for a certain period of time and accurate delineation of sand dune areas. The present research traces sand dune changes along the Bulgarian Black Sea coast over a 27 year period (1983-2010). This period includes also the time of expanded tourist boom and overbuilding of the coastal zone, and respectively presents the largest dune changes and reductions. Based on the landscape change analyst in GIS environment the study also aims to explore the importance of different natural and human factors in driving the observed dune alterations and destruction. To detect and assess dune changes during the last 3 decades, we used data for sand dunes derived from several sources at different time periods in order to compare changes in shoreline positions, dune contours and areas: i) Topographic maps in 1:5,000 scale from 1983; ii) Modern Very High Resolution orthophotographs from 2006 and 2010; iii) QuickBird Very High Resolution satellite images from 2009; iv) Statistical information for population and tourist infrastructure is also used to consider the influence of human pressure and hotel developments on the dune dynamics. In addition, for more detailed description and visualization of main dune types, digital photos have been taken at many parts of the Bulgarian coast. The study was performed in GIS environment. Based on the results obtained the dunes along the Bulgarian coast were divided into three main groups with relation to the general factors responsible for their alterations: i) Dunes that have decreased in result of shoreline retreat and erosion of the beach itself. Typically dunes are located behind sand beaches and they are part of the beach-dune systems. Such type of dune reduction could be driven by combination of many factors, both natural ones (such as severe storms, erosion, heavy rains or flooding) and human impacts (large number of installed coast-protection structures along the coast, which interrupt the sediment transport, create new sedimentary deficit and generate erosion). During the recent years most of the Bulgarian beaches have progressively eroded and their areas have significantly been decreased. ii) Dunes that have been reduced/damaged and lost due to expanded tourist and housing infrastructures/developments and due to afforestaion activities. The principal sources of human impacts on sand dunes in Bulgaria are rapid coastal urbanization over the recent years (i.e., hotel and residential constructions, roads, parking structures, and other related infrastructure), unregulated camping and "temporary" constructions on the dunes, a lax regulatory environment that tolerates the re-zoning of protected sand dunes to "agricultural" areas. At most recreational sites there were wide coastal dunes, which however have been destroyed during tourist constructions. Such are dunes at the most famous Bulgarian sea resorts of Golden Sands and Sunny Beach in the areas of Varna and Nessebar. As a consequence, major areas along the Bulgarian coast were completely urbanized by hotels and other infrastructures and large sand dune systems were damaged. iii) Dunes located at still undeveloped coastal sections: yet they are naturally preserved and unthreatened by human pressure boom. These are just a few dune sites: at the northernmost portion of the Bulgarian coast (in the area of Durankulak), at the central part in the region of the largest Bulgarian river, Kamchia River, and along the southernmost coastline (in the area of Veleka River). Although sand dunes in Bulgaria are protected areas and national reserves they have been exposed to large anthropogenic pressure in particu

  4. Seasonal erosion and restoration of Mars' northern polar dunes.

    PubMed

    Hansen, C J; Bourke, M; Bridges, N T; Byrne, S; Colon, C; Diniega, S; Dundas, C; Herkenhoff, K; McEwen, A; Mellon, M; Portyankina, G; Thomas, N

    2011-02-01

    Despite radically different environmental conditions, terrestrial and martian dunes bear a strong resemblance, indicating that the basic processes of saltation and grainfall (sand avalanching down the dune slipface) operate on both worlds. Here, we show that martian dunes are subject to an additional modification process not found on Earth: springtime sublimation of Mars' CO(2) seasonal polar caps. Numerous dunes in Mars' north polar region have experienced morphological changes within a Mars year, detected in images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter. Dunes show new alcoves, gullies, and dune apron extension. This is followed by remobilization of the fresh deposits by the wind, forming ripples and erasing gullies. The widespread nature of these rapid changes, and the pristine appearance of most dunes in the area, implicates active sand transport in the vast polar erg in Mars' current climate. PMID:21292976

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

    USGS Publications Warehouse

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

    1989-01-01

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

  6. Dune Morphometry in the Age of Digital Elevation Models

    NASA Astrophysics Data System (ADS)

    Lancaster, N.

    2014-12-01

    Dune patterns can be characterized in many different ways. Relationships between dune height, width and spacing, and the spatial variation in these parameters have been widely employed to provide quantitative information that can be used to describe dune patterns and make comparisons between dunes in widely separated areas, as well as to identify different generations of dunes. Digital elevation models (e.g. ASTER GDEM) provide a rich resource of data for analyses of dune patterns at landscape scales in several ways, including: (1) more extensive analyses using traditional measures, such as relationships between dune height and spacing, and the spatial variation in these parameters; and (2) estimation of sediment thickness on a regional scale. Analyses of data for Arabian and Namibian sand seas and dune fields show that dune height and spacing relationships are much more variable than previously reported and call into question existing models. Regional patterns of sediment thickness reveal areas of erosion, bypass, and accumulation that can be related to transport pathways and wind regimes. The widespread occurrence of complex dune patterns as well as the magnitude of the newly available data sets however requires more sophisticated analyses than simple extraction of dune morphometric parameters using GIS approaches. Geostatistical analyses using spatial autocorrelation, Fourier, and Wavelet methods have been employed in analyses of sub-aqueous bedforms and show promise for dune systems. Automated or semi-automated identification of dune length, width, spacing, and trends using advanced image analysis techniques such as linear segment detection is a potentially transformative approach. The strengths and weaknesses of these methods to provide pertinent geomorphic information are currently being evaluated, but they have the potential to provide new insights into the nature of dune patterns.

  7. The November 15, 2006 Kuril Islands-Generated Tsunami in Crescent City, California

    NASA Astrophysics Data System (ADS)

    Dengler, L.; Uslu, B.; Barberopoulou, A.; Yim, S. C.; Kelly, A.

    2009-02-01

    On November 15, 2006, Crescent City in Del Norte County, California was hit by a tsunami generated by a M w 8.3 earthquake in the central Kuril Islands. Strong currents that persisted over an eight-hour period damaged floating docks and several boats and caused an estimated 9.2 million in losses. Initial tsunami alert bulletins issued by the West Coast Alaska Tsunami Warning Center (WCATWC) in Palmer, Alaska were cancelled about three and a half hours after the earthquake, nearly five hours before the first surges reached Crescent City. The largest amplitude wave, 1.76-meter peak to trough, was the sixth cycle and arrived over two hours after the first wave. Strong currents estimated at over 10 knots, damaged or destroyed three docks and caused cracks in most of the remaining docks. As a result of the November 15 event, WCATWC changed the definition of Advisory from a region-wide alert bulletin meaning that a potential tsunami is 6 hours or further away to a localized alert that tsunami water heights may approach warning- level thresholds in specific, vulnerable locations like Crescent City. On January 13, 2007 a similar Kuril event occurred and hourly conferences between the warning center and regional weather forecasts were held with a considerable improvement in the flow of information to local coastal jurisdictions. The event highlighted the vulnerability of harbors from a relatively modest tsunami and underscored the need to improve public education regarding the duration of the tsunami hazards, improve dialog between tsunami warning centers and local jurisdictions, and better understand the currents produced by tsunamis in harbors.

  8. Green Tea Polyphenol (?)-Epigallocatechin-3-Gallate Restores Nrf2 Activity and Ameliorates Crescentic Glomerulonephritis

    PubMed Central

    Zhou, Jason K.; Peng, Ai; Vaziri, Nosratola D.; Mohan, Chandra; Xu, Yan; Zhou, Xin J.

    2015-01-01

    Crescentic glomerulonephritis (GN) is the most severe form of GN and is associated with significant morbidity and mortality despite aggressive immunotherapy with steroids, cytotoxic drugs, and plasmapheresis. We examined the therapeutic efficacy of the green tea polyphenol (?)-epigallocatechin-3-gallate (EGCG, 50 mg/kg BW/day x3weeks), a potent anti-inflammatory and anti-oxidant agent, on experimental crescentic GN induced in 129/svJ mice by administration of rabbit anti-mouse glomerular basement membrane sera. Routine histology and key molecules involved in inflammatory and redox signaling were studied. EGCG treatment significantly reduced mortality, decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. The improvements in renal function and histology were accompanied by the restoration of Nrf2 signaling (which was impaired in vehicle-treated mice) as shown by increased nuclear translocation of Nrf2 and cytoplasmic glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and glutathione peroxidase. EGCG-treated mice also showed reduction in p-Akt, p-JNK, p-ERK1/2 and p-P38 as well as restoration of PPAR? and SIRT1 levels. Lower dose of EGCG (25 mg/kg BW/day x2 weeks) treatment also significantly decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. Thus, our data illustrate the efficacy of EGCG in reversing the progression of crescentic GN in mice by targeting multiple signaling and inflammatory pathways as well as countering oxidative stress. PMID:25785827

  9. Green tea polyphenol (-)-epigallocatechin-3-gallate restores Nrf2 activity and ameliorates crescentic glomerulonephritis.

    PubMed

    Ye, Ting; Zhen, Junhui; Du, Yong; Zhou, Jason K; Peng, Ai; Vaziri, Nosratola D; Mohan, Chandra; Xu, Yan; Zhou, Xin J

    2015-01-01

    Crescentic glomerulonephritis (GN) is the most severe form of GN and is associated with significant morbidity and mortality despite aggressive immunotherapy with steroids, cytotoxic drugs, and plasmapheresis. We examined the therapeutic efficacy of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG, 50 mg/kg BW/day x3 weeks), a potent anti-inflammatory and anti-oxidant agent, on experimental crescentic GN induced in 129/svJ mice by administration of rabbit anti-mouse glomerular basement membrane sera. Routine histology and key molecules involved in inflammatory and redox signaling were studied. EGCG treatment significantly reduced mortality, decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. The improvements in renal function and histology were accompanied by the restoration of Nrf2 signaling (which was impaired in vehicle-treated mice) as shown by increased nuclear translocation of Nrf2 and cytoplasmic glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and glutathione peroxidase. EGCG-treated mice also showed reduction in p-Akt, p-JNK, p-ERK1/2 and p-P38 as well as restoration of PPAR? and SIRT1 levels. Lower dose of EGCG (25 mg/kg BW/day x2 weeks) treatment also significantly decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. Thus, our data illustrate the efficacy of EGCG in reversing the progression of crescentic GN in mice by targeting multiple signaling and inflammatory pathways as well as countering oxidative stress. PMID:25785827

  10. Membranous glomerulonephritis and cellular crescents induced by levamisole-adulterated cocaine abuse: a case report

    PubMed Central

    Moll-Guillen, Jose-Luis; Espí-Reig, Jordi; Blanes-Julia, Marino; García-Martínez, Ana-María; Pujol-Marco, Conrad; Hernández-Jaras, Julio

    2015-01-01

    Levamisole is illicitly employed as a cocaine adulterant. The consumption of levamisole-adulterated cocaine can provoke anti-neutrophil cytoplasmic antibody (ANCA)-associated syndromes. Patients carrying an HLAB27 allele are known to be at higher risk of developing agranulocytosis when treated with levamisole. Likewise, patients with ANCA-associated vasculitis (AAV) and internal organ involvement have typically been exposed to offending agents for prolonged periods of time, often on the order of years. Here, we report an unusual case of a patient in which kidney biopsy showed membranous glomerulonephritis with cellular crescents associated with levamisole-contaminated cocaine use. PMID:26605317

  11. Crescent-Shaped Retinal Defects Associated With Membrane Peeling With a Diamond-Dusted Membrane Scraper.

    PubMed

    Leung, Ella H; Flynn, Harry W; Rosenfeld, Philip J

    2016-01-01

    Membrane peeling is a common procedure for treating diseases of the vitreoretinal interface, such as macular holes and epiretinal membranes; however, potential complications include inner retinal dimples and inner retinal optic neuropathy. The current case series describes five patients who developed large, crescentic inner retinal defects after membrane peeling with diamond-dusted membrane scrapers. The changes visualized by en face optical coherence tomography were outside the fovea and followed the expected contours of membrane scrapers being used intraoperatively. The visual acuities at the last follow-up were 20/40 or better in all five patients. [Ophthalmic Surg Imaging Lasers Retina. 2016;47:90-93.]. PMID:26731218

  12. Manipulation of yeast cells with DOE-modulated crescent-shaped and optical bottle laser beams

    NASA Astrophysics Data System (ADS)

    Rykov, Mikhail A.; Skidanov, Roman V.

    2013-09-01

    The work is a study of micromanipulation techniques using DOE-modulated laser beams. Two kinds of crescentshaped and optical bottle beam kinds are covered. The numerical model and experimental results on the trapping and manipulating of yeast cells with modulated laser beams are presented. They show that modulated beams are sometimes more efficient than common Gaussian beam: crescent beams are able to achieve better trap stiffness at the price of altered spatial distribution of that stiffness. Optical bottles are beneficial for their ability to hold the trapped object by its edges therefore decreasing amount of energy absorbed by the microbiological sample.

  13. Valles Marineris dune fields as compared with other martian populations: Diversity of dune compositions, morphologies, and thermophysical properties

    NASA Astrophysics Data System (ADS)

    Chojnacki, Matthew; Burr, Devon M.; Moersch, Jeffrey E.

    2014-02-01

    Planetary dune field properties and their bulk bedform morphologies relate to regional wind patterns, sediment supply, climate, and topography. On Mars, major occurrences of spatially contiguous low-albedo sand dunes are primarily found in three major topographic settings: impact craters, high-latitude basins, and linear troughs or valleys, the largest being the Valles Marineris (VM) rift system. As one of the primary present day martian sediment sinks, VM holds nearly a third of the non-polar dune area on Mars. Moreover, VM differs from other regions due to its unusual geologic, topographic, and atmospheric setting. Herein, we test the overarching hypothesis that VM dune fields are compositionally, morphologically, and thermophysically distinct from other low- and mid-latitude (50°N-50°S latitude) dune fields. Topographic measurements of dune fields and their underlying terrains indicate slopes, roughnesses, and reliefs to be notably greater for those in VM. Variable VM dune morphologies are shown with topographically-related duneforms (climbing, falling, and echo dunes) located among spur-and-gully wall, landslide, and chaotic terrains, contrasting most martian dunes found in more topographically benign locations (e.g., craters, basins). VM dune fields superposed on Late Amazonian landslides are constrained to have formed and/or migrated over >10s of kilometers in the last 50 My to 1 Gy. Diversity of detected dune sand compositions, including unaltered ultramafic minerals and glasses (e.g., high and low-calcium pyroxene, olivine, Fe-bearing glass), and alteration products (hydrated sulfates, weathered Fe-bearing glass), is more pronounced in VM. Observations show heterogeneous sand compositions exist at the regional-, basinal-, dune field-, and dune-scales. Although not substantially greater than elsewhere, unambiguous evidence for recent dune activity in VM is indicated from pairs of high-resolution images that include: dune deflation, dune migration, slip face modification (e.g., alcoves), and ripple modification or migration, at varying scales (10s-100s m2). We conclude that VM dune fields are qualitatively and quantitatively distinct from other low- and mid-latitude dune fields, most readily attributable to the rift's unusual setting. Moreover, results imply dune field properties and aeolian processes on Mars can be largely influenced by regional environment, which may have their own distinctive set of boundary conditions, rather than a globally homogenous collection of aeolian sediment and bedforms.

  14. Pooh Bear rock and Mermaid Dune

    NASA Technical Reports Server (NTRS)

    1997-01-01

    One of the two forward cameras aboard Sojourner imaged this area of Martian terrain on Sol 26. The large rock dubbed 'Pooh Bear' is at far left, and stands between four and five inches high. Mermaid Dune is the smooth area stretching horizontally across the top quarter of the image. The Alpha Proton X-Ray Spectrometer (APXS) instrument aboard Sojourner will be deployed on Mermaid Dune, and the rover will later use its cleated wheels to dig into it.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages and Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

  15. Extension d'une valuation # Michel Vaquie

    E-print Network

    Extension d'une valuation # Michel Vaquiâ??e Abstract We want to determine all the extensions of a valuation # of a field K to a monogenic extension L of K, i.e. L = K(x) is the field of rational functions valuation for a given valuation µ of K[x], and has shown how we can recover any extension to L of a discrete

  16. Annual monsoon rains recorded by Jurassic dunes.

    PubMed

    Loope, D B; Rowe, C M; Joeckel, R M

    2001-07-01

    Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events. PMID:11452305

  17. Impact of the winter 2013-2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments

    NASA Astrophysics Data System (ADS)

    Castelle, Bruno; Marieu, Vincent; Bujan, Stéphane; Splinter, Kristen D.; Robinet, Arhur; Sénéchal, Nadia; Ferreira, Sophie

    2015-06-01

    The winter of 2013/2014 was characterized by a striking pattern of temporal and spatial extreme storm wave clustering in Western Europe. The 110-km long Gironde coast, SW France, was exposed to the most energetic wave conditions over the last 18 years. The period was outstanding in terms of the available energy to move sediment and cause large-scale erosion with the 2-month average significant wave height (Hs) exceeding 3.6 m, just below the 0.95 quantile, and 4 distinct 10-year return period storms with Hs > 9 m. These storm waves caused unprecedented beach and dune erosion along the Gironde coast, including severely damaged sea defences at the coastal towns. At the end of the winter, dune erosion scarp height was highly variable alongshore and often exceeded 10 m. Megacusp embayments were observed along the Gironde coast with an average alongshore spacing of 1000 m in the south progressively decreasing to 500 m in the north, with an average cross-shore amplitude of 20 m. While beach megacusps were previously observed to systematically couple to the inner bar along the Gironde coast during low- to moderate-energy wave conditions, severe storm-driven megacusp embayments cutting the dune were found to be enforced and coupled to the outer crescentic bar. A detailed inspection of the 1500 m-long bimonthly topographic surveys of Truc Vert beach shows that in early January 2014 the outstanding shore-normal incident storm swell 'Hercules', with Hs and peak wave period Tp peaking at 9.6 m and 22 s, respectively, triggered the formation of a localized megacusp embayment with the erosion scarp height exceeding 6 m in its centre where the dune retreat reached 30 m. The subsequent storms progressively smoothed the megacusp by the end of the winter, mostly through severe erosion of the megacusp horns. Because of the very long period (16 s < Tp < 23 s) storm waves with persistent shore-normal incidence, the well-developed outer crescentic bar observed prior to the winter did not straighten. Instead, the outer-bar three-dimensionality developed further, particularly during 'Hercules'. Our observations indicate that both the antecedent outer sandbar morphology and storm wave characteristics, including period and angle of incidence, govern patterns of beach and dune erosion along open multiple-barred sandy coasts during severe storms.

  18. Pauci-immune necrotizing crescentic glomerulonephritis with crescentic and full moon extracapillary proliferation: clinico-pathologic correlation and follow-up study.

    PubMed

    Unlu, Mehtat; Kiremitci, Saba; Ensari, Arzu; Ozluk, Yasemin; Kilicaslan, Isin; Ozdemir, Binnaz Handan; Ates, Deniz; Ertoy Baydar, Dilek; Gonul, Ipek Isik; Memis, Leyla; Sarsik, Banu; Sen, Sait; Akkaya, Bahar; Orhan, Diclehan; Gonlusen, Gulfiliz; Ellidokuz, Hulya; Ada, Sibel; Cavdar, Caner; Akagun, Tulin; Kamali, Sevil; Aksu, Kenan; Yazisiz, Veli; Paydas, Saime; Soylu, Alper; Sarioglu, Sulen

    2013-02-15

    The prognostic value of the type and extent of extracapillary proliferation (ECP) in pauci-immune necrotizing crescentic glomerulonephitis (PIGN) was evaluated in this study. In 141 PIGN cases, all glomeruli with ECP were grouped according to type (cellular, fibrocellular and fibrous) and extent of the lesions in Bowman's space; (segmental, semicircumferential and circumferential, which might be termed full moon-FM). Cases with cellular and fibrous lesions involving ? 50% of glomeruli with ECP were classified as cellular and fibrous groups, respectively, while the remaining cases were classified as fibrocellular. Cases with segmental and circumferential (FM glomerulus) lesions involving ? 50% of glomeruli with ECP were classified as ECPI and ECPIII (FM) groups, respectively, while the rest were classified as ECPII. All the cases were classified according to Berden et al. Significant results were only nearly obtained for the FM group, including the need for dialysis. The Cox regression model revealed a 2.6-fold risk for FM cases regarding dialysis requirement. We propose that the percentage of FM glomeruli should be noted in the pathology report, and cases with more than 50% of FM glomeruli (FM group) should be identified in the group with increased risk of dialysis requirement. Our series also suggests that classification according to Berden et al. is of clinical relevance. PMID:23246377

  19. Trophic status and assessment of non-point nutrient enrichment of Lake Crescent Olympic National Park

    USGS Publications Warehouse

    Boyle, Terence P.; Beeson, David R.

    1991-01-01

    A limited effort study was conducted in Lake Crescent, Olympic National Park to determine the trophic status and assess whether non-point nutrients were leaching into the lake and affecting biological resources. The concentration of chlorophyll a, total nitrogen concentration, and Secchi disk transparency used as parameters of the Trophic Status Index revealed that Lake Crescent in Olympic National Park was in the oligotrophic range. Evaluation of the nitrogen to phosphorous ration revealed that nitrogen was the nutrient limiting to overall lake productivity. Single species and community bioassays indicated that other nutrients, possibly iron, had some secondary control over community composition of the algal community. Assessment of six near-shore sites for the presence and effects of non-point nutrients revealed that La Poel Point which formerly was the site of a resort had slightly higher algal bioassay and periphyton response than the other sites. No conditions that would require immediate action by resource management of Olympic National Park were identified. The general recommendations for a long term lake monitoring plan are discussed.

  20. Object-based Dune Analysis: Automated dune mapping and pattern characterization for Ganges Chasma and Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Vaz, David A.; Sarmento, Pedro T. K.; Barata, Maria T.; Fenton, Lori K.; Michaels, Timothy I.

    2015-12-01

    A method that enables the automated mapping and characterization of dune fields on Mars is described. Using CTX image mosaics, the introduced Object-based Dune Analysis (OBDA) technique produces an objective and reproducible mapping of dune morphologies over extensive areas. The data set thus obtained integrates a large variety of data, allowing a simple cross-analysis of dune patterns, spectral and morphometric information, and mesoscale wind models. Two dune fields, located in Gale crater and Ganges Chasma, were used to test and validate the methodology. The segmentation of dune-related morphologies is highly efficient, reaching overall accuracies of 95%. In addition, we show that the automated segmentation of slipface traces is also possible with expected accuracies of 85-90%. A qualitative and quantitative comparison of the final outputs with photointerpretations is performed, and the precision of the directional characterization of the dune patterns is evaluated. We demonstrate a good agreement between the OBDA outputs and the photointerpreted dune morphologies, with local trend deviations below 45° for 80-95% of the mapped areas. Because the developed algorithm is tuned for the recognition of linear features from the imagery, the slipfaces of small barchans can be preferentially overlooked owing to their small extent at the spatial resolution of the CTX mosaics. Dune types composed of longer linear morphologies are much better represented, including correct mapping of secondary structures. Having proved the effectiveness and accuracy of the mapping procedure, we discuss its future applications for the improvement of dune catalogs on Mars.

  1. The effects of psammophilous plants on sand dune dynamics

    E-print Network

    Golan Bel; Yosef Ashkenazy

    2013-08-30

    Psammophilous plants are special plants that flourish in sand moving environments. There are two main mechanisms by which the wind affects these plants: (i) sand drift exposes roots and covers branches--the exposed roots turn into new plants and the covered branches turn into new roots; both mechanisms result in an enhanced growth rate of the psammophilous plant cover of the dunes; (ii) strong winds, often associated with sand movement, tear branches and seed them in nearby locations, resulting in new plants and an enhanced growth rate of the psammophilous plant cover of the dunes. Despite their important role in dune dynamics, to our knowledge, psammophilous plants have never been incorporated into mathematical models of sand dunes. Here, we attempt to model the effects of these plants on sand dune dynamics. We construct a set of three ordinary differential equations for the fractions of surface cover of regular vegetation, biogenic soil crust and psammophilous plants. The latter reach their optimal growth under (i) specific sand drift or (ii) specific wind power. We show that psammophilous plants enrich the sand dune dynamics. Depending on the climatological conditions, it is possible to obtain one, two, or three steady dune states. The activity of the dunes can be associated with the surface cover--bare dunes are active, and dunes with significant cover of vegetation, biogenic soil crust, or psammophilous plants are fixed. Our model shows that under suitable precipitation rates and wind power, the dynamics of the different cover types is in accordance with the common view that dunes are initially stabilized by psammophilous plants that reduce sand activity, thus enhancing the growth of regular vegetation that eventually dominates the cover of the dunes and determines their activity.

  2. Submarine sand dunes and sedimentary environments in Oceanographer Canyon.

    USGS Publications Warehouse

    Valentine, P.C.; Cooper, R.A.; Uzmann, J.R.

    1984-01-01

    Reveals an extensive field of large sand dunes on the canyon floor. The dunes are medium to coarse sand, are oriented across the axis, and the largest of them are as high as 3m and have wavelengths up to 15m. Their asymmetry, grain size, and height suggest that they are formed by axial currents flowing up- and downcanyon and that the largest dunes require flows of at least 70 cm/sec.-from Authors

  3. From landform to process: Morphology and formation of lake-bed barchan dunes, Makgadikgadi, Botswana

    NASA Astrophysics Data System (ADS)

    Burrough, Sallie L.; Thomas, David S. G.; Bailey, Richard M.; Davies, Lauren

    2012-08-01

    A suite of crescentic landforms is visible from remotely sensed imagery within the Ntwetwe panPan in the Makgadikgadi basin, Botswana. We investigate the most distinct of these landforms using morphometric measurements, sedimentary data and Optically Stimulated Luminescence (OSL) signal analysis. Comparative analysis with previously published barchan morphological data sets suggest the Ntwetwe features fall within the spectrum of morphometric parameters found in a range of barchan dunefields from around the world. There is currently insufficient comparative morphometric data from sub-aqueous dunefields to be able to distinguish the particular formative environment of the dune. OSL signal analyses however, support the hypothesis of Grove (1969) [Grove, A.T., 1969. Landforms and climatic change in the Kalahari and Ngamiland. Geographical Journal, 135: 191-212] that the last deposition of the sediments within the Ntwetwe forms was most likely aeolian in origin. Luminescence signal analysis is employed to investigate potential transport and bleaching environments of the sediments forming the features, but results in this case do not shed further light on the formative conditions of these enigmatic landforms.

  4. Barchan dunes in two dimensions: experimental tests for minimal models.

    PubMed

    Groh, Christopher; Wierschem, Andreas; Aksel, Nuri; Rehberg, Ingo; Kruelle, Christof A

    2008-08-01

    A well-defined two-dimensional single barchan dune under the force of a shearing water flow is investigated experimentally. From an initially prepared triangular heap a rapid relaxation to a steady-state solution is observed with constant mass, shape, and velocity. This attractor exhibits all characteristic features of barchan dunes found in nature, namely a gently inclined windward side, crest, brink, and steep lee face. The relaxation time towards the steady state increases with mass. For small dunes we find significant deviations from a fixed height-length aspect ratio. As predicted by recent theoretical models, the migration velocity scales reciprocal to the length of the dune. PMID:18850828

  5. Digital mapping of the extent of global dune systems

    NASA Astrophysics Data System (ADS)

    Hesse, Paul; Lancaster, Nicholas; Telfer, Matt

    2015-04-01

    Inland dune systems occur on all continents and at all latitudes, yet until now there is no digital map of their location and extent. We have compiled a new digital map of the extent of inland dune systems worldwide from published and unpublished sources, supplemented by manual digitizing of additional sand seas and dune fields. The digital database is compiled in ArcGIS, allowing mapping at scales from global to regional. The database contains spatial information on approximately 200 dune fields and sand seas ranging in size from less than 2 square km to as much as 630,000 sq km, covering a total global area of 29.4 million sq km. It includes both currently active unvegetated sand seas and dune fields, as well as partially vegetated and vegetated areas of dunes and sand sheets. Where available, the database contains information on dune type and status (active or stabilized). Manual digitizing of dune and sand sheet areas, as well as correction of existing digital coverages was accomplished mainly using ESRI imagery resources, with constant reference to ancillary information from publications and previous mapping. Compilation of the database required extensive research on the geographic names for different dune areas, as well as dunefield status and extent. The database and maps derived from it will be available online at http://inquadunesatlas.dri.edu/. We envisage it will be a dynamic and ongoing project and solicit corrections and additional information, including new and revised digital coverages, from the scientific community.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  7. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  9. Classification of satellite time series-derived land surface phenology focused on the northern Fertile Crescent

    NASA Astrophysics Data System (ADS)

    Bunker, Brian

    Land surface phenology describes events in a seasonal vegetation cycle and can be used in a variety of applications from predicting onset of future drought conditions, to revealing potential limits of historical dry farming, to guiding more accurate dating of archeological sites. Traditional methods of monitoring vegetation phenology use data collected in situ. However, vegetation health indices derived from satellite remote sensor data, such as the normalized difference vegetation index (NDVI), have been used as proxy for vegetation phenology due to their repeated acquisition and broad area coverage. Land surface phenology is accessible in the NDVI satellite record when images are processed to be intercomparable over time and temporally ordered to create a time series. This study utilized NDVI time series to classify areas of similar vegetation phenology in the northern Fertile Crescent, an area from the middle Mediterranean coast to southern/south-eastern Turkey to western Iran and northern Iraq. Phenological monitoring of the northern Fertile Crescent is critical due to the area's minimal water resources, susceptibility to drought, and understanding ancient historical reliance on precipitation for subsistence dry farming. Delineation of phenological classes provides areal and temporal synopsis of vegetation productivity time series. Phenological classes were developed from NDVI time series calculated from NOAA's Advanced Very High Resolution Radiometer (AVHRR) imagery with 8 × 8 km spatial resolution over twenty-five years, and by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) with 250 × 250 m spatial resolution over twelve years. Both AVHRR and MODIS time series were subjected to data reduction techniques in spatial and temporal dimensions. Optimized ISODATA clusters were developed for both of these data reduction techniques in order to compare the effects of spatial versus temporal aggregation. Within the northern Fertile Crescent study area, the spatial reduction technique showed increased cluster cohesion over the temporal reduction method. The latter technique showed an increase in temporal smoothing over the spatial reduction technique. Each technique has advantages depending on the desired spatial or temporal granularity. Additional work is required to determine optimal scale size for the spatial data reduction technique.

  10. 76 FR 68503 - Ungulate Management Plan/Environmental Impact Statement, Great Sand Dunes National Park and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-04

    ...Environmental Impact Statement, Great Sand Dunes National Park and Preserve, CO AGENCY...for the Ungulate Management Plan, Great Sand Dunes National Park and Preserve...for the Ungulate Management Plan, Great Sand Dunes National Park and Preserve,...

  11. Mars Global Digital Dune Database: MC2-MC29

    USGS Publications Warehouse

    Hayward, Rosalyn K.; Mullins, Kevin F.; Fenton, L.K.; Hare, T.M.; Titus, T.N.; Bourke, M.C.; Colaprete, Anthony; Christensen, P.R.

    2007-01-01

    Introduction The Mars Global Digital Dune Database presents data and describes the methodology used in creating the database. The database provides a comprehensive and quantitative view of the geographic distribution of moderate- to large-size dune fields from 65? N to 65? S latitude and encompasses ~ 550 dune fields. The database will be expanded to cover the entire planet in later versions. Although we have attempted to include all dune fields between 65? N and 65? S, some have likely been excluded for two reasons: 1) incomplete THEMIS IR (daytime) coverage may have caused us to exclude some moderate- to large-size dune fields or 2) resolution of THEMIS IR coverage (100m/pixel) certainly caused us to exclude smaller dune fields. The smallest dune fields in the database are ~ 1 km2 in area. While the moderate to large dune fields are likely to constitute the largest compilation of sediment on the planet, smaller stores of sediment of dunes are likely to be found elsewhere via higher resolution data. Thus, it should be noted that our database excludes all small dune fields and some moderate to large dune fields as well. Therefore the absence of mapped dune fields does not mean that such dune fields do not exist and is not intended to imply a lack of saltating sand in other areas. Where availability and quality of THEMIS visible (VIS) or Mars Orbiter Camera narrow angle (MOC NA) images allowed, we classifed dunes and included dune slipface measurements, which were derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. For dunes located within craters, the azimuth from crater centroid to dune field centroid was calculated. Output from a general circulation model (GCM) is also included. In addition to polygons locating dune fields, the database includes over 1800 selected Thermal Emission Imaging System (THEMIS) infrared (IR), THEMIS visible (VIS) and Mars Orbiter Camera Narrow Angle (MOC NA) images that were used to build the database. The database is presented in a variety of formats. It is presented as a series of ArcReader projects which can be opened using the free ArcReader software. The latest version of ArcReader can be downloaded at http://www.esri.com/software/arcgis/arcreader/download.html. The database is also presented in ArcMap projects. The ArcMap projects allow fuller use of the data, but require ESRI ArcMap? software. Multiple projects were required to accommodate the large number of images needed. A fuller description of the projects can be found in the Dunes_ReadMe file and the ReadMe_GIS file in the Documentation folder. For users who prefer to create their own projects, the data is available in ESRI shapefile and geodatabase formats, as well as the open Geographic Markup Language (GML) format. A printable map of the dunes and craters in the database is available as a Portable Document Format (PDF) document. The map is also included as a JPEG file. ReadMe files are available in PDF and ASCII (.txt) files. Tables are available in both Excel (.xls) and ASCII formats.

  12. Extraterrestrial dunes: An introduction to the special issue on planetary dune systems

    E-print Network

    Bourke, Mary C.

    and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, United Kingdom c Desert Research Center for Earth and Planetary Studies, MRC 315, National Air and Space Museum, Smithsonian Institution further investigation. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Aeolian sand dune systems

  13. GEOLOGY | Volume 43 | Number 11 | www.gsapubs.org 1027 Sediment flux from the morphodynamics of elongating linear dunes

    E-print Network

    Narteau, Clément

    from remote imagery rely essentially on the migration speed of barchan dunes, but not on the dynamics to the barchan dune crests in zones of unidirectional wind. INTRODUCTION Linear dunes are the most common dune

  14. 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.

  15. Titan dune heights retrieval by using Cassini Radar Altimeter

    NASA Astrophysics Data System (ADS)

    Mastrogiuseppe, M.; Poggiali, V.; Seu, R.; Martufi, R.; Notarnicola, C.

    2014-02-01

    The Cassini Radar is a Ku band multimode instrument capable of providing topographic and mapping information. During several of the 93 Titan fly-bys performed by Cassini, the radar collected a large amount of data observing many dune fields in multiple modes such as SAR, Altimeter, Scatterometer and Radiometer. Understanding dune characteristics, such as shape and height, will reveal important clues on Titan's climatic and geological history providing a better understanding of aeolian processes on Earth. Dunes are believed to be sculpted by the action of the wind, weak at the surface but still able to activate the process of sand-sized particle transport. This work aims to estimate dunes height by modeling the shape of the real Cassini Radar Altimeter echoes. Joint processing of SAR/Altimeter data has been adopted to localize the altimeter footprints overlapping dune fields excluding non-dune features. The height of the dunes was estimated by applying Maximum Likelihood Estimation along with a non-coherent electromagnetic (EM) echo model, thus comparing the real averaged waveform with the theoretical curves. Such analysis has been performed over the Fensal dune field observed during the T30 flyby (May 2007). As a result we found that the estimated dunes' peak to trough heights difference was in the order of 60-120 m. Estimation accuracy and robustness of the MLE for different complex scenarios was assessed via radar simulations and Monte-Carlo approach. We simulated dunes-interdunes different composition and roughness for a large set of values verifying that, in the range of possible Titan environment conditions, these two surface parameters have weak effects on our estimates of standard dune heights deviation. Results presented here are the first part of a study that will cover all Titan's sand seas.

  16. Riverine Eolian Dunes in Uruguay: OSL Ages and Paleoenvironmental Significance

    NASA Astrophysics Data System (ADS)

    Leigh, D. S.; Suarez, R.; Brook, G. A.

    2012-12-01

    Relict parabolic dunes occur along Rio Negro and Rio Tacuarembó in Uruguay under the current humid temperate climate. These dunes offer important terrestrial evidence of drier conditions in the past and may provide foresight about landscape consequences of future climate change. The ages of these dunes previously had not been measured by any absolute dating technique. Two dune fields were selected for optically stimulated luminescence (OSL) dating using the single aliquot regeneration method, including four samples along Rio Negro near Pueblo de la Arena and three samples along Rio Tacuarembó near Ansina. Results indicate that the dunes were active during the late Pleistocene, with five of the OSL ages in the 22 ka to 12 ka range. One OSL age at the Ansina dune field returned an age of 6 ka, indicating the possibility of limited dune reactivation during the Holocene. There is clear evidence of historical dune activation (e.g. buried fences) at both the Rio Negro and Rio Tacuarembó sites; one OSL sample from Rio Negro dunes confirms an historical age of 107 years BP. However, human land disturbance rather than climatic factors may explain the historical reactivation. Late Pleistocene dune activity in central Uruguay indicates much drier and windier paleoclimate (at least seasonally) than present, and correlates well with eolian activity in more arid parts of South America in western Argentina. Age and paleoenvironment of the riverine dunes in Uruguay are remarkably similar to those of the southeastern United States (USA), indicating similar patterns of paleoclimate in both hemispheres. Such similarities help to resolve the spatial patterns of global scale climate change.

  17. Deep crescentic features caused by subglacial boulder point pressure on jointed rock; an example from Virkisjökull, SE Iceland

    NASA Astrophysics Data System (ADS)

    Krabbendam, M.; Bradwell, T.; Everest, J.

    2012-04-01

    A variety of subglacially formed, erosional crescentic features (e.g. crescentic gouges, lunate fractures) have been widely reported on deglaciated bedrock surfaces. They are characterised by a conchoidal fracture that dips in the same direction as the palaeo-ice flow direction, and a steeper fracture that faces against the ice flow. They are generally interpreted as being formed by point pressure exerted by large boulders entrained in basal ice. They are significant in that they record palaeo-ice flow even if shallower glacial striae are obliterated by post-glacial weathering [1, 2, 3]. This contribution reports on deep scallop-shaped, crescentic depressions observed on abraded surfaces of roche moutonnées and whalebacks recently (<10yrs) exposed beneath the actively retreating Virkisjökull, an outlet glacier of the Oraefajökull ice cap in southeast Iceland. The substrate comprises hard rhyolitic rock (relatively rare in Iceland compared to more common basalt and hyaloclastite) with polygonal, columnar jointing. The crescentic depressions at Virkisjökull are cut into smoothed, abraded surfaces festooned with abundant glacial striae. Differences with previously reported crescentic features are: • The scallop-shaped depressions are considerably deeper (5-20 cm); • The steep fracture facing ice flow coincides in all cases with a pre-existing joint that cuts the entire whaleback. The steep joints developed thus before the conchoidal fracture, whilst in reported crescentic features they develop after the conchoidal fracture. We suggest the following formation mechanism. A boulder encased in basal ice exerts continuous pressure on its contact point as it moves across the ice-bedrock contact. This sets up a stress field in the bedrock that does not necessarily exceed the intact rock strength (other crescentic features are rare to absent at Virkisjökull). However, as the stress field migrates (with the transported boulder) and encounters a subvertical, pre-existing joint, stress concentrations build up that do exceed the intact rock strength, resulting in a new (conchoidal) fracture, 'spalling' off a thick, scallop-shaped fragment. The significance of the deep scallop-shaped crescentic depressions is that: • in common with other crescentic features they appear to be robust ice-flow indicators and indicate that former basal ice was rich in coarse, cobble/boulder-sized debris; • they are deeper and represent more significant erosion than previously reported crescentic features; during continuous subglacial erosion they thus (re)introduce a significant roughness on smoothed abraded surfaces, resulting in faster subglacial erosion; • assuming our proposed formation mechanism is correct, they could develop at lower stress (?thinner ice, [3]) than other crescentic features, as they utilise pre-existing weaknesses in the rock. The observations were made as part of the British Geological Survey's Virkisjökull Observatory Project. [1] Gilbert, GK, 1906. Bull. Geo. Soc. Am, v. 17, 303-313. [2] Harris, SE, 1943. J. Geology, v. 51, 244-258. [3] Wintges, T. 1985. J. Glaciology, v. 31, 340-349.

  18. Evidence for community structure and habitat partitioning in coastal dune stiletto flies at the Guadalupe-Nipomo dunes system, California

    PubMed Central

    Holston, Kevin C.

    2005-01-01

    This study provides empirical evidence for habitat selection by North American species of stiletto flies (Diptera: Therevidae), based on local distributions of adults and immatures, and the first hypothesis of community assemblages proposed for a stiletto fly community. Sites at three localities within the Guadalupe-Nipomo dune system were sampled for stiletto flies in 1997 and 2001 by sifting sand, malaise trapping, and hand netting. Nine species were collected from four ecological zones and three intermediate ecological zones: Acrosathe novella (Coquillett), Brachylinga baccata (Loew), Nebritus powelli (Webb and Irwin), Ozodiceromyia sp., Pherocera sp., Tabudamima melanophleba (Loew), Thereva comata Loew, Thereva elizabethae Holston and Irwin, and Thereva fucata Loew. Species associations of adults and larvae with habitats and ecological zones were consistent among sites, suggesting that local distributions of coastal dune stiletto fly species are influenced by differences in habitat selection. In habitats dominated by the arroyo willow,Salix lasiolepsis, stiletto fly larvae of three species were collected in local sympatry, demonstrating that S. lasiolepsis stands along stabilized dune ridges can provide an intermediate ecological zone linking active dune and riparian habitat in the Guadalupe-Nipomo dune system. Sites dominated by European beach grass, Ammophilia arenaria, blue gum, Eucalyptus globulus, and Monterey cypress, Cupressus macrocarpa, are considered unsuitable for stiletto flies, which emphasizes the importance of terrestrial habitats with native vegetation for stiletto fly species. The local distributions of stiletto fly species at the Guadalupe-Nipomo dune system allow the community to be divided into three assemblages; active dune, pioneer scrub, and scrub-riparian. These assemblages may be applicable to other coastal dune stiletto fly communities, and may have particular relevance to stiletto fly species collected in European coastal dunes. The results from this study provide a descriptive framework for studies testing habitat selection in coastal dune stiletto fly species and inform conservation of threatened dune insects. PMID:17119624

  19. Particle tracking and mean residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, Deguo; Narteau, Clement; Rozier, Olivier

    2013-04-01

    We analyze sediment particles motions in steady-state barchan dunes by tracking individual cells of a 3-D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan dune shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchan dunes. Then, for different flow strength and dune size, we find that the mean residence time of sediment particles in barchan dunes is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan dune morphodynamics. Finally, we initiate a discussion about sediment transport and memory in presence of bedforms using the advantages of the particle tracking technique.

  20. Narrowing the gap between real and simulated barchan dune dynamics

    NASA Astrophysics Data System (ADS)

    Hugenholtz, C.; Barchyn, T. E.

    2011-12-01

    There are a growing number of computer simulation models capable of reproducing many of the morphological characteristics and dynamics of real barchan sand dunes. While these models offer tremendous insight and opportunities to develop hypotheses, there is a relative paucity of empirical observations to use as a basis for validation. To address this issue we present empirical observations of barchan dune dynamics using high-resolution, multi-temporal satellite imagery from locations in Peru, Namibia, and Mauritania. We highlight the response of barchan dunes to collisions, wind direction variability, interactions with bedrock topography, and depletion of sediment supply. First, we document the process of dunes emerging from the slipfaces of barchan dunes. In the past, this process was only observed in numerical models or interpreted from single-date imagery. We also show that collisions can result in calving or shedding of dunes from the horns. Second, we present the first empirical evidence of barchans changing into dome and "wedge" dunes under the influence of bimodal winds. Third, we show that barchans break down when they encounter uphill topography. However, they can re-form in the lee of a bedrock obstacle if sediment supply is sufficient. Finally, we show that, in the absence of collisions, small barchans can disappear quickly when they lose upwind sediment supply. Altogether, our observations add to the empirical record of barchan dune dynamics and are useful for evaluating the behaviour of numerical models.

  1. 36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 36 Parks, Forests, and Public Property 1 2013-07-01 2013-07-01 false Sleeping Bear Dunes National... INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes National... applicable State law is allowed. (c) Bicycling. (1) The Sleeping Bear Heritage Trail, approximately 27...

  2. cologie et conservation d'une steppe mditerranenne

    E-print Network

    van Tiggelen, Bart

    Écologie et conservation d'une steppe méditerranéenne La plaine de Crau Laurent Tatin, Axel Wolff des coussouls de Crau. Les paysages des steppes marquent les esprits, à l'évocation de celles du plus singulières au monde. En France, entre la Camargue et les Alpilles, une steppe d'une rare richesse

  3. Mechanism of acoustic emissions from booming sand dunes

    E-print Network

    Zhen-Ting Wang

    2013-05-10

    The classical elastic mechanics shows that the fundamental frequency of a sand grain chain is similar to the typical frequency of acoustic emission generated by the booming dunes. The "song of dunes" is therefore considered to originate from the resonance of grain chains occurring within a solid layer only several centimeters thick.

  4. 36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Sleeping Bear Dunes National Lakeshore. 7.80 Section 7.80 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes...

  5. 36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 1 2011-07-01 2011-07-01 false Sleeping Bear Dunes National Lakeshore. 7.80 Section 7.80 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes...

  6. 36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 36 Parks, Forests, and Public Property 1 2012-07-01 2012-07-01 false Sleeping Bear Dunes National Lakeshore. 7.80 Section 7.80 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes...

  7. 36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 36 Parks, Forests, and Public Property 1 2014-07-01 2014-07-01 false Sleeping Bear Dunes National... INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes National... applicable State law is allowed. (c) Bicycling. (1) The Sleeping Bear Heritage Trail, approximately 27...

  8. Coastal Dune Forest Development and the Regeneration of Millipede Communities

    E-print Network

    Pretoria, University of

    Coastal Dune Forest Development and the Regeneration of Millipede Communities Bereket H. Redi,1, the similarity of millipede assemblages on the two chrono- sequences to those on three sets of reference sites farther away. Key words: coastal dune forests, millipedes, regeneration, rehabilitation, succession

  9. Biogenic crust dynamics on sand dunes Shai Kinast,1

    E-print Network

    Ashkenazy, Yossi "Yosef"

    addressed the question of sand-dune stability in relation to climate change and anthropogenic disturbances erosion. Since most sandy soils are located in dry- lands where the vegetation is patchy and generally and agricultural fields [11, 12]. Sand dunes are also stabilized by biogenic soil crusts. These crusts comprise

  10. Methane storms as a driver of Titan's dune orientation

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clément; Lebonnois, Sébastien; Rodriguez, Sébastien; Courrech Du Pont, Sylvain; Lucas, Antoine

    2015-05-01

    The equatorial regions of Saturn's moon Titan are covered by linear dunes that propagate eastwards. Global climate models (GCMs), however, predict westward mean surface winds at low latitudes on Titan, similar to the trade winds on Earth. This apparent contradiction has been attributed to Saturn's gravitational tides, large-scale topography and wind statistics, but none of these hypotheses fully explains the global eastward propagation of dunes in Titan's equatorial band. However, above altitudes of about 5 km, Titan's atmosphere is in eastward super-rotation, suggesting that this momentum may be delivered to the surface. Here we assess the influence of equatorial tropical methane storms--which develop at high altitudes during the equinox--on Titan's dune orientation, using mesoscale simulations of convective methane clouds with a GCM wind profile that includes super-rotation. We find that these storms produce fast eastward gust fronts above the surface that exceed the normal westward surface winds. These episodic gusts generated by tropical storms are expected to dominate aeolian transport, leading to eastward propagation of dunes. We therefore suggest a coupling between super-rotation, tropical methane storms and dune formation on Titan. This framework, applied to GCM predictions and analogies to some terrestrial dune fields, explains the linear shape, eastward propagation and poleward divergence of Titan's dunes, and implies an equatorial origin of dune sand.

  11. 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

  12. 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

  13. 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.

  14. The effects of psammophilous plants on sand dune dynamics

    E-print Network

    Bel, Golan

    2013-01-01

    Psammophilous plants are special plants that flourish in sand moving environments. There are two main mechanisms by which the wind affects these plants: (i) sand drift exposes roots and covers branches--the exposed roots turn into new plants and the covered branches turn into new roots; both mechanisms result in an enhanced growth rate of the psammophilous plant cover of the dunes; (ii) strong winds, often associated with sand movement, tear branches and seed them in nearby locations, resulting in new plants and an enhanced growth rate of the psammophilous plant cover of the dunes. Despite their important role in dune dynamics, to our knowledge, psammophilous plants have never been incorporated into mathematical models of sand dunes. Here, we attempt to model the effects of these plants on sand dune dynamics. We construct a set of three ordinary differential equations for the fractions of surface cover of regular vegetation, biogenic soil crust and psammophilous plants. The latter reach their optimal growth u...

  15. Where to dig for gold? - Density segregation inside migrating dunes

    NASA Astrophysics Data System (ADS)

    Groh, Christopher; Rehberg, Ingo; Kruelle, Christof A.

    2013-06-01

    If a fluid streams over an extended area of sand, the grains will self-organize by forming complex structures like ripples or dunes. Below the surface, the inner structure of a dune is determined by the individual fate of the particles. In general, agitated granular matter is known to show de-mixing whenever particles differ in size or density, and indeed size segregation is a well-known feature for dunes, called reverse grading. Here we report results of a recent experimental investigation with two particle species differing not in size but in density. Our experimental setup consists of a stadium-shaped flow channel which is filled with water. Measurements are made with a CCD-camera, placed in front of the straight part, recording side views of the dunes migrating downstream. From an initially prepared triangular heap a rapid relaxation to a steady-state solution is observed with constant mass, shape, and velocity. This attractor exhibits all characteristic features of barchan dunes found in nature, namely a gently inclined windward side, crest, brink, and steep lee face. In addition, if the dune consists of a bi-dense mixture of particles, the heavier particles accumulate at the top of migrating dunes whereas light particles are buried at its bottom. This insight into the sedimentology of dunes composed of different types of sand has, loosely speaking, the implication, that in a dune mixed of gold and sand, gold nuggets are likely to be found at the top of the dune, close to the surface at its crest.

  16. Large-eddy simulation of unidirectional turbulent flow over dunes

    NASA Astrophysics Data System (ADS)

    Omidyeganeh, Mohammad

    We performed large eddy simulation of the flow over a series of two- and three-dimensional dune geometries at laboratory scale using the Lagrangian dynamic eddy-viscosity subgrid-scale model. First, we studied the flow over a standard 2D transverse dune geometry, then bedform three-dimensionality was imposed. Finally, we investigated the turbulent flow over barchan dunes. The results are validated by comparison with simulations and experiments for the 2D dune case, while the results of the 3D dunes are validated qualitatively against experiments. The flow over transverse dunes separates at the dune crest, generating a shear layer that plays a crucial role in the transport of momentum and energy, as well as the generation of coherent structures. Spanwise vortices are generated in the separated shear; as they are advected, they undergo lateral instabilities and develop into horseshoe-like structures and finally reach the surface. The ejection that occurs between the legs of the vortex creates the upwelling and downdrafting events on the free surface known as "boils". The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which may cause secondary flow across the stream. The mean flow is characterized by a pair of counter-rotating streamwise vortices, with core radii of the order of the flow depth. Staggering the crestlines alters the secondary motion; two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The flow over barchan dunes presents significant differences to that over transverse dunes. The flow near the bed, upstream of the dune, diverges from the centerline plane; the flow close to the centerline plane separates at the crest and reattaches on the bed. Away from the centerline plane and along the horns, flow separation occurs intermittently. The flow in the separation bubble is routed towards the horns and leaves the dune at the tips. Barchan dunes induce two counter-rotating streamwise vortices, along each of the horns, which direct high-momentum fluid toward the symmetry plane and low-momentum fluid near the bed away from the centerline.

  17. Late Pleistocene dune activity in the central Great Plains, USA

    USGS Publications Warehouse

    Mason, J.A.; Swinehart, J.B.; Hanson, P.R.; Loope, D.B.; Goble, R.J.; Miao, X.; Schmeisser, R.L.

    2011-01-01

    Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of cold, short growing seasons with relatively low precipitation and low atmospheric CO2 that increased plant moisture stress, limiting the ability of vegetation to stabilize active dune sand. The apparent coexistence of large mobile dunes with boreal forest taxa suggests a Late Pleistocene environment with few modern analogs. ?? 2011 Elsevier Ltd.

  18. Feasibility of using sand dunes as archives of old air

    NASA Astrophysics Data System (ADS)

    Severinghaus, Jeffrey P.; Keeling, Ralph F.; Miller, Benjamin R.; Weiss, Ray F.; Deck, Bruce; Broecker, Wallace S.

    1997-07-01

    Large unaltered samples of the atmosphere covering the past century would complement the history of atmospheric gases obtained from bubbles in ice cores, enabling measurement of geochemically important species such as O2, 14CH4, and 14CO. Sand dunes are a porous media with interstitial air in diffusive contact with the atmosphere, somewhat analogous to the unconsolidated layer of firn atop glaciers. Recent studies have demonstrated the value of firn as an archive of old air [Battle et al., 1996; Bender et al., 1994a]. Unlike firn, sand dunes are incompressible and so remain permeable to greater depths and may extend the firn record into the past century. To evaluate the feasibility of using sand dunes as archives of old air, we drilled 60 m deep test holes in the Algodones Dunes, Imperial Valley, California. The main objective was to see if the air in a sand dune is as old as predicted by a diffusion model, or if the dune is rapidly flushed by advective pumping during windstorms and barometric pressure changes. We dated the air with chlorofluorocarbons and krypton-85, anthropogenic tracers whose atmospheric concentrations are known and have been increasing rapidly in the past half century. These tracer data match the pure diffusion model well, showing that advection in this dune is negligible compared to diffusion as a transport mechanism and that the mean age of the air at 61 m depth is ˜10 years. Dunes therefore do contain old air. However, dunes appear to suffer from two serious drawbacks as archives. Microbial metabolism is evident in elevated CO2 and N2O and depressed CH4 and O2 concentrations in this dune, corrupting the signals of interest in this and probably most dunes. Second, isotopic analyses of N2 and O2 from the dune show that fractionation of the gases occurs due to diffusion of water vapor, complicating the interpretation of the O2 signal beyond the point of viability for an air archive. Sand dunes may be useful for relatively inert gases with large atmospheric concentration changes such as chlorofluorocarbons.

  19. The Epidemiology of Hepatitis C Virus in the Fertile Crescent: Systematic Review and Meta-Analysis

    PubMed Central

    Chemaitelly, Hiam; Chaabna, Karima; Abu-Raddad, Laith J.

    2015-01-01

    Objective To characterize hepatitis C virus (HCV) epidemiology in countries of the Fertile Crescent region of the Middle East and North Africa (MENA), namely Iraq, Jordan, Lebanon, Palestine, and Syria. Methods We systematically reviewed and synthesized available records of HCV incidence and prevalence following PRISMA guidelines. Meta-analyses were implemented using a DerSimonian-Laird random effects model with inverse weighting to estimate the country-specific HCV prevalence among the various at risk population groups. Results We identified eight HCV incidence and 240 HCV prevalence measures in the Fertile Crescent. HCV sero-conversion risk among hemodialysis patients was 9.2% in Jordan and 40.3% in Iraq, and ranged between 0% and 3.5% among other populations in Iraq over different follow-up times. Our meta-analyses estimated HCV prevalence among the general population at 0.2% in Iraq (range: 0–7.2%; 95% CI: 0.1–0.3%), 0.3% in Jordan (range: 0–2.0%; 95% CI: 0.1–0.5%), 0.2% in Lebanon (range: 0–3.4%; 95% CI: 0.1–0.3%), 0.2% in Palestine (range: 0–9.0%; 95% CI: 0.2–0.3%), and 0.4% in Syria (range: 0.3–0.9%; 95% CI: 0.4–0.5%). Among populations at high risk, HCV prevalence was estimated at 19.5% in Iraq (range: 0–67.3%; 95% CI: 14.9–24.5%), 37.0% in Jordan (range: 21–59.5%; 95% CI: 29.3–45.0%), 14.5% in Lebanon (range: 0–52.8%; 95% CI: 5.6–26.5%), and 47.4% in Syria (range: 21.0–75.0%; 95% CI: 32.5–62.5%). Genotypes 4 and 1 appear to be the dominant circulating strains. Conclusions HCV prevalence in the population at large appears to be below 1%, lower than that in other MENA sub-regions, and tending towards the lower end of the global range. However, there is evidence for ongoing HCV transmission within medical facilities and among people who inject drugs (PWID). Migration dynamics appear to have played a role in determining the circulating genotypes. HCV prevention efforts should be targeted, and focus on infection control in clinical settings and harm reduction among PWID. PMID:26296200

  20. Chondrocalcinose articulaire révélatrice d'une hypercalcémie hypocalciurique familiale: à propos d'une observation

    PubMed Central

    Frikha, Faten; Snoussi, Mouna; Salah, Raida Ben; Loukil, Hanen; Bahloul, Zouhir

    2015-01-01

    L'hypercalcémie hypocalciurique familiale (HHF) est une maladie bénigne à transmission autosomique dominante, caractérisée par une hypercalcémie persistante béhigne, une hypocalciurie, et des concentrations de parathormone (PTH) normales ou modérément élevées, sans complication secondaire à l'hypercalcémie. Nous rapportons l'observation d'un patient ayant présenté une chondrocalcinose articulaire révélatrice d'une HHF. A travers cette observation nous essayons de décrire les aspects épidémiologiques, les caractéristiques cliniques, et paracliniques de cette association. PMID:26090016

  1. Vegetation controls on the maximum size of coastal dunes

    PubMed Central

    Durán, Orencio; Moore, Laura J.

    2013-01-01

    Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand “dune-building” species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought. PMID:24101481

  2. Numerical simulation of the flow over Barchan dunes

    NASA Astrophysics Data System (ADS)

    Omidyeganeh, Mohammad; Piomelli, Ugo; Christensen, Kenneth T.; Best, Jim

    2012-11-01

    We performed large-eddy simulation of the turbulent flow over a typical barchan dune model. The configuration is similar to that of experiments carried out at the University of Illinois, but the Reynolds number based on the free-surface velocity and the dune height is one fifth of the experiment. The simulation adopts the volume-of-fluid technique to model the dune. The use of periodic boundary conditions in the streamwise and spanwise directions implies that we are considering a fully developed flow over one dune in an infinite array. The height of the domain is close to the thickness of the approaching boundary layer, upstream of the dunes in the experiment. The resolution used is close to a typical DNS; ?x+ < 20 . 7 , ?y+ < 0 . 8 , and ?z+ < 10 . 3 . The approaching flow to the dune accelerates over the stoss (upstream) side and rises up to the crest, while at the same time diverging slowly in the spanwise direction toward the closest horn. The separated flow either reattaches on the plane or moves helically inside the recirculation zone toward the closest horn. The separated shear-layer extends downstream and toward the free-surface and contribute to downstream dunes. The agreement of the turbulence statistics with the experiment is good.

  3. Vegetation controls on the maximum size of coastal dunes.

    PubMed

    Durán, Orencio; Moore, Laura J

    2013-10-22

    Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand "dune-building" species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought. PMID:24101481

  4. Is Titan's Dune Orientation Controlled by Tropical Methane Storms?

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clément; Lebonnois, Sébastien; Rodriguez, Sébastien; Courrech du Pont, Sylvain; Lucas, Antoine

    2014-11-01

    Titan’s equatorial regions are covered by eastward oriented linear dunes. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds on Earth [1, 2].Here, we propose that Titan’s dune orientation is actually determined by equinoctial tropical methane storms producing a coupling with superrotation and dune formation. Using meso-scale simulations of convective methane clouds [3, 4] with a GCM wind profile featuring the superrotation [5, 6], we show that Titan’s storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind roses and analogies with terrestrial dune fields [7], we show that Titan's dune growth occurs eastward under these conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major features of Titan's dunes (i.e. divergence from the equator, size and spacing).References:[1] Lorenz et al.: The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes, Science (2006)[2] Lorenz & Radebaugh: Global pattern of Titan’s dunes: Radar survey from the Cassini prime mission, Geophysical Research Letter (2009)[3] Barth & Rafkin.: TRAMS: A new dynamic cloud model for Titan’s methane clouds, Geophysical Research Letter (2007)[4] Barth & Rafkin.: Convective cloud heights as a diagnostic for methane environment on Titan, Icarus (2010)[5] Charnay & Lebonnois: Two boundary layers in Titan's lower troposphere inferred from a climate model, Nature Geoscience (2012)[6] Lebonnois et al.: Titan global climate model: A new 3-dimensional version of the IPSL Titan GCM, Icarus (2012)[7] Courrech du Pont, Narteau & Gao: Two modes for dune orientation, Geology (2014)

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

    USGS Publications Warehouse

    Denny, Charles Storrow; Owens, James Patrick

    1979-01-01

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

  6. Titan's dunes and interdunes: new insights from Cassini Radar observations

    NASA Astrophysics Data System (ADS)

    Le Gall, A. A.; Janssen, M. A.; Lorenz, R. D.; Wye, L.; Callahan, P. S.; Hayes, A. G.; Paganelli, F.; Zebker, H. A.

    2008-12-01

    Since 2004, the Cassini Titan RADAR Mapper instrument, a multimode microwave multiple-beam sensor has observed the surface of Titan at 13.78 GHz. This instrument can operate as a high-resolution synthetic- aperture radar (SAR) imager, profiling altimeter, scatterometer, and radiometer, the latter able to observe simultaneously with, or separately from, the active measurements. The comparison of the data collected in these different modes of operation addresses a number of compositional and geological questions. In particular, radiometry observations near closest approach provide a powerful complement to SAR reflectivity measurements, despite the difference in the resolution. Among the 23 flybys of the Cassini prime mission for which SAR measurements were performed, 14 provided observations of Titan's linear dunes. They revealed that the fields of dunes cover a large portion of Titan's surface, mainly in low-latitudes, within ± 30°. They are radar-dark and exhibit a very high emissivity (with brightness temperatures from 3 to 5 K above that of their surroundings), consistent with a smooth surface and a low dielectric constant. Yet, many questions remain relative to their composition and geometry. We will present the results of our investigation of the correlation between the radar backscatter and the brightness temperature of the dune fields that suggests that interdunes are flat and with a higher dielectric constant than the dunes. This interpretation is supported by data from scatterometry and altimetry. It also accounts for the fact that the look direction seems to have no significant importance in the identification of the dunes. Also, both the emissivity and the reflectivity of the dune fields depend on the incidence (or emission) angle and the look direction. A few dunes were observed with a variety of geometries, especially the ones at the overlap of several swaths. The backscatter properties of these dunes as a function of the look geometry are examined to provide an estimate of the dunes slopes.

  7. Interleukin 17 signaling drives Type I Interferon induced proliferative crescentic glomerulonephritis in lupus-prone mice.

    PubMed

    Ramani, Kritika; Biswas, Partha S

    2016-01-01

    Crescentic glomerulonephritis (cGN) is a severe clinical manifestation in a subset of patients with Systemic lupus erythematosus. Lack of understanding of the pathogenesis of cGN act as a major constraint in treating these patients. Emerging evidence suggest a critical role of IL-17 in the pathogenesis of membranoproliferative glomerulonephritis in lupus. However, the role of IL-17 receptor (IL-17RA) signaling in cGN is unknown. Here, we developed a model of poly I:C-induced Type I Interferon (IFN-I)-dependent cGN in B6.MRL-Faslpr/J (B6.lpr) mice. B6.lpr mice deficient in IL-17RA were protected from IFN-I-dependent cGN. While systemic response was unabated, renal infiltration of alternatively activated macrophages was severely impaired in IL-17RA(-/-) mice. Finally, we show that IL-17 differentially regulates the expression of macrophage chemo-attractant genes in renal tubular epithelial cells and macrophages in association with IFN-I. These results suggest that neutralization IL-17 may confer better protection in SLE patients with high IFN-I gene signature and cGN. PMID:26556529

  8. Climate change in the Fertile Crescent and implications of the recent Syrian drought

    PubMed Central

    Kelley, Colin P.; Mohtadi, Shahrzad; Cane, Mark A.; Seager, Richard; Kushnir, Yochanan

    2015-01-01

    Before the Syrian uprising that began in 2011, the greater Fertile Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and unsustainable agricultural and environmental policies, the drought had a catalytic effect, contributing to political unrest. We show that the recent decrease in Syrian precipitation is a combination of natural variability and a long-term drying trend, and the unusual severity of the observed drought is here shown to be highly unlikely without this trend. Precipitation changes in Syria are linked to rising mean sea-level pressure in the Eastern Mediterranean, which also shows a long-term trend. There has been also a long-term warming trend in the Eastern Mediterranean, adding to the drawdown of soil moisture. No natural cause is apparent for these trends, whereas the observed drying and warming are consistent with model studies of the response to increases in greenhouse gases. Furthermore, model studies show an increasingly drier and hotter future mean climate for the Eastern Mediterranean. Analyses of observations and model simulations indicate that a drought of the severity and duration of the recent Syrian drought, which is implicated in the current conflict, has become more than twice as likely as a consequence of human interference in the climate system. PMID:25733898

  9. Climate change in the Fertile Crescent and implications of the recent Syrian drought.

    PubMed

    Kelley, Colin P; Mohtadi, Shahrzad; Cane, Mark A; Seager, Richard; Kushnir, Yochanan

    2015-03-17

    Before the Syrian uprising that began in 2011, the greater Fertile Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and unsustainable agricultural and environmental policies, the drought had a catalytic effect, contributing to political unrest. We show that the recent decrease in Syrian precipitation is a combination of natural variability and a long-term drying trend, and the unusual severity of the observed drought is here shown to be highly unlikely without this trend. Precipitation changes in Syria are linked to rising mean sea-level pressure in the Eastern Mediterranean, which also shows a long-term trend. There has been also a long-term warming trend in the Eastern Mediterranean, adding to the drawdown of soil moisture. No natural cause is apparent for these trends, whereas the observed drying and warming are consistent with model studies of the response to increases in greenhouse gases. Furthermore, model studies show an increasingly drier and hotter future mean climate for the Eastern Mediterranean. Analyses of observations and model simulations indicate that a drought of the severity and duration of the recent Syrian drought, which is implicated in the current conflict, has become more than twice as likely as a consequence of human interference in the climate system. PMID:25733898

  10. SIMULATION OF THE EFFECT OF WIND SPEEDUP IN THE FORMA-TION OF TRANSVERSE DUNE FIELDS

    E-print Network

    Carretero, Ricardo

    . Some progress has already been made especially with isolated barchan dunes as in the works of Howard et, they succeeded in reproducing a barchan dune with a good geometrical agreement to natural dunes. However and deformational shaping by gravity. Both these models succeeded in reproducing some types of dunes such as barchan

  11. PLANT ASSEMBLAGE STRUCTURE ON BARRIER ISLAND `PIMPLE' DUNES AT THE VIRGINIA COAST RESERVE

    E-print Network

    Lawrence, Deborah

    PLANT ASSEMBLAGE STRUCTURE ON BARRIER ISLAND `PIMPLE' DUNES AT THE VIRGINIA COAST RESERVE LONG ASSEMBLAGE STRUCTURE ON BARRIER ISLAND `PIMPLE' DUNES AT THE VIRGINIA COAST RESERVE LONG-TERM ECOLOGICAL', small, rounded dunes forming along main dune ridges of the barrier islands. There are distinct plant

  12. Dating of Sand Dunes Using Cosmogenic Chlorine-36: An Example From the Nebraska Sand Hills, USA

    E-print Network

    Zreda, Marek

    Dating of Sand Dunes Using Cosmogenic Chlorine-36: An Example From the Nebraska Sand Hills, USA- ing sand dunes based on the accumulation of cosmogenic chlorine-36 in sand grains. The concen- tration of chlorine-36 in a stable sand dune primarily depends on the length of time the dune has been exposed

  13. Interdisciplinary research produces results in understanding planetary dunes

    USGS Publications Warehouse

    Titus, Timothy N.; Hayward, Rosalyn K.; Dinwiddie, Cynthia L.

    2012-01-01

    Third International Planetary Dunes Workshop: Remote Sensing and Image Analysis of Planetary Dunes; Flagstaff, Arizona, 12–16 June 2012. This workshop, the third in a biennial series, was convened as a means of bringing together terrestrial and planetary researchers from diverse backgrounds with the goal of fostering collaborative interdisciplinary research. The small-group setting facilitated intensive discussions of many problems associated with aeolian processes on Earth, Mars, Venus, Titan, Triton, and Pluto. The workshop produced a list of key scientifc questions about planetary dune felds.

  14. Earth Desert Analogues for Titan's Large Linear Dunes

    NASA Astrophysics Data System (ADS)

    Radebaugh, J.; Lorenz, R. D.; Barnes, J. W.; Hayes, A. G.; Farr, T. G.; Heggy, E.; Wall, S. D.; Aharonson, O.

    2013-09-01

    Large seas of linear dunes on Titan have analogues in the Saharan, SW African, Australian and Arabian deserts of Earth. Analogue field studies of these more accessible terrestrial locations can provide insight into the formation of linear dunes in general and of surface, wind and climate conditions on Titan. Initial studies in these remote desert regions using various methods have revealed that linear dune systems have dynamic surfaces subject to continual reworking by recent winds. Given similar morphologies on Titan, similar conditions may prevail.

  15. Field and Laboratory Investigations of Coastal Dune Morphodynamics

    NASA Astrophysics Data System (ADS)

    Ruggiero, P.; Maddux, T.; Kaminsky, G.; Palmsten, M.; Holman, R.; Cox, D.

    2007-12-01

    Coastal dunes are important features along many coastlines, owing to their role in sediment budgets, their use as ecologically unique habitat, and their ability to protect onshore resources from wave attack. Skillful predictions of the erosion and overtopping rates of these features are needed to quantify coastal vulnerability during major storm events. Knowledge of post-storm recovery and subsequent dune growth rates is critical to developing quantitative sediment budgets and ultimately for predicting future shoreline positions. We have been conducting both long-term field and large-scale laboratory studies to improve our understanding of dune morphodynamics and will present results of dune behavior, including various feedback mechanisms, at scales ranging from individual storm events to decadal trends. A large-scale physical model study of dune erosion was recently performed at Oregon State University's O.H. Hinsdale Wave Research Laboratory producing a comprehensive, near prototype-scale data set of hydrodynamics, sediment transport, and morphological evolution during extreme dune erosion events. The laboratory moveable bed beach/dune system was brought to equilibrium with pre-storm random wave conditions. It was subsequently subjected to attack from steadily increasing water levels and offshore wave heights simulating a natural storm surge hydrograph. Observations made include inner surf zone and swash free surface and velocities as well as wave-by-wave estimates of topographical change at high spatial resolution through the use of stereo video imagery. Initial results suggest strong feedbacks between the evolution of the foreshore profile during the storm and episodic dune slumping events. Beach topographic data have been collected quarterly along southwest Washington and northwest Oregon since 1997 resolving the seasonal to interannual morphological variability of a nearly 160-km long high-energy dissipative coastline. Major climate events (such as El Ninos) cause region-wide dune erosion/scarping due to high water levels and increased storminess. However, subsequent dune recovery rates have been variable and appear linked to variations in short-term shoreline change rates and sediment budgets. At interannual scale regions of high shoreline progradation rates experience relatively high dune growth rates. At longer time scales, overall dune morphology is again linked to shoreline change rates but with the highest foredune ridges occurring in areas of relative stable shorelines at decadal scale.

  16. Quantifying energy and water fluxes in dry dune ecosystems of the Netherlands

    NASA Astrophysics Data System (ADS)

    Voortman, B. R.; Bartholomeus, R. P.; van der Zee, S. E. A. T. M.; Bierkens, M. F. P.; Witte, J. P. M.

    2015-04-01

    Coastal and inland dunes provide various ecosystem services that are related to groundwater, such as drinking water production and biodiversity. To manage groundwater in a sustainable manner, knowledge of actual evapotranspiration (ETa) for the various land covers in dunes is essential. Aiming at improving the parameterization of dune vegetation in hydro-meteorological models, this study explores the magnitude of energy and water fluxes in an inland dune ecosystem in the Netherlands. Hydro-meteorological measurements were used to parameterize the Penman-Monteith evapotranspiration model for four different surfaces: bare sand, moss, grass and heather. We found that the net longwave radiation (Rnl) was the largest energy flux for most surfaces during daytime. However, modelling this flux by a calibrated FAO-56 Rnl model for each surface and for hourly time steps was unsuccessful. Our Rnl model, with a novel sub-model using solar elevation angle and air temperature to describe the diurnal pattern in radiative surface temperature, improved Rnl simulations considerably. Model simulations of evaporation from moss surfaces showed that the modulating effect of mosses on the water balance is species dependent. We demonstrate that dense moss carpets (Campylopus introflexus) evaporate more (5%, +14 mm) than bare sand (total of 258 mm in 2013), while more open structured mosses (Hypnum cupressiforme) evaporate less (-30%, -76 mm) than bare sand. Additionally, we found that a drought event in the summer of 2013 showed a pronounced delayed signal on lysimeter measurements of ETa for the grass and heather surfaces respectively. Due to the desiccation of leaves after the drought event, and their feedback on the parameters of the Penman-Monteith equation, the potential evapotranspiration in the year 2013 dropped with 9% (-37mm) and 10% (-61 mm) for the grass and heather surfaces respectively, which subsequently led to lowered ETa of 8% (-29 mm) and 7% (-29 mm). These feedbacks are of importance to water resources, especially during a changing climate with increasing number of drought days. Therefore, such feedbacks need to be integrated into a coupled plant physiological and hydro-meteorological model to accurately simulate ETa. In addition, our study showed that groundwater recharge in dunes can be increased considerably by promoting moss vegetation, especially of open structured moss species.

  17. Quantifying energy and water fluxes in dry dune ecosystems of the Netherlands

    NASA Astrophysics Data System (ADS)

    Voortman, B. R.; Bartholomeus, R. P.; van der Zee, S. E. A. T. M.; Bierkens, M. F. P.; Witte, J. P. M.

    2015-09-01

    Coastal and inland dunes provide various ecosystem services that are related to groundwater, such as drinking water production and biodiversity. To manage groundwater in a sustainable manner, knowledge of actual evapotranspiration (ETa) for the various land covers in dunes is essential. Aiming at improving the parameterization of dune vegetation in hydrometeorological models, this study explores the magnitude of energy and water fluxes in an inland dune ecosystem in the Netherlands. Hydrometeorological measurements were used to parameterize the Penman-Monteith evapotranspiration model for four different surfaces: bare sand, moss, grass and heather. We found that the net longwave radiation (Rnl) was the largest energy flux for most surfaces during daytime. However, modeling this flux by a calibrated FAO-56 Rnl model for each surface and for hourly time steps was unsuccessful. Our Rnl model, with a novel submodel using solar elevation angle and air temperature to describe the diurnal pattern in radiative surface temperature, improved Rnl simulations considerably. Model simulations of evaporation from moss surfaces showed that the modulating effect of mosses on the water balance is species-dependent. We demonstrate that dense moss carpets (Campylopus introflexus) evaporate more (5 %, +14 mm) than bare sand (total of 258 mm in 2013), while more open-structured mosses (Hypnum cupressiforme) evaporate less (-30 %, -76 mm) than bare sand. Additionally, we found that a drought event in the summer of 2013 showed a pronounced delayed signal on lysimeter measurements of ETa for the grass and heather surfaces, respectively. Due to the desiccation of leaves after the drought event, and their feedback on the surface resistance, the potential evapotranspiration in the year 2013 dropped by 9 % (-37 mm) and 10 % (-61 mm) for the grass and heather surfaces, respectively, which subsequently led to lowered ETa of 8 % (-29 mm) and 7 % (-29 mm). These feedbacks are of importance for water resources, especially during a changing climate with an increasing number of drought days. Therefore, such feedbacks need to be integrated into a coupled plant physiological and hydrometeorological model to accurately simulate ETa. In addition, our study showed that groundwater recharge in dunes can be increased considerably by promoting moss vegetation, especially of open-structured moss species.

  18. Solar Energy Study Areas in Colorado Map Prepared June 5, 2009

    E-print Network

    Laughlin, Robert B.

    Refuge Baca National Wildlife Refuge Monte Vista National Wildlife Refuge Great Sand Dunes National Park and Implement Agency-Specific Programs for Solar Energy Development Platoro Reservoir Alamosa National Wildlife

  19. Song of the dunes as a self-synchronized instrument.

    PubMed

    Douady, S; Manning, A; Hersen, P; Elbelrhiti, H; Protière, S; Daerr, A; Kabbachi, B

    2006-07-01

    Since Marco Polo it has been known that some sand dunes have the peculiar ability to emit a loud sound with a well-defined frequency, sometimes for several minutes. The origin of this sustained sound has remained mysterious, partly because of its rarity in nature. It has been recognized that the sound is not due to the air flow around the dunes but to the motion of an avalanche, and not to an acoustic excitation of the grains but to their relative motion. By comparing singing dunes around the world and two controlled experiments, in the laboratory and the field, we prove that the frequency of the sound is the frequency of the relative motion of the sand grains. Sound is produced because moving grains synchronize their motions. The laboratory experiment shows that the dune is not needed for sound emission. A velocity threshold for sound emission is found in both experiments, and an interpretation is proposed. PMID:16907409

  20. Song of the Dunes as a Self-Synchronized Instrument

    NASA Astrophysics Data System (ADS)

    Douady, S.; Manning, A.; Hersen, P.; Elbelrhiti, H.; Protière, S.; Daerr, A.; Kabbachi, B.

    2006-07-01

    Since Marco Polo it has been known that some sand dunes have the peculiar ability to emit a loud sound with a well-defined frequency, sometimes for several minutes. The origin of this sustained sound has remained mysterious, partly because of its rarity in nature. It has been recognized that the sound is not due to the air flow around the dunes but to the motion of an avalanche, and not to an acoustic excitation of the grains but to their relative motion. By comparing singing dunes around the world and two controlled experiments, in the laboratory and the field, we prove that the frequency of the sound is the frequency of the relative motion of the sand grains. Sound is produced because moving grains synchronize their motions. The laboratory experiment shows that the dune is not needed for sound emission. A velocity threshold for sound emission is found in both experiments, and an interpretation is proposed.

  1. Methane storms as a driver of Titan's dune orientation

    E-print Network

    Charnay, Benjamin; Rafkin, Scot; Narteau, Clément; Lebonnois, Sébastien; Rodriguez, Sébastien; Pont, Sylvain Courrech du; Lucas, Antoine

    2015-01-01

    Titan's equatorial regions are covered by eastward propagating linear dunes. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs), which are oriented westward at these latitudes, similar to trade winds on Earth. Different hypotheses have been proposed to address this apparent contradiction, involving Saturn's gravitational tides, large scale topography or wind statistics, but none of them can explain a global eastward dune propagation in the equatorial band. Here we analyse the impact of equinoctial tropical methane storms developing in the superrotating atmosphere (i.e. the eastward winds at high altitude) on Titan's dune orientation. Using mesoscale simulations of convective methane clouds with a GCM wind profile featuring superrotation, we show that Titan's storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport, allowing dunes to extend eastward. This analysis therefore suggests a coupling between superrotation, tro...

  2. 25. Wide view from the dune to the southeast, showing ...

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

    25. Wide view from the dune to the southeast, showing from right to left, surf, beach, bluff, stilwell Hall. - Fort Ord, Soldiers' Club, California State Highway 1 near Eighth Street, Seaside, Monterey County, CA

  3. Ground Penetrating Radar Stratigraphy of Megaflood Gravel Dune

    NASA Astrophysics Data System (ADS)

    Carling, P. A.; Bristow, C. S.; Litvinov, A.; Nield, J. M.

    2010-12-01

    Undulating terrain in Altai Mountains of S. Siberia was interpreted in 1996 by Carling as large gravel dunes; the Kuray dunefield. The dunes relate to the catastrophic emptying of the ice-dam glacial Lake Kuray-Chuja in the late Pleistocene. Detail of the internal structure of the features will ensure the correct geomorphological interpretation. A ground penetrating radar survey was made of the largest, 16m high asymmetric ridge of wavelength 180m. The initial stratigraphic interpretation is consistent with gravel dune bedding due to a flood. The five flow-parallel GPR transects are pre-processed and corrected for the topography. Note the ridge is asymmetry with a longer, less steep stoss slope as opposed to a shorter, steeper lee slope. The radar reflections within the dune are mainly inclined reflections which dip downstream from right to left. These reflections are interpreted to be from cross-stratification within a dune. At the base is a sharp, irregular reflection interpreted as a basal erosion surface. Reflections from cross-strata downlap onto this surface as the dune migrated downstream. Within the inclined reflections there are lower angle inclined reflections that truncate underlying reflections & are in turn downlapped by overlying reflections, these surfaces are interpreted as bounding surfaces where there has been a break in deposition a with a reshaping of the bedform. The packages of cross-strata separated by bounding surfaces indicate a vertical stacking of strata; not just a simple downstream translation of a migrating bedform. This could be a response to a rapidly changing flood hydrograph where the bedform wavelength and height tries to adjust to the fluctuating discharge. The rising hydrograph is marked by the basal scour and initial dune construction. During peak discharge the dune forms & migrates downstream generating sets of large cross-strata. As the discharge declines and flow depth decreases smaller dunes are formed but their development is constrained by the existing giant dune morphology so the small dunes generate bounding surfaces & smaller sets at the crest and downstream margins of the giant bedforms.

  4. 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.

  5. Habitat change in a perched dune system along Lake Superior

    USGS Publications Warehouse

    Loope, Walter L.; McEachern, A. Kathryn

    1998-01-01

    Episodes of habitat change, driven by changes in levels of the Great Lakes, must be considered when assessing human effects upon coastal vegetation and rare species. Paleoecological studies, baseline inventories, and long-term monitoring programs within the Grand Sable Dunes, a perched-dune system along Lake Superior, provide a window on vegetation change at different spatial and temporal scales and also provide an illustrative case study.

  6. Percutaneous Screw Fixation of Crescent Fracture-Dislocation of the Sacroiliac Joint.

    PubMed

    Shui, Xiaolong; Ying, Xiaozhou; Mao, Chuanwan; Feng, Yongzeng; Chen, Linwei; Kong, Jianzhong; Guo, Xiaoshan; Wang, Gang

    2015-11-01

    Crescent fracture-dislocation of the sacroiliac joint (CFDSIJ) is a type of lateral compression pelvic injury associated with instability. Open reduction and internal fixation is a traditional treatment of CFDSIJ. However, a minimally invasive method has never been reported. The purpose of this study was to assess the outcome of closed reduction and percutaneous fixation for different types of CFDSIJ and present their clinical outcome. The authors reviewed 117 patients diagnosed with CFDSIJ between July 2003 and July 2013. Closed reduction and percutaneous fixation was performed in 73 patients. Treatment selection was based on Day's fracture classification. For type I fractures, fixation perpendicular to the fracture line were performed. For type II fractures, crossed fixation was performed. For type III fractures, fixation was performed with iliosacral screws. Forty-four patients were treated by open reduction and plate fixation. Demographics, fracture pattern distribution, blood loss, incision lengths, revision surgeries, radiological results, and functional scores were compared. All 117 patients were followed for more than 6 months (mean, 14 months [range, 6-24 months]). Blood loss, extensive exposure, duration of posterior ring surgery, duration of hospital stay, and infection rates were lower in the closed group (P<.01). Patients in the closed group achieved better functional performance (P<.01). There were no significant differences in reduction quality (P=.32), revision surgery rates (P=.27), and iatrogenic neurologic injuries (P=.2) between the 2 groups. The authors' results indicate that closed reduction and percutaneous fixation is a safe and effective surgical method for CFDSIJ. [Orthopedics. 2015; 38(11):e976-e982.]. PMID:26558677

  7. Barchan dune corridors: field characterization and investigation of control parameters

    E-print Network

    Hicham Elbelrhiti; Bruno Andreotti; Philippe Claudin

    2007-07-10

    The structure of the barchan field located between Tarfaya and Laayoune (Atlantic Sahara, Morocco) is quantitatively investigated and compared to that in La Pampa de la Joya (Arequipa, Peru). On the basis of field measurements, we show how the volume, the velocity and the output sand flux of a dune can be computed from the value of its body and horn widths. The dune size distribution is obtained from the analysis of aerial photographs. It shows that these fields are in a statistically homogeneous state along the wind direction and present a `corridor' structure in the transverse direction, in which the dunes have a rather well selected size. Investigating the possible external parameters controlling these corridors, we demonstrate that none among topography, granulometry, wind and sand flux is relevant. We finally discuss the dynamical processes at work in these fields (collisions and wind fluctuations), and investigate the way they could regulate the size of the dunes. Furthermore we show that the overall sand flux transported by a dune field is smaller than the maximum transport that could be reached in the absence of dunes, i.e. in saltation over the solid ground.

  8. Simulation model of erosion and deposition on a barchan dune

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    Erosion and deposition over a barchan dune near the Salton Sea, California, are modeled by bookkeeping the quantity of sand in saltation following streamlines of transport. Field observations of near surface wind velocity and direction plus supplemental measurements of the velocity distribution over a scale model of the dune are combined as input to Bagnold type sand transport formulas corrected for slope effects. A unidirectional wind is assumed. The resulting patterns of erosion and deposition compare closely with those observed in the field and those predicted by the assumption of equilibrium (downwind translation of the dune without change in size or geometry). Discrepancies between the simulated results and the observed or predicted erosional patterns appear to be largely due to natural fluctuations in the wind direction. The shape of barchan dunes is a function of grain size, velocity, degree of saturation of the oncoming flow, and the variability in the direction of the oncoming wind. The size of the barchans may be controlled by natural atmospheric scales, by the age of the dunes, or by the upwind roughness. The upwind roughness can be controlled by fixed elements or by sand in the saltation. In the latter case, dune scale is determined by grain size and wind velocity.

  9. A COMPARATIVE ANALYSIS OF BARCHAN DUNES IN THE INTRA-CRATER DUNE FIELDS AND THE NORTH POLAR SAND SEA. M.C. Bourke1

    E-print Network

    Bourke, Mary C.

    A COMPARATIVE ANALYSIS OF BARCHAN DUNES IN THE INTRA-CRATER DUNE FIELDS AND THE NORTH POLAR SAND studied in detail in Viking 1 and 2 Orbiter im- ages have been classified as barchan, barchanoid of a morphometric analysis of barchan dunes in two of these locations: the North Polar Sand Sea (NPSS) and intra

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  11. Measuring Possible Tsunami Currents from the April 1, 2014 Mw 8.2 Chile Earthquake in Crescent City, California

    NASA Astrophysics Data System (ADS)

    Admire, A. R.; Crawford, G. B.; Dengler, L. A.

    2014-12-01

    Crescent City, California has a long history of damaging tsunamis. Thirty-nine tsunamis have been recorded since 1933, including five that caused damage. Crescent City's harbor and small boat basin are particularly vulnerable to strong currents. Humboldt State University has installed Acoustic Doppler Profilers (ADPs) in order to directly measure water pressure fluctuations and currents caused by tsunamis. An instrument in Humboldt Bay, ~100 km south of Crescent City, recorded tsunamis generated by the 2010 Mw 8.7 Chile and 2011 Mw 9.0 Japan earthquakes and demonstrated the usefulness of ADPs in measuring tsunami currents. In 2013, an ADP was deployed in Crescent City's harbor adjacent to the NOAA tide gauge. On April 1, 2014, a Mw 8.2 earthquake occurred in northern Chile, producing a modest Pacific-wide tsunami and a 16 cm peak amplitude on the Crescent City tide gauge. We analyze the ADP data before and during the expected arrival of the April 2 tsunami to see if a tsunami signal is present. Tidal currents are generally small (5 cm/s or less). For two months before the tsunami, intermittent, high-frequency variability is present in velocity and pressure at periods on the order of 20, 9 and 5 min, which compare favorably to modal periods predicted using some simplified models of open-ended basins. For several hours after the tsunami arrival on April 2, spectral power levels in velocity and pressure around the 20 min period are notably enhanced. These results suggest that: (1) the observed periods of enhanced variability represent the first three modes (n=0, 1 and 2) of free oscillations in the harbor, (2) the dominant period of (non-tidal) oscillations observed during the April 2, 2014 tsunami (~20 min) and during previous tsunamis (e.g., the water level record for the March 11, 2011 tsunami; also ~20 min) represents harbor resonance corresponding to the lowest order mode, and (3) this event is very near the ADP limit of detectability with peak tsunami currents of 5-10 cm/s and higher frequency variability and instrument noise root-mean-squared amplitude of 4-5 cm/s.

  12. Large Eddy Simulation of Flow and Sediment Transport over Dunes

    NASA Astrophysics Data System (ADS)

    Agegnehu, G.; Smith, H. D.

    2012-12-01

    Understanding the nature of flow over bedforms has a great importance in fluvial and coastal environments. For example, a bedform is one source of energy dissipation in water waves outside the surf zone in coastal environments. In rivers, the migration of dunes often affects the stability of the river bed and banks. In general, when a fluid flows over a sediment bed, the sediment transport generated by the interaction of the flow field with the bed results in the periodic deformation of the bed in the form of dunes. Dunes generally reach an equilibrium shape, and slowly propagate in the direction of the flow, as sand is lifted in the high shear regions, and redeposited in the separated flow areas. Different numerical approaches have been used in the past to study the flow and sediment transport over bedforms. In most research works, Reynolds Averaged Navier Stokes (RANS) equations are employed to study fluid motions over ripples and dunes. However, evidences suggests that these models can not represent key turbulent quantities in unsteady boundary layers. The use of Large Eddy Simulation (LES) can resolve a much larger range of smaller scales than RANS. Moreover, unsteady simulations using LES give vital turbulent quantities which can help to study fluid motion and sediment transport over dunes. For this steady, we use a three-dimensional, non-hydrostatic model, OpenFOAM. It is a freely available tool which has different solvers to simulate specific problems in engineering and fluid mechanics. Our objective is to examine the flow and sediment transport from numerical stand point for bed geometries that are typical of fixed dunes. At the first step, we performed Large Eddy Simulation of the flow over dune geometries based on the experimental data of Nelson et al. (1993). The instantaneous flow field is investigated with special emphasis on the occurrence of coherent structures. To assess the effect of bed geometries on near bed turbulence, we considered different dune geometries based on dune height and wave length. We will also examine the role of near bed turbulence on sediment transport over dunes. For validation, profiles of velocities, turbulent intensities, and sediment transport calculated by the numerical model will be compared with available experimental measurements.

  13. Modeling the large-scale structure of a barchan dune field

    E-print Network

    S. Worman; A. B. Murray; R. Littlewood; B. Andreotti; P. Claudin

    2013-07-12

    In nature, barchan dunes typically exist as members of larger fields that display striking, enigmatic structures that cannot be readily explained by examining the dynamics at the scale of single dunes, or by appealing to patterns in external forcing. To explore the possibility that observed structures emerge spontaneously as a collective result of many dunes interacting with each other, we built a numerical model that treats barchans as discrete entities that interact with one another according to simplified rules derived from theoretical and numerical work and from field observations: (1) Dunes exchange sand through the fluxes that leak from the downwind side of each dune and are captured on their upstream sides; (2) when dunes become sufficiently large, small dunes are born on their downwind sides (`calving'); and (3) when dunes collide directly enough, they merge. Results show that these relatively simple interactions provide potential explanations for a range of field-scale phenomena including isolated patches of dunes and heterogeneous arrangements of similarly sized dunes in denser fields. The results also suggest that (1) dune field characteristics depend on the sand flux fed into the upwind boundary, although (2) moving downwind, the system approaches a common attracting state in which the memory of the upwind conditions vanishes. This work supports the hypothesis that calving exerts a first-order control on field-scale phenomena; it prevents individual dunes from growing without bound, as single-dune analyses suggest, and allows the formation of roughly realistic, persistent dune field patterns.

  14. Reply to ``Comment on `Minimal size of a barchan dune' ''

    NASA Astrophysics Data System (ADS)

    Parteli, E. J. R.; Durán, O.; Herrmann, H. J.

    2007-12-01

    We reply to the preceding comment by Andreotti and Claudin [Phys. Rev. E 76, 063301 (2007)] on our paper [Phys. Rev. E 75, 011301 (2007)]. We show that the equations of the dune model used in our calculations are self-consistent and effectively lead to a dependence of the minimal dune size on the wind speed through the saturation length. Furthermore, we show that Meridiani Planum ripples are probably not a good reference to estimate the grain size of Martian dune sands: the soil in the ripple troughs at the landing site is covered with nonerodible elements (“blueberries”), which increase the minimal threshold for saltation by a factor of 2.0. We conclude that, in the absence of large fragments as the ones found at the landing site, basaltic grains of diameter d=500±100?m that compose the large, typical dark Martian dunes [K. S. Edgett and P. R. Christensen, J. Geophys. Res. 96, 22765 (1991)] probably saltate during the strongest storms on Mars. We also show that the wind friction speed u??3.0m/s that we found from the calculations of Martian dunes is within the values of maximum wind speeds that occur during Martian storms a few times a decade [R. E. Arvidson , Science 222, 463 (1983); H. J. Moore, J. Geophys. Res. 90, 163 (1985); R. Sullivan , Nature (London) 436, 58 (2005); D. J. Jerolmack , J. Geophys. Res. 111, E12S02 (2006)]. In this manner, the dune model predicts that Martian dunes can be formed under present Martian conditions, with no need to assume other conditions of wind and atmosphere that could have prevailed in the past.

  15. The intense 2007-2009 drought in the Fertile Crescent: Impacts and associated atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Trigo, Ricardo M.; Gouveia, Celia; Barriopedro, David

    2010-05-01

    The historical region of Fertile Crescent area (FC hereafter) was hit by an intense and prolonged drought episode in both 2008 and 2009 as a consequence of the very low values of precipitation registered during the two hydrological years comprised between 2007 and 2009. This drought event had major socio-economic impacts in several countries located within the affected area; Iraq, Jordan, Syria and Iran. The economic impact was mostly due to the steep decline in agricultural productivity in the highly populated areas of the Euphrates and Tigris river basins. Traditional methods of drought assessment and monitoring depend heavily on the availability of rainfall data as recorded in meteorological and hydrological networks. The recent availability of reliable satellite imagery covering wide regions over long periods of time has progressively strengthen the role of remote sensing in environmental studies, in particular in those related to drought episodes. In particular, large-scale impacts in vegetation dynamics as well as in lake level can be now achieved with in near real-time with different satellite platforms. The aim of this work is to characterize the temporal and spatial extent of this extreme drought event for the two consecutive hydrological drought years of 2007-2008 and 2008-2009 at the monthly and seasonal scales and to evaluate some of hydrological and vegetative impacts of this event using appropriate satellite information. We confirm that this is the most intense 2-year drought event since 1940 (although just marginally below the 1998-2000 event). Furthermore, the Lake Tharthar (Iraq) is currently reaching its lowest values, similar to those achieved at the end of the prolonged drought between 1998 and 2001. The exceptionality of the 2000 and 2008 events were outstanding, not only because the large amount of pixels with more than 5 months in vegetation stress, but also due to the fact that the persistent drought affect a large amount of pixels belonging to cultivated areas, that are responsible for wheat and barley productions in FC. The impact of drought is clearly visible during the 2000 and 2008 in both wheat and barley productions, with significant economic losses in the affected countries.

  16. Differing Abundances of Gypsum in the Primary and Secondary Dunes of the Martian Dune Field Olympia Undae

    NASA Astrophysics Data System (ADS)

    Szumila, I. T.; Bishop, J. L.; Fenton, L. K.; Brown, A. J.

    2012-12-01

    We report on a compositional study in Olympia Undae, located around the polar cap of Mars. Gypsum has been detected throughout the sand sea but with a decline in abundance westward (Langevin et al., 2005). Dune crests are the regions of highest apparent gypsum concentration in CRISM images. Olympia Undae consists of primary dunes formed transverse to circumpolar easterly winds and secondary dunes which lie almost orthogonal to the primary dunes (Ewing et al. 2010). METHODS: We examined a number of CRISM and HiRISE images across the dune field. We focused our preliminary study on FRT0000C31A and FRT0000C2FC, which exhibited the best spectral signatures. Gypsum was identified in CRISM images by its unique 1.45/1.49/1.54 ?m triplet, ~1.94-1.95 ?m band, 2.22/2.27 ?m doublet and 2.49 ?m band with a 2.42 ?m shoulder. Spectra were acquired from regions of interest (ROIs) created along the crests of primary dunes and the low-relief crests of the secondary dunes (Fig. 1). FINDINGS: CRISM spectra of primary and secondary dune crest ROIs from FRT0000C2FC are compared with a gypsum-rich unit in FRT0000CA5C (Fig. 2). The I/F of gypsum-bearing regions is much darker than pure gypsum indicating a mixture composition containing darker components. The depth of the ~1.95 ?m hydration band is ~20-30% stronger for primary dune crests relative to the secondaries, which suggests a similar relationship among the gypsum abundance of these features, assuming similar components and grain sizes. Semi-quantitative analyses are underway to measure this in more detail. Continuing studies are planned with additional images as well. Figure 1 A map-projected view of CRISM image FRT0000C2FC with ROI locations for the primary (P) and secondary (S) dune crests marked. Figure 2 CRISM I/F spectra of gypsum-bearing units in Olympia Undae compared with laboratory reflectance spectra of minerals.

  17. Two-dimensional airflow modeling underpredicts the wind velocity over dunes

    NASA Astrophysics Data System (ADS)

    Michelsen, Britt; Strobl, Severin; Parteli, Eric J. R.; Pöschel, Thorsten

    2015-11-01

    We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune’s symmetry axis — that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected.

  18. Two-dimensional airflow modeling underpredicts the wind velocity over dunes

    PubMed Central

    Michelsen, Britt; Strobl, Severin; Parteli, Eric J. R.; Pöschel, Thorsten

    2015-01-01

    We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune’s symmetry axis — that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected. PMID:26572966

  19. Airborne gamma-ray spectrometer and magnetometer survey, Crescent quadrangle (Oregon). Volume II. Final report

    SciTech Connect

    Not Available

    1981-01-01

    Seventeen uranium anomalies meet the minimum statistical requirements as defined in Volume I. These anomalies are listed and are shown on the Uranium Anomaly Interpretation Map. Potassium (%K), equivalent Uranium (ppM eU), equivalent Thorium (ppM eT), eU/eT, eU/K, eT/K, and magnetic Pseudo Contour Maps are presented in Appendix E. Stacked Profiles showing geologic strip maps along each flight-line, together with sensor data, and ancillary data are presented in Appendix F. All maps and profiles were prepared on a scale of 1:250,000, but have been reduced to 1:500,000 for presentation in Volume II. Anomaly No. 1 is over Pliocene-Pleistocene basalt and andesite (Qtba). Anomaly No. 2 is over the contact zone between rhyolitic rocks of the John Day formation (Tmor) and Quaternary alluvium (Qal). Anomaly No. 3 is over the contact area between Tertiary silicic ash-flow tuff (Tat) and Quaternary alluvium (Qal). Anomalies No. 4, No. 5, No. 6 are over Recent pumice and ash-flow deposits (Qrp). Anomalies No. 7, No. 8, No. 9, and No. 10 are over Pliocene/Pleistocene basalt (Qtb). Anomaly No. 11 is over the contact area between Pliocene basalt (Tpb), and Pliocene/Pleistocene basalt (Qtb). Anomaly No. 12 is over Quaternary terrace deposits (Qpn). Anomalies No. 13, and No. 14 are over Pleistocene basalt (Tpb). Anomaly No. 15 is over tuffaceous sedimentary rocks (Ts). Anomaly No. 16, the largest in the quadrangle, is over tuffaceous sedimentary rocks (Ts), dune sands (Qd), silicic vent rocks (Tvs), and Quaternary lacustrine rocks (Q1). Anomaly No. 17 is over silicic vent rocks and Quaternary lacustrine sediments (Q1).

  20. The Mediterranean Coastal Dunes in Egypt: An Endangered Landscape

    NASA Astrophysics Data System (ADS)

    Batanouny, K. H.

    1999-08-01

    The Mediterranean coast in Egypt extends almost 900 km, the major part of which is bordered by sand dunes of different natures and types. Along the coastline between Alexandria and El-Alamein, a distance of some 100 km, the sand dunes represent a particular landscape with special characteristics and features, and consequently plants with particular attributes. In this area, the belt of sand dunes has developed immediately south of the shore and these dunes may rise up to 10 m in height and extend about 0·5-1·5 km inland from the shore. These dunes are famous as a habitat for the fig (Ficus carica L.) cultivation depending on the irregular rainfall. They also represent a landing station and a cross-road for birds such as quail migrating from Europe in the north. In the past, summer resort areas were confined to limited areas with few people, these same areas support the growth of some important plant species, for example, sand binders, medicinal and range plants. For more than two decades, there has been considerable socio-economic change and an open-door policy in the economy of the country has been adopted. One of the consequences of this change is that a great part of the coastal dune belt west of Alexandria till El-Alamein, has been subjected to destruction, due to the continuous construction of summer resort villages. These were built at a distance of about 100 m of the shoreline, extending 400-600 m inland and a breadth of 400 m or more along the shoreline. The area already covered by the dunes is now almost occupied by new buildings, gardens and other infrastructure. The consequences of these human activities are numerous and include impacts on the soil, water resources, the flora and the fauna, migrating birds, trends of the indigenous people, and the cultural environment. The present paper gives a concise environmental setting of the dune belt before the advent of the new activities, and the socio-economic and political attitudes which threaten the dunes. The ecological consequences of the recent human activities and recommendations are presented.

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

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-18

    ...Record of Decision for the Approved Imperial Sand Dunes Recreation Area Management Plan and...announces the availability of the Imperial Sand Dunes Recreation Area Record of Decision...SUPPLEMENTARY INFORMATION: The Imperial Sand Dunes Recreation Area (ISDRA) and...

  2. Linear and nonlinear wave propagation in booming sand dunes

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    The current field study examines linear and non-linear acoustic waves found in large desert sand dunes using field measurements of wave speed, frequency content, dispersion, and polarization. At the dune fields visited, an avalanching of sand can trigger a loud booming or rumbling sound with narrow peak frequencies centered between 70 and 105 Hz with higher harmonics. Prior to the onset of the nearly monotone booming, the emission consists of short bursts or burps of sound of smaller amplitude and over a significantly broader range of frequencies. These burps created at dune sites have similar frequency content to sounds generated by small-scale shearing in laboratory-scale experiments. By investigating the wave characteristics of both burping and booming emissions, this manuscript demonstrates that booming and burping correspond with the transmission of different waves within the dune. The burping sounds correspond to a surface Rayleigh wave with nonlinear and dispersive properties. The booming emission results from a linear, non-dispersive P-wave, which supports an earlier analysis where booming is modeled as the trapping of the body waves in the dune's surficial layer. Besides characterizing the booming and burping emissions, this manuscript illustrates the effect of scale in the wave propagation of granular materials, when non-linear, dispersive waves across small scales transition to linear, non-dispersive waves across larger scales.

  3. Origin and lateral migration of linear dunes in the Qaidam Basin of NW China revealed by dune sediments, internal structures, and optically stimulated luminescence ages, with implications for linear dunes on Titan: discussion

    USGS Publications Warehouse

    Rubin, David M.; Rubin, Alan M.

    2013-01-01

    Zhou et al. (2012) proposed that longitudinal dunes in the Qaidam Basin, China, formed like yardangs: by erosion into sediment that was not deposited by those dunes. Because erosion occurs on the upwind flanks of most migrating dunes (Rubin and Hunter, 1982, 1985), the key to demonstrating a yardang-like origin is to show that the dunes did not deposit the strata that they contain. Zhou et al. made this argument by proposing that: (1) The dunes have not deposited cross-strata in the past 810 yr. (2) Cross-bedding within the dunes was not deposited by the dunes on the present-day land surface, but rather by older dunes that had a different morphology. (3) The present dunes are a later generation, “most likely of erosional origin similar to yardangs with orientations controlled by strikes of joints,” (p. 1147). (4) Rates of deflation in the dune field have been extremely high for the past 810–2440 yr. This commentary reviews these conclusions, reviews contradictory observations, and considers alternative interpretations.

  4. Morphology and dynamics of large subtidal dunes in Bahia Blanca estuary, Argentina

    NASA Astrophysics Data System (ADS)

    Minor Salvatierra, Marta; Aliotta, Salvador; Ginsberg, Silvia Susana

    2015-10-01

    The purpose of this paper is to carry out a detailed analysis of subtidal dune morphology and temporal variability and to estimate dune migration rate to improve knowledge of this topic, and so enhance the existing data on different marine environments in the world and especially in South America where this information is limited. Two swath bathymetry surveys were conducted across a dune field in the Bahia Blanca Estuary (Argentina). Morphometric parameters and migration rate according to the dune type, were analyzed. The field is composed of large dunes exhibiting two morphological configurations, which are differentiated into sinuous and barchan dunes. The dunes studied are the largest of the estuary, with heights and wavelengths greater than 5 m and 130 m, respectively. The crests of the large dunes are arranged with an orientation perpendicular to the axis of the channel. From geometrical analysis of the parameters, the dunes show a weakly positive correlation between dune height and wavelength as too between dune height and water depth. No clear relationship was observed between maximum height and wavelength parameters with water depth. Across the estuary, the bedforms migrate in the ebb direction, with mean rate of 43 m year- 1. Comparison of our results with previous data shows that during three decades the western boundary of dune field has been displaced 900 m towards the outer estuary, however the dune field configuration and distribution of diverse types of bedform appear to be relatively stable.

  5. A model of Barchan dunes including lateral shear stress.

    PubMed

    Schwämmle, V; Herrmann, H J

    2005-01-01

    Barchan dunes are found where sand availability is low and wind direction quite constant. The two dimensional shear stress of the wind field and the sand movement by saltation and avalanches over a barchan dune are simulated. The model with one dimensional shear stress is extended including surface diffusion and lateral shear stress. The resulting final shape is compared to the results of the model with a one dimensional shear stress and confirmed by comparison to measurements. We found agreement and improvements with respect to the model with one dimensional shear stress. Additionally, a characteristic edge at the center of the windward side is discovered which is also observed for big barchans. Diffusion effects reduce this effect for small dunes. PMID:15688141

  6. Advanced InSAR imaging for dune mapping

    NASA Astrophysics Data System (ADS)

    Havivi, Shiran; August, Yitzhak; Blumberg, Dan G.; Rotman, Stanley R.

    2015-04-01

    Aeolian morphologies are formed in the presence of sufficient wind energy and available particles. These processes occur naturally or are further enhanced or reduced by human intervention. The dimensions of change are dependent primarily on the wind energy and surface properties. Since the 1970's, remote sensing imagery both optical and radar, are used for documentation and interpretation of the geomorphologic changes of sand dunes. Remote sensing studies of Aeolian morphologies is mostly useful to document major changes, yet, subtle changes, occurring in a period of days or months in scales of centimeters, are very difficult to detect in imagery. Interferometric Synthetic Aperture Radar (InSAR) is an imaging technique for measuring Earth's surface topography and deformation. InSAR images are produced by measuring the radar phase difference between two separated antennas that view the same surface area. Classical InSAR is based on high coherence between two images or more. The output (interferogram) can show subtle changes with an accuracy of several millimeters to centimeters. Very little work has been done on measuring or identifying the changes in dunes using InSAR. The reason is that dunes tend to be less coherent than firm, stable, surfaces. This research aims to demonstrate how interferometric decorrelation, or, coherence change detection, can be used for identifying dune instability. We hypothesize and demonstrate that the loss of radar coherence over time on dunes can be used as an indication of the dune's instability. When SAR images are acquired at sufficiently close intervals one can measure the time it takes to lose coherence and associate this time with geomorphic stability. To achieve our goals, the Nitzanim coastal dunes along the Mediterranean, 40 km south of Tel-Aviv, Israel, were chosen as a case study. The dunes in this area are of varying levels of stability and vegetation cover and have been monitored meteorologically, geomorphologically and extensively in the field. High resolution TerraSAR-X (TSX) images, covering the entire research area were acquired for the period of October 2011 to July 2012 (15 images in total). All images were co-registreted, the first image was used as the master image. A coherence index was calculated for all the images. Analysis was performed in GIS software. The results display minor changes (coherence index in range of 0.4-0.65) on dune crests depending on the dune location relative to its distance from the sea and distance from the city. In addition, field results indicate erosion / deposition of sand in a cumulatively amount of approximately 30mm annually. The results of this study confirm that it is possible to monitor subtle changes in dunes and to identify dune stability or instability, only by the use of SAR images.

  7. Defrosting Polar Dunes--'They Look Like Bushes!'

    NASA Technical Reports Server (NTRS)

    1999-01-01

    'They look like bushes!' That's what almost everyone says when they see the dark features found in pictures taken of sand dunes in the polar regions as they are beginning to defrost after a long, cold winter. It is hard to escape the fact that, at first glance, these images acquired by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) over both polar regions during the spring and summer seasons, do indeed resemble aerial photographs of sand dune fields on Earth--complete with vegetation growing on and around them! Of course, this is not what the features are, as we describe below and in related picture captions. Still, don't they look like vegetation to you? Shown here are two views of the same MGS MOC image. On the left is the full scene, on the right is an expanded view of a portion of the scene on the left. The bright, smooth surfaces that are dotted with occasional, nearly triangular dark spots are sand dunes covered by winter frost.

    The MGS MOC has been used over the past several months (April-August 1999) to monitor dark spots as they form and evolve on polar dune surfaces. The dark spots typically appear first along the lower margins of a dune--similar to the position of bushes and tufts of grass that occur in and among some sand dunes on Earth.

    Because the martian air pressure is very low--100 times lower than at Sea Level on Earth--ice on Mars does not melt and become liquid when it warms up. Instead, ice sublimes--that is, it changes directly from solid to gas, just as 'dry ice' does on Earth. As polar dunes emerge from the months-long winter night, and first become exposed to sunlight, the bright winter frost and snow begins to sublime. This process is not uniform everywhere on a dune, but begins in small spots and then over several months it spreads until the entire dune is spotted like a leopard.

    The early stages of the defrosting process--as in the picture shown here--give the impression that something is 'growing' on the dunes. The sand underneath the frost is dark, just like basalt beach sand in Hawaii. Once it is exposed to sunlight, the dark sand probably absorbs sunlight and helps speed the defrosting of each sand dune.

    This picture was taken by MGS MOC on July 21, 1999. The dunes are located in the south polar region and are expected to be completely defrosted by November or December 1999. North is approximately up, and sunlight illuminates the scene from the upper left. The 500 meter scale bar equals 547 yards; the 300 meter scale is also 328 yards.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  8. A Probabilistic Tsunami Hazard Assessment Methodology and Its Application to Crescent City, CA

    NASA Astrophysics Data System (ADS)

    Gonzalez, F. I.; Leveque, R. J.; Waagan, K.; Adams, L.; Lin, G.

    2012-12-01

    A PTHA methodology, based in large part on Probabilistic Seismic Hazard Assessment methods (e.g., Cornell, 1968; SSHAC, 1997; Geist and Parsons, 2005), was previously applied to Seaside, OR (Gonzalez, et al., 2009). This initial version of the method has been updated to include: a revised method to estimate tidal uncertainty; an improved method for generating stochastic realizations to estimate slip distribution uncertainty (Mai and Beroza, 2002; Blair, et al., 2011); additional near-field sources in the Cascadia Subduction Zone, based on the work of Goldfinger, et al. (2012); far-field sources in Japan, based on information updated since the 3 March 2011 Tohoku tsunami (Japan Earthquake Research Committee, 2011). The GeoClaw tsunami model (Berger, et. al, 2011) is used to simulate generation, propagation and inundation. We will discuss this revised PTHA methodology and the results of its application to Crescent City, CA. Berger, M.J., D. L. George, R. J. LeVeque, and K. T. Mandli, The GeoClaw software for depth-averaged flows with adaptive refinement, Adv. Water Res. 34 (2011), pp. 1195-1206. Blair, J.L., McCrory, P.A., Oppenheimer, D.H., and Waldhauser, F. (2011): A Geo-referenced 3D model of the Juan de Fuca Slab and associated seismicity: U.S. Geological Survey Data Series 633, v.1.0, available at http://pubs.usgs.gov/ds/633/. Cornell, C. A. (1968): Engineering seismic risk analysis, Bull. Seismol. Soc. Am., 58, 1583-1606. Geist, E. L., and T. Parsons (2005): Probabilistic Analysis of Tsunami Hazards, Nat. Hazards, 37 (3), 277-314. Goldfinger, C., Nelson, C.H., Morey, A.E., Johnson, J.E., Patton, J.R., Karabanov, E., Gutiérrez-Pastor, J., Eriksson, A.T., Gràcia, E., Dunhill, G., Enkin, R.J., Dallimore, A., and Vallier, T. (2012): Turbidite event history—Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone: U.S. Geological Survey Professional Paper 1661-F, 170 p. (Available at http://pubs.usgs.gov/pp/pp1661f/). González, F.I., E.L. Geist, B. Jaffe, U. Kânoglu, H. Mofjeld, C.E. Synolakis, V.V Titov, D. Arcas, D. Bellomo, D. Carlton, T. Horning, J. Johnson, J. Newman, T. Parsons, R. Peters, C. Peterson, G .Priest, A. Venturato, J. Weber, F. Wong, and A. Yalciner (2009): Probabilistic Tsunami Hazard Assessment at Seaside, Oregon, for Near- and Far-Field Seismic Sources, J. Geophys. Res., 114, C11023, doi:10.1029/2008JC005132. Japan Earthquake Research Committee, (2011): http://www.jishin.go.jp/main/p_hyoka02.htm Mai, P. M., and G. C. Beroza (2002): A spatial random field model to characterize complexity in earthquake slip, J. Geophys. Res., 107(B11), 2308, doi:10.1029/2001JB000588. SSHAC (Senior Seismic Hazard Analysis Committee) (1997): Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts, Main Report Rep. NUREG/CR-6372 UCRL-ID-122160 Vol. 1, 256 pp, U.S. Nuclear Regulatory Commission.

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

    USGS Publications Warehouse

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

    2009-01-01

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

  10. Reply to comment by B. Andreotti et al. on ``Solving the mystery of booming sand dunes''

    E-print Network

    Clayton, Robert W.

    Reply to comment by B. Andreotti et al. on ``Solving the mystery of booming sand dunes'' Nathalie M to comment by B. Andreotti et al. on ``Solving the mystery of booming sand dunes,'' Geophys. Res. Lett., 35

  11. Comment on ``Solving the mystery of booming sand dunes'' by Nathalie M. Vriend et al.

    E-print Network

    Clayton, Robert W.

    Comment on ``Solving the mystery of booming sand dunes'' by Nathalie M. Vriend et al. B. Andreotti), Comment on ``Solving the mystery of booming sand dunes'' by Nathalie M. Vriend et al., Geophys. Res. Lett

  12. Comment on "Relevant Length Scale of Barchan Dunes"

    E-print Network

    Klaus Kroy; Xiang Guo

    2004-04-05

    In a recent experimental breakthrough, Hersen et al. [1] demonstrated that by changing the agitating medium from air to water, one can obtain, on laboratory scale, dunes that are downsized copies of desert dunes, thereby overcoming a major obstacle for their systematic study. Here we argue in two steps (i),(ii) that an alternative data analysis leads to some conclusions that are qualitatively and quantitatively different from Hersen et al.'s but justify their similarity hypothesis on different grounds. [1] P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89 (2002) 264301

  13. Defrosting Polar Dunes--Changes Over a 26-Day Period

    NASA Technical Reports Server (NTRS)

    1999-01-01

    As the retreat of the south polar winter frost cap became visible in June 1999, high resolution images from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) began to show dark spots forming on the surfaces of frost-covered sand dunes. Immediately, the MOC science team began to plan to observe several dune fields more than once, should that opportunity arise, so that the evolution of these dark spots could be documented and studied. Such work will eventually lead to abetter understanding of how the martian polar caps retreat as winter ends and spring unfolds in each hemisphere.

    MGS is in a polar orbit, which means that, unlike many other places on Mars, the spacecraft has more opportunities to take pictures of the same place. Dune fields near 87o latitude can be repeatedly viewed; dunes near the equator are not likely to be photographed more than once during the entire MGS mission.

    The pictures presented here show changes on a set of nearly pear-shaped sand dunes located on the floor of an unnamed crater at 59oS, 353oW. The picture on the left shows the dunes as they appeared on June 19, 1999, the picture on the right shows the same dunes on July 15, 1999. The dark spots in the June 19picture--indicating areas where frost has sublimed away--became larger by July 15th. In addition, new spots had appeared as of mid-July. If possible, these dunes will be photographed by MOC again in mid-August and each month until the frost is gone.

    The pictures shown in (B) (above) are expanded views of portions of the pictures in (A). The 200 meter scale bar equals 656 feet; the 100 meter bar is 328 feet (109 yards) long. All images are illuminated from the upper left; north is toward the upper right.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  14. The Herschel DUNES Open Time Key Programme

    NASA Technical Reports Server (NTRS)

    Danchi, William C.

    2009-01-01

    We will use the unique photometric capabilities provided by Herschel to perform a deep and systematic survey for faint, cold debris disks around nearby stars. Our sensitivity-limited Open Time Key Programme (OTKP) aims at finding and characterizing faint extrasolar analogues to the Edgeworth-Kuiper Belt (EKB) in an unbiased, statistically significant sample of nearby FGK main-sequence stars. Our target set spans a broad range of stellar ages (from 0.1 to 10 Gyr) and is volume-limited (distances < 20 pc). All stars with known extrasolar planets within this distance are included; additionally, some M- and A-type stars will be observed in collaboration with the Herschel DEBRIS OTKP, so that the entire sample covers a decade in stellar mass, from 0.2 to 2 solar masses. We will perform PACS and SPIRE photometric observations covering the wavelength range from 70 to 500 microns. The PACS observations at 100 microns have been designed to detect the stellar photospheres down to the confusion limit with a signal-to-noise ratio > 5. The observations in the other Herschel bands will allow us to characterize, model, and constrain the disks. As a result, it will be possible for us to reach fractional dust luminosities of a few times 10-7, close to the EKB level in the Solar System. This will provide an unprecedented lower limit to the fractional abundance of planetesimal systems and allow us to assess the presence of giant planets, which would play dynamical roles similar to those played by Jupiter and Neptune in the Solar System. The proposed observations will provide new and unique evidence for the presence of mature planetary systems in the solar neighbourhood and, in turn, will address the universality of planet/planetary system formation in disks around young stars.

  15. Relevant Length Scale of Barchan Dunes Pascal Hersen, Stephane Douady, and Bruno Andreotti

    E-print Network

    Relevant Length Scale of Barchan Dunes Pascal Hersen, Ste´phane Douady, and Bruno Andreotti 1 barchan dunes under water: some sand is put on a tray moving periodically and asymmetrically in a water tank, and barchans rapidly form. We measure basic morphological and dynamical properties of these dunes

  16. Morphodynamics of barchan and transverse dunes using a cellular automaton model

    E-print Network

    Narteau, Clément

    Morphodynamics of barchan and transverse dunes using a cellular automaton model D. Zhang,1 C for stabilizing the shape of isolated barchan dunes. We measure the propagation speed of superimposed bedforms on steady state barchan dunes and show how they contribute to the formation and detachment of smaller

  17. Mars Global Digital Dune Database and initial science results Rosalyn K. Hayward,1

    E-print Network

    Bourke, Mary C.

    volume of $3,600 km3 . This area, when combined with polar dune estimates, suggests moderate- to large Camera narrow-angle (MOC NA) images allow, we classify dunes and include dune slipface measurements-resolution images like Mars Global Surveyor (MGS) Mars Orbiter Camera narrow-angle (MOC NA) [Malin et al., 1992

  18. 76 FR 57074 - Transfer of Administrative Jurisdiction at or Near Great Sand Dunes National Park

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-15

    ...Administrative Jurisdiction at or Near Great Sand Dunes National Park AGENCY: National Park...lands acquired for the benefit of Great Sand Dunes National Park, Baca National Wildlife...interests in land for the benefit of Great Sand Dunes National Park, Baca National...

  19. 44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 2014-10-01 false Evaluation of sand dunes in mapping coastal flood hazard areas...HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas...vegetative cover, such as the placement of sand materials in a dune-like...

  20. 44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 2010-10-01 false Evaluation of sand dunes in mapping coastal flood hazard areas...HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas...vegetative cover, such as the placement of sand materials in a dune-like...

  1. 44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 2013-10-01 false Evaluation of sand dunes in mapping coastal flood hazard areas...HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas...vegetative cover, such as the placement of sand materials in a dune-like...

  2. 44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 2011-10-01 false Evaluation of sand dunes in mapping coastal flood hazard areas...HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas...vegetative cover, such as the placement of sand materials in a dune-like...

  3. 44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 2011-10-01 true Evaluation of sand dunes in mapping coastal flood hazard areas...HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas...vegetative cover, such as the placement of sand materials in a dune-like...

  4. J. Zool., Lond. (1996) 238, 703 712 Millipede communities in rehabilitating coastal dune forests

    E-print Network

    Pretoria, University of

    1996-01-01

    J. Zool., Lond. (1996) 238, 703 712 Millipede communities in rehabilitating coastal dune forestsI' a known-aged series of stands representative or coastal dune ["orest suceesslun. A survey of the millipede-specific millipede COIII III unity variables on rehabilitating dunes with those recorded in relatively undisturbed d

  5. Dunes on Mars, `Venus', Earth, and subaqueous ripples: a scaling law for their elementary size

    E-print Network

    Claudin, Philippe

    Dunes on Mars, `Venus', Earth, and subaqueous ripples: a scaling law for their elementary size P as snow, dunes under water, but also dunes on Mars or Titan. Summarising our work published in [1], we from the bed, (ii) the grain inertia that controls the length needed for one grain to reach its

  6. A Holocene history of dune-mediated landscape change along the southeastern shore of Lake Superior

    E-print Network

    Fisher, Timothy G.

    stream piracy, breaching of dune dams, and aerial exposure and forestation of infilled lakebeds to events of dune damming and subsequent dam breaching. The interrelated late Holocene events apparent of Lake Superior with dune building, stream damming and diversion and reservoir impoundment and infilling

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

    PubMed Central

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

    2015-01-01

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

  8. Geospatial analysis of a coastal sand dune field evolution: Jockey's Ridge, North Carolina

    E-print Network

    Mitasova, Helena

    Sciences, North Carolina State University, Raleigh, NC 27695, USA b Department of Civil, Construction the dune migration and forcing growth in dune elevation. Understanding the causes of the current movements 2005 Elsevier B.V. All rights reserved. Keywords: DEM; Sand dunes; Migration rates; Lidar; GIS; North

  9. Pauci-Immune Necrotizing and Crescentic Glomerulonephritis with Membranous Lupus Nephritis, Fifteen Years after Initial Diagnosis of Secondary Membranous Nephropathy

    PubMed Central

    Burkhart, Ryan; Shah, Nina; Abel, Michael; Oliver, James D.; Lewin, Matthew

    2015-01-01

    Renal involvement in systemic lupus erythematosus (SLE) is usually immune complex mediated and may have multiple different presentations. Pauci-immune necrotizing and crescentic glomerulonephritis (NCGN) refers to extensive glomerular inflammation with few or no immune deposits that may result in rapid decline in renal function. We report a case of a 79-year-old Hispanic male with a history of secondary membranous nephropathy (diagnosed by renal biopsy 15 years previously) who was admitted with acute kidney injury and active urinary sediment. P-ANCA titers and anti-myeloperoxidase antibodies were positive. The renal biopsy was diagnostic for NCGN superimposed on a secondary membranous nephropathy. A previous diagnosis of SLE based on American College of Rheumatology criteria was discovered via Veteran's Administration records review after the completion of treatment for pauci-immune NCGN. ANCAs are detected in 20–31% of patients with SLE. There may be an association between SLE and ANCA seropositivity. In patients with lupus nephritis and biopsy findings of necrotizing and crescentic glomerulonephritis, without significant immune complex deposition, ANCA testing should be performed. In patients with secondary membranous nephropathy SLE should be excluded. PMID:26558120

  10. Environmental Controls and Eco-geomorphic Interactions of the Barchan-to-parabolic Dune Stabilisation and the Parabolic-to-barchan Dune Reactivation

    NASA Astrophysics Data System (ADS)

    Yan, Na; Baas, Andreas

    2015-04-01

    Parabolic dunes are one of a few common aeolian landforms which are highly controlled by eco-geomorphic interactions. Parabolic dunes, on the one hand, can be developed from highly mobile dune landforms, barchans for instance, in an ameliorated vegetation condition; or on the other hand, they can be reactivated and transformed back into mobile dunes due to vegetation deterioration. The fundamental mechanisms and eco-geomorphic interactions controlling both dune transformations remain poorly understood. To bridge the gap between complex processes involved in dune transformations on a relatively long temporal scale and real world monitoring records on a very limited temporal scale, this research has extended the DECAL model to incorporate 'dynamic' growth functions and the different 'growth' of perennial shrubs between growing and non-growing seasons, informed by field measurements and remote sensing analysis, to explore environmental controls and eco-geomorphic interactions of both types of dune transformation. A non-dimensional 'dune stabilising index' is proposed to capture the interactions between environmental controls (i.e. the capabilities of vegetation to withstand wind erosion and sand burial, the sandy substratum thickness, the height of the initial dune, and the sand transport potential), and establish the linkage between these controls and the geometry of a stabilising dune. An example demonstrates how to use the power-law relationship between the dune stabilising index and the normalised migration distance to assist in extrapolating the historical trajectories of transforming dunes. The modelling results also show that a slight increase in vegetation cover of an initial parabolic dune can significantly increase the reactivation threshold of climatic impact (both drought stress and wind strength) required to reactivate a stabilising parabolic dune into a barchan. Four eco-geomorphic interaction zones that govern a barchan-to-parabolic dune transformation and a parabolic-to-barchan dune transformation have been identified. These zones exhibit different characteristics and dynamics that are sensitive to changes in environmental forces, and can be potentially used as a proxy to monitor the mobility of a dune system.

  11. SPATIAL VARIATIONS IN SUSPENDED SEDIMENT TRANSPORT OVER DUNES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The magnitude of the lateral variations in the concentration of suspended sediment over dunes in an alluvial sand-bed channel are poorly known. Characterizing the lateral distributions of suspended sediment is important for understanding its causes and for accurate measurement of the rate of sedim...

  12. Alphabetisation conscientisante comme base d'une education permanente

    NASA Astrophysics Data System (ADS)

    Ndimurukundo, Nicephore

    1994-05-01

    D'après la pratique et les enseignements vécus, nous pensons qu'une alphabétisation fonctionnelle et conscientisante est susceptible de constituer la base d'une éducation permanente (life long education), à condition que: Une philosophie et une anthropologie de la libération de l'homme soient le fondement de 1'alphabétisation;

  13. Lateral variations in suspended sediment concentration over dunes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The magnitude of the lateral variations in the concentration of suspended sediment over dunes in an alluvial sand-bed channel are poorly known. Characterizing the lateral distributions of suspended sediment is important for understanding its causes and for accurate measurement of the rate of sedim...

  14. Rivers, Lakes, Dunes, and Rain: Crustal Processes in Titan's

    E-print Network

    Reiners, Peter W.

    Rivers, Lakes, Dunes, and Rain: Crustal Processes in Titan's Methane Cycle Jonathan I. Lunine1-6597/09/0530-0299$20.00 Key Words hydrology, climate, hydrocarbons, atmospheres, planets, clouds Abstract Titan exhibits ample SETTING FOR A METHANE CYCLE ON TITAN Titan is Saturn's largest natural satellite and the second

  15. Analysis of Coastal Dunes: A Remote Sensing and Statistical Approach.

    ERIC Educational Resources Information Center

    Jones, J. Richard

    1985-01-01

    Remote sensing analysis and statistical methods were used to analyze the coastal dunes of Plum Island, Massachusetts. The research methodology used provides an example of a student project for remote sensing, geomorphology, or spatial analysis courses at the university level. (RM)

  16. Climate and coastal dune vegetation: disturbance, recovery, and succession

    E-print Network

    Miller, Thomas E.

    Science+Business Media B.V. 2009 Abstract The sand dune habitats found on barrier islands and other coasts, especially on barrier islands, are particularly dynamic environ- ments because of interactions. A nine-year census of 294 plots on St. George Island, Florida suggests that the major climatic drivers

  17. Low-flying Helicopter Scanning Great Sand Dunes National Park

    USGS Multimedia Gallery

    Citizens and visitors should not be alarmed if they witness a low-flying helicopter, with a large wire-loop contraption hanging from a cable underneath, flying over the Great Sand Dunes National Park in the next couple of weeks. Starting on or about Monday, Oct. 10, and lasting for one to two weeks...

  18. Discussion. Cemented horizon in subarctic Alaskan sand dunes.

    USGS Publications Warehouse

    Galloway, J.P.; Koster, E.A.; Hamilton, T.D.

    1985-01-01

    Exception is taken to the conclusions (M.A. 84M/4465) concerning the distribution, age and origin of the cementing materials of carbonate crusts in the eaeolian sand deposits of the dune field in the central Kobuk Valley. (Following abstract)-M.S.

  19. Extension d'une valuation * Michel Vaqui'e

    E-print Network

    Extension d'une valuation * Michel Vaqui'e Abstract We want to determine all the extensions of a valuation of a field K to valuation for a given valuation ~ of K[x], and has shown how we can recover any extension to L

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    A LiDAR-derived digital elevation model (DEM) of a representative portion of the White Sands Dune Field, New Mexico, allows for characterization of an unprecedented range of dune-field parameters and serves as a basis for pattern analysis. Dune-field parameters were measured and statistically analyzed for populations of dunes selected at random and occurring along transects. Populations sampled by these two different methods are comparable, but highlight the sensitivity of transect placement in a dune field that has pattern heterogeneity. Based upon coefficients of variation, pattern emerges at White Sands primarily because of a strong fabric of crestline orientation, and secondarily because of the regularity of spacing between dunes of similar shape as defined by sinuosity, height and length. Linear regression of dune parameters shows that dune geometric relationships vary primarily with crestline length, but there is little correlation between other parameters, including dune spacing and height. This result highlights the sensitivity of identifying topographic heterogeneity in a LiDAR-derived DEM, given that mean ratios conform to global averages. Stripping off the dunes in Matlab shows a terraced surface, which is interpreted to represent paleo-shorelines formed during relative still stands in the overall retreat of Lake Otero. Elevated bands of higher, more closely spaced dunes occur just leeward of the paleo-shorelines. A revised model for the White Sands Dune Field consists of the basinward progradation of successive dune-field segments. Each segment is associated with a paleo-shoreline, and consists of an upwind dune ridge, represented by the elevated bands, and a leeward dune field.

  1. The Influence of Physical & Biological Cohesion on Dune Development

    NASA Astrophysics Data System (ADS)

    Schindler, Robert; Parsons, Daniel; Ye, Leiping; Baas, Jaco; Hope, Julie; Manning, Andy; Malarkey, Jonathan; Aspden, Rebecca; Lichtman, Dougal; Thorne, Peter; Peakall, Jeff; Patterson, David; Davies, Alan; Bass, Sarah; O'Boyle, Louise

    2014-05-01

    Existing predictions for dune bedforms are based on simplified physical parameters, with assumptions that sediment consists only of cohesionless sand. They do not include the complexities of mud: physical cohesion is imparted by cohesive clays and biological cohesion is created by the presence of organisms which, among other things, generate extra-cellular polymers (EPS). Using controlled experiments we show the profound influence on the size, development and equilibrium morphology of dune bedforms of both physical and biological cohesion. Experiments were completed at the Total Environment Simulator facility at Hull University, UK in a 10 x 2 m channel. A flat sediment bed was laid to 0.15 m depth. A unidirectional flow of 0.25 m depth was passed over the sediment for 10 h. In Phase 1 eight different sand:clay mixes were examined, where clay content was 18.0 - 2.1%. In Phase 2, the same mixtures were used with additions of EPS. A velocity of 0.8 m s-1 was used throughout, corresponding to the dune regime for the selected sand. Bedform development was monitored via ultrasonic ranging transducers, sediment cores and water samples. Phase 1 showed substantial differences in bedform type with clay content, with size inversely related to clay content, e.g. Run 1 (18.0% clay) generated 2D ripples; Run 7 (2.1% clay) generated 3D dunes. Transitional forms, included dunes with superimposed ripples, were present between these extremes. In Phase 2, EPS contents equivalent to only 1/30th of 1% by mass prevented the development of bedforms. Bedforms were generated in sediments with 1/20th and 1/10th of 1%, with an inverse relationship between bedform size and EPS content. Comparison of Phase 1 and Phase 2 runs with equal sand:mud ratios reveals that EPS acts to severely inhibit bedform development compared with the mud-only case. We can conclude that (1) the ripple-dune transition can occur under constant flow conditions, i.e. clay content may dictate bedform type, that (2) EPS can severely constrain the development of bedforms, at masses two orders of magnitude smaller than mud, ultimately preventing their development in conditions that would yield dunes in non-cohesive sands and that (3) biological cohesion appears to be greater than physical cohesion at ratios found in natural estuaries. We can conclude that, if the effects of physical and biological cohesion are not included when they are present, predictive models describing bedform growth, morphological equilibrium and migration will be inaccurate and in many cases misleading.

  2. Volcaniclastic dunes from the 2006 deposits of Tungurahua volcano, Ecuador

    NASA Astrophysics Data System (ADS)

    Douillet, G.; Hanson, J. B.; Goldstein, F.; Kueppers, U.; Tsang-Hin-Sun; Bustillos, J.; Robin, C.; Dingwell, D. B.

    2010-12-01

    Tungurahua volcano has been in eruption intermittently since 1999 and showed peaks in activity in 2006, 2008, and 2010. This study focuses on the deposits from August 2006 small volume pyroclastic density currents (PDC). These deposits show two different facies types, due to interaction with topography. A poorly sorted coarse unit of blocks and ash is mainly found within valleys that had confined the PDCs and was driven by gravity, probably traveling partially fluidized. A stratified, coarse depleted, ash unit, up to 5 meters in thickness, is usually found outside the valleys on outer sides of curves, or at changes of topography. The difference in emplacement position shows that inertial forces were more important than gravity forces for the ash unit. Deposition of the coarse depleted unit is caused by a hydraulic jump. The main characteristic feature of the ash unit is the presence of fields of dunes on its surface. Dunes (also referred as sand waves) produced in PDCs have been reported in various places and several types can be characterized. Their length ranges from 1 to several tens of meters for a length/ height ratio (L/H) that is usually in the range of 10 to 20. Grain size varies from fine ash to lapilli sizes. Most volcanic dunes are interpreted as deposited by supercritical flow (antidunes) because of the occurrence of upstream side aggradation and the low angle slopes. However, dunes were sometimes related with high depositional rates because of the occurrence of a climbing structure (Taal volcano). Tungurahua type dunes are atypical. They are much steeper with L/H=5, for length ranging from 1 to 8 meters. Interestingly, the steepest slope is usually the one facing to the vent. The largest dunes have linear transverse shapes, smaller ones also show lunate shapes. Internally, cross stratification is well defined by layers of fine ash alternating with layers of coarse ash. The structure exhibits different patterns, showing aggradation on the downslope, on the upslope, or both sides (climbing dunes). Usually, Tungurahua dunes don't show migration of the entire structure as commonly observed in fluvial or aeolian conditions. Here, stoss side reworking of deposited material by the flow is minor, only the position of the crest is migrating. Two scenarios are possible for the observed features: 1) A very high deposition rate in low wind conditions, leading to climbing structures (high deposition) and steep slopes (low wind). These conditions are in agreement with the presence of a hydraulic jump. 2) The occurrence of a large scale backflow (flowing upslope) due to the detachment of the entire flow from the ground in some places. This latter interpretation explains why the upslope side (thus lee side!) is steeper, the upward crest migration of climbing dunes, and the low L/H ratio, but is more difficult to imagine. From our data set we infer that in both cases the dunes at Tungurahua volcano result from highly depositional conditions but are not antidunes. Experimental and simulational approaches to understanding the deposition of these structures are being developed.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  4. Two-dimensional airflow modeling underpredicts the wind velocity over dunes.

    PubMed

    Michelsen, Britt; Strobl, Severin; Parteli, Eric J R; Pöschel, Thorsten

    2015-01-01

    We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected. PMID:26572966

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

    USGS Publications Warehouse

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

    2009-01-01

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

  6. Marine litter in Mediterranean sandy littorals: Spatial distribution patterns along central Italy coastal dunes.

    PubMed

    Poeta, Gianluca; Battisti, Corrado; Acosta, Alicia T R

    2014-12-15

    Sandy shores are generally considered important sinks for marine litter and the presence of this litter may represent a serious threat to biotic communities and dune integrity mostly due to cleaning activities carried out through mechanical equipment. In spring (April-May) 2012 we sampled 153 2×2m random plots to assess the spatial distribution patterns of litter on Central Italy sandy shores. We analysed the relationship between the presence of litter and coastal dune habitats along the sea-inland gradient. Our results showed that the most frequent litter items were plastic and polystyrene. Differences of marine litter spatial distribution were found between upper beach and fore dune habitats and fixed dune habitats: embryo dune and mobile dune habitats show the highest frequency of litter, but, surprisingly, marine litter did not impact fixed dune habitats, these possibly acting as a natural barrier protecting the inner part of the coast from marine litter dispersion. PMID:25455823

  7. An analysis of the moon's surface using reflected illumination from the earth during a waning crescent lunar phase

    NASA Technical Reports Server (NTRS)

    Hammond, Ernest C., Jr.; Linton-Petza, Maggie

    1989-01-01

    There have been many articles written concerning the lunar after-glow, the spectacular reflection from the moon's surface, and the possible observation of luminescence on the dark side of the moon. The researcher, using a 600 mm cassegrain telescope lense and Kodak 400 ASA T-Max film, photographed the crescent moon whose dark side was clearly visible by the reflected light from earth. The film was digitized to a Perkin-Elmer 1010M microdensitometer for enhancement and enlargement. The resulting pictures indicate a completely different land pattern formation than observed during a full moon. An attempt is made to analyze the observed structures and to compare them to the pictures observed during the normal full moon. There are boundaries on the digitized dark section of the moon that can be identified with structures seen during the normal full moon. But, these variations do change considerably under enhancement.

  8. Morphodynamic-numerical Simulation of River Bars and Dunes

    NASA Astrophysics Data System (ADS)

    Mewis, P.

    2003-04-01

    It is well accepted in Hydromechnics, Meteorology and Oceanography that instabilities are responsible for the generation of turbulence, cyclones and Golf Stream rings. In the morphodynamic behavior several instabilities have been identified that generate ripples, dunes, antidunes, alternate bars and tidal ridges respectively (Callander, Kennedy, Fredsoe, Hulscher a.o.). These can be modelled numericaly using the right set of equations and appropriate numerical schemes. The instabilities predicted mostly by linear stability analysis are simulated fully nonlinear using a numerical model. Problems arise due to a decoupling within the numerical solution of the system of first order partial differential equations resulting in short waves with a length of twice the mesh spacing that grow unbounded. This decoupling badly distorts the physically sound generation of bedforms. It is shown that, like in the case of pressure coupled equations, special care is needed in the numerical formulation of the model. Upwinding techniques are usefull to prevent the decoupling and yield good results. Other methods to cope with the decoupling problem are shown and discussed shortly. The strong influence of commonly applied smoothing techniques including the upwinding on the numerical result is demonstrated. Using a threedimensional hydrostatic flow model, coupled with a morphodynamic module alternate bars and also dunes can be simulated. The morphodynamic-numerical model SMOR is applied to simulate the generation of alternate bars like in Tubinos experiment. The same model is used to simulate scour overdeepening in river curves for the experiment of Odgaard. The generation of dunes is a more complicated mechanism that is nevertheless inherent in threedimensional models. Thus the generation of dunes has been simulated. The shape and dimensions of the dunes seem to be reasonable. The results are compared with observations and discussed. A very simple extension for depth integrated (2D) morphodynamic models to account for secondary flow by the water level gradient is presented. Applying this extention not only in the transverse but also in the streamwise direction leads to the generation of dunes in 2D models.

  9. Sensitivity of the Automatic Determination of Sand Transport Direction and Rate to Dune Morphology (Invited)

    NASA Astrophysics Data System (ADS)

    Scheidt, S. P.; Lancaster, N.

    2010-12-01

    Measurements of rates of dune migration and sand flux are important to understanding the dynamics of aeolian systems, including sand encroachment, desertification, and response to changes in climate. The recent development of the Coregistration of Optically Sensed Images and Correlation (COSI-Corr) algorithm allows a unique remote-sensing approach for measuring dune migration rates. Fast- and slow-moving dunes have been analyzed by previous researchers using the algorithm, but the technique has mostly been tested on simple dune forms, which lack second-order geomorphic features that might cause errors. Our work tested the algorithm’s sensitivity to different dune types and evaluated the performance of the algorithm by making comparisons to previous studies and manual traces of the dunes in a GIS. Different parameters were chosen when applying the COSI-Corr algorithm, which were set according to the expected magnitude of dune displacement and the dune size with respect to image resolution. The dunes under study were chosen from the Namib Desert in locations where dune migration rates had previously been measured. These areas included (1) barchan dunes in Walvis Bay, (2) linear dunes just south of the Kuiseb River and (3) convoys of barchan dunes in the southern Namib. Orthorectified ASTER data from different dates were used to study the incremental and maximal changes between 1967 and 2009. These and other dune areas were studied to understand how varied geographic conditions (e.g.., the presence of coastlines, topography and background surface reflectance) affect the algorithm results. Walvis Bay dune migration vectors indicate rates between 3 and 30 m/yr to the north-northeast, which compares well to the range of previously reported values (2-27 m/yr). Individual dune migration rates between 1961 and 2005 also compared well to distances measured from dune crests in a GIS. Some vectors are overestimated because of interdune albedo effects, resulting from variable soil moisture. Northerly migration of dunes located along barchan convoys in the Southern Namib Desert was determined to be between 9 and 38 m/yr. This compared well to previously published migration rates of ten individually tracked dunes. Migration rate is found to vary with dune size in this area, although the COSI-Corr results have a number of interpretation challenges because of changes in dune shape. Between 2000 and 2006, the overall displacement of small dunes superimposed on linear dunes is between 3-11 m/yr to the north. Interdune displacement vectors in the linear dune area are noisy, which is probably the result of variable vegetation that causes seasonal differences in albedo. The north-south oriented crestline of the linear dunes changes laterally with season by only a few meters, but the magnitude of seasonal crest movement could not be accurately determined due to the error resulting from image spatial resolution; improved results are expected with accurately orthorectified, high spatial resolution imagery of the dunes.

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

    NASA Astrophysics Data System (ADS)

    Bristow, Charlie; Armitage, Simon

    2015-04-01

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

  11. 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, provenance and tectonic history of the sand dunes. Geochemical analysis indicated that most of sand dunes are quartz arenite type, except in the Red sea, basement related central Saudi Arabia and Najran areas, the sand dunes are sub-arkoses, sub-litharenite and litharenite. The concentration of major,trace and rare elements showed active continental margins as a tectonic setting of Red sea, basement related Najran and central Arabia sand dune. In contrast, passive continental margins for the other locations. The distribution of major, trace and rare earth elements showed similarity in chemical composition between basement related sand dunes in Red sea, Najran and central Arabia.

  12. Dynamics of Unusual Debris Flows on Martian Sand Dunes

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  13. Reconstruction d’une Carbonisation du Pouce par Lambeau Chinois

    PubMed Central

    Khales, A.; Achbouk, J.A.; Moussaoui, A.; Belmir, R.; Tourabi, K.; Oufkir, A.; Ihrai, H.

    2010-01-01

    Summary La main en tant qu’organe majeur de la préhension peut être le siège de brûlures graves qui compromettent sa fonction. Bien qu’elle ne représente que 2% de la surface corporelle la brûlure de la main est grave et difficile à traiter, vu la vulnérabilité et la complexité de son appareil locomoteur. Nous rapportons dans ce travail le cas d’un patient victime d’une carbonisation de la main. Huit mois après le parage et la couverture par lambeau inguinal, le patient bénéficie d’une reconstruction du pouce par lambeau chinois associé à une greffe osseuse. Le résultat s’est avéré satisfaisant. Le lambeau chinois prouve par son apport vasculaire et par sa facilité technique qu’il est un moyen très intéressant dans la reconstruction du pouce - ou des doigts en général - surtout dans un contexte de brûlure. PMID:21991226

  14. Soins primaires des personnes victimes d’une lésion médullaire

    PubMed Central

    McColl, Mary Ann; Aiken, Alice; McColl, Alexander; Sakakibara, Brodie; Smith, Karen

    2012-01-01

    Résumé Objectif Effectuer une étude de la portée des données empiriques, entre 1980 et 2009, concernant les soins primaires aux adultes victimes d’une lésion médullaire (LME). Sources des données Une recension dans des revues révisées par des pairs de1980 à 2009 à l’aide de CINAHL, PubMed-MEDLINE, EMBASE, PsycINFO, Social Sciences Abstracts et Social Work Abstracts. Sélection des études La recherche électronique au moyen de mots-clés a permis de cerner 42 articles sur les soins primaires et les LME. Des critères d’inclusion ont servi à réduire la liste à un ensemble de 21 articles publiés en anglais qui portaient sur un échantillon de plus de 3 et présentaient une analyse empirique. Synthèse Environ 90 % des personnes atteintes d’une LME ont identifié leur médecin de famille comme étant leur docteur habituel; 63 % avaient un spécialiste des LME. Les personnes vivant à long terme avec une LME développent des rubriques complexes pour naviguer dans leurs systèmes de soins de santé personnels. Les données scientifiques ne sont pas unanimes quant à l’efficacité des programmes d’intervention directe pour le maintien de la santé et la prévention des complications à la suite d’une LME. Les données appuient cependant le suivi périodique par une équipe spécialisée et un bilan de santé annuel complet. La recherche fait valoir un fort degré d’uniformité dans l’identification des problèmes les plus courants soulevés par les personnes atteintes d’une LME en soins primaires, dont la plupart concernent l’incapacité, plus précisément les complications secondaires, comme la dysfonction intestinale ou vésicale et la douleur. Il existe aussi de bonnes données probantes à l’effet que de nombreux problèmes de santé généraux exigent de l’attention dans une telle population, comme les problèmes de la densité osseuse, la dépression et les questions entourant la santé sexuelle et la reproduction. Il y a des données de niveaux 4 et 5 concernant des besoins en matière de santé non satisfaits qu’ont des personnes victimes d’une LME vivant dans la communauté. En dépit du fait que les patients atteints d’une LME utilisent beaucoup les soins primaires et les services de santé en général, les données scientifiques font valoir que les besoins de renseignements de ces patients en particulier ne sont pas adéquatement satisfaits. Conclusion Un solide système de soins primaires représente la meilleure assurance de bons résultats sur le plan de la santé et d’une utilisation raisonnable des services de santé chez les personnes victimes d’une LME, notamment un bilan de santé annuel complet, un recours approprié aux autres spécialistes et une attention accordée à l’accessibilité et aux besoins insatisfaits.

  15. Comment on ``Minimal size of a barchan dune''

    NASA Astrophysics Data System (ADS)

    Andreotti, B.; Claudin, P.

    2007-12-01

    It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their “minimal size” scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Durán, and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus cannot decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Planet. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500?m) , were formed in the past under very strong winds. We emphasize that this saltating grain size, estimated from thermal diffusion measurements, is far from straightforward. Moreover, the microscopic photographs taken by the rovers on Martian Aeolian bedforms show a grain size of 87±25?m together with hematite spherules at millimeter scale. As those so-called “blueberries” cannot be entrained more frequently than a few hours per century, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli

  16. Comment on "Minimal size of a barchan dune".

    PubMed

    Andreotti, B; Claudin, P

    2007-12-01

    It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their "minimal size" scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Durán, and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus cannot decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Planet. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500 microm), were formed in the past under very strong winds. We emphasize that this saltating grain size, estimated from thermal diffusion measurements, is far from straightforward. Moreover, the microscopic photographs taken by the rovers on Martian Aeolian bedforms show a grain size of 87+/-25 microm together with hematite spherules at millimeter scale. As those so-called "blueberries" cannot be entrained more frequently than a few hours per century, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli. PMID:18233886

  17. Comment on "Minimal size of a barchan dune"

    E-print Network

    B. Andreotti; P. Claudin

    2007-05-24

    It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their `minimal size' scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Duran and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus can not decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Pla. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500 micrometers), were formed in the past under very strong winds. We show that this saltating grain size, estimated from thermal diffusion measurements, is not reliable. Moreover, the microscopic photographs taken by the rovers on Martian aeolian bedforms show a grain size of 87 plus or minus 25 micrometers together with hematite spherules at millimetre scale. As those so-called ``blueberries'' can not be entrained by reasonable winds, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli et al.

  18. Evidence for sensitivity of dune wetlands to groundwater nutrients.

    PubMed

    Rhymes, Jennifer; Wallace, Hilary; Fenner, Nathalie; Jones, Laurence

    2014-08-15

    Dune slacks are seasonal wetlands, high in biodiversity, which experience considerable within-year and between-year variations in water-table. They are subject to many pressures including climate change, land use change and eutrophication. Despite their biological importance and the threats facing them, the hydrological and nutrient parameters that influence their soil properties and biodiversity are poorly understood and there have been no empirical studies to date testing for biological effects in dune systems resulting from groundwater nutrients at low concentrations. In this study we examined the impact of groundwater nutrients on water chemistry, soil chemistry and vegetation composition of dune slacks at three distance classes (0-150 m, 150-300 m, 300-450 m) away from known (off-site) nutrient sources at Aberffraw dunes in North Wales, whilst accounting for differences in water-table regime. Groundwater nitrate and dissolved inorganic nitrogen (DIN) and soil nitrate and nitrite all had significantly higher concentrations closest to the nutrient source. Multivariate analysis showed that although plant species composition within this site was primarily controlled by water table depth and water table fluctuation, nitrogen from groundwater also influenced species composition, independently of water table and soil development. A model containing all hydrological parameters explained 17% of the total species variance; an additional 7% was explained following the addition of NO3 to this model. Areas exposed to elevated, but still relatively low, groundwater nutrient concentrations (mean 0.204 mg/L+/-0.091 of DIN) had greater abundance of nitrophilous species and fewer basipholous species than in areas with lower concentrations. This shows that clear biological impact occurs below previously suggested DIN thresholds of 0.20-0.40 (mg/L). PMID:24846404

  19. 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.

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

    PubMed

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

    2015-02-15

    Land surface emissivity (LSE) in the thermal infrared depends mainly on the ground cover and on changes in soil moisture. The LSE is a critical variable that affects the prediction accuracy of geophysical models requiring land surface temperature as an input, highlighting the need for an accurate derivation of LSE. The primary aim of this study was to test the hypothesis that diurnal changes in emissivity, as detected from space, are larger for areas mostly covered by biocrusts (composed mainly of cyanobacteria) than for bare sand areas. The LSE dynamics were monitored from geostationary orbit by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) over a sand dune field in a coastal desert region extending across both sides of the Israel-Egypt political borderline. Different land-use practices by the two countries have resulted in exposed, active sand dunes on the Egyptian side (Sinai), and dunes stabilized by biocrusts on the Israeli side (Negev). Since biocrusts adsorb more moisture from the atmosphere than bare sand does, and LSE is affected by the soil moisture, diurnal fluctuations in LSE were larger for the crusted dunes in the 8.7 ?m channel. This phenomenon is attributed to water vapor adsorption by the sand/biocrust particles. The results indicate that LSE is sensitive to minor changes in soil water content caused by water vapor adsorption and can, therefore, serve as a tool for quantifying this effect, which has a large spatial impact. As biocrusts cover vast regions in deserts worldwide, this discovery has repercussions for LSE estimations in deserts around the globe, and these LSE variations can potentially have considerable effects on geophysical models from local to regional scales. PMID:25437760

  1. The focal plane instrumentation for the DUNE mission

    E-print Network

    Jeff Booth; Mark Cropper; Frank Eisenhauer; Alexandre Refregier; the DUNE collaboration

    2008-07-25

    DUNE (Dark Universe Explorer) is a proposed mission to measure parameters of dark energy using weak gravitational lensing The particular challenges of both optical and infrared focal planes and the DUNE baseline solution is discussed. The DUNE visible Focal Plane Array (VFP) consists of 36 large format red-sensitive CCDs, arranged in a 9x4 array together with the associated mechanical support structure and electronics processing chains. Four additional CCDs dedicated to attitude control measurements are located at the edge of the array. All CCDs are 4096 pixel red-enhanced e2v CCD203-82 devices with square 12 $\\mu$m pixels, operating from 550-920nm. Combining four rows of CCDs provides a total exposure time of 1500s. The VFP will be used in a closed-loop system by the spacecraft, which operates in a drift scan mode, in order to synchronize the scan and readout rates. The Near Infrared (NIR) FPA consists of a 5 x 12 mosaic of 60 Hawaii 2RG detector arrays from Teledyne, NIR bandpass filters for the wavelength bands Y, J, and H, the mechanical support structure, and the detector readout and signal processing electronics. The FPA is operated at a maximum temperature of 140 K for low dark current of 0.02e$-$/s. Each sensor chip assembly has 2048 x 2048 square pixels of 18 $\\mu$m size (0.15 arcsec), sensitive in the 0.8 to 1.7 $\\mu$m wavelength range. As the spacecraft is scanning the sky, the image motion on the NIR FPA is stabilized by a de-scanning mirror during the integration time of 300 s per detector. The total integration time of 1500 seconds is split among the three NIR wavelengths bands. DUNE has been proposed to ESA's Cosmic Vision program and has been jointly selected with SPACE for an ESA Assessment Phase which has led to the joint Euclid mission concept.

  2. Defrosting Polar Dunes--Dark Spots and Wind Streaks

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The first time that the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC)team saw dark spots on defrosting dune surfaces was in August and September of 1998. At that time, it was the north polar seasonal frost cap that was subliming away (more recent images from 1999 have shown the south polar frosts). This picture (above) shows a small portion of the giant dune field that surrounds the north polar region, as it appeared on August 23, 1998. At the time, it was early northern spring and the dunes were still covered with winter frost.

    Dark spots had appeared on the north polar dunes, and many of them exhibited a radial or semi-radial pattern of dark streaks and streamers. At first, there was speculation that the streaks indicated that the defrosting process might somehow involve explosions! The dark spots seemed to resemble small craters with dark, radial ejecta. It seemed possible that frozen carbon dioxide trapped beneath water ice might somehow heat up, turn to gas, expand, and then 'explode' in either a small blast or at least a 'puff' of air similar to that which comes from the blowhole of a surfacing whale or seal.

    The image shown here changed the earlier impression. The dark spots and streaks do not result from explosions. The spots--though not well understood--represent the earliest stages of defrosting on the sand dunes. The streaks, instead of being caused by small explosions, are instead the result of wind. In this picture, the fine, dark streaks show essentially identical orientations from spot to spot (e.g., compare the spots seen in boxes (a) and (b)). Each ray of dark material must result from wind blowing from a particular direction--for example, all of the spots in this picture exhibit a ray that points toward the upper left corner of the image, and each of these rays indicates the same wind regime. Each spot also has a ray pointing toward the lower right and top/upper-right. These, too, must indicate periods when the wind was strong enough to move materials, consistently, in only one direction.

    The sand that makes up the north polar dunes is dark. Each spot and streak is composed of the dune sand. The bright surfaces are all covered with frost. This picture is located near 76.9oN, 271.2oW, in the north polar sand sea. Illumination is from the lower left. The 200 meter scale also indicates a distance of 656 feet.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  3. Spatial and temporal variations in the sediment state of North American dune fields

    NASA Astrophysics Data System (ADS)

    Halfen, Alan F.; Lancaster, Nicholas; Wolfe, Stephen

    2015-04-01

    This research evaluates geomorphic and chronologic data from the INQUA Dune Atlas for three areas of North America: 1) the Prairie, Parkland and 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. Chronometric data for periods of dune activity and stability are compared with palaeoenvironment reconstructions to assess dune system response to changes in sediment supply, availability, and mobility. Dune fields in the northern Great Plains were formed 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. In the Central Great Plains, many dune fields are closely linked to fluvial sediment sources. Sediment supply was high in these dune fields 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 short but repeated intervals during the late Holocene. Despite spatial and temporal gaps in chronometric data, 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, being the primary driver of dune activity during the Holocene.

  4. Constructing notches in foredunes: Effect on sediment dynamics in the dune hinterland

    NASA Astrophysics Data System (ADS)

    Riksen, Michel J. P. M.; Goossens, Dirk; Huiskes, Hendrik P. J.; Krol, Johan; Slim, Pieter A.

    2016-01-01

    Measurements were carried out on the island of Ameland (The Netherlands) to determine whether notches cut into foredunes stimulated the supply of fresh calcareous beach and dune sand into the white and grey dune habitats behind the dunes, increasing these habitats' biological quality. Sediment characteristics and dynamics (deposition flux and grain size properties) as well as aspects of the vegetation (occurrence, composition and cover density) were studied along six transects, three behind an intact foredune and three behind a foredune with a notch cut into it. Compared to an intact foredune, the notched foredune exhibited higher deposition and accumulation behind the dune. The extra supply of sand was small, however, and for the notches studied, limited to the zone within approximately 50-60 m of the foredune's crest. Farther away from the dune, the effect of the notches became negligible. The presence of a notch did affect the grain size composition of sediment deposited behind the foredune. For intact foredunes, the grain size composition behind the dune was similar to that on the dune itself. When a notch had been cut, the sediment was finer behind the foredune, gradually coarsening away from the dune. Sand spray (deposition of sand eroded from the dune and transported in modified saltation during heavy winds) explains these granulometric results. The effect of the notches on the vegetation in the grey dune habitat behind the foredune was small and, for the notches studied, limited to the first approximately 35 m of the grey dune area, between 30 and 65 m from the foredune's crest. The notches had a greater effect on the white dune habitat but - in the opinion of the authors - this remained disproportionately small relative to the effort required for notch excavation and maintenance.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  7. Ripple migration and dune activity on Mars: Evidence for dynamic wind processes

    NASA Astrophysics Data System (ADS)

    Silvestro, S.; Fenton, L. K.; Vaz, D. A.; Bridges, N. T.; Ori, G. G.

    2010-10-01

    In this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in Nili Patera on Mars. The measured average migration of ˜1.7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area. In addition, we document widespread changes in the dune base-ground surface contact and in the slip face structures, showing that not only the ripples, but the whole dunes are actually migrating in the present-day atmospheric setting. These results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on Mars may also be active.

  8. Two independent dune growth mechanisms: from laboratory to landscape-scale experiments

    NASA Astrophysics Data System (ADS)

    Narteau, Clement; Ping, Lv; Courrech Du Pont, Sylvain; Dong, Zhibao; Cascales-Fernandez, Laura; Rodriguez, Sébatien

    2015-04-01

    Using laboratory subaqueous experiments, we show that a single bidirectional flow regime can lead to two different dune orientations depending on sediment availability. The erodibility of the bed selects the overriding mechanism for the formation of dunes. Then, dunes may either (1) increase in height from the destabilization of a sand bed with no restriction in sediment availability or (2) grow by extension away from a localized sand source in zones of low sand availability. These results are used to develop a new set of landscape-scale experiments in the Tengger desert (Inner Mongolia, China). Exposed to bimodal winds, this site is unique because it allows multiparametric analysis of dune morphodynamics in a natural environment (16 hectares) under well-controlled initial and boundary conditions. The orientation of dunes as a function of the wind regime and the coupling between flow and topography are currently investigated in three experiments that provide empirical support for the coexistence of two independent dune growth mechanisms. In both laboratory and landscape scale experiments, we find that dunes that are transport-limited select an orientation that maximizes the normal to crest components of transport. In zones of limited sand supply, dunes elongate in the direction of the resultant sand flux at the crest. We show how these results can be used to quantitatively predicts the orientation of primary and secondary dune patterns in modern terrestrial sand seas but also on Mars and Titan.

  9. Dunes on Saturn’s moon Titan as revealed by the Cassini Mission

    NASA Astrophysics Data System (ADS)

    Radebaugh, Jani

    2013-12-01

    Dunes on Titan, a dominant landform comprising at least 15% of the surface, represent the end product of many physical processes acting in alien conditions. Winds in a nitrogen-rich atmosphere with Earth-like pressure transport sand that is likely to have been derived from complex organics produced in the atmosphere. These sands then accumulate into large, planet-encircling sand seas concentrated near the equator. Dunes on Titan are predominantly linear and similar in size and form to the large linear dunes of the Namib, Arabian and Saharan sand seas. They likely formed from wide bimodal winds and appear to undergo average sand transport to the east. Their singular form across the satellite indicates Titan’s dunes may be highly mature, and may reside in a condition of stability that permitted their growth and evolution over long time scales. The dunes are among the youngest surface features, as even river channels do not cut through them. However, reorganization time scales of large linear dunes on Titan are likely tens of thousands of years. Thus, Titan’s dune forms may be long-lived and yet be actively undergoing sand transport. This work is a summary of research on dunes on Titan after the Cassini Prime and Equinox Missions (2004-2010) and now during the Solstice Mission (to end in 2017). It discusses results of Cassini data analysis and modeling of conditions on Titan and it draws comparisons with observations and models of linear dune formation and evolution on Earth.

  10. Hydrogeology and hydrochemistry of dunes and wetlands along the southern shore of Lake Michigan, Indiana

    USGS Publications Warehouse

    Shedlock, Robert J.; Cohen, D.A.; Imbrigiotta, T.E.; Thompson, T.A.

    1994-01-01

    The dunes and the wetlands along the southern shore of Lake Michigan are underlain by a complex aquifer system composed of unconsolidated glacial, lacustrine, and eolian deposits. Surficial dune, beach, and glacial lacustrine sands compose an extensive surficial aquifer. The underlying drift contains three major confined sand aquifers. Potentiometric and hydrochemical data are consistent with a conceptual model in which regional and intermediate flow systems, recharged in end moraines south of the dune-beach complexes, discharge into Lake Michigan and the Great Marsh by upward leakage through unconsolidated sediments. Local flow systems in the surficial aquifer, recharged in the major dune-beach complexes, discharge into streams, ditches, and ponded areas in the adjacent interdunal wetlands. Shallow ground water discharges directly into Lake Michigan only north of a water-table divide that underlies the dune-beach complex along the shoreline. The position of ground-water seepage faces is affected by transient water-table mounds observed in the dune-beach complexes at the margins of wetlands. Substantial recharge to the dune complexes probably occurs near these dune-wetland margins. In the dune-beach complexes and intradunal wetlands, the shallow ground and wetland waters are dilute calcium bicarbonate and calcium bicarbonate sulfate types. More mineralized bicarbonate water types having variable proportions of calcium, magnesium, and sodium are found in interior parts of the Great Marsh because this area is probably a discharge zone for the regional and intermediate flow systems.

  11. Temporal variation of soil seed banks in two different dune systems in northeastern Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Yan, Q. L.; Liu, Z. M.; Zhu, J. J.

    2009-08-01

    To assess the potential contribution of soil seed banks to seedling recruitment, and to the vegetative processes of dune systems in semi-arid areas, a comparison of temporal variation in soil seed bank was made between active and stabilized dune systems in northeastern Inner Mongolia, China. The results showed that between-year difference in seed density for the stabilized system was smaller than that for the active one, but there were similar variations with season in seed bank for both dune systems. Furthermore, seed densities of the dominant species on the respective dune type (i.e., annuals on the stabilized dune and psammophytes on the active dune) varied more sharply with season, but more gently in annual variation than those of other phytogroups. These findings suggest that (1) seeds of annuals in the soil of the stabilized dune, or seeds of psammophytes in the soil of the active dune contributed much to seedling recruitment or plant species colonization, (2) the relationship between soil seed bank and seedling recruitment was complex in both dune systems.

  12. 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.

  13. A second look at western Sinai seif dunes and their lateral migration

    USGS Publications Warehouse

    Rubin, D.M.; Tsoar, H.; Blumberg, D.G.

    2008-01-01

    Tsoar et al. [Tsoar, H., Blumberg, D.G., Stoler, Y., 2004. Elongation and migration of sand dunes. Geomorphology 57, 293-302.] reported that seif dunes in the western Sinai Desert did not migrate laterally between 1973 and 1999. If the planform sinuosities of the dunes are removed by filtering, spatial averaging, or linear regression, however, it is evident that the dunes did, in fact, migrate laterally roughly 13??m during this 26-year period. The measured migration distance is 1-2 orders of magnitude greater than the rms co-registration error Tsoar et al. determined for the first and last air photos that were used to map the dunes. The western Sinai dunes provide another example demonstrating that linear dunes can migrate laterally, and they illustrate some of the difficulties in documenting systematic lateral motion. Lateral migration of a dune can be important geologically or geomorphologically, even where migration is too slow to detect from repeated topographic surveys. This article explains the wind conditions for the lateral migration of seif dunes in western Sinai and the possible wind occurrences that would not lead to such a migration.

  14. A second look at western Sinai seif dunes and their lateral migration

    NASA Astrophysics Data System (ADS)

    Rubin, David M.; Tsoar, Haim; Blumberg, Dan G.

    2008-01-01

    Tsoar et al. [Tsoar, H., Blumberg, D.G., Stoler, Y., 2004. Elongation and migration of sand dunes. Geomorphology 57, 293-302.] reported that seif dunes in the western Sinai Desert did not migrate laterally between 1973 and 1999. If the planform sinuosities of the dunes are removed by filtering, spatial averaging, or linear regression, however, it is evident that the dunes did, in fact, migrate laterally roughly 13 m during this 26-year period. The measured migration distance is 1-2 orders of magnitude greater than the rms co-registration error Tsoar et al. determined for the first and last air photos that were used to map the dunes. The western Sinai dunes provide another example demonstrating that linear dunes can migrate laterally, and they illustrate some of the difficulties in documenting systematic lateral motion. Lateral migration of a dune can be important geologically or geomorphologically, even where migration is too slow to detect from repeated topographic surveys. This article explains the wind conditions for the lateral migration of seif dunes in western Sinai and the possible wind occurrences that would not lead to such a migration.

  15. Functional Traits Differ between Cereal Crop Progenitors and Other Wild Grasses Gathered in the Neolithic Fertile Crescent

    PubMed Central

    Cunniff, Jennifer; Wilkinson, Sarah; Charles, Michael; Jones, Glynis; Rees, Mark; Osborne, Colin P.

    2014-01-01

    The reasons why some plant species were selected as crops and others were abandoned during the Neolithic emergence of agriculture are poorly understood. We tested the hypothesis that the traits of Fertile Crescent crop progenitors were advantageous in the fertile, disturbed habitats surrounding early settlements and in cultivated fields. We screened functional traits related to competition and disturbance in a group of grass species that were increasingly exploited by early plant gatherers, and that were later domesticated (crop progenitors); and in a set of grass species for which there is archaeological evidence of gathering, but which were never domesticated (wild species). We hypothesised that crop progenitors would have greater seed mass, growth rate, height and yield than wild species, as these traits are indicative of greater competitive ability, and that crop progenitors would be more resilient to defoliation. Our results show that crop progenitors have larger seed mass than wild species, germinate faster and have greater seedling size. Increased seed size is weakly but positively correlated with a higher growth rate, which is primarily driven by greater biomass assimilation per unit leaf area. Crop progenitors also tend to have a taller stature, greater grain yield and higher resilience to defoliation. Collectively, the data are consistent with the hypothesis that adaptations to competition and disturbance gave crop progenitors a selective advantage in the areas surrounding early human settlements and in cultivated environments, leading to their adoption as crops through processes of unconscious selection. PMID:24489941

  16. Natural versus Urban dunes along the Emilia-Romagna coast, Northern Adriatic (Italy)

    NASA Astrophysics Data System (ADS)

    Corbau, Corinne; Simeoni, Umberto

    2014-05-01

    Beach-dune interaction models can be precious tools for land managers and policymakers. However, if the models are inaccurate, land use policies may be designed based on false pretences or assumptions leading to poor land management, long-term erosion and sustainability issues, and increased difficulties in maintaining the dynamic coastal systems. From the literature, it appears that even the most reliable beach-dunes interactions models are not applicable to all coastal systems (Short and Hesp, 1982; Psuty, 1988; Sherman and Bauer, 1993). The study aims to identify the morphological evolution of the Emilia-Romagna coastal dunes according to its natural and "human" characteristics and to classify groups of dunes with similar evolutionary patterns. The coastal area consists essentially of 130 km of low sandy coast, interrupted by vast lagoon areas, harbor jetties and numerous hard coastal defense structures that were built during the first half of the 20th century to protect the Emilia-Romagna coast against erosion. Today about 57% of the littoral is protected by hard defenses, which have modified the morphodynamic characteristics of the beach without inverting the negative coastal evolution's trend. From recent aerial photographs (2011), 62 coastal dunes have been identified and mapped. Furthermore, the dune analysis shows a variability of the "physical characteristics" of coastal-dune systems along the Emilia-Romagna coast. The dune height varies from 1 to 7 meters, the width of the beach and of the active dunes range respectively from 10 to 150 m and from 10 to 65 m. Three main factors may explain the variability of the "physical characteristics": 1- Firstly the frontal dunes may be of different states according to the classification of Hesp (2002) since they correspond to incipient foredunes, well-developed foredunes, blowouts, residual foredunes as well as reactivated relict foredunes, 2- This could also be related to a different orientation of the coastline and foredune's line to the dominant onshore winds and, 3- Human impacts may also explain this variability since most of the dune-beach systems of Emilia-Romagna are characterized by important anthropogenic features that do not adequately describe beach-foredune interactions. A factor analysis of the coastal dunes has allowed formulating hypotheses about their evolutionary trends according to the importance and interference of factors, both natural and anthropic, acting on the beach-dune system. Four groups of dunes have been identified corresponding to natural dunes, semi-anthropic dunes with major natural features, semi-anthropic dunes with major anthropic feature and "urban" dunes. Furthermore, while human activities impede the formation and development of new incipient dunes, other human activities favor the conservation and development of the human-altered foredunes. Hesp, P., 2002: Foredunes and blowouts: initiation, geomorphology and dynamics, Geomorphology, 245-268. Psuty, N. P. 1988. Sediment budget and dune/beach interaction. Journal of Coastal Research Special Issue 3: 1-4. Sherman, D. J., and B. O. Bauer. 1993. Dynamics of beach-dune systems. Progress in Physical Geography 17 (4): 413-447 Short, A. D., and P. A. Hesp. 1982. Wave, beach and dune interactions in South Eastern Australia. Marine Geology 48: 259-284.

  17. Constraints on coastal dune invasion for a notorious plant invader.

    PubMed

    Griffith, Alden B; Ahmed, Tania; Hildner, Abigail L G; Kuckreja, Shivani; Long, Shuangxou

    2015-01-01

    Although most biological invasions are not successful, relatively few studies have examined otherwise notorious invaders in systems where they are not highly problematic. The annual grass Bromus tectorum is a dominant invader in western North America, but is usually confined to human-dominated and disturbed systems (e.g. roadsides and parking lots) in the East where it remains virtually unstudied. This study aims to address fundamental ecological questions regarding B. tectorum in a Cape Cod dune ecosystem. (i) What is the range of variation in population dynamics and the potential for population growth? (ii) Which factors influence its local abundance and distribution? We observed substantial variation in population dynamics over 3 years, with the number of adult B. tectorum individuals increasing substantially between the first 2 years (? = 9.24) and then decreasing (? = 0.43). Population growth in terms of total seeds was similarly variable, but to a lesser extent (? = 2.32 followed by ? = 0.32). Experimental soil disturbance led to a more than 10-fold increase in mean seedling emergence, and high sensitivity to differences in emergence carried this effect through the life cycle. In contrast, barriers to seed dispersal had no effect on population dynamics, suggesting limited dispersal in this system. Across the landscape, the presence of B. tectorum was associated with areas of higher plant diversity as opposed to those with a strong dominant (e.g. the foredune, dominated by Ammophila breviligulata, or low heathlands, characterized by Hudsonia tomentosa and Arctostaphylos uva-ursi). Overall, we find that B. tectorum is capable of both substantial population growth and decline in a dune ecosystem, but is likely limited without disturbance and dispersal agents. Thus, management actions that restrict dune access (e.g. for nesting habitat) likely have the co-benefit of limiting the invasive potential of B. tectorum. PMID:26558705

  18. Constraints on coastal dune invasion for a notorious plant invader

    PubMed Central

    Griffith, Alden B.; Ahmed, Tania; Hildner, Abigail L. G.; Kuckreja, Shivani; Long, Shuangxou

    2015-01-01

    Although most biological invasions are not successful, relatively few studies have examined otherwise notorious invaders in systems where they are not highly problematic. The annual grass Bromus tectorum is a dominant invader in western North America, but is usually confined to human-dominated and disturbed systems (e.g. roadsides and parking lots) in the East where it remains virtually unstudied. This study aims to address fundamental ecological questions regarding B. tectorum in a Cape Cod dune ecosystem. (i) What is the range of variation in population dynamics and the potential for population growth? (ii) Which factors influence its local abundance and distribution? We observed substantial variation in population dynamics over 3 years, with the number of adult B. tectorum individuals increasing substantially between the first 2 years (? = 9.24) and then decreasing (? = 0.43). Population growth in terms of total seeds was similarly variable, but to a lesser extent (? = 2.32 followed by ? = 0.32). Experimental soil disturbance led to a more than 10-fold increase in mean seedling emergence, and high sensitivity to differences in emergence carried this effect through the life cycle. In contrast, barriers to seed dispersal had no effect on population dynamics, suggesting limited dispersal in this system. Across the landscape, the presence of B. tectorum was associated with areas of higher plant diversity as opposed to those with a strong dominant (e.g. the foredune, dominated by Ammophila breviligulata, or low heathlands, characterized by Hudsonia tomentosa and Arctostaphylos uva-ursi). Overall, we find that B. tectorum is capable of both substantial population growth and decline in a dune ecosystem, but is likely limited without disturbance and dispersal agents. Thus, management actions that restrict dune access (e.g. for nesting habitat) likely have the co-benefit of limiting the invasive potential of B. tectorum. PMID:26558705

  19. Post-storm beach and dune recovery: Implications for barrier island resilience

    NASA Astrophysics Data System (ADS)

    Houser, Chris; Wernette, Phil; Rentschlar, Elizabeth; Jones, Hannah; Hammond, Brianna; Trimble, Sarah

    2015-04-01

    The ability of beaches and dunes to recover following an extreme storm is a primary control of barrier island response to sea-level rise and changes in the frequency and/or magnitude of storm surges. Whereas erosion of the beach and dune occurs over hours and days, it can be years to decades before the beach and dune are able to recover to their pre-storm state. As a consequence, there are numerous descriptions of near-instantaneous beach and dune erosion due to storms, the immediate onshore transport of sand, and the initial phases of beach and dune recovery following a storm, but a paucity of data on long-term beach and dune recovery. A combination of previously published data from Galveston Island, Texas and new remotely sensed data from Santa Rosa Island, Florida is used in the present study to quantify the rate of dune recovery for dissipative and intermediate beach types, respectively. Recovery of the dune height and volume on Galveston Island was observed within two years following Hurricane Alicia (1983) and was largely complete within six years of the storm, despite extensive washover. In contrast, the dunes on Santa Rosa Island in Northwest Florida began to recover four years after Hurricane Ivan (2004), and only after the profile approached its pre-storm level and the rate of vegetation recovery (regrowth) was at a maximum. Results show that complete recovery of the largest dunes (in height and volume) will take approximately 10 years on Santa Rosa Island, which suggests that these sections of the island are particularly vulnerable to significant change in island morphology if there is also a change in the frequency and magnitude of storm events. In contrast, the areas of the island with the smallest dunes before Hurricane Ivan exhibited a rapid recovery, but no further growth in profile volume and dune height beyond the pre-storm volume and height, despite continued recovery of the largest dunes to their pre-storm height. A change in storm magnitude and/or frequency is a potential threat to barrier island resilience, particularly for those sections of the island where dune recovery has historically taken the longest time. Further study is required to determine how and why dune recovery varies for the dissipative and intermediate beaches of Galveston Island and Santa Rosa Island, respectively.

  20. Late Quaternary stratigraphy and geochronology of the western Killpecker Dunes, Wyoming, USA

    USGS Publications Warehouse

    Mayer, J.H.; Mahan, S.A.

    2004-01-01

    New stratigraphic and geochronologic data from the Killpecker Dunes in southwestern Wyoming facilitate a more precise understanding of the dune field's history. Prior investigations suggested that evidence for late Pleistocene eolian activity in the dune field was lacking. However, luminescence ages from eolian sand of ???15,000 yr, as well as Folsom (12,950-11,950 cal yr B.P.) and Agate Basin (12,600-10,700 cal yr) artifacts overlying eolian sand, indicate the dune field existed at least during the latest Pleistocene, with initial eolian sedimentation probably occurring under a dry periglacial climate. The period between ???13,000 and 8900 cal yr B.P. was characterized by relatively slow eolian sedimentation concomitant with soil formation. Erosion occurred between ???8182 and 6600 cal yr B.P. on the upwind region of the dune field, followed by relative stability and soil formation between ???5900 and 2700 cal yr B.P. The first of at least two latest Holocene episodes of eolian sedimentation occurred between ???2000 and 1500 yr, followed by a brief (???500 yr) episode of soil formation; a second episode of sedimentation, occurring by at least ???700 yr, may coincide with a hypothesized Medieval warm period. Recent stabilization of the western Killpecker Dunes likely occurred during the Little Ice Age (???350-100 yr B.P.). The eolian chronology of the western Killpecker Dunes correlates reasonably well with those of other major dune fields in the Wyoming Basin, suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late Quaternary. Similar to dune fields on the central Great Plains, dune fields in the Wyoming Basin have been active under a periglacial climate during the late Pleistocene, as well as under near-modern conditions during the latest Holocene. ?? 2003 University of Washington. All rights reserved.

  1. Iron mineralogy and bioaccessibility of dust generated from soils as determined by reflectance spectroscopy and magnetic and chemical properties--Nellis Dunes recreational area, Nevada

    USGS Publications Warehouse

    Goldstein, Harland L.; Reynolds, Richard L.; Morman, Suzette A.; Moskowitz, Bruce; Kokaly, Raymond F.; Goossens, Dirk; Buck, Brenda J.; Flagg, Cody; Till, Jessica; Yauk, Kimberly; Berquó, Thelma S.

    2013-01-01

    Atmospheric mineral dust exerts many important effects on the Earth system, such as atmospheric temperatures, marine productivity, and melting of snow and ice. Mineral dust also can have detrimental effects on human health through respiration of very small particles and the leaching of metals in various organs. These effects can be better understood through characterization of the physical and chemical properties of dust, including certain iron oxide minerals, for their extraordinary radiative properties and possible effects on lung inflammation. Studies of dust from the Nellis Dunes recreation area near Las Vegas, Nevada, focus on characteristics of radiative properties (capacity of dust to absorb solar radiation), iron oxide mineral type and size, chemistry, and bioaccessibility of metals in fluids that simulate human gastric, lung, and phagolysosomal fluids. In samples of dust from the Nellis Dunes recreation area with median grain sizes of 2.4, 3.1, and 4.3 micrometers, the ferric oxide minerals goethite and hematite, at least some of it nanosized, were identified. In one sample, in vitro bioaccessibility experiments revealed high bioaccessibility of arsenic in all three biofluids and higher leachate concentration and bioaccessibility for copper, uranium, and vanadium in the simulated lung fluid than in the phagolysosomal fluid. The combination of methods used here to characterize mineral dust at the Nellis Dunes recreation area can be applied to global dust and broad issues of public health.

  2. Evaluating Aeolian Sand Transport Vectors In Dune Blowouts 

    E-print Network

    Randolph, Janelle

    2013-02-13

    National Seashore The dune blowout system specific to this study is a trough-shaped blowout, which Cooper (1958) described as one of the two major categories of blowout types. The trough blowout is more elongated than the saucer blowout and has longer...-shaped blowouts. However, extensive research of saucer-shaped blowouts has identified characteristics of wind movement and transport. Gares and Nordstrom (1987) found wind speeds were lowest in a small saucer-shaped blowout base and highest on the upwind...

  3. Visualization of Marine Sand Dune Displacements Utilizing Modern Gpu Techniques

    NASA Astrophysics Data System (ADS)

    Gierlinger, T.; Brodtkorb, A. R.; Stumpf, A.; Weiler, M.; Michel, F.

    2015-08-01

    Quantifying and visualizing deformation and material fluxes is an indispensable tool for many geoscientific applications at different scales comprising for example global convective models (Burstedde et al., 2013), co-seismic slip (Leprince et al., 2007) or local slope deformation (Stumpf et al., 2014b). Within the European project IQmulus (http://www.iqmulus.eu) a special focus is laid on the efficient detection and visualization of submarine sand dune displacements. In this paper we present our approaches on the visualization of the calculated displacements utilizing modern GPU techniques to enable the user to interactively analyze intermediate and final results within the whole workflow.

  4. Interdune areas of the back-island dune field, North Padre Island, Texas

    NASA Astrophysics Data System (ADS)

    Hummel, Gary; Kocurek, Gary

    1984-04-01

    The small, young (about 100 yrs) back-island dune field on north Padre Island, south Texas, consists of fairly persistant oblique dunes (up to 6 m high) with well-developed interdune areas that grade northwestward to small, ephemeral transverse and barchan dunes with interconnected "interdune" areas, thence sheet sand areas. The subhumid climate is marked by rain associated with frontal systems and tropical storms. Winds are seasonally bimodal—prevailing southeasterly are punctuated by northerly and northwesterly winds with the passage of frontal systems in winter. The entire dune field and individual oblique dunes show a net migration of about 15 m yr -1 to the northwest. The dunes however are on a seasonally reversing track, changing their slipface direction and migration direction with frontal systems. One year of monitoring shows sand transport in the dune-interdune system to be complex and cyclic. During the wind reversals of winter, dunes are very ineffecfive sand traps owing to loss of flow separation, and much sand is lost to the interdune areas. Interdune areas store sand during these wet winter months as a result of the wind reversals and higher moisture content. During the summer, the interdune areas deflate and the dunes build in size. The overall dune field deposit appears to consist of three laterally contiguous zones from southeast to northwest: (1) continuous, climbing oblique dune and interdune deposits; (2) discontinuous lenses of dune sand in overall "interdune layers"; and (3) a chaotic mixture of dune and horizontal deposits of the sheet sand areas. One year's mapping and trenching documents that interdune sedimentary structures are extremely variable laterally and vertically reflecting specific microenvironments within the interdune flat. Wet-surface features consist of current and wave ripples, channel fill, miniature deltas, wrinkle marks, mini-ripples, rills, algae and sand volcanoes. Abundant adhesion structures, rain-impacted ripples, brecciated surfaces and microtopography reflect damp-surface deposits. Dry-surface features are predominately wind ripples; others include small isolated barchan and shadow dunes, organic debris lag surfaces, deflation scours, beetle bioturbation, plant-root structures associated with shadow-dunes, and grainfall from the adjacent dunes. Interdune deposits account for about 40% of the total dune field deposits, which seems reasonable compared to some ancient examples. By virtue of occupying a relative "basin", interdune deposits are selectively preserved compared to dune deposits. In general, interdune sedimentation is enhanced by non-eolian depositional mechanisms, a high water table, early evaporatic cements, and a variable wind regime. The actual thicknesses of individual dune and interdune deposits are less on Padre than ancient examples, reflecting the relative scale of the bedforms. In many respects, sequences of sedimentary structure in Padre Island interdune deposits are typical of ancient, coastal interdune strata, but some marked departures occur. Adhesion structures, relatively rare in some ancient examples but abundant within Padre interdune deposits, seem favored by the small size of dune and interdune area, the climate and a variable wind regime. Penecontemporaneous deformation, absent in Padre interdune deposits but pronounced in some ancient examples, probably reflects dune size and the nature of the deposits. Wavy laminae in ancient interdune deposits probably result from many causes, but seem best represented by modern examples of evaporitic algal/bacterial-formed structures.

  5. The Effect of Vegetation Density on the Resilience of Coastal Dune Systems Against Wave-Induced Erosion 

    E-print Network

    Tyler, Robert Cory

    2013-09-28

    by coastal managers and stakeholders. Dunes with healthy vegetation growth are believed to provide an even higher resilience against wave-induced erosion. However, very little research currently exists on quantifying the effect that plants have on dune...

  6. 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

  7. Reply to "Comment on `Minimal size of a barchan dune' " E. J. R. Parteli,1

    E-print Network

    Claudin, Philippe

    Reply to "Comment on `Minimal size of a barchan dune' " E. J. R. Parteli,1 O. Durán,2 and H. J of the minimal size of barchan dunes. This model, which consists of a coupled set of equations for the wind

  8. LONGEVITY OF DUNE LARKS IN THE NAMIB DESERT Jos B Williams

    E-print Network

    de Villiers, Marienne

    LONGEVITY OF DUNE LARKS IN THE NAMIB DESERT Jos B Williams Percy Fitzparrick Institute of African-sea of the Namib Desert, a hyperarid region where rainfall is scant and primary production is verv low (Lancaster BANDED IN THE NAMIB DESERT a l. Banded and recaptured in East Dunes atea of Namib-Naukluft park 23"47 ' S

  9. A Beach and Dune Community. 4-H Marine Science. Member's Guide. Activity I. MSp 1.

    ERIC Educational Resources Information Center

    Auburn Univ., AL. Cooperative Extension Service.

    The investigation in this booklet is designed to provide 4-H members with opportunities to identify common plants and animals found on beaches and sand dunes and to determine the role of the plants and animals in this community. Learners are provided with a picture of a hypothetical beach and sand dune and a list of organisms (included in the…

  10. 77 FR 62476 - Special Regulations; Areas of the National Park System, Sleeping Bear Dunes National Lakeshore...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-15

    ..., Sleeping Bear Dunes National Lakeshore, Bicycling AGENCY: National Park Service, Interior. ACTION: Proposed rule. SUMMARY: The National Park Service proposes to designate the Sleeping Bear Heritage Trail currently under construction within Sleeping Bear Dunes National Lakeshore as a route for bicycle use....

  11. AEOLIAN DUNE FIELDS OF KANSAS AND THEIR RESPONSE TO LATE-QUATERNARY DROUGHT

    E-print Network

    Halfen, Alan Frederick

    2012-12-31

    of past dune field activity, which in many cases, is the result of drought. Based on a drought-aeolian activity relationship, the timing of past dune activity can, therefore, be used as a proxy for prehistoric drought. This dissertation presents three...

  12. Mars Global Digital Dune Database: Distribution in North Polar Region and Comparison to Equatorial Region

    NASA Astrophysics Data System (ADS)

    Hayward, R. K.; Fenton, L. K.; Tanaka, K. L.; Mullins, K. F.; Titus, T. N.; Bourke, M. C.; Hare, T. M.; Christensen, P. R.

    2008-03-01

    The north polar portion of the Mars Global Digital Dune Database (MGD3) extends coverage of medium to large-size dark dunes to include the region from 65°N to 90°N, building on the previously released equatorial portion that spans 65°S to 65°N.

  13. 76 FR 62087 - Draft Conservation Plan and Draft Environmental Assessment; Dunes Sagebrush Lizard, Texas

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-06

    ... application includes the draft Texas Conservation Plan for the Dunes Sagebrush Lizard (TCP). The draft TCP... range in Texas. The Applicant proposes to implement conservation measures for this species by removing... addition to a larger conservation effort for the dunes sagebrush lizard across its range within Texas...

  14. Interisland Variability of Dune Plant Community Structure on Virginia's Barrier Islands

    E-print Network

    Lawrence, Deborah

    Interisland Variability of Dune Plant Community Structure on Virginia's Barrier Islands by Justin VARIABILITY OF DUNE PLANT COMMUNITY STRUCTURE ON VIRGINIA'S BARRIER ISLANDS Justin K. Shafer Old Dominion University, 2010 Director: Dr. Frank P. Day The barrier islands of the Virginia Coast Reserve LTER site

  15. Morphological barrier island changes and recovery of dunes after Hurricane Dennis, St. George Island, Florida

    E-print Network

    Fagherazzi, Sergio

    Morphological barrier island changes and recovery of dunes after Hurricane Dennis, St. George September 2009 Keywords: Dune recovery LiDAR Overwash Hurricane Dennis Barrier island During the summer barrier island chain located along the Florida Panhandle. In this paper, LiDAR-based morphological changes

  16. Using Long-Term Census Data to Inform Restoration Methods for Coastal Dune Vegetation

    E-print Network

    Ronquist, Fredrik

    /Published online: 17 April 2013 # Coastal and Estuarine Research Federation 2013 Abstract Barrier islands Barrier Island . Coastal ecology . Dune zone . Disturbance . Dune vegetation . Storm response Introduction Barrier Islands are a common landform along the eastern and Gulf coasts of North America (Hayes 1979

  17. LONG TERM RESIDUAL EFFECTS OF A NUTRIENT ADDITION ON A BARRIER ISLAND DUNE ECOSYSTEM

    E-print Network

    Lawrence, Deborah

    LONG TERM RESIDUAL EFFECTS OF A NUTRIENT ADDITION ON A BARRIER ISLAND DUNE ECOSYSTEM by Susan M EFFECTS OF A NUTRIENT ADDITION ON A BARRIER ISLAND DUNE ECOSYSTEM Susan M. Heyel Old Dominion University Island, part of the Virginia Coast Reserve Long Term Ecological Research site, to examine plant community

  18. 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.

  19. Decline of Birds in a Human Modified Coastal Dune Forest Landscape in South Africa

    E-print Network

    Pretoria, University of

    Decline of Birds in a Human Modified Coastal Dune Forest Landscape in South Africa Morgan J rainfall may have contributed to bird declines. However, other possibilities warrant further investigation) Decline of Birds in a Human Modified Coastal Dune Forest Landscape in South Africa. PLoS ONE 6(1): e16176

  20. Modeling the SAR backscatter of linear dunes on Earth and Titan

    NASA Astrophysics Data System (ADS)

    Paillou, Ph.; Bernard, D.; Radebaugh, J.; Lorenz, R.; Le Gall, A.; Farr, T.

    2014-02-01

    We modeled the Synthetic Aperture Radar (SAR) response of linear dunes of the Great Sand Sea in Egypt using a single surface scattering term, based on Integral Equation and Physical Optics Models. Using multi-frequency SIR-C/X-SAR radar scenes and topography obtained from the Shuttle Radar Topography Mission (SRTM), we were able to estimate reasonable values for the parameters describing the surface roughness of the dunes. As the linear dunes of the Great Sand Sea are relevant analogs for the linear dunes observed on Titan by the Cassini Radar instrument, these results were thus used as a starting point to simulate the radar response of Titan's dunes, as imaged by the Radar instrument onboard the Cassini spacecraft during the T8 flyby in October 2005. We show that a single surface scattering term is not sufficient to simulate the radar signal backscattered by the dunes on Titan: one has to add a diffuse scattering term, indicating that Titan's dunes are likely to have somewhat inhomogeneous internal structures related to porosity and/or internal layering. Our results also indicate that the dunes on Titan should be close to perfectly smooth, possibly because of the formation of smaller ripples than on Earth, plus smoothing resulting from precipitation events.

  1. Namib Desert dune/interdune transects exhibit habitat-specific edaphic bacterial communities

    PubMed Central

    Ronca, Sandra; Ramond, Jean-Baptiste; Jones, Brian E.; Seely, Mary; Cowan, Don A.

    2015-01-01

    The sand dunes and inter-dune zones of the hyper-arid central Namib Desert represent heterogeneous soil habitats. As little is known about their indigenous edaphic bacterial communities, we aimed to evaluate their diversity and factors of assembly and hypothesized that soil physicochemistry gradients would strongly shape dune/interdune communities. We sampled a total of 125 samples from 5 parallel dune/interdune transects and characterized 21 physico-chemical edaphic parameters coupled with 16S rRNA gene bacterial community fingerprinting using T-RFLP and 454 pyrosequencing. Multivariate analyses of T-RFLP data showed significantly different bacterial communities, related to physico-chemical gradients, in four distinct dune habitats: the dune top, slope, base and interdune zones. Pyrosequencing of 16S rRNA gene amplicon sets showed that each dune zone presented a unique phylogenetic profile, suggesting a high degree of environmental selection. The combined results strongly infer that habitat filtering is an important factor shaping Namib Desert dune bacterial communities, with habitat stability, soil texture and mineral and nutrient contents being the main environmental drivers of bacterial community structures. PMID:26388839

  2. A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples

    E-print Network

    Claudin, Philippe

    A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples Philippe Claudin (Martian dunes). The difficulty is to determine the diameter of saltating grains on Mars. A first estimate at which these bed instabilities develop and propagate on Mars. © 2006 Elsevier B.V. All rights reserved

  3. Modeling removal of bacteriophages MS2 and PRD1 by dune recharge at Castricum, Netherlands

    E-print Network

    Hassanizadeh, S. Majid

    of safe drinking water. Drinking water is consid- ered to be safe if certain maximum allowable by dune recharge was studied at a field site in the dune area of Castricum, Netherlands. Recharge water% of the total drinking water production relies on pretreated surface water that is artificially recharged

  4. ~WOVEGROUND BIOMASS AND NET PRIMARY PRODUCTION ALONG .A VIRGINIA BARRIER ISLAND DUNE CHRONOSEQUENCE

    E-print Network

    Lawrence, Deborah

    ~WOVEGROUND BIOMASS AND NET PRIMARY PRODUCTION ALONG .A VIRGINIA BARRIER ISLAND DUNE CHRONOSEQUENCE BIOMASS AND NET PRIMARY PRODUCTION ALONG A VIRGINIA BARRIER ISLAND DUNE CHRONOSEQUENCE John Joseph DiLustro Old Dominion University, 1994 Director: Dr. Frank P. Day Jr. Aboveground biomass was examined along

  5. Water Use for Cultivation Management of Watermelon in Upland Field on Sand Dune

    NASA Astrophysics Data System (ADS)

    Hashimoto, Iwao; Senge, Masateru; Itou, Kengo; Maruyama, Toshisuke

    Early-maturing cultivation of watermelon in a plastic tunnel was invetigated in upland field on sand dune on the coast of the Japan Sea to find water use to control blowing sand and to transplant seedlings. This region has low precipitation, low humidity, and strong wind in March and April, when sand is readily blown in the field. Water is used to control blowing sand on days with precipitation below 5 mm, minimum humidity below the meteorological average in April, and maximum wind velocity above the meteorological average in April. For the rooting and growth of watermelon seedlings, soil temperature needs to be raised because it is low in April. Ridges are mulched with transparent, porous polyethylene films 10 or more days before transplanting the seedlings and irrigated with sprinklers on fine days for the thermal storage of solar energy. The stored heat steams the mulched ridges to raise soil temperature to 15°C or higher on the day of transplanting the seedlings. The total amount of irrigation water used for watermelon cultivation was 432.7 mm, of which 23.6 mm was for blowing sand control and 26.6 mm was for transplanting the seedlings. The combined amount, 50.2 mm, is 11.6% of the total amount of water used for cultivation management.

  6. Hydrology of the dunes area north of Coos Bay, Oregon

    USGS Publications Warehouse

    Robison, J.H.

    1973-01-01

    Hydrology of a 20-square-mile area of dunes along the central Oregon coast was studied. The area is underlain by 80 to 150 feet of Quaternary dune and marine sand which overlies Tertiary marine clay and shale. Ground water for industrial and municipal use is being withdrawn at a rate of 4 million gallons per day. Original plans to withdraw as much as 30 million gallons per day are evidently limited by the prospect of excessive lowering of levels in shallow lakes near the wells, and possibly sea-water intrusion, if water-level gradients are reversed. At the present stage of development there are 18 production wells, each capable of producing 200-300 gallons per minute from the lower part of the sand deposits. Except for thin layers of silt, clay, and organic matter, the deposits of sand are clean and uniform; horizontal permeability is two orders of magnitude times the vertical permeability. Because of the low vertical permeability, drawdown cones are not evident in the upper part of the aquifer adjacent to the wells. However, present pumping lowers general water levels in the lakes and the shallow ground-water zone as much as several feet. A two-layer electric analog model was built to analyze effects of present and projected development as well as any alternate plans. Model results were used to develop curves for short-term prediction of water levels.

  7. Dew fall in sand dune areas of India

    NASA Astrophysics Data System (ADS)

    Subramaniam, A. R.; Kesava Rao, A. V. R.

    1983-09-01

    An attempt has been made to study the significance of dew in the sand dune areas of India. Dew data recorded by Duvdevani dew gauges at three India Meteorological Stations (Bikaner, Jaisalmer and Ganganagar) with dew so recorded at four different heights i.e., 5 cm, 25 cm, 50 cm and 100 cm above the ground from 1973 to 1976 is taken for analysis. Mean monthly dew amount per dew night for the three stations at all the four heights is presented and discussed. Variation of mean seasonal (September to April) dew amount with height is also presented. It is found that higher amounts of dew deposit occur during the three months December to February. The data for the year having maximum dew fall (1975 76) is taken and analysed in terms of rainfall and potential evapotranspiration during the season. Ganganagar shows highest percentage of dew in 1975 76 when compared to actual seasonal rainfall (37%) and normal seasonal rainfall (27%); which is about 14% of the actual potential evapotranspiration and 18% of the normal potential evapotranspiration. Techniques standardized for afforesting shifting sand dunes are mentioned and recommended tree species for afforestation are presented.

  8. Sargassum as a Natural Solution to Enhance Dune Plant Growth

    NASA Astrophysics Data System (ADS)

    Williams, Amy; Feagin, Rusty

    2010-11-01

    Many beach management practices focus on creating an attractive environment for tourists, but can detrimentally affect long-term dune integrity. One such practice is mechanical beach raking in which the wrack line is removed from the beach front. In Texas, Sargassum fluitans and natans, types of brown alga, are the main components of wrack and may provide a subsidy to the ecosystem. In this study, we used greenhouse studies to test the hypothesis that the addition of sargassum can increase soil nutrients and produce increased growth in dune plants. We also conducted an analysis of the nutrients in the sargassum to determine the mechanisms responsible for any growth enhancement. Panicum amarum showed significant enhancement of growth with the addition of sargassum, and while Helianthus debilis, Ipomoea stolonifera, Sporobolus virginicus, and Uniola paniculata responded slightly differently to the specific treatments, none were impaired by the addition of sargassum. In general, plants seemed to respond well to unwashed sargassum and multiple additions of sargassum, indicating that plants may have adapted to capitalize on the subsidy in its natural state directly from the ocean. For coastal managers, the use of sargassum as a fertilizer could be a positive, natural, and efficient method of dealing with the accumulation of wrack on the beach.

  9. Forme atypique d'une maladie de Lyme

    PubMed Central

    Mahfoudhi, Madiha; Turki, Sami; Kheder, Adel

    2015-01-01

    La maladie de Lyme est une zoonose qui se manifeste essentiellement par des signes cutanés, articulaires, neurologiques et cardiaques. Elle peut exceptionnellement mimer une dermatomyosite. Nous rapportons l'observation d'une patiente âgée de 37 ans qui a présenté des myalgies et un érythroedème de la face et en péri-orbitaire. Une dermatomyosite a été fortement suspectée devant une élévation des enzymes musculaires. Elle a été traitée par une corticothérapie à forte dose. L’évolution a été marquée par l'aggravation des myalgies et l'apparition d'un déficit musculaire. Elle a été alors hospitalisée dans notre service. Les enzymes musculaires étaient élevées. L’électromyogramme était sans anomalies. Le bilan immunologique était négatif. Une enquête infectieuse a été réalisée retrouvant une sérologie de Lyme positive. Après administration d'une antibiothérapie adaptée, l’évolution était bonne avec disparition du tableau clinico-biologique de dermatomyosite. La précocité du diagnostic et l'instauration d'un traitement efficace permet d’éviter des complications graves. PMID:26516401

  10. Reticulated Origin of Domesticated Emmer Wheat Supports a Dynamic Model for the Emergence of Agriculture in the Fertile Crescent

    PubMed Central

    Civá?, Peter; Ivani?ová, Zuzana; Brown, Terence A.

    2013-01-01

    We used supernetworks with datasets of nuclear gene sequences and novel markers detecting retrotransposon insertions in ribosomal DNA loci to reassess the evolutionary relationships among tetraploid wheats. We show that domesticated emmer has a reticulated genetic ancestry, sharing phylogenetic signals with wild populations from all parts of the wild range. The extent of the genetic reticulation cannot be explained by post-domestication gene flow between cultivated emmer and wild plants, and the phylogenetic relationships among tetraploid wheats are incompatible with simple linear descent of the domesticates from a single wild population. A more parsimonious explanation of the data is that domesticated emmer originates from a hybridized population of different wild lineages. The observed diversity and reticulation patterns indicate that wild emmer evolved in the southern Levant, and that the wild emmer populations in south-eastern Turkey and the Zagros Mountains are relatively recent reticulate descendants of a subset of the Levantine wild populations. Based on our results we propose a new model for the emergence of domesticated emmer. During a pre-domestication period, diverse wild populations were collected from a large area west of the Euphrates and cultivated in mixed stands. Within these cultivated stands, hybridization gave rise to lineages displaying reticulated genealogical relationships with their ancestral populations. Gradual movement of early farmers out of the Levant introduced the pre-domesticated reticulated lineages to the northern and eastern parts of the Fertile Crescent, giving rise to the local wild populations but also facilitating fixation of domestication traits. Our model is consistent with the protracted and dispersed transition to agriculture indicated by the archaeobotanical evidence, and also with previous genetic data affiliating domesticated emmer with the wild populations in southeast Turkey. Unlike other protracted models, we assume that humans played an intuitive role throughout the process. PMID:24312385

  11. Analysis of simple sequence repeats (SSRs) in wild barley from the Fertile Crescent: associations with ecology, geography and flowering time.

    PubMed

    Ivandic, Victor; Hackett, Christine A; Nevo, Eviatar; Keith, Richard; Thomas, William T B; Forster, Brian P

    2002-01-01

    Wild barley, Hordeum spontaneum C. Koch, is the progenitor of cultivated barley, Hordeum vulgare. The centre of diversity is in the Fertile Crescent of the Near East, where wild barley grows in a wide range of conditions (temperature, water availability, day length, etc.). The genetic diversity of 39 wild barley genotypes collected from Israel, Turkey and Iran was studied with 33 SSRs of known map location. Analysis of molecular variance (AMOVA) was performed to partition the genetic variation present within from the variation between the three countries of origin. Using classification tree analysis, two (or three) specific SSRs were identified which could correctly classify most of the wild barley genotypes according to country of origin. Associations of SSR variation with flowering time and adaptation to site-of-origin ecology and geography were investigated by two contrasting statistical approaches, linear regression based on SSR length variation and linear regression based on SSR allele class differences. A number of SSRs were significantly associated with flowering time under four different growing regimes (short days, long days, unvernalised and vernalised). Most of the associations observed could be accounted for by close linkage of the SSR loci to earliness per se genes. No associations were found with photoperiodic and vernalisation response genes known to control flowering in cultivated barley suggesting that different genetic factors may be active in wild barley. Novel genomic regions controlling flowering time in wild barley were detected on chromosomes 1HS, 2HL, 3HS and 4HS. Associations of SSRs with site-of-origin ecological and geographic data were found primarily in genomic regions determining plant development. This study shows that the analyses of SSR variation by allele class and repeat length are complementary, and that some SSRs are not necessarily selectively neutral. PMID:11999832

  12. Sand transverse dune aerodynamics: 3D Coherent Flow Structures from a computational study

    E-print Network

    Bruno, Luca

    2015-01-01

    The engineering interest about dune fields is dictated by the their interaction with a number of human infrastructures in arid environments. The aerodynamic behaviour of sand dunes in atmospheric boundary layer belongs to the class of bluff bodies. Because of their simple geometry and their frequent occurrence in desert area, transverse sand dunes are usually adopted in literature as a benchmark to investigate dune aerodynamics by means of both computational or experimental approach, usually in nominally 2D setups. The writers suspect the flow in the wake is characterised by 3D features and affected by wind tunnel setup - e.g. blockage effect, duct side wall boundary layer, incoming velocity profile - when experimental studies are carried out. The present study aims at evaluating the 3D flow features of an idealised transverse dune under different setup conditions by means of computational simulations and to compare the obtained results with experimental measurements.

  13. Short-term changes in mobile dunes at Port Alfred, South Africa

    NASA Astrophysics Data System (ADS)

    Lubke, Roy A.; Sugden, Jean

    1990-03-01

    Development along the western beachfront of Port Alfred, which is situated along a sandy shoreline, increased markedly in the 1960s as the coastal town became a popular holiday resort. This development included the removal of coastal vegetation, which resulted in the destabilization of dunes and migration of sand westerly onto the road, West Beach parking lot, and lawns of the cabanas. Sand traps were constructed to collect sand blowing across the dunes over set periods, and the net sand movement along the mobile dune belt was calculated using Hunter's equation. The dunes show an easterly movement of sand at a rate of 3.5 m/yr, which is comparable with figures recorded along other areas of this coastline. Considering the wind regime and amount of sand movement along this coast, it is inappropriate to clear vegetation and develop within the dune region.

  14. Dune Morphodynamics on a Semi-Arid, Wave-Dominated Barrier Island: South Padre Island, Texas

    NASA Astrophysics Data System (ADS)

    Del Angel, D. C.; Gibeaut, J. C.

    2012-12-01

    Spatial and temporal dune accretion along the barrier island of South Padre Island (SPI),Texas was examined using a combination of field measurements and lidar elevation data. Volume change rates derived from the data were compared to potential sediment transport rates derived from Hsu's (1974 & 1977) model using local wind-gauge data. A statistical model was then used to investigate controls on foredune accretion. Dune volume change was estimated from cross-shore profile measurements acquired during the summer of 2009, spring of 2010, and fall of 2010. For summer 2009 to spring 2010, dune volume change ranged from -18 to 12.5 m^3/m. The onshore potential drift for the same time period was estimated to be 6.6 m^3/m. In comparison, volume change ranged from -5.5 to 5.3 m^3/m for spring to fall 2010 with most dunes experiencing erosion. The estimated onshore drift was much higher at 22.5 m^3/m. The high drift potential associated with the spring and summer months is attributed to the predominant wind direction and the occurrence of tropical storms. Dune volume change was also observed on a longer time scale using lidar DEMs for the years 2000, 2005, and 2009. From 2000 to 2005, most natural dunes experienced accretion with a mean of 17.67 m^3/m, whereas between 2005 and 2009, the majority of dunes experienced volume loss with a mean change of -4.16 m^3/m. Overall, the mean volume change from 2000 to 2009 was 13.51 m^3/m. Onshore drift for 2000 to 2005 was estimated to be 16.44 m^3/m, which is a good approximation to the observed volume change. In contrast, onshore drift for 2000 to 2009 was estimated to be 80.4 m^3/m, which is substantially higher than the mean volume change observed during the period. The discrepancy between the modeled and observe value is partly due to dune volume loss from storm surge erosion. In addition, there was a significant increase in onshore drift potential from 2006 to 2008. Stepwise backward regression was used to find significant correlations (p-values < 0.01) between observed values in dune volume change and beach and dune morphometric parameters. Examined parameters include beach width, beach height, beach slope, shoreline orientation, the long-term rate of shoreline displacement, and aeolian dune form (washover terrace, dune terrace, dune ridge and active dunes). Model results show that dune type, beach width, and shoreline orientation were significant contributors. A hierarchical partitioning method provided further insight by showing that dune type explains most of the variation (57%), followed by beach width (30%) and lastly, orientation (< 2%). Based on the volumetric change analysis, results observed from 2000 to 2005 provide a good estimate of the average dune accretion for SPI because of the low impact of storms. But, from the wind models, potential transport has yearly fluctuations which can affect accretion rates. Furthermore, accretion will continue to be interrupted by the periodic occurrence of storms. Spatial variability of dune volume change is related to the existing dune form and beach morphology as evidenced by the statistical analysis. It is expected that the relative occurrence of washovers, terraces, ridges, and active dunes will vary in time as storms, drought and anthropogenic stresses change.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  16. Solar astronomy

    NASA Technical Reports Server (NTRS)

    Rosner, Robert; Noyes, Robert; Antiochos, Spiro K.; Canfield, Richard C.; Chupp, Edward L.; Deming, Drake; Doschek, George A.; Dulk, George A.; Foukal, Peter V.; Gilliland, Ronald L.

    1991-01-01

    An overview is given of modern solar physics. Topics covered include the solar interior, the solar surface, the solar atmosphere, the Large Earth-based Solar Telescope (LEST), the Orbiting Solar Laboratory, the High Energy Solar Physics mission, the Space Exploration Initiative, solar-terrestrial physics, and adaptive optics. Policy and related programmatic recommendations are given for university research and education, facilitating solar research, and integrated support for solar research.

  17. British Geomorphological Research Group, Annual Meeting, Oxford, 2003. An analysis and classification of 'barchan' dunes on Mars.

    E-print Network

    Bourke, Mary C.

    and classification of 'barchan' dunes on Mars. Bourke, M.C., and Balme, M. School of Geography and the Environment, studied in detail in Viking 1 and 2 Orbiter images have been classified as barchan, barchanoid, transverse of a morphometric analysis of `barchan' dunes in the North polar sand sea and intra-crater dune fields. We find that

  18. Species Diversity of Seed-Eating Desert Rodents in Sand Dune Habitats Author(s): James H. Brown

    E-print Network

    Brown, James H.

    Species Diversity of Seed-Eating Desert Rodents in Sand Dune Habitats Author(s): James H. Brown DIVERSITY OF SEED-EATING DESERT RODENTS IN SAND DUNE HABITATS' JAMES H. BROWN Department of Biology of semistabilized,wind- drifted sand in eastern California, Nevada, and western Utah. These dunes were similar

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

    NASA Astrophysics Data System (ADS)

    Yan, Na; Baas, Andreas C. W.

    2015-01-01

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

  20. 75 FR 45653 - Notice of Re-Opening of Comment Period for the Draft Imperial Sand Dunes Recreation Area...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-03

    ...of Comment Period for the Draft Imperial Sand Dunes Recreation Area Management Plan and...the comment period on the Draft Imperial Sand Dunes Recreation Area Management Plan...California 92243. Copies of the Draft Imperial Sand Dunes RAMP/EIS are available in the...

  1. 77 FR 36871 - Endangered and Threatened Wildlife and Plants; Withdrawal of the Proposed Rule To List Dunes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-19

    ... review classifying the sand dune lizard (dunes sagebrush lizard) as a Category 2 species (47 FR 58454... dunes sagebrush lizard as a Category 3C species (50 FR 37958). Category 3C status included taxa that... status had changed. Therefore, in our notice of review on November 21, 1991 (56 FR 58804), the...

  2. Characteristics of dune-paleosol-sequences in Fuerteventura. - What should be questioned?

    NASA Astrophysics Data System (ADS)

    Faust, Dominik; Willkommen, Tobias; Yanes, Yurena; Richter, David; Zöller, Ludwig

    2013-04-01

    Characteristics of dune-paleosol-sequences in Fuerteventura. - What should be questioned? Dominik Faust, TU Dresden, Germany Tobias Willkommen, TU Dresden, Germany Yurena Yanes, CSIC Granada/Cincinatti, Spain/USA David Richter, TU Dresden, Germany Ludwig Zöller, Uni Bayreuth, Germany The northern part of Fuerteventura is characterized by large dune fields. We investigated dune-paleosol-sequences in four pits to establish a robust stratigraphy and to propose a standard section. An interaction of processes like dune formation, soil formation and redeposition of soils and sand are most important to understand the principles of landscape development in the study area. To our mind a process cycle seem to be important: First climbing-dunes are formed by sand of shelf origin. Then soil formation could have taken place. Soil and/or sand were then eroded and deposited at toe slope position. This material in turn is the source of new sand supply and dune formation. The described cycle may be repeated several times and this ping-pong-process holds on. The results are sections composed of dune layers, paleosols and colluvial material interbedded. Fundamental questions still remain unanswered: Is climate change responsable for changes in process combination (e.g. from dune formation to soil formation)? Or are these features due to divergence phenomenon, where different effects/results (dune and soils) may be linked to similar causes (here: climate)? Assuming that different features (soils and dunes) were formed under one climate, increasing soil forming intensity could be mainly a function of decreasing sand supply. This in turn could be caused by reduced sand production (s. ZECH et al. accepted). However geochemical data and mollusc assemblages point to changing environments in space and even climate modifications in time.

  3. Flood-formed dunes in Athabasca Valles, Mars: Morphology, modeling, and implications

    USGS Publications Warehouse

    Burr, D.M.; Carling, P.A.; Beyer, R.A.; Lancaster, N.

    2004-01-01

    Estimates of discharge for martian outflow channels have spanned orders of magnitude due in part to uncertainties in floodwater height. A methodology of estimating discharge based on bedforms would reduce some of this uncertainty. Such a methodology based on the morphology and granulometry of flood-formed ('diluvial') dunes has been developed by Carling (1996b, in: Branson, J., Brown, A.G., Gregory, K.J. (Eds.), Global Continental Changes: The Context of Palaeohydrology. Geological Society Special Publication No. 115, London, UK, 165-179) and applied to Pleistocene flood-formed dunes in Siberia. Transverse periodic dune-like bedforms in Athabasca Valles, Mars, have previously been classified both as flood-formed dunes and as antidunes. Either interpretation is important, as they both imply substantial quantities of water, but each has different hydraulic implications. We undertook photoclinometric measurements of these forms, and compared them with data from flood-formed dunes in Siberia. Our analysis of those data shows their morphology to be more consistent with dunes than antidunes, thus providing the first documentation of flood-formed dunes on Mars. Other reasoning based on context and likely hydraulics also supports the bedforms' classification as dunes. Evidence does not support the dunes being aeolian, although a conclusive determination cannot be made with present data. Given the preponderance of evidence that the features are flood-formed instead of aeolian, we applied Carling's (1996b, in: Branson, J., Brown, A.G., Gregory, K.J. (Eds.), Global Continental Changes: The Context of Palaeohydrology. Geological Society Special Publication No. 115, London, UK, 165-179) dune-flow model to derive the peak discharge of the flood flow that formed them. The resultant estimate is approximately 2??106 m3/s, similar to previous estimates. The size of the Athabascan dunes' in comparison with that of terrestrial dunes suggests that these martian dunes took at least 1-2 days to grow. Their flattened morphology implies that they were formed at high subcritical flow and that the flood flow that formed them receded very quickly. ?? 2004 Elsevier Inc. All rights reserved.

  4. Formation of Linear Dunes and Other Secrets of the Simpson Desert, Australia

    NASA Astrophysics Data System (ADS)

    Craddock, R. A.; Hutchinson, M. F.; Tooth, S.; Maxwell, T. A.; Stein, J. A.; Howard, A. D.; Irwin, R. P.; Wilson, S.

    2006-12-01

    It is estimated that linear dunes represent 40 percent of all dunes on Earth. Linear dunes have also been found on every terrestrial planet with an appreciable atmosphere, including Mars, Venus and Titan. Remarkably, however, despite how prevalent they are very little is known about their formation, chronology and their interaction with adjacent sediment sources. There are two basic hypotheses regarding the origin of linear dunes. The "wind rift" concept suggests that linear dunes are swept together from local material. In this model wind moves across the surface as horizontal vortices scouring or channeling out alluvial sand deposits [Pell et al., 1999; 2000]. The linear nature of the dunes is attributed to the parallel direction of the vortices. In the "depositional" concept sand is thought to come from a few depositional sources which can then be transported great distances. In this model linear dunes are a result of bidirectional winds that blow the sand together from either direction [Wopfner and Twidale, 2001]. Recently we began a series of studies in the Simpson Desert of Australia to tests these competing hypotheses. The Simpson Desert is located in the Lake Eyre basin and borders the Northwest Territory, Queensland and South Australia. Typically the area receives less than 150 mm (6 inches) of rain annually, and the rivers that drain into the Simpson Desert terminate in a series of floodout deposits where the flood waters simply debouch into the desert and seep into the sand leaving behind fresh sediment deposits. There is evidence indicating that these alluvial sediments are subsequently reworked into new dunes [Hollands et al., 2006]; however, the mechanism and timing of these processes is poorly understood. Using Differential Global Positioning System (DGPS) equipment we conducted a series of topographic surveys of linear dunes located in the western and southern parts of the Simpson Desert. Several of these dunes were staked so that we can monitor changes in dune morphometry over time. Results of the DGPS survey were also compared to Shuttle Radar Topographic Mission (SRTM) data as a way of verifying the accuracy of these data so that dune morphometry can be studied in a more systematic way. Our results will help us to better understand how linear dunes form and the environmental conditions necessary to generate them on Earth and on other terrestrial planets.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    With the increase of the annual sand demand for the construction industry the excessive excavation of river sand is becoming a serious environmental problem in Sri Lanka. Therefore, it is necessary to explore the possibility for an alternative to stop or at least to minimize river sand mining activities. Dune sand is one of the available alternative materials to be considered instead of river sand in the country. Large quantities of sand dunes occur mainly along the NW and SE coastal belt which belong to very low rainfall Dry Zone coasts. The height of dune deposits, vary from 1m to about 30 meters above sea level. The objective of this paper is to indicate some studies and facts on the dune sand deposits of Sri Lanka. Laboratory studies were carried out for visual observations and physical properties at the initial stage and then a number of tests were carried out according to ASTM standards to obtain the compressive strength of concrete cylinders and mortar cubes mixing dune sand and river sand in different percentages keeping a constant water cement ratio. Next the water cement ratio was changed for constant dune sand and river sand proportion. Microscopic analysis shows that the dune sand consist of 95 % of quartz and 5 % of garnet, feldspar, illmenite and other heavy minerals with clay, fine dust, fine shell fragments and organic matters. Grains are sub-rounded to angular and tabular shapes. The grain sizes vary from fine to medium size of sand with silt. The degree of sorting and particle size observed with dune sands are more suited with the requirement of fine aggregates in the construction industry. The test result indicates that dune sand could be effectively used in construction work without sieving and it is ideal for wall plastering due to its'-uniformity. It could also be effectively used in concrete and in mortars mixing with river sand. The best mixing ratio is 75% dune sand and 25% river sand as the fine aggregate of concrete. For mortar the mixing percentage is 50%. The best water cement ratio for mix proportion is 0.45. It was observed that the available amount of dune sand can be extracted to meet the demand for sand in construction industry. However, the extraction of dune sand from the areas close to the sea will cause several social, environmental and legal problems. Therefore sand mining from dunes must be commenced after making a detailed Environmental Impact Assessment.

  6. Shaping a dune with wind and frost in Matara crater, Mars

    NASA Astrophysics Data System (ADS)

    Diniega, S.

    2013-12-01

    Matara crater dune field exhibits a complex and fascinating geologic history. It first gained scientific attention when dune gullies (of alcove-channel-apron morphology, a few hundred meters to 3 km in length) were observed in MOC and HiRISE images to be actively evolving during the last Mars decade. Additionally, aeolian processes are clearly active within this field as the dune brinks are quite crisp in appearance, ripples on the surfaces of these dunes have been observed to migrate, and ripples have formed within sediment recently remobilized by dune-gully activity. This study seeks to understand how sediment has been redistributed/mobilized through both aeolian processes and seasonal processes leading to gully and ripple evolution. In particular, we focus on how ripples form and grow due to the wind, and are sometimes erased due to new deposition within the gully apron. We primarily focus on one very large dune-gully apron in Matara crater, where we have observed both dune-gully activity and new ripple formation over the last few Mars years. By mapping out regions with different ripple wavelengths - indicative of different ripple ages, we will examine how seasonal frost and aeolian processes have interacted over the last few decades to centuries.

  7. Eolian deposition cycles since AD 500 in Playa San Bartolo lunette dune, Sonora, Mexico: Paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Ortega, Beatriz; Schaaf, Peter; Murray, Andrew; Caballero, Margarita; Lozano, Socorro; Ramirez, Angel

    2013-12-01

    Records of past climatic changes in desert environments are scarce due to the poor preservation of biological proxies. To overcome this lack we consider the paleoenvironmental significance and age of a lunette dune at the eastern rim of Playa San Bartolo (PSB) in the Sonoran Desert (Mexico). Thermoluminescence and optical stimulated luminescence (TL and OSL) provide the chronology of lunette dune development. Mineralogical, geochemical (major, trace and REE element concentrations) and rock magnetic analyses allow for the assessment of sediment provenance and changes in the composition of the PSB dune over time. The upper 6 m of dune accumulation occurred over the past 1.5 ka, largely during AD 500-1200, a period that correlates with the Medieval climatic anomaly (AD 300-1300). Variability in composition of dune sediments is attributed to changes in sediment sources. Sand sized deposits are mainly eroded from granitoids from nearby outcrops. Sandy silt deposits, rich in evaporative minerals, resulted after the flooding of PSB, later deflation and accumulation of both detritic and authigenic components in the dune. These findings suggest that main dune accretion occurred during regionally extended drought conditions, disrupted by sporadic heavy rainfall.

  8. Water resources of Sleeping Bear Dunes National Lakeshore, Michigan

    USGS Publications Warehouse

    Handy, A.H.; Stark, J.R.

    1984-01-01

    Sleeping Bear Dunes National Lakeshore in a water-rich area. It borders Lake Michigan and several small streams flow through the park to the lake. Small lakes are numerous within the park and near its boundaries. Ground water is available at most places in the park and wells yield as much as 100 gallons per minute. Water from streams, lakes, wells, and springs is of good quality. Dissolved solids range from 35 to 180 mg/L in lakes, from 145 to 214 mg/L in streams, and from 136 to 468 mg/L in groundwater. Analyses of samples for pesticides and trace metals indicate that no pesticides are present in the water, and that concentrations of trace metals do not exceed recommended drinking-water standards. Surface and ground water are available in sufficient quantity in most areas of the park for the development of water supplies for visitor 's centers, campgrounds, picnic areas, and other park facilities. (USGS)

  9. Comment on "Solving the mystery of booming sand dunes"

    E-print Network

    B. Andreotti; L. Bonneau; E. Clement

    2007-10-30

    We show here that the standard physical model used by Vriend et al. to analyse seismograph data, namely a non-dispersive bulk propagation, does not apply to the surface layer of sand dunes. According to several experimental, theoretical and field results, the only possible propagation of sound waves in a dry sand bed under gravity is through an infinite, yet discrete, number of dispersive surface modes. Besides, we present a series of evidences, most of which have already been published in the literature, that the frequency of booming avalanches is not controlled by any resonance as argued in this article. In particular, plotting the data provided by Vriend et al. as a table, it turns out that they do not present any correlation between the booming frequency and their estimate of the resonant frequency.

  10. Une hanche douloureuse révélatrice d'une histiocytose osseuse multifocale

    PubMed Central

    Lahrach, Kamal; Alaoui, Adil; el Kadi, Khalid Ibn; Marzouki, Amine; Boutayeb, Fawzi

    2014-01-01

    L'histiocytose langerhansienne est une maladie rare qui touche principalement l'enfant et l'adulte jeune. Elle peut prendre plusieurs aspects, L'atteinte osseuse peut être uni- ou multifocale. Nous rapportons une observation d'histiocytose langerhansienne osseuse multifocale, révélée chez un patient âgé de 23 ans et ayant touché le col fémoral droit. La scintigraphie osseuse a permis de retrouver plusieurs localisations: l'os temporal, humérale et scapulaire droite. En raison du risque fracturaire, le patient a bénéficié d'une ostéosynthèse par vis-plaque DHS avec curetage biopsie de la lésion. L'examen histologique a révélé une histiocytose langerhansienne. L'évolution fut favorable après chimiothérapie par voie générale. PMID:25018840

  11. Etude numerique du sillage tourbillonnaire d'une eolienne

    NASA Astrophysics Data System (ADS)

    Sibuet Watters, Christophe

    Cette these formalise le concept de la surface actuatrice (SA) et en presente l'implantation dans deux methodes de mecanique des fluides assistee par ordinateur (CFD) bidimensionnelle (2D) et tridimensionnelle (3D), la validation et l'application au probleme de modelisation du sillage tourbillonnaire d'une eolienne. En termes cinetiques, une SA est une nappe tourbillonnaire qui resulte en une discontinuite de vitesse tandis qu'en termes dynamiques, elle est associee a un systeme de forces dont la composante dans la direction normale a la SA resulte en une discontinuite de pression. Les methodes CFD utilisees sont des methodes aux volumes finis, adaptees pour prendre en compte l'action de la SA sur l'ecoulement. L'approche de la SA est validee pour des problemes 2D: aile infinie et disque actuateur, ainsi que pour le probleme 3D de l'aile en translation (aile effilee), avant d'etre appliquee a plusieurs eoliennes.

  12. Seepage measurements from Long Lake, Indiana Dunes National Lakeshore

    USGS Publications Warehouse

    Isiorho, S.A.; Beeching, F.M.; Stewart, P.M.; Whitman, R.L.

    1996-01-01

    Long Lake, located near Lake Michigan within the dune-complexes of Indiana Dunes National Lakeshore, USA, was formed some time during the Pleistocene and Holocene epochs. A surficial aquifer underlies Long Lake, which is either a source or sink for the later. The hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural, municipal, and industrial development of the region. Limited data suggest that the organisms of Long Lake have elevated levels of several contaminants. This study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality. Seepage measurements and minipiezometric tests were used to determine seepage within the lake. Seepage measurements and minipiezometric tests suggest that water seeps out of Long Lake, thus recharging the groundwater that flows southwest away from the lake. There is a great deal of variability in the seepage rate, with a mean of 11.5×10-4±11.2×10-4 m d-1. The mean seepage rate of 0.3 m yr-1 for Long Lake is greater than the 0.2 m yr-1 recharge rate estimated for the drainage basin area. The Long Lake recharge volume of 2.5 × 105 m3 yr-1 is approximately 22% of the volume of the lake and is significant when compared to the total surface recharge volume of 4.8 × 105 m3 yr-1 to the upper aquifer of the drainage area. There is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions.

  13. Correlation of Dune Field Stabilization with Mineralogy in the Southern Hemisphere of Mars

    NASA Astrophysics Data System (ADS)

    Fenton, L. K.; Hayward, R. K.; Horgan, B. H.; Titus, T. N.

    2013-12-01

    Because of its relatively dust-free surfaces, aeolian sand on Mars is a prime target for remote sensing compositional studies. It is not yet known how sand composition may be influenced by transport or the presence of ground ice. However, Ruff and Christensen (2007) identified a shift in dune field composition poleward of 50°S, which may reflect a latitudinal shift in source composition, transport, or weathering. This compositional shift coincides with a latitudinal trend in dune field morphology that was interpreted to signify an increase in dune stabilization with proximity to the pole (Fenton and Hayward, 2010). We present preliminary results from linear spectral unmixing of Thermal Emission Spectrometer (TES) data for 24 dune fields in the southern hemisphere of Mars (located 40°-80°S) using the spectral library of Rogers and Fergason (2011). There is a great deal of variation in the resulting abundances, but most dune fields have a lower percentage of olivine and pyroxene than that identified closer to the equator, in Iapygia and Tyrrhena Terrae (60°-100°E, 0-30°S; Rogers and Fergason, 2011). As identified by Ruff and Christensen (2007), there is a shift at ~60°S from more mafic materials (olivine and pyroxene) to less mafic materials (feldspar and high-silica phases) that corresponds with the transition from active-appearing dune fields (red in figure) to those displaying the first signs of stabilization (orange in figure). Dune fields displaying further signs of stability have abundances intermediate between these two ranges, suggesting that compositional variations related to dune field stability are only significant where the first signs of stability appear. In addition, there is typically a wide range of abundances within individual dune fields, suggesting that, at least to some degree, compositional variation is controlled by local processes (e.g., local sources or wind patterns).

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

    NASA Astrophysics Data System (ADS)

    Marsh, William M.

    1990-09-01

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

  15. The origin of collapse features appearing in a migrating parabolic dune along the southern coast of Lake Michigan

    NASA Astrophysics Data System (ADS)

    Argyilan, Erin P.; Avis, Peter G.; Krekeler, Mark P. S.; Morris, Charles C.

    2015-12-01

    Dune decomposition chimneys are collapse features formed when migrating dunes encroach on a forest and buried trees subsequently decay, leaving a temporarily stable open hole. The recent appearance of holes on the stoss slope of Mount Baldy at the Indiana Dunes National Lakeshore provided an opportunity for study of such features. Mount Baldy is a large parabolic dune that is rapidly migrating onshore over a late Holocene landscape with stabilized relict parabolic dunes that supported oak (Quercus spp.) trees visible on the 1939 aerial photo. Individual holes were mapped to locations on the dune surface that would directly overlie the arm of a buried relict parabolic dune. Analyses of buried trees and surrounding sediment indicated that saprotrophic wood decay fungi continue to actively decompose trees after burial and biomineralization of a calcium-carbonate-rich cement occurs at the contact between organic material and sands. Scanning electron microscopy of the cement showed neoformed authigenic minerals and organic structures consistent in morphology with fungal hyphae. We propose that, within the dune, portions of the decayed trees progressively collapse and infill, and open holes are temporarily stabilized by the calcium-carbonate-rich cement. Further, holes can exist undetected at the surface, covered by a thin veneer of sand. Migrating dune systems are observed in many coastal and inland areas. Ongoing work must address the relative contributions of individual environmental factors on the formation of dune decomposition chimneys, including the biomineralization of cement, sand mineralogy, rate of dune movement, tree species, climate, and the composition of fungal communities.

  16. Nucléation, ascension et éclatement d'une bulle de champagne

    NASA Astrophysics Data System (ADS)

    Liger-Belair, G.

    2006-03-01

    People have long been fascinated by bubbles and foams dynamics, and since the pioneering work of Leonardo da Vinci in the early 16th century, this subject has generated a huge bibliography. However, only quite recently, much interest was devoted to bubbles in Champagne wines and carbonated beverages. Since the time of the benedictine monk dom Pierre Perignon (1638-1715), champagne is the wine of celebration. This fame is largely linked to the elegance of its effervescence and foaming properties. In this book, the latest results about the chemical physics behind the bubbling properties of Champagne and sparkling wines are collected and fully illustrated. The first chapter is devoted to the history of champagne and to a presentation of the tools of the physical chemistry of interfaces needed for a whole comprehension of the book. Then, the three main steps of a fleeting champagne bubble's life are presented in chronological order, that is, the bubble nucleation on the glass wall (Chap.2), the bubble ascent and growth through the liquid matrix (Chap.3), and the bursting of bubbles at the liquid surface (Chap.4), which constitutes the most intriguing, functional, and visually appealing step. L'objectif général de ce travail consacré à l'étude des processus physicochimiques liés à l'effervescence des vins de Champagne était de décortiquer les différentes étapes de la vie d'une bulle de champagne en conditions réelles de consommation, dans une flûte. Nous résumons ci-après les principaux résultats obtenus pour chacune des étapes de la vie de la bulle, depuis sa naissance sur les parois d'une flûte, jusqu'à son éclatement en surface. Nucléation À l'aide d'une caméra rapide munie d'un objectif de microscope, nous avons pu mettre à mal une idée largement répandue. Ce ne sont pas les anfractuosités de la surface du verre ou de la flûte qui sont responsable de la nucléation hétérogène des bulles, mais des particules adsorbées sur les parois du verre ou de la flûte. Dans la majorité des cas, il s'agit de fibres de cellulose creuses dont les propriétés géométriques permettent le piégeage d'une poche d'air en leur sein au moment du versement. Un modèle de piégeage a été construit et met en avant le rôle fondamental joué par la vitesse du versement. Plus cette vitesse augmente, plus on augmente la probabilité de piéger des poches d'air au sein de ces fibres, provoquant ainsi une effervescence plus importante. La dynamique de production des bulles a également été filmée in situ à l'aide de la caméra, puis modélisée en utilisant les équations de la diffusion adaptées à la géométrie de notre fibre supposée approximativement cylindrique. Nous avons montré que le temps caractéristique de production d'une bulle par la fibre est largement gouverné par la croissance de cette petite poche de gaz par diffusion du CO{2} dissous vers la poche. Nous avons démontré que la convection du liquide joue un rôle essentiel lors du transfert de masse du CO{2} dissous vers la poche. En effet, un modèle purement diffusif ne permet pas du tout de reproduire la dynamique de croissance expérimentale de ces poches de gaz piégées au cœur des fibres. Nous avons également pu mettre en évidence des changements spectaculaires dans la dynamique de bullage de certains sites de nucléation suivis au cours du temps pendant le processus de dégazage. Ces observations font de la fibre de cellulose immergée dans le champagne le plus petit système de bullage non-linéaire observé à ce jour. Dynamique ascensionnelle Pour mesurer la vitesse d'une bulle tout au long de son trajet vers la surface libre du champagne, nous avons tiré profit de la production répétitive de bulles au niveau des sites de nucléation. Par la mise en place d'un dispositif expérimental simple qui associe une lumière stroboscopique et un appareil photographique muni de bagues macros, nous avons pu accéder à l'observation fine des trains de bulles ainsi qu'à la détermination de la vitesse ascensionnelle des bulles. Les m

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

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  18. Mineral resources of the North Algodones Dunes Wilderness Study Area (CDCA-360), Imperial County, California

    SciTech Connect

    Smith, R.S.U.; Yeend, W.; Dohrenwend, J.C.; Gese, D.D.

    1984-01-01

    This report presents the results of a mineral survey of the North Algodones Dunes Wilderness Study Area (CDCA-360), California Desert Conservation Area, Imperial County, California. The potential for undiscovered base and precious metals, and sand and gravel within the North Algodones Dunes Wilderness Study Area is low. The study area has a moderate potential for geothermal energy. One small sand-free area between the Coachella Canal and the west edge of the dune field would probably be the only feasible exploration site for geothermal energy. The study area has a moderate to high potential for the occurrence of undiscovered gas/condensate within the underlying rocks. 21 refs.

  19. The behavioural ecology of two sympatric talitrid species, Talitrus saltator (Montagu) and Orchestia gammarellus (Pallas) on a Tyrrhenian sandy beach dune system

    NASA Astrophysics Data System (ADS)

    Colombini, Isabella; Fallaci, Mario; Gagnarli, Elena; Rossano, Claudia; Scapini, Felicita; Chelazzi, Lorenzo

    2013-01-01

    The behavioural ecology of a sub-population of Talitrus saltator living on the sandy shore of the Maremma Regional Park (Italy) was compared with that of Orchestia gammarellus inhabiting the retrodunal dune slack area. Monthly monitoring over a year determined the mean distribution patterns, their changes and whether these overlapped. Standard pitfall traps were placed along transects across the beach-dune-dune slack area. Experiments analysed the diel activity rhythms during spring and the activity patterns of the different age classes and the two sexes were compared within and between species. Local environmental conditions were registered with a microclimatic station. During May and September, plant hummocks were monitored to see whether surface movements of O. gammarellus could be restricted to certain periods of the year and to estimate densities within the vegetation. The plant biomass and moisture conditions within the hummocks were also recorded and substratum samples were collected at the base of the shrubs for laboratory analysis. To test for visual cues, orientation experiments with and without landscape view were carried out on the beach during morning and afternoon hours and contemporaneously for each species. Experiments to test the diel variation of scototaxis to a black shape were also performed over a 24 h period of time under controlled conditions. There was a spatial partitioning of the two species, with T. saltator moving along a sea-land axis according to diel and seasonal changes and with some individuals reaching the back of the dune in particular environmental conditions. No spatial overlap with the zonation patterns of O. gammarellus was observed, which was restricted to the dune slack area. Nocturnal surface activity was observed for both species with juveniles peaking at dawn and with O. gammarellus being strictly more nocturnal than T. saltator. Orientation experiments showed a higher ability of T. saltator to orient towards the shoreline using solar and local cues, whereas O. gammarellus seemed to have a stronger scototaxis. Differences in the behavioural responses are discussed in terms of the species ecological adaptations to their particular habitats.

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

    NASA Astrophysics Data System (ADS)

    Hoose, M.; Pelletier, J. D.

    2013-12-01

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

  1. Solar Lentigo

    MedlinePLUS

    newsletter | contact Share | Solar Lentigo Information for adults A A A This image displays many solar lentigos due to the patient having many sunburns as a child and teenager. Overview A solar lentigo (plural, solar lentigines), also known as a ...

  2. A legacy of divergent fishery management regimes and the resilience of rainbow and cutthroat trout populations in Lake Crescent, Olympic National Park, Washington

    USGS Publications Warehouse

    Brenkman, Samuel J.; Duda, Jeffrey J.; Kennedy, Philip R.; Baker, Bruce M.

    2014-01-01

    As a means to increase visitation, early fisheries management in the National Park Service (NPS) promoted sport harvest and hatchery supplementation. Today, NPS management objectives focus on the preservation of native fish. We summarized management regimes of Olympic National Park's Lake Crescent, which included decades of liberal sport harvest and hatchery releases of 14.3 million salmonids. Notably, nonnative species failed to persist in the lake. Complementary analyses of annual redd counts (1989–2012) and genetics data delineated three sympatric trout (one rainbow; two cutthroat) populations that exhibited distinct spatial and temporal spawning patterns, variable emergence timings, and genetic distinctiveness. Allacustrine rainbow trout spawned in the lake outlet from January to May. Cutthroat trout spawned in the major inlet tributary (Barnes Creek) from February to June and in the outlet river (Lyre) from September to March, an unusual timing for coastal cutthroat trout. Redd counts for each species were initially low (rainbow = mean 89; range 37–159; cutthroat = mean 93; range 18–180), and significantly increased for rainbow trout (mean 306; range 254–352) after implementation of catch-and-release regulations. Rainbow and cutthroat trout reached maximum sizes of 10.4 kg and 5.4 kg, respectively, and are among the largest throughout their native ranges. Morphometric analyses revealed interspecific differences but no intraspecific differences between the two cutthroat populations. Genetic analyses identified three distinct populations and low levels (9–17%) of interspecific hybridization. Lake Crescent rainbow trout were genetically divergent from 24 nearby Oncorhynchus mykiss populations, and represented a unique evolutionary legacy worthy of protection. The indigenous and geographically isolated Lake Crescent trout populations were resilient to overharvest and potential interactions with introduced fish species.

  3. Blowing in the wind: the dynamics of small laboratory-scale dunes

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; van de Water, Willem

    2011-11-01

    Barchan dunes can be found in the desert under steady wind conditions where they translate unaltered in the direction of the wind. These remarkable natural patterns are the result of the interaction between sand and wind where the wind deposits the sand in heaps, which, in turn, change the properties of the turbulent wind. The length scales of these dunes, set by saltation of the grains, can be reduced dramatically by oscillating gravity. This makes laboratory experiments possible. We study the fate of tiny dunes sitting on an oscillating table in the turbulent boundary layer of a wind tunnel. Growth or death of these dunes depends on the influx of sand. Paradoxically, more influx can lead to more erosion. We explain this through a continuum model, and link its unknowns to detailed measurements of grain dynamics.

  4. Initiation and early development of barchan dunes: A case study of the Moroccan Atlantic Sahara desert

    NASA Astrophysics Data System (ADS)

    Elbelrhiti, Hicham

    2012-02-01

    This paper describes field measurements that document the formation of barchan dunes in the Moroccan Atlantic Sahara desert. The first mechanism described is the transformation of patches and proto-dunes at Cap Juby beach to barchan dunes of elementary size. This transformation is discussed in relation to the wind speed and saturation length. The second mechanism is the ejection of small barchans of elementary size by other small barchans in response to the perturbation of the target barchan by two other impacting small barchans. This remote initiation is discussed in relation to the bulk flux transported by the barchan dunes involved in this interaction and to their morphology. Other modes of barchan initiation observed in the field are also presented.

  5. STUDIES OF DUNE CHANGE ON MARS COMBINING MOC AND HIRISE IMAGES. M. C. , A. Philippoff1

    E-print Network

    Bourke, Mary C.

    examined included dome (16%), elongated dome (7%), modified dome (two slip faces, 2%), proto-barchan (23%), barchan (40%) and megabarchan (12%). The mean width of newly sampled dunes was 333 m with a range between

  6. Probing CP violation signal at DUNE in presence of non-standard neutrino interactions

    E-print Network

    Masud, Mehedi; Mehta, Poonam

    2015-01-01

    We discuss the impact of non-standard neutrino matter interactions (NSI) in propagation on the determination of CP phase in the context of the long baseline accelerator experiments such as Deep Underground Neutrino Experiment (DUNE). DUNE will mainly address the issue of CP violation in the leptonic sector. Here we study the role of NSI and its impact on the question of observing the CP violation signal at DUNE. We consider two scenarios of oscillation with three active neutrinos in absence and presence of NSI. We elucidate the importance of ruling out subdominant new physics effects introduced by NSI in inferring CP violation signal at DUNE by considering NSI terms collectively as well as by exploiting the non-trivial interplay of moduli and phases of the NSI terms. We demonstrate the existence of NSI-SI degeneracies which need to be eliminated in reliable manner in order to make conclusive statements about the CP phase.

  7. 77 FR 56671 - Draft Shoreline Restoration Management Plan and Environmental Impact Statement for Indiana Dunes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-13

    ...Dunes National Lakeshore, 1100 N. Mineral Springs Road, Porter, Indiana 46304; telephone (219) 926-7561, extension...public inspection in their entirety. Dated: July 27, 2012. Michael T. Reynolds, Regional Director, Midwest Region. [FR...

  8. SiPMs characterization and selection for the DUNE far detector photon detection system

    E-print Network

    Sun, Yujing

    2015-01-01

    The Deep Underground Neutrino Experiment (DUNE) together with the Long Baseline Neutrino Facility (LBNF) hosted at the Fermilab will provide a unique, world-leading program for the exploration of key questions at the forefront of neutrino physics and astrophysics. CP violation in neutrino flavor mixing is one of its most important potential discoveries. Additionally, the experiment will determine the neutrino mass hierarchy and precisely measure the neutrino mixing parameters which may potentially reveal new fundamental symmetries of nature. Moreover, the DUNE is also designed for the observation of nucleon decay and supernova burst neutrinos. The photon detection (PD) system in the DUNE far detector provides trigger for cosmic backgrounds, enhances supernova burst trigger efficiency and improves the energy resolution of the detector. The DUNE adopts the technology of liquid argon time projection chamber (LArTPC) that requires the PD sensors, silicon photomultipliers (SiPM), to be carefully chosen to not only...

  9. Petrology of dune sand derived from basalt on the Ka'u Desert, Hawaii

    NASA Technical Reports Server (NTRS)

    Gooding, J. L.

    1982-01-01

    Dune sand from the Ka'u Desert, southwest flank of Kilauea volcano, Hawaii, is moderately well-sorted (median = 1.60 Phi, deviation = 0.60, skewness = 0.25, kurtosis = 0.68) and composed mostly of frosted subangular particles of basalt glass ('unfractionated' olivine-normative tholeitte), olivine, lithic fragments (subophitic and intersertal basalts; magnetite-ilmenite-rich basalts), reticular basalt glass, magnetite, ilmenite, and plagioclase, in approximately that order of abundance. Quantitative lithological comparison of the dune sand with sand-sized ash from the Keanakakoi Formation supports suggestions that the dune sand was derived largely from Keanakakoi ash. The dune sand is too well sorted to have been emplaced in its present form by base-surge but could have evolved by post-eruption reworking of the ash.

  10. Lymphangioléiomyomatose pulmonaire de révélation inhabituelle au cours d'une sclérose en plaque

    PubMed Central

    Jaafoura, Neirouz Ghannouchi; Guigua, Ahmed; Zaghouani, Houneida; Atig, Amira; Bakir, Dajla; Khalifa, Mabrouk; Bahri, Fethi

    2015-01-01

    La lymphangioléiomyomatose pulmonaire est une pathologie rare de la femme jeune, caractérisée par une prolifération de cellules musculaires lisses immatures, aboutissant à la destruction kystique des poumons avec possibilité d’évolution vers l'insuffisance respiratoire chronique. La découverte est souvent fortuite lors de la prise en charge d'une autre pathologie pulmonaire. Son association à une sclérose en plaque n'a jamais été rapportée, de même que l'embolie pulmonaire in situ comme manifestation inaugurale. Nous rapportons l'observation d'une patiente âgée de 39 ans, suivie pour sclérose en plaque depuis 20 ans, chez qui le diagnostic d'une lymphangioléiomyomatose pulmonaire a été posé, à l'occasion d'une broncho-pneumopathie bilatérale avec une embolie pulmonaire associée motivant la réalisation d'un angioscanner thoracique. PMID:26185588

  11. Probing CP violation signal at DUNE in presence of non-standard neutrino interactions

    E-print Network

    Mehedi Masud; Animesh Chatterjee; Poonam Mehta

    2015-10-28

    We discuss the impact of non-standard neutrino matter interactions (NSI) in propagation on the determination of CP phase in the context of the long baseline accelerator experiments such as Deep Underground Neutrino Experiment (DUNE). DUNE will mainly address the issue of CP violation in the leptonic sector. Here we study the role of NSI and its impact on the question of observing the CP violation signal at DUNE. We consider two scenarios of oscillation with three active neutrinos in absence and presence of NSI. We elucidate the importance of ruling out subdominant new physics effects introduced by NSI in inferring CP violation signal at DUNE by considering NSI terms collectively as well as by exploiting the non-trivial interplay of moduli and phases of the NSI terms. We demonstrate the existence of NSI-SI degeneracies which need to be eliminated in reliable manner in order to make conclusive statements about the CP phase.

  12. Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice

    NASA Technical Reports Server (NTRS)

    Petrich, Chris; Eicken, Hajo; Polashenski, Christopher M.; Sturm, Matthew; Harbeck, Jeremy P.; Perovich, Donald K.; Finnegan, David C.

    2012-01-01

    The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

  13. Conceptual Design and Physical Model Tests of a Levee-in-Dune Hurricane Barrier 

    E-print Network

    West, Nicholas Allan

    2014-12-04

    In an effort to protect the Greater Houston Metropolitan Area from hurricane storm surge damage, four Levee-in-Dune concepts are studied as part of the Ike Dike project. The Ike Dike is a proposed hurricane surge barrier ...

  14. 77 FR 62476 - Special Regulations; Areas of the National Park System, Sleeping Bear Dunes National Lakeshore...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-15

    ...people visit the Lakeshore annually. SLBE's main visitor attractions include the Dune Climb (330,000+ visitors/year...and is not at issue in this proposal. Compliance With Other Laws and Executive Orders Regulatory Planning and Review...

  15. The impact of devegetated dune fields on North American climate during the late Medieval Climate Anomaly

    NASA Astrophysics Data System (ADS)

    Cook, B. I.; Seager, R.; Miller, R. L.

    2011-07-01

    During the Medieval Climate Anomaly, North America experienced severe droughts and widespread mobilization of dune fields that persisted for decades. We use an atmosphere general circulation model, forced by a tropical Pacific sea surface temperature reconstruction and changes in the land surface consistent with estimates of dune mobilization (conceptualized as partial devegetation), to investigate whether the devegetation could have exacerbated the medieval droughts. Presence of devegetated dunes in the model significantly increases surface temperatures, but has little impact on precipitation or drought severity, as defined by either the Palmer Drought Severity Index or the ratio of precipitation to potential evapotranspiration. Results are similar to recent studies of the 1930s Dust Bowl drought, suggesting bare soil associated with the dunes, in and of itself, is not sufficient to amplify droughts over North America.

  16. The Impact of Devegetated Dune Fields on North American Climate During the Late Medieval Climate Anomaly

    NASA Technical Reports Server (NTRS)

    Cook, B. I.; Seager, R.; Miller, R. L.

    2011-01-01

    During the Medieval Climate Anomaly, North America experienced severe droughts and widespread mobilization of dune fields that persisted for decades. We use an atmosphere general circulation model, forced by a tropical Pacific sea surface temperature reconstruction and changes in the land surface consistent with estimates of dune mobilization (conceptualized as partial devegetation), to investigate whether the devegetation could have exacerbated the medieval droughts. Presence of devegetated dunes in the model significantly increases surface temperatures, but has little impact on precipitation or drought severity, as defined by either the Palmer Drought Severity Index or the ratio of precipitation to potential evapotranspiration. Results are similar to recent studies of the 1930s Dust Bowl drought, suggesting bare soil associated with the dunes, in and of itself, is not sufficient to amplify droughts over North America.

  17. Burrowing mayflies (Hexagenia) as indicators of ecosystem health at Sleeping Bear Dunes National Lakeshore, Michigan

    USGS Publications Warehouse

    Edsall, Thomas A.; Phillips, William E.

    2004-01-01

    The present study describes the provisional use of burrowing mayflies (Hexagenia [Ephemeroptera: Ephemeridae]) as an indicator organism to assess and monitor the health of the Loon Lake and lower Platte River ecosystem within Sleeping Bear Dunes National Lakeshore, Michigan.

  18. Dune-forming winds on Titan and the influence of topography

    NASA Astrophysics Data System (ADS)

    Tokano, Tetsuya

    2008-03-01

    Numerous extended dunes on Saturn's moon Titan detected by the Cassini RADAR constrain the long-term pattern of surface winds. We analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model (GCM) in order to constrain surface wind predictions of this GCM by dune observations. The model shows that modern winds are sufficient for saltation and dune formation at low latitudes, in agreement with the presence of dunes there. The best condition for the dune-forming wind occurs with a threshold friction speed of 0.02 m s -1 or slightly less. The equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the Hadley circulation. The cross-equatorial wind is steady, and is characterised by a high Weibull shape parameter ( k˜4). The wind pattern at higher latitudes is more complex and gusty, and neither longitudinal nor transversal dunes would be able to form. Putative large-scale topography is found to have a profound influence on the near-surface wind pattern. Generally mountains cause a convergence and speeding up on the flank, while basins weaken the wind and cause a divergent flow. Longitudinal dunes can be deflected on the foot of mountains by up to 90°. If Xanadu is a hypothetical large mountain, a wind pattern converging in Xanadu that entirely disagrees with the dune observations is predicted. If instead Xanadu is a large basin, the wind arcs clockwise north of Xanadu and anti-clockwise west and southwest of Xanadu, in agreement with the dune orientations in the vicinity of Xanadu. The albedo pattern has comparatively little influence on the wind field. Isolated mountain chains cause only local-scale change in the wind pattern. However, the persistent surface easterlies in Belet, which are in conflict with the dune orientations, do not disappear by any combination of large-scale topography.

  19. Sand dunes monitoring using remote sensing and GIS techniques for some sites in Iraq

    NASA Astrophysics Data System (ADS)

    Fadhil, Ayad Mohammed

    This study is aimed at monitoring, mapping and assessing the sand dune encroachment in the northern central part of Iraq. The study area includes six districts suffering from the increasing prevalence of sand dunes, particularly in the recent years, which are characterized by dry weather and a reduction in rainfall averages. Remote sensing "RS" and in particular, Earth observation satellites besides Geographical Information Systems "GIS" provide significant contributions to monitoring sand dunes encroachment. Two Landsat TM images acquired on July of 1988, and July of 2009 were assembled and used to extract the research indices. Satellite image based indices; the Normalized Difference Vegetation Index "NDVI", the Tasseled Cap Wetness Indicator "TCW", the Land Surface Temperature "LST", and the Normalized Difference Sand Index "NDSI" (a new index which has been proposed in this study) with RS and GIS techniques were used for monitoring the sand dune encroachment at two sites in the northern central part of Iraq. The results showed an increase in the sand dunes accumulations by 2,020.6 km2 and 291.1 km2 throughout the 21 years from 1988 to 2009 in Baiji and Al-Aith sites in the region, respectively. Sand dunes movement rates for the same period were 1,155.9 m year-1 and 494.2 m year-1 in the two mentioned sites, respectively. The results showed that the study area in general is exposed to a high risk of sand dune encroachment. The means of soil conditioners and windbreaks has been proposed to mitigate the impacts of sand dune encroachment.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  2. Quantification of Dune Response over the Course of a 6-Day Nor'Easter, Outer Banks, NC

    NASA Astrophysics Data System (ADS)

    Brodie, K. L.; Spore, N.; Swann, C.

    2014-12-01

    The amount and type of foredune morphologic change during a storm event primarily scales with the level of inundation during that event. Specifically, external hydrodynamic forcing (total water level) can be compared with antecedent beach and foredune morphology to predict an impact regime that relates to the type of expected morphologic evolution of the system. For example, when total water levels are above the dune toe, but below the dune crest, the impact regime is classified as "collision" and the expected morphology response is slumping or scarping of the dune face. While the amount of dune retreat scales largely with the duration of wave attack to the dune face, characteristics of the dune other than its crest or toe elevation may also enhance or impede rates of morphologic change. The aftermath of Hurricane Sandy provided a unique opportunity to observe alongshore variations in dune response to a 6-day Nor'Easter (Hs >4 m in 6 m depth), as a variety of dunes were constructed (or not) by individual home owners in preparation for the winter storm season. Daily terrestrial lidar scans were conducted along 20 km of coastline in Duck, NC using Coastal Lidar And Radar Imaging System (CLARIS) during the first dune collision event following Sandy. Foredunes were grouped by their pre-storm form (e.g. vegetated, pushed, scarped, etc) using automated feature extraction tools based on surface curvature and slope, and daily rates of morphologic volume change were calculated. The highest dune retreat rates were focused along a 1.5 km region where cross-shore erosion of recently pushed, un-vegetated dunes reached 2 m/day. Variations in dune response were analyzed in relation to their pre-storm morphology, with care taken to normalize for alongshore variations in hydrodynamic forcing. Ongoing research is focused on identifying specific metrics that can be easily extracted from topographic DEMs to aid in dune retreat predictions.

  3. Efficient fog harvesting by Stipagrostis sabulicola (Namib dune bushman grass)

    NASA Astrophysics Data System (ADS)

    Roth-Nebelsick, A.; Ebner, M.; Miranda, T.

    2010-07-01

    Stipagrostis sabulicola is an endemic species of the central Namib Desert which settles on extremely arid dune fields. Due to its ability to persistence even during exceptionally dry years it is generally assumed that water supply of this species is substantially based on fog water. In this contribution, the results of a study investigating the capability of S. sabulicola for fog harvesting are presented. For this purpose, stem flow rates of S. sabulicola during fog events, spatial gradient of soil water content (SWC) close to mounds of S. sabulicola and its leaf water potential (LWP) before and after fog events were monitored together with climate parameters. According to the data obtained during this study, S. sabulicola is able to harvest substantial amounts of water by fog catchment from nocturnal fog events. Since culms of S. sabulicola are often stiff with an upright habitus, fog harvesting occurs via stemflow that conducts water directly towards the root zone of a plant. According to this mechanism, the stem runoff is concentrated within the area of the mound. A medium-sized mound of S. sabulicola is able to collect an amount of about 4 l per fog night. This fog harvesting leads to a considerable spatial gradient of soil water content with values decreasing with increasing distance from the mound. As a result of the water input by fog drip, SWC within the mound increases significantly, particularly close to the culm bases where SWC values increased to 2.2 % after a fog event. Due to the uneven distribution of water by stemflow, SWC within a mound shows high spatial heterogeneity which is also illustrated by the numerous outliers and extreme values of SWC within the mound region. This heterogeneity is also due to the fact that several sagging leaves are always present causing fog drip which more or less irregularly scatters moisture. For bare soil outside of a mound, the water content is not substantially increased, amounting to 0.78 % on average during dry days and 0.89 % after fog events. Fog harvesting affects also leaf water potential: whereas leaf water potential declines during dry days, it remains more or less constant on days following fog events. Since mounds of S. sabulicola provide shelter and food for various other organisms such as ants and lizards, their ability for nocturnal fog catchment is of high significance for the ecosystem of the Namib dunes.

  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. Mycorrhizal fungal communities in coastal sand dunes and heaths investigated by pyrosequencing analyses.

    PubMed

    Botnen, Synnøve; Kauserud, Håvard; Carlsen, Tor; Blaalid, Rakel; Høiland, Klaus

    2015-08-01

    Maritime sand dunes and coastal ericaceous heaths are unstable and dynamic habitats for mycorrhizal fungi. Creeping willow (Salix repens) is an important host plant in these habitats in parts of Europe. In this study, we wanted to assess which mycorrhizal fungi are associated with S. repens in four different coastal vegetation types in Southern Norway, three types from sand dunes and one from heaths. Moreover, we investigated which ecological factors are important for the fungal community structure in these vegetation types. Mycorrhizal fungi on S. repens root samples were identified by 454 pyrosequencing of tag-encoded internal transcribed spacer 1 (ITS1) amplicons. Significantly higher fungal richness was observed in hummock dunes and dune slacks compared to eroded dune vegetation. The compositional variation was mainly accounted for by location (plot) and vegetation type and was significantly correlated to content of carbon, nitrogen and phosphorus in soil. The investigated maritime sand dunes and coastal ericaceous heaths hosted mycorrhizal taxa mainly associated with Helotiales, Sebacinales, Thelephorales and Agaricales. PMID:25597300

  6. Mediterranean coastal dune systems: Which abiotic factors have the most influence on plant communities?

    NASA Astrophysics Data System (ADS)

    Ruocco, Matteo; Bertoni, Duccio; Sarti, Giovanni; Ciccarelli, Daniela

    2014-08-01

    Mediterranean coastal dunes are dynamic and heterogeneous ecosystems characterised by a strong interaction between abiotic and biotic factors. The present study aimed to adopt a multidisciplinary approach - integrating data on dune morphology, sediment texture and soil parameters as well as shoreline trend - in order to define which are the abiotic factors that most affect the distribution and composition of Mediterranean plant dune communities. The study was carried out in two protected areas, located in central Italy, subjected to different shoreline trends in recent years. 75 plots were identified along eleven randomly positioned cross-shore transects, starting from the beach continuing up to the plant communities of the backdunes. In each plot floristic and environmental data - such as distance to the coastline, plot altitude, inclination, shoreline trend, mean grain-size, sorting, pH, conductivity and organic matter concentration - were collected. The analyses revealed significant changes of vegetational cover, dune morphology and geopedological features along the coast-to-inland gradient. Relationships between vegetation composition and environmental factors were investigated through Canonical Correspondence Analysis (CCA). Four factors - distance to the coastline, mean grain-size, shoreline trend and organic matter - were found to be closely correlated with the floristic composition of plant communities. Finally, soil properties were highlighted as the most determinant factors of community zonation in these Mediterranean coastal dune ecosystems. These results could be taken into account by local managers in conservation actions such as protecting the eroding foredunes as well as in artificial dune reconstructions.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  8. Global mapping and characterization of Titan's dune fields with Cassini: Correlation between RADAR and VIMS observations

    NASA Astrophysics Data System (ADS)

    Rodriguez, S.; Garcia, A.; Lucas, A.; Appéré, T.; Le Gall, A.; Reffet, E.; Le Corre, L.; Le Mouélic, S.; Cornet, T.; Courrech du Pont, S.; Narteau, C.; Bourgeois, O.; Radebaugh, J.; Arnold, K.; Barnes, J. W.; Stephan, K.; Jaumann, R.; Sotin, C.; Brown, R. H.; Lorenz, R. D.; Turtle, E. P.

    2014-02-01

    Vast fields of linear dunes have been observed in the equatorial regions of Titan, Saturn's largest moon. As the Cassini mission, in orbit around Saturn since July 2004 and extended until May 2017, carries on, the high-resolution coverage of Titan's surface increases, revealing new dune fields and allowing refinements in the examination of their properties. In this paper, we present the joint analysis of Cassini's microwave and infrared global scale observations of Titan. Integrating within an up-to-date global map of Titan all the Cassini RADAR and VIMS (Visual and Infrared Mapping Spectrometer) images - the latter being empirically corrected for atmospheric scattering and surface photometry, from July 2004 through July 2013 and June 2010 respectively, we found very good qualitative and quantitative spatial matching between the geographic distribution of the dune fields and a specific infrared spectral unit (namely the “dark brown” unit). The high degree of spatial correlation between dunes and the “dark brown” unit has important implications for Titan's geology and climate. We found that RADAR-mapped dunes and the “dark brown” unit are similarly confined within the equatorial belt (±30° in latitudes) with an equivalent distribution with latitude, suggesting an increasing sediment availability and mobility at Titan's tropics relative to higher latitudes, compatible with the lower ground humidity predicted in equatorial regions by General Circulation Models. Furthermore, the strong correlation between RADAR-mapped dunes and the VIMS “dark brown” unit (72%) allows us to better constrain the total surface area covered by dune material, previously estimated from the extrapolation of the RADAR observations alone. According to our calculations, dune material cover 17.5 ± 1.5% of Titan's surface area, equivalent to a total surface area of 14.6 ± 1.2 million km2 (˜1.5 times the surface area of Earth's Sahara desert). The VIMS “dark brown” coloration of the dune material is here confirmed at large spatial scale. If the sand particle composition is dominated by solid organics produced in and settling from the atmosphere, as supported by our spectral modeling and by previous spectral analysis, microwave radiometric data and atmospheric modeling, dune fields are one of the major surface hydrocarbon reservoirs on Titan. Assuming two possible scenarios for the sand distribution (either the sand is (1) entirely trapped in dune landforms, or (2) trapped in dunes at places where dune landforms are firmly observed and in sand sheets elsewhere), we estimate the volume of hydrocarbons trapped in the dune sediment to be comprised between 1.7 and 4.4 × 105 km3, corresponding to an average total mass of 230,000 GT, in comparison with ˜4000-30,000 GT of hydrocarbons in the polar lakes and seas. This indicates a maximum age for the dune sediments of ˜730-Myr, consistent with estimations of the ages of the current Titan's atmospheric methane and surface.

  9. A 45-year time series of Saharan dune mobility from remote sensing

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2012-04-01

    Decadal trends in the aeolian dust record of the Sahara affect the global climate system and the nutrient budget of the Atlantic Ocean. One proposed cause of these trends are changes in the frequency and intensity of dust storms, which have hitherto been hard to quantify. Because sand flux scales with the cube of wind speed, dune migration rates can be used as a proxy for storminess. Relative changes in the storminess of the Sahara can thus be monitored by tracking the migration rates of individual sand dunes over time. The Bodélé Depression of northern Chad was selected as a target area for this method, because it is the most important point-source of aeolian dust on the planet and features the largest and fastest dunes on Earth. A collection of co-registered Landsat, SPOT, and ASTER scenes, combined with declassified American spy satellite images was used to construct a 45 year record of dune migration in the Bodélé Depression. One unexpected outcome of the study was the observation of binary dune interactions in the imagery sequence, which reveals that when two barchan dunes collide, a transfer of mass occurs so that one dune appears to travel through the other unscathed, like a solitary wave. This confirms a controversial numerical model prediction and settles a decade-old debate in aeolian geomorphology. The COSI-Corr change detection method was used to measure the dune migration rates from 1984 until 1987, 1990, 1996, 2000, 2003, 2005, 2007, 2008, 2009, and 2010. An algorithm was developed to automatically warp the resulting displacement fields back to a common point in time. Thus, individual image pixels of a dune field were tracked over time, allowing the extraction of a time series from the co-registered satellite images without further human intervention. The automated analysis was extended further back into the past by comparison of the 1984 image with declassified American spy satellite (Corona) images from 1965 and 1970. Due to the presence of specks of dust as well as image distortions caused by shrinking of the photographic film, it was not possible to automatically measure the dune displacements of these scenes with COSI-Corr. Instead, the image was georeferenced and coregistered to the 1984 Landsat imagery by third order polynomial fits to 531 tie points, and the displacements of ten large barchan dunes were measured by hand. Thanks to the 19-year time lapse between the two images used for these 'analog' measurements, their precision is better than 5%, which is comparable with that of the automated COSI-Corr analysis. The resulting dune celerities are identical to the automated measurements, which themselves show little or no temporal variability over the subsequent 26 years. The lack of any trend in the time series of dune celerity paints a picture of remarkably stable dune mobility over the past 45 years. None of the distributions fall outside the overall average of 25m/yr. The constant dune migration rates resulting from our study indicate that there has been no change in the storminess of the Sahara over the past 45 years. The observed dust trends are therefore caused by changes in vegetation cover, which in turn reflect changes in precipitation and land usage. This work highlights the importance of the hyper-arid Bodélé Depression, which provides a steady but finite supply of aeolian dust to the atmosphere without which nutrient fluxes and terrestrial albedo would be more variable than they are today.

  10. A case of a 6-year-old girl with anti-neutrophil cytoplasmic autoantibody-negative pauci-immune crescentic glomerulonephritis.

    PubMed

    Shimizu, Maki; Sekiguchi, Takanori; Kishi, Natsuko; Goji, Aya; Takahashi, Tomoko; Kozan, Hiroko; Sakaguchi, Zenichi; Kinoshita, Yukiko; Matsuura, Sato; Suga, Kenichi; Urushihara, Maki; Kondo, Shuji; Kagami, Shoji; Ohara, Katsuaki

    2011-08-01

    A 6-year-old girl was admitted to our hospital with proteinuria, hematuria, skin rash and joint pain of the lower limbs. Due to rapid progression of renal insufficiency, hemodialysis and peritoneal dialysis were performed. She was diagnosed with rapidly progressive glomerulonephritis. Kidney biopsy showed severe crescent formation (50% of glomeruli) and no deposition of any immunoglobulins or complements. Serologically, anti-neutrophil cytoplasmic autoantibody (ANCA) was negative not only by ELISA against proteinase-3 and myeloperoxidase-ANCA but also by indirect immunofluorescent assay against cytoplasmic and perinuclear ANCA. Anti-glomerular basement membrane antibody was also negative. In the acute phase, proinflammatory cytokines such as soluble tumor necrosis factor receptor 1 (sTNFR1), soluble interleukin (IL)-2 receptor (sIL2R), IL-6 and chemokine IL-8 were elevated. The patient was diagnosed with ANCA-negative pauci-immune crescentic glomerulonephritis (CrGN). Intensive treatment with methylprednisolone pulse therapy, plasma exchange, and multiple drug therapy including prednisolone and cyclophosphamide resulted in histopathological improvement and complete remission of proteinuria. There was a possibility that sTNFR1, sIL2R, IL-6 and IL-8 might be involved in the initiation and progression of ANCA-negative pauci-immune CrGN, and to remove and suppress these cytokines might be an effective way to treat ANCA-negative pauci-immune CrGN. PMID:21360022

  11. Nuclear Factor Erythroid 2-Related Factor 2 Drives Podocyte-Specific Expression of Peroxisome Proliferator-Activated Receptor ? Essential for Resistance to Crescentic GN.

    PubMed

    Henique, Carole; Bollee, Guillaume; Lenoir, Olivia; Dhaun, Neeraj; Camus, Marine; Chipont, Anna; Flosseau, Kathleen; Mandet, Chantal; Yamamoto, Masayuki; Karras, Alexandre; Thervet, Eric; Bruneval, Patrick; Nochy, Dominique; Mesnard, Laurent; Tharaux, Pierre-Louis

    2016-01-01

    Necrotizing and crescentic rapidly progressive GN (RPGN) is a life-threatening syndrome characterized by a rapid loss of renal function. Evidence suggests that podocyte expression of the transcription factor peroxisome proliferator-activated receptor ? (PPAR?) may prevent podocyte injury, but the function of glomerular PPAR? in acute, severe inflammatory GN is unknown. Here, we observed marked loss of PPAR? abundance and transcriptional activity in glomerular podocytes in experimental RPGN. Blunted expression of PPAR? in podocyte nuclei was also found in kidneys from patients diagnosed with crescentic GN. Podocyte-specific Ppar? gene targeting accentuated glomerular damage, with increased urinary loss of albumin and severe kidney failure. Furthermore, a PPAR? gain-of-function approach achieved by systemic administration of thiazolidinedione (TZD) failed to prevent severe RPGN in mice with podocyte-specific Ppar? gene deficiency. In nuclear factor erythroid 2-related factor 2 (NRF2)-deficient mice, loss of podocyte PPAR? was observed at baseline. NRF2 deficiency markedly aggravated the course of RPGN, an effect that was partially prevented by TZD administration. Furthermore, delayed administration of TZD, initiated after the onset of RPGN, still alleviated the severity of experimental RPGN. These findings establish a requirement for the NRF2-PPAR? cascade in podocytes, and we suggest that these transcription factors have a role in augmenting the tolerance of glomeruli to severe immune-complex mediated injury. The NRF2-PPAR? pathway may be a therapeutic target for RPGN. PMID:25999406

  12. Wind Erosion and Dune Formation on High Frozen Bluffs

    NASA Technical Reports Server (NTRS)

    Marsh, W. M.; Marsh, B. D.

    1984-01-01

    Frost penetration increases upslope on barren, windswept bluffs in cold environments. Along the south shore of Lake Superior, near the brow of 100 m high bluffs it typically exceeds 5 m. Frost increases the shear strength of damp sand to a level comparable to that of concrete, making winter slopes highly stable despite undercutting by waves and ground-water sapping along the footslope. Sublimation of interparticle ice in the slope face increases with wind speed and lower vapor pressures. The cold and dry winter winds of Lake Superior ablate these slopes through loss of binding ice. Wind erosion rates, based on measurements of sand accumulation on the forest floor downwind of the brow, show most airborne sand falls out within several meters of the brow, forming a berm 1 to 3 m high after many years. The spatial pattern of sand deposition, however, varies considerably over distances of several hundred meters along the top bluffs in response to frost conditions and the build-up of gravel lag on the slope face, sand exposure from mass movements, and local aerodynamics of the crest slope. The formation of perched sand dunes in the Great Lakes region is clearly related to wind erosion of sand from high bluffs in winter. Broadly similar processes may operate on Mars.

  13. 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

  14. Eye development in the Cape dune mole rat.

    PubMed

    Nikitina, Natalya V; Kidson, Susan H

    2014-03-01

    Studies on mammalian species with naturally reduced eyes can provide valuable insights into the evolutionary developmental mechanisms underlying the reduction of the eye structures. Because few naturally microphthalmic animals have been studied and eye reduction must have evolved independently in many of the modern groups, novel evolutionary developmental models for eye research have to be sought. Here, we present a first report on embryonic eye development in the Cape dune mole rat, Bathyergus suillus. The eyes of these animals contain all the internal structures characteristic of the normal eye but exhibit abnormalities in the anterior chamber structures. The lens is small but develops normally and exhibits a normal expression of ?- and ?-crystallins. One of the interesting features of these animals is an extremely enlarged and highly pigmented ciliary body. In order to understand the molecular basis of this unusual feature, the expression pattern of an early marker of the ciliary zone, Ptmb4, was investigated in this animal. Surprisingly, in situ hybridization results revealed that Ptmb4 expression was absent from the ciliary body zone of the developing Bathyergus eye. PMID:24570380

  15. Remotely sensed dune sand flux measurements in the dustiest place on Earth (Bodélé, Chad)

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2009-12-01

    The Bodélé Depression of northern Chad is the dustiest place on Earth, thanks to a unique combination of two factors. First, the Bodélé is located downwind of a narrow gap between the Tibesti and Ennedi mountain ranges, which act as a funnel creating the strong winds of the Bodélé Low Level Jet. Second, the depression forms the deepest part of palaeo-lake Megachad, which once rivaled the Caspian Sea in size. When the lake dried out during the Holocene, it left behind thick deposits of diatomite, which currently provide an abundant and readily available source of dust. Previous work has shown that dust is primarily produced by eddies near the horns of barchan dunes. Using a new remote sensing technique called COSI-Corr, these barchans were shown to be not only the largest, but also the fastest on Earth, featuring the highest sand fluxes. Quantifying sand flux with field measurements is an expensive and time-consuming process. COSI-Corr -which stands for 'Co-registration of Optically Sensed Images and Correlation' and was originally developed for the purpose of detecting surface deformation caused by earthquakes- offers an alternative approach to measuring sand flux, using remote sensing. From pairs of ASTER imagery, dune migration in the Bodélé depression was successfully measured over time intervals of one month to 6.5 years. The displacement maps produced by COSI-Corr can be used to automatically distinguish dunes from interdunes, which is a crucial step towards calculating sand flux. Dune heights and volumes were obtained by interpolating a surface between the interdune areas and subtracting it from a digital elevation model. Multiplying height with celerity yields a pixel-by-pixel estimate of the sand flux. Applying this method to large diatomite dunes in the Bodélé confirms that these are some of the world’s fastest moving barchans. Plotting dune height against inverse celerity reveals sand flux at the dune crest of >200 m3/m/yr. Average dune sand flux values for the eastern and western Bodélé are 76 and 99 m3/m/yr, respectively. The contribution of the dunes to the total area-averaged sand flux is 24-29 m3/m/yr, which is ~10% of the saltation flux determined by previously published field measurements. The displacement field of quartz dunes in the northeastern Bodélé displayed as a vector field.

  16. Controls on coastal dune morphology, shoreline erosion and barrier island response to extreme storms

    USGS Publications Warehouse

    Houser, C.; Hapke, C.; Hamilton, S.

    2008-01-01

    The response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore. While it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge, the underlying causes of the alongshore variation remain poorly understood. This study examines the alongshore variation in dune morphology along a 11??km stretch of Santa Rosa Island in northwest Florida and relates the variation in morphology to the response of the island during Hurricane Ivan and historic and storm-related rates of shoreline erosion. The morphology of the foredune and backbarrier dunes was characterized before and after Hurricane Ivan using Empirical Orthogonal Function (EOF) analysis and related through Canonical Correlation Analysis (CCA). The height and extent of the foredune, and the presence and relative location of the backbarrier dunes, varied alongshore at discrete length scales (of ~ 750, 1450 and 4550??m) that are statistically significant at the 95% confidence level. Cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner-shelf, the backbarrier cuspate headlands, and the historical and storm-related trends in shoreline change. Sections of the coast with little to no dune development before Hurricane Ivan were observed in the narrowest portions of the island (between headlands), west of the transverse ridges. Overwash penetration tended to be larger in these areas and island breaching was common, leaving the surface close to the watertable and covered by a lag of shell and gravel. In contrast, large foredunes and the backbarrier dunes were observed at the widest sections of the island (the cuspate headlands) and at crest of the transverse ridges. Due to the large dunes and the presence of the backbarrier dunes, these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper-shoreface. It is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace. Since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface, it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively. These findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during Hurricane Ivan. ?? 2008 Elsevier B.V. All rights reserved.

  17. The internal structure of modern barchan dunes of the Ebro River Delta (Spain) from ground penetrating radar

    NASA Astrophysics Data System (ADS)

    Gómez-Ortiz, D.; Martín-Crespo, T.; Rodríguez, I.; Sánchez, M. J.; Montoya, I.

    2009-06-01

    Ground penetrating radar is a non-invasive technique that allows the study of the structure of dune systems when outcrops are limited or protected. GPR response of sand dunes of the Holocene aeolian dunes of the Ebro River Delta (Spain) has been analyzed in this study in order to: characterise their internal architecture, determine their development and recent evolution, and calculate electromagnetic (EM) waves mean velocities in fine-grained sedimentary deposits. Several GPR profiles carried out in different representative areas have revealed the existence of different reflector packages that are related to differences in barchan-type dune activity. The area with a highest sand movement activity is characterized by small dunes, with overlapping reflector packages exhibiting reflections which dip up to 25°. When dune activity is moderate, dunes are higher (up to 5 m height) and their internal structure shows low-angle dip reflections except for the avalanche face, where dips up to 22° are identified. The area with the lowest sand movement, nearest to the coast line, is represented by small dunes with internal geometry consisting of partially overlapping elongated reflector packages defined by subhorizontal reflections. In all cases, a reflection associated to the location of the water table has been recognized at about 0.7 m depth. The results obtained from the GPR survey have allowed us to improve our knowledge about the dynamics of the coastal dune field and its relative evolution. They have shown that the morphology and geometry of the dune bodies adapt themselves to wind conditions, which permits the construction of coastal dune development models in order to establish the evolution of dunes.

  18. Luminescence dating of Holocene dune complexes along the shore of northern France (Picardy)

    NASA Astrophysics Data System (ADS)

    Lauer, Tobias; Frechen, Manfred; Meurisse-Fort, Murielle; Gosselin, Guillaume; van Vliet-Lanoë, Brigitte

    2010-05-01

    The Holocene dune and peat complexes along the shore of northern France (Picardy) had already been studied in detail by Meurisse et al. (2005) and Meurisse-Fort (2009). Information about the palaeodevelopment of those dune fields is hence given due to existing 14C data as well as by sedimentological and morphological analyses. Due to the results from radiocarbon dating, different types of aeolian bodies could be correlated along the Picardy coastline and a regional stratigraphic sequence could be established (Meurisse-Fort, 2009). The aim of the ongoing study is to get a higher chronological resolution for the different phases of dune activity in Picardy by luminescence dating what is a powerful tool to determine the time of last sunlight exposure of grains before burial (this information yields important information about dune movement). Samples for OSL dating were taken from dune bodies located in Tardinghen, Hardelot, Saint-Frieux and Saint-Gabriel. For dating, a single aliquot regenerative dose (SAR) protocol (Murray & Wintle 2003) is applied to coarse grained quartz. First tests concerning the signal intensity, the purity of the quartz OSL signal and the bleaching properties showed that quartz OSL dating works well for the dunes of the northern France coastline. The new luminescence ages will help to better unravel the phases of sand dune activity and stabilisation mainly controlled by climate changes and human impact. References: Meurisse, M., Van Vliet-Lanoë, B., Talon, B. & Recourt, P. (2005): Complexes dunaires et tourbeux holocènes du littoral du Nord de la France. - Geoscience, 337 : 675-684. Meurisse-Fort, M. (2009): Enregistrement haute résolution des massifs dunaires ; Manche, mer du Nord et Atlantique - Le rôle des tempêtes. Thèse de Doctorat soutenue en juin 2007, Université de Lille1. Coll. Recherches - Sciences (Sciences de la Terre). EPU-Publibook (ed.), Paris, 310 pp. Murray, A.S. & Wintle, A.G. (2003): The single aliquot regenerative dose protocol: potential for improvements in reliability. - Radiat. Meas., 37: 377-381.

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

    NASA Astrophysics Data System (ADS)

    Lancaster, N.; Halfen, A. F.

    2012-12-01

    Sand seas and dune fields are globally significant sedimentary deposits, which archive the effects of climate and sea level change on a variety of temporal and spatial scales. Dune systems provide a valuable source of information on past climate conditions, including evidence for periods of aridity and unique data on past wind regimes. Researchers have compiled vast quantities of geomorphic and chronological data from these dune systems for nearly half a century, however, these data remain disconnected, making comparisons of dune systems challenging at global and regional scales. The primary goal of this project is to develop a global digital database of chronologic information for periods of desert sand dune accumulation and stabilization, as well as, pertinent stratigraphic and geomorphic information. This database can then be used by scientists to 1) document the history of aeolian processes in arid regions with emphasis on dune systems in low and mid latitude deserts, 2) correlate periods of sand accumulation and stability with other terrestrial and marine paleoclimatic proxies and records, and 3) develop an improved understanding of the response of dune systems to climate change. The database currently resides in Microsoft Access format, which allows searching and filtering of data. The database includes 4 linked tables containing information on the site, chronological control (radiocarbon or luminescence), and the pertinent literature citations. Thus far the database contains information for 838 sites world wide, comprising 2598 luminescence and radiocarbon ages, though these numbers increase regularly as new data is added. The database is only available on request at this time, however, an online, GIS database is being developed and will be available in the near future. Data outputs from the online database will include PDF reports and Google Earth formatted data sets for quick viewing of data. Additionally, data will be available in a gridded format for wider use in data-model comparisons. Sites in database August 2012

  20. High-Resolution Monitoring of Coastal Dune Erosion and Growth Using an Unmanned Aerial Vehicle

    NASA Astrophysics Data System (ADS)

    Ruessink, G.; Markies, H.; Van Maarseveen, M.

    2014-12-01

    Coastal foredunes lose and gain sand through marine and aeolian processes, but coastal-evolution models that can accurately predict both wave-driven dune erosion and wind-blown dune growth are non-existing. This is, together with a limited understanding of coastal aeolian process dynamics, due to the lack of adequate field data sets from which erosion and supply volumes can be studied simultaneously. Here, we quantify coastal foredune dynamics using nine topographic surveys performed near Egmond aan Zee, The Netherlands, between September 2011 and March 2014 using an unmanned aerial vehicle (UAV). The approximately 0.75-km long study site comprises a 30-100 m wide sandy beach and a 20-25 m high foredune, of which the higher parts are densely vegetated with European marram grass. Using a structure-from-motion workflow, the 200-500 photographs taken during each UAV flight were processed into a point cloud, from which a geo-referenced digital surface model with a 0.25 x 0.25 m resolution was subsequently computed. Our data set contains two dune-erosion events, including that due to storm Xaver (December 2013), which caused one of the highest surge levels in the southern North Sea region for the last decades. Dune erosion during both events varied alongshore from the destruction of embryonic dunes on the upper beach to the slumping of the entire dune face. During the first storm (January 2012), erosion volumes ranged from 5 m3/m in the (former) embryonic dune field to over 40 m3/m elsewhere. During the subsequent 11 (spring - autumn) months, the foredune accreted by (on average) 8 m3/m, again with substantial alongshore variability (0 - 20 m3/m). Intriguingly, volume changes during the 2012-2013 winter were minimal. We will compare the observed aeolian supply rates with model predictions and discuss reasons for their temporal variability. Funded by the Dutch Organisation for Scientific Research NWO.

  1. A meta-analysis of plant facilitation in coastal dune systems: responses, regions, and research gaps.

    PubMed

    Castanho, Camila de Toledo; Lortie, Christopher J; Zaitchik, Benjamin; Prado, Paulo Inácio

    2015-01-01

    Empirical studies in salt marshes, arid, and alpine systems support the hypothesis that facilitation between plants is an important ecological process in severe or 'stressful' environments. Coastal dunes are both abiotically stressful and frequently disturbed systems. Facilitation has been documented, but the evidence to date has not been synthesized. We did a systematic review with meta-analysis to highlight general research gaps in the study of plant interactions in coastal dunes and examine if regional and local factors influence the magnitude of facilitation in these systems. The 32 studies included in the systematic review were done in coastal dunes located in 13 countries around the world but the majority was in the temperate zone (63%). Most of the studies adopt only an observational approach to make inferences about facilitative interactions, whereas only 28% of the studies used both observational and experimental approaches. Among the factors we tested, only geographic region mediates the occurrence of facilitation more broadly in coastal dune systems. The presence of a neighbor positively influenced growth and survival in the tropics, whereas in temperate and subartic regions the effect was neutral for both response variables. We found no evidence that climatic and local factors, such as life-form and life stage of interacting plants, affect the magnitude of facilitation in coastal dunes. Overall, conclusions about plant facilitation in coastal dunes depend on the response variable measured and, more broadly, on the geographic region examined. However, the high variability and the limited number of studies, especially in tropical region, indicate we need to be cautious in the generalization of the conclusions. Anyway, coastal dunes provide an important means to explore topical issues in facilitation research including context dependency, local versus regional drivers of community structure, and the importance of gradients in shaping the outcome of net interactions. PMID:25699214

  2. Changes in plant species composition of coastal dune habitats over a 20-year period

    PubMed Central

    Del Vecchio, Silvia; Prisco, Irene; Acosta, Alicia T. R.; Stanisci, Angela

    2015-01-01

    Coastal sandy ecosystems are increasingly being threatened by human pressure, causing loss of biodiversity, habitat degradation and landscape modifications. However, there are still very few detailed studies focussing on compositional changes in coastal dune plant communities over time. In this work, we investigated how coastal dune European Union (EU) habitats (from pioneer annual beach communities to Mediterranean scrubs on the landward fixed dunes) have changed during the last 20 years. Using phytosociological relevés conducted in 1989–90 and in 2010–12, we investigated changes in floristic composition over time. We then compared plant cover and the proportion of ruderal, alien and habitat diagnostic species (‘focal species’) in the two periods. Finally, we used Ellenberg indicator values to define the ‘preferences’ of the plant species for temperature and moisture. We found that only fore dune habitats showed significant differences in species cover between the two time periods, with higher plant cover in the more recent relevés and a significant increase in thermophilic species. Although previous studies have demonstrated consistent habitat loss in this area, we observed that all coastal dune plant communities remain well represented, after a 20-year period. However, fore dunes have been experiencing significant compositional changes. Although we cannot confirm whether the observed changes are strictly related to climatic changes, to human pressure or to both, we hypothesize that a moderate increment in average yearly temperature may have promoted the increase in plant cover and the spread of thermophilic species. Thus, even though human activities are major driving forces of change in coastal dune vegetation, at the community scale climatic factors may also play important roles. Our study draws on re-visitation studies which appear to constitute a powerful tool for the assessment of the conservation status of EU habitats. PMID:25750408

  3. Dune-dammed lakes of the Nebraska Sand Hills: Geologic setting and paleoclimatic implications

    SciTech Connect

    Loope, D.B.; Swinehart, J.B. )

    1992-01-01

    Within the western half of this grass-stabilized dunefield, about 1,000 interdune lakes are grouped into two clusters here named the Blue and Birdwood lake basins. In the lake basins, those parts of the valley not filled by dune sand are occupied by modern lakes and Holocene lake sediments. The Blue Creek dam is mounded transverse to flow; spill-over of the lake basin takes place over bedrock on the east side of the dam when lake level is 2 m higher than present. The permeability of dune sand prevents massive overflow, and thereby contributes to the integrity and longevity of the dam. Preserved lake sediments in the basin indicate that Blue Creek was obstructed prior to 13,000 yr BP, probably during glacial maximum (18,000 yr BP). Extensive peats dated at 1,500-1,000 yr BP lie directly on fluvial sand and gravel along the Calamus River, a stream that presently discharges a nearly constant 350 cfs. These sediments indicate blockage of streams also took place when linear dunes were active in the eastern Sand Hills in Late Holocene time. With the onset of an arid episode, dunes forming an interfluves curtail the severity of runoff events. As the regional water table drops, drainages go dry and dunes move uncontested into blocking positions. Although drainages of the eastern Sand Hills appear to have repeatedly broken through sand-blocked channels, the Blue and Birdwood lake basins are still blocked by Late Pleistocene dune dams. The repeated episodes of stream blockage and interbedded lake sediments and dune sands behind the extant dams record several strong fluctuations in Holocene climate. Recently proposed climatic models indicate that the northward flow of warm, moist air from the Gulf of Mexico is enhanced when the Gulf's surface temperature is low and the Bermuda high is intensified and in a western position. When the Bermuda high moves eastward, the core of the North American continent becomes desiccated.

  4. Changes in plant species composition of coastal dune habitats over a 20-year period.

    PubMed

    Del Vecchio, Silvia; Prisco, Irene; Acosta, Alicia T R; Stanisci, Angela

    2015-01-01

    Coastal sandy ecosystems are increasingly being threatened by human pressure, causing loss of biodiversity, habitat degradation and landscape modifications. However, there are still very few detailed studies focussing on compositional changes in coastal dune plant communities over time. In this work, we investigated how coastal dune European Union (EU) habitats (from pioneer annual beach communities to Mediterranean scrubs on the landward fixed dunes) have changed during the last 20 years. Using phytosociological relevés conducted in 1989-90 and in 2010-12, we investigated changes in floristic composition over time. We then compared plant cover and the proportion of ruderal, alien and habitat diagnostic species ('focal species') in the two periods. Finally, we used Ellenberg indicator values to define the 'preferences' of the plant species for temperature and moisture. We found that only fore dune habitats showed significant differences in species cover between the two time periods, with higher plant cover in the more recent relevés and a significant increase in thermophilic species. Although previous studies have demonstrated consistent habitat loss in this area, we observed that all coastal dune plant communities remain well represented, after a 20-year period. However, fore dunes have been experiencing significant compositional changes. Although we cannot confirm whether the observed changes are strictly related to climatic changes, to human pressure or to both, we hypothesize that a moderate increment in average yearly temperature may have promoted the increase in plant cover and the spread of thermophilic species. Thus, even though human activities are major driving forces of change in coastal dune vegetation, at the community scale climatic factors may also play important roles. Our study draws on re-visitation studies which appear to constitute a powerful tool for the assessment of the conservation status of EU habitats. PMID:25750408

  5. Mars Global Digital Dune Database (MGD3): North polar region (MC-1) distribution, applications, and volume estimates

    USGS Publications Warehouse

    Hayward, R.K.

    2011-01-01

    The Mars Global Digital Dune Database (MGD3) now extends from 90??N to 65??S. The recently released north polar portion (MC-1) of MGD3 adds ~844 000km2 of moderate- to large-size dark dunes to the previously released equatorial portion (MC-2 to MC-29) of the database. The database, available in GIS- and tabular-format in USGS Open-File Reports, makes it possible to examine global dune distribution patterns and to compare dunes with other global data sets (e.g. atmospheric models). MGD3 can also be used by researchers to identify areas suitable for more focused studies. The utility of MGD3 is demonstrated through three example applications. First, the uneven geographic distribution of the dunes is discussed and described. Second, dune-derived wind direction and its role as ground truth for atmospheric models is reviewed. Comparisons between dune-derived winds and global and mesoscale atmospheric models suggest that local topography may have an important influence on dune-forming winds. Third, the methods used here to estimate north polar dune volume are presented and these methods and estimates (1130km3 to 3250km3) are compared with those of previous researchers (1158km3 to 15 000km3). In the near future, MGD3 will be extended to include the south polar region. ?? 2011 by John Wiley and Sons, Ltd.

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

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.

    2013-12-01

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

  7. Coastal change-potential assessment of Sleeping Bear Dunes, Indiana Dunes, and Apostle Islands National Lakeshores to lake-level changes

    USGS Publications Warehouse

    Pendleton, Elizabeth A.; Thieler, E. Robert; Williams, S. Jeffress

    2007-01-01

    A change-potential index (CPI) was used to map the susceptibility of the shoreline to future lake-level change within Apostle Islands, Indiana Dunes, and Sleeping Bear Dunes National Lakeshores (NL) along Lake Superior and Lake Michigan. The CPI in the Great Lakes setting ranks the following in terms of their physical contribution to lake-level related coastal change: geomorphology, regional coastal slope, rate and direction (i.e., rise and fall) of relative lake-level change, historical shoreline change rates, annual ice cover and mean significant wave height. The rankings for each input variable were combined, and an index value calculated for 1-minute bins covering the parks. The CPI highlights those regions where the physical effects of lake-level and coastal change might be the greatest. This approach combines the coastal system's potential for change with its natural ability to adapt to changing environmental conditions, yielding a quantitative, although relative, measure of the parks' natural susceptibility to the effects of lake-level variation. The CPI provides an objective technique for evaluation and long-term planning by scientists and park managers. The CPI is applied to the National Lakeshores of Apostle Islands, Indiana Dunes, and Sleeping Bear Dunes to test this methodology in lake settings. The National Lakeshores in this study consist of sand and gravel beaches, rock outcrops, and dune and glacial bluffs. The areas within these Great Lakes parks that are likely to experience the most lake-level-related coastal change are areas of unconsolidated sediment where regional coastal slope is low and wave energy is high.

  8. Solar Cookers.

    ERIC Educational Resources Information Center

    King, Richard C.

    1981-01-01

    Describes the use of solar cookers in the science classroom. Includes instructions for construction of a solar cooker, an explanation of how solar cookers work, and a number of suggested activities. (DS)

  9. Tracking Topographic Changes from Multitemporal Stereo Images, Application to the Nili Patera Dune Field

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The High Resolution Imaging Science Experiment (HiRISE) in orbit around Mars provides images with a nominal ground resolution of 25cm. Its agility allows imaging a same scene with stereo view angles thus allowing for for Digital elevation Model (DEM) extraction through stereo-photogrammetry. This dataset thus offers an exceptional opportunity to measure the topography with high precision and track its eventual evolution with time. In this presentation, we will discuss how multi-temporal acquisitions of HiRISE images of the Nili Patera dune field allow tracking ripples migration, assess sand fluxes and dunes activity. We investigated in particular the use of multi-temporal DEMs to monitor the migration and morphologic evolution of the dune field. We present here the methodology used and the various challenges that must be overcome to best exploit the multi-temporal images. Two DEMs were extracted from two stereo images pairs acquired 390 earth days apart in 2010-2011 using SOCET SET photogrammetry software, with a 1m post-spacing and a vertical accuracy of few tens of centimeters. Prior to comparison the DEMs registration, which was not precise enough out of SOCET-SET, was improved by wrapping the second DEM onto the first one using the bedrock only as a support for registration. The vertical registration residual was estimated at around 40cm RMSE and is mostly due to CCD misalignment and uncorrected spacecraft attitudes. Changes of elevation over time are usually determined from DEMs differentiation: provided that DEMs are perfectly registered and sampled on the same grid, this approach readily quantifies erosion and deposition processes. As the dunes have moved horizontally, they are not physically aligned anymore in the DEMs, and their morphologic evolution cannot be recovered easily from differentiating the DEMs. In this particular setting the topographic evolution is best recovered from correlation of the DEMs. We measure that the fastest dunes have migrated by up to 1meter per Earth year as a result of lee front deposition and stoss slope erosion. DEMs differentiation, after correction for horizontal migration, provides and additional information on dune morphology evolution. Some dunes show a vertical growth over the 390 days spanning the 2 DEMs, but we cannot exclude a bias due to the acquisition parameters. Indeed, the images of the two stereo pairs were acquired 22 and 5 days apart, respectively. During that time, the ripples laying on the dune surface have probably migrated. As the DEMs extraction is based on feature tracking and parallax, this difference in DEMs elevation may be only, or in part, due to the ripple migration between the acquisition times that biased the actual dune elevations.

  10. Lee Slope Processes on a Small Artificial Flow-Transverse Dune

    NASA Astrophysics Data System (ADS)

    Cupp, K. C.; Lancaster, N.; Nickling, W. G.

    2005-12-01

    Sand is primarily deposited on the upper lee slope of dunes by grainfall and is transported downslope by reptation and grainflow (avalanching). Grainfall occurs as saltating sand grains from the stoss slope are blown over the dune crest and fall on the lee slope. Reptation and grainflow then transport these sand grains downslope. The resulting grainflows deposit lobes of sand, primarily on the lower lee slope, which are often preserved in the rock record. An understanding of the processes and conditions that produce lower lee slope deposits could provide important information regarding dune morphology, sand availability and transport rates as well the depositional environment. Despite their importance there have been few studies of grainfall, reptation, and grainflow because the lee slope is a fragile and easily disturbed environment. To overcome these obstacles the Wind Erosion Laboratory, Department of Geography, University of Guelph and the Desert Research Institute have constructed a dune simulation wind tunnel. The wind tunnel contains a small, but true-scale artificial flow-transverse sand dune that is 9 m long, 1.2 m high, and 1 m wide. Experiments in the wind tunnel were run at wind speeds ranging from 5 to 8 m/s measured 30 cm above the dune crest. The dune simulation wind tunnel provides an opportunity to study lee slope processes in a well-constrained environment by controlling wind speeds and direction, dune geometry and composition, and allows for extensive instrumentation and close observation of depositional processes. Experiments on the lee slope in the dune simulation wind tunnel indicate that grainfall decreases exponentially with distance from the crest. Grainfall distance downslope and magnitude increases with increasing wind speeds. Reptation transports and redistributes sand from grainfall primarily on the upper lee slope. Measurements of reptation rates and slope profiles show the formation of a large sediment bulge on the upper lee slope. Grainflow frequency increases with increasing wind speeds. Grainflows commonly originate at or near the point of reattachment of the return cell, in the area between the upper and lower lee slope. The point of reattachment of the return cell and the exponential decay rate of grainfall are two important factors in the location of the point of grainflow origination.

  11. A Dune Simulation Wind Tunnel for Studies of Lee Face Processes

    NASA Astrophysics Data System (ADS)

    Cupp, K.; Lancaster, N.; Nickling, W. G.

    2004-12-01

    Sand is deposited on the lee slope of dunes by grainfall, avalanching (grainflow), and wind ripple migration. These processes play major roles in the formation of aeolian cross strata. Grainfall is produced by saltating grains that are blown over the dune crest and fall on the lee slope. Avalanching occurs when sand on the lee slope fails and the resulting grainflow will deposit tongues of sand downslope. Lee slope deposits are often preserved in the rock record and an understanding of the conditions that produce them as well as avalanche frequency and magnitude could provide important information about dune morphology, sediment flux and availability, air flow, and the environment of deposition. Despite their importance there have been very few studies of grainfall and avalanching because the lee slope of dunes is a very fragile and easily disturbed environment. Designing research strategies to study these processes presents significant technical challenges. To overcome these obstacles construction and testing of a dune simulation wind tunnel was recently completed as a joint project between the Wind Erosion Laboratory, Department of Geography, University of Guelph and the Desert Research Institute. This wind tunnel contains a small, but true-scale sand dune that is 8.5 m long, 1.2 m high, and 1 m wide and is capable of producing wind speeds of 16 m/s at 30cm above the dune crest. The wind tunnel provides an opportunity to study lee slope processes in a well-constrained environment by controlling wind speeds and direction, dune geometry and composition, and allows for extensive instrumentation and close observation of depositional processes. Preliminary experiments in the dune simulation wind tunnel indicate that avalanche frequency is predictable: increased wind speeds resulted in more frequent avalanches. Avalanches commonly originate in the mid-lee slope region at or near the point of reattachment of the return cell caused by flow separation at the crest. Downslope saltation and/or reptation on the lee slope surface appear to slow at the point of reattachment and appears to be an important factor in the location of avalanche origination. Preliminary measurements of the distribution of sediment deposited by grainfall at three different wind speeds suggest a possible depositional bulge in the mid-lee slope region. Research supported by NSF EAR-0207833

  12. Experimental and numerical study of turbulent flow associated with interacting barchan dunes

    NASA Astrophysics Data System (ADS)

    Barros, J. M., Jr.; Blois, G.; Anderson, W.; Tang, Z.; Best, J.; Christensen, K. T.

    2014-12-01

    Barchan dunes are naturally occurring three-dimensional topographic features that have been observed on the surface of several planets. They occur both in aeolian and in subaqueous environments. Barchans typically form in fields having a broad distribution in dune size and migration rates. This results in variable bedform spacing and eventually dynamic bedform-bedform interactions that involve morphodynamic processes (e.g. collision, merging, splitting). These processes are controlled by complex feedback mechanisms mutually linking three key elements: fluid flow, sediment transport and bed morphology. The aim of this work is to contribute to the understanding of the fluid-flow mechanisms responsible for the formation, migration and interaction of these dunes. To this end, we study the three-dimensional flow generated by the interactions between fixed barchan-dune models arranged in tandem in collision and ejection scenarios via experiments in an optically-accessible flow environment using planar particle-image velocimetry (PIV) measurements of the flow field. These measurements are complemented by targeted large-eddy simulations (LES) meant to provide a three-dimensional view of the flow processes for these fixed dune arrangements.

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

    USGS Publications Warehouse

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

    2013-01-01

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

  14. A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples

    NASA Astrophysics Data System (ADS)

    Claudin, Philippe; Andreotti, Bruno

    2006-11-01

    The linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength ? at which the bed destabilises to form dunes should scale with the drag length Ldrag=?/s ?f d . This scaling law is tested using existing and new measurements performed in water (subaqueous ripples), in air (aeolian dunes and fresh snow dunes), in a high pressure CO2 wind tunnel reproducing conditions close to Venus' atmosphere and in the low pressure CO2 Martian atmosphere (Martian dunes). The difficulty is to determine the diameter of saltating grains on Mars. A first estimate comes from photographs of aeolian ripples taken by the rovers Opportunity and Spirit, showing grains whose diameters are smaller than on Earth dunes. In addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds. It confirms that the small grains visualised by the rovers should be grains experiencing saltation. Finally, we show that, within error bars, the scaling of ? with Ldrag holds over almost five decades. We conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on Mars.

  15. A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples

    E-print Network

    Philippe Claudin; Bruno Andreotti

    2006-08-07

    The linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength $\\lambda$ at which the bed destabilises to form dunes should scale with the drag length $L_{\\rm drag} = \\frac{\\rho_s}{\\rho_f} d$. This scaling law is tested using existing and new measurements performed in water (subaqueous ripples), in air (aeolian dunes and fresh snow dunes), in a high pressure CO$_2$ wind tunnel reproducing conditions close to the Venus atmosphere and in the low pressure CO$_2$ martian atmosphere (martian dunes). A difficulty is to determine the diameter of saltating grains on Mars. A first estimate comes from photographs of aeolian ripples taken by the rovers Opportunity and Spirit, showing grains whose diameters are smaller than on Earth dunes. In addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds. It confirms that the small grains visualised by the rovers should be grains experiencing saltation. Finally, we show that, within error bars, the scaling of $\\lambda$ with $L_{\\rm drag}$ holds over almost five decades. We conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on Mars.

  16. Quaternary eolian dunes in the Savannah River valley, Jasper County, South Carolina, USA

    NASA Astrophysics Data System (ADS)

    Swezey, Christopher S.; Schultz, Arthur P.; González, Wilma Alemán; Bernhardt, Christopher E.; Doar, William R.; Garrity, Christopher P.; Mahan, Shannon A.; McGeehin, John P.

    2013-09-01

    Sand hills in the Savannah River valley in Jasper County (South Carolina, USA) are interpreted as the remnants of parabolic eolian dunes composed of sand derived from the Savannah River and stabilized by vegetation under prevailing climate conditions. Optically stimulated luminescence ages reveal that most of the dunes were active ca. 40 to 19 ka ago, coincident with the last glacial maximum (LGM) through early deglaciation. Modern surface winds are not sufficient for sustained eolian sand transport. When the dunes were active, winds blew at velocities of at least 4 m/s from west to east, and some vegetation was present. The ratio of annual precipitation to potential evapotranspiration (P:PE) was less than the modern ratio of 1.23 and may have been < 0.30, caused by stronger winds (which would have resulted in greater evaporation) and/or reduced precipitation. The Savannah River dunes are part of a larger assemblage of eolian dunes that were active in the eastern United States during and immediately after the LGM, suggesting that eolian sediment behavior in this region has been controlled by regional forcing mechanisms during the Quaternary.

  17. A ˜200 ka record of climatic change and dune activity in the Thar Desert, India

    NASA Astrophysics Data System (ADS)

    Singhvi, A. K.; Williams, M. A. J.; Rajaguru, S. N.; Misra, V. N.; Chawla, S.; Stokes, S.; Chauhan, N.; Francis, T.; Ganjoo, R. K.; Humphreys, G. S.

    2010-11-01

    An 18.4 m excavated dune section in the Thar Desert of India with a chronology based on 12 TL ages and a basal age of ˜190 ka has preserved 12 cycles of dune accretion, soil formation, calcrete development, and subsequent erosion, together with the presence of stone artefacts ranging in age from Lower Palaeolithic to Mesolithic, coeval with more humid climatic interludes. Phases of soil development and carbonate precipitation were relatively wet and phases of dune accretion relatively dry, so that there were 12 significant moist intervals separated by 11 drier intervals during the past ˜190 ka. The calculated time interval between successive phases of dune sand accumulation ranged from 22.2 ka to 15.8 ka, with a mean of 19.0 ka. These values are consistent with a precessional influence on dune activity and on the associated onset of early monsoonal activity in this region. Carbon isotopes measured on organic matter within the sand profiles show consistent values close to -21.6 ± 1‰, pointing to deposition during a transitional climatic regime characterized by a change from open C3 grassland to C4 woodland or forest.

  18. Reassessment of the record of linear dune activity in Tasmania using optical dating

    NASA Astrophysics Data System (ADS)

    Duller, G. A. T.; Augustinus, P. C.

    2006-10-01

    Stabilized linear dunes in northeastern Tasmania have previously been dated using luminescence signals from quartz (Duller G.A.T, Augustinus, P., 1997 Luminescence studies of dunes from north-eastern Tasmania. Quaternary Geochronology (QSR) 16, 357-365.) and gave ages from 44±4 to 29±3 ka. Unexpectedly, no evidence was found for dune activity at the last glacial maximum (LGM). The ages were obtained using analytical methods available at the time, including multiple aliquot methods. In recent years the single aliquot regenerative dose (SAR) procedure has been developed, and this method gave ages from 23.8±1.6 to 21.8±1.3 ka for the same samples. A further seven samples from other linear dunes in the area gave ages from 16.8 to 19.7 ka. These ages are strong evidence that linear dunes in northeastern Tasmania were last active at, or immediately after, the LGM, consistent with evidence for enhanced aridity through large parts of the Australian continent at that time. Earlier methods of optical dating using quartz did not explicitly check for changes in luminescence sensitivity and thus their reliability must be suspect. For samples measured here, the largest discrepancy in equivalent dose between the sensitivity corrected and non-sensitivity corrected data is 84%, while for the remainder it is much smaller. These results demonstrate the importance of checking the validity of previously published optical dating results which were obtained using methods that did not explicitly check for sensitivity change.

  19. Radar scattering of linear dunes and mega-yardangs: Application to Titan

    E-print Network

    Paillou, Philippe; Radebaugh, Jani; Wall, Stephen

    2015-01-01

    The Ku-band (13.8 GHz - 2.2 cm) RADAR instrument onboard the Cassini-Huygens spacecraft has revealed the richness of the surface of Titan, as numerous seas, lakes, rivers, cryo-volcanic flows and vast dune fields have been discovered. Linear dunes are a major geomorphological feature present on Titan, covering up to 17% of its surface, mainly in equatorial regions. However, the resolution of the RADAR instrument is not good enough to allow a detailed study of the morphology of these features. In addition, other linear wind-related landforms, such as mega-yardangs (linear wind-abraded ridges formed in cohesive rocks), are likely to present a comparable radar signature that could be confused with the one of dunes. We conducted a comparative study of the radar radiometry of both linear dunes and mega-yardangs, based on representative terrestrial analogues: the linear dunes located in the Great Sand Sea in western Egypt and in the Namib Desert in Namibia, and the mega-yardangs observed in the Lut Desert in easter...

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

    PubMed

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

    2015-01-01

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