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.

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China.

PubMed

Fan, Baoli; McHugh, Allen David; Guo, Shujiang; Ma, Quanlin; Zhang, Jianhui; Zhang, Xiaojuan; Zhang, Weixing; Du, Juan; Yu, Qiushi; Zhao, Changming

2018-03-01

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air-filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-05

Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 27652 Latitude: 80.983 Longitude: 170.458 Instrument: VIS Captured: 2008-03-09 04:03 https://photojournal.jpl.nasa.gov/catalog/PIA22288

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.

Observation and numerical modeling of tidal dune dynamics

NASA Astrophysics Data System (ADS)

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

2018-05-01

Tidal sand dune dynamics is observed for two tidal cycles in the Arcachon tidal inlet, southwest France. An array of instruments is deployed to measure bathymetric and current variations along dune profiles. Based on the measurements, dune crest horizontal and vertical displacements are quantified and show important dynamics in phase with tidal currents. We observed superimposed ripples on the dune stoss side and front, migrating and changing polarity as tidal currents reverse. A 2D RANS numerical model is used to simulate the morphodynamic evolution of a flat non-cohesive sand bed submitted to a tidal current. The model reproduces the bed evolution until a field of sand bedforms is obtained that are comparable with observed superimposed ripples in terms of geometrical dimensions and dynamics. The model is then applied to simulate the dynamics of a field of large sand dunes of similar size as the dunes observed in situ. In both cases, simulation results compare well with measurements qualitatively and quantitatively. This research allows for a better understanding of tidal sand dune and superimposed ripple morphodynamics and opens new perspectives for the use of numerical models to predict their evolution.

Control parameters of the martian dune field positions at planetary scale: tests by the MCD

NASA Astrophysics Data System (ADS)

allemand, pascal

2016-04-01

The surface of Mars is occupied by more than 500 dunes fields mainly located inside impact craters of the south hemisphere and near the north polar cap. The questions of the activity of martian dunes and of the localization of the martian dune fields are not completely solved. It has been demonstrated recently by image observation and image correlation that some of these dune fields are clearly active. The sand flux of one of them has been even estimated. But there is no global view of the degree of activity of each the dune fields. (2)The topography of impact craters in which dune fields are localized is an important factor of their position. But there is no consensus of the effect of global atmospheric circulation on dune field localization. These two questions are addressed using the results of Mars Climate Database 5.2 (MCD) (Millour, 2015; Forget et al., 1999). The wind fields of the MCD have been first validated against the observations made on active dune fields. Using a classical transport law, the Drift Potential (DP) and the Relative Drift Potential (RDP) have been computed for each dune fields. A good correlation exists between the position of dune fields and specific values of these two parameters. The activity of each dune field is estimated from these parameters and tested on some examples by image observations. Finally a map of sand flow has been computed at the scale of the planet. This map shows that sand and dust is trapped in specific regions. These regions correspond to the area of dune field concentration.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-12

This VIS image of Olympia Undae was collected during north polar summer. The dunes are now completely frost free and are dark in color due to being made of basaltic sand. The surface between the dunes, where visible, is a bright tone. In some regions of dense dunes, the bright material may be a deposit on the dunes rather than the underlying surface. The presence of gypsum has been suggested for Olympia Undae, gypsum is a lighter tone than basalt in this filter of the THEMIS VIS camera. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 12614 Latitude: 80.8745 Longitude: 174.688 Instrument: VIS Captured: 2004-10-18 00:23 https://photojournal.jpl.nasa.gov/catalog/PIA22293

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-13

This VIS image of Olympia Undae was collected during north polar summer. The dunes are now completely frost free and are dark in color due to being made of basaltic sand. The surface between the dunes, where visible, is a bright tone. In some regions of dense dunes, the bright material may be a deposit on the dunes rather than the underlying surface. The presence of gypsum has been suggested for Olympia Undae, gypsum is a lighter tone than basalt in this filter of the THEMIS VIS camera. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 21125 Latitude: 81.5387 Longitude: 181.591 Instrument: VIS Captured: 2006-09-18 18:07 https://photojournal.jpl.nasa.gov/catalog/PIA22294

Geomorphology and drift potential of major aeolian sand deposits in Egypt

NASA Astrophysics Data System (ADS)

Hereher, Mohamed E.

2018-03-01

Aeolian sand deposits cover a significant area of the Egyptian deserts. They are mostly found in the Western Desert and Northern Sinai. In order to understand the distribution, pattern and forms of sand dunes in these dune fields it is crucial to analyze the wind regimes throughout the sandy deserts of the country. Therefore, a set of wind data acquired from twelve meteorological stations were processed in order to determine the drift potential (DP), the resultant drift potential (RDP) and the resultant drift direction (RDD) of sand in each dune field. The study showed that the significant aeolian sand deposits occur in low-energy wind environments with the dominance of linear and transverse dunes. Regions of high-energy wind environments occur in the south of the country and exhibit evidence of deflation rather than accumulation with the occurrence of migratory crescentic dunes. Analysis of the sand drift potentials and their directions help us to interpret the formation of major sand seas in Egypt. The pattern of sand drift potential/direction suggests that the sands in these seas might be inherited from exogenous sources.

Modeling aeolian dune and dune field evolution

NASA Astrophysics Data System (ADS)

Diniega, Serina

Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations. In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models. By elucidating the qualitative and quantitative connections between environmental conditions, physical processes, and resultant dune and dune field morphologies, this research furthers our ability to interpret spacecraft images of dune fields, and to use present-day observations to improve our understanding of past terrestrial and martian environments.

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

NASA Astrophysics Data System (ADS)

Parker Gay, S.

1999-03-01

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

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-06

This VIS image of Olympia Undae was collected early in north polar spring. The crests of the dunes are light colored, indicative of a frost covering. As the season changes into summertime, the dune crests will lose the frost and reveal the darker sand beneath. The margin of the north polar cap is visible at the top of the image. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 10293 Latitude: 83.0224 Longitude: 174.743 Instrument: VIS Captured: 2004-04-09 22:04 https://photojournal.jpl.nasa.gov/catalog/PIA22289

Earth-like sand fluxes on Mars.

PubMed

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

2012-05-09

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

Onset and Dynamics of a Subaqueous Dune Field in a Tideless Erosional Deltaic Shoreface: an Analog for the Initial Development of Sand Ridges

NASA Astrophysics Data System (ADS)

Guerrero, Q.; Guillén, J.; Durán, R.; Urgeles, R.

2016-12-01

A subaqueous dune field located over a retreating deltaic lobe in the Ebro delta (NW Mediterranean) is morphodynamically characterized by analyzing three sets of co-located, multibeam bathymetric data acquired in 2004, 2013 and 2015, measurements of near-bottom currents and suspended sediment concentrations, high-resolution seismic profiles and aerial photographs. The dunes, made of fine sand, extend from 5 to 15 m water depth, have straight crestlines and maximum heights and wavelengths of 2.5 and 350 m, respectively (Fig. 1). Results suggest that the onset of dune field development is closely related to the contemporary evolution of the Ebro delta. A change in the main river channel in the 1940s led to the progressive abandonment of the former river mouth, severe coastal retreatment ( 37 m·y-1) and increased sediment availability. The characteristic NW winds of the region induce near-bottom currents flowing towards the SE which are able to rework and transport these sediments. The dune field developed over the shoreface of the abandoned river mouth and is currently active with mean SE migration rates of 10 m·y-1, most likely when high-energetic currents occur. The morphology of the dune field and crestline obliquity to shoreline orientation agree well with that observed in sand ridges of continental shelves worldwide. Mid-outer shelf sand ridges have been interpreted as sedimentary bodies formed in coastal waters and detached from the coast during sea level rise. The studied dune field could therefore be an example of the initial stages of sand ridges development when large amounts of sand are suddenly available. The field developed when the river mouth switched, favored by a pre-existing seafloor irregularity. Despite the time-scale for the genesis and evolution of shoreface sand ridges has been set in time-scales of hundreds/thousands of years, this study shows that shoreface sand ridges can develop during shorter time-scales (tens of years). Furthermore, it is discussed that, in absence of a rapid sea level rise, these sand ridges probably will vanish as a consequence of sediment scarcity and wave reworking.

Optical Dating of Holocene Dune Sands in the Ferris Dune Field, Wyoming

NASA Astrophysics Data System (ADS)

Stokes, Stephen; Gaylord, David R.

1993-05-01

Optical dating of late Quaternary quartz dune sands from the Clear Creek portion of Ferris dune field, Wyoming, demonstrates the considerable potential of the technique as a chronostratigraphic tool. A sequence of radiocarbon-dated Holocene interdune strata permit optical dating of the intercalated dune sand to be tested; the concordance is good. The optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at Clear Creek peaked during two relatively short phases at ca. 8500 and 4000 yr B.P. The dates indicate that aeolian accumulation maxima (at least in the Clear Creek area) may not be synchronous with previously defined phases of marked aridity.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-08

This VIS image of Olympia Undae was collected during north polar spring. The crests of the dunes and other surfaces are light colored, indicative of a frost covering. At the top right of the image is a region of smooth surfaces. This is the ejecta from Jojutla Crater. The ejecta is a higher elevation than the rest of the surface, and dunes are "climbing" or "skirting" the ejecta regions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time, and, in this case, the presence of different surface elevations. As the season changes into summertime, the dune crests will lose the frost and reveal the darker sand beneath. This loss of frost is just starting to be visible at the bottom of the image. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 27352 Latitude: 80.9139 Longitude: 185.126 Instrument: VIS Captured: 2008-02-13 11:10 https://photojournal.jpl.nasa.gov/catalog/PIA22291

Holocene beach buildup and coastal aeolian sand incursions off the Nile littoral cell

NASA Astrophysics Data System (ADS)

Roskin, Joel; Sivan, Dorit; Shtienberg, Gilad; Porat, Naomi; Bookman, Revital

2017-04-01

Israel's coastal plain is abundant with sand originating from the Nile littoral cell. The inland windblown loose sand has formed 3-6 km wide lobe-like sand and dune fields currently comprised of foredunes, linear and northeasterly facing transverse and parabolic dunes that are currently stabilized by vegetation. This study reviews the architecture and history of the these dune fields aiming to: (a) Date the timings of beach accretion, and sand and dune incursions. (b) Discriminate between natural and human-induced forcing factors of sand mobilization and stabilization in time and space. (c) Present a model of the dunescape development. (d) Assess scenarios of sand transport in the future charcaterized by intense human impact and climate change. Luminescence ages, radiocarbon dates and relative ages from previously published geological and archaeological reports, historical texts, together with new optically stimulated luminescence (OSL) ages and stratigraphic and sedimentological data are analyzed. The deposition, mobilizations and preservation of the sand bodies, initially induced by the decline in sea level rise at 6-4 ka, were later controlled by historic land-use intensity and modern land-use/negligence practices. At 6 ka, beach sand buildup rapidly started. Where aeolianite ridges bordered the coast, pulses of sand with biogenic carbonate grains unconformably draped the ridges and rapidly consolidated into a distinct sandy calcarenite unit. Further east, sand sheets and low dunes partly pedogenized following their incursion, but did not cement. The water retention capacities of the sand sheets enabled the establishment of a sand-stabilizing vegetation cover that probably became an attractive environment for fuel and grazing. The growing Hellenistic-Roman-Byzantine ( 2.4-1.3 ka) populations probably led to increased consumption and massive destruction of sand stabilizing vegetation, enabling sand erodibility and mobilization during winter storms. The sand gradually expanded to the current limits of today's dune fields. The gradual but unsteady post-Byzantine demographic drop enabled reestablishment of natural vegetation and rapid regosol development. This drop occurred differentially along the coast due to governance and land-use practices. We suggest that dune construction mainly evolved around the 19th century from the existing sand sheets and low dunes that intermittently developed since 6-5 ka. Human (Bedouin grazing influx and ethnic settlements) destruction of vegetation, in conjuction with the rapid 19th-20th century population growth made the sand prone to "in situ" transverse and linear dune formation in response to powerful winds further supported by increased storminess at this time. Inland dune mobilization and the artificial establishment of vegetated foredunes along the coast in the 1930's-1940's partly scalped the sand deposits by the coast.

Megadroughts and late Holocene dune activation at the eastern margin of the Great Plains, north-central Kansas, USA

NASA Astrophysics Data System (ADS)

Hanson, P. R.; Arbogast, A. F.; Johnson, W. C.; Joeckel, R. M.; Young, A. R.

2010-01-01

Optical and radiocarbon dating indicates that alluvium underlying dunes near Abilene was deposited at or before ˜45 ka, and that the overlying dunes were active at ˜1.1-0.5 ka. Geochemical data indicate that the Abilene dune sand is immature and was derived from the underlying Pleistocene alluvium, and not from Holocene age Smoky Hill River deposits. These findings suggest that dune activation was a response to increased aridity and local reduction in vegetation cover as opposed to changes in sediment availability from nearby rivers. The time interval of dune activation at Abilene overlaps Medieval Warm Period megadroughts, similar to the larger and more westerly dune fields on the Great Plains, including the Nebraska Sand Hills and the Great Bend Sand Prairie. The activation of smaller dune fields such as the Abilene dunes near the more humid eastern margin of the Great Plains shows the geographic extent and severity of paleodrought events. Unlike the Duncan dunes, another plains-marginal dune field, however, the Abilene dunes show no evidence for multiple drought events during the Holocene. This difference in dune activity, if it is not a result of sampling or preservation bias, indicates variations in the extent and severity of older drought events at the eastern margin of the Great Plains.

Evidence of Active Dune Sand on the Great Plains in the 19th Century from Accounts of Early Explorers

NASA Astrophysics Data System (ADS)

Muhs, Daniel R.; Holliday, Vance T.

1995-03-01

Eolian sand is extensive over the Great Plains of North America, but is at present mostly stabilized by vegetation. Accounts published by early explorers, however, indicate that at least parts of dune fields in Nebraska, Colorado, Kansas, New Mexico, and Texas were active in the 19th century. Based on an index of dune mobility and a regional tree-ring record, the probable causes for these periods of greater eolian activity are droughts, accompanied by higher temperatures, which greatly lowered the precipitation-to-evapotranspiration ratio and diminished the cover of stabilizing vegetation. In addition, observations by several explorers, and previous historical studies, indicate that rivers upwind of Great Plains dune fields had shallow, braided, sandy channels, as well as intermittent flow in the 19th century. Wide, braided, sandy rivers that were frequently dry would have increased sand supplies to active dune fields. We conclude that dune fields in the Great Plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high, with or without greenhouse warming.

Eolian sand transport pathways in the southwestern United States: Importance of the Colorado River and local sources

USGS Publications Warehouse

Muhs, D.R.; Reynolds, R.L.; Been, J.; Skipp, G.

2003-01-01

Geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions. Along such pathways, sediment transport by wind can surmount topographic obstacles and cross major drainages. Recent studies have suggested that three distinct eolian sand transport pathways exist (or once existed) in the Mojave and Sonoran Desert regions of the southwestern United States. One hypothesized pathway is colian sand transport from the eastern Mojave Desert of California into western Arizona, near Parker, and would require sand movement across what must have been at least a seasonally dry Colorado River valley. We tested this hypothesis by mineralogical, geochemical and magnetic analyses of eolian sands on both sides of the Colorado River, as well as sediment from the river itself. Results indicate that dunes on opposite sides of the Colorado River are mineralogically distinct: eastern California dunes are feldspar-rich whereas western Arizona dunes are quartz-rich, derived from quartz-rich Colorado River sediments. Because of historic vegetation changes, little new sediment from the Colorado River is presently available to supply the Parker dunes. Based on this study and previous work, the Colorado River is now known to be the source of sand for at least three of the major dune fields of the Sonoran Desert of western Arizona and northern Mexico. On the other hand, locally derived alluvium appears to be a more important source of dune fields in the Mojave Desert of California. Although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields, few empirical data actually exist to support this theory. The results presented here demonstrate that a major river system in the southwestern United States is a barrier to the migration of some dune fields, but essential to the origin of others. Published by Elsevier Science Ltd.

Sand Sheet on Crater Floor

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

As with yesterday's image, this dune field is located inside a crater, in this case an unnamed crater at 26 degrees North latitude. In this VIS image the dunes are coalescing into a sand sheet, note the lack of dune forms to the north of the small hills. The presence of ridges and hills in the area is affecting the dune shapes.

Image information: VIS instrument. Latitude 26.4, Longitude 62.7 East (297.3 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.

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

NASA Astrophysics Data System (ADS)

Edgett, Kenneth S.

1996-10-01

INTRODUCTION: On Earth, aeolian sand dunes are used as tools of scientific inquiry. Holocene and Pleistocene dunes preserve clues about Quaternary climate variations and human activities ranging from Ice Age hunting practices to Twentieth Century warfare. Modern dunes contain the sedimentary textures and structures necessary for interpreting ancient sandstones, and they provide natural laboratories for investigation of aeolian physics and desertification processes. The dunes of Mars can likewise be used as scientific tools. Dunes provide relatively dust-free surfaces. From a remote sensing perspective, martian dunes have much potential for providing clues about surface mineralogy and the interaction between the surface and atmosphere. Such information can in turn provide insights regarding crust composition, volcanic evolution, present and past climate events, and perhaps weathering rates. The Mars Global Surveyor Thermal Emission Spectrometer (TES) is expected to reach the planet in September 1997. TES will provide 6 to 50 micrometer spectra of the martian surface at ground resolutions of 3 to 9 km. Sandy aeolian environments on Mars might provide key information about bedrock composition. To prepare for the TES investigation, I have been examining a thermal infrared image of a Mars-composition analog dune field in Christmas Lake Valley, Oregon. COMPOSITION AND GEOLOGIC SETTING: The "Shifting Sand Dunes" dune field is located at the eastern end of Christmas Lake Valley, in what was once the Pleistocene Fort Rock Lake [1]. Much of the sand that makes up the Shifting Sand Dunes dune field is reworked Mt. Mazama airfall from its terminal eruption 6,800 years ago, plus material deflated from the lake bed [1, 2]. The main constituents of the dunes are volcanic glass and devitrified glass fragments, plagioclase crystals, basalt lithic fragments, aggregates of silt and clay-size volcanic ash, pyroxenes, opaque oxide minerals (mostly magnetite), and trace occurrences of fossil fragments and other minerals [3]. THERMAL INFRARED IMAGE: The thermal infrared images used in this study was obtained by the NASA Ames Research Center C-130 Earth Resources airborne Thermal Infrared Multispectral Scanner (TIMS) on 21 September 1991. The image has 6 spectral bands between 8 and 12 micrometers and a ground resolution of 9 m/pixel. The raw image was converted to calibrated radiance, from which normalized emittance was computed for each of the six bands, following the method of Realmutto [4]. Atmospheric effects were corrected using an empirical method described by Edgett and Anderson [5]. The resulting 6-band image provides quantitative determination of the surface emissivity. Dune spectra in the image match spectra obtained in our laboratory using samples collected from the field area [3, 5]. ACTIVE DUNES, INACTIVE DUNES, AND INTERDUNE AREAS FROM EMISSIVITY VARIATION: This study shows that in a modern dune field, the location of active dunes, interdune surfaces, and inactive dunes can be mapped using emissivity in the thermal infrared band that shows the most spectral variation [6]. In this case, TIMS band 3 (9.2 micrometers) had the most variation, although the entire emissivity range was only from 0.89 to 1.0. Active dunes had the lowest emissivities (0.89 to 0.91), inactive dunes were distinguished by higher emissivities (.094 to 1.0), and interdune surfaces had intermediate values (0.90 to 0.95). These emissivity variations result from differences in particle size, as inactive dunes tend to have finer-grained silt and dust on them. LINEAR UNMIXING USING IMAGE ENDMEMBERS: Quantitative estimates of thermal infrared spectral emissivity are ideally suited to unmixing analysis. For grains larger than the wavelength (e.g., dune sand), a linear unmixing approach provides geologically useful results [7]. In the present study, image endmembers were selected for a preliminary unmixing study: (1) "regular sand," which contains nearly 50% plagioclase and nearly 20% volcanic glass; (2) "dark sand, which consists mainly of basalt clasts (> 25%) and glass (> 30%); (3) "mud chips," which are volcanic ash aggregates broken into sand-sized pieces, (4) sagebrush and grass; and (5) thick vegetation, such as an alfalfa farm near the dunes. The most important result of this preliminary unmixing work is an image that shows the distribution of ash aggregates and "dark sand," both of which vary throughout the dune field as a function of proximity to the source. The volcanic ash aggregates, in particular, are locally eroded from a layer that caps the Pleistocene lake beds that underlie the dunes [3]. SUMMARY: This study highlights the use of thermal infrared spectra to map local contributions of sand to a dune field, and to distinguish active versus inactive dune fields. Mapping of local contributions to active dune fields on Mars using TES or other multispectral images has potential to provide indications of local bedrock composition. REFERENCES: [1] Allison, I. S. (1979) Oregon Dept. Geol. Minl. Res. Spec. Pap. 7. [2] Dole, H. M. (1942) M.S. Thesis, Oregon State, Corvallis, Or. [3] Edgett, K. S. (1994) in Ph.D. Diss., pp. 145-201, Arizona State, Tempe, AZ. [4] Realmutto, V. J. (1990) in JPL Publ. 90-55, pp. 31-35. [5] Edgett, K. S., and D. L. Anderson (1995) in JPL Publ. 95-1, v. 2, pp. 9-12. [6] Edgett, K. S. et al. (1995) in JPL Publ. 95-1, v. 2, pp. 13-16. [7] Ramsey, M. S. (1996) Ph.D. Diss, Arizona State, Tempe, AZ.

The influence of groundwater depth on coastal dune development at sand flats close to inlets

NASA Astrophysics Data System (ADS)

Silva, Filipe Galiforni; Wijnberg, Kathelijne M.; de Groot, Alma V.; Hulscher, Suzanne J. M. H.

2018-05-01

A cellular automata model is used to analyze the effects of groundwater levels and sediment supply on aeolian dune development occurring on sand flats close to inlets. The model considers, in a schematized and probabilistic way, aeolian transport processes, groundwater influence, vegetation development, and combined effects of waves and tides that can both erode and accrete the sand flat. Next to three idealized cases, a sand flat adjoining the barrier island of Texel, the Netherlands, was chosen as a case study. Elevation data from 18 annual LIDAR surveys was used to characterize sand flat and dune development. Additionally, a field survey was carried out to map the spatial variation in capillary fringe depth across the sand flat. Results show that for high groundwater situations, sediment supply became limited inducing formation of Coppice-like dunes, even though aeolian losses were regularly replenished by marine import during sand flat flooding. Long dune rows developed for high sediment supply scenarios which occurred for deep groundwater levels. Furthermore, a threshold depth appears to exist at which the groundwater level starts to affect dune development on the inlet sand flat. The threshold can vary spatially depending on external conditions such as topography. On sand flats close to inlets, groundwater is capable of introducing spatial variability in dune growth, which is consistent with dune development patterns found on the Texel sand flat.

Controls on desert dune activity - a geospatial approach

NASA Astrophysics Data System (ADS)

Lancaster, N.; Hesse, P. P.

2017-12-01

Desert and other inland dunes occur on a wide spectrum of activity (defined loosely as the proportion of the surface area subject to sand movement) from unvegetated to sparsely vegetated "active" dunes through discontinuously vegetated inactive dunes to completely vegetated and degraded dunes. Many of the latter are relicts of past climatic conditions. Although field studies and modeling of the interactions between winds, vegetation cover, and dune activity can provide valuable insights, the response of dune systems to climate change and variability past, present, and future has until now been hampered by the lack of pertinent observational data on geomorphic and climatic boundary conditions and dune activity status for most dune areas. We have developed GIS-based approach that permits analysis of boundary conditions and controls on dune activity at a range of spatial scales from dunefield to global. In this approach, the digital mapping of dune field and sand sea extent has been combined with systematic observations of dune activity at 0.2° intervals from high resolution satellite image data, resulting in four classes of activity. 1 km resolution global gridded datasets for the aridity index (AI); precipitation, satellite-derived percent vegetation cover; and estimates of sand transport potential (DP) were re-sampled for each 0.2° grid cell, and dune activity was compared to vegetation cover, sand transport potential, precipitation, and the aridity index. Results so far indicate that there are broad-scale relationships between dunefield mean activity, climate, and vegetation cover. However, the scatter in the data suggest that other local factors may be at work. Intra-dune field patterns are complex in many cases. Overall, much more work needs to be done to gain a full understanding of controls at different spatial and temporal scales, which can be faciliated by this spatial database.

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-01-24

This VIS image of Kaiser Crater shows individual dunes and where the dunes have coalesced into longer dune forms. The addition of sand makes the dunes larger and the intra-dune areas go from sand-free to complete coverage of the hard surface of the crater floor. With a continued influx of sand the region will transition from individual dunes to a sand sheet with surface dune forms. Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southern part of the crater floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 1423 Latitude: -46.9573 Longitude: 18.6192 Instrument: VIS Captured: 2002-04-10 16:44 https://photojournal.jpl.nasa.gov/catalog/PIA22173

Barchan Pac-Man

NASA Image and Video Library

2018-05-14

This image from NASA's Mars Reconnaissance Orbiter shows barchan sand dunes, common on Mars and often forming vast dune fields within very large (tens to hundreds of kilometers) impact basins. The regions upwind of barchans are usually devoid of sandy bedforms, so if you were walking in a downwind direction, then the barchans would seem to appear out of nowhere. As you walk downwind, you would notice the barchans link up ("joining arms") and eventually slope into featureless sand sheets. We call this progression of dunes a "Herschel-type dune field" named after the first place this sequence was described: Herschel Crater. But here is something interesting: a barchan dune filling the upwind portion of a small impact crater in a Pac-Man-like shape. This "dune-in-a-crater" is nearly at the highest extent of the field. It is also probably a rare configuration, and over the next few tens of thousands of years the sand will be blown out of the crater. https://photojournal.jpl.nasa.gov/catalog/PIA22456

Geochemical evidence for a complex origin for the Kelso dunes, Mojave National Preserve, California USA

USGS Publications Warehouse

Muhs, Daniel; Lancaster, Nicholas; Skipp, Gary L.

2017-01-01

The Kelso Dune field in southern California is intriguing because although it is of limited areal extent (~ 100 km2), it has a wide variety of dune forms and contains many active dunes (~ 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

A complex origin for the Kelso Dunes, Mojave National Preserve, California, USA: A case study using a simple geochemical method with global applications

NASA Astrophysics Data System (ADS)

Muhs, Daniel R.; Lancaster, Nicholas; Skipp, Gary L.

2017-01-01

The Kelso Dune field in southern California is intriguing because although it is of limited areal extent ( 100 km2), it has a wide variety of dune forms and contains many active dunes ( 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

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

NASA Technical Reports Server (NTRS)

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

1995-01-01

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

Dune-slope activity due to frost and wind throughout the north polar erg, Mars

PubMed Central

DINIEGA, SERINA; HANSEN, CANDICE J.; ALLEN, AMANDA; GRIGSBY, NATHAN; LI, ZHEYU; PEREZ, TYLER; CHOJNACKI, MATTHEW

2018-01-01

Repeat, high-resolution imaging of dunes within the Martian north polar erg have shown that these dune slopes are very active, with alcoves forming along the dune brink each Mars year. In some areas, a few hundred cubic metres of downslope sand movement have been observed, sometimes moving the dune brink ‘backwards’. Based on morphological and activity-timing similarities of these north polar features to southern dune gullies, identifying the processes forming these features is likely to have relevance for understanding the general evolution/modification of dune gullies. To determine alcove-formation model constraints, we have surveyed seven dune fields, each over 1–4 Mars winters. Consistent with earlier reports, we found that alcove-formation activity occurs during the autumn–winter seasons, before or while the stable seasonal frost layer is deposited. We propose a new model in which alcove formation occurs during the autumn, and springtime sublimation activity then enhances the feature. Summertime winds blow sand into the new alcoves, erasing small alcoves over a few Mars years. Based on the observed rate of alcove erasure, we estimated the effective aeolian sand transport flux. From this, we proposed that alcove formation may account for 2–20% of the total sand movement within these dune fields. PMID:29731538

Dune-slope activity due to frost and wind throughout the north polar erg, Mars.

PubMed

Diniega, Serina; Hansen, Candice J; Allen, Amanda; Grigsby, Nathan; Li, Zheyu; Perez, Tyler; Chojnacki, Matthew

2017-01-01

Repeat, high-resolution imaging of dunes within the Martian north polar erg have shown that these dune slopes are very active, with alcoves forming along the dune brink each Mars year. In some areas, a few hundred cubic metres of downslope sand movement have been observed, sometimes moving the dune brink 'backwards'. Based on morphological and activity-timing similarities of these north polar features to southern dune gullies, identifying the processes forming these features is likely to have relevance for understanding the general evolution/modification of dune gullies. To determine alcove-formation model constraints, we have surveyed seven dune fields, each over 1-4 Mars winters. Consistent with earlier reports, we found that alcove-formation activity occurs during the autumn-winter seasons, before or while the stable seasonal frost layer is deposited. We propose a new model in which alcove formation occurs during the autumn, and springtime sublimation activity then enhances the feature. Summertime winds blow sand into the new alcoves, erasing small alcoves over a few Mars years. Based on the observed rate of alcove erasure, we estimated the effective aeolian sand transport flux. From this, we proposed that alcove formation may account for 2-20% of the total sand movement within these dune fields.

Cassini SAR, radiometry, scatterometry and altimetry observations of Titan's dune fields

USGS Publications Warehouse

Le, Gall A.; Janssen, M.A.; Wye, L.C.; Hayes, A.G.; Radebaugh, J.; Savage, C.; Zebker, H.; Lorenz, R.D.; Lunine, J.I.; Kirk, R.L.; Lopes, R.M.C.; Wall, S.; Callahan, P.; Stofan, E.R.; Farr, Tom

2011-01-01

Large expanses of linear dunes cover Titan's equatorial regions. As the Cassini mission continues, more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation (SAR, radiometry, scatterometry, altimetry) and with an increasing variety of observational geometries. In this paper, we report on Cassini's radar instrument observations of the dune fields mapped through May 2009 and present our key findings in terms of Titan's geology and climate. We estimate that dune fields cover ???12.5% of Titan's surface, which corresponds to an area of ???10millionkm2, roughly the area of the United States. If dune sand-sized particles are mainly composed of solid organics as suggested by VIMS observations (Cassini Visual and Infrared Mapping Spectrometer) and atmospheric modeling and supported by radiometry data, dune fields are the largest known organic reservoir on Titan. Dune regions are, with the exception of the polar lakes and seas, the least reflective and most emissive features on this moon. Interestingly, we also find a latitudinal dependence in the dune field microwave properties: up to a latitude of ???11??, dune fields tend to become less emissive and brighter as one moves northward. Above ???11?? this trend is reversed. The microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion (relative to that of the dune), roughness and degree of sand cover. In agreement with radiometry and scatterometry observations, SAR images suggest that the fraction of interdunes increases northward up to a latitude of ???14??. In general, scattering from the subsurface (volume scattering and surface scattering from buried interfaces) makes interdunal regions brighter than the dunes. The observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north, thus allowing wave penetration in the underlying substrate. Altimetry measurements over dunes have highlighted a region located in the Fensal dune field (???5?? latitude) where the icy bedrock of Titan is likely exposed within smooth interdune areas. The hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and/or an increase in the ground humidity toward the north, which could be related to Titan's asymmetric seasonal polar insolation. Alternatively, it may indicate that either the wind pattern or the topography is less favorable for dune formation in Titan's northern tropics. ?? 2011 Elsevier Inc.

Holden Crater Dune Field

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

A common location for dune fields on Mars is in the basin of large craters. This dune field is located in Holden Crater at 25 degrees South atitude.

Image information: VIS instrument. Latitude -25.5, Longitude 326.8 East (33.2 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.

Mars global digital dune database: MC-30

USGS Publications Warehouse

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

2012-01-01

The Mars Global Digital Dune Database (MGD3) provides data and describes the methodology used in creating the global database of moderate- to large-size dune fields on Mars. The database is being released in a series of U.S. Geological Survey Open-File Reports. The first report (Hayward and others, 2007) included dune fields from lat 65° N. to 65° S. (http://pubs.usgs.gov/of/2007/1158/). The second report (Hayward and others, 2010) included dune fields from lat 60° N. to 90° N. (http://pubs.usgs.gov/of/2010/1170/). This report encompasses ~75,000 km2 of mapped dune fields from lat 60° to 90° S. The dune fields included in this global database were initially located using Mars Odyssey Thermal Emission Imaging System (THEMIS) Infrared (IR) images. In the previous two reports, some dune fields may have been unintentionally excluded for two reasons: (1) incomplete THEMIS IR (daytime) coverage may have caused us to exclude some moderate- to large-size dune fields or (2) resolution of THEMIS IR coverage (100 m/pixel) certainly caused us to exclude smaller dune fields. In this report, mapping is more complete. The Arizona State University THEMIS daytime IR mosaic provided complete IR coverage, and it is unlikely that we missed any large dune fields in the South Pole (SP) region. In addition, the increased availability of higher resolution images resulted in the inclusion of more small (~1 km2) sand dune fields and sand patches. To maintain consistency with the previous releases, we have identified the sand features that would not have been included in earlier releases. While the moderate to large dune fields in MGD3 are likely to constitute the largest compilation of sediment on the planet, we acknowledge that our database excludes numerous small dune fields and some moderate to large dune fields as well. Please note that the absence of mapped dune fields does not mean that dune fields do not exist and is not intended to imply a lack of saltating sand in other areas. Where availability and quality of THEMIS visible (VIS), Mars Orbiter Camera (MOC) narrow angle, Mars Express High Resolution Stereo Camera, or Mars Reconnaissance Orbiter Context Camera and High Resolution Imaging Science Experiment images allowed, we classified dunes and included some dune slipface measurements, which were derived from gross dune morphology and represent the approximate prevailing wind direction at the last time of significant dune modification. It was beyond the scope of this report to look at the detail needed to discern subtle dune modification. It was also beyond the scope of this report to measure all slipfaces. We attempted to include enough slipface measurements to represent the general circulation (as implied by gross dune morphology) and to give a sense of the complex nature of aeolian activity on Mars. The absence of slipface measurements in a given direction should not be taken as evidence that winds in that direction did not occur. When a dune field was located within a crater, the azimuth from crater centroid to dune field centroid was calculated, as another possible indicator of wind direction. Output from a general circulation model is also included. In addition to polygons locating dune fields, the database includes ~700 of the THEMIS VIS and MOC images that were used to build the database.

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.

Determining mineralogical variations of aeolian deposits using thermal infrared emissivity and linear deconvolution methods

USGS Publications Warehouse

Hubbard, Bernard E.; Hooper, Donald M.; Solano, Federico; Mars, John C.

2018-01-01

We apply linear deconvolution methods to derive mineral and glass proportions for eight field sample training sites at seven dune fields: (1) Algodones, California; (2) Big Dune, Nevada; (3) Bruneau, Idaho; (4) Great Kobuk Sand Dunes, Alaska; (5) Great Sand Dunes National Park and Preserve, Colorado; (6) Sunset Crater, Arizona; and (7) White Sands National Monument, New Mexico. These dune fields were chosen because they represent a wide range of mineral grain mixtures and allow us to gauge a better understanding of both compositional and sorting effects within terrestrial and extraterrestrial dune systems. We also use actual ASTER TIR emissivity imagery to map the spatial distribution of these minerals throughout the seven dune fields and evaluate the effects of degraded spectral resolution on the accuracy of mineral abundances retrieved. Our results show that hyperspectral data convolutions of our laboratory emissivity spectra outperformed multispectral data convolutions of the same data with respect to the mineral, glass and lithic abundances derived. Both the number and wavelength position of spectral bands greatly impacts the accuracy of linear deconvolution retrieval of feldspar proportions (e.g. K-feldspar vs. plagioclase) especially, as well as the detection of certain mafic and carbonate minerals. In particular, ASTER mapping results show that several of the dune sites display patterns such that less dense minerals typically have higher abundances near the center of the active and most evolved dunes in the field, while more dense minerals and glasses appear to be more abundant along the margins of the active dune fields.

Determining mineralogical variations of aeolian deposits using thermal infrared emissivity and linear deconvolution methods

NASA Astrophysics Data System (ADS)

Hubbard, Bernard E.; Hooper, Donald M.; Solano, Federico; Mars, John C.

2018-02-01

We apply linear deconvolution methods to derive mineral and glass proportions for eight field sample training sites at seven dune fields: (1) Algodones, California; (2) Big Dune, Nevada; (3) Bruneau, Idaho; (4) Great Kobuk Sand Dunes, Alaska; (5) Great Sand Dunes National Park and Preserve, Colorado; (6) Sunset Crater, Arizona; and (7) White Sands National Monument, New Mexico. These dune fields were chosen because they represent a wide range of mineral grain mixtures and allow us to gauge a better understanding of both compositional and sorting effects within terrestrial and extraterrestrial dune systems. We also use actual ASTER TIR emissivity imagery to map the spatial distribution of these minerals throughout the seven dune fields and evaluate the effects of degraded spectral resolution on the accuracy of mineral abundances retrieved. Our results show that hyperspectral data convolutions of our laboratory emissivity spectra outperformed multispectral data convolutions of the same data with respect to the mineral, glass and lithic abundances derived. Both the number and wavelength position of spectral bands greatly impacts the accuracy of linear deconvolution retrieval of feldspar proportions (e.g. K-feldspar vs. plagioclase) especially, as well as the detection of certain mafic and carbonate minerals. In particular, ASTER mapping results show that several of the dune sites display patterns such that less dense minerals typically have higher abundances near the center of the active and most evolved dunes in the field, while more dense minerals and glasses appear to be more abundant along the margins of the active dune fields.

Earth Observations taken by the Expedition 31 Crew

NASA Image and Video Library

2012-05-11

ISS031-E-030783 (11 May 2012) --- Linear dunes in the Great Sand Sea in southwest Egypt are featured in this image photographed by an Expedition 31 crew member on the International Space Station. In southwestern Egypt, deep in the Sahara Desert, the action of wind dominates landscapes today much as it has done for the past several thousand years. Winds blowing from the north have fashioned sands into large dunes, aligned parallel with these winds. The so-called linear dunes?shown here in the Great Sand Sea?are easily seen from space and local maps show that they rise 20?30 meters above the surrounding flat plains. The distance between individual linear dunes is interestingly regular, at 1.5?2.5 kilometers, suggesting some equilibrium exists between the formative wind strength and the sand supply. It is possible that linear dunes may relate to earlier times when winds were stronger than they are today, or sand more plentiful. The dark patch of rock outcrop at upper right sticks up above the surface on which the dunes lie by as much as 150 meters. The north winds have been deflected around this high zone, and smaller secondary linear dunes can be seen along the right side of the image, aligned with local winds that become ever more northeasterly with nearness to the outcrops. A dune-free zone on the protected downwind (south-southeast) side of the outcrop gives a sense of the sand movement (generally from the bottom of the image towards the top). At first glance, the large linear dunes appear to be the major landform in the image; however a complex pattern of even smaller dunes can be seen perched on top of the largest dunes (inset). The sand that comprises many dune fields usually, according to scientists, derives from some larger river not very distant upwind, supplied from the dry river bed (exposed to the wind during dry seasons of low river flow, or regional change to a more arid climate). Inland dune fields thus lie downwind of the source river. A large, unnamed river once flowed to the Mediterranean Sea situated west of the dunes shown in this picture, dumping its sand load 300 kilometers northwest of the area shown. It is likely that this river, the evidence of which is now almost completely obliterated, was the source of the sand in the linear dunes, the scientists say.

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.

Dune mobility in the St. Anthony Dune Field, Idaho, USA: Effects of meteorological variables and lag time

NASA Astrophysics Data System (ADS)

Hoover, R. H.; Gaylord, D. R.; Cooper, C. M.

2018-05-01

The St. Anthony Dune Field (SADF) is a 300 km2 expanse of active to stabilized transverse, barchan, barchanoid, and parabolic sand dunes located in a semi-arid climate in southeastern Idaho. The northeastern portion of the SADF, 16 km2, was investigated to examine meteorological influences on dune mobility. Understanding meteorological predictors of sand-dune migration for the SADF informs landscape evolution and impacts assessment of eolian activity on sensitive agricultural lands in the western United States, with implications for semi-arid environments globally. Archival aerial photos from 1954 to 2011 were used to calculate dune migration rates which were subsequently compared to regional meteorological data, including temperature, precipitation and wind speed. Observational analyses based on aerial photo imagery and meteorological data indicate that dune migration is influenced by weather for up to 5-10 years and therefore decadal weather patterns should be taken into account when using dune migration rates as proxies from climate fluctuation. Statistical examination of meteorological variables in this study indicates that 24% of the variation of sand dune migration rates is attributed to temperature, precipitation and wind speed, which is increased to 45% when incorporating lag time.

Crater Floor Dune Field

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

Our final dune image shows a small dune field inside an unnamed crater south of Nili Fossae.

Image information: VIS instrument. Latitude 20.6, Longitude 79 East (281 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.

Glimpse of Bagnold Dunes Edging Mount Sharp

NASA Image and Video Library

2015-11-16

The dark band in the lower portion of this Martian scene is part of the "Bagnold Dunes" dune field lining the northwestern edge of Mount Sharp, inside Gale Crater. The view combines multiple images taken with the Mast Camera (Mastcam) on NASA's Curiosity Mars rover on Sept. 25, 2015, during the 1,115th Martian day, or sol, of Curiosity's work on Mars. The images are from Mastcam's right-eye camera, which has a telephoto lens. The view is toward south-southeast. Curiosity will visit examples of the Bagnold Dunes on the rover's route to higher layers of Mount Sharp. The informal name for the dune field is a tribute to British military engineer Ralph Bagnold (1896-1990), a pioneer in the study of how winds move sand particles of dunes on Earth. The dune field is evident as a dark band in orbital images of the area inside Gale Crater where Curiosity has been active since landing in 2012, such as a traverse map at PIA20162. Dunes are larger than wind-blown ripples of sand or dust that Curiosity and other rovers have visited previously. The scene is presented with a color adjustment that approximates white balancing, to resemble how the rocks and sand would appear under daytime lighting conditions on Earth. http://photojournal.jpl.nasa.gov/catalog/PIA19929

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-18

The majority of the dune field in Rabe Crater consists of a sand sheet with dune forms on the surface. The sand sheet is where a thick layer of sand has been concentrated. As continued winds blow across the sand surface it creates dune forms. The depth of the sand sheet prevents excavation to the crater floor and the dune forms all appear connected. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 58024 Latitude: -43.6954 Longitude: 34.8236 Instrument: VIS Captured: 2015-01-12 09:48 https://photojournal.jpl.nasa.gov/catalog/PIA22144

Northern Sand Sea

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

This VIS image was taken at 82 degrees North latitude during Northern spring. The image is completely dominated by dunes. In sand seas, it is very common for a single type of dune to occur, and for a single predominate wind to control the alignment of the dunes.

Image information: VIS instrument. Latitude 82.2, Longitude 152.5 East (207.5 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.

Ganges Chasma Sand Sheet

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

Today's sand sheet is located in the Ganges Chasma portion of Valles Marineris. As with yesterday's image, note that the dune forms are seen only at the margin and that the interior of the sand sheet at this resolution appears to completely lack dune forms.

Image information: VIS instrument. Latitude -6.4, Longitude 310.7 East (49.3 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.

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

USGS Publications Warehouse

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

2003-01-01

Proctor Crater is a 150 km diameter crater in Noachis Terra, within the southern highlands of Mars. The analysis leading to the sedimentary history incorporates several data sets including imagery, elevation, composition, and thermal inertia, mostly from the Mars Global Surveyor mission. The resulting stratigraphy reveals that the sedimentary history of Proctor Crater has involved a complex interaction of accumulating and eroding sedimentation. Aeolian features spanning much of the history of the crater interior dominate its surface, including large erosional pits, stratified beds of aeolian sediment, sand dunes, erosional and depositional streaks, dust devil tracks, and small bright bed forms that are probably granule ripples. Long ago, up to 450 m of layered sediment filled the crater basin, now exposed in eroded pits on the crater floor. These sediments are probably part of an ancient deposit of aeolian volcaniclastic material. Since then, some quantity of this material has been eroded from the top layers of the strata. Small, bright dune forms lie stratigraphically beneath the large dark dune field. Relative to the large dark dunes, the bright bed forms are immobile, although in places, their orientations are clearly influenced by the presence of the larger dunes. Their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill. Dust devil tracks form during the spring and summer, following a west-southwesterly wind. Early in the spring the dust devils are largely restricted to dark patches of sand. As the summer approaches, dust devil tracks become more plentiful and spread to the rest of the crater floor, indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils. The dark dunes contain few dust devil tracks, suggesting that accumulated dust is swept away directly by saltation, rather than by the passage of dust devils. Spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt-like materials. The average thermal inertia calculated from Thermal Emission Spectrometer bolometric temperatures is 277 ?? 17 J m-2 s-0.5 K-1, leading to an effective grain size of 740 ?? 170 ??m, which is consistent with coarse sand and within the range expected for Martian sand. The coarse sand that composes the large dune field may have originated from outside the crater, saltating in from the southwest. Most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried. The sand was transported to the east center of the crater floor, where beneath the present-day dunes a 50 m high mound of sand has accumulated. Dune slip faces indicate a wind regime consisting of three opposing winds. Some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms. The combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime, which produces the large reversing transverse and star dunes that dominate the dune field. The dark dunes have both active slip faces and seemingly inactive slip faces, suggesting that the dunes vary spatially in their relative activity. Nevertheless, the aeolian activity that has dominated the history of Proctor Crater still continues today. Copyright 2003 by the American Geophysical Union.

Recent eolian activity and paleoclimate fluctuations in the Ferris Lost Soldier Area, South-Central Wyoming

NASA Astrophysics Data System (ADS)

Gaylord, D. R.

1983-09-01

The Ferris Dune Fields were examined. Sand dunes are especially valuable in paleoclimate reconstructions because they: (1) bury and preserve datable materials and artifacts; (2) respond to even subtle changes in wind velocity and direction as reflected both in external morphology and internal structures; and (3) remain unconsolidated, making them amenable to easy textural and compositional examination. The valley of Clear Creek in the Ferris Dunes reveals a relatively continuous Holocene section of interbedded dune and interdunal pond deposits. Radiocarbon dates from the interdunal pond strata at Clear Creek, theoretical sand dune migration rates, compositional analysis of periglacial sand wedges, and relative dating of actively migrating parabolic dunes reveals a general sequence of geologic-climatic events that affected the Ferris-Lost Soldier area. The most recent major reactivaton of dunes occurred approximately 290 years ago.

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.

A seismic search for the paleoshorelines of Lake Otero beneath White Sands Dune Field, New Mexico

NASA Astrophysics Data System (ADS)

Wagner, P. F.; Reece, R.; Ewing, R. C.

2014-12-01

The Tularosa Basin, which now houses White Sands Dune Field, was once occupied by Pleistocene Lake Otero. Several paleoshorelines of Lake Otero have been identified throughout the basin by field surveys and remote sensing using digital elevation models. Up to four shorelines may be buried beneath White Sands Dune Field and it has been posited that the current upwind margin of White Sands coincides with a one of these shorelines. Here we employ a novel geophysical instrument and method to image the subsurface: the seismic land streamer. The land streamer utilizes weighted base plates and one-component vertical geophones in a towed array. With a seisgun acoustic source, we imaged in the Alkali Flats area near the upwind margin, one potential location of paleoshorelines, as well as the Film Lot closer to the center of the dune field. Surfaces in both locations are indurated gypsum playa, which made seismic imaging possible and successful. We collected one SW-NE trending seismic line at each location, which matches the dominant wind and dune migration directions. Based on initial data analysis we find some subsurface structure that may coincide with the paleo lake bed of Lake Otero. The successful demonstration of this new method provides the foundation for an expanded regional subsurface study to image the strata and structure of the Tularosa Basin.

'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.

Nili Patera Dune Field

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

This VIS image shows a dune field within Nili Patera, the northern caldera of a large volcanic complex in Syrtis Major.

Image information: VIS instrument. Latitude 9, Longitude 67 East (293 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.

Geochemical evidence for an Eolian sand dam across the North and South Platte rivers in Nebraska

USGS Publications Warehouse

Muhs, Daniel R.; Swinehart, James B.; Loope, David B.; Been, Josh; Mahan, Shannon; Bush, Charles A.

2000-01-01

Geochemical and geomorphic data from dune fields in southwestern Nebraska provide new evidence that the Nebraska Sand Hills once migrated across the North and South Platte rivers and dammed the largest tributary system to the Missouri River. The Lincoln County and Imperial dune fields, which lie downwind of the South Platte River, have compositions intermediate between the Nebraska Sand Hills (quartz-rich) and northeastern Colorado dunes (K-feldspar-rich). The most likely explanation for the intermediate composition is that the Lincoln County and Imperial dunes are derived in part from the Nebraska Sand Hills and in part from the South Platte River. The only mechanism by which the Nebraska Sand Hills could have migrated this far south is by complete infilling of what were probably perennially dry North Platte and South Platte river valleys. Such a series of events would have required an extended drought, both for activation of eolian sand and decreased discharges in the Platte River system. A nearby major tributary of the North Platte River is postulated to have been blocked by eolian sand about 12,000 14C yr B.P. We propose that an eolian sand dam across the Plattes was constructed at about this same time.

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.

The persistence of large-scale blowouts in largely vegetated coastal dune fields

NASA Astrophysics Data System (ADS)

Delgado-Fernandez, Irene; Smyth, Thomas; Jackson, Derek; Davidson-Arnott, Robin; Smith, Alexander

2016-04-01

Coastal dunes move through natural phases of stability and instability during their evolution, displaying various temporal and spatial patterns across the dune field. Recent observations, however, have shown exceptionally rapid rates of stability through increased vegetative growth. This progressive vegetation colonisation and consequent loss of bare sand on coastal dune systems has been noted worldwide. Percentage reductions in bare sand of as much as 80% within just a few decades can been seen in examples from South Africa, Canada and Brazil as well as coastal dune sites across NW Europe. Despite these dramatic trends towards dune stabilisation, it is not uncommon to find particular examples of large-scale active blowouts and parabolic dunes within largely vegetated coastal dunes. While turbulence and airflow dynamics within features such as blowouts and other dune forms has been studied in detail within recent years, there is a lack of knowledge about what maintains dune mobility at these specific points in otherwise largely stabilized dune fields. This work explores the particular example of the 'Devil's Hole' blowout, Sefton Dunes, NW England. Approximately 300 m long by 100 m wide, its basin is below the water-table which leads to frequent flooding. Sefton Dunes in general have seen a dramatic loss of bare sand since the 1940s. However, and coinciding with this period of dune stabilisation, the 'Devil's Hole' has not only remained active but also grown in size at a rate of 4.5 m year-1 along its main axis. An exploration of factors controlling the maintenance of open bare sand areas at this particular location is examined using a variety of techniques including Computational Fluid Dynamics (CFD) airflow modelling and in situ empirical measurements of (short-term experiments) of wind turbulence and sand transport. Field measurements of wind parameters and transport processes were collected over a 2 week period during October 2015. Twenty three 3D ultrasonic anemometers were deployed at 0.5 m elevations over a grid covering sections of the blowout walls, deflation basin and depositional lobe. A number of high resolution sand traps and wenglor sensors were co-located with anemometers in the walls and basin, and a terrestrial laser scanner was used to collect high-resolution topographic data both before and after the strongest transport event recorded during the study period. Preliminary results indicate significant transport differences in operation at each of the two blow out walls as well as complex interactions between turbulence, superficial moisture content and up-wind sediment sources. This study represents a comprehensive examination of both wind and sediment flux patterns at high spatial and temporal resolution inside a large trough blowout feature; and reveals insights into why such systems are maintained as erosional features for long time periods.

Dune Transition in the High Southern Latitudes

NASA Image and Video Library

2017-04-19

Sand dune populations on Mars can vary widely with respect to morphology, relief, and activity. One of the most striking examples occurs with the many dune fields of the high Southern latitudes. When we venture south of -60 degrees latitude, we see increasing signs of dune degradation, with subdued dune brinks and broad sandy aprons, rather than sharp, dune crests and distinct boundaries. Dunes this far south are also very modest in height, often consisting solely of flat sand sheets. Additionally, global monitoring campaigns are revealing a noticeable lack of changes in these bedform positions, whereas many dunes and ripples to the north are migrating across the surface. This image shows a moderate sized dune field (-72 degrees latitude) that displays most of these morphologic features and a noticeable absence of dune crests. This transition is likely related to polar processes, ground ice, and changes in regional climate relative to the rest of the planet. https://photojournal.jpl.nasa.gov/catalog/PIA21595

Investigating Mars: Arabia Terra Dunes

NASA Image and Video Library

2018-03-21

This image is located southeast of the region of the large sand dune deposit. Here there is still limited amounts of available sand and the dunes formed are smaller individual features. The rocky floor of the crater is visible between the dunes. In some places the floor is relatively free of hills and mesas, while other locations are dense with features. The hills and mesas in the crater can range up to several hundreds of meters tall. Located in eastern Arabia is an unnamed crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of what is probably fine-grain sand. The shape of the dunes indicate that prevailing winds have come from different directions over the years. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 37799 Latitude: 26.2544 Longitude: 63.1648 Instrument: VIS Captured: 2010-06-22 17:06 https://photojournal.jpl.nasa.gov/catalog/PIA22300

Ground-Water Flow Direction, Water Quality, Recharge Sources, and Age, Great Sand Dunes National Monument, South-Central Colorado, 2000-2001

USGS Publications Warehouse

Rupert, Michael G.; Plummer, Niel

2004-01-01

Great Sand Dunes National Monument is located in south-central Colorado along the eastern edge of the San Luis Valley. The Great Sand Dunes National Monument contains the tallest sand dunes in North America; some rise up to750 feet. Important ecological features of the Great Sand Dunes National Monument are palustrine wetlands associated with interdunal ponds and depressions along the western edge of the dune field. The existence and natural maintenance of the dune field and the interdunal ponds are dependent on maintaining ground-water levels at historic elevations. To address these concerns, the U.S. Geological Survey conducted a study, in collaboration with the National Park Service, of ground-water flow direction, water quality, recharge sources, and age at the Great Sand Dunes National Monument. A shallow unconfined aquifer and a deeper confined aquifer are the two principal aquifers at the Great Sand Dunes National Monument. Ground water in the unconfined aquifer is recharged from Medano and Sand Creeks near the Sangre de Cristo Mountain front, flows underneath the main dune field, and discharges to Big and Little Spring Creeks. The percentage of calcium in ground water in the unconfined aquifer decreases and the percentage of sodium increases because of ionic exchange with clay minerals as the ground water flows underneath the dune field. It takes more than 60 years for the ground water to flow from Medano and Sand Creeks to Big and Little Spring Creeks. During this time, ground water in the upper part of the unconfined aquifer is recharged by numerous precipitation events. Evaporation of precipitation during recharge prior to reaching the water table causes enrichment in deuterium (2H) and oxygen-18 (18O) relative to waters that are not evaporated. This recharge from precipitation events causes the apparent ages determined using chlorofluorocarbons and tritium to become younger, because relatively young precipitation water is mixing with older waters derived from Medano and Sand Creeks. Major ion chemistry of water from sites completed in the confined aquifer is different than water from sites completed in the unconfined aquifer, but insufficient data exist to quantify if the two aquifers are hydrologically disconnected. Radiocarbon dating of ground water in the confined aquifer indicates it is about 30,000 years old (plus or minus 3,000 years). The peak of the last major ice advance (Wisconsin) during the ice age occurred about 20,000 years before present; ground water from the confined aquifer is much older than that. Water quality and water levels of the interdunal ponds are not affected by waters from the confined aquifer. Instead, the interdunal ponds are affected directly by fluctuations in the water table of the unconfined aquifer. Any lowering of the water table of the unconfined aquifer would result in an immediate decrease in water levels of the interdunal ponds. The water quality of the interdunal ponds probably results from several factors, including the water quality of the unconfined aquifer, evaporation of the pond water, and biologic activity within the ponds.

The role of streamline curvature in sand dune dynamics: evidence from field and wind tunnel measurements

NASA Astrophysics Data System (ADS)

Wiggs, Giles F. S.; Livingstone, Ian; Warren, Andrew

1996-09-01

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

Mastcam Telephoto of a Martian Dune Downwind Face

NASA Image and Video Library

2016-01-04

This view combines multiple images from the telephoto-lens camera of the Mast Camera (Mastcam) on NASA's Curiosity Mars rover to reveal fine details of the downwind face of "Namib Dune." The site is part of the dark-sand "Bagnold Dunes" field along the northwestern flank of Mount Sharp. Images taken from orbit have shown that dunes in the Bagnold field move as much as about 3 feet (1 meter) per Earth year. Sand on this face of Namib Dune has cascaded down a slope of about 26 to 28 degrees. The top of the face is about 13 to 17 feet (4 to 5 meters) above the rocky ground at its base. http://photojournal.jpl.nasa.gov/catalog/PIA20283

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

USGS Publications Warehouse

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

1995-01-01

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

Parabolic dune development modes according to shape at the southern fringes of the Hobq Desert, Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Guan, Chao; Hasi, Eerdun; Zhang, Ping; Tao, Binbin; Liu, Dan; Zhou, Yanguang

2017-10-01

Since the 1970s, parabolic dunes at the southern fringe of the Hobq Desert, Inner Mongolia, China have exhibited many different shapes (V-shaped, U-shaped, and palmate) each with a unique mode of development. In the study area, parabolic dunes are mainly distributed in Regions A, B, and C with an intermittent river running from the south to the north. We used high-resolution remote-sensing images from 1970 to 2014 and RTK-GPS measurements to study the development modes of different dune shapes; the modes are characterized by the relationship between the intermittent river and dunes, formation of the incipient dune patterns, the predominant source supply of dunes, and the primary formation of different shapes (V-shaped, U-shaped, and palmate). Most parabolic dunes in Region A are V-shaped and closer to the bank of the river. The original barchans in this region exhibit "disconnected arms" behavior. With the sand blown out of the riverbed through gullies, the nebkhas on the disconnected arms acquire the external sand source through the "fertile island effect", thereby developing into triangular sand patches and further developing into V-shaped parabolic dunes. Most parabolic dunes in Regions B and C are palmate. The residual dunes cut by the re-channelization of river from transverse dune fields on the west bank are the main sand source of Region B. The parabolic dunes in Region C are the original barchans having then been transformed. The stoss slopes of V-shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape. The dune crest of V-shaped parabolic dune is the deposition area, which forms the "arc-shaped sand ridge". Their two arms are non-parallel; the lateral airflow of the arms jointly transport sand to the middle part of dunes, resulting in a narrower triangle that gradually becomes V-shaped. Palmate parabolic dunes have a steeper stoss slope and height. The dune crest of the palmate parabolic dune is the erosion area, which forms a long and narrow trough between nebkhas by the "funnelling effect". This process forces sand towards lee slopes, which transform from concave (original barchans) into convex, ultimately resulting in the formation of palmate parabolic dunes.

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-01-23

Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southeastern part of the crater floor. Most of the individual dunes in Kaiser Crater are barchan dunes. Barchan dunes are crescent shaped with the points of the crescent pointing downwind. The sand is blown up the low angle side of the dune and then tumbles down the steep slip face. This dune type forms on hard surfaces where there is limited amounts of sand. Barchan dunes can merge together over time with increased sand in the local area. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 1036 Latitude: -46.7795 Longitude: 20.2075 Instrument: VIS Captured: 2002-03-09 20:07 https://photojournal.jpl.nasa.gov/catalog/PIA22172

Investigating Mars: Arabia Terra Dunes

NASA Image and Video Library

2018-03-20

The bottom of this image shows the hills and mesas within the crater. The dunes at the top of the image are engulfing and covering the hills. In some locations the hills are still a substantial obstacle to the wind. In these cases the wind is blowing sand up against the windward side, but the hill is causing chaotic wind flow around the hill and rather than depositing sand, the wind is actually removing sand on the leeward side of the hill. With continued winds and sand movement the deposition of material will eventually build up along the leeward side of the hill and then engulf the hill on all sides. Located in eastern Arabia is an unnamed crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of what is probably fine-grain sand. The shape of the dunes indicate that prevailing winds have come from different directions over the years. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 11781 Latitude: 26.3693 Longitude: 62.693 Instrument: VIS Captured: 2004-08-10 10:40 https://photojournal.jpl.nasa.gov/catalog/PIA22299

Dunes in Brashear

NASA Image and Video Library

2006-01-08

This Mars Global Surveyor MGS Mars Orbiter Camera MOC image shows a field of dark sand dunes on the northwestern floor of Brashear Crater. The dunes formed largely from winds that blew from the southeast lower right

Visible/near-infrared spectral diversity from in situ observations of the Bagnold Dune Field sands in Gale Crater, Mars

NASA Astrophysics Data System (ADS)

Johnson, Jeffrey R.; Achilles, Cherie; Bell, James F.; Bender, Steve; Cloutis, Edward; Ehlmann, Bethany; Fraeman, Abigail; Gasnault, Olivier; Hamilton, Victoria E.; Le Mouélic, Stéphane; Maurice, Sylvestre; Pinet, Patrick; Thompson, Lucy; Wellington, Danika; Wiens, Roger C.

2017-12-01

As part of the Bagnold Dune campaign conducted by Mars Science Laboratory rover Curiosity, visible/near-infrared reflectance spectra of dune sands were acquired using Mast Camera (Mastcam) multispectral imaging (445-1013 nm) and Chemistry and Camera (ChemCam) passive point spectroscopy (400-840 nm). By comparing spectra from pristine and rover-disturbed ripple crests and troughs within the dune field, and through analysis of sieved grain size fractions, constraints on mineral segregation from grain sorting could be determined. In general, the dune areas exhibited low relative reflectance, a weak 530 nm absorption band, an absorption band near 620 nm, and a spectral downturn after 685 nm consistent with olivine-bearing sands. The finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest 530 nm bands, highest relative reflectances, and weakest red/near-infrared ratios, consistent with a combination of crystalline and amorphous ferric materials. Coarser-grained samples were the darkest and bluest and exhibited weaker 530 nm bands, lower relative reflectances, and stronger downturns in the near-infrared, consistent with greater proportions of mafic minerals such as olivine and pyroxene. These grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands. Sieved dune sands exhibited progressive decreases in reflectance with increasing grain size, as observed in laboratory spectra of olivine size separates. The continuum of spectral features observed between the coarse- and fine-grained dune sands suggests that mafic grains, ferric materials, and air fall dust mix in variable proportions depending on aeolian activity and grain sorting.

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

USGS Publications Warehouse

Draut, Amy E.

2012-01-01

Connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions. This study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid Colorado River corridor, southwestern USA. By quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources, this work demonstrates for the first time that the flow- and sediment-limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line. Dune fields decoupled from fluvial sand supply have more ground cover (biologic crust and vegetation) and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply. The proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach (Marble–Grand Canyon, Arizona) than in a much less regulated reach with otherwise similar environmental conditions (Cataract Canyon, Utah). The interconnections shown here among river flow and sediment, aeolian sand transport, and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments. Because fluvial–aeolian coupling is common globally, it is likely that similar sediment-transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously.

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.

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.

Geologic and paleoecologic studies of the Nebraska Sand Hills

USGS Publications Warehouse

Ahlbrandt, Thomas S.; Fryberger, S.G.; Hanley, John H.; Bradbury, J. Platt

1980-01-01

PART A: The Nebraska Sand Hills are an inactive, late Quaternary, most probably Holocene, dune field (covering 57,000 km 2 ) that have been eroded along streams and in blowouts, resulting in excellent lateral and vertical exposures of the stratification of dune and interdune sediments. This paper presents new data on the geometry, primary sedimentary structures, modification of sedimentary structures, direction of sand movement, and petrography of these eolian deposits. Eolian deposits of the Sand Hills occur as relatively thin (9-24 m) 'blanket' sands, composed of a complex of dune and discontinuous, diachronous interdune deposits unconformably overlying fluviolacustrine sediments. The internal stratification of large dunes in the Sand Hills (as high as 100 m), is similar to the internal stratification of smaller dunes of the same type in the Sand Hills, differing only in scale. Studies of laminae orientation in the Sand Hills indicate that transverse, barchan, and blowout dunes can be differentiated in rocks of eolian origin using both the mean dip angle of laminae and the mean angular deviation of dip direction. A variety of secondary structures modify or replace primary eolian stratification in the Sand Hills, the more common of which are dissipation structures and bioturbation. Dissipation structures in the Sand Hills may develop when infiltrating water deposits clay adjacent to less permeable layers in the sand, or along the upper margins of frozen layers that form in the sands during winter. Cross-bed measurements from dunes of the Nebraska Sand Hills necessitate a new interpretation of the past sand transport directions. The data from these measurements indicate a general northwest-to-southeast drift of sand, with a more southerly drift in the southeast part of the Sand Hills. A large area of small dunes < 100 m high) described by Smith (1965) as linear or seif in the central part of the Sand Hills was interpreted by him on the basis of morphology only. We interpret these as transverse-ridge dunes that were generally moving to the south. Further, our measurements indicate that dunes in the western part of the Sand Hills did not develop in response to present-day effective wind regimes. The presence of 'transverse' and en echelon barchan dunes in the Sand Hills corresponds to a developmental sequence of barchan to linear dunes proposed by Tsoar (1978). Dune and interdune deposits of the Sand Hills are subfeldsarenites to feldsarenites. Sand grains are commonly coated with montmorillonitic clay, which may be the local source of the clay concentrated in the dissipation structures. Textures of sand samples taken from adjacent layers within a dune were as dissimilar as textures of samples taken from widely separated dunes. This common occurrence indicates that textural data must be used carefully and in combination with other data to recognize ancient rocks of eolian origin. Organic material derived from a variety of flora and fauna that inhabit the interdunes (chapters B and C) generated both oil and gas upon heating. Thus, interdune sediments may be an indigenous hydrocarbon source if buried in eolianites. The twofold stratigraphy of loess and correlative dune deposits in the Sand Hills proposed by Reed and Dreeszen (1965) could not be confirmed by the present study. Rather, available data indicate that the dunes represent a single formation as suggested by Lugn (1935). PART B: Three assemblages of nonmarine Mollusca from paleointerdune deposits in the Nebraska Sand Hills inhabited shallow, quiet, vegetated, subpermanent or temporary, freshwater interdune ponds and adjacent terrestrial habitats. Analysis of factors affecting the taxonomic composition, diversity, and abundance of species in living assemblages of mollusks support this interpretation. The mollusks have long biostratigraphic ranges and broad biogeographic distributions. They fail to establish precise age relations of the faunas othe

Field measurements of mean and turbulent airflow over a barchan sand dune

NASA Astrophysics Data System (ADS)

Weaver, Corinne M.; Wiggs, Giles F. S.

2011-05-01

Advances in our knowledge of the aeolian processes governing sand dune dynamics have been restricted by a reliance on measures of time-averaged airflow, such as shear velocity ( u*). It has become clear that such measures are incapable of explaining the complete dynamics of sediment transport across dune surfaces. Past evidence from wind tunnel and modelling studies has suggested that in some regions on a dune's surface the sediment transport might be better explained through investigations of the turbulent nature of the airflow. However, to date there have been no field studies providing data on the turbulent characteristics of the airflow around dunes with which to support or refute such hypotheses. The field investigation presented here provides mean and turbulent airflow measurements across the centre-line of a barchan sand dune in Namibia. Data were collected using arrays of sonic anemometers and were compared with sand flux data measured using wedge-shaped traps. Results support previously published data derived from wind tunnels and numerical models. The decline in mean wind velocity at the upwind toe of the dune is shown to coincide with a rise in turbulence, whilst mean velocity acceleration on the upper slope corresponds with a general decline in measured turbulence. Analysis of the components of Reynold shear stress ( -u'¯w'¯) and normal stresses ( u¯ and w2 ¯) supports the notion that the development of flow turbulence along the dune centre-line is likely to be associated with the interplay between streamline curvature and mean flow deceleration/acceleration. It is suggested that, due to the nature of its calculation, turbulence intensity is a measure of less practical use than direct assessments of the individual components of Reynolds stress, particularly the instantaneous horizontal streamwise component ( u2 ¯) and shear stress ( -uw¯). Whilst, increases in Reynolds shear stress and the horizontal streamwise component of stress in the toe region of the dune may effectively explain the maintenance of sand flux in a region of declining mean velocity, they have much less explanatory power for sand flux on the upper windward slope and in the crestal region of the dune. Here, it is suggested that mean flow acceleration is likely to provide the most significant driving force on sand flux, possibly augmented by a rise in the horizontal streamwise component of Reynolds stress ( u2 ¯) in the crest/brink region. Therefore, although wind turbulence is considered to be of fundamental importance in explaining the sediment transport dynamics across the dune's surface it is recognised that the interaction between mean flow deceleration/acceleration, streamline curvature and individual components of Reynolds stress is complex and the identification of a single element of flow that offers a panacea for accounting for sand flux and dune dynamics is difficult to find.

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

USGS Publications Warehouse

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

2014-01-01

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.

Dune growth under multidirectional wind regimes

NASA Astrophysics Data System (ADS)

Gadal, C.; Rozier, O.; Claudin, P.; Courrech Du Pont, S.; Narteau, C.

2017-12-01

Under unidirectional wind regimes, flat sand beds become unstable to produce periodic linear dunes, commonly called transverse dunes because their main ridges are oriented perpendicular to the air flow. In areas of low sediment availability, the same interactions between flow, transport and topography produce barchan dunes, isolated sand-pile migrating over long distances with a characteristic crescentic shape. For the last fifteen years, barchan dunes and the instability at the origin of transverse dunes have been the subject of numerous studies that have identified a set of characteristic length and time scales with respect to the physical properties of both grains and fluid. This is not the case for dunes developing under multidirectional wind regimes. Under these conditions, dune orientation is measured with respect to the direction of the resultant sand flux. Depending on the wind regime, dunes do not always line up perpendicularly to the resultant sand flux, but can also be at an oblique angle or even parallel to it. These oblique and longitudinal dunes are ubiquitous in all deserts on Earth and planetary bodies because of the seasonal variability of wind orientation. They are however poorly constrained by observations and there is still no complete theoretical framework providing a description of their orientation and initial wavelength. Here, we extend the linear stability analysis of a flat sand of bed done in two dimensions for a unidirectional flow to three dimensions and multidirectional flow regimes. We are able to recover transitions from transverse to oblique or longitudinal dune patterns according to changes in wind regimes. We besides give a prediction for the initial dune wavelength. Our results compare well to previous theory of dune orientation and to field, experimental and numerical data.

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.

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

NASA Astrophysics Data System (ADS)

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

2014-11-01

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

Investigating Mars: Arabia Terra Dunes

NASA Image and Video Library

2018-03-23

This is a false color image of the dune field in the Arabia Terra crater. In this combination of bands, sand appears as a blue to dark blue color. In this image, the smaller areas of sand are easily visible and indicate the large amount of available material for creating dunes. Located in eastern Arabia is an unnamed crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of what is probably fine-grain sand. The shape of the dunes indicate that prevailing winds have come from different directions over the years. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 45125 Latitude: 26.6761 Longitude: 62.9345 Instrument: VIS Captured: 2012-02-15 20:32 https://photojournal.jpl.nasa.gov/catalog/PIA22302

Effects of prolonged drought on the vegetation cover of sand dunes in the NW Negev Desert: Field survey, remote sensing and conceptual modeling

NASA Astrophysics Data System (ADS)

Siegal, Z.; Tsoar, H.; Karnieli, A.

2013-06-01

Luminescence dating of stable sand dunes in the large deserts of the world has shown several episodes of mobility during the last 30 k years. The logical explanation for the mobility of fixed dunes is severe drought. Though drought length can be estimated, the level of precipitation drop is unknown. The stabilized sand dunes of the northwestern Negev Desert, Israel have been under an unprecedented prolonged drought since 1995. This has resulted in a vast decrease of shrubs cover on the fixed sand dunes, which changes along the rainfall gradient. In the north, an average of 27% of the shrubs had wilted by 2009, and in the drier southern area, 68% of the shrubs had withered. This loss of shrubbery is not expected to induce dune remobilization because the existing bio-crust cover is not negatively affected by the drought. Eleven aerial photographs taken over the drier southern area from 1956 to 2005 show the change in shrub cover due to human impact and the recent severe drought.

'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.

Dome and Barchan Dunes in Newton Crater

NASA Image and Video Library

2014-10-01

This observation from NASA Mars Reconnaissance Orbiter shows both dome and barchan dunes in a small sand dune field on the floor of Newton Crater, an approximately 300 kilometer 130 mile wide crater in the Southern hemisphere of Mars.

Eolian features in the Western Desert of Egypt and some applications to Mars.

USGS Publications Warehouse

El-Baz, F.; Breed, C.S.; Grolier, M.J.; McCauley, J.F.

1979-01-01

Relations of landform types to wind regimes, bedrock composition, sediment supply, and topography are shown by field studies and satellite photographs of the Western Desert. This desert provides analogs of Martian wind-formed features and sand dunes, alternating light and dark streaks, knob 'shadows' and yardangs. Surface particles have been segregated by wind into dunes, sand sheets, and light streaks, that can be differentiated by their grain size distributions, surface shapes, and colors. Throughgoing sand of mostly fine to medium grain size is migrating S in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing W winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. -from Authors

Isolated Northern Dunes

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

This VIS image was taken at 81 degrees North latitude during Northern spring. In this region, the dunes are isolated from each other. The dunes are just starting to emerge from the winter frost covering appearing dark with bright crests. These dunes are located on top of ice.

Image information: VIS instrument. Latitude 82.1, Longitude 191.3 East (168.7 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.

Vegetation of semi-stable rangeland dunes of the Navajo Nation, Southwestern USA

USGS Publications Warehouse

Thomas, Kathryn A.; Redsteer, Margaret H.

2016-01-01

Dune destabilization and increased mobility is a worldwide issue causing ecological, economic, and health problems for the inhabitants of areas with extensive dune fields. Dunes cover nearly a third of the Navajo Nation within the Colorado Plateau of southwestern USA. There, higher temperatures and prolonged drought beginning in 1996 have produced significant increases in dune mobility. Vegetation plays an important role in dune stabilization, but there are few studies of the plants of the aeolian surfaces of this region. We examined plant species and their attributes within a moderately vegetated dune field of the Navajo Nation to understand the types and characteristics of plants that stabilize rangeland dunes. These dunes supported a low cover of mixed grass-scrubland with fifty-two perennial and annual species including extensive occurrence of non-native annual Salsola spp. Perennial grass richness and shrub cover were positively associated with increased soil sand composition. Taprooted shrubs were more common on sandier substrates. Most dominant grasses had C4 photosynthesis, suggestive of higher water-use efficiencies and growth advantage in warm arid environments. Plant cover was commonly below the threshold of dune stabilization. Increasing sand movement with continued aridity will select for plants adapted to burial, deflation, and abrasion. The study indicates plants tolerant of increased sand mobility and burial but more investigation is needed to identify the plants adapted to establish and regenerate under these conditions. In addition, the role of Salsola spp. in promoting decline of perennial grasses and shrubs needs clarification.

North Polar Erg

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

This VIS image was taken at 82 degrees North latitude during Northern spring. As with yesterday's image, the dunes are still partially frost covered. This region is part of the north polar erg (sand sea), note the complexity and regional coverage of the dunes.

Image information: VIS instrument. Latitude 81.2, Longitude 118.2 East (241.8 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.

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

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2009-12-01

ISS022-E-005258 (1 Dec. 2009) --- This detailed hand-held digital camera?s image recorded from the International Space Station highlights sand dunes in the Fachi-Bilma erg, or sand sea, which is part of the central eastern Tenere Desert. The Tenere occupies much of southeastern Niger and is considered to be part of the larger Sahara Desert that stretches across northern Africa. Much of the Sahara is comprised of ergs ? with an area of approximately 150,000 square kilometers, the Fachi-Bilma is one of the larger sand seas. Two major types of dunes are visible in the image. Large, roughly north-south oriented transverse dunes fill the image frame. This type of dune tends to form at roughly right angles to the dominant northeasterly winds. The dune crests are marked in this image by darker, steeper sand accumulations that cast shadows. The lighter-toned zones between are lower interdune ?flats?. The large dunes appear to be highly symmetrical with regard to their crests. This suggests that the crest sediments are coarser, preventing the formation of a steeper slip face on the downwind side of the dune by wind-driven motion of similarly-sized sand grains. According to NASA scientists, this particular form of transverse dune is known as a zibar, and is thought to form by winnowing of smaller sand grains by the wind, leaving the coarser grains to form dune crests. A second set of thin linear dunes oriented at roughly right angles to the zibar dunes appears to be formed on the larger landforms and is therefore a younger landscape feature. These dunes appear to be forming from finer grains in the same wind field as the larger zibars. The image was taken with digital still camera fitted with a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center.

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.

Dunes Around Khnifiss Lagoon (Tarfaya, SW of Morocco): Composition, Itinerary In Dune Fields, Effects on Dunes' Colours and Morphodynamic

NASA Astrophysics Data System (ADS)

Adnani, M.; Azzaoui, M. A.; Elbelrhiti, H.; Ahmamou, M.; Masmoudi, L.

2015-12-01

Dunes around Khnifiss lagoon (28° 3'N, 12°13'W) show different colors ranging from black at the beach, whitish yellow in transverse dunes near the beach to reddish at the mega barchans situated few kilometers in the SW. The scientific question is about the abundance of different dunes in the same environmental conditions. The present work aims to investigate the factors that influence dunes color change, and then at which degree these factors could control dunes stability. To highlight the difference in color observed at the dune fields then to characterize dunes mineralogy, Landsat TM images were used in addition to mineralogical analysis that was carried out for the black grains samples originated from megabarchans. Optic Microscope and SEM- EDS data was adopted, in addition to physico-chemical analysis provided by Electronic Microprobe. Grain size and shape analysis were conducted to characterize the different types of grains of sand. 3/1 Landsat image band ratio allowed iron oxide distinction, the results revealed the importance of iron oxide concentration. Furthermore, mineralogical and physico-chemical analysis revealed (i) a high grade of oxides (Rutile, Ilmenite, Magnetite, Ulvöspinel) in samples, (ii) silicates (Quartz, Clinopyroxene, feldspar, Zircon), (iii) phosphate (apatite) and (iv) carbonate (calcite). The grain size analysis of the sand originated from the megabarchans reveals that there are three populations of sand. Black grains with a diameter less than 100μm and dominated by the magnetite, red ones composed mainly by the quartz with diameter between 100 and 180 μm and grains with diameter more than 180 μm are white and composed by carbonates. The threshold of motion of these different grains was calculated. It shows that these different grains have the same threshold of motion, which means that the grain size compensates the density. This explains the abundance of different populations of sand in the same environment. The dominance of iron oxides justified the color black in sand. However, the whitish yellow and reddish color observed in dunes could be attributed to iron oxide clay coating, produced under weathering conditions, covering the grains of quartz. Key words: black sand, Landsat, Iron Oxide, Khnifiss beach, megadunes, Tarfaya, Morocco

Overview of Initial Results From Studies of the Bagnold Dune Field on Mars by the Curiosity Rover

NASA Astrophysics Data System (ADS)

Bridges, Nathan; Ehlmann, Bethany; Ewing, Ryan; Newman, Claire; Sullivan, Robert; Conrad, Pamela; Cousin, Agnes; Edgett, Kenneth; Fisk, Martin; Fraeman, Abigail; Johnson, Jeffrey; Lamb, Michael; Lapotre, Mathieu; Le Mouélic, Stéphane; Martinez, German; Meslin, Pierre-Yves; Thompson, Lucy; van Beek, Jason; Vasavada, Ashwin; Wiens, Roger

2016-04-01

The Curiosity Rover is currently studying the Bagnold Dunes in Gale Crater. Here we provide a general overview of results and note that other EGU presentations will focus on specific aspects. The in situ activities have not yet occurred as of this writing, but other analyses have been performed approaching and within the dunefield. ChemCam passive spectra of Bagnold Dune sands are consistent with the presence of olivine. Two APXS spots on the High Dune stoss slope margin, and two others in an engineering test sand patch, show less inferred dust, greater Si, and higher Fe/Mn than other "soils" in Gale Crater. ChemCam analyses of more than 300 soils along the Curiosity traverse show that both fine and coarse soils have increasing iron and alkali content as the Bagnold Dunes are approached, a trend that may reflect admixtures of local rocks (alkalis + iron) to the fines, but also a contribution of Bagnold-like sand (iron) that increases toward the dunefield. MAHLI images of sands on the lower east stoss slope of High Dune show medium and coarse sand in ripple forms, and very fine and fine sand in ripple troughs. Most grains are dark gray, but some are also brick-red/brown, white, green translucent, yellow, brown" colorless translucent, or vitreous spheres HiRISE orbital images show that the Bagnold Dunes migrate on the order of decimeters or more per Earth year. Prior to entering the dune field, wind disruption of dump piles and grain movement was observed over multi-sol time spans, demonstrating that winds are of sufficient strength to mobilize unconsolidated material, either through direct aerodynamic force or via the action of smaller impacting grains. Within the dune field, we are, as of this writing, engaged in change detection experiments with Mastcam and ChemCam's RMI camera. Data we have so far, spanning 8 sols from the same location, shows no changes. Mastcam and RMI images of the stoss sides of Namib, Noctivaga, and High Dune show that the "ripples" seen with HiRISE are more akin to ˜1 m scale wavelength bedforms that exhibit clear stoss slopes, sinuous crests, slip faces, and grain flow and fall features. One interpretation is that these are fluid drag bedforms that form in an aeolian regime distinct from that on Earth due to the large viscous sub-layer in the low density Martian atmosphere. Superimposed on these bedforms are more definitive ripples of ˜10 cm wavelength, similar to impact dune ripples on Earth. The slipface of Namib Dune shows distinct flow lobes, bounded at the top by alcoves and at the bottom by lobate toes, with prominent detachment scars. Ripples upon and oriented orthogonal to the slipface indicate sand transport from winds within the dune recirculation zone. Some of the flow lobes have few ripples, indicating recent avalanching. The internal structure and stratigraphy of the edge Namib Dunes will likely be forthcoming in the trenching at the first in situ stop and will be reported at EGU.

Two Sizes of Ripples on Surface of Martian Sand Dune

NASA Image and Video Library

2016-06-30

Two sizes of wind-sculpted ripples are evident in this view of the top surface of a Martian sand dune. Sand dunes and the smaller type of ripples also exist on Earth. The larger ripples -- roughly 10 feet (3 meters) apart -- are a type not seen on Earth nor previously recognized as a distinct type on Mars. The Mast Camera (Mastcam) on NASA's Curiosity Mars rover took the multiple component images of this scene on Dec. 13, 2015, during the 1,192nd Martian day, or sol, of the rover's work on Mars. That month, Curiosity was conducting the first close-up investigation ever made of active sand dunes anywhere other than Earth. The larger ripples have distinctive sinuous crest lines, compared to the smaller ripples. The location is part of "Namib Dune" in the Bagnold Dune Field, which forms a dark band along the northwestern flank of Mount Sharp. The component images were taken in early morning at this site, with the camera looking in the direction of the sun. This mosaic combining the images has been processed to brighten it and make the ripples more visible. The sand is very dark, both from the morning shadows and from the intrinsic darkness of the minerals that dominate its composition. http://photojournal.jpl.nasa.gov/catalog/PIA20755

Curiosity Self-Portrait at Martian Sand Dune

NASA Image and Video Library

2016-01-29

This self-portrait of NASA's Curiosity Mars rover shows the vehicle at "Namib Dune," where the rover's activities included scuffing into the dune with a wheel and scooping samples of sand for laboratory analysis. The scene combines 57 images taken on Jan. 19, 2016, during the 1,228th Martian day, or sol, of Curiosity's work on Mars. The camera used for this is the Mars Hand Lens Imager (MAHLI) at the end of the rover's robotic arm. Namib Dune is part of the dark-sand "Bagnold Dune Field" along the northwestern flank of Mount Sharp. Images taken from orbit have shown that dunes in the Bagnold field move as much as about 3 feet (1 meter) per Earth year. The location of Namib Dune is show on a map of Curiosity's route at http://mars.nasa.gov/msl/multimedia/images/?ImageID=7640. The relationship of Bagnold Dune Field to the lower portion of Mount Sharp is shown in a map at PIA16064. The view does not include the rover's arm. Wrist motions and turret rotations on the arm allowed MAHLI to acquire the mosaic's component images. The arm was positioned out of the shot in the images, or portions of images, that were used in this mosaic. This process was used previously in acquiring and assembling Curiosity self-portraits taken at sample-collection sites, including "Rocknest" (PIA16468), "Windjana" (PIA18390) and "Buckskin" (PIA19807). For scale, the rover's wheels are 20 inches (50 centimeters) in diameter and about 16 inches (40 centimeters) wide. Other Curiosity self-portraits are available at http://photojournal.jpl.nasa.gov/catalog/PIA20316

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.

The role of vegetation in shaping dune morphology

NASA Astrophysics Data System (ADS)

Duran Vinent, O.; Moore, L. J.; Young, D.

2012-12-01

Aeolian dunes naturally emerge under strong winds and sufficient sand supply. They represent the most dynamical feature of the arid and/or coastal landscape and their evolution has the potential to either increase desertification or reduce coastal vulnerability to storms. Although large-scale dune morphology mainly depends on the wind regime and sand availability, vegetation plays an important role in semiarid and/or coastal areas. It is well known that under certain conditions vegetation is able to stabilize dunes, driving a morphological transformation from un-vegetated mobile crescent dunes to static vegetated "parabolic" dunes, de facto paralyzing desertification and initiating land recovery. Furthermore, vegetation is also the primary ingredient in the formation of coastal foredunes, which determine vulnerability to storms, as low dunes are prone to storm-induced erosion and overwash. In both cases, the coupling of biological and geomorphic (physical) processes, in particular vegetation growth and sand transport, governs the evolution of morphology. These processes were implemented in a computational model as part of a previous effort. It was shown that, for a migrating dune, this coupling leads to a negative feedback for dune motion, where an ever denser vegetation implies ever lesser sand transport. The model also predicted the existence of a "mobility index", defined by the vegetation growth rate to sand erosion rate ratio, that fully characterizes the morphological outcome: for indices above a certain threshold biological processes are dominant and dune motion slows after being covered by plants; for lower indices, the physical processes are the dominant ones and the dune remains mobile while vegetation is buried or rooted out. Here, we extend this model to better understand the formation of coastal dunes. We include new physical elements such as the shoreline and water table, as well as different grass species and potential competition among them. Consistent with field observations, we find that basic dune morphology is primarily determined by grass species, with linear or hummocky dunes being built by some species, while others may prevent dune formation. We also find that the evolution of coastal dune morphology is controlled by at least two bio-geomorphic couplings: (1) between vegetation growth and sand transport, which leads to a positive feedback for dune growth, as certain beach grasses maximize growth under sand accretion, which means that an ever denser vegetation implies an ever higher accretion rate; and (2) between vegetation growth and shoreline position through the sand influx. While the first coupling is responsible for dune formation, the second one determines when dunes stop growing and thus controls final dune size. This is particularly relevant for accreting/eroding coastlines where we find that dune size, and thus coastal protection, is maximized for relatively small accretion rates while larger accretion rates lead to formation of a new, smaller dune ridge at the beach.

Earth observation views of the Sahara Desert taken from OV-105 during STS-99

NASA Image and Video Library

2000-03-09

STS099-729-045 (11-22 February 2000) ---This Earth scene from the Space Shuttle Endeavour features linear dunes in the Algerian Saharan sand sea known as the Erg Chech. The dunes, according to NASA scientists, have been built up over thousands of years into masses elongated roughly parallel with the prevailing northeast winds. Dune chains in the northern (upper) half of the view are 5-8 kilometers apart. A slight change in orientation and an increase in the density of dunes appear across the middle of the view. Such changes usually relate to changes in sand supply, and also to topographic scarps over which the dunes pass. Obstacles like scarps and hills locally cause a leftward deflection (in the Northern Hemisphere) in wind direction, an effect that can be seen here in the dune orientation in the middle of the photo. Dunes in the lower part of the view are 2-5 kilometers apart. White patches are small dry lakes at low points in the underlying rock surface. The strong red color in some dunes near the edge of the dune field (left margin) is iron staining derived from sand particles blown into the dunes from the underlying iron-rich soils. A dune-free area appears in the lower left corner.

Morphodynamics of Planetary Deserts: A Laboratory Approach

NASA Astrophysics Data System (ADS)

Garcia, A.; Courrech Du Pont, S.; Rodriguez, S.

2014-12-01

Earth deserts show a rich variety of dune shapes from transverse to barchan, star and linear dunes depending on the history of wind regimes (strength and variability) and sand availability [1]. In desert, exposed to one wind direction, dunes perpendicular to the wind direction are found to be transverse or barchans, only sand availability plays a key role on their formation and evolution. However, the evolution time scale of such structures (several years) limits our investigation of their morphodynamics understanding. We use here, a laboratory experiment able to considerably reduce space and time scales by reproducing millimeter to centimeter subaqueous dunes by controlling environmental parameters such as type of wind (multi-winds, bimodal, quasi-bimodal or unidirectional wind) and amount of sediment [2,3]. This set up allows us to characterize more precisely the different modes of dune formation and long-term evolution, and to constrain the physics behind the morphogenesis and dynamics of dunes. Indeed, the formation, evolution and transition between the different dune modes are better understood and quantified thanks to a new setting experiment able to give a remote sediment source in continuous (closer to what happens in terrestrial desert): a sand distributor that controls the input sand flow. Firstly, in a one wind direction conditions, we managed to follow and quantify the growth of the instability of transverse dunes that break into barchans when the sand supply is low and reversely when the sand supply is higher, barchan fields evolve to bars dunes ending to form transverse. The next step will be to perform experiments under two winds conditions in order to better constrain the formation mode of linear dunes, depending also only on the input sand flux. Previous experiments shown that linear "finger" dunes can be triggered by the break of transverse dunes and then the elongating of one barchan's arm [4]. These studies can farther explain more precisely in different wind history and sand supply, these patterns state that should emerge and, by applying the relevant scale law, to apply this laboratory work to terrestrial and planetary (Mars and Titan) desert dynamics. [1] Bagnold R.A. (1941). [2] Hersen P. (2004). [3] Reffet E. (2010). [4] Courrech Du Pont S. et al. (2014).

Dune Variety

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

Our final look at the north polar erg was taken at 80 degrees North latitude during Northern summer. This image is of lower resolution than the previous images, but covers a much larger area. The dunes have very little remaining frost cover. Note the large extent of coverage, and the different dune forms.

Image information: VIS instrument. Latitude 80.8, Longitude 184.6 East (175.4 West). 19 meter/pixel resolution.

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

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

UAV-imaging to model growth response of marram grass to sand burial: Implications for coastal dune development

NASA Astrophysics Data System (ADS)

Nolet, Corjan; van Puijenbroek, Marinka; Suomalainen, Juha; Limpens, Juul; Riksen, Michel

2018-04-01

Vegetated coastal dunes have the capacity to keep up with sea-level rise by accumulating and stabilizing wind-blown sand. In Europe, this is attributed to marram grass (Ammophila arenaria), a coastal grass species that combines two unique advantages for dune-building: (1) a very high tolerance to burial by wind-blown sand, and (2) more vigorous growth due to positive feedback to sand burial. However, while these vegetation characteristics have been demonstrated, observational data has not been used to model a function to describe the growth response of Ammophila to sand burial. Studies that model coastal dune development by incorporating positive feedback, as a result, may be hampered by growth functions that are unvalidated against field data. Therefore, this study aims to parameterize an empirical relationship to model the growth response of Ammophila to burial by wind-blown sand. A coastal foredune along a nourished beach in the Netherlands was monitored from April 2015 to April 2016. High-resolution geospatial data was acquired using an Unmanned Aerial Vehicle (UAV). Growth response of Ammophila, expressed by changes in Normalized Difference Vegetation Index (Δ NDVI) and vegetation cover (Δ Cover), is related to a sand burial gradient by fitting a Gaussian function using nonlinear quantile regression. The regression curves indicate an optimal burial rate for Ammophila of 0.31 m of sand per growing season, and suggest (by extrapolation of the data) a maximum burial tolerance for Ammophila between 0.78 (for Δ Cover) and 0.96 m (for Δ NDVI) of sand per growing season. These findings are advantageous to coastal management: maximizing the potential of Ammophila to develop dunes maximizes the potential of coastal dunes to provide coastal safety.

Earth Observations taken during Expedition 16 / STS-120 Joint Operations

NASA Image and Video Library

2007-10-26

ISS016-E-006986 (26 Oct. 2007) --- Great Sand Dunes National Park and Preserve, Colorado is featured in this image photographed by an Expedition 16 crewmember on the International Space Station. The Sangre de Cristo Mountains of south-central Colorado stretch dramatically from top left to lower right of this image, generally outlined by the dark green of forests with white snow-capped peaks on the highest elevations. Dun-colored dunes, covering an area of 80 square kilometers, are banked up on the west side of the mountains and comprise the Great Sand Dunes National Park and Preserve. Originally established in 1932 as a National Monument, it was reauthorized as a National Park in 2004. The park contains dunes over 750 feet (227 meters) high -- among the highest in North America. Sand grains that make up the dunes are small enough to be moved along by the wind (a process known as saltation), although much of the dunefield is now anchored by vegetation. Predominant winds blow broadly to the east, so that sand in the San Luis valley (part of which appears at lower left) is driven towards and piled against the Sangre de Cristo Mts. The sand of the dunes is mostly derived from ancient exposed lakebed sediments - now the floor of the San Luis valley - formed by erosion of rocks in the Sangre de Cristo and San Juan Mountains (located to the west). The action of streams and occasional storms today returns some of the impounded sand back to the valley, where the prevailing winds begin the sand's migration to the dunefield anew. Interestingly, the specific location of the sand field appears to be related to a locally lower altitude sector of the Sangre de Cristo Mts. Altitudes can be inferred from the distribution of snow cover on the day this image was taken. Areas to the north (Cleveland Peak and northward) of the dunefield, and to the south around Blanca Peak, are higher than the ridgeline next to the dune field where almost no snow is visible. Since winds are preferentially channeled over the lower parts of any range (hundreds of meters lower here than ridgelines to north and south), sand grains are carried up to (but not over) the low point of the range.

Textures Where Curiosity Rover Studied a Martian Dune

NASA Image and Video Library

2017-05-04

This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover shows two scales of ripples, plus other textures, in an area where the mission examined a linear-shaped dune in the Bagnold dune field on lower Mount Sharp. The scene is an excerpt from a 360-degree panorama acquired on March 24 and March 25, 2017, (PST) during the 1,647th Martian day, or sol, of Curiosity's work on Mars, at a location called "Ogunquit Beach." Crests of the longer ripples visible in the dark sand of the dune are several feet (a few meters) apart. This medium-scale feature in active sand dunes on Mars was one of Curiosity's findings at the crescent-shaped dunes that the rover examined in late 2015 and early 2016. Ripples that scale are not seen on Earth's sand dunes. Overlaid on those ripples are much smaller ripples, with crests about ten times closer together. Textures of the local bedrock in the foreground -- part of the Murray formation that originated as lakebed sediments -- and of gravel-covered ground (at right) are also visible. The image has been white-balanced so that the colors of the colors of the rock and sand materials resemble how they would appear under daytime lighting conditions on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA11242

Modification and Mobility of Dunes and Ripples in Middle and High Southern Latitude Dune Fields

NASA Astrophysics Data System (ADS)

Banks, M.; Fenton, L. K.; Chojnacki, M.; Silvestro, S.

2017-12-01

Change detection analyses of aeolian bedforms (dunes and ripples), using multi-temporal images (0.25 m/pixel) acquired by the High Resolution Imaging Science Experiment (HiRISE), reveal changes and migration of some bedforms. We now have a database of 200 dune fields with migration rates for bedforms that are mobile. Results show that most northern (N) hemisphere bedforms show movement, while 50% of southern (S) hemisphere bedforms show no detectable changes. In particular, bedforms located >70° N are consistently mobile and exhibit high sand fluxes while S hemisphere bedforms progressively decrease in mobility with proximity to the S pole. We analyze HiRISE image pairs covering dune fields south of 40° S for evidence of movement and apply a dune stability index (SI) based on the presence/lack of superposed non-aeolian features and degree of degradation by non-aeolian processes (0-6, higher numbers indicating increasing evidence of stability/modification). Combining mobility data and SI for 71 dune fields, we find a clear trend of decreasing sand mobility and increasing SI with latitude: 1) both dunes and ripples are more commonly mobile at lower latitudes, although some high-latitude ripples are migrating, 2) dune fields with low SIs (≤3) tend to be active while those with higher SIs tend to be inactive, and 3) ripple migration rates decrease slightly with increasing latitude and SI, although this may be attributable to regional variations. The elevation of dune fields generally increases with increasing S latitude suggesting elevation, and decreasing pressure, may contribute to decreasing mobility. A change in dominance of active to inactive bedforms and a morphological shift to higher SIs (SI=2) both occur at 60º S and coincide with the edge of high concentrations of H2O-equivalent hydrogen content observed by the Neutron Spectrometer. This is consistent with previous studies suggesting stabilizing agents (e.g., ground ice), likely limit sediment movement (i.e. sand availability). Active dune fields with morphologies consistent with stability (i.e. migrating ripples with SI=3) may indicate possible competing influences of aeolian and non-aeolian processes (i.e. polar processes), or perhaps a temporal shift from earlier conditions dominated by polar processes to recent increases in aeolian activity.

Change Observed in Martian Sand Dune

NASA Image and Video Library

2015-11-16

This animation flips back and forth between views taken in 2010 and 2014 of a Martian sand dune at the edge of Mount Sharp, documenting dune activity. The images are from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. They cover an area about 740 feet (about 225 meters) wide, showing a site called "Dune 2" in the "Bagnold Dunes" dune field. NASA's Curiosity Mars rover will observe this dune up close on the rover's route up Mount Sharp. North is toward the top. The edge of the dune at the crescent-shaped slip face on the south edge advances slightly during the four-year period between the dates of the images. Figure A is an annotated version with an arrow indicating the location of this change. The lighting angle is different in the two images, resulting in numerous changes in shadows. http://photojournal.jpl.nasa.gov/catalog/PIA20161

Rover Track in Sand Sheet Near Martian Sand Dune

NASA Image and Video Library

2015-12-10

The rippled surface of the first Martian sand dune ever studied up close fills this view of "High Dune" from the Mast Camera (Mastcam) on NASA's Curiosity rover. This site is part of the "Bagnold Dunes" field along the northwestern flank of Mount Sharp. The dunes are active, migrating up to about one yard or meter per year. The component images of this mosaic view were taken on Nov. 27, 2015, during the 1,176th Martian day, or sol, of Curiosity's work on Mars. The scene is presented with a color adjustment that approximates white balancing, to resemble how the sand would appear under daytime lighting conditions on Earth. The annotated version includes superimposed scale bars of 30 centimeters (1 foot) in the foreground and 100 centimeters (3.3 feet) in the middle distance. Malin Space Science Systems, San Diego, built and operates Curiosity's Mastcam. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, built the rover and manages the project for NASA's Science Mission Directorate, Washington. http://photojournal.jpl.nasa.gov/catalog/PIA20169

Central Asian sand seas climate change as inferred from OSL dating

NASA Astrophysics Data System (ADS)

Maman, Shimrit; Tsoar, Haim; Blumberg, Dan; Porat, Naomi

2014-05-01

Luminescence dating techniques have become more accessible, widespread, more accurate and support studies of climate change. Optically stimulated luminescence (OSL) is used to determine the time elapsed since quartz grains were last exposed to sunlight, before they were buried and the dune stabilized. Many sand seas have been dated extensively by luminescence, e.g., the Kalahari, Namib the Australian linear dunes and the northwestern Negev dune field, Israel. However, no ages were published so far from the central Asian sand seas. The lack of dune stratigraphy and numerical ages precluded any reliable assessment of the paleoclimatic significance of dunes in central Asia. Central Asian Sand seas (ergs) have accumulated in the Turan basin, north-west of the Hindu Kush range, and span from south Turkmenistan to the Syr-Darya River in Kazakhstan. These ergs are dissected by the Amu-Darya River; to its north lies the Kyzylkum (red sands) and to its south lies the Karakum (black sands). Combined, they form one of the largest sand seas in the world. This area is understudied, and little information has been published regarding the sands stabilization processes and deposition ages. In this study, OSL ages for the Karakum and Kyzylkum sands are presented and analysis of the implications of these results is provided. Optical dates obtained in this study are used to study the effects climatic changes had on the mobility and stability of the central Asian sand seas. Optically stimulated luminescence ages derived from the upper meter of the interdune of 14 exposed sections from both ergs, indicate extensive sand and dune stabilization during the mid-Holocene. This stabilization is understood to reflect a transition to a warmer, wetter, and less windy climate that generally persisted until today. The OSL ages, coupled with a compilation of regional paleoclimatic data, corroborate and reinforce the previously proposed Mid-Holocene Liavliakan phase, known to reflect a warmer, wetter, and less windy climate that persists until today and resulted in dune stabilization around the Mid-Holocene. This study, solidifies our results regarding the Kyzylkum and Karakum sand seas dynamics, ages, and emphasizes the importance of regional climatic control on aeolian activity.

Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux.

PubMed

Ayoub, F; Avouac, J-P; Newman, C E; Richardson, M I; Lucas, A; Leprince, S; Bridges, N T

2014-09-30

Coupling between surface winds and saltation is a fundamental factor governing geological activity and climate on Mars. Saltation of sand is crucial for both erosion of the surface and dust lifting into the atmosphere. Wind tunnel experiments along with measurements from surface meteorology stations and modelling of wind speeds suggest that winds should only rarely move sand on Mars. However, evidence for currently active dune migration has recently accumulated. Crucially, the frequency of sand-moving events and the implied threshold wind stresses for saltation have remained unknown. Here we present detailed measurements of Nili Patera dune field based on High Resolution Imaging Science Experiment images, demonstrating that sand motion occurs daily throughout much of the year and that the resulting sand flux is strongly seasonal. Analysis of the seasonal sand flux variation suggests an effective threshold for sand motion for application to large-scale model wind fields (1-100 km scale) of τ(s)=0.01±0.0015 N m(-2).

Desert Patterns

NASA Image and Video Library

2017-12-08

Desert Patterns - April 13th, 2003 Description: Seen through the "eyes" of a satellite sensor, ribbons of Saharan sand dunes seem to glow in sunset colors. These patterned stripes are part of Erg Chech, a desolate sand sea in southwestern Algeria, Africa, where the prevailing winds create an endlessly shifting collage of large, linear sand dunes. The term "erg" is derived from an Arabic word for a field of sand dunes. Credit: USGS/NASA/Landsat 7 To learn more about the Landsat satellite go to: landsat.gsfc.nasa.gov/ NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

North Polar Erg

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

Our topic for the weeks of April 4 and April 11 is dunes on Mars. We will look at the north polar sand sea and at isolated dune fields at lower latitudes. Sand seas on Earth are often called 'ergs,' an Arabic name for dune field. A sand sea differs from a dune field in two ways: 1) a sand sea has a large regional extent, and 2) the individual dunes are large in size and complex in form.

This VIS image was taken at 81 degrees North latitude during Northern spring. This region of the north polar erg is dominated by a different form of dunes than yesterday's image.

Image information: VIS instrument. Latitude 81.4, Longitude 121.9 East (238.1 West). 19 meter/pixel resolution.

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

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

Provenance and recycling of Arabian desert sand

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vermeesch, Pieter; Andò, Sergio; Vezzoli, Giovanni; Valagussa, Manuel; Allen, Kate; Kadi, Khalid; Al-Juboury, Ali

2013-04-01

This study seeks to determine the ultimate origin of aeolian sand in Arabian deserts by high-resolution petrographic and heavy-mineral techniques combined with zircon U-Pb geochronology. Point-counting is used here as the sole method by which unbiased volume percentages of heavy minerals can be obtained. A comprehensive analysis of river and wadi sands from the Red Sea to the Bitlis-Zagros orogen allowed us to characterize all potential sediment sources, and thus to quantitatively constrain provenance of Arabian dune fields. Two main types of aeolian sand can be distinguished. Quartzose sands with very poor heavy-mineral suites including zircon occupy most of the region comprising the Great Nafud and Rub' al-Khali Sand Seas, and are largely recycled from thick Lower Palaeozoic quartzarenites with very minor first-cycle contributions from Precambrian basement, Mesozoic carbonate rocks, or Neogene basalts. Instead, carbonaticlastic sands with richer lithic and heavy-mineral populations characterize coastal dunes bordering the Arabian Gulf from the Jafurah Sand Sea of Saudi Arabia to the United Arab Emirates. The similarity with detritus carried by the axial Tigris-Euphrates system and by transverse rivers draining carbonate rocks of the Zagros indicates that Arabian coastal dunes largely consist of far-travelled sand, deposited on the exposed floor of the Gulf during Pleistocene lowstands and blown inland by dominant Shamal northerly winds. A dataset of detrital zircon U-Pb ages measured on twelve dune samples and two Lower Palaeozoic sandstones yielded fourteen identical age spectra. The age distributions all show a major Neoproterozoic peak corresponding to the Pan-African magmatic and tectonic events by which the Arabian Shield was assembled, with minor late Palaeoproterozoic and Neoarchean peaks. A similar U-Pb signature characterizes also Jafurah dune sands, suggesting that zircons are dominantly derived from interior Arabia, possibly deflated from the Wadi al-Batin fossil alluvial fan or even from Mesozoic sandstones of the Arabian margin accreted to the Cenozoic Zagros orogen. Due to extensive recycling and the fact that zircon is so resistant to weathering and erosion, the U-Pb age signatures are much less powerful a tracer of sedimentary provenance than framework petrography and heavy minerals. Actualistic provenance studies of dune fields at subcontinental scale shed light on the generation and homogenization of aeolian sand, and allow us to trace complex pathways of multistep sediment transport, thus providing crucial independent information for accurate palaeogeographic and palaeoclimatic reconstructions.

Provenance and recycling of Arabian desert sand

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vermeesch, Pieter; Andò, Sergio; Vezzoli, Giovanni; Valagussa, Manuel; Allen, Kate; Kadi, Khalid A.; Al-Juboury, Ali I. A.

2013-05-01

This study seeks to determine the ultimate origin of aeolian sand in Arabian deserts by high-resolution petrographic and heavy-mineral techniques combined with zircon U-Pb geochronology. Point-counting is used here as the sole method by which unbiased volume percentages of heavy minerals can be obtained. A comprehensive analysis of river and wadi sands from the Red Sea to the Bitlis-Zagros orogen allowed us to characterize all potential sediment sources, and thus to quantitatively constrain provenance of Arabian dune fields. Two main types of aeolian sand can be distinguished. Quartzose sands with very poor heavy-mineral suites including zircon occupy most of the region comprising the Great Nafud and Rub' al-Khali Sand Seas, and are largely recycled from thick Lower Palaeozoic quartzarenites with very minor first-cycle contributions from Precambrian basement, Mesozoic carbonate rocks, or Neogene basalts. Instead, carbonaticlastic sands with richer lithic and heavy-mineral populations characterize coastal dunes bordering the Arabian Gulf from the Jafurah Sand Sea of Saudi Arabia to the United Arab Emirates. The similarity with detritus carried by the axial Tigris-Euphrates system and by transverse rivers draining carbonate rocks of the Zagros indicates that Arabian coastal dunes largely consist of far-travelled sand, deposited on the exposed floor of the Gulf during Pleistocene lowstands and blown inland by dominant Shamal northerly winds. A dataset of detrital zircon U-Pb ages measured on twelve dune samples and two Lower Palaeozoic sandstones yielded fourteen identical age spectra. The age distributions all show a major Neoproterozoic peak corresponding to the Pan-African magmatic and tectonic events by which the Arabian Shield was assembled, with minor late Palaeoproterozoic and Neoarchean peaks. A similar U-Pb signature characterizes also Jafurah dune sands, suggesting that zircons are dominantly derived from interior Arabia, possibly deflated from the Wadi al-Batin fossil alluvial fan or even from Mesozoic sandstones of the Arabian margin accreted to the Cenozoic Zagros orogen. Due to extensive recycling and the fact that zircon is so resistant to weathering and erosion, the U-Pb age signatures are much less powerful a tracer of sedimentary provenance than framework petrography and heavy minerals. Actualistic provenance studies of dune fields at subcontinental scale shed light on the generation and homogenization of aeolian sand, and allow us to trace complex pathways of multistep sediment transport, thus providing crucial independent information for accurate palaeogeographic and palaeoclimatic reconstructions.

Submarine sand dunes and sedimentary environments in Oceanographer Canyon.

USGS Publications Warehouse

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

1984-01-01

Observations from research submersibles in the northern part of Oceanographer Canyon reveal the presence of 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 3 m and have wavelengths up to 15 m. 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. Shelf sand, low in silt and clay content, is transported by currents down and along the canyon walls onto the canyon floor. As the sand enters the canyon, it is mixed with immobile gravel deposits on the canyon rim; lower on the walls, the sand is mixed with silt and clay burrowed by organisms from the semiconsolidated sandy silt that underlies the canyon walls and floor. Upon reaching the canyon floor, the sand is sculpted into bed forms by currents, and the fines are winnowed out and transported out of the canyon. At present, the shelf and canyon walls are being eroded by bottom currents and burrowing organisms, whereas the canyon floor is covered by mobile sand that moves both up and down the axis in this part of the canyon.

A bright intra-dune feature on Titan and its implications for sand formation and transport

NASA Astrophysics Data System (ADS)

MacKenzie, Shannon; Barnes, Jason W.; Rodriguez, Sebastien; Cornet, Thomas; Brossier, Jeremy; Soderblom, Jason M.; Le Mouélic, Stephane; Sotin, Christophe; Brown, Robert H.; Buratti, Bonnie J.; Clark, Roger Nelson; Nicholson, Philip D.; Baines, Kevin

2017-10-01

Organic sands cover much of Titan’s equatorial belt, gathered into longitudinal dunes about a kilometer wide and hundreds of kilometers long. At the end of the Cassini era, questions of how such a vast volume of saltable material is or was created on Titan remain unanswered. At least two possible mechanisms suggested for forming sand-sized particles involve liquids: (1) evaporite deposition and erosion and (2) flocculation of material within a lake. Transporting sand from the lakes and seas of Titan’s poles to the equatorial belt is not strongly supported by Cassini observations: the equatorial belt sits higher than the poles and no sheets or corridors of travelling sand have been identified. Thus, previous sites of equatorial surface liquids may be of interest for understanding sand formation, such as the suggested paleoseas Tui and Hotei Regio. A newly identified feature in the VIMS data sits within the Fensal dune field but is distinct from the surrounding sand. We investigate this Bright Fensal Feature (BFF) using data from Cassini VIMS and RADAR. Specifically, we find spectral similarities between the BFF and both sand and Hotei Regio. The RADAR cross sectional backscatter is similar to neighboring dark areas, perhaps sand covered interdunes. We use this evidence to constrain the BFF’s formation history and discuss how this intra-dune feature may contribute to the processes of sand transport and supply.

Once in a Blue Dune

NASA Image and Video Library

2018-06-11

Sand dunes often accumulate in the floors of craters. In this region of Lyot Crater NASA's Mars Reconnaissance Orbiter (MRO) shows a field of classic barchan dunes. Just to the south of the group of barchan dunes is one large dune with a more complex structure. This particular dune, appearing like turquoise blue in enhanced color, is made of finer material and/or has a different composition than the surrounding. https://photojournal.jpl.nasa.gov/catalog/PIA22512

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

USGS Publications Warehouse

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

2010-01-01

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

Dunes and microdunes on Venus: Why were so few found in the Magellan data?

NASA Technical Reports Server (NTRS)

Weitz, Catherine M.; Plaut, Jeffrey J.; Greeley, Ronald; Saunders, R. Steven

1994-01-01

A search through cycle 1, 2, and 3 Magellan radar data covering 98% of the surface of Venus revealed very few dunes. Only two possible dune fields and several areas that may contain microdunes smaller than the resolution of the images (75 m) were identified. The Aglaonice dune field was identified in the cycle 1 images by the specular returns characteristic of dune faces oriented perpendicular to the radar illumination. Cycle 1 and 2 data of the Fortuna-Meshkenet dune field indicate that there has been no noticeable movement of the dunes over an 8-month period. The dunes, which are oriented both parallel and perpendicular to the radar illumination, appear to be dark features on a brighter substrate. Bright and dark patches that were visible in either cycle 1 or 2 data, but not both, allowed identification of several regions in the southern part of Venus that may contain microdunes. The microdunes are associated with several parabolic crater deposits in the region and are probably similar to those formed in wind tunnel experiments under Venus-like conditions. Bragg scattering and/or subpixel relfections from the near-normal face on asymmetric microdunes may account for these bright and dark patches. Look-angle effects and the lack of sufficient sand-size particles seem to be most likely reasons so few dunes were identified in Magellan data. Insufficient wind speeds, thinness of sand cover, and difficulty in identifying isolated dunes may also be contributors to the scarcity of dunes.

Dunes and Microdunes on Venus: Why Were So Few Found in the Magellan Data?

NASA Technical Reports Server (NTRS)

Weitz, Catherine M.; Plaut, Jeffrey J.; Greeley, Ronald; Saunders, R. Steven

1994-01-01

A search through cycle 1, 2, and 3 Magellan radar data covering 98% of the surface of Venus revealed very few dunes. Only two possible dune fields and several areas that may contain microdunes smaller than the resolution of the images (75 m) were identified. The Aglaonice dune field was identified in the cycle I images by the specular returns characteristic of dune faces oriented perpendicular to the radar illumination. Cycle 1 and 2 data of the Fortuna-Meshkenet dune field indicate that there has been no noticeable movement of the dunes over an 8-month period. The dunes, which are oriented both parallel and perpendicular to the radar illumination, appear to be dark features on a brighter substrate. Bright and dark patches that were visible in either cycle 1 or 2 data, but not both, allowed identification of several regions in the southern part of Venus that may contain microdunes. The microdunes are associated with several parabolic crater deposits in the region and are probably similar to those formed in wind tunnel experiments under Venus-like conditions. Bragg scattering and/or subpixel reflections from the near-normal face on asymmetric microdunes may account for these bright and dark patches. Look-angle effects and the lack of sufficient sand-size particles seem to be the most likely reasons so few dunes were identified in Magellan data. Insufficient wind speeds, thinness of sand cover, and difficulty in identifying isolated dunes may also be contributors to the scarcity of dunes.

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

NASA Astrophysics Data System (ADS)

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

2004-03-01

Contrasting wind, sediment and frost precipitation regimes contribute to different dune scale and form on Mars. Isolated barchans in the NPSS are smaller but assume a classic barchan form. Intra-crater barchans are larger and more variable in form.

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.

Investigating Mars: Moreux Crater

NASA Image and Video Library

2017-11-22

This image of Moreux Crater shows the western floor of the crater and the multitude of sand dunes that are found on the floor of the crater. A large sand sheet with surface dunes forms is located at the top of the image, and smaller individual dunes stretch from the bottom of the sand sheet to the bottom of the image. In this false color image sand dunes are "blue". Moreux Crater is located in northern Arabia Terra and has a diameter of 138 kilometers. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 10384 Latitude: 41.841 Longitude: 44.087 Instrument: VIS Captured: 2004-04-17 10:07 https://photojournal.jpl.nasa.gov/catalog/PIA22035

Possibility of star (pyramid) dune development in the area of bimodal wind regime

NASA Astrophysics Data System (ADS)

Biejat, K.

2012-04-01

Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star dunes located in E and W parts of the erg allow inferring that there must have been differences in supply of the aeolian sand. Eastern slopes of compound star dunes developed in the W part of the erg are inclined 10-15°. This shows that significant delivery of the sand must have occurred also from NE. Eastern slopes of compound star dunes located in the E part of the erg are inclined 20-30°. It can be therefore inferred that they have functioned mainly as lee slopes and the sand was delivery from SW. This proves that location of the dunes within the erg plays a significant role in shaping wind directions responsible for delivery of the sand. Orientation of subsidiary arms does not show any relationship with general wind regime, which leads to conclusion that the subsidiary arms develop due to local diversified regime of nearsurface wind flow. This is governed by barriers such as the star dunes themselves and not by other topographic obstacles.

Earth observation taken by the Expedition 28 crew

NASA Image and Video Library

2011-09-08

ISS028-E-044444 (8 Sept. 2011) --- This image, photographed by an Expedition 28 crew member on the International Space Station, highlights a sand dune field within the Burqin-Haba River-Jimunai Desert near the borders of China, Mongolia, Russia and Kazakhstan. The dune field (approximately 32 kilometers long) is located immediately to the west-northwest of the city of Burqin (not shown), and is part of the Junggar Basin, a region of active petroleum production in northwestern China. The Irtysh River, with associated wetlands and riparian vegetation (appearing grey-green in the image) flows from its headwaters in the Altay Mountains to the east towards Siberia to the west (right to left). Tan sandy linear dunes at center on the south side of the Irtysh River dominate the view. The linear dunes are formed from mobile barchan (crescent-shaped) dunes moving from left to right in this view; the barchans eventually merge to form the large linear dunes some of which reach 50-100 meters in height. Sand moving along the southern edge of the dune field appears to be feeding a southeastern lobe with a separate population of linear dunes (lower right). The Burqin-Haba River-Jimunai Desert area also includes darker gravel covered surfaces that form pavements known locally as gobi. These are somewhat indistinguishable from vegetated areas arresting some of the dunes at the resolution of the image, but tend to be located on the flat regions between the dunes.

Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations: Bagnold Dune Sands Composition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprisingmore » >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2O.« less

Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations: Bagnold Dune Sands Composition

DOE PAGES

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.; ...

2017-06-12

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprisingmore » >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2O.« less

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.

Aeolian Landscapes of Titan from Cassini RADAR Reveal Winds, Elevation Constraints and Sediment Characteristics

NASA Astrophysics Data System (ADS)

Radebaugh, J.; Lewis, R. C.; Bishop, B.; Christiansen, E. H.; Kerber, L.; Rodriguez, S.; Narteau, C.; Le Gall, A. A.; Lucas, A.; Malaska, M.

2017-12-01

Similar to terrestrial bodies with atmospheres, a significant portion of the surface of Titan is covered in aeolian landscapes, now imaged by Cassini RADAR at close to 50% coverage. While the compositions of the wind-carried and wind-carved sediments are under discussion, their characteristics, such as being rounded, loose and capable of being saltated, or being fine, soft and forming easily erodible deposits, can be discerned from the geomorphology. Large duneforms are similar to those in Earth's big deserts, formed by particles in strict size and shape limits, and steep, badlands-like morphologies of yardang regions indicate soft rocks with armored features. Shapes and orientations of dunes and yardangs can also reveal wind directions and effects of elevation and topographic obstacles. Recent studies of dunes in the Belet Sand Sea of Titan's equatorial trailing hemisphere reveal dunes are generally wider and with greater spacing near the center, similar to dunes in the Namib Sand Sea of Earth. Dune-to-interdune ratios decrease toward higher latitudes, as was previously observed, and are slightly higher in regions of low elevation, which may relate to elevation affecting winds and sand transport capacity. However, this relationship is not as strong for the Namib. Furthermore, the effects of the location of dunes with respect to sand sea margins on dune parameter values has only begun to be explored. The European ERA-Interim (observations plus model) wind results for the Namib reveal vector sum winds are several degrees away from down the dune long axis, consistent with the fingering mode of dune growth, and allowing for down-axis sand transport. We assume similar model winds for the dunes of Titan. Model winds for the yardangs of the Lut desert of Earth are directly down axis, which means wind directions should be able to be determined in the isolated yardang fields of Titan's northern midlatitudes. Further studies of dune parameters on Titan from Cassini can help reveal the reasons for the extent of the sand seas and how (and whether) sands are transported across them. Further studies of winds and sediment properties of yardangs on Earth will reveal expected winds, material requirements and relative ages of the yardangs with respect to other landforms of Titan.

View of chains of star sand dunes in eastern Algeria from Skylab

NASA Image and Video Library

1973-12-31

SL4-138-3820 (31 Dec. 1973) --- An north-looking oblique view of chains of star sand dunes in eastern Algeria as seen from the Skylab space station in Earth orbit. This picture was taken by one of the Skylab 4 crewmen with a hand-held 70mm Hasselblad camera. The low sun angle of about 25 degrees above horizontal enhances the detail in this picture. The coordinates of the center of the photograph are approximately 29.5 degrees north latitude and 5.0 degrees east longitude in the Grand Erg Oriental. The field of view at the base of the photograph is approximately 200 kilometers (125 miles). The individual dunes are roughly star-shaped rather than simple crescents which are common in dune fields. In this region the stars are aligned along ridges. The causes of these and a wide variety of other dune forms are little understood. Descriptions and photographs from Skylab 4 will be used by the U.S. Geological Survey in their world-wide study of dunes. Photo credit: NASA

Field measurement and analysis of climatic factors affecting dune mobility near Grand Falls on the Navajo Nation, southwestern United States

USGS Publications Warehouse

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

2015-01-01

Aeolian sand covers extensive areas of the Navajo Nation in the southwestern United States. Much of this sand is currently stabilized by vegetation, although many drier parts of these Native lands also have active and partly active dunes. Current prolonged drought conditions that started in the mid-1990s are producing significant changes in dune mobility. Reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations, agriculture, grazing, and infrastructure. To understand and document the current and future potential for mobility, seasonally repeated surveys were used to track the location of multiple active barchan dunes. By utilizing Real-Time Kinematic GPS field surveys and simultaneously collecting in-situ meteorological data, it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences. Through analysis of the recorded data, we examined the fit of various climate parameters, and demonstrate that under the current prolonged drought, wind power is the dominant factor controlling dune mobility.

Sand dune tracking from satellite laser altimetry

NASA Astrophysics Data System (ADS)

Dabboor, Mohammed

Substantial problems arise from sand movement in arid and semi-arid countries. Sand poses a threat to infrastructure, agricultural and urban areas. These issues are caused by the encroachment of sand on roads and railway tracks, farmland, towns and villages, and airports, to name a few. Sand movement highly depends on geomorphology including vegetation cover, shape and height of the terrain, and grain size of the sand. However, wind direction and speed are the most important factors that affect efficient sand movement. The direction of the movement depends on the main direction of the wind, but it has been shown that a minimum wind speed is required, e.g. wind gusts, to initiate sand transport. This fact prevents a simple calculation of sand transport from conventional wind data as wind records rarely contain sub-minute intervals masking out any wind gusts. An alternative of predicting sand transport is the direct observation of sand advance by in situ measurements or via satellite. Until recently, satellite imagery was the only means to compare dune shape and position for predicting dune migration over several years. In 2003, the NASA laser altimetry mission ICESat became operational and monitors elevations over all surface types including sand dunes with an accuracy of about 10-20 cm. In this study, ICESat observations from repeat tracks (tracks overlapping eachother within 50 m) are used to derive sand dune advance and direction. The method employs a correlation of the elevation profiles over several dunes and was sucessfully validated with synthetic data. The accuracy of this method is 5 meters of dune advance. One of the most active areas exhibiting sand and dune movement is the area of the Arabian Peninsula. Approximately one-third of the Arabian Peninsula is covered by sand dunes. Different wind regimes (Shamal, Kaus) cause sand dune movement in the selected study area in the eastern part of the Arabian Peninsula between 20-25 degrees North and 45-55 degrees East. Two different dune types can be distinguised which exhibit a 6 m and 26 m average dune advance over a 6 months time period. Wind speed/direction data and the observed dune advance agree well and indicate that dune tracking from space is a viable alternative to in situ or model data.

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.

A gradient-based approach for automated crest-line detection and analysis of sand dune patterns on planetary surfaces

NASA Astrophysics Data System (ADS)

Lancaster, N.; LeBlanc, D.; Bebis, G.; Nicolescu, M.

2015-12-01

Dune-field patterns are believed to behave as self-organizing systems, but what causes the patterns to form is still poorly understood. The most obvious (and in many cases the most significant) aspect of a dune system is the pattern of dune crest lines. Extracting meaningful features such as crest length, orientation, spacing, bifurcations, and merging of crests from image data can reveal important information about the specific dune-field morphological properties, development, and response to changes in boundary conditions, but manual methods are labor-intensive and time-consuming. We are developing the capability to recognize and characterize patterns of sand dunes on planetary surfaces. Our goal is to develop a robust methodology and the necessary algorithms for automated or semi-automated extraction of dune morphometric information from image data. Our main approach uses image processing methods to extract gradient information from satellite images of dune fields. Typically, the gradients have a dominant magnitude and orientation. In many cases, the images have two major dominant gradient orientations, for the sunny and shaded side of the dunes. A histogram of the gradient orientations is used to determine the dominant orientation. A threshold is applied to the image based on gradient orientations which agree with the dominant orientation. The contours of the binary image can then be used to determine the dune crest-lines, based on pixel intensity values. Once the crest-lines have been extracted, the morphological properties can be computed. We have tested our approach on a variety of images of linear and crescentic (transverse) dunes and compared dune detection algorithms with manually-digitized dune crest lines, achieving true positive values of 0.57-0.99; and false positives values of 0.30-0.67, indicating that out approach is generally robust.

Defrosting Polar Dunes--"They Look Like Bushes!"

NASA Image and Video Library

2000-05-26

"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. http://photojournal.jpl.nasa.gov/catalog/PIA02300

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

USGS Publications Warehouse

Draut, Amy E.

2011-01-01

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

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

Temporal and spatial patterns of Holocene dune activity on the Great Plains of North America: megadroughts and climate links

NASA Astrophysics Data System (ADS)

Forman, Steven L.; Oglesby, Robert; Webb, Robert S.

2001-05-01

The Holocene record of eolian sand and loess deposition is reviewed for numerous presently stabilized dune fields on the Great Plains of North America. Dune field activity reflects decade-to-century-scale dominance of drought that exceeded historic conditions, with a growing season deficit of precipitation >25%. The largest dune fields, the Nebraska Sand Hills and ergs in eastern Colorado, Kansas and the Southern High Plains showed peak activity sometime between ca. 7 and 5 cal. ka. Loess deposition between ca. 10 and 4 cal. ka also signifies widespread aridity. Most dune fields exhibit evidence for one or more reactivation events sometime in the past 2 cal. ka; a number of localities register two events post 1 cal. ka, the latest potentially after 1400 AD. However, there is not a clear association of the latest dune remobilization events with up to 13 droughts in the past 2 cal. ka identified in dendroclimatic and lacustrine records. Periods of persistent drought are associated with a La Niña-dominated climate state, with cooling of sea surface temperatures in the tropical Pacific Ocean and later of the tropical Atlantic Ocean and the Gulf of Mexico that significantly weakens cyclogenesis over central North America. As drought proceeds, reduced soil moisture and vegetation cover would lessen evaporative cooling and increase surface temperatures. These surface changes strengthen the eastward expansion of a high-pressure ridge aloft and shift the jet stream northward, further enhancing continent-wide drought. Uncertainty persists if dune fields will reactivate in the future at a scale similar to the Holocene because of widespread irrigation, the lack of migratory bison herds, and the suppression of prairie fires, all of which enhance stabilization of dune fields in the Great Plains.

The Bagnold Dunes in Southern Summer: Active Sediment Transport on Mars Observed by the Curiosity rover

NASA Astrophysics Data System (ADS)

Baker, M. M.; Lapotre, M. G. A.; Bridges, N. T.; Minitti, M. E.; Newman, C. E.; Ehlmann, B. L.; Vasavada, A. R.; Edgett, K. S.; Lewis, K. W.

2017-12-01

Since its landing at Gale crater five years ago, the Curiosity rover has provided us with unparalleled data to study active surface processes on Mars. Repeat imaging campaigns (i.e. "change-detection campaigns") conducted with the rover's cameras have allowed us to study Martian atmosphere-surface interactions and characterize wind-driven sediment transport from ground-truth observations. Utilizing the rover's periodic stops to image identical patches of ground over multiple sols, these change-detection campaigns have revealed sediment motion over a wide range of grain sizes. These results have been corroborated in images taken by the rover's hand lens imager (MAHLI), which have captured sand transport occurring on the scale of minutes. Of particular interest are images collected during Curiosity's traverse across the Bagnold Dune Field, the first dune field observed to be active in situ on another planet. Curiosity carried out the first phase of the Bagnold Dunes campaign (between Ls 72º and 109º) along the northern edge of the dune field at the base of Aeolis Mons, where change-detection images showed very limited sediment motion. More recently, a second phase of the campaign was conducted along the southern edge of the dune field between Ls 312º to 345º; here, images captured extensive wind-driven sand motion. Observations from multiple cameras show ripples migrating to the southwest, in agreement with predicted net transport within the dune field. Together with change-detection observations conducted outside of the dune field, the data show that ubiquitous Martian landscapes are seasonally active within Gale crater, with the bulk of the sediment flux occurring during southern summer.

Morphological response of coastal dunes to a group of three typhoons on Pingtan Island, China

NASA Astrophysics Data System (ADS)

Yang, Lin; Dong, Yuxiang; Huang, Dequan

2018-06-01

Pingtan Island (Fujian, China) was severely impacted by a group of three typhoons in a sequence of Nepartak, Meranti, and Megi during the summer of 2016. Field investigations were conducted on the island before and after the typhoons using high-precision RTK GPS technology and surveying methods, and we analyzed the morphological responses of three types of coastal dunes (coastal foredunes, climbing dunes, and coastal sand sheets) to the typhoon group. The maximum height decrease among coastal foredunes was 2.89 m after the typhoon group landed; dune volume increased by 0.9%, and the windward side showed a slight height increase, whereas that of the slope crest and leeward slope were slightly lower than the values before the typhoon group landed. The maximum height decrease among climbing dunes was 1.43 m, and dune volume decreased slightly by 0.1%; the height change among climbing dunes differed in magnitude between sites. Among coastal sand sheets, the maximum height increase was 0.75 m, and dune volume increased by 1.5%; the height of frontal coastal sand sheets increased markedly as result of storm surge washover deposits, whereas the heights barely changed at the middle and trailing edges. The above results suggest that the typhoon group imposed significant morphological changes on coastal dunes. However, the features of morphological responses differed between the three types of coastal dunes studied, and also among dunes of the same type based on local characteristics. Furthermore, coastal dunes showed no cumulative effects in their responses to the typhoon group, despite the individual typhoon impacts on coastal dune morphology.

Seasonal Changes in Northern Mars Dune Field

NASA Image and Video Library

2011-02-03

Three images of the same location, taken by NASA Mars Reconnaissance Orbiter at different times on Mars, show seasonal activity causing sand avalanches and ripple changes on a Martian dune. Time sequence of the images progresses from top to bottom.

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.

Summary of the Second International Planetary Dunes Workshop: Planetary Analogs - Integrating Models, Remote Sensing, and Field Data, Alamosa, Colorado, USA, May 18-21, 2010

USGS Publications Warehouse

Fenton, L.K.; Bishop, M.A.; Bourke, M.C.; Bristow, C.S.; Hayward, R.K.; Horgan, B.H.; Lancaster, N.; Michaels, T.I.; Tirsch, D.; Titus, T.N.; Valdez, A.

2010-01-01

The Second International Planetary Dunes Workshop took place in Alamosa, Colorado, USA from May 18-21, 2010. The workshop brought together researchers from diverse backgrounds to foster discussion and collaboration regarding terrestrial and extra-terrestrial dunes and dune systems. Two and a half days were spent on five oral sessions and one poster session, a full-day field trip to Great Sand Dunes National Park, with a great deal of time purposefully left open for discussion. On the last day of the workshop, participants assembled a list of thirteen priorities for future research on planetary dune systems. ?? 2010.

Self-Synchronization of Numerical Granular Flows: A Key to Musical Sands?

NASA Astrophysics Data System (ADS)

Staron, L.

2011-12-01

In some rare circumstances, sand flows at the surface of dunes are able to produce a loud sound known as "the song of dunes". The complex mechanisms at the source of these singing properties are far from fully understood. In this study, granular flows are simulated in two dimensions using the discrete Contact Dynamics algorithm. We show that the motion of grains at the surface of the flows exhibits a well-defined oscillation, the frequency of which is not described by the natural frequencies of the system, and does not depend on the rigid or erodible bottom condition. To explain this oscillation, we propose a simple synchronization model based on the existence of coherent structures, or clusters, at the surface of the flow, which yields successful prediction of the numerically observed frequencies. Our analysis gives consistent results when compared with field data from booming dunes, offers a possible explanation for the field observation of sound-generation velocity threshold, and provides new keys to the understanding of musical sands.

Changing Dunes and Ripples in Olympia Undae

NASA Image and Video Library

2014-04-30

Olympia Undae is a large field of sand dunes surrounding Mars North Polar ice cap. High latitude covers them with water and carbon dioxide frost in the winter so they are illuminated. NASA Mars Reconnaissance Orbiter views these best in summer.

Sand incursion into temperate (Lithuania) and tropical (the Bahamas) maritime vegetation: Georadar visualization of target-rich aeolian lithosomes

NASA Astrophysics Data System (ADS)

Buynevich, Ilya V.; Savarese, Michael; Curran, H. Allen; Bitinas, Albertas; Glumac, Bosiljka; Pupienis, Donatas; Kopcznski, Karen; Dobrotin, Nikita; Gnivecki, Perry; Boush, Lisa Park; Damušytė, Aldona

2017-08-01

Interaction of windblown sand with maritime vegetation, either as dune migration or episodic grain transport is a common phenomenon along many sandy coasts. Vegetation introduces antecedent surface roughness, especially when scaled to the landform height, but its role may be concealed if overwhelmed by aeolian incursion and burial. Where field observations and cores lack detail for characterizing this complex process, ground-penetrating radar (GPR) offers continuous visualization of aeolian sequences. Along the Curonian Spit, Lithuania, dune reactivation phases resulted in massive invasion of siliciclastic sand triggered by natural perturbations and land clearance. Massive (>30 m high) dunes entombed mature pine, oak, and alder stands and this process is ongoing. Mid-frequency (200 MHz) georadar surveys reveal landward-dipping lateral accretion surfaces interrupted by high-amplitude point-source anomalies produced by recently buried trees. In tropical regions, dense vegetation and potential for rapid lithification of carbonate sand results in more complex internal structures. Along the windward coast of San Salvador Island, the Bahamas, a massive dune has buried several generations of maritime scrubland, resulting in highly chaotic reflection pattern and high target density. On a nearby Little Exuma Island, numerous reentrants in aeolianites promoted formation of blowouts and incursion of windblown sand 10-25 m into a silver thatch palm forest. High-frequency (800 MHz) GPR images resolve diffractions from trunks and roots buried by > 2 m of oolitic sand. Basal refection morphology helps differentiate the irregular dune/beachrock surface from a smooth palm-frond mat. Aside from detecting and mapping buried vegetation, geophysical images capture its effect on sediment accumulation. This has the potential for differentiating its effect from other discordant structures within dunes (clasts, dissolution voids, trunk molds, burrows, and cultural remains).

Which processes form the volcanic sands on Mars?

NASA Astrophysics Data System (ADS)

Grégoire, M.; Baratoux, D.; Mangold, N.; Arnalds, O.; Platvoet, B.; Bardinzeff, J.; Pinet, P.

2007-12-01

Volcanic sands are common at the surface of Mars. They are usually of basaltic composition. Occurrence of sands, mostly recognized as dark dune fields include numerous impact craters in the southern hemisphere [1], several volcanic provinces such as Cerberus and Syrtis Major[2], several impact craters in the northern hemisphere, the large basins (Hellas and Argyre), Valles Marineris, and the poles [3]. In most cases, the sands are of basaltic composition [2,4], at the exception of the polar dunes which are made of sulfates [3]. It is interesting to note that dunes have been found on the Hesperian volcanic plateau of Systis Major, while they are not reported on Tyrrhena Terra, a volcanic province similar in age and morphology to Syrtis. It seems thus that the formation of sand from volcanic material is not systematic and thus requires particular conditions. These different situations which will be presented raise the following questions. When did these volcanic sands form in the Martian history? Did they result from a long-standing and slow process operating in the present cold conditions or did they result from several episodes associated for instant to climate changes? We review several mechanisms which could account for the formation of volcanic sand on Mars from the volcanic material. In particular, we focus on the role of cold-climate processes from an analysis of terrestrial analogs in Iceland. In this case, the advance and retreat of glaciers over a recent erupted shield volcano associated with the strong catabatic winds have resulted in the rapid formation (less than few thousands years) of large volumes of sands. [1] Fenton, L. K. (2005), Potential sand sources for the dune fields in Noachis Terra, Mars, J. Geophys. Res. 110, E11004, doi :10.1029/2005JE002436. [2] Vaucher et. al, in revision for Icarus [3] Langevin et. al, (2005), Science, 307, 1584-1586 [4] Poulet F., Mangold N. and Erard S. (2003), Astron. & Astrophys. 412, L19-L23.

Bedform dynamics in a large sand-bedded river using multibeam echo sounding

NASA Astrophysics Data System (ADS)

Elliott, C. M.; Jacobson, R. B.; Erwin, S.; Eric, A. B.; DeLonay, A. J.

2014-12-01

High-resolution repeat multibeam Echo Sounder (MBES) surveys of the Lower Missouri River in Missouri, USA demonstrate sand bedform movement at a variety of scales over a range of discharges. Understanding dune transport rates and the temporal and spatial variability in sizes across the channel has implications for how sediment transport measurements are made and for understanding the dynamics of habitats utilized by benthic organisms over a range of life stages. Nearly 800 miles of the Lower Missouri River has been altered through channelization and bank stabilization that began in the early 1900's for navigation purposes. Channelization of the Lower Missouri River has created a self-scouring navigation channel with large dunes that migrate downstream over a wide range of discharges. Until the use of MBES surveys on the Missouri River the spatial variability of dune forms in the Missouri River navigation channel was poorly understood. MBES surveys allow for visualization of a range of sand bedforms and repeat measurements demonstrate that dunes are moving over a wide range of discharges on the river. Understanding the spatial variability of dunes and dune movement across the channel and in different channel settings (bends, channel cross-overs, near channel structures) will inform emerging methods in sediment transport measurement that use bedform differencing calculations and provide context for physical bedload sediment sampling on large sand-bedded rivers. Multiple benthic fish species of interest including the endangered pallid sturgeon utilize Missouri River dune fields and adjacent regions for migration, feeding, spawning, early development and dispersal. Surveys using MBES and other hydroacoustic tools provide fisheries biologists with broad new insights into the functionality of bedforms as habitat for critical life stages of large river fish species in the Missouri River, and similar sand-bedded systems.

Earth Observations taken by the Expedition 18 Crew

NASA Image and Video Library

2008-12-20

ISS018-E-014770 (20 Dec. 2008) --- Sand dunes in the Marzuq Sand Sea, southwest Libya are featured in this image photographed by an Expedition 18 crewmember on the International Space Station. This detailed view, taken from low Earth orbit, shows classic large and small sand masses of the Central Sahara where wind is a more powerful land-forming agent than water. ?Draa? dunes (from the Arabic for ?arm?) are very large masses of sand and appear here as the broad network of yellow-orange sand masses (the image covers a region approximately 9.4 kilometers wide), with smooth-floored, almost sand-free basins between them. These sand masses lie in the western part of Libya?s vast Marzuq Sand Sea (greater than 60,000 square kilometers, centered at 24.5N 12W). Geologists think that the draa of the Marzuq have probably been formed by winds different from the dominant north/northeast winds of today. Numerous smaller dunes can be seen developed on the backs of the draa. Three distinct dune types can be identified: longitudinal dunes (formed essentially parallel with formative winds from the north); transverse dunes, usually more curved, formed at right angles to the formative wind; and star dunes, in which several linear arms converge towards a single peak. The upwind side of the sand masses appears smoother than the more rippled downwind side. Wind is moving sand grains almost all the time. This means that the draa and the dunes are all moving -- as sand is added on the upwind side and blown off the downwind side. It is well known that small sand masses move much faster than large sand masses. This means that the draa are almost stationary, but that the smaller dunes are moving relatively quickly across their backs. When the dunes reach the downwind side of the draa they are obliterated, their sand being blown across the basins as individual grains.

75 FR 77801 - Endangered and Threatened Wildlife and Plants; Endangered Status for Dunes Sagebrush Lizard

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-14

... December 30, 1982, we published our notice of review classifying the sand dune lizard (dunes sagebrush... listing actions for the southern Idaho ground squirrel, sand dune lizard, or Tahoe yellow cress. The court... by the common name of sand dune lizard (e.g., Degenhardt et al. 1996, p. 159); however, the currently...

Earth Observations taken by the Expedition 17 Crew

NASA Image and Video Library

2008-08-12

ISS017-E-013025 (12 Aug. 2008) --- The Tifernine Dune Field in Algeria is featured in this image photographed by an Expedition 17 crewmember on the International Space Station. The Tifernine Dune Field is located at the southernmost tip of the Grand Erg Oriental, a "dune sea" that occupies a large portion of the Sahara Desert in eastern Algeria. This view illustrates the interface between the yellow-orange sand dunes of the field and adjacent dark brown consolidated rocks of the Tinrhert Plateau to the south and east (right). NASA scientists point out that three distinct landform types are visible in the image, each providing information about past and present climate in the area. The oldest landform is represented by the rocks of the Tinrhert Plateau, which are characterized by a number of incised channels in the bedrock -- these formed during a wet and cool climate period, most probably by glacial meltwater streams. As the present dry and hot climate that characterizes the Sahara became established, water ceased to flow in these channels, and large amounts of drying sediment (sand, silt, and clay) were eroded and transported by predominantly northeast-southwest winds -- forming large linear dunes that roughly parallel the prevailing wind direction (center). The present climate regime is still hot and dry, but current wind directions are more variable, leading to the formation of star dunes -- recognizable by a starfish-like pattern when seem from above -- that are modifying the older large linear dunes. White to grey regions within the dune field are exposed deposits of silt and clay, together with evaporite minerals (such as halite, or common table salt) formed by evaporation of water that collected in small basins between the dunes.

Expression of terrain and surface geology in high-resolution helicopter-borne gravity gradient (AGG) data: examples from Great Sand Dunes National Park, Rio Grande Rift, Colorado

USGS Publications Warehouse

Drenth, Benjamin J.

2013-01-01

Airborne gravity gradient (AGG) data are rapidly becoming standard components of geophysical mapping programs, due to their advantages in cost, access, and resolution advantages over measurements of the gravity field on the ground. Unlike conventional techniques that measure the gravity field, AGG methods measure derivatives of the gravity field. This means that effects of terrain and near-surface geology are amplified in AGG data, and that proper terrain corrections are critically important for AGG data processing. However, terrain corrections require reasonable estimates of density for the rocks and sediments that make up the terrain. A recommended philosophical approach is to use the terrain and surface geology, with their strong expression in AGG data, to the interpreter’s advantage. An example of such an approach is presented here for an area with very difficult ground access and little ground gravity data. Nettleton-style profiling is used with AGG data to estimate the densities of the sand dunefield and adjacent Precambrian rocks from the area of Great Sand Dunes National Park in southern Colorado. Processing of the AGG data using the density estimate for the dunefield allows buried structures, including a hypothesized buried basement bench, to be mapped beneath the sand dunes.

The Mars Science Laboratory (MSL) Bagnold Dunes Campaign, Phase I: Overview and introduction to the special issue

NASA Astrophysics Data System (ADS)

Bridges, Nathan T.; Ehlmann, Bethany L.

2018-01-01

The Bagnold dunes in Gale Crater, Mars, are the first active aeolian dune field explored in situ on another planet. The Curiosity rover visited the Bagnold dune field to understand modern winds, aeolian processes, rates, and structures; to determine dune material composition, provenance, and the extent and type of compositional sorting; and to collect knowledge that informs the interpretation of past aeolian processes that are preserved in the Martian sedimentary rock record. The Curiosity rover conducted a coordinated campaign of activities lasting 4 months, interspersed with other rover activities, and employing all of the rover's science instruments and several engineering capabilities. Described in 13 manuscripts and summarized here, the major findings of the Bagnold Dunes Campaign, Phase I, include the following: the characterization of and explanation for a distinctive, meter-scale size of sinuous aeolian bedform formed in the high kinetic viscosity regime of Mars' thin atmosphere; articulation and evaluation of a grain splash model that successfully explains the occurrence of saltation even at wind speeds below the fluid threshold; determination of the dune sands' basaltic mineralogy and crystal chemistry in comparison with other soils and sedimentary rocks; and characterization of chemically distinctive volatile reservoirs in sand-sized versus dust-sized fractions of Mars soil, including two volatile-bearing types of amorphous phases.

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.

Numerical simulation of wind-sand movement in the reversed flow region of a sand dune with a bridge built downstream.

PubMed

He, Wei; Huang, Ning; Xu, Bin; Wang, Wenbo

2018-04-23

A bridge built inside the reversed flow region of a sand dune will change the characteristics of wind-sand movement in this region. The Reynolds-averaged Navier-Stokes simulation and discrete particle tracing are used to simulate the wind-sand movement around a sand dune with a bridge built inside the reversed region. Three cases with different bridge positions are studied. The results show that 1) compared with the isolated dune case, a tall bridge built at the leeward toe leads to an increase in the deposition rate on the leeward slope and a longer reversed flow region downstream of the sand dune; meanwhile, the high speed of crosswind on the bridge indicates that some measures should be taken to protect trains from strong crosswind; 2) a low bridge at the leeward toe has little effect on the sand deposition and reversed flow region of the dune; however, low sand transport rate and crosswind speed on the bridge show that anti-crosswind/sand measures should be taken according to the actual situation and 3) a low bridge on the leeward slope has little effect on the length of reversed flow region, however, high crosswind speed and sand flux on the bridge reveal the need of anti-crosswind/sand measures on the bridge. Moreover, the bridges in the reversed flow region increase the sand flux near the leeward crest; as a result, the moving patterns of the sand dune are changed.

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.

Comparison of the mineral composition of the sediment found in two Mars dunefields: Ogygis Undae and Gale crater - three distinct endmembers identified

NASA Astrophysics Data System (ADS)

Charles, Heather; Titus, Timothy; Hayward, Rosalyn; Edwards, Christopher; Ahrens, Caitlin

2017-01-01

The composition of two dune fields, Ogygis Undae and the NE-SW trending dune field in Gale crater (the "Bagnold Dune Field" and "Western Dune Field"), were analyzed using thermal emission spectra from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Mars Odyssey Thermal Emission Imaging System (THEMIS). The Gale crater dune field was used as a baseline as other orbital compositional analyses have been conducted, and in situ sampling results will soon be available. Results from unmixing thermal emission spectra showed a spatial variation between feldspar mineral abundances and pyroxene mineral abundances in Ogygis Undae. Other datasets, including nighttime thermal inertia values, also showed variation throughout the dune field. One explanation proposed for this variation is a bimodal distribution of two sand populations. This distribution is seen in some terrestrial dune fields. The two dune fields varied in both mineral types present and in uniformity of composition. These differences point to different source lithologies and different distances travelled from source material. Examining these differences further will allow for a greater understanding of aeolian processes on Mars.

SL3-34-056

NASA Image and Video Library

1973-07-01

SL3-34-056 (July-September 1973) --- A near vertical view of an 8,000 square-mile area of the Grand Erg Oriental in east central Algeria as photographed from Earth orbit by one of the six lenses of the Itek-furnished S190-A Multispectral Photographic Facility Experiment in the Multiple Docking Adapter of the Skylab space station. The Grand Erg contains vast areas of sand dunes and sand plains. This photograph illustrates the variety of surface features that are characteristic of the Sahara Desert. The dark areas are relatively sand free, and may contain rock outcrops along which travel is considerably easier. Sand dunes are abundant in this picture, and their size, shape, location and pattern are due to the underlying topography and direction of the prevailing winds. Scientists interested in study of dune fields will be able to use this photograph for detailed analysis of the dune features, especially their characteristics adjacent to the sand-free areas. Federal agencies participating with NASA on the EREP project are the Departments of Agriculture, Commerce, Interior, the Environmental Protection Agency and the Corps of Engineers. All EREP photography is available to the public through the Department of Interior?s Earth Resources Observations Systems Data Center, Sioux Falls, South Dakota, 57198. Photo credit: NASA

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

PubMed

Govaerts, Yves M

2015-02-03

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

The effects of psammophilous plants on sand dune dynamics

NASA Astrophysics Data System (ADS)

Bel, Golan; Ashkenazy, Yosef

2014-07-01

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

3D Airflow patterns over coastal foredunes: implications for aeolian sediment transport

NASA Astrophysics Data System (ADS)

Jackson, Derek W. T.; Cooper, Andrew G.; Baas, Andreas C. W.; Lynch, Kevin; Beyers, Meiring

2010-05-01

A fundamental criterion for the development of coastal sand dunes is usually highlighted as a significant onshore wind component of the local wind field. The presence of large sand dune systems on coasts where the predominant wind blows offshore is therefore difficult to explain and usually they are attributed to the past occurrence of onshore winds and, by implication, subsequent changes in climate. Recent studies have shown that offshore winds can be deflected or 'steered' by existing dunes so that their direction changes. This can occur to such an extent that a process known as 'flow reversal' can arise, whereby the initially offshore wind actually flows onshore at the beach. This process is important because it can cause sand to be blown from the beach and into the dunes, causing them to grow. This may be central in explaining the presence of extensive dunes on coasts where the dominant wind is offshore, but is also important in how dunes recover after periods of wave erosion during storms. Offshore winds have traditionally been excluded from sediment budget calculations for coastal dunes, but when they do transport sand onshore, this may have been an important oversight leading to significant underestimates of the volume of sand being transported by wind. This work investigates the controls on the processes and the mechanisms involved in deformation of the flow and resulting sediment transport at coastal foredunes in Northern Ireland. We use a combination of field measurement of wind and sediment transport coupled with state-of-the-art aerodynamic modelling using computational fluid dynamics (CFD) and 3-D sonic anemometry. Our working hypothesis is that offshore winds contribute substantially to foredune behaviour on leeside coasts. Preliminary results show strong reverse flow eddies in the seaward side of the foredunes during offshore wind events. These secondary flow reversals have been above velocity threshold and are transport capable. Using CFD modelling across a high resolution LIDAR surface of the dunes and beach we have isolated key areas of wind direction and velocity patterns which are important in aeolian transport budgets. Results are particularly important in post-storm recovery of foredunes damaged under wave action as offshore winds can initiate significant onshore transport, re-supplying the backbeach and foredune zones.

The Geologic Exploration of the Bagnold Dune Field at Gale Crater by the Curiosity Rover.

PubMed

Chojnacki, Matthew; Fenton, Lori K

2017-11-01

The Mars Science Laboratory rover Curiosity engaged in a monthlong campaign investigating the Bagnold dune field in Gale crater. What represents the first in situ investigation of a dune field on another planet has resulted in a number of discoveries. Collectively, the Curiosity rover team has compiled the most comprehensive survey of any extraterrestrial aeolian system visited to date with results that yield important insights into a number of processes, including sediment transport, bed form morphology and structure, chemical and physical composition of aeolian sand, and wind regime characteristics. These findings and more are provided in detail by the JGR-Planets Special Issue Curiosity's Bagnold Dunes Campaign, Phase I.

The Geologic Exploration of the Bagnold Dune Field at Gale Crater by the Curiosity Rover

PubMed Central

Chojnacki, Matthew; Fenton, Lori K.

2018-01-01

The Mars Science Laboratory rover Curiosity engaged in a monthlong campaign investigating the Bagnold dune field in Gale crater. What represents the first in situ investigation of a dune field on another planet has resulted in a number of discoveries. Collectively, the Curiosity rover team has compiled the most comprehensive survey of any extraterrestrial aeolian system visited to date with results that yield important insights into a number of processes, including sediment transport, bed form morphology and structure, chemical and physical composition of aeolian sand, and wind regime characteristics. These findings and more are provided in detail by the JGR-Planets Special Issue Curiosity’s Bagnold Dunes Campaign, Phase I. PMID:29564198

Analysis of beachgrass ecomorphodynamics and foredune morphology along US Pacific Northwest coastal sand dunes using a Bayesian network

NASA Astrophysics Data System (ADS)

Biel, R.; Hacker, S.; Ruggiero, P.

2016-12-01

Coastal dunes provide valuable infrastructure for mitigating flooding and erosion hazard exposure by dissipating wave energy. Although vegetation is essential for foredune establishment and growth by facilitating sand deposition and stabilization, few have examined how plant distribution and abundance relates to foredune morphology in the field. The US Pacific Northwest coastal dune system presents an excellent case study for examining ecomorphodynamic processes on sand dunes. It exhibits a diverse array of geomorphological conditions, including a range of dissipative to reflective beaches and highly varied foredune morphology. Ecologically, the region contains two invasive, dune-building beachgrasses of the same genus (Ammophila arenaria and A. breviligulata). To explore how geomorphological and ecological drivers alter foredune morphology, we used a Bayesian network to assess the role of nearshore bathymetry, sand supply (measured as shoreline change rate), and beachgrass species identity and density in determining foredune morphology. At a finer scale, we also examined whether beachgrass density and species identity altered sand accretion between 2012 and 2014 at multiple points across the foredune using a mixed model. Our Bayesian network analysis indicates that nearshore slope, shoreline change rate, beach width, and beachgrass density directly or indirectly affect foredune width, slope, and height. However, we observed no relationships between species identity and foredune morphology. When examining the finer-scale relationship between beachgrass density and sand accretion at points along the foredune, we found that sand accretion was correlated with beachgrass stem density in 2012, new stem growth between 2012 and 2014, beach width, and elevation. Moreover, A. arenaria accreted more sand than A. breviligulata on the foredune face, suggesting that subtle differences in beachgrass morphology or growth patterns may produce differing accretion patterns across the foredune. Both analyses indicate that beachgrass density alters foredune morphology. Although A. arenaria and A. breviligulata exhibit differing sand accretion patterns at points across the foredune face, it is unclear whether these fine-scale differences produce coarse-scale changes in foredune morphology.

The Changing Dunes of Wirtz Crater

NASA Image and Video Library

2017-01-19

The large dark feature is a classic Martian sand dune. Most sand on Earth is made from the mineral quartz, which is white and bright. On Mars, most sand is composed of dark basalt, a volcanic rock. For this reason, dunes on Mars are darker than those on Earth. The dunes in this observation, within Wirtz Crater, are known as "barchans." The steepest slope is on the eastern (right) side, partially in shadow, and represents the direction the dune is migrating as the sand is blown and transported by the wind. Small ripples are visible on much of the dune surface. The dark streaks on the dune are tracks left by passing vortices known to us as dust devils. These raise dust off the dune, revealing a darker substrate. http://photojournal.jpl.nasa.gov/catalog/PIA12289

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.

WIND VELOCITIES AND SAND FLUXES IN MESQUITE DUNE-LANDS IN THE NORTHERN CHIHUAHUAN DESERT: A COMPARISON BETWEEN FIELD MEASUREMENTS AND THE QUIC (QUICK URBAN AND INDUSTRIAL COMPLEX) MODEL

EPA Science Inventory

The poster shows comparisons of wind velocities and sand fluxes between field measurements and a computer model, called QUIC (Quick Urban & Industrial Complex). The comparisons were made for a small desert region in New Mexico.

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

USGS Publications Warehouse

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

2010-01-01

The recent increase in dune studies in North America has been heavily focused in the Great Plains, while less attention has historically been given to the dune fields east of the Mississippi River. Here we report ages and suggest a potential sediment source for sand dunes in the Green River Lowland, Illinois, which may provide a better understanding of the dynamic interactions between eolian, glacial, lacustrine and fluvial processes that shaped the landscapes of the upper Midwest. Seven coherent optically stimulated luminescence ages (OSL, or optical ages) obtained from four sites suggest that major dune construction in the Green River Lowland occurred within a narrow time window around 17,500 ago. This implies either an enhanced aridity or an episodic increase of sediment supply at 17,500 years ago, or combination of the both. Contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the Lake Michigan Lobe retreated from the area, we propose that Green River Lowland dunes sand originated from the Green Bay Lobe through the Rock River. Specifically, sediment supply increased in the Rock River valley during drainage of Glacial Lake Scuppernong, which formed between ???18,000 and 17,000 years ago, when the Green Bay Lobe retreated from its terminal moraine. The lake drained catastrophically through the Rock River valley, providing glacial sediment and water to erode the preexisting sandy sediments. Throughout the remainder of the late Pleistocene, the Laurentide Ice Sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys. Therefore, the dunes in the Green River Lowland formed only during the catastrophic drainage of Glacial Lake Scuppernong, but were stabilized through the remainder of the Pleistocene. This scenario explains the abrupt dune construction around 17,500 years ago, and explains the lack of later dune activity up to the Pleistocene-Holocene transition. OSL and radiocarbon ages also indicate that dunes were reactivated during the early, middle and late Holocene. Some eolian activation occurred within well-defined dry intervals in the upper Midwest, suggesting that increased aridity may have been the primary driver in mobilizing sand. However, many ages do not correspond to drier periods. In contrast to the relative coherency of the Pleistocene OSL ages from multiple study sites, the Holocene OSL ages do not overlap from one site to another, suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the Holocene. Therefore, we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the Holocene. The multiple periods of eolian activity during the Holocene suggest a high potential for future sand activation in the region, and these results are informative for environmental prediction and potential future mitigation.

Proctor Crater Dunes

NASA Technical Reports Server (NTRS)

2002-01-01

[figure removed for brevity, see original site]

This image, located near 30E and 47.5S, displays sand dunes within Proctor Crater. These dunes are composed of basaltic sand that has collected in the bottom of the crater. The topographic depression of the crater forms a sand trap that prevents the sand from escaping. Dune fields are common in the bottoms of craters on Mars and appear as dark splotches that lean up against the downwind walls of the craters. Dunes are useful for studying both the geology and meteorology of Mars. The sand forms by erosion of larger rocks, but it is unclear when and where this erosion took place on Mars or how such large volumes of sand could be formed. The dunes also indicate the local wind directions by their morphology. In this case, there are few clear slipfaces that would indicate the downwind direction. The crests of the dunes also typically run north-south in the image. This dune form indicates that there are probably two prevailing wind directions that run east and west (left to right and right to left).

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.

Xylocopa bees in tropical coastal sand dunes: use of resources and their floral syndromes.

PubMed

Figueiredo, N; Gimenes, M; de Miranda, M D; Oliveira-Rebouças, P

2013-06-01

Large bees such as species from Xylocopa Latreille are usually associated with pollination in tropical sand dune areas, which frequently present shrubby herbaceous vegetation adapted to conditions of high salinity, high solar radiation and strong winds. We report on the diversity of Xylocopa and the plants they visited to collect nectar and pollen, focusing on the floral syndromes they present in these plants and on the breadth of the trophic niche in a tropical sand dune fragment over the year. The field work was carried out monthly in Baixio (Bahia, Brazil; Northern Coast Environmental Protection Area) from April 2008 to March 2009, over two consecutive days, from 06:30 AM to 05:00 PM. The medium-large body sized Xylocopa (Neoxylocopa) cearensis Ducke and Xylocopa (Schonnherria) subcyanea Pérez were noticeable for their frequency, constancy on the flowers and sharing of plant species. Xylocopa spp. visited plants with flowers of different shapes, colors, inflorescence arrangement and syndromes. However, their resource collections were mainly concentrated on Cuphea brachiata, Waltheria cinerascens, Croton sellowii and Chamaecrista ramosa, which may be considered key species for Xylocopa spp. maintenance in coastal sand dune and restinga environments in Northeast Brazil.

Giant Linear Dunes as the Formation Pathway to Megabarchan Chains: Titan and the Rub 'Al Khali

NASA Astrophysics Data System (ADS)

Lorenz, R. D.; Radebaugh, J.

2015-05-01

We suggest megabarchans cannot grow from barchans. Rather sand accumulates as giant linear dunes in a bidirectional regime which has since become more unidirectional. We see this pattern on Titan and in the field in the .United Arab Emirates.

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.

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.

Comparison of the mineral composition of the sediment found in two Mars dunefields: Ogygis Undae and Gale crater – three distinct endmembers identified

USGS Publications Warehouse

Charles, Heather; Titus, Timothy N.; Hayward, Rosalyn; Edwards, Christopher; Ahrens, Caitlin

2016-01-01

The composition of two dune fields, Ogygis Undae and the NE–SW trending dune field in Gale crater (the “Bagnold Dune Field” and “Western Dune Field”), were analyzed using thermal emission spectra from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Mars Odyssey Thermal Emission Imaging System (THEMIS). The Gale crater dune field was used as a baseline as other orbital compositional analyses have been conducted, and in situ sampling results will soon be available.Results from unmixing thermal emission spectra showed a spatial variation between feldspar mineral abundances and pyroxene mineral abundances in Ogygis Undae. Other datasets, including nighttime thermal inertia values, also showed variation throughout the dune field. One explanation proposed for this variation is a bimodal distribution of two sand populations. This distribution is seen in some terrestrial dune fields.The two dune fields varied in both mineral types present and in uniformity of composition. These differences point to different source lithologies and different distances travelled from source material. Examining these differences further will allow for a greater understanding of aeolian processes on Mars.

The Quantification and Evolution of Resilience in Integrated Coastal Systems

DTIC Science & Technology

2012-08-01

for natural protection when protective beaches and sand dunes are destroyed or overtopped. Protects a beach or sand dune that fronts backshore from...dredged material on a beach, dune , barrier island, or sand berm located in the near- shore zone. Stabilize the location of an eroding beach, dune ...waves will erode beaches and dunes . Table 5. Components and processes that are part of an ecosystem restoration subsystem defined by an oyster

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.

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.

The Enigmatic Longevity of Granular Materials on Mars: The Case for Geologically Episodic Dune Formation

NASA Technical Reports Server (NTRS)

Marshall, J.

1999-01-01

Martian sand dunes are concentrated in vast sand seas in the circumpolar belt of the planet's northern hemisphere, but they are also pervasive over the whole planet. Their occurrence is to be expected on a super-arid planetary surface subjected to boundary layer drag from a continually active atmosphere. Whilst their occurrence is to be expected, their survival is enigmatic. But the enigma only arises if the martian system is considered similar to Earth's --where sand is moved highly frequently, more or less on a seasonal basis. Experimentally it is readily demonstrated that active sand will soon wear down to small grains and eventually diminish to below the critical sand size required to sustain dune formation. According to conventional wisdom, sand moves at higher speeds on Mars than on Earth, and if it were to move as frequently as it does on Earth, then the dune-forming sand population should have long since disappeared, given the great longevity of the martian aeolian system (Sagan coined the term "kamikaze" grains to express this disappearance). No supply of sand could keep pace with this depletion, especially in light of the fact that Mars does not have very active weathering, nor significant crustal differentiation. On Earth, plate tectonics, magmatic activity, and general crustal differentiation over geological time have produced great concentrations of quartz crystals in the continental crustal masses. Not only are these quartz grains chemically and mechanically resilient, they are about the right size for being transported by either wind or water. Add to this, the geologically recent contribution of glacial grinding, and it is easy to see why there are dune field on Earth. So what are the martian dunes composed of, and how does the material survive the eons of attrition? In addition to experimental demonstrations of sand comminution in laboratory aeolian simulations, the problem can be approached from first principles. Sagan showed that by simple considerations of material strength versus mechanical work applied to the material, comminution to sub-sand size would be inevitable. Another semi-analytical approach might be taken by considering that the archetypal aeolian sand surface texture is an irregularly pitted ("frosted") surface composed of chipping hollows approximately 10 microns in diameter, 5 microns deep. Their volume = about 250 cubic microns, or about 1/25000 of the volume of a 100 micron diameter dune grain. Because a saltating grain always strikes another grain, then two surfaces are impacted. Thus each grain undergoes two impacts for every one saltation leap, when the impact statistics are considered for a closed dune system (it can be calculated that a grain can never undergo <1 impact, and never >2 per saltation leap). Hence, if we conservatively assume that there is damage to a grain each time it bounces, but with the minimum damage of only 2 microscopic craters per impact, then approximately 12,500 impacts are required to completely eliminate the grain. Of course, it would require only a fraction of this amount to reduce the grain to below sand size. A grain will make only several tens of saltation leaps on the stoss side of a dune before becoming buried on the lee slope. The dune then has to move its full length before the grain is exhumed again for abrasion. Even with this hiatus in transport, it is easy to see that terrestrial dunes need resupplying with sand in order to survive. In recent theoretical work it has been shown that martian aeolian transport may be initiated with high-speed grains, but this converts to a lower energy dynamic transport equilibrium in which a reptation population dominates grain transport (on Earth, at least half of the flux is by reptation and creep). On Mars, therefore, average grain speeds may be lower than those on Earth, or at least comparable. This would permit greater longevity for martian sands, but it would not go far enough to solve the survival problem. It may, however, explain why martian dunes are about the same size as terrestrial dunes. If martian saltation leaps were significantly longer than on Earth (as usually assumed), then a dune's lee slope would have to be correspondingly longer in order to trap the sand; this would scale up the whole dune structure. But with shorter trajectories in a reptation population, larger dunes would be unnecessary. Additional information is contained in the original.

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

USGS Publications Warehouse

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

2009-01-01

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

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-09-07

ISS013-E-78506 (7 Sept. 2006) --- Sand dunes near Mongolia's Har Lake are featured in this image photographed by an Expedition 13 crewmember on the International Space Station. Har (or Black) Lake is located in the western part of the country within the Valley of Lakes--part of a system of closed basins that stretches across central Asia. According to scientists, these basins are the remnants of larger paleolakes that had begun to shrink in size by approximately five thousand years ago as regional climate became drier. Today, the Valley of Lakes is an important ecological resource for study of steppe grasslands, and as resting points for large numbers of migratory birds. Portions of the basin are designated as national parks or other protected areas, and Har Lake itself is an ecotourism destination (usually by horseback). This oblique view captures the dynamic nature of the landscape of Har Lake. The lake is encircled by sand dune fields which encroach on the lower slopes of the Tobhata Mountains to the west and south. Gaps in the mountains have been exploited by sand dunes moving eastward (indicating westerly winds) -- the most striking example being a series of dunes entering Har Lake along its southwestern shoreline. Here, the dune forms reflect the channeling of winds through the break in the mountain ridgeline, leading to dune crests oriented transverse to northwesterly winds. Another well-developed line of dunes is visible between Har and Baga Lakes. While these dunes appear to cut across a lake surface, the dunes have in fact moved across a narrow stream channel.

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

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

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 (σ0). 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.

Airflow-terrain interactions through a mountain gap, with an example of eolian activity beneath an atmospheric hydraulic jump

NASA Astrophysics Data System (ADS)

Gaylord, David R.; Dawson, Paul J.

1987-09-01

The integration of atmospheric soundings from a fully instrumented aircraft with detailed sedimentary and geomorphic analyses of eolian features in the Ferris dune field of south-central Wyoming lends insight into the manner in which topography interacts with airflow to modify eolian activity. Topographically modified airflow results in zones of airflow deceleration, acceleration, and enhanced atmospheric turbulence, all of which influence the surface morphology and sedimentology. Extreme lateral confluence of prevailing airflow produces accelerated, unidirectional winds. These winds correlate with unusually continuous and elongate parabolic dunes that extend into a mountain gap (Windy Gap). Persistently heightened winds produced at the entrance to Windy Gap have resulted in a concentration of active sand dunes that lack slipfaces. Common development of a strongly amplified atmospheric wave analogous to a hydraulic jump in the gap contributes to the formation of a variety of eolian features that mantle the surface of Windy Gap and the Ferris dune field tail. Heightened, unidirectional winds in this zone promote grain-size segregation, the formation of elongated and aligned sand drifts, climbing and falling dunes, elongate scour streaks, and parabolic dunes that have low-angle (<20°) cross-stratification. Deflation of bedrock and loose sediment has been enhanced in the zone of maximum turbulence beneath the hydraulic jump.

Diurnal emissivity dynamics in bare versus biocrusted sand dunes.

PubMed

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

2015-02-15

Land surface emissivity (LSE) in the thermal infrared depends mainly on the ground cover and on changes in soil moisture. The LSE is a critical variable that affects the prediction accuracy of geophysical models requiring land surface temperature as an input, highlighting the need for an accurate derivation of LSE. The primary aim of this study was to test the hypothesis that diurnal changes in emissivity, as detected from space, are larger for areas mostly covered by biocrusts (composed mainly of cyanobacteria) than for bare sand areas. The LSE dynamics were monitored from geostationary orbit by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) over a sand dune field in a coastal desert region extending across both sides of the Israel-Egypt political borderline. Different land-use practices by the two countries have resulted in exposed, active sand dunes on the Egyptian side (Sinai), and dunes stabilized by biocrusts on the Israeli side (Negev). Since biocrusts adsorb more moisture from the atmosphere than bare sand does, and LSE is affected by the soil moisture, diurnal fluctuations in LSE were larger for the crusted dunes in the 8.7 μm channel. This phenomenon is attributed to water vapor adsorption by the sand/biocrust particles. The results indicate that LSE is sensitive to minor changes in soil water content caused by water vapor adsorption and can, therefore, serve as a tool for quantifying this effect, which has a large spatial impact. As biocrusts cover vast regions in deserts worldwide, this discovery has repercussions for LSE estimations in deserts around the globe, and these LSE variations can potentially have considerable effects on geophysical models from local to regional scales. Copyright © 2014 Elsevier B.V. All rights reserved.

Hardened Dunes in Arcadia Planitia

NASA Image and Video Library

2014-10-29

NASA Mars Reconnaissance Orbiter HiRISE, with its high resolution and eight years in orbit about Mars, has shown that many dunes and ripples on the planet are active. This demonstrates that in some areas sand is loose enough and winds strong enough, that significant change can occur. Nevertheless, other Martian dunes are clearly *inactive*. This image in Arcadia Planitia shows dunes in a crater. Unlike active dunes on the planet, those here are bright, and, zooming in, there are several lines of evidence indicating that the dunes have become indurated, that is, hardened into cohesive sediment or even into sandstone rock. For example, the dune field at the southern edge is cut off by a step cliff, indicating erosion of hard material. Although fine scale ripples on the original dune surface are preserved, we also see large scale fluting from southwest to northeast, a common texture associated with wind-induced sand abrasion. How these dunes became indurated is unknown. One possibility is that this area of Mars was buried and then exhumed, a process that seems to have occurred many times in the Martian past over various areas of the planet. During burial, compaction and possibly ground water circulation would have indurated the dunes, leaving them as a hard sandstone that, when exhumed, was subsequently partially eroded. http://photojournal.jpl.nasa.gov/catalog/PIA18890

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

NASA Astrophysics Data System (ADS)

Sotiropoulos, Fotis; Khosronejad, Ali

2016-02-01

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

XRD and mineralogical analysis of gypsum dunes at White Sands National Monument, New Mexico and applications to gypsum detection on Mars

NASA Astrophysics Data System (ADS)

Lafuente, B.; Bishop, J. L.; Fenton, L. K.; King, S. J.; Blake, D.; Sarrazin, P.; Downs, R.; Horgan, B. H.

2013-12-01

A field portable X-ray Diffraction (XRD) instrument was used at White Sands National Monument to perform in-situ measurements followed by laboratory analyses of the gypsum-rich dunes and to determine its modal mineralogy. The field instrument is a Terra XRD (Olympus NDT) based on the technology of the CheMin (Chemistry and Mineralogy) instrument onboard the Mars Science Laboratory (MSL) rover Curiosity which is providing the mineralogical and chemical composition of scooped soil samples and drilled rock powders collected at Gale Crater [1]. Using Terra at White Sands will contribute to 'ground truth' for gypsum-bearing environments on Mars. Together with data provided by VNIR spectra [2], this study clarifies our understanding of the origin and history of gypsum-rich sand dunes discovered near the northern polar region of Mars [3]. The results obtained from the field analyses performed by XRD and VNIR spectroscopy in four dunes at White Sands revealed the presence of quartz and dolomite. Their relative abundance has been estimated using the Reference Intensity Ratio (RIR) method. For this study, particulate samples of pure natural gypsum, quartz and dolomite were used to prepare calibration mixtures of gypsum-quartz and gypsum-dolomite with the 90-150μm size fractions. All single phases and mixtures were analyzed by XRD and RIR factors were calculated. Using this method, the relative abundance of quartz and dolomite has been estimated from the data collected in the field. Quartz appears to be present in low amounts (2-5 wt.%) while dolomite is present at percentages up to 80 wt.%. Samples from four dunes were collected and prepared for subsequent XRD analysis in the lab to estimate their composition and illustrate the changes in mineralogy with respect to location and grain size. Gypsum-dolomite mixtures: The dolomite XRD pattern is dominated by an intense diffraction peak at 2θ≈36 deg. which overlaps a peak of gypsum, This makes low concentrations of dolomite difficult to quantify in mixtures with high concentration of gypsum. Dolomite has been detected in some locations at dune 3 as high as 80 wt.%. Gypsum-quartz mixtures: The intensity of the main diffraction peak of quartz at 2θ≈31 deg. decreases progressively with the decrease of the amount of quartz in the mixtures. Samples from dune 1 and 2 show quartz abundance at 5.6 and 2.6 wt.% respectively . [1] Blake et al. Space Sci. Rev. (2012). doi:10.1007/s11214-012-9905-1. [2] King et al. (2013) AGU, submitted. [3] Langevin et al. (2005). Science 307, 1584-1586.

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

USGS Publications Warehouse

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

2008-01-01

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

Compositional variations in sands of the Bagnold Dunes, Gale Crater, Mars, from visible-shortwave infrared spectroscopy and comparison with ground truth from the Curiosity Rover

USGS Publications Warehouse

Lapotre, Mathieu G.A.; Ehlmann, B. L.; Minson, Sarah E.; Arvidson, R. E.; Ayoub, F.; Fraeman, A. A.; Ewing, R. C.; Bridges, N. T.

2017-01-01

During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single scattering albedo spectra and a Markov-Chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that XRD-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are non-unique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold dunes, consistent with a mafic enrichment of sands with cumulative transport distance by sorting of olivine, pyroxene, and plagioclase grains during aeolian saltation. Furthermore, the large variations in Fe and Mg abundances (~20 wt%) at the Bagnold Dunes suggest that compositional variability induced by wind sorting may be enhanced by local mixing with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones.

Mineralogy of Eolian Sands at Gale Crater

NASA Technical Reports Server (NTRS)

Achilles, C. N.; Vaniman, D. T.; Blake, D. F.; Bristow, T. F.; Rampe, E. B.; Ming, D. W.; Chipera, S. J.; Morris, R. V.; Morrison, S. M.; Downs, R. T.;

Which Came First?

NASA Image and Video Library

2015-09-16

The workings of the Martian winds are visible in this image of sand dunes trapped inside an unnamed crater in southern Terra Cimmeria captured by NASA Mars Reconnaissance Orbiter spacecraft. Many of the craters in the Southern highlands of Mars contain sand dunes, and HiRISE is still in the process of mapping these dunes and determining how active they are today. So far, the dunes in these craters appear to be a mixed bunch, with some dunes actively advancing while others seem to be frozen in place. This image will be compared to a previous picture, to see how these dunes have changed since 2008. The sand dunes are the large, branched ridges and dark patches that are conspicuous against the bright background, particularly in the northwest corner of our picture. There are also signs of two other wind-related processes: smaller, brighter ridges line the floor of the crater in regularly spaced rows. These are also windblown deposits, mysterious "transverse aeolian ridges" or TARs that are more common in the Martian tropics. Faint, irregular dark lines cross the dunes and the TARs, marking the tracks of dust devils that vacuum the surface during southern summer. So, which came first? We can untangle the history of these processes by looking at the picture more closely. Over most of the image, it is obvious that the dark sand dunes bury the bright TARs, meaning that the sand dunes are younger than the TARs. But this relationship is not so clear for the southernmost dune we see in this picture. Here, the TARs look like they extend into the dune and merge with ripples on the dune's surface, suggesting that the TARs might be younger than the dunes. The question can be resolved by carefully examining an enhanced color cutout. The TARs are brighter and redder than the sand dunes and this color persists on the crests of the TARs as the sand encroaches, burying the valleys first and then the slopes and finally the TAR crests. This tells us that the unusual appearance of the dune margin is caused by burial and exposure of the older TARs by the younger sand. Finally, you can trace the tracks of dust devils crossing over the dunes, telling us that they are younger than the dunes. So, first came the TARs, next the dunes, and last the dust devils -- probably within the last few months! http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia19941

Demography and monitoring of Welsh's milkweed (Asclepias welshii) at Coral Pink Sand Dunes

Treesearch

Brent C. Palmer; L. Armstrong

2001-01-01

Results are presented of a 12-year monitoring program on the Coral Pink Sand Dunes and Sand Hills populations of the threatened Welsh's milkweed, Asclepias welshii N & P Holmgren. The species is an early sera1 member of the dune flora, colonizing blowouts and advancing with shifting dunes. When an area stabilizes and other vegetation encroaches, A. welshii is...

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-04-01

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

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

PubMed Central

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

2016-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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

Relating sedimentary processes in the Bagnold Dunes to the development of crater basin aeolian stratification

NASA Astrophysics Data System (ADS)

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M. D.; Stein, N.; Rubin, D. M.; Sullivan, R. J., Jr.; Banham, S.; Thomas, N. M.; Lamb, M. P.; Gupta, S.; Fischer, W. W.

2017-12-01

Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under martian conditions. Exploration of the Bagnold Dunes by the Curiosity Rover in Gale Crater, Mars provided the first opportunity to make in situ observations of martian dunes from the grain-to-dune scale. We used the suite of cameras on Curiosity, including Navigation Camera, Mast Camera, and Mars Hand Lens Imager. We measured grainsize and identified sedimentary processes similar to processes on terrestrial dunes, such as grainfall, grainflow, and impact ripples. Impact ripple grainsize had a median of 0.103 mm. Measurements of grainflow slopes indicate a relaxation angle of 29° and grainfall slopes indicate critical angles of at least 32°. Dissimilar to terrestrial dunes, large, meter-scale ripples form on all slopes of the dunes. The ripples form both sinuous and linear crestlines, have symmetric and asymmetric profiles, range in height between 12cm and 28cm, and host grainfall, grainflow, and impact ripples. The largest ripples are interpreted to integrate the annual wind cycle within the crater, whereas smaller large ripples and impact ripples form or reorient to shorter term wind cycling. Assessment of sedimentary processes in combination with dune type across the Bagnold Dunes shows that dune-field pattern development in response to a complex crater-basin wind regime dictates the distribution of geomorphic processes. From a stratigraphic perspective, zones of highest potential accumulation correlate with zones of wind convergence, which produce complex winds and dune field patterns thereby limiting the potential distribution of types of aeolian stratification preserved within crater basins.

Grain-size variations on a longitudinal dune and a barchan dune

NASA Astrophysics Data System (ADS)

Watson, Andrew

1986-01-01

The grain-size characteristics of the sand upon two dunes—a 40 m high longitudinal dune in the central Namib Desert and a 6.0 m high barchan in the Jafurah sand sea of Saudi Arabia—vary with position on the dunes. On the longitudinal dune, median grain size decreases, sorting improves and the grain-size distributions are less skewed and more normalized toward the crest. Though sand at the windward toe is distinct, elsewhere on the dune the changes in grain-size characteristics are gradual. An abrupt change in grain size and sorting near the crest—as described by Bagnold (1941, pp. 226-229)—is not well represented on this dune. Coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest. Avalanching down slipfaces at the crest acts only as a supplementary grading mechanism. On the barchan dune median grain size also decreases near the crest, but sorting becomes poorer, though the grain-size distributions are more symmetric and more normalized. The dune profile is a Gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling. Grain size increases and sorting improves down the dune's slipface. However, this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion. On both dunes, height and morphology appear to influence significantly the grain-size characteristics.

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-08-08

ISS013-E-65526 (8 Aug. 2006) --- Issaouane Dune Sea, Eastern Algeria is featured in this image photographed by an Expedition 13 crewmember on the International Space Station. This view from one of the smaller dune seas in the central Sahara shows the complex but regular patterns produced by winds in deserts where abundant sand is available. Geologists now know that dune seas (also called ergs) comprise at least three orders of dune size. In this image the largest and oldest appear here as chains oriented about 60 degrees apart, that is, one oriented almost north-south, the other southwest-northeast. The "streets" between the dune chains (also called mega-dunes) are swept clean of sand in places, revealing the original surface, with light colored muds and salt derived from very occasional rains. The chains have probably taken hundreds of thousands of years to accumulate, starting when the Sahara began to become significantly dry roughly 2.5 million years ago. Rivers became smaller, failed to reach the sea and deposited their sand load in the desert. Wind did the rest, blowing the sand into aerodynamic dune forms. According to scientists, chain trends coincide with two of the four major trends identified in the Great Eastern Sand Sea immediately to the north. Each trend likely implies a different formative wind direction--attesting to the climate shifts that have occurred since sand began to accumulate in the central Sahara. Smaller dunes are superimposed on the mega-dunes. Sinuous crest lines are the mesoscale (intermediate in size) forms, forming octopus-like crests, especially evident as the arms of star dunes. Whereas the mega-dunes are apparently stationary, studies based on aerial photographs in other parts of the world show that these dune crests move in the course of decades. The smallest dunes appear in patches on the eastern sides of the mega-dunes as a tracery of closely spaced crests. Small dunes move fast and reform quickly as stronger winds shift with the seasons. Sand grains are blown continuously from upwind dunes, across the dune-free flats. Small dunes form when the grains slow down and accumulate at the next large dune. The small dunes ride up and over the backs of the mega- and meso-dunes. Interestingly the crest orientation of the small dunes is different from that of the mesoscale dunes throughout the image. This is a common effect of wind direction shifting locally depending on dune height: the increased friction caused by larger dunes causes formative winds to blow to the left of the (weaker) winds that form the small dunes. The friction effect of larger dunes is to the right in the southern hemisphere, well illustrated on the coast of the Namib Desert.

High Dune is First Martian Dune Studied up Close

NASA Image and Video Library

2015-12-10

The rippled surface of the first Martian sand dune ever studied up close fills this view of "High Dune" from the Mast Camera (Mastcam) on NASA's Curiosity rover. This site is part of the "Bagnold Dunes" field along the northwestern flank of Mount Sharp. The dunes are active, migrating up to about one yard or meter per year. The component images of this mosaic view were taken on Nov. 27, 2015, during the 1,176th Martian day, or sol, of Curiosity's work on Mars. The scene is presented with a color adjustment that approximates white balancing, to resemble how the sand would appear under daytime lighting conditions on Earth. The annotated version includes superimposed scale bars of 30 centimeters (1 foot) in the foreground and 100 centimeters (3.3 feet) in the middle distance. Malin Space Science Systems, San Diego, built and operates Curiosity's Mastcam. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, built the rover and manages the project for NASA's Science Mission Directorate, Washington. http://photojournal.jpl.nasa.gov/catalog/PIA20168

Earth observations taken from the shuttle Challenger during STS-41C

NASA Image and Video Library

2009-06-25

41C-31-990 (6-13 April 1984) --- Southwestern Algeria's Erg Chech shows long lines of parallel sand dunes called siefs. The Erg (sand desert) is in a remote (26.5 degrees north by 1.5 degrees west) of harsh desert, uninhabited and rarely visited. These parallel sand dunes are about 100 miles in length and 5 to 10 miles apart and are found in very few areas of the Earth. Most sand dunes are traverse dunes, or perpendicular to the general direction of the wind.

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.

Sand dune of Ruby, Arizona, an anthropogenically created biodiversity hotspot for wasps and their velvet ant parasitoids

Treesearch

Justin O. Schmidt

2013-01-01

A large artificial sand dune composed of finely crushed mine tailings was produced by deep mining operations at Ruby, Arizona. Today, the ghost town of Ruby is an important historical location and biodiversity refuge, with the newly formed dune forming the core of the refuge. The dune provides ideal nesting habitat for at least 13 species of sand-loving wasps,...

Exploring the Sandy Province of Herschel Crater

NASA Image and Video Library

2017-09-04

This view from NASA's Mars Reconnaissance Orbiter shows the downwind stretches of a sand sheet in central part of the much larger Herschel Crater. This sandy province began kilometers upwind in a string of barchan sand dunes. As the north-to-south blowing wind weakened downwind, it could no longer fashion the sand into dunes but rather into amorphously-shaped sand sheets. While perhaps not awe-inspiringly beautiful, sand sheets can tell us about Mars' current and past environmental conditions as a piece of the puzzle for understanding habitability. Having dunes upwind of sheets is the opposite situation Earth has, where upwind sand sheets evolve downwind into sand dunes. This mystery is receiving ongoing research to to understand these sandy differences between Earth and Mars. https://photojournal.jpl.nasa.gov/catalog/PIA21933

Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf

USGS Publications Warehouse

Correggiari, A.; Field, M.E.; Trincardi, F.

1996-01-01

The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form. We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20-24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.

Global map of Titan's dune fields

NASA Astrophysics Data System (ADS)

Le Corre, L.; Le Mouélic, S.; Sotin, C.; Barnes, J. W.; Brown, R. H.; Baines, K.; Buratti, B.; Clark, R.; Nicholson, P.

2008-09-01

Introduction Methane is the second major constituent of Titan's atmosphere; but it should be totally removed at least in ten million years by photochemistry in the stratosphere and condensation in the troposphere [1]. The first process produces hydrocarbons which form the haze and can condensate onto the surface. The second process causes methane rains on the surface, which carve channels networks. The loss of methane is possibly balanced by outgassing during cryovolcanic event [2]. But hydrocarbons grains deposited onto the surface cannot be recycled. They may be stored in the dunes [3], which were first seen by SAR (Synthetic Aperture Radar) [4]. We focus our study on the mapping of the dune fields in order to determine their global distribution. The aim is to constrain the amount of hydrocarbon material existing in the dunes, and to relate it to the duration of the methane cycle. Data from the Visual and Infrared Mapping Spectrometer (VIMS) and RADAR instruments onboard Cassini spacecraft can be used to map Titan's surface. Infrared images, which are mainly sensitive to composition and grain size, are very complementary to the microwave measurements which depend mainly on roughness and topography. We used spectral criteria after empirical correction of aerosols to map the distribution of heterogeneous units on Titan [5]. These units are compared with SAR images in overlapping regions. Titan's surface mosaics with VIMS VIMS probes the first ten of microns of the ground in seven narrow atmospheric windows in the 0.88 to 5.11 μm wavelength range. We built infrared mosaics with cubes sorted by spatial resolution, by keeping cubes corresponding to favorable observing conditions (incidence, emergence, phase and time exposure). Band ratios were computed and combined in false color composite images (red as 1.59/1.27-μm, green as 2.03/1.27-μm and blue as 1.27/1.08-μm). Band ratios are useful to minimize the effect of illuminating conditions and albedo variations [6]. Mosaics of Titan's surface were created using images acquired during 42 flybys from Ta (October 26th 2004) to T42 (March 25th 2008). These images have been integrated into a Geographic Information System (GIS). Global maps of band ratios appear fuzzy at high latitudes due to a low spatial resolution and to the presence of haze and clouds. The unfavorable observing geometry, with high incidence angles, induces a very strong scattering by the aerosols in these regions. On the contrary, equatorial and mid-latitudes regions have been covered at a medium resolution, in better observing conditions. In our color composites, most of Titan surface appears either in brown units, bluish units or bright units. We observed that brown units cover 18% of the whole Titan's surface and are found in equatorial regions. Dark blue units cover roughly 2% of Titan's surface. They are systematically associated with bright terrains and are never found isolated within brown units (Fig. 1a). Dune patterns were first observed in the infrared with VIMS during the closest approach at T4 and T20 flybys [7, 8]. The detailed study of dune fields by [8] shows that dune patterns are found mainly in brown units and interdunes can account for the observed spectral variability. Dunes with Radar SAR dataset We also use the RADAR data in SAR mode, mainly sensitive to roughness, surface topography and dielectric constant variations. It is independent of solar light conditions and of the presence of clouds. We retrieved the radar swaths from Ta to T25 (February 22nd 2007) flybys from the PDS website and reprojected the data using the ISIS2 software. The spatial resolution of the SAR images allows the direct imaging of the dunes. Most of Titan's dunes appear longitudinal and resemble terrestrial dunes, such as the ones found in Namibia [4]. Detailed morphologic analysis was performed in [9], who inferred a dominant wind eastward to account for their formation. Two kinds of dunes have been observed: sand seas and small dunes in low sand supply zones. Most of the aeolian sand deposits are found in sand seas. In addition, isolated groups of "cat scratches", very sinuous short dunes [9] and sand sheets [10] (visible as dark uniform terrains) are recognized. Their emplacement is most probably related to the available sand supply. Comparison of infrared and SAR units Sand seas and small dunes match different kind of terrains in the infrared. Radar dune fields boundaries in the infrared. The dune fields in SAR images generally end at the limit between infrared brown and bright units (Fig. 1b and 1c). Dunes can also be found on dark blue terrains as seen by [7] and [11]. 82% of SAR dunes are located in brown units and 4.5% in dark blue units. The remnant dunes corresponding to "cat scratches" or not well defined dune fields appear in infrared bright units as isolated patches. These dunes may form with a low sand supply, thus VIMS detects a bright terrain because of the lower resolution than SAR. It could account for some of the 13.5% radar dunes found on bright areas. It should be noted that the limit between SAR dunes and brown units is sometimes shifted by about 20 km. This could be due to the obliquity and spin rate of Titan, which are not taken into account in our georeferenced images [12]. An accurate model of Titan obliquity and spin rate would be needed to correct this effect. But yet, there is a significant overlapping between VIMS brown units and dunes seen with the RADAR at global scale. The relationship seems to be more complex for the dark blue terrains, since dunes overlap this unit or are stopped at the border. Dark blue units may correspond to an aeolian deposit younger than the dunes [6]. By using a mean height of 150 m for the dunes [3, 10] and an average thickness of 20 m [3], we find a total amount of dune material in the brown units of 3.01 105 km3. This is consistent with the estimation from [3]. Conclusion From the global mapping, we inferred that dunes in the RADAR data are highly correlated with brown infrared terrains, and can overlap dark blue areas. Observations of brown infrared terrains by VIMS will complete the dune fields coverage found by SAR: the total SAR surface coverage at the end of the extended mission will be ~40%, whereas VIMS will achieve a near global coverage at 15-20 km/pixel in average. Therefore, the integration of both datasets will improve the estimation of amount of hydrocarbons present in solid state on Titan. References [1] Atreya, S. K. et al. (2006) PSS, 54, 1177-1187. [2] Sotin, C. et al. (2005) Science, 435, 786-789. [3] Lorenz, R. D. et al. (2008), GRL, 35, L02206. [4] Lorenz, R. D. et al. (2006) Science, 312, 724-727. [5] Le Mouélic, S. et al. (2008) LPSC XXXIX, abstract 1730. [6] Le Mouélic, S. et al. (2008) JGR, 113, E04003. [7] Barnes, J. W. et al. (2007) Icarus, 186, 242-258. [8] Barnes, J. W. et al. (2008) Icarus, 195, 400-414. [9] Radebaugh, J. et al. (2008) Icarus, 194, 690-703. [10] Lunine, J. I. et al. (2008) Icarus, 195, 415-433. [11] Soderblom, L. A. et al. (2007) PSS, 55, 2025-2036. [12] Stiles, B. W. et al (2008) The Astronomical Journal, 135, 1669-1680.

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

USGS Publications Warehouse

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

2007-01-01

Visible and Near-Infrared (VNIR) through Short Wavelength Infrared (SWIR) (0.4-2.5????m) AVIRIS data, along with laboratory spectral measurements and analyses of field samples, were used to characterize grain size variations in aeolian gypsum deposits across barchan-transverse, parabolic, and barchan dunes at White Sands, New Mexico, USA. All field samples contained a mineralogy of ?????100% gypsum. In order to document grain size variations at White Sands, surficial gypsum samples were collected along three Transects parallel to the prevailing downwind direction. Grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621????m, which were subjected to spectral measurements. Absorption band depths of the size fractions were determined after applying an automated continuum-removal procedure to each spectrum. Then, the relationship between absorption band depth and gypsum size fraction was established using a linear regression. Three software processing steps were carried out to measure the grain size variations of gypsum in the Dune Area using AVIRIS data. AVIRIS mapping results, field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits. In contrast, the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits. Based on laboratory estimates, a representative barchan-transverse dune (Transect 1) has a mean grain size of 1.16 ??{symbol} (449????m). The error bar results show that the error ranges from - 50 to + 50????m. Mean grain size for a representative parabolic dune (Transect 2) is 1.51 ??{symbol} (352????m), and 1.52 ??{symbol} (347????m) for a representative barchan dune (Transect 3). T-test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas. The t-test results also show that there are no significant differences between modeled and laboratory-measured grain size values. Hyperspectral grain size modeling can help to determine dynamic processes shaping the formation of the dunes such as wind directions, and the relative strengths of winds through time. This has implications for studying such processes on other planetary landforms that have mineralogy with unique absorption bands in VNIR-SWIR hyperspectral data. ?? 2006 Elsevier B.V. All rights reserved.

Sedimentary differentiation of aeolian grains at the White Sands National Monument, New Mexico, USA

NASA Astrophysics Data System (ADS)

Fenton, Lori K.; Bishop, Janice L.; King, Sara; Lafuente, Barbara; Horgan, Briony; Bustos, David; Sarrazin, Philippe

2017-06-01

Gypsum (CaSO4·2H2O) has been identified as a major component of part of Olympia Undae in the northern polar region of Mars, along with the mafic minerals more typical of Martian dune fields. The source and age of the gypsum is disputed, with the proposed explanations having vastly different implications for Mars' geological history. Furthermore, the transport of low density gypsum grains relative to and concurrently with denser grains has yet to be investigated in an aeolian setting. To address this knowledge gap, we performed a field study at White Sands National Monument (WSNM) in New Mexico, USA. Although gypsum dominates the bulk of the dune field, a dolomite-rich [CaMg(CO3)2] transport pathway along the northern border of WSNM provides a suitable analog site to study the transport of gypsum grains relative to the somewhat harder and denser carbonate grains. We collected samples along the stoss slope of a dune and on two coarse-grained ripples at the upwind margin of the dune field where minerals other than gypsum were most common. For comparison, additional samples were taken along the stoss slope of a dune outside the dolomite transport pathway, in the center of the dune field. Visible and near-infrared (VNIR), X-ray powder diffraction (XRD), and Raman analyses of different sample size fractions reveal that dolomite is only prevalent in grains larger than ∼1 mm. Other minerals, most notably calcite, are also present in smaller quantities among the coarse grains. The abundance of these coarse grains, relative to gypsum grains of the same size, drops off sharply at the upwind margin of the dune field. In contrast, gypsum dominated the finer fraction (<∼1 mm) at all sample sites, displaying no spatial variation. Estimates of sediment fluxes indicate that, although mineralogical differentiation of wind-transported grains occurs gradually in creep, the process is much more rapid when winds are strong enough to saltate the ⩾1 mm grains. The observed grain segregation is consistent with the WSNM dune field formative friction velocity (0.39 m/s) proposed by Jerolmack et al. (2011): winds significantly weaker than this value would not lift the large grains into differentiation-inducing saltation, whereas the observed differentiated trend would be obliterated by significantly stronger winds. When applied to Olympia Undae, a similar sediment flux analysis suggests that the strongest winds modeled by the Mars Climate Database (MCD) are consistent with the observed concentration of gypsum at dune crests. Density-driven differentiation in transport should not influence sediment fluxes of finer grains (<1 mm) as strongly on Earth, suggesting that the high ratio of fine gypsum grains to other minerals at WSNM is caused by a relatively high production and/or abrasion rate of gypsum sand. The observed preferential transport of coarse-grained gypsum in the dune field conceals a broader range of coarse-grained minerals present on Alkali Flat, contributing to the problem that mineralogy determined through both remote sensing of dune fields and analysis of dune foresets does not fully represent that of the source regions. Unlike quartz, the concentration of gypsum in WSNM occurs not because it is more resistant to weathering and erosion than other minerals, but rather because it is more readily produced (in the case of finer grains) and transported (in the case of coarser grains) than other minerals present in the region.

Stratigraphic Architecture of Aeolian Dune Interactions

NASA Astrophysics Data System (ADS)

Brothers, S. C.; Kocurek, G.

2015-12-01

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

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations.

PubMed

Ehlmann, B L; Edgett, K S; Sutter, B; Achilles, C N; Litvak, M L; Lapotre, M G A; Sullivan, R; Fraeman, A A; Arvidson, R E; Blake, D F; Bridges, N T; Conrad, P G; Cousin, A; Downs, R T; Gabriel, T S J; Gellert, R; Hamilton, V E; Hardgrove, C; Johnson, J R; Kuhn, S; Mahaffy, P R; Maurice, S; McHenry, M; Meslin, P-Y; Ming, D W; Minitti, M E; Morookian, J M; Morris, R V; O'Connell-Cooper, C D; Pinet, P C; Rowland, S K; Schröder, S; Siebach, K L; Stein, N T; Thompson, L M; Vaniman, D T; Vasavada, A R; Wellington, D F; Wiens, R C; Yen, A S

2017-12-01

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H 2 O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H 2 O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H 2 O.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

NASA Astrophysics Data System (ADS)

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.; Achilles, C. N.; Litvak, M. L.; Lapotre, M. G. A.; Sullivan, R.; Fraeman, A. A.; Arvidson, R. E.; Blake, D. F.; Bridges, N. T.; Conrad, P. G.; Cousin, A.; Downs, R. T.; Gabriel, T. S. J.; Gellert, R.; Hamilton, V. E.; Hardgrove, C.; Johnson, J. R.; Kuhn, S.; Mahaffy, P. R.; Maurice, S.; McHenry, M.; Meslin, P.-Y.; Ming, D. W.; Minitti, M. E.; Morookian, J. M.; Morris, R. V.; O'Connell-Cooper, C. D.; Pinet, P. C.; Rowland, S. K.; Schröder, S.; Siebach, K. L.; Stein, N. T.; Thompson, L. M.; Vaniman, D. T.; Vasavada, A. R.; Wellington, D. F.; Wiens, R. C.; Yen, A. S.

2017-12-01

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized ( 45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H2O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O.

Microbial Characterization of Qatari Barchan Sand Dunes

PubMed Central

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

2016-01-01

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

Data Analysis and Synthesis for the ONR Undersea Sand Dunes in the South China Sea Field Experiments

DTIC Science & Technology

2015-09-30

understanding of coastal oceanography by means of applying simple dynamical theories to high-quality observations obtained in the field. My primary...area of expertise is physical oceanography , but I also enjoy collaborating with biological, chemical, acoustical, and optical oceanographers to work... oceanography , and impact of the bottom configuration and physical oceanography on acoustic propagation. • The space and time scales of the dune

Earth Observations taken by the Expedition 15 Crew

NASA Image and Video Library

2007-06-28

ISS015-E-15323 (27 June 2007) --- Part of Bechar Basin, Algeria is featured in this image photographed by an Expedition 15 crewmember on the International Space Station. The Bechar Basin of northwestern Algeria reaches depths of 8,000 meters, and is a producing hydrocarbon region. According to scientists, the basin was formed as Paleozoic (approximately 250-540 million years old) sedimentary layers were folded and faulted during much later collision of the continents of Africa and Europe during the Tertiary Period (approximately 2-65 million years ago). Hydrocarbon reservoirs are located within clastic (formed of variably-sized pieces of pre-existing rock) sedimentary rocks and fossilized coral reefs. Dark brown to tan folded ridges of these Paleozoic sedimentary layers extend across this view from top to bottom. Sand dunes are visible to the north, south, and west of the city of Bechar (gray-blue region to the left of the fold ridges) at center. Wadis (river channels) are dry most of the year in the arid climate of the region. Unconsolidated (loose) sands left in the channels by intermittent streams are transported by surface winds after the water is gone. This leads to the formation of individual dunes and larger dune fields (both bright tan in color) along the wadi courses, which also concentrate sands from other sources; dune fields are visible to the south of Bechar and at lower right. The oblique -- looking at an angle from the International Space Station, versus looking straight down - view of this photo accentuates cliff and dune shadows, providing a sense of the topography of the region.

Morphology, spatial pattern and sediment of Nitraria tangutorum nebkhas in barchans interdune areas at the southeast margin of the Badain Jaran Desert, China

NASA Astrophysics Data System (ADS)

Yang, YanYan; Liu, LianYou; Shi, PeiJun; Zhang, GuoMing; Qu, ZhiQiang; Tang, Yan; Lei, Jie; Wen, HaiMing; Xiong, YiYing; Wang, JingPu; Shen, LingLing

2015-03-01

To understand the characteristics of the nebkhas in barchan interdune areas, isolated barchan dunes at the southeast margin of the Badain Jaran Desert in China and Nitraria tangutorun nebkhas in the interdune areas were selected, and the morphometric parameters, spatial patterns, and granulometric characteristics of the nebkhas in various interdune zones were compared. According to the locations relative to barchan dunes, the interdune areas were divided into three zones: the windward interdune zone (Zw), the leeward interdune zone (Zl), and the horn interdune zone (Zh). The zone that is proximal to barchan dunes and has never been disturbed by barchan dunes was also selected (Zi). The morphometric parameters were measured through a satellite image and field investigation. The population density and spatial patterns were analyzed using the satellite image, and surface sediment samples of the nebkhas and barchan dunes were collected for grain size analysis. The morphometric parameters of Nitraria tangutorun nebkhas in the interdune zones differ significantly. The nebkhas in Zh are larger than those observed in the other zones, and the nebkhas are the smallest in Zl. In all of the zones, the long-axis orientation of the nebkhas is perpendicular to the prevailing wind direction. The population density of the nebkhas in Zw is relatively higher, whereas the density in Zh and Zl becomes obviously lower. The spatial distribution of nebkhas in all of the zones can be categorized as a dispersed pattern. The sediments of the nebkhas are coarsest in Zh and finest in Zl. In addition, the sediments of the nebkhas in all of the zones are finer than those of barchan dunes. The amount of sand captured by the nebkhas in the interdune areas is approximately 20% of the volume of barchan dunes. The variations of the nebkhas' sizes, spatial pattern and sediment are subjected to migration, flow field and sand transport of barchan dunes and sand accumulation with plant growth in the interdune areas, which suggest complex mutual interactions between barchan dunes and the nebkhas in the interdune areas.

Geochemical evidence for the provenance of aeolian deposits in the Qaidam Basin, Tibetan Plateau

NASA Astrophysics Data System (ADS)

Du, Shisong; Wu, Yongqiu; Tan, Lihua

2018-06-01

The main purpose of this study is to analyse the material source of different grain-size components of dune sand in the Qaidam Basin. We determined the trace and rare earth element (REE) compositions and Sr-Nd isotopic compositions of the coarse (75-500 μm) and fine (<75 μm) fractions of surface sediment samples. The comparison of the immobile trace element and REE compositions, Sr-Nd isotopic compositions and multidimensional scaling (MDS) results of the dune sands with those of different types of sediments in potential source areas revealed the following information. (1) The fine- and coarse-grained fractions of dune sands in the Qaidam Basin exhibit distinctly different elemental concentrations, elemental patterns and characteristic parameters of REE. Moreover, Sr-Nd isotopic differences also exist between different grain-size fractions of aeolian sand, which means that different grain-size fractions of these dune sands have different source areas. (2) The geochemical characteristics of the coarse particles of dune sand exhibit obvious regional heterogeneity and generally record a local origin derived from local fluvial sediments and alluvial/proluvial sediments. The coarse- and fine-grained dune sand in the southern Qaidam Basin mainly came from Kunlun Mountains, whereas the coarse- and fine-grained dune sand in the northeastern Qaidam Basin mainly came from Qilian Mountains. (3) The fine-grained fractions of sediments throughout the entire Qaidam Basin may have been affected by the input of foreign materials from the Tarim Basin.

Flowing Dunes of Shangri-La Denoised

NASA Image and Video Library

2016-09-07

This radar image of the Shangri-La Sand Sea on Titan from NASA's Cassini spacecraft shows hundreds of sand dunes are visible as dark lines snaking across the surface. These dunes display patterns of undulation and divergence around elevated mountains (which appear bright to the radar), thereby showing the direction of wind and sand transport on the surface. Sands being carried from left to right (west to east) cannot surmount the tallest obstacles; instead, they are directed through chutes and canyons between the tall features, evident in thin, blade-like, isolated dunes between bright some features. Once sands have passed around the obstacles, they resume their downwind course, at first collecting into small, patchy dunes and then organizing into larger, more pervasive linear forms, before being halted once again by obstacles. These patterns reveal the effects not only of wind -- perhaps even modern winds if the dunes are actively moving today -- but also the effects of underlying bedrock and surrounding topography. Dunes across the solar system aid in our understanding of underlying topography, winds and climate, past and present. Similar patterns can be seen in dunes of the Great Sandy Desert in Australia, where dunes undulate broadly across the uneven terrain and are halted at the margins of sand-trapping lakes. The dune orientations correlate generally with the direction of current trade winds, and reveal that winds must have been similar back when the dunes formed, during the Pleistocene glacial and interglacial periods. The image was taken by the Cassini Synthetic Aperture radar (SAR) on July 25, 2016 during the mission's 122nd targeted Titan encounter. The image has been modified by the denoising method described in A. Lucas, JGR:Planets (2014). http://photojournal.jpl.nasa.gov/catalog/PIA20711

Flowing Dunes of Shangri-La

NASA Image and Video Library

2016-09-07

The Shangri-La Sand Sea on Titan is shown in this image from the Synthetic Aperture radar (SAR) on NASA's Cassini spacecraft. Hundreds of sand dunes are visible as dark lines snaking across the surface. These dunes display patterns of undulation and divergence around elevated mountains (which appear bright to the radar), thereby showing the direction of wind and sand transport on the surface. Sands being carried from left to right (west to east) cannot surmount the tallest obstacles; instead, they are directed through chutes and canyons between the tall features, evident in thin, blade-like, isolated dunes between bright some features. Once sands have passed around the obstacles, they resume their downwind course, at first collecting into small, patchy dunes and then organizing into larger, more pervasive linear forms, before being halted once again by obstacles. These patterns reveal the effects not only of wind -- perhaps even modern winds if the dunes are actively moving today -- but also the effects of underlying bedrock and surrounding topography. Dunes across the solar system aid in our understanding of underlying topography, winds and climate, past and present. Similar patterns can be seen in dunes of the Great Sandy Desert in Australia, where dunes undulate broadly across the uneven terrain and are halted at the margins of sand-trapping lakes. The dune orientations correlate generally with the direction of current trade winds, and reveal that winds must have been similar back when the dunes formed, during the Pleistocene glacial and interglacial periods. An annotated version of this radar image is also available.at the Photojournal. North on Titan is up in the image. Radar illuminates the scene from upper right at a 27-degree incidence angle. http://photojournal.jpl.nasa.gov/catalog/PIA20710

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.

Depositional environments of some Pleistocene coastal terrace deposits, southwestern Oregon - case history of progradational beach and dune sequence.

USGS Publications Warehouse

Hunter, R.E.

1980-01-01

These deposits comprise a basal gravelly unit and 3 overlying sandy units, each with mud beds, a paleosol, or the modern soil in its uppermost part. The gravelly unit is interpreted as a progradational deposit. The main parts of the sandy units are made up of 1) a crossbedded sand facies, the dominant structure in which is medium-scale crossbedding (interpreted as the product of small eolian dunes), and 2) an irregularly bedded sand facies, which is locally pebbly and is dominated by scour-and-fill structures, interpreted as deposits of interdune ephemeral streams, ephemeral ponds, and wet to dry subaerial flats. The mud beds and paleosols represent times of temporary stabilization of the dune field.- from Author

78 FR 11981 - Special Regulations; Areas of the National Park System, Sleeping Bear Dunes National Lakeshore...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-21

... complex of coastal sand dunes, the Lakeshore features white sand beaches, steep bluffs reaching as high as... most notable feature--the ancient sand dunes--are products of wind, ice, and water action over... National Lakeshore'' (NPS Environmental Quality Division--May 2012), available for review at http://www.nps...

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

77 FR 11061 - Endangered and Threatened Wildlife and Plants; Proposed Endangered Status for the Dunes Sagebrush...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-24

... Agreement for the Lesser Prairie-Chicken (Tympanuchus pallidicinctus) and Sand Dune Lizard (Sceloporus... Conservation Agreement for the Lesser Prairie-Chicken (Tympanuchus pallidicinctus) and Sand Dune Lizard...

Backscatter modelling and inversion from Cassini/SAR data: Implications for Titan's sand seas properties and climatic conditions

NASA Astrophysics Data System (ADS)

Lucas, A.; Rodriguez, S.; Lemonnier, F.; Paillou, P.; Le Gall, A. A.; Narteau, C.

2015-12-01

Sand seas on Titan may reflect the present and past climatic conditions. Understanding the morphodynamics and physicochemical properties of Titan's dunes is therefore essential for a better comprehension of the climatic and geological history of the largest Saturn's moon. We derived quantitatively surface properties (texture, composition) from the modelling of microwave backscattered signal and Monte Carlo inversion of despeckled Cassini/SAR data over the equatorial sand seas. We show that dunes and inter-dunes have significantly different physical properties. Absorption is more efficient in the dunes compared to the inter-dunes. The inter-dunes are smoother with an higher dielectric constant than the dunes. Considering the composition, the inter-dunes are in between the dunes and the bright inselbergs, suggesting the presence of a shallow layer of sediment in between the dunes. Additionally potential secondary bedforms may have been detected. Implications for dune morphodynamics, sediment inventory and climatic conditions occurring on Titan will be discussed.

A study of global sand seas

USGS Publications Warehouse

McKee, Edwin D.

1979-01-01

The birth of the idea that led to this publication on "Global Sand Seas" dates back to the late 1920's. At that time I was engaged in a study of the Coconino Sandstone of Arizona's Grand Canyon. Considerable controversy existed then as to whether this sandstone was a subaqueous deposit or was composed of wind-formed dunes. It became apparent that definitive literature was sparse or lacking on types of dunes, global distribution of these types, the mechanics of their development, the precise nature of their internal structure of cross-stratificiation, and the relation of wind systems to these sand forms. Especially lacking were data on criteria that could confidently be used in the recognition of ancient dunes. The common denominator in this publication is eolian sand bodies. Although the book is concerned primarily with desert sand seas, the subject matter is not restricted to deserts; it includes many references to deposits of coastal sand and to sand bodies in humid climates. Nor does the book deal exclusively with dunes, which, according to most definitions, involve mounds or hills. Many references are made to sand sheets, sand stringers, and other types of sand deposits that have no prominent topographic expression. All sand bodies accumulated by the action of wind are discussed. Chapters A-J of this publication are primarily topical. Chapters cover the grain texture, the color, and the structure of modern dunes and other eolian sands. Special treatment is given to the relation of wind data to dune interpretation, the evolution of form in current-deposited sand bodies as determined from experimental studies, and the discriminant analysis technique for differentiating between coastal and inland desert sands. This topical part of the publication also includes an analysis of criteria used in ancient deposits to interpret their eolian genesis and a consideration of economic application of the principles described, including a discussion of potentials and problems associated with eolian hydrocarbon reservoirs. The final chapters present a discussion of the morphology and distribution of dunes as determined largely from Landsat images.Chapter K of the publication is devoted to descriptions of major sand seas based largely on thematic maps derived from Landsat (ERTS) mosaics. Although inclusion herein of the actual mosaics proved to be impractical, the maps derived from them do show the distribution and abundance of various dune types and the relations of these types to certain associated features, such as bedrock, water bodies, and juxtaposed dunes. Furthermore, sand roses included with each of these maps enable the user to draw conclusions on the probable relations of wind strength and direction to dune type in a particular area.Regional studies (chapter K) were a team effort. Analysis of the Landsat (ERTS) mosaics and mapping boundaries of individual dune types were by Carol Breed. Synthesis of the rather voluminous literature and preparation of abstracts covering it was by Camilla MacCauley. Actual preparation of maps was by Franci Lennartz and later by Sarah Andrews. The gathering of data on wind, the calculation of wind roses, and the interpretation of their relations to sand bodies were by Steven Fryberger, assisted by Gary Dean.

Effects of sand burial on the survival and growth of two shrubs dominant in different habitats of northern China.

PubMed

Qu, Hao; Zhao, Ha-Lin; Zhao, Xue-Yong; Zuo, Xiao-An; Wang, Shao-Kun; Chen, Min

2017-04-01

Plants that grow in dune ecosystems always suffer from sand burial. Shrubs play implications on the healthy functioning of dune ecosystems due to control blowing sand. However, the survival and growth responses of shrubs to sand burial remain poorly understood. The survival rate and seedling height of two shrubs (Artemisia halodendron and Lespedeza davurica) along with the soil properties under different burial depths were examined in order to reveal the causing ecophysiological attributes of sand burial on shrubs in the desertified region. It was found that A. halodendron can survive a burial depth of 6 cm greater than its seedling height, which is a dominant shrub in mobile dunes with intense burial, whereas a burial depth equivalent to three fourths of its seedling height is detrimental to L. davurica, which is dominant in fixed dunes with less burial. The reasons for the shrub death under sand burial were associated with the physical barrier to vertical growth and the reduction in photosynthetic area. In conclusion, A. halodendron can facilitate the stabilization of mobile dunes because of their high tolerance to the frequent and intensive sand burial, while L. davurica can be beneficial for the recovery process because of their higher survival rates under shallow burial following restoration of mobile dunes.

Namib Desert, Namibia, Africa

NASA Image and Video Library

1990-04-29

One of the driest regions on Earth, the Namib Desert, Namibia, Africa (23.0N, 15.0E) lies adjacent to the Atlantic coast but the upwelling oceanic water causes a very stable rainless atmosphere. The few local inland rivers do not reach the sea but instead, appear as long indentations where they penetrate the dune fields and end as small dry lakes. The vast dune fields are the result of sands deposited over millions of years by the stream flow.

Namib Desert, Namibia, Africa

NASA Technical Reports Server (NTRS)

1990-01-01

One of the driest regions on Earth, the Namib Desert, Namibia, Africa (23.0N, 15.0E) lies adjacent to the Atlantic coast but upwelling oceanic water causes a very stable rainless atmosphere. The few local inland rivers do not reach the sea but instead appear as long indentations where rivers penetrate the dune fields and end as small dry lakes. The vast dune fields are the result of sands deposited over millions of years by the stream flow.

Namib Desert, Namibia, Africa

NASA Technical Reports Server (NTRS)

1990-01-01

One of the driest regions on Earth, the Namib Desert, Namibia, Africa (23.0N, 15.0E) lies adjacent to the Atlantic coast but the upwelling oceanic water causes a very stable rainless atmosphere. The few local inland rivers do not reach the sea but instead, appear as long indentations where they penetrate the dune fields and end as small dry lakes. The vast dune fields are the result of sands deposited over millions of years by the stream flow.

Holocene coastal dune fields used as indicators of net littoral transport: West Coast, USA

USGS Publications Warehouse

Peterson, C.D.; Stock, E.; Hart, R.; Percy, D.; Hostetler, S.W.; Knott, J.R.

2010-01-01

Between Point Grenville, Washington, and Point Conception, California (1500 km distance) 21 dune fields record longshore transport in 20 littoral cells during the late Holocene. The direction of predominant littoral transport is established by relative positions of dune fields (north, central, or south) in 17 representative littoral cells. Dune field position is north of cell midpoints in northernmost Oregon and Washington, but is south of cell midpoints in southern Oregon and California. Downdrift sand trapping occurs at significant changes in shoreline angle and/or at bounding headlands that project at least 2.5 km seaward from the general coastal trend. Sand bypassing occurs around small headlands of less than 0.5 km in projection distance. A northward shift of the winter low-pressure center in the northeast Pacific Ocean is modeled from 11 ka to 0 ka. Nearshore current forcing in southern Oregon and northern California switched from northward in earliest Holocene time to southward in late Holocene time. The late Holocene (5-0 ka) is generally characterized by net northward littoral drift in northernmost Oregon and Washington and by net southward littoral drift in southernmost Oregon and California. A regional divergence of net transport direction in central Oregon, i.e. no net drift, is consistent with modeled wind and wave forcing at the present time (0 ka). ?? 2009 Elsevier B.V.

Do Sahara dunes make dust? Some dunes do and some dunes don't

NASA Astrophysics Data System (ADS)

Bristow, Charlie

2017-04-01

The Sahara desert is responsible for producing around half of the atmospheric mineral dust on Earth. While most of the Sahara has the potential to produce dust some areas have been identified using remote sensing as especially prolific dust sources such as the Bodélé Depression in Chad which is described as the dustiest place on Earth. Geomorphological analysis indicates that these areas are usually topographic lows, such as the Bodélé, as well as regions on the flanks of topographic highs. This view was challenged by Crouvi et al. (2012) who suggest that active sand dunes are the most frequent dust sources. In this paper we use an experimental dust chamber to generate dust from dune sediments collected from the crest of active sand dunes across the Sahara including samples from the Bodélé depression, as well as dune sands from Algeria, Egypt, Libya, Morocco and Tunisia. The experiments produced a wide range of results indicating that some dune sands, including those from the Bodélé produce much more dust than others.

Dynamic dune management, integrating objectives of nature development and coastal safety: Examples from the Netherlands

NASA Astrophysics Data System (ADS)

Arens, Sebastiaan M.; Mulder, Jan P. M.; Slings, Quirinus L.; Geelen, Luc H. W. T.; Damsma, Petra

2013-10-01

This paper discusses and compares results of management interventions to remobilise dunes and obtain more autonomous changes in foredunes resulting from a change in coastal defence policy. In recent decades, nature conservation managers tried to restore aeolian dynamics and dune mobility landward of foredunes to maintain threatened, rare pioneer species. Results indicate that destabilisation activities yielded an important increase of blowing sand and its effects on ecology but with a limited effect on the desired integral remobilization of dunes. Roots remaining in the sand after removal of vegetation and soil is one of the main problems. Follow up removal of roots for 3 to 5 years seems to be essential, but it is not clear whether the dunes will remain mobile in the long term. In 1990 the Dutch government decided to maintain the position of the coastline by artificial sand nourishment. An intensive management of the foredunes was no longer required. Consequently, natural processes in the foredunes revived, and the sediment budget of the beach-dune system changed. Two main types of responses are visible. In some areas, increased input of sand resulted in the development of embryonic dunes seaward of the former foredunes, leading to increased stabilisation of the former foredunes. In other areas, development of embryonic dunes was insignificant despite the increased sand input, but wind erosion features developed in the foredunes, and the environment was more dynamic. The reasons for the differences are not clear, and the interaction between shoreface, beach and dunes is still poorly understood. Until now, attempts to mobilise the inner dunes were independent of changes made to the foredunes. We argue that an integrated, dynamic approach to coastal management, taking account of all relevant functions (including safety and natural values) and the dune-beach system as a whole, may provide new and durable solutions. An integrated approach would ideally provide fresh sand to the system by sand nourishment; define a wide safety zone, which enables the transition zone of beach to foredunes to develop freely; reserve space for natural processes without restrictions; and stimulate natural redistribution of sand within the system and restore inland transport of sand by removing vegetation behind the foredunes. A long time scale (several decades) is needed for this approach to be successful.

Earth Observations taken by the Expedition 27 Crew

NASA Image and Video Library

2011-05-16

ISS027-E-034290 (16 May 2011) --- Ar Rub al Khali Sand Sea, Arabian Peninsula is featured in this image photographed by an Expedition 27 crew member on the International Space Station. The Ar Rub al Khali, also known as the “Empty Quarter”, is a large region of sand dunes and interdune flats known as a sand sea (or erg). This photograph highlights a part of the Ar Rub al Khali located close to its southeastern margin in the Sultanate of Oman. Reddish-brown, large linear sand dunes alternate with blue-gray interdune salt flats known as sabkhas at left. The major trend of the linear dunes is transverse to northwesterly trade winds that originate in Iraq (known as the Shamal winds). Formation of secondary barchan (crescent-shaped) and star dunes (dune crests in several directions originating from a single point, looking somewhat like a starfish from above) on the linear dunes is supported by southwesterly winds that occur during the monsoon season (Kharif winds). The long linear dunes begin to break up into isolated large star dunes to the northeast and east (right). This is likely a result of both wind pattern interactions and changes in the sand supply to the dunes. The Empty Quarter covers much of the south-central portion of the Arabian Peninsula, and with an area of approximately 660,000 square kilometers it is the largest continuous sand desert on Earth. The Empty Quarter is so called as the dominantly hyperarid climate and difficulty of travel through the dunes has not encouraged permanent settlement within the region. There is geological and archeological evidence to support cooler and wetter past climates in the region together with human settlement. This evidence includes exposed lakebed sediments, scattered stone tools, and the fossils of hippopotamus, water buffalo, and long-horned cattle.

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

USGS Publications Warehouse

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

2009-01-01

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

Earth observations taken by the Expedition Seven crew

NASA Image and Video Library

2003-09-21

ISS007-E-15177 (21 September 2003) --- This view, photographed by an Expedition 7 crewmember onboard the International Space Station (ISS), features a small part of the coastal dune field which is now protected as the Lencois Maranhenses National Park, on Brazil’s north coast, about 700 kilometers east of the Amazon River mouth. Persistent winds blow off the equatorial Atlantic Ocean onto Brazil from the east, driving white sand inland from 100 kilometers stretch of coast, to form a large field of dunes. The dark areas between the white dunes are fresh water ponds that draw fishermen to this newly established park.

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

NASA Astrophysics Data System (ADS)

Mahdavi, P.; Bergmeier, E.

2016-07-01

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

Effects of sand fences on coastal dune vegetation distribution

NASA Astrophysics Data System (ADS)

Grafals-Soto, Rosana

2012-04-01

Sand fences are important human adjustments modifying the morphology of developed shores. The effects of sand fences on sediment transport and deposition in their initial stages have been well studied, but little is known about the effect of deteriorated sand fences that have become partially buried low scale barriers within the dune, potentially benefiting vegetation growth by protecting it from onshore stress. Data on vegetation, topography and fence characteristics were gathered at three dune sites in Ocean City, New Jersey on September 2007 and March 2008 to evaluate the effect of fences within the dune on vegetation distribution. Variables include: distance landward of dune toe, degree of sheltering from onshore stressors, net change in surface elevation (deposition or erosion), vegetation diversity and density, presence of remnant fence, and distance landward of fence. Results for the studied environment reveal that 1) vegetation diversity or density does not increase near remnant fences because most remnants are lower than average vegetation height and can not provide shelter; but 2) vegetation distribution is related to topographic variables, such as degree of sheltering, that are most likely the result of sand accretion caused by fence deployment. Fence deployment that prioritizes the creation of topographically diverse dunes within a restricted space may increase the diversity and density of the vegetation, and the resilience and value of developed dunes. Managers should consider the benefits of using sand fences on appropriately wide beaches to create a protective dune that is also diverse, functional and better able to adapt to change.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

PubMed Central

Edgett, K. S.; Sutter, B.; Achilles, C. N.; Litvak, M. L.; Lapotre, M. G. A.; Sullivan, R.; Fraeman, A. A.; Arvidson, R. E.; Blake, D. F.; Bridges, N. T.; Conrad, P. G.; Cousin, A.; Downs, R. T.; Gabriel, T. S. J.; Gellert, R.; Hamilton, V. E.; Hardgrove, C.; Johnson, J. R.; Kuhn, S.; Mahaffy, P. R.; Maurice, S.; McHenry, M.; Meslin, P.‐Y.; Ming, D. W.; Minitti, M. E.; Morookian, J. M.; Morris, R. V.; O'Connell‐Cooper, C. D.; Pinet, P. C.; Rowland, S. K.; Schröder, S.; Siebach, K. L.; Stein, N. T.; Thompson, L. M.; Vaniman, D. T.; Vasavada, A. R.; Wellington, D. F.; Wiens, R. C.; Yen, A. S.

2017-01-01

Abstract The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45–500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust‐covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt‐sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse‐sieved fraction of Bagnold sands, corroborated by visible/near‐infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand‐sized fraction (represented by Bagnold) that are Si‐enriched, hydroxylated alteration products and/or H2O‐ or OH‐bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O. PMID:29497589

Aeolian dune sediment flux heterogeneity in Meridiani Planum, Mars

PubMed Central

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

2018-01-01

It is now known unambiguously that wind-driven bedform activity is occurring on the surface of Mars today, including early detections of active sand dunes in Meridiani Planum’s Endeavour crater. Many of these reports are only based on a few sets of observations of relatively isolated bedforms and lack regional context. Here, we investigate aeolian activity across central Meridiani Planum and test the hypothesis that dune sites surrounding Endeavour crater are also active and part of region-wide sediment migration driven by northwesterly winds. All 13 dune fields investigated clearly showed evidence for activity and the majority exhibited dune migration (average rates of 0.6 m/Earth-year). Observations indicate substantial geographic and temporal heterogeneity of dune crest fluxes across the area and per site. Locations with multiple time steps indicate dune sand fluxes can vary by a factor of five, providing evidence for short periods of rapid migration followed by near-stagnation. In contrast, measurements at other sites are nearly identical, indicating that some dunes are in a steady-state as they migrate. The observed sediment transport direction was consistent with a regional northeasterly-to-northwesterly wind regime, revealing more variations than were appreciated from earlier, more localized studies. Craters containing shallow, degraded, flat-floored interiors tended to have dunes with high sediment fluxes/activity, whereas local kilometer-scale topographic obstructions (e.g., central peaks, yardangs) were found to be inversely correlated with dune mobility. Finally, the previous, more limited detections of dune activity in Endeavour crater have been shown to be representative of a broader, region-wide pattern of dune motion. PMID:29576818

Aeolian dune sediment flux heterogeneity in Meridiani Planum, Mars.

PubMed

Chojnacki, Matthew; Urso, Anna; Fenton, Lori K; Michaels, Timothy I

2017-06-01

It is now known unambiguously that wind-driven bedform activity is occurring on the surface of Mars today, including early detections of active sand dunes in Meridiani Planum's Endeavour crater. Many of these reports are only based on a few sets of observations of relatively isolated bedforms and lack regional context. Here, we investigate aeolian activity across central Meridiani Planum and test the hypothesis that dune sites surrounding Endeavour crater are also active and part of region-wide sediment migration driven by northwesterly winds. All 13 dune fields investigated clearly showed evidence for activity and the majority exhibited dune migration (average rates of 0.6 m/Earth-year). Observations indicate substantial geographic and temporal heterogeneity of dune crest fluxes across the area and per site. Locations with multiple time steps indicate dune sand fluxes can vary by a factor of five, providing evidence for short periods of rapid migration followed by near-stagnation. In contrast, measurements at other sites are nearly identical, indicating that some dunes are in a steady-state as they migrate. The observed sediment transport direction was consistent with a regional northeasterly-to-northwesterly wind regime, revealing more variations than were appreciated from earlier, more localized studies. Craters containing shallow, degraded, flat-floored interiors tended to have dunes with high sediment fluxes/activity, whereas local kilometer-scale topographic obstructions (e.g., central peaks, yardangs) were found to be inversely correlated with dune mobility. Finally, the previous, more limited detections of dune activity in Endeavour crater have been shown to be representative of a broader, region-wide pattern of dune motion.

The physics of wind-blown sand and dust.

PubMed

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

2012-10-01

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

The physics of wind-blown sand and dust

NASA Astrophysics Data System (ADS)

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

2012-10-01

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

Exploring elements that influence stewardship in the eastern Lake Ontario dune and wetland area

Treesearch

Diane Kuehn; James Smahol

2010-01-01

Th e Eastern Lake Ontario Dune and Wetland Area (ELODWA) is a 17-mile stretch of sand dunes, wetlands, and woodlands along the eastern shore of Lake Ontario in New York State. Reductions in negative, visitor-caused impacts on the dunes (e.g., trampling of dune vegetation and sand erosion) are thought to be due in part to the extensive visitor education efforts of...

Origins of late- Pleistocene coastal dune sheets, Magdalena and Guerrero Negro, from continental shelf low-stand supply (70-20 ka), under conditions of southeast littoral- and eolian-sand transport, in Baja California Sur, Mexico

NASA Astrophysics Data System (ADS)

Peterson, Curt D.; Murillo-Jiménez, Janette M.; Stock, Errol; Price, David M.; Hostetler, Steve W.; Percy, David

2017-10-01

Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits.

Sand Dunes of Nili Patera in 3-D

NASA Technical Reports Server (NTRS)

2001-01-01

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

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

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

NASA Astrophysics Data System (ADS)

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

2008-03-01

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

Curiosity heads to active Martian dunes on This Week @NASA – November 20, 2015

NASA Image and Video Library

2015-11-20

NASA’s Curiosity rover is making an unscheduled stop on its way up Mount Sharp on Mars, for a close-up look at a collection of actively moving sand dunes. Images from orbit indicate that the Bagnold Dunes are migrating as much as about 3 feet per Earth year, and includes one particular dune that is about two-stories high and as broad as a football field. Researchers plan to have the rover take samples for analysis. No active dunes have ever been visited anywhere else in the solar system besides Earth. Also, Orion cone panels welded, Launch approaches for Cygnus, Student CubeSat onboard Cygnus, New crew access tower components and more!

Investigating Mars: Coprates Chasma

NASA Image and Video Library

2017-10-04

Coprates Chasma is one of the numerous canyons that make up Valles Marineris. The chasma stretches for 960 km (600 miles) from Melas Chasma to the west and Capri Chasma to the east. Landslide deposits, layered materials and sand dunes cover a large portion of the chasma floor. This image is located in eastern Coprates Chasma. The branching features near the bottom of the image are spurs of rock in the cliff face. The rock is more resistant to erosion that fine materials like sand and dust. Those materials are visible below the spurs, and then onto the canyon floor. Unlike the large landslide deposits, these small fans of material build up over time as the material above erodes. There are sand dunes along the edge of the fans in this image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 36294 Latitude: -14.7055 Longitude: 303.066 Instrument: VIS Captured: 2010-02-18 17:20 https://photojournal.jpl.nasa.gov/catalog/PIA21998

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

PubMed

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

2007-01-01

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

Biological soil crust formation under artificial vegetation effect and its properties in the Mugetan sandy land, northeastern Qinghai-Tibet Plateau

NASA Astrophysics Data System (ADS)

Li, Y. F.; Li, Z. W.; Jia, Y. H.; Zhang, K.

2016-08-01

Mugetan sandy land is an inland desertification area of about 2,065 km2 in the northeastern Qinghai-Tibet Plateau. In the ecological restoration region of the Mugetan sandy land, different crusts have formed under the action of vegetation in three types of sandy soil (i.e. semi-fixed sand dune, fixed sand dune and ancient fixed aeolian sandy soil). The surface sand particle distribution, mineral component and vegetation composition of moving sand dunes and three types of sandy soil were studied in 2010-2014 to analyze the biological crust formation properties in the Mugetan sandy land and the effects of artificial vegetation. Results from this study revealed that artificial vegetation increases the clay content and encourages the development of biological curst. The fine particles (i.e. clay and humus) of the surface layer of the sand dunes increased more than 15% ten years after the artificial vegetation planting, and further increased up to 20% after one hundred years. The interaction of clay, humus, and other fine particles formed the soil aggregate structure. Meanwhile, under the vegetation effect from the microbes, algae, and moss, the sand particles stuck together and a biological crust formed. The interconnection of the partial crusts caused the sand dunes to gradually be fixed as a whole. Maintaining the integrity of the biological crust plays a vital role in fixing the sand under the crust. The precipitation and temperature conditions in the Mugetan sandy land could satisfy the demand of biological crust formation and development. If rational vegetation measures are adopted in the region with moving sand dunes, the lichen-moss-algae biological curst will form after ten years, but it still takes more time for the sand dunes to reach the nutrient enrichment state. If the biological curst is partly broken due to human activities, reasonable closure and restoration measures can shorten the restoration time of the biological crust.

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 particular over the last decade. There is an increased demand now of proper management and urgent conservation activities. Such measures first require an accurate understanding of dune properties/behaviour, assessment of anthropogenic factors affecting dune persistence and identification of coastal areas most sensitive to risk of destruction. This research has been undertaken with the support of National Science Fund - Ministry of Education, Youth and Science, (Republic of Bulgaria); Contract No: DNTS 02/11 from 29.09.2010 in the frame of a Joint Research Project between Bulgaria and Romania (2010-2012). The Ministry of Agriculture and Food (Republic of Bulgaria) is deeply acknowledged for providing the modern orthophoto and satellite image data needed and useful also for implementation of the project activities.

Earth Observations taken by the Expedition 35 Crew

NASA Image and Video Library

2013-03-25

ISS035-E-009454 (25 March 2013 ) --- One of the Expedition 35 crew members aboard the Earth-orbiting International Space Station used a 400 millimeter lens to photograph this view of the Great Sandy Desert, northwestern Australia on March 25. It bears evidence that much of Australia is arid. In northwest Australia the Great Sandy Desert holds great geological interest as a zone of active sand dune movement; strings of narrow lakes that represent very ancient rivers are also present. While a variety of dune forms can be seen in the region, this photograph features numerous linear dunes (approximately 25 meters high) separated in a roughly regular fashion (0.5?1.5 kilometers), and aligned closely to the winds that generated them?that is, winds blowing from east to west. Where linear dunes converge, dune confluences point downwind. One of the main visual impressions flying over such tropical dune fields ? both from an airplane or from the orbital station outpost?apart from the dune patterns are fire scars where thin vegetation has been burned off the dunes. The result is dunes that appear red from the underlying sand (image top left and top right), and darker areas where the vegetation remains (image lower left and lower right). The white feature visible down the center of the image is Lake Auld, the white color being the result of a cemented combination of fine clayey sediment and salts from evaporation of flood waters that occasionally fill the lake. Wider views of the area show that this lake is part of what is now known to have been a major, ancient river system in northwest Australia, draining northwest to the Indian Ocean. Such sinuous lakes are also known in Australia as ?river lakes.? Scientists point out that the river system is remarkably well preserved considering that the rivers were probably active in the Paleocene Epoch more than 55 million years ago. Australia then lay much further south in a wetter climatic zone. Today?s desert climate results in almost all rivers in the Great Sandy Desert being dry. Linear dunes can be seen entering Lake Auld on the east side. During flooding events, the sand of the dune noses is dispersed, becoming incorporated into the lake floor sediments together with muds and salts. During the long intervening dry periods, sand can blow across the lake floor to build thinner, smaller dunes visible as linear accumulations on the west side of the lake.

Agglomeration of a comprehensive model for the wind-driven sand transport at the Belgian Coast

NASA Astrophysics Data System (ADS)

Strypsteen, Glenn; Rauwoens, Pieter

2016-04-01

Although a lot of research has been done in the area of Aeolian transport, it is only during the last years that attention has been drawn to Aeolian transport in coastal areas. In these areas, the physical processes are more complex, due to a large number of transport limiting parameters. In this PhD-project, which is now in its early stage, a model will be developed which relates the wind-driven sand transport at the Belgian coast with physical parameters such as the wind speed, humidity and grain size of the sand, and the slope of beach and dune surface. For the first time, the interaction between beach and dune dynamics is studied at the Belgian coast. The Belgian coastline is only 67km long, but densely populated and therefore subject to coastal protection and safety. The coast mostly consists of sandy beaches and dikes. Although, still 33km of dunes exist, whose dynamics are far less understood. The overall research approach consists of three pathways: (i) field measurements, (ii) physical model tests, and (iii) numerical simulations. Firstly and most importantly, several field campaigns will provide accurate data of meteo-marine conditions, morphology, and sand transport events on a wide beach at the Belgian Coastline. The experimental set-up consists of a monitoring station, which will provide time series of vegetation cover, shoreline position, fetch distances, surficial moisture content, wind speed and direction and transport processes. The horizontal and vertical variability of the event scale Aeolian sand transport is analyzed with 8 MWAC sand traps. Two saltiphones register the intensity and variations of grain impacts over time. Two meteo-masts, each with four anemometers and one wind vane, provide quantitative measurements of the wind flow at different locations on the beach. Surficial moisture is measured with a moisture sensor. The topography measurements are typically done with laser techniques. To start, two sites are selected for measurement campaigns: one consists of the typical beach - dike system, a second site involves the dunes. First results of the measured data will be presented at the conference, together with a comparison to empirical correlations available in literature. Next to the field measurements, we propose physical model tests to provide data that is difficult to measure in the field. They will be used to determine the shear velocity and critical shear velocity in function of the transport flux. The effect of surficial moisture, vegetation and morphologic landforms will also be investigated in the model tests. Numerical simulations will provide a better insight in the physical processes of the Aeolian events and will be validated with the experimental results from the field campaigns and the physical model tests. The ultimate goal of the PhD is to obtain a sand transport model for the Belgian Coast, which can be used to assess the stability of nourishments in a quantitative matter, but it also will gain a better insight in the beach and dune interactions with the changing climate.

Mid-Holocene stabilization of the Karakum and Kyzylkum sand seas, central Asia - evidence from OSL ages

NASA Astrophysics Data System (ADS)

Maman, Shimrit; Tsoar, Haim; Blumberg, Dan G.; Porat, Naomi

2013-04-01

Sand seas (ergs) are large areas of deserts covered by wind-swept sand with varying degrees of vegetation cover. The Kyzylkum and Karakum ergs have accumulated in the Turan basin, northwest of the Hindu Kush range, and span from south Turkmenistan to the Syrdarya River in Kazakhstan. These ergs are dissected by the Amudarya River; To the north lies the Kyzylkum (red sands) and to the south the Karakum (black sands). This area is understudied, and little information has been published regarding the sands stabilization processes and deposition ages. This research focuses on identifying and mapping the ergs of Central Asia and analyzing the climate factors that set the dunes into motion and that stabilized them. A variety of spaceborne imagery with varying spectral and spatial resolutions was used. These images provide the basis for mapping sand distribution, dune forms, and vegetation cover. Wilson (1973) defined these ergs as active based on precipitation. Our results show that they are mostly stabilized, with an estimated area of ~260,000 sq. Km for Kara-Kum , and ~195,500 sq. Km for the Kyzyl-Kum . Meteorological analysis of wind and precipitation data indicate a low wind energy environment (DP<200) and sufficient rainfall (>100 mm) to which is essential for vegetation cover. We present the first optically stimulated luminescence (OSL) ages from the upper meter of 14 exposed sections from both ergs. The age of the sand samples was determined as ~Mid-Holocene by OSL, which provides an insight into past climate characteristics. These ages indicate extensive sand and dune stabilization during the Mid-Holocene. GIS analysis was performed in parallel with field work to validate and verify the results. The OSL ages, coupled with a compilation of regional palaeoclimatic data, corroborate and reinforce the previously proposed Mid-Holocene Liavliakan phase, known to reflect a warmer, wetter, less windy climate than persists today and that resulted in dune stabilization around Mid-Holocene. This study emphasizes the importance of regional climatic control on aeolian activity and is the first to show when these vast sand seas were stabilized.

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

NASA Astrophysics Data System (ADS)

Mader, Detlef

The spectrum of aeolian depositional subenvironments in the upper Middle Buntsandstein Karlstal-Schichten sequence in the Eifel North-South-zone at the western margin of the Mid-European Triassic Basin comprises trains of larger and higher narrowly-spaced dunes in sand seas, isolated smaller and lower widely-spaced dunes in floodplains and interdune playas, dry interdune sheet sands, damp interdune adhesive sandflats, wet interdune playa lakes, rainfall runoff watercourses and ephemeral channels cutting through the dune belt, and deflation gravel lag veneers. Distinction of aeolian and fluvial sediments within the succession of closely intertonguing wind- and water-laid deposits is possible by independent analysis of the conventional criteria and the more modern stratification styles. Thick cross-bedded aeolian sand sequences originate as barchanoid-type dunes which accumulate and migrate in the regime of narrow to wide unimodal southeasterly to southwesterly trade winds in low northern palaeolatitude in summer when the intertropical convergence zone is shifted to the north. The predominantly transverse-ridge dunes accrete mainly by grainfall and subcritical climbing of wind ripples, subordinately also by grainflow interfingering with grainfall. Horizontal-laminated aeolian sands form as sand sheets in dry interdune playas by subcritical migration of wind ripple trains, rarely also by plane bed accretion. Thin cross-bedded dune sands or horizontal-laminated aeolian sands capping fluvial cyclothems originate by deflation of emerged alluvial bar sands during low-water stages and subsequent accumulation of the winnowed sand as widely-spaced dunelets or chains of wind ripples in desiccated parts of the adjoining floodplain. The aeolian sand layers at the base of lacustrine cyclothems record migration of isolated little dunes across the dry playa floor at the beginning of a wetting-upwards cyclothem, with the sand deriving from deflation of fluvial incursions or representing residual sand not having been incorporated into larger dunes of the surrounding sand sea. Damp interdune deposits originate by trapping of loose sand that is blown across a moist playa surface as adhesion ripples and warts. The adhesion structures form both in aeolian sheet sand environments with increasing moisture of the substrate and on fluvial channel bars and stream bottoms with declining dampness during subaerial exposure. Wet interdune deposits originate by settling of suspension fines in periodic shallow lakes between the dunes following heavy ephemeral rainfall or forming by rising ground water table, and by aquatic redeposition of aeolian sand due to washout after atmospheric precipitation and alluvial invasion. Deflationary interdune deposits form by winnowing of the sandy matrix from fluvial sheet or bar conglomerates thereby leaving the dispersed gravel as more or less tightly-packed residual veneer on the degradation surface providing bed armour against further aeolian or aquatic erosion. Aeolian deposition is at the top of the Middle Buntsandstein rather rapidly terminated by fluvial inundation of the erg, erosion and partial resedimentation of dune sands and burial of the more or less degraded aeolian bedforms under a carpet of alluvial deposits. At the beginning of the Upper Buntsandstein, a change to semi-arid climate results in stabilization of emerging overbank plains and channels by palaeosol formation and plant growth thus completely inhibiting further accumulation of aeolian sands. The range of modes of origin of dune sands and interdune deposits, the spatial and temporal variability of their accumulation and preservation and the distribution of water-laid intercalations provide a base for independent evaluation of the dynamics of the aeolian system and its controls as well as for comparative assessment of the behaviour of the aeolian environment and the fluvial milieu in a system of intertonguing sand sea and river belt and of the mechanisms triggering and governing the interference pattern.

Monitoring Sand Sheets and Dunes

NASA Image and Video Library

2017-06-12

NASA's Mars Reconnaissance Orbiter (MRO) captured this crater featuring sand dunes and sand sheets on its floor. What are sand sheets? Snow fall on Earth is a good example of sand sheets: when it snows, the ground gets blanketed with up to a few meters of snow. The snow mantles the ground and "mimics" the underlying topography. Sand sheets likewise mantle the ground as a relatively thin deposit. This kind of environment has been monitored by HiRISE since 2007 to look for movement in the ripples covering the dunes and sheets. This is how scientists who study wind-blown sand can track the amount of sand moving through the area and possibly where the sand came from. Using the present environment is crucial to understanding the past: sand dunes, sheets, and ripples sometimes become preserved as sandstone and contain clues as to how they were deposited The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 25 centimeters (9.8 inches) per pixel (with 1 x 1 binning); objects on the order of 75 centimeters (29.5 inches) across are resolved.] North is up. https://photojournal.jpl.nasa.gov/catalog/PIA21757

Dune-dammed lakes of the Nebraska Sand Hills: Geologic setting and paleoclimatic implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 themore » 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.« less

On the Internal Structure of Mobile Barchan Sand Dunes due to Granular Processes

NASA Astrophysics Data System (ADS)

Vriend, N. M.; Arran, M.; Louge, M. Y.; Hay, A. G.; Valance, A.

2017-12-01

In this work, we visualize the internal structure of mobile barchan desert dunes at the avalanche scale. We reveal an intriguing history of dune building using a novel combination of local sand sampling and advanced geophysical techniques resulting in high resolution measurements of individual avalanche events. Due to progressive rebuilding, granular avalanching, erosional and depositional processes, these marching barchan dunes are reworked every few years and a characteristic zebra-pattern (figure 1a), orientated parallel to the slipface at the angle of repose, appears at regular intervals. We present scientific data on the structure obtained from several mobile barchan dunes of different sizes during recent desert field campaigns (2014, 2015, 2017) in a mobile barchan dune field in Qatar (25.01°N, 51.34°E in the AlWakrah municipality). The site has been equipped with a weather station and has been regularly visited by a multidisciplinary research team in recent years (e.g. [1]). By applying high-frequency (1200 MHz) ground penetrating radar (GPR) transects across the midline (figure 1b) we map the continuous evolution of this cross-bedding at high resolution deep within the dune. The GPR reveals a slope reduction of the slipface near the base of the dune; evidence of irregular wind reversals; and the presence of a harder aeolian cap around the crest and extending to the brink. The data is supplemented with granulometry from layers stabilized by dyed water injection and uncovered by excavating vertical walls perpendicular to old buried avalanches. We attribute visible differences in water penetration between adjacent layers to fine particle segregation processes in granular avalanches. This work was made possible by the support of NPRP grant 6-059-2-023 from the Qatar National Research Fund to MYL and AGH, and a Royal Society Dorothy Hodgkin Research Fellowship to NMV. We thank Jean-Luc Métayer for performing detailed particle size distribution measurements. References: [1] Louge, M. Y., A. Valance, A. Ould el-Moctar, J. Xu, A. G. Hay, and R. Richer, Temperature and humidity within a mobile barchan sand dune, implications for microbial survival, J. Geophys. Res. 118, doi:10.1002/2013JF002839 (2013).

Spectroscopy, morphometry, and photoclinometry of Titan's dunefields from Cassini/VIMS

USGS Publications Warehouse

Barnes, J.W.; Brown, R.H.; Soderblom, L.; Sotin, Christophe; Le, Mouelic S.; Rodriguez, S.; Jaumann, R.; Beyer, R.A.; Buratti, B.J.; Pitman, K.; Baines, K.H.; Clark, R.; Nicholson, P.

2008-01-01

Fine-resolution (500 m/pixel) Cassini Visual and Infrared Mapping Spectrometer (VIMS) T20 observations of Titan resolve that moon's sand dunes. The spectral variability in some dune regions shows that there are sand-free interdune areas, wherein VIMS spectra reveal the exposed dune substrate. The interdunes from T20 are, variously, materials that correspond to the equatorial bright, 5-??m-bright, and dark blue spectral units. Our observations show that an enigmatic "dark red" spectral unit seen in T5 in fact represents a macroscopic mixture with 5-??m-bright material and dunes as its spectral endmembers. Looking more broadly, similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes. The presence of interdunes indicates that Titan's dunefields are both mature and recently active. The spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of Titan; various organics are consistent with the dunes' measured reflectivity. We measure a mean dune spacing of 2.1 km, and find that the dunes are oriented on the average in an east-west direction, but angling up to 10?? from parallel to the equator in specific cases. Where no interdunes are present, we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m. These results pave the way for future exploration and interpretation of Titan's sand dunes. ?? 2007 Elsevier Inc. All rights reserved.

Thermophysical Variation within Dune Fields in the Southern Hemisphere of Mars

NASA Astrophysics Data System (ADS)

Courville, S. W.; Putzig, N. E.; Hoover, R.; Fenton, L. K.

2016-12-01

The activity and composition of Martian sand dunes, which are relatively young features, provide insight into the current and recent climate state of Mars. This study investigates small-scale variations of thermophysical properties within dune fields across the southern hemisphere of Mars to better understand near-surface composition. Previous morphological studies of southern hemisphere dune fields on Mars indicate a trend of decreasing activity with increasing latitude. We observe a corresponding trend in thermal properties. To investigate the thermal behavior of the dunes, we use apparent thermal inertia (ATI) derived from the Mars Odyssey's Thermal Emission Imaging System (THEMIS), which has a resolution of 100 meters per pixel. Overlaying THEMIS ATI values on images and digital terrain models from the High Resolution Imaging Science Experiment (HiRISE) allows us to compare ATI with small-scale dune morphology and slopes. In general, we observe three types of ATI behavior: (1) fields with exposed ground between dunes display lower ATI on the dunes themselves, consistent with dunes of relatively low thermal inertia resting upon a wind-resistant consolidated bed with higher thermal inertia; (2) fields with little or no inter-dune exposures exhibit ATI in dune troughs that is 100 tiu or more lower than along crests, counterintuitively suggesting that dune trough material is finer than that along dune crests; and (3) fields with highly degraded dunes typically display uniform ATI values, indicating that their properties do not vary laterally at the resolution of THEMIS images or vertically within a seasonal skin depth. These ATI behaviors correspond to the activity state of the dune field with type 1 being the most active and occurring toward the equator, while type 3 is the least active and found mostly at high southern latitudes. To consider alternative explanations for the ATI variation observed in Type 2 fields, we created thermal models of slopes, lateral mixtures of two particle sizes, and layering of two particle sizes. However, these models are unable to explain the observed ATI, suggesting that the composition and/or activity of these dunes are more complicated than allowed by two-component models.

Gypsum at Olympia Undae

NASA Technical Reports Server (NTRS)

2006-01-01

This Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) 'targeted image' shows a region of sand dunes surrounding the Martian north polar cap. CRISM, an instrument on NASA's Mars Reconnaissance Orbiter, acquired the image at 1811 UTC (2:11 p.m. EDT) on Oct. 1, 2006. The imaged site is near 80.0 degrees north latitude, 240.7 degrees east longitude. It covers an area about 12 kilometers (7.5 miles) square. At the center of the image, the spatial resolution is as good as 20 meters (65 feet) per pixel. The image was taken in 544 colors covering 0.36 to 3.92 micrometers.

CRISM's sister instrument on the Mars Express spacecraft, OMEGA, has spectrally mapped Mars at lower spatial resolution and discovered that several regions of the planet are rich in sulfate minerals formed by liquid water. Surprisingly, one of the sulfate-rich deposits is a part of the giant field of sand dunes surrounding the north polar cap. CRISM is remapping the dune field at about five times higher resolution than OMEGA, and imaging selected regions at 50 times higher resolution. This image is the first of the high-resolution images of the dune field.

This visualization includes two renderings of the data, both map-projected. The left images are false-color representations showing brightness of the surface at selected infrared wavelengths. The right images show strength of an absorption band at 1900 nanometers wavelength, which indicates the relative abundance of the sulfate mineral gypsum. Brighter areas have more gypsum, and darker areas have less gypsum. The bottom views are enlargements of the central part of the two versions of the image shown at top.

Gypsum is a light-colored, whitish mineral, so it was anticipated that gypsum-rich parts of the sand dunes would be light in color. In fact, there are light-colored areas in the left images, but the images of the gypsum absorption at right show that the light areas have only low gypsum abundance. The dark sand dunes contain most of the gypsum, which is particularly concentrated at the dune crests. CRISM's scientists are taking more high-resolution images of the dune fields to see if this pattern is prevalent, and to attempt to track down the source of the gypsum that makes an arid dune field so rich in minerals formed long ago in liquid water.

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.

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.

NASA's Jet Propulsion Laboratory, a division of the Califonia Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor and built the spacecraft.

Radar-visible wind streaks in the Altiplano of Bolivia

NASA Technical Reports Server (NTRS)

Greeley, R.; Christensen, P.

1984-01-01

Isolated knobs that are erosional remnants of central volcanoes or of folded rocks occur in several areas of the Altiplano are visible on both optical and images. The optically visible streaks occur in the immediate lee of the knobs, whereas the radar visible streaks occur in the zone downwind between the knobs. Aerial reconnaissance and field studies showed that the optically visible streaks consist of a series of small ( 100 m wide) barchan and barchanoid dunes, intradune sand sheets, and sand hummocks (large shrub coppice dunes) up to 15 m across and 5 m high. On LANDSAT images these features are poorly resolved but combine to form a bright streak. On the radar image, this area also appears brighter than the zone of the radar dark streak; evidently, the dunes and hummocks serve as radar reflectors. The radar dark streak consists of a relatively flat, smooth sand sheet which lacks organized aerolian bedforms, other than occasional ripples. Wind velocity profiles show a greater U value in the optically bright streak zone than in the radar dark streak.

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

NASA Astrophysics Data System (ADS)

Kilibarda, Zoran; Kilibarda, Vesna

2016-12-01

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

Geologic map of Great Sand Dunes National Park, Colorado

USGS Publications Warehouse

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

2016-10-20

Geologic mapping was begun after a range fire swept the area of what is now the Great Sand Dunes National Park in April 2000. The park spans an area of 437 square kilometers (or about 169 square miles), of which 98 percent is blanketed by sediment of Quaternary age, the Holocene and Pleistocene Epochs; hence, this geologic map of the Great Sand Dunes National Park is essentially a surficial geologic map. These surficial deposits are diverse and include sediment of eolian (windblown), alluvial (stream and sheetwash), palustrine (wetlands and marshes), lacustrine (lake), and mass-wasting (landslides) origin. Sediment of middle and late Holocene age, from about 8,000 years ago to the present, covers about 80 percent of the park.Fluctuations in groundwater level during Holocene time caused wetlands on the nearby lowland that bounds the park on the west to alternately expand and contract. These fluctuations controlled the stability or instability of eolian sand deposits on the downwind (eastern) side of the lowland. When groundwater level rose, playas became lakes, and wet or marshy areas formed in many places. When the water table rose, spring-fed streams filled their channels and valley floors with sediment. Conversely, when groundwater level fell, spring-fed streams incised their valley floors, and lakes, ponds, and marshes dried up and became sources of windblown sand.Discharge in streams draining the west flank of the Sangre de Cristo Range is controlled primarily by snowmelt and flow is perennial until it reaches the mountain front, beyond which streams begin losing water at a high rate as the water soaks into the creek beds. Even streams originating in the larger drainage basins, such as Sand and Medano Creeks, generally do not extend much more than 4 km (about 2.5 miles) beyond where they exit the mountains.The Great Sand Dunes contain the tallest dunes (maximum height about 750 feet, or 230 m) in North America. These dunes cover an area of 72 square kilometers (28 square miles) and contain an estimated 10–13 billion cubic meters (2.4 to 3.1 cubic miles) of sand. The dunes accumulated in an embayment that formed where the trend of the Sangre de Cristo Range changes from southeasterly to southwesterly. They owe their exceptional height to a combination of factors including range-front geometry, topography, an abundant sand supply from the nearby basin, a complex wind regime, and the Sangre de Cristo Range, which prevents continued eastward migration of dune sand deposited by the prevailing southwesterly and westerly winds. Although the sand on the surface of the Great Sand Dunes is of late Holocene age, most of this massive sand body is a complex of deposits that accumulated episodically for more than 130,000 years.

Analytical mesoscale modeling of aeolian sand transport

NASA Astrophysics Data System (ADS)

Lämmel, Marc; Kroy, Klaus

2017-11-01

The mesoscale structure of aeolian sand transport determines a variety of natural phenomena studied in planetary and Earth science. We analyze it theoretically beyond the mean-field level, based on the grain-scale transport kinetics and splash statistics. A coarse-grained analytical model is proposed and verified by numerical simulations resolving individual grain trajectories. The predicted height-resolved sand flux and other important characteristics of the aeolian transport layer agree remarkably well with a comprehensive compilation of field and wind-tunnel data, suggesting that the model robustly captures the essential mesoscale physics. By comparing the predicted saturation length with field data for the minimum sand-dune size, we elucidate the importance of intermittent turbulent wind fluctuations for field measurements and reconcile conflicting previous models for this most enigmatic emergent aeolian scale.

Environmental differences in substrate mechanics do not affect sprinting performance in sand lizards (Uma scoparia and Callisaurus draconoides).

PubMed

Korff, Wyatt L; McHenry, Matthew J

2011-01-01

Running performance depends on a mechanical interaction between the feet of an animal and the substrate. This interaction may differ between two species of sand lizard from the Mojave Desert that have different locomotor morphologies and habitat distributions. Uma scorparia possesses toe fringes and inhabits dunes, whereas the closely related Callisaurus draconoides lacks fringes and is found on dune and wash habitats. The present study evaluated whether these distribution patterns are related to differential locomotor performance on the fine sand of the dunes and the course sand of the wash habitat. We measured the kinematics of sprinting and characterized differences in grain size distribution and surface strength of the soil in both habitats. Although wash sand had a surface strength (15.4±6.2 kPa) that was more than three times that of dune sand (4.7±2.1 kPa), both species ran with similar sprinting performance on the two types of soil. The broadly distributed C. draconoides ran with a slightly (22%) faster maximum speed (2.2±0.2 m s(-1)) than the dune-dwelling U. scorparia (1.8±0.2 m s(-1)) on dune sand, but not on wash sand. Furthermore, there were no significant differences in maximum acceleration or the time to attain maximum speed between species or between substrates. These results suggest that differences in habitat distribution between these species are not related to locomotor performance and that sprinting ability is dominated neither by environmental differences in substrate nor the presence of toe fringes.

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

NASA Astrophysics Data System (ADS)

Bourke, Mary; McGaley-Towle, Zoe

2014-05-01

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

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-09-02

ISS013-E-75141 (2 Sept. 2006) --- Erg Oriental, Algeria is featured in this image photographed by an Expedition 13 crewmember onboard the International Space Station. One of the main interests of rainless regions like the Sahara Desert to landscape science is that the work of flowing water--mainly streams and rivers--becomes less important than the work of wind. According to scientists, over millennia, and if enough sand is available, winds can generate dunes of enormous size, arranged in regular patterns. Long, generally north-south trending linear dunes stretch across much of northeast Algeria covering a vast tract (approximately 140,000 kilometers square) of the Sahara Desert known as the Erg Oriental. Erg means dune sea in Arabic, and the term has been adopted into modern geology. Spanning this image diagonally are a series of two kilometer-wide linear dunes, comprised of red sand, from a point on the southwest margin of the erg (center point 28.9N 4.8W). The dune chains are more than 100 meters high. The "streets" between the dunes are grayer areas free of sand. Linear dune chains are usually generated roughly parallel with the dominant winds. It also seems to be true that linear dunes are built by stronger winds. This detailed view shows that smaller dunes, known as star dunes, are built on top of the linear dunes. By contrast, star dunes seem to form in weak wind regimes, with winds from different directions in each season -- resulting in characteristic "arms" snaking away from a central point. Some scientists therefore think the dunes in this image were generated in two earlier climatic phases, different from that of today. (1) During a phase when winds were stronger and dominantly from one direction (the south), major linear sand masses accumulated. (2) Later, when wind strengths declined, the star dunes formed. Modern features--known as wind streaks--on the edge of the present erg (not shown), younger than either the linear or star dunes, show that present-day sand-moving winds blow from the southwest.

Sand dune effects on seismic data

NASA Astrophysics Data System (ADS)

Arran, M.; Vriend, N. M.; Muyzert, E. J.

2017-12-01

Ground roll is a significant source of noise in land seismic data, with cross-line scattered ground roll particularly difficult to suppress. This noise arises from surface heterogeneities lateral to the receiver spread, and in desert regions sand dunes are a major contributor. However, the nature of this noise is poorly understood, preventing the design of more effective data acquisition or processing techniques. Here, we present numerical simulations demonstrating that sand dunes can act as resonators, scattering a seismic signal over an extensive period of time. We introduce a mathematical framework that quantitatively describes the properties of noise scattered by a barchan dune, and we discuss the relevance of heterogeneities within the dune. Having identified regions in time, space, and frequency space at which noise will be more significant, we propose the possibility of reducing dune-scattered noise through careful survey design and data processing.

A complicated story of frost and wind: Present-day gully activity within the north polar erg, Mar

NASA Astrophysics Data System (ADS)

Diniega, Serina; Hansen, Candice; Allen, Amanda; Grisby, Nathan; Li, Zheyu Joey

2016-10-01

Analyses of high-resolution observations have shown that the dunes within the martian north polar erg (AKA Olympia Undae) are currently very active on seasonal and yearly timescales, with 20-60% of the dunes within five polar dune fields undergoing the formation of alcove-apron features each Mars year. Previous studies have hypothesized formation mechanisms, based on observations of when new alcove and alcove-apron features form within an individual field through one Mars year. However, results are ill-constrained (and thus different hypotheses have been proposed) as the polar hood and winter night mean very few images are taken during the actual period of activity. In this study, we mitigate this limitation by examining several fields over several Mars years -- thus bringing aggregated results as well as detailed correlation checks against environmental conditions and seasonal processes to bear on the problem. From this, we propose a new process that appears consistent with all observations: (1) small alcoves form along the dune brink in the autumn (under the polar hood) due to instabilities induced by the night-formation and morning-sublimation of frost. As autumn progresses, the seasonal frost layer builds over the altered dune slope. (2) In the early spring, sublimation activity is concentrated and/or enhanced over these alcoves, causing further erosion and the formation of larger alcove-apron features. From the planform dimensions of the newly formed alcoves, we can estimate the volume of sand moved down the dune slope during one period of activity and estimate the aeolian sediment flux by looking at how quickly the alcoves are erased. We find that, over a Mars year, the amount of material moved via alcove-apron activity and via the wind are both comparable to aeolian sand flux estimates over dunes within lower-latitude regions of Mars. Thus it appears that the formation of alcoves-aprons is a significant mechanism for dune advancement and evolution within the north polar erg, and understanding it better will add to our understanding of polar processes, aeolian sediment transport, and dune evolution on Mars.

Exploring the contributions of vegetation and dune size to early dune development using unmanned aerial vehicle (UAV) imaging

NASA Astrophysics Data System (ADS)

van Puijenbroek, Marinka E. B.; Nolet, Corjan; de Groot, Alma V.; Suomalainen, Juha M.; Riksen, Michel J. P. M.; Berendse, Frank; Limpens, Juul

2017-12-01

Dune development along highly dynamic land-sea boundaries is the result of interaction between vegetation and dune size with sedimentation and erosion processes. Disentangling the contribution of vegetation characteristics from that of dune size would improve predictions of nebkha dune development under a changing climate, but has proven difficult due to the scarcity of spatially continuous monitoring data. This study explored the contributions of vegetation and dune size to dune development for locations differing in shelter from the sea. We monitored a natural nebkha dune field of 8 ha, along the coast of the island Texel, the Netherlands, for 1 year using an unmanned aerial vehicle (UAV) with camera. After constructing a digital surface model and orthomosaic we derived for each dune (1) vegetation characteristics (species composition, vegetation density, and maximum vegetation height), (2) dune size (dune volume, area, and maximum height), (3) degree of shelter (proximity to other nebkha dunes and the sheltering by the foredune). Changes in dune volume over summer and winter were related to vegetation, dune size and degree of shelter. We found that a positive change in dune volume (dune growth) was linearly related to initial dune volume over summer but not over winter. Big dunes accumulated more sand than small dunes due to their larger surface area. Exposed dunes increased more in volume (0.81 % per dune per week) than sheltered dunes (0.2 % per dune per week) over summer, while the opposite occurred over winter. Vegetation characteristics did not significantly affect dune growth in summer, but did significantly affect dune growth in winter. Over winter, dunes dominated by Ammophila arenaria, a grass species with high vegetation density throughout the year, increased more in volume than dunes dominated by Elytrigia juncea, a grass species with lower vegetation density (0.43 vs. 0.42 (m3 m-3) week-1). The effect of species was irrespective of dune size or distance to the sea. Our results show that dune growth in summer is mainly determined by dune size, whereas in winter dune growth was determined by vegetation type. In our study area the growth of exposed dunes was likely restricted by storm erosion, whereas growth of sheltered dunes was restricted by sand supply. Our results can be used to improve models predicting coastal dune development.

Sand Dunes with Frost

NASA Technical Reports Server (NTRS)

2004-01-01

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

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

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-04

...(a) of the Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et seq.), which are: (a... Dunes are a small complex of crescent-shaped dunes (WildEarth Guardians 2010, p. 8). The highest dune...]C) (Rust 1981, pp. 13, 27; Rust and Hanks 1982, p. 324). The Sand Mountain serican scarab is active...

Recent Aeolian Dune Change on Mars

NASA Technical Reports Server (NTRS)

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

2007-01-01

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

[Geostatistics analyzing to cause of formation of circle distribution of plant communities in Horqin Sandy Land].

PubMed

He, Xingdong; Gao, Yubao; Zhao, Wenzhi; Cong, Zili

2004-09-01

Investigation results in the present study showed that plant communities took typical concentric circles distribution patterns along habitat gradient from top, slope to interdune on a few large fixed dunes in middle part of Korqin Sandy Land. In order to explain this phenomenon, analysis of water content and its spatial heterogeneity in sand layers on different locations of dunes was conducted. In these dunes, water contents in sand layers of the tops were lower than those of the slopes; both of them were lower than those of the interdunes. According to the results of geostatistics analysis, whether shifting dune or fixed dune, spatial heterogeneity of water contents in sand layers took on regular changes, such as ratios between nugget and sill and ranges reduced gradually, fractal dimension increased gradually, the regular changes of these parameters indicated that random spatial heterogeneity reduced gradually, and autocorrelation spatial heterogeneity increased gradually from the top, the slope to the interdune. The regular changes of water contents in sand layers and their spatial heterogeneity of different locations of the dunes, thus, might be an important cause resulted in the formation of the concentric circles patterns of the plant communities on these fixed dunes.

A case study on dune response to infragravity waves

NASA Astrophysics Data System (ADS)

Li, Wenshan; Wang, Hui; Li, Huan; Wu, Shuangquan; Li, Cheng

2017-08-01

A series of numerical simulations were conducted using the process-based model XBeach to investigate dune response under normal and getting rid of infragravity wave conditions with different slopes. Erosion volume upside the dune toe and dune top recession are set as indicators for dune vulnerability as well as defence capacity for its front-beach. Results show that both dune erosion volume and dune top recession decrease with gentler dune slopes. Of all the simulation cases, dune with a face slope of 1/1 lost most sand and supplied most sand for lower-bed. The presence of infragravity waves is validated to be crucial to dune vulnerability. The dune erosion volume is shown to decrease by 44.5%∼61.5% and the dune top recession decreased by 0%∼45.5% correspondingly, in the case that infragravity motion is not taken into account during simulation for different dune slopes.

Advanced Interferometric Synthetic Aperture Imaging Radar (InSAR) for Dune Mapping

NASA Astrophysics Data System (ADS)

Havivi, Shiran; Amir, Doron; Schvartzman, Ilan; August, Yitzhak; Mamman, Shimrit; Rotman, Stanely R.; Blumberg, Dan G.

2016-04-01

Aeolian morphologies are formed in the presence of sufficient wind energy and available lose 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 1970s, remote sensing imagery, both optical and radar, have been 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 or more images. 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 methods. The reason is that dunes tend to be less coherent than firm, stable, surfaces. This work aims to demonstrate how interferometric decorrelation 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 coherence change detection method was used, in order to identify dune stability or instability and the dune activity level. The Nitzanim-Ashdod 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 studied extensively in the field. High resolution TerraSAR-X (TSX) images covering the entire research area were acquired for the period of 2011 to 2012. Analysis was performed in imaging processing and GIS software. The coherence results display minor changes on the dune crest (0.42-0.49), compared to bigger changes in windward slope (0.31-0.37). The level of change depends on the dune location relative to its distance from the sea. Furthermore, the coherence results show decreasing over time. Field results indicate erosion/deposition of sand ranging from -99 to 137 mm/year. The results of this study confirm that it is possible to monitor subtle changes in sand dunes and to identify dune stability or instability, only by the use of SAR images, even in areas characterized by low coherence.

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

USGS Publications Warehouse

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

2010-01-01

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

North Polar Gypsum Dunes in Olympia Undae

NASA Image and Video Library

2016-07-15

These sand dunes are a type of aeolian bedform and partly encircle the Martian North Pole in a region called Olympia Undae. Unlike most of the sand dunes on Mars that are made of the volcanic rock basalt, these are made of a type of sulfate mineral called gypsum. Whence the sand? Well, gypsum is a mineral that can often form from the evaporation of water that has sulfur and calcium dissolved in it. This sand was probably sourced from a northern region on Mars that used to be quite wet. The boxy gridding of the dunes indicates that the wind blows in multiple directions. Note: "Aeolian" means wind-blown and "bedform" means piles of sediment shaped by a flowing fluid (liquid or gas). http://photojournal.jpl.nasa.gov/catalog/PIA20743

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

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-24

... Imperial Sand Dunes Recreation Area (ISDRA) Subgroup of the California Desert District Advisory Council... Dunes Recreation Area Subgroup of the California Desert District Advisory Council (DAC) to the Bureau of... meeting for the California Desert District Advisory Council ISDRA Subgroup, c/o Bureau of Land Management...

Denivation Features of Polar Dunes: An Earth Analogue for Morphological Indicators of Solid Water on Mars

NASA Astrophysics Data System (ADS)

McGowan, H. A.; Neil, D.

2005-12-01

The identification of sources of water on Mars will be critical to the successful exploration of the planet and the establishment of a permanent presence by humans. While the Martian polar ice caps contain up to 70% water by mass, the extreme climate of these regions means that they may not be suitable for habitation. As a result, other sites must be identified where access to water is possible. Recent evidence has emerged that suggests sand dunes on Mars may contain 40-50% water by mass (Bourke 2005). In this paper, we present niveo-aeolian features observed in the sand dunes of the Victoria Valley, Antarctica, which have long been considered an Earth analogue for those on Mars (Morris et al. 1972). These features include cornices of permafrosted sand in dune-crest deflation hollows, exposed erosion resistant frozen water and sand lenses, wet sand flows and seeps. We also report on the morphological characteristics of sand sink holes which form in chains above layers of buried, melting and/or sublimating snow. This process is apparently reliant on the melting of inter-grain ice bonds and subsequent formation of a dry mobile sand layer on the dune surface. These micro-morphological features associated with summertime denivation of the Victoria Valley sand dunes, which are 5 to 10 m high and several hundred meters in crest length, are too small to identify on air photographs, satellite imagery and LIDAR DEMS of these transverse barchanoid ridges. However, on Mars where sand dunes are 1 to 2 orders of magnitude larger, these features may be identifiable if solid water exists within them, as suggested by Bourke (2005). Perhaps of greater importance, they may indicate the presence of buried palaeo-snow layers which have been preserved beneath the erosion resistant permafrosted sand dunes on Mars. We believe that the formation and subsequent exposure of these snow layers is the primary cause of the denivation features present in the polar dunes of the Victoria Valley, Antarctica. References: Bourke, M.C. 2005: Water on Mars. The Halstead Lecture, British Association for the Advancement of Science, Trinity College, Dublin, September 2005. Morris, E.C., Mutch, T.A. and Holt, H.E. 1972: Atlas of geologic features in the Dry Valleys of South Victoria Land, Antarctica: Possible analogs of Martian surface features. Interagency report: Astrogeology 52. Prepared under NASA contract L-9718 by the Geological Survey.

The Effect of the Kind of Sands and Additions on the Mechanical Behaviour of S.C.C

NASA Astrophysics Data System (ADS)

Zeghichi, L.; Benghazi, Z.; Baali, L.

The sand is an inert element essential in the composition of concrete; its use ensures granular continuity between the cement and gravel for better cohesion of concrete. This paper presents the results of a study that investigated the influence of sand quality on the properties of fresh and hardened self-compacting concrete (SCC). The dune sands are very fine materials characterized by a high intergranular porosity, high surface area and low fineness modulus; on the other hand crushed (manufactured) sand has a high rate into thin and irregular shapes which are influencing the workability of concrete. The amount of dune sand varies from (0% 50%, to 100%) by weight of fine aggregates. The effect of additions is also treated (blast furnace slag and lime stone) The results show that the rheological properties favour the use of dune sands; however the mechanical properties support the use of crushed sand.

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

USGS Publications Warehouse

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

2006-01-01

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

Dunes of the Southern Highlands

NASA Image and Video Library

2017-03-23

Sand dunes are scattered across Mars and one of the larger populations exists in the Southern hemisphere, just west of the Hellas impact basin. The Hellespontus region features numerous collections of dark, dune formations that collect both within depressions such as craters, and among "extra-crater" plains areas. This image displays the middle portion of a large dune field composed primarily of crescent-shaped "barchan" dunes. Here, the steep, sunlit side of the dune, called a slip face, indicates the down-wind side of the dune and direction of its migration. Other long, narrow linear dunes known as "seif" dunes are also here and in other locales to the east. NB: "Seif" comes from the Arabic word meaning "sword." The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 25.5 centimeters (10 inches) per pixel (with 1 x 1 binning); objects on the order of 77 centimeters (30.3 inches) across are resolved.] North is up. http://photojournal.jpl.nasa.gov/catalog/PIA21571

Poster 17: Methane storms as a driver of Titan's dune orientation.

NASA Astrophysics Data System (ADS)

Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clement; Lebonnois, Sebastien; Rodriguez, Sebastien; Courech Du Pont, Sylvain; Lucas, Antoine

2016-06-01

Titan's equatorial regions are covered by eastward oriented linear dunes [1,2]. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds on Earth. We propose that Titan's dune orientation is actually determined by equinoctial tropical methane storms producing a coupling with superrotation and dune formation [3]. Using meso-scale simulations of convective methane clouds [4] with a GCM wind profile featuring the superrotation [5,6], we show that Titan's storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind calculations and analogies with terrestrial dune fields [7], we show that Titan's dune propagation occurs eastward under these conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major features of Titan's dunes as the divergence from the equator or the dune size and spacing. It also implies an equatorial origin of Titan's dune sand and a possible occurence of dust storms.

Titan's Sand Seas properties from the modelling of microwave-backscattered signal of Cassini/SAR

NASA Astrophysics Data System (ADS)

Lucas, Antoine; Rodriguez, Sébastien; Lommonier, Florentin; Ferrari, Cécile; Paillou, Philippe; Le Gall, Alice; Narteau, Clément

2016-04-01

Titan's sand seas may reflect the current and past surface conditions. Assessing the physicochemical properties and the morphodynamics of the equatorial linear dunes is a milestone in our comprehension of the climatic and geological history of the largest Saturn's moon. Based on enhanced SAR processing leading to despeckled Cassini RADAR data sets, we analyzed quantitatively the surface properties (e.g., slopes, texture, composition...) over the sand seas. First, using a large amount of overlaps and a wide range of incidence angle and azimuths, we show that the radar cross-section over the inter-dunes strongly differs from the one over the dunes. This strongly suggests significant difference in the physical properties between these two geomorphic units. Then, we derived quantitatively the surface properties from the modelling of microwave-backscattered signal using a Monte-Carlo inversion. Our results show that dunes are globally more microwaves absorbent than the inter-dunes. The inter-dunes are smoother with a higher dielectric constant than the dunes. Considering the composition, the inter-dunes are in between the dunes and the bright inselbergs mainly composed of water ice, suggesting the presence of a shallow layer of sediment in between the dunes. This may suggest that Titan dunes are developing over a coarser sediment bed similarly to what is observed in some terrestrial sand seas such as in Ténéré desert (Niger, see also contribution #EGU2016-13383). Additionally, potential secondary bedforms (such as ripples) as well as avalanche faces may have been detected.

Southern Sand Dunes

NASA Image and Video Library

2003-01-15

At first glance, this NASA Mars Odyssey image showing impact craters and linear ridges and troughs is typical of the southern highlands. However, upon closer examination migrating sand dunes are observed within the troughs.

Dynamics of a cliff top dune

NASA Astrophysics Data System (ADS)

Rasmussen, K. R.

2012-12-01

Morphological changes during more than 100 years have been investigated for a cliff-top dune complex at Rubjerg at the Danish North Sea coast. Here the lower 50 m of the cliff front is composed of Pleistocene steeply inclined floes of silt and clay with coarse sand in between which gives it a saw-tooth appearance. On top of this the dunes are found for several kilometres along the coastline. Due to erosion by the North Sea the cliff has retreated about 120 m between approximately 1880 and 1970 as indicated from two national surveys, and recent GPS-surveys indicate that erosion is continuing at a similar rate. Nevertheless the cliff top dune complex has survived, but its morphology has undergone some changed. The old maps indicate that around 1880 the dune complex was composed of several up to about 20 m high dunes streamlined in the East-West direction which is parallel to the prevailing wind direction. When protective planting started during the first half of the 20th Century the cliff top dunes gradually merged together forming a narrow, tall ridge parallel to the shore line with the highest part reaching about 90 m near 1970. In 1993 the highest points along the ridge was almost 95 m high, but then the protective planting was considerably reduced and recent annual GPS-surveys indicate that the dunes respond quickly to this by changing their morphology towards the original appearance. It is remarkable that despite the mass wasting caused by the constant erosion of the cliff front the dunes have remained more or less intact. Theoretical studies of hill flow indicate given the proper geometry of the cliff then suspension of even coarse grains can be a very effective agent for carrying sand from the exposed parts of the cliff front to and beyond the cliff-top. Mostly the sand grains are deposited within some hundred meters downwind of the cliff dune while silt is often carried more than 10 km inland. Field observations indicate that where the dislodged floes and beds of coarse sand are missing the cliff is steep and dunes are absent at the cliff top. On the other hand when floes are present then some parts of the cliff are less steep and where sand is abundant cliff top dunes seem to be abundant, too. In order to investigate how flow conditions at the cliff front responds to its geometry, scale models of the cliff front approximately 1:10, but with different steepness have been tested in a boundary layer wind tunnel. All runs have been made with proper roughness scaling and besides a variation in their longitudinal profiles some variation in their transverse profiles has also been tested. The surface-near flow has been mapped with high resolution 2-D laser-Doppler profiling, and one of the important aims is to demonstrate the interaction between sediment and geological structure on one side and flow and dune state on the other side. A particular aim is to investigate if and how the separation bubble may have a profound control on mobilization and transport of sediment.

Lunar and Planetary Science XXXV: Martian Aeolian and Mass Wasting Processes: Blowing and Flowing

NASA Technical Reports Server (NTRS)

2004-01-01

The session Martian Aeolian and Mass Wasting Processes: BLowing and Flowing included the following topics: 1) Three Decades of Martian Surface Changes; 2) Thermophysical Properties of Isidis Basin, Mars; 3) Intracrater Material in Eastern Arabia Terra: THEMIS, MOC, and MOLA Analysis of Wind-blown Deposits and Possible High-Inertia Source Material; 4) Thermal Properties of Sand from TES and THEMIS: Do Martian Dunes Make a Good Control for Thermal Inertia Calculations? 5) A Comparative Analysis of Barchan Dunes in the Intra-Crater Dune Fields and the North Polar Sand Sea; 6) Diluvial Dunes in Athabasca Valles, Mars: Morphology, Modeling and Implications; 7) Surface Profiling of Natural Dust Devils; 8) Martian Dust Devil Tracks: Inferred Directions of Movement; 9) Numerical Simulations of Anastomosing Slope Streaks on Mars; 10) Young Fans in an Equatorial Crater in Xanthe Terra, Mars; 11) Large Well-exposed Alluvual Fans in Deep Late-Noachian Craters; 12) New Evidence for the Formation of Large Landslides on Mars; and 13) What Can We Learn from the Ages of Valles Marineris Landslides on Martian Impact History?

Dunes with Frost

NASA Technical Reports Server (NTRS)

2004-01-01

31 May 2004 Springtime for the martian northern hemisphere brings defrosting spots and patterns to the north polar dune fields. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example located near 76.7oN, 250.4oW. In summer, these dunes would be darker than their surroundings. However, while they are still covered by frost, they are not any darker than the substrate across which the sand is slowly traveling. Dune movement in this case is dominated by winds that blow from the southwest (lower left) toward the northeast (upper right). The picure covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.

Slip Face on Downwind Side of Namib Sand Dune on Mars

NASA Image and Video Library

2016-01-04

This view from NASA's Curiosity Mars Rover shows the downwind side of "Namib Dune," which stands about 13 feet (4 meters) high. The site is part of Bagnold Dunes, a band of dark sand dunes along the northwestern flank of Mars' Mount Sharp. The component images stitched together into this scene were taken with Curiosity's Navigation Camera (Navcam) on Dec. 17, 2015, during the 1,196th Martian day, or sol, of the rover's work on Mars. In late 2015 and early 2016, Curiosity is conducting the first up-close studies ever made of active sand dunes anywhere but on Earth. Under the influence of Martian wind, the Bagnold Dunes are migrating up to about one yard or meter per Earth year. The view spans from westward on the left to east-southeastward on the right. It is presented as a cylindrical perspective projection. http://photojournal.jpl.nasa.gov/catalog/PIA20281

Downwind Side of Namib Sand Dune on Mars, Stereo

NASA Image and Video Library

2016-01-04

This stereo view from NASA's Curiosity Mars Rover shows the downwind side of "Namib Dune," which stands about 13 feet (4 meters) high. The image appears three-dimensional when viewed through red-blue glasses with the red lens on the left. The site is part of Bagnold Dunes, a band of dark sand dunes along the northwestern flank of Mars' Mount Sharp. The component images stitched together into this scene were taken with Curiosity's Navigation Camera (Navcam) on Dec. 17, 2015, during the 1,196th Martian day, or sol, of the rover's work on Mars. In late 2015 and early 2016, Curiosity is conducting the first up-close studies ever made of active sand dunes anywhere but on Earth. Under the influence of Martian wind, the Bagnold Dunes are migrating up to about one yard or meter per Earth year. http://photojournal.jpl.nasa.gov/catalog/PIA20282

Investigating Mars: Coprates Chasma

NASA Image and Video Library

2017-09-28

Coprates Chasma is one of the numerous canyons that make up Valles Marineris. The chasma stretches for 960 km (600 miles) from Melas Chasma to the west and Capri Chasma to the east. Landslide deposits, layered materials and sand dunes cover a large portion of the chasma floor. This image is located in eastern Coprates Chasma. The image shows a relatively smooth floor, with a group of sand dune forms located against the wall of the chasma (bottom of image). The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 27061 Latitude: -13.9602 Longitude: 301.82 Instrument: VIS Captured: 2008-01-20 10:39 https://photojournal.jpl.nasa.gov/catalog/PIA21993

Earth observations taken during the STS-103 mission

NASA Image and Video Library

1999-12-24

STS103-710-084 (19-27 December 1999)--- One of the astronauts aboard the Earth-orbiting Space Shuttle Discovery used a handheld 70mm camera to photograph the great sand seas which occupy northern Algeria. They are Grand Erg Oriental (Eastern Sand Sea) and Grand Erg Occidental (Western Sand Sea). Both sand seas occupy depressions that are separated by a north-south rise called Mizab. Ergs are areas of large accumulations of sand that take the form of actively shifting dunes, fossilized dunes, or extensive sand sheets.

Full-Circle Vista With a Linear Shaped Martian Sand Dune

NASA Image and Video Library

2017-02-27

The left side of this 360-degree panorama from NASA's Curiosity Mars rover shows the long rows of ripples on a linear shaped dune in the Bagnold Dune Field on the northwestern flank of Mount Sharp. The view is a mosaic of images taken with Curiosity's Navigation Camera (Navcam) on Feb. 5, 2017, during the 1,601st Martian day, or sol, of the rover's work on Mars. The view is centered toward west-southwest, with east-southeast on either end. A capped mound called "Ireson Hill" is on the right. http://photojournal.jpl.nasa.gov/catalog/PIA21268

Suspended and Bedload Sand dynamics in the Mekong River Channel and Export to the Coastal Ocean

NASA Astrophysics Data System (ADS)

Stephens, J. D.; Di Leonardo, D. R.; Weathers, H. D., III; Allison, M. A.

2016-02-01

Two field campaigns were conducted in the tidal and estuarine reach of the Song Hau distributary of the Mekong River to examine the dynamics of sand transport and export to the coastal ocean. This study examines variation in suspended sand concentration and net transport with respect to changes in discharge between the October 2014 high discharge and March 2015 low discharge studies, and over semi-diurnal and spring-neap tidal cycles between Can Tho and the Tran De and Dinh An distributary channels in the Mekong Delta. Suspended sand concentrations were measured using a P-61 isokinetic suspended sediment sampler and a Sequoia Scientific LISST-100X used in vertical profiling mode. Stationary ADCP data are used to examine bed stress at cast sites. Bed load transport rates were calculated using a repeat multibeam transect methodology and dune translation rates with flow. Preliminary results indicate that suspended sand concentration increases towards the bed and is positively correlated with increasing shear stress controlled by river discharge and tides. However, sites with non-sandy bottoms, as indicated by multibeam bathymetry, have low suspended sand concentrations, suggesting a close linkage with a bed sand source. Bed load transport rates vary cross-sectionally with shear stress and are linked to dune size. Most bed load transport is taking place in or near the thalweg. The reduction in ebb flows at low discharge and the mantling of sand fields by salinity driven mud deposition, is suspected to control the low suspended sand concentrations observed in March. Results to date suggest that net sand export (suspended plus bed load) to the ocean occurs predominantly during the high discharge monsoon season.

76 FR 62087 - Draft Conservation Plan and Draft Environmental Assessment; Dunes Sagebrush Lizard, Texas

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-06

... known as the sand dune lizard, and the lesser prairie-chicken, among the Service, the Bureau of Land... southeastern New Mexico and west Texas. The species only occurs in sand dune complexes associated with shinnery... direct, indirect, and cumulative impacts of the TCP on the quality of the human environment and other...

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.

Overview of the 2015 Algodones Sand Dunes field campaign to support sensor intercalibration

NASA Astrophysics Data System (ADS)

McCorkel, Joel; Bachmann, Charles M.; Coburn, Craig; Gerace, Aaron; Leigh, Larry; Czapla-Myers, Jeff; Helder, Dennis; Cook, Bruce

2018-01-01

Several sites from around the world are being used operationally and are suitable for vicarious calibration of space-borne imaging platforms. However, due to the proximity of these sites (e.g., Libya 4), a rigorous characterization of the landscape is not feasible, limiting their utility for sensor intercalibration efforts. Due to its accessibility and similarities to Libya 4, the Algodones Sand Dunes System in California, USA, was identified as a potentially attractive intercalibration site for space-borne, reflective instruments such as Landsat. In March 2015, a 4-day field campaign was conducted to develop an initial characterization of Algodones with a primary goal of assessing its intercalibration potential. Five organizations from the US and Canada collaborated to collect both active and passive airborne image data, spatial and temporal measurements of spectral bidirectional reflectance distribution function, and in-situ sand samples from several locations across the Algodones system. The collection activities conducted to support the campaign goal is summarized, including a summary of all instrumentation used, the data collected, and the experiments performed in an effort to characterize the Algodones site.

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.

The Karakum and Kyzylkum sand seas dynamics; mapping and palaeoclimatic interpretations

NASA Astrophysics Data System (ADS)

Maman, Shimrit; Blumberg, Dan G.; Tsoar, Haim; Porat, Naomi

2015-04-01

Sand seas are large basins in deserts that are mantled by wind-swept sand and that exhibit varying degrees of vegetation cover. Wilson (1973) was the first to globally map and classify sand seas. Beyond Wilson's maps, however, little research has been published regarding the Karakum and Kyzylkum sand seas of Central Asia. Wilson's maps delineate active ergs from inactive ergs based solely on precipitation. His assumption of annual average rainfall as a factor determining mobility vs. stability of sand seas is too simplistic and does not take into consideration other factors such as biogenic soil crusts and wind power, both of which are known to have major effects on the dynamics of sand dunes. Literature related to mapping and classifying the Central Asian ergs by remote sensing or sand sea classification state (stable/active) is lacking. Moreover, the palaeoclimatic significance of dunes in Central Asia is difficult to assess, as there has been few studies of dune stratigraphy and numerical ages are lacking. Optically stimulated luminescence (OSL) is a firm optical dating method that is used to determine the elapsed time since quartz grains were last exposed to sunlight, thus, their burial. Yet, absolute ages indicating mobilization and stabilization of these sands, are still inadequately known and are here under discussion. The broad concern of this research was to determine the dynamics of the Central Asian sand seas and study the palaeoclimatic changes that brought to their stabilization. As there are no reliable maps or aeolian discussion of these sands, establishment of a digital data base was initially conducted, focusing on identifying and mapping these sand seas. The vast area and inaccessibility make traditional mapping methods virtually impossible. A variety of space-borne imagery both optical and radar, with varying spectral and spatial resolutions was used. These images provided the basis for mapping sand distribution, dune forms, and vegetation cover. GIS analysis was performed in parallel with field work to obtain validation and verification. The remote sensing and GIS results show that these ergs are mostly stabilized, with the estimated sand mantled area for the Karakum desert ~260,000 km2, and for the Kyzylkum it is ~195,500 km2. Meteorological analysis of wind and precipitation data indicate a low wind power environment (DP< 200) and sufficient rainfall (>100 mm) to support vegetation. Thus, these sands are indicative of past periods during which the climate in this region was different than today, enabling aeolian sand activity. Optically stimulated luminescence ages derived from the upper meter of the interdune of 14 exposed sections from both ergs, indicate sand stabilization during the mid-Holocene. This stabilization is understood to reflect a transition to a warmer, wetter, and less windy climate that generally persisted until today. The OSL ages, coupled with a compilation of regional palaeoclimatic data, corroborate and reinforce the previously proposed Mid-Holocene Liavliakan phase, known to reflect a warmer, wetter, and less windy climate that persists until today and resulted in dune stabilization around the Mid-Holocene.

Environmental forcing metrics to quantify short-term foredune morphodynamics

NASA Astrophysics Data System (ADS)

Spore, N.; Conery, I.; Brodie, K. L.; Palmsten, M.

2016-12-01

Coastal foredunes evolve continuously due to competing aeolian and hydrodynamic processes. Onshore to shore-parallel winds transport sand to the dune while storm-driven surge and wave runup remove sand from the dune. Dune-growth requires periods of time when the wind exceeds a threshold velocity to initiate transport and the relative geometry of the dry beach to the wind direction to create large fetches. This study aims to derive an aeolian transport potential (ATP) metric from the precipitation, available fetch (a function of wind angle and dry-beach width), and a threshold wind speed to initiate transport. ATP is then combined with a hydrodynamic transport potential (HTP) metric, defined as the number of hours of wave impact to the foredune or upper beach, to assess the time-dependent magnitude of the forcing factors affecting morphological evolution of the foredune between monthly terrestrial lidar surveys.This study focuses on two distinctly different dune fields and their frontal or incipient dune ridges in Duck, NC at the USACE Field Research Facility (FRF): (1) an undisturbed, tall and narrow recently impacted dune with a near vertical face; and (2) an undisturbed, shorter and wider dune with gentler and more hummocky slopes. The two sites are separated by < 1km alongshore and experience similar environmental forcings due to their close proximity. We used hourly precipitation, wind, wave, and imagery-derived runup data from the FRF and surrounding weather stations as inputs to ATP and HTP for each site. We scanned each site at monthly intervals for 18 months with high-resolution terrestrial lidar and generated 10 cm digital elevation models (DEM) for each scan. Incremental and cumulative changes in elevation, volume, and dune toe position were extracted from the DEMs and compared to the ATP and HTP values between the surveys to evaluate the dominant factors affecting sediment flux to the system.

Origin of the Sinai-Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history

USGS Publications Warehouse

Muhs, Daniel R.; Roskin, Joel; Tsoar, Haim; Skipp, Gary; Budahn, James R.; Sneh, Amihai; Porat, Naomi; Stanley, Jean-Daniel; Katra, Itzhak; Blumberg, Dan G.

2013-01-01

The Sinai–Negev erg occupies an area of 13,000 km2 in the deserts of Egypt and Israel. Aeolian sand of this erg has been proposed to be derived from the Nile Delta, but empirical data supporting this view are lacking. An alternative source sediment is sand from the large Wadi El Arish drainage system in central and northern Sinai. Mineralogy of the Negev and Sinai dunes shows that they are high in quartz, with much smaller amounts of K-feldspar and plagioclase. Both Nile Delta sands and Sinai wadi sands, upstream of the dunes, also have high amounts of quartz relative to K-feldspar and plagioclase. However, Sinai wadi sands have abundant calcite, whereas Nile Delta sands have little or no calcite. Overall, the mineralogical data suggest that the dunes are derived dominantly from the Nile Delta, with Sinai wadi sands being a minor contributor. Geochemical data that proxy for both the light mineral fraction (SiO2/10–Al2O3 + Na2O + K2O–CaO) and heavy mineral fraction (Fe2O3–MgO–TiO2) also indicate a dominant Nile Delta source for the dunes. Thus, we report here the first empirical evidence that the Sinai–Negev dunes are derived dominantly from the Nile Delta. Linkage of the Sinai–Negev erg to the Nile Delta as a source is consistent with the distribution of OSL ages of Negev dunes in recent studies. Stratigraphic studies show that during the Last Glacial period, when dune incursions in the Sinai–Negev erg began, what is now the Nile Delta area was characterized by a broad, sandy, minimally vegetated plain, with seasonally dry anastomosing channels. Such conditions were ideal for providing a ready source of sand for aeolian transport under what were probably much stronger glacial-age winds. With the post-glacial rise in sea level, the Nile River began to aggrade. Post-glacial sedimentation has been dominated by fine-grained silts and clays. Thus, sea level, along with favorable climatic conditions, emerges as a major influence on the timing of dune activity in the Sinai–Negev erg, through its control on the supply of sand from the Nile Delta. The mineralogy of the Sinai–Negev dunes is also consistent with a proposed hypothesis that these sediments are an important source of loess in Israel.

A Late Pleistocene linear dune dam record of aeolian-fluvial dynamics at the fringes of the northwestern Negev dunefield

NASA Astrophysics Data System (ADS)

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

2017-04-01

The paper presents a late Pleistocene aeolian-fluvial record within a linear dune-like structure that partway served as a dune dam. Situated along the southern fringe of the northwestern Negev desert dunefield (Israel) the structure's morphology, orientation, and some of its stratigraphic units partly resemble adjacent west-east extending vegetated linear dunes. Uneven levels of light-colored, fine-grained fluvial deposits (LFFDs) extend to the north and south from the flanks of the studied structure. Abundant Epipalaeolithic sites line the fringes of the LFFDs. The LFFD microstructures of fine graded bedding and clay blocky peds indicate sorting and shrinking of saturated clays in transitional environments between low energy flows to shallow standing water formed by dunes damming a mid-sized drainage system. The structure's architecture of interchanging units of sand with LFFDs indicates interchanging dominances between aeolian sand incursion and winter floods. Sand mobilization associated with powerful winds during the Heinrich 1 event led to dune damming downstream of the structure and within the structure to in-situ sand deposition, partial fluvial erosion, reworking of the sand, and LFFD deposition. Increased sand deposition led to structure growth and blockage of its drainage system that in turn accumulated LFFD units up stream of the structure. Extrapolation of current local fluvial sediment yields indicate that LFFD accretion up to the structure's brim occurred over a short period of several decades. Thin layers of Geometric Kebaran (c. 17.5-14.5 ka cal BP) to Harifian (12-11 ka BP) artifacts within the structure's surface indicates intermittent, repetitive, and short term camping utilizing adjacent water along a timespan of 4-6 kyr. The finds directly imply that the NW Negev LFFDs formed in dune-dammed water bodies which themselves were formed following events of vegetated linear dune elongation. LFFD accumulation persisted as a result of dune dam maintenance by smaller sand mobilization events. Wetter climates increased flood events boosting LFFD buildup rates but shortened dune dam longevity. The abundance and recurrence of water bodies in middle and large basins deteriorated after Harifian times when reduced wind power during the post-Younger Dryas constrained dune dam maintenance. Eventually, dune dam incision began as a result of overland flow after accommodation space dissipated due to LFFD accretion. Altogether, fluctuating high wind power and precipitation during a glacial-interglacial time window and high availability of fine-grained fluvial sediment yield from eroded middle to late Pleistocene upstream highlands loess mantles, combined to create a trio of aeolian-fluvial forcing factors supporting short-term but amplified dune-dammed fluvial depositional conditions.

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.

The Geodiversity in Drift Sand Landscapes of The Netherlands

NASA Astrophysics Data System (ADS)

van den Ancker, Hanneke; Jungerius, Pieter Dirk; Riksen, Michel

2015-04-01

The authors carried out detailed field studies of more than twelve drift sand landscapes in The Netherlands. The objective of these studies was to restore Natura-2000 values by restoring the wind activity. Active drift sands occur almost exclusively in The Netherlands, Natura 2000 habitat 2330 'Inland dunes with open Corynephorus and Agrostis grasslands', for which reason our country is largely responsible for this European landscape. Active drift sands had almost disappeared for two reasons: first, the stabilization of the drift sands by air pollution, mainly nitrogen, which stimulates the growth of algae and grasses that initiate soil formation, and second, by the growth of forests surrounding the sands, which decreases the wind force. The restoration studies revealed differences in the geodiversity between and within the drift sand areas. Whereas the drift sands on geological and soil maps show as almost homogenous areas, they have in fact highly variable geo-conditions of which examples will be given. These geodiversity aspects concern differences in geomorphological structure, origin, sediments and age of the drift sands. Differences in wind and water erosion, trampling and soil formation add to the geodiversity within the drift sand areas. Especially in the primary stages of succession the differences in geodiversity are relevant for the Natura-2000 values. We discerned three main types of active sands. Firstly, the impressive drift sands with large parabolic dune structures, often consisting of series of interlocking parabolic dunes. They developed from the northeast towards the southwest, against the direction of the dominant wind, and must have taken centuries to develop. Small parts of these systems are still active, other parts show different degrees of soil formation. Their origin is still unclear but probably dates from medieval times (Heidinga, 1985, Jungerius & Riksen, 2008). Second are the drift sand areas with irregular hills from 0.5 to about 2 metres high. They are common near villages. They originated through sand blown from fallow agricultural fields and local overgrazing. They vary in age from prehistoric to modern time and are now mostly planted with forests. Third are the linear drift sand areas with one to three metre high ridges that align old roads and originated through dust whirled up by horses and carriages over many centuries. They also occurs within drift sands of the first system. In the re-stabilization of reactivated drift sands, differences in geodiversity on a still more detailed scale are important (Ancker, Jungerius et al. 2013). Even a small change in slope can cause primary dunes to develop and stop wind erosion. Gradually the geodiversity aspects are recognized as relevant for the management of active and fossil drift sands, and also is becoming a management issue in itself. An important future research issue is the completion of the Drift Sand Atlas, a project that describes the geodiversity aspects of all drift sand areas of The Netherlands. This project has been retarded by lack of means. Knowledge of the geodiversity also is important for correct sampling of C14 and luminescence data. Other future research includes the processes that caused the formation of 'randwallen' (rim walls), rates of water and wind erosion and soil formation and links between flora, fauna and Natura 2000 species. References

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

PubMed

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

2015-11-15

Concentrations of nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in beach and dune sands from thirteen Havana (Cuba) resorts were estimated by X-ray fluorescence analysis. Determined mean metal contents (in mg·kg(-1)) in beach sand samples were 28±12 for Ni, 35±12 for Cu, 31±11 for Zn and 6.0±1.8 for Pb, while for dune sands were 30±15, 38±22, 37±15 and 6.8±2.9, respectively. Metal-to-iron normalization shows moderately severe and severe enrichment by Cu. The comparison with sediment quality guidelines shows that dune sands from various resorts must be considered as heavily polluted by Cu and Ni. Almost in every resort, the Ni and Cu contents exceed their corresponding TEL values and, in some resorts, the Ni PEL value. The comparison with a Havana topsoil study indicates the possible Ni and Cu natural origin. Copyright © 2015 Elsevier Ltd. All rights reserved.

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

PubMed

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

2015-12-30

Concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in dune sands from six urban and suburban Matanzas (Cuba) resorts and Varadero beach were estimated by X-ray fluorescence analysis. Ranges of metal contents in dune sands show a strong variation across the studied locations (in mg/kg(-1)): 20-2964 for Cr, 17-183 for Ni, 17-51 for Cu, 18-88 for Zn and 5-29 for Pb. The values of contamination factors and contamination degrees how that two of the studied Matanzas's resorts (Judio and Chirry) are strongly polluted. The comparison with Sediment Quality Guidelines shows that dune sands from Judio resort represent a serious risk for humans, due to polluted Cr and Ni levels, while sands from the rest of the studied resorts, including Varadero beach, do not represent any risk for public use. Copyright © 2015 Elsevier Ltd. All rights reserved.

Deep learning for the detection of barchan dunes in satellite images

NASA Astrophysics Data System (ADS)

Azzaoui, A. M.; Adnani, M.; Elbelrhiti, H.; Chaouki, B. E. K.; Masmoudi, L.

2017-12-01

Barchan dunes are known to be the fastest moving sand dunes in deserts as they form under unidirectional winds and limited sand supply over a firm coherent basement (Elbelrhiti and Hargitai,2015). They were studied in the context of natural hazard monitoring as they could be a threat to human activities and infrastructures. Also, they were studied as a natural phenomenon occurring in other planetary landforms such as Mars or Venus (Bourke et al., 2010). Our region of interest was located in a desert region in the south of Morocco, in a barchan dunes corridor next to the town of Tarfaya. This region which is part of the Sahara desert contained thousands of barchans; which limits the number of dunes that could be studied during field missions. Therefore, we chose to monitor barchan dunes with satellite imagery, which can be seen as a complementary approach to field missions. We collected data from the Sentinel platform (https://scihub.copernicus.eu/dhus/); we used a machine learning method as a basis for the detection of barchan dunes positions in the satellite image. We trained a deep learning model on a mid-sized dataset that contained blocks representing images of barchan dunes, and images of other desert features, that we collected by cropping and annotating the source image. During testing, we browsed the satellite image with a gliding window that evaluated each block, and then produced a probability map. Finally, a threshold on the latter map exposed the location of barchan dunes. We used a subsample of data to train the model and we gradually incremented the size of the training set to get finer results and avoid over fitting. The positions of barchan dunes were successfully detected and deep learning was an effective method for this application. Sentinel-2 images were chosen for their availability and good temporal resolution, which will allow the tracking of barchan dunes in future work. While Sentinel images had sufficient spatial resolution for the detection of mid-size to large size barchans, we noted that it was relatively difficult to detect smaller barchan dunes. Overall, deep learning allowed us to achieve a high accuracy in the detection of barchan dunes. The tracking of hundreds of barchans using this detection method would provide an insight into the understanding of the dynamics of this natural phenomenon.

Richat Structure, Mauritania, Anaglyph, Landsat Image over SRTM Elevation

NASA Technical Reports Server (NTRS)

2004-01-01

The prominent circular feature seen here, known as the Richat Structure, in the Sahara desert of Mauritania, is often noted by astronauts because it forms a conspicuous 50-kilometer-wide (30-mile-wide) bull's-eye on the otherwise rather featureless expanse of the desert. Initially mistaken for a possible impact crater, it is now known to be an eroded circular anticline (structural dome) of layered sedimentary rocks.

Extensive sand dunes occur in this region and the interaction of bedrock topography, wind, and moving sand is evident in this scene. Note especially how the dune field generally ends abruptly short of the cliffs as wind from the northeast (upper right) apparently funnels around the cliff, sweeping clean areas near the base of the cliff (particularly at the cliff point to the northwest, upper left, of the Richat Structure). Note also the isolated peak within the dune field. That peak captures some sand on its windward side, but mostly deflects the wind and sand around its sides, creating a sand-barren streak that continues far downwind.

To the west (left), a north-south trending bedrock ridge breaks up the sand field, and downwind from the ridge, streaks of dunes occur at certain locations. Upon close inspection, these streaks can be seen to be associated with saddles (low points) along the ridge, where sand preferentially passes over the ridge. This again shows how topographic features control the distribution of sand across the terrain.

This anaglyph was created by draping a Landsat reflectance infrared image over an SRTM elevation model, and then generating two differing perspectives, one for each eye. When viewed through special glasses, the anaglyph is a vertically exaggerated view of the Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and cover the right eye with a blue filter For vertical scale, note that the prominent cliffs (image center) are about 300 meters (about 1000 feet) tall, the central rings of the Richat structure are about 80 meters (about 260 feet) tall, and the sand dunes rise about 80 meters (about 260 feet) above the adjacent terrain across the center of the image.

Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Geospatial-Intelligence Agency (NGA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.

Size: 174.6 kilometers (108.3 miles) by 112.5 kilometers (69.8 miles) Location: 21.4 degrees North latitude, 12.0 degrees West longitude Orientation: North toward the top Image Data: Landsat band 7 Date Acquired: February 2000 (SRTM), January 13, 1987 (Landsat)

Meroe Patera

NASA Image and Video Library

2002-11-26

This image is located in Meroe Patera (longitude: 292W/68E, latitude: 7.01), which is a small region within Syrtis Major Planitia. Syrtis Major is a low-relief shield volcano whose lava flows make up a plateau more than 1000 km across. These flows are of Hesperian age (Martian activity of intermediate age) and are believed to have originated from a series of volcanic depressions, called calderas. The caldera complex lies on extensions of the ring faults associated with the Isidis impact basin toward the northeast - thus Syrtis Major volcanism may be associated with post-impact adjustments of the Martian crust. The most striking feature in this image is the light streaks across the image that lead to dunes in the lower left region. Wind streaks are albedo markings interpreted to be formed by aeolian action on surface materials. Most are elongate and allow an interpretation of effective wind directions. Many streaks are time variable and thus provide information on seasonal or long-term changes in surface wind directions and strengths. The wind streaks in this image are lighter than their surroundings and are the most common type of wind streak found on Mars. These streaks are formed downwind from crater rims (as in this example), mesas, knobs, and other positive topographic features. The dune field in this image is a mixture of barchan dunes and transverse dunes. Dunes are among the most distinctive aeolian feature on Mars, and are similar in form to barchan and transverse dunes on Earth. This similarity is the best evidence to indicate that martian dunes are composed of sand-sized material, although the source and composition of the sand remain controversial. Both the observations of dunes and wind streaks indicate that this location has a windy environment - and these winds are persistent enough to product dunes, as sand-sized material accumulates in this region. These features also indicate that the winds in this region are originating from the right side of the image, and moving towards the left. http://photojournal.jpl.nasa.gov/catalog/PIA04012

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-01-29

This VIS image of Kaiser Crater shows a region of the dunes with varied appearances. The different dune forms developed due to different amounts of available sand, different wind directions, and the texture of the crater floor. The dune forms change from the bottom to the top of the image - large long connected dunes, to large individual dunes, to the very small individual dunes at the top of the image. Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southern part of the crater floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 17686 Latitude: -46.6956 Longitude: 19.8394 Instrument: VIS Captured: 2005-12-09 13:25 https://photojournal.jpl.nasa.gov/catalog/PIA22261

Low Albedo Surfaces and Eolian Sediment: Mars Orbiter Camera Views of Western Arabia Terra Craters and Wind Streaks

NASA Technical Reports Server (NTRS)

Edgett, Kenneth S.

2001-01-01

High spatial resolution (1.5 to 12 m/pixel) Mars Global Surveyor Mars Orbiter Camera images obtained September 1997 through June 2001 indicate that the large, dark wind streaks of western Arabia Terra each originate at a barchan dune field on a crater floor. The streaks consist of a relatively thin coating of sediment deflated from the dune fields and their vicinity. This sediment drapes a previous mantle that more thickly covers nearly all of western Arabia Terra. No dunes or eolian bedforms are found within the dark wind streaks, nor do any of the intracrater dunes climb up crater walls to provide sand to the wind streaks. The relations between dunes, wind streak, and subjacent terrain imply that dark-toned grains finer than those which comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain. Such grains are most likely in the silt size range (3.9-62.5 micrometers). The streaks change in terms of extent, relative albedo, and surface pattern over periods measured in years, but very little evidence for recent eolian activity (dust plumes, storms, dune movement) has been observed.

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

USGS Publications Warehouse

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

2013-01-01

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

Crew Earth Observations (CEO) taken during Expedition Five on the ISS

NASA Image and Video Library

2002-08-25

ISS005-E-11189 (25 August 2002) --- Calanscio Sand Sea, Libya is featured in this digital image photographed by an Expedition 5 crewmember on the International Space Station (ISS). A plume of black smoke blowing westward is silhouetted against yellow linear dunes in the great sand sea of northeast Libya. Smoke from flares at remote well heads is commonly seen by astronauts flying over the Sahara Desert. NASA scientists studying the Station imagery had the following observations about the image. The plume dispersal pattern visible at the left edge of the image may be due to upper-level winds or gravitational settling of heavier particulates. The regular pattern of linear dunes is generated by two major winds: the dominant north wind (north is towards the top right) determines the orientation of the sand dunes. Gentler easterly winds, as were blowing when this view was taken, make the dunes asymmetric, with a gentle windward (west) slope and an over steeped downwind slope. Some over steepened slopes even cast shadows in the early morning light. One mound of sand (top right), due north of the well head, does not fit the pattern of linear dunes. This type is known as a star dune.

Large-eddy simulation of sand dune morphodynamics

NASA Astrophysics Data System (ADS)

Khosronejad, Ali; Sotiropoulos, Fotis; St. Anthony Falls Laboratory, University of Minnesota Team

2015-11-01

Sand dunes are natural features that form under complex interaction between turbulent flow and bed morphodynamics. We employ a fully-coupled 3D numerical model (Khosronejad and Sotiropoulos, 2014, Journal of Fluid Mechanics, 753:150-216) to perform high-resolution large-eddy simulations of turbulence and bed morphodynamics in a laboratory scale mobile-bed channel to investigate initiation, evolution and quasi-equilibrium of sand dunes (Venditti and Church, 2005, J. Geophysical Research, 110:F01009). We employ a curvilinear immersed boundary method along with convection-diffusion and bed-morphodynamics modules to simulate the suspended sediment and the bed-load transports respectively. The coupled simulation were carried out on a grid with more than 100 million grid nodes and simulated about 3 hours of physical time of dune evolution. The simulations provide the first complete description of sand dune formation and long-term evolution. The geometric characteristics of the simulated dunes are shown to be in excellent agreement with observed data obtained across a broad range of scales. This work was supported by NSF Grants EAR-0120914 (as part of the National Center for Earth-Surface Dynamics). Computational resources were provided by the University of Minnesota Supercomputing Institute.

Seismic and acoustic emissions of a booming dune. [in lunar, planetary and terrestrial sand motion

NASA Technical Reports Server (NTRS)

Criswell, D. R.; Lindsay, J. F.; Reasoner, D. L.

1975-01-01

Acoustic and seismic spectra of booming sand dunes that emit low-frequency musical resonances when the dunes slump or undergo forced shearing are analyzed and described. Previous studies of booming, squeaking, screeching, and roaring sands with pure outputs resembling those of musical instruments, or more turbulent acoustic outputs such as the sound of low-flying propeller aircraft, are reviewed. The possibility of similar phenomena on the moon (thermal moonquakes) or nearby planets (Mars, Venus) is considered on the basis of planetary topography, soil mechanics, and atmosphere.

Investigating Mars: Melas Chasma

NASA Image and Video Library

2017-11-30

Melas Chasma is part of the largest canyon system on Mars, Valles Marineris. At only 563 km long (349 miles) it is not the longest canyon, but it is the widest. Located in the center of Valles Marineris, it has depths up to 9 km below the surrounding plains, and is the location of many large landslide deposits, as will as layered materials and sand dunes. There is evidence of both water and wind action as modes of formation for many of the interior deposits. Today's image of the southern section of the canyon shows a large region of sand dunes. The presence of dunes indicates wind action as the most recent geologic process modifying the canyon. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 18513 Latitude: -12.752 Longitude: 288.597 Instrument: VIS Captured: 2006-02-15 15:24 https://photojournal.jpl.nasa.gov/catalog/PIA22131

Constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast

NASA Astrophysics Data System (ADS)

Kaplan, Kayla L.; Nordstrom, Karl F.; Jackson, Nancy L.

2016-10-01

Landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them. This field study evaluates how buildings and sand-trapping fences change the direction of wind approach, reduce wind speed, and restrict fetch distances for sediment entrainment, thereby reducing the potential for aeolian transport and development of dunes in enclaves. Field data were gathered in an 80 m long, 44 m deep beach enclave on the ocean shoreline of New Jersey, USA. Comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses, increasing the relative importance of longshore winds. Vertical arrays of anemometers on the foredune crest, foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore, with strongest winds on the berm crest. Vertical cylindrical traps on the foredune crest, foredune toe, mid-backshore, berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest. Sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes. Strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes. The length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth. The landward edge of the enclave (defined by a sand fence near the dune toe) is sheltered along its entire length from winds blowing at an angle to the shoreline of 25° or less. A foredune set back this distance in an enclave the length of an individual lot (about 20 m) would be sheltered at an angle of 57° or less, reducing the opportunity for dune building by onshore winds. Reduced potential for aeolian transport in enclaves implies that human actions may be required to build dunes artificially to protect buildings and roads from storm overwash.

Morphologic characteristics and migration rate assessment of barchan dunes in the Southeastern Western Desert of Egypt

NASA Astrophysics Data System (ADS)

Hamdan, M. A.; Refaat, A. A.; Abdel Wahed, M.

2016-03-01

This work explores the morphologic characteristics of aeolian dune sand in the southeastern part of Western Desert of Egypt. It aims to assess the movement of barchan dunes and evaluate their environmental influence on the Toshka Project. Morphometric investigation of barchan dunes in the Toshka area revealed that most barchans have high length/width (a/c) ratios (fat to pudgy), while one-fifth of the studied barchans have lower a/c ratios and so appear normal in their morphologic forms. Statistical analysis of the main parameters of barchan dunes in Toshka and other desert regions in the Kharga (Egypt), Kuwait, Southern Morocco, California and Southern Peru demonstrates that barchans of the Toshka area are distinctive in their appearance. They are characterized by distinct aspect with higher values of length and width and greater growth in height. The high-energy wind environment in addition to the large amount of drifting sand are principal factors responsible for the unique shape of Toshka barchans. The migration rate of barchan dunes in four chosen test locations, within the central and western Toshka area, ranges from about 3 to 10.82 m/year. The calculated average migration rate of these dunes is about 6 m/year in a SSW direction. Sand encroachment is more extensive in the central and western parts of the investigated Toshka area. Risk evaluation of sand dune movements in the southeastern part of the Western Desert points to medium to high sand encroachment risk values. These may represent serious hazards to the newly-established Toshka Project, threatening roads, as well as cultivated lands in the area.

Windblown Sand in Ganges Chasma

NASA Image and Video Library

2017-04-25

Dark, windblown sand covers intricate sedimentary rock layers in this image captured by NASA's Mars Reconnaissance Orbiter (MRO) from Ganges Chasma, a canyon in the Valles Marineris system. These features are at once familiar and unusual to those familiar with Earth's beaches and deserts. Most sand dunes on Earth are made of silica-rich sand, giving them a light color; these Martian dunes owe their dark color to the iron and magnesium-rich sand found in the region. https://photojournal.jpl.nasa.gov/catalog/PIA21600

Simulation of Effects of the Saffman Force and the Magnus Force on Sand Saltation in Turbulent Flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Zhongquan C.; Zou, Xueyong; Yang, Xiaofan

2011-12-11

The effects of both the Saffman force and Magnus force on sand saltation are investigated. Turbulent flows in a channel and over a barchans dune are considered with sand particles injected into the flow. The results show that both of the forces increase the height and skipping distance of sand saltation, with the Magnus force giving more significant effect on the height. These forces can also increase the sand settling at the lee side of the barchans dune.

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.

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

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

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

USGS Publications Warehouse

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

2013-01-01

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

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

... such as Empire, Glen Arbor, and Frankfort are closer. Named after a complex of coastal sand dunes, the Lakeshore features white sand beaches, steep bluffs reaching as high as 450 feet above Lake Michigan, thick maple and beech forests, and clear inland lakes. The Lakeshore's most notable features--the ancient sand...

Origin of intraformational folds in the Jurassic Todilto Limestone, Ambrosia Lake uranium mining district, McKinley and Valencia counties, New Mexico

USGS Publications Warehouse

Green, M.W.

1982-01-01

The Todilto Limestone of Middle Jurassic age in the Ambrosia Lake uranium mining district of McKinley and Valencia Counties, New Mexico, is the host formation for numerous small- to medium-sized uranium deposits in joints, shear zones, and fractures within small- to large-scale intraformational folds. The folds probably were formed as a result of differential sediment loading when eolian sand dunes of the overlying Summerville Formation of Middle Jurassic age migrated over soft, chemically precipitated, lime muds of the Todilto shortly after their deposition in a regressive, mixed fresh and saline lacustrine or marine environment of deposition. Encroachment of Summerville eolian dunes over soft Todilto lime muds was apparently a local phenomenon and was restricted to postulated beltlike zones which trended radially across the Todilto coastline toward the receding body of water. Intraformational folding is believed to be confined to the pathways of individual eolian dunes or clusters of dunes within the dune belts. During the process of sediment loading by migrating sand dunes, layers of Todilto lime mud were differentially compacted, contorted, and dewatered, producing both small- and large-scale plastic deformation structures, including convolute laminations, mounds, rolls, folds, and small anticlines and synclines. With continued compaction and dewatering, the mud, in localized areas, reached a point of desaturation at which sediment plasticity was lost. Prolonged loading by overlying dune sands thus caused faulting, shearing, fracturing, and jointing of contorted limestone beds. These areas or zones of deformation within the limestone became the preferred sites of epigenetic uranium mineralization because of the induced transmissivity created by sediment rupture. Along most of the prograding Todilto coastline, adjacent to the eolian dune belts, both interdune and coastal sabkha environments dominated during Todilto-Summerville time. Sediments in coastal areas consisted mainly of clay, silt, sandy silt, and very fine-grained sand, which was apparently derived from the winnowing of the finer grained fraction of sediment from adjacent dune fields during periods of eolian activity. Most of the sabkha sediments were probably carried in airborne suspension to the low-lying, ground-water-saturated coastal areas, where they were deposited as relatively uniform blanket-like layers. Deposition of sabkha deposits was apparently slow and uniform over most of the Todilto coastal areas and crested only small-scale deformation features in underlying Todilto rocks. Large-scale deformation features and uranium deposits are both notably absent in the Todilto where it is overlain by finer textured sabkha deposits in the Summerville.

Autumn Frost, North Polar Sand Dunes

NASA Technical Reports Server (NTRS)

1999-01-01

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

Dark Polar Dunes

NASA Image and Video Library

2006-09-01

This MOC image shows dunes in the martian north polar region. The dunes are composed of dark, coarse sand. The white areas around the dunes are the last remaining areas of seasonal carbon dioxide frost cover

Seed bank dynamics of blowout penstemon in relation to local patterns of sand movement on the Ferris Dunes, south-central Wyoming

Treesearch

Kassie L. Tilini; Susan E. Meyer; Phil S. Allen

2017-01-01

Plants restricted to active sand dunes possess traits that enable both survival in a harsh environment and local migration in response to a shifting habitat mosaic. We examined seed bank dynamics of Penstemon haydenii S. Watson (blowout penstemon) in relation to local sand movement. We measured within-year sand movement along a 400 m transect and examined plant density...

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

NASA Astrophysics Data System (ADS)

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

2012-03-01

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

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.

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…

Small Dunes

NASA Image and Video Library

2011-06-06

As wind is the only active geologic process on Mars today, sand and dust continue to be moved around the surface. Most craters host a sand dune or two, like this unnamed crater in Tyrrhena Terra. This image is from NASA 2001 Mars Odyssey.

Investigating Mars: Coprates Chasma

NASA Image and Video Library

2017-09-22

Coprates Chasma is one of the numerous canyons that make up Valles Marineris. The chasma stretches for 960 km (600 miles) from Melas Chasma to the west and Capri Chasma to the east. Landslide deposits, layered materials and sand dunes cover a large portion of the chasma floor. This image is located on the eastern side of Coprates Chasma, near Capri Chasma. The image shows multiple landslide features, which form lobed shaped deposits at the bottom of the canyon cliff face. Sand dunes are visible both on the landslide deposit and other parts of the canyon floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 16628 Latitude: -15.4094 Longitude: 304.726 Instrument: VIS Captured: 2005-09-13 10:38 https://photojournal.jpl.nasa.gov/catalog/PIA21990

Investigating Mars: Coprates Chasma

NASA Image and Video Library

2017-09-26

Coprates Chasma is one of the numerous canyons that make up Valles Marineris. The chasma stretches for 960 km (600 miles) from Melas Chasma to the west and Capri Chasma to the east. Landslide deposits, layered materials and sand dunes cover a large portion of the chasma floor. This image is located on the eastern side of Coprates Chasma, near Capri Chasma. The image shows multiple landslide features, which form lobed shaped deposits at the bottom of the canyon cliff face. Sand dunes are visible both on the landslide deposit and other parts of the canyon floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 16653 Latitude: -14.2759 Longitude: 303.707 Instrument: VIS Captured: 2005-09-15 12:01 https://photojournal.jpl.nasa.gov/catalog/PIA21991

Detection of sand encroachment patterns in desert oases. The case of Erg Chebbi (Morocco).

PubMed

Puy, Arnald; Herzog, Manuel; Escriche, Pedro; Marouche, Amou; Oubana, Yousef; Bubenzer, Olaf

2018-06-11

Desert oases are fragile agrarian areas, very vulnerable to sand encroachment by wind. Ensuring their conservation highly depends on our capacity to identify sand encroachment patterns, e.g. the origin of sand and its spatial distribution in the irrigated plots. Here we show how to tackle this issue using the case study of Erg Chebbi (Morocco), where two oases (Hassilabiad and Merzouga) are surrounded by dunes, Hamada and alluvial sediments from the Wadi Ziz. We combine field interviews with the study of wind dynamics, sediment sampling, Particle Size Distribution (PSD) tests and End-Member Modelling Analysis (EMMA). We observe that the most relevant contributor to sand encroachment is the Wadi Ziz (30%), followed by the Hamada (28%), an undetermined source of dust (25%), and the Erg dunes (16%). These genetically different sediments cluster unevenly in the oases, indicating the existence of areas with contrasting degrees of exposure to sedimentary sources. The results allow to define on solid grounds which sand source areas should be stabilized first in order to obtain the greatest reduction in sand encroachment. Our approach also provides policy-makers with better tools to identify which spots are specially vulnerable to accumulate a specific sediment, thus allowing for a more nuanced management of sand in oasis environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Comparison of geology of Jurassic Norphlet Mary Ann field, Mobile Bay, Alabama, to onshore regional Norphlet trends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marzono, M.; Pense, G.; Andronaco, P.

The geology of the Mary Ann field is better understood in light of regional studies, which help to establish a depositional model in terms of both facies and thickness variations. These studies also illustrate major differences between onshore and offshore Norphlet deposits concerning topics such as diagenesis, hydrocarbon trapping, and migration. The Jurassic Norphlet sandstone was deposited in an arid basin extending from east Texas to Florida by a fluvial-eolian depositional system, prior to the transgression of the Smackover Formation. Until discovery of the Mary Ann field in 1979, Norphlet production was restricted to onshore areas, mostly along the Pickens-Pollardmore » fault system in Mississippi, Alabama, and Florida. The Mary Ann field is a Norphlet dry-gas accumulation, and was the first offshore field in the Gulf of Mexico to establish economic reserves in the Jurassic. The field is located in Mobile Bay, approximately 25 mi (40 km) south of Mobile, Alabama. Formed by a deep-seated (more than 20,000 ft or 6096 m) faulted salt pillow, Mary Ann field produces from a series of stacked eolian dune sands situated near the Norphlet paleocoastline. Five lithofacies have been recognized in cores from the Mobil 76 No. 2 well. Each lithofacies has a distinct reservoir quality. Optimum reservoir faces are the dune and sheet sands. Nonreservoir facies are interdune (wet and dry), marine reworked, and evaporitic sands. Following deposition, these sediments have undergone varying amounts of diagenesis. Early cementation of well-sorted sands supported the pore system during compaction. However, late cementation by chlorite, silica, and alteration of liquid hydrocarbons to an asphaltic residue have completely occluded the pore system in parts of the reservoir.« less

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.

Investigating Mars: Siton Undae

NASA Image and Video Library

2017-09-19

Siton Undae is a large dune field located in the northern plains near Escorial Crater. Siton Undae is west of the crater and is one of three dune fields near the crater. The nearby north polar cap is dissected by Chasma Boreale, which exposes an ice free surface. This image was collected during the middle of northern hemisphere summer. There is no frost left on the dunes and they appear dark. These dunes are likely formed of basaltic sand. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 12909 Latitude: 76.1809 Longitude: 298.105 Instrument: VIS Captured:2004-11-11 07:20 https://photojournal.jpl.nasa.gov/catalog/PIA21959

Investigating Mars: Russell Crater

NASA Image and Video Library

2017-08-03

This image shows the western section of the large sand ridge on the floor of Russell Crater. This is also the northern extent of the dune field. The crest of the large ridge runs from lower right to upper left. Smaller dune ridges intersect the large ridge perpendicular to the crest. Russell Crater is located in Noachis Terra. A spectacular dune ridge and other dune forms on the crater floor have caused extensive imaging. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 26659 Latitude: -54.0179 Longitude: 12.8638 Instrument: VIS Captured: 2007-12-18 08:26 https://photojournal.jpl.nasa.gov/catalog/PIA21801

Terrestrial analogs of the hellespontus dunes, Mars

USGS Publications Warehouse

Breed, C.S.

1977-01-01

Geomorphic features in the Hellespontus region, Mars, were compared with dunes of the crescentic ridge type in numerous terrestrial sand seas quantitatively by dimensional analysis of dune lengths, widths, and wavelengths. Mean values for the Hellespontus dunes are close to mean values derived from measurements of all sampled terrestrial sand seas. Terrestrial analogs of form and areal distribution of the Hellespontus dunes are shown by comparison of scale ratios derived from the measurements. Dunes of similar form occur in South West Africa, in Pakistan, in the southeastern Arabian peninsula, in the Sahara, in eastern USSR and northern China, and in western North America. Terrestrial analogs closest to form and areal distribution of the Hellespontus dunes are in the Kara Kum Desert, Turkmen SSR, and in the Ala Shan (Gobi) Desert, China. ?? 1977.

APXS-derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average

NASA Astrophysics Data System (ADS)

O'Connell-Cooper, C. D.; Spray, J. G.; Thompson, L. M.; Gellert, R.; Berger, J. A.; Boyd, N. I.; Desouza, E. D.; Perrett, G. M.; Schmidt, M.; VanBommel, S. J.

2017-12-01

We present Alpha-Particle X-ray Spectrometer (APXS) data for the active Bagnold dune field within the Gale impact crater (Mars Science Laboratory (MSL) mission). We derive an APXS-based average basaltic soil (ABS) composition for Mars based on past and recent data from the MSL and Mars Exploration Rover (MER) missions. This represents an update to the Taylor and McLennan (2009) average Martian soil and facilitates comparison across Martian data sets. The active Bagnold dune field is compositionally distinct from the ABS, with elevated Mg, Ni, and Fe, suggesting mafic mineral enrichment and uniformly low levels of S, Cl, and Zn, indicating only a minimal dust component. A relationship between decreasing grain size and increasing felsic content is revealed. The Bagnold sands possess the lowest S/Cl of all Martian unconsolidated materials. Gale soils exhibit relatively uniform major element compositions, similar to Meridiani Planum and Gusev Crater basaltic soils (MER missions). However, they show minor enrichments in K, Cr, Mn, and Fe, which may signify a local contribution. The lithified eolian Stimson Formation within the Gale impact crater is compositionally similar to the ABS and Bagnold sands, which provide a modern analogue for these ancient eolian deposits. Compilation of APXS-derived soil data reveals a generally homogenous global composition for Martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time.

Occurrence of flow parallel and flow transverse bedforms in Fehmarn Belt (SW Baltic Sea) related to the local palaeomorphology

NASA Astrophysics Data System (ADS)

Feldens, P.; Diesing, M.; Schwarzer, K.; Heinrich, C.; Schlenz, B.

2015-02-01

This study describes the spatial distribution of flow-parallel sand ribbons and flow-transverse large and very large subaqueous dunes in the south-western Baltic Sea offshore Fehmarn Island between 13 m and 20 m water depth, based on hydroacoustic and grain size data. The system of sand ribbons and dunes is intermittently active due to currents induced during major inflows of the North Sea water into the Baltic Sea. The sand ribbons are located on a lag deposit on top of glacial till, while the dunes rest on top of drowned Holocene nearshore deposits. The sand ribbons reach heights between 0.4 m and 0.6 m, with widths varying between 60 m and several hundreds of metres. The observed dunes have heights between 0.09 m and 2.35 m, while their wavelengths range from 17 m to 120 m. Offshore Fehmarn Island, the transition from sand ribbons to dunes is most likely linked to a contrast in sediment supply, as reworked drowned nearshore deposits provide sediment available for transport in significantly larger amounts than glacial till. Similar to an earlier approach for river bed states, the dimensionless thickness of sediment available for transport is able to differentiate between the bed states.

Fog Bank, Namib Desert, Namibia, Africa

NASA Image and Video Library

1991-12-01

Fog is the only source of moisture for desert dwelling animals and plants living in the Namib Desert sand dune field, Namibia (23.5N, 15.0E). Coastal stratus clouds provide most of the life supporting moisture as fog droplets in this arid land where the usual annual rainfall is less than a quarter of an inch for decades at a time. In this view, the stratus clouds over the coast conform to the dune pattern proving that the fog is in ground contact.

Fog Bank, Namib Desert, Namibia, Africa

NASA Technical Reports Server (NTRS)

1991-01-01

Fog is the only source of moisture for desert dwelling animals and plants living in the Namib Desert sand dune field, Namibia (23.5N, 15.0E). Coastal stratus clouds provide most of the life supporting moisture as fog droplets in this arid land where the usual annual rainfall is less than a quarter of an inch for decades at a time. In this view, the stratus clouds over the coast conform to the dune pattern proving that the fog is in ground contact.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-02-01

This VIS image of the floor of Kaiser Crater contains several sand dune shapes and sizes. The "whiter" material is the hard crater floor surface. Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southern part of the crater floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 39910 Latitude: -46.9063 Longitude: 19.8112 Instrument: VIS Captured: 2010-12-13 11:17 https://photojournal.jpl.nasa.gov/catalog/PIA22264

Investigating Mars: Russell Crater

NASA Image and Video Library

2017-08-08

This image shows part of the dune field just south of the large sand ridge - which is visible on the very top of the image. There is a huge range of dune sizes on the floor of Russell Crater. In this image the small sizes are at the bottom of the image and transition to larger dunes at the top. Russell Crater is located in Noachis Terra. A spectacular dune ridge and other dune forms on the crater floor have caused extensive imaging. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 34544 Latitude: -54.6035 Longitude: 12.6071 Instrument: VIS Captured: 2009-09-27 15:35 https://photojournal.jpl.nasa.gov/catalog/PIA21805

Numerical modelling of flow structures over idealized transverse aeolian dunes of varying geometry

NASA Astrophysics Data System (ADS)

Parsons, Daniel R.; Walker, Ian J.; Wiggs, Giles F. S.

2004-04-01

A Computational Fluid Dynamics (CFD) model (PHOENICS™ 3.5) previously validated for wind tunnel measurements is used to simulate the streamwise and vertical velocity flow fields over idealized transverse dunes of varying height ( h) and stoss slope basal length ( L). The model accurately reproduced patterns of: flow deceleration at the dune toe; stoss flow acceleration; vertical lift in the crest region; lee-side flow separation, re-attachment and reversal; and flow recovery distance. Results indicate that the flow field over transverse dunes is particularly sensitive to changes in dune height, with an increase in height resulting in flow deceleration at the toe, streamwise acceleration and vertical lift at the crest, and an increase in the extent of, and strength of reversed flows within, the lee-side separation cell. In general, the length of the separation zone varied from 3 to 15 h from the crest and increased over taller, steeper dunes. Similarly, the flow recovery distance ranged from 45 to >75 h and was more sensitive to changes in dune height. For the range of dune shapes investigated in this study, the differing effects of height and stoss slope length raise questions regarding the applicability of dune aspect ratio as a parameter for explaining airflow over transverse dunes. Evidence is also provided to support existing research on: streamline curvature and the maintenance of sand transport in the toe region; vertical lift in the crest region and its effect on grainfall delivery; relations between the turbulent shear layer and downward forcing of flow re-attachment; and extended flow recovery distances beyond the separation cell. Field validation is required to test these findings in natural settings. Future applications of the model will characterize turbulence and shear stress fields, examine the effects of more complex isolated dune forms and investigate flow over multiple dunes.

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.

Design and initial testing of a piezoelectric sensor to quantify aeolian sand transport

NASA Astrophysics Data System (ADS)

Raygosa-Barahona, Ruben; Ruiz-Martinez, Gabriel; Mariño-Tapia, Ismael; Heyser-Ojeda, Emilio

2016-09-01

This paper describes a sensor for measuring the mass flux of aeolian sand transport based on a low-cost piezo-electric transducer. The device is able to measure time series of aeolian sand transport. Maximum fluxes of 27 mg per second can be achieved. The design includes a sand trap, an electronic amplifier circuit and an embedded system for data collection. A field test was performed, where the basis for signal interpretation and the corresponding measurements of aeolian sand transport are presented. The sensor successfully measures fluxes driven by sea breezes of 10 ms-1, showing the importance of this process for dune-building in the region.

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

USGS Publications Warehouse

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

2006-01-01

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

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

PubMed

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

2006-05-05

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

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

2011-02-04

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.

Seasonal erosion and restoration of Mars' northern polar dunes

USGS Publications Warehouse

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.

2011-01-01

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.

A field study of flow turbulence and sediment transport dynamics on a beach surface in the lee of a coastal foredune under offshore winds

NASA Astrophysics Data System (ADS)

Baas, A. C.; Jackson, D.; Cooper, J. A.; Lynch, K.; Delgado-Fernandez, I.; Beyers, M.; Lee, Z. S.

2010-12-01

The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune (‘against’ the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u’, v’, w’). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that shear velocity obtained using traditional wind profile approaches does not correlate with transport as additional stresses are generated due to turbulent structures.

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.

Reorientation Timescales and Pattern Dynamics for Titan's Dunes: Does the Tail Wag the Dog or the Dragon?

NASA Astrophysics Data System (ADS)

Hayes, A. G.; Ewing, R. C.; Cassini Radar Science Team, T.

2011-12-01

Fields of bedform patterns persist across many orders of magnitude, from cm-scale sub-aqueous current ripples to km-scale aeolian dunes, and form with surprisingly little difference in expression despite a range of formative environments. Because of the remarkable similarity between and among patterns, extracting information about climate and environment from these patterns is a challenge. For example, crest orientation is not diagnostic of a particular flow regime; similar patterns form under many different flow configurations. On Titan, these challenges have played out with many attempts to reconcile dune-field patterns with modeled and expected wind regimes. We propose that thinking about the change in dune orientation, rather than the orientation itself, can provide new insights on the long-term stability of the dune-field patterns and the formative wind regime. In this work, we apply the re-orientation model presented by Werner and Kocurek [Geology, 1997] to the equatorial dune fields of Titan. We measure variations in pattern parameters (crest spacing, crest length and defect density, which is the number of defect pairs per total crest length) both within and between Titan's dune fields to describe pattern maturity and identify areas where changes in dune orientation are likely to occur (or may already be occurring). Measured defect densities are similar to Earth's largest linear dune fields, such as the Namib Sand Sea and the Simpson Desert. We use measured defect densities in the Werner and Kocurek model to estimate crestline reorientation rates. We find reorientation timescales varying from ten to a hundred thousand times the average migration timescale (time to migrate a bedform one meter, ~1 Titan year according to Tokano (Aeolian Research, 2010)). Well organized patterns have the longest reorientation time scales (~10^5 migration timescales), while the topographically or spatially isolated patches of dunes show the shortest reorientation times (~10^3 migration timescales). In addition, comparisons between spacing and defect density of Titan's dunes and some of the largest fields observed on Earth and Mars reveal that dune patterns on all three planets are geometrically similar, suggesting that growth and organization share common pattern dynamics. Our results suggest that Titan's dunes may react to gross bedform transport averaged over orbital timescales, relaxing the requirement that a single modern wind regime is required to produce the observed pattern.

Grain Size Measurements of Eolian Ripples in Gale Crater, Mars

NASA Astrophysics Data System (ADS)

Weitz, C. M.; Sullivan, R. J., Jr.; Lapotre, M. G. A.; Rowland, S. K.; Edgett, K. S.; Grant, J. A., III; Yingst, R. A.

2017-12-01

The Curiosity rover team has explored several different eolian sand targets in Gale crater, including dunes and ripples. Using Curiosity's Mars Hand Lens Imager (MAHLI), we measured the size of grains on or near ripple crests within dunes, ripple fields, and in isolated ripples. The Barby target (Sol 1184) is on the crest of a ripple on the lower stoss slope of the barchan High dune. Flume Ridge (Sol 1604) and Avery Peak (Sol 1651) are smaller ripples on the Nathan Bridges and Mount Desert Island linear dunes. Schoolhouse Ledge (Sol 1688) is an isolated megaripple not associated with either a dune or ripple field. Enchanted Island (Sol 1751) is a ripple contained within a larger ripple field near the Vera Rubin Ridge. Our results show the grains of the Avery Peak and Flume Ridge targets are mostly 75-150 µm in size and grain motion was observed during each MAHLI imaging sequence. Barby is dominated by 250-450 µm grains assumed to be active based upon the lack of a dust coating, though grain motion was not observed. The Enchanted Island target has slightly larger grains than Barby, with most between 300-500 µm. The grains have some dust aggregates on their surfaces, suggesting they have been less active in recent months or years relative to the ripples examined within the Bagnold dune field. Finally, grains along the crest of Schoolhouse Ledge are the largest, 400-600 µm, and all of the grain surfaces have a thin dust coating, indicating the ripple is not currently active. Some of the ripple crests have similar grain sizes on both the stoss and lee sides (Schoolhouse Ledge, Barby) whereas other ripples showed larger grains concentrated on the stoss side (Enchanted Island, Avery Peak, Flume Ridge). Scuffing by the rover's front wheel revealed both Schoolhouse Ledge and Enchanted Island had coarser grains dominating the ripple surface with finer grains within the ripple interior. In general, the surfaces of active sand ripples have smaller grains compared to the inactive ripples which exhibit an armor of larger grains. Our results indicate grain sizes vary widely depending upon such factors as ripple activity, location along the ripple, ripple size, dune type, and orientation relative to the wind direction.

Aeolian Sediment Transport Pathways and Aerodynamics at Troughs on Mars

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

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

PubMed

Kok, Jasper F

2010-02-19

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

Multiple origins of linear dunes on Earth and Titan

USGS Publications Warehouse

Rubin, David M.; Hesp, Patrick A.

2009-01-01

Dunes with relatively long and parallel crests are classified as linear dunes. On Earth, they form in at least two environmental settings: where winds of bimodal direction blow across loose sand, and also where single-direction winds blow over sediment that is locally stabilized, be it through vegetation, sediment cohesion or topographic shelter from the winds. Linear dunes have also been identified on Titan, where they are thought to form in loose sand. Here we present evidence that in the Qaidam Basin, China, linear dunes are found downwind of transverse dunes owing to higher cohesiveness in the downwind sediments, which contain larger amounts of salt and mud. We also present a compilation of other settings where sediment stabilization has been reported to produce linear dunes. We suggest that in this dune-forming process, loose sediment accumulates on the dunes and is stabilized; the stable dune then functions as a topographic shelter, which induces the deposition of sediments downwind. We conclude that a model in which Titan's dunes formed similarly in cohesive sediments cannot be ruled out by the existing data.

Sand-grain micromorphology used as a sediment-source indicator for Kharga Depression dunes (Western Desert, S Egypt)

NASA Astrophysics Data System (ADS)

Woronko, B.; Dłużewski, M.; Woronko, D.

2017-12-01

Roundness and surface-feature characteristics of sand grains collected from two dune ridges in Kharga Depression (southern Egypt) were tested for potential use as source-to-sink indicators of dunes movement. Grain examination was accommodated through Scanning Electron Microscope (SEM) analysis. Five grain types were distinguished: A) fresh; B) sheet precipitated with ;raindrop; structures; C) platy precipitated; D) broken; and E) with chemically etched surfaces-each type diagnostic of a specific geomorphic inheritance. Regarding the level of sphericity, these grains were subdivided into nine roundness classes (0.1-0.9), where angular grains are marked by 0.1 and very well-rounded grains by 0.9. Significant roundness and grain-type surface variations are observed both along dune ridges and between them. Poorly and medium-rounded grain populations dominate, along with sheet-precipitated grains. The contribution of well- and very well-rounded grains is low. The northern part of both eastern and western dune ridges is characterized by grains that represent high-energy aqueous environments with well-rounded grains, whereas platy precipitated grains with a lower level of roundness are concentrated in the middle part of the dune ridges. The southern part of the Kharga Depression is again characterized by sheet-precipitated grains. Our results indicate that the northern part of dune ridges in the Kharga Depression is mainly built of sands that originate from beyond the depression (e.g., Ghard Abu-Maharik) and the weathered deposits of the Nubian and Moghra Sandstones. The dunes in central and southern part of the Kharga Depression also derive sand from a local depression bottom comprised of playa and fluvial deposits. The growing importance of the local sand source may be explained by the lowering of the local groundwater table, which resulted in playa drying. This groundwater loss resulted in the degradation of the vegetation cover, facilitating an increase in wind entrainment of playa sediments.

Insights from Askja sand sheet, Iceland, as a depositional analogue for the Bagnold Dune Field, Gale Crater, Mars.

NASA Astrophysics Data System (ADS)

Ukstins, I.; Sara, M.; Riishuus, M.; Schmidt, M. E.; Yingst, R. A.; Berger, J.

2017-12-01

Examining the compositional effect of aeolian transport and sorting processes on basaltic sands is significant for understanding the evolution of the Bagnold dune field, as well as other martian soils and sedimentary units. We use the Askja sand sheet, Iceland, as a testbed to quantify the nature of soil production and aeolian transport processes in a mafic system. Basalts from Askja and surrounding volcanic units, which can have high MgO (5-18 wt %) and high Fe2O3 (5-18 wt %), have been weathered to form mafic volcaniclastic deposits which are incorporated into a 40-km long sand sheet to the E-SE of the caldera, ranging from 10 cm to 10 m thick, and covering 240 km2. Ash and lava from the 2014-2015 Holuhraun eruption were emplaced onto the southeastern part of the sand sheet. The SW section is deflationary and defined by very fine to medium grained basaltic sand with ventifact cobbles and boulders. The central part is inflating and dominated by very fine-grained sand, relict lava fields, and small to large sand ripples (1 to 30 cm). The NE portion is also inflating but accumulation is limited to topographic depressions. Bulk chemistry of >200 sand samples are similar to Martian crust (SiO2: 48-52 wt %, MgO: 5-8 wt %, Fe2O3: 13-15 wt %). MgO concentrations vary with distance along the sand sheet, increasing by 1.5% over 10 km in the downwind direction (E, NE), then maintaining a relatively consistent concentration of 6.75 wt % over 18 km. Mean equancy of grains decreases 15 % to the E over 10 km followed by a plateau at 65 to 75 %. Material at depth tends to be of higher sphericity than material on or near the surface. Notably, MgO increases while the sphericity decreases and both data sets level off at 10 km, which suggests these two variables are related. These indicate input of material with prismoidal morphology around 10 km, and may be due to the Holuhraun eruption.

Modern sedimentary facies, depositional environments, and major controlling processes on an arid siliciclastic coast, Al qahmah, SE Red Sea, Saudi Arabia

NASA Astrophysics Data System (ADS)

Nabhan, Abdullah I.; Yang, Wan

2018-04-01

The facies and environments along the arid siliciclastic coast of Red Sea in Al Qahmah, Saudi Arabia are studied to establish a depositional model for interpretation of ancient rocks deposited in rift settings. Field and petrographic studies of 151 sediment samples in an area of 20 km2 define seven main facies types: beach, washover fan, tidal channel, dune, sabkha, delta, and wadi (seasonal stream). The wadi and delta facies are composed of poorly to moderately well-sorted, gravelly, medium-to-fine sands. Delta-front sands are redistributed by southward longshore currents to form a beach. Beach facies is composed of well-to-moderately sorted fine sands with minor gravels, which contain high concentrations of magnetite, ilmenite, garnet, pyroxene, amphibole, epidote, titanite, and apatite grains, indicating strong winnowing. Crabs and other burrowers destroy primary sedimentary structures and mix sediments in foreshore and backshore of the beaches. Wind and storm surge rework foreshore and backshore sediments to form washover fans. Sabkha facies occurs extensively in supratidal depressions behind beach, are flooded by rainstorms and spring tide, and capped by a 5-cm-thick crust composed of interlaminated halite, quartz, albite, minor gypsum and biotite, and rarely calcium carbonate. Halite occurs as thin sheets and gypsum as nodules with a chicken-wire structure. Clastic fraction in sabkha sediments ranges from coarse silt to coarse sand with moderate sorting, and is transported by currents and wind. Tidal inlets and tidal creeks assume abandoned wadis and are filled by muddy sand. Sand dunes and sand sheets are 1-7 m high and widely distributed due to variable wind directions. Fine-grained dune sands are moderately well sorted, whereas sheet sands are coarser and poorly sorted due to vegetation baffling. Most eolian sands are sourced from beach deposits. This suite of complex riverine, wave, tidal, wind, chemical, and biological processes form the facies mosaic along the arid Al Qahmah coast, which is strongly affected by climate-driven evaporation and wind action.

Fungal symbiosis and precipitation alter traits and dune building by the ecosystem engineer, Ammophila breviligulata.

PubMed

Emery, Sarah M; Bell-Dereske, Lukas; Rudgers, Jennifer A

2015-04-01

Ecosystem engineer species influence their community and ecosystem by creating or altering the physical structure of habitats. The function of ecosystem engineers is variable and can depend on both abiotic and biotic factors. Here we make use of a primary successional system to evaluate the direct and interactive effects of climate change (precipitation) and fungal endophyte symbiosis on population traits and ecosystem function of the ecosystem engineering grass species, Ammophila breviligulata. We manipulated endophyte presence in A. breviligulata in combination with rain-out shelters and rainfall additions in a factorial field experiment established in 2010 on Lake Michigan sand dunes. We monitored plant traits, survival, growth, and sexual reproduction of A. breviligulata from 2010-2013, and quantified ecosystem engineering as the sand accumulation rate. Presence of the endophyte in A. breviligulata increased vegetative growth by up to 19%, and reduced sexual reproduction by up to 46% across all precipitation treatments. Precipitation was a less significant factor than endophyte colonization for A. breviligulata growth. Reduced precipitation increased average leaf number per tiller but had no other effects on plant traits. Changes in A. breviligulata traits corresponded to increases in sand accumulation in plots with the endophyte as well as in plots with reduced precipitation. Sand accumulation is a key ecosystem function in these primary successional habitats, and so microbial symbiosis in this ecosystem engineer could lead to direct effects on the value of these dune habitats for humans.

Assessing the Importance of Cross-Stream Transport in Bedload Flux Estimates from Migrating Dunes: Colorado River, Grand Canyon National Park

NASA Astrophysics Data System (ADS)

Leary, K. P.; Buscombe, D.; Schmeeckle, M.; Kaplinski, M. A.

2017-12-01

Bedforms are ubiquitous in sand-bedded rivers, and understanding their morphodynamics is key to quantifying bedload transport. As such, mechanistic understanding of the spatiotemporal details of sand transport through and over bedforms is paramount to quantifying total sediment flux in sand-bedded river systems. However, due to the complexity of bedform field geometries and migration in natural settings, our ability to relate migration to bedload flux, and to quantify the relative role of tractive and suspended processes in their dynamics, is incomplete. Recent flume and numerical investigations indicate the potential importance of cross-stream transport, a process previously regarded as secondary and diffusive, to the three-dimensionality of bedforms and spatially variable translation and deformation rates. This research seeks to understand and quantify the importance of cross-stream transport in bedform three-dimensionality in a field setting. This work utilizes a high-resolution (0.25 m grid) data set of bedforms migrating in the channel of the Colorado River in Grand Canyon National Park. This data set comprises multi-beam sonar surveys collected at 3 different flow discharges ( 283, 566, and 1076 m3/s) along a reach of the Colorado River just upstream of the Diamond Creek USGS gage. Data were collected every 6 minutes almost continuously for 12 hours. Using bed elevation profiles (BEPs), we extract detailed bedform geometrical data (i.e. bedform height, wavelength) and spatial sediment flux data over a suite of bedforms at each flow. Coupling this spatially extensive data with a generalized Exner equation, we conduct mass balance calculations that evaluate the possibility, and potential importance, of cross-stream transport in the spatial variability of translation and deformation rates. Preliminary results suggest that intra-dune cross-stream transport can partially account for changes in the planform shape of dunes and may play an important role in spatially variable translation and deformation rates. Parameterization of cross-stream sediment transport could lead to accounting for ambiguities in bedload flux calculations caused by dune deformation, which in turn could significantly improve overall calculation of bedload and total load sediment transport in sand bedded rivers.

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

Introduction of European beach grass (Ammophila arenaria) to coastal dune systems of western North America induced significant changes to the transport and storage of sediment, and consequently the nesting habitat of the western snowy plover (Charadrius alexandrinus nivosus). At the Bodega Marine Reserve and Sonoma Coast State Park, Ammophila was introduced within the ~0.5 km2 dune area in the 1920's to limit the flux of sand through Bodega Harbor and agricultural land. To assess the potential impact of restoration efforts (Ammophila removal) on aeolian sediment flux, we measured sediment flux as a function of wind speeds and ground cover, and used these measurements to parameterize a spatial model for historical sand deposition Fine- to coarse-grained lithic to sub-lithic sand is delivered to the Bodega dune system from Salmon Creek beach, the down-shore terminus of a littoral system fed by the 3846 km2 Russian River catchment, several small (<100 km2) coastal catchments, and seacliff erosion. Littoral sediment traverses the 1.8 km wide dune system from NW to SE via aeolian transport. Ammophila colonization occurred initially adjacent to the shoreface, inducing deposition of a ~10 meter-high foredune and has subsequently encroached the ~0.5 km2 region between the foredune and Bodega Harbor. Comparison of historical topographic maps via raster subtraction indicates rapid construction of both the foredune and a ~15 meter-high transverse dune (Gaffney ridge) at the edge of the planted region. An average accumulation rate of ~4,000 m3/yr is indicated within the study swath by the preserved sediment volumes. Within the modern dune system, unvegetated areas exhibit 2-3 meter wavelength, ~1/2 meter amplitude mega-ripples, and the uppermost 2-10 cm consists of coarse-sand to granule-sized armor layer. In contrast, grain-sizes in vegetated areas are largely vertically homogenous. Open areas are typically 2-8 meters lower than adjacent vegetated areas, and show evidence for net lowering of the land surface (i.e., exposed fence posts, roots). Conversely, vegetated areas appear prone to sediment accumulation, particularly downwind of unvegetated areas. We measured sand transport using 0.5 m high traps deployed at 18 sites throughout the dune field, and used a linear mixed effects model to predict transport rate as a function of wind and ground cover class, taking into account random effects of sampling date and repeated measurements at each site. The analysis indicates up to 450-times higher transport rates in unvegetated areas relative to vegetated areas at peak wind conditions. We then used these results to parameterize a simple raster-based sediment flux model for the 0.5 km wide study area, using LIDAR-based topography and aerial orthophotography to classify ground cover. Due to the nearly complete compartmentalization of sediment flux by vegetative baffling, the model suggests that proposed restoration (removal of vegetative cover) of the seaward 1 km of the dune system would lead to significant increases in sediment transport in the treated area accompanied by accumulation along its vegetated downwind edge, but little to no change in sand flux within Ammophila-covered areas >0.2 km downwind of restored areas.

Sand Transport under Highly Turbulent Airflow on a Beach Surface

NASA Astrophysics Data System (ADS)

Baas, A. C. W.; Jackson, D. W. T.; Cooper, J. A. G.; Lynch, K.; Delgado-Fernandez, I.; Beyers, J. H. M.

2012-04-01

The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune ('against' the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u', v', w'). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that shear velocity obtained using traditional wind profile approaches does not correlate with transport as additional stresses are generated due to turbulent structures.

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

USGS Publications Warehouse

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

2006-01-01

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

Interaction of petroleum mulching, vegetation restoration and dust fallout on the conditions of sand dunes in southwest of Iran

NASA Astrophysics Data System (ADS)

Azoogh, Liela; Khalili moghadam, Bijan; Jafari, Siroos

2018-06-01

In the past half-century, petroleum mulching-biological fixation (PM-BF) practices have been employed to stabilize sand dunes in Iran. However, the effects of PM-BF practices on the attributes of sand dunes and the dispersion of heavy metals of mulch have been poorly understood. To this end, three regions treated with PM-BF for 5, 20, and 40 years and a control region with no PM-BF were studied. Samples of soil properties were taken at the depths of 0-10 cm and 10-50 cm, with three replications, in Khuzestan Province. The results showed that PM-BF practices promoted the restoration of vegetation cover in the sand dunes. In addition, these practices increased the deposition of dust particles, gradually increasing the magnitudes of palygorskite and smectite clays over time. The interactions between dust deposition and PM-BF practices significantly altered the chemical and physical properties of the dunes. PM-BF practices increased soil organic matter (184-287%), cation exchangeable capacity (142-209%), electrical conductivity (144-493%), clay content (134-196%), and penetration resistance (107-170%) compared to the region with no PM-BF practices. Furthermore, petroleum mulching significantly increased the amount of Ni (1.19%), Cd (1.55%), Pb (1.08%), Cu (1.34%), Zn (1.38%), Mn (1.66%), and Fe (1.15%). However, in the long term, these elements will probably leach linearly as a consequence of an increase in organic matter and soil salinity in the light texture of sand dunes.

Limited change in dune mobility in response to a large decrease in wind power in semi-arid northern China since the 1970s

USGS Publications Warehouse

Mason, J.A.; Swinehart, J.B.; Lu, H.; Miao, X.; Cha, P.; Zhou, Y.

2008-01-01

The climatic controls on dune mobility, especially the relative importance of wind strength, remain incompletely understood. This is a key research problem in semi-arid northern China, both for interpreting past dune activity as evidence of paleoclimate and for predicting future environmental change. Potential eolian sand transport, which is approximately proportional to wind power above the threshold for sand entrainment, has decreased across much of northern China since the 1970s. Over the same period, effective moisture (ratio of precipitation to potential evapotranspiration) has not changed significantly. This "natural experiment" provides insight on the relative importance of wind power as a control on dune mobility in three dunefields of northern China (Mu Us, Otindag, and Horqin), although poorly understood and potentially large effects of human land use complicate interpretation. Dune forms in these three regions are consistent with sand transport vectors inferred from weather station data, suggesting that wind directions have remained stable and the stations adequately represent winds that shaped the dunes. The predicted effect of weaker winds since the 1970s would be dune stabilization, with lower sand transport rates allowing vegetation cover to expand. Large portions of all three dunefields remained stabilized by vegetation in the 1970s despite high wind power. Since the 1970s, trends in remotely sensed vegetation greenness and change in mobile dune area inferred from sequential Landsat images do indicate widespread dune stabilization in the eastern Mu Us region. On the other hand, expansion of active dunes took place farther west in the Mu Us dunefield and especially in the central Otindag dunefield, with little overall change in two parts of the Horqin dunes. Better ground truth is needed to validate the remote sensing analyses, but results presented here place limits on the relative importance of wind strength as a control on dune mobility in the study areas. High wind power alone does not completely destabilize these dunes. A large decrease in wind power either has little short-term effect on the dunes, or more likely its effect is sufficiently small that it is obscured by human impacts on dune stability in many parts of the study areas. ?? 2008 Elsevier B.V. All rights reserved.

Investigating Mars: Moreux Crater

NASA Image and Video Library

2017-11-23

This image of Moreux Crater shows the eastern side of the central peak, as well as the nearby sand dunes. In this false color image sand dunes are "blue". Smaller patches of blue are located on the central peak materials and indicate where surface winds have moved fine materials on/off the peak deposits. The pitted and curvilinear morphology of the central peak deposits have been interpreted to have formed by glacial activity. Moreux Crater is located in northern Arabia Terra and has a diameter of 138 kilometers. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 12518 Latitude: 41.8223 Longitude: 44.7638 Instrument: VIS Captured: 2004-10-10 02:55 https://photojournal.jpl.nasa.gov/catalog/PIA22126

Investigating Mars: Moreux Crater

NASA Image and Video Library

2017-11-24

This image of Moreux Crater shows the highest elevations of the central peak, as well as the nearby sand dunes. In this false color image sand dunes are "blue". Smaller patches of blue are located on the central peak materials and indicate where surface winds have moved fine materials on/off the peak deposits. The pitted and curvilinear morphology of the central peak deposits have been interpreted to have formed by glacial activity. Moreux Crater is located in northern Arabia Terra and has a diameter of 138 kilometers. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 46786 Latitude: 41.7667 Longitude: 44.3482 Instrument: VIS Captured: 2012-07-01 13:41 https://photojournal.jpl.nasa.gov/catalog/PIA22127

Dunes in the Solar System : New Perspectives, Analogs and Challenges

NASA Astrophysics Data System (ADS)

Lorenz, R. D.

2016-12-01

These are exciting times for planetary Aeolian research. New paradigms opened up by numerical modeling backed by laboratory and field experimentation now permit a much higher-fidelity mapping of dune morphology to wind regime and sediment characteristics. The identification of the 'fingering mode' of bedform growth, and its association with limited sediment supply, now brings a systematic explanation of what was once bewildering complexity and opens the way to decoding more environmental detail from the landscape than was possible before. Much of this model work has been developed in parallel with, if not stimulated by, the discovery of vast fields of sand dunes on Titan a decade ago, and datasets of higher resolution and wider coverage on Mars and Earth. The pace of relevant discoveries has accelerated, with bedforms observed on comet 67P-Churyumov-Gerasimenko, periodic structures on Pluto's landscape, and a possibly new class of bedform discovered by the Curiosity rover's close inspection of the Bagnold dunes on Mars - all in the last two years! These features have all stimulated examination of transport physics at the particle and bedform scale, especially in rarified conditions.At the global scale, Titan's dune patterns have been broadly explained, and hint at Croll-Milankovich climate cycles. Yet the origin of the sand remains a mystery. Much work remains to understand regional transports on all worlds, which can be addressed with mesoscale and CFD models. Observationally, the greatest opportunity for progress will come with higher resolution views of the surfaces of Venus and Titan. Venus, a world on which aeolian transport was observed in only a couple of hours of surface observation, is in particular long overdue for further exploration. In all these cases, terrestrial analogs provide valuable insights.

Investigating Mars: Melas Chasma

NASA Image and Video Library

2017-12-07

Melas Chasma is part of the largest canyon system on Mars, Valles Marineris. At only 563 km long (349 miles) it is not the longest canyon, but it is the widest. Located in the center of Valles Marineris, it has depths up to 9 km below the surrounding plains, and is the location of many large landslide deposits, as will as layered materials and sand dunes. There is evidence of both water and wind action as modes of formation for many of the interior deposits. This VIS image is located along the northern cliff face of the chasma. The linear features are large landslide surfaces. A region of sand dunes is located along the change in elevation from the cliff face at the top of the image and the floor of the canyon at the bottom of the image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 31790 Latitude: -10.3951 Longitude: 290.141 Instrument: VIS Captured: 2009-02-12 20:47 https://photojournal.jpl.nasa.gov/catalog/PIA22137

Investigating Mars: Coprates Chasma

NASA Image and Video Library

2017-10-03

Coprates Chasma is one of the numerous canyons that make up Valles Marineris. The chasma stretches for 960 km (600 miles) from Melas Chasma to the west and Capri Chasma to the east. Landslide deposits, layered materials and sand dunes cover a large portion of the chasma floor. This image is located in central Coprates Chasma. In this image, there is a landslide deposit at the bottom of the image. The brighter material to the left of the landslide appears to be a rough surface likely etched by wind action. The chasma contains numerous regions of sand dunes, indicating that the wind plays a part in the erosion and deposition of fine materials in the canyon. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 35820 Latitude: -12.793 Longitude: 297.407 Instrument: VIS Captured: 2010-01-10 16:39 https://photojournal.jpl.nasa.gov/catalog/PIA21996

Investigating Mars: Melas Chasma

NASA Image and Video Library

2017-11-27

Melas Chasma is part of the largest canyon system on Mars, Valles Marineris. At only 563 km long (349 miles) it is not the longest canyon, but it is the widest. Located in the center of Valles Marineris, it has depths up to 9 km from the surrounding plains, and is the location of many large landslide deposits, as will as layered materials and sand dunes. There is evidence of both water and wind action as modes of formation for many of the interior deposits. This VIS image shows layered materials and sand dunes. The image is located on the mid elevations on the south side of the canyon. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 10838 Latitude: -12.7865 Longitude: 288.837 Instrument: VIS Captured: 2004-05-24 17:32 https://photojournal.jpl.nasa.gov/catalog/PIA22128

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

NASA Astrophysics Data System (ADS)

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.

2017-12-01

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were 29° where grainflows were present and 33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.

Environmental implications of the use of sulfidic back-bay sediments for dune reconstruction — Lessons learned post Hurricane Sandy

USGS Publications Warehouse

Plumlee, Geoffrey S.; Benzel, William M.; Hoefen, Todd M.; Hageman, Philip L.; Morman, Suzette A.; Reilly, Timothy J.; Adams, Monique; Berry, Cyrus J.; Fischer, Jeffrey; Fisher, Irene

2016-01-01

Some barrier-island dunes damaged or destroyed by Hurricane Sandy's storm surges in October 2012 have been reconstructed using sediments dredged from back bays. These sand-, clay-, and iron sulfide-rich sediments were used to make berm-like cores for the reconstructed dunes, which were then covered by beach sand. In November 2013, we sampled and analyzed partially weathered materials collected from the cores of reconstructed dunes. There are generally low levels of metal toxicants in the reconstructed dune materials. However oxidation of reactive iron sulfides by percolating rainwater produces acid-sulfate pore waters, which evaporate during dry periods to produce efflorescent gypsum and sodium jarosite salts. The results suggest use of sulfidic sediments in dune reconstruction has both drawbacks (e.g., potential to generate acid runoff from dune cores following rainfall, enhanced corrosion of steel bulwarks) and possible benefits (e.g., efflorescent salts may enhance structural integrity).

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-01-31

This VIS image of the floor of Kaiser Crater contains a large variety of sand dune shapes and sizes. The "whiter" material is the hard crater floor surface. Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southern part of the crater floor. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 35430 Latitude: -46.8699 Longitude: 19.4731 Instrument: VIS Captured: 2009-12-09 14:09 https://photojournal.jpl.nasa.gov/catalog/PIA22263

Barchan and Linear Dunes on Earth and Mars - Comparative Research

NASA Astrophysics Data System (ADS)

Tsoar, H.; Edgett, K. S.; Schatz, V.; Parteli, E. J.; Herrmann, H. J.

2007-05-01

High resolution images from MGS and MRO reveal, in detail, ripples and dunes on Mars that were not discerned in old Viking images. The two basic dune types known on Earth, barchan (and transverse) and seif (linear), are also common on Mars, although seif dunes are quite rare on that planet. Some Martian barchan and seif dunes have a different morphology, particularly as evident in the Martian north polar region. Some of the barchans have an elongated, elliptical shape, while some of the linear dunes lack the sinuosity commonly associated with terrestrial seif dunes. These barchan and linear dunes occur together, side-by-side, and in some cases are merged to create a single bed-form. Induration of the dunes, or crust formation, can explain the occurrence of these dunes of unusual morphology in the Martian north polar region. Crusts may form as water vapor diffuses into and out of the fine-grained materials on the planet's surface. Salts would be deposited as intergranular cement. Because these bedforms occur in the polar region, the cementing agent could be ice instead of salts; indeed, the dunes spend more than half each Martian year beneath a covering of seasonal frost, mostly frozen carbon dioxide. Elliptical shaped barchans were created artificially in Saudi Arabia by spraying advancing barchan dunes with crude oil to stabilize them until the dunes reached a streamlined body shape. Simulation work indicates that the same process can occur on the indurated Martian barchans, but by cementation of grains rather than introduction of oil. Short lee dunes that have a linear shape with a sharp-edged crest are known to form from sand accumulation at the lee side of obstacles. Once a dune is stabilized by induration or crust, it functions as an obstacle to the wind. Linear lee dunes stabilized by ice (water or carbon dioxide) or mineral crust may elongate and form a long linear dune that aligns parallel to the wind. Melting of the ice will set up a straight linear dune, with loose sand, parallel to the dominant wind. Field observations on terrestrial deserts show that such a dune can only be formed when it is covered by vegetation. If vegetation is removed the bare linear dune disintegrates into small barchans. Simulation also shows that linear dune is unstable and deforms until it takes the shape of a string of barchans, which are the stable shape under unidirectional winds.

Thermal behavior and ice-table depth within the north polar erg of Mars

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.; Mellon, Michael T.; Herkenhoff, Kenneth E.; Phillips, Roger J.; Davis, Brian J.; Ewer, Kenneth J.; Bowers, Lauren M.

2014-02-01

We fully resolve a long-standing thermal discrepancy concerning the north polar erg of Mars. Several recent studies have shown that the erg's thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice-cemented sand. Our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg, demonstrating that other likely forms of physical heterogeneity play only a minor role, and obviating the need to invoke exotic materials. Thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust-sized materials than with sand. Since theory and laboratory data show that dunes will only form out of sand-sized particles, exotic sand-sized agglomerations of dust have been invoked to explain the low values of thermal inertia. However, the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand-sized basaltic grains, whereas Martian dust deposits are generally lighter and redder. The alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the Mars Global Surveyor Thermal Emission Spectrometer and the Mars Odyssey Thermal Emission Imaging System and by forward modeling of physical heterogeneity. In addition, our results exclude a uniform composition of dark dust-sized materials, and they show that the thermal effects of the dune slopes and bright interdune materials evident in high-resolution images cannot account for the erg's thermal behavior.

Thermal behavior and ice-table depth within the north polar erg of Mars

USGS Publications Warehouse

Putzig, Nathaniel E.; Mellon, Michael T.; Herkenhoff, Kenneth E.; Phillips, Roger J.; Davis, Brian J.; Ewer, Kenneth J.; Bowers, Lauren M.

2014-01-01

We fully resolve a long-standing thermal discrepancy concerning the north polar erg of Mars. Several recent studies have shown that the erg’s thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice-cemented sand. Our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg, demonstrating that other likely forms of physical heterogeneity play only a minor role, and obviating the need to invoke exotic materials. Thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust-sized materials than with sand. Since theory and laboratory data show that dunes will only form out of sand-sized particles, exotic sand-sized agglomerations of dust have been invoked to explain the low values of thermal inertia. However, the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand-sized basaltic grains, whereas Martian dust deposits are generally lighter and redder. The alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the Mars Global Surveyor Thermal Emission Spectrometer and the Mars Odyssey Thermal Emission Imaging System and by forward modeling of physical heterogeneity. In addition, our results exclude a uniform composition of dark dust-sized materials, and they show that the thermal effects of the dune slopes and bright interdune materials evident in high-resolution images cannot account for the erg’s thermal behavior.

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

USGS Publications Warehouse

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

2016-08-11

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

Experimental investigation of cephapirin adsorption to quartz filter sands and dune sands

NASA Astrophysics Data System (ADS)

Peterson, Jonathan W.; O'Meara, Theresa A.; Seymour, Michael D.

2008-08-01

Batch experiments were performed to investigate cephapirin (a widely used veterinary antibiotic) adsorption on various size sands of low total organic carbon content (0.08-0.36 wt%). In the aqueous concentration range investigated (11-112 μmol/L cephapirin), adsorption to nearly pure quartz filter sands (0.50-3.35 mm diameter) is low. Isotherms are S-shaped and most display a region of minimum adsorption, where decreased adsorption occurs with increasing solution concentration, followed by increased adsorption at higher concentrations. Cephapirin adsorption to quartz-rich, feldspar-bearing dune sands (0.06-0.35 mm diameter), and the smallest quartz filter sand investigated (0.43-0.50 mm), can be described by linear sorption isotherms over the range of concentrations investigated. Distribution coefficients ( K d) range from 0.94 to 3.45 L/kg. No systematic relationship exists between grain size and amount of adsorption for any of the sands investigated. Cephapirin adsorption is positively correlated to the feldspar ratio (K-feldspar/(albite + Ca-plagioclase). Feldspar-ratio normalization of distribution coefficients was more effective than organic carbon normalization at reducing variability of K d values in the dune sands investigated.

Impacts of climate change on the formation and stability of late Quaternary sand sheets and falling dunes, Black Mesa region, southern Colorado Plateau, USA

USGS Publications Warehouse

Ellwein, Amy L.; Mahan, Shannon; McFadden, Leslie D.

2015-01-01

Widely used predictive models of eolian system dynamics are typically based entirely on climatic variables and do not account for landscape complexity and geomorphic history. Climate-only assumptions fail to give accurate predictions of the dynamics of this and many other dune fields. A growing body of work suggests that eolian deposits in wind-driven semiarid climates may be more strongly related to increases in sediment supply than to increases in aridity.

Ripples and Dunes in Proctor Crater

NASA Image and Video Library

2017-10-09

NASA's Mars Reconnaissance Rover (MRO) has observed two types of wind (aeolian) features in Proctor Crater: large, dark features that are sand dunes, made up of basaltic particles, and smaller, light-toned ripples that we call "TAR," or "transverse aeolian ridges." The origin of the TARs is a mystery. They might be dust deposits, or perhaps coarse grained ripples that are coated in bright dust. These TARs are less than 10 meters tall, and are much smaller than the sand dunes that reach impressive heights of over 130 meters. In other places on Mars, TARs are generally older than sand dunes, but here in Proctor Crater, it is not so obvious. How can we tell which came first, the TARs or the dunes? The dunes are situated on top of the TARs, and with this information, we can say the dunes are clearly the younger formations here in Proctor Crater. Fortunately, HiRISE has a tool that can solve this riddle. By taking stereo images of the same region from two different locations, we can estimate the topography of the region by measuring the displacement of surface features from one picture to the other. The result is a quantitative estimate of the local surface topography, called a digital terrain model. The dunes are situated on top of the TARs, and with this information, we can say the dunes are clearly the younger formations here in Proctor Crater. https://photojournal.jpl.nasa.gov/catalog/PIA22040

Investigating Mars: Candor Chasma

NASA Image and Video Library

2018-01-09

This image shows part of western Candor and the erosion of a large mesa. Layered materials are visible throughout the image. The dark material with the linear appearance in the middle of the image are sand dunes. Sand dunes are created by wind action. At the present time, wind is the active process shaping the surface. Candor Chasma is one of the largest canyons that make up Valles Marineris. It is approximately 810 km long (503 miles) and has is divided into two regions - eastern and western Candor. Candor is located south of Ophir Chasma and north of Melas Chasma. The border with Melas Chasma contains many large landslide deposits. The floor of Candor Chasma includes a variety of landforms, including layered deposits, dunes, landslide deposits and steep sided cliffs and mesas. Many forms of erosion have shaped Chandor Chasma. There is evidence of wind and water erosion, as well as significant gravity driven mass wasting (landslides). The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 6245 Latitude: -5.77639 Longitude: 284.339 Instrument: VIS Captured: 2003-05-12 14:49 https://photojournal.jpl.nasa.gov/catalog/PIA22161

On the formation and pattern coarsening of subaqueous ripples and dunes

NASA Astrophysics Data System (ADS)

Jarvis, P.; Vriend, N. M.

2017-12-01

The physical mechanisms governing formation, evolution and co-interaction of sand ripples and dunes are an active topic of investigation. Previous studies employed a variety of experimental and field observations and numerical and theoretical modelling, but a unified description of the physical mechanisms governing bedform morphology remains elusive. Specifically, the interactions between bedforms are poorly understood and experimental data for validation is scarce. We present results from a novel experimental setup where we study both (1) the early stage of subaqueous ripple formation from a flat, erodible bed, and (2) the later-time evolution of the system. Experiments are carried out in a periodic 2 m diameter circular channel of width 9 cm, containing a flat bed of sand overlain by water. Counter-rotation between the channel and a submerged paddle assembly drives a shear flow eroding and transporting sediment, thereby creating bed instabilities that evolve over time. By measuring the bed profile under varying grain size and flow velocity, we calculate the initial distribution of wavelengths in the bed disturbance, the growth rate of perturbations and the temporal evolution of the wavelength spectrum. We compare the early-time results with predictions from linear stability models as well as statistically quantifying the later-time coarsening behaviour. During the coarsening stage, we observe different modes of bedform interaction: coalescence and ejection. A further set of experiments are performed to investigate this in detail, whereby we study the interaction between a pair of dunes migrating on a non-erodible surface. By varying the sizes of the two dunes, we produce a phase-diagram for the coalescence and ejection modes. Combining the results of these binary collisions with the coarsening statistics from the flat-bed experiments we can develop a more complete understanding of the physics of dune interactions, as well as how interactions govern the development of entire dune fields.

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-20

This is a false color image of Rabe Crater. In this combination of filters "blue" typically means basaltic sand. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 52231 Latitude: -43.6665 Longitude: 34.2627 Instrument: VIS Captured: 2013-09-22 14:29 https://photojournal.jpl.nasa.gov/catalog/PIA22146

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-22

This is a false color image of Rabe Crater. In this combination of filters "blue" typically means basaltic sand. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 67144 Latitude: -43.5512 Longitude: 34.5951 Instrument: VIS Captured: 2017-02-01 12:57 https://photojournal.jpl.nasa.gov/catalog/PIA22148

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-19

This is a false color image of Rabe Crater. In this combination of filters "blue" typically means basaltic sand. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 51157 Latitude: -43.6787 Longitude: 34.3985 Instrument: VIS Captured: 2013-06-26 05:33 https://photojournal.jpl.nasa.gov/catalog/PIA22145

[Dynamic changes of surface soil organic carbon and light-fraction organic carbon after mobile dune afforestation with Mongolian pine in Horqin Sandy Land].

PubMed

Shang, Wen; Li, Yu-qiang; Wang, Shao-kun; Feng, Jing; Su, Na

2011-08-01

This paper studied the dynamic changes of surface (0-15 cm) soil organic carbon (SOC) and light-fraction organic carbon (LFOC) in 25- and 35-year-old sand-fixing Mongolian pine (Pinus sylvestris var. mongolica) plantations in Horqin Sandy Land, with a mobile dune as a comparison site. After the afforestation on mobile dune, the content of coarse sand in soil decreased, while that of fine sand and clay-silt increased significantly. The SOC and LFOC contents also increased significantly, but tended to decrease with increasing soil depth. Afforestation increased the storages of SOC and LFOC in surface soil, and the increment increased with plantation age. In the two plantations, the increment of surface soil LFOC storage was much higher than that of SOC storage, suggesting that mobile dune afforestation had a larger effect on surface soil LFOC than on SOC.

Earth observations taken during the STS-103 mission

NASA Image and Video Library

1999-12-26

STS103-728-022 (19-27 December 1999)--- One of the astronauts aboard the Earth-orbiting Space Shuttle Discovery used a handheld 70mm camera to photograph the Tifernine dunes (note, the dunes are below the "beak" of sandstone rock). According to NASA scientists studying the STS-103 photo collection, the dunes were created when the dark sandstone rocks trapped sand. Winds, they continued, then piled the sand into dunes up to 457.2 m (1,500 ft). The color of the sandstone is due to a desert varnish, the scientists reported. The varnish is composed of manganese, iron oxides, hydroxides, and clay minerals, they said.

Ripples and Dunes

NASA Technical Reports Server (NTRS)

2006-01-01

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

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

Studies of the Terrestrial Molecular Oxygen and Carbon Cycles in Sand Dune Gases and in Biosphere 2.

NASA Astrophysics Data System (ADS)

Severinghaus, Jeffrey Peck

Molecular oxygen in the atmosphere is coupled tightly to the terrestrial carbon cycle by the processes of photosynthesis, respiration, and burning. This dissertation examines different aspects of this coupling in four chapters. Chapter 1 explores the feasibility of using air from sand dunes to reconstruct atmospheric O_2 composition centuries ago. Such a record would reveal changes in the mass of the terrestrial biosphere, after correction for known fossil fuel combustion, and constrain the fate of anthropogenic CO_2. Test drilling in sand dunes shows that sand dunes do contain old air, as shown by the concentrations of chlorofluorocarbons and ^{85}Kr. Diffusion is shown to dominate mixing rather than advection. However, biological respiration in dunes corrupts the signal, and isotopic analysis of O_2 and N _2 shows that fractionation of the gases precludes use of sand dunes as archives. Chapter 2 further explores this fractionation, revealing a previously unknown "water vapor flux fractionation" process. A flux of water vapor out of the moist dune into the dry desert air sweeps out the other gases, forcing them to diffuse back into the dune. The heavy isotopes of N_2 and O_2 diffuse more slowly, creating a steady state depletion of heavy isotopes in the dune interior. Molecular diffusion theory and a laboratory simulation of the effect agree well with the observations. Additional fractionation of the dune air occurs via thermal diffusion and gravitational settling, and it is predicted that soil gases in general will enjoy all three effects. Chapter 3 examines the cause of a mysterious drop in O _2 concentrations in the closed ecosystem of Biosphere 2, located near Tucson, Arizona. The organic -rich soil manufactured for the experiment is shown to be the culprit, with CO_2 produced by bacterial respiration of the organic matter reacting with the extensive concrete surfaces inside. Chapter 4 examines the O_2:C stoichiometry of terrestrial soil respiration and photosynthesis, in the context of using atmospheric O_2 measurements to constrain the size of the "missing sink" of CO_2. Direct measurements of soil respiration and biomatter elemental abundance suggest a value of 1.1 +/- 0.05 oxygen molecules per CO_2 molecule.

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

Federal Register 2010, 2011, 2012, 2013, 2014

2012-09-07

...: Regular Mail: BLM Director (210), Attention: Brenda Hudgens- Williams, P.O. Box 71383, Washington, DC 20024-1383. Overnight Mail: BLM Director (210), Attention: Brenda Hudgens- Williams, 20 M Street SE...; and visual resources. The Proposed Imperial Sand Dunes RAMP and CDCA Plan Amendment/Final EIS includes...

Abrupt sand-dune accumulation at the northeastern margin of the Tibetan Plateau challenges the wet MIS3a inferred from numerous lake-highstands

PubMed Central

Long, Hao; Fuchs, Markus; Yang, Linhai; Cheng, Hongyi

2016-01-01

Over the Tibetan Plateau and adjacent regions, numerous 14C-based lake records revealed a ubiquitous wet climatic period during 40–25 ka (late MIS 3), which is in contradiction with the global pattern of generally cold and dry climates. This paper focuses on OSL dating results of a large set of sand dunes and alluvial sediments (50 OSL ages) from the Qinwangchuan (QWC) Basin at the northeast edge of the Tibetan Plateau, with the aim to test the validity of the anomalous wet condition for the late MIS 3 interval, evidenced by numerous lake highstands. The abrupt sand dune accumulation as indication of increased aridity in the study area was OSL dated to ~40–13 ka. This dry climatic inference of the sand dune system from QWC apparently shows no wet MIS 3a event. Thus, the anomalous wet conditions revealed by high lake levels for the late MIS 3 phase may not be a universal phenomena across entire western China. PMID:27172907

Salinization owing to evaporation from bare-soil surfaces and its influences on the evaporation

NASA Astrophysics Data System (ADS)

Shimojimaa, Eiichi; Yoshioka, Ryuma; Tamagawa, Ichiro

1996-04-01

To investigate the relationship between evaporation and salinization, the surfaces of three columns of uniform porous materials, desert dune sand, silica sand and glass beads, respectively, were exposed to a temperature-, humidity- and/or wind-speed-controlled ambient atmosphere. For the dune sand, chemicals such as Na +, Ca 2+, Cl - and SO 42-, dissolved mainly from CaSO 4, Na 2SO 4, CaCO 3 and NaC1 in the sand particles, caused marked salinization near the top surface. Slow dissolution of Na 2SO 4 and CaSO 4 influenced the development of concentration profiles for SO 42- and Na + markedly for months after the beginning of the experiment, while the profile of Cl - was not affected directly, because dissolution of NaCl was rapid. Concentration profiles of Cl - for the glass beads and for the silica sand columns filled with a high concentration of NaCI solution of (10 4 mg1 -1 for Cl -), were analysed similarly. Experimental results suggested that the vapour flux in a dry soil became larger because of the increase in the gradient of the vapour density caused by greater chemical enrichment near the top surface compared with that at the evaporation surface. The vapour flux also became smaller as the gradient of the vapour density decreased, owing to the markedly enriched evaporation surface. In the experiment with glass beads, filled with the NaCl solution, solute crystallization (4-10 mm thick) was observed. For the dune sand, only when a turbulent airflow was applied did a crust (a few millimetres in thickness) form entirely on the top surface. Such deposition led to a reduction in the flux of water vapour as the permeable cross-sectional area decreased. The resistance to transfer increased three to ten times for the glass beads but only by 30% for the dune sand. The lower increase for the dune sand may be due to penetration of the applied airflow into cracks in the crust.

Modeling and monitoring the hydrological effects of the Sand Engine.

NASA Astrophysics Data System (ADS)

Schaars, Frans; Hoogmoed, Merel; van Vliet, Frank; Stuyfzand, Pieter; Groen, Michel; van der Made, Kees-Jan; Caljé, Ruben; Auken, Esben; Bergsted Pedersen, Jesper

2013-04-01

Since 1887, Dunea Water Company produces high quality drinking water using the dune area at Monster (Province of South Holland, the Netherlands). Annually, 8 billion liters of water is produced here using artificial recharge and recovery with shallow wells and infiltration lakes. The dunes are an important step in producing drinking water serving as an underground buffer, leveling fluctuating in temperature and quality and removing bacteria and viruses from the infiltrated water in a natural way. Since space is limited in the Netherlands, the drinking water production of Dunea is closely matched with surrounding land uses and natural constraints. This prevents groundwater nuisance, upconing and intrusion of salt water and, in this case, movement of a nearby groundwater pollution. This is especially true in the Monster area where the dunes are fairly low and small; the coast is less than 350 meters from the recovery wells. The coast of Monster was identified as a weak link in the coastal defense of The Netherlands. Because of this, two coastal defense projects were carried out between 2009 and 2011. The first project involved creating an extra dune ridge in front of existing dunes which leads to intrusion of a large volume of seawater. Directly after completion, the Sand Engine was constructed. This hook shaped sand peninsula will supply the coast with sand for the coming decades due to erosion and deposition along the coast. These two large coastal defense projects would obviously influence the tightly balanced hydrological system of Monster. Without hydrological intervention, the drinking water production would no longer be sustainable in this area. To study the effects of these projects and to find a solution to combine coastal defense and drinking water supply, field research and effect (geochemical) modeling were used interactively. To prevent negative effects it was decided to construct interception wells on top of the new dune ridge (28 in total). A comprehensive monitoring system was built to keep track of the salt groundwater and the groundwater heads. The zero measurement included groundwater heads, water samples, but also geophysical methods such as SkyTEM and CVES. We will also show the monitoring system we use to keep track of the groundwater heads and salt water intrusion in the future.

Subsurface valleys and geoarcheology of the Eastern Sahara revealed by shuttle radar

USGS Publications Warehouse

McCauley, J.F.; Schaber, G.G.; Breed, C.S.; Grolier, M.J.; Haynes, C.V.; Issawi, B.; Elachi, C.; Blom, R.

1982-01-01

The shuttle imaging radar (SIR-A) carried on the space shuttle Columbia in November 1981 penetrated the extremely dry Selima Sand Sheet, dunes, and drift sand of the eastern Sahara, revealing previously unknown buried valleys, geologic structures, and possible Stone Age occupation sites. Radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand- and alluvium-filled valleys, some nearly as wide as the Nile Valley and perhaps as old as middle Tertiary. The nov-vanished maijor river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat, hyperarid region. Underfit and incised dry wadis, many superimposed on the large valleys, represent erosion by intermittent running water, probably during Quaternary pluvials. Stone Age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation. The presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present-day oases which have been centers of episodic human habitation. Radar penetration of dry sand and soils varies with the wavelength of the incident signals (24 centimeters for the SIR-A system), incidence angle, and the electrical properties of the materials, which are largely determined by moisture content. The calculated depth of radar penetration of dry sand and granules, based on laboratory measurements of the electrical properties of samples from the Selima Sand Sheet, is at least 5 meters. Recent (September 1982) field studies in Egypt verified SIR-A signal penetration depths of at least 1 meter in the Selima Sand Sheet and in drift sand and 2 or more meters in sand dunes. Copyright ?? 1982 AAAS.

DIVERSITY OF ARBUSCULAR MYCORRHIZAL FUNGI ALONG A SAND DUNE STABILIZATION GRADIENT: A CASE STUDY AT PRAIA DE JOAQUINA, ILHA DE SANTA CATARINA, SOUTH BRAZIL

EPA Science Inventory

Species diversity of abuscular mycorrhizal fungi (AMF) was assessed along a dunes stabilization gradient (embyonic dune, foredune and fixed dune) at Praia da Joaquina (Joaquina Beach), Ilha de Santa Catarina. These dunes served as a case study to assess whether diversity and myc...

Extraction of lidar-based dune-crest elevations for use in examining the vulnerability of beaches to inundation during hurricanes

USGS Publications Warehouse

Stockdon, H.F.; Doran, K.S.; Sallenger, A.H.

2009-01-01

The morphology of coastal sand dunes plays an important role in determining how a beach will respond to a hurricane. Accurate measurements of dune height and position are essential for assessing the vulnerability of beaches to extreme coastal change during future landfalls. Lidar topographic surveys provide rapid, accurate, high-resolution datasets for identifying the location, position, and morphology of coastal sand dunes over large stretches of coast. An algorithm has been developed for identification of the crest of the most seaward sand dune that defines the landward limit of the beach system. Based on changes in beach slope along cross-shore transects of lidar data, dune elevation and location can automatically be extracted every few meters along the coastline. Dune elevations in conjunction with storm-induced water levels can be used to predict the type of coastal response (e.g., beach erosion, dune erosion, overwash, or inundation) that may be expected during hurricane landfall. The vulnerability of the beach system at Fire Island National Seashore in New York to the most extreme of these changes, inundation, is assessed by comparing lidar-derived dune elevations to modeled wave setup and storm surge height. The vulnerability of the beach system to inundation during landfall of a Category 3 hurricane is shown to be spatially variable because of longshore variations in dune height (mean elevation 5.44 m, standard deviation 1.32 m). Hurricane-induced mean water levels exceed dune elevations along 70 of the coastal park, making these locations more vulnerable to inundation during a Category 3 storm. ?? 2009 Coastal Education and Research Foundation.

Coastal Studies for Primary Grades.

ERIC Educational Resources Information Center

Butler, Venetia R.; Roach, Ellen M.

1986-01-01

Describes a set of field trips for participants of the Coastal Environmental Education for Primary Grades program in Georgia. Includes a sample of the activities used by first- and second-grade students. Discusses follow-up activities and the need for more educational programs dealing with sand dunes and saltwater marshes. (TW)

Dunes - False Color

NASA Image and Video Library

2015-12-01

The THEMIS VIS camera contains 5 filters. Data from different filters can be combined in many ways to create a false color image. This image from NASA 2001 Mars Odyssey spacecraft shows sand dunes and sand materials in depressions near the south pole. The dark blue tone shows the location of sand transport from one depression to another. Orbit Number: 16870 Latitude: -75.1264 Longitude: 348.882 Instrument: VIS Captured: 2005-10-03 09:18 http://photojournal.jpl.nasa.gov/catalog/PIA20105

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars.

PubMed

Ewing, R C; Lapotre, M G A; Lewis, K W; Day, M; Stein, N; Rubin, D M; Sullivan, R; Banham, S; Lamb, M P; Bridges, N T; Gupta, S; Fischer, W W

2017-12-01

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.

Mars Global Digital Dune Database; MC-1

USGS Publications Warehouse

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

2010-01-01

The Mars Global Digital Dune Database presents data and describes the methodology used in creating the global database of moderate- to large-size dune fields on Mars. The database is being released in a series of U.S. Geological Survey (USGS) Open-File Reports. The first release (Hayward and others, 2007) included dune fields from 65 degrees N to 65 degrees S (http://pubs.usgs.gov/of/2007/1158/). The current release encompasses ~ 845,000 km2 of mapped dune fields from 65 degrees N to 90 degrees N latitude. Dune fields between 65 degrees S and 90 degrees S will be released in a future USGS Open-File Report. Although we have attempted to include all dune fields, 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), Mars Orbiter Camera narrow angle (MOC NA), or Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images allowed, we classified dunes and included some dune slipface measurements, which were derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. It was beyond the scope of this report to look at the detail needed to discern subtle dune modification. It was also beyond the scope of this report to measure all slipfaces. We attempted to include enough slipface measurements to represent the general circulation (as implied by gross dune morphology) and to give a sense of the complex nature of aeolian activity on Mars. The absence of slipface measurements in a given direction should not be taken as evidence that winds in that direction did not occur. When a dune field was located within a crater, the azimuth from crater centroid to dune field centroid was calculated, as another possible indicator of wind direction. Output from a general circulation model (GCM) is also included. In addition to polygons locating dune fields, the database includes 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 an ArcReader project 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 an ArcMap project. The ArcMap project allows fuller use of the data, but requires ESRI ArcMap(Registered) software. A fuller description of the projects can be found in the NP_Dunes_ReadMe file (NP_Dunes_ReadMe folder_ and the NP_Dunes_ReadMe_GIS file (NP_Documentation folder). For users who prefer to create their own projects, the data are available in ESRI shapefile and geodatabase formats, as well as the open Geography 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. (NP_Documentation folder) Documentation files are available in PDF and ASCII (.txt) files. Tables are available in both Excel and ASCII (.txt)

Floor of Baldet Crater

NASA Image and Video Library

2002-06-17

This NASA Mars Odyssey image shows a remarkable array of dunes on the floor of a large impact crater named Baldet. Many of the dunes in this region are isolated features with large, sand-free interdune surfaces between the individual dunes.

The dune effect on sand-transporting winds on Mars.

PubMed

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

2015-11-05

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

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

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.

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-21

This is a false color image of Rabe Crater. In this combination of filters "blue" typically means basaltic sand. This VIS image crosses the entire crater and demonstrates how extensive the dunes are on the floor of Rabe Crater. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 67013 Latitude: -43.2572 Longitude: 34.5875 Instrument: VIS Captured: 2017-01-21 18:25 https://photojournal.jpl.nasa.gov/catalog/PIA22147

Intensity of geodynamic processes in the Lithuanian part of the Curonian Spit

NASA Astrophysics Data System (ADS)

Česnulevičius, Algimantas; Morkūnaitė, Regina; Bautrėnas, Artūras; Bevainis, Linas; Ovodas, Donatas

2017-06-01

The paper considers conditions and intensity of aeolian and dune slope transformation processes occurring in the wind-blown sand strips of the dunes of the Curonian Spit. An assessment of the intensity of aeolian processes was made based on the analysis of climatic factors and in situ observations. Transformations in aeolian relief forms were investigated based on the comparison of geodetic measurements and measurements of aerial photographs. Changes in micro-terraces of dune slopes were investigated through comparison of the results of repeated levelling and measurements of aerial photographs. The periods of weak, medium, and strong winds were distinguished, and sand moisture fluctuations affecting the beginning of aeolian processes were investigated. The wind-blown sand movements were found to start when sand moisture decreased by 2 % in the surface sand layer and by up to 5 % at a depth of 10 cm. In 2004-2016, the wind-blown sand movements affected the size of reference deflation relief forms: scarp length by 8 %, scarp width by 35 %, pothole length by 80 %, pothole width by 80 %, roll length by 17 %, roll width by 18 %, hollow length by 17 %, and hollow width by 39 %. The elementary relief forms in the leeward eastern slopes of the dunes experienced the strongest transformations. During a period of 5 months, the height of micro-terraces of the eastern slope of the Parnidis Dune changed from 0.05 to 0.64 cm. The change was related to fluctuations in precipitation intensity: in July-August 2016 the amount of precipitation increased 1.6-fold compared with the multiannual average, thus causing the change in the position of terrace ledges by 21 %.

Identification of Radar Facies and Linked Process-Based Palaeo-environmental Interpretations, Cooloola Sand Mass, Queensland, Australia

NASA Astrophysics Data System (ADS)

Gontz, A. M.; McCallum, A. B.; Moss, P. T.; Shulmeister, J.

2015-12-01

During 2015 and 2014, nearly 60 km of high-resolution ground penetrating radar data were acquired on the Cooloola Sand Mass (CSM) in southeastern coastal Queensland. The CSM is part of the world's largest downdrift sand system. It contains three of the world's largest sand islands, several National Parks, a UNESCO World Heritage Site and covers 500 km of the eastern Australian coastline in northern New South Wales and southern Queensland. The large (>200 m) composite dunes of the CSM exhibit multiple activation phases, coastally eroding bluffs and dune development is not obvious from surficial exposures. This provides an ideal environment for ground penetrating radar. The dune sequences have been provisionally dated to the mid Quaternary through present and represent the potential for a large palaeo-environmental proxy dataset. GPR imagery was collected using a MALA GeoSciences Ground Explorer (GX) system with 160 and 450 MHz antennae from the numerous physiographic and ecological provinces as well as mapped surficial soil units at the CSM. These data were used to determine the subsurface architecture, identify radar facies and develop environmental interpretations. In the clean, aeolian quartz-rich sands, radar wave penetration exceeded 30 m (radar velocity = 0.07 m/ns) with the 160 MHz antenna. From the interpreted environmental units including palaeosol, dune slip face, dune stoss face, sand blow, beach, estuarine and fluvial, we are developing maps to relate the units and focus a detailed sampling regime that includes OSL, sediment geochemistry and sedimentology, The interpreted units, stratigraphic correlation and spatial distribution of the facies is the first step in a broader project to unravel the Quaternary environmental and climate records that are archived within the sediments of the CSM.

Investigating Mars: Candor Chasma

NASA Image and Video Library

2018-01-12

This image shows part of eastern Candor Chasma. In the middle of the image is a set of linear ridges and valleys. These features are called yardangs and are created by uniform winds that winnow away materials. Once the valleys are formed the wind then is funneled through the valley and erosion continues more in the valley than on the ridges. At the bottom of the valleys there are sand materials covering the slope between the valleys and the surrounding chasma floor. Beyond this coating of sand there are darker sand deposits where wind has accumulated the sand into larger dunes. The brighter mesa on the right side of the image has also been wind eroded into yardangs, but are aligned in a different direction than the larger yardangs. This indicates that wind directions within the canyon have changed over time. Candor Chasma is one of the largest canyons that make up Valles Marineris. It is approximately 810 km long (503 miles) and has is divided into two regions - eastern and western Candor. Candor is located south of Ophir Chasma and north of Melas Chasma. The border with Melas Chasma contains many large landslide deposits. The floor of Candor Chasma includes a variety of landforms, including layered deposits, dunes, landslide deposits and steep sided cliffs and mesas. Many forms of erosion have shaped Chandor Chasma. There is evidence of wind and water erosion, as well as significant gravity driven mass wasting (landslides). The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 10551 Latitude: -6.93639 Longitude: 288.562 Instrument: VIS Captured: 2004-05-01 02:24 https://photojournal.jpl.nasa.gov/catalog/PIA22165

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.

Breeding system and its consequence on fruit set of a rare sand dune shrub Eremosparton songoricum (Fabaceae: Papilionoideae): implications for conservation

USDA-ARS?s Scientific Manuscript database

The breeding system and its consequence on fruit set of Eremosparton songoricum (Litv.) Vass., a rare shrubby legume occurring in moving or semi-fixed sand dunes of Central Asian deserts, were examined by manipulative experiments and observational studies in natural populations during the period of ...

75 FR 20826 - Notice of Intent To Prepare a Draft Environmental Impact Statement on Beach and Dune Restoration...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-21

... restore the beach and dune by placing approximately 610,000 cubic yards of beach compatible sand along the proposed project's beach. The sand will be hopper-dredged from a relict shoal approximately three to six... analyze the following: aesthetics/visual quality, agricultural resources, air quality, biological...

Investigating Mars: Russell Crater - False Color

NASA Image and Video Library

2017-08-11

This image shows the western part of the dune field on the floor of Russell Crater. This is a false color image of Russell crater and it's surroundings. Sand Dunes usually appear "blue" in false color images. Russell Crater is located in Noachis Terra. A spectacular dune ridge and other dune forms on the crater floor have caused extensive imaging. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 59591 Latitude: -54.471 Longitude: 13.1288 Instrument: VIS Captured: 2015-05-21 10:57 https://photojournal.jpl.nasa.gov/catalog/PIA21808

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.

Analysis of wind-blown sand movement over transverse dunes.

PubMed

Jiang, Hong; Huang, Ning; Zhu, Yuanjian

2014-12-01

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

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

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

NASA Astrophysics Data System (ADS)

Weaver, C. M.; Wiggs, G.

2007-12-01

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

Connecting Brabant's cover sand landscapes through landscape history

NASA Astrophysics Data System (ADS)

Heskes, Erik; van den Ancker, Hanneke; Jungerius, Pieter Dirk; Harthoorn, Jaap; Maes, Bert; Leenders, Karel; de Jongh, Piet; Kluiving, Sjoerd; van den Oetelaar, Ger

2015-04-01

Noord-Brabant has the largest variety of cover sand landscapes in The Netherlands, and probably in Western Europe. During the Last Ice Age the area was not covered by land ice and a polar desert developed in which sand dunes buried the existing river landscapes. Some of these polar dune landscapes experienced a geomorphological and soil development that remained virtually untouched up to the present day, such as the low parabolic dunes of the Strabrechtse Heide or the later and higher dunes of the Oisterwijkse Vennen. As Noord-Brabant lies on the fringe of a tectonic basin, the thickness of cover sand deposits in the Centrale Slenk, part of a rift through Europe, amounts up to 20 metres. Cover sand deposits along the fault lines cause the special phenomenon of 'wijst' to develop, in which the higher grounds are wetter than the boarding lower grounds. Since 4000 BC humans settled in these cover sand landscapes and made use of its small-scale variety. An example are the prehistoric finds on the flanks and the historic towns on top of the 'donken' in northwest Noord-Brabant, where the cover sand landscapes are buried by river and marine deposits and only the peaks of the dunes protrude as donken. Or the church of Handel that is built beside a 'wijst' source and a site of pilgrimage since living memory. Or the 'essen' and plaggen agriculture that developed along the stream valleys of Noord-Brabant from 1300 AD onwards, giving rise to geomorphological features as 'randwallen' and plaggen soils of more than a metre thickness. Each region of Brabant each has its own approach in attracting tourists and has not yet used this common landscape history to connect, manage and promote their territories. We propose a landscape-historical approach to develop a national or European Geopark Brabants' cover sand landscapes, in which each region focuses on a specific part of the landscape history of Brabant, that stretches from the Late Weichselian polar desert when the dune landscapes were formed, through prehistoric, Roman and medieval times up to the post-modern nature building projects aimed at restoring biodiversity. A brochure was developed to raise awareness and promote interest for a landscape historical concept, in which each region profits from being part of a quality history.

Determination of erosion thresholds and aeolian dune stabilization mechanisms via robotic shear strength measurements

NASA Astrophysics Data System (ADS)

Qian, F.; Lee, D. B.; Bodek, S.; Roberts, S.; Topping, T. T.; Robele, Y.; Koditschek, D. E.; Jerolmack, D. J.

2017-12-01

Understanding the parameters that control the spatial variation in aeolian soil erodibility is crucial to the development of sediment transport models. Currently, in-situ measurements of erodibility are time consuming and lack robustness. In an attempt to remedy this issue, we perform field and laboratory tests to determine the suitability of a novel mechanical shear strength method to assess soil erodibility. These tests can be performed quickly ( 1 minute) by a semi-autonomous robot using its direct-drive leg, while environmental controls such as soil moisture and grain size are simultaneously characterized. The robot was deployed at White Sands National Monument to delineate and understand erodibility gradients at two different scales: (1) from dry dune crest to moist interdune (distance 10s m), where we determined that shear strength increases by a factor of three with increasing soil moisture; and (2) from barren barchan dunes to vegetated and crusted parabolics downwind (distance 5 km), where we found that shear strength was enhanced by a factor of two relative to loose sand. Interestingly, shear strength varied little from carbonate-crusted dune surfaces to bio-crust covered interdunes in the downwind parabolic region, indicating that varied surface crusts contribute similarly to erosion resistance. To isolate the control of soil moisture on erodibility, we performed laboratory experiments in a sandbox. These results verify that the observed increase in soil erodibility from barchan crest to interdune at White Sands is dominated by soil moisture, and the variation in parabolic dune and barchan interdune areas results from a combination of soil moisture, bio-activity, and crust development. This study highlights that spatial variation of soil erodibility in arid environments is large enough to significantly affect sediment transport, and that probing soil erodibility with a robot has the potential to improve our understanding of this multifaceted problem.

Changes in vegetation and biological soil crust communities on sand dunes stabilizing after a century of grazing on San Miguel Island, Channel Island National Park, California

USGS Publications Warehouse

Zellman, Kristine L.

2014-01-01

San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or cyclical succession pathways. Many of the dunes that have been stabilized the longest (since before 1929) are dominated by exotic grasses. Stands of biological soil crusts (cyanobacteria) are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting a closed vascular plant canopy, which may indicate that the role of soil crusts in dune stabilization on the island is transitory. Particle-size analyses of soil samples from the study area reveal that higher biological soil crust LOD is positively correlated with increasing fine grain content. The findings indicate that changes in vegetation communities may be the most rapid at earlier and later stages of dune stabilization and that regular monitoring of dunes may help to identify the interactions between vegetation and soil crusts, as well as the potential transitions between native and exotic plant communities.

Investigating Mars: Rabe Crater

NASA Image and Video Library

2017-12-15

This VIS image provides another instance where the topography of the upper floor material affects the winds and dune formation. At the edges of the dune field, the dunes become smaller and more separated, revealing the harder surface that the dunes are moving across. Rabe Crater is 108 km (67 miles) across. Craters of similar size often have flat floors. Rabe Crater has some areas of flat floor, but also has a large complex pit occupying a substantial part of the floor. The interior fill of the crater is thought to be layered sediments created by wind and or water action. The pit is eroded into this material. The eroded materials appear to have stayed within the crater forming a large sand sheet with surface dune forms as well as individual dunes where the crater floor is visible. The dunes also appear to be moving from the upper floor level into the pit. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 57843 Latitude: -43.3482 Longitude: 34.6454 Instrument: VIS Captured: 2014-12-28 12:37 https://photojournal.jpl.nasa.gov/catalog/PIA22143

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

PubMed Central

Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.

2017-01-01

Abstract The Mars Science Laboratory rover Curiosity visited two active wind‐blown sand dunes within Gale crater, Mars, which provided the first ground‐based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial‐like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large‐ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter‐scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune‐field pattern dynamics and basin‐scale boundary conditions will dictate the style and distribution of sedimentary processes. PMID:29497590

MODELING FLOW PATTERNS IN A SMALL VEGETATED AREA IN THE NORTHERN CHICHUAHUAN DESERT USING QUIC ( QUIC URBAN AND INDUSTRIAL COMPLEX )

EPA Science Inventory

Sandstorms are frequent in the northern Chihuahuan Desert in New Mexico, an area characterized by open areas lacking vegetation, individual mesquite bushes, and mesquite coppice dunes. Field measurements of sand fluxes and wind velocities over a two year period provided a descri...

Local variation of inundation, sedimentary characteristics, and mineral assemblages of the 2011 Tohoku-oki tsunami on the Misawa coast, Aomori, Japan

NASA Astrophysics Data System (ADS)

Nakamura, Yugo; Nishimura, Yuichi; Putra, Purna Sulastya

2012-12-01

The 2011 Tohoku-oki tsunami caused severe damage to the coastal regions of eastern Japan and left a sediment veneer over affected areas. We discuss differences in depositional characteristics of the 2011 Tohoku-oki tsunami from the viewpoint of the sediment source, coastal topography and flow height. The study area on the Misawa coast, northern Tohoku, includes a 20 km long coastline with sandy beaches, coastal dunes and a gently sloping lowland. This landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit. During field surveys conducted from April 10 to May 2, 2011, we described the thickness, facies, and structure of the tsunami deposit. We also collected sand samples at approximately 20 m intervals along 13 shore-perpendicular transects extending up to 550 m inland, for grain size and mineral assemblage analysis. The tsunami flow height was estimated by measuring the elevation of debris found in trees, broken tree limbs, or water marks on buildings. The nature of the coastal lowland affected the flow height and inundation distance. In the southern part of the study area, where there is a narrow, 100 m wide low-lying coastal strip, the run-up height reached 10 m on the landward terrace slopes. To the north, the maximum inundation reached 550 m with a run-up height of 3.2 m on the wider, low-lying coastal topography. The average flow height was 4-5 m. The tsunami eroded coastal dunes and formed small scarps along the coast. Immediately landward of the coastal dunes the tsunami deposit was more than 20 cm thick, but thinned markedly inland from this point. Close to the dunes the deposit was composed largely of medium sand (1-2 Φ) with planar and parallel bedding, but with no apparent upward fining or coarsening. The grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point. The mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand. At sites more than half the inundation distance inland, the thinner tsunami deposit consisted mainly of fine sand (2.375 Φ) with some upward fining. The difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes. We infer that the well-sorted, finer sediments were deposited out of suspension, whereas the relatively coarse sands were laid down from traction flows. The depositional characteristics of the 2011 Tohoku-oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point, as opposed to flow height.

Citizen Science: Dune Restoration with Sea Oats by Junior Friends of MacArthur Beach State Park

NASA Astrophysics Data System (ADS)

Allen, S.

2016-12-01

As a crucial part of the dune ecosystem, Sea Oats are a protected species in Florida. They provide excellent habitat for small birds and mammals and prevent dune erosion with their fibrous roots.Citizen science is a research and education tool that involves everyday people in real and meaningful forms of science. My volunteer group, Junior friends of Macarthur Beach State Park, used citizen science to restore dunes by growing and planting Sea Oats. Junior friends is a group of 6-12th grade students whose purpose is to support the park through monthly activities and special events. Junior Friends asked,what is the best way to germinate/grow/and plant Sea Oats to renourish the beach dune. Specifically, what planting medium is most conducive for maximizing growth of Sea Oats? We tested three scenarios: 100% potting soil, 100% sand from the beach, 50% sand-50% potting soil mixture.Using harvested Sea Oat seeds from Macarthur Beach State Park, we separated the seeds from their casings, known as spiklets. We then monitored the plant's weekly over the course of 14 weeks and charted their growth. All the seeds had similar growth rates, but the seeds that grew in 100% potting soil consistently grew the tallest. The second tallest Sea Oats were 100% sand; the 50% sand-50% potting soil mixture produced the least amount of growth. When seedlings reached their desired growth of 6-8 inches and established a root ball, we planted the Sea Oats on the dune for restoration. After planting them,we monitored the growth of the Sea Oats on the MacArthur Beach dune throughout the rest of the year, charting the height of the planted Sea Oats. Using Citizen science we had meaningful data that helped us have a better understanding of restoring Sea Oats on Florida dunes and will help further future restorations.

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

PubMed

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

2016-03-01

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

Cross-bedding set thickness and stratigraphic architecture of aeolian systems: An example from the Upper Permian Pirambóia Formation (Paraná Basin), southern Brazil

NASA Astrophysics Data System (ADS)

Dias, Kayo Delorenzo Nardi; Scherer, Claiton M. S.

2008-05-01

The Pirambóia Formation comprises an unconformity-bounded aeolian succession essentially composed of three facies associations: aeolian sand sheet, aeolian dune and interdune facies associations. The lower portion of the Pirambóia Formation is characterised by aeolian sand sheet deposits, which are overlain by aeolian dune and interdune strata, hence pointing to an overall increase in sand availability within the paleoerg. The dune and interdune successions can be further subdivided into two distinct stratigraphic intervals in terms of their mean set thickness. Intervals 1 and 2 display mean set thicknesses of 2.9 and 6.19 m, respectively. This increase in the mean set thickness reflects an increase of the angle of climb and/or dune size. In addition to improve the stratigraphic subdivision, the recognition and correlation of intervals with distinct mean set thicknesses provides a tool for reconstructing aeolian erg architecture from drill cores.

White Sands, New Mexico as seen from STS-60

NASA Image and Video Library

1994-02-09

STS060-83-016 (3-11 Feb 1994) --- White Sands National Monument (Park) is easily recognized in the center of this near-vertical color photograph. White Sands is the world's largest gypsum dune field. It represents an alabaster sea that covers nearly 300 square miles. The National Park Service has the responsibility to preserve this unique feature, allowing the dune world to unfold in its natural environment, but without interference from humans. White Sands lies within a spectacular, oblong geological depression called the Tularosa Basin bounded by the Sacramento Mountains on the east and the San Andres Mountains on the west. Climatically the basin is a true desert, averaging less than 10 inches of rainfall per year. In terms of topographic relief the Sacramento Mountains attain elevations greater than 9,000 feet above sea level, while the San Andres Mountains on the west exceed altitudes of 8,000 feet. At the southwest corner of the White Sands is dry lake, Lucero. This lake is the lowest point in the Tularosa Basin at 3,900 feet. In terms of cultural features the city of Alamogordo (over 20,000 population) and Holloman Air Force Base can be seen with great clarity on this photograph. The area is accessible by highways U.S.70 & 82 from Las Cruces, New Mexico, and U.S.54 from El Paso, Texas.

Murzuk Sand Sea, Sahara Desert, Libya, Africa

NASA Image and Video Library

1993-01-19

STS054-152-189 (13-19 Jan. 1993) --- This near-vertical color photograph shows the very diverse landscape that is part of the great Sahara Desert of north Africa. Specifically, the vast expanse of sand dunes, located in the extreme southwestern corner of Libya, is known as the Murzuk Sand Sea. Close inspection of this photograph shows the agricultural village of Murzuk as evidenced by the numerous center pivot irrigation patterns at the edge of the Murzuk Sand Sea. The very rugged, dissected terrain to the west of this sand sea is the eastern tip of the Tassili N'ajjer Mountains and the Tadrart Plateau that are in neighboring Algeria. Several smaller areas of sand dunes are interspersed between the major areas of rock outcrops. The photograph was taken with a Linhof camera.

Municipal initiatives for managing dunes in coastal residential areas: a case study of Avalon, New Jersey, USA

NASA Astrophysics Data System (ADS)

Nordstrom, Karl F.; Jackson, Nancy L.; Bruno, Michael S.; de Butts, Harry A.

2002-10-01

The characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values. Shoreline management zones include a naturally evolving, undeveloped segment; a noneroding, developed segment; eroding and noneroding segments of an "improved beach" where dunes have been built by artificial nourishment; and a privately built, artificially nourished dune on the shoreline of an inlet. A disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences, vegetation plantings, purchase of undeveloped lots, and sediment backpassing to maintain beach widths and dune elevations. The present nourished and shaped foredune in the improved beach is higher, wider, and closer to the berm crest than the natural dune. Restricted inputs of aeolian sand keep the surface flat and poorly vegetated. A stable section of this engineered shore has a wider beach, and sand fences have created a higher foredune with greater topographic diversity. The cross shore zonation of vegetation here is more typical of natural dunes, but the environmental gradient is much narrower. The privately built dune is low, narrow, and located where it could not be created naturally. Foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size (0.16-0.21 mm) and sorting (0.31-0.39 φ), but sediment on the surface of the nourished dune is coarser (28.1% gravel) with a more poorly sorted sand fraction (1.30 φ) representing lag elements on the deflation surface. Willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the Federal Emergency Management Agency (FEMA) to replace lost sediment, thus placing an economic value on dunes. Success of the management program is attributed to: (i) timing property-purchase and dune-building programs to periods immediately after storms (causing residents to accept high dunes that restrict access or views); (ii) instituting a vigorous education program (reminding residents of hazards during nonstorm periods); (iii) maintaining control over local sediment supplies (to keep pace with erosion and create new shoreline environments); (iv) investing private and municipal economic resources in landforms (qualifying them for external funds for replacement); and (v) maintaining, augmenting, or simply tolerating biodiversity and natural processes (retaining a natural heritage).

The Impact of Rainfall on Soil Moisture Dynamics in a Foggy Desert.

PubMed

Li, Bonan; Wang, Lixin; Kaseke, Kudzai F; Li, Lin; Seely, Mary K

2016-01-01

Soil moisture is a key variable in dryland ecosystems since it determines the occurrence and duration of vegetation water stress and affects the development of weather patterns including rainfall. However, the lack of ground observations of soil moisture and rainfall dynamics in many drylands has long been a major obstacle in understanding ecohydrological processes in these ecosystems. It is also uncertain to what extent rainfall controls soil moisture dynamics in fog dominated dryland systems. To this end, in this study, twelve to nineteen months' continuous daily records of rainfall and soil moisture (from January 2014 to August 2015) obtained from three sites (one sand dune site and two gravel plain sites) in the Namib Desert are reported. A process-based model simulating the stochastic soil moisture dynamics in water-limited systems was used to study the relationships between soil moisture and rainfall dynamics. Model sensitivity in response to different soil and vegetation parameters under diverse soil textures was also investigated. Our field observations showed that surface soil moisture dynamics generally follow rainfall patterns at the two gravel plain sites, whereas soil moisture dynamics in the sand dune site did not show a significant relationship with rainfall pattern. The modeling results suggested that most of the soil moisture dynamics can be simulated except the daily fluctuations, which may require a modification of the model structure to include non-rainfall components. Sensitivity analyses suggested that soil hygroscopic point (sh) and field capacity (sfc) were two main parameters controlling soil moisture output, though permanent wilting point (sw) was also very sensitive under the parameter setting of sand dune (Gobabeb) and gravel plain (Kleinberg). Overall, the modeling results were not sensitive to the parameters in non-bounded group (e.g., soil hydraulic conductivity (Ks) and soil porosity (n)). Field observations, stochastic modeling results as well as sensitivity analyses provide soil moisture baseline information for future monitoring and the prediction of soil moisture patterns in the Namib Desert.

The Impact of Rainfall on Soil Moisture Dynamics in a Foggy Desert

PubMed Central

Li, Bonan; Wang, Lixin; Kaseke, Kudzai F.; Li, Lin; Seely, Mary K.

2016-01-01

Soil moisture is a key variable in dryland ecosystems since it determines the occurrence and duration of vegetation water stress and affects the development of weather patterns including rainfall. However, the lack of ground observations of soil moisture and rainfall dynamics in many drylands has long been a major obstacle in understanding ecohydrological processes in these ecosystems. It is also uncertain to what extent rainfall controls soil moisture dynamics in fog dominated dryland systems. To this end, in this study, twelve to nineteen months’ continuous daily records of rainfall and soil moisture (from January 2014 to August 2015) obtained from three sites (one sand dune site and two gravel plain sites) in the Namib Desert are reported. A process-based model simulating the stochastic soil moisture dynamics in water-limited systems was used to study the relationships between soil moisture and rainfall dynamics. Model sensitivity in response to different soil and vegetation parameters under diverse soil textures was also investigated. Our field observations showed that surface soil moisture dynamics generally follow rainfall patterns at the two gravel plain sites, whereas soil moisture dynamics in the sand dune site did not show a significant relationship with rainfall pattern. The modeling results suggested that most of the soil moisture dynamics can be simulated except the daily fluctuations, which may require a modification of the model structure to include non-rainfall components. Sensitivity analyses suggested that soil hygroscopic point (sh) and field capacity (sfc) were two main parameters controlling soil moisture output, though permanent wilting point (sw) was also very sensitive under the parameter setting of sand dune (Gobabeb) and gravel plain (Kleinberg). Overall, the modeling results were not sensitive to the parameters in non-bounded group (e.g., soil hydraulic conductivity (Ks) and soil porosity (n)). Field observations, stochastic modeling results as well as sensitivity analyses provide soil moisture baseline information for future monitoring and the prediction of soil moisture patterns in the Namib Desert. PMID:27764203

Maunder Crater

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 24 May 2002) The Science This image is of a portion of Maunder Crater located at about 49 S and 358 W (2 E). There are a number of interesting features in this image. The lower left portion of the image shows a series of barchan dunes that are traveling from right to left. The sand does not always form dunes as can be seen in the dark and diffuse areas surrounding the dune field. The other interesting item in this image are the gullies that can be seen streaming down from just beneath a number of sharp ridgelines in the upper portion of the image. These gullies were first seen by the MOC camera on the MGS spacecraft and it is though that they formed by groundwater leaking out of the rock layers on the walls of craters. The water runs down the slope and forms the fluvial features seen in the image. Other researchers think that these features could be formed by other fluids, such as CO₂. These features are typically seen on south facing slopes in the southern hemisphere, though this image has gullies on north facing slopes as well. The Story Little black squigglies seem to worm their way down the left-hand side of this image. These land features are called barchan (crescent-shaped) dunes. Barchan dunes are found in sandy deserts on Earth, so it's no surprise the Martian wind makes them a common site on the red planet too. They were first named by a Russian scientist named Alexander von Middendorf, who studied the inland desert dunes of Turkistan. The barchan dunes in this image occur in the basin of Maunder crater on Mars, and are traveling from right to left. The sand does not always form dunes, though, as can be seen in the dark areas of scattered sand surrounding the dune field. Look for the streaming gullies that appear just beneath a number of sharp ridgelines in the upper portion of the image. These gullies were first discovered by the Mars Orbital Camera on the Mars Global Surveyor spacecraft. While most crater gullies are found on south-facing slopes in the southern hemisphere of Mars, you can see from this image that they occur on north-facing slopes as well. Comparing where gullies appear will help scientists understand more about the conditions under which they form. Some researchers are really excited about gullies on Mars, because they believe these surface tracings might be signs that groundwater has leaked out of the rock layers on the walls of craters. If that's true, the water runs down the slope and forms the flow-like features seen in the image. Scientists can get into some really hot debates, however. Other researchers think that these features could be formed by other fluids, such as carbon dioxide. No one knows for sure, so a lot of heads will be studiously bent over these images, continuing to study them closely. The neat thing about science is that the way you get closer to the truth is to hypothesize and then test, test, and test again. Debate for scientists is seen as an essential means of making sure that no wrong assumptions are made or that no important factor is left out. It's what keeps the field interesting and dynamic . . . and sometimes quite loud and entertaining!

A Wireless Sensor Network for the Real-Time Remote Measurement of Aeolian Sand Transport on Sandy Beaches and Dunes

PubMed Central

Cappelli, Irene; Mecocci, Alessandro; Alquini, Fernanda

2018-01-01

Direct measurements of aeolian sand transport on coastal dunes and beaches is of paramount importance to make correct decisions about coast management. As most of the existing studies are mainly based on a statistical approach, the solution presented in this paper proposes a sensing structure able to orient itself according to wind direction and directly calculate the amount of wind-transported sand by collecting it and by measuring its weight. Measurements are performed remotely without requiring human action because the structure is equipped with a ZigBee radio module, which periodically sends readings to a local gateway. Here data are processed by a microcontroller and then transferred to a remote data collection centre, through GSM technology. The ease of installation, the reduced power consumption and the low maintenance required, make the proposed solution able to work independently, limiting human intervention, for all the duration of the expected experimental campaign. In order to analyze the cause-effect relationship between the transported sand and the wind, the sensing structure is integrated with a multi-layer anemoscope-anemometer structure. The overall sensor network has been developed and tested in the laboratory, and its operation has been validated in field through a 48 h measurement campaign. PMID:29518060

A Wireless Sensor Network for the Real-Time Remote Measurement of Aeolian Sand Transport on Sandy Beaches and Dunes.

PubMed

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

2018-03-08

Direct measurements of aeolian sand transport on coastal dunes and beaches is of paramount importance to make correct decisions about coast management. As most of the existing studies are mainly based on a statistical approach, the solution presented in this paper proposes a sensing structure able to orient itself according to wind direction and directly calculate the amount of wind-transported sand by collecting it and by measuring its weight. Measurements are performed remotely without requiring human action because the structure is equipped with a ZigBee radio module, which periodically sends readings to a local gateway. Here data are processed by a microcontroller and then transferred to a remote data collection centre, through GSM technology. The ease of installation, the reduced power consumption and the low maintenance required, make the proposed solution able to work independently, limiting human intervention, for all the duration of the expected experimental campaign. In order to analyze the cause-effect relationship between the transported sand and the wind, the sensing structure is integrated with a multi-layer anemoscope-anemometer structure. The overall sensor network has been developed and tested in the laboratory, and its operation has been validated in field through a 48 h measurement campaign.

Biological soil crust as a bio-mediator alters hydrological processes in stabilized dune system of the Tengger Desert, China

NASA Astrophysics Data System (ADS)

Li, Xinrong

2016-04-01

Biological soil crust (BSC) is a vital component in the stabilized sand dunes with a living cover up to more than 70% of the total, which has been considered as a bio-mediator that directly influences and regulates the sand dune ecosystem processes. However, its influences on soil hydrological processes have been long neglected in Chinese deserts. In this study, BSCs of different successional stages were chose to test their influence on the hydrological processes of stabilized dune, where the groundwater deep exceeds 30m, further to explore why occur the sand-binding vegetation replacement between shrubs and herbs. Our long-term observation (60 years) shows that cyanobacteria crust has been colonized and developed after 3 years since the sand-binding vegetation has been established and dune fixation using planted xerophytic shrubs and made sand barrier (straw-checkerboard) on shifting dune surface, lichen and moss crust occurred after 20 years, and the cover of moss dominated crust could reach 70 % after 50 years. The colonization and development of BSC altered the initial soil water balance of revegetated areas by influencing rainfall infiltration, soil evaporation and dew water entrapment. The results show that BSC obviously reduced the infiltration that occurred during most rainfall events (80%), when rainfall was greater than 5 mm or less than 20 mm. The presence of BSC reduced evaporation of topsoil after small rainfall (<5 mm) because its high proportion of finer particles slowed the evaporation rate, thus keeping the water in the soil surface longer, and crust facilitated topsoil evaporation when rainfall reached 10 mm. The amount of dew entrapment increases with the succession of BSC. Moreover, the effect of the later successional BSC to dew entrapment, rainfall infiltration and evaporation was more obvious than the early successional BSC on stabilized dunes. In general, BSC reduced the amount of rainfall water that reached deeper soil (0.4-3m), which is where the roots of shrubs are primarily distributed. These changes in the soil moisture pattern induced shifting of sand-binding vegetation from initial planted xerophytic shrub communities with higher coverage (35%) to complex communities dominated by shallow-rooted herbaceous species with low shrub coverage (9%). In correspondence with these changes, soil water balance of the initial vegetation systems (mean soil water kept 3.5%) was turned into a new balance of current vegetation (mean soil water maintains 1.5%). Above findings provide an important enlightenment for future desertification control and sand hazards prevention by revegetation.

KSC-2014-2345

NASA Image and Video Library

2014-05-02

CAPE CANAVERAL, Fla. -- At the Kennedy Space Center in Florida, the sand dunes along a 1.2 mile stretch of shoreline near Launch Pads 39A and B were restored during a six-month effort using 90,000 cubic yards of sand. To help prevent future erosion, 180,000 shrubs, including grasses, sunflowers, vines, sea grapes and palmettos were planted. Constant pounding from tropical storms, such as Hurricane Sandy in October of 2012, other weather systems and higher than usual tides, destroyed sand dunes protecting infrastructure at the spaceport. Photo credit: NASA/Dan Casper

KSC-2014-2346

NASA Image and Video Library

2014-05-02

CAPE CANAVERAL, Fla. -- At the Kennedy Space Center in Florida, the sand dunes along a 1.2 mile stretch of shoreline near Launch Pads 39A and B were restored during a six-month effort using 90,000 cubic yards of sand. To help prevent erosion, 180,000 shrubs, including grasses, sunflowers, vines, sea grapes and palmettos were planted. Constant pounding from tropical storms, such as Hurricane Sandy in October of 2012, other weather systems and higher than usual tides, destroyed sand dunes protecting infrastructure at the spaceport. Photo credit: NASA/Dan Casper

KSC-2014-2808

NASA Image and Video Library

2014-05-15

CAPE CANAVERAL, Fla. -- At the Kennedy Space Center in Florida, the sand dunes along a 1.2 mile stretch of shoreline near Launch Pads 39A and B were restored during a six-month effort using 90,000 cubic yards of sand. To help prevent erosion, 180,000 shrubs, including grasses, sunflowers, vines, sea grapes and palmettos were planted. Constant pounding from tropical storms, such as Hurricane Sandy in October of 2012, other weather systems and higher than usual tides, destroyed sand dunes protecting infrastructure at the spaceport. Photo credit: NASA/Dan Casper

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

NASA Technical Reports Server (NTRS)

Mckee, E. D.; Breed, C. S.

1973-01-01

A description and classification of major types of sand seas on the basis of morphological pattern and lineation are discussed. The steps involved in analyzing the patterns of deposits on ERTS-1 imagery, where the visible forms are mostly dune complexes rather than individual dunes are outlined. After completion of thematic maps portraying the pattern and lineation of the sand bodies, data on directions and intensity of prevailing and other winds are plotted on corresponding bases, as a preliminary to determination of internal structures through ground truth.

Long-term sand supply to Coachella Valley Fringe-toed Lizard Habitat in the Northern Coachella Valley, California

USGS Publications Warehouse

Griffiths, Peter G.; Webb, Robert H.; Lancaster, Nicholas; Kaehler, Charles A.; Lundstrom, Scott C.

2002-01-01

The Coachella Valley fringe-toed lizard (Uma inornata) is a federally listed threatened species that inhabits active sand dunes in the vicinity of Palm Springs, California. The Whitewater Floodplain and Willow Hole Reserves provide some of the primary remaining habitat for this species. The sediment-delivery system that creates these active sand dunes consists of fluvial depositional areas fed episodically by ephemeral streams. Finer fluvial sediments (typically sand size and finer) are mobilized in a largely unidirectional wind field associated with strong westerly winds through San Gorgonio Pass. The fluvial depositional areas are primarily associated with floodplains of the Whitewater?San Gorgonio Rivers and Mission Creek?Morongo Wash; other small drainages also contribute fluvial sediment to the eolian system. The eolian dunes are transitory as a result of unidirectional sand movement from the depositional areas, which are recharged with fine-grained sediment only during episodic floods that typically occur during El Ni?o years. Eolian sand moves primarily from west to east through the study area; the period of maximum eolian activity is April through June. Wind speed varies diurnally, with maximum velocities typically occurring during the afternoon. Development of alluvial fans, alteration of stream channels by channelization, in-stream gravel mining, and construction of infiltration galleries were thought to reduce the amount of fluvial sediment reaching the depositional areas upwind of Uma habitat. Also, the presence of roadways, railroads, and housing developments was thought to disrupt or redirect eolian sand movement. Most of the sediment yield to the fluvial system is generated in higher elevation areas with little or no development, and sediment yield is affected primarily by climatic fluctuations and rural land use, particularly livestock grazing and wildfire. Channelization benefits sediment delivery to the depositional plains upwind of the reserves by minimizing in-channel sediment storage on the alluvial fans. The post-development annual sediment yield to the Whitewater and Mission Creek?Morongo Wash depositional areas are 3.5 and 1.5 million ft3/yr, respectively, covering each depositional area to a depth of 0.2 to 0.4 in. Given existing sand-transport rates, this material could be depleted by eolian processes in 8 to 16 months, a rate consistent with the presence of persistent sand dunes. However, these depletion times are likely minimum estimates, as some eolian sand is seen to persist in the immediate vicinity of depositional areas for longer time periods. Transport rates may be reduced by the presence of vegetation and other windbreaks. Because they are perpendicular to prevailing winds, the infiltration galleries on Whitewater River trap fluvial and eolian sediment, reducing sediment availability. Also, the presence of the railroad and Interstate 10 redirect eolian sand movement to the southeast along their corridors,potentially eliminating the Whitewater depositional area as a sand source for the Willow Hole Reserve. Using directional wind data, we discuss the potential for eolian sand transport from the Mission Creek?Morongo Wash depositional area to Willow Hole.

Investigating Mars: Candor Chasma

NASA Image and Video Library

2018-01-17

The bottom half of this image of central Candor Chasma shows a surface topography called chaos. Chaos is a region of small to medium sized mesas surrounded by valleys that are usually the same elevation. In this image sand and sand dunes are accumulating in the valleys and increasing in depth. Candor Chasma is one of the largest canyons that make up Valles Marineris. It is approximately 810 km long (503 miles) and has is divided into two regions - eastern and western Candor. Candor is located south of Ophir Chasma and north of Melas Chasma. The border with Melas Chasma contains many large landslide deposits. The floor of Candor Chasma includes a variety of landforms, including layered deposits, dunes, landslide deposits and steep sided cliffs and mesas. Many forms of erosion have shaped Chandor Chasma. There is evidence of wind and water erosion, as well as significant gravity driven mass wasting (landslides). The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 18251 Latitude: -6.45589 Longitude: 287.35 Instrument: VIS Captured: 2006-01-25 01:39 https://photojournal.jpl.nasa.gov/catalog/PIA22168

Investigating Mars: Candor Chasma

NASA Image and Video Library

2018-01-18

This image of central Candor Chasma shows a surface topography called chaos. Chaos is a region of small to medium sized mesas surrounded by valleys that are usually the same elevation. In this image sand and sand dunes have accumulated in the valleys near the top of the image, but are not as prevalent towards the bottom of the image. Candor Chasma is one of the largest canyons that make up Valles Marineris. It is approximately 810 km long (503 miles) and has is divided into two regions - eastern and western Candor. Candor is located south of Ophir Chasma and north of Melas Chasma. The border with Melas Chasma contains many large landslide deposits. The floor of Candor Chasma includes a variety of landforms, including layered deposits, dunes, landslide deposits and steep sided cliffs and mesas. Many forms of erosion have shaped Chandor Chasma. There is evidence of wind and water erosion, as well as significant gravity driven mass wasting (landslides). The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 69000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 26213 Latitude: -7.25478 Longitude: 287.032 Instrument: VIS Captured: 2007-11-11 14:48 https://photojournal.jpl.nasa.gov/catalog/PIA22169

Reconnaissance geology of the Jabal Shaqran Quadrangle, sheet 17/44 B, Kingdom of Saudi Arabia

USGS Publications Warehouse

Sable, Edward G.

1982-01-01

The Jabal Shaqran quadrangle lies in the southeastern Asir province, mostly within the westernmost part of the Rub al Khali desert, and is largely covered by Quaternary deposits. Proterozoic crystalline rocks are exposed as inselbergs or rock pediment surfaces along the western border of the quadrangle. The crystalline basement is metavolcanic rock intruded by plutonic to hypabyssal rocks consisting of diorite and gabbro, biotite tonalite gneiss, biotite-hornblende monzogranite, biotite-sodic amphibole granite, and syenogranite to quartz syenite, listed in the inferred order of emplacement. Rhyolite-dacite fels, associated with andesitic to basaltic metavolcanic flow rocks and minor amphibolite, is interpreted to have resulted from metasomatic alteration of the flow rocks during emplacement of granitic plutons. The Wajid Sandstone, of Cambrian to Ordovician age, is largely a coarse-grained quartz arenite with pebbly phases; common crossbedds indicate north-northwest to north-northeast directions of sand transport. Beds are cemented by iron oxide, carbonate, and minor quartz. The Wajid Sandstone is exposed only in the northwestern and northern parts of the quadrangle. Quaternary deposits record a climate that became increasingly more arid. They include Holocene and Pleistocene(?) alluvial and fluvial deposits of sand, gravel, and silt, minor carbonate crusts, and eolian sand and silt. Gravel terraces and gravel plains less than 10 m above the present major wadi channels are widespread and commonly are overlain by marly silt along the wadis. Between major wadis, which discharge into the Rub al Khali basin, gravel-topped surfaces are partly covered by a complex of low, sinuous, discontinuous, generally northwest trending transverse sand dunes. Normal to this trend, higher and more extensive linear dunes and dune complexes, including seif (irq) dunes as high as 50 m, have encroached southwestward. The transverse and linear dunes may represent two stages of advance separated by a pluvial cycle. Studies of aerial photographs indicate that the dunes have not changed appreciably in shape or size between 1951 and 1959, although some seif dunes have advanced their leading edges 15 to 25 m. No potentially economic mineral resources other than sand and gravel were found.

Details of Layers in Victoria Crater's Cape St. Vincent

NASA Technical Reports Server (NTRS)

2007-01-01

NASA's Mars Exploration Rover Opportunity rover spent about 300 sols (Martian days) during 2006 and 2007 traversing the rim of Victoria Crater. Besides looking for a good place to enter the crater, the rover obtained images of rock outcrops exposed at several cliffs along the way.

The cliff in this image from Opportunity's panoramic camera (Pancam) is informally named Cape St. Vincent. It is a promontory approximately 12 meters (39 feet) tall on the northern rim of Victoria crater, near the farthest point along the rover's traverse around the rim. Layers seen in Cape St. Vincent have proven to be among the best examples of meter scale cross-bedding observed on Mars to date. Cross-bedding is a geologic term for rock layers which are inclined relative to the horizontal and which are indicative of ancient sand dune deposits. In order to get a better look at these outcrops, Pancam 'super-resolution' imaging techniques were utilized. Super-resolution is a type of imaging mode which acquires many pictures of the same target to reconstruct a digital image at a higher resolution than is native to the camera. These super-resolution images have allowed scientists to discern that the rocks at Victoria Crater once represented a large dune field, not unlike the Sahara desert on Earth, and that this dune field migrated with an ancient wind flowing from the north to the south across the region. Other rover chemical and mineral measurements have shown that many of the ancient sand dunes studied in Meridiani Planum were modified by surface and subsurface liquid water long ago.

This is a Mars Exploration Rover Opportunity Panoramic Camera image acquired on sol 1167 (May 7, 2007), and was constructed from a mathematical combination of 16 different blue filter (480 nm) images.

Illustrative Experiments of the Erosion of Sand and Accompanying Theoretical Considerations

ERIC Educational Resources Information Center

Schneiderbauer, Simon

2012-01-01

Winds in desert regions form the well-known barchan dunes. Frequently, human settlements are threatened by the migration of these dunes. But why do these dunes move? And how is dune migration in deserts connected to scour development in the vicinity of pylons in river beds or to snow cornices in alpine regions? This paper introduces the topic of…

Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China

NASA Astrophysics Data System (ADS)

Long, Hao; Shen, Ji; Chen, Jianhui; Tsukamoto, Sumiko; Yang, Linhai; Cheng, Hongyi; Frechen, Manfred

2017-10-01

Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12-6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.

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

USGS Publications Warehouse

Zeigenfuss, Linda C.; Schoenecker, Kathryn A.

2015-08-07

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

Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars

NASA Astrophysics Data System (ADS)

Grotzinger, J. P.; Arvidson, R. E.; Bell, J. F.; Calvin, W.; Clark, B. C.; Fike, D. A.; Golombek, M.; Greeley, R.; Haldemann, A.; Herkenhoff, K. E.; Jolliff, B. L.; Knoll, A. H.; Malin, M.; McLennan, S. M.; Parker, T.; Soderblom, L.; Sohl-Dickstein, J. N.; Squyres, S. W.; Tosca, N. J.; Watters, W. A.

2005-11-01

Outcrop exposures of sedimentary rocks at the Opportunity landing site (Meridiani Planum) form a set of genetically related strata defined here informally as the Burns formation. This formation can be subdivided into lower, middle, and upper units which, respectively, represent eolian dune, eolian sand sheet, and mixed eolian sand sheet and interdune facies associations. Collectively, these three units are at least 7 m thick and define a "wetting-upward" succession which records a progressive increase in the influence of groundwater and, ultimately, surface water in controlling primary depositional processes. The Burns lower unit is interpreted as a dry dune field (though grain composition indicates an evaporitic source), whose preserved record of large-scale cross-bedded sandstones indicates either superimposed bedforms of variable size or reactivation of lee-side slip faces by episodic (possibly seasonal) changes in wind direction. The boundary between the lower and middle units is a significant eolian deflation surface. This surface is interpreted to record eolian erosion down to the capillary fringe of the water table, where increased resistance to wind-induced erosion was promoted by increased sediment cohesiveness in the capillary fringe. The overlying Burns middle unit is characterized by fine-scale planar-laminated to low-angle-stratified sandstones. These sandstones accumulated during lateral migration of eolian impact ripples over the flat to gently undulating sand sheet surface. In terrestrial settings, sand sheets may form an intermediate environment between dune fields and interdune or playa surfaces. The contact between the middle and upper units of the Burns formation is interpreted as a diagenetic front, where recrystallization in the phreatic or capillary zones may have occurred. The upper unit of the Burns formation contains a mixture of sand sheet facies and interdune facies. Interdune facies include wavy bedding, irregular lamination with convolute bedding and possible small tepee or salt-ridge structures, and cm-scale festoon cross-lamination indicative of shallow subaqueous flows marked by current velocities of a few tens of cm/s. Most likely, these currents were gravity-driven, possibly unchannelized flows resulting from the flooding of interdune/playa surfaces. However, evidence for lacustrine sedimentation, including mudstones or in situ bottom-growth evaporites, has not been observed so far at Eagle and Endurance craters. Mineralogical and elemental data indicate that the eolian sandstones of the lower and middle units, as well as the subaqueous and eolian deposits of the Burns upper unit, were derived from an evaporitic source. This indirectly points to a temporally equivalent playa where lacustrine evaporites or ground-water-generated efflorescent crusts were deflated to provide a source of sand-sized particles that were entrained to form eolian dunes and sand sheets. This process is responsible for the development of sulfate eolianites at White Sands, New Mexico, and could have provided a prolific flux of sulfate sediment at Meridiani. Though evidence for surface water in the Burns formation is mostly limited to the upper unit, the associated sulfate eolianites provide strong evidence for the critical role of groundwater in controlling sediment production and stratigraphic architecture throughout the formation.

Last Glacial Maximum Development of Parna Dunes in Panhandle Oklahoma, USA

NASA Astrophysics Data System (ADS)

Johnson, W. C.; Halfen, A. F.; McGowen, S.; Carter, B.; Fine, S.; Bement, L. C.; Simms, A. R.

2012-12-01

Though dunefields are a ubiquitous feature of the North American Great Plains, those studied to date have consisted primarily of sand grains. In Beaver County of the Oklahoma panhandle, however, upland dune forms consist of sand-sized aggregates of silt and clay. These aptly named parna dunes occur in two swarms, range in height from 10-15 m, and have asymmetrical dome morphologies with approximate north-south dune orientations. Despite their morphological similarities to sand dunes of the region, their origin and evolution is unknown. Documenting parna dune formation in the Oklahoma panhandle will help improve our understanding of prehistoric landscape instability and climate change, particularly in the central Great Plains where such records are limited. Panhandle parna dunes are typified by Blue Mound, our best documented parna dune thus far. Coring has documented a basal paleosol buried at a depth equivalent to the surrounding landscape—14C ages from this soil indicate its formation about 25-21 ka. The paleosol is a hydric Mollisol with a pronounced C3 isotopic signature reflecting hydric plant communities, rather than the regionally dominated C4 prairie vegetation. Hydric soils are associated with many of the playas on the surrounding landscape today, which suggests that they may have been more prevalent during the LGM. The overlying 8-10 m of parna is low in organic C and high in calcite, with indications of up to ten major episodes of sediment flux, which are documented with magnetic, isotope, soil-stratigraphic, particle-size, and color data. Near-surface luminescence (OSL) ages from Blue Mound are similar to the 14C ages from the basal paleosol, indicating rapid dune construction, with little or no Holocene accumulation of sediment. Marine isotope stage (MIS) 3 loess records indicate that upland areas of the region were relatively stable with attendant widespread pedogenesis prior to development of the parna dunes. At the onset of the LGM, however, the landscape destabilized, and aeolian processes dominated. Peoria Loess began accumulating throughout parts of Oklahoma and much of Kansas, Nebraska, and beyond, until landscape stabilization was re-attained about 14-13 ka. Our chronological and geomorphic data suggest that parna dune construction in the Oklahoma panhandle was the result of strong, northerly winds, which precipitated aeolian activity at the beginning of MIS 2. Furthermore, these features appear to be more analogous to the regional loess record than the sand dune activation record, and, with more research, may prove to be a reliable record of late-Quaternary landscape change in the central Great Plains.

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.

Contribution to the study of thermal properties of clay bricks reinforced by date palm fiber

NASA Astrophysics Data System (ADS)

Mekhermeche, A.; Kriker, A.; Dahmani, S.

2016-07-01

The Saharan regions of Algeria are characterized by a hot and dry climate. The most used cement materials such as theconcrete or the mortar blocks have bad thermal characteristic. However, these regions have several local materials: clay, dune sand and some natural fibers, which are formerly proved their thermal efficiency. The price of construction material used therefore depends on the international market constantly destabilized by theeconomic crisis coupled with the energy crisis in recent times. To produce a framework of life at a lower cost, it is important, therefore, to circumvent the influence of the cost of energy by upgrading the local materials of construction. In order to improve thermal performances in Saharan building materials this study was lanced. The aim of this research isthen to fabricate some bricks using three local materials: namely the clay, sand dune and the fibers of date palm. The percentage of sand and fibers varies from 0% to 40% and 0% to 3% by mass respectively. A sand dune of Ain El Beida of Ouargla of Algeria was used. Clay was extracted from Beldet Amer of Touggourt Ouargla Algérie. The fibers used in this study were vegetable fibers from date palm of Ouargla Algeria. The results showed that increasing in the mass fraction of sand and of fiber were beneficial for improving thermal properties. As function of increasing the percentage of sand dune and fibers there were: A decrease in: thermal conductivity, specific heat, heat capacity, thermal effusivity and thermal diffusivity and there were an increase in the thermal resistance.

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

USGS Publications Warehouse

Rubin, David M.

2012-01-01

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

Becquerel Crater Deposit

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 28 May 2002) The finely layered deposit in Becquerel crater, seen in the center of this THEMIS image, is slowly being eroded away by the action of windblown sand. Dark sand from a source north of the bright deposit is collecting along its northern edge, forming impressive barchan style dunes. These vaguely boomerang-shaped dunes form with their two points extending in the downwind direction, demonstrating that the winds capable of moving sand grains come from the north. Grains that leave the dunes climb the eroding stair-stepped layers, collecting along the cliff faces before reaching the crest of the deposit. Once there, the sand grains are unimpeded and continue down the south side of the deposit without any significant accumulation until they fall off the steep cliffs of the southern margin. The boat-hull shaped mounds and ridges of bright material called yardangs form in response to the scouring action of the migrating sand. To the west, the deposit has thinned enough that the barchan dunes extend well into the deeply eroded north-south trending canyons. Sand that reaches the south side collects and reforms barchan dunes with the same orientation as those on the north side of the deposit. Note the abrupt transition between the bright material and the dark crater floor on the southern margin. Steep cliffs are present with no indication of rubble from the obvious erosion that produced them. The lack of debris at the base of the cliffs is evidence that the bright material is readily broken up into particles that can be transported away by the wind. The geological processes that are destroying the Becquerel crater deposit appear active today. But it is also possible that they are dormant, awaiting a particular set of climatic conditions that produces the right winds and perhaps even temperatures to allow the erosion to continue.

Planet-wide sand motion on mars

USGS Publications Warehouse

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

2012-01-01

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

Coupled topographic and vegetation patterns in coastal dunes: Remote sensing observations and ecomorphodynamic implications

NASA Astrophysics Data System (ADS)

Yousefi Lalimi, F.; Silvestri, S.; Moore, L. J.; Marani, M.

2017-01-01

Vegetation plays a key role in stabilizing coastal dunes and barrier islands by mediating sand transport, deposition, and erosion. Dune topography, in turn, affects vegetation growth, by determining local environmental conditions. However, our understanding of vegetation and dune topography as coupled and spatially extensive dynamical systems is limited. Here we develop and use remote sensing analyses to quantitatively characterize coastal dune ecotopographic patterns by simultaneously identifying the spatial distribution of topographic elevation and vegetation biomass. Lidar-derived leaf area index and hyperspectral-derived normalized difference vegetation index patterns yield vegetation distributions at the whole-system scale which are in agreement with each other and with field observations. Lidar-derived concurrent quantifications of biomass and topography show that plants more favorably develop on the landward side of the foredune crest and that the foredune crestline marks the position of an ecotone, which is interpreted as the result of a sheltering effect sharply changing local environmental conditions. We conclude that the position of the foredune crestline is a chief ecomorphodynamic feature resulting from the two-way interaction between vegetation and topography.

ESTIMATING THE ECONOMIC VALUE OF NATIONAL PARKS WITH COUNT DATA MODELS USING ON-SITE, SECONDARY DATA: THE CASE OF THE GREAT SAND DUNES NATIONAL PARK AND PRESERVE

EPA Science Inventory

We estimate an individual travel cost model for Great Sand Dunes National Park and Preserve (GSD) in Colorado using on-site, secondary data. The purpose of the on-site survey was to help the National Park Service better understand the visitors of GSD; it was not intended for a t...

Microbial community composition but not diversity changes along succession in arctic sand dunes.

PubMed

Poosakkannu, Anbu; Nissinen, Riitta; Männistö, Minna; Kytöviita, Minna-Maarit

2017-02-01

The generality of increasing diversity of fungi and bacteria across arctic sand dune succession was tested. Microbial communities were examined by high-throughput sequencing of 16S rRNA genes (bacteria) and internal transcribed spacer (ITS) regions (fungi). We studied four microbial compartments (inside leaf, inside root, rhizosphere and bulk soil) and characterized microbes associated with a single plant species (Deschampsia flexuosa) across two sand dune successional stages (early and late). Bacterial richness increased across succession in bulk soil and leaf endosphere. In contrast, soil fungal richness remained constant while root endosphere fungal richness increased across succession. There was, however, no significant difference in Shannon diversity indices between early and late successional stage in any compartment. There was a significant difference in the composition of microbial communities between early and late successional stage in all compartments, although the major microbial OTUs were shared between early and late successional stage. Co-occurrence network analysis revealed successional stage-specific microbial groups. There were more co-occurring modules in early successional stage than in late stage. Altogether, these results emphasize that succession strongly affects distribution of microbial species, but not microbial diversity in arctic sand dune ecosystem and that fungi and bacteria may not follow the same successional trajectories. © 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

National assessment of hurricane-induced coastal erosion hazards: Southeast Atlantic Coast

USGS Publications Warehouse

Stockdon, Hilary F.; Doran, Kara S.; Thompson, David M.; Sopkin, Kristin L.; Plant, Nathaniel G.

2013-01-01

Beaches serve as a natural barrier between the ocean and inland communities, ecosystems, and natural resources. However, these dynamic environments move and change in response to winds, waves, and currents. During extreme storms, changes to beaches can be large, and the results are sometimes catastrophic. Lives may be lost, communities destroyed, and millions of dollars spent on rebuilding. During storms, large waves may erode beaches, and high storm surge shifts the erosive force of the waves higher on the beach. In some cases, the combined effects of waves and surge may cause overwash or flooding. Building and infrastructure on or near a dune can be undermined during wave attack and subsequent erosion. During Hurricane Ivan in 2004, a five-story condominium in Orange Beach, Alabama, collapsed after the sand dune supporting the foundation eroded. The September 1999 landfall of Hurricane Dennis caused erosion and undermining that destroyed roads, foundations, and septic systems. Waves overtopping a dune can transport sand inland, covering roads and blocking evacuation routes or emergency relief. If storm surge inundates barrier island dunes, currents flowing across the island can create a breach, or new inlet, completely severing evacuation routes. Waves and surge during the 2003 landfall of Hurricane Isabel left a 200-meter (m) wide breach that cut the only road to and from the village of Hatteras, N.C. Extreme coastal changes caused by hurricanes may increase the vulnerability of communities both during a storm and to future storms. For example, when sand dunes on a barrier island are eroded substantially, inland structures are exposed to storm surge and waves. Absent or low dunes also allow water to flow inland across the island, potentially increasing storm surge in the back bay, on the soundside of the barrier, and on the mainland. During Hurricane Isabel the protective sand dunes near the breach were completely eroded, increasing vulnerability to future storms.

National assessment of hurricane-induced coastal erosion hazards: Mid-Atlantic Coast

USGS Publications Warehouse

Doran, Kara S.; Stockdon, Hilary F.; Sopkin, Kristin L.; Thompson, David M.; Plant, Nathaniel G.

2013-01-01

Beaches serve as a natural buffer between the ocean and inland communities, ecosystems, and natural resources. However, these dynamic environments move and change in response to winds, waves, and currents. During extreme storms, changes to beaches can be large, and the results are sometimes catastrophic. Lives may be lost, communities destroyed, and millions of dollars spent on rebuilding. During storms, large waves may erode beaches, and high storm surge shifts the erosive force of the waves higher on the beach. In some cases, the combined effects of waves and surge may cause overwash (when waves and surge overtop the dune, transporting sand inland) or flooding. Building and infrastructure on or near a dune can be undermined during wave attack and subsequent erosion. During Hurricane Ivan in 2004, a five-story condominium in Orange Beach, Alabama, collapsed after the sand dune supporting the foundation eroded. Hurricane Sandy, which made landfall as an extra-tropical cyclone on October 29, 2012, caused erosion and undermining that destroyed roads, boardwalks, and foundations in Seaside Heights, New Jersey. Waves overtopping a dune can transport sand inland, covering roads and blocking evacuation routes or emergency relief. If storm surge inundates barrier island dunes, currents flowing across the island can create a breach, or a new inlet, completely severing evacuation routes. Waves and surge during Hurricane Sandy, which made landfall on October 29, 2012, left a breach that cut the road and bridge to Mantoloking, N.J. Extreme coastal changes caused by hurricanes may increase the vulnerability of communities both during a storm and to future storms. For example, when sand dunes on a barrier island are eroded substantially, inland structures are exposed to storm surge and waves. Absent or low dunes also allow water to flow inland across the island, potentially increasing storm surge in the back bay, on the soundside of the barrier, and on the mainland.

The Carolina Sandhills: Quaternary eolian sand sheets and dunes along the updip margin of the Atlantic Coastal Plain province, southeastern United States

USGS Publications Warehouse

Swezey, Christopher; Fitzwater, Bradley A.; Whittecar, G. Richard; Mahan, Shannon; Garrity, Christopher P.; Aleman Gonzalez, Wilma B.; Dobbs, Kerby M.

2016-01-01

The Carolina Sandhills is a physiographic region of the Atlantic Coastal Plain province in the southeastern United States. In Chesterfield County (South Carolina), the surficial sand of this region is the Pinehurst Formation, which is interpreted as eolian sand derived from the underlying Cretaceous Middendorf Formation. This sand has yielded three clusters of optically stimulated luminescence ages: (1) 75 to 37 thousand years ago (ka), coincident with growth of the Laurentide Ice Sheet; (2) 28 to 18 ka, coincident with the last glacial maximum (LGM); and (3) 12 to 6 ka, mostly coincident with the Younger Dryas through final collapse of the Laurentide Ice Sheet. Relict dune morphologies are consistent with winds from the west or northwest, coincident with modern and inferred LGM January wind directions. Sand sheets are more common than dunes because of effects of coarse grain size (mean range: 0.35–0.59 mm) and vegetation. The coarse grain size would have required LGM wind velocities of at least 4–6 m/sec, accounting for effects of colder air temperatures on eolian sand transport. The eolian interpretation of the Carolina Sandhills is consistent with other evidence for eolian activity in the southeastern United States during the last glaciation.

Avalanches of Singing Sand in the Laboratory

NASA Astrophysics Data System (ADS)

Dagois-Bohy, Simon; Courrech Du Pont, Sylvain; Douady, Stéphane

2011-03-01

The song of dunes is a natural phenomenon that has arisen travellers' curiosity for a long time, from Marco Polo to R.A. Bagnold. Scientific observations in the XXth century have shown that the sound is emitted during a shear flow of these particular grains, the free surface of the flow having coherent vibrations like a loud speaker. The sound emission is also submitted to a threshold effect with many parameters like humidity, flow speed, surface of the grains. The sound has been reproduced in laboratory avalanche experiments close to the natural phenomenon on field, but set in a channel with a hard bottom and a few centimeters of sand flowing, which contradicts explanations of the sound that involve a sand dune under the avalanche flow. Flow rates measurements also show the presence of a plug region in the flow above the sheared band, with the same characteristic length as the coherence zones of the sound. Finally we show experimentally that the Froude number, once modified to take into account the height of this plug band, is the parameter that sets the amplitude of the sound, and produces a threshold that depends on the grain type.

Rock Abrasion as Seen by the MSL Curiosity Rover: Insights on Physical Weathering on Mars

NASA Astrophysics Data System (ADS)

Bridges, N.; Day, M. D.; Le Mouelic, S.; Martin-Torres, F. J.; Newsom, H. E.; Sullivan, R. J., Jr.; Ullan, A.; Wiens, R. C.; Zorzano, M. P.

2014-12-01

Mars is a dry planet, with actively blowing sand in many regions. In the absence of stable liquid water and an active hydrosphere, rates of chemical weathering are slow, such that aeolian abrasion is a dominant agent of landscape modification where sand is present and winds above threshold occur at sufficient frequency. Reflecting this activity, ventifacts, rocks that have been abraded by windborne particles, and wind-eroded outcrops, are common. They provide invaluable markers of the Martian wind record and insight into climate and landscape modification. Ventifacts are distributed along the traverse of the Mars Science Laboratory Curiosity rover. They contain one or more diagnostic features and textures: Facets, keels, basal sills, elongated pits, scallops/flutes, grooves, rock tails, and lineations. Keels at the junction of facets are sharp enough to pose a hazard MSL's wheels in some areas. Geomorphic and textural patterns on outcrops indicate retreat of windward faces. Moonlight Valley and other depressions are demarcated by undercut walls and scree boulders, with the valley interiors containing fewer rocks, most of which show evidence for significant abrasion. Together, this suggests widening and undercutting of the valley walls, and erosion of interior rocks, by windblown sand. HiRISE images do not show any dark sand dunes in the traverse so far, in contrast to the large dune field to the south that is migrating up to 2 m per year. In addition, ChemCam shows that the rock Bathurst has a rind rich in mobile elements that would be removed in an abrading environment. This indicates that rock abrasion was likely more dominant in the past, a hypothesis consistent with rapid scarp retreat as suggested by the cosmogenic noble gases in Yellowknife Bay. Ventifacts and evidence for bedrock abrasion have also been found at the Pathfinder, Spirit, and Opportunity sites, areas, like the Curiosity traverse so far, that lack evidence for current high sand fluxes. Yardangs are also common on the planet, regardless of whether local sand is mobile. This suggest that abrasion on Mars is an episodic process driven by the passage of sand in which rock retreat rates, based on fluxes of current active dunes, may reach 10s of microns per year. Such a process has acted, over long time scales, to imprint upon the surface a record of sand activity.

Coastal dune dynamics in response to excavated foredune notches

NASA Astrophysics Data System (ADS)

Ruessink, B. G.; Arens, S. M.; Kuipers, M.; Donker, J. J. A.

2018-04-01

Dune management along developed coasts has traditionally focussed on the suppression of the geomorphic dynamics of the foredune to improve its role in sea defence. Because a stabilized foredune acts as an almost total barrier to aeolian transport from the beach, the habitat diversity in the more landward dunes has degraded. With the overarching objective to mitigate this undesirable loss in biodiversity, dune management projects nowadays increasingly intend to restore aeolian dynamics by reconnecting the beach-dune system with notches excavated through the foredune. Here, we use repeat topographic survey data to examine the geomorphic response of a coastal dune system in the Dutch National Park Zuid-Kennemerland to five notches excavated in 2012-2013 within an 850-m stretch of the 20-m high established foredune. The notches were dug in a V-shape (viewed onshore), with a width between approximately 50 and 100 m at the top, a (cross-dune) length between 100 and 200 m, and excavation depths between 9 and 12.5 m. The 1 × 1 m digital terrain models, acquired with airborne Lidar and UAV photogrammetry, illustrate that during the 3-year survey period the notches developed into a U-shape because of wall deflation, and that up to 8-m thick and 150-m long depositional lobes formed landward of the notches. Sand budget computations showed that the sand volume of the entire study area increased by about 22,750 m3/year, which, given the 850-m width of the study area, corresponds to an aeolian input from the beach of approximately 26.5 m3/m/year. Between 2006 and 2012 all wind-blown beach sand deposited on the seaward side of the foredune; since 2013, the notches have caused 75% of the sand to be deposited landward of the foredune. This highlights that the notches are highly effective conduits for aeolian transport into the back dunes. Future monitoring is required to determine for how long the notches will stimulate aeolian dynamics and if (and when) vegetation eventually starts to regrow and enforces the degeneration of the notches.

Sedimentary rhythms in coastal dunes as a record of intra-annual changes in wind climate (Łeba, Poland)

NASA Astrophysics Data System (ADS)

Ludwig, J.; Lindhorst, S.; Betzler, C.; Bierstedt, S. E.; Borówka, R. K.

2017-08-01

It is shown that coastal dunes bear a so far unread archive of annual wind intensity. Active dunes at the Polish coast near Łeba consist of two genetic units: primary dunes with up to 18 m high eastward-dipping foresets, temporarily superimposed by smaller secondary dunes. Ground-penetrating radar (GPR) data reveal that the foresets of the primary dunes are bundled into alternating packages imaged as either low- or high-amplitude reflections. High-amplitude packages are composed of quartz sand with intercalated heavy-minerals layers. Low-amplitude packages lack these heavy-mineral concentrations. Dune net-progradation is towards the east, reflecting the prevalence of westerly winds. Winds blowing parallel to the dune crest winnow the lee slope, leaving layers enriched in heavy minerals. Sediment transport to the slip face of the dunes is enhanced during the winter months, whereas winnowing predominantly takes place during the spring to autumn months, when the wind field is bi-directional. As a consequence of this seasonal shift, the sedimentary record of one year comprises one low- and one high-amplitude GPR reflection interval. This sedimentary pattern is a persistent feature of the Łeba dunes and recognized to resemble a sedimentary "bar code". To overcome hiatuses in the bar code of individual dunes and dune-to-dune variations in bar-code quality, dendrochronological methods were adopted to compile a composite bar code from several dunes. The resulting data series shows annual variations in west-wind intensity at the southern Baltic coast for the time period 1987 to 2012. Proxy-based wind data are validated against instrumental based weather observations.

Late Holocene eolian activity in the mineralogically mature Nebraska Sand Hills

USGS Publications Warehouse

Muhs, D.R.; Stafford, Thomas W.; Swinehart, J.B.; Cowherd, S.D.; Mahan, S.A.; Bush, C.A.; Madole, R.F.; Maat, P.B.

1997-01-01

The age of sand dunes in the Nebraska Sand Hills has been controversial, with some investigators suggesting a full-glacial age and others suggesting that they were last active in the late Holocene. New accelerator mass spectrometry radiocarbon ages of unaltered bison bones and organic-rich sediments suggest that eolian sand deposition occurred at least twice in the past 3000 14C yr B.P. in three widely separated localities and as many as three times in the past 800 14C yr at three other localities. These late Holocene episodes of eolian activity are probably the result of droughts more intense than the 1930s "Dust Bowl" period, based on independent Great Plains climate records from lake sediments and tree rings. However, new geochemical data indicate that the Nebraska Sand Hills are mineralogically mature. Eolian sands in Nebraska have lower K-feldspar (and K2O, Rb, and Ba) contents than most possible source sediments and lower K-feldspar contents than dunes of similar age in Colorado. The most likely explanation for mineralogical maturity is reduction of sand-sized K-feldspar to silt-sized particles via ballistic impacts due to strong winds over many cycles of eolian activity. Therefore, dunes of the Nebraska Sand Hills must have had a long history, probably extending over more than one glacial-interglacial cycle, and the potential for reactivation is high, with or without a future greenhouse warming. ?? 1997 University of Washington.

The contribution of Corynephorus canescens to the geodiversity of inland drift sands

NASA Astrophysics Data System (ADS)

Jungerius, Pieter Dirk; Riksen, Michel; van den Ancker, Hanneke; Kooistra, Maja

2016-04-01

Most dunes in the Netherlands are phytogenic, which means that plants are essential in their formation. This applies also to the dunes of the inland drift sand areas, which are nicknamed Atlantic deserts on account of their extreme climatic conditions. Daily temperatures on the bare sand surfaces may run up to 60° C on sunny summer days, dropping as low as below freezing point at night. Apart from blue and green algae, Corynephorus canescens, Grey hair-grass, it is the first conqueror of these active sands and plays an important role in the geomorphological development of the inland drift sands. C. canescens is a rapid colonizer and flourishes when it receives a regular supply of fresh sand, but is soon succeeded by competitor species. Like Ammophila arenaria (Marram grass), its vigour declines after some time, because its roots are affected. Therefore the plant requires a regular supply of fresh sand to outgrow the affected root zone. The growth of C. canescens is stimulated by two different geomorphological processes: aeolian and pluvial processes. Aboveground, the tussock architecture of the plant helps to trap sand and form small initial dunes. When formed by wind, these are called nabkahs; when formed by splash bush mounds. In a micro-morphological thin section both processes can often be recognized in one dune. The decline of C. canescens is caused by two soil-forming processes: reduction of permeability and accumulation of organic matter. Poor aeration and compaction restrict the growth of its roots. Increase in organic matter hampers the rate of root respiration and promotes conditions for the establishment of competitor species. In the nabkahs, thin slides show on the positive side for C. canescens there is little blown-in organic matter, but on the negative side that the grains upon aging develop a colourless organic coating formed by cyanobacteria (algae. For splashed sands on the positive side for Grey hairgrass there are few organic coatings, but on the negative side there are many organic fragments. So although different both sediments have the same effect. Under the present climate and level of air pollution, the phase of C. canescens is short-lived. Its disappearance marks the end of dune formation and after its decline slope development changes drastically. In conclusion, the interaction between Corynephorus canescens and the geomorphological and soil processes are important in the development and the geodiversity of inland drift sands.

The Evolution of a Snow Dune Field

NASA Astrophysics Data System (ADS)

Filhol, S.; Pirk, N.; Schuler, T.; Burkhart, J. F.

2017-12-01

On March 24, 2017 we observed the evolution of a snow dune field during a passing storm on the alpine plateau of Finse, Norway. With a terrestrial lidar we captured 15 high-resolution scans of the snow surface over an area of about 5000 m2 over the course of 7.5 hours from which we analyze morphological changes. An eddy covariance system located nearby at the Finse Alpine Research Station recorded wind and its turbulent structure, and measured the snow drifting flux with a FlowCapt sensor. This combined dataset provides novel insight into the responses and changes of the snow surface morphology exposed to storm constraints (e.g. wind speed, drifting flux). We found that individual dunes have moved 30 to 37 m over the course of 7.5 hours. The wavelength of the dunes varied from 10.3±3.1 m at the time of the first scan to 13.6±3.3 m at the last scan. Within this time period we observed individual dunes 1) migrating down wind, later becoming 2) temporarily nearly static as the wind speed dropped, and finally 3) migrating, growing, and merging into larger transverse dunes under strong wind conditions accompanied by large quantities of drifting snow. This dynamics can be considered analogous to sand dune behavior, however, on much shorter time scale (1h vs 10-100 years) and smaller spatial scale (10m vs 100m). The record of this event helps us to understand the morphological evolution of a snow surface during a blowing snow storm, and further illustrates the fate of self-sustained bedforms such as dunes in varying conditions. Such detailed description of erosion/deposition processes of the snow surface are crucial for improvements of land surface models, commonly applied to hydrological and ecological purposes.

Calculation of Beach Change Under Interacting Cross-Shore and Longshore Processes

DTIC Science & Technology

2010-01-01

the dune toe , berm width, and shoreline position are calculated, while maintaining longshore transport rates representative of the regional long-term...during growth together with the dune shape, the seaward movement of the dune toe ΔyDw for a given increase in dune volume ΔVDw is: ΔyDw = ΔVDw DD ð2Þ...Expressing Eq. (1) in terms of dune toe advance yields: dyDw dt = qw DD ð3Þ It is assumed that sand transport to the dune is related to thewidth of the

Use of remote sensing techniques to determine the effects of grazing on vegetation cover and dune elevation at assateague island national seashore: Impact of horses

USGS Publications Warehouse

De Stoppelaire, G. H.; Gillespie, T.W.; Brock, J.C.; Tobin, G.A.

2004-01-01

The effects of grazing by feral horses on vegetation and dune topography at Assateague Island National Seashore were investigated using color-infrared imagery, lidar surveys, and field measurements. Five pairs of fenced and unfenced plots (300 m2) established in 1993 on sand flats and small dunes with similar elevation, topography, and vegetation cover were used for this study. Color-infrared imagery from 1998 and field measurements from 2001 indicated that there was a significant difference in vegetation cover between the fenced and unfenced plot-pairs over the study period. Fenced plots contained a higher percentage of vegetation cover that was dominated by American beachgrass (Ammophila breviligulata). Lidar surveys from 1997, 1999, and 2000 showed that there were significant differences in elevation and topography between fenced and unfenced plot-pairs. Fenced plots were, on average, 0.63 m higher than unfenced plots, whereas unfenced plots had generally decreased in elevation after establishment in 1993. Results demonstrate that feral horse grazing has had a significant impact on dune formation and has contributed to the erosion of dunes at Assateague Island. The findings suggest that unless the size of the feral horse population is reduced, grazing will continue to foster unnaturally high rates of dune erosion into the future. In order to maintain the natural processes that historically occurred on barrier islands, much larger fenced exclosures would be required to prevent horse grazing. ?? 2004 Springer Science+Business Media, Inc.

Investigating Mars: Kaiser Crater Dunes

NASA Image and Video Library

2018-02-02

This is a false color image of Kaiser Crater. In this combination of filters "blue" typically means basaltic sand. This VIS image crosses 3/4 of the crater and demonstrates how extensive the dunes are on the floor of Kaiser Crater. Kaiser Crater is located in the southern hemisphere in the Noachis region west of Hellas Planitia. Kaiser Crater is just one of several large craters with extensive dune fields on the crater floor. Other nearby dune filled craters are Proctor, Russell, and Rabe. Kaiser Crater is 207 km (129 miles) in diameter. The dunes are located in the southern part of the crater floor. The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 66602 Latitude: -47.0551 Longitude: 19.446 Instrument: VIS Captured: 2016-12-18 21:42 https://photojournal.jpl.nasa.gov/catalog/PIA22265

KENNEDY SPACE CENTER, FLA. - The sand dunes facing the Atlantic Ocean near Launch Pad 39A (background) at KSC spill purple flowers down its banks. The beach is just south of the Canaveral National Seashore, managed by the National Wildlife Service.

NASA Image and Video Library

2003-08-19

KENNEDY SPACE CENTER, FLA. - The sand dunes facing the Atlantic Ocean near Launch Pad 39A (background) at KSC spill purple flowers down its banks. The beach is just south of the Canaveral National Seashore, managed by the National Wildlife Service.

Lunar and Planetary Science XXXV: Mars: Wind, Dust Sand, and Debris

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Mars: Wind, Dust Sand, and Debris" included: Mars Exploration Rovers: Laboratory Simulations of Aeolian Interactions; Thermal and Spectral Analysis of an Intracrater Dune Field in Amazonis Planitia; How High is that Dune? A Comparison of Methods Used to Constrain the Morphometry of Aeolian Bedforms on Mars; Dust Devils on Mars: Scaling of Dust Flux Based on Laboratory Simulations; A Close Encounter with a Terrestrial Dust Devil; Interpretation of Wind Direction from Eolian Features: Herschel Crater, Mars Erosion Rates at the Viking 2 Landing Site; Mars Dust: Characterization of Particle Size and Electrostatic Charge Distributions; Simple Non-fluvial Models of Planetary Surface Modification, with Application to Mars; Comparison of Geomorphically Determined Winds with a General Circulation Model: Herschel Crater, Mars; Analysis of Martian Debris Aprons in Eastern Hellas Using THEMIS; Origin of Martian Northern Hemisphere Mid-Latitude Lobate Debris Aprons; Debris Aprons in the Tempe/Mareotis Region of Mars;and Constraining Flow Dynamics of Mass Movements on Earth and Mars.

Temporal characteristics of coherent flow structures generated over alluvial sand dunes, Mississippi River, revealed by acoustic doppler current profiling and multibeam echo sounding

USGS Publications Warehouse

Czuba, John A.; Oberg, Kevin A.; Best, Jim L.; Parsons, Daniel R.; Simmons, S. M.; Johnson, K.K.; Malzone, C.

2009-01-01

This paper investigates the flow in the lee of a large sand dune located at the confluence of the Mississippi and Missouri Rivers, USA. Stationary profiles collected from an anchored boat using an acoustic Doppler current profiler (ADCP) were georeferenced with data from a real-time kinematic differential global positioning system. A multibeam echo sounder was used to map the bathymetry of the confluence and provided a morphological context for the ADCP measurements. The flow in the lee of a low-angle dune shows good correspondence with current conceptual models of flow over dunes. As expected, quadrant 2 events (upwellings of low-momentum fluid) are associated with high backscatter intensity. Turbulent events generated in the lower lee of a dune near the bed are associated with periods of vortex shedding and wake flapping. Remnant coherent structures that advect over the lower lee of the dune in the upper portion of the water column, have mostly dissipated and contribute little to turbulence intensities. The turbulent events that occupy most of the water column in the upper lee of the dune are associated with periods of wake flapping.

Environmental Processes and Spectral Reflectance Characteristics Associated with Soil Erosion in Desert Fringe Regions

NASA Technical Reports Server (NTRS)

Jacobberger, P. A.

1987-01-01

Results of analysis of spectral variation of sand dunes in El Ghorabi, Bahariya, Egypt; Tombouctou/Azaouad, Mali; and Tsodilo Hills, western Botswana are presented. Seasonal variations in dune extent and location of dune crests and their relationship to such factors as wind and weather variations are emphasized.

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.

Diversity and Community Composition of Vertebrates in Desert River Habitats

PubMed Central

Free, C. L.; Baxter, G. S.; Dickman, C. R.; Lisle, A.; Leung, L. K.-P.

2015-01-01

Animal species are seldom distributed evenly at either local or larger spatial scales, and instead tend to aggregate in sites that meet their resource requirements and maximise fitness. This tendency is likely to be especially marked in arid regions where species could be expected to concentrate at resource-rich oases. In this study, we first test the hypothesis that productive riparian sites in arid Australia support higher vertebrate diversity than other desert habitats, and then elucidate the habitats selected by different species. We addressed the first aim by examining the diversity and composition of vertebrate assemblages inhabiting the Field River and adjacent sand dunes in the Simpson Desert, western Queensland, over a period of two and a half years. The second aim was addressed by examining species composition in riparian and sand dune habitats in dry and wet years. Vertebrate species richness was estimated to be highest (54 species) in the riverine habitats and lowest on the surrounding dune habitats (45 species). The riverine habitats had different species pools compared to the dune habitats. Several species, including the agamid Gowidon longirostris and tree frog Litoria rubella, inhabited the riverine habitats exclusively, while others such as the skinks Ctenotus ariadnae and C. dux were captured only in the dune habitats. The results suggest that, on a local scale, diversity is higher along riparian corridors and that riparian woodland is important for tree-dependent species. Further, the distribution of some species, such as Mus musculus, may be governed by environmental variables (e.g. soil moisture) associated with riparian corridors that are not available in the surrounding desert environment. We conclude that inland river systems may be often of high conservation value, and that management should be initiated where possible to alleviate threats to their continued functioning. PMID:26637127

The response and recovery of coastal beach-dune systems to storms

NASA Astrophysics Data System (ADS)

Farrell, Eugene; Lynch, Kevin; Wilkes Orozco, Sinead; Castro Camba, Guillermo

2017-04-01

This two year field monitoring project examines the response and recovery of a coastal beach-dune system in the west coast of Ireland (The Maharees, Co. Kerry) to storms. Historic analyses were completed using maps, aerial photography, and DGPS surveys with the Digital Shoreline Analysis System. The results establish that the average shoreline recession along the 1.2 km site is 72 m during the past 115 years. The coastal monitoring experiment aims to link micro-scale aeolian processes and meso-scale beach-dune behaviour to identify and quantify sediment exchange between the beach and dune under different meteorological and hydrodynamic conditions. Geomorphological changes on the beach and near-shore bar migration were monitored using repeated monthly DGPS surveys and drone technology. Topographical data were correlated with atmospheric data obtained from a locally installed Campbell Scientific automatic weather station, oceanographic data from secondary sources, and photogrammetry using a camera installed at the site collecting pictures every 10 minutes during daylight hours. Changes in surface elevation on the top of the foredune caused by aeolian processes are measured using erosion pin transects. The preliminary results illustrate that natural beach building processes initiate system recovery post storms including elevated foreshores and backshores and nearshore sand bar migration across the entire 1.2 km stretch of coastline. In parallel with the scientific work, the local community have mobilized and are working closely with the lead scientists to implement short term coastal management strategies such as signage, information booklets, sand trap fencing, walkways, wooden revetments, dune planting in order to support the end goal of obtaining financial support from government for a larger, long term coastal protection plan.

Erosion of Coastal Foredunes: A Review on the Effect of Dune Vegetation

DTIC Science & Technology

2017-02-01

intensity, sustainable nature-based coastal protection measures are of growing interest. One of these considered features is coastal dunes, which... protection by sand banks, beaches, and dunes. Coastal Engineering 87:136–146. Hesp, P. 1991. Ecological processes and plant adaptations on coastal dunes...ERDC/CHL CHETN-I-94 February 2017 Approved for public release; distribution is unlimited. Erosion of Coastal Foredunes: A Review on the Effect

Sand aggregation by exopolysaccharide-producing Microbacterium arborescens--AGSB.

PubMed

Godinho, Aureen L; Bhosle, Saroj

2009-06-01

In the rhizosphere, exopolymers are also known to be useful to improve the moisture-holding capacity. The ability of the isolates from coastal sand dunes to produce exopolymers was determined. Among which the isolate, showing very high production of exopolysaccharide (EPS), Microbacterium arborescens--AGSB, a facultative alkalophile was further studied for exopolymer production. The isolate a gram-positive non-spore forming, slender rod, catalase positive, oxidase negative, showed growth in 12% sodium chloride. The culture was found to produce exopolymer which showed good aggregation of sand which has an important role in the stabilization of sand dunes. The exopolymer was further analysed. The cold isopropanol precipitation of dialysed supernatants grown in polypeptone yeast extract glucose broth produced partially soluble EPSs with glucose as the sole carbon source. Chemical analysis of the EPS revealed the presence of rhamnose, fucose, arabinose, mannose, galactose and glucose. On optimization of growth parameters (sucrose as carbon source and glycine as nitrogen source), the polymer was found to be a heteropolysaccharide containing mannose as the major component. It was interesting to note that the chemical composition of the exopolymers produced from both unoptimized and optimized culture conditions of Microbacterium arborescens--AGSB is different from those of other species from the same genera. This study shows that marine coastal environments such as coastal sand dunes, are a previously unexplored habitat for EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication especially in nutrient-limited environments such as the coastal sand dunes more so in the extreme conditions of pH. Such polysaccharides may help the bacteria to adhere to solid substrates and survive during the nutrient limitations.