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NASA NTRS1979

Morphology and distribution of common 'sand' dunes on Mars - Comparison with the earth

A comparative study of Martian and terrestrial dunes was made based on Viking Orbiter pictures and aerial pictures of terrestrial deserts. The morphological similarity between the Martian dunes and terrestrial crescentic dunes implies that the dynamics of dune formation are similar on the two planets, despite Martian constraints on dune formation that include much higher velocity winds required to move 'sand' in saltation, the possible inhibition of sand movement by absorbed water vapor, the seasonal 'snow' cover in the north circumpolar erg, and a probably sparse sand supply. The absence of longitudinal dunes and the restriction of massive crescentic dunes to a few sites on Mars suggests that Mars may have a long eolian history in which much of the sand suitable for saltation has already been transported to the north polar erg and crater floor fields.

Breed, C. S.↗

NASA NTRS1977

Simulation model of erosion and deposition on a barchan dune

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.

Howard, A. D.↗

NASA NTRS1977

Terrestrial analogs of the Hellespontus dunes, Mars

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.

Breed, C. S.↗

NASA NTRS2005

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

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.

Bourke, M. C.↗

NASA NTRS2007

Recent Aeolian Dune Change on Mars

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.

Bourke, M. C.↗

NASA NTRS2011

How Altitude and Latitude Control Dune Morphometry on Titan

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.

radar observations↗

NASA NTRS1983

Speculation on Martian north polar wind circulation and the resultant orientations of polar sand dunes

When seen at frost cap minimum, Martian north polar erg dunes north of 80 deg N record east winds, while those south of that latitude record west winds. Many of the transverse dunes are considered to be reversing dunes, and dunes in the two fields may have reversed at least once during the lifetime of the Viking Orbiters. It is proposed that the average polar winds are strong, off-pole northwest winds in the fall, moderate west winds in winter, latitude-dependent weak-to-strong off-pole northeast winds in spring, and weak west winds in summer, as has been largely confirmed by Viking images of near polar clouds. Over millenia, the combination of reversing west and east winds could produce the biomodal distributions of dune orientations observed at the north pole.

Ward, A. W.↗

NASA NTRS1995

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

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.

Edgett, Kenneth S.↗

NASA NTRS1995

Longitudinal dunes on Mars: Relation to current wind regimes

Longitudinal dunes are extremely rare on Mars, but constitute a substantial fraction of terrestrial desert dunes. We report finding isolated examples of longitudinal dunes on Mars and relate their occurence to expected sand transport regimes. Terrestrial longitudinal dunes form in bimodal and multimodal transport regimes. General circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on Mars. Thus the dearth of longitudinal dunes on Mars is consistant with their apparent formation conditions on Earth.

Lee, Pascal↗

NASA NTRS1995

Longitudinal dunes on Mars: Relation to current wind regimes

Longitudinal dunes are extremely rare on Mars, but constitute a substantial fraction of terrestrial desert dunes. We report finding isolated examples of longitudinal dunes on Mars and relate their occurrence to expected sand transport regimes. Terrestrial longitudinal dunes form in bimodal and multimodal transport regimes. General circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on Mars. Thus the dearth of longitudinal dunes on Mars is consistent with their apparent formation conditions on Earth.

Lee, Pascal↗

NASA NTRS2006

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

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

Bourke, M. C.↗

NASA NTRS2012

Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice

The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

arctic↗

NASA NTRS2011

They're Alive! Present-Day Evolution of Martian Dunes

The sharp brinks and margins, smooth and steep lee slopes, and lack of superimposed landforms (such as small impact craters) on many Martian sand dunes suggests that these features are geologically young clean brinks and smooth/steep lee slopes (HiRISE image PSP_010413_1920; 20 deg N,79 deg E; image widthis about 500m).Within the last decade, and often primarily through the detailed inspection of high-resolution (HiRISE) images, we have finally found clear evidence that many dunes of Mars are active -- through both aeolian and seasonal (frost) processes. However, it is yet unclear if active dune formation does occur or if we are observing surficial modification of dunes which formed under different climate conditions.

Mars↗

NASA NTRS1973

Eolian deposits and dunes on Mars.

A complex of coalescing ridges and diverse marginal features observed in Mariner 9 pictures of the Hellespontus region of Mars is identified as a dune mass. Many other possible dune features are recognized in midlatitudes and polar latitudes, and regional differences in the appearance of cratered terrains are attributed to modification by dune deposits. The morphology and temporal behavior of some Martian albedo features can be explained by dune-forming saltation processes. Eolian activity seems to be widespread, if not ubiquitous, on Mars and appears to produce major regional variations in the surface environment.

Cutts, J. A.↗

NASA NTRS1982

Petrology of dune sand derived from basalt on the Ka'u Desert, Hawaii

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.

Gooding, J. L.↗

NASA NTRS1982

Radar scatterometry of sand dunes and lava flows

Four frequency like polarized scatterometer data over a sand dune field and a volcanic field were analyzed to understand the scattering characteristics of these two terrain types as a function of frequency and incidence angle. For the frequency range studied (400 MHz to 13.3 GHz) unvegetated sand dunes are specular reflectors that return an echo to the radar antenna particularly when the geometry is such that the dune slope is nearly perpendicular to the antenna. Vegetation on the dunes can cause significant backscatter. Lava flows are strong diffuse scatterers which have backscatter values similar to coniferous forest at certain frequencies. Different observation frequencies are required for different situations. The scatterometer data correlate well with radar images.

Blom, R.↗

NASA NTRS1982

SIR-A radar images of sand dunes and volcanic fields

Shuttle Imaging Radar (SIR-A) synthetic aperture radar images of sand dunes and volcanic fields are presented and preliminary interpretation provided. The SIR-A images are compared with Seasat images where available. Unvegetated sand dunes are recorded as black areas on SIR-A images due to the specular reflection away from the sensor at the SIR-A incidence angle. Even a very small amount of vegetation provides some backscatter, however. Interdune areas frequently contain rough lag gravels which outline the dunes. Lava flows are typically very rough surfaces which are bright areas on radar images. Cinder cones are smooth and therefore black on the image unless they have a blocky crater rim at the SIR-A incidence angle. Ash dunes and ash fields are smooth and imaged as dark areas.

Blom, R.↗

NASA NTRS1989

Sand dune materials and polar layered deposits on Mars

The possible place of sand in the Martian polar layered deposits is examined. The erosional features in layered deposits and the morphologic relationship of dunes and the layered deposits are discussed. The colors of the polar dunes are shown to be similar to the colors of dunes at other latitudes, suggesting that the polar dunes can be explained without any special or exotic mechanism. Consideration is given to mixing and segregation of materials by eolian processes observed on Mars, showing that sand was probably carried to the polar regions during part of the formation of the layered deposits.

Thomas, Peter↗