Crescentic Dunes Research Articles

Giant solar farm planned for Nevada

California-based SolarReserve hopes to build in the Nevada desert what would be the world’s largest solar farm. The concentrated solar facility would cost $5 billion and be capable of generating 2 gigawatts of power. The firm’s technology, already deployed at the 110-MW Crescent Dunes Solar Energy Project near Las Vegas, uses thousands of mirrors, called heliostats, to focus the sun’s rays on a tower filled with molten salts. The 565 °C fluid creates steam that powers a turbine. SolarReserve is currently working to find a site and obtain financing.

Aeolian dune sediment flux variability over an annual cycle of wind

AbstractAeolian dune motion is thought to be driven by an annual cycle of sediment‐transporting wind events. Each wind event drives uneven motion of dune crestlines, yet dune crestlines align as a trend to an annual cycle of wind. Understanding the variability in dune motion over such a cycle aids the interpretation of aeolian cross‐stratification, often available only in the limiting exposure of core and outcrop. Digital elevation models obtained by light detection and ranging are used to estimate dune brink motion and sediment flux along the sinuous crestlines of crescentic dunes at White Sands gypsum dune field (south‐central New Mexico, USA) over an annual cycle of wind. In tandem, meteorological observations over the same annual cycle are used to drive a kinematic model of dune crestline motion. Wind‐driven kinematic modelling does well to predict the mean and overall variation in sediment flux with compass direction. Digital elevation model‐based estimations of brink motion and sediment flux reveal that dune motion and sediment flux very nearly follow a circular normal distribution. Dunes at White Sands were found to achieve steady mean values of lee surface dip direction, brink motion and sediment flux within a sample window the size of approximately six dunes of average crestline length. Due to the symmetrical distribution of dune motion about the average lee surface dip direction, uneven motion of dune crestlines averages to become motion of dune crestlines normal to a trend, as predicted by wind‐driven kinematic models.

Grain size distribution at four developmental stages of crescent dunes in the hinterland of the Taklimakan Desert, China

Although scientists have performed many studies on crescent (barchan) dunes in the Taklimakan Desert, few studies reported the changes in grain size at different development stages of crescent dunes. In order to evaluate the changing trends of surface sediment grain size with dune development, we investigated the grain size characteristics at four developmental stages (oval sand pile, shield dune, incipient crescent dune and mature crescent dune) of crescent dunes by measuring the morphology of sand dune and observing the near-surface wind regime. The dunes have developed in a wide inter-dune corridor between high compound longitudinal ridges in China’s Taklimakan Desert. The surface sediments at four developmental stages of the crescent dunes were primarily composed of fine sands, followed by very fine and medium sands. Mean grain sizes ranged from 2.8 to 3.1 φ, with a unimodal distribution. The sands were moderately well-sorted, their distribution varied from platykurtic to very platykurtic, and symmetrical or skewed towards the fine particles. From oval sand piles through shield and incipient crescent dunes to mature crescent dunes, incipient grain size gradually increased, particles became finer, sorting became better, kurtosis and skewness increased. Grain sizes on the surface layer became coarser upwards from the toe of the windward slope and then became finer towards the bottom of the leeward slope. We found that the coarsest particles at different positions at the four developmental stages were different. The coarsest particles were distributed at the top of the oval sand piles and shield dunes, versus at the middle of the windward slope of the incipient and mature crescent dunes. Correlations between the mean grain size and other grain size parameters showed that as mean grain size became finer, sorting became better and kurtosis became wider, but skewness changed only slightly. In addition, grain size variation in the surface sediments correlated with the movement speed of the dunes in the study area. In the open ground among tall-complex longitudinal ridges in the hinterland of the Taklimakan Desert where aeolian environment is characterized by comparatively strong wind and unsaturated sand flow, faster dune movement corresponded to coarser grain size.

Eolian deposits of the southwestern margin of the Botucatú paleoerg: Reconstruction of the Gondwana landscape in Central Northern Argentina

The Mesozoic Botucatú paleoerg at the southwestern margin of Gondwana includes a succession of eolian dunes cross-strata which are presently exposed in Otumpa Hills (Central Northern Argentina). Here, the architectural facies, petrology, and provenance of those rocks were studied in order to investigate depositional environments and paleoclimates. The stratigraphic sequence included basal eolian two-dimensional crescentic dunes (Slp) overlain by three-dimensional crescentic dunes of smaller scale (Smt). These were correlated with the Upper Member Rivera of the Tacuarembó Formation (Uruguay), or its equivalent in Brazil, the Botucatú Formation. These outcrops partially mark the southwestern margin of the Botucatú paleoerg along the Chaco–Paraná Basin boundary. The paleocurrents from the W, NW, and SW and the U–Pb ages of detrital zircons indicate a main Pampean cratonic and secondary Andean magmatic arc (180Ma) source. A detrital zircon of 180Ma by U–Pb limits a maximum depositional age at 180Ma (Toarcian) for facies Slp. Upwards, the phreatic silcrete and calcrete indicate semiarid conditions during the Paleocene, which are correlated with the Queguay Formation of Uruguay. A saprolite paleoweathering profile, recording wet tropical–hyper-tropical climate at the Early Eocene and representing the Gondwana landscape and climate conditions, crowns the sequence. This study represents the first provenance and surface texture analysis of minerals from the Botucatú paleoerg and was instrumental to unravel past environmental and sedimentary conditions.

High Capacity Factor CSP-PV Hybrid Systems

Tower concentrating systems with direct molten salt heat transfer and storage can deploy particularly inexpensive and scalable thermal storage, enabling cost-effective 24-hour generation using only solar energy. While typical capacity factors (CFs) for intermittent renewables are generally between 20% and 40%, the SolarReserve Crescent Dunes project will offer above 50%. This paper discusses how SolarReserve's CSP technology can cost-effectively produce a CF over 80%, and when hybridized with PV, can raise the CF further to roughly 90%. A detailed operational model of a hybrid system in Chile's Atacama Desert was produced, using localized data on weather and interconnection capacity, to illustrate this capability. Analysis of high CF CSP-PV hybrids leads to three important conclusions. First, it was found that effective configuration of high CF systems supported selection of fixed-tilt PV at a high angle, which is optimized for winter generation in order to minimize seasonal differences. Second, when a dispatch strategy was developed which incorporated multiple priority levels and which dispatched CSP in response to PV output, it enabled higher CF CSP-PV hybrid operations than the CSP accomplished alone. Third, it was found that average annual DNI was not a sufficient metric of solar resource, and that seasonal variability and consolidation of non-optimal days were also important to high CF designs. New metrics for solar resource measurement are proposed and discussed.

Dune deformation in a multi‐directional wind regime: White Sands Dune Field, New Mexico

AbstractAs with most dune fields, the White Sands Dune Field in New Mexico forms in a wind regime that is not unimodal. In this study, crescentic dune shape change (deformation) with migration at White Sands was explored in a time series of five LiDAR‐derived digital elevation models (DEMs) and compared to a record of wind direction and speed during the same period. For the study period of June 2007 to June 2010, 244 sand‐transporting wind events occurred and define a dominant wind mode from the SW and lesser modes from the NNW and SSE. Based upon difference maps and tracing of dune brinklines, overall dune behavior consists of crest‐normal migration to the NE, but also along‐crest migration of dune sinuosity and stoss superimposed dunes to the SE. The SW winds are transverse to dune orientations and cause most forward migration. The NNW winds cause along‐crest migration of dune sinuosity and stoss bedforms, as well as SE migration of NE‐trending dune terminations. The SSE winds cause ephemeral dune deformation, especially crestal slipface reversals. The dunes deform with migration because of differences in dune‐segment size, and differences in the lee‐face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation. Each wind event deforms dune shape, this new shape then serves as the boundary condition for the next wind event. Shared incidence‐angle control on dune deformation and lee‐face stratification types allows for an idealized model for White Sands dunes. Copyright © 2015 John Wiley & Sons, Ltd.

Molten salt tower reboots solar thermal power [News

Solar power projects intended to turn solar heat into steam to generate electricity have struggled to compete amid tumbling prices for solar energy from solid-state photovoltaic (PV) panels. But the first commercial-scale implementation of an innovative solar thermal design could turn the tide. Engineered from the ground up to store some of its solar energy, the 110-megawatt plant is nearing completion in the Crescent Dunes near Tonopah, Nev. It aims to simultaneously produce the cheapest solar thermal power and to dispatch that power for up to 10 hours after the setting sun has idled photovoltaics.

Morphology and formation mechanism of sand shadow dunes on the Qinghai-Tibet Plateau

The formation and development of dunes depend on wind-blown sand movement which is affected by the characteristics of sand material, topography, wind regimes and other factors. In this paper, we investigated two sand shadow dune groups in Shigatse and Za’gya Zangbo of Tibet and an individual dune in Da Qaidam of Qinghai, and analyzed their topographies and morphologies, and the physical characteristics of the sand, wind regime and sand transport. Formed under harsh conditions behind hills, these mature sand shadow dunes are hundreds of meters long, have significant ridges and crescent dunes downwind, and have a hill pass on one or both sides. Wind tunnel experiments revealed that the hill gap and wind velocity are important factors in the formation of these dunes. Sand shadow dunes formed only when the gap spacing is two-thirds of the hill height. When wind velocities are 20 m/s, the sand body is divided into two parts. The hill pass allows the transport of sand by wind, creating a “narrow-pipe effect”, which causes the transported material to gradually accumulate in the center of the shadow zone. We observed that the following are needed for sand shadow dunes to form: (1) strong winds, sufficient sand, suitable obstacles and a dry climate; (2) one or both sides of the obstacle forming the shadow zone must have a hill pass; and (3) the windward side of the obstacle must have a wide, flat area, providing adequate spacing for wind flow and transport of material and the leeward side must have a sufficiently broad, flat area to allow the release of the transported material. Research results on these newly discovered dunes on the Qinghai-Tibet Plateau could contribute to the understanding of dune geomorphology.

Wind regimes and aeolian geomorphology in the western and southwestern Tengger Desert, NW China

Wind is the primary control on the formation of aeolian geomorphology. In this study, we combined wind regime data from automated weather stations in the western and southwestern Tengger Desert of the Inner Mongolia region in China with remote-sensing data to analyse the relationship between the wind energy environment and aeolian geomorphology. Tengger Desert is one of the main dust storm sources in northwestern China. Therefore, efforts aimed at controlling desertification and dust storm require a deeper understanding of the processes that govern the formation and subsequent evolution of dunes in this area. Wind speed was largest in the northwest (3.3 m/s in the Xiqu station) and smallest in the southeast (1.2 m/s in the Haizitan station). Potential sand transport was also largest in the northwest (195 in the Jiahe station) and smallest in the southeast (33 in the Tumen station). The sand-driving wind (5.92 m/s) directions were from the NW and SE quadrant across the study area, at >76% of all sand-driving wind, reaching 99% in the Tumen station. The sand-driving wind in the NW quadrant reached >48%, and in the SE quadrant, >12% of all sand-driving wind in all stations. In the study area, sand dunes included crescent, dune networks, transverse, and coppice dunes. Dune crest directions had similar trends from upwind to downwind, at 133° in the middle region, and 124° in the southwestern region. Mean dune spacing changed with dune patterns; the maximum spacing for crescent dunes was 147 m, for dune networks 118 m, and for transverse dunes it was 77 m. The mean crest length was 124 m (maximum) for crescent dunes in the northwest, 121 m for transverse dunes, and 84 m for dune networks. However, because of gullies in the southern region, the mean crest length was only 58 m (least) for the crescent dunes in that area. The defect density ranged from 0.007 to 0.014. The spatial differences in dune patterns reflected the evolution of the dune field, where older dunes had been formed upwind and younger downwind. Copyright © 2014 John Wiley & Sons, Ltd.

Observations of coastal aeolian dune movements at Feicuidao, on the Changli Gold Coast in Hebei Province

High-precision RTK GPS technology was used to survey the movements of typical coastal dunes, including a coastal crescent dune and a coastal transverse ridge, in the Feicuidao region of the Changli Gold Coast in Hebei Province in 2006–2008. Our data provide information on the direction, type, and velocity of coastal dune movements, and indicate that the coastal dunes in this region are characterized as slow and landward advancing, with to-and-fro fluctuations. The bottom of the studied coastal transverse ridge was stable during the observation period but the position of its crest advanced eastward (seaward) during summer and autumn, and moved landward (westward) in winter and spring. Thus, its crest moved generally landward (westward) but fluctuated to-and-fro eastward and westward. In contrast, the entire coastal crescent dune advanced landward (westward) in a to-and-fro manner, and the velocity of its movement was faster than that of the transverse ridge dune. These results are mainly related to the wind conditions in the research area, the height and volume of the two types of coastal dunes.

A high spatio-temporal methodology for monitoring dunes morphology based on precise GPS-NRTK profiles: Test-case of Dune of Mónsul on the south-east Spanish coastline

Abstract The effects of erosion and accretion of sand dune systems are often underestimated due to the coarse spatial and temporal resolution data set. This paper shows a specific methodology to monitor, at local scale and high repeatability, the crescentic dune of Monsul in Almeria (SE Spain). Precise spatial information based on high resolution profiles has been obtained periodically by repeated GPS surveys. The dune morphology and associated changes due to erosion and accretion are investigated using the GPS methodology in RTK (Real Time Kinematic) mode. This technique introduces significant improvements compared to other techniques for monitoring small areas such as better repeatability, accuracy, reliability, etc. The availability of the Andalusian Positioning Network, an active network over the region, allowed us to monitor the dune throughout GPS profiles capturing its evolution for the period of April–September, 2010. Three GPS campaigns spaced over time were performed. The framework is established by the active network, avoiding the placement of a local control network in this protected area. The main objective of this study is to perform a control methodology based on NRTK (network RTK) positioning supported by a regional active network, with special emphasis on checking and filtering the surveyed data. The numerical and graphical results presented show a balance between the values of erosion and accretion of sand on the dune.

Decadal-scale evolution of a small dune field: Keeler Dunes, California 1944–2010

Aerial photographs and satellite images have been used to document the evolution of a small (<1km2) dunefield over the past 60–70years. Over this period, the dunefield has undergone significant changes, including development of well defined linear and crescentic dunes from an initial small area of partially vegetated dunes, resulting in an increase in the area of the dunes by a factor of 3 since 1944. The dune field continues to expand toward the southeast but its upwind margins are now experiencing significant erosion because the sand supply is now cut off by dust control measures in the source area and transport pathway. This study provides some information on the timescales of dune development in a high-energy aeolian environment, which formerly experienced an abundant supply of sand, with rapid development of crescentic dunes over a period of 20years. The complexity of dunefield development is also highlighted, even on decadal timescales, and the important role of episodic sediment supply in forming new generations of dunes. Periods of rapid dunefield change involving lagged input of additional sand from external sources appear to be linked to episodes of high flows in the Owens River, which is the main sediment source for the Keeler Dunes.

Dune field development, interactions and boundary conditions for crescentic and stellate megadunes of the Al Liwa Basin, the Empty Quarter

ABSTRACTWithin the greater Ar Rub' al Khali (Empty Quarter) sand sea lies an internal depocentre, the Al Liwa Basin, which comprises a variety of mega‐scale dune types. Crescentic dunes dominant the north of the basin while megadunes of stellate or star form are a major landform of the south‐eastern reaches. Their development into dune fields is determined by the style and rate of dune–dune interactions, the boundary conditions imposed by a multi‐modal wind regime, fluctuating groundwater levels, and sediment availability under an assortment of climatic conditions throughout the Quaternary. As a result, dune field patterns are a collective response to these perturbations in space, time and environment. The R‐statistic is a collective measure of these responses, and is a metric capable of identifying the degree of pattern maturity or self‐organization of the aeolian system, and the pathways from which patterns evolve. The spatial signature of the southerly located star dunes is characterized by two definitive patterns of organization: the first, one of complete spatial randomness, the second, a low degree of spatial uniformity. In isolation, these results appear to be unrelated to those for crescentic dunes of the region in which a significantly higher degree of pattern dispersion is the norm. However, when spatial statistical measures are integrated with the theoretical understanding of dune–dune interactions and the involvement of environmental agents, the complex morphodynamic pathways and linkages between regional dune fields is better understood. In this case, both constructive (e.g. merging, lateral linking) and regenerative activity (e.g. calving) have played important roles in the development of dune size, and associated adjustments in spacing, and dune numbers, and subsequently dune field patterns. Synergetic patterns are emblematic of this vast dunescape, whereby transitional geographic, morphologic, dimensional and environmental modifications exist between the mega‐crescentic and mega‐stellate dunes of the Empty Quarter. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Methodology for reconstructing wind direction, wind speed and duration of wind events from aeolian cross‐strata

A methodology for reconstructing wind direction, speed, and event duration from aeolian dune cross‐strata was developed from analysis of crescentic dunes at White Sands, New Mexico, during wind events. Dune lee faces were surveyed, lee‐face deposits mapped, deposition rates measured, grain size sampled by stratification type, and winds characterized from meteorological and field data. The spatial distribution of lee‐face stratification styles is a function of the incidence angle formed between the wind and the brinkline, with secondary controls by wind speed and dune sinuosity and height. Sets of wind‐ripple strata form at incidence angles of 25°–40°, grainfall/grainflow foresets over wind‐ripple bottomsets at 40°–70°, and grainflow/grainfall foresets at 70°–90°. Erosional reactivation surfaces form at incidence angles up to 15°; bypass surfaces up to 25°. The total sediment load is fractionated within lee‐face stratification types. Wind speed can be reconstructed from relationships between grain size, transport mode, shear velocity and grain‐settling velocity. Where the full range of grain transport modes occurs and grain size is limited by shear stress, the shear velocity and grain‐size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep, and the coarse fraction in grainfall traveled in saltation. The minimum duration of a wind event can be estimated using measures of shear velocity, dune height and dune forward migration. Method limitations arise with source‐area control on grain size, extremes in wind events, and severe truncation of sets of cross‐strata.

Feathered sand ridges in the Kumtagh Desert and their position in the classification system

Feathered sand ridges in the northeastern Kumtagh Desert in China cover an area of 4016 km2 and consist of crescent sand ridges and interridge tongue-shaped dunes. Differences in grain size, mineral composition and albedo between crescent sand ridges and tongue-shaped dunes, and between windward and leeward slopes of tongue-shaped dunes, result in their feathery appearance in aerial and satellite imagery. Measurements of the sand drift potential in the region show that the sand-moving wind for feathered sand ridges can be divided into three sectors; i.e. north-northeasterly, easterly and east-northeasterly sectors roughly corresponding to the southeast, northwest and southwest slip faces. Our findings suggests that the crescent sand ridges resulting from the connection of barchan dunes along the prevailing wind direction are longitudinal dune ridges rather than transverse ones. Tongue-shaped dunes and quasi-dune shapes have obvious distinctions and are new transverse dune types. According to McKee’s dune shape classification, the feathered sand ridges are not a deformation dune type but a complex one. According to Wu’s dune morphological and genetic classification, they are not dune ridges or compound dune ridges that form under the action of unidirectional winds or two winds intersecting at an acute angle, but are complex dune ridges that form under the action of three winds intersecting at an acute angle.

Aeolian scours as putative signatures of wind erosion and sediment transport direction on Mars

Obstacle marks, specifically current crescents (scours) formed by aeolian erosion, have not been previously identified on Mars from orbit. However, recent Mars Reconnaissance Orbiter images of an unnamed intracrater dune field within the Hellespontus region have shown innumerable meter-scale scours around fine and medium grade blocks. The types, relative numbers, and distributions of scour features served to determine, by proxy, the modes of surface wind direction and pathways of sediment transport across the crater floor. The orientations of scours of U-type morphology as well as the facing directions of leeward slopes for crescentic dunes (barchans and barchanoids) and megaripples were examined by statistical methods to determine their reference directions and dispersion of modal classes. We showed that although the dune field has evolved primarily under the influence of winds from the southwest, U-type scours have developed predominantly from a significant northwesterly wind direction. These data suggest that the dune field has evolved under the influence of a bimodal wind regime. Furthermore, such an aeolian system may help to explain the intermediary morphology between crescentic and linear for the central part of the dune field, in which the dunes appear to have undergone longitudinal as well as lateral sediment transport. In the absence of direct measurements of wind directions and strengths, current crescents offer detailed data from which planetary air flow at the surface–air interface can be better interpreted for the many intracrater settings across Mars.

Equilibrium versus disequilibrium of barchan dunes

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

Historical Dune Pattern Dynamics: White Sands Dune Field, New Mexico

Research efforts studying dune fields as spatial units are limited and the historical dynamics associated with dune field-scale pattern attributes are currently not well documented. Historical repeat aerial photography was used to quantify temporal changes in the crescentic dune pattern at the White Sands Dune Field, New Mexico. A Geographic Information System (GIS) was used to digitize ~ 14,000 dune crests from the combined photoset. Crest length, sinuosity, spacing, orientation, transport vector, and defect density were calculated from these measurements and statistically analyzed. The pattern analysis revealed that crest length, sinuosity, and defect density were highly variable pattern elements over a 60-year period. These dune pattern elements also exhibited temporal relationships, such as the inverse relationship between crest length and sinuosity over time. Defect density calculations revealed that the dune field is trending to a possible state of disorganization. This trend was temporarily interrupted in 1985 by a massive period of organization in which crest length was inversely related to defect density and defect density was proportionally related to sinuosity. The temporal variations in these pattern elements and the episodic organizational event in 1985 were likely climatically induced.

Aeolian sand sea development along the mid‐Cretaceous western Tethyan margin (Spain): erg sedimentology and palaeoclimate implications

AbstractThe existence of a mid‐Cretaceous erg system along the western Tethyan margin (Iberian Basin, Spain) was recently demonstrated based on the occurrence of wind‐blown desert sands in coeval shallow marine deposits. Here, the first direct evidence of this mid‐Cretaceous erg in Europe is presented and the palaeoclimate and palaeoceanographic implications are discussed. The aeolian sand sea extended over an area of 4600 km2. Compound crescentic dunes, linear draa and complex aeolian dunes, sand sheets, wet, dry and evaporitic interdunes, sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub‐tropical arid belt along the western Tethyan margin. Sub‐critically climbing translatent strata, grain flow and grain fall deposits, pin‐stripe lamination, lee side dune wind ripples, soft‐sediment deformations, vertebrate tracks, biogenic traces, tubes and wood fragments are some of the small‐scale structures and components observed in the aeolian dune sandstones. At the boundary between the aeolian sand sea and the marine realm, intertonguing of aeolian deposits and marine facies occurs. Massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events. The cyclic occurrence of soft sediment deformation is ascribed to intermittent (marine) flooding of aeolian dunes and associated rise in the water table. The aeolian erg system developed in an active extensional tectonic setting that favoured its preservation. Because of the close proximity of the marine realm, the water table was high and contributed to the preservation of the aeolian facies.A sand‐drift surface marks the onset of aeolian dune construction and accumulation, whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period. A prominent aeolian super‐surface forms an angular unconformity that divides the aeolian succession into two erg sequences. This super‐surface formed in response to a major tectonic reactivation in the basin, and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas.The location of the mid‐Cretaceous palaeoerg fits well to both the global distribution of other known Cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea‐level lowstand during early mid‐Cretaceous times. The occurrence of a sub‐tropical coastal erg in the mid‐Cretaceous of Spain correlates with the exposure of carbonate platforms on the Arabian platform during much of the Late Aptian to Middle Albian, and is related to this eustatic sea‐level lowstand.

Wind tunnel experiments of air flow patterns over nabkhas modeled after those from the Hotan River basin, Xinjiang, China (I): non-vegetated

A nabkha is a vegetated sand mound, which is typical of the aeolian landforms found in the Hotan River basin in Xinjiang, China. This paper compares the results of a series of wind tunnel experiments with an on-site field survey of nabkhas in the Hotan River basin of Xinjiang. Wind tunnel experiments were conducted on semi-spherical and conical sand mounds without vegetation or shadow dunes. Field mounds were 40 times as large as the size of the wind tunnel models. In the wind tunnel experiments, five different velocities from 6 to 14 m/s were selected and used to model the wind flow pattern over individual sand mound using clean air without additional sand. Changes in the flow pattern at different wind speeds resulted in changes to the characteristic structure of the nabkha surface. The results of the experiments for the semi-spherical sand mound at all wind velocities show the formation of a vortex at the bottom of the upwind side of the mound that resulted in scouring and deposition of a crescentic dune upwind of the main mound. The top part of the sand mound is strongly eroded. In the field, these dunes exhibited the same scouring and crescentic dune formation and the eroded upper surface was often topped by a layer of peat within the mound suggesting destroyed vegetation due to river channel migration or by possible anthropogenic forces such as fuel gathering, etc. Experiments for the conical mounds exhibit only a small increase in velocity on the upwind side of the mound and no formation of a vortex at the bottom of the upwind side. Instead, a vortex formed on the leeward side of the mound and overall, no change occurred in the shape of the conical mound. In the field, conical mounds have no crescentic dunes on the upwind side and no erosion at the top exposed below peat beds. Therefore, the field and laboratory experiments show that semi-spherical and conical sand mounds respond differently to similar wind conditions with different surface configuration and development of crescent-shaped upwind deposits when using air devoid of additional sediment.