Linear Dunes Research Articles

Fluvial-lacustrine influences on linear dune erosion at Lake Caroline in the Simpson Desert of Australia

Linear dunes are frequently examined with regard to their formation and maintenance; however, erosion or degradation of these landforms is less commonly addressed, due in part to the lack of observable changes in the geologic record. This study investigates the significant erosion of linear dunes along Lake Caroline, a playa in the northern Simpson Desert of central Australia. Field observations, laboratory analyses, and remote sensing imagery document recent fluvial and lacustrine interactions at Lake Caroline. Compositional and geochemical sediment analyses from three ∼2 m deep hand-augured sample sites indicate that the playa is primarily filled with sand from linear dunes, but also contains evaporite minerals and weathered local bedrock. Satellite images show that the playa has flooded at least 58 times since 2001. Our results indicate that present-day aeolian processes are sufficient to mobilize and transport sediment but are dominated by fluvial-lacustrine processes, resulting in the playa-adjacent dunes becoming isolated and starved of local sediment. As a result, the dunes are currently eroding into the playa which supports the conclusion that long-distance sediment transport is not responsible for the formation or maintenance of linear dunes as suggested by the linear due extension hypothesis. Burial dates from optically stimulated luminescence (OSL) indicate the linear dunes have been eroding for as much as 24 ka, and sediment samples from the playa near one linear dune suggest an onset of dune formation in the area before 58 ka. This work documents an instance in geologic time during the late Quaternary when aeolian, fluvial, and lacustrine processes are competing with one another, offering new insights into the dynamics of linear dunes in the arid Simpson Desert.

Holocene aeolian environmental dynamics in fixed and semi-fixed deserts over the arid Central Asia revealed by comprehensive sand-dune records

Fixed and semi-fixed deserts are widely distributed in arid Central Asia (ACA). Environmental changes in these deserts can affect the regional radiation balance, climate dynamics, and global climate through a series of feedback effects. This study analyzed luminescence dating from 37 sites, with a particular focus on dendritic dunes (a pattern of vegetated linear dunes) and the ancient dunes beneath them in the Gurbantunggut Desert and yielded the following insights. (1) Primary ridges of dendritic dunes originated approximately 1.0 ka, whereas secondary ridges predominantly formed at 8.5 ± 0.3 ka. The formation of the underlying ancient dunes commenced at least 11.0 ± 0.5 ka and ended between 8.5 ± 0.3 ka and 8.2 ± 0.4 ka. (2) During the Holocene, the Gurbantunggut Desert underwent two distinct environmental phases. From 11.7 ka to 8.1 ± 0.1 ka, the region was characterized by vigorous aeolian activity, marked by the prevalence of mobile dunes. Conversely, the period from 8.1 ± 0.1 ka to 0 ka exhibited substantial environmental amelioration, with limited aeolian activity and the intermittent partial development of vegetated linear dunes. (3) A comprehensive analysis of the principal factors affecting regional aeolian activity revealed that at 11.7 ka–8.1 ± 0.1 ka, moisture (precipitation) and near-surface wind intensity primarily governed aeolian activity in the Gurbantunggut Desert. At 8.1 ± 0.1 ka–0 ka, aeolian activity was mainly influenced by moisture (precipitation), near-surface wind intensity, and external sand supply. (4) Similar patterns of Holocene aeolian activity were observed in the fixed Bayanbulak, Karakum, and Kizil Kum Deserts within the ACA. On a suborbital scale, winter insolation served as the primary driving factor, along with the ice volume and atmospheric CO2 concentration. These factors collectively controlled regional winter temperatures, which determined moisture (precipitation) and near-surface wind intensity by affecting the winter westerlies and Siberian High, ultimately controlling regional aeolian activity.

Landscape evolution and hydrology at the Late Pleistocene archaeological site of Narabeb in the Namib Sand Sea, Namibia

The Namib Sand Sea (NSS) in Namibia is known to preserve a wide variety of Pleistocene-age archaeological sites. However, few Middle Stone Age (MSA) sites in this region have been systematically investigated and basic questions around chronology and technological organization remain open. Here we examine Narabeb, an open air MSA surface site exposed in an interdune pan, ∼30 km into the northern NSS. Narabeb was first documented in the 1970s, and then re-examined in 2021 and 2022 by members of this team. Lithic technological analysis combined with a geomorphological description of the site, palaeoenvironmental interpretation of fine-grain water-lain sediments, and luminescence ages from northern and southern locations on the Narabeb pan provide some of the first understanding of human-environmental interactions and estimates of chronology from the later-Middle and Late Pleistocene in the NSS. In addition, we apply a quantitative approach to aeolian linear dune accumulation and extension to explore possible scenarios for landscape development at this site, in order to better understand the former water course(s) affecting the area. The new chronology suggests this site contained standing water at, or just after, the MIS 7/6 transition, and again at, or just after, the end of MIS 6 into early MIS 5. The timing of greater phases of water availability have some overlap with the speleothem growth record at Rössing Cave, situated ∼90 km north of the NSS (and ∼135 km north of Narabeb). Our results provide the foundation for larger, regional-scale analyses of early human adaptive strategies in this unique environment within Southern Africa.

Morphological and sedimentary characteristics of raked linear dunes in the southeastern Taklimakan Desert, China

Raked linear dunes were rarely reported, except in the Kumtagh Desert, leaving little known about the dynamic process. However, numerous raked linear dunes have formed in the Kat Kum dunefield of the southeastern Taklimakan Desert, which provides a new case to study the morphodynamics of these dunes. We conducted a comprehensive analysis on the dune morphometry, wind regime, sedimentary characteristics, and sand availability of these dunes. We found that grain size variation is an essential factor affecting the formation of raked linear dunes in addition to wind regime and limited sand availability. These dunes in the Kat Kum present small scale and easily reshaped with fast migration rate compared with these in the Kumtagh Desert, and distributed in areas with low sand cover. The primary ridge extended obliquely to the resultant drift direction, whereas the subsidiary ridge extend is nearly parallel to this direction. The grain size of the primary ridge is noticeably coarser than that of the subsidiary ridge. These dunes seem to have evolved from barchans. Under a north-northeast wind, barchans reshaped to asymmetrical barchans by extending their southeast limbs and eroding their northwest limbs, causing the ridge to be oblique to the resultant drift direction. The strong east-northeast wind erodes and reshapes the primary ridge, transporting fine sand to the northwest and resulting in the formation of proto-subsidiary ridges. With the elongation and lateral movement of primary ridge, a continuous subsidiary ridge with regular dune spacing forms on the northwest flank.

Geomorphology of the Makgadikgadi Basin (Botswana): Insight Into the Propagation of the East African Rift System

AbstractThe Southwestern Branch of the East African Rift System propagates through the Central and Southern African plateaus and ends in the Okavango Makgadikgadi Zambezi Basin. This basin hosts the Okavango Graben and the Eiseb Graben, considered as the terminus of the Southwestern Branch of the rift. To the southeast, the Makgadikgadi Basin is affected by a series of normal faults forming the Makgadikgadi Rift Zone (MRZ) which regional geodynamic significance remains unclear. Based on fieldwork and geomorphic analysis, we revisited the geomorphological features associated with paleolakes and the fault pattern within the Makgadikgadi Basin to better constrain the dynamics of the MRZ. Fault scarps and offsets along linear dunes show normal‐dip kinematics of faults, indicating a NW‐SE extension direction in the area. Furthermore, lacustrine shorelines in the basin are undeformed, proving that they post‐date the fault activity. The previously published ages of these shorelines demonstrate that the MRZ currently has a low tectonic activity. Integrated in the geodynamic framework of the region, these results suggest that present‐day deformation shifts toward the Okavango Graben north of the MRZ. We therefore propose a “zip‐opening” model to explain the propagation of the Southwestern Branch of the East African Rift System where the tip of the system progressively progresses southwestward, driven by motions of the continental plates.

Yardang-controlled dune morphology and dynamics in the Qaidam Basin: Insight from remote sensing and numerical simulations

The yardang-dune coexistence and the control of yardangs on dune formation reveal the joint action of wind erosion and deposition. Yardangs exhibit distinctive characteristics of streamlining and clustering, which apply unique and complicated impacts on the wind field and sand transport. However, previous studies lack systematic investigation on how yardangs exert control over dune morphology, and the intricate wind dynamics and mechanisms involved remain unclear. In this study, the “yardang-controlled dune” is systematically illustrated, supported by thorough studies of the yardang-controlled dune morphology and dynamics. Through the monitoring of the 6722 km2 dunes in the Qaidam Basin (QB), three typical yardang-dune coexistence patterns are identified and summarized: Pattern I-windward dune, crescentic dunes form on the upwind sides of the sparsely arranged yardangs; Pattern II-corridor dune, crescentic dunes form beside the narrowly arranged yardangs in the corridors and migrate; Pattern III-leeward dune, linear dune forms on the downwind side from isolated yardang tail. Computational fluid dynamics (CFD) modeling is used to analyze the dynamics and mechanisms of the three patterns and the corresponding real yardang topographies. CFD simulations show that with the control of yardangs, the winds in the locations corresponding to the dunes have significantly low velocities, leading to the wind entrainment decrease, sand accumulation and subsequent dune formation. CFD also reveals that the aspect ratios of yardangs control the formations of wind shadows and linear dunes on the yardang tails. The simulation results agree well with the actual landforms observed in the QB of the three patterns. Additionally, the dune leeward slope width and migration velocity statistics based on remote sensing provide further support for the observations and simulations. This study sheds light on the intricate influences of yardangs on wind deposition, underscoring their role in shaping the landform of dunes.

Quantifying dune migration patterns and influencing factors in the central Sahara Desert

Based on Landsat images and ERA5 climate data, here we analyzed geomorphic dune patterns and the spatial characteristics of dune migration in the central Sahara Desert region (SW Libya, SE Algeria), using the COSI-Corr technique. Our results revealed clear observable drift potential (DP) and resultant drift potential (RDP) gradients, these decreasing from a northerly to southerly direction. Moreover, the annual average RDP/DP in most areas was <0.3 (i.e., highly variable). The main dune types in the study area included complex transverse ridges (22.82 %), linear dunes (19.87 %), barchan and barchanoid chains (16.95 %), and star dunes (13.55 %). Of these, barchans and barchanoid chains, as well as complex transverse ridges, appeared in areas of relatively high DP, while complex longitudinal ridges and honeycomb dunes were found in those of low DP. Linear dunes had a simpler wind composition, being mainly distributed in areas with intermediate wind variability. Both the honeycomb dunes and complex longitudinal ridges had nearly always formed in complex multi-directional wind environments. Dune migration displacement in dune fields ranged widely, from 0.5 to 23.57 m (mean = 6.71 m), during the 30-year study period (1993–2022). Barchans and barchanoid chains migrated fastest, with a mean value > 10 m/yr; in contrast, complex longitudinal ridges and honeycomb dunes had the slowest migration rate, always at < 5 m/yr. Overall, the dune migration rate was mainly related to dune height and wind regime. Spatially, the dune migration trend was basically consistent with that of the resultant drift direction (RDD), mainly in a northwesterly direction (28.36 %). The accuracy testing results indicated that the COSI-Corr displacement measurement accuracy was generally higher than the dune migration direction accuracy. This study provides not only valuable reference data for regional aeolian activities, but also insight into the developmental environments and migration dynamics of differing dune types, which could be used for prospective regional aeolian geomorphology research in the Sahara Desert.

Using Texture Statistics to Identify and Map Different Dune Types within the Rub’ al Khali

Understanding the movement, direction, and shape of sand dunes can contribute to reducing their impact on infrastructure and the environment. The Rub’ al Khali desert has a distribution of dune types. This study aims to identify and map the different types of dunes within the Rub’ al Khali using a texture analysis method based on a digital elevation model (DEM). Statistical texture analysis methods (variance, skewness, and kurtosis) show three different textures of sand dune shapes, according to the geography of the dunes, using data contained in global DEMs. The analysis presented in this study focused on the use of DEMs to investigate the varied dune morphology within the Rub’ al Khali. The GMTED2010 and EarthEnv_DEM90 digital elevation models were compared. Spatial variability in dune height, spatial variability in dune texture, and profile graphs were created to examine dune surfaces in cross-section. The results provided six different dune types within the sand sea: giant compound linear dunes, simple linear dunes, simple transverse dunes, compound crescentic dunes (megabarchans), huge star dunes, and many transitional forms that defy classification. The results showed that the compound linear dune and simple linear dune were the dominant dune types, covering 41.61% and 31.7% of the total study area, respectively. The maps of variance, using either 10 × 10 and 30 × 30 focal blocks, produced a fairly sharp distinction in dune texture. It is hoped that future research in aeolian geomorphology will greatly benefit from these results, which could easily be expanded with the use of more sophisticated pattern recognition software, which clearly shows the value of using such an approach.

Wind-reworked fluvial deposits as an archaeological environment: the Agnes Banks Sand of the Quaternary Hawkesbury–Nepean sequence of southeast Australia

ABSTRACT The deposits of Sydney’s rivers are thought to have experienced widespread aeolian modification during the Quaternary. The resultant sediments form archaeologically important landscapes upon which are found several of the oldest archaeological sites in the Sydney district. Unfortunately, little is known of the processes and products of aeolian reworking. The context of the archaeological discoveries is therefore enigmatic. This study focusses on the Agnes Banks Sand, a Cenozoic sand body that may represent the only sedimentary unit in the Sydney area that preserves reliable evidence of the action of aeolian processes on fluvial sediments. Our work confirms that the sands are indistinguishable from inland dune deposits worldwide, with the deposits reworked from alluvial sediments within and adjacent to the channel of the nearby Nepean River. The sands form east–west-aligned linear dunes, whilst the sediment body fines to the east, a pattern consistent with entrainment by westerly winds. Three other aeolian depositional bodies have been identified alongside the Hawkesbury–Nepean River. Together, these form an assemblage of source-bordering dunes that lies downwind of the river across the northern part of the Cumberland Basin. Deposition here began in Marine Isotope Stages 3–2 and continued into Marine Isotope Stage 1, a period corresponding with a general episode of dune activation across southeast Australia. Although it is widely believed that the Agnes Banks Sand was formed sometime between the Pliocene and the Middle Pleistocene, we present evidence that its deposition post-dates 65 ka and that the deposits are contemporaneous with the other fluvio-aeolian units in the catchment. The true importance of Agnes Banks, however, is as a type locality from which it has been possible to derive sedimentological and geomorphological signatures that may be applied to appraisals of the fluvio-aeolian record within (and perhaps beyond) the Sydney area.

Spatiotemporal analysis of dune stabilization in the Kyzylkum and Karakum sandy deserts

Sand seas and dune bedforms are climatic chronicles that have a wide range of scientific meanings. The Karakum and Kyzylkum sand seas in Central Asia span ∼500,000 km2, among the largest sand seas on Earth; yet, very little is known about their emergence and stabilization. Further, the internationally accessible literature lacks comprehensive studies on the interactions between contemporary climate and dune morphodynamics for this region. In this study, we applied the conventional approach for examining wind data—Fryberger’s drift equations and the latest Copernicus ERA5 wind reanalysis model—to demonstrate that the Karakum and Kyzylkum deserts had (and continue to have) low-energy environments during 1950–2019. Time-series multidimensional raster analysis and data mining indicated that 93% of surveyed desert areas were subjected to low-energy wind conditions during the last 70 years. The decrease in wind energy was further confirmed using the partitioning around medoids (PAM) unsupervised machine-learning clustering method and Getis-Ord Gi* statistics. Such an environmental setting promotes plant growth and biogenic crust development, and strengthens dune stability across the deserts. Furthermore, the results suggested that the spatial patterns of active dune morphologies (e.g., complex barchanoid ridges and overlaying superimpositions) were closely linked to the drift direction, power, and variability of contemporary winds, whereas stabilized aeolian formations (e.g., distinct formations of complex and compound vegetated linear dunes) indicated debatable disassociations. The relationship between the recognized orientation of the surveyed dune types and the computed resultant drift direction did not change significantly, suggesting that over time, the winds in these areas have most likely varied in strength, but not in direction. The calculated drift powers are not sufficient for the formation of registered mega profiles. Rather, they bolster dunes stability, stressing both deserts as indicative of earlier climatic eras that permitted aeolian sand activity and severe shifts that have initiated their steadiness. This is the first comprehensive study to statistically evaluate the links between the contemporary climate and dune morphologies of the Karakum and Kyzylkum deserts. Our study can serve as a foundation for future studies on climate change, dune mapping, and optically stimulated luminescence (OSL) dating, while offering a broad understanding of the region’s paleo and contemporary environmental systems dynamics.

Land Reclamation and its Impact on Agriculture-A Case in Tamil Nadu

Desertification is a significant global ecological problem. It is also common in many areas in the Theni district. The study villages in the Theni district are affected by the aeolian sand deposition, forming linear dunes along the Western Ghats. They have been so for hundreds of years. Arable/agricultural land has been covered by dunes for an area of 12,000 ha. There are even now high dunes stretching for almost 20-25 km all along the Western Ghats, after about 40 per cent of the area has been sand quarried in the last several years. The villages get very low rainfall of about 650 mm to 750 mm a year. Purpose of the Study. The purpose of the study is to look at what has happened after sand quarrying/mining of the area by the human agency and how the reclaimed areas used, particularly for small-scale agriculture, in the last several years. The Objectives of the Study. The objectives of the study are: (1) To examine the process of land reclamation in the study area through sand mining from the dunes and sand encroached areas; and (2) To analyse the use of reclaimed land for agriculture, particularly by the marginal and small farmers of the study villages. Land Reclamation and Agriculture of the Study Area. Land reclamation hereabouts has been happening for several years, but it has been primarily an individual effort. Some farmers have decided either on their own or the advice of someone or in some cases they have simply followed others. Lands of considerable extent have been reclaimed from the sands in the villages of Sillamarathupatti and Silamalai, which are our current focus. The paper speaks about the impacts of land reclamation on the agriculture of the villages from a questionnaire survey.

ZIBARS: Distribution, morphology and environmental controls

Zibar is an Arabic word for aeolian bedforms that are coarse-grained, of limited relief, have no slipfaces, and occur on sand sheets and within interdune corridors of many sand seas. They may also be called granule-armored dunes, undulations, transverse aeolian ridges, mega-ripples, giant ripples, and chevrons and whalebacks. Zibars, though very extensive, are by no means ubiquitous in the world’s aeolian environments. They occur in thirteen main locations in dry, warm deserts: Algodones, USA; Gran Desierto, Mexico; eastern Mauritania; Ubari, Libya; Libyan Desert; Erg of Fachi-Bilma/Tenéré; Selima, Sudan; Namib, Namibia; Lut, Iran; southern Rub’ al Khali, Arabia; Thar, India; Kumtagh, China; and Atacama, Peru. They can occur as transverse ridges, as parabolic shapes, and as oblique features. In many regions they tend to have a spacing of around 8 to 14 per km. They tend to be modest in height, varying between tens of centimeters to up to c 6–8 m. All researchers seem to agree that they are mound-like forms without slipfaces and that their slope angles are no more than 5-15o. Nearly all zibars occur in the interdunes between various types of linear dune. They are composed of ill-sorted sand, often with a large coarse component.

Reconstructing rainfall using dryland dunes: Assessing the suitability of the southern Kalahari for unsaturated zone hydrostratigraphies

Time-series of dryland rainfall over 100–1000 s of years are scarce but are needed to underpin improved predictions under future climate change. Dryland sand dunes are established Quaternary geomorphic archives, which also contain pore moisture as part of the unsaturated zone (USZ), with chemical tracers that provide a novel proxy for palaeomoisture. Chloride depth profiles, converted using a mass balance approach to temporal records, are known as hydrostratigraphies. Evaporative enrichment of meteoric chloride occurs in the near-surface zone and the established signature gets transported vertically via infiltration. This study explores the potential for this approach for southern Kalahari vegetated linear dunes comparing twelve (10–12 m deep) hydrostratigraphies across space and sampled in different years (2011, 2013, and 2016). Three further profiles sampled close to an interdune pan demonstrate that additional chloride is added locally to the dune closest to the pan. The remaining hydrostratigraphies show variable trends, with four broad groupings, leading us to suggest this region is unsuitable for this approach. Insights into this variable behavior were sought from simulating liquid and vapor flux using STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil). Simulations suggest the mixing zone can reach 10 m thick, which helps account for the variation in hydrostratigraphies. Heterogeneity may also arise from spatially-heterogenous receipt of convective rainfall events and non-uniform vegetation cover. Furthermore, the vegetated nature of the landscape leads to less uniform moisture movement within the dune sands. We call for future applications to include site-specific insights into moisture dynamics.

Last interglacial pressure pattern over the Mediterranean from aeolian sediments: A case study from Apulia

In this work, we reconstruct a change in the wind regime and sea level pressure pattern during marine isotope stage (MIS) 5.5.To obtain these results, we studied two elements of the landscape south of the city of Gallipoli (Apulia region, southern Italy), namely, the Carmine-Li Foggi palaeo-littoral ridge (CLlr) and a field of domal-longitudinal fossil dunes present in the Il Campo locality, both dating back to MIS 5.5, through the use of geological and geomorphological surveys together with geochronological analyses by Uranium series and amino acid racemization/epimerization. A detailed study was carried out on the aeolian units within CLlr (AU1 and AU2) and the fossil dunes of the Il Campo locality (AU3) to reconstruct the palaeo-directions of the winds and, possibly, the sea level pressure patterns. AU1 was the first aeolian unit to settle. The accumulation of AU1 at the northern and southern edges of CLlr and its internal structure indicate effective aeolian transport both towards the N and S. Based on the principle of actualism,the AU1 unit allows us to recognise a “first aeolian phase” characterised by the alternation of winds from the S and NW. It involves an autumn–winter pressure pattern characterised by an Atlantic footprint similar to the current pattern: the Atlantic depressions entering the Mediterranean caused, as occurs today over Apulia, the alternation of winds from the S and NW before and after the passage of the low-pressure minima, respectively. In spring–summer, the pressure fields were likely very similar to the current pressure fields, with the Azores high dominating the central–western Mediterranean and the low pressure dominating the eastern Mediterranean, with winds not able to significantly impact sand transport, just as occurs today; this summer regime left the prevailing imprint of the Atlantic winter regime and therefore NW–S bimodality.AU2 and AU3 settled later than AU1 in a “second aeolian phase” of MIS 5.5. AU2 is characterised by south-eastward-dipping foresets. AU3 consists of domal and linear dunes oriented in the NW–SE direction. We interpret AU2 and AU3 as coastal dunes originating in a prevailing NW wind regime.Based on the principle of actualism and on literature data, we conclude that AU2 and AU3 settled under a pressure pattern which in fall–winter was similar to the current pattern, that is, characterised by Atlantic cyclones transiting over the Mediterranean, and the consequent NW–S bimodality of the winds. In the spring–summer, instead, the pattern was characterised by a pressure gradient from west (high) to east (low) higher than the current pressure gradient; this gradient caused stronger NW winds compared to today over the Apulia, according to a similar (but increased) mechanism which today, on the Aegean Sea, causes the development of the Etesio-Meltemi summer winds.Such strong summer winds from the NW, which were effective for sand transport, coupled with the NW–S bimodality in fall–winter, caused the overall prevalence of NW winds during the “second aeolian phase”. This summer pressure gradient over the Mediterranean from west (high) to east (low) greater than today was caused by a summer strengthening of the east Mediterranean low-pressure branch, in turn caused by the northward shift of the intertropical convergence zone (ITCZ), which was widely documented during the sapropel S5 event and verified during MIS 5.5 after sea level had risen to the highstand.

Local Wind Regime Induced by Giant Linear Dunes: Comparison of ERA5-Land Reanalysis with Surface Measurements

Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. During the night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis. For the given dune orientation and measured wind regime, we link the observed wind deviation (over $$50^{\circ }$$ ) to the daily cycle of the turbulent atmospheric boundary layer. During the night, a shallow boundary layer induces a flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern.

Near-surface structure of a large linear dune and an associated crossing dune of the northern Namib Sand Sea from Ground Penetrating Radar: Implications for the history of large linear dunes on Earth and Titan

• Ground Penetrating Radar images obtained of a large Namib Sand Sea linear dune. • Strata up to ∼ 10 m depth show scouring and abrupt changes. • Alternating strata reveal changes in dominant wind direction. • Subsurface patterns reveal down-axis transport of sand. • Implications for wind direction and sand transport on Saturn’s moon Titan. We imaged the near-surface sedimentary structures of a large linear dune, flanking dune forms and an associated crossing linear dune never before studied in the northern Namib Sand Sea using 200-MHz Ground-Penetrating Radar (GPR). The dry, uniform sandy conditions and wavelength used allowed for highly detailed observations of sedimentary structures to depths of ∼ 12 m across a >1km lateral scan. Sedimentary features observed in the main linear dune include scouring and abrupt changes in strata such as trough cross stratification (TCS), onlap, downlap, truncation and avalanche-related bedding, all a result of complex sand transport conditions. Different phases of deposition have produced an opposed succession of strata on each side of the dune. These successions alternate 2-dimensional (2D), or bedform instability mode features with 3-dimensional (3D), or fingering mode features, separated by a clear process boundary. These alternating successions reflect a change in the dominant wind environment in the recent past. The changing winds may feed into the building and overall stability of this dune field and may be a model for conditions in other large linear/longitudinal dune fields. The subsurface structure of an oblique crossing linear dune demonstrates sand transport generally down the dune long axis in the direction predicted from modern, ERA-Interim model as well as paleoclimate model winds. This suggests relatively long-term stability of this intermediate-sized landform and the potential long-term coexistence of large dunes and secondary forms. These studies have implications for the extensive sand seas of Titan, where lack of large secondary forms may indicate a simple wind regime over long time periods.

Dune Field Patterns and Their Control Factors in the Middle Areas of China’s Hexi Corridor Desert

The middle areas of China’s Hexi Corridor Desert are distributed within or at the edge of oases in continental river basins in Northern China. Recently, researchers found that rivers can provide sediment material for dune formation and development, but the mechanism has not been investigated in detail. In this study, the relationships among the wind environment, spatial distribution of continental rivers, sand availability, and dune field patterns in the middle area of Hexi Corridor Desert were analyzed. In terms of the wind energy environment, the study area can be divided into three regions: high-energy environment in the north, intermediate-energy environment in the middle, and low-energy environment in the south. The results showed that the resultant drift potential is predominantly from the NW quadrant. The directional variability of wind is intermediate in the northern and middle region and low in the southern region. The directions of winds with critical speed are SW in the northern region, NW and WNW in the middle region, and NW in the southern region. The main dune types are barchans, reticulate dunes, star dunes, linear dunes, and coppice dunes, which differ from previous results (mainly barchans and coppice dunes). Dune field patterns are controlled by the wind energy environment. In addition, the spatial distribution of continental rivers and sand availability are important factors affecting dune formation and development. Sand dunes are distributed downwind of continental rivers, which confirms the hypothesis that rivers can provide sediment material for dune formation. The spatial distribution and different dune types in the middle area of Hexi Corridor Desert reveal that their formation and development are controlled by the wind regime and sediment supply.

The Effects of Wind Regime and Sand Supply on the Coexistence of Barchans and Linear Dunes in China’s Qaidam Basin

Dunes composed of granular materials are present in deserts and other environments, such as subaqueous environments and environments on other planets, with very different time and length scales for their evolution. In arid regions, barchans (transverse dunes) develop under a unimodal wind regime, and are oriented perpendicular to the sand transport direction, whereas linear (longitudinal) dunes develop under a bimodal wind regime and are oriented parallel to the sand transport direction. However, field survey results cannot be explained solely by the wind because barchans and linear dunes can coexist under the same wind regime. Here, we investigated China’s Qaidam Basin, where barchans and linear dunes coexist. We measured dune morphology, analyzed wind data, and quantified the sand supply (equivalent sand thickness) to describe their development environment, and focused on the effect of sand supply to explore the combined effects of wind regime and sand supply on the coexistence of barchans and linear dunes. In our study area, barchans and linear dunes had low heights. The wind regime was narrowly bimodal, with low directional variability. The sand supply was limited (low equivalent sand thickness), but was greater for barchan chains than for barchans, and linear dunes had the smallest supply; the equivalent sand thickness in the linear dune areas was half that in barchan areas and one-quarter that in barchan chain areas. Except in the presence of topographical barriers and cohesive sediments, a unimodal or bimodal wind regime with an acute angle allows barchans and linear dunes to coexist under a low sand supply. The linear dunes and the barchans migrated along the resultant drift direction. Though we studied aeolian dunes, these findings will increase our understanding of these similar bedforms that develop in other planetary environments (e.g., Mars).

Aeolian-fluvial processes control landscape evolution along dunefield margins of the northwestern Negev (Israel) since the late Quaternary

Dunefield margins are sensitive to aeolian-fluvial processes that record local environmental conditions and climatic events. A common aeolian-fluvial process along dunefield margins is dune-damming—marking aeolian domination over a fluvial system. This study reports on the character, controls, and chronology of a transition from a pre-dunefield environment to a fluvial-dominated environment, at the intersection of the northwestern Negev desert (Israel) dunefield margins with a medium-sized (100 km2) drainage basin. Relative and absolute Optically Stimulated Luminescence (POSL/OSL) dating along several radiocarbon dates and sedimentological analysis helped decipher the chronostratigraphy of nine sections in the drainage basin where it meets the dunefield, and reconstruct landscape evolution.The study reveals immediate and lagged fluvial response to aeolian domination during the Heinrich-1 and Younger-Dryas when the region was subject to exceptional wind power. The domination of vegetated linear dune encroachment over the drainage basin led to a temporal and spatial succession of dune-dammed waterbodies. Aeolian-dominated fluvial sedimentation resulted in a sequence of distinct event-based couplet depositions. Decreased wind power following the Younger-Dryas stabilized the properties of the dune-dams, while increasing fluvial activity during the early-Holocene, upon the stabilized dune-dams, led to aggregation of couplets in water bodies. These sediments formed the maximal extent of the dunefield margins alluvial plain. After the dune-dam breaching at the dunefield margins, fluvial penetration into the dunefield resulted in a mid-Holocene dune-damming impoundment within the dunefield. Altogether, the lagged fluvio-sedimentological response to aeolian-domination significantly contributed to the aggregation and extension of alluvial plains, shaping the dunefield margin landscape.

Titan’s Prevailing Circulation Might Drive Highly Intermittent, Yet Significant Sediment Transport

AbstractTitan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these aeolian processes are caused by the wind‐driven saltation of surface grains. It is still unclear, however, how saltation on Titan can occur despite the typically weak surface winds and the potentially cohesive surface grains. Here, we explore the hypothesis that saltation on Titan may be sustained at lower wind speeds than previously thought, primarily through granular splash rather than aerodynamic lifting of surface grains. We propose a saltation mass flux parameterization for Titan and use it to quantify sediment transport with a general circulation model. The results suggest that Titan's prevailing circulation can generate highly intermittent yet significant saltation, with mass fluxes of the order of 104 kg m−1 year−1, and that Titan dunes may be formed primarily by fine grains, approximately 0.1 mm in size.