Transverse Dunes Research Articles

Evolutionary stages of active to vegetated coastal transgressive dunefields in the San Matías Gulf coast, Argentina

The understanding of how active aeolian coastal dunes transform into fully vegetated forms, and the specific dune configurations that emerge, particularly within coastal dune systems, is limited. This study examines the changes in dune morphology associated with vegetation growth within transgressive dunefields in NE Patagonia, Argentina. The dunefields are located along the northern coast of the San Matías Gulf, ranging from relatively small to large, and dominantly active in the past ∼80 years. Satellite and aerial images were analyzed using GIS procedures to calculate vegetation cover changes and dune migration rates and identify different dune types and their evolutionary stages of fixation. Five stages were defined in relation to vegetation cover and dune shapes and patterns, from bare sand to fully vegetated dunes. Transverse or barchanoid ridges (sometimes with aklé [fish scale], or chaotic patterns) convert to partially vegetated sub-parabolic dunes and finish as parabolic dunes. In other cases, the dunes may convert to reticulate, aklé, or chaotic patterns, completely vegetated. Various stages span a continuous range from unvegetated to fully vegetated dunes across a wide array of timeframes. In some cases, it was possible to recognize changes from stage one to five in ∼20 years. Where the initial transverse dune is largely maintained during the stabilization process a distinctive pattern named “gusanos” (worms) was identified. The vegetated surface measured in some areas changed from 11 % to 51 % vegetation cover between 1961 and 2022, with migration rates decreasing from 9.53 m/year to zero between 1991 and 2020. The increase in vegetation growth also coincides with higher temperatures, weaker winds and decreasing grazing livestock within this Patagonia area. The recorded processes are similar to coastal dune and vegetation changes in some semiarid regions from the Southern Hemisphere between 30 and 60° S, especially in South Australia.

Morphometry of the Samalayuca dunes, northern Chihuahua, Mexico

The Samalayuca Dunes (SMD) (Médanos de Samalayuca), Chihuahua, México, are one of México’s largest and least studied dune fields, now managed as a Protected Area for their ecological characteristics. We present a morphometric characterization of the dune field based on remote sensing and field studies, to advance understanding of its physical environment. SMD’s generally-fine sands originate from shoreline deposits of Paleolake Palomas, transported eastward (downwind) along an aeolian corridor, accumulating primarily as echo dunes upwind of the sierras of Samalayuca and Presidio. A complex wind regime, with northerly and southerly winds complementing regionally-prevailing southwesterlies, modified by topographic effects, shapes the SMD’s morphology. The sand sea covers ~139.7 km2, with ~113.8 km2 in the main eastern body and ~25.9 km2 in a northwestern subfield. We describe six major dune forms: north to south straight-crested dunes, east to west straight-crested dunes, star dunes, vegetated parabolic dunes, relict transverse dunes, and “megastar” (draa) dunes. Mean interdune centroid spacing is 76.5 m. The active dunes, previously described as an “aklé” pattern, are predominantly straight-crested dune sets oriented near-perpendicular to each other with general north-south and east-west crest orientations, 4-5 m high, spaced ~67 m apart for north-south trending crests and ~53 m for east-west trending crests, representing a nearly perpendicular interference pattern in some locations. The active dunes are superimposed in a compound and complex arrangement on relict remnants of much larger north-northwest trending transverse dune ridges fanning out from south to north-northwest, spaced approximately ~1 km apart and ~50 m high. The easternmost dune ridge contains an active set of at least 15 active megastar and reversing dunes up to 120 m tall, increasing in size and complexity from south to north. As a protected area with historical and ecological value, additional geologic investigations should be performed at the SMD, to help conserve this remarkable geologic feature.

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.

Late Quaternary eolian dune-field mobilization and stabilization near the Laurentide Ice Sheet limit, New Jersey Pine Barrens, eastern USA

Well-preserved stabilized dune fields are widespread in the New Jersey Pine Barrens, northern Atlantic Coastal Plain, USA. In this area, which was unglaciated throughout the Quaternary, quartz-rich Miocene–Pleistocene age fluvial and marginal marine sands provided source sediments for eolian mobilization. Parabolic and transverse dunes within fluvial source-bordering dune fields in small-river watersheds migrated to the east-southeast (110–125°) over unconsolidated sands and gravels. The short eolian transport distance of most dune-field sand in the presence of moderately to sub-rounded quartz grains with low sphericity indicates eolian abrasion and dune-sand fashioning occurred within a short duration of transport. Although the absolute duration of eolian transport remains unknown, dune stabilization occurred about 23–17.5 ka, with a weighted mean of 19.5 ± 0.5 ka from six dated dunes. Dune stabilization coincided with northward retreat of the Laurentide Ice Sheet from its maximum position at ∼41.500° N (∼100 km north of the study area), to ∼41.375°N (∼200 km north). The well-preserved dune morphology and narrowly constrained ages suggest rapid dune stabilization. Dune-forming katabatic winds from the WNW declined abruptly with northward migration of the ice sheet, accompanied by climatic amelioration and stabilization by vegetation. A short-lived period of eolian mobilization may have been associated with a temporary increase in sand availability from adjacent fluvially derived sediments. Post-depositional processes included soil eluviation, with dissolution features and breakage blocks on quartz grains signifying long-term in-situ soil weathering.

Evolution and migration of the highest megadunes on Earth

Giant aeolian sand dunes, over 100 m high, occur in the major deserts on Earth, and they can provide valuable insights into past wind regimes and climatic conditions in desert areas. However, the formation and evolution of these megadunes remains poorly understood. The highest aeolian sand dunes on Earth are in the Badain Jaran Desert (BJD) in northwestern China, where hundreds of giant transverse dunes are at least 200–300 m high, with some as high as ∼500 m. We present sedimentary records from eight cores from five megadunes (200–400 m in height), including a 320-m drill core from a ∼ 430-m-high megadune in the centre of this desert, which is the first detailed investigation of Earth's tallest sand dune. The results of high-resolution optical dating show that these huge transversal dunes migrated downwind, with the dune migration taking some tens of thousands years to complete a single cycle of turnover. We present a model for the migration of the largest free-standing aeolian landform, which demonstrates that the formation and migration of megadunes is closely linked to global climate change. Although there was negligible dune migration during warm and humid interglacial periods, the dunes were still able to rapidly accrete vertically. The migration of these dunes occurred during the coldest and driest periods (e.g., Marine Isotope Stages 4 and 2), at the rate of a few centimeters per year, highlighting the slow net downwind transport of dunes in the Badain Jaran Desert. Our results highlight the role of global climate change over the last glacial cycle in the formation and migration of megadunes.

Evolution of a coastal transgressive dunefield to a parabolic dunefield, Canunda dunes, South Australia

Various studies have detailed the evolution of barchan dunes to parabolic dunes and a very few studies describe the evolution of coastal transgressive dunefields and continental sand seas to parabolic dunefields. This study examines the evolution and transformation of a 12 km long portion of a formerly large (~50 km along-coast), active, transgressive dunefield (coastal sand sea or erg) dominated by transverse dunes to a coastal barrier dominated by parabolic dunes. A GIS study of vegetation cover change from 1950 to 2017 was conducted, and a stereographic analyses of 1945 to 2020 aerial photography was carried out to determine morphological changes across the dune system. Historical rainfall, aeolian drift potentials, and rabbit numbers are examined as possible drivers of change, and rabbit numbers most strongly correlate with vegetation change. The vegetation cover of the greater dunefield increased in the study area from 26 % cover in 1950 to 54 % by 2020. A largely unvegetated transgressive dunefield dominated by transverse dunes evolved into a parabolic dunefield in <70 years. Vegetation colonisation primarily took place from landward slipfaces, by nebkha formation on dune lobe crests, from interdune swales and flats, and within deflation basins and plains. Vegetation colonisation also occurred above the backshore in the same period. Aeolian landform units such as marginal ridges, nebkha fields, deflation basins and plains, dune ridges, remnant knobs, parabolic dunes, and a foredune-blowout complex were formed as the dune field was colonised and stabilised by vegetation growth. The study provides far greater detail on how vegetational and morphological changes take place as a transgressive dunefield evolves into a parabolic dunefield.

Simulation of flow and shear stress distribution on the Oceano Dunes, implications for saltation and dust emissions

Wind-driven shear stresses drive saltation and dust emissions over sand dunes. However, the complex topography of coastal dunes and practical difficulties in measuring shear stresses in the presence of blowing sand make a detailed view of this important information difficult to obtain. We combine computational fluid dynamics with field instrumentation and high resolution topographic data to investigate the shear stresses resulting from on-shore winds on the ground surface for a flat sloping beach area, nebkha foredune, and transverse dune at Oceano Dunes, CA. This approach allows for paired simulations over measured and modified topographies using the same boundary condition. Shear values from scenarios that account for the effects of vegetation and aerodynamic form separately are presented. Using available dust emissions data, an accounting of the emissions from the surface was performed. Sparse vegetation on the nebkha in the foredune was found to play a significant role in modulating the shear on the surface and initial boundary layer modification of the onshore wind profile.

Factors controlling the development of cold-climate dune fields within the central part of the European Sand Belt – Insights from morphometry

The central part of the European Sand Belt is an area where intense aeolian processes led to the development of large dune fields in the Lateglacial. They have been studied principally in terms of their stratigraphy, with less attention given to their evolution and geomorphology. It is also uncertain whether large dune fields in cold areas arise analogously to those formed in other climatic zones. To fill this gap, we performed a morphometric analysis of 31 stabilized dune fields in Poland using high-resolution LiDAR data. We related the outcomes to the morphological zones associated with the extent of the ice sheet during the LGM, the position and basement shape of the dune fields. The results indicate that dune fields in cold areas evolve in the same way as in other climatic zones, as expressed in the preserved relation between crest length, spacing, and defect density. The study found that the investigated dune fields have simple patterns composed of single populations of transverse to parabolic dunes facing E-ESE, suggesting their simultaneous formation in the Younger Dryas. At the same time, the varying degree of dune fields pattern development indicates the different duration of aeolian processes that shaped individual dune fields. The dominance of transverse dunes transformed partially or completely into parabolic dunes reflects the increasing role of vegetation over time and the decreasing supply of sand. The development of the dune field patterns was not found to be correlated with the extent of the ice sheet during the LGM, the morphological position, and the basement shape of the dune fields.

Geomorphology of sand dunes in the Taklamakan Desert based on ERA5 reanalysis data

The characteristics of the wind regime and the development of dune morphology in the Taklamakan Desert have been the focus of scholars. In this study, we used ERA5 reanalysis wind data at a height of 10 m from 1979 to 2019 to examine the sand transport and wind regime characteristics of the entire Taklamakan Desert. We combined the two latest dune development modes, i.e., bed instability and elongation modes, and determined that: (1) Taklamakan Desert is overall characterized by a lower wind energy environment; the wind and sand activity intensities are highest in the eastern part of the desert, with a decreasing trend from the east to the west. The wind direction in the eastern region shows unimodal characteristics due to the backward easterly wind; the wind regime gradually becomes complicated from the northeast to the southwest; (2) the morphological alignments of dunes can be predicted by such modern wind regimes combined with the latest dune development modes. Large longitudinal dunes in the middle of the desert can be predicted with the elongation mode, whereas secondary transverse dunes, which derive from these composite dunes, can be predicted using the bed instability mode. Collectively, this paper fills the gap of the lack of uniform and standardized macro-scale wind data in the Taklamakan Desert, and the two modes of dune development derived from ERA5 reanalysis data can match the morphology and trend of most modern dunes.

Environmental factors controlling the Last Glacial multi-phase development of the Moravian Sahara dune field, Lower Moravian Basin, Central Europe

Aeolian sediments and landforms represent a unique source of proxy data allowing the detailed research of palaeoenvironmental changes. For example, dune morphology and dune field patterns could reflect an influence of a wide range of conditions from palaeowind directions to topography. The Moravian Sahara dune field located in southern Moravia represents a unique archive reflecting the effects of these environmental variables, lying far away from the European sand belt which is the main area of interest for aeolian research in Europe. Here, we present the complex geospatial analysis of the dunes and their topography performed on Digital Terrain Models (DTM) from which their basic morphometrics (crest orientation, spacings between the dunes, and others) were obtained. Two groups of differently oriented transverse dunes have been distinguished, suggesting a significant twist in atmospheric circulation connected with the retreat of ice sheets following the Last Glacial Maximum. In addition, other local conditions such as the topography and sediment supply were found to exert a strong influence on the formation of dune field patterns. Thus, the results of the high-resolution DTMs presented here show their applicability to the highly detailed study of the influence of environmental conditions on the development of the aeolian dune fields.

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).

Shaping effects of sand flow channels on aeolian geomorphology – a case study of the Badain Jaran, Tengger, and Ulan Buh Deserts, northern China

Based on the interactions between mountains, we identified three sand flow channels in the Badain Jaran, Tengger, and Ulan Buh Deserts, northern China. We found that the height difference of the terrain in these areas provided favorable conditions for the transportation of sand. Owing to the venturi effect of their geomorphologies, airflow was compressed in these channels, and their wind regimes were strong and unimodal. Compared with the interior of the desert, the sand transport potential was relatively large in these areas, and westerly and northwest winds prevailed. We found that the wind accelerated in the sand flow channels, resulting in faster-moving dunes. The dune types that developed in these channels were relatively simple owing to the unimodal wind regimes; they mainly comprised barchan and transverse dunes. We also identified a transition landscape from barchan dunes to transverse, or complex dunes. Based on their sediment characteristics and the prevailing wind directions, we found that the sand flow channels provided a direct sand supply between the three deserts. The sand flow channels connected these independent deserts to an entire desert system. Similar sand flow channels can also be found in other deserts globally. Collectively, these sand flow channels reflect interactions between deserts.

Grain size analysis of the latest Quaternary Kordofan Sand of Central Sudan: Depositional environment and mode of transportation

Grain size analysis is a powerful tool for determining the depositional environment. Grain size analysis for 48 samples from four sections along a 280 km long, nearly north–south-trending transect, has been conducted in the mainly Holocene Kordofan Sand in the Kordofan Region of Central Sudan. In these sections, this part of the Kordofan Sand comprises three pedosedimentary sequences. The lower sequence (∼13–10 kyr) has been pedogenized during the African Humid Period and ends up farther West with lacustrine or palustrine carbonates. The middle sequence (∼6–3 kyr) is represented by sand with low degree of pedogenesis and corresponds to the African Humid Period. The upper sequence was deposited after a hiatus lasting from ∼3.3 to 1.1 ka BP, and constitutes the present-day surficial deposits, showing little or no pedogenesis. Spatial grain size distribution and mode of transport show a southward fining trend, indicating that the sandy sediments were transported from north to south. This interpretation is supported by the results of mean grain size – sorting, and sorting – skewness interrelations, which provided a linear relationship. Vertical variation in grain size distribution in the studied sections shows variable energy over time in the north and constant, low energy in the south. The dominance of saltation as a transport mode confirms that the studied sediments were deposited in aeolian environment. The low sorting degree, the presence of coarse grains, and the still active transverse dunes and barchans in the North, indicate that the Late Pleistocene part of the Kordofan Sandstone is submitted to reworking until now. Consequently, the mainly Holocene sand sequences were fed both by distal, fine-grained Saharan material and by proximal, coarser-grained sand proceeding from the Late Pleistocene aeolian dunes.

Depositional timing and palaeoclimate interpretation of the Tamala Limestone aeolianites in Shark Bay, Western Australia

• AAR dating shows an aging of the Tamala Limestone aeolianites towards the east. • The Tamala Limestone aeolianites are landward-advancing (i.e., transverse) dunes that have migrated from west to east. • Dune accumulation occurred during dry/cold glacials of the Pleistocene period. • Dune activity in the region is strongly linked to a weak Leeuwin Current. • Dune accumulation occurred during a northward shift of both the Hadley and Ferrel cells. The carbonate units grouped under the name “Tamala Limestone” outcrop for a thousand kilometres along the coast of Western Australia. The extensive Zuytdorp Cliffs shaping the northern half of the coastline up to Shark Bay expose and offer an exceptional access to the stratigraphy of this formation. The regional survey of the Shark Bay region, which combines both stratigraphic and sedimentological analyses, reveals that the Tamala Limestone is a dry accumulating aeolian system composed of large transverse dunes migrating parallel to the prevailing winds. Accordingly, the amino acid-data show an aging of the units towards the east. Episodes of carbonate aeolian sedimentation correlate with the successive glacial intervals of the Pleistocene whilst paleosols are correlated with breaks in the sedimentation during interglacial intervals. Palaeoclimate reconstructions reveal that sea level and sea surface temperature of the Indo-Pacific Warm Pool were lower during glacial intervals. The weakened Leeuwin Current, which flows along the western coast of Australia and is the main source of precipitation, contributed to the aridification of the region. Consequently, and associated with a northward migration of the Hadley and Ferrel cells, periods of glaciation were drier. By contrast, paleosols developed through dissolution of the carbonate units during more humid interglacial intervals.

Coarsening Dynamics of 2D Subaqueous Dunes

AbstractFluid flow over an initially flat granular bed leads to the formation of a surface‐wave instability. The sediment bed profile coarsens and increases in amplitude and wavelength as disturbances develop from ripples into dunes. We perform experiments and numerical simulations to quantify both the temporal evolution of bed properties and the relationship between the initial growth rate and the friction velocity u∗. Experimentally, we study underwater bedforms originating from a thin horizontal particle layer in a narrow and counter‐rotating annular flume. We investigate the role of flow speed, flow depth and initial bed thickness on dune evolution. Bedforms evolve from small, irregular disturbances on the bed surface to rapidly growing connected terraces (2D equivalent of transverse dunes) before splitting into discrete dunes. Throughout much of this process, growth is controlled by dune collisions which are observed to result in either coalescence or ejection (mass exchange). We quantify the coarsening process by tracking the temporal evolution of the bed amplitude and wavelength. Additionally, we perform Large Eddy Simulations (LES) of the fluid flow inside the flume to relate the experimental conditions to u∗. By combining the experimental observations with the LES results, we find that the initial dune growth rate scales approximately as . These results can motivate models of finite‐amplitude dune growth from thin sediment layers that are important in both natural and industrial settings.

The late Miocene eolian record at the eastern margin of the Puna Plateau, NW Argentina: Evidence of upper-tropospheric paleocirculation

ABSTRACT The Puna–Altiplano Plateau of the Central Andes is the second-highest plateau in the world (after Tibet), with a mean elevation of 4000 m.a.s.l. and an arid to hyperarid climate. Uplift of the Puna–Altiplano Plateau has affected lower-level atmospheric circulation, acting as a barrier to humid easterly winds from the Amazon basin and favoring an across-strike precipitation gradient resulting in a humid climate towards the east of the plateau and an arid to hyperarid climate in the orogen's interior. In the modern climate, the Bolivian High anticyclone regulates upper troposphere circulation, but little is known about the high-altitude tropospheric circulation of the past. This work focuses on the eolian record of the San Antonio de los Cobres basin along the eastern border of the Puna Plateau, NW Argentina, with the aim of analyzing its origin and thus elucidating the late Miocene winds. The eolian deposits are constrained by 7.8 Ma (K/Ar and U/Pb) and 6.4 Ma (U/Pb) ignimbrites at the nearly basal and upper contacts, respectively. Based on stratigraphic, sedimentological, and provenance analysis of the eolian units, we have identified three main facies associations (FAs): FA1) cross-stratified sandstones with large- to small-scale tabular, planar cross-bedding and with trough cross-stratification; FA2) sandstones with planar to low-angle stratification associated with thinly laminated ripple sandstone strata; FA3) medium- to coarse-grained massive sandstones associated with pebbly to bouldery, matrix-supported conglomerates and clast-supported conglomerates. The lateral and vertical facies assemblages indicate a dune field confined to topographic depressions dominated by transverse dunes with straight and sinuous crestlines that laterally grade into sandsheets associated with ephemeral streams. Paleoflows, lithotypes, and grain-size determinations indicate a persistent north-northwest provenance and wind velocities of 24–38 km/h (with maximum velocities of 55–75 km/h). The results of our analysis coupled with data from previous studies indicates that, for at least the last ca. 8 Myr, the winds have been blowing constantly from the north-northwest with an intensity similar to the present. This implies that the paleo-atmospheric circulation had a similar pattern to the present-day one. Therefore, we conclude that the upper-troposphere circulation in the Puna Plateau of NW Argentina was already regulated by the Bolivian High anticyclone during the Miocene, generating constant north-northwesterly winds.

The morphodynamics of transverse dunes on the coast of South Africa

Transverse sand dunes located within the supratidal zones of beaches are a significant geomorphic feature along sand-dominated coasts worldwide and are generated by strong alongshore winds in areas of high sediment availability. Transverse dunes are present along the South African coast, and these are known to migrate dynamically in response to wind forcing. However, the detailed dynamics of individual dune systems along the same coastal stretch have not been compared to one another, and the relationship of transverse dunes to their hosting beach systems has also not been examined. This study examines the properties and dynamics of transverse supratidal dunes from three systems along the coast of South Africa, using remote sensing methods. Results show that, although the underlying beach system appears to be relatively stable over the time period of analysis, there is a dominant aeolian-driven migration of transverse dunes towards the northeast, following prevailing wind direction, countered by less dominant movement to the southwest. There are also considerable variations in calculated annual dune migration rates between adjacent systems, between summer and winter seasons, and between dunes within a single site. This highlights that, although beach and dune landforms can be conceptually considered as part of the same sediment system, there is not a clear relationship between phases of beach aggradation and phases of dune aggradation. Instead, a primary control appears to be beachface erosion by waves that reduces beach width and influences dune morphodynamics, independent of sediment supply.

Wind regime and aeolian sand transport in Khuzestan Sand Sea

The Khuzestan Sand Sea extends from the Wasit and Maysan provinces in Iraq (22%) to the Ilam (10%) and Khuzestan (68%) provinces in Iran. In order to determine wind regimes and sand transport characteristics, hourly wind data records from 21 meteorological stations for the period 2000–2016 were analyzed using aeolian-sediment transport methods. The analysis of the wind energy based on drift potential (DP) revealed rather large spatial variations in the Khuzestan Sand Sea. The Iraqi part of the desert, as well as the southern regions of the Ilam province and the western edge of the Khuzestan province were characterized by particularly high wind energy (DP greater than 400), while towards the central area of the Khuzestan Sand Sea near Ahvaz city a sharp decrease to DP less than 200 was detected. In the southern and southeastern parts of the Khuzestan Province, the wind energy increased again and the DP reached more than 200 vector units. The temporal analysis of the DP showed no considerable temporal trends between 2000 and 2014 in this study area. The dune morphology analysis revealed a bimodal wind regime, which was also supported by the dominance of sand sheets and transverse dunes. Additionally, the local topography has an important influence on the formation of topographic dunes in the southeastern parts of the Sand Sea.

Geomorphology of aeolian dunes in the western Sahara Desert

Although the western Sahara Desert is dominated by aeolian dunes, research on the geomorphology of aeolian dunes throughout this region as a unit has been limited compared with other large deserts. In the present study, comprehensive research is conducted on the geomorphology of dunes in the western Sahara Desert based on aeolian parameters and dune growth mechanisms. We identified the controlling factors on the dune morphology and formation of superimposed dunes. The results suggest that the spatial patterns of dune morphology are closely correlated with the drift potential (DP) and dune orientation. A well-defined gradient of declining DP, resultant drift potential (RDP), and directional wind variability from north to south was found, indicating a gradual weakening trend in the DP along the sand flow path. Linear and transverse dunes are distributed on the central part of the desert. Barchan dunes are distributed on the western coastal areas and desert margins. Lastly, star dunes are distributed in the upwind on the northern desert margin. We concluded that the wind regime and sand availability directly impact the dune morphology in the western Sahara Desert by considering the growth mechanisms. This study provides valuable reference data on regional aeolian activities that can be used by subsequent regional aeolian geomorphology studies in the western Sahara Desert.

Degradation of a transgressive coastal Dunefield by pines plantation and strategies for recuperation (Lagoa Do Peixe National Park, Southern Brazil)

The transgressive dunefield of the Lagoa de Peixe Natural Park was modified drastically due to intensive pine plantation and the leeward development of the associated degraded areas. The present study analyzed the disturbances in the dunefield of the Lagoa do Peixe Natural Park due to pine tree plantation and the impact of the subsequent deforestation program conducted in the region. Aerial photographs, satellite images, and DGPS topographic data collected over a 70-year-long period were retrieved, analyzed, and compared, which allowed the observation of the geomorphological evolution of the dunefield. In addition, a profile of GPR on the inlet (during a period with the channel closed) was analyzed. In 1948, the surface of the sand barrier was occupied by high transverse dunes and low barchan dunes. Pine tree plantation on the inner side fixed the transgressive dunes and, consequently, avoided the filling of the shallow lagoon, although degraded areas were generated on the lee side of the pines. Simultaneous pine plantations in the backshore avoided the aeolian sediment input to the dunefield, generating a large interdune area along with the development of a few parabolic dunes, which resulted in cannibalization of the transgressive dunes. In 2001, pine trees occupied 15.03% of the total area analyzed in the present study, while the degraded area accounted for 10.81% of the total area. Progressive deforestation was performed (ring bound technique for tree gradual death), maintaining three lines of pines in contact with the dunes, to promote autochthonous vegetation growth, thereby preventing the filling of the adjacent lagoon with aeolian sediments. By the year 2018, the pine tree plantation area reduced to 3.25%, the dunefield area was 79.03%, and the extension of the degraded areas had increased and reached 17.71% of the total area. The pine tree plantation and the deforestation for conservation purposes are the main factors explaining the degradation of the dunefield during the period between 1948 and 2018, while regional climatic oscillations contributed as the secondary factor. Although internationally controversial, the present case study demonstrates that the removal of this exotic vegetation, through dune vegetation recovery programs, is often unsuccessful and may generate more degraded areas. However, in the case presented here, it was essential to remove the forest to ensure the dune field geodynamics and, therefore, the base (biotope) of the natural system (maintenance of the lagoon and the dunefield).