Article

Mega‐Yardangs: A Global Analysis

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Abstract

Yardangs, analogues of which occur on Mars and possibly on Venus, are wind moulded landforms that develop in the world's drylands. Mega-yardangs (wind-abraded, ridge, and swale features of regional extent) are easily identified on satellite images and these have been employed to map their global distribution. Areas where they are present include Central Asia, the Lut Desert of Iran, northern Saudi Arabia, Bahrain, the Libyan Desert in Egypt, the central Sahara, the Namib Desert, the high Andes and the Peruvian Desert. These features develop in a wide range of rock types, including sandstones, ignimbrites, limestones and basement rocks, occur in hyper-arid areas, form where winds tend to be unimodal in direction, are best developed in areas of sand transport rather than sand accumulation, and occur in plains rather than in mountainous areas.

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... Recently, Late Ordovician glacial deposits and exhumed subglacial mega-lineations (MLs) and landforms were reported from southeast Egypt over the Neoproterozoic basement rocks of the Arabian Nubian Shield (Elhebiry et al., 2020). On the other side of the Red Sea, and along the postulated extension of the newly reported glacial MLs, similar east-northeast-trending streamlined ridges in northwest Arabia over the Neoproterozoic basement of the Arabian Nubian Shield and the Cambro-Ordovician Saq Sandstone were interpreted as mega-yardangs formed by wind erosion (Brown et al., 1989;Goudie, 2007;Vincent and Kattan, 2006). ...
... Earlier studies which considered these streamlined landforms as mega-yardangs (Brown et al., 1989;Goudie, 2007;Vincent and Kattan, 2006) were biased by the presence of transverse barchan dunes along and orthogonal to the extension of the MLs in the northern part of the study area (Fig. 3A). Here, we provide evidence in support of a Late Ordovician glacial origin of these streamlined landforms and argue against an aeolian origin. ...
... Here, we provide evidence in support of a Late Ordovician glacial origin of these streamlined landforms and argue against an aeolian origin. First, the streamlined beds are sub parallel to the prevailing wind directions (southwest to northeast; inferred from the barchan dunes orientation in An Nafud desert) in the northern part of the study area (Goudie, 2007;Vincent and Kattan, 2006) (Fig. 3A), but not in the central and southern sections, where the MLs are at high angles to the prevailing wind direction (from northwest to south-east; inferred from the longitudinal dune trends; Fig. 3B). Second, the mapped MLs were identified over the preglacial rock units (Neoproterozoic basement and the Cambro-Ordovician Saq Sandstone) but not over glacial or post-glacial deposits (Figs. ...
Article
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Mega-streamlined landforms on Earth and Mars have been attributed to aeolian, glaciogenic, fluvial, and tectonic processes. Identifying the forces that shaped these landforms is paramount for understanding landscape evolution and constraining paleo-climate models and ice sheet reconstructions. In Arabia, east-northeast trending, kilometer-scale streamlined landforms were interpreted to have been formed by Quaternary aeolian erosion. We provide field and satellite-based evidence for a Late Ordovician glacial origin for these streamlined landforms, which were exhumed during Red Sea-related uplift. Then we use Late Ordovician paleo-topographic data to reconstruct the Late Ordovician ice sheet using identified and previously reported glacial deposits and landforms. Our reconstruction suggests these glacial features are part of a major, topographically controlled, marine-terminating ice stream, with a minimum length of 1000 km extending from the southeast Egypt to northern and central Arabia and possibly more than twice this length if the glaciomarine and iceberg deposits in the present-day western Iran are part of this system. Our results support models that advocate for a single, major, and highly dynamic ice sheet and provide new morphological-based constraints for Late Ordovician climate models.
... In addition to wind erosion, the lithology of the strata must also be considered. Yardangs can develop in a variety of lithologies, ranging from sedimentary (e.g., Xia, 1987;Breed et al., 1989;Dong et al., 2012), magmatic (e.g., De Silva, 1989;Inbar and Risso, 2001;De Silva, et al., 2010) and metamorphic (e.g., Goudie, 2007). However, sedimentary rocks are especially important for yardang formation because of their weaker diagenesis and lower resistance to wind deflation in https://doi.org/10.1016/j.aeolia. ...
... During field investigations, we found that the profiles of eroded yardang bodies in Loulan were concavo-convex and that there were numerous collapsed convex layers around the yardangs. This differential erosion of yardangs occurs widely in the Loulan region; it is rarely found in other areas and differs from other yardangs cited in the literature which generally erode more rapidly at their base (e.g., Goudie, 2007). Therefore, questions arise regarding how this pattern of differential erosion arises, and how the controlling factors differ from those associated with general erosion. ...
... Abrasion and deflation are two important types of erosional process. Abrasion, which is caused by the friction generated by moving particles, results mainly in undercutting at the foot of the slope ( Goudie, 2007). The strongest dynamics and the maximum flux of saltating sand particles occur at a certain height, changing with wind velocity and decreasing with increasing height ( Sharp, 1964;Zou et al., 2001;Dong et al., 2004). ...
Article
Yardangs are a type of wind-sculpted landform which generally form in hyper-arid regions. Several factors affect the development of yardangs, and the relative importance of these factors likely varies with differences in regional environmental factors. In the Loulan region of Lop Nur, wind dynamics are the principal factor affecting the development of yardangs. However, layered yardangs, which have undergone a unique form of differential erosion, are common in the region. These erosional landforms differ from typical yardangs which are eroded solely by abrasion and deflation. We conducted field and laboratory investigations of layered yardangs to determine their origin. The results indicate that there are two types of strata comprising the yardangs: uncompacted sand-silt layers, with a lower carbonate content; and compacted clay-silt layers, with a higher carbonate content. Both types of strata are horizontal and occur in alternating layers. This type of structure enables the wind to more easily erode the less resistant sand-silt layers at different heights, leaving the more resistant compacted clay-silt layers relatively intact. Eventually the undercut remnant clay-silt layers collapse once the weight of the suspended strata exceeds their elastic resistance (more than 90% of the fallen blocks have length/thickness ratios between 1.2 and 2.5). Therefore, in addition to wind dynamics, the lithology and structure of the strata are important factors affecting the development of the layered yardangs. This type of differential erosion accelerates the development of the yardangs in the Loulan region.
... Earlier studies focused on yardang morphology (e.g., Halimov and Fezer, 1989), and the morphological simulation relied on wind tunnel experiments (Ward and Greeley, 1984). In recent years, the improvement of analytical techniques, such as erosion rate testing Rohrmann et al., 2013), luminescence dating (Washington et al., 2006;Dong et al., 2012;Niu et al., 2013;Ding et al., 2020), exposure dating (Sebe et al., 2011;Wu et al., 2019), numerical modeling (Barchyn and Hugenholtz, 2015;Pelletier, 2018;Wu et al., 2019), remote sensing (RS) and geographic information system (GIS) (Goudie, 2007;Ehsani and Quiel, 2008;Li et al., 2016b;Hu et al., 2017;Wang et al., 2018a;Yuan et al., 2020), has promoted the diversity and comprehensiveness of yardang research. For example, age of yardangs has been more precisely constrained (Wu et al., 2019), controls on yardang development have been simulated (Barchyn and Hugenholtz, 2015;Pelletier, 2018), mega-yardangs have been extensively studied (Goudie, 2007), and identification of yardangs has been carried out using unmanned aerial vehicle (UAV)/RS images and digital elevation model (DEM) (Ehsani and Quiel, 2008;Zhao et al., 2018;Yuan et al., 2020). ...
... In recent years, the improvement of analytical techniques, such as erosion rate testing Rohrmann et al., 2013), luminescence dating (Washington et al., 2006;Dong et al., 2012;Niu et al., 2013;Ding et al., 2020), exposure dating (Sebe et al., 2011;Wu et al., 2019), numerical modeling (Barchyn and Hugenholtz, 2015;Pelletier, 2018;Wu et al., 2019), remote sensing (RS) and geographic information system (GIS) (Goudie, 2007;Ehsani and Quiel, 2008;Li et al., 2016b;Hu et al., 2017;Wang et al., 2018a;Yuan et al., 2020), has promoted the diversity and comprehensiveness of yardang research. For example, age of yardangs has been more precisely constrained (Wu et al., 2019), controls on yardang development have been simulated (Barchyn and Hugenholtz, 2015;Pelletier, 2018), mega-yardangs have been extensively studied (Goudie, 2007), and identification of yardangs has been carried out using unmanned aerial vehicle (UAV)/RS images and digital elevation model (DEM) (Ehsani and Quiel, 2008;Zhao et al., 2018;Yuan et al., 2020). Yardangs on Earth are distributed in numerous deserts of low to middle latitudes, and carved into different lithologies, such as unconsolidated fluvial/lacustrine sediments, consolidated bedrocks, or loose aeolian sands ( Fig. 1 and Table S1). ...
... Evolution of Earth yardangs plays a key role in understanding geomorphological processes on Earth (Goudie, 2008;Pullen et al., 2017) and Mars (de Silva et al., 2010;Xiao et al., 2017;Wang et al., 2018a), as well as global climatic changes (Kapp et al., 2011;Pullen et al., 2017), and dust transportation (Washington et al., 2006;Bristow et al., 2009;Pullen et al., 2017). Studies of yardang evolution have been conducted in Asia (Halimov and Fezer, 1989;Xia, 1987;Zheng et al., 2002;Al-Dousari et al., 2009;Dong et al., 2012;Wang et al., 2018a), Africa (Brookes, 2001), Europe (Gutiérrez-Elorza et al., 2002;Sebe et al., 2011), Northern America (Ward and Greeley, 1984;Clarke et al., 1996;Whitney et al., 2015;Pelletier et al., 2018), Southern America (Inbar and Risso, 2001), and even around the world (Goudie, 2007;Laity, 2011). These studies expounded yardang landform in terms of origins, morphologic changes and controlling factors, and obtained various achievements: (1) different influence factors have been examined (e.g., Ward and Greeley, 1984;Al-Dousari et al., 2009;Pelletier et al., 2018) and summarized (Laity, 2011); (2) several evolutionary patterns have been proposed based on local conditions (Halimov and Fezer, 1989;Brookes, 2001;Dong et al., 2012); ...
Article
Yardangs, as typical aeolian landforms, are extensively identified in arid/hyper-arid areas on Earth and other terrestrial bodies. In this review, based on analyses of morphology, distribution, age, climate, and geologic condition of yardangs worldwide, we (1) assess the impacts of various controlling factors on yardang development to generalize a model based on morphology; (2) illustrate the climate-driven mechanism for yardangs; (3) propose a geomorphological evolutionary model of yardang fields; and (4) discuss potential implications of the above two models of yardang evolution on Earth to Mars. It is demonstrated that both deflation and abrasion work on yardang development, and it is the lithology to determine which one will be more effective. In addition, the wind action dominates the general aerodynamic form of yardangs, while non-aeolian factors account for the diversity in yardang morphology. Thus, a model including four stages and initiating mechanisms is generalized for yardang processes, from initiation to demise. The synthetic analyses of meteorological data, chronology, and paleoclimatic proxies show that yardang development is mostly controlled by westerlies, and would be accelerated during glacial periods and interrupted by lake formation during interglacial periods due to dry-humid fluctuations and changes in atmospheric circulation, driven by variations in solar radiation at orbital scales. This leads to the zonal distributions of yardangs near 30° in both hemispheres. Depressions would be created or enlarged in yardang fields during glacial period, along with activities of dust release and transport, leading to aeolian deposition (e.g. loess) downwind. The depressions, then, could be turned into lakes during wet phase of interglacial period and evolved into new yardangs in the following glacial period due to wind erosion. This climate-controlled geomorphological process under glacial-interglacial cycles suggests that high accumulation rate in sediments from enclosed inland basins (e.g. the Qaidam Basin) doesn't mean high-resolution climatic record due to the hiatus by wind erosion, indicating the significance of robust chronology establishment before any climatic correlation. Under the rules of Earth-based yardang evolution, it is potential to identify the specific level of development and explore the geomorphological processes as well as the climatic background for yardangs on Mars.
... Yardang is a typical wind-erosional landform in the arid and hyper-arid areas on the Earth (Goudie, 2007;Al-Dousari et al., 2009), and is a common landform on the Mars as well (Xiao et al., 2017, Anglés andLi, 2017;Wang et al., 2018). Studies on the evolution of Yardang have made significant progress attributed to the development of methods, e.g. ...
... Studies on the evolution of Yardang have made significant progress attributed to the development of methods, e.g. remote sensing and geographic information system (Goudie, 2007), exposure dating (Wu et al., 2019) and erosion rate testing (Rohrmann et al., 2013) of 10 Be. ...
Article
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The Qaidam Basin preserves the largest Yardang field on Earth, and yardangs are intriguing landforms for studies of the paleo-environment and aeolian processes. Formation of yardangs involved both the initial lacustrine deposition and the subsequent wind-erosion processes. However, the timings of both processes in the Qaidam Basin are still controversial due to limited age data and unsuitable dating methodology. In this paper, we first compared two optical dating methods to determine the suitable one for the study area, then investigated the geomorphic processes based on the new ages. Two-step post-IR IRSL (pIRIR) and multi-elevated-temperature pIRIR (MET-pIRIR) methods of feldspar, were applied to date lacustrine sediments on the top parts of yardangs to decipher the transition time from depositional to an erosional environment. Comparisons of the two methods demonstrated that the influence from anomalous fading was very minimal thus negligible for MET-pIRIR method, as proved by the De plateau between MET-pIRIR 250 and MET-pIRIR 290 ; while the pIR50IR 250 signals suffered from fading obviously, which was difficult to be corrected due to the high De close to saturation. Consequently, the chronology in this study was based on the MET-pIRIR 250 method, potentially offering reliable ages of over 200 ka. Seven MET-pIRIR 250 ages of 201–336 ka suggested that a mega-Qaidam Lake (>2714 m a.s.l. on Google Earth) maintained until Marine Isotopic Stage (MIS) 7. The absence of sediments since ca . 200 ka implied wind-erosion and yardang formation since MIS6. This transition from lacustrine to a wind-erosion environment was interpreted as a response to the glacial-interglacial scale climatic changes.
... In the absence of changes in wind speed the Skeleton Coast Dunefield is found to consist of a set of juxtaposed barchan corridors. The large-scale aeolian erosional lineations which Goudie (2007) referred to as mega-yardangs are located precisely at the point at which the surface winds rapidly accelerate as the coastal convexity is approached, which leads to erosion of the Skeleton Coast barchans and a resurgence of high-energy sandflow. Note that immediately north of the aeolian lineations the MBL height is abruptly reduced north of the convexity in the coastline. ...
... In places within the NAEB and to the south of the Cunene Dunefield on the Skeleton Coast the development of macro-erosional grooves has led to the formation of large fields of aeolian lineations (termed mega-yardangs by Goudie, 2007) cut into the hard bedrock floor. Although the spatial stability of counterrotating helical vortices has been questioned in the past, this study has shown that both hydraulic and coherent turbulent flow structures can be topographically fixed to create stable high-energy linear pathways through aeolian systems such as the NAS. ...
Article
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Exploration for aeolian diamond placers within the southern Sperrgebiet requires a thorough understanding of aeolian transport across a broad range of scales from a systemic regional level to a micro-topographic-scale at the individual particle level. Within this arid zone the transport of coarse-grained aeolian bedload, including diamonds, is driven by the impact of saltating sandflow, which produces a uniquely characteristic diamond dispersal pattern as well as a variety of coarse-grained bedload features, textures and fabrics. For the first time the Namibian Aeolian System (NAS : see Annex 1 for abbreviations) which runs along the entire continental margin from the Orange River in the south to southern Angola in the north can be studied within the context of the recently discovered Benguela Low-Level Coastal Jet (BLLCJ). The structures produced in response to the hydraulic behaviour of the BLLCJ flow are shown to influence strongly the location of zones of high-energy erosion and aeolian sand accumulation throughout the system. The boundary conditions of the Namib Aeolian Erosion Basin are redefined to include the influence of the BLLCJ on the architecture and dynamics of sandflow pathways through this high-energy aeolian erosion landscape. Empirical sandflow measurements were previously used to identify narrow, linearly extensive Aeolian Transport Corridors characterised by high sandflow conditions. The corridors are commonly marked by the development of mono-trains of large barchan dunes along their length. The advent of Google Earth Engine time-lapse video provides an observational platform enabling spatial and temporal changes in sandflow and bedforms to be examined over a 32 year period. It thus provides many new insights into sandflow-dune and dune-dune interaction throughout this large-scale system down to the resolution of individual protobarchan genesis. The influence of the hydraulic behaviour of the BLLCJ flow together with localised effects of topography on surface wind flow structure is examined through analysis of a unique 10 km wide regional Airborne Laser Scanner (ALS) dataset stretching 170 km from Chameis Bay in the south to Schmidtfeld, to the north of Lüderitz. Aeolian bedforms and erosional features and patterns of coarse-grained aeolian bedload textural features and fabrics are mapped in detail throughout the Sperrgebiet. Changes in bedform interaction are shown to reflect variation in the pattern of surface flow created by localised topographic blocking and steering effects. The new system-wide perspective on the pattern of sandflow that feeds into, and maintains, the present-day Namib Sand Sea shows clear evidence of the influence of the BLLCJ as well as a variety of different types of vortices, which is a newly recognised element in the boundary conditions of this high-energy system. It is concluded that favourable conditions exist for the formation of horizontal rolls and vortex structures of varying length-scales within the Marine Boundary Layer (MBL) associated with the BLLCJ. It is proposed that these strongly influence both the development of the erosional aeolian landscape and the pattern of bedforms that develop within Aeolian Transport Corridors in response to surface wind flow over complex topography.
... The degree to which eolian processes shape the landscape morphology of arid regions is a long-standing point of contention (Brock & Twidale, 2011;Goudie, 2012), albeit one renewed by the exploration of wind-dominated planetary surfaces and their terrestrial analogues (e.g., Xiao et al., 2017). Wind erosion may outpace fluvial incision of bedrock in hyperarid regions, and wind can enhance the erosion of favorably oriented bedrock canyons (Perkins et al., 2015). ...
... Although it is difficult to imagine how fluvial or tectonic processes could produce these mesas, our wind erosion hypothesis provides a potential explanation. The mesas are larger and smoother than megayardangs described in indurated ignimbrites nearby on the Puna Plateau and in Northern Chile Goudie, 2007) but are similar in planform shape to megayardangs in Crommelin crater, Mars, that developed in canyon networks reworked by wind erosion (Perkins et al., 2015, and Figure 1b therein). As evidenced by the lack of boulder-sized colluvium, the lithologic composition of the smooth mesas is more friable than well-indurated ignimbrite and not capable of supporting the near-vertical slopes characteristic of some megayardangs . ...
Article
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Wind erosion is integral to the evolution of arid landscapes on Earth and Mars, but the nature of long‐term wind erosion of bedrock is poorly understood. Here we describe the Salina del Fraile (SdF) depression in the Puna Plateau of the Central Andes, NW Argentina, as a landform excavated by wind over several million years. New structural cross sections and a compilation of chronostratigraphic ages rule out the hypothesis that the depression was created by transtensional tectonics. Dated remnant lacustrine and alluvial deposits in the floor of the depression constrain the rate and timing of erosion. Late Oligocene‐Miocene compressional folding uplifted friable strata that were preferentially eroded, resulting in the high‐relief (900 m) depression. Up to 1.95 km and an average of 1.05 km of strata were eroded during the last 8.2 to 17 Ma, at rates of 0.06 to 0.23 mm/yr. These rates are similar to long‐term average wind erosion rates reported in other regions. Coarse‐grained eolian megaripples, yardangs, and elongated ridges indicate ongoing eolian abrasion and deflation, aided by salt weathering, of the floor of the depression. Megaripple migration across stony lag surfaces exposes fresh bedrock to continued erosion. The SdF also contains kilometer‐scale mesas and ridges that we interpret as erosional remnants. These landforms are similar to megayardangs and erosional topography identified on the lower flanks of Mount Sharp, Gale crater, Mars. In such hyperarid landscapes characterized by lithologic heterogeneities, high‐relief landforms can be generated and sustained by wind erosion, without significant fluvial or glacial incision.
... Their shape resembles an inverted boat, although some yardangs have instead a flat Landscapes Developed on Ignimbrites top. These features may occur in a wide variety of lithological types (Goudie 1989(Goudie , 2004. The outcrops of the Portezuelo Ignimbrite are eroded by the wind, forming yardangs of a depth of 3-6 m. ...
... In geomorphological literature, there are other terms that are used as equivalent to those cited here, such as mushroom rocks, pedestal rocks, chimney rocks, earth pillars, yardangs, demoiselles, and hoodoos, among others. In general, these names are applied according to specific geographical regions; for instance, in Utah (USA), the term "hoodoo" (Goudie 2004) is used to describe landforms of the chimney type, which in France they are known as "demoiselles". These terms point out mostly anthropomorphic shapes than their true genesis. ...
Chapter
This paper analyses the landforms and landscapes developed on ignimbrites outcropping in different regions of Argentina : Portezuelo (province of Mendoza) , Lihuel Calel (province of La Pampa) , Pilcaniyeu (province of Río Negro) , Barda Colorada (province of Chubut) and Chon Aike (province of Santa Cruz) . Some of these localities show clear resemblance to landforms which are typical of sedimentary rock landscapes , whereas others expose landforms typical of granitic rock landscapes . Systems of macro- and micro-landforms have been observed, such as inselbergs , bornhardts , nubbins , castle koppies , tors , crests and pinnacles , low cliffs , whale backs , and many other, associated minor features. Landforms of micro-modelling are shown at the base of vertical slopes, as cavities of the alveolar hollows and tafoni types, with subsequent evolution to caves , caverns and rock shelters . Besides, sometimes peculiar landforms such as yardangs , mushrooms and hoodoos are observed. The dominant agents that are responsible for these features are chemical and physical weathering and aeolian erosion . The micro-modelling affecting the different ignimbrite units is a direct consequence of their particular textural and structural conditions, on which a varied set of processes and erosion mechanisms have acted and defined their shape. In other cases, the orientation of the prevailing winds and the exposure of the ignimbrite flows have a decisive contribution to their genesis and ensuing development. It is herein concluded that the heterogeneity of these rocks, mostly due to changes in the welding degree , generates diverse types of macro- and micro-landforms .
... However, field evidence (e.g., Bonifay, 1962Bonifay, , 1965 and the development of mature erosional landforms (yardangs, pans) strongly suggest that deflation and aeolian deposition occurred during older periods, probably during most of the middle Pleistocene glacial phases. Many studies have indicated that the formation of yardangs and pans is a slow process that takes several thousand to hundreds of thousands years (e.g., McCauley et al., 1977;Halimov and Fezer, 1989;Washington et al., 2006;Goudie, 2007;Al-Dousari et al., 2009;Sebe et al., 2011;Laity and Bridges, 2013). This suggests that the aeolian system in the study region developed within a long period of time, presumably during several glacial phases of the Pleistocene like other European systems, such as in southwestern France (Sitzia et al., 2015;Bosq et al., in press) and the Danube valley . ...
Thesis
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Depuis presque un siècle, d’importants dépôts éoliens pléistocènes ont été reconnus dans la branche méridionale du rift cénozoïque ouest-européen, i.e. la basse vallée du Rhône et celles de ses affluents alpins. Ces lœss, déconnectés des deux principaux systèmes éoliens européens (la ceinture lœssique nord-européenne et le bassin du Danube), constituent un enregistrement clé pour documenter l’évolution des paléoenvironnements glaciaires péri-méditerranéens. L’étude de leur répartition spatiale couplée à une analyse sédimentologique et géochimique a montré que leurs principales caractéristiques (mode grossier autour de 60 µm, distribution granulométrique polymodale, taux de carbonate élevé, épaisseur localement importante (> 5 m), distribution spatiale discontinue et bioturbation abondante) peuvent être expliquées par la persistance d’un couvert végétal arbustif dans un contexte climatique moins rigoureux que celui des régions nordiques, permettant la capture simultanée des particules transportées par saltation et par suspension depuis les sources alluviales. À l’échelle européenne, la composition géochimique des lœss varie d’une région à l’autre mais garde une certaine homogénéité au sein d’un même bassin versant. Nos résultats suggèrent que cette variabilité est principalement contrôlée par la lithologie des zones englacées. Une analyse multi-proxy et chronostratigraphique à haute résolution a été réalisée sur deux séquences de lœss-paléosols : la séquence de Collias (~ 8 m) qui couvre la quasi-totalité du dernier cycle glaciaire et celle de Lautagne (~ 4 m) qui fournit un enregistrement détaillé du Pléniglaciaire supérieur. À l’échelle régionale, la principale période de sédimentation éolienne a été datée entre 37,5 ka et 12 ka avec un maximum de sédimentation entre 26 ka et 25 ka, synchrone de l’avancée maximale de la calotte alpine. Ce résultat suggère que les fluctuations des glaciers ont été le principal moteur de l’accumulation lœssique en modulant la production de particules susceptibles d’être transportées par la déflation.
... In arid, coastal, and periglacial environments on earth, wind-carried solid particles can slowly shape many types of rocks, such as basalt, marble, carbonate, and dolerite etc., to form ventifacts with one or more facets separated by sharp keels over long time periods [9][10][11][12]. Another common erosive morphological feature in arid environments is yardangs, often having beautiful streamlined shapes [13,14]. Our knowledge of Mars has been advanced extraordinarily over the past several decades. ...
Article
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The erosion of perfectly brittle materials under low speed impacts is studied by the combination of the Hertzian contact theory and the maximum stress criterion. It is found that the fractional erosion per impact is proportional to the product of the square root of the yield strain and the ratio of the kinetic energy per volume of the impacting body to the critical strain energy density of the target. The novel formula is conceptually extended to the erosion of cracked brittle materials.
... The power of wind erosion can form unexpected shapes or nearly sculptures out of sandstone or siltstone, known as Yardangs (Fig. 1). These landforms occur in environments with strong prevailing winds, in hyper-arid areas and they are shaped by abrasive sediments carried by the wind [2]. The ever-changing landscapes of deserts are also formed by the effects of the wind that causes the migration of sand dunes. ...
Conference Paper
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Living organisms have been constantly adapting to the specific environmental conditions of the most diverse places in the world and have developed a balanced relationship with nature that is particularly interesting to observe in extreme conditions. The landscapes are continually influenced, even shaped by natural forces. Many of the beautiful natural formations are created by the water and wind erosion. The creations of humans are quite a different case. Architecture hasn't evolved yet to be a natural part of its environment. The wind, for instance, is a powerful natural force that not only shapes the landscapes but is also a factor that could greatly affect building's shape and the design of public spaces around it. A brief overview of selected examples of architectural and design prototypes, ideas and realized projects that are responding to the changes in the environment, particularly to the wind effects, is made. Average global wind flow and occurrence is analyzed and depicted on the world map. An architectural shape is designed using the parametric modeling tool Grasshopper. It is a shelter in the Sahara desert, inspired by the wind creations and is almost literally formed by the wind. The designed shape is subsequently analyzed in the CFD analysis software. The wind speed is changed from the average values up to the extreme values. The resulting wind isocurves are compared. The wind swirls are observed to better understand the space around the shelter and the places of sand accumulation.
... The size of ARTs presents important differences in initiation and morphology compared to yardangs. Yardangs attain heights from meters to tens of meters for meso-yardangs, and hundreds of meters for mega-yardangs (Cooke and Warren, 1993;Goudie, 2007). The size of meso-and mega-yardangs means that they project well above the saltation cloud, which commonly is approximately 1 m high on Earth (Laity, 1994). ...
Article
Aeolian rat-tails (ARTs) are a previously undocumented, regionally-ubiquitous aeolian abrasion feature observed on matrix-supported ignimbrite surfaces in the Puna Plateau of Northwest Argentina. ARTs consist of an abrasion-resistant lithic clast projecting above the surface with a lee tail or ‘keel’ in the more erodible matrix. Size is controlled by the dimensions of the windward lithic clast, ranging from centimetre to meter scale; spatial density varies with clast content, which may reflect variations in ignimbrite facies. Field observations suggest ARTs follow a definable evolutionary sequence. First, an abrasion-resistant lithic clast contained within the ignimbrite is exposed to abrasion at the surface. Impacts from abrading particles erode the softer ignimbrite matrix adjacent to the clast. The clast shelters the leeward surface under a unimodal abrasion direction, creating a tail that tapers downwind and elongates as the clast emerges. Clasts become dislodged from the matrix as the surrounding surface erodes, ultimately destroying the feature if the clast is small enough to be mobilized directly by wind or impacting particles. This evolutionary sequence explains the morphology of ARTs and the presence of loose clasts on the ignimbrite surface, which contributes to the development of other landforms in the region, such as periodic bedrock ridges, yardangs, and megaripples. Satellite and rover images suggest similar features also exist on Mars. Because the formation and preservation of ARTs is contingent on unimodal abrasion direction, their orientation can be used as an indicator of long-term aeolian sediment transport direction.
... Yardangs are linear wind-parallel erosional landforms in cohesive material, and mostly occur in hyperarid to semiarid areas on Earth (McCauley et al., 1977;Breed et al., 1989;Brookes, 2001;Ritley, 2004;Goudie, 2007;Panah et al., 2007;Ehsani and Quiel, 2008;Al-Dousari et al., 2009;Bristow et al., 2009;Dong et al., 2012). Yardangs are also present on Mars (Ward, 1979;Mandt et al., 2009;Bridges et al., 2010;Zimbelman and Griffin, 2010;Bishop, 2011;Day and Kocurek, 2015), Venus (Trego, 1990;Arvidson et al., 1991;Trego, 1992;Greeley et al., 1995), and Titan (Paillou and Radebaugh, 2013). ...
Article
The hyperarid Qaidam Basin features extensive fields of yardangs (covering an area of ~ 40,000km²) sculpted in tectonically folded sedimentary rocks. We extracted the geometries of 16,749 yardangs, such as length-to-width ratio (L/W), spatial density, and spacing, from multi-source remote sensing data provided by Google Earth™. We classified the yardangs into four types based on their L/W: short-axis (1–2), whale-back (2–6), hogsback (6–10) and long-ridge (10 − 210). We interpreted the yardang geometries in the context of their geologic setting (bedding orientation, location along anticline crests or syncline troughs, and lithologic heterogeneity). Our results show that the yardang geometries in the Qaidam Basin are mainly controlled by the structural geology and rheology of the sedimentary rocks (e.g., strike and dip of bedding, the presence or absence of interbedded soft and hard beds, and structural position with folds), the angle between geomorphically-effective wind directions and the strike of bedding, and the relative cumulative wind shear force where two geomorphically-effective wind directions are present. Our analysis revealed the following: 1) nearly 69% of the yardangs with long-ridge and hogsback geometries are distributed in syncline areas whereas 73% of the yardangs with short-axis geometries are distributed in anticline areas; 2) the L/W ratio of yardangs exposed along the windward limbs of anticlines is lower than that of yardangs exposed along the leeward limbs; and 3) in the westernmost parts of the basin, yardangs are locally sculpted into mounds by two geomorphically-effective wind directions.
... Yardangs with similar aspect ratios and lengths are geographically clustered (Fig. 8). Lithology, induration, bedding orientation, and the length of time since the yardang developed are widely considered to impart first-order controls on yardang morphology (e.g., Grolier et al., 1980;Goudie, 2007;de Silva et al., 2010;Vincent and Kattan, 2006). Because the nature of the bedrock that constitutes the yardangs in the field area is relatively homogeneous (i.e., mostly sandstone to siltstone), and induration and bedding orientation vary little across the field area, we attribute the wide distribution in yardang aspect ratios to geographical differences in the timing of yardang development. ...
Article
Here, we present a stratigraphic and geomorphologic study of the northern part of the hyperarid and internally drained Hami Basin, located south of the Tian Mountains in northwestern China. The Hami Basin exposes wind-eroded Neogene sedimentary bedrock and was potentially an important source of atmospheric dust transported by westerly winds and deposited in the northern Pacific Ocean in the past. The northern Hami Basin exposes at least 430 m of subhorizontal (dipping locally < 1° to the south) Neogene strata. The strata consist of interbedded paleosol, siltstone, sandstone, and massive and cross-bedded matrix- and clast-supported pebble conglomerate associated with alluvial-fan to playa deposition. The Neogene strata are sculpted into widespread ( > 2000 km²) but spatially discontinuous fields of megayardangs, separated and locally overlain by spatially extensive (1 × 10⁴-10⁶ m²) subhorizontal planar surfaces of unconsolidated gravel. These gravel surfaces are topographically tiered and coincide spatially with prominent conglomerate beds within the wind-eroded Neogene stratigraphy. Conversely, the yardang fields developed in finer-grained and presumably more easily eroded intervals of the stratigraphy between the conglomerate beds. Unconsolidated gravels are also exposed within interyardang corridors, on yardang flanks and tops, in Pleistocene-Holocene ephemeral stream channels, and atop fluvial terraces. There is a scarcity of unconsolidated sediment composed of sand- to smaller-sized particles, which implies the basin is sandstarved and/or that near-surface winds are efficient in removing sand and fine-grained sediment from the basin. We suggest that the rate of eolian-dominated downcutting through the heterogeneous lithologies within the Neogene strata was modulated, in part, by the distribution of conglomerate beds. The distribution of conglomerates, which are more abundant in the lower part of the wind-eroded section, would be consistent with initially higher wind erosion rates and a decreasing trend through time as gravel surfaces coalesced, armored the landscape, and suppressed wind deflation. We estimate a minimum vertically integrated average of 178 m of erosion based on the projection of wind-eroded strata within the field area. We infer that the abundance of dark-colored (low-albedo) unconsolidated gravels in the Hami Basin has contributed to its anomalously high land skin temperatures and frequent extreme near-surface wind events.
... Signaling the presence of rock-or at least indurated material-kharafish is an Egyptian term that encompasses the full range of aeolian erosional forms [149], from kilometer-scale mega-yardangs [150], to centimeter-scale ridges and grooves [151] (p. 68), and millimeterscale flutes [152]. ...
Article
Full-text available
Sedimentary rocks provide records of past surface and subsurface processes and environments. The first step in the study of the sedimentary rock record of another world is to learn to recognize their occurrences in images from instruments aboard orbiting, flyby, or aerial platforms. For two decades, Mars has been known to have sedimentary rocks; however, planet-wide identification is incomplete. Global coverage at 0.25–6 m/pixel, and observations from the Curiosity rover in Gale crater, expand the ability to recognize Martian sedimentary rocks. No longer limited to cases that are light-toned, lightly cratered, and stratified—or mimic original depositional setting (e.g., lithified deltas)—Martian sedimentary rocks include dark-toned examples, as well as rocks that are erosion-resistant enough to retain small craters as well as do lava flows. Breakdown of conglomerates, breccias, and even some mudstones, can produce a pebbly regolith that imparts a “smooth” appearance in satellite and aerial images. Context is important; sedimentary rocks remain challenging to distinguish from primary igneous rocks in some cases. Detection of ultramafic, mafic, or andesitic compositions do not dictate that a rock is igneous, and clast genesis should be considered separately from the depositional record. Mars likely has much more sedimentary rock than previously recognized.
... Present-day examples(Goudie 2007) showing spectacular geometries similar to the circular structures of Weymouth Bay are well developed in the landscape of the Qaidam Basin, China, where they are spaced every few hundreds of metres and have tens of metres of relief (Kapp et al. 2011). Pronounced bedding and gentle stratal dips in the Qaidam examples produce concentric sets of circular structures as observed in the north-east of the studied area in Weymouth Bay. ...
Article
Full-text available
Many sedimentary rock successions contain plan-view circular structures such as impacts, diapirs and carbonate buildups. When remotely sensed, it can be difficult to discriminate between their formation mechanisms. Here we examine this problem by assessing the origins of circular structures imaged in high-resolution multibeam bathymetric data from Weymouth Bay (UK). The imagery shows 30-150 m across, concave-down structures within the upper Purbeck Limestone Group on the southern limb of the Purbeck Anticline. Similar structures have not been identified in the extensive outcrops around the Bay. The morphology and geological setting of the structures are consistent with three different interpretations; carbonate mounds, periclinal folds and evaporite diapirs. However, none of these structures have been previously recorded in the upper Purbeck Limestone Group outcrops of this internationally renowned geological region. We apply a scoring system to 25 features of the circular structures to discriminate between these three alternative interpretations. This analysis indicates that evaporite diapirs are the least likely and carbonate mounds the most likely origin of the structures. The presence of carbonate mounds revises the upper Purbeck palaeofacies distribution in its type area and provides an analogue for the exploration for hydrocarbon reservoirs in lacustrine mounds.
... However, field evidence (e.g., Bonifay, 1962Bonifay, , 1965 and the development of mature erosional landforms (yardangs, pans) strongly suggest that deflation and aeolian deposition occurred during older periods, probably during most of the middle Pleistocene glacial phases. Many studies have indicated that the formation of yardangs and pans is a slow process that takes several thousand to hundreds of thousands years (e.g., McCauley et al., 1977;Halimov and Fezer, 1989;Washington et al., 2006;Goudie, 2007;Al-Dousari et al., 2009;Sebe et al., 2011;Laity and Bridges, 2013). This suggests that the aeolian system in the study region developed within a long period of time, presumably during several glacial phases of the Pleistocene like other European systems, such as in southwestern France (Sitzia et al., 2015;Bosq et al., in press) and the Danube valley (Marković et al., 2015). ...
Article
In the Rhône Valley, a north-south oriented Cenozoic rift in southeast France, thick Pleistocene loess deposits have been recognized since the beginning of the last century. These loess records, which are disconnected from the North European Loess Belt (NELB), are of significant interest to document the evolution of perimediterranean landscapes and environments during the Last Glacial. To overcome the poor precision of available aeolian distribution maps, aeolian deposits were mapped using the topsoil textural database provided by the Land Use and Cover Area frame Statistical Survey project (LUCAS). The grain-size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops. Then, the areas showing a similar grain-size composition were extracted from the LUCAS rasters. The resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess, in better agreement with the known distribution of outcrops. The map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits. The deflation-related landforms, i.e., yardangs, closed depressions (pans), and desert pavements, are widespread south of narrowings of the Rhône Valley between latitudes 44°N and 45°N. They indicate palaeowinds blowing from the north/northwest. Aeolian sand, loessic sand, sandy loess, and loess deposits successively spread on both sides of the Rhône River. The loess is characterized by a coarse texture (main mode around 60 μm), strong local thickness (>5 m), limited extension, and abundant bioturbation. This preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the Last Glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources.
... Although it has been suggested that the basin supplied large quantities of loess to the Loess Plateau (Kapp et al., 2011), and salt crusts on the remains of at least two of the playa lakes in the Qaidam Basin formed about 1.0 ka B.P. so that subsequent erosion of about 800 m of strata from the basin could not have taken place. Strata in the basin are over 3,000 m thick, and yardangs are present on ridges near the western end (Goudie, 2007). It was these yardangs that prompted the suggestion that this area was the source of the loess on the Loess Plateau. ...
Article
Full-text available
The Qinghai-Tibet Plateau has developed into a vast fortress-like structure that has recently presented a barrier limiting the egress of moisture-bearing air masses. Lower sea levels also affected the climate. This paper examines their effects on the current evidence for the timing of past glaciations, and the development and evolution of permafrost. There are two theories regarding glaciation on the Qinghai-Tibet Plateau (QTP). Kuhle suggested that there was a major, unified ice-cap during the Last Glacial Maximum (LGM), whereas major Chinese glaciologists and others have not found or verified reliable evidence for this per se. There have been limited glaciations during the last 1.1 Ma B.P. but with increasing dominance of permafrost including both primary and secondary tessellons infilled with rock, sand or loess. The East Asia Monsoon was absent in this area during the main LGM, starting at >30 ka B.P. on the plateau, with sufficient precipitation reappearing about 19 ka B.P. to produce ice-wedges. A weak Megathermal event took place between 8.5 and 6.0 ka B.P., followed by Neoglacial events exhibiting peak cold at 5.3-4.7 ka, 3.1-1.5 ka, and the Little Ice Age (LIA) after 0.7 ka. Subsequently, mean annual air temperature has increased by 4 °C.
... • Table S1 • Table S2 • Table S3 • Table S4 • Figure S1 • Figure S2 America, and the coastal Peru and Chile (cf. Goudie, 2007;McCauley et al., 1977a), all host yardangs. They have also been identified on other planets, that is, Venus (Greeley et al., 1992), Titan (Paillou & Radebaugh, 2013), and especially on Mars (Carr, 2006), where yardangs typically occur in equatorial regions, including the Medusae Fossae Formation (MFF), Ares Vallis, Sacra Sulci, Candor Chasma, Iapygia, and some paleolake basins within impact craters (Day & Kocurek, 2016;Desai & Murty, 2016;Greeley & Iversen, 1987;Kite et al., 2013;Tanaka et al., 2014;Ward, 1979). ...
Article
Full-text available
Wind-eroded ridges known as yardangs are common in most arid desert regions on Earth, as well as on other planets, notably in the Medusae Fossae Formation (MFF) and Gale Crater on Mars. However, the formation and evolution of these various yardangs are not well understood, which, therefore, requires further studies by more terrestrial analogues. Here we report a detailed investigation of the terrestrial yardang fields in the Qaidam Basin, northeastern Tibetan Plateau, China. Most of them are distributed in the northwestern and central eastern parts, with dominant orientations northwest to north-northeast and approximately west to east, respectively. Based on their morphologies and distributions, yardangs within the Qaidam Basin have been classified into 11 different types out of four main groups. Wind is the dominant driver of yardang erosion, but water, salt, and mass wasting may also have played important roles in their formation and modification. A four-step evolution model, including embryonic, adolescent, mature, and receding stages, is proposed to reveal their formation and evolution in the basin. Meanwhile, yardangs in the MFF and Gale Crater on Mars have morphologic and geometric characteristics that show striking similarities to those in the Qaidam Basin. The fact that some yardang fields in MFF on Mars also show overlapping relationships suggests that they possibly have experienced a multistage evolution, during which the evolution processes may have been interrupted at some stages due to differences in the competence of rocks and/or the changes of the environment.
... Eolian action on non-cohesive sediment leads to the formation of sand ripples (Andreotti Remarkably similar ripples can be observed on snow surfaces (Filhol and Sturm (2015); Kosugi et al. (1992), Fig. 1.2c). Another ice pattern created by the wind are the sastrugi, or yardangs (Goudie (2007), Fig. 1.2d). ...
Thesis
The interactions between a fluid, such as water or air, and a deformable surface, such as rock, ice or sand, create marvelous natural patterns. The desert dunes generated by the winds, the cave speleothems shaped by thin water films and the sediment patterns on a river bed are just some examples. The branch of fluid mechanics devoted to the study of these patterns is the so-called morphodynamics. In this thesis, some morphological patterns from different natural environments are analytically modelled through stability analysis. This mathematical approach, commonly used to study every morphological pattern, addresses the stability of the spatially uniform solution to a small spatial perturbation. In unstable conditions, the perturbation grows in time to eventually form a finite-amplitude pattern. This thesis focuses on alternate bars, which are macro-scale river patterns, and on some small-scale ice and karst patterns. In first place, bar formation in rivers with considerable amount of suspended load is investigated. Closed forms relations for the wavelength (linear stability analysis) and the finite amplitude (weakly nonlinear analysis through Center Manifold Projection) are achieved. Results show that suspension plays a destabilizing role in bar instability and it affects both the bar wavelength and amplitude. The theoretical outcomes are validated with field observations. In second place, the conditions for vegetation spreading on finite-amplitude bars are mathematically framed in a model that also includes flow stochasticity. Flow unsteadiness is identified as the main factor discouraging vegetation growth, up to the point that, above a certain threshold, plant spread is completely inhibited. Comparison with field data demonstrates that the model captures the physical conditions heralding the transition between bare and vegetated fluvial states. Small-scale patterns in karst and glacial environments are usually generated by a falling liquid film. In some cases, the resulting patterns are so similar that a unified approach for the two environments is possible. This happens in the case of the longitudinally oriented organ-pipe-like structures, called flutings, which are widespread in caves and in ice-falls. In this thesis, an analytical model for fluting formation is proposed and closed form relations for the wavelength and the finite-amplitude (linear and weakly nonlinear analyses) are provided. The theoretical results are confirmed by numerical simulations of the fully nonlinear equations. The last part of this thesis deals with the problem of icicle formation. Recent experiments have revealed that small amounts of dissolved impurities are required for radial ripples to appear on icicle surface. This is contrary to existing theories, which would predict ripples on icicles formed by pure water. The theoretical model here proposed shows that icicles made by pure water do not develop ripples. Moreover, some considerations on the reason why dissolved impurities drive the ripple instability are presented.
... This type of landform develops on soft sediments, such as river and lake deposits, and is dominated by streamlines or long ridges (Niu, 2011). Today, yardang research, pertaining to its definition (Ward, 1979;Goudie et al., 1999), distribution (Mandt et al., 2009;Silva et al., 2010;Qu et al., 2014), classification (Halimov and Fezer, 1989;Cooke et al., 1993), morphological characteristics (Whitney, 1985;Goudie, 1999), formative conditions (Haynes, 2001;Goudie, 2007), evolutionary processes (Ward and Greeley, 1984;Xia, 1987;Dong et al., 2012), formative age (El-Baz et al., 1979;Al-Dousari et al., 2009;Niu et al., 2013), and environments (Dong and Chen, 1997), has gradually matured both in China and abroad. ...
... In the Dakhla Depression, Egypt, and the Lop-Nor region in China, ridges formed from re-exposed meanders and former stream channels are accompanied by yardangs (Fig. 32). Yardangs are wind-eroded landforms that provide insights useful for reconstructing past and present wind regimes (e.g., McCauley et al., 1977;Goudie, 2007). In eastern Saudi Arabia, many hollows extending to tens of meters in diameter accompany these ridges. ...
Article
Full-text available
Orbiting and landed spacecraft have provided vast amounts of data on fluvial and fluvial-related landforms and sediments on Mars. One variant of these landforms consists of ridges interpreted to be remnants of ancient fluvial activity, observed at thousands of Martian locales, suggesting extensive precipitation and runoff on early Mars. The importance of these ridges increased after the selection of the Jezero crater and the Oxia Planum landing sites for NASA's Perseverance and ESA's Rosalind Franklin rovers because these locations preserve fluvial sediments in ancient, lithified deltaic landforms. To further understand Martian fluvial ridges, this contribution presents an inventory of 104 sites of fluvial ridges on Earth, offering Upper Ordovician to late Holocene examples that are analogous to their Martian counterparts. The Earth global dataset provides environmental contexts for the formation mechanisms and conditions that accompanied channel and valley formation, erosion, and inversion. We describe four pathways by which channel and valley forms became ridges after materials adjacent to channels were eroded away: (1) twenty-seven cases of volcanic rock-capped ridges; (2) sixty examples of duricrust-capped ridges (eogenesis); (3) four examples of ridge sites formed through armoring by large clasts; and (4) thirteen locations where ridges were formed by erosion after deep burial and tectonic return to the Earth's surface (mesogensis). Water erosion, wind erosion, and mass wasting all play a role in removing the surrounding terrain, leaving the channel deposits or valley fills standing as ridges. Such ridges can contain as little as 0% and up to 100% fluvial sediments deposited in paleochannels and paleovalleys. Many of Earth's fluvial ridges that preserve channel fill sediments were formed as a response to short-duration seasonal or intermittent fluvial events (i.e. a few thousand to tens of thousands of years). Ridges formed from stacked channel-belts mark vertical aggradation and lateral migration occurring over more prolonged periods of fluvial activity (i.e. millions of years). Underlying materials can be older alluvial or fluvial, aeolian and lacustrine deposits, and weathered bedrock. The wide range of fluvial ridge composition and formational pathways on Earth suggests that the accumulation of the Martian fluvial deposits in paleo-channels and paleo-valleys (now expressed as ridges) also likely developed by both short-lived and long-lived fluvial activity. Although true duricrust has yet to be identified on Mars, the prevalence of duricrust-capped ridges on Earth might suggest that these occur on Mars and are important in preserving the record there. Volcanic rock-capped fluvial ridges are also common on Earth, but very few have been identified on Mars. Tectonism, compared to Earth, plays a negligible role in returning buried materials to the Martian surface. The discrimination of ridges exposed by erosion after deep burial (mesogenesis) versus those never buried nor exhumed (eogenesis) is not feasible based on remotely-sensed data unless cross-cutting relationships are visible in plan view. Our observations on preserved fluvial deposits compared with the underlying materials in terrestrial ridges infer that uncertainties could be significant in the case of paleohydraulic reconstructions made using measurements of the geomorphic parameters of ridges from high-spatial-resolution orbiter images.
... In this statistical test, the objective was to identify a trend line direction rather than the actual correlation (R 2 ), because there were too few observations of each variable to be statistically significant (p > 0.05). (Goudie, 2007, Koeberl, 1994, Koeberl et al., 2005, McCauley et al., 1977, Mchone et al., 2002 Badain Jaran Linear bright depositional and linear dark nondepositional streaks, with both types being located behind small mountains (Dong et al., 2013, Mason et al., 2008, Wang et al., 2005, Wang et al., 2015, Yang et al., 2012 Pali Aike Linear bright wind streaks emanating from craters Brown et al., 2004;L.L. Brown et al., 2004;Paruelo et al., 1998, Rodriguez et al., 2010, Zárate, 2003, Zolitschka et al., 2006 Registan Loess and lacustrine present on site (Balsan, 1972, Shroder, 2014, Whitney, 2006 Selima Sand Sheet Linear dark depositional streak Prevailing winds from northnortheast Flat surface covered by unvegetated sand and granules Sand enriched by clay and iron-rich material Precambrian rock overlaid by Paleozoic and ...
Article
Wind streaks are common aeolian features observed on terrestrial planets. They were first identified on Mars; thus, the associated terminology is based on Mars-related observations usually describing surface patterns with distinct albedos. However, terms related to reflected tones are only relevant to past knowledge for Mars, and not necessarily suitable for description of radar-visible streaks located on Venus, Titan, or Earth. Furthermore, the sensor type used to observe wind streaks can influence the subsequent data analysis. The purpose of this study was to examine the effects of sensor type on wind streak identification and interpretation. Six case studies featuring wind streaks on Earth were performed, using imaging by both radar and optical sensors. The results indicate that wind streak identification is constrained to a specific combination of sensor settings appropriate for the local surface properties. Only half the optically visible wind streaks considered in this study were also radar-visible, but all the wind streaks observable in the radar images also appeared in the optical images. Furthermore, "bright" and "dark" (reflectance and backscatter) are relative terms and should be used with caution. These results suggest that the Venusian wind streak database is most likely far from complete and that many more streaks exist.
... The largest continuous Yardangs on Earth are > 100 km long and are Abbasi, et al. Aeolian Research 41 (2019) 100539 located in the western part of the Lut desert (Ehsani and Quiel, 2008;Goudie, 2007;Radebaugh et al., 2017), while the tallest star dunes can be found in the southeast of the Yalan sand sea (Lorenz et al., 2015). More differentiated results were obtained when the LMI classified dunes as active due to a high potential evapotranspiration, e.g. in the southern Lut desert (Rahmatabad Rigan) and the eastern part of Jazmorian (Bampoor and Iranshahr). ...
Article
Sand dune movement causes severe damage to infrastructure and rural settlements in Iran every year. Identifying active dunes and monitoring areas with migrating sand are important prerequisites for mitigating these damages. With regard to this objective, the spatial variation of the wind energy environment based on the sand drift potential (DP) was calculated from 204 meteorological stations. Three commonly used dune activity models-the Lancaster mobility index (1988), the Tsoar mobility index (2005), and the index developed by Yizhaq et al. (2009)-were used for the evaluation of Iran's sand dune activity. The analysis of the indices showed that the dune activity was characterized by great spatial variation across Iran's deserts. All three models identified fully active dunes in the Sistan plain, the whole of the Lut desert, as well as in the Zirkuh Qaien and Deyhook regions, while the dunes in the northern part of Rig Boland, Booshroyeh and in the Neyshabor dunefields were categorized as stabilized dunes. For other dunes, the models show a less unified activity classification , with the Lancaster and Yizhaq models having more similar results while the Tsoar model stands more apart. Based on these model results and fields observations, a modified Lancaster mobility index has been applied to show a more realistic spatial variation of sand dunes activity in Iran's desert areas.
... These include provenance, transport media, sedimentary environments, and deposition processes. Some studies have inferred that yardang sedimentary environments are mainly composed of fluvial, lacustrine (McCauley et al., 1977;Wang, 1987;Xia, 1987;Zheng et al., 2002;Wu, 2003;Yang, 2009), alluvial (Goudie, 2007;, and aeolian (Goudie, 1989;Li et al., 2012) environments, according to the lithologic characteristics of yardang sedimentary facies, among which the fluvial and lacustrine sedimentary environments have been recognized as sources by numerous scholars, while sources from alluvial and aeolian environments remain controversial. With respect to yardang provenance, only a few studies based on paleogeographic conditions have indicated that the Lop Nur, Shule River, and Beishan Mountain may have provided the material for the formation of yardang structures through lake regression as well as perennial river and temporary flooding processes (Qu et al., 2004;Qu et al., 2014); however, there remains a lack of convincing quantitative evidence to corroborate such theories. ...
... In the Dakhla Depression, Egypt, and the Lop-Nor in China, exhumed meanders and channels are accompanied by yardangs (Fig. 21). Yardangs are erosional landforms that provide insights useful for reconstructing past and present wind regimes (e.g., McCauley et al., 1977;Goudie, 2007). In eastern Saudi Arabia, many hollows extending to tens of meters in diameter accompany inverted streams. ...
Preprint
Data from orbiting and landed spacecraft have provided vast amounts of information regarding fluvial and fluvial-related landforms and sediments on Mars. One variant of these landforms are sinuous ridges that have been interpreted to be remnant evidence for ancient fluvial activity, observed at hundreds of martian locales. In order to further understanding of these martian landforms, this paper inventories the 107 known and unknown inverted channel sites on Earth; these offer 114 different examples that consist of materials ranging in age from Upper Ordovician to late Holocene. These examples record several climatic events from the Upper Ordovician glaciation to late Quaternary climate oscillation. These Earth examples include inverted channels in deltaic and alluvial fan sediment, providing new analogs to their martian counterparts. This global dataset provides environmental context regarding the formation mechanisms and conditions that accompanied channel formation and inversion. There are five documented processes by which channel sediment and valley fill become consolidated and inverted after adjacent floodplain sediments are eroded away: (1) channel fill cementation during near-surface, early diagenesis; (2) channel fill lithification during burial diagenesis in the subsurface; (3) filling of a channel or valley by extrusive volcanism (lavas, tuffs); (4) channel surface armouring of coarse clasts by aeolian and fluvial processes; (5) compaction of bank-forming peat, which can lead to early inversion without removal of floodplain material. On Earth, early diagenesis (shallow surficial cementation) dominates among inverted fluvial channels (59%), volcanism is an important contributor (23%), and deep burial diagenesis, surface armouring, compaction of bank-forming peat are comparatively minor (11%, 6%, and 1% respectively). Water erosion, wind erosion, and exhumation due to tectonic activity play an important role in removing the surrounding terrain, leaving the channel deposits standing as a ridge. Wind erosion rates involved in causing topographic inversion range from 10 mm/year in the Bodélé Depression, Chad, to 0.21 mm/year in the Kumtagh Desert, China. These observations have important implications for understanding the formation and paleoclimate associated with similar landforms on Mars. Shallow, near-subsurface cementation of channel sediment could be prevalent on Mars due to a favorable climate like that of where they occur on Earth (tropical and subtropical climates), particularly because most Martian examples are not capped by volcanic materials and because tectonism, as compared to Earth, plays a negligible role in returning buried materials to the surface. Studying inverted channels on Mars at the global scale will bring new information on the early climate of Mars, particularly transition from wet to dry conditions. Finally, we propose that inverted deltaic deposits, which occur around the margins of the Pleistocene Tushka paleolake, in Egypt, are an excellent terrestrial analogue for fan-shaped deposits in relief inversion on Mars, particularly the deltaic deposits in Jezero crater, the landing site for NASA’s Mars 2020 rover.
... The morphologies of yardangs are the feedback results of the topographies, wind regimes and sediment types when they formed, which makes them critical paleoclimatic and paleoenvironmental indicators [12][13][14]. Significant work has been done regarding yardang morphologies and their spatial distributions, evolution processes and controlling factors [5,12,[15][16][17][18][19][20][21]. ...
Article
Full-text available
The morphological characteristics of yardangs are the direct evidence that reveals the wind and fluvial erosion for lacustrine sediments in arid areas. These features can be critical indicators in reconstructing local wind directions and environment conditions. Thus, the fast and accurate extraction of yardangs is key to studying their regional distribution and evolution process. However, the existing automated methods to characterize yardangs are of limited generalization that may only be feasible for specific types of yardangs in certain areas. Deep learning methods, which are superior in representation learning, provide potential solutions for mapping yardangs with complex and variable features. In this study, we apply Mask region-based convolutional neural networks (Mask R-CNN) to automatically delineate and classify yardangs using very high spatial resolution images from Google Earth. The yardang field in the Qaidam Basin, northwestern China is selected to conduct the experiments and the method yields mean average precisions of 0.869 and 0.671 for intersection of union (IoU) thresholds of 0.5 and 0.75, respectively. The manual validation results on images of additional study sites show an overall detection accuracy of 74%, while more than 90% of the detected yardangs can be correctly classified and delineated. We then conclude that Mask R-CNN is a robust model to characterize multi-scale yardangs of various types and allows for the research of the morphological and evolutionary aspects of aeolian landform.
... The largest continuous Yardangs on Earth are > 100 km long and are Abbasi, et al. Aeolian Research 41 (2019) 100539 located in the western part of the Lut desert (Ehsani and Quiel, 2008;Goudie, 2007;Radebaugh et al., 2017), while the tallest star dunes can be found in the southeast of the Yalan sand sea (Lorenz et al., 2015). More differentiated results were obtained when the LMI classified dunes as active due to a high potential evapotranspiration, e.g. in the southern Lut desert (Rahmatabad Rigan) and the eastern part of Jazmorian (Bampoor and Iranshahr). ...
... They are typically three or more times longer than wide, and when viewed from above, resemble the hull of a boat with a steep, blunt, upwind face that gradually gets lower and narrower towards the lee end (Livingstone and Warren, 1996). Mega-yardangs can be up to several kilometres long and cover extensive areas, up to hundreds of square kilometres (Inbar and Risso, 2001;Goudie, 2007). The Nullarbor features are not yardangs because they do not exhibit the "ship hull" profile and are longer and more extensive than any known yardangs. ...
Article
The southern Nullarbor Plain is covered by low amplitude (generally 1–2 m) parallel ridges and swales with variable wavelength (300–900 m). The ridges are stony; the swales hold thin deposits of unconsolidated silt and clay. The ridges and swales have previously been attributed to joint control but are not parallel to joints exposed in cave roofs. Instead, they have a striking similarity to central Australian linear sand dunes: they are parallel, regularly spaced and most importantly, fork in a consistent direction. They are here explained as the etched footprints of an extensive linear dune system that once covered much of the southern Nullarbor. Rainwater collecting in the troughs between the sand dunes dissolved the underlying limestone to produce the swales. Recognition of this dune field fills a major gap in the distribution of linear dunes across Australia. The dunes have subsequently disappeared, apart from red aeolian sand in dolines in the southeastern part of the Nullarbor; most of the sand was probably blown offshore. The ridge and swales are oriented predominantly north-south in the west, and northeast-southwest and northwest-southeast in the centre and east, due to deposition by northerly and westerly winds respectively, as shown by directions of forking. The north-south Nullarbor dunes are probably older and may have been deposited in the arid climate of the late Neogene; this would make them the oldest linear dunes in Australia, remnants of an early phase of linear dune activity that has been removed or overprinted elsewhere. The change in wind direction shown by the dune orientation could represent northward migration of sub-tropical high-pressure systems during the late Neogene.
... The fact that the ridges are mostly carved into the bedrock narrows down the possible formation process to aeolian erosion. Candidate resulting landforms are either yardangs, which are streamlined hills eroded by wind, or periodic bedrock ridges (PBRs), which are bedform-like erosional features (Goudie, 2007;Hugenholtz et al., 2015;Laity, 2009;Montgomery et al., 2012). The crestlines of the ridges are not streamlined, have Y junction terminations (typical in aeolian bedforms (McKee, 1979;Werner & Kocurek, 1999)), and do not resemble yardangs at any of their formational stages (Wang et al., 2018). ...
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Wind‐formed features are abundant in Oxia Planum (Mars), the landing site of the 2022 ExoMars mission, which shows geological evidence for a past wet environment. Studies of aeolian bedforms at the landing site were focused on assessing the risk for rover trafficability, however their potential in recording additional climatic fluctuations has not been explored. Here we show that the landing site experienced multiple climatic changes in the Amazonian, which are recorded by an intriguing set of ridges that we interpret as Periodic Bedrock Ridges (PBRs). Clues for a PBR origin result from ridge regularity, defect terminations and the presence of preserved megaripples detaching from the PBRs. PBR orientation differs from superimposed transverse aeolian ridges pointing toward a major change in wind regime. Our results provide constrains on PBR formation mechanisms and offer indications on paleo winds that will be crucial for understanding the landing site geology.
... A compass plot from between 1970 and 2003 of the annual wind direction and magnitude in the Lut Desert, north of the study area, reflects the predominance of unidirectional northwesterly winds (Ehsani and Quiel, 2008) (Fig. 2a and b). A regional wind system called "the wind of 120 days" predominates from May to September in east-central Iran (Goudie, 2007), and is best illustrated by the wind near the primary dune field north of the Fahraj Plain. ...
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The biogeomorphology of nebkha dunes, was investigated in the Fahraj Plain, which is located in southern part of the Lut Plain in southeastern Iran. Field investigations were performed to determine nature of nebkha dunes, whose genesis and growth involves the trapping of aeolian sand within the body of a plant. This study demonstrated that Tamarix, a shrub/tree in the Tamaricaceae family, has played a major role in reducing dust and sand storms in the region by trapping aeolian sediments and accumulating them in the form of nebkhas. In contrast, another tree/shrub that grows in the area, Prosopis cineraria (a variety of mesquite in the Fabaceae family), due to its structure seems not to have played an important role in aeolian sediment accumulation or in shaping any nebkha dunes in the area. Whereas previous investigations indicated that the highest nebkhas, which are located at the western margin of the Lut basin on the Takab plain, were no more than 12 m in height, our field investigations and measurements revealed that on the Fahraj plain there are nebkhas greater than 20 m in height. This would suggest that some of these nebkhas are among the largest and highest that have been reported in the world. Some were connected by rows of Tamarix and formed very long ridges more than 200 m in length. It seems that their form may be due to human activity. During our survey of nebkhas in the region we observed ongoing and increasing degradation in the nebkha field that we were examining. This seemed to be due to current climate variability and human impact. Investigation of the past climate of this region reveals that the Indian monsoon is and has been a major factor. Examination of this history also reveals the relationship between climate and sand movement in the region, and the inferred past history of nebkha dunes. Past analogue conditions from that history can provide a scenario of future nebkha evolution, and reveal if their current, ongoing degradation is a long-term trend or simply a short-term cycle.
... Bedrock outcrops north of Jubail belong to the Dam Fm and comprise limestone, sandstone, marl and shale (Alkhaldi et al., 2020). Within the southeastern coastal area wind faceted yardangs (sensu Goudie, 2007) are common features of the landscape, which are often found on low-lying outcrops and ridges of the Rus, Dammam and Hofuf Formations as well as being well developed in Quaternary carbonate aeolianite formations. ...
Article
This paper presents the key findings of a multidisciplinary study investigating the nature and timing of coastal landscape evolution in eastern Saudi Arabia during the Holocene. To date, most sea level reconstructions for the Arabo-Persian Gulf are based on uncalibrated 14C ages without correction for marine reservoir effects, or lack precision with regard to the effects of neotectonic changes, indicators of sea level used, errors in elevation of sedimentary units used, and the relationship with actual tides. As a consequence, the nature and timing of relative sea level (RSL) changes during the Late Pleistocene and Holocene remain poorly understood. To help address this, we use sea level index points (SLIPs) based on calibrated 14C ages to present a RSL curve for the central-southern Gulf of Saudi Arabia from coastal sabkha deposits near the rchaeological site of Dosariyah. The sediments record rapid transgression during the early Holocene with a mid-Holocene high-stand immediately prior to 6880e6560 cal. BP when the upper limit for the palaeo Mean Highest High tide water (MHHW) was 2.8-3.10 m above present day mean sea level. Transgression continued until shortly after 5575-5310 cal. BP with an upper limit to the palaeo-MHHW of 3.75 m above present sea levels. Thereafter a fall in RSL was recorded, with the regression leading to the progradation of the coastal system and the development of coastal sabkhas. Nonetheless later transgressions are recorded in the region between 4848-4536 and 4335-3949 cal BP. Radiometric dating results from archaeological excavations at Dosariyah, one of the most important Neolithic coastal sites in the Gulf, suggest that occupation of the site during the Neolithic coincides with the mid-Holocene marine transgression (ca. 7200-6500 cal. BP). Whilst the close proximity of the site to the sea may have facilitated maritime exchange activities, occupation of the site was short-lived and the phase of abandonment occurred during a period of rapid RSL rise, which would have transformed the area around Dosariyah into an island or certainly cut it off tidally from the mainland.
... 700 km in length with a maximum width of ∼300 km and occupies ∼120,000 km 2 with a mean elevation of 2700 m (Chen and Bowler, 1986). The geomorphology of the Qaidam Basin is characterized by widespread eolian features including migrating dunes, deflecting pans, and mega-yardangs due to extremely arid climate and severe wind erosion (Goudie, 2007). The lake system in the modern Qaidam Basin comprises more than 20 discrete salt lakes and playas and occupies a quarter of the total basin area (Chen and Bowler, 1986). ...
Article
The Qaidam Basin marks a crucial boundary between the Westerlies and the Asian summer monsoons. Previous studies in the Qaidam Basin have advanced our knowledge of the paleoclimate over glacial to interglacial cycles. However, our understanding of the paleoclimatic sensitivity of the Qaidam Basin to the relative strength of these two climatic driving forces remains limited due to the lack of regional paleoclimatic reconstructions. The Qaidam Basin is proposed as a regional and global eolian dust source during the glacial periods, during which a cold, dry climate is associated with the equatorward shift of the jet stream. On the contrary, paleoshoreline records suggest that a highstand lake stage prevailed in late Marine Isotope Stage 3 (MIS 3) and lasted until 15 ka. To address this conundrum, we have applied an integrated approach to reconstructing the regional paleoclimatic history by combining compound-specific isotope analysis, lake temperature reconstruction, and numerical modeling. Our results show varying paleoclimate associated with the dynamic climate boundary since 45 ka: (1) a wet climate during late MIS 3, when the Asian summer monsoons are strengthened under high summer insolation and penetrate further into Central Asia; (2) a general cold, dry but wetter than at present climate in the Last Glacial Maximum (LGM), when the Asian summer monsoons retreat and the Westerlies become dominant; and (3) three short periods of extreme aridity corresponding to the Younger Dryas and Heinrich 2 and 4 events, when the normal moisture transport via the Westerlies and Asian summer monsoons is interrupted. The numerical modeling supports an increase in the effective precipitation during the LGM due to reduced evaporation under low summer insolation. These results suggest that the Westerlies and Asian summer monsoons alternately controlled the climate in the Qaidam Basin in response to precessional forcing during the late Pleistocene.
... One of the most evident weather factors markedly shaping natural surroundings is the wind [11]. In the context of architecture, the wind can "form" the built environment, or, in other words, the wind fluxes interact with the built scenery, which, when unnoticed during the design process, can lead to creating zones with absent wind or, reversely, zones with high-speed wind, accompanied by turbulent flow. ...
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In the climate change era, the tendency to utilize computer-aided strategies in architectural design enables the incorporation of the influences of ambient conditions into the design process. Such a design strategy can consequently contribute to creating nature-based, sustainable architectural, and urban solutions. In this paper, it will be shown that the built environment can be designed, already from the first concepts, to affect and consequentially improve the local wind microclimate by addressing the unfavorable wind effects and proposing solutions for transforming them into an advantage. Utilizing the iterative Research Through Design (RTD) approach, the proposed data-driven wind-oriented shape optimization is introduced in a case study located in Stockholm. Three complex architectural shapes, resulting from the wind-oriented design approach, are parametrically designed in Grasshopper for Rhino and subsequently analyzed in a Computational Fluid Dynamics (CFD) plug-in Swift for Grasshopper.
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Parameters of geomorphological characteristics are critical for research on yardangs. However, which are low-cost, accurate, and automatic or semi-automatic methods for extracting these parameters are limited. We present here semi-automatic techniques for this purpose. They are object-based image analysis (OBIA) and Canny edge detection (CED), using free, very high spatial resolution images from Google Earth. We chose yardang fields in Dunhuang of west China to test the methods. Our results showed that the extractions registered an overall accuracy of 92.26% with a Kappa coefficient of agreement of 0.82 at a segmentation scale of 52 using the OBIA method, and the exaction of yardangs had the highest accuracy at medium segmentation scales (138, 145). Using CED, we resampled the experimental image subset to a series of lower spatial resolutions for eliminating noise. The total length of yardang boundaries showed a logarithmically decreasing (R2 = 0.904) trend with decreasing spatial resolution, and there was also a linear relationship between yardang median widths and spatial resolutions (R2 = 0.95). Despite the difficulty of identifying shadows, the CED method achieved an overall accuracy of 89.23%with a kappa coefficient of agreement of 0.72, similar to that of the OBIA method at medium segmentation scale (138).
Article
New work by Pelletier et al. (2018) and Pelletier (2018) quantitatively explains how arid landscapes can be sculpted into regular ‘teardrop’ shaped hills known as yardangs. A diversity of theories have been proposed to explain these perplexing hills. Pelletier (2018) helpfully clarifies that the most likely suite of mechanisms involves an interplay between wind‐ and water‐driven erosion. Using detailed field measurements from Ocotillo Wells, California, a model is developed that explains how yardangs achieve their characteristic form and spacing. Although couched around the iconic yardang, the work contributes a general and robust template for understanding landscapes where both wind and water erosion are present. Pelletier et al. present a comprehensive treatment of the evolution of yardangs Yardang evolution is driven by denudation and wind erosion
Chapter
Soil formation is a complex phenomenon. The role of geology is mostly prominent through the influence of lithology in the production of parent material and tectonics in the geoform of structural origin. Geomorphology plays an important role in soil formation through relief, surface morphodynamics, morphoclimatic context, weathering and time (age). The geological zones and their related geomorphic features are dealt with, as related to soil distribution. The Iranian Plateau is divided to eight structural zones. The Zagros mountain chain contains the most important sedimentary basins comprised mainly of calcareous detrital sediments. Karst features are the major expression of the Zagros landscape. The other mountain chain --Alborz zone-- is composed of sedimentary rocks including limestone, dolomitic and clastic rocks. Large areas in northern Iran, are covered by loess deposits with a thickness of 30 to 70 m. Central Iran is composed of a series of inland basins and more than 60 playas. Makran zone, in East and Southeast of Iran, is composed of uplands with varying width and altitude, irregular in trend and physiography. Various landforms such as fans, terraces, valleys, outwash deposits, etc studied in several case studies from different regions of Iran are reviewed to show the close relationship between soils and geomorphology.
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Isolated landscapes largely shaped by aeolian processes can occur on Earth, while the majority of Mars’ recent history has been dominated by wind-driven activity. Resultantly, Martian landscapes often exhibit large-scale aeolian features, including yardang landforms carved from sedimentary-layered deposits. High-resolution orbital monitoring has revealed that persistent bedform activity is occurring with dune and ripple migration implying ongoing abrasion of the surface. However, little is known about the interaction between dunes and the topography surrounding them. Here we explore dune-yardang interactions in Becquerel crater in an effort to better understand local landscape evolution. Dunes there occur on the north and south sides of a 700-m-tall sedimentary deposit, which displays numerous superposed yardangs. Dune and yardang orientations are congruent suggesting they both were formed under a predominantly northerly wind regime. Migration rates and sediment fluxes decrease as dunes approach the deposit and begin to increase again downwind of the deposit where the effect of topographic sheltering decreases. Estimated sand abrasion rates (16-40 μm yr-1) would yield a formation time of 1.8-4.5 million years for the 70-m-deep yardangs. This evidence for local aeolian abrasion also helps explain the young exposure ages of deposit surfaces, as estimated by the crater size-frequency distribution. Comparisons to terrestrial dune activity and yardang development begin to place constraints on yardang formation times for both Earth and Mars. These results provide insight into the complexities of sediment transport on uneven terrain and are compelling examples of contemporary aeolian-driven landscape evolution on Mars.
Article
Here I present a set of mathematical modeling results, constrained by the results of the companion paper, aimed at improving our understanding of yardang development and controls on yardang morphology. The classic model for yardang development posits that yardangs evolve to an aspect ratio of ≈ 4 in order to minimize aerodynamic drag. Computational fluid dynamics (CFD) model results presented here, however, demonstrate that yardangs with an aspect ratio of 4 do not minimize drag. As an alternative, I propose that yardang aspect ratios are primarily controlled by the lateral downwind expansion of wind and wind‐blown sediments focused into the troughs among yardangs, which can be quantified using previous studies of wall‐bounded turbulent jets. This approach predicts yardangs with aspect ratios in the range of 5 to 10, i.e., similar to those of natural yardangs. In addition to aerodynamics, yardang aspect ratios are influenced by the strikes and dips of strata, as demonstrated in the companion paper. To better understand the aerodynamic and bedrock structural controls on yardang morphology, I developed a landscape evolution model that combines the physics of boundary layer flow and abrasion by aeolian sediment transport with a model for the erosion of the tops and lee sides of yardangs by water‐driven erosional processes. Yardang formation in the model is enhanced in substrates with greater heterogeneity (i.e., alternating strong and weak strata). Yardang morphology is controlled by the strikes and dips of strata as well as the topographic diffusivity associated with water‐driven erosional processes. Yardangs with an aspect ratio (AR) of 4 are not minimum‐drag forms. Yardang ARs are controlled by bedrock structure and the aerodynamics of turbulent jets. Numerical modeling illustrates the importance of water‐driven processes and bedrock structure.
Thesis
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Sand and dust storms are among the biggest environmental problems in the Tarim Basin. In the eastern Tarim Basin, however, the natural riparian vegetation reduces the frequency and magnitude of these events. This contributes to the important ecosystem service of protecting the National Highway 218 leading through this area against drifting sand. The degradation of these so-called Tugai forests due to water scarcity now endangers this ecosystem service. One Chinese project and the Sino-German project SuMaRiO are now working on the restora-tion of the lower reaches of the Tarim River and the maintenance of its ecosystem services. This master thesis now treats the influence of natural riparian vegetation on aeolian process-es and the consequent ecosystem service within a biogeomorphological approach. Sediment flux measurements and a modelling approach are combined to have a spatial explicit estima-tion of the sediment retention by riparian vegetation. For an investigation area of ca. 10km² in the eastern Tarim Basin the model predicts an overall sediment retention of 11656kg/h. following this, about 73% of the length of the National Highway within the investigation area are protected against drifting sand. Beside this, the potential influence of the so-called ‘eco-logical water’ on the sediment retention is investigated. As result, this water transfer can maintain the actual sediment retention but due to the missing rejuvenation and therefore missing expansion of the forest standings on a larger scale only a small increase can be ex-pected. Furthermore there is an aeolian redistribution of sediment within the Tugai ecosys-tem. The measurements show that fine alluvial sediment is eroded, while coarse aeolian sed-iment is accumulated. Consequences of this process remain unclear in the moment. All in all the natural riparian vegetation has a big influence on aeolian processes and contrib-utes therefore to the important ecosystem service of protecting the National Highway 218 against drifting sand. The restoration efforts with the transfer of ‘ecological water’ can help maintaining the retention potential of the vegetation, the potential for an increase is limited under the current circumstances.
Article
Geotourism implicitly implies geologic and geomorphologic characteristics as the base for tourism/recreation activities and geographic situations. The Lut desert and its environmental system have many potential and outstanding universal values including the highest and longest yardangs (kaluts) and very high sand dunes and nebkhas. It is necessary to explore and introduce internationally the values of the Lut desert. In this research, we have initially listed tourism attractions of the Lut desert. Subsequently, their scientific, educational, and tourism value, and degradation risks have been evaluated by Brilha (2016) method. The suitable areas for geotourism development have been determined by the fuzzy AHP method and the optimal areas have also been selected and surveyed based on an assessment of geosites. The results of the geosite evaluation of the Lut desert indicate that the geosites of Shur River, mega-yardangs (kaluts), linear dunes, basalt plateau of Gandom Beryan, and the dreamy city of the Lut (Shahr-e Khialy-ye Lut) have the highest values for geotourism. The results of zonation by fuzzy AHP have also indicated that west, northeast, and southeast parts of the Lut have more suitable conditions for geotourism development. Finally, through the integration of the assessments and zoning of suitable areas for geotourism development with a field survey in a new approach, we have selected eight suitable areas for the geotourism development in the Lut desert.
Chapter
An abraded landscape forms predominantly by the mechanical wear of coherent material by saltating sand grains, with deflation removing particles and soils by wind shear. Abraded systems range from small wind-scoured areas to the vast landscape assemblages of the Sahara Desert and the planet Mars. Landforms include ventifacts, yardangs, deflation basins, and inverted terrain. Wind-abraded landscapes require strong and generally sustained winds, abrasive sediment, and sparse vegetation. These conditions occur in desert, cold (periglacial and paraglacial), and coastal environments, with the most extensive features on Earth formed in the hyperarid environments of Asia and Africa. Many of the same landforms occur on Mars.
Chapter
Hydro-aeolianAeolian features are among those landformsLandforms that can be seen in micro-, meso-, and macro-scales in the southeast IranIran. The landform is called yardangYardang or named kalutKalut for unique kinds of that. In fact, the most kalutsKalut of IranIran are developed in the Lut DesertLut Desert as the highest yardangYardang of the world. However, there are many embryonic kalutsKalut in Rafsanjan, south Semnan, south Sabzevar, and many parts of the country. The high diversity of the landformsLandforms made kalutsKalut as one of the most attractive geosites of IranIran.
Article
A major physical process shaping bedrock landforms in fluvial, coastal, and aeolian environments is abrasion by sediment‐carrying fluid flows. A unifying formula to describe the rate of abrasion occurring in these environments has not been presented, the exploration of which is the purpose of this study. Considering the threshold concept the formulation is made including erosivity of fluid flows and erodibility of bedrock. The formula is described as dΓ/dt = C [(FA/FR) – 1], where Γ is the amount of erosion, i.e. eroded length (distance), volume, mass, or weight, t is the time, dΓ/dt is the erosion rate, FA (= A x [fluid force]) is the assailing force of sediment‐laden fluid flows used as an index of the flow erosivity, FR (= B x [bedrock strength]) is the resisting force representing the bedrock erodibility, C is a coefficient with the same unit as that of dΓ/dt, and A and B are dimensionless coefficients. The equation is confirmed by existing laboratory abrasion data and its applicability is examined using existing laboratory data of fluvial and aeolian abrasion experiments and field data from a coastal area. Examinations applying fluvial and aeolian abrasion data indicate that the coefficient C is found to represent the amount of sediment working as abrasives in fluid flows and the hardness of sediment relative to bedrock; and A is presented to reflect the particle size of the sediment. The coefficient B is a conversion factor from conventional mechanical strength of rocks to the resisting force. Selecting appropriate physical quantities for FA and FR enables the application of this equation to abrasion studies on various landforms in these environments. © 2018 John Wiley & Sons, Ltd.
Chapter
The surface compositions and atmospheric conditions of Titan and Pluto, the solid outer solar system bodies with significant atmospheres, are notably dissimilar to those of Earth. Yet the Cassini mission to the Saturn system and the New Horizons mission to Pluto during the past decades have revealed dune forms similar to Earth's in shape, landscape interactions and even size. Geomorphological analyzes, coupled with strong recent advances in dune evolution modeling, have revealed important connections between atmospheric and surface processes on these bodies. The compositions and behaviors of dunes in the outer solar system greatly inform dune studies, including on Earth and inner solar system bodies.
Article
Research over approximately 200 yr on the geomorphic effects of the force of water, wind, waves and ice is reviewed. In a changed scientific, technological, institutional and socio-political context, several trends emerge. Increased focus on measurement of processes from the 1930s onwards was facilitated by new technologies, leading eventually to a blurring of disciplinary boundaries and the emergence of geomorphology as an Earth system science. Human impact research and applications have blossomed and are contributing to an emerging understanding of the Anthropocene. Absolute dating techniques have reinvigorated landform and landscape evolution research, while remote sensing and geospatial science generally have enhanced observation, measurement and modeling of terrestrial and planetary surface and subsurface forms and processes. The historical record demonstrates that geomorphology has attained scientific vigour and societal relevance through fascinating journeys of curiosity, exploration, mapping, measurement, modeling and explanation.
Article
Dunhuang UNESCO Global Geopark (DHGG) is rich in geoheritage and contains scientific value for studying the sedimentation environments and paleoclimates of Western China. The Geopark is also notable for its aesthetic, cultural, artistic, and recreational value for tourism development. Since geographer Sven Hedin's discovery of a yardang landform around Lop Nur in 1903, the area has been heavily studied. After the site was designated a National Geopark, geoconservation and geotourism began to rapidly develop and problems associated with these changes emerged. This study characterizes some of DHGG's typical geoheritage, existing geoconservation, launched geotourism, and also describes some of the area's challenges. In addition, the opportunities and challenges of DHGG arising from the construction of the Silk Road Economic Belt and 21st-Century Maritime Silk Road (B&R) are discussed. To benefit the sustainable development of DHGG, it is prudent to continue promoting geodiversity, geoconservation, and geotourism by making use of the advantages brought by the B&R.
Article
A number of major factors have driven the volume and nature of aeolian geomorphology in the second half of the twentieth century: the growth of process studies, the availability of remote sensing, the development of new dating techniques (e.g. optical dating), the utilisation of new technologies (e.g. data loggers and global positioning systems),computer modelling of dune forms and wind action and sediment movement, the recognition of the importance of aeolian forms and processes in extra-terrestrial settings (especially Mars), the role of aeolian dust in atmospheric processes, the search for analogues for ancient hydrocarbon-bearing strata, the appreciation of the importance of climatic changes in desert areas, a concern with what may happen to arid environments in a warmer world, and an increasing realisation that aeolian phenomena could be hazardous. This chapter does not deal with coastal dunes, but concentrates on those of the major lower latitude drylands. It discusses the main controls on dune forms, the nature of sand seas, ancient and modern, and the nature of dune sediments. It also shows that during the 1970s there was a burgeoning interest in dust storms. In addition, with the availability of remote sensing imagery it was possible to see for the first time that wind-furrowed yardangs were striking features with a wide global distribution. The origin of closed depressions (pans) generated a large literature and hypotheses for their formation were put forward which included wind erosion, solution, excavation by animals, karstic and pseudo-karstic solution, and tectonic subsidence. Remote sensing showed just how important they were in drylands. Other phenomena that attracted attention and some controversy were stone pavements and peri-desert loess. Finally, it is suggested that the nature of aeolian processes and forms will be modified in a warmer world.
Article
Yardangs are streamlined ridges that form in arid environments on Earth and Mars through wind‐driven abrasion of consolidated substrates. Currently, there is limited consensus on the mechanisms that initiate and establish patterns of yardangs on the landscape. In this work, we examine the spatial organization of yardangs in the Campo de Piedra Pómez ignimbrite deposit of northwestern Argentina and identify evidence of antecedent controls on yardang patterns and formation. We mapped 14,826 yardangs in the region using a high‐resolution digital elevation model (DEM) and satellite imagery. We classified yardangs as points using a two‐stage decision rule based on morphology and spectral characteristics. Point pattern analysis shows that yardangs in the study area are not randomly distributed and commonly exhibit directional anisotropy in point pattern. The anisotropic pattern manifests as bands of closely‐spaced yardangs oriented transverse to the dominant northwesterly wind direction. We hypothesize that banding is controlled by pre‐existing antecedent topography in the bedrock, such as fumaroles or ridges associated with pyroclastic flow deposits. We present evidence from other locations on Earth and Mars to illustrate that the transverse banding is a common pattern in yardang landscapes.
Article
Yardangs are typical aeolian erosion landforms, which are attracting more and more attention of geomorphologists and geologists for their various morphology and enigmatic formation mechanisms. In order to clarify the aeolian environments that influence the development of long-ridge yardangs in the northwestern Qaidam Basin of China, the present research investigated the winds by installing wind observation tower in the field. We found that the sand-driving winds mainly blow from the north-northwest, northwest and north, and occur the most frequent in summer, because the high temperature increases atmospheric instability and leads to downward momentum transfer and active local convection during these months. The annual drift potential and the ratio of resultant drift potential indicate that the study area pertains to a high-energy wind environment and a narrow unimodal wind regime. The wind energy decreases from northwest to southeast in the Qaidam Basin, with the northerly winds in the northwestern basin changing to more westerly in the southeastern basin. The strong and unidirectional wind regime for the long-ridge yardangs in the northwestern Qaidam Basin results from the combined effects of topographic obstacles such as the Altun Mountains and of the interaction between the air stream and the yardang bodies. Present study suggests that yardang evolution needs such strong and unidirectional winds in high- or intermediate-energy wind environments. This differs from sandy deserts or sandy lands, which usually develop at low- or intermediate-energy wind environments. Present study clarifies the wind regime corresponding to the long-ridge yardangs’ development, and lays firm foundation to put forward the formation mechanisms for yardangs in the Qaidam Basin.
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The aeolian system within the 0–20 km wide coastal tract of the southern Namib deflation basin is governed by unimodal southwesterly to south-southeasterly surface windflow. A strong seasonality characterizes the wind energy of the system, with the peak occurring from September to March, when gusting at 80–100 km h⁻¹ is common.
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The growing concern over climate change and decertification stresses the importance of aeolian process prediction. In this paper the use of a general circulation model to predict current aeolian features is examined. A GCM developed at NASA/Goddard Space Flight Center was used in conjunction with White`s aeolian sand flux model to produce a global potential aeolian transport map. Surface wind shear stress predictions were used from the output of a GCM simulation that was performed as part of the Atmospheric Model Intercomparison Project on 1979 climate conditions. The spatial resolution of this study (as driven by the GCM) is 4° X 5°; instantaneous 6-hourly wind stress data were saved by the GCM and used in this report. A global map showing potential sand transport was compared to drift potential directions as inferred from Landsat images from the 1980s for several sand seas and a coastal dune field. Generally, results show a good correlation between the simulated sand drift direction and the drift direction inferred for dune forms. Discrepancies between the drift potential and the drift inferred from images were found in the North American deserts and the Arabian peninsula. An attempt to predict the type of dune that would be formed in specific regions was not successful. The model could probably be further improved by incorporating soil moisture, surface roughness, and vegetation information for a better assessment of sand threshold conditions. The correlation may permit use of a GCM to analyze {open_quotes}fossil{close_quotes} dunes or to forecast aeolian processes. 48 refs., 8 figs.
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Sandstone ridges along the marine-eolian boundary of the Middle Jurassic Page Sandstone (eolian) with the lower Carmel Formation (restricted marine) in south-central Utah have been identified as erosional remnants consisting of strata of siliciclastic sabkha and eolian origin. The ridges lie within two distinct units of the Thousand Pockets Tongue of the Page. Two equally plausible models explain the genesis of these ridges. One model involves (1) early cementation of eolian and sabkha strata, (2) wind erosion leading to development of yardangs and unconformities, (3) yardang tilting due to evaporite dissolution, and (4) renewed deposition and burial. The alternative model explains ridge development through (1) subsidence, with tilting, of eolian and sabkha strata into evaporites due to loading from linear dunes, (2) evaporite dissolution and unconformity development, and (3) renewed deposition and burial. These models provide important clues about the nature of a missing part of the rock record. Reconstruction of units that were deposited but later eroded improves paleogeographic interpretation and here indicates that the Carmel paleo-shoreline was considerably farther to the northwest than previously believed.
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The Lut Desert of Iran is an elongated valley oriented north-northwest to south-southeast. The valley descends southward to the Jaz Murian dry lake through a pass. The Navy's Coupled Ocean-Atmosphere Mesoscale Prediction System is used to study a northerly low-level jet in the valley and across the dry lake. The dynamics of the jet are investigated with force balance and Froude numbers to determine the contribution of various mechanisms to the jet formation and maintenance. The jet is initiated as a channeled gap flow in the convergent topography of the Lut valley by the valley-parallel pressure gradients generated by the large-scale processes and by the presence of cold air over the valley's sloping terrain. The pressure gradient is mainly counteracted by the frictional force. The imbalance between them controls the intensity and persistence of the jet in the valley. Farther south, the jet evolves into a downslope flow resembling a hydraulic jump on the steep slope of the dry lake. A transition of subcritical situation to supercritical faster flow is found at the mountain crest between the Lut valley and dry lake. The depth of stably stratified cold layer, the static stability of upstream inversion, and magnitude of upstream winds all determine the jet configuration over the dry lake. The lee troughing over the Gulf of Oman and the Persian Gulf, as the large-scale inland flow crosses the coastal mountains, supports this low-level jet through the increased along-jet pressure gradient. The jet is also influenced by diurnal forcing. being strong at night and weak during daytime.
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Yardangs are streamlined, wind-eroded hills common to most deserts. Yardangs at Rogers Lake, Mojave Desert, California, have streamlined forms characteristic of objects eroded by moving fluids, a teardrop shape that approaches an ideal 1:4 width-to-length ratio. In wind-tunnel simulations, miniature forms of various shapes changed sequentially by erosion of the windward corners, erosion of the windward slope, erosion of the leeward corners and flanks, and erosion of the leeward slope. Prominent mechanisms in yardang evolution apparently are abrasion at the windward end and deflation and reverse air flow near the middle and at the downstream end. Width-to-length ratios of yardangs are grossly similar to those of some fluvial and glacial streamlined landforms. Refs.
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Archaeological sites associated with the Holocene playas in Farafra Oasis were occupied primarily by foragers. Intensive utilization of wild sorghum, originally dated to 6700 yr B.P., has now been pushed back to 7600 yr B.P. Sheep and goats, originating in the Levant, were introduced in Farafra Oasis ca. 6700 yr B.P. The playas were episodically sustained by surface runoff and wadi activity under wet/moist climatic conditions with frequent dry oscillations from approximately 9650 to 6000 radiocarbon yr B.P. A shift toward drier climatic conditions associated with colluvial reworking of older cultural material is evident from 7300 to 6000 yr B.P. This shift precipitated a significant change in settlement strategy. The main phase of playa formation ended ca. 6000 yr B.P. under cold conditions and increasing aridity. © 2001 John Wiley & Sons, Inc.
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Mean annual dust storm frequencies are mapped for south-west Asia (Iran, Afghanistan, Pakistan and India) showing areas of greatest activity in two regions: an area at the convergence of the borders of Iran, Afghanistan and Pakistan that comprises the Seistan Basin, Registan and north-western Baluchistan; and the plains of Afghan Turkestan. The highest average annual number of dust storm days is 80.7 at Zabol in Iranian Seistan. Little dust-raising activity occurs on the Indian peninsula. Dust storms occur principally during the dry season months of spring and summer. Local and regional meteorological conditions associated with dust storms are described, ranging from the short-lived dust devil measuring tens of metres across to dust plumes visible on satellite imagery. Dust is transported from the region north to Asian states of the U.S.S.R., south over the Arabian Sea and east over south-east Asia. The importance of soils in the wind erosion system is indicated. Dust storms commonly occur on fine-grained material, particularly loess, alluvium, silt, clay and other outwash sediments. Dust storms have received a variety of names locally in the region. Dust storm frequency during the peak season in northern India is found to be poorly related to mean rainfall, mean wind speed and a climatic wind erosion factor, C developed by Chepil et al. (1962).
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1] The nature and origin of the Medusae Fossae Formation (MFF) on Mars has been debated since the return of the first Viking images. The MFF's young age, distinctive surface texture, and lack of obvious source have prompted multiple hypotheses for its origin. This study uses data from the Mars Global Surveyor (MGS) mission to examine the MFF at all available scales. We discuss and quantify observations from Mars Orbiter Laser Altimeter (MOLA) topography and Mars Orbiter Camera (MOC) images to better constrain the origin of the MFF. Topographic grid estimates yield a present extent of 2.1 Â 10 6 km 2 and a volume of 1.4 Â 10 6 km 3 ; however, remnant yardang deposits observed far from the thicker lobes of MFF material suggest that it may have once covered up to 5 Â 10 6 km 2 . We do not find compelling evidence for extensive fluvial reworking of the MFF; however, in several regions, buried channels are apparent in the MFF because the formation is draped over underlying topography. Layering is apparent at all scales, from submeter to hundreds of meters, with variable resistance to weathering. Continuity of layers appears to be local to regional, but not likely formation-wide. Yardangs form both parallel and bidirectional patterns, with resistant layers and jointing probably influencing their orientations. A comparative study of MFF regional topography and surface expression indicates that the MFF is quantitatively dissimilar to Martian polar layered deposits. The material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin.
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Deflation, mass movement and abrasion of hydro-aeolian deposits within former lake basins of the North-eastern Sahara have produced a series of spectacular yardang landforms which attest to high rates of aeolian abrasion and erosion in response to strong prevailing northerly trade winds. The deposits were previously interpreted in a descriptive fashion via both field and remote sensing survey. We analysed the yardang features of the Kharga Oasis by undertaking a morphometric survey using high precision Global Positioning System Kinematic Surveys. Yardang morphology is more complex than has previously been interpreted. Alignment of clusters of yardangs as en echelon suites of N-S swarms is commonplace. To fully understand the morphology and evolution of these features a more detailed assessment of yardang sets rather than individual forms is required. Erosion of the yardangs is observed to be occurring via aeolian abrasion at the windward tip, but more significantly via mass failures which exploit cracking within the fines-rich sediment matrix.
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Yardangs are perhaps, the most neglected and misunderstood of the Earth's landforms. The existence of large fields of yardangs ranging from meters to kilometers in length is not well known to American geologists. In the United States many early workers overstated the role of the wind in landscape development, leaving a legacy of uncertainty about the effectiveness of the wind as an agent of surface sculpture. New field and experimental modeling data suggests that deflation is far more important in yardang development than previously realized. -from Authors
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Concentrates on recent articles concerned with eolian sand dunes and related phenomena. -K.Clayton
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A multidisciplinary group of sixteen scientists visited the southwestern desert of Egypt to verify interpretations of Earth-orbital photographs. The two-week journey started at Kharga Oasis and proceeded south-southwest to Bir Tarfawi, west to the Gilf Kebir plateau, and then to Gebel Uweinat, on the border between Egypt, Libya and Sudan. Members of the expedition discovered sites of prehistoric human settlements ranging in age from approximately 3000 to perhaps 200 000 years ago. The condition of plant remains in the Gilf Kebir area indicated a prolonged period of dryness of up to 20 years. However, a cloud mass observed on a weather satellite image in mid-December 1977 may have provided rainwater for numerous plants in the Uweinat region. The geological findings, including prospects for economic mineral deposits, were valuable. Fluvial and aeolian erosional patterns were studied at Gilf Kebir and also at Uweinat. Many of the desert landforms display similarities to those recently identified on Mars. Correlations of features in the Egyptian desert with those on the Martian surface will help us to a better understanding of surface processes on both Earth and Mars.
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Data from field studies and satellite photographs of the Western Desert of Egypt, which provides analogs of Martian wind-formed features, including sand dunes, alternating light and dark streaks, knob shadows and yardangs, are considered. Thoroughgoing sand of mostly fine to medium grain size is migrating southward in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing northerly winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. Attention is given to the streamlined yardangs carved in crystalline limestone that constitute one of the largest yardang fields on earth.
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Yardangs are streamlined erosional wind forms, similar in form to inverted boat hulls, that in terrestrial deserts range from meters to kilometers in length. On Mars the best examples are seen in the equatorial region. In the Amazonis region, hundreds of ridges and sawtooth-edged mesas have been wind sculptured in layered rocks. Individual ridges are tens of kilometers long with intervening valleys nearly 1 km wide. The wind-stripped surface seems to be relatively young and therefore must be easily erodible. Possible lithologies include ignimbrites, mudflows, or lithified regolith. Other wind-sculpted features occur in the Aeolis region, in Ares Valles, and in the Iapygia region. White Rock, a light-colored plateau inside a crater, is interpreted to be a yardang cluster eroded in a deposit inside the host crater. White Rock may be a jointed, wind-eroded pyroclastic deposit. Yardangs on Mars, especially when they are sculpted in young geologic units, demonstrate that much of the observed eolian erosion is recent. Yardang azimuths often are not parallel with wind streak directions, indicating that the yardangs were formed by different (older or weaker) winds from those that formed the streaks.
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Aeolian erosion develops through two principal processes: deflation (removal of loosened material and its transport as fine grains in atmospheric suspension) and abrasion (mechanical wear of coherent material). The relative significance of each of these processes appears to be a function of the properties of surface materials and the availability of abrasive particles. The landforms that result from aeolian erosion include ventifacts, ridge and swale systems, yardangs, desert depressions, and inverted relief.
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Potassium-rich feldspars separated from aeolian sands from the East and West Cronese Basin have been dated by infra-red stimulated luminescence. Sands from shoreline-reworked aeolian dune ridges in the West Cronese Basin suggest that Late Holocene playa lakes have existed in the basin within the last 2000 years. Four dates from these ridges suggest that a phase of aeolian deposition and stabilisation occurred 150–250 years ago. A date of 250 ± 75 years on a yardang formed from horizontally bedded sand, however, implies that at least a metre of erosion in the West Cronese Basin has occurred since that time, in response to a dominant southwesterly wind. Late Pleistocene dates ranging from 18,850 to 23,350 years were obtained from an aeolian unit in the East Cronese Basin giving limiting ages on wavecut shorelines formed in the deposit. This aeolian sand appears to have been deposited and stabilised at a similar time to part of the nearby Cat Dune sand ramp.
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The objectives of this study were to: 1) develop a global data base of aeolian features by searching Magellan coverage for possible time-variable wind streaks, 2) analyze the data base to characterize aeolian features and processes on Venus, 3) apply the analysis to assessments of wind patterns near the surface and for comparisons with atmospheric circulation models, 4) analyze shuttle radar data acquired for aeolian features on Earth to determine their radar characteristics, and 5) conduct geological mapping of two quadrangles. Wind, or aeolian, features are observed on Venus and aeolian processes play a role in modifying its surface. Analysis of features resulting from aeolian processes provides insight into characteristics of both the atmosphere and the surface. Wind related features identified on Venus include erosional landforms (yardangs), depositional dune fields, and features resulting from the interaction of the atmosphere and crater ejecta at the time of impact. The most abundant aeolian features are various wind streaks. Their discovery on Venus afforded the opportunity to learn about the interaction of the atmosphere and surface, both for the identification of sediments and in mapping near-surface winds.
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This article looks at the paleoclimatic record of winds recorded in the deposits of dust grains in the deep sea. Such grains are carried to the sea by the wind. The strength of the wind is indicated by the size of dust grains observed, larger grains requiring stronger winds to effect transport from arid regions. The number of the dust grains provides an indication of the aridity of land masses at the times in question. The record indicates that wind varies on the Milankovitch cycles of orbital variability, but also on time scales shorter than the 100kyr cycles associated with glaciation and aridity.
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Yardangs of different sizes were developed in the Payun Matru Volcanic Field, a semiarid area east of the southern Andes mountains. Yardangs from volcanic terrains have not been described previously from Earth, although studies from Mars interpreted linear ridges found by Mariner and Viking images as yardangs. The Payun Matru Volcanic Field is an extensive plateau at 2000 m a.s.l. covered by basaltic lava and ignimbrite flows. Strong westerly winds affect the extensive plateau. Micro- and mesoyardangs are formed on the ignimbrite rock blanket, and macroforms or megayardangs, several kilometres in length, are developed in the basaltic lava flows as long parallel troughs. They all have a distinctive 320° azimuth, which is the prevailing wind direction. No yardang features are noted in the more recent lava flows, younger than 1000 years, indicating that their formation needed a longer time or they developed in earlier periods with stronger winds. The yardang development is explained by the strong unidirectional winds, the poor vegetational cover due to the aridity of the region, the available quartz sand and volcanic ash particles as abrasive agents, and the volcanic lithology texture and flow structure. Copyright
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In Canyonlands National Park, south-east Utah, at least 29 partly exhumed, aligned sandstone ridges trending generally N20°W occur at the upper unconformable surface of the Lower Permian (Leonardian) White Rim Sandstone. The ridges are at least 1·5 km long, 250 m wide and have up to 14 m of vertical relief (mean of 9 m). A thin lag of coarse sandstone that contains wind-ripple laminae and granule ripples directly overlies the ridges. Angular blocks of sandstone within the lag and sand-filled fissures immediately below the lag, within the ridges, attest to early cementation of the ridge-forming material. SE-dipping aeolian cross-strata within the White Rim Sandstone and within the lag closely parallel the ridge trend. The ridges are interpreted as wind-sculpted desert landforms (yardangs) that developed on the lithified upper surface of the White Rim Sandstone during an extended period of hyperaridity towards the end of the Permian.
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With observational data spanning 1961–1999 from 90 meteorological stations in Xinjiang, China, the spatial and temporal characteristics of sandstorms and strong winds, and the contribution of strong winds to the occurrence of sandstormsare analyzed. Moreover, the dominant wind direction and minimumwind speeds during sandstorm periods are discussed. The research shows that although possessing similar climatic trends, sandstorms and strong winds in Xinjiang have opposite geographical distributions, i.e. places with more sandstorms show fewer strong winds. The contribution of strongwinds to sandstorms in northern Xinjiang is larger than that insouthern Xinjiang. The dominant wind directions clearly indicatethe paths of the weather systems that introduced the sandstorms.The minimum wind speeds in the sandstorms were over 10 ms-1in northern and eastern Xinjiang and in the Turpan and Yanqi Basins of southern Xinjiang. In Tarim Basin of southern Xinjiang,however, the minimum wind speed was about 6–8 ms-1, and even 6 ms-1 at its southern edge.
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Dakhla Oasis (25.5°N, 29°E) occupies a structurally localized depression at 90–140 m above sea level, ∼1200 km2 in area, below a 300 m escarpment bordering the Libyan Plateau, Western Desert of Egypt. Semi-arid intervals of the Quaternary period generated eight sedimentary formations, separated by erosion during hyper-arid intervals. Sediments comprise three generations of colluvial/fluvial fanglomerates, two generations of tabular spring-laid clastic and chemical sediments, two generations of mound springs and basinal sediments. of fluvio-lacustrine, evaporitic, pluvio-aeolian and aeolian origins. Discussion of these sediments is organized according to geomorphic region, from north to south, plateau, scarp and piedmont, lowland and cuesta plain.Chronological evidence is restricted to many radiocarbon dates of Holocene cultural material associated with playa sediments (9−4.5 ka), a isochron age of ∼62.0 ±7.6 ka for basinal evaporites, and two ages of ∼176 and ∼170 ka for a boulder of derived travertine. The regional Quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces. It is broadly similar to sequences earlier reconstructed in the topographically similar Kharga Oasis region 150 km to the east, and Kurkur Oasis, 400 km to the south-southeast. Speculations on chronology and driving mechanism are offered in conclusion.
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This paper presents results of a study of aeolian erosion at the landscape scale. There have been few such studies in desert geomorphology compared to those focused on individual landforms and on rock surface sculpture.The present study area lies in the southern part of the Libyan Desert in south-central Egypt, between 25° and 27°N, 29° and 30°E. Bedrock comprises Paleogene limestone of various lithologies. Climate is hyperarid.The following topics are treated.(i) Correspondences between rock outcrop belts and belts of terrain lineated by aeolian erosion and unlineated terrain.(ii) The effect of lithology on aeolian lineation, which works through the presence or absence of chert in the limestones. Lineation is produced by aeolian erosion in chert-free/poor rocks, whereas erosion of chert-rich rocks produces a desert pavement that armors the surface, suppressing erosion.(iii) The effect of large valleys eroded upwind of lineated terrain, which deflect winds and trap sand, ending erosion, so that downwind lineations are reduced and finally erased by weathering.(iv) Sample lineated landscapes in the area show stages of evolution, arranged in the time domain into a proposed cycle of aeolian erosion; the cycle progresses from initial smooth plain to grooves separating long, blade-shaped ridges, to segmentation of ridges into shorter blades along diagonal joints, to streamlining of shorter blades and size reduction, to final planation. In any one wind-parallel swath of lineated terrain, stages in the cycle progress downwind in the space domain, so that upwind landscapes are more advanced in the cycle.(v) The structure of air flow responsible for lineation is still uncertain, but initial grooving may respond to stable longitudinal horseshoe vortices, or self-organized regularity of erosion by random vortices; subsequently, the erosion pattern is fixed by evolving relief.(vi) Large, smooth basins within the lineated terrain were carved by aeolian erosion before Oxygen Isotope Stage (OIS) 5 (70–130 ka), as were similar basins along the Dakhla piedmont below the scarp; little geomorphic change has occurred since, so in this field of aeolian erosional lineations (AELs) the aeolian erosion cycle may have occupied 10 times as long. Since continental scale aridity set in at ca. 2.4 Ma, there have been only two cycles in this area. A completed cycle earlier than the current incomplete one is indicated by rare small yardangs riding ‘piggyback’ on larger ones.
Article
This work reveals the existence of yardangs in the central sector of the semiarid Ebro Depression of Spain. Almost all the documented yardang fields are located in extreme arid environments. The yardangs are developed in horizontal tertiary gypsum and limestone. More than 100 closed depressions (solution dolines) have been formed in the soluble sediments of this area, some of them hosting saline lakes or playas. All the yardangs occur on the leeward margin of the larger playas and their mean orientation (N122E) coincides with the prevalent direction of the strong local wind called Cierzo. Two main types of yardang have been identified; 44 rock yardangs formed in the Miocene bedrock and six yardangs developed in unconsolidated lacustrine deposits. Nebkha dunes have been recognized and yardang-like morphologies in building rubble accumulations on the floor of a playa (<100 years old). The generation of yardangs in this semiarid area is related to the presence of playas, which constitute the source of abrading particles during dry periods. At the present time, the yardangs developed in the lacustrine terraces, nebkhas and rubble accumulations are active landforms, whereas the rock yardangs are considered to be inactive.
Article
A comparative study of Martian and terrestrial dunes was made based on Viking Orbiter pictures and aerial pictures of terrestrial deserts. The morphological similarity between the Martian dunes and terrestrial crescentic dunes implies that the dynamics of dune formation are similar on the two planets, despite Martian constraints on dune formation that include much higher velocity winds required to move 'sand' in saltation, the possible inhibition of sand movement by absorbed water vapor, the seasonal 'snow' cover in the north circumpolar erg, and a probably sparse sand supply. The absence of longitudinal dunes and the restriction of massive crescentic dunes to a few sites on Mars suggests that Mars may have a long eolian history in which much of the sand suitable for saltation has already been transported to the north polar erg and crater floor fields.
An expedition to the Gilf Kebir and ‘Uweinat (1938)
  • Bagnold
Yardangs in South Dakota badlands
  • Baker
The Geomorphology of Egypt, Volume 1. Cairo, Egypt: The Egyptian Geographical Society
  • N S Embabi
  • N S Embabi
Yardangs of the Western Desert
  • M. J. Grolier
  • M. J. Grolier
Aolische sedimente und formen als indikatoren der spatpleistozanen bis aktuellen landschaftentwicklung beispiele aus den trockengebiete syriens
  • Rosner
Yardangs Geomorphology in arid regions
  • J F Mccauley
  • M F Grolier
  • C S Breed
  • J F Mccauley
  • M F Grolier
  • C S Breed
The landscape in aridity
  • Peel
Yardangs of Peru and other desert regions
  • J. F. McCauley
  • M. F. Grolier
  • C. S. Breed
  • J. F. McCauley
  • M. F. Grolier
  • C. S. Breed
Yardangs in South Dakota badlands An Egyptian oasis (Kharga) A comparison of general circulation model predic-tions to sand drift and dune orientations
  • C L Baker
  • H J L Beadnell
Baker, C. L. (1951). Yardangs in South Dakota badlands. Bulletin Geological Society of America 62, p. 1532. Beadnell, H. J. L. (1909). An Egyptian oasis (Kharga). London: John Murray. Blumberg, D. G., and Greeley, R. (1966). A comparison of general circulation model predic-tions to sand drift and dune orientations. Journal of Climate 9, pp. 3248 –3259.