Aeolian landscapes in arid regions are highly sensitive to global climate changes and play a critical role in Earth’s environmental systems through various feedback mechanisms. Their evolution, driven by multi-scale and multi-factor interactions, often involves complex processes such as multiple stable state transitions and self-organized criticality. This presentation focuses on the extensive deserts and dune fields in northern China, which provide a unique setting for investigating the evolution of wind-driven sedimentary systems and their responses to climatic fluctuations, including significant cooling or warming events over glacial-interglacial cycles.
Spanning multiple timescales, this presentation first reviews the long-term evolution of northern China's aeolian systems, from the late Cenozoic to the late Quaternary and the Last Glacial Maximum. Key findings reveal how dramatic temperature fluctuations and monsoon variations at tectonic and orbital scales have shaped aeolian activity and landscape stability. Special attention is given to the spatial heterogeneity and nonlinear responses of semi-arid dune systems since the Holocene, with a focus on the dune bistability phenomenon, where active and stabilized dunes coexist under similar conditions for millennia. By synthesizing remote sensing data, stratigraphic evidence, and numerical modeling, this study further identifies critical transitions in dune systems, highlighting their nonlinear behaviors and potential trajectories under future climate scenarios.
By integrating theoretical models, machine learning approaches, and field data, this interdisciplinary approach deepens understanding of the dynamic processes governing aeolian landscapes. The findings also provide valuable insights into the evolution and resilience of aeolian systems under changing environmental conditions, particularly in cold-climate and arid regions.
How to cite: Xu, Z.: Complex Processes and Nonlinear Evolution of Aeolian Landscapes in Response to Climate Change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4903, https://doi.org/10.5194/egusphere-egu25-4903, 2025.
Dunes and ripples are markers of eolian activity. Dunes arise and evolve from the action of wind blowing on sand grains and can thus provide information on past and current wind regime. They constantly adjust and adapt their shape through feedback between the bed topography and the near-surface air flow. This interaction modulates erosion of the stoss side and deposition on the lee side, and eventually results in the dune migration. Here, we present a workflow that quantitatively relates the rate of barchan dunes migration, which can be measured from remote sensing, to the wind velocity, either measured at a meteorological station or extracted from reanalysis data. We validate this workflow using data from Earth and apply it on Mars.
The workflow requires the selection of a sand transport law and the use of computational fluid dynamic (CFD) modeling. This modeling is used to estimate the effect of the local topography on the near surface airflow, namely the speed-up effect. We compare the dune migration rate predicted through the workflow to remote sensing observations, at two barchan dune fields located along the southern rim of the Arabia Gulf. After validating this workflow on Earth, we apply it to a barchan dune field on Mars. The dune migration is used to derive a wind speed distribution, averaged over one Martian year. Finally, we use ripple migration, that is much faster than dune migration, to derive the sub-annual variation of the wind speed.
How to cite: Daudon, C., Avouac, J.-P., Beyers, M., and Jackson, D.: Inferring wind speed from ripple and dune migration on Mars, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-748, https://doi.org/10.5194/egusphere-egu25-748, 2025.
Aeolian ripple patterns shape nearly every wind-exposed sand surface. Despite the different formation origins of megaripples, impact ripples and the newly discovered aerodynamic ripples on Earth [1], their disappearance under strong winds is conventionally blamed on the same mechanism, by the fluid-entrainment hypothesis. By revealing its shortcomings and inconsistencies, the need for an update of our understanding of ripple flattening is pointed out. Based on recently discovered grain-scale characteristics of aeolian sand transport [2], we propose a robust new hypothesis for impact ripple disappearance, which we call surface-melting hypothesis. It states that impact ripples cannot form when mid-air collisions play a substantial role in the transport process. Since the latter is correlated with a scaling crossover in the total mass-transport rate as a function of surface shear stress [2], the surface-melting hypothesis predicts an upper bound on the wind- strength regime that allows impact ripples to form. We will show that it stands up well to a comparison with original and literature data, does not suffer from conflicts and inconsistencies with the disappearance of other ripple types and thus allows for a coherent and profound understanding of the stability regimes of aeolian ripples in general. We present and discuss a tentative phase diagram of ripple existence in the parameter space of Shields-number and grain diameter which, in addition to summarizing our theoretical and experimental findings, predicts the disappearance of the recently introduced aerodynamic ripples in the aerodynamically rough regime, characterized by Re𝑝 ≳ 20.
[1] Yizhaq, H., Tholen, K., Saban, L. et al. Coevolving aerodynamic and impact ripples on Earth. Nat. Geosci. 17, 66–72 (2024).
[2] T. Pähtz and O. Durán. Unification of Aeolian and Fluvial Sediment Transport Rate from Granular Physics. Phys. Rev. Lett. 124, 168001 (2020).
How to cite: Rein, C., Tholen, K., Saban, L., Katra, I., Yizhaq, H., and Kroy, K.: Flattening of Aeolian Ripples, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16709, https://doi.org/10.5194/egusphere-egu25-16709, 2025.
During the Last Glacial Maximum (approximately 20,000 years BP), intensified mineral dust activity significantly impacted the Earth’s climate system and aerosol dynamics. While increased emissions from traditional dust sources are often cited as the primary cause of this intensification, direct evidence linking specific source regions to observed dust patterns remains limited. Ice core records from Greenland suggest an increase in East Asian dust storms. However, recent loess sedimentary records from Europe reveal substantial dust accumulation, aligning closely with the timing and intensity of the Greenland records.
Our study seeks to resolve long-standing uncertainties regarding the origins of European loess and its potential connection to Greenland dust deposits. By analyzing geochemical data from 16 European loess profiles along a longitudinal transect from Western France to Ukraine, we demonstrate that Europe was influenced by a remote dust source distinct from local deposits. Notably, elemental signatures in different grain size fractions trace this source to North Africa. Supporting this, atmospheric model simulations confirm an influx of African dust during the coldest phases of the glacial period, underscoring its far-reaching impact on northern latitudes.
This research provides a groundbreaking perspective on the atmospheric dust cycle during the Last Glacial Maximum, identifying—for the first time—a remote dust source active over Europe. Moreover, the findings suggest that this African dust may have reached northern high latitudes, including Greenland, as corroborated by Earth system model simulations. These results challenge the prevailing assumption that East Asian deserts were the dominant contributors to glacial dust, offering a fresh framework to reexamine aerosol-driven biogeochemical processes during this period. This study advances our understanding of the dust cycle’s complexity and its role in abrupt climate shifts during the Last Glacial Maximum.
Ref: Rousseau, D.-D. et al. (2025) A remote input of African dust to Last Glacial Europe, submitted.
How to cite: Rousseau, D.-D., Chauvel, C., Hopcroft, P., Gutiérrez, P., Saulnier-Copard, S., Antoine, P., Fuchs, M., and Ustrzycka, A.: A remote input of African dust to Last Glacial Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3549, https://doi.org/10.5194/egusphere-egu25-3549, 2025.
The morphological analysis of aeolian dunes from satellite and spacecraft imagery has traditionally relied on human expert interpreters. This approach has been often impeded by the need for manual input, which limits the breadth of scope, and could be sensitive to human bias [1-3]. In recent years, machine learning techniques have revolutionized the automatic analysis of images, particularly for the purpose of object detection [4, 5] – but require optimization (“training”) on large manually labeled datasets. In this study, we use an autoencoder, a convolutional neural network which learns from context – and does not require manual labels – to analyze the morphology of dunes in the north polar erg of Mars.
Like the better-known principal component analysis technique (PCA), an autoencoder synthesizes information through dimensionality reduction. By compressing input data and reconstructing it back from the compressed version, the autoencoder effectively extracts important features from non-linear data like images (similar to principal components of a linear PCA) without human guidance. In this study, we employ an autoencoder to analyze images of martian dunes obtained from the global mosaic processed from calibrated images obtained by the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) (5 m/px) [6]. After optimizing the model weights on 8000 images, we use the autoencoder to automatically classify dune morphology.
The compact representation of images of martian dunes in this principal component space shows clustering by dune morphology (Figure 1); not only by dune type, but also by varying morphology of the same type of dunes. Our synthesized data, which does not require discrete categorical classification (unlike, e.g., [7]) demonstrates the continuous transition between isolated barchan dunes and connected barchanoidal ridges. For example, our model identifies the higher density of barchanoidal ridges in Olympia Undae and near Escorial crater, which is in the convergence between Chasma Borelae and the circumpolar erg (red points), previously manually mapped [8].
In the meeting, we will present refined autonomous mapping and morphological analysis of dunes on Mars using a state-of-the-art Mask Autoencoder [9] and apply our model to satellite images of terrestrial dunes.
References:
[1] Bond et al., GSA (2007).
[2] Robbins et al., Icarus (2014).
[3] Bergen et al., Science (2019).
[4] Rubanenko et al., IEEE JSTARS (2021).
[5] Ali-Dib et al., Icarus (2020).
[6] Dickson et al., ESS (2024).
[7] Du Pont et al., ESR (2024).
[8] Hayward et al., Journal of Geophysical Research: Planets (2007).
[9] Kaiming et al., Proceedings of the IEEE/CVF conference on computer vision and pattern recognition (2022).
Plain-language Summary
We propose using machine learning, specifically autoencoders, to analyze the morphology of aeolian dunes on Mars in satellite imagery without manual labeling. By training the model on thousands of images, we automatically identified and grouped dune morphologies, revealing transitions like those between isolated barchan dunes and connected ridges. Key findings include clustering of specific dune types in regions like Olympia Undae and Escorial Crater. This method provides an efficient, unbiased approach to studying Martian and terrestrial dunes.
How to cite: Hayat, Y. and Rubanenko, L.: Automatic Classification of Aeolian Dunes on Mars Using an Autoencoder, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18934, https://doi.org/10.5194/egusphere-egu25-18934, 2025.
This study investigates the mechanisms of aeolian (wind) ripple formation through controlled experiments in the open-circuit boundary wind tunnel at Ben-Gurion University, focusing on how interactions between different grain sizes and wind velocities influence the development and evolution of impact and aerodynamic ripples.
We measured ripple morphology, including wavelength and sinuosity, using 3D scanning (EinScan Pro HD) and time-lapse photography, and analyzed the vertical sand flux, using an array of saltation traps. These measurements were conducted across various wind velocities (u* = 0.22-0.9 m/s) with glass beads and natural dune sands with median grain sizes of d50 = 90, 170, 230, 248, and 375 µm. We observed distinct differences in ripple formation patterns by systematically altering these parameters.
The results reveal distinct ripple regimes and transitions driven by grain size and wind velocity. For fine-grain sand beds, two ripple scales emerged: smaller (λ = 0.3-3 cm) linear impact ripples superimposed on the larger (λ = 5-55 cm) aerodynamic ripples. Increasing wind velocity led to the disappearance of impact ripples and transformed the aerodynamic ripples into more complex wavy patterns with higher sinuosity (SI = 1.28-1.74). These aerodynamic ripples share morphological similarities with current (subaqueous) ripples, particularly in terms of their increased sinuosity and development stages, supporting that their origin is due to hydrodynamic instability (Yizhaq et al., 2024). In comparison, coarser grains produced only one-scale regular impact ripple with lower sinuosity (SI ≈ 1), and their wavelength increased with wind velocity.
Sand flux measurements revealed a nonlinear relationship with wind velocity in agreement with Martin and Kok, 2017 formulation, demonstrated the critical influence of grain size on transport rates, and can offer insights into sediment transport mechanisms and existing sediment transport models.
By distinguishing between aerodynamic and impact regimes and spatiotemporal dynamics, we provide a fresh look at ripple formation in terrestrial and extraterrestrial environments, including the debated origins of the large Martian ripples.
How to cite: saban, L., katra, I., Durán, O., Rein, C., Kroy, K., and Yizhaq, H.: Aerodynamic and Impact ripple dynamics: The influence of grain size and wind velocity on morphology and sand flux., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10467, https://doi.org/10.5194/egusphere-egu25-10467, 2025.
Barchans are crescent-shaped sand dunes found in desert areas with little sand and a consistent seasonal wind direction. The characteristic parts at the tips of the leeward side of the barchan is called horns, from which sand flows out. Since barchans exist in groups, the expelled sand is supplied to the barchans located on the leeward side. Therefore, when considering the movement of barchans, it is important to consider the interaction between barchans due to such sand flow. In spite of this importance, there has been little research on the indirect interaction of sand between barchans. A previous research on the indirect interaction has used a cell model to calculate the movement of sand on each grid. According to the study, when the same amount of sand that flows out from a barchan is supplied to a point on the windward side away from the central axis, the apex of the barchan moves smoothly in a direction perpendicular to the wind direction while maintaining its shape and volume, at the same time as moving downwind. And it finally reaches the sand supply source [1]. However, the cell model just simulates the dynamics of barchans and further theoretical analysis of the mechanism of barchan movement is beyond the scope of the model. Therefore, in order to mathematically analyze the movement of barchans due to sand supply, the crest line model has been proposed[2]. The crest line model focuses on the cross section of the barchan and is a differential equation-based mathematical approach to dune dynamics using only two variables, the height h of the apex of the triangle of the cross section and the position x of it (Figure1). In the sense, the crest line model is a minimal model which enables us mathematical treatment of the dynamics of dune. This model has mainly been applied to analyze the shape stability of transverse dunes. As the first new aspect of this study, we have extended this model to the barchans with influx (Figure2). The research results can provide new insights into the mathematical solution of barchan migration due to sand supply and further understandings the dynamics of barchan collisions.
[1] A. Kastuki, et al., Simulation of barchan dynamics with inter-dune sand streams, New Journal of Physics (2011)
[2] L. Guignier, et al., Sand dunes as migrating strings, Physical Review E (2013)
How to cite: Navarro Yabe, S., Shiraishi, M., and Nishimori, H.: Sand influx effect on barchan dynamics using crest line model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12029, https://doi.org/10.5194/egusphere-egu25-12029, 2025.
Snow bedforms range in size from centimeters to kilometers and exhibit a variety of morphologies. They are critical in understanding the local surface energy balance as they modulate interactions between the snow or ice surface and the atmosphere, making them an important component of Earth’s croysphere. Despite their significance, especially given that snow covers more than 10% of Earth’s surface annually, snow bedforms have been the subject of relatively few studies, particularly in subarctic environments. Here we discuss the formation and evolution of snow bedforms using rectified coastal imagery collected in subarctic and arctic Alaska, USA. Visible images were captured during daylight hours (2018–present) in the communities of Golovin, Unalakleet, and Utqiagvik, Alaska, using two tower-mounted fixed cameras with overlapping fields of view at each location. We documented multiple formation events of ripples and transverse dunes on nearshore sea ice and their evolution to barchanoid bedforms, often at wind speeds lower than those previously presented in the literature. The length scales of these features increased with wind-event duration. In general, their migration rates were greater than those observed in other environments at equivalent wind speeds. In addition, the normalized widths of observed snow barchans were greater than snow and sand barchans reported in other studies. We present several case studies of creation, migration, and morphological evolution of snow bedforms, highlighting a variety of morphologies, and compare their characteristics to those found in other environments, such as Antarctica. In addition, snow sintering prolonged bedform lifespans, often enabling these features to persist in-place through multiple wind events, highlighting the key role of sintering in snow transport and bedform evolution.
How to cite: Nowacki, D. and Poizat, M.: Nearshore snow-bedform dynamics determined from imagery in the subarctic and arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14031, https://doi.org/10.5194/egusphere-egu25-14031, 2025.
Posters on site: Fri, 2 May, 10:45–12:30 | Hall X2
The shape, orientation, and spacing of sand ripples provide insights into local sand transport conditions. Consequently, mapping ripple patterns can enhance our understanding of wind regimes on Mars and Earth, especially in areas lacking local wind observations. However, manually mapping these ripple patterns is time-consuming and subjective, underscoring the need for automated methods to analyze large areas consistently. Our goal was to automatically quantify three types of ripple patterns—straight ripples, sinuous ripples, and complex textures—and to map their distribution over barchan dunes. We introduce two innovative and complementary methods for identifying these ripple patterns in high-resolution satellite imagery of Martian dunes. The efficacy of both approaches was assessed on 42 barchan dunes across 6 HiRISE sites.
The first method, a machine learning model known as U-Net, proved to be more reliable in classifying the ripple patterns, achieving 86% precision, 82% recall, and 82% F1-score for image tiles, as well as 82% precision, 77% recall, and 79% F1-score for complete dune mappings. The second method, a spatial autocorrelation analysis called the 2D semi-variogram, performed poorly in classifying ripple patterns over entire dunes, with precision reaching up to 56%, recall at 45%, and F1-score at 39%. However, it excelled in accurately measuring ripple spacing (R² = 0.78) and orientation (R² = 0.98). By combining the U-Net model's efficiency in ripple classification with the 2D semi-variogram’s precision in measuring spacing and orientation, we can conduct extensive analyses of ripples and local wind regimes across Mars. Furthermore, these methods hold potential for application in drone imagery of terrestrial dunes, paving the way for further research and exploration.
How to cite: Delobel, L., Moffat, D., and Baas, A.: Automatic Mapping and Characterising Of Ripple Patterns on Sand Dunes using U-Net and 2D Semi-Variogram., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6353, https://doi.org/10.5194/egusphere-egu25-6353, 2025.
Aeolian dunes are formed by the accumulation of wind-blown sand and its movement over time. While their shape may reflect wind directions during the period of formation, stratigraphic features in aeolian dunes record past climate and environments. In northern Fennoscandia, abundant dune fields serve as detailed records of Holocene arctic climate change. Specifically, buried soil and charcoal layers observed in mostly parabolic dunes preserve a rich history of past changes in climate, environment, fire history and land use. Understanding the evolution of the dunes in the face of these changes is crucial to project how Arctic environments respond to future climate change. Such studies require knowledge on the location, size, and shape of the aeolian sand dunes, which involves mapping them as polygon features. However, manual mapping of these landforms is very time-consuming. Semi-automatization can be used to develop a transferable, reproducible and scalable mapping approach, overcoming this issue.
Here we utilize a semi-automatic method involving machine learning models to map aeolian sand dunes in two study areas in northern Finland. While we rely on manual mapping based on a 2 m digital elevation model (DEM), its hillshade and Google satellite imagery for establishing a training dataset, segmentation and classification of sand dune objects is carried out using DEM derivatives such as slope, convergence index, general curvature, and topographic position index through support vector machines and random forest algorithms. We validate the training dataset and mapping results during field campaigns. Our semi-automatic object-based mapping method enables a mostly correct identification of dune objects, including attribute information on their size, shape, and morphological characteristics, compared to our field investigation. False positives occur at locations of great similarity between parabolic dunes and other topographic features. Future steps include reducing the false positives and transferring the approach to additional areas to ultimately develop a method for automated, regional-scale mapping of aeolian sand dunes in Arctic Fennoscandia.
How to cite: Campo, L., Hölbling, D., Stammler, M., Stevens, T., Abad, L., and Baykal, Y.: Semi-automated mapping of aeolian sand dunes: A case study from northern Finland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5666, https://doi.org/10.5194/egusphere-egu25-5666, 2025.
The postglacial landscape of Northern Fennoscandia is characterised by abundant depositional landforms, including eskers and aeolian sand dunes. Stratigraphic markers in sand dunes, such as buried soils or charcoal bands, record past environmental and climatic changes, preserving a history of landscape instability and sand movement caused by climate, fire, and land use changes. Although the shape and orientation of the dunes reflect the dominant wind direction during their formation, the mapping of aeolian sand dunes in Fennoscandia remains limited to a few studies and is generally not conducted at the polygon level. To systematically analyse the location, shape, and orientation of dunes over large areas, scalable and reproducible semi-automated mapping approaches based on remote sensing data are needed, with results validated in the field.
While analysing and interpreting digital elevation models, derived hillshades, satellite imagery, and aerial photographs, we observed features we referred to as ‘double-dune ridges’; dunes appearing in direct proximity to each other that mimic each other’s shape and orientation. Ground-truthing fieldwork showed that the ridges are unlikely to represent two separate, quasi-parallel dunes but rather the remnants of single dunes where the crests have been eroded and excavated. In their present form, these mostly parabolic dunes can be described by stable, vegetation-covered windward (stoss) and leeward (lee) sides, with open to low pioneer vegetation covering areas where the former crest once existed.
We discuss this example of dune degradation in Northern Fennoscandia and illustrate how an interdisciplinary approach can provide valuable insights into the dynamics involved. We strongly believe that integrating detailed mapping with chronostratigraphic, tree ring, and remote sensing data is essential for understanding the processes leading to the excavation of the former crest of dunes and, more broadly, to landscape evolution and degradation.
How to cite: Hölbling, D., Stammler, M., Stevens, T., Baykal, Y., and Campo, L.: What causes aeolian sand dunes in Northern Fennoscandia to lose their crests? From mapping and dating to process understanding, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11579, https://doi.org/10.5194/egusphere-egu25-11579, 2025.
Aeolian parabolic dunes in Arctic Fennoscandia are widely scattered across diverse biomes from tundra to mountain birch and pine forest, with many systems in more sparsely vegetated locations still showing signs of current degradation or partial activity. Dune stratigraphy reveals that these dunes have also undergone multiple phases of Holocene activity and reactivation, following initial dune formation immediately post deglaciation. Multiple buried soil, charcoal and homogenous dune sand layers demonstrate that dune stability is repeatedly interrupted by multiple fire events and dune reworking episodes during the Holocene. As such, these systems have great potential as archives of Arctic landscape, climate and fire history in a highly sensitive environment, and over a range of biomes.
However, few of these dunes, especially in Sweden, have been independently dated using modern luminescence and radiocarbon techniques in order to constrain the timing of phases of dune stability, fire activity and reworking. As such, there is limited understanding of whether fire frequency or landscape degradation episodes have changed over the Holocene, whether there are wider patterns in these events over Arctic Fennoscandia, and if so what the climatic or anthropogenic drivers of such changes may be. Luminescence dating of aeolian sands constrains the timing of dune sand movement (or rather the cessation of movement), allowing direct dating of reworking events, while radiocarbon dating of charcoal constrains the timing of fires that may have marked the end of periods of stability, and the initiation of dune degradation and reworking.
Here we address this by applying detailed quartz optical stimulated luminescence (OSL) and feldspar post infrared - infrared stimulated luminescence (pIR-IRSL) dating to cross bedded (initial dune form) and homogenous sand (reactivation layers) units in multiple dunes in Arctic Sweden and Finland over a diverse range of biomes. We also apply detailed AMS 14C dating to multiple charcoal fragments from charcoal bands exposed in the stratigraphy of these dunes, which often separate dune reactivation sand units. In this way, not only can we cross check multiple independent chronological techniques, but we can also construct detailed local dune development and reworking histories across a wide area of Arctic Europe. Combining these histories allows testing of potential wider climatic and human drivers for fire and landscape changes in Arctic Fennoscandia over the Holocene. Our results show that the choice of best luminescence dosimeter mineral varies substantially by location, and that scattered charcoal fragments exposed in dune sands are often reworked from previous fires. However, our detailed, multi-technique approach allows development of detailed fire and reactivation histories for these dunes, and reveals substantial differences in these histories across biome type and location. Despite these differences, some wider trends are also apparent, notably a substantial increase in fire and dune activity after the Holocene Optimum and in recent centuries. We discuss possible causes for these changes.
How to cite: Stevens, T., Yi, S., Wang, Y., Baykal, Y., Oehler, S., Stammler, M., Hölbling, D., Campo, L., Kaakinen, A., and Possnert, G.: Joint luminescence and radiocarbon dating of Holocene fire history and dune activity in Arctic Fennoscandia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9029, https://doi.org/10.5194/egusphere-egu25-9029, 2025.
The Otindag dune field, located on the Inner Mongolia Plateau and covers an area of approximately 52,000 km², ranks among the four largest dune fields in China. Located near the northern boundary of the East Asian monsoon, this region exhibits a cold temperate monsoon climate that transitions from semi-arid to arid conditions. The mean annual temperature ranges from 0 to 3 °C, while winter temperatures average approximately -18.3 °C, with an extreme minimum of -36.6 °C, reflecting the region’s significant seasonal thermal variation. In the southern Otindag dune field, nebkhas, a distinctive biogeomorphological aeolian landform created by the accumulation of sand around vegetation are distributed. The relatively thick sand layers within nebkha dunes are excellent sedimentary archives with great potential to capture past climate and environmental changes that occurred during the historical period and the Anthropocene. However, establishing a robust chronological framework for nebkha sediments remains a significant challenge due to limitations in existing dating methods.
In this study, we employed both luminescence and Cs-137 dating techniques to establish a chronology for nebkha sediments in the Otindag dune field. Luminescence dating results demonstrate that quartz luminescence signals from nebkhas are relatively strong and well-suited for age framework construction. The ages derived from the Central Age Model (CAM) and Minimum Age Model (MAM) are largely consistent, indicating effective bleaching of the quartz luminescence signals. Conversely, single-aliquot K-feldspar dating results exhibit a significant overestimation of ages. To address this discrepancy, we applied single-grain (SG) techniques in conjunction with the Minimum Age Model (MAM) to refine the dating of K-feldspar samples, yielding ages in agreement with quartz results. Cs-137 dating further validated the chronology, revealing that the primary development of nebkhas occurred within the past 100 years, which may be attributed to climate-driven or human-induced aridification in this region. Compared to other dune field regions in northern China, such as the Mu Us dune field, quartz from the Otindag dune field exhibits higher luminescence sensitivity, whereas K-feldspar signals display significant bleaching challenges. This study hypothesizes that regional variations in mineral luminescence properties may be attributed to differences in sediment provenance, which will be further investigated in future research. This study enhances the applicability of luminescence dating techniques for young nebkha sediments, providing a methodological framework for other nebkha fields across the globe.
How to cite: Yi, S., Wang, Y., Xu, Z., and Li, S.: Multi-method dating of typical nebkha sediments in the Otindag dune field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17100, https://doi.org/10.5194/egusphere-egu25-17100, 2025.
Aeolian processes on planetary surfaces are governed by atmospheric dynamics and surface properties, yielding similar landforms across a wide range of environments. On Earth, recent climate change, particularly the decline in near-surface wind speeds (terrestrial stilling) and variations in other climatic factors, has significantly influenced aeolian landscapes. In the inland deserts of Central and East Asia, these changes have led to reduced dune migration, dune stabilization and transformation, fewer dust storms, and increased vegetation recovery in the drylands.
This study investigates the coupled effects of wind speed reduction and vegetation restoration on the mobility and stability of sand dunes in northern China, located at the junction of the Gobi, Badain Jaran, and Tengger deserts. Vegetation changes were assessed using multiple NDVI time series, which revealed a general increase in vegetation across the study area, despite notable spatial heterogeneity. This greening trend is primarily driven by wetter, warmer, and less windy climatic conditions during the past few decades, further amplified by large-scale ecological restoration programs. While vegetation expansion has not fully stabilized the dunes in most areas, it has contributed to reduced migration rates and altered dune morphology.
In extreme arid zones with negligible vegetation growth over the past decades, dune migration rates were analyzed using Landsat satellite imagery (1986–2021) and the COSI-Corr procedure, constructing a 35-year time series across multiple sites. The results demonstrate a consistent decline in dune migration rates, aligning with the trend of terrestrial stilling. This suggests that recent adjustments in atmospheric circulation under global climate change have significantly slowed dune migration. Model calculations further reveal reduced sand flux under declining wind speeds, consistent with the cubic relationship between wind speed and sand transport, validating theoretical sand transport laws at larger spatial scales.
These findings underscore the critical role of atmospheric circulation in shaping aeolian landforms and emphasize the combined effects of climate change and human activities in stabilizing sand dunes. By integrating these terrestrial insights into planetary aeolian research, this study offers valuable analogues for understanding dune dynamics under varying atmospheric conditions across planetary surfaces.
How to cite: Wang, L. and Xu, Z.: Dune Slowdown and Stabilization in Inland Deserts of East Asia: The Role of Wind Stilling and Vegetation Recovery over Four Decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6569, https://doi.org/10.5194/egusphere-egu25-6569, 2025.
Wind erosion is a major driver shaping landscape patterns in drylands. Vegetation is known to provide protection from wind erosion by sheltering the ground surface, extracting wind momentum, and trapping sediment. Significant progress has been made in parameterizing the protective effect of vegetation elements as a function of vegetation cover for wind erosion model development. However, the influence of single vegetation elements on shear stress patterns at the surface in two dimensions, particularly in the spanwise direction where increases in surface shear stress and subsequent soil erosion have commonly been observed, has not been included in drag partition schemes to date. Studies on wind speed around a shrub (or other obstacles) in the spanwise direction underscore the potential role of vegetation in intensifying erosion issues, e.g., dust emissions, desertification and challenges in land management. Here, we quantify wind erosivity patterns around a single shrub within a semi-arid rangeland environment for a range of wind velocity and plant phenology. Field data were collected 2/7/2023-7/19/2023 and 2/12/2024-6/20/2024 at the National Wind Erosion Research Network site at the USDA Jornada Experimental Range in south-central New Mexico, USA. A total of 18 Irwin sensors were installed around a honey mesquite shrub (Prosopis glandulosa Torr.), mainly perpendicular to the dominant wind direction, to quantify surface shear velocity (u*s, m/s). A sonic anemometer, installed at 1 m above the surface 3 m upwind of the shrub measured turbulent shear velocity (u*, m/s). We use the shear stress ratio (SSR= u*s/u*) to delineate and quantify shelter and acceleration zones around the shrub. Our objectives were to: 1) compare the spatial patterns of erosivity; 2) examine the shelter and acceleration effects around the shrub at different wind speeds; and 3) examine the plant phenological influence on shelter and acceleration effects around the shrub. Results show that the shrub's impact on erosivity patterns varied depending on its phenological phase. On average, the largest SSR, approximately 1.5 times greater than that at the upwind location, occurred during the dormant and green-up phases, at a spanwise distance of 2 meters (about twice the shrub height) from the shrub center. The smallest SSR, about 39% of that at the upwind location, occurred closest to the shrub during the green-up phase in the spanwise direction and during the leaf-on phase at the downwind location. In the dormant phase, the shape of the shelter zones became more streamlined as wind speed increased. In the green-up phase, the size of the shelter area increased with wind speed, reaching its maximum extent. In the leaf on phase, the acceleration zone expanded as wind speed increased. Our results suggest that incorporating the 2-D surface shear velocity impacts around vegetation, i.e., including both acceleration and shelter effects, is needed to increase the accuracy of wind erosion models in vegetated dryland ecosystems.
How to cite: Zhang, P., Edwards, B., Webb, N., Gillies, J. (., Trautz, A., Nikolich, G., Ziegler, N., Okin, G., Van Zee, J., and Wheeler, B.: The impact of a single shrub on the distribution of surface shear velocity in a semi-arid rangeland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13657, https://doi.org/10.5194/egusphere-egu25-13657, 2025.
The relationships between aeolian sediments in dune fields and adjacent sedimentary environments are critical for understanding arid landscapes. They provide valuable proxies for paleoclimatic reconstructions, as shown in various desert regions worldwide. Studies have highlighted how aeolian environments modulate sediment transport in fluvial systems, acting as buffers (e.g., East et al., 2015), an essential consideration for comprehensive source-to-sink sediment budgets. While research has primarily focused on fluvial-aeolian interactions, studies on alluvial fan-aeolian interactions are limited. Alluvial fans, when not bypassed, are excellent sedimentary archives for reconstructing paleoclimates in arid regions. It is known that increased aridity tends to expand aeolian coverage over fan surfaces, whereas increased runoff activity restricts aeolian environments to distal fan areas, which then serve as sediment sources for sand dune fields. However, there is a gap in understanding how fans and aeolian sediments interact when both operate simultaneously, independent of climatic variability. To address this, we studied alluvial fans in the Atacama Desert, where prolonged aridity provides a natural laboratory to explore interactions between aeolian and alluvial fan processes, with exceptional preservation of surface morphologies. Rare episodic storms generate runoff that transports sediments from catchments to alluvial fans, which may be partially or fully covered by aeolian sands. The selected fans exhibit debris flow lobes across all fan segments, not just at the apex.
Our study investigates how fan morphology (e.g., roughness and relief) (Cook and Pelletier, 2007) controls saltation transport processes and pathways, and examines the interactions between dune formation and debris flow lobes. By analyzing surface grain size and topography and leveraging Synthetic Aperture Radar (SAR) backscatter intensity data from C and L Bands, calibrated with field grain size distributions and laboratory analyses, we automated the mapping of fan sediment cover. Our findings reveal that aeolian covers, including barchan dunes, do not prevent debris flows from reaching mid and distal fan areas on fans with gradients of ~10°. This contrasts with observations from the southwestern US fans, where star dunes can obstruct debris flow pathways (Anderson and Anderson, 1990). The interactions we have identified are relevant for improving debris flow runout modelling, interpreting past fan sedimentary arrangements, and understanding fan evolution and sediment fluxes in arid environments. These insights have broader implications for the evolution of arid landscapes, sheeding light on the dynamic interplay between aeolian and alluvial fan processes.
How to cite: Cabré, A., Mather, A., Bufe, A., and Lang, A.: Interactions between aeolian dune fields and debris flows in alluvial fans., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13192, https://doi.org/10.5194/egusphere-egu25-13192, 2025.
In the Alxa Plateau of China, there is a narrow sand belt composed of sparse barchan dunes between Badain Jaran Desert and Ulan Buhe Desert. However, the dynamics of sand dunes and the age of formation of the sand belt are still unclear, and it is even thought that this sand belt is the result of recent desertification. Based on the regional meteorological observation data of the past 20 years, we analyzed the rate and direction of dune migration and morphological changes of sand dunes. The results show that the movement and morphological changes of sand dunes in this sand belt have obvious spatio-temporal variation due to topography, wind conditions and the shape and size of sand dunes. The dune migration rate ranged from 2.09 to 40.93 m·a-1, and the direction was 102°~152°. Under the influence of terrain, the dune migration rate in the piedmont area is higher than that in the high plain area. Over time, the sand movement rate in each region decreased, and the direction tended to be northward in the high plain, and southward in the foothill; Most of dunes in the belt are slim and normal in shape, with only a few being short-fat and fat. However, there are differences in the dune morphology parameters in each region, with the main area of the high plain sand transport belt generally having larger parameters than other areas. In the process of dune movement, the dune circumference and area on the north and south sides of the high plain sand transport belt fluctuated slightly, while the main area and the foothill belt tended to increase. The length of the dune and their windward slope increased to different degrees, the height decreased, and the southern wing prolonged obviously. The external environment and its own morphology jointly affected the change of dune morphology. Considering the width of the sand transport belt and the proportion of dunes, the sand transport flux calculated in the high plain area reached 138.04 t·m-1·a-1, and the foothill zone was 95.20 t·m-1·a-1, which provided an estimate that the Badain Jaran Desert contributed nearly 773,800 tons of sand to the Yamaleike Desert annually through sand transport, and nearly 550,000 tons of sand contributed to the Ulan Buh Desert through the pedimont zone.
How to cite: Hasi, E. and Wu, Y.: Dynamics of Barchan dune in the sand belt between Badain Jaran and Ulan Buh Desert, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4811, https://doi.org/10.5194/egusphere-egu25-4811, 2025.
Emergence and growth of sand dunes result from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. At night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis.
For the given dune orientation and measured wind regime, we link the observed wind deviation to the daily cycle of the turbulent atmospheric boundary layer. At night, a shallow boundary layer induces flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern.
Published article: Gadal, C., Delorme, P., Narteau, C., Wiggs, G. F., Baddock, M., Nield, J. M., & Claudin, P. (2022). Local wind regime induced by giant linear dunes: comparison of ERA5-land reanalysis with surface measurements. Boundary-Layer Meteorology, 185(3), 309-332.
How to cite: Gadal, C., Delorme, P., Narteau, C., Wiggs, G. F. S., Baddock, M., M. Nield, J., and Claudin, P.: Local wind regime induced by giant linear dunes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6096, https://doi.org/10.5194/egusphere-egu25-6096, 2025.
The transport of sand by wind has been the subject of extensive research. Despite numerous efforts, however, substantial discrepancies persist among theoretical models, wind tunnel experiments, and field observations concerning the magnitude of the critical threshold necessary to induce sand movement over heterogeneous surfaces.
In this study, we conducted field experiments to quantify surface shear velocities and wind velocities across seven heterogeneous surfaces characterized by a broad range of grain sizes. Surface shear velocities were measured using flush-mounted Irwin sensors (IS), while wind velocities were measured using a thermal anemometer (TA) positioned 30 mm above the surface and a 3-D ultrasonic anemometer (UA) 0.6 m above the surface. A high-resolution video camera monitored the surface to document sand motion. IS and TA sensors were emplaced within the view field of the camera. Reptating sand grains were captured using adhesive-coated plastic sticks. A total of 46, quality-controlled, threshold event data sets were acquired from the IS and TA measurements and 39 from the UA measurements.
For each event, surface shear velocities and wind velocities were block-averaged at 1-second intervals. Maximum and minimum values of shear (IS) and wind velocities (TA) were determined for each threshold event. Maxima are defined as the fastest shear and wind velocities without sand movement in the 5 seconds before an event, and minima are defined as the slowest velocities with movement in the 10 seconds before an event. Shear velocities in the constant stress layer (UA) were estimated with 2 minute-averaged Reynolds stress derivations. Median grain sizes for each event were estimated via photosieving. This approach enabled the estimation of threshold conditions corresponding to specific grain sizes, bracketed by their respective maximum and minimum values.
Our results from surface and near-surface data indicate no statistically-significant relationship between threshold shear or wind velocities and median grain sizes ranging from 131 to 475 µm. The mean of the maximum and minimum surface shear velocities for the 1-second block averages is 0.17 m/s (standard deviation, 0.02 m/s). The respective wind velocity threshold is 5.28 m/s (standard deviation, 1.64 m/s). Testing longer averaging intervals (1.5, 2, and 3 seconds) yielded consistent results, with a reduction in the differences between maximum and minimum values as the interval increased, but yielding no significant relationships. The shear velocity estimates from the ultrasonic anemometer data indicate a statistically significant, Bagnold-type relationship for the threshold, but with an “A” coefficient of 0.14 (standard deviation, 0.05) for the fluid threshold.
These findings support the concept of equal mobility, whereby a single threshold shear or wind velocity can initiate sand motion for a range of grain sizes on heterogeneous surfaces. The findings also indicate a decoupling of threshold conditions as measured at or near the surface and those as measured typically in the constant stress layer.
How to cite: Bae, J. and Sherman, D. J.: Field Estimates of Thresholds for Aeolian Sand Transport, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13976, https://doi.org/10.5194/egusphere-egu25-13976, 2025.
Previously, studies of barchans in Algeria have been limited to those close to In-Salah in the centre of the country and Mali has been entirely overlooked. This is primarily because the aeolian bedforms in these countries are predominantly linear dunes. However, 150-250km N-NE of Taoudenni, Mali one can find a number of barchans and megabarchans which straddle the Mali-Algeria border. To our knowledge, these dunes have not previously been studied. The widths of the dunes range from around 30m for the smallest barchans to 1.6km for the largest megabarchan, allowing us to test the robustness of scaling laws typically applied to barchans and the similarity between barchans and megabarchans. In this poster, we present preliminary analyses of the morphology and migration rates of the dunes measured using Google Earth imagery.
How to cite: Robson, D. and Baas, A.: Morphology and Migration of Megabarchans on the Mali-Algeria Border, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19261, https://doi.org/10.5194/egusphere-egu25-19261, 2025.
In this study, we analyze the surface aeolian record around the Coprates rise region, an extensive area that includes Thaumasia and Bosporos Planae as well as the western Noachis Terra lowlands. The main goals are: a) to test the systematic mapping of aeolian bedforms (PBRs, TARs, and/or paleo-megaripples ) at medium resolutions using CTX mosaics and the techniques introduced by Vaz et al. ( 2023); b) to evaluate the spatial distribution of aeolian bedforms and identify different populations in this large area; c) to use GCM predictions and state-of-the-art bedform formation models to test how well the mapped features fit the predicted current-day surface aeolian dynamics.
The automated methodology accurately maps various sets of linear and periodic bedforms. We estimate that about 50% of the mapped bedforms are associated with or controlled by local topography, showing clear spatial associations with specific topographic settings: craters, incised valleys, grabens and wrinkle ridges. These were excluded from a comparative analysis with the GCM-derived predictions.
We identified eight sets of bedforms with very different characteristics (e.g. trends, wavelength, morphologies, and preservation state). We found significant disparities between the mapped bedform trends and the GCM-based predictions, suggesting that most of the mapped sets are incompatible with current surface aeolian dynamics, as predicted from the GCM outputs.
References
Vaz, D. A., Silvestro, S., Chojnacki, M., & Silva, D. C. A. (2023). Constraining the mechanisms of aeolian bedform formation on Mars through a global morphometric survey. Earth and Planetary Science Letters, 614, 118196. https://doi.org/10.1016/j.epsl.2023.118196
How to cite: Vaz, D. A., Cardoso, R., Torres, I., Bahia, R. S., Bohacek, E., and Silvestro, S.: Large-scale systematic mapping of paleo-bedforms in the Thaumasia Planum – western Noachis Terra region, Mars, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13879, https://doi.org/10.5194/egusphere-egu25-13879, 2025.
The ESA ExoMars mission will land at Oxia Planum to search for signs of life on Mars [1, 2]. In this study, we compare automated and manual mapping of aeolian features in CTX (6 m/pixel), CaSSIS (5 m/pixel), and HiRISE (25 cm/pixel) images in the landing site with potential sand fluxes from the NASA Ames GCM. Bright-toned wind streaks (n = 85) were manually mapped and were formed by winds originating from the NNW–NNE, the return flows of the Hadley cell circulation. A few dark-toned streaks (n = 2), formed by winds from the E–ESE, were also identified. Bright bedforms (trasverse aeolian ridges [TARs]) were automatically mapped. They are widespread [3, 4] and exhibit dark banding on their SE-facing slopes [4] which might be caused by aeolian sorting of loose sands with varying granulometry and/or composition. Ridges (periodic bedrock ridges [PBRs]) were automatically mapped as well. Together with the PBRs we identified a potentially new class of WNW–ESE-oriented cratered ridges (“ridges 2”). These features, located inside degraded impact craters, display Y-junctions and may be locally covered by boulders from nearby impacts [4]. However, unlike PBRs, they do not appear to be directly carved into the underlying bedrock. The orientations of wind streaks in the study area suggest at least two wind regimes at play. Interestingly, a bimodal sand flux direction is also predicted by the GCM, with one mode (~172°–188°) closely matching the observed bright-toned wind streak orientations. Bright bedforms (TARs) are likely relict features shaped by past wind conditions [3-5]. This is supported by the GCM-predicted bedform orientation, which does not align with either the observed TARs’ orientation or that of the older periodic bedrock ridges (PBRs) [3-5]. The newly identified “ridge 2” class of landform has previously been interpreted as precursor bedforms that initiated the formation of the underlying PBRs [4]. However, the ridge 2 class can be found even on a flat bedrock surface not in association with PBRs. This observation suggests that these features may represent a later episode of aeolian deposition or erosion, occurring after the formation of the PBRs [4]. The morphology of the “ridge 2” class varies across the study area, with some ridges appearing subdued and eroded. A ghost-dune pit origin [6] or an erosional-scarf/bedform assemblage, similar to observations at Meridiani Planum [7], cannot be ruled out.
Detailed examination of the relationships among ridges, PBRs, and TARs by the ESA Rosalind Franklin rover will be crucial for advancing our understanding of PBR formation mechanisms, the winds responsible for shaping TARs, and broader Martian climatic changes.
[1] Vago J. et al. (2017). Astrobiology, 17. [2] Quantin et al. (2021), Astrobiology, 21. [3] Silvestro S. et al. (2021), GRL, 48. [4] Favaro E. et al. (2021), JGR, 126. [5] Favaro E. et al. (2024), EPSL, 626. [6] Day M.D. & Catling D.C. (2018), JGR, 123. [7] Fenton L.K. et al. (2018), JGR, 123, 1–15.
How to cite: Silvestro, S., Vaz, D. A., Grasso, F. M., Fenton, L., Cardoso, R., Pacifici, A., Tirsch, D., Favaro, E., Tao, Y., Salese, F., Franzese, G., Popa, C., Mongelluzzo, G., Porto, C., Pajola, M., Rizza, U., and Esposito, F.: Aeolian Landforms in the EXOMARS 2028 Landing Site in Oxia Planum (Mars), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15981, https://doi.org/10.5194/egusphere-egu25-15981, 2025.
