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Geomorphological evidence of catastrophic glacial floods has been discovered in many formerly glaciated areas of North America, in the mountains of Siberia and Central Asia, and in northern Europe. Within the area of the last Scandinavian Ice Sheet in the European Lowland a wide range of landforms related to glacial meltwater flows have been documented but no unequivocal evidence of cataclysmic glacial outburst floods exist. Here we discuss a landform signature of Late Weichselian glacial megafloods in the Suwałki Lakeland, north-eastern Poland. These landforms are oversized ice-marginal spillways, scabland-like features, expansion bars, megadunes, obstacle marks, and clusters of kettle holes. This unique glacial landscape was probably generated by at least two separate glacial megafloods (the older event ca 19 ka ago and the younger event shortly after ca 16 ka ago). Palaeohydraulic calculations based on the morphometric characteristics of the flood landforms suggest that one of those megafloods had water depth of at least 19 m and flow velocity of around 15–17 ms−1. The flood flow regime was from subcritical to supercritical. The calculated maximum flood discharge range was between 0.5 × 106 and 2.2 × 106 m3s−1 with the most likely value of around 2 × 106 m3s−1. These numbers place this megaflood among the largest glacial megafloods worldwide, with a possible impact on global climate through rapid release of large volumes of freshwater into the Atlantic Ocean following a transfer across the European Lowland through prominent ice-marginal meltwater spillways. [ABSTRACT FROM AUTHOR]

Abstract The Utracán paleo-dune field (La Pampa Province, Argentina, southern South America) was examined by remote sensing, morphometric analyses and field surveys as a case study of complex megadunes of inland deserts. The paleo-dune field is within the Utracán-Argentino valley, one of the transverse valleys of La Pampa Province excavated into a regional structural plain. Similar paleo-dune fields occur within these valleys. Utracán dunes are mostly stabilized by grasses, deeply disturbed by cattle grazing and agriculture. The paleo-dune field is formed by complex parabolic megadunes with superimposed dunes. Parabolic megadunes present lengths of trailing arms of 3.3–12.9 km, widths between them of 2–2.9 km and heights of 7–38 m. The position of the dune noses at the northeastern tip of the bedform and measured SW-NE orientation of arms indicate a mean transport direction to azimuth 68.2°. Above the parabolic arms, and isolated in the paleo-dune field, there are compound blowout dunes (clusters of several blowouts forming a larger bedform). They show the depositional lobes to the NE, with a measured mean transport direction to azimuth 58.1°. The SW-NE longitudinal length varies between 324 and 1302 m and the NW-SE transverse length between 114 and 622 m. Other parabolic arms show low (<3 m) barchanoid dunes, with crest lengths of 48–811 m, a mean crest spacing of 74 m and a transport direction to azimuth 28.2°. The paleo-dune field also shows smaller, simple parabolic and blowout dunes. We hypothesize that the parabolic and blowout dunes are the basic bedforms that emerged under the boundary conditions of the Utracán dune field, related to a high sediment supply coupled with a partial vegetation cover, in a valley that provided accommodation space by means of well-defined depression and wind deceleration due to a change in the longitudinal valley slope direction. The west-to-east spatial progression of dune morphologies along the Utracán-Argentino valley, the general transport direction of dunes to the NE, and the petrographic sand composition allow us the infer that the transverse valleys of La Pampa Province worked as sand transport pathways. These pathways transferred fine to very fine sand from the eastern Andean piedmont to the Pampean plain, likely during the Quaternary. Graphical abstract Unlabelled Image Highlights • Complex parabolic megadunes develop in inland deserts. • Complex parabolic megadunes show superimposed compound blowout dunes and barchanoid dunes. • Megadunes respond to a partially vegetated sandy landscape with high sand supply. • Transverse valleys of southwestern Pampas work as aeolian sand transport pathways. [ABSTRACT FROM AUTHOR]

Giant aeolian sand dunes, over 100 m high, occur in the major deserts on Earth, and they can provide valuable insights into past wind regimes and climatic conditions in desert areas. However, the formation and evolution of these megadunes remains poorly understood. The highest aeolian sand dunes on Earth are in the Badain Jaran Desert (BJD) in northwestern China, where hundreds of giant transverse dunes are at least 200–300 m high, with some as high as ∼500 m. We present sedimentary records from eight cores from five megadunes (200–400 m in height), including a 320-m drill core from a ∼ 430-m-high megadune in the centre of this desert, which is the first detailed investigation of Earth's tallest sand dune. The results of high-resolution optical dating show that these huge transversal dunes migrated downwind, with the dune migration taking some tens of thousands years to complete a single cycle of turnover. We present a model for the migration of the largest free-standing aeolian landform, which demonstrates that the formation and migration of megadunes is closely linked to global climate change. Although there was negligible dune migration during warm and humid interglacial periods, the dunes were still able to rapidly accrete vertically. The migration of these dunes occurred during the coldest and driest periods (e.g., Marine Isotope Stages 4 and 2), at the rate of a few centimeters per year, highlighting the slow net downwind transport of dunes in the Badain Jaran Desert. Our results highlight the role of global climate change over the last glacial cycle in the formation and migration of megadunes. • The largest dune on Earth is composed entirely of undifferentiated aeolian sand. • Optical dating demonstrates that mega transversal dunes recycling at 30–100 ka. • Megadunes migrated slowly but accumulated higher in warm/humid interglacial periods. • Megadunes migrated quickly during the cold/dry periods during the glacial cycle. [ABSTRACT FROM AUTHOR]

Complex interactions between katabatic winds and the cryosphere may lead to the formation of sedimentation waves at the surface of ice sheets. These have been first described and named snow megadunes in Antarctica. Here we use topographic data, optical images, subsurface radar soundings and spectroscopic data acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves have similarities with Antarctic snow megadunes regarding their surface morphology, texture, grain size asymmetry, and internal stratigraphic architecture. Both sets of Martian sedimentation waves present young ice and occasional sastrugi fields, indicative of net accumulation, on their shallow-dipping upwind sides, their tops and the intervening troughs. Old layers of dusty ice, indicative of net ablation, are exhumed on the steep-dipping downwind sides of the larger waves. Smooth surfaces of coarse-grained ice, indicative of reduced accumulation associated with sublimation metamorphism, cover the steep-dipping downwind sides of the smaller waves. These surface characteristics and the internal stratigraphy revealed by radar soundings are consistent with the interpretation that both sets of Martian sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. The recognition of these sedimentation waves provides the basis for the development of a common model of ice/wind interaction at the surface of Martian and terrestrial glaciers. Martian smaller waves, characterized by reduced net accumulation on their downwind sides, are analogous to Antarctic snow megadunes that have been described so far. A terrestrial equivalent remains to be discovered for the larger Martian waves, characterized by net ablation on their downwind sides. [ABSTRACT FROM AUTHOR]

Abstract: Laser altimetry from satellites such as ICESat provides high-resolution data for remote parts of the Earth, such as Antarctica and Greenland. Due to the large amount of data that must be processed to determine multi-temporal height variations, algorithm optimization is crucial. Modelling satellite tracks as great circle arcs on a sphere allows the application of vector algebra and spherical trigonometry in searching crossovers and near-shots for height variation analysis. Two programs written in Fortran 90/95 are presented: the former reads and filters ICESat data from input GLA12 binary files, while the latter implements the search for multi-temporal height variations. The analysis of inter-annual height variations in a megadune field of East Antarctica shows decimetre-scale changes possibly related to wind-driven accumulation and erosion processes. [Copyright &y& Elsevier]

Abstract Field observations demonstrate that calc-sinters occurred in the lakes of Badain Jaran Desert. 87Sr/86Sr ratios, 14C, δ13C and mineral compositions of calc-sinters, and ³He/4He, 4He/20Ne, δ18O, δD, pH and TDS of water from springs and lakes are analyzed in detail. The results indicate that the lake water is supplied through deep fault zone. The "kernel" of stabilized dunes in the Badain Jaran Desert perhaps consists of calc-sinters and calcareous cementation layers. Deep-seated groundwater effuses from this "kernel" and recharges to lakes in desert. Precipitation and snowmelt water from the Qinghai-Tibet Plateau is fed into the Badain Jaran Desert, Gurinai, Wentougaole and Ejinqi areas through the Xigaze-Langshan Fault zone. The isotopic compositions of groundwater in the Alax Plateau are abnormal due to the strong evaporation of the Gyaring and Ngoring lake water in the headstream of the Yellow River. Groundwater dissolves dissoluble fractions of rocks during its transportation through the fault zone and flows out of the mouth of spring in the Badan Jaran Desert. The dissoluble fractions are finally developed into calc-sinters and calcareous cementation layers around the spring. Calci-sinters are gradually largened and eventually emerge on the surface of lake water. Eolian sands accumulate on the surfaces of calc-sinters and calcareous cementation layers, and eventually develop into dunes. Invasion of magma causes an increase in the temperature of groundwater within the faults. Groundwater evaporation provides water vapor for the formation of humid stabilized dunes during its upwelling. Rhizoconcretions found in Yihejigede indicate that the dune was formed and remained immovable 4700 years ago. The height of the megadunes is proportional to thermal quantity carried by the groundwater. [ABSTRACT FROM AUTHOR]

The Badain Jaran Desert features the highest megadunes on Earth, and a unique megadune-lake alternation landscape. Based on field survey and interpretation of aerial photographs, this paper examines the general characteristics of the Badain Jaran megadunes, their morphometry and formation, as well as the formation of megadune-lake alternation landscape. It is suggested that the megadunes in the Badain Jaran Desert were developed in a low wind energy environment. The compound transverse megadunes, the dominant megadune type, have a similar wind regime to barchanoid dunes, and the compound star megadunes, which occur near the mountains, have a similar wind regime to star dunes. Similar to the barchanoid dunes, the height, base area and spacing of the compound transverse megadunes show reasonably good inter-correlation. The base area of the megadunes and the area of the leeward interdune lake basins are also inter-correlated. The alignment and spacing of the Badain Jaran megadunes implies that wind is the most important factor in their development; the morphology underneath the megadunes does not determine the general pattern of the megadunes as previously suggested. Repetitions of dune fixation and reactivation in the development process played an important role in increasing the megadunes'' height, hence their size. The interdune lakes in the megadune area were mainly formed by talus springs and are only partly fed by atmospheric precipitation. [Copyright &y& Elsevier]

Cenozoic tectono-geomorphic growth processes of the Yabrai Fault (YBF) along Yabrai Mountain (YM) and their impacts on the landscape formation of Badain Jaran Desert (BJD) during the late Quaternary are still unsolved, and yet are crucial to exploring the tectonic evolution of the boundary between the northeastern Tibetan Plateau and southern Gobi Alxa block. This study addresses these issues using information extraction-based interpretations of multiple satellite images coupled with field observations. The 138 km-long NE-NEE striking YBF can be divided into 3 segments: southwestern, central, and northeastern segments all characterized by left-lateral faulting with normal faulting components. Apatite (U-Th)/He thermochronology and calcite (U-Th) dating integrated with regional tectonic evolution history provides new geochronological evidence for understanding the multi-stage evolution of the YM and YBF. (1) Before the late Cretaceous (135–72 Ma), the mountain experienced rapid cooling and uplift. (2) During the late Cretaceous to Eocene (ca. 70–33.9), the YM is likely to have experienced denudation and flattening. (3) From the Oligocene to early Pliocene (33.9–5 Ma), the YBF underwent ~47 km of left-lateral displacement that accommodated the slip of Altyn Tagh Fault (ATF). (4) Since the Pliocene (5 ± 1 Ma), the YBF is characterized by left-lateral strike-slip faulting with a normal faulting component. The normal faulting resulted in uplift and the creation of topography along the central segment of the YBF. This has impeded the southeastward migration of sand dunes, building the world's highest megadune within the BJD. The tectono-geomorphic growth of the YM and YBF plays a key role in formation of the unique megadune-lake pattern and in preventing the merging of the BJD and Tengger Desert (TD). • Tectonic geomorphological study of the Yabrai Mountain, NE Tibetan Plateau margin • Uses remote sensing, fieldwork, apatite thermochronology and fault-dating methods • Thermochronology reveals Cenozoic uplift, erosion and faulting. • Yabrai faulting is dominantly strike slip but with a normal component along central segment. • Faulting-uplift affects air-water circulation aiding desert and megadune-lake formation. [ABSTRACT FROM AUTHOR]

• Height of Earth's tallest megadunes in the Badain Jaran Desert is increasing. • Base of the megadune windward slope is eroding and the top is accumulating. • On the windward slope the modern eolian sand layer thickens from the base upwards. • Increased humidity and reduced wind speed favor the growth of megadunes. The Badain Jaran Desert (BJD) in NW China is well known for its unique landscape of megadunes coexisting with permanent lakes. The megadunes are already the tallest sand dunes on earth, and some of them are up to 400 m high. However, it is unclear whether or not the height of the megadunes is continuing to increase under present climatic and environmental conditions. In order to determine the growth status of the megadunes, we collected 26 samples from the windward slopes of two megadunes for optically stimulated and infrared stimulated luminescence dating. The results show that the thickness of the modern eolian sand layers increases from the lower part of the windward slopes, with a thickness of less than 1 m, to more than 2 m in the middle, and to 9 m in the upper part. This indicates that the height of the megadunes is continuing to increase under modern conditions. The surface sediments from the base of the windward slope and the adjacent lake basin have relatively old ages of 6–7 ka, indicating that these areas are eroding. The recent eolian sands of the upper part of the megadunes likely originated from the base of the dunes or from the lake basin. The megadunes in the BJD are currently becoming increasingly high and steep due to the upward migration and accumulation of sand particles. Increased humidity and a weakened wind regime in northern China, related to ongoing climatic warming, are likely the main factors in maintaining the growth of the megadunes. [ABSTRACT FROM AUTHOR]