Aeolian Erosion Research Articles

Topographic variation in burning-induced loss of carbon from organic soils in Tasmanian moorlands

Although it is known that cool fire can result in carbon loss in organic soils, data are lacking on the effects of such fire on the distinctive lowland organic soils of the southern hemisphere and on the relationship of fire-induced carbon loss to topography. We established an experiment to determine the effects of a low severity burn on organic and total mass of soils, the position of the water table and vegetation cover. We recorded soil losses directly after the fire, after the first rain and after 4 years. We also recorded losses as a result of the first rain and at 4 years after a wildfire at another locality with the same vegetation and topography. We compared soil surface temperatures over summer between burned and unburned moorland. The planned fire resulted in substantial soil and carbon losses, which, up to 4 years after the wildfire, occurred mostly as a result of the fire itself and the first rains. The topographic wetness index was strongly related to soil and organic matter loss for the pooled data for both sites, while fire severity, slope and vegetation cover were less predictive. Burning increased dissolved organic material in streams; the depth of the water table; and, soil temperatures. The continuing soil loss on slopes 18 years after fire contrasts with faster recovery on the shelves and in the basins, reflecting a strong topographic component in variation. Fire is a major influence on the depth of the organic soils of the southern hemisphere, as in the northern hemisphere. The influence of fire on soils varies markedly between topographic positions, with the time interval between fires that would maintain organic soils in basins being markedly less than that necessary to maintain organic soils on slopes. The topographic effect appears to be a consequence of relative drying rather than relative exposure to water or aeolian erosion or differences in fire severity.

Slope hummock development, Fosheim Peninsula, Ellesmere Island, Nunavut, Canada

Slope hummocks, a type of nonsorted patterned ground, are composed of stratified, organic, silty sand, and develop through the interaction of niveo-eolian deposition, solifluction, slopewash, and vegetation growth. Fields of hummocks show consistent patterns: forms on convex slopes increase in height downslope until the channel is reached, whereas those on convexo-concave slopes increase on the upper convexity but are buried by niveo-eolian deposition downslope of the snowbank remnant. These trends can be reproduced using a simple numerical model based on measured slope and snow depth profiles, sediment concentrations in the snow and solifluction rates. The model indicates that hummocks transit slopes of 20–40 m in about 2–4 ka, a time-frame that is plausible given site emergence, measured rates of solifluction, and published dates for organic horizons within hummocks on northern Ellesmere Island. Sensitivity analyses show that long-term effect of climate warming on hummock heights may differ depending on whether it is accompanied by precipitation increase or decrease. The required combination of two-sided freezing to promote plug-like movement, incomplete vegetation cover and thin snow that enable eolian erosion during winter and spring, and vegetation growth in snow-bed sites to stabilize niveo-eolian deposits may explain why these forms are important regionally but apparently are not present throughout the Arctic.

Particle size distributions of South Tunisian soils erodible by wind

180 samples representative of surface soils erodible by wind were collected in South Tunisia to retrieve their grain size distribution. Dry sieving using 13 sieves was favour to preserve as much as possible the soil aggregates in their natural state. Two different methods were used to characterize the grain size distribution; the f method of moments and the use of a combination of log-normal statistical functions. Both methods underline the ubiquitous and dominant presence of a very fine sand population (around 100 μm in diameter), very well sorted (σ =1,23) which corresponds to the grain size range for which the wind energy required for initiating the aeolian erosion is minimum. This clearly suggests that most of the soils in South Tunisia have the potential to be easily eroded by wind. However, in about 1/3 of the samples mainly those located in Dahars and in the vicinity of mountains, a secondary population of coarse grains (1500 μm in diameter) is also observed. This coarse mode could significantly reduce the wind erosion of the soils where it is present by covering a part of the surface and by limiting the efficiency of the wind transfer to the surface.

Wind tunnel experiments on vertical distribution of wind-blown sand flux and change of the quantity of sand erosion and deposition above gravel beds under different sand supplies

Wind tunnel experiments were carried out with respect to the vertical distributions of wind-blown sand flux and the processes of aeolian erosion and deposition under different wind velocities and sand supplies above beds with different gravel coverage. Preliminary results revealed that the vertical distribution of wind-blown sand flux was a way to determine whether the gobi sand stream was the saturated one or not. It had different significances to indicate characteristics of transport and deposition above gobi beds. Whether bed processes are of aeolian erosion or deposition was determined by the sand stream near the surface, especially within 0–6 cm height, while the sand transport was mainly influenced by the sand stream in the saltating layer above the height of 6 cm. The degree of the abundance of sand supply was one of the important factors to determine the saturation level of sand stream, which influenced the characteristic of aeolian erosion and deposition on gravel beds. Given the similar wind condition, the sand transport rates controlled by the saturated flow were between 2 and 8 times of the unsaturated one. Those bed processes controlled by the saturated flow were mainly of deposition, and the amount of sand accumulation increased largely as the wind speed increased. In contrast, the bed processes controlled by the unsaturated flow were mainly of aeolian erosion. Meanwhile, there was an obvious blocking sand ability within the height of 0–2 cm, and the maximal value of sand transport occurred within the surface of 2–5 cm height.

Preservation of earthen heritage sites on the Silk Road, northwest China from the impact of the environment

The Silk Road played an important role in the economic and cultural exchanges between central China, Europe and Central Asia. A number of heritage sites with significant values still remain throughout the Gobi Desert and other desert regions in Northwest China. Most of the heritage sites composed of adobeern materials and the earthen structures have been impacted by adverse environmental conditions for thousands of years causing severe damage with only a small proportion of the structures left surviving to the present day. Analysis of the main environmental factors affecting the heritage sites such as temperature difference, wind storms, rain storms, and the freeze–thaw process and a study of the mechanism of the deterioration are the main topics presented in this paper. The authors have concluded that a Potassium–Silica solution PS invented by one of the authors has been effective in improving the intrinsic properties of heritage site earthen structures with regard to reducing the impact of environmental damage. The results of comparative tests show that samples treated by using the PS solution have performed well, particularly in protecting structures from aeolian erosion and heavy rainfall. Some findings on the effect of PS treatment on earthen structures at heritage sites are discussed in detail in the present paper.

Atmospheric distribution and deposition of mercury in the Idrija Hg mine region, Slovenia

The atmospheric distribution and deposition of Hg in the area of the former Idrija Hg-mine, Slovenia, were investigated. Mapping of air Hg 0 concentrations was performed to assess the spatial distribution and major sources of mercury to the atmosphere in the area. In addition, analyses of mercury speciation in the air over Idrija were performed during a 4-day sampling campaign in September 2006 to better understand the fate and transformation of Hg in the atmosphere of this specific mercury polluted site. The speciation results were then compared to the results of mercury speciation in the wet and throughfall deposition sampled on a precipitation event basis from October 2006 to September 2007. The Hg 0 concentration in air was mostly below 10 ng m −3, with the highest concentration in the area of the former smelter complex exceeding 5000 ng m −3. Mercury-bearing airborne particles (TPM) seem to dominate the atmospheric Hg deposition, which revealed noticeable variations between precipitation events (11–76 ng m −2 day −1), mostly as a function of the amount of precipitation. Hg in precipitation was largely (∼50%) associated with the particulate phase (THg P). No correlation was found between the THg P and the dissolved phases (THg D), suggesting that particulate phase Hg is mostly the result of dry deposition. In the throughfall, significantly higher (2–10 fold) Hg concentrations than in associated event precipitation were observed, mostly due to Hg in the particulate phase (∼70% THg). As shown by SEM/EDXS microscopy, an important amount of mercury in the precipitation and throughfall samples is due to the presence of cinnabar particles as a result of the aeolian erosion of cinnabar-containing surfaces in the area.

Aeolian scours as putative signatures of wind erosion and sediment transport direction on Mars

Obstacle marks, specifically current crescents (scours) formed by aeolian erosion, have not been previously identified on Mars from orbit. However, recent Mars Reconnaissance Orbiter images of an unnamed intracrater dune field within the Hellespontus region have shown innumerable meter-scale scours around fine and medium grade blocks. The types, relative numbers, and distributions of scour features served to determine, by proxy, the modes of surface wind direction and pathways of sediment transport across the crater floor. The orientations of scours of U-type morphology as well as the facing directions of leeward slopes for crescentic dunes (barchans and barchanoids) and megaripples were examined by statistical methods to determine their reference directions and dispersion of modal classes. We showed that although the dune field has evolved primarily under the influence of winds from the southwest, U-type scours have developed predominantly from a significant northwesterly wind direction. These data suggest that the dune field has evolved under the influence of a bimodal wind regime. Furthermore, such an aeolian system may help to explain the intermediary morphology between crescentic and linear for the central part of the dune field, in which the dunes appear to have undergone longitudinal as well as lateral sediment transport. In the absence of direct measurements of wind directions and strengths, current crescents offer detailed data from which planetary air flow at the surface–air interface can be better interpreted for the many intracrater settings across Mars.

Numerical modelling of aeolian erosion over rough surfaces

AbstractThe presence of non‐erodible roughness elements on erodible surfaces has the effect of absorbing part of the wind shear stress and thus protecting the erodible surface from wind erosion. This paper examines the shear stress distribution over roughness arrays of varying density, representing the progress of erosion on a bed of erodible and non‐erodible particles. Three‐dimensional numerical simulations, simulating wind flow over a bed of particles covered by roughness elements, were conducted in order to investigate the effect of roughness elements on the shear stress near the surface. The results of these simulations confirm that the erosion of soil by wind is strongly attenuated by the presence of roughness elements on the surface and depends on the geometric properties of the roughness elements. Based on the new numerical results obtained, a refinement of existing theoretical approaches is developed to describe the dependence of the friction velocity upon roughness frontal area and real exposed cover rate. The new formulation proposed will allow a more accurate evaluation of shear stress partitioning as a function of topographic changes. Copyright © 2010 John Wiley & Sons, Ltd.

Mobilization of lead-zinc rich particles from mine tailings in northern Tunisia by aeolian and run-off processes

Abstract Dispersion of metal rich particles from mine tailings is an important hazard for the environment. Specially, in Mediterranean context, this is potentially more risky because of the violence of climatic events. Northern Tunisia includes about 50 mining districts with an ore mineralogy consisting mainly of galena, iron sulphides and subordinate sphalerite embedded in a calcitic and baritic gangue. A century of mining exploitation left waste rich in potentially toxic elements (PTE) with values up to 46900 mg/kg for Pb and 49501 mg/kg for Zn, stored in uncontrolled and untreated deposits. The PTE contents observed in the surrounding soils generally devoted to agricultural activities are as high as 12488 mg/kg for Pb, 3485 mg/kg for Zn and 15 mg/kg for Cd. The contents in sediments downstream are also high, in the range of 47800 mg/kg for Pb, 5767 mg/kg for Zn and 36 mg/kg for Cd. PTE-bearing phases are mainly sulphides, carbonates and iron oxyhydroxydes. Because of the lack of vegetation and the presence of fine particles in the mining wastes, PTE were dispersed to nearby areas, resulting in the contamination of agricultural soils and river sediments. Under the Mediterranean climate which includes a long dry summer with windy episodes and heavy rainfall in the winter, mine tailings are exposed to two types of erosion: hydraulic erosion with transport during heavy rainfall events and aeolian erosion inducing fine particle dispersion. Dispersion of the PTE from mine tailings in northern Tunisia presents a risk of environmental contamination and of toxicity by inhalation for the habitants near the former mining districts. Furthermore these PTE can be transferred from agricultural soils surrounding the tailings to the cultivated plants (mainly cereals).

A modeling study of Aeolian erosion enhanced by surface wind confluences over Mexico City

Abstract Using wind erosion and air quality models, a study on the effect of PM10 from aeolian erosion episodes in Mexico City is presented. The important contribution of aeolian erosion on urban air quality, its genesis, morphology, location and regional implications such as the role played by surface confluences, the dry Lake of Texcoco and agricultural lands to the east and south-east of Mexico City is established. All analyzed episodes showed that wind erosion is a major cause of high PM10 concentrations in Mexico City. The wind erosion and air quality models used here provide useful computational tools to study the aeolian erosion phenomenon, its sources and impact on urban regions.

Numerical and wind tunnel modeling on the windbreak effectiveness to control the aeolian erosion of conical stockpiles

There are many industrial sites where open aggregate conical piles exist to store granular materials, like coal, industrial residuals, or other minerals. Usually these storage piles are placed in open areas, making them susceptible to wind erosion, which can create health, environmental, and/or economical concerns. It is common to minimize the dust emission through the placement of windbreaks in the vicinity of the storage piles, which reduces the wind speed in the vicinity of the pile’s surface. In this work, some experimental results from a wind tunnel study on the erosion of a conical sand pile, exposed or protected by a fence with porosities of 0, 70, and 83%, are shown. For the sheltered cases, the windbreak was placed at several distances from the pile’s leading edge, ranging from H to 4H, where H is the initial height of the non-eroded pile. The evolution of the shape of the sand pile is shown, at different instances in time, and the pile deformation quantified, using a novel experimental setup developed for wind erosion studies. This information might be regarded as a useful dataset for the benchmark of computational models aiming to produce the transient simulation of the aeolian erosion of stockpiles. The CFD results are comprised of the modeling of several experimental scenarios. The computational results for the surface wind velocity show a good correlation with the initial deformation of the pile. Based on the results, the isocontours of (u s /u r ) presented might be regarded as a good basis for the estimation of the pile shear velocity.

Origin of coarsely crystalline gypsum domes in a saline playa environment at the White Sands National Monument, New Mexico

Dome‐like structures up to 3 m in height, composed predominantly of coarse crystals of selenite gypsum, occur on the surface of Alkali Flat, a saline playa lake in White Sands National Monument, New Mexico. The structures were investigated using field observations, aerial images, and geochemical methods. The domes are inferred to be remnants of lake sediments that have been preserved from Holocene eolian erosion due to higher cementation resulting from crystallization of large gypsum (selenite) crystals in the playa's clay‐rich sediments. Low δ2H values of the selenite, from −90 to −69 ‰, suggest precipitation from saturated solutions associated with groundwater seepage in the playa related to the upward flows of groundwater, primarily fed by meteoric water rather than the evaporation of the playa water. Values of δ34S for selenite range from 12.1 to 13.8 ‰ (median 13.0 ‰) and are notably higher than the dissolved sulfate in the modern groundwater system that has δ34S values from 10.2 to 11.8 ‰ (median 11.4 ‰). The two main regional sources of sulfate are Middle Permian evaporites with median δ34S values of 12.0 ‰ and Lower Permian evaporites with median δ34S values of 13.0 ‰. The δ34S values measured in domes suggest their formation during a period of time when groundwater seepage might have been dominated by deeply circulating water that interacted with Lower Permian evaporites buried in the basin center. The apparent alignments of domes suggest that past groundwater seepage was controlled by fractures beneath Alkali Flat which are associated with a regional fault system in the area.

Aeolian erosion and sand transport over the Mejillones Pampa in the coastal Atacama Desert of northern Chile

The Mejillones Peninsula in the coastal Atacama Desert of northern Chile is a region in which ocean–atmosphere–land interactions are particularly strong, resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea. Because the aeolian particles in the laminated sediments at the bottom of Mejillones Bay record long-term changes in the intensity of prevailing southerly winds, it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions. The aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the Mejillones Peninsula, the Mejillones Pampa, including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles, through field measurements. In addition, we test the ability of an existing saltation model (MB95) to reproduce the variability of the erosion process during the field experiment. Soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200–300 µm and 100–150 µm size ranges. Aeolian particles collected in BSNE sand traps located at different heights near the surface, exhibit a bimodal size distribution similar to that of the erodible fraction of the soils; the abundance of the fine class increasing with height. Small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion. The mineralogical composition of moving particles is similar to that of the soils, with quartz, feldspar and calcite as the most important minerals, followed by clay minerals, gypsum and amphibole. A value of u* t is calculated for each soil particle size class. Subsequently, the elementary contribution of each size class to the horizontal flux is calculated using White (1979)'s equation and the total flux is finally obtained by integration. The saltation model successfully reproduces the variability of the wind erosion process during the field experiment, but over-estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude.

Relationships of aeolian erosion and deposition with LiDAR-derived landscape surface roughness following wildfire

The reduction of vegetation by wildfire can subject stable soil surfaces to increased aeolian transport. Vegetation and associated microtopography function as surface roughness elements that influence the entrainment, transport, and deposition of sediment by wind in burned and unburned semiarid shrublands. We examined whether surface roughness derived from LiDAR can explain variability in aeolian surface change following wildfire in loess soils of a cold desert shrub steppe in SE Idaho, USA. Erosion bridges were installed in Fall 2007, following a late summer wildfire to monitor soil surface change at sites in burned and downwind unburned areas. Surface elevation measurements were made when the erosion bridges were installed and again in Fall 2008. Surface change was determined from the difference in relative elevation between the two dates. Airborne LiDAR data were acquired in Fall 2007 following erosion bridge installation. Surface roughness was calculated at 2-m raster resolution using the standard deviation of all LiDAR elevations within the 2-m cells, after elevations were detrended to remove the effects of topographic slope. Surface change varied as a function of surface roughness among burned and unburned surfaces, with net erosion occurring on the relatively smooth, burned surfaces and net deposition occurring on the rough, unburned surfaces. Site mean surface change decreased linearly as a function of the inverse of site mean surface roughness ( r 2 = 0.77, p < 0.00). Quantile regression analysis indicated that changes in surface roughness were related to proportionally greater changes in erosion compared to deposition. Analysis of surface change at finer spatial scales suggested that aeolian processes occurred with strong spatial patterns on burned, but not unburned surfaces. Future research to examine relationships between aeolian transport and fine spatial resolution topographic variability, for example from ground-based LiDAR systems, is recommended.

Geology of the Selk crater region on Titan from Cassini VIMS observations

Observations of Titan obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) have revealed Selk crater, a geologically young, bright-rimmed, impact crater located ∼800 km north-northwest of the Huygens landing site. The crater rim-crest diameter is ∼90 km; its floor diameter is ∼60 km. A central pit/peak, 20–30 km in diameter, is seen; the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on Ganymede and Callisto, all of which are dome craters. The VIMS data, unfortunately, are not of sufficient resolution to detect such a dome. The inner rim of Selk crater is fluted, probably by eolian erosion, while the outer flank and presumed ejecta blanket appear dissected by drainages (particularly to the east), likely the result of fluvial erosion. Terracing is observed on the northern and western walls of Selk crater within a 10–15 km wide terrace zone identified in VIMS data; the terrace zone is bright in SAR data, consistent with it being a rough surface. The terrace zone is slightly wider than those observed on Ganymede and Callisto and may reflect differences in thermal structure and/or composition of the lithosphere. The polygonal appearance of the crater likely results from two preexisting planes of weakness (oriented at azimuths of 21° and 122° east of north). A unit of generally bright terrain that exhibits similar infrared-color variation and contrast to Selk crater extends east-southeast from the crater several hundred kilometers. We informally refer to this terrain as the Selk “bench.” Both Selk and the bench are surrounded by the infrared-dark Belet dune field. Hypotheses for the genesis of the optically bright terrain of the bench include: wind shadowing in the lee of Selk crater preventing the encroachment of dunes, impact-induced cryovolcanism, flow of a fluidized-ejecta blanket (similar to the bright crater outflows observed on Venus), and erosion of a streamlined upland formed in the lee of Selk crater by fluid flow. Vestigial circular outlines in this feature just east of Selk’s ejecta blanket suggest that this might be a remnant of an ancient, cratered crust. Evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the Belet dune field. We conclude that this feature either represents a relatively high-viscosity, fluidized-ejecta flow (a class intermediate to ejecta blankets and long venusian-style ejecta flows) or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west-northwest.

Land degradation in drylands: Interactions among hydrologic–aeolian erosion and vegetation dynamics

Land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality. Climate change, shifts in vegetation composition, accelerated soil erosion processes, and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification. Even though the role of hydrologic–aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized, most studies have concentrated only on the role of one or two of these components, and not on the interactions among all three. Drawing on relevant published studies, here we review recent contributions to the study of biotic and abiotic drivers of dryland degradation and we propose a more holistic perspective of the interactions between wind and water erosion processes in dryland systems, how these processes affect vegetation patterns and how vegetation patterns, in turn, affect these processes. Notably, changing climate and land use have resulted in rapid vegetation shifts, which alter the rates and patterns of soil erosion in dryland systems. With the predicted increase in aridity and an increase in the frequency of droughts in drylands around the world, there could be an increasing dominance of abiotic controls of land degradation, in particular hydrologic and aeolian soil erosion processes. Further, changes in climate may alter the relative importance of wind versus water erosion in dryland ecosystems. Therefore acquiring a more holistic perspective of the interactions among hydrologic–aeolian erosion and vegetation dynamic processes is fundamental to quantifying and modeling land degradation processes in drylands in changing climate, disturbance regimes and management scenarios.

Formation, erosion and exposure of Early Amazonian dikes, dike swarms and possible subglacial eruptions in the Elysium Rise/Utopia Basin Region, Mars

Hundreds of narrow, linear ridge segments are found in the transition zone between the Elysium Rise and the Utopia basin, occurring as both single and multiple ridges. The ridges are distinctive because of their very linear, steep-sided nature, their often sharp ridge crest (which sometimes is fractured), their association with stubby flows, their continuity over long distances and their cross-cutting of different terrain. The linear ridges are interpreted to be single dikes and dike swarms, either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption. Five dike swarms are identified, having lengths ranging from 10–45 km and being between 1–7 km wide, while single ridges are up to 20 km long and 100–500 m wide. In the areas of dike swarms, crustal dilatation is estimated to vary from 15–60%. Dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area. The ridges both modify and constrain Early Amazonian flows and flood plain deposits suggesting intense dike emplacement in the Early Amazonian. The association with different stages of inverted craters, as well as some features of ice-related origin (possible ice-cauldron and tindar-like features), indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement.

Imprint of North-Atlantic abrupt climate changes on western European loess deposits as viewed in a dust emission model

Western European loess sequences of the last glaciation (∼100,000–15,000 years BP) exhibit strong, cyclic variations of the sedimentation rate, which are coeval to the Greenland stadial/interstadial cycles and the Heinrich events. These North-Atlantic rapid climate changes appear, thus, as a potential cause for the sedimentation variations, via changes in dust intensity cycle. Here we make a first step in testing this hypothesis, by modelling the impact of the North-Atlantic abrupt climate variations on dust emission. Our dust emission calculations use meteorological fields generated by the LMDZ atmospheric general circulation model at a resolution down to 60 km over Western Europe. Three numerical experiments are run, representing a Greenland stadial, an interstadial and a Heinrich event. Orbital parameters and ice-sheet configuration correspond to conditions from Marine Isotope Stage 3 (∼60,000–25,000 years BP), a period characterized by strong millennial-scale climate variability. The only differences we impose in the boundary conditions regard the North-Atlantic surface temperature and sea-ice cover in the latitudinal band 30°–63°N. The changes in wind, precipitation, soil moisture and snow cover from one simulated state to another result in small differences in dust emission intensity. In contrast, when the inhibition of the aeolian erosion by vegetation is taken into account, the dust fluxes for the cold climate states (Greenland stadial and Heinrich event) become generally more than twice higher than those for the relatively warmer Greenland interstadial, in agreement with the loess data. These results support the hypothesis that the North-Atlantic millennial-scale variability is imprinted in Western European loess profiles, and point to vegetation changes as the main factor responsible for millennial-scale sedimentation variations. An analysis for the English Channel and southern North Sea areas, major potential dust sources, shows that the seasonality of dust emission is not controlled by the wind speed, as in modern large deserts, but by the surface conditions. Consequently, the dusty season lasts from late winter to early summer, with maximum activity in April–May, and is shifted towards summer when the climate is colder.

Numerical modeling of flow structures over various flat-topped stockpiles height: Implications on dust emissions

Fugitive dust emissions from open stock yards for bulk materials, such as coal or ores, can represent a significant part of overall estimated atmospheric emission on industrial site, as example on steel plant sites. Stockpile topography is known to modify the near field uptake force of the wind through changes of the mean flow. Various studies have shown that aeolian erosion strongly occurs on the stockpile crest, so it appears relevant to carry out a study to analyze the effect on the dust emissions of the stockpile clipping. Three-dimensional numerical simulations were done with the aim of simulating wind flow over different flat-topped pile scenarios, corresponding to a constant material volume. Various wind flow directions were tested to determine its impact on particle emissions. Data obtained from Computational Fluid Dynamics simulations were then integrated in order to estimate the effect of the clipping on the stockpiles dust emission rates by using the EPA's emission factors method. Results provide evidence to suggest that clipping stockpiles does not reduce dust emissions. This study provides to industrial operators some informations on the best geometrical pile characteristics in order to limit particles emissions.

Using airborne geophysics to define the 3D distribution and landscape evolution of Quaternary valley-fill deposits around the Jamestown area, South Australia

The combined analysis of airborne electromagnetics, airborne gamma-ray spectrometry, magnetics and a digital elevation model with ground-based calibration has enabled construction of a 3D architectural and landscape evolution model of valley-fill deposits around the township of Jamestown in South Australia. The valley-fill sediments consist of traction, suspension and debris-flow deposits that range in age (optically stimulated luminescence dating) from 102 ± 12 ka to the present day. A sediment isopach map generated from the airborne electromagnetics dataset reveals the 3D structure of the valley-fill deposits. The sediments are up to 40 m thick in asymmetrical valleys and are the result of colluvial fan, floodplain and sheet-wash processes. The sediments fine upwards with a higher proportion of coarser bedload deposits toward the base and fine sand, silt and clay towards the top of the sequence. A strong linear correlation between airborne K response and soil texture allowed the percentage of surface silt to be modelled over the depositional landforms. The sediments are thought to have been derived by a combination of eolian dust accessions, and weathering and erosion of bedrock materials within the catchment. Older drainage lines reflected in the distribution of relatively closely spaced and well-connected ‘magnetic channels’ differ markedly from present-day streams that are largely ephemeral and interrupted. This is thought to reflect a change in local hydrology and associated geomorphic processes from relatively high to lower energy conditions as the valley alluviated. These hydrological changes are likely to be associated with a drying climate, lower recharge and runoff.