Aeolian Erosion Research Articles

05/00020 Wind tunnel study of coal dust release from train wagons: Ferreira, A. D. and Vaz, P. A. Journal of Wind Engineering and Industrial Aerodynamics, 2004, 92 (7–8), 565–577.

The paper presents a wind tunnel study to assess the coal dust released due to aeolian erosion from wagons equipped with two different shelter cover systems. A 1:25 scale model was used, and it comprises one locomotive and four train wagons with a 3.55 m maximum length. Several tests were conducted for different train configurations, and two initial load levels, with an undisturbed flow velocity of 13.4 m/s. Experiments showthe use of covers reduces the amount of dust released to be less than 20% of the quantity eroded from the uncovered wagon. Results are primarily related to time series of released mass, for different conditions. Free-surface time evolution inside the last wagon is shown to illustrate marked differences by using the two distinct cover systems. r 2004 Elsevier Ltd. All rights reserved.

Tillage techniques to reactivate aeolian erosion on inland drift-sand

The inland drift-sand areas in northern Europe are characterised by a rapid decline in both aeolian activity and areal size. Many former drift-sand surfaces have become immobilised by natural or man-induced processes, such as conversion into forest or other terrain for agricultural, economic or societal purposes. The sharp reduction of these areas automatically implies the disappearance in Western Europe of a unique landscape with a high natural and cultural-historic value. Therefore, it is necessary to investigate how drift-sand areas can be preserved, how the balance between the active areas and those colonised with drift-sand vegetation can be kept under control, and how introducing techniques that reactivate, or benefit, the aeolian processes can counteract irreversible immobilisation by subsequent colonisation. Four such techniques (rotary cultivator, beach sand cleaner, disk harrow and excavator) were evaluated during an 8-month experiment on drift-sand stabilised by grey hair grass and algae crusts at Kootwijkerzand, The Netherlands. The effect of the techniques was measured using five key-parameters: the raising and lowering of the surface due to aeolian activity, the horizontal sediment transport flux, the vertical sediment accumulation flux, changes in the grain size of the top layer due to aeolian processes, and changes in the organic matter content of the topsoil. The effect of each technique on soil compaction, surface roughness and the amount of plant residue left on the field is also discussed. The highest aeolian activity (horizontal and vertical flux, surface lowering) was observed on test fields treated with the beach sand cleaner and the rotary cultivator. The changes in grain size and organic matter content of the top layer were also highest in these fields. Of the four techniques tested, the beach sand cleaner and the rotary cultivator are thus the most recommendable methods to reactivate drift-sand stabilised by grey hair grass and algae crusts. The disk harrow and the excavator may also lead to a reactivation, but they are less effective and therefore less recommendable.

Effect of Mars analogue dust deposition on the automated detection of calcite in visible/near-infrared spectra

We have developed an artificial neural net detector for use on board Mars rovers that correctly identifies calcite under Mars analogue dust (JSC Mars-1 regolith simulant) layers up to ∼ 100 μm thickness and 80% aerial coverage. Both the detector output and the band depth of the ∼ 2300 nm CO = 3 absorption are linearly related to the surface area of exposed calcite. This detector provides a means for rapid and robust automated recognition of calcite on Mars in areas of active aeolian erosion.

Wind tunnel study of coal dust release from train wagons

The paper presents a wind tunnel study to assess the coal dust released due to aeolian erosion from wagons equipped with two different shelter cover systems. A 1:25 scale model was used, and it comprises one locomotive and four train wagons with a 3.55 m maximum length. Several tests were conducted for different train configurations, and two initial load levels, with an undisturbed flow velocity of 13.4 m/s. Experiments show the use of covers reduces the amount of dust released to be less than 20% of the quantity eroded from the uncovered wagon. Results are primarily related to time series of released mass, for different conditions. Free-surface time evolution inside the last wagon is shown to illustrate marked differences by using the two distinct cover systems.

Geomorphic and Environmental Change Around a Large, Aging Reservoir: Lake C. W. McConaughy, Western Nebraska, USA

Lake C. W. McConaughy, a 63-year-old manmade reservoir in the North Platte Valley of western Nebraska, is the largest standing body of water in the state. From the time that Kingsley Dam was completed in 1941 until the present day (2004), many geomorphic and environmental changes have occurred along the shores and within the North Platte Valley. Erosion on the southeastern shoreline of the lake had been perceived as a problem for landowners and managers for at least three decades, but the full scale of erosion was revealed only after a cumulative 18-m drawdown in lake level: bedrock platforms, extending from cliffs on headlands, as well as minor caves, alcoves, potholes, and beach erosion scarps were revealed. Actual headland retreat since 1941 has probably been on a scale of magnitude of tens of meters. Erosional platforms, however, are as much as 266 m in length, indicating that they are, collectively, the results of a combination of pre-reservoir geomorphic conditions, erosion during reservoir filling, and wave erosion after filling. Serial observations of the shoreline made in the period 1999–2002 demonstrated that shoreline erosion continues. Depositional features such as pocket beaches and beach ridges have formed de novo in bays between headlands. Also, a delta that prograded at least 4 km from the North Platte River into the lake between 1952 and 1993 continues to grow, and major morphometric changes have occurred on the North Platte River immediately upstream since 1941 in response to the elevation of the local base level by the lake; most of the change in channel patterns in the river upstream from the delta took place in a mere 8 years from 1952 to 1960. Since 1999, some emergent beaches and areas of exposed lake floor have developed sand dunes; eolian erosion and re-deposition is widespread elsewhere in these areas during periods of high winds, which are frequent in western Nebraska. The water table beneath lands adjacent to the reservoir generally rose until 1953 as the lake was filling. The far-flung irrigation system of which Lake McConaughy is the key element has elevated water tables as far as 250 km from the lake. Since at least 2000, soil salinization (episodic thenardite accumulation) has developed in exposed lake sediments at the western end of the lake. On a smaller scale, groundwater has been discharging lakeward along shoreline beach scarps through springs and seeps while lake levels have been low. Slightly lowering the operating level of Lake McConaughy could slow some of the more dramatic effects of shoreline erosion when the lake returns to its pre-drought volume, but erosion will continue, particularly at the ends of headlands on the southeastern shore, which are exposed to strong waves driven by northerly to northwesterly winds. Eolian erosion and re-deposition will, on the other hand, continue as long as lake level remains particularly low as a result of drought and the removal of irrigation waters. Salinization can be considered an ephemeral phenomenon, dependent on future management of the lake, but it indirectly represents the potential for larger-scale changes in hydrogeologic systems. The longer-term effects of lake-related water-table changes, both near the lake and downstream in irrigated lands, as well as the ability of the lake to supply irrigation water if drought conditions continue, remain to be seen.

The MAGO experiment for dust environment monitoring on the Martian surface

Among the main directions identified for future Martian exploration, the study of the properties of dust dispersed in the atmosphere, its cycle and the impact on climate are considered of primary relevance. Dust storms, dust devils and the dust “cycle” have been identified and studied by past remote and in situ experiments, but little quantitative information is available on these processes, so far. The airborne dust contributes to the determination of the dynamic and thermodynamic evolution of the atmosphere, including the large-scale circulation processes and its impact on the climate of Mars. Moreover, aeolian erosion, redistribution of dust on the surface and weathering processes are mostly known only qualitatively. In order to improve our knowledge of the airborne dust evolution and other atmospheric processes, it is mandatory to measure the amount, mass-size distribution and dynamical properties of solid particles in the Martian atmosphere as a function of time. In this context, there is clearly a need for the implementation of experiments dedicated to study directly atmospheric dust. The Martian atmospheric grain observer (MAGO) experiment is aimed at providing direct quantitative measurements of mass and size distributions of dust particles, a goal that has never been fully achieved so far. The instrument design combines three types of sensors to monitor in situ the dust mass flux (micro balance system, MBS) and single grain properties (grain detection system, GDS + impact sensor, IS). Technical solutions and science capabilities are discussed in this paper.

Full-scale measurements for evaluation of coal dust release from train wagons with two different shelter covers

The paper describes a full-scale study performed to evaluate the amount of coal dust released by eolian erosion from partly covered train wagons over runs of 350 km. The experimental setup designed for this study is described along with the effectiveness assessment of two types of dust collectors. Airflow statistics are reported for the region immediately above the top level of the wagons. Visualisation tests for the fugitive dust indicate that most of it leaves each wagon primarily through the rear end. The releases from the partly covered wagons are compared against those from the uncovered wagons, to assess the performance of the covers in what concerns the reduction of fugitive dust. The amounts of dust collected after being treated through an error analysis yields an estimate for the total amount of coal released from each wagon under consideration. The uncertainties resulting from a full-scale study based on actual operating conditions were taken into account and the major contribution of this study is toward the quantification of the fugitive dust release, which seems to have been overlooked in studies appearing in the open literature. The value of less than 0.001% of the 60 tons net load of coal for partly covered wagons, using a 95% confidence interval, over a particular 350 km run, may be representative of many other similar situations. This value tends to be lower than the values usually quoted in different contexts, and primarily within environmental impact assessments.

Remarks on the definition and estimation of the aeolian erosion threshold friction velocity

Theoretical equations and numerical models of wind erosion processes include threshold (the lowest friction velocity at which soil movement is initiated) as a basic parameter. Stout (1998) showed that the averaging time of a wind speed measurement affects the observed threshold. Turbulence leads to intermittent saltation, a process characterised by bursts with periods of inactivity. Using Weibull and Gaussian distributions for the horizontal wind speed, it is found that the averaging time, the variance and the form of horizontal wind speed distribution affects the observed threshold. Furthermore, theoretical calculations reveal that the sediment transport rate and its increase with the friction velocity above the apparent threshold, depends on the variance and the form of horizontal wind speed distribution. The proportionality between streamwise sand flux and friction velocity cubed is a result of distribution function of the wind strength. Predictive formulae must include the variance of horizontal wind speed.

Palaeofluvial estimates from exhumed meander scrolls, Taref Formation (Turonian), Dakhla Region, Western Desert, Egypt

An array of meander scroll sets (point bar complexes) is exposed over a land surface eroded across the dip slope of sandstones of the Nubia Group, Taref Formation (Turonian) around the southern fringe of Dakhla Oasis, Egypt (25.5°N, 29°E). These sandstones are thus interpreted as fluvially deposited. Using published equations, bankfull channel width, depth, as well as sinuosity are estimated from radii of meander curvature. With a reasonable assumption of velocity, bankfull discharge is then estimated. This is found to be comparable with bankfull discharge values estimated from published plots of hydraulic geometry (width and depth) against discharge. Both approaches result in mean bankfull discharge estimates of 4.4–7.0×10 3 m 3s −1. Using mean radius of meander curvature, sinuosity is estimated at 1.66. In this hyperarid climatic region aeolian erosion has carved yardangs into the Taref sandstone, the flanks of which expose uniform, tabular cross-beds of coarse, clean quartz sand. From the palaeofluvial estimates, from other features of the exhumed meander scrolls, and from the character of the sandstone, channels in which the Taref sands were deposited are inferred to have been wide and shallow, of low sinuosity, rapidly migrating laterally, with minimal overbank deposition of muds, and rapid vertical accretion. Published indications of a tropical monsoon climate over Egypt in the Turonian are harmonized with the absence of fossil flora from the Taref with reference to indications of a rapidly changing fluvial landscape.

The role of overland flow in sediment and nitrogen budgets of mesquite dunefields, southern New Mexico

Rainfall-simulation experiments were conducted within the Jornada Experimental Range, southern New Mexico, on small plots located on mesquite nabkha and interdune spaces. Data from these experiments were used to determine runoff, sediment and nitrogen losses, and to measure the effect of soil crusts in interdune spaces on these quantities. Results show that runoff from the nabkha plots amounted to only 7·8% of the applied rainfall, whereas from the interdune plots it was 75·7%, rising to 90·8% from plots where the soil crust was protected from raindrop impact. Sediment yield from the nabkha plots averaged 0·24gm −2s −1 and from the interdune plots it averaged 0·70gm −2s −1, with no difference between the protected and unprotected plots. Nitrogen losses in runoff averaged 1·45mgl −1 from the nabkha plots and 0·61mgl −1 from the interdune plots. However, because of the much greater runoff from the interdune areas total nitrogen loss from interdune plots was three times that from the nabkha plots. Rates of annual sediment loss by runoff are estimated to be similar to rates of aeolian erosion, but rates of dissolved nitrogen loss are estimated at only between 2% and 7% of total atmospheric deposition and less than 1% of nitrogen fixation by mesquite.

Inverted clast stratigraphy in an eolian archaeological environment

AbstractUnderstanding the geomorphic history of eolian basins is important in interpreting the archaeological record and human responses to past environments. One hundred forty soil profiles were excavated and described in southern New Mexico and West Texas. Seven major late Quaternary stratigraphic units were found: La Mesa, eolian Jornada (I, II), eolian Isaacks' Ranch, eolian Organ (I, II, and III), Historical Blowsand, and the playa deposits of Petts Tank and Lake Tank. Each unit represents a period of landscape instability, eolian erosion, and concurrent deposition, followed by landscape stability and soil formation. Eolian erosion can form local surficial lag deposits if materials larger than the competence of the wind are present. However, erosional processes alone cannot explain the presence of older clasts at the surface with intact, younger deposits underneath. We propose a combination of processes: deflation in eolian windows, followed by lateral movement of clasts over areas that have not been deflated. The effects of these processes on artifact stratigraphy and archaeological interpretations could be significant. © 2002 Wiley Periodicals, Inc.

Implications of Water Supply for Indigenous Americans during Holocene Aridity Phases on the Southern High Plains, USA

Springs in the 40 to 50 large lake basins (>15 km 2) on the southern portion of the Southern High Plains (SHP) were active during periods of aridity in the Holocene when there may have been human habitation of the area. Eolian erosion of the lake floors and lunette accretion occurred as groundwater levels declined in response to decreased groundwater recharge. The declining lake floor associated with eolian erosion allowed groundwater evaporative discharge to continue, thus maintaining a groundwater gradient toward the lake. This hydrologic condition was favorable for a relatively continuous spring discharge to the lake, independent of the elevation of the lake floor. To evaluate the postulated dynamic equilibrium critical to this conclusion, 17 optically stimulated ages were determined from a 17.7-m deep core of a lunette adjacent to Double Lakes, Texas (33°13′15″N, 101°54′08″W). The core yielded sediment accumulation dates of 11,500±1100, 6500±700, and 4900±500 yr B.P., corresponding broadly with periods of aridity known from other evidence. Based on analysis of this lunette, it is concluded that springs in Double Lakes basin probably existed throughout the Holocene with discharges similar to those observed historically. We assumed that similar dynamic equilibrium existed in the other large lake basins in the SHP and that these springs could have provided a continuous source of water for indigenous peoples during periods of prolonged aridity. The dynamic equilibrium that is proposed in this study is applicable not only to other arid and semiarid geographic areas with wind-erodible material but also over different geologic times.

Nebkha dunes in the Molopo Basin, South Africa and Botswana: formation controls and their validity as indicators of soil degradation

Nebkha dunes have been proposed as a reliable rapid indicator of aeolian erosion and dryland degradation. This paper tests the applicability of these links for the Molopo Basin, southern Africa where it is shown that nebkha sediments are largely locally derived from interdune areas and are significantly enriched in available inorganic nutrients. Feedbacks with the bush canopy are the most likely cause of the enrichment, such that this can occur without associated declines in nutrient availability in surrounding source areas. Thus, although the nebkhas indicate aeolian transport of sediment, the immediate association with soil degradation is over-simplistic.

Overgrazing effects on vegetation cover and properties of volcanic ash soil in the páramo of Llangahua and La Esperanza (Tungurahua, Ecuador)

Abstract. The páramo is a high‐altitude ecosystem of the northern Andes. The vegetation is continuous, with grasses as the dominant groundcover. Because of their high water retention, páramos play a fundamental role in water availability for all the population of the inter‐Andean valleys. There are many studies of this specific ecosystem, but very few are focussed on overgrazing and its effect on vegetation and soil properties. Intensive grazing started less than 20 years ago and was studied in a representative area in the western Cordillera of central Ecuador covered by recent volcanic ash deposits. Intensive sheep grazing has led to a strong decline in the number of plant species, the replacement of the tussock grass vegetation by a short carpet grass vegetation, and an increase of bare land. In that area, the upper 50 cm of Andisols are deeply affected by a convergent decrease of Al and Fe oxalate and pyrophosphate in soil extracts, carbon contents decrease from 100 g kg–1 to less than 50 g kg–1 in the humid zone, from 70 to 40 g kg–1 in the dry zone and a reduction of water‐retention capacity at −33 kPa matrix potential from 800 g kg–1 to 200 g kg–1 in humid zones, from 350 to less than 100 g kg–1 in drier areas. They showed also a decrease in the macrostructure and the development of a highly water repellent microstructure. All these important transformations favour the development of aeolian erosion in dry areas, runoff on bare surfaces, and gully erosion on slopes. The role of the páramo in water‐regulation of this ecosystem seems to have been adversely affected for the future.

Eolian Dust Erosion from an Agricultural Field on the North Carolina Coastal Plain

Eolian erosion typically has not been considered a significant process on the humid southeastern coastal plain of the United States. A preliminary study of eolian erosion from an agricultural field was undertaken during the late winter of 2002 and early spring of 1999. During those times local agricultural practices leave fields bare while frontal systems produce frequent high wind events. Dust emissions were measured with two samplers; modified Wilson and Cooke passive dust traps and high-volume air samplers. Results of the study indicate that wind erosion is a significant process on agricultural fields of the North Carolina Coastal plain. Dust flux off of the field during the largest of five measured events was estimated as high as 126 kg/m with total losses of 3070 kg/ha. Atmospheric concentrations of suspended material were measured at 58,815 μgm-3. Sediment erosion was not evenly distributed across the field. Erosion was focused over soils that are better drained. Low levels of soil moisture did not eliminate erosion but instead produced pulses of sediment emission as sustained wind continually dried then activated sequential layers of the field surface. Soil moisture and topography appear to be the primary controls on spatial erosion differences and soil characteristics likely play a secondary role.

Selected Physico-Chemical Properties of Zinc and Lead Ore Tailings and their Biological Stabilisation

The following work focuses on problems and possibilities for revegetation of zinc and lead ore tailings in the Mining and Metallurgic Plant ‘Boleslaw’ in Poland, and on selected physical and chemical properties also regarding the vegetation, which spontaneously appears on the ponds. It was found that main factors impeding the development of vegetation are excessive contents of Zn, Pb, and Cd, as well as eolian erosion and deficiency of macroelements. The results of biological fertilisation tests were discussed in particular with regard to the deficiency of macroelements and the immobilisation of Zn, Pb, and Cd. Pot and field experiments permitted determination of this kind of interaction with doses of mineral fertilization ensuring plant growth. Plants were introduced to the sediment without a layer of insulation. The obtained results, along with some thorough research into the conditions prevailing on the sedimentation ponds, may be used as a basis for the biological stabilisation of this kind of waste material.

Aeolian erosional lineations in the Libyan Desert, Dakhla Region, Egypt

This paper presents results of a study of aeolian erosion at the landscape scale. There have been few such studies in desert geomorphology compared to those focused on individual landforms and on rock surface sculpture. The present study area lies in the southern part of the Libyan Desert in south-central Egypt, between 25° and 27°N, 29° and 30°E. Bedrock comprises Paleogene limestone of various lithologies. Climate is hyperarid. The following topics are treated. (i) Correspondences between rock outcrop belts and belts of terrain lineated by aeolian erosion and unlineated terrain. (ii) The effect of lithology on aeolian lineation, which works through the presence or absence of chert in the limestones. Lineation is produced by aeolian erosion in chert-free/poor rocks, whereas erosion of chert-rich rocks produces a desert pavement that armors the surface, suppressing erosion. (iii) The effect of large valleys eroded upwind of lineated terrain, which deflect winds and trap sand, ending erosion, so that downwind lineations are reduced and finally erased by weathering. (iv) Sample lineated landscapes in the area show stages of evolution, arranged in the time domain into a proposed cycle of aeolian erosion; the cycle progresses from initial smooth plain to grooves separating long, blade-shaped ridges, to segmentation of ridges into shorter blades along diagonal joints, to streamlining of shorter blades and size reduction, to final planation. In any one wind-parallel swath of lineated terrain, stages in the cycle progress downwind in the space domain, so that upwind landscapes are more advanced in the cycle. (v) The structure of air flow responsible for lineation is still uncertain, but initial grooving may respond to stable longitudinal horseshoe vortices, or self-organized regularity of erosion by random vortices; subsequently, the erosion pattern is fixed by evolving relief. (vi) Large, smooth basins within the lineated terrain were carved by aeolian erosion before Oxygen Isotope Stage (OIS) 5 (70–130 ka), as were similar basins along the Dakhla piedmont below the scarp; little geomorphic change has occurred since, so in this field of aeolian erosional lineations (AELs) the aeolian erosion cycle may have occupied 10 times as long. Since continental scale aridity set in at ca. 2.4 Ma, there have been only two cycles in this area. A completed cycle earlier than the current incomplete one is indicated by rare small yardangs riding ‘piggyback’ on larger ones.

Location and sampling of aqueous and hydrothermal deposits in martian impact craters.

Do large craters on Mars represent sites that contain aqueous and hydrothermal deposits that provide clues to astrobiological processes? Are these materials available for sampling in large craters? Several lines of evidence strongly support the exploration of large impact craters to study deposits important for astrobiology. The great depth of impact craters, up to several kilometers relative to the surrounding terrain, can allow the breaching of local aquifers, providing a source of water for lakes and hydrothermal systems. Craters can also be filled with water from outflow channels and valley networks to form large lakes with accompanying sedimentation. Impact melt and uplifted basement heat sources in craters > 50 km in diameter should be sufficient to drive substantial hydrothermal activity and keep crater lakes from freezing for thousands of years, even under cold climatic conditions. Fluid flow in hydrothermal systems is focused at the edges of large planar impact melt sheets, suggesting that the edge of the melt sheets will have experienced substantial hydrothermal alteration and mineral deposition. Hydrothermal deposits, fine-grained lacustrine sediments, and playa evaporite deposits may preserve evidence for biogeochemical processes that occurred in the aquifers and craters. Therefore, large craters may represent giant Petri dishes for culturing preexisting life on Mars and promoting biogeochemical processes. Landing sites must be identified in craters where access to the buried lacustrine sediments and impact melt deposits is provided by processes such as erosion from outflow channels, faulting, aeolian erosion, or excavation by later superimposed cratering events. Very recent gully formation and small impacts within craters may allow surface sampling of organic materials exposed only recently to the harsh oxidizing surface environment.

Quaternary palaeohydrological evolution of a playa lake: Salada Mediana, central Ebro Basin, Spain

Sedimentary features, mineralogy, bulk geochemical composition, stable isotope analyses and pollen data from sediment cores were used to reconstruct the Late Quaternary depositional evolution of the Salada Mediana playa lake (central Ebro Basin, northeastern Spain). The 150‐cm‐long sediment core sequence is composed of gypsum‐ and dolomite‐rich muds (Lower and Middle sections) and black, laminated, calcite‐bearing sediments (Upper section). The Salada Mediana formed as a karstic depression in the Miocene gypsum substratum during the Late Pleistocene. The Lower section was deposited in a sulphate–carbonate saline lake that ended with a period of desiccation and basin floor deflation. Subsequent deposition (Middle section) took place in a playa‐lake system. Two cycles of lower water table and expanded saline mud flats occurred. The Holocene sequence is missing, probably as a result of aeolian erosion. Sedimentation resumed only a few centuries ago, and saline pan environments dominated until modern times. The Salada Mediana facies succession was mainly governed by fluctuations in the hydrological balance, brine composition, and salinity; however, aeolian processes (detrital input and deflation) and recycling of previously precipitated salts also played a significant role.

Possible Frost Mounds in an Ancient Martian Lake Bed

Circular to elongated mounds are observed in Gusev crater in the Aeolis subquadrangle of Mars. They are arranged in a large cluster and show different stages of evolution, from fresh to scar structures. Their morphology and morphometric ratios are comparable to those of terrestrial frost mounds. This study shows how the paleolacustrine environment of the Ma'adim Vallis/Gusev crater hydrogeologic system may have provided a suitable environment for the formation of frost mounds. Alternate hypotheses of formation including volcanism, fluvial erosion, and eolian erosion are discussed. Other features such as heavings, curvilinear troughs, hills, ridges, and depressions support the idea of a sediment/ice interaction. The typology of the mounds and plausible mechanisms for their formation are proposed. Their presence could support the model of a massive water body in Gusev during the Amazonian and provide indicators of paleoenvironmental conditions at the time of their formation.