Aeolian Research最新文献

The fluvial-aeolian interaction field of the Guandacol valley (northwest Argentina) is studied through different methodologies that comprise satellite, drone and GPR images, bedform descriptions, and grain-size analysis. The obtained information allowed the recognition of five depositional subenvironments: 1. Dune patches; 2. Aeolian sand sheets; 3. Muddy plains; 4. Active channels; and 5. Abandoned and secondary channels. Moreover, the lithofacies pattern, sedimentary structures and geometry of the beds permitted the definition of ten architectural elements in both channel and interchannel areas. The channel architectural elements comprise active channels with intercalations of aeolian deposits (CHe), abandoned or secondary channels (CHa), aeolian sand ramp (CHsr), lateral bars (CHlb), and aeolian mesoforms (CHem). The architectural elements in the interchannel area include active dunes (Fad), fixed or low-migration rate dunes (Fsd), partially flooded interdunes (Ffd), sandy flats (Fsf), and muddy plains (Fmp). A model of the evolution of fluvial-aeolian interaction environment is proposed in which three types are recognized: dry, intermediate, and wet. Migratory dunes and sand sheets environments dominate the dry interaction systems in the floodplain (Fad, Fsf). At the same time, during the intermediate stage, Fsd and Fsf architectures prevail, together with fluvial bars with thin aeolian intercalations into the channels (CHe and CHa). The wet systems consist of flooded interdunes, muddy plains, and different types of aeolian mesoforms in the channel (Fmp, Ffd and CHem).

The analysis of present-day depositional subenvironments in the Guandacol valley and the definition of architectural elements serve as a potential analogue for studying ancient fluvial-aeolian interaction environments.

The carbonate units grouped under the name “Tamala Limestone” outcrop for a thousand kilometres along the coast of Western Australia. The extensive Zuytdorp Cliffs shaping the northern half of the coastline up to Shark Bay expose and offer an exceptional access to the stratigraphy of this formation.

The regional survey of the Shark Bay region, which combines both stratigraphic and sedimentological analyses, reveals that the Tamala Limestone is a dry accumulating aeolian system composed of large transverse dunes migrating parallel to the prevailing winds. Accordingly, the amino acid-data show an aging of the units towards the east. Episodes of carbonate aeolian sedimentation correlate with the successive glacial intervals of the Pleistocene whilst paleosols are correlated with breaks in the sedimentation during interglacial intervals.

Palaeoclimate reconstructions reveal that sea level and sea surface temperature of the Indo-Pacific Warm Pool were lower during glacial intervals. The weakened Leeuwin Current, which flows along the western coast of Australia and is the main source of precipitation, contributed to the aridification of the region. Consequently, and associated with a northward migration of the Hadley and Ferrel cells, periods of glaciation were drier. By contrast, paleosols developed through dissolution of the carbonate units during more humid interglacial intervals.

Aeolian dune morphology was characterized quantitatively in three dimensions to map and classify the Keeler Dunes complex (Keeler Dunes) in Owens Valley, California, from 1944 to 2012, providing a spatially and temporally resolved understanding of dune development and evolution during this period. The three-dimensional (3D) quantitative methods applied in this study provide an opportunity to build on previous two-dimensional (2D) work on dunefield evolution at this site (Lancaster and McCarley-Holder, 2013 [LM2013]). The 3D quantitative methods permitted the identification and quantification of two specific regions of the Keeler Dunes not previously described or considered. With the two new regions included in the time-series analysis, the Keeler Dunes are shown to be stable from a volume perspective since the mid-1990s, with a decrease between the late 1970s and mid-1990s. These results differ from the threefold increase reported during the same timeframe using 2D techniques by LM2013. While the Keeler Dunes were found to be stable from a volume perspective, they underwent significant geomorphological changes during this period. As the semi-active and vegetated dune mounds reactivated, depositional aprons of newly mobile sand advanced downwind. Over time, the depositional aprons formed linear dunes (in the northern dunefield) and crescentic dunes (in the southern dunefield) that are still present today. Fundamentally, the quantitative photogrammetric-based approach in this work provides significant new insight into the evolution and origin of the modern Keeler Dunes. In addition, this work underscores the importance of 3D quantitative techniques to fully characterize the temporal evolution of dynamic dunefields.

Fugitive dust sources within the Keeler Dunes, a small shoreline dune system in the northeast corner of Owens (dry) Lake in Owens Valley, California, U.S.A. were investigated. PM₁₀ flux potential was quantified using measurements from a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). Stratified random sampling was used to evaluate potential PM₁₀ fluxes from eight landforms, as determined by high-resolution satellite imagery and ground observations, found within the vicinity of the Keeler Dunes. Within each landform, potential PM₁₀ flux for one or more representative surface types was measured. A total of seven surface types were identified, several of which existed on different landforms. The results indicate that the major determinant of potential PM₁₀ flux is the landform type. Furthermore, the highest potential PM₁₀ fluxes are from landforms characterized by surface deposition of alluvial sediment. Within the Keeler Dunes Complex, these landforms are associated with the severely eroded 1944 shoreline coppice dunes, flash flood channels, and flash flood deposits. In the Owens Valley, studies of dust emissions have tended to focus on aeolian landforms. However, similar to measurements of potential PM₁₀ flux from desert landforms across the globe, this investigation points to the importance of alluvial landforms as major sources of dust emissions within the Owens Valley region. This article is a part of a larger investigation into the modern destabilization and migration of the Keeler Dunes (Schaaf et al. this issue).

Studying the role of vegetation in regulating aeolian sediment transport is complicated by the diversity of plant geometry and spatial distribution. Using Unmanned Aerial Systems (UAS) surveys of four partially vegetated sand dunes in the Simpson Desert, this study explored statistical associations between vegetation and the location and quantity of aeolian ripples. Employing mosaic image classifications, Digital Surface Models (DSM), and Canopy Height Models (CHM), four core independent metrics were computed: The fractional cover (f_c); frontal area index (λ), mean gap length (L), and shadow casting or Shadow Area Ratio (SAR). The strongest predictor of aeolian ripple abundance was the mean scaled gap length (individually scaled by the lesser of an adjacent plant’s width or height) ($\stackrel{-}{L_{\mathrm{sf}}}$) (R² = 0.83). $\stackrel{-}{L_{\mathrm{sf}}}$ (and $\stackrel{-}{L_h}$, which only used plant height) effectively resolved the spatial and structural distribution of vegetation, which was partially governed by the composition of functional plant types. f_c was also strongly associated with ripple abundance (R² = 0.81). Ripple cover varied continuously with f_c without a clear threshold for the onset of sand transport, though the curve flattened above f_c ≈ 25–30%. Moderate associations were found for SAR (R² ≤ 0.57) and λ (R² = 0.63). Shadow lengths (in units of plant height) of 1–3 best explained the location of ripples. The efficacy of shadow casting was affected by the signal to noise ratio in the DSMs at the scale of very small plants. UAS data nevertheless displayed strong potential for advancing the study of vegetation and aeolian activity.

Gobis (gravel deserts) cover large areas in northwestern China and other parts of the world, but sediment transport above gobi surfaces has not been widely investigated; thus, there is insufficient empirical data to support dust source identification. In the present study, we used the LDDSEG vertically segmented sediment sampler to collect sediment transport data above a gobi surface. The results demonstrated that the sediment transport rate above the gobi surface was larger than that above a sandy surface, with rates as high as 9.7 kg m^-1h⁻¹. The transport flux can be expressed as a Gaussian peak function, with the maximum sediment transport at 0.05 to 0.09 m above the surface. Principal-components analysis (PCA) indicated that the mean grain size of the transported sediment was controlled mainly by the content of silt and clay (<63 μm) and fine sand (125 to 250 μm); this explains the inflection height for sediment transport. PCA also indicated that dry lacustrine deposits were the main sediment source in the study region. About 90% of the cumulative sediment transport occurs at a height below 0.65 m. Our results indicate that sediment transported over a gobi surface has higher trajectories and longer distances than above a sandy surface. The larger silt and clay component (about 30%) of the sediment transported over the gobi surface means that gobi surfaces are important dust sources in northern China, although the dust likely originated from dry lacustrine sites upwind of the study site.

This study aimed to develop a method for the management of petroleum pollutants released into the environment using modified bentonite and to evaluate the use of petroleum-impregnated modified bentonite, as an eco-friendly and resistant mulch to stabilize mobile sands exposed to wind erosion. Bentonite was modified using hexa-decyl-tri-methyl-ammonium bromide to increase its capacity for petroleum adsorption. The resistivity to breakdown of the produced mulch was determined against wind, runoff, and by drainage water caused by simulated rainfall. Results showed that the basal spacing of the modified bentonite increased 162% compared to unmodified bentonite and it was able to adsorb petroleum, 5 times its base weight. The produced mulch was resistant against wind flows up to 16.7 m s⁻¹ with no soil loss during 5 min, while the untreated sandy soil started to move at a threshold speed of 10.3 m s⁻¹ (with a soil loss rate of 53 g m⁻² s⁻¹) and the tray of soil was fully eroded after 135 s. Analysis of the drainage waters which passed through the mulch showed that mulch 2 (ratio 5:1, sandy soil: modified clay + unmodified clay (1:1) mixed by petroleum) retained more polycyclic aromatic hydrocarbons compounds, compared to mulches 1 (ratio of 5:1 sandy soil: unmodified bentonite mixed with petroleum) and 3 (ratio 5:1:0.5, sandy soil: unmodified clay: modified clay mixed by petroleum). Analysis of the runoff water samples also showed that PAHs retention in mulch 2 is significantly higher than the amounts retained by mulches 1 and 3.

Sand dunes could have bistable states based on the observation that bare dunes and vegetation-stabilized dunes can coexist in the same area under the same environmental conditions. So far, more quantitative evidence on such an interesting phenomenon has remained elusive. In this study, the vegetation coverage and spatial distribution of dunes in the semi-arid Mu Us dune field, north-central China, were investigated by different remote sensing indices derived from the Landsat images using the Google Earth Engine platform, and the results were verified using the aerial images. Frequency distribution of vegetation coverage in many sub-regions (5 km × 5 km) across the dune field clearly shows two dominant peaks, one around 5% and the other around 40%, representing active and stabilized dune states, respectively. The boundaries between the patches of these two states are sharp, and have hardly shifted during the last twenty years. Such coexistence of bistable states is mostly distributed across a precipitation gradient from 200 to 400 mm in the study area. The relative portion of active dunes in total is reduced with increasing precipitation, while the dominant peaks of vegetation coverage for two dune states remain largely unchanged. All these lines of evidence are in accordance with the theory of alternative stable states and model predictions. Because the reversal would be difficult once the dunes shifted into an undesired state from the standpoint of environmental management, detecting and monitoring these transitions, which are often abrupt, is important for better process-based understanding of the mechanisms involved and anticipating future transitions.

We tested the longstanding (but untested) premise that loess cover (thickness and texture) positively impact the value of land parcels. To do this, we visited 1178 upland sites across 12 counties in Wisconsin with a mix of land uses; each site was underlain by loess of varying thickness. We sampled the loess at each site with a 195-cm long hand auger, and measured its thickness. The per-acre value of each parcel was then determined, where possible, using an online website. Parcels that contained buildings and structures, those whose per-acre values were not listed on the web site, and sites for which we lacked accurate thickness data (because the loess was > 195 cm thick) were eliminated from the dataset, resulting in a final count of 461 sites for analysis. The data, compared statistically using simple linear and logarithmic regressions, indicate that land values are highest on sites with thicker and siltier loess. This conclusion is in agreement with observations made on the ground while sampling. The strongest correlation (R² = 0.268; P-value <0.001) with land value occurred on a composite variable, developed to mimic the total mass of fine and medium silt in a 1 cm² column of loess from the soil surface to the bottom of the loess, indicating that the most prized land in the study area occurs on sites with the thickest and the most “fine-silty” loess.

The Mars Surface Wind Tunnel at NASA Ames Research Center is used to simulate windblown (aeolian) movement of sand and dust on the martian surface. Because objects weigh less on Mars, the tunnel employs lighter sand in the form of crushed walnut shell to compensate for Earth’s higher gravity. The tunnel is thus operated on the principle of ‘grain-weight similitude’. This approach enables successful replication of transport thresholds but it leads to major discrepancies for other aspects of grain behavior.