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Yardangs are streamlined ridges that form in arid environments on Earth and Mars through wind‐driven abrasion of consolidated substrates. Currently, there is limited consensus on the mechanisms that initiate and establish patterns of yardangs on the landscape. In this work, we examine the spatial organization of yardangs in the Campo de Piedra Pómez ignimbrite deposit of north‐western Argentina and identify evidence of antecedent controls on yardang patterns and formation. We mapped 14,826 yardangs in the region using a high‐resolution digital elevation model (DEM) and satellite imagery. We classified yardangs as points using a two‐stage decision rule based on morphology and spectral characteristics. Point pattern analysis shows that yardangs in the study area are not randomly distributed and commonly exhibit directional anisotropy in point pattern. The anisotropic pattern manifests as bands of closely‐spaced yardangs oriented transverse to the dominant northwesterly wind direction. We hypothesize that banding is controlled by pre‐existing antecedent topography in the bedrock, such as fumaroles or ridges associated with pyroclastic flow deposits. We present evidence from other locations on Earth and Mars to illustrate that the transverse banding is a common pattern in yardang landscapes. [ABSTRACT FROM AUTHOR]

Mars hosts three scales of superimposed aeolian bedforms: small decimeter‐scale impact ripples, large meter‐scale ripples, and dunes. The formation mechanism for large meter‐scale ripples is enigmatic and debated. This debate is largely informed by two questions: (a) Are large ripples similar to any features on Earth? and (b) Do they have the same grain size distribution as dunes and impact ripples? We address these questions using a novel digitizing approach to produce the largest known data set of Mars ripple sand grain size to date. We find a distinction between the grain size distributions of small ripples and large ripples and suggest that analogous bedforms are found on Earth. Despite an inability to perform rigorous sedimentology on Mars, results help resolve outstanding questions in bedform physics and support a hypothesis that aeolian ripples on Mars develop by a terrestrially analogous impact mechanism. Plain Language Summary: Mars and Earth have many different sizes of sand ripples and sand dunes. The Curiosity rover took pictures of large sand ripples with one meter spacing between crests. On Earth these large ripples are often called "megaripples". However, it is hard to know if the meter‐scale ripples observed by Curiosity form in the same way as Earth's megaripples. To help solve this problem, we measured more than twenty thousand sand grains from close‐up images of the ripples taken by the Mars Hand Lens Imager on Curiosity. The method we used to measure the imaged grains simulates the measurement method used for real sand samples on Earth. Using a method like this is important because it allows for direct comparison between Earth sand and Mars sand. With this method, we find that the large ripples observed by Curiosity have larger sand grains than the smaller ripples. Earth's megaripples also have larger grains than smaller ripples. The difference in sand grain size we measured provides evidence that large Martian ripples form in a way that is similar to Earth's "megaripples". Key Points: A new data set of surface sediment texture is used to test the fluid drag and impact hypotheses of large wind‐formed Martian ripplesLarge wind ripples have coarser and more poorly sorted surface sediment than nearby smaller ripplesThe surface sediment of large wind ripples on Mars is consistent with an impact mechanism, not fluid drag [ABSTRACT FROM AUTHOR]

The effects of large floods on river morphology are variable and poorly understood. In this study, we apply multi-temporal datasets collected with small unmanned aircraft systems (UASs) to analyze three-dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 June 2013 on the Elbow River, Alberta. We documented reach-scale spatial patterns of erosion and deposition using high-resolution (4-5 cm/pixel) orthoimagery and digital elevation models (DEMs) produced from photogrammetry. Significant bank erosion and channel widening occurred, with an average elevation change of −0.24 m. The channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments. To test the extent to which geomorphic changes can be predicted from initial conditions, we compared shear stresses from a two-dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes. We found no relation between modeled normalized shear stresses and patterns of scour and fill, confirming the complex nature of sediment mobilization and flux in high-magnitude events. However, comparing modeled peak flows through the pre- and post-flood topography showed that the flood resulted in an adjustment that contributes to overall stability, with lower percentages of bed area below thresholds for full mobility in the post-flood geomorphic configuration. Overall, this work highlights the potential of UAS-based remote sensing for measuring three-dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Throughout the northern Great Plains of North America, there are large tracts of vegetation-stabilized aeolian dune fields; some have transformed from desert-like conditions to grassland only within the last 200 years. Here, we examine how this transformation has affected vadose zone hydrology by comparing infiltration and soil moisture on stabilized and active dunes at a dune field in Saskatchewan, Canada. At one active and one stabilized dune, we measured soil moisture dynamics throughout the 2010 growing season with time-domain reflectometry sensors installed at four depths down to 200 cm below the surface. We also acquired soil samples from two active and two stabilized dunes ten times throughout the 2010 growing season to measure soil moisture dynamics down to 500 cm below the surface. Results indicate that while soil moisture was elevated at 25 cm depth in the stabilized dunes during the 2010 growing season, below that level soil, moisture was significantly lower than the active dunes and also more variable down to 500 cm. A comparison of surface hydraulic conductivity between one active dune and one stabilized dune showed that it was more than one order of magnitude greater at the former, presumably due to the elevated levels of silt, clay, and organics at the surface of the stabilized dune, which reduce the infiltration rate. Overall, we interpret the main difference in soil moisture dynamics to be caused by the presence of transpiring vegetation, as well as changes in soil properties attributed to the establishment of vegetation. Therefore, the results of this study suggest that during dune stabilization, the establishment of vegetation reduces profile soil moisture recharge. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article focuses on the analysis of chinook windstorm events in Alberta, Canada in November 2011. It states that several salient synoptic features arises in November 2011 that pose clear understandings on probable drivers of chinook windstorms including the development of light to moderate La Niña. It mentions that, in November 23, a second windstorm that was more intense hit, southern Alberta and a lee trough, classic characteristic of a cross-barrier flow, remain in the region.

ABSTRACT The introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes. Models can mimic this planform inversion, but little is known about the specific processes and mechanisms responsible. Here we outline a minimalist, quantitative, and process-based hypothesis to explain the barchan-parabolic transformation. The process is described in terms of variations in the stabilization of wind-parallel cross-sectional dune slices. We hypothesize that stabilization of individual 'dune slices' is the predictable result of feedbacks initiated from colonization of vegetation on the slipface, which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation. Under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates. Initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune, which rotates the planform brinkline angle from concave- to convex-downwind. This reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre. The planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization. Our hypothesis raises several important questions for future study: (i) are parabolic dunes transitional landforms between active and vegetation-stabilized dune states? (ii) should stabilization modelling of parabolic dune fields be treated differently than linear dunes? and (iii) are stabilized parabolic dune fields 'armoured' against re-activation? Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Progress in some areas of process-based aeolian sediment transport research is hampered by limited opportunities for data comparison, synthesis, and integration. This is partially due to a lack of reliable comparison methods. Many comparison methods are forms of calibration that are either restrictive (e.g., time-averages only) or non-existent (e.g., for field-based sediment transport thresholds or vertical mass flux profiles). It is believed that the adoption of standard methods for common measurements may improve inter-study comparison, add value and longevity to data, and advance integrative modeling efforts. Examples of approaches in allied disciplines where standards are used routinely are reviewed and we discuss how the mutual benefits of standardized data could outweigh perceived disadvantages. Overall, the goal of this commentary is to encourage discussion, self-assessment, and forethought with regard to measurement methods used in process-based aeolian geomorphology. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study on the topographic changes of a supply-limited inland parabolic sand dune from 2003-2009 in Bigstick Sand Hills of southwestern Saskatchewan. The study intends to determine the impact of the diminishing local sand supply on dune stabilization. The geographic information system (GIS) analysis of volumetric changes was conducted to be able to determine the reduction of local sand supply.

The article presents a study which focuses on the analysis of sand dunes using advanced spaceborne thermal emission and reflection radiometer global digital elevation model (ASTER GDEM). It says that ASTER GDEM does not only provides expanded spatial coverage, but it also gives better resolution. It states that analysis methods are used to illustrate data applications to discriminate dune generations. It concludes that the new topographic dataset holds opportunity for dune research.

The article presents a study on the airflow dynamics of an aeolian saucer blowout for better knowing the form-flow interactions and morphodynamics in the Bigstick Sand Hills of Saskatchewan, Canada. The study reveals the expansion and deceleration of airflow that passes over the saucer blowout's windward rim which contributes to flow separation and a minor re-circulation area on sheltered lee slopes. It shows that saucer blowout airflow patterns including oblique winds and axis-parallel winds presents significant contributions in the development and sand transport. It notes that wind tunnel experimentation, computer simulations and fieldwork on wind speed and direction are needed to understand the impacts of form-flow interactions on the morphodynamics and sand transport forms of blowouts.

The article discusses a study on the use of floodplain stratigraphy as a method in assessing ice jam flood frequency in Yukon River, which stretches from Yukon Territory to Alaska. The study focuses on the development of an ice jam flood record for northern rivers for the last 2000 years based on three study locations at the river as well as investigates natural variability and the changes of flood frequency in response to climactic factors. The benefit of the sedimentary record for future studies on flood frequency monitoring is also discussed.

Strong winds can be a dominant characteristic of the climate in the alpine biogeographic zone and can reach speeds capable of causing people to lose balance or even blowing them over. However, in contrast to urban settings, where a considerable body of literature has examined mechanical effects of wind on people, in alpine zones the hazard associated with wind is almost entirely based on anecdotal evidence and remains largely unquantified. In this article we use archival weather station data to determine the wind hazard in the alpine zone above treeline (2543m amsl) along a popular hiking trail in the Kananaskis region of Alberta, Canada. Drawing on pedestrian wind research, we define hazardous wind at this location as any recorded wind speed >22.5ms−1. We assess wind hazard based on hourly wind speed and daily maximum gust speed for the periods 2000-2013 and 2008-2013, respectively. Results indicate that hazardous winds are almost always southwesterly, consistent with the prevailing wind, and can occur at any time of the year, but are most common in autumn and winter. Daily maximum gusts >22.5ms−1 occurred every other day on average, while hourly wind speed >22.5ms−1 occurred for 1.3-6.4% of the year. Also noteworthy is that category 1 and 2 hurricane-level wind speeds (33-42 and 43-49ms−1, respectively) were recorded at this site. The peak of category 1 wind speeds occurred in 2011 (103h in total or 1.2% of the year), while the peak in category 2 wind speeds occurred in 2009 (10h total or 0.1% of the year). A review of synoptic conditions during strong wind events suggests they are likely driven by downslope winds associated with mountain wave amplification and lee cyclogenesis. Overall, this study serves as an example to demonstrate that wind hazard in the alpine zone can be considerable and should be assessed in greater detail at all locations where people are likely to encounter strong winds. [ABSTRACT FROM AUTHOR]