Controls on the large‐scale spatial variations of dune field properties in the barchanoid portion of White Sands dune field, New Mexico

Abstract

Previous studies have shown that sediment fluxes and dune sizes are a maximum near the upwind margin of the White Sands dune field and decrease, to first order, with increasing distance downwind. These patterns have alternatively been attributed to a shear-stress overshoot associated with a roughness transition localized at the upwind margin and to the influence of long-wavelength topography on the hydrology and hence erodibility of dune field sediments. I point out an issue that compromises the shear-stress overshoot model and further test the hypothesis that long-wavelength topographic variations, acting in concert with feedbacks among aerodynamic, granulometric, and geomorphic variables, control dune field properties at White Sands. Building upon the existing literature, I document that the mean and variability of grain sizes, sand dryness, aerodynamic roughness lengths, bed shear stresses, sediment fluxes, and ripple and dune heights all achieve local maxima at the crests of the two most prominent scarps in the dune field, one coincident with the upwind margin and the other located 6-7 km downwind. Computational fluid dynamics (CFD) modeling predicts that bed shear stresses, erosion rates, and the supply of relatively coarse, poorly sorted sediments are localized at the two scarps due to flow line convergence, hydrology, and the spatially distributed adjustment of the boundary layer to variations in dune size. As a result, the crests of the scarps have larger ripples due to the granulometric control of ripple size. Larger grain sizes and/or larger ripples lead to larger dunes and hence larger values of bed shear stress in a positive feedback.

The Imprint of Vegetation on Desert Dune Dynamics

“…We make use of repeat aerial LIDAR topographic data collected in September 2009 and June 2010, to construct digital elevation models (DEMs) with horizontal and vertical resolutions of 1 and 0.1 m, respectively (see section 4). The dunes at White Sands have characteristic lengths of ∼100 m, heights of several meters, and migration rates of several meters per year, so structure and dynamics are well resolved with this data set (Barchyn & Hugenholtz, 2015;Pelletier, 2015;Xia & Dong, 2016). We assume that the rates of dune migration for the 2009-2010 windy season are typical of the migration that would occur in any other given year.…”

“…Beginning around the location x ≈ 7 km, the barchanoids rapidly become colonized by vegetation and invert their shape-over a scale of 1 km-to a parabolic morphology (Barchyn & Hugenholtz, 2015;Durán & Herrmann, 2006b;Jerolmack et al, 2012;Reitz et al, 2010) (Figures 1b-1d). Region III is associated with parabolic dunes that become increasingly vegetated, elongated, and slower moving as they progress downwind (Jerolmack et al, 2012;Pelletier, 2015).…”

Migrating meter-scale bedforms on Martian dark dunes: Are terrestrial aeolian ripples good analogues?

“…This type of transition, with higher sedimentary fluxes near the upwind edge of the dune field is common on terrestrial dune fields and was interpreted to be the result of a roughness transition which creates an internal boundary layer decreasing the shear stress downwind (Jerolmack et al, 2012). This view is not agreed upon; Pelletier (2015) argues in favor of a feedback between long-wavelength topography and the dunes. In the same manner, our observations demonstrate that topography plays a fundamental role causing a km-scale spatial modulation of the dune's migration rate and morphology.…”

“…This demonstrates an effective association between dune patterns and topography. It is out of the scope of this paper to investigate and prove the reasons for this relation in the case of Herschel, but it is known from our planet that long-wavelength topography influences wind flow, sediment availability and/or dune field roughness, factors that can control dune patterns at large spatial scales (Jerolmack et al, 2012;du Pont et al, 2014;Pelletier, 2015).…”

Morphological characterization of landforms produced by springtime seasonal activity on Russell Crater megadune, Mars

“…Wind is the most common trigger for slip face avalanches on Earth, yet wind strength does not significantly influence the angle required to trigger slip face avalanches (Sutton et al 2013;Pelletier, 2015). Given that the slip-faces of dunes on Mars have been measured to have similar angles to on Earth (Ewing et al, 2017;Atwood-Stone and McEwen 2013), similarly steep (>30°) slopes should be required to trigger such avalanches on Mars.…”