Multiscale bed form interactions and their implications for the abruptness and stability of the downwind dune field margin at White Sands, New Mexico, USA

Abstract

The downwind margin of White Sands dune field is an abrupt transition from mobile aeolian dunes to a dune-free vegetated surface. This margin is also relatively stable; over the past 60 years it has migrated several times more slowly than the slowest dunes within the dune field, resulting in a zone of dune coalescence, aggradation, and, along most of the margin, development of a dune complex (i.e., dunes superimposed on draas). Repeat terrestrial laser scanning surveys conducted over a 3 month period demonstrate that sediment fluxes within the dune complex decrease on approach to the margin. Computational fluid dynamics modeling indicates that this decrease is due, in part, to a decrease in mean turbulent bed shear stress on the lee side of the dune complex as a result of flow line divergence or sheltering of the lee-side dunes by the stoss side of the dune complex. Conservation of mass demands that this decrease in bed shear stress causes aggradation. We speculate that aggradation on the lee side of the dune complex further enhances the sheltering effect in a positive feedback, contributing to the growth and/or maintenance of the dune complex and a relatively abrupt and stable dune field margin. Our model and data add to a growing body of evidence that aeolian dune field patterns are influenced by feedbacks that occur at scales larger than individual dunes.

Controls on the aerodynamic roughness length and the grain‐size dependence of aeolian sediment transport

“…near the upper end of the values we measured), and x is the distance downwind of the roughness transition. Our approach for estimating shear velocities (u * ) and aerodynamic roughness lengths (z 0 ) based on four cup anemometers is similar to the methodology described by Pelletier and Jerolmack (2014). Field measurements and observations took place during three monitoring periods on 14-15 May (15:30-7:00), 21-22 May (17:02-10:36), and 22-23 May (15:21-11:15).…”

“…The distribution of measuring heights was selected to give approximately equal logarithmic spacing. Our approach for estimating shear velocities (u * ) and aerodynamic roughness lengths (z 0 ) based on four cup anemometers is similar to the methodology described by Pelletier and Jerolmack (2014). Wind direction was measured at 2.80 m above the bedform using an electronic wind vane.…”

Stratigraphic architecture resulting from dune interactions: White Sands Dune Field, New Mexico

“…These transition from constructive interactions (for example, merging and lateral linking) at the upwind field margin where most pattern emergence occurs to neutral interactions (for example, defect and bedform repulsion) in the dune field centre where this study was undertaken. Both the progression and overall dynamic pattern are influenced by field-scale boundary conditions, including line-sediment sources defined by the antecedent beach ridges (Ewing & Kocurek, 2010b;Baitis et al, 2014) and the feedback between surface roughness created by the dune field and the atmospheric boundary layer (Jerolmack et al, 2012;Anderson & Chamecki, 2014;Pelletier & Jerolmack, 2014).…”

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

“…The White Sands dune field in New Mexico (Figure 1) has been a particular focus of dune studies during the past decade [e.g., Kocurek et al, 2007;Ewing and Kocurek, 2010;Reitz et al, 2010;Jerolmack et al, 2011Jerolmack et al, , 2012Anderson and Chamecki, 2014;Baitis et al, 2014;Pelletier and Jerolmack, 2014], building on classic studies by McKee [1966] and McKee and Douglass [1971]. Models for the large-scale self-organization of this dune field has figured prominently in the aeolian dune literature [e.g., Ewing and Kocurek, 2010;Jerolmack et al, 2011Jerolmack et al, , 2012Baitis et al, 2014].…”