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Evaluation of Aeolian Bedform Growth and Evolution at Multiple Scales
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  • James Zimbelman,
  • Stephen Scheidt,
  • Andrew Valdez,
  • Alexander Morgan,
  • Andrew Johnston
James Zimbelman
Smithsonian Institution

Corresponding Author:zimbelmanj@si.edu

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Stephen Scheidt
Planetary Science Institute
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Andrew Valdez
National Park Service
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Alexander Morgan
Smithsonian Institution
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Andrew Johnston
Adler Planetarium
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Windblown sand produces distinctive bedforms at scales ranging from normal sand ripples to large reversing sand dunes. We explore how aeolian bedforms evolve at both extremes of this range. An investigation of the transition from sand ripples (<1 cm height) to granule-coated megaripples (25 cm height) is underway at Great Sand Dunes National Park and Preserve (GSDNPP) in central Colorado. Sand-to-megaripple transitions at GSDNPP were documented in May and Sept of 2019 using stereophotogrammetry that produced digital terrain models that resolved granule (1-2 mm) particles as well as some sand grains; these data show the spatial distribution of particles across sand ripples whose crests merge directly into crests of megaripples. To date we have not observed that sand ripples are a necessary prerequisite for the initiation and growth of megaripples; the spatial density of granule particles appears to influence the evolution of megaripples. Reversing sand dunes are being monitored using differential navigation satellite system data at GSDNPP (up to 10 m height) and at Bruneau Dunes State Park (BDSP) in central Idaho (individual dunes >100 m height). Surveys of the crests of reversing dunes at GSDNPP reveal a northeastward migration of individual dunes along the southern margin of the main dune mass, consistent with dominant local winds, yet the symmetric reversing dune profile is maintained during the translation. Surveys of the crests of large reversing dunes at BDSP reveal variable adjustments of the crests that may be affected by wind flow altered by the bulk of the dunes themselves, sheltering the southern end of the dunes from one of the seasonal bimodal winds. Results to date indicate that the deformable shape of aeolian bedforms affect wind flow at all spatial scales, influencing the evolution of the features over diverse time scales.