Wind-formed gravel bed forms, Wright Valley, Antarctica

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Abstract

[1] Bed forms composed of gravel size particles (≈50% of particles >4 mm) are observed in the Wright Valley of the McMurdo Dry Valley system in Antarctica. These bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0.025 (standard deviation 0.005), mean wavelength of 2.7 m (±0.49 m), and a mean height of 0.06 m (±0.01 m). Particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0.5 mm and 0.25 mm. Time-integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles ≥4 mm during the two-year monitoring period was extremely low. Measurements of the horizontal displacement of tracer particles (14 mm, 12 mm, 10 mm, 8 mm, and 6 mm diameter) placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles. The bed forms share form and grain size characteristics with both ripples and mega-ripples, showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples, but their sinuosity suggest that transverse instabilities affect their formation similar to mega-ripples. Based on the data for the prevailing environmental conditions it can be argued that the Wright Valley form is an expression of gravel particles moved solely by highly intermittent creep processes. This also argues for the need for a very long period of time for their evolution, on the order of centuries.

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