Avalanche grainflow on a simulated aeolian dune

Abstract

[1] Avalanches maintain the slipface of aeolian dunes, which alters their airflow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel under wind velocities of 8-11 m s -1 . Changes in slipface topography were observed photographically and measured utilizing a 3-D laser scanner with 1 mm 2 spatial resolution. Avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32 ı ) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed. This independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport.

Dynamics of sediment storage and release on aeolian dune slip faces: A field study in Jericoacoara, Brazil

“…Our data are broadly consistent with the results of Sutton et al [, ], who found that the frequency of grain flows generated in a laboratory dune depended on the sediment flux over the brinkline (formalized in our equation ). They also demonstrated that the relaxation angle controls the frequency of quasiperiodic cycles of storage and release of sediment from the upper slope in a manner that is also consistent with our equation .…”

“…Specifically, under dry‐sand conditions the 30 m tall slip face had < θ c > = 32.2°–32.35° and the 17 m tall slip face had < θ c > = 32.2°–33°, with larger values (and hence larger differences) associated with slower winds. Combining these data with the < θ c > value of 34° from the 1.2 m tall slip face of the Sutton et al [, ], available data suggest that < θ c > varies inversely with slip‐face height, although this relationship must be valid only to some limit. The relaxation angle also has an inverse relationship with slip‐face height, reflecting an inverse relationship of the critical angle with height but no such relationship for the angle of repose. The 30 m tall slip face had a < θ c > − < θ r > value of ≈0.1°, the 17 m tall slip‐face had < θ c > − < θ r > values in the range of 0.2°–0.8°, and the 1.2 m tall slip face of Sutton et al [, ] had a < θ c > − < θ r > value of ≈2°.…”

Aeolian dune sediment flux heterogeneity in Meridiani Planum, Mars

“…Even subtle differences in barchan dune morphology may contribute to migration rate variations. For example, dunes possessing more concave slip faces may produce convergent avalanches advancing the lee slope faster than a comparable sized planar-shaped barchan (Sutton et al, 2013). A spectrum of slip face concavity can be observed across the study area; although it is unclear how much of a factor this was as moderate fluxes (~5m 3 m −1 yr −1 ) were observed for dunes with both concave and planar slip faces (e.g., Figs.…”

Morphometric analysis of slipface processes of an aeolian dune: Implications for grain‐flow dynamics

“…The frequency of grain flows is thought to be dependent on factors such as the depositional rate (correlated to wind velocity) and sediment characteristics or environmental conditions which may affect grain movement or angle of repose (e.g. Allen, , ; Sweet & Kocurek,; McDonald & Anderson, , ; Nickling et al ., ; Cupp et al ., ; Breton et al ., ; Sutton, ; Sutton et al ., ,b; Pelletier et al ., ; Nield et al ., ). However, the mechanism of formation and initiation of grain flows is more complex.…”