Aeolian slipface dynamics and grainflow morphologies on Earth and Mars

In 2015, an active dune field on Mars was visited up close by the Curiosity rover in Gale Crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital-based imagery. For the first time, these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations. The image data from the slipface on the Namib dune within the Bagnold dune field shows grainflow morphologies
that are similar to dunes on Earth. Quantitative estimates of flow thickness, based on shadow length are presented for the grainflows on the Namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the Maspalomas dune field located in Gran Canaria, Spain. Using observations from Maspalomas to support interpretations of martian slipface dynamics, we discuss implications for the local wind regime, style of grainflow, seasonal activity, and dune migration. The presence of multiple large-magnitude grainflows on the Namib slipface suggests an active aeolian environment, capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope. However, the thinness of grainflows on the Namib dune, the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment, at least for the most recent slipface activity. Large, actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events. This mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies, both young and old, which are otherwise quickly erased on Earth due to sediment redistribution and grainfall.