Unravelling raked linear dunes to explain the coexistence of bedforms in complex dunefields

Abstract

Raked linear dunes keep a constant orientation for considerable distances with a marked asymmetry between a periodic pattern of semi-crescentic structures on one side and a continuous slope on the other. Here we show that this shape is associated with a steady-state dune type arising from the coexistence of two dune growth mechanisms. Primary ridges elongate in the direction of the resultant sand flux. Semi-crescentic structures result from the development of superimposed dunes growing perpendicularly to the maximum gross bedform-normal transport. In the particular case of raked linear dunes, these two mechanisms produces primary and secondary ridges with similar height but with different orientations, which are oblique to each other. The raked pattern develops preferentially on the leeward side of the primary ridges according to the direction of propagation of the superimposed bedforms. As shown by numerical modelling, raked linear dunes occur where both these oblique orientations and dynamics are met.

Geology and Physical Properties Investigations by the InSight Lander

“…). Recent laboratory experiments, numerical simulations and field measurements have demonstrated that a multidirectional wind regime can produce two dune trends depending on sand supply(Courrech du Pont et al 2014;Gao et al 2015;Lü et al 2017). As shown by Courrech du Pont et al(2014), this is because there are two competing dune growth mechanisms.…”

Reconstruction of linear dunes from ancient aeolian successions using subsurface data: Permian Auk Formation, Central North Sea, UK

“…Mountney et al, 1999). One present-day system containing dunes of a type similar to those envisaged for the Auk Formation is in the Kumtagh Desert of north-western China where linear draa have superimposed barchanoid dunes migrating along their lower flanks (Lü et al, 2017).…”

Understanding Snow Bedform Formation by Adding Sintering to a Cellular Automata Model

“…This robust coupling between the flow, its modification due to the undulating surface, and the evolution of the surface itself is the defining feature of the RESCAL model and thus makes it perhaps one of the best cellular automata models for simulating surface morphology that exist. This can be evidenced from the successful application of the RESCAL model to simulate various complex sand bedforms on Earth (Zhang et al, 2010;Ping et al, 2014;Lü et al, 2017) and Mars (Zhang et al, 2012) and also gives us the confidence of introducing this model to the cryospheric science community.…”