Interpretation of the complex dune morphology on Mars: dune activity, modelling and a terrestrial analogue

In this work we analyze a dark erg on Mars that could be considered a mega-dune (draa) where secondary dunes of different morphology are superposed over a main crescent-shaped bedform (primary dune). The presence of a complex, multi-directional wind regime is indicated as one of the main causes for the accumulation of a tall draa, presenting an analogy to the Great Sand Dunes in Colorado. In both cases, main regional winds from the SW blow in opposition to winds from the NE which are enhanced by the topography. Such a complex wind regime leads to the development of star and reversing dunes and is accurately predicted by atmospheric models on a regional and local scale. Signs of activity in the form of grainflow scars are also noted over the slip faces of many dunes, suggesting that easterly winds are actively shaping the study draa in the present-day climatic setting. The presence of this draa on Mars suggests a complex interaction between regional and local topographically controlled flows and a consistent availability of sand. The future study of an analogue terrestrial site such as the Great Sand Dunes could be fundamental for understanding the evolution of similar Martian dune fields. Copyright (C) 2012 John Wiley & Sons, Ltd.