MARTIAN AEOLIAN SYSTEMS

In most regions of Mars, aeolian processes dominate landscape evolution, slowly wearing down volcanic flows, impact craters, river channels, and polar ice caps. Areas of net erosion are marked by vast fields of coarse-grained ripples and yardangs. Dark dunes composed mainly of mafic sands are common, always superposed by ~3 m wide bedforms that are thought to be analogous to sand ripples on Earth. Enigmatic Transverse Aeolian Ridges (TARs), which are similar in size to simple transverse dunes, but that have morphologies more consistent with ripples, are much more common than the dark dunes. Sandstones and duststones, some of which are billions of years old, attest to the continued work of the wind throughout much of martian history. Although the work on Mars is yet in its infancy, the same principles used to study terrestrial aeolian systems may be applied to understand how martian aeolian systems developed. Three examples from markedly different martian environments illustrate the wide range in aeolian system history on Mars.

1) In the great northern polar sand sea, Ewing et al. (2010) used pattern analysis to show that at least one part of the vast Olympia Undae was produced in two constructional events. An older, well-organized generation of transverse dunes, formed by circumpolar easterly winds, is slowly being reworked by a new influx of sand eroding from the edge of the nearby polar cap.

2) Deep in Ganges Chasma, an offshoot of the extensive Valles Marineris, lie several dune fields and sand sheets. The largest, with an area of ~400 km², abuts a ~5 km high scarp. Combined application of the principle of maximum gross bedform-normal transport (MGBNT) and a mesoscale atmospheric model shows that sand converged upon this spot from four directions, under transport-limited conditions.

3) Meridiani Planum is a flat plain pocked by impact craters. The plains are covered by coarse-grained ripples, whereas TARs and dark dunes formed on the crater floors. Pattern and MGBNT analysis reveals four generations of bedform construction within ~300 Ma, each formed by a distinct wind regime. Uniform bedform size suggests the coarse-grained ripples formed from erosion of the ~3 billion year sediments which they superpose. Bedform construction occurred during brief transport-limited conditions that likely correspond to variations in climate.