Aeolian bed forms are formed by wind action. Wind action is one of the most surface-forming processes on Mars. Dust storms and dust devils are currently observable on Mars and subject of many studies e.g. [Ryan and Sharman, 1981; Cantor et al., 2001; Cantor et al., 2006]. There are many processes associated to wind erosion, such as aeolian fretting or pitting and deflation, resulting in multiple different erosional features. Examples for these are fretted surfaces, ventifacts (wind-faceted stones and rocks with flattened polished surfaces) and deflation surfaces. An overview of these processes and terrestrial analogues is given by [Thomas et al., 2005]. Aeolian processes do not only result in erosional features but do create multiple aeolian bed forms. The best known of them are dunes but also smaller features such as wind tails or moats can be found on Mars and Earth.
On Mars as on Earth many different dune shapes can be found, e.g. barchan and transverse dunes, barchanoid ridges, longitudinal dunes, ripples and star dunes [e.g. Breed et al., 1979; Hayward et al., 2007] . On Earth, dunes are typically formed in deserts of arid or semiarid regions or in coastal areas. On Mars, sand dunes are almost globally distributed. Most of the dunes are found on the floors of impact craters or other depressions such as grabens or channels, in polar regions, and also near the calderas of highland volcanoes. In opposite to the yellowish quartz-rich terrestrial dunes, the majority of the Martian dunes consists of dark mafic sands.
Images 1(a) and 1(b) show examples for barchan dunes on Earth and Mars, respectively. These crescent dunes whose horns point downwind were built by constant unidirectional winds and indicate a limited sand supply [Pye and Tsoar, 1990]. They can become many tens of meters high and exceed widths of several kilometres [Breed, 1977; Bourke et al., 2006]. This dune type is the most common on Earth and Mars [Breed et al., 1979].
Images 2(a) and 2(b) show star dunes on Mars and Earth, respectively. They were built in a multidirectional wind regime and have a pyramid-like shape. This dune type is characterised by three or more slip faces on arms radiating from the high centre of the mound. On Mars, they can be found on the margins of huge and complex dune fields on crater floors. This is analogue to Earth, where star dunes mostly occur around the margins of sand sees [Breed, 1977].
Moats develop through the non-accumulation of particles on the upwind side (luv) of small obstacles caused by flow acceleration in the local wind patterns [Greeley et al., 2002]. On the central upwind side of the obstacle, the moat typically has its deepest part, while is becomes shallower extending down from both flanks. Images 1(a) and 1(b) give examples for moats on Earth and Mars, respectively.
Besides such impressive aeolian bed forms like dunes, numerous smaller types of aeolian accumulations similar to Earth can be found on Mars. Images 1(a) and 1(b) show wind tails on Mars and Earth, respectively. These drift deposits develop in the lee of topographic obstacles, such as small rocks. The tapered end of the wind tail points downwind.
Aeolian Analogues:
Dunes:
Moats:
Windtails:
Aeolian Analogues:
Dunes:
Last update: 07/06/2010 13:37
