Gullies result from linear erosion caused by different process such as surface runoff, different types of mass movements (e.g. debris flows, mud flows), regressive erosion, or a combination of these activities. Gravitative mass movements of loose rock and/or solid rock in association with water is known to be the fundamental process for the building of gullies [Reiss, 2006]. Thus the discovery of gullies on Martian crater walls was a further indication for water-associated processes on Mars. Terrestrial gullies can be found in almost every climatic zone. Figure 1 presents an example for gullies in the Antarctic Dry Valleys, a region which is used as a Mars-analog study site from many researchers.
Martian gullies (Fig. 2) can preferably be found on crater walls. Reiss (2006) revealed that most of the Martian gullies can be found in the southern hemisphere concentrated in a band between 35°S and 71°S. The northern hemisphere exhibits a much lower gully occurrence.
There is a number of proposed origins for gullies on Mars, such as groundwater seepage and subsequent surface runoff [Malin and Edgett, 2000], melting of near surface ground ice [Costard et al., 2002], melting of water-rich snow deposits [Christensen, 2003], dry flow of aeolian material [Treiman, 2003], and CO2-supported debris flows [Hoffman, 2000]. Martian gullies are typically less than a few kilometers long and tens of meters wide [Komatsu, 2007]. Recently, Malin et al. (2006) revealed that some Martian gullies have been active even within the past decade. If this is the case, it would imply that liquid water flows on the surface of Mars occasionally even under the current climate [Malin et al., 2006; Komatsu, 2007].
The morphology of gullies on Earth and Mars is similar. Both, terrestrial and Martian gullies show the 3 typical morphological features: (1) The zone of origin, called alcove, (2) the zone of transport, called channel/-s, and the zone of deposition, called apron (Fig. 3).
Last update: 07/06/2010 14:31
