Recent Surface Runoff on a Dune Slope within the Last Martian Year ?

Kurzfassung

Rill erosion on a dune slope in the Russell Crater dune field was detected on a high resolution Mars Orbiter Camera (MOC)-NA image. The identified erosional morphology differs from previously observed gully erosion [1] elsewhere on Mars. The observation indicates that the extremely fresh appearing erosion is caused by recent surface runoff within the last Martian year. The erosion features were found in the high resolution MOC-NA image M1901170. They are located on a 350m high dune slope with a dip of about 8° in the Russell Crater dune field at 54.5°S and 347.3°W. The erosion starts in small alcoves in a dendritic pattern at the dune crest and merges after a short distance into main channels, which have a parallel pattern following the slope topography. In contrast to all other observed gullies on Mars they run out and abruptly end at the dune base without a depositional apron. The morphological forms show strong affinity to rill erosion on Earth [2], except from the lack of an apron. The morphology of the rills indicates that overland flow might have caused the erosion. The image was acquired in mid autumn at LS 50°. The very fresh appearing rills suggest that the erosion took place by a defrosting process between late winter and mid spring indicated by TES albedo and temperature data. We favour an erosion process by liquid water: the rills are located in absolute elevations of ~200m and the retreat of the south polar cap leads to an increase of the atmospheric pressure in the southern spring [3, 4] which could allow liquid water to be stable in this region [5]. The lack of a depositional apron may be caused by compaction of the dust material with potentially simultaneous sublimation of the fluid. Alternatively it is possible that the rills might have been formed by an unknown process of CO2-sublimation in late winter up to early spring. Further observations will be made to identify and understand seasonal erosion processes.