Geologic settings of Martian gullies: Implications for their origins
Article first published online: 8 MAR 2003
Copyright 2003 by the American Geophysical Union.
Journal of Geophysical Research: Planets (1991–2012)
Volume 108, Issue E4, April 2003
How to Cite
2003), Geologic settings of Martian gullies: Implications for their origins, J. Geophys. Res., 108, 8031, doi:10.1029/2002JE001900, E4.(
- Issue published online: 8 MAR 2003
- Article first published online: 8 MAR 2003
- Manuscript Accepted: 4 OCT 2002
- Manuscript Revised: 13 SEP 2002
- Manuscript Received: 1 MAR 2002
- debris flow;
- granular flow
 Martian gullies are found on steep slopes of all origins, on all sorts of terrains of all ages, scattered across nearly all of Mars. Gullies are observed on all manner of substrates (layered, massive, shattered, rubble), with or without nearby mantling deposits. Gullies are most common in the southern midlatitudes but also occur in the northern hemisphere, in near polar terrain, on equatorial volcanoes, and on northern plains. Most gullies in the southern hemisphere are on south-facing slopes, but they occur on slopes of all orientations. Gullies are among the youngest features on Mars but locally are overlain by eolian deposits and cut by faults. Old or eroded gullies are rare, and those found have been partially stripped from slopes, leaving no rock debris behind. Most gully deposits contain no detectable rocks. These data are inconsistent with published hypotheses of gully formation, including seeps and breakouts of water or brine, hydrothermal activity, cryovolcanism, and breakouts from liquid carbon dioxide. The data are consistent with gullies being dry flows of eolian material (dust and silt), comparable to climax snow avalanches on Earth. Eolian sedimentation should be correlated little with underlying geology: cause of slope, age of terrain, type of terrain, or the nature of the rocks. Eolian sedimentation should be correlated with wind deceleration (which will cause suspended sediment to drop), and areas with common gullies are those with strong wind deceleration (predicted by global circulation model). In such areas, sediment will be deposited preferentially in the lee of obstacles; for the gully-rich areas of the southern midlatitudes, winds blow from the NNW, so that sediment is deposited on SSE-facing slopes (i.e., poleward). These predictions are in accord with observations.