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Geologic settings of Martian gullies - Implications for their
origins
Treiman, A.H.
Journal of Geophysical Research. E. Planets. Vol. 108, no. E4.
Feb. 2003
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, and 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.
 Descriptors: Mars exploration | Mars surface | Planetary geology | Planetary
structure | Remote sensing | Landforms | Weathering | Wind effects | Surface properties | Erosion | Topology | Mars | Space exploration
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