Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p31b0436y&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P31B-0436
Other
6225 Mars
Scientific paper
Since Mars gullies were first revealed with the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 2000, they rapidly became a hotspot in Mars studying in that some of them are very young features on Mars surface. The previous studies focused on their formation and erosion mechanisms. As a result, several mechanisms have been proposed. But none of them can interpret the formation of all gullies perfectly. High resolution HiRISE images give us a good opportunity to examine it. In this study, we propose that wind could play an important role in some of the gullies formation. Wind is the most important agent acting on Mars surface (Fenton, 2003) and produced many features on Mars surface, including ubiquitous dunes, yardangs, deflation pits, dust storms, and dust deposits. Similarly, wind can also affect the inner edge of craters and valleys, where the gullies have been found mostly. Under the erosion of wind, the small channel will turn to a big gully. Wind could be a major reason to explain (1) why gullies formed in one side of a crater wall, while small wind-blown sand deposits in the opposite side of the same crater, as found in the crater of this HiRISE image (PSP_001697_1390_RED.JP2) and (2) why two craters next to each other, but only the big one has gullies developed. The reason for this is that big crater can form a strong wind circulation. In another HiRISE image (PSP_001330_1395_RED.JP2), we found a rock in the lower end of a gully course in a crater wall, for which we explain this gully is in the process of formation. This rock could be moving down and carving in to form the course due to the wind force. Based on the common characteristics of wind abrasion mechanics (Greeley and Iversen, 1985), we propose the following processes of gully formation by wind: (1) Embryonic stage: one side of a crater wall or valley wall was "softened" by the wind storm and formed some irregular and V-shaped fractured channels. (2) Youthful stage: small impact pits formed due to wind storm increase in numbers and coalesce due to lateral growth of the pits. In the same time, the abrasion channels grew longer down the wall. (3) Advanced stage: under the influence of gravity and wind abrasion, mass materials on the upper wall begin to avalanche in the downwind side, while wind-blown sands deposit in the upwind side of the valley or crater under the circulation of wind. (4) Mature stage: complete removal of the sands in the channels and the gullies are completely exposed. Sands continue to deposit on to the upwind side of the crater or valley.
Xie Hehu
Yue Zhiguo
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