Physics
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jgr...10623737w&link_type=abstract
Journal of Geophysical Research, Volume 106, Issue E10, p. 23737-23752
Physics
32
Planetology: Solid Surface Planets: Erosion And Weathering, Planetology: Solid Surface Planets: Remote Sensing, Planetology: Solar System Objects: Mars
Scientific paper
Morphometric measurements of martian valley networks using Mars Orbiter Laser Altimeter (MOLA) topographic data yield mean valley width values of x+/-σ:2040+/-1548m and depth values of x+/-σ:109+/-137m. Our analysis of changes in valley shape with latitude and wall slope with depth indicate infilling and mass wasting processes have not greatly altered the original valley shape; thus valley network morphometry is dominantly due to channel formation mechanisms. Both U-and V-shaped profiles are observed, commonly within the same valley network system. The average U-shaped valley is slightly deeper (18 m) and significantly wider (1313 m) than its V-shaped counterpart. Valley networks have decreasing width-to-depth ratios and increasing wall slopes as valley depth increases. Our observations are consistent with a two-phase valley network formation model. (1) Valleys initially form via surface runoff, a process that creates V-shaped profiles and quasi-dendritic form. The observed linear correlation of top width and depth (below 125 m depth) suggests the depth of vertical incisement governs top width. (2) Reactivation of the same valleys by headward extending sapping processes widens the channel to form U-shaped cross sections in downstream reaches. The availability of liquid water within a few hundred meters of the surface appears to be a necessary requirement for valley network formation. Mean valley depth decreases by ~50 m from equatorial to higher latitudes (~50°), contrary to the relationship predicted if the sapping depth was governed by the ice-water boundary. Deeper equatorial valley networks may result from latitudinal variations in the availability of water or formation efficiency.
Phillips Roger J.
Williams Rebecca M. E.
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