Mathematics – Logic
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p21d..07w&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #P21D-07
Mathematics
Logic
1815 Erosion And Sedimentation, 1824 Geomorphology (1625), 5415 Erosion And Weathering, 5499 General Or Miscellaneous, 6225 Mars
Scientific paper
In the Xanthe Terra region of Mars, unique fan-shaped landforms are observed associated with the walls of 60-km diameter `Mojave' Crater in high-resolution Mars Orbiter Camera (MOC) images. These 500-m radial length fans have many morphologic attributes consistent with formation of fans by water and gravity-driven alluvial sedimentation. The purpose of this investigation is to obtain precise topographic measurements of terrestrial alluvial fans that will provide constraints for further evaluating hypothesized formation processes (debris versus fluvial flows) of the `Mojave' Crater fans. Longitudinal and transverse profiles for six alluvial fans in southwestern California were acquired to compare with similarly-scaled fan-shaped landforms found at `Mojave' Crater. The fans surveyed represent a continuum of formation processes: fluvial-dominated alluvial fans, composite fans and debris cones. Five of the fans are located on the eastern side of Soda Mountains, near Zzyzx, CA, while a sixth fan is on the eastern flank of Eagle Mountain south of Death Valley Junction, CA. Topographic data was acquired using a Differential Global Positioning System (DGPS). The Trimble 4800 Total Station and roving receiver yields topographic data with <4 cm horizontal and vertical accuracy. Several potentially useful attributes of fan morphology were observed. The radial slope of fans where debris flow processes dominated is constant while a concave-upward is associated with fluvially-fed fans. Several thousand years may be needed for fluvial modification of a composite fan to generate a weak concavity. The length of the fan radii and the fan surface gradient are inversely correlated. In these examples, shorter fans (<200 m) resulted from debris flows and have a steeper average fan slope (>15 degrees) relative to longer (>400 m), shallower (<7 degrees) fans formed via fluvial flow. Convex transverse profiles indicative of a semi-conical form were typically observed for end-member fans (fluvial or debris-flow dominated), whereas composite fans were characterized by irregular profiles.
Johnston Andrew K.
Williams Rosa M.
Zimbelman James R.
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