HR: 17:50h
AN: P34A-07    [Abstracts]
TI: Dunes Versus Ripples: Topographic Profiling Across Terrestrial Examples, With Application to the Interpretation of Features on Mars
AU: * Zimbelman, J R
EM: zimbelmanj@si.edu
AF: Smithsonian Institution, CEPS/NASM MRC 315, Washington, DC 20013-7012, United States
AU: Williams, S H
EM: williamssh@si.edu
AF: Smithsonian Institution, Education/NASM MRC 310, Washington, DC 20013-7012, United States
AB: Topographic profiles were collected for several aeolian bedform types throughout the western United States, ranging from sand ripples to transverse dunes. Profiles were measured perpendicular to bedform crests for features ranging over three orders of magnitude in wavelength, including sand ripples, granule-covered sand ripples, granule ripples, active transverse dunes, and partially stabilized transverse dunes. The data collection technique used depended on the size of the bedform. When the terrestrial topographic profiles are normalized by the measured wavelength of the features, in both horizontal and vertical dimensions, the profiles show a progression of shapes from sand ripples to granule ripples to transverse dunes. Current sampling does not allow a determination of whether the observed profile changes represent a smooth progression of profile shape or that the profiles fall into discreet classes. As a test of the use of the scaled profile approach to features on Mars, topographic information was derived through simple photoclinometry on the first publicly-released, full- resolution HiRISE image, which happens to reveal an abundance of aeolian bedforms. When scaled by the feature wavelength, as was done for the terrestrial examples, the profile across a 50-m-wavelength martian bedform has the characteristic shape of a granule ripple. However, the scaled height of the martian feature (0.17) is greater than the largest scaled height of any of our measured terrestrial features (0.13, for a sand ripple). If the heights from the martian profile are reduced by a factor of 0.38, the ratio of martian to terrestrial gravity, the martian profile then conforms very closely to the scaled profile of a terrestrial granule ripple. Numerous granule ripples have been imaged by both the Spirit and Opportunity rovers during more than 3 years of operation on Mars, but to date the rovers have not investigated a feature of 50 m wavelength. Topographic profiles should be obtained for additional terrestrial and martian aeolian bedforms, but our initial results imply that scaled topographic profiles can be of great assistance in evaluating whether 10- to 100-m-wavelength martian bedforms are more likely to be either small sand dunes or large granule-coated ripples.
DE: 1824 Geomorphology: general (1625)
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly