Energy Tranfer of Saltating Sand Onto Rock Surface on Earth and Mars: Implications for Rock Morphology and Abrasion Rates

Details Energy Tranfer of Saltating Sand Onto Rock Surface on Earth and Mars: Implications for Rock Morphology and Abrasion Rates Energy Tranfer of Saltating Sand Onto Rock Surface on Earth and Mars: Implications for Rock Morphology and Abrasion Rates

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p13b0151b&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P13B-0151

Physics

5415 Erosion And Weathering, 5499 General Or Miscellaneous

Scientific paper

The interaction between saltating sand grains and rock surfaces is quantified to gauge relative abrasion potential as a function of rock shape, wind speed, grain size, and planetary environment. As facet slope becomes more horizontal, the flux of ascending vs. descending grains and impact angle decrease, altering the shape and decreasing the magnitude of the kinetic energy profile. Many kinetic energy height profiles for impacts exhibit a distinctive increase, or kink, a few centimeters above the surface, consistent with previous field, wind tunnel, and theoretical investigations. The height of the kink observed in natural and wind tunnel settings is greater than predictions by a factor of 2 or more, probably because of enhanced bouncing off hard ground surfaces. The KE profiles we present provide a relative measure of kinetic energy for two particle diameters (150 and 600 μm) at several freestream speeds (10, 25, and 50 m s-1 for Earth and 25 and 50 m s-1 for Mars) providing predictions for rock shape evolution over time. Rebounded grains increase the effective flux and relative kinetic energy for intermediate slope angles. Whether abrasion occurs, as opposed to simple grain impact with little or no mass lost from the rock, depends on whether the grain kinetic energy (EG) exceeds a critical value (EC), as well as the flux of grains with energies above EC. In abrading environments, rock facets of most or all but the shallowest slopes will be abraded. The result will be rocks with abrasion features on most or all facets facing the wind. A lower, steep face may be present if saltation ceases, but this can be eroded over time, producing a sloping basal region beneath a region of even greater slope. Abrasion may ultimately cease or slow down when the rock slope is shallow enough such that EG is close to EC. Examples of rocks with these characteristics are found on Earth and at the Pathfinder and Spirit landing sites. Considering the potential range of particle sizes and wind speeds, the predicted kinetic energies of saltating sand hitting rocks overlap on Earth and Mars. However, when limited to the most likely grain sizes and threshold conditions, our results agree with previous work and show that kinetic energies are about an order of magnitude greater on Mars.

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