ROCK ABRASION AND VENTIFACT FORMATION ON EARTH AND MARS USING WIND TUNNEL STUDIES

We describe an initial set of experiments coupled with theoretical models and field studies that address rock abrasion and ventifact formation on Mars and Earth. Rock analog materials are being abraded under terrestrial, Martian, and high particle flux conditions to determine the effects of target and atmospheric properties on ventifact morphology. The relation between the target properties and experimental conditions and the resulting morphological forms produced provide the formulation of models of ventifact formation on actual rocks. These models are being coupled to theoretical treatments of abrasion energy due to saltation. These resulting models will eventually provide estimates for the rates of ventifact formation and the link between morphology and geologic and aeolian factors in rocks on Earth and Mars. Much of our initial efforts have involved calibration of the ASU and Ames/Marswit wind tunnels. In particular, we are examining the flux from a hopper and trying to reproduce, as best as possible, the trajectory angle and kinetic energy of saltating sand grains (a sand bed source is not used because the high flux needed for abrasion, which a hopper provides, cannot be achieved). Some initial experiments in terrestrial atmosphere have been run in which a fixed volume of sand is fed from the hopper and sand is collected in traps that span the vertical dimension of the tunnel. The collectors are positioned where, based on theoretical considerations, hopper sand is predicted to best match the trajectory and kinetic energy of saltating sand for a similar wind speed and particle size. We are using computer models of hopper trajectories in the wind tunnels and saltation trajectories on Earth and Mars. This is being done in order to determine the optimum particle sizes and wind speeds needed to best simulate saltation trajectories and kinetic energies using a hopper. These models, when combined with the determination of sand flux , can be used to determine the total kinetic energy participating in abrasion.