UCLA

Wind-driven sediment transport dominates landscape evolution in arid environments as observed on modern Mars and in many regions on Earth, both in the present day and throughout the geologic past. Desertification continues to increase around Earth, leaving more of our planet under the influence of aeolian processes, thus making studying the landforms created by wind ever more important. Sand-transporting winds can be depositional, creating ripples and dune fields, or erosional, creating yardangs and ventifacts. Collectively, these features, created by wind-driven sediment transport, record a history of local winds integrated over both modern and recent geologic time. Chapter 1 of this thesis provides a background of wind-driven sediment transport and places my three investigations regarding various aspects of aeolian geomorphology in this broader context. These studies range from addressing the factors that affect a landscape’s sediment budget to analyzing the landforms wind-blown sediment can create to lastly quantifying sand’s destructive force via abrasion with distance away from a sand source. Chapter 2 investigates the question of when a crater basin transitions from being a sink to source of sediment by analyzing 116 crater walls in Arabia Terra on Mars. Mars, once very-much Earth like and dominated by water, is now primarily evolving by wind. This transition has altered the degradation rates of craters on Mars and thus how much sediment is added or subtracted from the planet’s overall sediment budget. In this work, we showed that a crater transitions from sink to source when the crater wall has degraded to a slope of ~15�. We compared these results to other work completed in other regions on Mars as well as other measurements made in similar environments on Earth, showing an agreement in each. In chapter 3, we explored a transitioning wet-to-dry environment on Earth as an analog for similar transitioning environments that once occurred on Mars. We focused on crescentic shaped features formed at the wet-to-dry transition in Deep Springs, CA, and determined that although they are strikingly similar to barchan sand dune strata formed in aeolian environments, they are formed by the inflow and outflow of groundwater into the playa lake. These results, and others in the work, show that we should proceed with caution in evaluating the dominant formation process in similar environments on Mars as observed in satellite imagery and those collected on the surface. In Chapter 4, we quantified the magnitude of abrasion on gypsum with distance away from a sand source. The data collected here over ~1.5 years shows agreement with previous studies quantifying rates of abrasion with height and suggest that the magnitude of abrasion decreases exponentially from the sand source with a proportionality of ~-3x10-4 while sediment flux decreases linearly away from a sand source with distance.