CAN SLOPE-DEPENDENT SEDIMENT TRANSPORT EXPLAIN MARTIAN CRATER PROFILES?

Martian impact craters have rims and walls that have been modified by surface processes. Indeed, the craters on Mars vary drastically in age as well as size and degree of degradation. Of the many mechanisms of mass transport, we chose a simple model of downslope gravity driven transport as a testable hypothesis. We constructed a numerical model in a spreadsheet of how a crater profile would change over time. We assume that sediment transport rate varies according to slope magnitude, and this results in a diffusive-like model. The mathematical elevation profile evolves through time based on spatial changes of sediment transport rate.The model has seven variables that must be specified including initial elevation; diffusivity; time step size; spacing between nodes in the solution; two boundary flux conditions; and duration of a simulation. We performed sensitivity tests in order to see how each variable affected the mathematical profile. We found a moderate range in forms can develop in the model, with the dominant control exerted by boundary flux conditions. Old craters, if they evolve according to a slope-dependent transport model, should smoothly fill from the edges inward, relief and slope should decline over time, and the point on the profile which divides the eroding section from the depositing section should very slowly migrate toward the crater center over time. The profile evolves toward a constant boundary between erosion-deposition areas early in the evolution, coincident with ~0.5 crater relief. Thus, no bedrock should be visible below that height. We test these predictions against a cohort of Martian crater profiles extracted from Mars Orbiter Laser Altimeter data that range in degree of degradation. Relief and slope covary for the craters, with lower slope coinciding with lower crater relief, consistent with the model. We are initiating a search of HiRise imagery to test the erosion-deposition transition location.