AGENTS OF PLANETARY GEOMORPHIC CHANGE: MARTIAN AEOLIAN MORPHODYNAMICS AND THE EMPLACEMENT OF CRATER EJECTA
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Date
2017-05-11
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Johns Hopkins University
Abstract
High resolution images of planetary surfaces, such as of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera, reveal a landscape shaped by wind and impact cratering. Wind is the most formative geologic agent on Mars today and impact cratering is the most pervasive geologic process over the lifetime of the Solar System’s solid worlds.
In this thesis, I examine the geomorphology and morphodynamics of aeolian geology on Mars and the emplacement of impact crater ejecta on solid worlds with an eye toward the Moon. I provide an introduction to these topics and planets in Chapter 1. In Chapter 2, I present a model for predicting sand flux changes downwind within a dune field by invoking internal boundary layer flow and topographic wind speed changes. These predictions are consistent with measured sand fluxes and changes in dune geomorphology as a function of downwind distance. Chapter 3 builds off this work to explain the existence of Martian sand sheets as deriving from erosion via sand suspension of upwind dunes, in contrast to Earth’s dunes and sheets. These results and insights were facilitated by atmospheric circulation models combined with automatic and manual ripple and dune change detection methods. Chapter 4 unveils a new method for studying the dynamics and resulting geomorphology of the emplacement of impact crater ejecta. Along with presenting this new method, I also present geologic results from the initial experiments which reveal ejecta emplacement to be both erosive and depositional, analogous to terrestrial debris flows. The consequences of heterogeneous ejecta emplacement provide an interpretive framework for analyzing spectral datasets, samples, and stratigraphic relations for the Moon and other solid worlds.
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Keywords
planetary aeolian geology, impact crater ejecta emplacement