Date of Award

Summer 8-14-2015

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Peter Koons

Second Committee Member

Christopher Gerbi

Third Committee Member

Sean Smith

Abstract

The surface of the Earth retains an imperfect memory of the diverse geodynamic, climatic, and surface transport processes that cooperatively drive the evolution of Earth. In this thesis I explore the potential of using topographic analysis and landscape evolution models to unlock past and/or present evidence for geodynamic activity. I explore the potential isolated effects of geodynamics on landscape evolution, particularly focusing on two byproducts of tectonic strain: rock displacement and damage. Field evidence supports a strong correlation between rock damage and erodibility, and a numerical sensitivity analysis supports the hypothesis that an order of magnitude weakening in rock, well within naturally occurring weakening levels, can have significant effects on the rates and patterns of landscape evolution. More specifically, weak zones associated with fault damage erode relatively quickly and hence attract a greater proportion of surface runoff, causing many rivers to become confined to the exposed structures of fault zones. In many cases this influence is independent of how evolved a landscape is prior to weak zone introduction. When combined, displacement and damage along a fault cooperatively control the drainage network pattern, hillslopes, and channel gradients. Quantitative methods for measuring topographic anisotropy indicate signature patterns associated with specific scale-dependent geodynamic and geomorphic processes that could otherwise go unnoticed when attempting to identify features from raw topographic data alone. The sharp relief associated with weak zone erosion leads to a significant perturbation of the near surface stress field that can potentially localize crustal failure under active tectonic conditions. Models used to study interactions between climate, surface processes, and crustal tectonics suggest a strong positive feedback between erosion and strain caused by the mechanical link between rock damage and erodibility. The rapid erosion of shear zones leads to greater topographic stress and hence greater strain localization. The link between erodibility and strain localization scales with greater damage, particularly due to structurally confined drainage patterns focusing a greater degree of fluvial incision in regions that already accommodate the majority of strain, resulting in a greater concentration and greater longevity of strain in narrow shear zones.

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