Topography and surface processes in compressional orogens

The topography of the Earth reflects the long-term history of both tectonics and climate. In this dissertation, I explore some of the physical mechanisms for the origin and evolution of mountain topography.;Much of the Earth's topography is directly attributable to fluvial processes. The observation that topography is fractal, regardless of climate or tectonic setting, suggests that scale invariance is fundamental to these fiuvial processes. A diffusion-limited aggregation (DLA) model presented here provides a robust means of generating fractal drainage patterns. The inherent "shielding" of the DLA model results in drainage networks with fractal dimensions slightly less than the space-filling condition D = 2.0, a feature in good agreement with real networks.;While continental plateaus, such as Tibet or the Bolivian Altiplano, lie in rain shadows, the margins of these plateaus can experience extremely heavy orographic precipitation. A combination of modeling and observation suggests that the present topography of Nepal and the Beni basin in Bolivia is directly attributable to the intense precipitation, erosion, and subsequent isostatic response. This "erosion machine" may be self-perpetuating. Actual rates of Neogene erosion may be calculated by summing volumes of sediment in basins. Such calculations indicate that up to 70% of the Neogene tectonic influx into the Himalaya has been removed due to erosion, and that erosion rates in the Amazonian Andes may have increased during the Plio-Pleistocene.;Topography can also reflect a purely tectonic origin. In the Tibetan plateau, Mio-Pleistocene grabens are bounded by uplifted rift flanks. The analysis of digital topography suggests that these uplifts are flexural in origin, indicating a flexural rigidity of ;Minimization of work may provide an intuitive and realistic way to model the deformation associated with mountain building. A numerical least-work model presented here highlights the competition between gravitational and frictional work. A result of this competition is the formation of a tapered topographic wedge, with the topographic slope proportional to the friction coefficient.