Tectonics, topography, climate, and erosion: Analysis of Himalayan digital elevation data and numerical modeling

Plate collision drives complex interactions among uplift, climate, and erosion involving feedbacks over many space and time scales. This dissertation investigates these processes and interactions through analysis of digital topographic data, imagery, and geologic data from the Himalayas, and through numerical modeling.; A numerical model of continental collision and breakup is used to investigate properties of the global plate tectonic system due to kinematic constraints. Characteristics of the model are determined by the dimensionless parameter {dollar}T = Omegatau, (Omega{dollar} is mean angular continent speed; {dollar}tau{dollar} is mean time between plumes). Using reasonable values for {dollar}Omega{dollar} and {dollar}tau{dollar}, the model produces plausible distributions of continental sizes, mean free paths, numbers of continents, and continent coalescence times.; We map the full-glacial extent of valley glaciation in central Nepal by analyzing valley form throughout the drainage network to identify down-valley transitions from U-shaped glacial to V-shaped fluvial forms. We map modern glacier termini using Landsat MSS imagery. Terminus elevations are converted to ELA estimates using a THAR of 0.5. Modern and full-glacial ELAs differ by 500-650 m, as found previously in the central Himalayas. This difference is much smaller than for other regions, suggesting reduced full-glacial precipitation consistent with other evidence for a weaker full-glacial monsoon.; Varying Himalayan topography is used to separate the roles of tectonics, climate, lithology, and erosion. We conclude that precipitation patterns do not correspond to the variations, that surface lithology exerts no systematic control on topography except in low-relief zones, and that steep frontal topography and streams generally correspond to inferred active fault ramps. These results support a model of the Himalayas as an "erosion machine" in which coupled orogenic, climatic, and erosional processes operate at extreme rates in a narrow zone of high relief and high mass flux, and differences among topographic profiles represent short-lived departures from a state of mass balance. Factors such as erodibility and precipitation are not of primary importance here. Evidence from other compressional mountain belts and results of physical and numerical modeling indicate that this view is probably not unique to the Himalayas.