Constraining tectonic and climatic controls on glacial/postglacial landscape evolution using numerical modeling

• Main Author: Lai, Jingtao
• Other Authors: Anders, Alison M, Liu, Lijun, Guenthner, William, Tomkin, Jonathan
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: Geomorphology; Glacial; Postglacial; Landscape evolution; Tectonics; Climate; Cold-based glacier
• Online Access: http://hdl.handle.net/2142/109417

Earth’s dynamic surface is shaped by the interactions between surface processes, tectonics, and climate. During the Late Cenozoic, repeated glaciations have affected the landscapes of many high-latitude regions and mountain ranges around the world, including both active subduction belts and stable continental interiors. The glacial/interglacial climate perturbations have caused repeated transitions between glacial and fluvial processes. During cold glacial periods, erosion and deposition by ice sheets and glaciers has left a clear imprint on Earth’s surface, creating unique landforms such as flat till plains, wide U-shaped valleys, steep mountain peaks, and deep fjords. As the climate transitioned into warm interglacial periods, these unique landforms further influenced the pace and style of postglacial fluvial and hillslope processes. How do tectonic and climatic conditions impact the rates and spatial patterns of glacial erosion? How do the inherited glacial landforms influence the development of postglacial landscapes? To answer these questions, my work focuses on exploring the sensitivity of landscape characteristics to variability in climate, tectonics, and surface process regime using numerical landscape evolution modeling. I model the hydrological connection of upland closed depressions to growing channels (via filling and spilling or through shallow subsurface flow) in postglacial low-relief till plains. My models show that connection leads to greater rates of channel network expansion and distinctive channel morphologies as compared with cases in which those closed depressions remain hydrologically isolated. To model glacial landscape evolution, I couple a sliding-dependent glacial erosion model with a sophisticated ice dynamics model. I investigate the impact of climatic and tectonic conditions on glacier basal thermal regimes and glacial erosion. Numerical simulations reveal that glacial erosion patterns follow the patterns of the basal thermal regime determined by geothermal heat and climate. I find a robust tendency for increasing glacial erosion with increasing geothermal heat flux. As geothermal heat flux increases, the area of significant glacial erosion expands into higher elevations and the location of maximum erosion migrates up-valley because high geothermal heat flux creates warm-based areas in high elevations. Climate conditions also influence the distribution of warm- and cold-based ice and, consequently, patterns of glacial erosion. Cold temperatures create cold-based glacier areas at high elevations, while high precipitation rates tend to cause warm-based conditions by increasing the thickness of glaciers and lowering the melting point of ice. As a result, glaciers in a cold and dry climate result in limited erosion at high elevations, and most glacial erosion focuses at low elevations in major valleys. In contrast, a warm and wet climate causes a large amount of erosion at high elevations. My model results suggest that climate controls the spatial patterns of glacial erosion primarily through changing the basal thermal regime rather than altering the equilibrium line altitudes of glaciers. In addition to numerical modeling, I also analyze global digital elevation data. My analysis suggests that glacial erosion significantly increases ridge-valley relief compared with fluvial incision. The results also show that relief increases with latitude, implying that high elevation ridges might be protected from erosion by cold-based glaciers in high latitude regions. By combining numerical modeling with observations, my research provides important insights into the feedbacks and interactions between tectonics, climate, and surface processes.