Tectonic uplift and subsidence of rocks, together with their erosion, redistribution, and deposition by atmospheric, biologic, and gravitational processes shapes the topography of Earth’s surface. Studying the rates and mechanics of such processes and how they vary in space and time is critical to understanding the dynamic environment in which we live.

Topographic change is most dramatic along convergent plate boundaries in continental settings. Here, single faults and folds can uplift at rates of several millimeters per year and can present a significant seismic hazard. Understanding the rates of growth and propagation of contractional structures is integral to an assessment of such hazards, as well as to modeling the development of continental collision zones. Whereas point measurements of deformation rates are commonly possible, constraining the full temporal and spatial evolution of structures remains challenging.

Competing with rock-uplift that elevates Earth’s surface, landscape lowering is driven by the incision of rivers into bedrock. Rivers can also bevel laterally into bedrock, thereby planating topography and creating topographic markers, such as fluvial strath terraces, which are commonly used to infer climatic and tectonic changes. Significant uncertainties remain in understanding the mechanics of such lateral erosion by rivers and of strath-terrace formation in uplifting landscapes.

Three studies in this thesis address the competition between surface uplift and lateral erosion, as well as the temporal and spatial patterns of fold growth. Chapter 1 presents results from physical experiments on the interactions between alluvial rivers with a zone of uplift. From these experiments, a simple parameter emerges that predicts the width of active beveling as a function of the uplift rate and the mobility of channels. Chapter 2 describes a field-study of the extensive lateral planation of actively uplifting folds by rivers in the foreland of the Tian Shan, northwestern China. Here, geomorphic mapping and dating of Late Quaternary terraces reveals that, contrary to existing models of strath-terrace formation, changes in lateral erosion rates of 1-3 orders of magnitude strongly control formation of planation surfaces. The dated fluvial terraces presented in this chapter do not only constrain rates of bedrock erosion, but also add to the growing database of Quaternary shortening and rock-uplift rates of contractional structures along the deforming eastern Pamir-Tian Shan collision zone. In order to explore how these rapidly deforming structures evolve both in time- and space, new decadal uplift rates obtained from interferometric synthetic aperture radar time-series analyses are presented in Chapter 3. These data place constraints on the spatial patterns of surface- and rock-uplift rates. In combination with rock-uplift rates measured over geologic timescales, a probabilistic model shows that, where significant (mm/y) changes in peak rock-uplift rate occurred across the Quaternary, gradual variations in those rates are more likely than sudden, step-like changes.

Intermontane basins are illuminating stratigraphic archives of deformation, denudation, and environmental conditions within the heart of actively growing mountain ranges. Commonly, however, it is difficult to determine from the sedimentary record of an individual basin whether basin formation, aggradation, and dissection were controlled primarily by climatic, tectonic, or lithological changes and whether these drivers were local or regional in nature. By comparing the onset of deposition, sediment-accumulation rates, incision, deformation, changes in fluvial connectivity, and sediment provenance in two interrelated intermontane basins, we can identify diverse controls on basin evolution. This work focuses on the Humahuaca basin and the Casa Grande basin, two adjacent intermontane basins currently connected by a bedrock gorge through the Sierra Alta, in the Eastern Cordillera of NW Argentina at ~23-24°S. We combine detailed geologic mapping, stratigraphic analysis of measured sections, provenance data, and geochronology to reconstruct the history of deformation, deposition, basin isolation, and incision in these basins. The exceptional time control provided by U-Pb geochronology of numerous volcanic ashes contained within the Neogene-Quaternary basin fill combined with an unambiguous magnetostratigraphic record in the Humahuaca basin enables the comparison of multiple types of datasets, e.g., sediment-accumulation rates, timing of deformation on individual faults, detrital zircon provenance, paleocurrents ,and sedimentary facies, from both basins to discriminate between potential controls on specific events in each basin’s history.

In both basins, sediment accumulation occurred ~4 – 0.8 Ma in response to renewed uplift of ranges that had already experienced an earlier phase of deformation. Both basins experienced temporary channel defeat at the outlet of the basin ~2.5 Ma as a result of increased aridity in the rain shadow of the growing ranges to the east. In the Humahuaca basin, channel defeat resulted in ponding at the outlet, deposition of fine-grained fluvial and lacustrine strata over a larger area, and an increase in sediment-accumulation rates from 2.5 Ma until 2.1 Ma. This event apparently contributed to the integration of the northern Humahuaca subbasin with the southern Humahuaca subbasin, such that rivers previously flowing east into the Andean foreland were diverted south. In the Casa Grande basin, its isolation is recognized from the loss of a distinctive, Casa Grande-specific detrital zircon age peak in the downstream Humahuaca basin. Casa Grande’s isolation lasted from ~2.4-2.1 Ma until <1.7 Ma. Despite the similar timing of deposition, sediment-accumulation rates in the Humahuaca basin were an order of magnitude higher than in the Casa Grande basin. Additionally, the Casa Grande basin strata are relatively undeformed, whereas faults in the Humahuaca basin were active from ~4.4-5 Ma until <1.6 Ma. Segmentation of faults on the western side of the Humahuaca basin results from the presence of E-W-striking Cretaceous normal faults that bounded Mesozoic grabens. The timing of deformation in the Humahuaca basin and bounding ranges is similar to the main phases of deformation in the Eastern Cordillera and broken foreland ~200 km to the south, and large-scale differences in the style and spatial distribution of deformation in these two regions probably reflect differences in the position of each region relative to the Cretaceous Salta rift and the orientation of rift-related normal faults.

Oversteepened, convex segments of stream channels called knickpoints have been utilized as markers that commonly migrate upstream and delineate abrupt changes in erosional efficiency influenced by base-level fall, changes in rock strength, or strong spatial variations in discharge. Currently, few analyses based on DEMs enable discrimination among migrating knickpoints related to changes in external forcing (baselevel fall, stream capture, and climate) versus fixed knickpoints related to internal forcing within a catchment (resistant bedrock units, coarse debris flow run-outs at tributary junctions, or landslide dams). Furthermore, few analyses have characterized the extent that migratory knickpoints steepen downstream-adjacent hillslopes. To study these interactions, we exploit a 1-m resolution LiDAR DEM of Santa Cruz Island (SCI), CA and a new algorithm that automatically extracts and measures the dimensions of any knickpoint in a regional DEM. The algorithm reduces knickpoint selection time by >99% and removes selection bias from the traditional means of regional knickpoint identification that relies on visual inspections of individual longitudinal profiles.

The spatial pattern of knickpoints located by the algorithm highlight three dominant knickpoint-forming processes on SCI: knickpoints fixed to contacts between rocks of different strength, knickpoints migrating upstream from an incision pulse caused by a significant stream capture event, and mobile knickpoints stemming from relative sea-level fall and wave erosion of sea-cliffs. Nearly 36% of the hillslope area downstream from migratory knickpoints has slopes above threshold values of 35˚, and on average, these regions display a 4-6˚ steeper median hillslope-gradient than hillslopes upstream from migratory knickpoints. Hillslope-gradient histograms are nearly identical upstream and downstream from knickpoints fixed to spatial changes in rock strength or when re-analyzing hillslopes surrounding migratory knickpoints with a 10-m resolution DEM. From regionally extensive map of stream knickpoints, geological context, and hillslope attributes extracted from a 1-m resolution DEM, new insights emerge on the controls of landscape evolution; insights that would be much harder to obtain through individual knickpoint selection or lower resolution imagery.