Identifying Topographic Signatures of River Network Development in Varied Terrains of the Pacific Northwest, USA
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Date
2024-01-09
Authors
Klema, Nathaniel
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Geomorphology leverages the competition between processes of uplift and erosion to infer geologic time-scale forcing on the earth's upper crust. While this framework has revolutionized our understanding of global mountain building, it has mostly been applied to relatively simple tectonic landscapes and few tools exist for applying such analysis to more complex volcanic terrains. Such settings, and particularly continental volcanic arcs, make up some of the earths most geologically active landscapes and are thus of broad scientific interest (Hilley et al., 2022). In this work we focus on varied terrains of the pacific northwestern region of the USA to develop tools and workflows that can applied to the study of the Cascade Volcanic arc.
In Chapter II we derive a land form classification scheme based on classical surface theory that can be used as an objective means of studying topography. We focus this analysis on the Oregon Coast range, a region studied for it's assumed steady-state characteristics. We show the efficacy of our curvature-based approach in identifying process regimes that define the evolution of fluvial landscapes, and show how land surface geometry varies as a function of drainage area.
In Chapter III we apply the methods used in Chapter II to probe timescales of fluvial development in the Central Oregon Cascades. Here a well known state-shift in hydrology is driven by weathering processes in aging volcanic bedrock and so the degree of fluvial development can inform both bedrock age and hydrologic regime (Jefferson et al., 2010). We show that this evolution is marked by an increase in the magnitude of land surface curvatures providing an objective means of studying this state-shift that does not depend on modern catchment delineations. We show that a full transition from volcanic constructional to fluvially dissected topography occurs over ~1 My, which is consistent with past estimates (Jefferson et al., 2010).
In Chapter IV we use an interdisciplinary approach to show how magmatism is expressed in mountain range scale land forms of the Columbia River Gorge where a cross section of the Cascade Arc has been exposed by persistent incision of the Columbia River. We combine modeling of fluvial knickpoints with a flexural uplift model applied to a geologic structural datum to show the relative influence of intrusive and extrusive magmatism to land form development. We also show how our model for the magmatic origin of this section of the Cascades is supported by heat flow, bouguer gravity, and surface wave tomography data.
Together the chapters of this dissertation show how through multidisciplinary approaches geomorphology can aid in disentangling the landscape evolution history of complex volcanic terrains.