Geological Sciences Theses and Dissertations

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The Cenozoic Evolution of Morphological and Ecological Diversity in Holarctic Rodents Within the Context of Tectonic and Climatic Change
(University of Oregon, 2024-08-07) Peng, Amanda; Hopkins, Samantha
The evolution of mammalian biodiversity is a complicated process with many complex drivers and mechanisms. It has been a topic of unique interest for several centuries and has been explored from multiple angles. Frequently, biodiversity is measured through some aspect of total species richness, which captures the abundances of some taxonomic unit. But study has been complicated by the fact that biodiversity is comprised not only of taxonomic diversity, but also morphological, ecological, and genetic attributes, with genetic attributes being less relevant in the fossil record. Morphological and ecological diversity are descriptors of functional diversity, which describe the total diversity in the physical characteristics (size, shape, etc.) and ecological role (diet, locomotion, etc.) of a mammal. This work seeks to discover the role that morphological and ecological diversity play in the evolution and distribution of mammals, and how this diversity evolves in response to abiotic drivers, like tectonism and climatic change. I investigate this topic using rodents as a case study. Rodents are uniquely suited to studies of this type for several reasons: they are abundant on the landscape and in the fossil record and respond rapidly to environmental changes. In my first chapter, I examined the relationship between taxonomic diversity and morphological disparity in Neogene rodents of North America. I investigated the role that climate change, tectonic activity, and subsequent landscape heterogeneity play in driving both taxonomic and morphologic diversity, as well as their relationship to one another. I found that taxonomic and morphologic diversity do not respond to tectonism or topographic complexity in a predictable way, and that morphologic diversity in homogeneous landscapes surpasses that of heterogeneous landscapes for much of the Neogene in North America, contrary to what is observed in taxonomic diversity. In my next chapter, I examined the role of morphological diversity in the modern latitudinal diversity gradient. Latitudinal diversity gradients, more aptly described as taxonomic diversity gradients, describe the change in taxonomic diversity with increasing distance from the equator. These gradients are ubiquitous across the tree of life but have rarely been measured in non-taxonomic diversity terms. I explored the relationship between morphological diversity, latitude, and climatic factors, including temperature, precipitation, and solar radiation to deduce the role of these variables in shaping the modern distribution of rodent diversity. I found that latitude does not have strong controls on morphological diversity, rather, latitude appears to correlate with taxonomic diversity more strongly. This suggests that taxonomic and morphologic diversity appear to be driven by separate processes in deep time and in the modern day. In my last chapter, I probed the ecomorphological history of rodents in Asia for parallels with the tectonic and climatic record. I did this by examining ecomorphospace occupation in tandem with significant events in the geologic history of Asia. I find that ecomorphospace occupation in Asian rodents has evolved in a stepwise manner through the Cenozoic. Ecomorphospace tends to contract across aridification events and expand across events of intensified dust transportation, which could be informative for modern predictive efforts in the face of human-mediated climatic and environmental change. Together, these works progressively narrow in on the role that abiotic factors play in shaping the morphologic and ecologic evolution of rodents. These studies suggest that tectonic, environmental, and climatic drivers have some control on the evolution of ecomorphological diversity in rodents, which has progressed independently to taxonomic diversity for much of the Cenozoic. Future work will continue to examine the drivers of diversity in rodents, and attempt to parse the separate drivers of morphological, ecological, and taxonomic diversity. This dissertation includes previously published coauthored material. One supplemental file is included with this dissertation, which contains Asian fossil rodent occurrences and ecological data from the New and Old Worlds database, supplemented with morphological and ecological data collected for this dissertation.
Embargo
Influence of Landscape Weathering and Fire on Soil Contaminant Reactivity in Western Oregon
(University of Oregon, 2024-08-07) Obeidy, Chelsea; Polizzotto, Matthew
Soil and water quality are global concerns that significantly impact human health and the environment. As the demand for soil and water resources increases, it is essential to understand the reactions that govern the fate of contaminants in the environment. Contaminants like arsenic (As), chromium (Cr), nickel (Ni), and manganese (Mn) can pose significant threats to soil and water quality, and complex landscape-scale processes influence their fate. However, understanding how these processes impact soil contaminant reactivity can be complicated due to the inherent spatial and temporal heterogeneity of earth surface processes. For example, soil weathering controls the pedogenic minerals that can react with contaminants and can release metals from parent materials into soils - processes that ultimately occur at the molecular scale but play out across landscapes over large time scales. External perturbations to soil systems, such as wildfires, can further influence soil and water quality by impacting soil contaminant cycling and the minerals governing these reactions. Wildfires are becoming more frequent and severe; hence, it is crucial to understand the landscape controls that drive contaminant reactivity.The objectives of this work were to (1) understand how soil weathering influences contaminant reactivity (2) quantify fire-induced Cr and Cr-reactive mineral generation and transport from burned soils as a function of landscape position; (3) determine how multiple contaminants (Co, Mn, Ni, and V) are impacted and transported from burned soils across a landscape. Data reveal that amorphous-pedogenic minerals, driven and maintained by soil weathering, greatly influence soil contaminant reactivity. When subjected to fire, amorphous phases associated with contaminants increase before transforming into more crystalline phases with reduced sorption capacities. Furthermore, Cr(VI), a Class A carcinogen, was generated during burning and correlated with amorphous soil minerals that varied across a landscape. Contaminants released and transported from burned soils exceeded drinking water standards for Cr(VI), Mn, and Ni; the degree and persistence of contamination depended on landscape position. These findings assist in understanding how soil contaminants are influenced by weathering across a landscape and the subsequent transformations and transport that can occur after fire. This dissertation includes previously published and unpublished coauthored materials.
Open Access
MAPPING ROCKFALL SUSCEPTIBILITY IN THE STEEP ROCKY SLOPES OF SKAGWAY, ALASKA
(University of Oregon, 2024-08-07) Wachino, Ian; Roering, Joshua
Rockfall is a common occurrence in steep mountainous terrain which poses a hazard to nearby communities. It is useful to determine the likelihood of rockfall initiating from a given location, or rockfall susceptibility, which is largely controlled by discontinuities in the rock mass. Rockfall susceptibility can be evaluated by identifying unfavorably oriented discontinuities that intersect with the face of a rock slope, a technique called kinematic analysis. Modern kinematic analyses use Digital Elevation Models to identify common failure modes and rockfall susceptible slopes at the scale of entire valleys.The area of interest for this study is the rugged topography surrounding Skagway, a small town in southeast Alaska that has been threatened by rockfalls that initiate from its steep valley walls. The aim of this study is to identify areas with high rockfall susceptibility, and compare the results to mapped talus deposits which are a proxy for past rockfall activity. In the granodiorite bedrock, two steeply dipping orthogonal joint sets, and a third set of sheeting joints were identified. The most prominent joint set dips steeply to the southeast, which predisposes northwest-facing rock slopes to block toppling failure. Kinematic tests show block toppling failure is more common than planar slide failure in the study area, particularly on the eastern sides of Skagway valley and Nahku Bay that generally face northwest. These findings are consistent with the more abundant talus deposits on the eastern sides Skagway valley Nahku Bay. Three distinct areas with particularly high rockfall susceptibility, and known rockfall source areas, were identified for further investigation and mitigation.
Open Access
Insights from Mapping Distributed and Focused Volcanism
(University of Oregon, 2024-08-07) Bussard, Rebecca; Dufek, Josef
This dissertation utilizes a variety of mapping techniques to explore surface and subsurface processes at different volcanic systems. As each volcanic system is unique, it is important to understand which mapping methods can be applied to vents contained within the system and which will face more challenges. This dissertation details the use of statistical analysis and remote sensing for addressing questions of magma transport/storage as well as volcanic surface change at distributed and focused systems.To begin, Voronoi tessellations are used to map the area between vents in a variety of distributed volcanic fields. The distributions of vent areas are then compared to distributions of areas between randomly simulated vents. If the distribution of vent areas across a volcanic field differs from a random distribution, then clustering is occurring in this field; from this, causes of clustering such as regional tectonic forces, magma supply rates, and magma storage can be explored. Five of the six fields analyzed experience clustering and visualize the length scale at which clustering occurs through Kernel Density Estimation. The work then shifts from distributed to focused volcanism, specifically Mt. St. Helens, a stratovolcano in southwest Washington. A computationally inexpensive neural network developed with open access code classifies snow cover in optical imagery covering the Mt. St. Helens region through time. The snow cover estimates produced through classification are then compared with coherence maps from Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data to quantify how snow cover effects coherence (signal strength). Snow cover reduces coherence up to 70% and widespread snow cover can almost entirely mask out uplift greater than one centimeter from an inflating magma source. Finally, InSAR timeseries and velocity data over Medicine Lake volcano measures ground deformation from 2017-2021. The vertical velocity data shows subsidence across the broad edifice that increases in magnitude within the volcano’s central caldera to ~ 1 cm/yr. Markov Chain Monte Carlo (MCMC) modeling constrains several parameters of a potential volume loss source at depth beneath the volcano, including depth and volume change for a point source and depth, length, wide, opening, and strike for a rectangular sill. The highest likelihood point source sits at 7.7 km depth with a volume decrease of 0.0013 km3/yr, and for the sill source sits at 10.1 km depth with a volume decrease of 0.0016 km3/yr. Subsidence due to edifice loading is also analytically modeled and is assumed to occur (subtracted from the InSAR vertical deformation signal). When the MCMC is rerun taking loading into account, source depths become shallower and volume changes decrease. This dissertation includes previously submitted and unpublished co-authored material.
Open Access
From Terminus to Sill: Feedbacks between Fjord Stratification, Subglacial Discharge, and Glacier Ice
(University of Oregon, 2024-08-07) Abib, Nicole; Sutherland, David
Mass loss from tidewater glaciers worldwide has increased in recent decades, partially attributed to changes occurring at the ice-ocean interface. The melting of the Greenland and Antarctic Ice Sheets have contributed up 14 mm of sea level rise over the past 20 years, and there remains large uncertainty into how these numbers will evolve into the future. At present, ~one-half of the ice lost annually from the Greenland Ice Sheet is due to frontal ablation, or the combination of submarine melting and iceberg calving, with similar percentages observed in Antarctica and other locations where glaciers reach the ocean. Frontal ablation changes the geometry of a glacier’s terminus, influencing glacier dynamics, the fate of upwelling plumes, and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice-ocean processes. In this dissertation, I use both remotely sensed and field-based observations to investigate the processes that contribute to tidewater glacier evolution. In Chapter II, I combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent environmental conditions to show that the terminus morphology is predominately overcut despite high multibeam sonar-derived melt rates. This finding challenges the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting and suggests that important glacier-ocean feedbacks are missing from current submarine melt rate theory. In Chapter III and IV, I examine one currently understudied piece of glacial fjord dynamics – the input of meltwater from ice mélange in the upper layers of the water column. I use field observations collected before and after an ephemeral ice mélange event in front of Kangilliup Sermia, Greenland, to directly investigate the extent to which ice mélange meltwater can modify glacier-adjacent water properties. I show that ice mélange can cause substantial cooling and freshening of the water column, leading to a stratification change down to the depth of the outflowing discharge plume and substantial modification of upper layer hydrography. I then expand this analysis to a suite of glacial fjords in Central West Greenland to investigate the conditions under which ice mélange forms and dissipates, finding that for glacial fjords with a deep grounding line, ice mélange breakup date is highly correlated with subglacial discharge plume evolution. This implies that future changes to ocean stratification or subglacial discharge magnitude will alter the duration over which ice mélange is present, thereby changing the timing of its meltwater injection into the proglacial fjords on which it sits and the length of time it is able to supply buttressing force to glacier termini. This dissertation includes previously published and unpublished co-authored material.
Open Access
Integrating Rupture and Tsunami Modeling to Study Large Subduction Zone Earthquakes
(University of Oregon, 2024-08-07) Small, David; Melgar, Diego
This dissertation focuses on studying past and future large subduction zone earthquakes through creating and utilizing a stochastic slip rupture modeling technique in combination with deformation and tsunami modeling. Here, I created a method for incorporating fault zone specific characteristics, like interseismic coupling, into the stochastic slip rupture modeling approach. With this method, output rupture models are informed as to where slip may be more likely to occur based on the specific pattern of coupling. I use the Cascadia subduction zone as a case study to then show how including coupling for rupture generation can impact the resultant tsunami hazards for an area when compared to the traditional approach for stochastic modeling. I find that imposing coupling into the workflow creates noticeable effects on the coastal tsunami hazards.Next, I validate this approach for earthquake modeling in its ability to model M9+ earthquakes. Prior to this, stochastic slip rupture modeling had not been validated in its ability to create “realistic” slip distributions for such large magnitude events. Here, I compare the dissimilarity of a suite of slip distributions created to previously published finite fault models for 4 recent and historic M9+ earthquakes. These stochastic models are completely blind to the events we compare them to, however, the stochastic slip modeling approach is able to produce ruptures that have similar slip distributions, and therefore “realistic”, to all 4 earthquakes. Additionally, when coupling models are available, the amount and similarity of “realistic” slip distributions can increase. However, the converse could also be true depending on the a priori assumption of coupling included, so a warning should be heeded. Then, with the validated method for producing coupling informed stochastic slip models, I constrain potential slip distributions for the last great Cascadia earthquake. Unlike any previous attempt, here I incorporate 3 different paleoseismic proxies associated with the event and compare them to results from tsunami and coastal deformation modeling. I specifically compare previously estimated tsunami arrival heights in Japan, subsidence estimates across the coastal Pacific Northwest, and locations of onshore tsunami sand deposits at 7 coastal marsh and lacustrine environments to those produced by the synthetic rupture models. By utilizing all 3 constraints, I find 7 unique but similar, wall-to-wall heterogeneous slip distributions. I also find that sequences of 3 or 4 closely time (years to a few decades) events can satisfy all 3 constraints equally well. While both modes of failure fit the constraints, I favor the full margin events because adequate sequences require specific extreme tidal conditions to inundate many coastal sites and their fits to the geologic observations are weaker. This dissertation includes previously published and unpublished co- authored material.
Open Access
Melt Generation and Evolution of Magmatic Systems in Extensional Settings on Venus: A Semi-Analytical Modeling Approach
(University of Oregon, 2024-08-07) Lien, Rudi; Dufek, Josef
The planet Venus appears to be the only geologically active planet in the solar system at present, aside from Earth. This long-sustained activity is reflected by globally distributed tectonic and volcanic features and evidence for ongoing volcanism. Here, I investigate magma production in the interior of Venus to better understand what thermal conditions are required to source active volcano-tectonic interactions. I developed a two-dimensional semi-analytical model to quantify melt production rates and the thermal evolution of the Venusian interior due to thinning of the lithosphere. Results indicate that large-scale melting (10^-5–10^-2 m^3/m^2/yr) is possible under present-day Venusian conditions for a broad range of parameters, although the melt production rates are consistently lower (by at least one order of magnitude) than those at similar geologic settings on Earth. This work characterizes the interior processes that may drive magmatism, volcanism, and tectonism on Venus, which has greater implications for planet evolution.This thesis includes unpublished co-authored material.
Open Access
Modeling of Earthquake Ground Motion: From the Source to the Site.
(University of Oregon, 2024-08-07) Nye, Tara; Sahakian, Valerie
This dissertation investigates different approaches for improving modeling ofearthquake ground motion by focusing efforts on the different physical properties which are traditionally thought to contribute to shaking–– the source, the path, and the site. The robustness and informativeness of earthquake simulations and empirically-derived ground motion models rely on accurate modeling of these different components. Methods to improve ground motion modeling are highly studied; however, due to the complexity of processes that contribute to shaking intensities and uncertainty, much is still left poorly understood, especially when modeling rare or atypical events. This dissertation utilizes both simulated and real earthquake data to better constrain source, path, and site parameters. In this dissertation, we use a one-dimensional semistochastic model to simulate data for the 2010M7.8 Mentawai tsunami earthquake, as well as for 112 moderate-to-large arbitrary Cascadia Subduction Zone (CSZ) events. Tsunami earthquakes and CSZ ruptures are scarce, which results in minimal data to analyze and thus a poorer understanding of the rupture physics. However, a future occurrence of either scenario is likely to result in significant damage. With the paucity of real data, simulations are necessary to train and test earthquake and tsunami early warning algorithms. We use near-field observed data from the Mentawai tsunami earthquake to ascertain source parameter values needed to simulate tsunami earthquake-type events. With the absence of recordings from a CSZ interface event, we use global ground motion and scaling models to validate and tune modeling of the source and path in the simulation model. Through our analyses, we find the simulations to be well-modeled and representative of these uncommon events. Finally, we constrain site effects in the seismically-active San Francisco Bay Area (SFBA) by using real recordings of small-to-moderate earthquakes to estimate the high frequency attenuation parameter (κ) and its site contribution (κ0). We develop an automated algorithm for selecting the frequency bounds used to estimate κ, and we find spatial trends in κ0 to be consistent with regional anelastic attenuation models and shallow geology. Through ground motion analyses, we find κ0 to reasonably model regional ground motion and is thus a valuable contribution to future ground motion studies in the SFBA. This dissertation includes previously published and unpublished co-authored material.
Open Access
CHEMICAL CONTROLS ON THE BIOTIC AND ABIOTIC RELEASE OF CHROMIUM AND VANADIUM
(University of Oregon, 2024-03-25) Balogun, Fatai; Polizzotto, Matthew
Contamination of ground and well water by Cr and V from anthropogenic and geogenic sources has gained considerable attention over the last few decades due to environmental and public health concerns. The specific threat of Cr and V contamination is dictated by their redox speciation. In the natural environment, redox active phases such as ubiquitous Iron and manganese (oxyhydr)oxides are known to modulate mechanisms responsible for the mobility and bioavailability of Cr and V. Also, Cr and V availability is dependent on the reactivity of natural organic matter, which may serve as a major reductant of oxidized species, sorbent, and facilitator of mineral dissolution. Despite this knowledge, the specific constraints on the mechanisms of Cr and V oxidation, release, and retention by different organic carbon types, Fe and, Mn(oxyhydr)oxides in model and natural systems are not well understood. Accordingly, the objectives of this work were to (1) gain a more detailed mechanistic understanding of how organic carbon proxies and Mn-oxide influence Cr oxidation and release; (2) determine the host phases for Cr and V in aquifer materials and quantify their adsorption capacities; (3) determine the impact of organic matter and Mn-oxide proxies on the biotic and abiotic release of Cr and V in aquifer materials. Our experiments showed that aliphatic citric acid produced 8.5 times less Cr(VI) than aromatic gallic acid. In chemically variable saprolites, the affinity for V was 8 – 11 times greater than for Cr. Amorphous phases were inferred to be the major host phases for Cr and V. Lastly, organic carbon abiotically released Cr and V from solid host phases, while Mn-oxide influenced the release of Cr and V only in Redlair saprolite. This work underscores the need to integrate organic carbon types and mineralogical controls into predictive models for redox-sensitive metal dynamics and environmental availability. This dissertation includes previously published and unpublished coauthored material.
Open Access
Investigating the Magnetospheric Dynamics of Quadrupole Magnetic Fields: Applications to Geomagnetic Reversals and Ice Giant Magnetospheres
(University of Oregon, 2024-01-10) Caggiano, Joseph; Paty, Carol
Planetary magnetic fields in our Solar System exhibit a wide range of configurations, from unmagnetized Venus and Mars to the complex dipole magnetic fields of Uranus and Neptune. This dissertation investigates the influence of magnetic quadrupoles on magnetospheric dynamics, particularly in the inner magnetosphere, where quadrupole fields are the strongest. Studying the impact of quadrupole magnetic fields is essential for understanding the ice giant magnetosphere systems and for anticipating the effects of Earth's geomagnetic reversal events, which could reduce the longevity of satellites in orbit around Earth, and enhance radiation in the atmosphere, potentially deplete the ozone layer and increase the presence of harmful compounds in the troposphere. Using analytical and multi-fluid magnetohydrodynamic (MHD) models, this dissertation examines how a quadrupole magnetosphere behaves differently from a dipole magnetosphere in the context of Earth during a pole reversal and how a strong quadrupole moment can affect plasma dynamics in ice giant planets like Uranus. The research demonstrates the nature of magnetospheric convection within a quadrupole-dominated magnetosphere and how a quadrupole lacking rotational symmetry can displace plasma in the inner magnetosphere. This may have consequences for a society heavily reliant on technology during pole reversal events. These findings are novel and contribute to the understanding of magnetospheric behavior during a pole reversal, potentially helping to assess the effects on satellites, power grids, and overall health. Additionally, this research may guide observations for the upcoming Uranus Orbiter and Probe mission and future missions to ice giant systems.
Open Access
Those Queer Amphibious Animals: Digging into the Fossil Record of Otarioid Pinnipeds to Investigate their Early Diversification, Locomotor Evolution, and Conservation Biogeography
(University of Oregon, 2024-01-10) Tate-Jones, Kellum; Davis, Edward
Seals, sea lions, walruses, and their extinct relatives and ancestors have played a critical role in marine ecosystems for over 25 million years. Known collectively as pinnipeds, these secondarily aquatic animals are unique among modern marine mammals for their obligatorily amphibious lifestyle and display remarkable ecological diversity, employing a range of strategies for aquatic locomotion and occupying coastal and pelagic habitats from the tropics to the poles. In addition to their extant representatives, their fossil record contains over a hundred named pinniped species, although the majority of these species are relatively derived members of the Phocidae (true seals), Otariidae (eared seals, including sea lions and fur seals), and Odobenidae (walruses). In my first chapter, I contributed to our understanding of early pinniped evolution by describing the new species Eodesmus condoni and performing a phylogenetic analysis to determine its placement within Pinnipedia. My analysis resolved E. condoni as the most basal species yet described of the extinct pinniped family Desmatophocidae. I then explored the evolution of aquatic locomotion in otarioid pinnipeds (otariids, odobenids, and desmatophocids) by using three-dimensional geometric morphometric analyses to first investigate the relationship between humerus morphology and swimming modes and then to predict the swimming mode used by fossil otarioid taxa. My results supported the plesiomorphy of hindlimb-dominated propulsion in all pinnipeds as well as the Otarioidea, with forelimb propulsion evolving three separate times: in the lineages of desmatophocid Allodesmus kernensis, odobenid Pontolis barroni, and an ancestor of modern Otariidae, likely through exaptation of humeral structures that first evolved for pinniped terrestrial locomotion. Finally, I use ecological niche modeling to compare the range of environmental conditions inhabited by the sole surviving walrus Odobenus rosmarus during the Pleistocene to the conditions in which it currently resides. This study reveals that during the Pleistocene, the regions where O. rosmarus lived encompassed warmer conditions than its current range. Contrary to predominant narrative about walrus response to climate change, these findings suggest that O. rosmarus may indeed be able to survive in the seasonally ice-free conditions that will characterize the Arctic in the coming decades. This dissertation includes previously published and unpublished coauthored material.
Open Access
Using Deep Learning to Backcast Hydrologic Response and Inform Landslide Early Warning Systems
(University of Oregon, 2024-01-09) Sheppard, Jonathan; Roering, Joshua
Landslides are difficult to predict due to the influence of variable geologic and environmental factors, such as geomechanical properties, rainfall, ground saturation, topography, and earthquakes, exert on the probability of a slope failure. Deep learning (DL) models can accurately predict the site-specific hydrologic response on hillslopes using soil moisture, pore pressure, and rainfall monitoring data. Landslide early warning systems can utilize empirical thresholds from deep learning-derived soil hydrology properties to improve landslide hazard prediction accuracy. We study the possibility of improving a logistical regression-based landslide early warning system being used in Sitka, AK by incorporating pore pressure responses that correspond to past known landslide events. Because pore pressure records for past known events are nonexistent, we must backcast soil hydrology timeseries from weather records, without including antecedent soil hydrology as initial conditions. We assess the accuracy of predictions at various rainfall intensity thresholds made by a Long Short-Term Memory (LSTM) DL model trained on weather features compared to a model that includes antecedent soil hydrology conditions. We find that the average accuracy of our model decreases by up to 20% for important, high-intensity rainfall events.
Open Access
Stable Isotope Systematics of Calcite
(University of Oregon, 2024-01-09) Olsen, Ellen; Watkins, James
The oxygen isotopic composition of calcite is widely used in paleoclimate studies to infer the temperatures of carbonate formation across a wide range of geologic environments including hydrothermal veins, caves, lakes, surface oceans, and in marine sediments. Carbonate-based temperature reconstructions depend on empirical d18O-T relationships that are affected by factors such as carbonate growth rate, solution composition, pH, and source(s) of dissolved inorganic carbon (DIC). We carried out calcite growth experiments over a range of pH (7.5-12.8), temperature (T = 10-25°C), ionic strength (I = 0.1-1.6; [NaCl] = 0-1.4 M) and concentration of the enzyme carbonic anhydrase ([CA] = 0-3 μM). The enzyme CA promotes isotopic equilibration of the DIC pool, which in turn, has a strong influence on the isotopic composition of the mineral. We divide the experimental results into two categories: (1) calcite grown from an equilibrated DIC pool, and (2) calcite grown from a non-equilibrated DIC pool. Results from (1) are used to determine the kinetic isotope effects (KIEs) attending the crystal growth reaction as a function of pH and ionic strength. No evidence of an ionic strength effect on oxygen isotope partitioning between calcite and DIC was found for NaCl concentrations up to 0.35 M, but in higher ionic strength solutions, NaCl was found to inhibit the efficacy of CA and prevent complete isotopic equilibration of the DIC pool, resulting in lower and more variable oxygen isotope fractionations. The oxygen isotope partitioning between calcite and water was found to systematically decrease with increasing pH. Results from (2) are used to determine the KIEs attending the CO2 hydration and hydroxylation reactions as a function of T, pH, ionic strength and [CA]. This study is the first to separately quantify the kinetic fractionation factors (KFFs) for CO2 and OH- separately during CO2 hydroxylation. The experimental results have been used to develop a generalizable model of oxygen isotope effects in the CaCO3-DIC-H2O system. The model can be used to predict the d18O of calcites grown from variably-equilibrated DIC pools and can explain why different experimental setups have yielded different d18O-T relationships for inorganic calcite.This dissertation includes previously published and unpublished co-authored material.
Embargo
Identifying Topographic Signatures of River Network Development in Varied Terrains of the Pacific Northwest, USA
(University of Oregon, 2024-01-09) Klema, Nathaniel; Karlstrom, Leif
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.
Open Access
High-Resolution Grain-Size Distributions: Insight into Tephra Dispersal and Sedimentation during Plinian Eruptions
(University of Oregon, 2024-01-09) Wiejaczka, Joshua; Giachetti, Thomas
Detailed field studies of past eruptions contribute to constraining the input parameters used to forecast tephra dispersion and mitigate potentially fatal volcanic hazards. It is thus of the utmost importance to understand the relationships between the characteristics of tephra deposits and these input Eruption Source Parameters (ESPs). In this dissertation, I determine the ESPs for the ~7.7 ka Cleetwood eruption of Mount Mazama (Crater Lake/giiwas, Oregon, USA). This eruption is an important historic eruption because it immediately preceded the climactic caldera-forming eruption, at the same location, and is similar to the only observed silicic volcanic eruptions that have transitioned from explosive to effusive activity (2008 Chaitén and 2011-2012 Cordón Caulle, [Chile]). The Cleetwood eruptive sequence consisted of two consecutive VEI 4 eruptions: the main lower Cleetwood unit and smaller upper Cleetwood units, in order from oldest to youngest. The lower Cleetwood phase alone, produced a ~14.4 km plume and emplaced ~0.85 km3 of tephra. Altogether, the explosive phase of the Cleetwood eruption deposited ~1.1 km3 (non-DRE) of material and transitioned to an effusive stage that emplaced a ~0.6 km3 rhyodacitic lava flow. Furthermore, I develop a novel approach which combines laser diffraction and dynamic image analysis to produce a continuous set of high-resolution grain-size distributions (HR-GSDs) for samples spanning a range of sizes of ejected tephra from less than a micron to a few centimeters. Through this approach, I show the ability for these HR-GSDs to provide insights into magma fragmentation and tephra transport. Next, through detailed wind analysis and the use of these ESPs as the inputs for Tephra2, a volcanic ash transport and dispersal model, I estimate the geometry and dimensions of the volcanic plume that emplaced the lower Cleetwood unit. Here, I show the standard version of Tephra2, which uses a vertical line source, does well to reproduce mass loads and grain-size distributions separately but fails to fit both simultaneously with a single set of empirical inputs. To overcome this, I adapt Tephra2 outputs to simulate deposition via an umbrella cloud. Applying this adaptation and a grid search approach over reasonable plume heights and umbrella cloud geometries gives the best results for a plume with a 4x40 km2 elliptical geometry. This approach improves overall GSDs without degrading mass loads. Lastly, I combine detailed componentry and HR-GSDs on samples I collected from the products of hybrid phase of the 2011-2012 eruption at Cordón Caulle. This analysis suggests that ash sintering after fragmentation produced a dense plug that obstructed the shallow conduit. This caused the system to re-pressurize and subsequently shatter pieces of the plug during the next explosive event. This pattern continued until permeable outgassing dominated over re-pressurization, facilitating the transition to a solely effusive stage.
Open Access
Geology of Mt. McLoughlin
(University of Oregon, 1974-06) Maynard, Leroy Carson
The purpose of this investigation is to contribute information about High Cascade volcanoes by studying one of them, Mt. McLoughlin, in detail. The study provides data on 1) the distribution and abundance of rock types, 2) the geologic history of the area, 3) the structural and contact relation of the High Cascades to the Western Cascades, and 4) the variation and evolution of rock types.
Open Access
The History and Petrography of the Basalts of Oregon
(University of Oregon, 1931-06) Fisk, Harold N.
Open Access
Machine Learning in Large and Small Earthquakes: from Rapid Large Earthquake Characterization to Slow Fault Zone Processes
(University of Oregon, 2023-03-24) Lin, Jiun-Ting; Thomas, Amanda
This dissertation summarizes the work of integrating machine-learning and traditional seismic analysis techniques into large and small earthquake problems. Earthquake early warning for large magnitude earthquakes is one of the most challenging problems in seismology. Here I develop an algorithm, called M-LARGE, that harnesses machine-learning, rupture simulations, and GNSS data to rapidly predict magnitude without saturation issue with an accuracy of 99%, outperforming other similar methods. I then show how M-LARGE can predict finite fault parameters and their evolution when rupture unfolds for fast and accurate ground motion forecasting.This dissertation will demonstrate how machine-learning can be used as a data mining tool to detect small magnitude seismicity buried in noisy waveforms. I will show its application to detect LFEs, a special class of small earthquakes typically occur down-dip of the seismogenic zone. The model detects more than five times the number of events than the original catalog in Vancouver Island and can apply to unseen stations, which provides a more flexible way to refine the temporal resolution of subduction zone processes. Finally, I will show how do small and slow earthquakes link to large and fast events and their implication on earthquake hazard assessment. With jointly inverted GNSS, strong motion, and tsunami data of the 2018 M7.1 Hawaii earthquake, I find that fast slip ruptures into the area previously hosts slow slip. The result is further validated by rupture simulations, where we find that the effective stress can be a factor that exerts a dominant control on the rupture extent. This reinforces the idea that an individual section of fault can host a variety of distinct slip behaviors, and slow slip should be considered as rupture extent for a more accurate hazard assessment. This dissertation includes previously published and unpublished co-authored material.
Open Access
Ancient soils of Earth and Mars
(University of Oregon, 2023-03-24) Broz, Adrian; Roering, Josh
Three to four billion years ago the surface of Mars may have been habitable. Ancient martian rocks that were subject to aqueous alteration in near-surface environments may store a record of this habitable paleoclimate, and they may also be favorable environments for the preservation of biosignatures. Some of the oldest altered rocks on Mars appear to be similar in mineralogy and geochemistry to ancient, buried soils (paleosols) on Earth. By using terrestrial paleosols as an analog for Mars, this dissertation seeks to constrain the organic preservation potential of martian paleosols. This is a first step towards understanding if putative martian paleosols should be considered high priority targets for in-situ drilling campaigns and sample return to Earth.The objectives of this work were to a) identify the factors that have led to enhanced preservation of organic matter in terrestrial paleosols from throughout Earth’s 3.7 billion year old geological record; b) determine if the mineralogy and alteration history of Eocene (33 million-year-old) paleosols from eastern Oregon can be identified with Mars rover-like instruments; and c) determine if trace amounts of organic carbon in the Oregon paleosols can be detected with evolved gas analysis (EGA), a technique currently employed by the NASA Curiosity Mars Rover to search for past signs of life on Mars. A data compilation of previously published organic matter content of paleosols spanning ~3 billion years of Earth history showed that soil redox state before burial was a major factor that was associated with enhanced preservation of organic matter in paleosols. Chemically reduced paleosols were found to preserve organic carbon at abundances two to three orders of magnitude greater than oxidized paleosols. Next, evolved gas analysis, spectroscopy, and x-ray diffraction were determined to be suitable techniques for constraining the mineralogy and alteration history of 33-million-year-old paleosols from Oregon. Very low amounts of organic carbon (~0.01 wt. %) and fragments of organic molecules in oxidized paleosols were able to be observed with EGA, suggesting these techniques may be suitable for detecting low amounts of organic carbon in similar materials on Mars. This work indicates that putative paleosols / weathering profiles on Mars should be considered high priority targets for in-situ biosignature detection and eventual sample return to Earth.
Open Access
From the Subglacial Environment to the Coastal Ocean: Exploring Feedbacks Between Glacial Meltwater and Tidewater Glacier Dynamics.
(University of Oregon, 2023-03-24) Hager, Alexander; Sutherland, David
Mass loss from the Antarctic and Greenland ice sheets has accelerated in recent decades and is predicted to contribute < 40 cm of mean sea level rise in the 21st Century. However, there is significant uncertainty in projections of ice sheet mass balance arising from unknowns in the dynamic response of tidewater glaciers to ocean forcing. At both the ice-ocean and ice-bed boundaries, glacial meltwater plays a vital role in governing the dynamics of tidewater glaciers, yet many meltwater processes are difficult to observe and are subsequently parameterized with unvalidated approximations in ice sheet models. Here, I employ a suite of numerical modeling experiments and observations to investigate how glacial meltwater at the bed and in the ocean affects the susceptibility of tidewater glaciers in Antarctica, Alaska, and Greenland to enhanced ocean forcing. It has historically been assumed that the formation of channelized subglacial drainage beneath Antarctic ice sheets is not possible, leading to the use of simplifying parameterizations of subglacial drainage under Antarctic ice sheets. However, recent observations have suggested subglacial channels exist beneath some Antarctic tidewater glaciers and could have a substantial impact on ice shelf ablation and glacier dynamics. In Chapter II, I pair numerical modeling experiments with observed radar specularity content from Thwaites Glacier, West Antarctica, to demonstrate that enough basal meltwater exists to form subglacial channels, which increase frontal ablation and basal friction beneath Thwaites Glacier. In Chapter III and IV, I transition to investigating the impact of glacial meltwater on glacial fjord dynamics. Leveraging numerical modeling with hydrographic observations from LeConte Bay, Alaska, I show that the sill-driven mixing and buoyancy forcing of subglacial discharge drives strong seasonal circulation regimes in LeConte Bay and may impede ice sheet models from accurately parameterizing ocean thermal forcing of tidewater glaciers. I then run further modeling experiments to test the accuracy ocean thermal forcing parameterizations in Greenland ice sheet models. By identifying the dominant local controls on local water transformation, I develop simple improvements to existing thermal forcing parameterizations that decrease parameterization error by < 89%. This dissertation includes previously published and co-authored material.