RSS 1.0Geosciences
Recent Submissions
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Finding solutions to the world's pending critical minerals supply crisis: developing new geochemical analytical methods and evaluating the potential for Te and Bi extraction from existing Au minesBismuth (Bi) and tellurium (Te) are technologically critical elements (TCEs), also known as critical minerals, primarily recovered as byproducts in the extraction of lead (Pb) and copper (Cu), respectively. Global demand for Bi and Te is expected to rise signicantly in the coming decades as energy production becomes carbon neutral. In order to meet this demand, alternative sources of Bi and Te must be identifed. Bismuth and Te are commonly enriched in granitoid-related gold (Au) deposits and epithermal Au-Ag-Te deposits but are not presently recovered. Identifying which Bi and Te minerals are present throughout the Au extraction process is essential to determining where these elements might be recovered and in what quantities. Concurrent with the need to identify potential sources of TCEs is the need to validate advancements in analytical geochemical methods. Energy Dispersive Spectrometry (EDS) methods have become a go-to mineralogical identication tool in the mineral exploration and mining industries due to their rapid automated analysis. However, little cross-validation has been done to verify the results and determine the limitations of these tools. Here I present the results of three studies: 1) an EDS bulk mineralogy phase mapping method validation study on Au and Cu mill processing samples; 2) a detailed elemental composition and mineralogical analysis of samples from the Pogo Mine Mill (Interior Alaska, USA) identifying potential annual byproduct recovery of 13.5 and 7.5 metric tonnes of Bi and Te, respectively; and 3) a detailed elemental composition and mineralogical analysis of mill samples from the Golden Sunlight Mine Mill (Whitehall, Montana, USA) identifying Te primarily hosted in pyrite. Using this approach for similar metallurgical studies at other Au mines with known signicant Bi and Te could yield additional targets for recovery and provide a framework for identifying other potential TCEs/critical minerals in other deposits.
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Acoustic and seismic signature of sustained volcanic eruptionsVolcanic eruptions of any size can pose a significant risk to the life and livelihood of humans, as well as to infrastructure and the economy. Understanding the dynamics of an eruption is crucial to providing timely and accurate assessments of the eruption and associated hazard. Ideally the monitoring of volcanic unrest and eruption dynamics is done remotely to minimize exposure to volcanologists and maximize the spatial monitoring coverage of instruments. Another important factor is to have real-time data to facilitate rapid analysis and interpretation. Seismic and acoustic (infrasound) waves have proven useful in terms of remote real-time volcano monitoring. However, accurate interpretation of these signals is a challenge due to the complexity of each volcano and each eruption. In this dissertation I present three projects that aim to improve the interpretation of seismic and acoustic signals, specifically their spectral properties, generated by multiphase flow during an eruption. In Chapter 2 we derive a seismic tremor model for a source underground but above the fragmentation level where the gas and particles rush through the volcanic conduit. This physical model assumes ash particles and gas turbulence impact the conduit wall and exert a force that generates seismic waves and is recorded as eruption tremor. We show that it is possible to model the seismic spectral amplitude and shape of a large sustained volcanic eruption, the eruption of Pavlof Volcano in 2016, with particle impacts and turbulence as seismic sources. Our modeling provides a framework to 1) narrow down the parameters associated with eruption dynamics and source processes, and 2) highlight that seismic amplitude and mass eruption rate are not necessarily correlated. Both findings are crucial for the successful interpretation of seismic data during a sustained eruption. In Chapter 3 we move further up above the vent to investigate the acoustic expression of sustained eruptions. The rapid discharge of the multiphase flow through the relatively small vent has been successfully compared to jetting in the past. We develop an algorithm to automatically fit laboratory-derived jet noise spectral shapes (similarity spectra) to the spectrum of three volcanic eruptions: Mount St. Helens 2005, Tungurahua 2006 and Kīlauea 2018. Our quantitative analysis of the misfit between the jet noise spectra and volcanic eruption shows that: 1) the jet noise spectra show a very good fit during the eruption, so we can assume it produces a volcanic form of jet noise, 2) we can distinguish between non-eruptive noise and eruption by the higher misfit of the former and the lower misfit of the latter, and 3) changes in spectral shape correspond to changes in eruption dynamics, which are highlighted by changes in the misfit in time and frequency space. To further look into how changes in spectral properties correspond to changes in eruption dynamics, Chapter 4 focuses in detail on the eruption of fissure 8 on Kilauea volcano in 2018. With the knowledge that the eruption produced jet noise (Chapter 3) we apply jet noise scaling laws and develop a model that relates the changes in infrasound amplitude and peak frequency to changes in jet velocity and diameter. Our analysis shows that in mid-June the infrasound amplitude peaks and the peak frequency decreases. Our jet noise scaling model explains this change through a decrease in jet velocity and increase in jet diameter. This interpretation fits video observations that show a decrease in lava fountain height and a widening of the fountain base around the same time. Our work demonstrates the potential to estimate lava fountain dimensions from infrasound recordings that could be useful for real-time, remote monitoring.
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Processes in the percolation zone in southwest Greenland: challenges in modeling surface energy balance and melt, and the role of topography in the formation of ice slabsIncreased surface melt in the percolation zone of Greenland causes significant changes in the firn structure, directly affecting the surface mass balance of the ice sheet and the amount and timing of meltwater runoff. Thick impermeable layers, referred to as ice slabs, are preventing melt water percolation and refreezing in the firn favoring lateral movement of water and direct runoff to the oceans. The objective of this dissertation is to enhance the understanding of these processes by modeling the surface energy balance and resulting melt, and investigating the spatial and temporal changes in firn surface properties and associated water movement in the percolation zone in southwest Greenland. Extensive fieldwork was carried out in this region between 2017 and 2019, including a collection of 19 shallow firn cores at several sites and the operation of two weather stations. A surface-energy balance model was forced with automatic weather station data from two sites (2040 and 2360 m a.s.l.). Extensive model validation and sensitivity analysis reveal that the skin layer formulation used to compute the surface temperature by closing the energy balance leads to a consistent overestimation of melt by more than a factor of two or three depending on the site. The results indicate that the energy available for melt is highly sensitive to small changes in surface temperature and suggests caution is needed in modeling Greenland melt from weather data. Furthermore, the spatial and temporal variability in air temperature bias of two regional climate models, MAR and RACMO, is assessed over the entire ice sheet. Model results are compared to 35 automatic weather stations over more than 25 years. Both models perform well in the ablation zone (< 1500 m a.s.l.) where most of the melt happens. However, a warm bias is found in both MAR and RACMO at the higher elevations percolation zone (> 1500 m a.s.l.). The seasonal evolution and interannual variability of near-surface firn characteristics in the percolation zone of southwest Greenland can be tracked with Sentinel-2 optical imagery. Fully saturated seasonal snow (blue slush) and lateral movement of water are strongly correlated with local topography. Furthermore there is evidence of water movement from higher to lower elevations, following surface slope, even after the halting of melt in the second half of August. This suggests that the formation of ice slabs is a self-sustained feedback process increasing the efficiency of the runoff networks in the percolation zone. Ice slabs form and become thicker in areas with smaller surface slope than the surroundings where melt water ponds on top of the impermeable layer, flows, and refreezes during fall, adding to the ice slab. This dissertation provides useful insights on the processes driving ongoing changes in the percolation zone of Greenland due to global warming. However, several questions remain still open. Melt is the main driver of changes. Accurately modeling it, solving the uncertainties in observed and modeled sensible and ground heat flux, is essential. Furthermore, more ground truth and field observations are necessary in the region where blue slush forms on top of ice slabs to quantitatively determine how much water leaves the ice sheet and how much instead refreezes thickening the ice slabs.
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Improved computational tools for infrasound analysisInfrasound describes low frequency (≤ 20 Hz) acoustic waves that can propagate long ranges (≥ 1000 km) through wave guides in the atmosphere. This characteristic makes infrasonic waves a useful monitoring technology for a variety of violent phenomena such as volcanic eruptions. However, source processes may be complex, and infrasound waves are continually modified as they interact with the ground and dynamic atmosphere along their propagation path. Additionally, infrasound still has a data quantity problem: vast amounts of raw data are now continuously generated from permanent arrays distributed around the world, but ground truth information, when possible, may be difficult to obtain. Globally-recorded events are more rare still. Under these conditions, computationally intensive approaches are an increasingly necessary tool to further exploit the information contained in infrasonic waveforms. This dissertation focuses on advanced computational approaches to infrasound analysis. Infrasound arrays may be located in remote environments, and an in-situ indicator of data quality would be useful to ensure a properly working array. Assuming that acoustic signals traverse the array as a plane wave, we document how some elements in both International Monitoring System and Alaska Volcano Observatory arrays produce outliers in inter-element travel time. These outliers, due to timing errors or other issues that cause an apparent deviation from plane wave behavior, produce inaccurate plane wave parameters (back-azimuth and trace velocity) when processed with conventional least squares time-domain array processing. In Chapter 2, we investigate how robust statistical regression methods, particularly least trimmed squares, M-estimation, and L1-norm regression, perform for time-domain infrasound array processing. Least trimmed squares processing returns accurate values across a variety of synthetic tests by using a subset of element pairs to estimate optimal back-azimuth and trace velocity values. By examining the element pairs not included in the subset, we find that the element producing outlying travel times can be identified and removed. We proceed to show how least trimmed squares processing improves infrasound array processing results at arrays I53US, I55US, and ADKI. We investigate the effect of terrain on infrasound propagation in Chapter 3. However, here our emphasis is on finite-frequency effects, specifically diffraction, on propagation ranges longer than 100 km. Simulations in the geometric acoustics approximation have shown that realistic terrain can reflect acoustic waves into shadow zones and scatter acoustic energy from tropospheric ducts. However, finite-frequency effects such as partial reflection and diffraction are not modeled under this approximation. We develop a finite-difference timedomain method to simulate linearized, inviscid, Euler equations for infrasound propagation. We first compare our finite-difference results with ray predictions with both flat terrain and a Gaussian hill at different ranges. We note an extended spatial footprint on the ground for our finite-frequency method compared to ray tracing, and evidence of partial reflections from the tropospheric duct. We build on these findings to investigate infrasound recordings from an explosion at the Utah Testing and Training Range. We examine recordings of this 2012 explosion on two infrasound arrays, NOQ and WMU, which are located at approximately 84 km and 148 km from the source respectively. Evidence from array processing suggests propagation paths through the troposphere, but no eigenrays were identified due to the weak tropospheric ducting conditions at the time of the explosion. We predict infrasonic signals at these arrays with our finite-difference method which show qualitative matches in waveform shape. Moreover, we track changes in waveform shape from source to receiver due to diffraction over terrain along the propagation path. Our results suggest that geometric acoustics underestimates acoustic arrivals through the troposphere, and that terrain along the propagation path affects waveform shape at distances greater than 100 km. As noted above, propagating acoustic waves frequently interact with the ground as they travel over sometimes complex topography. As part of this interaction, infrasound waves are commonly recorded to couple into the ground and are recorded on seismometers. Acoustic to seismic coupling is not commonly considered in simulations of infrasound propagation. In Chapter 4, we quantify the amount of acoustic to seismic coupling that occurs over both flat topography and meshed, complex, topography using a spectral element method. In the course of this research, we also derive expressions relating a seismic moment tensor to an acoustic quadrupole as well as conditions for elastic particle motion from the ground coupled airwave to switch from retrograde to prograde at the surface of an elastic halfspace. Using a suite of Earth models that span a range of specific acoustic impedances, we find a wide variety of energy admittances as a function of incidence angle (≤ 1% to ≈ 78%). However, in simulations over the complex terrain of Sakurajima Volcano, we find that the effect of coupling reduces peak acoustic amplitudes over a 15 km distance from the volcano by ≤ 2%. While this value is relatively small, the cumulative effect over long ranges, and multiple acoustic bounce points, may be nontrivial.
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Dendro-geomorphological analyses of the Slate Creek landslide, AlaskaHillslopes cover much of the Earth's surface, and mass movement is one of the main ways hillslopes re-adjust their profiles in response to the changing climate. Over the next few decades, the impacts of climate changes on mass movements are predicted to be pronounced at high latitudes where temperatures are warming rapidly, permafrost is thawing, and precipitation is increasing. More frequent mass movements have the potential to threaten critical infrastructure in Interior Alaska, particularly in areas of steep slopes and discontinuous permafrost like the Alaska Range. With these concerns in mind, I investigated the dynamics of a complex landslide that is encroaching on the Parks Highway near Slate Creek along the northern front of the Alaska Range. I used dendrochronology to document the extent and timing of this landslide's movements over the past century. To quantify general and seasonal rates of movement, I analyzed aerial photography and LiDAR imagery and obtained geographical positional measurements on a network of datum points established on the landslide's surface. I sought to test the hypothesis that climate controls the activity of the Slate Creek Landslide by comparing dendrochronology and rate-of-movement data to weather records. Results indicate that different parts of the landslide are moving at rates ranging from 0.2 cm/year to 8m/year. Dendrochronological data indicate there were periods of enhanced landslide movement occurring in 1967, 1973, 1977, 1980, and 2017. It remains unclear what triggered the initiation of this landslide and what factors have controlled its recent movement rates. Possibilities include disturbance of the landslide's toe, periods of increased precipitation, a past wildfire, permafrost thaw, or some combination of these factors.
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Temporal links between ductile shearing, widespread plutonism, and tectonic exhumation near the boundary of parautochthonous and allochthonous terranes in the northern Cordillera, AlaskaUnderstanding the relationship of accreted terranes with pericratonic North America is critical for unraveling the complex, polydeformational history of the North American Cordillera. The Cordillera represents a multi-accretionary system that has been fundamentally active since the Jurassic. The allochthonous Yukon-Tanana Terrane is an extensive and heterogeneous accreted terrane in the northern Cordillera. The tectonic boundary separating the Yukon-Tanana Terrane from pericratonic North America is exposed in eastern Alaska and is defined by a northward-dipping and low-angle ductile shear zone. This shear zone is interpreted to have exposed the structurally lower assemblages of parautochthonous North America during top-to-the-southeast directed exhumation in the Cretaceous. This interpretation is based on muscovite, biotite, and hornblende metamorphic cooling ages (ca. 100-120) of amphibolitefacies rock samples collected within the parautochthon. Historically, ⁴⁰Ar/³⁹Ar thermochronology has been a major resource, along with quartz c-axis petrofabric analysis, in identifying the boundaries of the shear zone. However, temporal relationships between shear zone formation, exhumation, and magmatism have remained incompletely understood. Targeted geologic mapping and petrochronology using a more robust chronometer, such as monazite, can aid these previous radiometric and kinematic interpretations. U-Th-Pb monazite petrochronology of samples within and outside the shear zone have placed better constraints on the age of shearing and exhumation. These analyses and observations support that exhumation of the parautochthonous assemblages occurred during the Cretaceous. Additionally, the ductile shear zone which facilitated juxtaposition of allochthonous and parautochthonous assemblages was active ca. 108 Ma. The northern Cordillera is also home to widespread Cretaceous, voluminous, and metallogenically important magmatism in both Alaska and the Yukon Territory. U-Pb zircon geochronology analyzed from 12 mid-Cretaceous plutons has better refined the crystallization history of these granitic bodies (ca. 115-100 Ma). Together, the monazite and zircon geochronology show that the shear zone and granitic plutons are linked, and that top-to-the-southeast crustal extension placed both spatial and temporal controls on the emplacement of mid-Cretaceous magma.
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Mapping bottomfast sea ice in Arctic lagoons using Sentinel-1 interferometerySea ice is an important component of Arctic coastal ecosystems. Where the water is shallow enough, it can extend all the way to the seafloor and become bottomfast sea ice (BSI), the lateral extent of which depends upon ice thickness and the regional nearshore slope. Sea ice thickness is a well-known indicator of climate change in the Arctic and in areas with gently sloping seafloors, we expect the extent of BSI to be a sensitive indicator of changes in ice thickness. Contact with the seafloor can help cool and aggregate subsea permafrost and restrict under-ice habitats. It also prevents or reduces motion experienced by floating landfast ice in response to wind, ocean, and ice forcing. Bottomfast ice is in turn more stable than floating ice with implications for human activities on ice. BSI cannot easily be distinguished from floating landfast ice using optical imagery and synthetic aperture radar (SAR) is not typically able to penetrate to the bottom of saline ice. As a result, large-scale mapping of BSI has previously been limited to brackish waters near Arctic deltas, where (SAR) can detect the ice-water interface. However, recent work has demonstrated that SAR interferometry (InSAR) can be used to delineate BSI based on an absence of small-scale surface motion over time. Here, we utilize the Alaska Satellite Facility's Hybrid Pluggable Processing Pipeline (HyP3): A cloud-based infrastructure to process interferograms from the entire Sentinel-1 record over three lagoon systems across the Beaufort Sea coast of Alaska near Utqiagvik, Prudhoe Bay, and Kaktovik. We develop and test a mapping approach that discriminates bottomfast ice based on a near-zero gradient in interferometric phase change, which on floating lagoon ice is primarily caused by surface motion from tides and thermal stress. This enables the comparison of the date of onset, maximum extent, and seasonal evolution of BSI between the lagoons from 2016-2020. We also evaluate the use of electromagnetic sounding in tandem with in-situ drilling to verify BSI extent with greater detail. Based on this work, we argue that mapping BSI could significantly improve our understanding of Arctic lagoons in terms of detailed bathymetry, winter habitats, and saline stress on benthic communities, and the thermal regime of the underlying permafrost.
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Bedrock geologic mapping of the Willow Creek area and deformational history of the Hatcher Pass schist, southern Talkeetna Mountains, AlaskaThe Willow Creek area in the southernmost Talkeetna Mountains of south-central Alaska is the southern extent of the Wrangellia composite terrane (WCT). Most of south-central Alaska represents a subduction-accretion complex built upon the southern WCT. The purpose of this project is to better constrain the origin and evolution of the Hatcher Pass schist (HPs), a regionally retrogressed chlorite-muscovite schist with plagioclase and garnet porphyroblasts in the Willow Creek area. I conducted bedrock mapping of the Willow Creek area along with structural and petrographic analyses to better constrain the petrogenetic and structural history of the HPs, its contact with forearc sediments that lie structurally above (Arkose Ridge Fm), and mid-Cretaceous Willow Creek plutonism to the north. I determined the following tectonic evolution for the HPs: subduction and incorporation into a subduction channel occurred no later than 75 Ma. The oldest known foliation (S₁) underwent isoclinal recumbent folding (F₂) that resulted in the development of the regionally dominant fabric (S₂). Fragmented boudins, porphyroblast asymmetry, and rare S-C geometries indicate top-to-the-east shearing during D₂. Two sets of open and upright folds, with largely SW-NE and NW-SE trending fold axes, postdate the development of S₂ and define a type 1 interference pattern. I interpret F₃₋₄ to have formed during doming (F₃) and continued tectonic exhumation (corrugations; F₄) along a south-vergent detachment responsible for the juxtaposition of the HPs with the overlaying Arkose Ridge Fm. Based on my detrital zircon data (MDA = 80 Ma), the HPs is interpreted to be a subducted equivalent of the accretionary complex (Valdez Group) exhumed above a slab window formed from slab breakoff of the Kula Plate.
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Documenting coastal change and community-based observations in Alaska communitiesClimate change is causing rapid and unprecedented environmental changes in Alaska coastal communities. These changes are impacting community infrastructure, travel access and subsistence activities for Indigenous people. Many communities lack access to relevant data products which can inform potential climate change mitigation strategies. Relevant data products can be developed through community engagement to identify research priorities and culturally appropriate community-based research methodologies to document community-based observations. Relevant coastal data products were produced for communities participating in two community-based monitoring programs: The Stakes for Stakeholders erosion monitoring program and the Alaska Arctic Observatory and Knowledge Hub monitoring network. Lessons learned from working with these two community-based monitoring networks were identified and discussed in detail. These lessons can be used to inform current and future community-based research partnerships in Alaska Indigenous communities. Researchers interested in further insight on these topics can build on insights coming directly from various Indigenous organizations who are voicing their perspectives on the current state of climate change research in Alaska.
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InSAR-derived thermoelastic lava flow compaction following the 2014-2015 Holuhraun fissure eruptionThe Icelandic volcano Bárðarbunga experienced a caldera collapse and a fissure eruption at Holuhraun from 16 August, 2014 to 27 February, 2015 (Sigmundsson et al., 2015). This eruption produced about 1.44 km³ of lava deposited over an 84 km² area on the Holuhraun plain north of the Vatnajokull Glacier (Pedersen et al., 2017), making it the second largest Icelandic eruption since the 1783-1784 Laki eruption (Gudmundsson et al., 2016). Since basaltic lava flows erupt at high temperatures (1100 to 1250 °C), they contract as they cool over time, which can manifest as measurable deformation of the lava flow surface. Remote sensing observations with high spatio-temporal resolution afford us with an opportunity to capture and analyze such post-eruptive processes. Here, we use Synthetic Aperture Radar (SAR) observations from 2015-2020 captured by the European Space Agency's Sentinel-I A/B satellite pair to perform Interferometric Synthetic Aperture Radar (InSAR) time series analysis on descending and ascending tracks that cover the Holuhraun lava field. Two Short Baseline Analysis (SBAS) are computed, and modeled deformation from plate tectonics and glacial isostatic adjustment is removed from these line-of-sight (LOS) velocity fields. We leverage the dual-view geometry of the estimated LOS InSAR velocity fields to infer effective vertical and east-west velocities of the lava flow surface. The effective vertical velocity field constrains a model linking lava flow compaction to cooling. The InSAR-inferred average velocities indicate higher rates of motion at lava tubes, eruptive centers, and "distributary centers" (as defined by Pedersen et al., 2017) where lava pooled before entering lava tubes during the eruption. We hypothesize that the different emplacement history of individual lobes and features of the lava field, as well as inconsistent compaction amounts of the Holuhraun alluvial plain, have caused the heterogenous cooling that manifests in a highly varying surface deformation field.
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Melt on Antarctic ice shelves: observing surface melt duration from microwave remote sensing and modeling the dynamical impacts of subshelf meltingMelt on the surface and underside of Antarctic ice shelves are important to the mass balance and stability of the ice sheet, and therefore pose significance to global sea levels. Satellite-based passive microwave observations provide daily or near-daily coarse resolution surface observations from 1978 on, and we use this record to identify days in which melt water is present on the ice sheet and ice shelf surfaces, called melt days. There are significant differences in the results of melt detection methods however, and we evaluate four different passive microwave melt detection algorithms. There is a lack of sufficient ground truth observations, so we use Google Earth Engine to build time series of Sentinel-1 Synthetic Aperture Radar images from which we can also detect melt to serve as a comparison dataset. A melt detection method using a Kmeans clustering algorithm developed here is shown to be the most effective on ice shelves, so we further apply this method to quantify melt days across all Antarctica ice shelves for every year from 1979/80 to 2019/20. The highest sums of melt days occur on the Antarctic Peninsula at 89 melt days per year, and we find few linear trends in the annual melt days on ice shelves around the continent. The primary mode of spatial variability in the melt day dataset is closely related to the Southern Annular Mode, a climate index for the southward migration of Southern Westerly Winds, which has been increasing in recent decades. Positive Southern Annular Mode index values are associated with decreased melt days in some regions of Antarctica. We also present a novel application of passive microwave analysis to detect changes in firn structure due to unusually large melt events in some regions and we show how this method detects ice lens formation and grain growth on specific ice shelves. To study the impacts of subshelf melt we focus on the Filchner-Ronne region of Antarctica, which contains the second largest ice shelf on the continent. We performed an ensemble of ice sheet model runs for a set of ocean warming scenarios. Each ensemble used a realistic range of physical parameters to control ice dynamics and sliding, generated by a Bayesian analysis of a surrogate model and observed velocities. Increased ocean temperatures were associated with increased mass loss, and by the year 2100 this region contributed 14 mm to sea level per degree of ocean warming at depth between +0°C and +4°C of ocean potential temperature. Beyond +4°C, the rate mass loss increased substantially. This mass loss corresponded to grounding line retreat across the region.
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Novel applications of remote sensing and GIS in mass wasting hazard assessments for two fjords of South-Central AlaskaThe fjords of South-Central Alaska are dynamic environments and host to a number of natural hazards that have not received much attention from the research community. The cities of Seward and Whittier are two of Alaska's most important marine transportation hubs, home to commercial fishing fleets, termini of the Alaska Railroad, and home to thousands of residents. This doctoral research focuses on landslides and their associated hazards in these under-studied areas. Chapter 2 involves surficial mapping of the study areas and documents the role of the underlying geologic processes that threaten the safety of people and infrastructure in the Passage Canal-Portage Valley area (including the town of Whittier), to better inform community planning, mitigation, and emergency response activities. Chapter 3 builds on the successes and lessons learned from the mapping efforts made in Chapter 2. A surficial geology and landslide inventory map were made using very high resolution orthoimagery, DEMs, and 3D models which were viewed in an immersive Virtual Reality (iVR) system. Chapter 4 examines the hazards associated with large amounts of sediment entering the alluvial fan system from further upslope. A collection of six Digital Elevation Models (DEMs) and meteorological data collected over a ten-year period were used to estimate flood-related sedimentation. Uncertainties in each DEM were accounted for, and a DEMs of Difference (DoD) technique was used to quantify the amount and pattern of sediment introduced, redistributed, or exiting the system. The study shows that the DoD method and using multiple technologies to create DEMs is effective in quantifying the volumetric change and general spatial patterns of sediment redistribution between the acquisition of DEMs. Correlations of the changes in sediment budget with rainfall data and flood events were made. During the years of average rainfall, the reaches in the corridor experienced an overall decrease in sediment load, while heavy rainfall events both saw large influx of new sediment and the reworking of existing sediment. This research is the first to collect and use high resolution data for generating digital elevation models, for using a DoD method for mapping elevation changes over time, and for using these products along with available ancillary data for a hazard assessment in these regions. This doctoral work lays out a solid foundation for further work in hazard assessment that will also guide decision-makers in the future on mitigation measures in these important population centers in south central Alaska.
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Coastal wetland carbon and mineral responses to storm and climate change through time, at Cape Espenberg AlaskaThe Arctic is experiencing warming and ecological shifts due to climate change and the compounded effects of polar amplification. There is a deficit of information surrounding the carbon cycle response in Arctic Alaskan coastal marsh environments to these forces. The Cape Espenberg barrier beach system has been mostly preserved through time as a shoreline-parallel, linear geometry prograding geomorphic feature. This study determines the Arctic carbon and mineral accumulation trends in marsh environments at Cape Espenberg for both paleo (pre 1850 AD) and modern (post 1850 AD) timeframes. This project makes connections between the responses of carbon and mineral materials to paleo and modern climate changes, and how this relationship may have evolved through time. Analytical analyses through radioisotope ¹³⁷Cs and ²¹⁰Pb, ¹⁴C, stable isotope spectrometry (δ¹³C), elemental (%C, %N, C:N), and dry bulk density and carbon density measurements yield a comprehensive physical and chemical dataset. Radioisotope dating techniques in the Arctic have proved challenging due to the dynamism of the environment. However, the combination of Constant Rate of Supply and Constant Initial Concentration age depth models has helped constrain ages to sediment cores even under variable conditions. Results indicate carbon and mineral accumulations have increased from paleo to modern times which indicates better growing and/or preservation conditions for organic matter (OM) under a modern climate. This agrees well with paleoclimate trends in the Medieval Climate Anomaly (MCA), and warm periods interspersed within the Little Ice Age (LIA), which correlate to greater productivity of terrestrial organic matter and isotopically lighter δ¹³C values (a terrestrial signature). Cold climate periods within the Little Ice Age correlate with increased aquatic organic matter sourcing and heavier δ¹³C values. Modern warming will likely continue to drive carbon sourcing towards terrestrial signatures as future temperatures are predicted to rise with global climate change. If the swale environments at Cape Espenberg can maintain ideal growing conditions (i.e. wet/anoxic soils and lower salinity to limit organic material decay, higher temperatures to promote growth) then Cape Espenberg will likely remain a viable carbon reservoir in the future. However, the question of whether the barrier system as a whole will continue to prograde under a regime of rising sea levels and increased storm impacts is unclear. The results of this study contribute towards understanding the dynamism of Arctic coastline mineral and carbon cycling and their ecological response to the current warming climate.
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Shallow surface thermogenic hydrocarbon migration over western Prudhoe Bay Region, Alaska"Hydrocarbons leak from petroleum reservoirs to the surface. In continuous permafrost regions like the Alaska North Slope, surface migration of thermogenic hydrocarbons may be hindered by the presence of ground ice. However, suitable permeable migration pathways in the permafrost can exist. Unfrozen sediments at the bottom of the lakes, or open faults can facilitate thermogenic hydrocarbon migration. I studied the nature and distribution of gaseous alkanes (C1 to C6) and helium in the shallow permafrost cores (2 m depth); depth profiles of alkanes (C1 to C7) in the two wells (1500 m deep); and stable isotopes of CH₄ trapped in lake gas bubbles, to trace the presence of thermogenic hydrocarbons and their migration pathways. Geostatistical analysis of the alkane and helium distributions shows that most anomalies occur along northwest-southeast oriented lineaments, roughly corresponding to the trend of the Eileen fault mapped at 2675 m depth, high fault density zones of the Kuparuk Formation, and northwest-southeast trending Sagavanirktok faults mapped at 457 m depth. The anomalies above the Eileen fault can be explained by a fluid-flow model in a dilational jog along a wrench fault. This model agrees with the movements along the Eileen fault"--Leaf iii
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Non-volcanic tremor in the Alaska/Aleutian subduction zone and its relationship to slow-slip events"We document non-volcanic tremor (NVT) in Southcentral Alaska and the Aleutian Arc in terms of durations and locations. In Southcentral Alaska, we tabulate NVT events occurring during the summer months of each year between 1999 and 2001 to test for a relationship with a slow-slip event that occurred during this time frame. We tabulate NVT events in the Aleutians starting in the summer of 2005 through the summer of 2008. The observed NVT events in both Southcentral Alaska and the Aleutian arc are sequences of emergent pulses with frequencies of 1-10 Hz. The majority of the events have durations ranging from 5-15 minutes. In Southcentral Alaska, the majority of the NVT events locate in the region of the slow-slip event and the quantity of events decreases significantly by the summer of 2001, coinciding with the end of the slow-slip event. Locating NVT events in the Aleutians is problematic due to the linearity and sparse distribution of seismic stations. General locations are established simply by the distribution of volcano seismic networks on which the signal is observed and the strength of that signal. These general locations appear to coincide with regions where the plate interface is locked or is transitioning from creeping to locked. Furthermore, several episodes of NVT in the Aleutians occurring during times of heightened volcanic and seismic activity in the arc, suggesting large regional stress changes possibly caused by undetected slow-slip events"--Leaf iii
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Holocene vegetation and climate change at Canyon Lake, Copper River basin, Alaska"The regional vegetation response to Holocene warming and the recession of glacial Lake Atria is recorded by environmental proxies in cores from Canyon Lake, near the northern limit of the Copper River Basin. Pollen, spores, plant macrofossils, and stable isotope analyses of C, N and H indicate that conditions in the northern margins stabilized fairly quickly following the recession of Lake Atria around 10740 cal yr BP. The development of a shallow lake ecosystem surrounded by Betula (birch) shrub-tundra was followed by the migration of Picea (spruce) and Alnus (alder) into the Copper River Basin around 9800 cal yr BP and the eventual development of the Picea-dominated boreal forest that persists to this day. The stable isotope record indicates that lake systems are more sensitive to neoglacial cooling, Medieval warming, and the Little Ice Age than the surrounding boreal forest during the middle to late Holocene. The magnitude and severity of these events may have been limited in the Copper River Basin, but climate and vegetation change may have had significant effects on the available resources to the human populations of the region"--Leaf iii
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Platinum group element enriched hydrothermal magnetite of the Union Bay Alaska-type ultramafic intrusion, Southeast Alaska"The Union Bay Alaskan-type Complex represents a completely different type of platinum group element (PGE) concentration from the classic Alaskan-type Complex PGE mineralization model, with PGEs localized in vein/veinlet magnetite, commonly within the olivine + pyroxene portions of the body. PGE concentrations of 18 g/t occur in magnetite veins and pods which cross magmatic layering and have an irregular morphology in both outcrop and thin section. Fe-Ti oxide geothermometry indicates that this mineralization formed at temperatures between 675-475°C. A variation in the amount of ilmenite and Mg-Al spinel exsolution in magnetite correlates with temperature estimates, lower temperature magnetite has less exsolution. Magnetite veins with a formation temperature of less than 600°C are surrounded by an alteration envelope of hydrous silicates that vary with temperature and contain appreciable amounts of Cl. Interaction of a PGE-Fe-Cl rich fluid with clinopyroxene and olivine increased the fluids pH and decreased PGE and Fe solubility depositing a PGE enriched magnetite within the wehrlite and clinopyroxenite of the Union Bay Alaskan-type complex. Potentially this fluid remobilized the PGE from disseminated euhedral magnetite of the peripheral units to form PGE enriched magnetite veins in the near-central portion of the complex"--Leaf iii
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Tectonic geomorphology of the Chukchi borderland: constraint for tectonic reconstruction models"The Chukchi Borderland is a region of extended continental crust within the Amerasia Basin and is bounded on one side by oceanic crust of the Canada Basin. Because of its central location within the basin, tectonic models for the reconstruction of the Arctic Ocean, must include the Chukchi Borderland although there is no consensus about its pre-rift location or kinematic development. In recent years bathymetric data have been collected that can offer constraint on the tectonic evolution of the Amerasia Basin by providing details about the geomorphology of the intra-basinal ridges allowing comparison of bathymetric features to those in other ocean basins. Bathymetric information in conjunction with multi-channel seismic and chirp sub-bottom profiler data show the location and strike of inferred faults used to determine rift directions which then provide constraint on tectonic reconstructions. The central Amerasia Basin, which includes the Chukchi Borderland, Mendeleev Ridge and south central Alpha Ridge, has experienced significant extension in generally the same direction and probably during one event. This type of plate boundary scale extension requires the development of accommodation faulting or transfer zones that facilitate the amalgamation of long fault segments. Features consistent with this type of faulting are observed throughout the Chukchi Borderland. There is no evidence of compression along the Northwind Ridge nor is there any indication of a strike-slip boundary within the Northern Chukchi Borderland as some tectonic models suggest. Whichever model is preferred, the geomorphology of the intra-basinal ridges must be taken into account and used as constraint for the reconstruction of the Amerasia Basin"--Leaf iii
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Character and controls of fold-and-thrust deformation from pre-orogenic to foreland basin deposits: an example from the Gilead creek region of the Northeastern Brooks Range, Alaska"The character of structures in the Gilead Creek region is influenced by the mechanical stratigraphy in the area. Shortening is distributed throughout the mechanical stratigraphy along detachments in the incompetent Kayak, Kavik, Kingak, and Hue Shales. Detachment intervals separate competent Lisburne Group, Echooka Formation, Ledge Sandstone/Shublik Formation, Gilead sandstone, and moderately competent Seabee Formation from each other and allow the competent units to fold at distinct wavelengths according to their mechanical properties. Thick, competent units tend to form long-wavelength folds. Thin, competent units form relatively short-wavelength folds. Thin, competent units that are structurally bound to a thicker, structurally more dominant unit, adhere to the structural style of the dominant unit unless there is some detachment between them. Strain is distributed through shale intervals in the moderately competent units, allowing short-wavelength folds in the thin competent beds. The dominant trend of structures in the area is northeast overprinted on east. East-trending structures formed during the ~60 Ma event that formed the main axis of the Brooks Range and its foothills. Northeast-trending structures formed during the formation of the northeastern Brooks Range dated at ~45 Ma, ~35 Ma, and ~27 Ma, manifest locally by the compressional uplift of the Echooka anticlinorium southeast of Gilead Creek"--Leaf iii.
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Relating deep magmatic processes to eruptive behavior at arc volcanoes through an analysis of deep seismicity"In this thesis, the seismicity at depths greater than 15 km beneath two sets of volcanic centers, the Klyuchevskoy Volcanic Group (KVG), Russia and Mount Spurr, Alaska is examined. In both regions, a pulsing pattern of deep seismicity is observed with many cycles following eruptive activity or periods of unrest. The bulk of the seismicity beneath the KVG is comprised of long-period events many of which share a similar appearance. Cross correlation of the waveforms for events occurring between 12/24/2007 and 12/31/2008 show a number of event families occurring over long time spans. New relative locations for these families which better constrain their spatial extent are derived. The pulsing pattern of seismicity seen here is in close keeping with the expected cyclic nature of melt segregation which occurs as melt leaves the site of generation and ascends to shallower levels. Based on evidence in the data, a model is proposed whereby melt segregation on the time scales necessary to facilitate eruptions is attributable to a pressure response in the deep system induced by the removal of material in the shallow chamber during an eruptive cycle"--Leaf iii.
