The Late Cretaceous (late Campanian, ca. 72.8 Ma) Prince Creek Formation on the North Slope of Alaska is well-known for preserving the highest latitude dinosaur fauna in either hemisphere. Within this diverse dinosaurian fauna, a single tyrannosaurid theropod has been described: Nanuqsaurus hoglundi. Little work has been devoted to the taxon since 2014, when it was initially described based on three fragmentary cranial bones. Notably, it was characterized as a "diminutive" taxon, thought to have been substantially smaller than related Late Cretaceous tyrannosaurid species. New cranial and postcranial material attributable to the taxon collected by and housed at the University of Alaska Museum, challenges many aspects of its anatomy, size, and paleobiology. Here, I incorporate new specimens and critically reanalyze the holotype material to address the taxonomic validity of Nanuqsaurus. Further, I conduct the first quantitative analysis to assess body size and test the hypothesis that the Alaskan tyrannosaurid is a diminutive taxon. New material (such as the proximal condyle of a metatarsal and a complete dorsal rib) allowed for the first histological analysis of the Alaskan taxon to be performed to better understand growth dynamics for the taxon and the ontogenetic status of these key specimens. Both specimens are revealed to have been at least 14 years of age at the time of their death and lack an external fundamental system, suggesting that growth had not stopped. New data also facilitates a critical taxonomic re-evaluation of N. hoglundi, which results in a more robust phylogenetic analysis and designation of the taxon as a nomen dubium. Direct proportional scaling of new material suggests a body size comparable to other Late Cretaceous tyrannosaurid taxa, such as Albertosaurus, Gorgosaurus, and Daspletosaurus (all 9 - 10 m body length). Application of theropod regression equations suggests a body size approaching these taxa (at approximately 8 m in length), and a much larger body mass than originally hypothesized (1615 - 1900 kg). The updated size warrants an examination of previously drawn paleobiological conclusions, such as a decrease in body size to reach an "optimal predator size" or as a response to a lack of resources. Regardless of the validity of the taxon, these data collectively provide new insights into the ecology and life history strategies of the northernmost large-bodied theropod known.

The frequency and pattern of eruptions at Augustine volcano makes it an ideal natural laboratory. The 2006 eruption produced deposits that were petrologically and compositionally similar to the 1976 and 1986 eruptions. Olivine phenocrysts have up to a 500-pm thick rim of intergrown orthopyroxene and magnetite. Petrologic data constrained Augustine magmatic conditions, which were then recreated in the laboratory to determine what conditions favor the growth of symplectite reaction rims on olivine. Oxygen fugacity (fO2) of Augustine magmas, recorded by Fe-Ti oxides, is -8.51 to -10.72 log units, which is slightly above the Re-ReO2 (RRO) buffer. Experiments were set up to investigate the effect of high fO2 on the formation of olivine rims. They involved seeding rhyodacite powder with high- to med-Mg olivine and placing it into Rene-style furnaces at 850°C and 150 MPa for 1 to 4 weeks at RRO. The full symplectite was not recreated, but high fO2 changed the rim texture and increased growth rate by nearly a factor of 10, relative to similar experiments run at Ni-NiO. Experiments and petrologic data suggest the natural symplectite rims took years to grow and that they did not result from mixing immediately prior to or during the 2006 eruption.

The regional response of vegetation to global atmospheric circulation patterns and human influence throughout the Holocene is recorded by environmental proxies in sediment cores from Lake Khargal in northern Mongolia. Pollen, spores, total organic carbon, and grain size analysis indicate that conditions in the watershed were moderately humid at ~11500 cal yr B.P. The vegetation community surrounding Lake Khargal consists of mainly of Artemisia (sage), Poaceae (grass), and Betula (birch) with a modest amount of extra-local Pinus (pine) from nearby boreal forests. Fluctuations in the ratios of these and other taxa show that aridity increased after ~10000 cal yr B.P., reaching its maximum at ~7900 cal yr B.P., which coincides with a global cooling event. Regional moisture availability gradually increases after ~7900 cal yr B.P., reaching its peak at ~2100 cal yr B.P., then decreases toward the present. Evidence of regional human activity appears in the taxonomic record around 5500 cal yr B.P. and persists into today.

From November 30 to December 2, 2020, an atmospheric river event brought high winds, heavy precipitation, and unseasonably warm temperatures to Southeast Alaska. In a 48-hour period, weather stations located in the Haines, Alaska, area recorded record-breaking amounts of precipitation. This resulted in 160 landslides around the community, some of which cut off evacuation routes and access to the community's fuel supply, and caused power outages and evacuations. The largest of the landslides occurred along Beach Road on December 2, 2020; it destroyed or severely damaged four residences and killed two occupants. This report focuses on 58 of the landslides, chosen based on their proximity and impact to road corridors or private property. During field investigations in 2021 and 2022, I observed and described landslides, took in situ strength measurements, and sampled soils that I subsequently tested in the laboratory for engineering index properties such as soil classification, moisture content, and organic content. I mapped landslide extents and evidence of previous landslides using high-resolution lidar data. Using all of these data, I developed a landslide catalog of the 58 landslides, which contains information about location, impact on the road system in 2020, field observations, stratigraphy, laboratory test results, landslide classification, maps, and relevant photographs. Analysis of the collected data suggests that the most significant factor that contributed to the December 2020 landslides was the amount and intensity of precipitation. This precipitation exacerbated the preexisting condition of high slope angles in the surrounding area, and resulted in excess pore pressure in soil types that usually drain well. Anthropogenic factors, such as removal of vegetation and the toe of slopes, also likely played a role in the distribution of the landslides. Recommendations for further study based on results in this report are: 1) to date previous landslides in the study area to determine the frequency of these events; 2) to install additional weather stations in the Haines area for widespread real-time weather monitoring and studying effects of localized high precipitation and/or wind on landslide occurrence; and 3) to conduct additional strength testing on soil and bedrock within the failed areas.

With an area of over 19 million acres, the Arctic National Wildlife Refuge is situated in the northeastern region of Alaska and stands as the largest federally protected refuge in the United States. The region supports a variety of wildlife and plants and is culturally significant to the indigenous populations of nearby Iñupiat and Gwich'in villages who rely on the land and wildlife for their way of life. The discovery of oil near this region in 1968, prompted local, state, and federal interest in understanding the oil and gas potential of the region. Oil and gas surveys in the 1980s estimated that a portion of the Arctic Coastal Plain, known as the "1002 Area", could contain more than seven trillion barrels of recoverable oil, making it one of the largest deposits in the world. In 2017, Congress passed the Tax Cuts and Jobs Act which mandated lease sales and the development of an environmental impact statement (EIS) to understand the potential impacts of an oil and gas program within the Arctic National Wildlife Refuge. The purpose of this research is to effectively communicate to resource managers about spatial and temporal changes in aufeis distribution in the Arctic National Wildlife Refuge. Aufeis fields are important features of rivers and streams in the Arctic National Wildlife Refuge that often form downstream from perennial groundwater springs. Over the course of a winter, these fields of ice can grow to be tens of kilometers long, kilometers wide, and up to ten meters thick. Perennial springs and aufeis play a crucial role in maintaining the hydrologic system during winter by contributing liquid water, which not only supports fish habitat but also ensures a consistent water supply during summer, thus enhancing connectivity along aquatic migratory corridors. At locations identified by the US Fish and Wildlife Service as perennial groundwater springs or known fish habitat, a remote sensing analysis of Landsat data was performed. Landsat imagery was analyzed during the melt season (May 14th - August 15th) between 1985 and 2021 to determine seasonal and interannual changes to the overall aufeis extent and the melt rate of aufeis. Based on the available imagery, aufeis between 2010 and 2021 appears to be melting at a significantly faster rate than between 1985 and 2009. An ArcGIS StoryMap was developed to effectively communicate this analysis by allowing users to interact directly with geospatial data. In presenting information in this format, scientific information is effectively communicated to resource managers to help inform their decision making process in a way that is relevant to known problems, is credible by conforming to scientific standards of rigor, and is legitimate by presenting information in an unbiased manner.

Synthetic Aperture Radar (SAR), a microwave-based active remote sensing technique, has had a rich and contemporary history. Because such platforms can measure both the phase and intensity of the reflected signal, interferometric SAR (InSAR) has proliferated and allowed geodesists to measure topography and millimeter-to-centimeter scale deformations of the Earth's surface from space. Applications of InSAR range from measuring the inflation of volcanoes caused by magma movement to measuring the subsidence in permafrost environments caused by the thawing of ground ice. Advancements in InSAR time series algorithms and speckle models have allowed us to image such movements at increasingly high precision. However, analysis of closure phases (or phase triplets), a quantification of inconsistencies thought to be caused by speckle, reveal systematic behaviors across many environments. Systematic closure phases have been linked to changes in the dielectric constant of the soil (generally thought to be a result of soil moisture changes), but existing models require strong constraints on structure and sensitivity to moisture content. To overcome this obstacle and decompose the closure phase into a systematic and stochastic part, we present a data-driven approach based on the SAR intensities. Intensity observations are also sensitive to surface dielectric changes. Thus, we have constructed an intensity triplet that mimics the algebraic structure of the closure phase. A regression between such triplets allows us to predict the systematic part of the closure phase, which is associated with dielectric changes. We estimate the corresponding phase errors using a minimum-norm inversion of the systematic closure phases to inspect the impact of such systematic closure phases on deformation measurements. Correction of these systematic closure phases that correlate with our intensity triplet can account for millimeter-scale fluctuations of the deformation time series. In permafrost environments, they can also account for displacement rate biases up to a millimeter a month. In semi-arid environments, these differences are generally an order of magnitude smaller and are less likely to lead to displacement rate biases. From nearby meteorological stations, we attribute these errors to snowfall, freeze-thaw, as well as seasonal moisture trends. This kind of analysis shows great potential for correcting the temporal inconsistencies in InSAR phases related to dielectric changes and enabling even finer deformation measurements, particularly in permafrost tundra.

Volcanic 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.

Infrasound 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.

Understanding 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.

The 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.