Now showing items 1-20 of 311

    • Characterization of geohazards via seismic and acoustic waves

      Toney, Liam; Fee, David; Tape, Carl; Haney, Matthew; Grapenthin, Ronni (2023-08)
      Earth processes, such as large landslides and volcanic eruptions, occur globally and can be hazardous to life and property. Geophysics -- the quantitative study of Earth processes and properties -- is used to monitor and rapidly respond to these geohazards. In particular, seismoacoustics, which is the joint study of seismic waves in the solid Earth and acoustic waves in Earth's atmosphere, has been proven effective for a variety of geophysical monitoring tasks. Typically, the acoustic waves studied are infrasonic: They have frequencies less than 20 hertz, which is below the threshold of human hearing. In this dissertation, we use seismic and acoustic waves and techniques to characterize geohazards, and we examine the propagation of the waves themselves to better understand how seismoacoustic energy is transformed on its path from a given source to the measurement location. Chapter 1 provides a broad overview of seismoacoustics tailored to this dissertation. In Chapter 2, we use seismic and acoustic waves to reconstruct the dynamics of two very large, and highly similar, ice and rock avalanches occurring in 2016 and 2019 on Iliamna Volcano (Alaska). We determine their trajectories using seismic data from distant stations, demonstrating the feasibility of remote seismic landslide characterization. Chapter 3 details the application of machine learning to a rich volcano infrasound dataset consisting of thousands of explosions recorded at Yasur Volcano (Vanuatu) over six days in 2016. We automatically generate a labeled catalog of infrasound waveforms associated to two different locations in Yasur's summit crater, and use this catalog to test different strategies for transforming the waveforms prior to classification model input. In Chapter 4, we use the coupling of atmospheric waves into the Earth to leverage a dense network of about 900 seismometers around Mount Saint Helens volcano (Washington state) as a quasi-infrasound network. We use buried explosions from a 2014 experiment as sources of infrasound. The dense spatial wavefield measurements permit detailed examination of the effects of wind and topography on infrasound propagation. Finally, in Chapter 5 we conclude with some discussion of future work and additional seismoacoustic topics.
    • A reinterpretation of Nanuqsaurus hoglundi (Tyrannosauridae) from the late cretaceous Prince Creek formation, northern Alaska

      Perry, Zackary R.; Druckenmiller, Patrick; Fowell, Sarah; McCarthy, Paul (2023-08)
      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.
    • Examination of volcanism and impact cratering on terrestrial bodies

      Knicely, Joshua J. C.; Herrick, Robert R.; Glaze, Lori; Larsen, Jessica; Meyer, Franz (2023-08)
      Exploring and expanding our understanding of the planets (i.e., planetary science) encompasses a vast array of topics and disciplines. This dissertation concentrates on the surficial processes of and examination of terrestrial planets, primarily via the study of volcanism and impact cratering. The first project starts with an exploration of NIR remote sensing techniques as applied to Venus. This work found that NIR remote sensing at the clement conditions just beneath the cloud deck provide vastly improved imaging capability. This improved visibility is most notable for the tesserae, regions of Venus of great interest to the scientific community. Radar imagery and derived data products were then used to survey 21 mid-sized volcanoes on the surface of Venus. Similar to volcanoes at larger diameters, the midsized volcanoes of Venus are significantly flatter than those on other terrestrial bodies. Several of these volcanoes also show deformation that requires a negligibly thin lithosphere some time after the emplacement of the construct. The third project then evaluates the hazards involved with safely placing a lander on the Venusian tesserae and examines potential methods by which to detect and then avoid these hazards. Safely placing a suite of scientific instruments on tesserae is necessary to answer long-standing questions about Venus. Current technologies put relevant hazards at the edge of detection (i.e., zero fault tolerance) and can execute divert maneuvers of only a few tens of meters. Investment in hazard detection and avoidance technologies is necessary to bring safety margins to acceptable levels; data from future missions - while helpful - will be insufficient to select safe landing zones prior to launch. Oblique impact cratering is a ubiquitous event (approximately half of all impacts are at 45 or less). Our poor understanding of this process leaves a significant amount of information buried and waiting to be uncovered. Low-velocity oblique impact experiments were conducted at John's Hopkins University's Applied Physics Laboratory Planetary Impact Lab to better understand the oblique impact process and prepare for high velocity experiments at similar impact angles. These experiments also sought to understand the effect of target tilt, which is currently necessary at existing experimental facilities in order to simulate changes in impact angle smaller than 15°. These experiments show that target tilt significantly amplifies oblique characteristics (e.g., aspect ratio, butterfly ejecta). The time-delayed and spatially offset transference of energy from the impactor to the target is important in determining the excavation process and final crater morphology and ejecta distribution.
    • An investigation of symplectite-rimmed olivine and magmatic processes during the 2006 eruption of Augustine Volcano, Alaska

      Tilman, Mariah Roberts (2008-05)
      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.
    • Coastal hazard analyses and projections for Arctic Alaska communities

      Buzard, Richard M.; Maio, Christopher; Kinsman, Nicole; Jones, Benjamin; Erikson, Li (2023-08)
      Storms and a changing climate can cause disasters for coastal communities. This is particularly felt in the Arctic, where temperatures are rising faster than the global average and sea ice decline has led to a longer open-water period when storms can make landfall. Communities in western and northern Alaska have experienced decades of frequent flooding and erosion. Climate change is a significant contributor today and for the future, but the current prevalence of disaster loss is more closely related to the continued development within hazard-prone areas. This dissertation maps areas prone to erosion and flooding to provide decision-making products for adaptation planning. Long-term erosion rates are projected 60 years into the future to compute the time until infrastructure is undermined. Flood histories are quantified to map hazard areas and improve storm impact forecasts. Record flood levels are estimated to support floodplain mapping. These studies are primarily exposure analyses that compare existing hazards to existing infrastructure to identify at-risk and safe areas around communities. However, as climate change progresses, existing hazards will change in unanticipated ways. The erosion history of Port Heiden tells an important story about how an unexpected change in coastal barrier islands led to rapid erosion and forced the community to relocate inland. This dissertation fills in the long-standing baseline data gaps about hazards in Arctic Alaska coastal communities. These results will help communities develop outside of hazard prone areas. However, the next iterations of hazard analyses will need to build off this baseline and carefully apply climate-informed approaches to predict changing hazards. Moreover, risk assessments must address community priorities and be improved by incorporating more of the values of mixed subsistence economies common to this region. Through community collaboration, hazard exposure analyses like this dissertation, and improving geophysical models, a roadmap is being built for communities to navigate towards a safer future.
    • An 11,600-year reconstruction of vegetation communities, moisture availability, and land use changes at Lake Khargal, northern Mongolia

      Barna, Joshua A.; Fowell, Sarah J.; Bigelow, Nancy H.; Mann, Daniel H. (2023-08)
      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.
    • Improved boreal vegetation mapping using imaging spectroscopy to aid wildfire management, Interior Alaska

      Badola, Anushree; Panda, Santosh K.; Bhatt, Uma S.; Roberts, Dar A.; Waigl, Christine F.; Jandt, Randi R. (2023-08)
      Wildfires are a natural and essential part of Alaska ecosystems, but excessive wildfires pose a risk to the ecosystem's health and diversity, as well as to human life and property. To manage wildfires effectively, vegetation/fuel maps play a critical role in identifying high-risk areas and allocating resources for prevention, suppression, and recovery efforts. Furthermore, vegetation/fuel maps are an important input for fire behavior models, along with weather and topography data. By predicting fire behavior, such as spread rate, intensity, and direction, fuel models allow fire managers to make informed decisions about wildfire suppression, management, and prevention. Traditionally used vegetation/fuel maps in Alaska are inadequate due to a lack of detailed information since they are primarily generated using coarser resolution (30m) multispectral data. Hyperspectral remote sensing offers an efficient approach for better characterization of forest vegetation due to the narrow bandwidth and finer spatial resolution. However, the high cost associated with data acquisition remains a significant challenge to the widespread application of hyperspectral data. The aim of this research is to create accurate and detailed vegetation maps and upscale them for the boreal region of Alaska. The study involves hyperspectral data simulation using Airborne Visible InfraRed Imaging Spectrometer - Next Generation (AVIRIS-NG) data and publicly available Sentinel-2 multispectral data, ground spectra convolved to Sentinel-2 and AVIRIS-NG using the spectral response function of each sensor. Simulated data captured the minute details found in the real AVIRIS-NG data and were classified to map vegetation. Using the ground data from Bonanza Creek Long-Term Ecological Research sites, we compared the new maps with the two existing map products (the LANDFIRE's Existing Vegetation Type (EVT) and Alaska Vegetation and Wetland Composite). The maps generated using simulated data showed an improvement of 33% in accuracy and are more detailed than existing map products. In addition to fuel maps, we performed sub-pixel level mapping to generate a needleleaf fraction map, which serves fire management needs since needleleaf species are highly flammable. However, validating the sub-pixel product was challenging. To overcome this, we devised a novel validation method incorporating high-resolution airborne hyperspectral data (1m) and ground data. The study addresses the limitations of traditional fuel/vegetation maps by providing a more detailed and accurate representation of vegetation/fuel in Alaska. The methods and findings advance fuel and vegetation mapping research in Alaska and offer a novel pathway to generate detailed fuel maps for boreal Alaska to aid wildfire management.
    • An analysis of cataloged December 2020 landslides near Haines, Alaska

      Nelson, Victoria A.; Darrow, Margaret; Stevens, De Anne; Kidanu, Shishay (2023-05)
      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.
    • Variability of hydrogeochemistry and chemical weathering regimes in high latitude glacierized coastal catchments

      Jenckes, Jordan R.; Munk, Lee Ann; McCarthy, Paul; Klein, Eric; Boutt, David; Trainor, Thomas (2023-05)
      Accelerated modifications to the hydrology, driven by global climate change, will alter the timing and amount of freshwater discharged from coastal catchments to the intertidal and nearshore habitats of the Gulf of Alaska. Coastal glacierized catchments are important sources of both inorganic and organic matter to the nearshore ecosystem. The Gulf of Alaska is an ecologically diverse ecosystem, that supports commercial, mariculture, and subsistence lifestyles. However, the coastal catchments of the Gulf of Alaska are relatively understudied with respect to solute generation, seasonal cycles of major cations and anions, and chemical weathering regimes. To close the knowledge gap, the present study utilizes a unique set of stream samples compiled from field-based activities and the USGS NWIS from stream sites across the Gulf of Alaska watershed. First, we find that watershed characteristics such as slope, elevation and relief drive the variation in concentration-discharge relationships, while glacier coverage controls solute yields. Second, though glaciers control overall solute yields, the climate dictates the timing of seasonal solute yields. Additionally, we find across the Gulf of Alaska lithology and climate are important controls on major cation and anion concentrations. Finally, we implement a solute mass balance model to estimate fractional contributions to solute flux from silicate, carbonate and precipitation. We find that carbonate weathering is the dominant source of weathering derived solutes, however there are several streams across the Gulf of Alaska in which silicate weathering is an important source of solutes. Overall, the results of this work illustrate the variability in stream chemistry across the Gulf of Alaska, and changing climate regimes will alter the fluxes of solutes and nutrients in the future.
    • Communicating remote sensing surveys of aufeis in northeast Alaska with land managers

      Dann, Julian; Bolton, W. Robert; Zwieback, Simon; Leonard, Paul; Timm, Kristin (2023-05)
      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.
    • Community-based monitoring: shoreline change in southwest Alaska

      Christian, Jessica Ellen; Maio, Christopher V.; Spellman, Katie L.; Buzard, Richard M. (2023-05)
      Arctic amplification has resulted in increased coastal hazards such as erosion in Alaska. The remoteness of the southwest Alaska coastline hinders frequent coastal hazard surveys, requiring alternate methods for measuring change throughout the year. This study documents and evaluates a community-based monitoring program in two southwestern Alaskan communities including Chignik Bay and Dillingham. The program entitled, Stakes for Stakeholders, has been running successfully since 2016 and continues to engage with rural communities to measure and map coastal change. The Stakes for Stakeholders program promotes self-advocacy and equips local participants with the tools, information, and resources needed to respond to increasing coastal hazards. This method engages local partners through data collection, training, and reviewing and revising resulting products to address local priorities. Community engagement consists of biannual video conference meetings, annual site visits, and miscellaneous communication (i.e., calls, text messaging, and emails). Baseline data was collected with community partners in the form of coastal topographic profiles and measurements collected at locally identified monitoring sites. The process of establishing, operating, and maintaining these sites is documented in various protocols and workflows produced in this study. As part of the research, locally prioritized data products were created. One such product was a hazard assessment report that was drafted for the community of Chignik Bay outlining all relevant coastal hazards to which the community is susceptible. Assessment rubrics were drafted and used to evaluate the efficacy of the program. These evaluations highlighted some of the most relevant community-based monitoring takeaways and pointed towards areas that needed improvement. Results from this study document a successful community-based monitoring (CBM) program and serve as a model for State and Federal research agencies and Arctic and sub-Arctic communities looking to respond to global climate change.
    • An intensity triplet for the prediction of systematic InSAR closure phases

      Biessel, Rowan; Zwieback, Simon; Meyer, Franz J.; Tape, Carl (2023-05)
      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.
    • 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 mines

      Spaleta, Karen Joy; Newberry, Rainer J.; Hayes, Sarah M.; Keskinen, Mary J.; Piatak, Nadine M.; Trainor, Thomas P. (2022-12)
      Bismuth (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.
    • Acoustic and seismic signature of sustained volcanic eruptions

      Gestrich, Julia E.; Fee, David; Tape, Carl; Haney, Matthew; Larsen, Jessica (2022-12)
      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.
    • 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 slabs

      Covi, Federico; Hock, Regine; Tedesco, Marco; Truffer, Martin; Sturm, Matthew (2022-12)
      Increased 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.
    • Improved computational tools for infrasound analysis

      Bishop, Jordan W.; Fee, David; Szuberla, Curt A. L.; Tape, Carl; Lyons, John (2022-12)
      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.
    • Dendro-geomorphological analyses of the Slate Creek landslide, Alaska

      Young, Mackenzie E.; Mann, Daniel; Gaglioti, Benjamin; Darrow, Margaret (2022-08)
      Hillslopes 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.
    • Temporal links between ductile shearing, widespread plutonism, and tectonic exhumation near the boundary of parautochthonous and allochthonous terranes in the northern Cordillera, Alaska

      Wildland, Alec D.; Regan, Sean; Nadin, Elisabeth; Jones, James V. III (2022-08)
      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.
    • Mapping bottomfast sea ice in Arctic lagoons using Sentinel-1 interferometery

      Pratt, Jacob W.; Mahoney, Andy; Iken, Katrin; Kasper, Jeremy; Romanovsky, Vladimir (2022-08)
      Sea 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.
    • Bedrock geologic mapping of the Willow Creek area and deformational history of the Hatcher Pass schist, southern Talkeetna Mountains, Alaska

      Muller, Isabella P.; Regan, Sean; Nadin, Elisabeth; Mezger, Jochen (2022-08)
      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.