Now showing items 1-20 of 316

    • Exploring competing gold system models in the Valdez Creek region, Clearwater Mountains, Alaska

      Suhey, Jane Marguerite; Regan, Sean; Nadin, Elisabeth; Kreiner, Douglas (2023-12)
      Gold deposits located within the accretionary and subduction-related tectonic environment of south-central Alaska are interpreted to have formed via devolatilization of hydrous assemblages through regional metamorphism (orogenic model) or by intrusion-related hydrothermal processes (intrusion-related gold system model). The Valdez Creek mining district is located in the southern Clearwater Mountains of south-central Alaska along the intermontane-insular belt suture of the North American Cordillera. The 67-56 Ma south-vergent Valdez Creek shear zone resulted in the thrusting of North American-derived Maclaren schist (intermontane) structurally above lower greenschist-facies rocks of the Clearwater metasediments (Insular). The ~ 5km thick ductile shear zone preserves a complete inverted Barrovian metamorphic gradient ranging from lower greenschist-facies conditions in the south to upper-amphibolite-facies in the north. This event records the terminal suturing of the Wrangellia composite terrane with the North American margin. Placer gold mining and lode gold exploration is currently focused within the footwall of the Valdez Creek shear zone. The region also contains previously undated Cretaceous intrusive rocks associated with gold-in-soil geochemical anomalies. Here, competing gold system models were investigated to identify the predominant mineralization process. This information is used to improve exploration strategies in the area and further develop our understanding of gold formation in the Clearwater Mountains, Alaska. Constraining mechanisms of gold mineralization through integrating structural analysis, geochemistry, and a multiphase geochronologic framework provides a robust tool to determine dominant ore-forming mechanisms. ⁴⁰Ar/³⁹Ar and ²⁰⁶Pb/²³⁸U geochronological methods were used to determine the timing of gold mineralization and constrain ages of igneous rocks associated with known lode sources. Detrital gold geochemistry methods were used to compare placer gold and lode gold compositions. Bulk rock major and trace element geochemical methods were also used to evaluate a primary gold-model by investigating compositional differences of gold-like elements across the Valdez Creek shear zone. Detailed mapping and structural analysis were completed to test if gold mineralization is compatible with shear zone activity (supporting an orogenic model) or if mineralization was unrelated to regional metamorphism and overprinted by the shear zone from 67-56 Ma (supporting an intrusion-related gold system model). The ²⁰⁶Pb/²³⁸U zircon data collected from the alkali pluton suite and the placer system indicates gold-hosting veins were localized within and adjacent to alkaline plutons in the region. These data also indicate that detritus in the placer system was locally derived. White mica ⁴⁰Ar/³⁹Ar geochronology integration ages from undeformed gold-bearing quartz veins proximal to intrusions supports a young mineralization age for gold between 62.11 Ma to 66.58 Ma. Similarities in gold chemistry were also identified within placer gold samples collected from current mining operations and a lode gold location within the catchment. Structural observations show gold-bearing mineralization in quartz veins is likely synchronous with the penetrative deformation associated with the Valdez Creek shear zone. Discrete and network vein orientations throughout the shear zone have geometries compatible with top-to-the-south shear sense of the Valdez Creek shear zone. These results are compatible with a local gold lode source for the Valdez Creek placer deposit that formed coeval with the Valdez Creek shear zone. Bulk rock major and trace element geochemistry results from across the Valdez Creek shear zone metamorphic gradient show a systematic decrease in As, Cu, Ni, Zn, Pb, and Au across the greenschist-amphibolite facies transition indicating that auriferous fluids may have been derived from the shear zone. We hypothesize that metamorphic fluids generated from the dehydroxylation of chlorite occurred simultaneously with shearing along the Valdez Creek shear zone. In this system, auriferous fluids were likely concentrated within or proximal to rigid intrusion(s) in the footwall of the shear zone, coinciding with vein development and fluid channelization, similar in process to the Juneau Gold Belt.
    • Volcanic gas quantification under suboptimal conditions

      Kushner, D. Skye; Lopez, Taryn; Kern, Christoph; Larsen, Jessica; Simpson, William (2023-12)
      Volcanic gas emissions are challenging to quantify. Achieving high confidence in gas composition, column concentrations, and emission rates acquired using remote sensing techniques is thought to require optimal atmospheric conditions. These conditions are often not met, creating a reluctance to preform measurements under non-ideal atmospheric conditions with inherent uncertainty about how useful those measurements may be. In the case of volcanic eruptions, the hazardous nature of the volcanic plume creates an environment where it is often not safe to collect measurements. This dissertation presents three projects which aim to constrain the quantity of two specific volcanic gases, mercury (Hg) and sulfur dioxide (SO₂), released under non-ideal measurement conditions. Specifically, chapter 2 aims to constrain Hg emission during volcanic eruptions, chapter 3 aims to characterize the uncertainty in SO₂ emission rates acquired under specific non-ideal atmospheric conditions, and chapter 4 aims to improve constraints on plume altitude for scanning remote sensing measurements of SO₂ emission rates acquired from a single instrument. Ash is a potential sink of volcanically-sourced atmospheric mercury, and the concentration of particle-bound Hg may provide constraints on Hg emissions during eruptions. In Chapter 2, the Hg concentrations in 227 bulk ash samples from the Mt. Spurr (1992), Redoubt (2009), and Augustine (2006) volcanic eruptions are examined to investigate large-scale spatial, temporal, and volcanic-source trends. No significant difference in Hg concentrations is found in bulk ash by distance from the eruption source or for discrete eruptive events at each volcano, suggesting that in-plume reactions converting gaseous Hg⁰ to adsorbed Hg²⁺ are happening on timescales shorter or longer than considered in this study (minutes to hours) and any additional in-plume controls may be masked by intra-volcanic sample variability. A significant difference is found in Hg concentration in ash among volcanic sources, which indicates that specific volcanoes may emit comparatively high or low quantities of Hg. These findings allow for the calculation of minimum, first-order estimates of volcanic Hg emissions during eruption in combination with total mass estimates of ashfall deposits. Mt. Spurr is found to be a high Hg emitting volcano such that its 1992 particulate Hg emissions likely contributed substantially to the global eruptive volcanic Hg budget for that year. Based on this study, previous approaches that used long-term Hg/SO₂ mass ratios to estimate eruptive total Hg under-account for Hg emitted in explosive events, and global volcanogenic Total Hg estimates need revisiting. A large source of error in SO₂ emission rates derived from mobile differential optical absorption spectroscopy (DOAS) is the uncertainty in atmospheric light paths between the scattered sunlight and the instrument, particularly under non-ideal atmospheric conditions such as the presence of clouds beneath the volcanic plume. In Chapter 3, numerical simulations using the McArtim model are used to examine the radiative transfer associated with zenith-facing mobile DOAS traverses for scenarios where there is a cloud layer between the instrument and the volcanic plume. In total, 217 permutations of atmospheric optical conditions are considered, allowing for the determination of errors associated with atmospheric scattering. Objective criteria are also developed for selecting SO₂ baselines and plume limits for each simulated traverse. This study then applies models to a real-world dataset from the 2021 Cumbre Vieja eruption to explore the effects of ground-level haze on a measured SO₂ column densities for the volcanic plume. All modeling results find large modifications in the shape of the analyzed plume SO₂ column density versus distance curve, even under scenarios with translucent clouds. Despite modification of the plume shape, the presence of a low cloud or haze layer is typically not a large source of error in determination of the total SO₂ quantity measured over the entirety of the traverse, which suggests that fairly accurate SO₂ emission rate measurements can be obtained even under non-ideal atmospheric measurement conditions. The real-world dataset from Cumbre Vieja is found to be best explained by a layer of ground-level laze containing SO₂ and a volcanic plume located between 2 - 4 km altitude. A large source of uncertainty in SO₂ emission rates derived from scanning DOAS instruments is the cross-sectional area of the detection, which is determined from the vertical and horizontal distance of the plume from the instrument. In Chapter 4, a novel method is employed to estimate plume altitude based on modeled wind speed data and validated against available webcam imagery at Cleveland Volcano in the Aleutian Islands, Alaska. This estimated plume altitude is used to calculate SO2 emission rates from single-station campaign scanning DOAS measurements at Cleveland Volcano, Gareloi Volcano, and Korovin Volcano (Alaska) in 2019, where the instrument was deployed for several days at each site. This method is also applied to a long-term dataset of scanning SO2 measurements acquired from a permanent scanning DOAS instrument installed at Cleveland Volcano September 2022 - June 2023. It is found that the method of estimating plume altitude in the long-term dataset produces a lower emission rate and a smaller sample variance than assuming a fixed summit plume altitude. The remaining variance in the data is then interpreted to represent variability in SO₂ emissions during times of relative quiescence at each studied volcano.
    • The effects of summer snowfall on Arctic sea ice radiative forcing

      Chapman-Dutton, Hannah; Webster, Melinda; Sturm, Matthew; Ballinger, Thomas; Zweiback, Simon (2023-12)
      The decline in Arctic sea ice has had major impacts on the climate system, particularly relating to the ice-albedo feedback. Since fresh snow on top of bare or melting sea ice increases the surface albedo on local scales, the impact of summer snow events can have a negative radiative forcing effect, which could inhibit sea ice surface melt. In this study, we compared snow depth and meteorological data from buoys and satellite retrievals of surface and atmospheric conditions to identify and characterize summer snow accumulation case studies across the Arctic from 2003 to 2017. Clouds and Earth's Radiant Energy System (CERES) retrievals were used to quantify the changes in surface albedo before and after the snow accumulation events. Information from these case studies was then scaled up to find similar events on a pan-Arctic scale using a Lagrangian sea ice parcel database. In this way, we characterized the frequency, magnitude, and duration of summer snow accumulation events similar to those observed by buoys. Finally, a simple radiative transfer model was used to quantify the impact of summer snowfall events on the surface and top-of-atmosphere radiative forcing over the entire Arctic region. The following work provides new information on observed snow accumulation events over Arctic sea ice in summer by combining multiple sources of in situ, satellite, and modeled data. Such results will be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice.
    • The relationship between fracturing, asymmetric folding, and normal faulting in Lisburne Group carbonates: West Porcupine Lake Valley, Northeastern Brooks Range, Alaska

      Shackleton, John Ryan (2003-05)
      The distribution of fold related fractures and other mesoscopic structures in asymmetrically folded Mississippian to Pennsylvanian Lisbume Group carbonates gives clues concerning the mechanism of folding. Since fracture sets pre-date and post-date folding, it is important, but sometimes difficult, to determine which fracture sets are related to folding. Higher density of fold related fractures and dissolution cleavage in the hinges than limbs of two folds in the study area is evidence for fixed hinge detachment folding. However, geometric modeling of box shaped folds in the study area suggests that some folds may have formed by either detachment folding or trishear fault propagation folding. Formulaic modeling of fracture density in a stratigraphic section using stratigraphic attributes such as lithology, bed thickness, and chert content predicts general trends in fracture density, but other factors such as slip along bed contacts may obscure the relationship between fracture density, lithology and bed thickness.
    • Instability and retreat of a lake-calving terminus, Mendenhall Glacier, Southeast Alaska

      Boyce, Eleanor (2006-05)
      Mendenhall Glacier is a lake-calving glacier in southeastern Alaska that is experiencing substantial thinning and increasingly rapid recession. Long-term mass wastage linked to climatic trends is responsible for thinning of the lower glacier and leaving the terminus vulnerable to buoyancy-driven calving and accelerated retreat. Bedrock topography may play a role in stabilizing the terminus between periods of rapid calving and retreat. Lake-terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues, with some similarities to both groups. Lacustrine termini experience fewer perturbations (e.g. tidal flexure, high subaqueous melt rates) and are therefore inherently more stable than tidewater termini. At Mendenhall, rapid thinning and simultaneous retreat into a deeper basin leci to floatation conditions along approximately 50% of the calving front. This unstable terminus geometry lasted for ~ 2 years anci culminated in large-scale calving and terminus collapse during summer 2004. We used a 1-dimensional viscoelastic model to investigate the transient response of a floating glacier tongue to buoyant forcing. Results suggest that creep may be capable of accommodating buoyant torque if it is applied gradually. As unresolved bending stresses approach the tensile strength of ice, small rapidly applied perturbations may cause buoyancy-driven calving.
    • 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.