• The 1931 eruption of Aniakchak volcano, Alaska: deposit characteristics and eruption dynamics

      Nicholson, Robert Stokes (2003-12)
      The 1931 eruption of Aniakchak progressed through several eruptive phases from multiple vents that totaled 1.4 x 10⁸ m³ dense rock equivalent of magma. The sequence of phases began with a sub-plinian eruption followed by a phreatomagmatically-influenced vulcanian phase originating from the primary vent. Effusive activity from two separate vents occurred simultaneously with the vulcanian phase. The eruption from the main vent progressed to strombolian in nature and eventually subsided into an effusive eruption. The composition of the magma ranged from trachydacite at the onset of the eruption to basaltic andesite at its conclusion. Volcanoes commonly exhibit variations in eruptive style similar to those seen at Aniakchak. Previous studies at other volcanoes have attributed changes in the nature of an eruption to such factors as the compositional variation in magma, magma flux, the presence of external water, conduit and surface morphology, and volatile degassing behavior. The differences in style of the 1931 Aniakchak eruption are the result of variations in magma flux, the presence or absence of external water, and differences in magma composition. Evidence of a zoned magma chamber indicates that properties associated with the magma chamber might have indirectly influenced the eruption style at Aniakchak.
    • 60,000 year climate and vegetation history of Southeast Alaska

      Wilcox, Paul S.; Fowell, Sarah; Bigelow, Nancy; Mann, Daniel; Dorale, Jeffrey (2017-08)
      Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until ~14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between ~13,000 and ~11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 ± 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on δ¹³C and δ¹⁸O values spanning the interval from ~60,000 yr. BP to ~11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative δ¹³C values are attributed to predominance of angiosperms in the vegetation above the cave at ~22,000 yr. BP and between ~53,000 and ~46,000 yr. BP while more positive δ¹³C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data suggest limited or no ice cover above El Capitan Cave for the duration of the record, possibly indicating that this region was a nunatak during glacial periods.
    • An 8 ka record of vegetation cover, fire history and moisture availability from North-Central Mongolia

      Molhoek, Emily (2007-05)
      Analysis of pollen, charcoal, and stable carbon and nitrogen isotopes ([delta]¹³C and [delta]¹⁵N) from a sediment core of Mongolian Lake Terhiyn-Tsagaan show increases in moisture availability coincident with mid- to late Holocene expansion of the Asian monsoon. The lake is freshwater and located in an intermontane depression on the flanks of the Hangai Range of north-central Mongolia. The site lies within the forest-steppe biome ~400 m below tree line. The low C:N of the sediments indicates that organic matter is primarily composed of autochthonous material. Artemisia and Chenopodiaceae pollen are indicators of dry steppe and semi-desert vegetation, whereas Poaceae pollen is more abundant in humid meadow-steppe or forest-steppe assemblages. An aridity index, calculated by dividing Artemisia + Chenopodiaceae by Poaceae pollen, is used to identify changes in moisture availability. High aridity indices and spikes of charcoal influx record relatively humid conditions at the site between 8.0 and 5.5 k years BP. Low charcoal influx rates and peak values of the aridity index between 4.5 and 4.0 k years BP correspond to a documented interval of drought in southern Asia and northern Africa attributed to a weak Asian monsoon. A decrease in charcoal influx since 7.5 k years BP combined with progressive increase in [delta]¹⁵N indicates increasing aridification from the mid-Holocene to nearly the present. Intervals of humidification at Lake Terhiyn-Tsagaan are thus synchronous with the waxing and waning of the Asian monsoon and out of phase with humid intervals recorded at Lake Telmen, approximately 250 km to the northwest. It is possible that the Terhiyn-Tsagaan drainage lies at the northern and/or western edge of the region that received precipitation from an expanded Holocene summer monsoon.
    • A comparative study of contrasting structural styles in the range-front region of the northeastern Arctic National Wildlife Refuge, northeastern Brooks Range, Alaska

      Hanks, Catherine Leigh; Stone, David B.; Crowder, R. Keith; Keskinen, Mary J.; Watts, Keith W.; Ave Lallemant, Hans G.; Mull, C. G. (1991)
      The range front of the northeastern Brooks Range in the Arctic National Wildlife Refuge (ANWR) is defined by anticlinoria cored by a 'basement' complex of weakly metamorphosed sedimentary, volcanic and intrusive rocks. These anticlinoria are interpreted to reflect horses in a northward-propagating regional duplex between a floor thrust at depth in the 'basement' complex and a roof thrust near the base of the cover sequence. Lateral variations in the geometry of these range-front anticlinoria reflect changes in lithology and deformational style of both the 'basement' and its cover. Two distinct structural geometries are displayed along the range front of northeastern ANWR. To the east, the large range-front anticlinorium is interpreted to reflect multiple horses of Cenozoic age within the stratified, slightly metamorphosed sedimentary and volcanic rocks of the pre-Mississippian 'basement'. During Cenozoic thrusting, these mechanically heterogeneous rocks deformed primarily via thrusting and related folding with minor penetrative strain. The Mississippian and younger cover sequence shortened via both thrust duplication and detachment folding above a detachment in the Mississippian Kayak Shale. In contrast, to the west the pre-Mississippian rocks consist primarily of the mechanically homogeneous Devonian Okpilak batholith. The batholith was transported northward during Cenozoic thrusting and now forms a major topographic and structural high near the range front. The batholith probably shortened during thrusting as a homogeneous mass via penetrative strain. Because the Kayak Shale is thin to absent in the vicinity of the batholith, Mississippian and younger rocks remained attached to the batholith and shortened via penetrative strain and minor imbrication. These two range-front areas form the central portion of two regional transects through northeastern ANWR. General area-balanced models for both transects suggest that the amount of total shortening is governed by the structural topography and the geometry of the basal detachment surface. While the structural topography of northeastern ANWR is reasonably well-constrained, the geometry of the basal detachment is not. Given a range in reasonable basal detachment geometries, shortening in both transects ranges from 16% to 61%. Detailed balanced cross sections based on subsurface and surface geologic data yield 46-48% shortening for both transects.
    • Active Tectonics In Southern Alaska And The Role Of The Yakutat Block Constrained By Gps Measurements

      Elliott, Julie; Freymueller, Jeff (2011)
      GPS data from southern Alaska and the northern Canadian Cordillera have helped redefine the region's tectonic landscape. Instead of a comparatively simple interaction between the Pacific and North American plates, with relative motion accommodated on a single boundary fault, the margin is made up of a number of small blocks and deformation zones with relative motion distributed across a variety of structures. Much of this complexity can be attributed to the Yakutat block, an allochthonous terrane that has been colliding with southern Alaska since the Miocene. This thesis presents GPS data from across the region and uses it to constrain a tectonic model for the Yakutat block collision and its effects on southern Alaska and eastern Canada. The Yakutat block itself moves NNW at a rate of 50 mm/yr. Along its eastern edge, the Yakutat block is fragmenting into small crustal slivers. Part of the strain from the collision is transferred east of the Fairweather -- Queen Charlotte fault system, causing the region inboard of the Fairweather fault to undergo a distinct clockwise rotation into the northern Canadian Cordillera. About 5% of the relative motion is transferred even further east, causing small northeasterly motions well into the northern Cordillera. Further north, the GPS data and model results indicate that the current deformation front between the Yakutat block and southern Alaska runs along the western side of the Malaspina Glacier. The majority of the ~37 mm/yr of relative convergence is accommodated along a narrow band of thrust faults concentrated in the southeastern part of the St. Elias orogen. Near the Bering Glacier, the tectonic regime abruptly changes as crustal thrust faults give way to subduction of the Yakutat block beneath the western St. Elias orogen and Prince William Sound. This change aligns with the Gulf of Alaska shear zone, implying that the Pacific plate is fragmenting in response to the Yakutat collision. The Bering Glacier region is undergoing internal deformation and may represent the final stage of accretion of the Yakutat block sedimentary layers. Further west, modeled block motions suggest the crust is laterally escaping along the Aleutian forearc.
    • Airborne hyperspectral imaging for wetland mapping in the Yukon Flats, Alaska

      Graham, Patrick Ryan; Prakash, Anupma; Rosselló, Jordi Cristóbal; Gens, Rudiger (2020-05)
      This study involved commissioning HySpex, a hyperspectral imaging system, on a single-engine Bush Hawk aircraft; using it to acquire images over selected regions of the Yukon Flats National Wildlife Refuge; establishing a complete processing flow to convert raw data to radiometrically and geometrically corrected hypercubes, and further processing the data to classify wetlands. Commissioning involved designing a customized mount to simultaneously install two-camera systems, one operating in the visible and near infrared region, and the other operating in the shortwave infrared region. Flight planning incorporated special considerations in choosing the flight direction, speed, and time windows to minimize effects of the Bidirectional Reflection Distribution Function (BRDF) that are more dominant in high latitudes. BRDF effects were further minimized through a special processing step, that was added to the established hyperspectral data processing chain developed by the German Space Agency (DLR). Instrument commissioning included a test flight over the University of Alaska Fairbanks for a bore-sight calibration between the HySpex system's two cameras, and to ensure the radiometric and geometric fidelity of the acquired images. Calibration resulted in a root mean square error of 0.5 pixels or less for images acquired from both cameras at 1-meter spatial resolution for each geometrically corrected flight line. Imagery was radiometrically corrected using the ATCOR-4 software package. No field spectra of the study areas were collected due to logistics constraints. However, a visual comparison between current spectral libraries and acquired hyperspectral image spectra was used to ensure spectral quality. For wetlands mapping, a 6-category legend was established based on previous United States Geological Survey and United States Fish and Wildlife Service information and maps, and three different classification methods are used in two selected areas: hybrid classification, spectral angle mapper, and maximum likelihood. Final maps were successfully classified using a maximum likelihood method with high Kappa values and user's and producer's accuracy are more than 90% for nearly all categories. The maximum likelihood classifier generated the best wetland classification results, with a Kappa index of about 0.90. This was followed by the SAM classifier with a Kappa index of about 0.57 and lastly by the hybrid classifier that achieved a Kappa index of only 0.42. Recommendations for future work include using higher-accuracy GPS measurements to improve georectification, building a spectral library for Alaskan vegetation, collection of ground spectral measurements concurrently with flight image acquisition, and acquisition of LiDAR or RGB-photo derived digital surface models to improve classification efforts.
    • Alaska Shorefast Ice: Interfacing Geophysics With Local Sea Ice Knowledge And Use

      Druckenmiller, Matthew L.; Eicken, Hajo (2011)
      This thesis interfaces geophysical techniques with local and traditional knowledge (LTK) of indigenous ice experts to track and evaluate coastal sea ice conditions over annual and inter-annual timescales. A novel approach is presented for consulting LTK alongside a systematic study of where, when, and how the community of Barrow, Alaska uses the ice cover. The goal of this research is to improve our understanding of and abilities to monitor the processes that govern the state and dynamics of shorefast sea ice in the Chukchi Sea and use of ice by the community. Shorefast ice stability and community strategies for safe hunting provide a framework for data collection and knowledge sharing that reveals how nuanced observations by Inupiat ice experts relate to identifying hazards. In particular, shorefast ice break-out events represent a significant threat to the lives of hunters. Fault tree analysis (FTA) is used to combine local and time-specific observations of ice conditions by both geophysical instruments and local experts, and to evaluate how ice features, atmospheric and oceanic forces, and local to regional processes interact to cause break-out events. Each year, the Barrow community builds trails across shorefast ice for use during the spring whaling season. In collaboration with hunters, a systematic multi-year survey (2007--2011) was performed to map these trails and measure ice thickness along them. Relationships between ice conditions and hunter strategies that guide trail placement and risk assessment are explored. In addition, trail surveys provide a meaningful and consistent approach to monitoring the thickness distribution of shorefast ice, while establishing a baseline for assessing future environmental change and potential impacts to the community. Coastal communities in the region have proven highly adaptive in their ability to safely and successfully hunt from sea ice over the last 30 years as significant changes have been observed in the ice zone north of Alaska. This research further illustrates how Barrow's whaling community copes with year-to-year variability and significant intra-seasonal changes in ice conditions. Hence, arctic communities that have coped with such short-term variability may be more adaptive to future environmental change than communities located in less dynamic environments.
    • Alaska's shrinking glaciers: integrated glaciological research for hydrological, ecological, and environmental education applications

      Young, Joanna; Pettit, Erin; Arendt, Anthony; Conner, Laura; Hood, Eran (2020-05)
      As air temperatures in Alaska are rising, glacier melt is accelerating and affecting hydrological resources and downstream ecosystem function. The extent to which glacier loss may change hydrological regimes in coastal climates, and how that may impact nearshore marine conditions, is uncertain. Moreover, from a social-ecological standpoint, many citizens today are disconnected from these types of environmental changes, in part due to isolation from visible climate change impacts. This dissertation addresses the dual need for examining recent Alaska glacier changes and resulting hydrological and marine impacts, and for exploring education strategies that leverage glacier changes for environmental identity development. In Chapter One, I present a conceptual framework that links the physical and social sciences research herein as equal components of a social-ecological system. In Chapter Two, I use a glacio-hydrological model to uncover that coastal glaciers of the Juneau Icefield have yet to pass `peak water' delivery. I also find that between 1980 to 2016, glacier ice melt increased annually (+10%, p = 0.14) and in spring (+16%, p = 0.05), leading to changing freshwater composition. In Chapter Three, I compare modeled Mendenhall River discharge to nearshore oceanographic measurements, finding that salinity and density in the upper 15 m are strongly glacially-inuenced (10 to 30 PSU and 1010 to 1023 kg m⁻³), and that glacier runoff exerts a stronger control (r² = 0.66) than total runoff. Large, signicant trends are also detected for 1997 to 2016 August modeled glacier runoff (p = 0.02, + 15%) and observed salinity (p = 0.01, -3.2 PSU), linking these phenomena and revealing ongoing changes. Finally, in Chapter Four, I analyze social science data from youth participants in a science outreach program in a climate-impacted glacier landscape. I find that better understanding ecosystem linkages and seeing the scale of glacier loss first-hand promote environmental identity development by building relatedness and pro-environmental motivation. Together, the glaciological and environmental education research herein provides diverse perspectives on improving both scientic and citizen understanding of glacier mass loss in a changing climate.
    • An Interdisciplinary Computational Study Of Magnetosphere-Ionsphere Coupling And Its Visual And Thermal Impact In The Auroral Region

      Styers, John; Newby, Greg (2012)
      A three-dimensional, three-fluid simulation (ions, electrons, and neutrals) was explicitly parallelized, facilitating the study of small-scale magnetospheric-ionospheric (M-I) coupling processes. The model has ionization and recombination, self-consistently (semi-empirically) determined collision frequencies, and a height resolved ionosphere. Inclusion of ion inertial terms in the momentum equation enables the propagation of Alfven waves. Investigation at small scales required large system domains, and thus fast parallel computers. The model was explicitly parallelized---enabling investigations of M-I coupling processes on very small temporal and spatial scales. The generation, reflection, and propagation of Alfven waves is of importance to the understanding of M-1 coupling processes---it is, in fact, the primary means of communication of physical processes in the coupled system. Alfvenic reflections were modeled for two different boundary conditions, and it was shown that the deformation of the current layer was Alfvenic in character. Visualizations of the data obtained appear to be consistent with the visual characteristics of actual discrete aurora in nature. The model reproduces qualitatively, and semi-quantitatively, in a self-consistent manner, some the behaviors of the formation and time-evolution of discrete arcs. These include the narrowness of arcs; electric fields extending parallel outward from the arcs; and fast (plasma) flows in the region of discrete arcs. Large-scale models---due to inevitable limitations of computational resources---need to make large-scale averages of computed properties. In regions of active small-scale structure, significant under-representation of the Joule heating occurs. It has been shown that the under-representation of the Joule heating in the region of active aurora can be as large as a factor of 8. This work includes a computer-based study of a quantitative approximation of this underrepresentation of the Joule heating by global, large-scale models and experimental observations.
    • An Investigation Into Argon-40/Argon-39 Radiogenic Dating And X-Ray Analysis Of Shales And Clays From Northern Alaska

      Munly, Walter Campbell; Layer, Paul (2004)
      In this thesis I develop a new 40Ar/39Ar dating technique for measuring ages and estimating cooling histories of potassium-bearing minerals within shales and clays. To overcome problems of argon recoil, small shale or clay flakes (possessing diameters less than 2 mm) were encapsulated within microampoules under vacuum. Encapsulation ensures that argon that recoils from tiny crystals during irradiation in a nuclear reactor cannot escape and will therefore be detected during 40Ar/39Ar laser step-heating. The step heating method is effective in differentiating between, and dating neoformed and detrital illite components. My use of this method has revealed a significant age difference across the Toyuk thrust, Brooks Range, northern Alaska. Devonian shales from south of the thrust yield relatively flat age spectra indicative of a younger illitic component, and argon retention ages around 225 Ma. Shale samples from north of the thrust yield staircase age spectra indicative of a detrital illite component, and older retention ages (233--391 Ma). Modeling of these spectra across the Toyuk also suggests that argon loss and subsequent cooling occurred at about 140 Ma. Retention ages across the Toyuk thrust may reflect differences in depths of tectonic burial, or differing ages of crystallization of neoformed illite during initial deposition and burial. 40Ar/39Ar age spectra from the Colville basin, North Slope, Alaska, illites are generally dominated by detrital illite, yielding high temperature step-heat ages up to 475 Ma. Illite crystallization ages from the NPRA (National Petroleum Reserve in Alaska) range between 205 and 225 Ma. These ages are older than depositional ages and therefore suggest that this illite was transported from outside the Colville basin, perhaps from the Brooks Range. The Colville basin samples also reveal argon loss at ~45 Ma. Paleocene samples from the Exxon Alaska State A-1 well yield illite crystallization ages of about 205 Ma, and argon loss ages around 40 Ma. X-ray diffraction of the Colville basin samples indicates the presence of multiple clay phases, including detrital and neoformed illite. This complex mineralogy precluded estimating when the host shales were within the oil generation window.
    • Analysis and interpretation of volcano deformation in Alaska: Studies from Okmok and Mt. Veniaminof volcanoes

      Fournier, Thomas J.; Freymueller, Jeffrey; Larsen, Jessica; Cervelli, Peter; Christensen, Douglas; McNutt, Stephen (2008-12)
      Four studies focus on the deformation at Okmok Volcano, the Alaska Peninsula and Mt. Veniaminof. The main focus of the thesis is the volcano deformation at Okmok Volcano and Mt. Veniaminof, but also includes an investigation of the tectonic related compression of the Alaska Peninsula. The complete data set of GPS observations at Okmok Volcano are investigated with the Unscented Kalman Filter time series analysis method. The technique is shown to be useful for inverting geodetic data for time dependent non-linear model parameters. The GPS record at Okmok from 2000 to mid 2007 shows distinct inflation pulses which have several months duration. The inflation is interpreted as magma accumulation in a shallow reservoir under the caldera center and approximately 2.5km below sea level. The location determined for the magma reservoir agrees with estimates determined by other geodetic techniques. Smaller deflation signals in the Okmok record appear following the inflation pulses. A degassing model is proposed to explain the deflation. Petrologic observations from lava erupted in 1997 provide an estimate for the volatile content of the magma. The solution model VolatileCalc is used to determine the amount of volatiles in the gas phase. Degassing can explain the deflation, but only under certain circumstances. The magma chamber must have a radius between ~1and 2km and the intruding magma must have less than approximately 500ppm CO2. At Mt. Veniaminof the deformation signal is dominated by compression caused by the convergence of the Pacific and North American Plates. A subduction model is created to account for the site velocities. A network of GPS benchmarks along the Alaska Peninsula is used to infer the amount of coupling along the mega-thrust. A transition from high to low coupling near the Shumagin Islands has important implications for the seismogenic potential of this section of the fault. The Shumagin segment likely ruptures in more frequent smaller magnitude quakes. The tectonic study provides a useful backdrop to examine the volcano deformation at Mt. Veniaminof. After being corrected for tectonic motion the sites velocities indicate inflation at the volcano. The deformation is interpreted as pressurization occurring beneath the volcano associated with eruptive activity in 2005.
    • Analysis of composition and chronology of dome emplacement at Black Peak Volcano, Alaska utilizing aster remote sensing data and field-based studies

      Adleman, Jennifer Nicole (2005-05)
      Black Peak volcano is a 3̃.5km-diameter caldera located on the Alaska Peninsula that formed 4̃,600 years ago in an eruption that excavated>km³ of material. The caldera floor is occupied by at least a dozen overlapping dacitic to andesitic lava domes and flows. Examination of XRF results and observations of the domes in and around the caldera reveals a range of 57-65wt% SiO₂ and variations in amphibole content. Evidence for magma mixing includes vesicular enclaves and geochemical trends that indicate involvement of a more mafic magma into a dacitic reservoir. The purpose of this study is to investigate if, and how, these differences in composition and mineralogy are detectable in satellite emissivity and TIR data (ASTER) and compare the results to ground-based field observations to discern changes in the mineralogical and chemical properties of the domes. This study incorporates the use of decorrelation-stretch image processing techniques and the deconvolution of laboratory emissivity spectra to assess the viability of discriminating variations in the lithologies observed at Black Peak volcano. Compositional results from XRD and electron microprobe analyses are comparable to those obtained through deconvolution processing. Surfaces of <10% amphibole and SiO₂ of 60-65wt% and those that correspond to>1̲0% and <61 wt% SiO₂ are distinguishable in the ASTER data.
    • An analysis of volcanic ash plume movement and dispersion within the North Pacific

      Papp, Kenneth R.; Dean, Kenneson; Sharpton, Virgil; Dehn, Jonathan; Schneider, David (2002-08)
      This study analyzes the movement and dispersion of airborne volcanic ash within the North Pacific region by simulating volcanic plumes from 22 volcanoes using the PUFF ash-tracking model. The model is run hourly using archived wind field data between 1994-2001 and the results are analyzed with statistical and GIS software. Maps and statistics are generated revealing the distribution of simulated airborned ash particles at 6 and 24 hr intervals, constraining the likely direcion and distance a volcanic ash cloud may propagate from a given volcano. The results indicate wind field charactistics during and after an eruption may have a larger effect on volcanic cloud growth rate than the eruption dynamics. Wind field and statistical analyses show North Pacific ash cloud distribution is strongly affected by the intensity, migration, and location of the Polar jet stream and associated cyclones. Although often used operationally during an eruption crisis, the PUFF model can also be used as an effective research tool and provide airborne ash hazard mitigation for towns, airports, and air traffic within the North Pacific region.
    • Anisotropy in the Alaska subduction zone: shear-wave splitting observations from local and teleseismic earthquakes

      Richards, Cole; Tape, Carl; West, Michael; Freymueller, Jeffrey (2020-05)
      Shear-wave splitting observations can provide insight to mantle flow due to the link between the deformation of mantle rocks and their direction dependent seismic wave velocities. We identify shear-wave anisotropy in the Cook Inlet segment of the Alaska subduction zone by analyzing splitting parameters of S phases from local intraslab earthquakes between 50 and 200 km depths and SKS waves from teleseismic events. These earthquakes were recorded from 2015-2017 (local S) and 2007-2017 (SKS) by stations from SALMON (Southern Alaska Lithosphere and Mantle Observation Network), TA (EarthScope Transportable Array), MOOS (Multidisciplinary Observations Of Subduction), AVO (Alaska Volcano Observatory), and the permanent network. Automatic phase picking (dbshear) of 12095 local earthquakes (Ml ≥ 1.5) recorded at 84 stations yielded 678 high-quality splitting measurements (filtered 0.2-1 Hz). Teleseismic SKS phases recorded at 112 stations with 26,143 event-station pairs resulted in 360 high-quality SKS splitting measurements (filtered 0.02-1 Hz and 0.01-1 Hz). Measurements for both datasets were made using the SC91 minimum eigenvalue method with software package MFAST. We compare local S and SKS splitting patterns both from previous studies and our own analysis and find that they are most similar in the far forearc, at the Kenai Peninsula, below which there is no mantle wedge. Anisotropy in the subducting Pacific lithosphere and subslab asthenosphere is likely here as both S and SKS display plate convergence fast directions and SKS measurements exhibit delay times too long (∼2 s) to be explained solely by lithospheric anisotropy. Large splitting delay times (∼0.5 s) for local measurements that mainly sample slab further indicate that the Pacific slab lithosphere contains significant anisotropy. We also observe anisotropy in the mantle wedge indicated by an increase in delay time as focal depth increases for stations with ray paths dominantly sampling wedge. These measurements display trench-perpendicular and plate convergence fast directions consistent with 2D corner flow in the mantle wedge. Both datasets show trench-parallel splitting directions in select areas of the arc/forearc that overlie parts of the mantle wedge and nose. B-type olivine in the mantle nose, subslab asthenospheric flow, flow around the slab edge, and anisotropy in the Pacific lithosphere all could be invoked to explain this pattern. While we are unable to distill the anisotropy to a single responsible structure, the sharp transition in the local S data splitting pattern from trench-perpendicular in the backarc to trench-parallel across the arc suggests B-type olivine in the mantle nose. For an overall model, we favor 2D corner flow of A-type olivine in the mantle wedge induced by downdip motion of the slab, B-type olivine in the nose, and plate convergence parallel anisotropy in the subslab asthenosphere and subducting Pacific lithosphere to explain the observed splitting patterns. It is clear that the subducting slab's structure and motion are the dominant influence on anisotropy and mantle flow regimes here. The differences in local S and SKS splitting results motivate further study on frequency dependence of splitting measurements and emphasize the need for a better understanding of which earth structures are responsible for the observed splitting patterns globally. This study constitutes the first comprehensive local splitting study in Alaska and refutes the common interpretation of along arc flow in the mantle wedge proposed by many previous splitting studies in Alaska.
    • Applicability of synthetic aperture radar for investigating river breakup on the Kuparuk River, Northern Alaska

      Floyd, Angelica L. (2012-12)
      A combined use of remote sensing techniques and field measurements is a pragmatic approach to study Arctic hydrology, given the vastness, complexity, and logistical challenges posed by most Arctic watersheds. This study investigates the use of synthetic aperture radar (SAR) to define spring breakup of the Kuparuk River on the North Slope of Alaska. A time series (years 2001-2010) of SAR images was assembled at the river mouth on the Arctic Coastal Plain. A statistical analysis was used and was limited to three variables: image brightness, variance in brightness over the river length, and a rank order analysis accomplished by segmenting the river and ranking segments in order of relative brightness. Variance was the only reliable breakup indicator of the three tested. A shorter one year temporal stack was assembled at the river's headwaters for a visual interpretation, which had limited success. Results from both analyses were calibrated with in-situ stream gauge data. River ice breakup is a highly complex process which may be defined differently by the remote sensing community and hydrologists, due to the sensitive nature of SAR, which may indicate surficial changes on the river before any discharge is recorded.
    • Applying a model of orographic precipitation to improve mass balance modeling of the Juneau Icefield

      Roth, Aurora; Hock, Regine; Truffer, Martin; Aschwanden, Andy (2016-12)
      Mass loss from glaciers in Southeast Alaska is expected to alter downstream environmental conditions such as streamflow patterns, riverine and coastal ecological systems, and ocean properties. To investigate these potential changes under future climate scenarios, accurate climate data are needed to drive glacier mass balance models. However, assessing and modeling precipitation in mountainous regions remains a major challenge in glacier mass balance modeling. We have used a linear theory of orographic precipitation model (LT model) to downscale precipitation from both the Weather Research and Forecasting (WRF) model and the European Centre for Medium-RangeWeather Forecasts interim reanalysis (ERA-Interim) to the Juneau Icefield, one of the largest icefields in North America (4149 km2), over the period 1979--2013. The LT model is physically-based, combining airflow dynamics and simple cloud microphysics to simulate precipitation in complex terrain. Cloud microphysics is parameterized as a function of user-defined snow and rain fall speeds which are then used to calculate the cloud time delay, t, at every time step. We established a model reference run using literature values of snow fall speed and rain fall speed. The model was run using a 1 km digital elevation model and 6 hour timesteps. Due to a lack of precipitation observations, we validated the model with point net accumulation observations along an 8.5 km transect on Taku glacier, one of the largest and best-studied outlet glaciers of the icefield. The observations occurred in late July of 1998, 2004, 2005, 2010, and 2011. We extracted the snow portion from the modeled precipitation and accounted for melt using a temperature-index model prior to comparing results to the observations. The latter was necessary since the observations were taken when substantial melt of the winter snow cover had occurred. The results of the reference run show reasonable agreement with the available glaciological observations (r2 = 0.89). We assessed the LT model results in terms of the icefield-wide average winter (October-March) precipitation amount and its spatial pattern for the 1979-2013 time period. To express the latter we calculated a precipitation index map where each grid cell of average winter precipitation was divided by the icefield-wide spatial mean. The downscaled precipitation pattern produced by the LT model is consistent with the expected orographic precipitation pattern with substantially reduced precipitation on the eastern lee-side portion of the icefield, a pattern that is absent in the coarse resolution WRF and ERA-Interim precipitation fields. To investigate the robustness of the LT model results, we performed a series of sensitivity experiments varying the LT model parameters of snow fall speed and rain fall speed, as well as the horizontal resolution of the underlying grid, and the climate input data. The precipitation pattern produced by the LT model was stable regardless of the parameter combination, horizontal resolution, and climate input data, but the precipitation amount varied strongly with these factors. For the range of snow fall speeds tested and holding all other parameters constant, the average winter precipitation spatial mean varied from 2.5 m to 4.4 m. We were unable to constrain the precipitation amount due to the scarcity of validation data. However, given the stability of the winter precipitation pattern produced by the LT model, we suggest a winter precipitation index map calculated from the LT model reference run results be used in combination with a distributed mass balance model for future mass balance modeling studies of the Juneau Icefield. More observations of total precipitation are needed to further validate the precipitation pattern of the LT model results, constrain the model parameters, and improve the estimation of total precipitation amounts by the LT model. We suggest three locations for potential weather stations that would be most beneficial for validating LT model results. The LT model could be applied to other regions in Alaska and elsewhere with strong orographic effects for improved glacier mass balance modeling and/or hydrological modeling.
    • Architectural analysis and fold geometry of syntectonic fluvial conglomerate in the Nanushuk Formation, Brooks Range foothills, Alaska

      Finzel, Emily Suzanne (2004-12)
      The fluvial style and syntectonic deposition of conglomerate in the upper part of the Nanushuk Formation are resolved using facies architectural analysis and structural geometry. Along the Kanayut River in the northern foothills of the Brooks Range, Alaska, fluvial conglomerate is exposed as benches on the north and south flanks of the Arc Mountain anticline. Photo mosaics of each bench on the north side, along with thirty-three detailed measured sections, were used to evaluate facies architecture. Eight lithofacies were described that characterize six facies associations including longitudinal and transverse gravel bars, diffuse gravel sheets, sediment gravity flow deposits, crevasse splay and floodplain deposits, and scour fills of a gravel-bed braided river. Strata on the south limb of the anticline show characteristics of syndeformational deposition during the growth of the south limb of the Arc Mountain anticline. These structural data provide new evidence for syndepositional contractional deformation during the mid-Cretaceous at this locality in the northern foothills of the Brooks Range. These results provide clues to the character and extent of potential reservoir rocks from the Nanushuk Group that are present in the subsurface of the National Petroleum Reserve in Alaska, which is important for continued recovery of natural resources on the North Slope.
    • Arctic landscape dynamics: modern processes and pleistocene legacies

      Farquharson, Louise M.; Mann, Daniel; Romanovsky, Vladimir; Grosse, Guido; Jones, Benjamin M.; Swanson, David (2017-12)
      The Arctic Cryosphere (AC) is sensitive to rapid climate changes. The response of glaciers, sea ice, and permafrost-influenced landscapes to warming is complicated by polar amplification of global climate change which is caused by the presence of thresholds in the physics of energy exchange occurring around the freezing point of water. To better understand how the AC has and will respond to warming climate, we need to understand landscape processes that are operating and interacting across a wide range of spatial and temporal scales. This dissertation presents three studies from Arctic Alaska that use a combination of field surveys, sedimentology, geochronology and remote sensing to explore various AC responses to climate change in the distant and recent past. The following questions are addressed in this dissertation: 1) How does the AC respond to large scale fluctuations in climate on Pleistocene glacial-interglacial time scales? 2) How do legacy effects relating to Pleistocene landscape dynamics inform us about the vulnerability of modern land systems to current climate warming? and 3) How are coastal systems influenced by permafrost and buffered from wave energy by seasonal sea ice currently responding to ongoing climate change? Chapter 2 uses sedimentology and geochronology to document the extent and timing of ice-sheet glaciation in the Arctic Basin during the penultimate interglacial period. Chapter 3 uses a combination of surficial geology mapping and remote sensing to explore the distribution and vulnerability of modern day landscapes on the North Slope of Alaska to thermokarst caused by rapid warming. Chapter 4 uses high spatial and temporal resolution remote sensing data and field surveys to show how sea ice decline is causing AC coastlines to become more geomorphologically dynamic. Together the results of this research show that the AC is a highly dynamic system that can respond to climate warming in complex and non-linear ways. Chapter 2 provides terrestrial evidence that ice-sheet glaciation occurred offshore in the Arctic Ocean in the later stages of the last interglacial period at a time when lower latitude sections of the Laurentide and Cordilleran were in retreat. These findings have important implications for how Arctic ice sheets respond to increased moisture availability caused by sea ice decline and atmospheric warming. This study also provides a new approach to reconstructing and establishing an absolute chronology for periods of Arctic Ocean glaciation during the mid- to late-Pleistocene. Chapter 3 illustrates how Pleistocene-legacy effects exert important influences over the vulnerability of Arctic lowlands to climate warming. Striking differences are revealed in Holocene thermokarst activity between different surficial geology units. During the Holocene, regions of marine silts have been the most susceptible to thermokarst, while regions of ice-poor aeolian sand have seen the least thermokarst activity. In future decades, areas of ice-rich aeolian silt will be most vulnerable to rapid warming because these areas contain large amounts of ground ice that have so far undergone little thermokarst development during the Holocene. Findings from this study have important implications for understanding future landscape evolution and carbon cycling in the Arctic. Chapter 4 shows that permafrost coastlines in the Kotzebue Sound region are already responding to ongoing climate change. Remote sensing data demonstrates that declines in the extent and timing of sea ice are causing an increasingly dynamic coastal system. Rates of change along the coast are more dynamic now than at any time during the past 64 years, and these geomorphic responses to sea ice decline are non-linear. Furthermore, future coastal change will not necessarily be characterized by higher erosion rates, because accretion rates are simultaneously rising. In general, the research described in this dissertation illustrates that the future response of AC components to ongoing climate change will be complex and nonlinear. These results serve to emphasize the value of using past responses of the AC to better understand its possible future trajectories. They also highlight the importance of taking into account a wide variety of processes operating across a wide range of spatial and temporal scales to refine future projected changes.
    • Arctic sea ice trafficability: new strategies for a changing icescape

      Dammann, Dyre Oliver; Eicken, Hajo; Mahoney, Andrew R.; Meyer, Franz J.; Bhatt, Uma S.; Meek, Chanda L. (2017-08)
      Sea ice is an important part of the Arctic social-environmental system, in part because it provides a platform for human transportation and for marine flora and fauna that use the ice as a habitat. Sea ice loss projected for coming decades is expected to change ice conditions throughout the Arctic, but little is known about the nature and extent of anticipated changes and in particular potential implications for over-ice travel and ice use as a platform. This question has been addressed here through an extensive effort to link sea ice use and key geophysical properties of sea ice, drawing upon extensive field surveys around on-ice operations and local and Indigenous knowledge for the widely different ice uses and ice regimes of Utqiaġvik, Kotzebue, and Nome, Alaska. A set of nine parameters that constrain landfast sea ice use has been derived, including spatial extent, stability, and timing and persistence of landfast ice. This work lays the foundation for a framework to assess and monitor key ice-parameters relevant in the context of ice-use feasibility, safety, and efficiency, drawing on different remote-sensing techniques. The framework outlines the steps necessary to further evaluate relevant parameters in the context of user objectives and key stakeholder needs for a given ice regime and ice use scenario. I have utilized this framework in case studies for three different ice regimes, where I find uses to be constrained by ice thickness, roughness, and fracture potential and develop assessment strategies with accuracy at the relevant spatial scales. In response to the widely reported importance of high-confidence ice thickness measurements, I have developed a new strategy to estimate appropriate thickness compensation factors. Compensation factors have the potential to reduce risk of misrepresenting areas of thin ice when using point-based in-situ assessment methods along a particular route. This approach was tested on an ice road near Kotzebue, Alaska, where substantial thickness variability results in the need to raise thickness thresholds by 50%. If sea ice is thick enough for safe travel, then the efficiency of travel is relevant and is influenced by the roughness of the ice surface. Here, I develop a technique to derive trafficability measures from ice roughness using polarimetric and interferometric synthetic aperture radar (SAR). Validated using Structure-from-Motion analysis of imagery obtained from an unmanned aerial system near Utqiaġvik, Alaska, I demonstrate the ability of these SAR techniques to map both topography and roughness with potential to guide trail construction efforts towards more trafficable ice. Even when the ice is sufficiently thick to ensure safe travel, potential for fracturing can be a serious hazard through the ability of cracks to compromise load-bearing capacity. Therefore, I have created a state-of-the-art technique using interferometric SAR to assess ice stability with capability of assessing internal ice stress and potential for failure. In an analysis of ice deformation and potential hazards for the Northstar Island ice road near Prudhoe Bay on Alaska's North Slope I have identified a zone of high relative fracture intensity potential that conformed with road inspections and hazard assessments by the operator. Through this work I have investigated the intersection between ice use and geophysics, demonstrating that quantitative evaluation of a given region in the ice use assessment framework developed here can aid in tactical routing of ice trails and roads as well as help inform long-term strategic decision-making regarding the future of Arctic operations on or near sea ice.
    • Argon isotopes and geochemistry of El Chichón Volcano, Chiapas, Mexico

      Jones, Daniel A. (2007-12)
      Argon isotope systematics can be highly insightful for the investigation of magmatic processes, as the isotopic ratios of different terrestrial reservoirs vary greatly and argon diffuses rapidly at magmatic temperatures. In an effort to understand the dynamics of argon systematics in volcanic systems, the major phases of the eruptive products of EI Chichón volcano were subjected to argon isotopic and bulk chemical analysis. While glass analyses were typically atmospheric in composition, phenocrysts display variation in both concentration and isotopic composition, both within and between the eruptive units, with a major change in behavior noted around 1500 YBP. This same event is recorded in trace element variation, and while little variation is seen in major oxide composition, fractionation trends are apparent. Correlations among argon isotopes, Ca and Cl reveal that the bulk of the argon resides within melt inclusions, but different reservoirs within phenocrysts contain differing isotopic ratios. Variations in the amount and isotopic composition of argon within a phenocryst are likely a function of crystal residence and the isotopic signature of the magma chamber during phenocryst growth. ⁴⁰Ar/³⁹Ar geochronology shows pre-Holocene eruptive activity had an approximate 100 ka interval and spanned at least 370 ka.