Recent Submissions

  • Melt on Antarctic ice shelves: observing surface melt duration from microwave remote sensing and modeling the dynamical impacts of subshelf melting

    Johnson, Andrew Carl; Hock, Regine; Fahnestock, Mark; Aschwanden, Andy; Bueler, Ed (2021-12)
    Melt on the surface and underside of Antarctic ice shelves are important to the mass balance and stability of the ice sheet, and therefore pose significance to global sea levels. Satellite-based passive microwave observations provide daily or near-daily coarse resolution surface observations from 1978 on, and we use this record to identify days in which melt water is present on the ice sheet and ice shelf surfaces, called melt days. There are significant differences in the results of melt detection methods however, and we evaluate four different passive microwave melt detection algorithms. There is a lack of sufficient ground truth observations, so we use Google Earth Engine to build time series of Sentinel-1 Synthetic Aperture Radar images from which we can also detect melt to serve as a comparison dataset. A melt detection method using a Kmeans clustering algorithm developed here is shown to be the most effective on ice shelves, so we further apply this method to quantify melt days across all Antarctica ice shelves for every year from 1979/80 to 2019/20. The highest sums of melt days occur on the Antarctic Peninsula at 89 melt days per year, and we find few linear trends in the annual melt days on ice shelves around the continent. The primary mode of spatial variability in the melt day dataset is closely related to the Southern Annular Mode, a climate index for the southward migration of Southern Westerly Winds, which has been increasing in recent decades. Positive Southern Annular Mode index values are associated with decreased melt days in some regions of Antarctica. We also present a novel application of passive microwave analysis to detect changes in firn structure due to unusually large melt events in some regions and we show how this method detects ice lens formation and grain growth on specific ice shelves. To study the impacts of subshelf melt we focus on the Filchner-Ronne region of Antarctica, which contains the second largest ice shelf on the continent. We performed an ensemble of ice sheet model runs for a set of ocean warming scenarios. Each ensemble used a realistic range of physical parameters to control ice dynamics and sliding, generated by a Bayesian analysis of a surrogate model and observed velocities. Increased ocean temperatures were associated with increased mass loss, and by the year 2100 this region contributed 14 mm to sea level per degree of ocean warming at depth between +0°C and +4°C of ocean potential temperature. Beyond +4°C, the rate mass loss increased substantially. This mass loss corresponded to grounding line retreat across the region.
  • Novel applications of remote sensing and GIS in mass wasting hazard assessments for two fjords of South-Central Alaska

    Balazs, Matthew S.; Prakash, Anupma; Wolken, Gabriel; Meyer, Franz; Darrow, Margaret (2021-12)
    The fjords of South-Central Alaska are dynamic environments and host to a number of natural hazards that have not received much attention from the research community. The cities of Seward and Whittier are two of Alaska's most important marine transportation hubs, home to commercial fishing fleets, termini of the Alaska Railroad, and home to thousands of residents. This doctoral research focuses on landslides and their associated hazards in these under-studied areas. Chapter 2 involves surficial mapping of the study areas and documents the role of the underlying geologic processes that threaten the safety of people and infrastructure in the Passage Canal-Portage Valley area (including the town of Whittier), to better inform community planning, mitigation, and emergency response activities. Chapter 3 builds on the successes and lessons learned from the mapping efforts made in Chapter 2. A surficial geology and landslide inventory map were made using very high resolution orthoimagery, DEMs, and 3D models which were viewed in an immersive Virtual Reality (iVR) system. Chapter 4 examines the hazards associated with large amounts of sediment entering the alluvial fan system from further upslope. A collection of six Digital Elevation Models (DEMs) and meteorological data collected over a ten-year period were used to estimate flood-related sedimentation. Uncertainties in each DEM were accounted for, and a DEMs of Difference (DoD) technique was used to quantify the amount and pattern of sediment introduced, redistributed, or exiting the system. The study shows that the DoD method and using multiple technologies to create DEMs is effective in quantifying the volumetric change and general spatial patterns of sediment redistribution between the acquisition of DEMs. Correlations of the changes in sediment budget with rainfall data and flood events were made. During the years of average rainfall, the reaches in the corridor experienced an overall decrease in sediment load, while heavy rainfall events both saw large influx of new sediment and the reworking of existing sediment. This research is the first to collect and use high resolution data for generating digital elevation models, for using a DoD method for mapping elevation changes over time, and for using these products along with available ancillary data for a hazard assessment in these regions. This doctoral work lays out a solid foundation for further work in hazard assessment that will also guide decision-makers in the future on mitigation measures in these important population centers in south central Alaska.
  • Coastal wetland carbon and mineral responses to storm and climate change through time, at Cape Espenberg Alaska

    Smith, Lindsey Michelle; Maio, Chris; Bigelow, Nancy; Eagle, Meagan (2022-05)
    The Arctic is experiencing warming and ecological shifts due to climate change and the compounded effects of polar amplification. There is a deficit of information surrounding the carbon cycle response in Arctic Alaskan coastal marsh environments to these forces. The Cape Espenberg barrier beach system has been mostly preserved through time as a shoreline-parallel, linear geometry prograding geomorphic feature. This study determines the Arctic carbon and mineral accumulation trends in marsh environments at Cape Espenberg for both paleo (pre 1850 AD) and modern (post 1850 AD) timeframes. This project makes connections between the responses of carbon and mineral materials to paleo and modern climate changes, and how this relationship may have evolved through time. Analytical analyses through radioisotope ¹³⁷Cs and ²¹⁰Pb, ¹⁴C, stable isotope spectrometry (δ¹³C), elemental (%C, %N, C:N), and dry bulk density and carbon density measurements yield a comprehensive physical and chemical dataset. Radioisotope dating techniques in the Arctic have proved challenging due to the dynamism of the environment. However, the combination of Constant Rate of Supply and Constant Initial Concentration age depth models has helped constrain ages to sediment cores even under variable conditions. Results indicate carbon and mineral accumulations have increased from paleo to modern times which indicates better growing and/or preservation conditions for organic matter (OM) under a modern climate. This agrees well with paleoclimate trends in the Medieval Climate Anomaly (MCA), and warm periods interspersed within the Little Ice Age (LIA), which correlate to greater productivity of terrestrial organic matter and isotopically lighter δ¹³C values (a terrestrial signature). Cold climate periods within the Little Ice Age correlate with increased aquatic organic matter sourcing and heavier δ¹³C values. Modern warming will likely continue to drive carbon sourcing towards terrestrial signatures as future temperatures are predicted to rise with global climate change. If the swale environments at Cape Espenberg can maintain ideal growing conditions (i.e. wet/anoxic soils and lower salinity to limit organic material decay, higher temperatures to promote growth) then Cape Espenberg will likely remain a viable carbon reservoir in the future. However, the question of whether the barrier system as a whole will continue to prograde under a regime of rising sea levels and increased storm impacts is unclear. The results of this study contribute towards understanding the dynamism of Arctic coastline mineral and carbon cycling and their ecological response to the current warming climate.
  • Non-volcanic tremor in the Alaska/Aleutian subduction zone and its relationship to slow-slip events

    Peterson, Chloe L. (2008-12)
    "We document non-volcanic tremor (NVT) in Southcentral Alaska and the Aleutian Arc in terms of durations and locations. In Southcentral Alaska, we tabulate NVT events occurring during the summer months of each year between 1999 and 2001 to test for a relationship with a slow-slip event that occurred during this time frame. We tabulate NVT events in the Aleutians starting in the summer of 2005 through the summer of 2008. The observed NVT events in both Southcentral Alaska and the Aleutian arc are sequences of emergent pulses with frequencies of 1-10 Hz. The majority of the events have durations ranging from 5-15 minutes. In Southcentral Alaska, the majority of the NVT events locate in the region of the slow-slip event and the quantity of events decreases significantly by the summer of 2001, coinciding with the end of the slow-slip event. Locating NVT events in the Aleutians is problematic due to the linearity and sparse distribution of seismic stations. General locations are established simply by the distribution of volcano seismic networks on which the signal is observed and the strength of that signal. These general locations appear to coincide with regions where the plate interface is locked or is transitioning from creeping to locked. Furthermore, several episodes of NVT in the Aleutians occurring during times of heightened volcanic and seismic activity in the arc, suggesting large regional stress changes possibly caused by undetected slow-slip events"--Leaf iii
  • Holocene vegetation and climate change at Canyon Lake, Copper River basin, Alaska

    Shimer, Grant (2009-05)
    "The regional vegetation response to Holocene warming and the recession of glacial Lake Atria is recorded by environmental proxies in cores from Canyon Lake, near the northern limit of the Copper River Basin. Pollen, spores, plant macrofossils, and stable isotope analyses of C, N and H indicate that conditions in the northern margins stabilized fairly quickly following the recession of Lake Atria around 10740 cal yr BP. The development of a shallow lake ecosystem surrounded by Betula (birch) shrub-tundra was followed by the migration of Picea (spruce) and Alnus (alder) into the Copper River Basin around 9800 cal yr BP and the eventual development of the Picea-dominated boreal forest that persists to this day. The stable isotope record indicates that lake systems are more sensitive to neoglacial cooling, Medieval warming, and the Little Ice Age than the surrounding boreal forest during the middle to late Holocene. The magnitude and severity of these events may have been limited in the Copper River Basin, but climate and vegetation change may have had significant effects on the available resources to the human populations of the region"--Leaf iii
  • Platinum group element enriched hydrothermal magnetite of the Union Bay Alaska-type ultramafic intrusion, Southeast Alaska

    Van Treeck, Christopher Jared (2009-08)
    "The Union Bay Alaskan-type Complex represents a completely different type of platinum group element (PGE) concentration from the classic Alaskan-type Complex PGE mineralization model, with PGEs localized in vein/veinlet magnetite, commonly within the olivine + pyroxene portions of the body. PGE concentrations of 18 g/t occur in magnetite veins and pods which cross magmatic layering and have an irregular morphology in both outcrop and thin section. Fe-Ti oxide geothermometry indicates that this mineralization formed at temperatures between 675-475°C. A variation in the amount of ilmenite and Mg-Al spinel exsolution in magnetite correlates with temperature estimates, lower temperature magnetite has less exsolution. Magnetite veins with a formation temperature of less than 600°C are surrounded by an alteration envelope of hydrous silicates that vary with temperature and contain appreciable amounts of Cl. Interaction of a PGE-Fe-Cl rich fluid with clinopyroxene and olivine increased the fluids pH and decreased PGE and Fe solubility depositing a PGE enriched magnetite within the wehrlite and clinopyroxenite of the Union Bay Alaskan-type complex. Potentially this fluid remobilized the PGE from disseminated euhedral magnetite of the peripheral units to form PGE enriched magnetite veins in the near-central portion of the complex"--Leaf iii
  • Tectonic geomorphology of the Chukchi borderland: constraint for tectonic reconstruction models

    Brumley, Kelley (2009-08)
    "The Chukchi Borderland is a region of extended continental crust within the Amerasia Basin and is bounded on one side by oceanic crust of the Canada Basin. Because of its central location within the basin, tectonic models for the reconstruction of the Arctic Ocean, must include the Chukchi Borderland although there is no consensus about its pre-rift location or kinematic development. In recent years bathymetric data have been collected that can offer constraint on the tectonic evolution of the Amerasia Basin by providing details about the geomorphology of the intra-basinal ridges allowing comparison of bathymetric features to those in other ocean basins. Bathymetric information in conjunction with multi-channel seismic and chirp sub-bottom profiler data show the location and strike of inferred faults used to determine rift directions which then provide constraint on tectonic reconstructions. The central Amerasia Basin, which includes the Chukchi Borderland, Mendeleev Ridge and south central Alpha Ridge, has experienced significant extension in generally the same direction and probably during one event. This type of plate boundary scale extension requires the development of accommodation faulting or transfer zones that facilitate the amalgamation of long fault segments. Features consistent with this type of faulting are observed throughout the Chukchi Borderland. There is no evidence of compression along the Northwind Ridge nor is there any indication of a strike-slip boundary within the Northern Chukchi Borderland as some tectonic models suggest. Whichever model is preferred, the geomorphology of the intra-basinal ridges must be taken into account and used as constraint for the reconstruction of the Amerasia Basin"--Leaf iii
  • Character and controls of fold-and-thrust deformation from pre-orogenic to foreland basin deposits: an example from the Gilead creek region of the Northeastern Brooks Range, Alaska

    Speeter, Garrett (2010-12)
    "The character of structures in the Gilead Creek region is influenced by the mechanical stratigraphy in the area. Shortening is distributed throughout the mechanical stratigraphy along detachments in the incompetent Kayak, Kavik, Kingak, and Hue Shales. Detachment intervals separate competent Lisburne Group, Echooka Formation, Ledge Sandstone/Shublik Formation, Gilead sandstone, and moderately competent Seabee Formation from each other and allow the competent units to fold at distinct wavelengths according to their mechanical properties. Thick, competent units tend to form long-wavelength folds. Thin, competent units form relatively short-wavelength folds. Thin, competent units that are structurally bound to a thicker, structurally more dominant unit, adhere to the structural style of the dominant unit unless there is some detachment between them. Strain is distributed through shale intervals in the moderately competent units, allowing short-wavelength folds in the thin competent beds. The dominant trend of structures in the area is northeast overprinted on east. East-trending structures formed during the ~60 Ma event that formed the main axis of the Brooks Range and its foothills. Northeast-trending structures formed during the formation of the northeastern Brooks Range dated at ~45 Ma, ~35 Ma, and ~27 Ma, manifest locally by the compressional uplift of the Echooka anticlinorium southeast of Gilead Creek"--Leaf iii.
  • Relating deep magmatic processes to eruptive behavior at arc volcanoes through an analysis of deep seismicity

    George, Ophelia A. (2010-12)
    "In this thesis, the seismicity at depths greater than 15 km beneath two sets of volcanic centers, the Klyuchevskoy Volcanic Group (KVG), Russia and Mount Spurr, Alaska is examined. In both regions, a pulsing pattern of deep seismicity is observed with many cycles following eruptive activity or periods of unrest. The bulk of the seismicity beneath the KVG is comprised of long-period events many of which share a similar appearance. Cross correlation of the waveforms for events occurring between 12/24/2007 and 12/31/2008 show a number of event families occurring over long time spans. New relative locations for these families which better constrain their spatial extent are derived. The pulsing pattern of seismicity seen here is in close keeping with the expected cyclic nature of melt segregation which occurs as melt leaves the site of generation and ascends to shallower levels. Based on evidence in the data, a model is proposed whereby melt segregation on the time scales necessary to facilitate eruptions is attributable to a pressure response in the deep system induced by the removal of material in the shallow chamber during an eruptive cycle"--Leaf iii.
  • Geochemistry, sedimentology, and stratigraphy of the Lower Cretaceous pebble shale unit, northeastern Alaska

    van der Kolk, Dolores A.; Whalen, Michael T.; McCarthy, Paul J.; Newberry, Rainer J.; Wartes, Marwan A. (2010-05)
    "Organic-rich, marine mudstone known informally as the Lower Cretaceous (Barremian-Aptian) pebble shale unit (PSU) is exposed in the northeastern Brooks Range. Outcrops were examined along the Canning River, an unnamed tributary of the Katakturuk River, and Marsh Creek. Gamma-ray data was measured for each stratigraphic section in order to correlate outcrop with wire-line well logs. Samples of the PSU were collected for thin section petrography, lithostratigraphy, biostratigraphy, total organic carbon (TOC), Rock-Eval II, vitrinite reflectance (R₀), and X-ray Fluorescence. The PSU contains bioturbated and laminated mudstones with thin-bedded siltstones interpreted as interbedded hemipelagites and turbidites. PSU foraminifers were deposited on the outer shelf and upper slope. Intervals with high TOC (2 to 6 wt %) indicate good source-rock quantity in the PSU; however, Rock Eval results suggest poor source-rock quality related to elevated thermal maturities (1.3 to 1.8 %R₀). The PSU is depleted in metals relative to average black shale"--Leaf iii
  • Effusion rates at Kliuchevskoi and Pavlof volcanoes: a comparison of eruptions

    Puchrik, Rachel Ann (2010-05)
    "Kliuchevskoi and Pavlof Volcanoes in Kamchatka, Russia and Alaska, USA respectively, are two of the most active stratovolcanoes in the North Pacific Region. Effusion rates were calculated and analyzed for the most recent eruptions by balancing the radiative energy with the thermodynamic properties of the lava with data from three near-polar orbiting satellite sensors to establish a trend in the eruptive behavior of these volcanoes. Effusion rates for the 1994, 2005, 2007 eruptions of Kliuchevskoi reached 8.0 m³ s⁻¹ with cumulative lava volumes as high as 0.033 km³. Effusion rates for the 1996 and 2007 Pavlof eruptions were as high as 7.3 m³ s⁻¹ with cumulative volumes as high as 0.036 km³. Effusion rates and cumulative lava volumes for Kliuchevskoi increased with each eruption, where as the Pavlof volumes and rates decreased. Eruptions with the longest thermal precursors produced the largest volumes of lava"--Leaf iii
  • Geothermometry and cathodoluminescence of quartz reveal crystallization histories of Katmai magmas

    Payne, Allison L. (2010-05)
    "This study combines electron microprobe analysis of titanium and aluminum in quartz, cathodoluminescence imagery, and titanium-in-quartz geothermometry to constrain the growth histories of quartz grains from three magmatic rock suites of Katmai, Alaska: (1) high-silica rhyolite from the 1912 Novarupta lava dome; (2) the Mageik rhyolite sills, suggested as an analog for Novarupta's feeder; and (3) the Pinnacle Porphyry granodiorite, which has mingled field relations with the Mageik sills. Oscillatory zoning and constant titanium concentrations across Novarupta quartz phenocrysts suggest continuous growth at temperatures of ~800-850°C. Thin, aluminum-rich, high-cathodoluminescence intensity rims may represent rapid growth during magmatic ascent or dome emplacement. Euhedral matrix quartz of the Mageik sills has cores enriched in both titanium and aluminum, yielding minimum temperatures of ~900°C, and possibly representing rapid growth. Titanium-poor rims likely represent continued growth to subsolidus temperatures after emplacement of the sills. Quartz in the Pinnacle Porphyry show early crystallization at minimum temperatures of ~820-870°C, followed by partial resorption and continued growth at ~800-815°C. Magma mixing events, as evidenced by mafic enclaves, may be responsible for the dissolution, while ascent and uninterrupted crystallization to solidus may be responsible for resumed growth at lower temperatures"--Leaf iii
  • Fracture evolution in a fold-and-thrust belt and the adjacent foreland basin: an example from the Northeastern Brooks Range, Alaska

    Loveland, Andrea M. (2010-05)
    "Fracture networks can enhance permeability in a reservoir, creating pathways for fluid migration. This study uses detailed surface and subsurface mapping, new and existing thermal and geochronologic data as well as observations of fractures in outcrop provide a framework for fracture development in the range front region along a surface to subsurface transect in the western part of the northeastern Brooks Range. Set 1 fractures formed prior to 45 Ma at>6 km depth, ahead of the Brooks Range mountain front in response to elevated pore fluid pressure and low differential stress. Set 2 fractures developed during the early stages of folding at a depth of ~7 km. Both Sets 1 and 2 developed synchronously with hydrocarbon generation and may have been early migration pathways, but were likely destroyed during advancement of the thrust belt. Late fracture Sets 3 and 4 formed at shallow depths in the absence of fluids and are probably related to the onset of uplift at ~25 Ma. These late sets postdate regional generation and migration, but may enhance reservoir permeability"--Leaf iii
  • Temporal-spatial micro-scale investigations of shallow silicic conduits: late-stage degassing, crystallization, and alteration

    Almberg, Leslie D. (2010-05)
    "Conduit samples from Unzen Volcano, obtained a decade after the 1991-1995 eruption, exhibit important physical and mineralogical differences, and subtle differences in bulk chemistry from erupted samples. These differences reflect emplacement confining pressures, maintenance at hypersolidus temperature, and subsequent subsolidus hydrothermal alteration. In contrast, extruded lava underwent decompression to ~1 atm., ~complete loss of magmatic water and rapid cooling. The resulting hypabyssal conduit texture is distinct from both eruptive and plutonic rocks. The low temperature of the conduit, <200°C when sampled by drilling, requires swift post-emplacement textural development. Significant changes in bulk composition were Mg, Fe and Na depletion and C and S enrichment. Trace-element concentrations of the conduit and the last-emplaced lava of the spine indicate a common derivation. Investigating three aspects of magma transport and post-emplacement evolution at Unzen, in conjunction with observations from comparable dome-forming volcanoes, quantifies the processes working in concert to produce the resultant textures. First, we constrain magmatic ascent rates and crystallization depth of the Unzen dacite via decompression crystallization experiments. Our results indicate that slow effusion rates (<̲20 m/hr) are required for both spine and conduit. Second, we present mineralogical evidence for extremely rapid alteration beneath Unzen, related to temperature, permeability within and volatile flux through the volcanic edifice. We describe meter-scale variations in alteration conditions, and conclude that maintenance of permeability to low porosity allows basalt-derived volatiles to traverse the conduit zone promoting extremely rapid alteration, orders of magnitude greater than predicted by models for larger/deeper intrusions. This suggests that despite convective hydrothermal heat removal, chemical effects were limited to early loss of magmatic water and later addition of magmatic volatiles. The extensive alteration within Unzen's conduit contrasts the minimal alteration beneath Obsidian Dome, considered as a 'control'. Finally, we present anisotropy measurements and three-dimensional visualizations of degassing structures from four volcanoes: Bezymianny, Unzen, Mount St. Helens and Obsidian Dome. Our novel approach, employing X-ray computed tomography and percolation models, indicates that gas loss at depth is more efficient in sheared regions (anisotropic), than in those that contain no evidence for shearing (isotropic)"--Leaves iii-iv
  • Periods of heightened volcanic seismicity across the Aleutian Arc, Alaska

    Christensen, Branden Carl (2010-08)
    "Data from the Alaska Volcano Observatory and Alaska Earthquake Information Center catalogs are applied to four research initiatives. In Chapter 1, the distinction between mainshock-aftershock sequences and swarms is made on the basis of how the total elastic energy is partitioned between the largest and smaller magnitude earthquakes. Chapter 2 establishes that multiplets are ubiquitous to periods of heightened volcano-seismicity across the Aleutian Islands and argues that they arise from the diffusion of heat and/ or pore fluids through the system and not from an increase in stress. The attributes of the 2008 Kasatochi eruption and pre-eruptive swarm are discussed in Chapter 3. Cross-correlation techniques are employed to root out additional waveforms that were either below the threshold of the detection or location algorithms used. The onset time of the pre-eruptive swarm is redefined and its temporal development more fully characterized. Chapter 4 integrates seismic and acoustic data to analyze the Continuous Phase of the 2006 eruption of Augustine Volcano. The Continuous Phase is shown to be a scaled-down version of the Explosive Phase. What was perceived by remote sensing observations as a continuous, unperturbed eruption is shown here to be a rapid succession of discrete blasts"--Leaf iii
  • Impacts of climate change on mass movements in Denali National Park and Preserve, Alaska

    Robert, Zena V.; Mann, Daniel; Farquharson, Louise; Romanovsky, Vladimir; Meyer, Franz; Maio, Chris (2021-08)
    The northeastern portion of Denali National Park and Preserve (DENA) is a high-altitude (800 m - 1400 m asl), subarctic (63°N) environment where climate is now changing rapidly. This landscape is underlain by discontinuous permafrost (perennially frozen ground), and the recent surge of mass movements occurring there could be the result of permafrost thaw. Some of these mass movements have the potential to damage the Denali Park Road, alter the flow of groundwater and stream systems, destroy vegetation cover, and endanger the half a million visitors that DENA receives every year. The purpose of this study to understand how mass movements in DENA are being affected by different aspects of climate change, to assess the role of permafrost thaw in their dynamics, to determine when DENA's landscape experienced periods of geomorphic instability in the past, and to better understand the potential trajectory of the landscape changes now occurring. Results show that many ongoing mass movements in DENA are reactivations of landslides that were active earlier in the Holocene (the last 11,700 years). A representative example is the Mile 35 landslide, a complex mass movement initiated along the Park Road during the summer of 2016 after a quiescent period of around 4000 years. I use a combination of remote sensing and field surveys to establish a four-year timeline of this landslide's movements and then compared these observations to records of weather and climate. Results suggest that freeze/thaw processes and extreme rainfall events strongly affect the initiation and subsequent movements of the Mile 35 landslide. Looking farther back in time, lichenometric dating of rockfalls in DENA suggests their frequency peaked 100 to 200 years ago during the initial stages of climate warming at the end of the Little Ice Age. These findings suggest that warming climate triggers a predictable sequence of mass movement responses in DENA, with the initial warming triggering a bout of more frequent rockfalls, and then, as warming penetrates deeper into the ground, causes deep-seated mass movements like the Mile 35 landslide. These results suggest that cycles of hillslope stability and instability in response to climate change are characteristic, long-term features of DENA's ecosystems and dynamic ecosystems and landscapes.
  • The mineralogical associations, distribution, and mineral zoning of cobalt in the Bornite deposit, southwest Brooks Range, AK

    Mahaffey, Zachary B.; Newberry, Rainer; Schrader, Christian; Regan, Sean (2021-08)
    The Bornite Cu-Co deposit is predominately hosted in dolomitic marble with interstratified phyllite; the mineral resource is restricted to the Upper, Lower and South Reefs. Cobalt is primarily from carrollite (ideally CuCo₂S₄), cobaltite (ideally CoAsS), and cobaltiferous pyrite ((Fe,Co)S₂). The Co minerals can contain significant Ni, and the Ni rich endmembers, millerite (NiS) and gersdroffite (ideally NiAsS), also rarely occur. Detailed handheld XRF analyses on 15 drill holes, coupled with reflected light petrography, electron microprobe-based compositional maps, and electron microprobe analyses (EPMA) have shown complex compositions, textures, associations, and spatial distribution of the Co minerals in the Bornite deposit. Carrollite compositions and textures vary with the Cu-sulfide assemblage: carrollite with bornite is commonly porphyroblastic and approximated by Cu(Co,Ni)₂S₄, whereas carrollite lacking associated bornite is interstitial and represented by (Cu,Ni)(Co,Ni)₂S₄. Cobaltite occurs in two generations: early As-depleted, Ni-poor, and metastable ((Co,Fe)As₀.₅S₁.₅ to (Co,Fe,Ni₀.₀₆)As₀.₈₈S₁.₁₂), and late near stoichiometric ((Co,Fe,Ni₀.₀₁)As₀.₉S₁.₁ to (Co,Fe,Ni₀.₉₄)As₁S₁). The latter rims and (or) replaces the former. The virtual lack of cobaltite in assemblages containing bornite + pyrite, along with carrollite compositions, suggest a gradient in Cu and Co activity that increased with increasing fS₂. Distinct carrollite zones associated with higher Cu grades are present in the high-grade zone (Number One Orebody) of the Upper Reef and the South Reef. Decreasingly Cu-rich assemblages dominated by chalcopyrite + pyrite and cobaltite are outside the carrollite zones. The Lower Reef has lower Cu grades, lacks a carrollite zone, and variably contains cobaltite. Due to these different Co mineral distributions, the Bornite deposit cannot represent dismemberment of a single homogeneous body. Bornite pyrite can contain Ni and Cu (both inversely correlated to Co) and As (maximum 5.6%, generally correlates with Co). Compositions of Co-pyrite lacking significant As (up to 8.5% Co) and late cobaltite suggest temperatures of 400-500℃, consistent with Upper Blueschist to Greenschist conditions. Pyrite compositions can be extremely variable within a single sample and even within a single grain: nearly half of all EPMA pyrite analyses yield < 0.25% Co. Clearly metamorphic (porphyroblastic) pyrite displays concentric oscillatory Co + As zonation. Average Co content in pyrite generally increases with Cu grade, which suggests Devonian Co and Cu deposition occurred simultaneously. Co deportment is a function of location in the deposit, which correlates with Cu grade and Co mineral zonation. Based on metal balance calculations, more than half (on average 57%) of the Co in South Reef intervals with > 0.5% Cu is due to Co-pyrite. In the Lower Reef the proportion is much higher: 55-93%. High Cu grade intervals typically yield increased carrollite abundance and decreased cobaltite. Carrollite consistently reports to the Cu concentrate, however, cobaltite recovery is variable and can report to the tails with Co-pyrite. Thus, maximizing Co recovery from Bornite will require producing a pyrite concentrate in addition to the Cu concentrate.
  • Advancing wildfire fuel mapping and burn severity assessment in Alaskan boreal forest using multi-sensor remote sensing

    Smith, Christopher William; Panda, Santosh; Bhatt, Uma; Meyer, Franz (2021-05)
    Wildfires in Alaska have been increasing in frequency, size, and intensity putting a strain on communities across the state, especially remote communities lacking firefighting infrastructure to address large scale fire events. Advances in remote sensing techniques and data provide an opportunity to generate high quality map products that can better inform fire managers to allocate resources to areas of most risk and inform scientists how to predict and understand fire behavior. The overarching goal of this thesis is therefore to build insight into methods that can be applied to create highly detailed fire statistic map products in Alaska. To address this overarching goal we tested several methods for generating fire fuel, burn severity, and wildfire hazard maps that were validated using data collected in the field. Applying the Random Forest classifier on Airborne Visible/ Infrared Imaging Spectrometer Next-Generation (AVIRIS-NG) hyperspectral data we were able to produce a fire fuel map with an 81% accuracy. We then tested two supervised machine learning classifiers, post fire standard spectral indices, and differenced spectral indices for their performance in assessing burn severity. We found that supervised machine learning classifiers outperform other algorithms when there is an adequate amount of training data. Using the support vector machine and random forest classifiers we were able to generate burn severity maps with 83% accuracy at the 2019 Shovel Creek Fire. Lastly, we looked for a relationship between burn severity and environmental conditions prevalent during the Shovel Creek and Nugget Creek fires. Overall, these products can be used by fire managers and scientists to assess fire risk, limit the damages caused by wildfires through adequate resource allocation, and provide the guidelines for creating future high quality fire fuel maps.
  • Atmospheric modeling of natural hazards

    Hirtl, Marcus; Stuefer, Martin; Webley, Peter; Simpson, William; Grell, Georg (2021-05)
    Airborne hazards either in gaseous form or particulate matter can originate from a variety of sources. The most common natural airborne hazards are ash and SO₂ released during volcanic eruptions, smoke emitted caused by wildfires and dust storms. Once released into the atmosphere they can have a significant impact on different parts of the environment e.g. air quality, soil and water, as well as air traffic and ground transportation networks. This latter field is an important aspect of everyday life that is affected during hazardous events. Aviation is one of the most critical ways of transport in this century. Even short interruptions in flight schedules can lead to major economic damages. Volcanic eruptions comprise one of the most important airborne hazards to aviation. These are considered rare as compared to severe weather, but with an extremely high impact. This dissertation focusses on dispersion modeling tools and how they can support emergency response during different phases of volcanic eruption events. The impact of the volcanic ash cloud on the prediction of meteorological parameters and furthermore the dispersion of the ash is demonstrated by applying the Weather Research Forecasting (WRF) model with on-line integrated chemical transport (WRF-Chem) to simulate the 2010 Eyjafjallajökull eruption in Iceland. Comprehensive observational data sets have been collected to evaluate the model and to show the added value of integrating direct-feedback processes into the simulations. The case of the Eyjafjallajökull eruption showed the necessity to further develop the volcanic emission preprocessor of WRF-Chem which has been extended for flexible and complex ash and SO₂ source terms. Furthermore, the thesis describes how scientists could support operational centers to mitigate hazards during a large volcanic eruption event. The author of the dissertation coordinated a large exercise including experts across all Europe within a project funded by the European Union. The exercise aimed to develop and test new tools, models, and data to support real-time decision making in aviation flight planning during a volcanic crisis event. New state-of-the-art modeling applications were integrated into a flight planning software during a fictitious eruption of the Etna volcano in Italy with contributions from scientists, the military and the aviation community.
  • Blood falls, Taylor Glacier, Antarctica: subglacially-sourced outflow at the surface of a cold polar glacier as recorded by time-lapse photography, seismic data, and historical observations

    Carr, Chris G.; Pettit, Erin; Carmichael, Joshua; Truffer, Martin; Tape, Carl (2021-05)
    Blood Falls forms when iron-rich, hypersaline, subglacially-sourced brine flows from a crack in the surface of Taylor Glacier, Antarctica. If air temperatures are low enough, the brine freezes to form a fan-shaped icing deposit. In chapter two, historical observations (including photos, oral histories, written descriptions, and field sketches) are evaluated using a confidence assessment framework to compile a history of brine icing deposit presence or absence during summer field seasons between 1903-1904 and 1993-1994. Additionally, an alternative explanation for a small, localized advance of a portion of the terminus is proposed: rather than temperature-driven ice viscosity changes, rising lake level drove temporary, localized basal sliding which induced advance, thinning, and collapse of a part of the terminus previously grounded on a proglacial moraine. In chapter three, time-lapse imagery is used to document a 2014 wintertime brine release that occurred in the absence of surface melt. This suggests that meltwater-driven fracture propagation of surface crevasses downward into the glacier was not a likely factor in this brine release event, as has been previously proposed. Further, there is no evidence for an increase in Rayleigh-wave activity prior to or during the brine release that would be characteristic of shallow seismic sources. Together, this suggests that sufficient pressure is built in the subglacial system to trigger basal crevassing and fracture propagation upward to allow brine release at the surface. In chapter four, two different seismic detectors that use ratios of short-term to long-term seismic energy variance to identify seismic events are compared. The detectors use different statistical distributions to determine what constitutes a large enough ratio to trigger an event detection. Differences between what the two detectors identify as events rather than background noise are interpreted as environmental microseismicity with a distinct diurnal and seasonal occurrence. Minimum detectable event sizes over 3-day time windows are compared. Together, these studies provide context for the history of brine release events, wintertime brine release characteristics, and descriptions of the local seismic environment at Taylor Glacier.

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