RSS 1.0Geosciences
Recent Submissions
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Early considerations and estimates for the performance of an Alaska-based earthquake early warning systemThe complexity of Alaska presents several challenges for earthquake early warning systems. These include the presence of offshore earthquakes, transform boundaries and crustal faults extending hundreds of kilometers, deep earthquakes, and a complicated coastline. This variety, combined with population centers spread far apart, makes it challenging to anticipate an earthquake early warning system's performance and to design a network accordingly. As Alaska begins to plan for earthquake early warning, our objective is to envision how and how well it might function in Alaska. We present here sets of scenarios with warning time and ground motion estimates for a variety of communities. These scenarios are designed to be meaningful test cases for Alaska earthquake early warning while also exploring how changes in source characteristics--such as magnitude, depth, location, and fault system--impact the timeliness of warnings. We combine travel time estimates, source time models, and the current seismic network to model hypothetical detection and alert times. We compare warning times to peak ground motions to determine the warning effectiveness. Our results suggest the potential for timely warnings up to Modified Mercalli Intensity 6 in the case of shallow earthquakes. More ideal scenarios, including deep earthquakes, could receive advanced warning for shaking up to intensity 8. Informed by these results, we discuss where we expect an Alaska earthquake early warning system to excel and what challenges should be tackled to improve other areas. Finally, we offer ways in which our results and insights can inform future works related to earthquake early warning in Alaska.
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Ice velocity and basal motion evolution of mountain glaciers on multi-decadal to centennial timescalesThe surface velocity of a glacier or ice sheet consists of two components, viscous deformation throughout the ice column and basal motion comprised of sliding along the bed and the deformation of subglacial till. Changes in basal motion on multi-decadal to centennial timescales could result in either a positive or negative feedback which accelerates or delays ice mass loss rates. Most glacier systems maintain a relatively stable ice flux, while surge type glaciers are prone to large flow instabilities between their surging and quiescent phases. How fast and how much basal motion will change in response to higher temperatures is not well understood. In this dissertation, my coauthors and I utilized models, modern observations of ice deformation, and a 50-year-old baseline dataset from Athabasca Glacier, Alberta, Canada. We used recent field observations of Athabasca Glacier borehole deformation from tiltmeters to constrain the internal ice velocity and basal motion in the modern day. Both our modeling and field observations show that the surface velocity of the glacier has decreased over this period and reduced basal motion is mostly responsible for the observed slow-down. Lower basal velocities could result in a stabilizing feedback, which reduces the rate of ice mass loss in the coming decades. We then investigated the dynamics of the 2020-22 Henteel No’ Loo’ (Muldrow Glacier), Alaska, USA surge. My coauthors and I utilized satellite data, GPS stations, and a ground-based radar interferometer to observe the surface velocity before, during, and after, the surge. We find that the surge reached maximum velocities of 20-25 meters per day and find evidence suggesting this may be an upper velocity limit for the surge. This dissertation shows that basal motion is a primary control on glacier velocities for both surging and non-surging glaciers over multi-decadal to centennial timescales.
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Pinpointing magma processes in time and spaceVolcanic eruptions pose major threats to society, including loss of human life, negative economic impacts, and environmental ramifications. As the global population continues to grow, so does the amount of people living in proximity to volcanoes. Volcanic eruptions are often triggered by perturbations in the magmatic system, which are caused by a variety of magmatic processes, such as magma recharge, magma ascent, and magma mingling. We applied diffusion chronometry, the technique of modeling chemical diffusion across mineral zones, to the 2009 eruption of Redoubt, and the 2016-2017 eruption of Bogoslof, in order to determine and date the pre- and syn-eruptive magmatic processes that triggered and drove the recent eruptions of these two, high-threat, Alaskan volcanoes. At Redoubt, our results, combined with multidisciplinary observations preceding the 2009 eruption, indicate that Redoubt experienced protracted magma recharge between the 1989-1990 and 2009 eruptions, with notably drastic increases in monitoring parameters occurring 3-4 months before the 2009 eruption. At Bogoslof, we analyze both the first and final products from the 9-month long 2016-2017 eruption. Analyses of the early products indicate that pre- eruptive magma recharge occurred in the weeks to months before eruption onset. This interpretation is supported by the seismic swarm that occurred approximately two months before the eruption began. Conversely, our analyses of the final erupted products of Bogoslof reveal that the distinct boundaries in mineral phases formed due to magma decompression caused by the shallow emplacement of magma occurring throughout the second phase of the eruption. The oldest crystal timescales from the second eruptive phase correspond to March 2017, correlating with increases in both seismicity and SO2 emissions. By determining and pinpointing the magma processes associated with volcanic eruptions in time and space, we gain insights into the pre- and syn-eruptive nature of the magma system. Our results aid in interpreting interdisciplinary monitoring data, and contribute to the development of new eruption forecasting tools.
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Tectonic controls on the emplacement of the McGonagall Pluton, Alaska Range, AlaskaThe role lithospheric-scale strike-slip faults play during the transport and emplacement of plutonic systems is widely debated. The 2000 km long dextral strike-slip Denali fault hosts a suite of Eocene calc-alkaline plutons emplaced directly adjacent to the fault, including the 33-43 Ma structurally complex McGonagall pluton. Detailed mapping, petrographic analysis, geochemistry, and geochronology work was completed to determine the role tectonic control played on the emplacement of the McGonagall pluton. Mapping conducted perpendicular to strike of the Denali fault yielded two high resolution strip maps. Two major textural units were mapped: an equigranular biotite-hornblende-plagioclase granodiorite (Eogd) and a texturally heterogeneous porphyritic hornblende-plagioclase granodiorite (Eogdp). Contacts between these units occur along SW striking faults/shear zones preserving sinistral asymmetric unit displacement. The McGonagall pluton was emplaced shallowly, evident from fine-grained crystallization textures and the presence of volcanic rocks in faulted contact within the pluton. Geochemical analyses of the two units indicate a common origin, with textural variations controlled by differing cooling histories. Field relationships paired with new zircon U-Pb LA- ICP-MS and CA-ID-TIMS ages indicate that the McGonagall pluton was built incrementally, even within the same unit. Analyses from the McGonagall pluton overlap with published geochronology and geochemistry data from the nearby Mt Galen volcanics, establishing them as an intrusive-extrusive system. The geometry of the internal contacts within the McGonagall pluton as well as the distribution of units are consistent with emplacement during dextral slip along the Denali fault. The McGonagall pluton was emplaced via dilational bookshelf faulting between dextral strike-slip faults during strain partitioning through clockwise rotation. Given the asymmetric spatial distribution of major units, geochemistry, and geochronology results about the Denali fault, the McGonagall pluton is an example of a kinematically-controlled pluton emplaced during active dextral deformation along the Denali Fault.
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Continuous landfast ice climatology from 1996-2023 and interferometric classification of landfast ice stability along the Outer Alaska Continental ShelfLandfast ice in Alaska is experiencing rapid changes in extents and duration, impacting the safety and utility of the ice for Arctic coastal communities. This study presents findings from an updated landfast ice dataset spanning from 1996 to 2023, comprising 7797 Seaward Landfast Ice Edge (SLIE) images derived from a combination of sources including prior work by Mahoney et al. (2014) and new analysis of operational ice charts produced by the National Weather Service Alaska Sea Ice Program (ASIP) and National Ice Center (NIC). We referred to this new dataset as the EM2024 dataset. Analysis of the entire EM2024 dataset reveals a declining trend in landfast ice extent and season length across Alaska. To better understand the nature of these changes and explore options for more robust detection of landfast ice for future datasets, we compared the EM2024 data for the winter period of 2017-2021 with SLIE data derived from Interferometric Synthetic Aperture Radar (InSAR). We used coherence to identify areas of landfast ice and the interferograms to derive the phase gradient as a proxy for estimating the relative stability of the landfast ice. We built on a pervious study by Dammann et al. (2019) by assigning quantitative phase gradient values to identify 3 distinct stability regimes of landfast ice: Bottomfast (|▽ϕ| < 0.14 radians/pixel), Stabilized (0.14 ≤ |▽ϕ| ≤ 0.47 radians/pixel), and Nonstabilized (|▽ϕ| > 0.47 radians/pixel). The monthly average phase gradient decreases as the season progresses, achieving the maximum stability in April or May depending on the region. This study provides an updated assessment of landfast ice conditions in Alaska and introduces a novel approach to identify relatively stable areas of landfast ice using InSAR. These findings have implications for enhancing the safety and planning of activities on landfast ice for Arctic coastal communities.
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Inferring eruption dynamics from seismometer-derived ground tilt measurements: a case study of two end-member volcanic systemsModern broadband seismometers are inertial sensors, and are sensitive to ground tilt as a conse quence of this design. We use broadband seismometers positioned on Mt. Erebus on Ross Island, Antarctica, and Augustine Volcano in the Lower Cook Inlet, Alaska, to recover tilt measurements during individual volcanic explosions to investigate the magmatic system configuration of each volcano. At Mt. Erebus, thought to be an end-member open conduit volcanic system, we find no evidence of tilting associated with the Strombolian explosions produced by the volcano. Because tilt preceding Strombolian explosions has been observed at other volcanoes, we interpret the lack of tilt at Erebus as evidence that its conduit system lacks any viscous plugging or mechanical re strictions that are necessary to generate explosion-related tilt. At Augustine Volcano we are able to measure tilt changes associated with each of the thirteen events during the explosive phase of its 2006 eruption. We use the tilt changes to invert for a dual deformation source model of a depressur izing open conduit above a depressurizing prolate spheroid. This deflation source geometry is in agreement with an existing magmatic system model developed with petrologic, seismic, and GPS data, offering further support to the existing model.
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Isotopic, geochemical and petrographic analysis of the Otuk Formation, Northern AlaskaThe Triassic-Jurassic boundary is associated with one of the big five Phanerozoic mass extinction events and is characterized by global negative δ13C excursions, indicating a major disruption in the carbon cycle. The end-Triassic extinction event was caused by Central Atlantic Magmatic Province volcanism, that initiated the breakup of the supercontinent Pangea. Abundant greenhouse gas emissions, including CO2 and CH4, from the volcanic activity, affected multiple environmental factors. Global warming, ocean acidification, deoxygenation, mass mortality, and lithological change are documented across the boundary. These environmental fluctuations are also observed due to human-induced global climate change, making understanding the end-Triassic extinction significant. Northern Alaska during the Late Triassic has evidence of being the location of an upwelling zone, influencing redox conditions on the sea floor. I hypothesize that isotopic, geochemical and petrographic analyses into Northern Alaska’s Late Triassic Otuk Formation will give a better understanding of the depositional environments in which it formed. Our research has documented the Triassic-Jurassic boundary using carbon and nitrogen isotopes in the rock record, where previously it was not well recorded in Alaska. Research into the Otuk Formation also helped identify the high petroleum potential of these organic-rich rocks. Late-Triassic Northern Alaska rocks were deposited in marine oxic to anoxic conditions, impacting organic burial and paleo¬ redox conditions. Paleo-redox conditions of euxinic environments were identified through the presence of pyrite framboids. A negative carbon isotope excursion was identified in the Otuk Formation, also corresponding with a change in lithofacies and fossil size and abundance. Sedimentary petrology and TOC values documented environmental changes from oxic bivalve¬ rich facies to dark, low-oxygen, organic shales across the Triassic-Jurassic boundary. The Triassic- Jurassic boundary is observed in Northern Alaska, and can act as a marker for multiple environmental changes at that time.
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Iceberg calving dynamics of Jakobshavn Isbræ, GreenlandJakobshavn Isbræ, a fast-flowing outlet glacier in West Greenland, began a rapid retreat in the late 1990's. The glacier has since retreated over 15 km, thinned by tens of meters, and doubled its discharge into the ocean. The glacier's retreat and associated dynamic adjustment are driven by poorly-understood processes occurring at the glacier-ocean interface. These processes were investigated by synthesizing a suite of field data collected in 2007 2008, including timelapse imagery, seismic and audio recordings, iceberg and glacier motion surveys, and ocean wave measurements, with simple theoretical considerations. Observations indicate that the glacier's mass loss from calving occurs primarily in summer and is dominated by the semi-weekly calving of full-glacier-thickness icebergs, which can only occur when the terminus is at or near flotation. The calving icebergs produce long-lasting and far reaching ocean waves and seismic signals, including "glacial earthquakes". Due to changes in the glacier stress field associated with calving, the lower glacier instantaneously accelerates by ~3% but does not episodically slip, thus contradicting the originally proposed glacial earthquake mechanism. We furthermore showed that the predominance of calving during summer can be attributed to variations in the strength of the proglacial ice melange (dense pack of sea ice and icebergs). Sea ice growth in winter stiffens the melange and prevents calving; each summer the mélange weakens and calving resumes. Previously proposed calving models are unable to explain the terminus dynamics of Jakobshavn Isbræ (and many other calving glaciers). Using our field observations as a basis, we developed a general framework for iceberg calving models that can be applied to any calving margin. The framework is based on mass continuity, the assumption that calving rate and terminus velocity are not independent, and the simple idea that terminus thickness following a calving event is larger than terminus thickness at the event onset. Although the calving framework does not constitute a complete calving model, it provides a guide for future attempts to define a universal calving law.
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The avialan fauna of the late Cretaceous Prince Creek Formation, AlaskaModern polar regions are critical breeding grounds for over 250 species of birds. Some migrate to high latitudes for access to seasonally abundant resources during reproductive periods, whereas others are year-round residents. Despite the major role these birds play in polar ecosystems, we know very little of the origins of the utilization of polar ecosystems for nesting due to the rarity of avialan fossils from high latitudes. The avialan fossil record spans 150 million years, yet evidence for high-latitude bird reproduction extends only to the Eocene La Meseta Formation of Antarctica (56-33.6 Ma). Here, we report a remarkable polar avifauna from the northernmost fossil-bearing Late Cretaceous ecosystem in the world, the Prince Creek Formation of northern Alaska (PCF). The PCF was deposited at 80-85°N paleolatitude, where continuous summer daylight would have lasted nearly six months. It preserves an ancient polar ecosystem including avian and non-avian dinosaurs, mammals, and fishes. The PCF avialan material was found as part of a decade-long microfossil analysis of channel lag deposits. Numerous skeletal elements, representing almost the entire avialan skeleton, constitute one of the most comprehensive and well-preserved Late Cretaceous avifaunas in the world. These fossils share morphological affinities with hesperornithines, ichthyornithines, and crown birds. Further, abundant perinatal fossils represent the youngest-known growth stages of Mesozoic euornithines. This is the oldest direct evidence for polar bird reproduction and demonstrates that multi ---taxic bird nesting has occurred in the High Arctic for at least 73 million years--nearly half the tenure for birds on Earth. Likewise, these fossils demonstrate that this behavior originated in the Mesozoic ancestors of modern birds, millions of years before the radiation of crown group birds following the end-Cretaceous mass extinction.
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Sediment characteristics and economic potential of large methane seeps in Esieh Lake, NWMy thesis evaluates lake sediment characteristics and how they have been affected as large geologic methane (CH₄) seeps formed in Esieh Lake (informal name), a lake in Northwest Alaska. I provide extensive background of the lake, including a synthesis of studies and reports that characterize the geology around this lake which, to date, contains the largest known CH₄ seeps in the Arctic. In addition to providing background information on Esieh Lake and characterizing the lake's sediments, I evaluate the economic potential for the CH₄ seeps and compare flux values to natural gas projects which were previously completed in Alaska and Canada. The evidence suggests the possibility that CH₄ seeps initiated in Esieh Lake sometime within the last century via an explosive event that formed large pockmarks in the lake bottom. Rapid expansion of the seep field occurred between 1952 and 1972. Seepage continued after the blowout event and is still present today, albeit at a more quiescent stage. An economic evaluation of the seep as an energy source found that the capital cost for infrastructure to transport gas to a nearby community resulted in high energy costs, higher than the current cost of electricity in Noatak from imported diesel. However, if infrastructure capital costs were not a factor, then the cost of electricity for Noatak using Esieh Lake seepage as natural gas, would be much lower that current electricity costs. Through existing technologies, Esieh Lake is not economically viable as a resource but as technology progresses, developing a very small-scale gas resource may become a viable option.
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Deep learning detection and quantification of volcanic thermal signals in infrared satellite dataVolcanic eruptions pose hazards to human lives and livelihoods (Loughlin et al., 2015). To mitigate these hazards, volcano monitoring groups aim to detect signs of unrest and eruption as early as possible. Prior to eruption volcanoes may show various signals of unrest, including: increased surface temperatures, surface deformation, increased seismicity, increased degassing, and more. Here we focus on one approach to monitor volcanic unrest: detecting high-temperature localized volcanic heat emissions, otherwise known as hotspots. The presence of hotspots can indicate subsurface and surface volcanic processes that precede, or coincide with, eruptions. Space-borne infrared sensors can identify hotspots in near-real-time; however, automatic hotspot detection systems are needed to efficiently analyze the large quantities of data produced. While hotspots have been automatically detected for over 20 years with simple thresholding algorithms, new computer vision technologies, such as convolutional neural networks (CNNs), enable improved detection capabilities. Here we introduce HotLINK: the Hotspot Learning and Identification Network, a CNN-based model to detect volcanic hotspots in VIIRS (Visible Infrared Imaging Radiometer Suite) imagery. We find that HotLINK achieves an accuracy of 96% when evaluated on a validation dataset of ~1,700 unseen images from Mount Veniaminof and Mount Cleveland volcanoes, Alaska, and 95% when evaluated on a test dataset of ~3,000 images from six additional Alaska volcanoes (Augustine Volcano, Bogoslof Island, Okmok Caldera, Pavlof Volcano, Redoubt Volcano, Shishaldin Volcano). Additional testing on ~700 labeled MODIS images demonstrates that our model is applicable to this sensor's data as well, achieving an accuracy of 98%. We apply HotLINK to 10 years of VIIRS data and 22 years of MODIS data for the eight aforementioned Alaska volcanoes. From these time series we find that HotLINK accurately characterizes background and eruptive periods, similar to a threshold-based method, MIROVA, but also detects more subtle warming signals, potentially related to volcanic unrest. In particular, analysis of the Mount Veniaminof record demonstrates that HotLINK is able to detect subtle hotspot signals that are coincident with elevated seismicity, potentially indicative of surface heating due to shallow magma intrusion and/or degassing. We identify three advantages to our model over its predecessors: (1) the ability to detect more subtle volcanic hotspots and produce fewer false positives, especially in daytime imagery; (2) the incorporation of probabilistic predictions for each detection that provide a measure of detection confidence; and (3) its transferability to multiple sensors and multiple volcanoes without the need for threshold tuning, suggesting the potential for global application. HotLINK is able to identify eruptions and potentially precursory warming signals in infrared satellite data, making it a valuable tool for monitoring volcanoes and tracking their heat released over time.
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Statistical analysis of stream sediments in the Mt. Freegold area of the Dawson Range, Central Yukon Territory, CanadaThe study uses data and samples from a 2009 and 2012 stream sediment sampling program, conducted in part by the author. With the aim to identify gold-bearing prospects, a data set of 417 samples was digested with aqua regia and analyzed using inductively coupled plasma mass spectrometry (ICP-MS). I had leftover material from the original samples reanalyzed by ICP-MS after 4 acid (nitric + hydrochloric + hydrofluoric + perchloric) digestion. I compared the compositional data for the two sample sets (308 samples, 45 elements). Accuracy and precision (reproducibility) for all elements of the aqua regia sample set is noticeable lower than that of the 4 acid digestion set. Accuracy is computed by the relative error that compares the assay of the standard sample to the known concentration of the standard. Precision is an estimate of the reproducibility of the sampling and analytical system. Precision is calculated by fractional uncertainty. Field duplicates are produced by splitting samples in two. Fractional uncertainty is calculated for each pair of original sample and field duplicate. Gold shows the lowest precision of all elements for both data sets, most likely due to the nugget effect. Using a paired sample T-Test I concluded that the mean concentrations of 42 elements are different for aqua regia versus 4 acid digestions. Only for three elements (sulphur, bismuth and copper) were non-distinguishable average element concentrations found for both digestion methods. A negative t-statistic (based on aqua regia vs. 4 acid digestion-based compositions) implies higher elemental recovery by 4 acid digestion. The aqua regia data set record only a portion (presented in brackets) of the values for 4 acid digestions for these elements: Na (1%), Hf (2%), Zr (3%), K (4%), Nb (5%), Sr (7%), Al (11%), Ti (12%), Rb (14%), Ba (16%) and Ca (19%). The digestion method determines the degree of element recovery from the solids (i.e., dissolution into solution) and consequently 'trustworthiness' of a given element's concentrations. This, in turn, dictates the element's usefulness for identifying prospective targets. The digestion method sets the frame for the spectrum of possible discoveries. As demonstrated 4 acid digestion has a high trustworthiness of a given element's concentrations over a broad spectrum of rock composition. Since the majority of elements have a high recovery, it is tempting to incorporate all analyzed elements in an analytical scheme for the evaluation of prospective targets. Thus I developed a new statistical method Mahalanobis Principal Component Analysis (MPCA) that considers element associations for all elements. Mahalanobis distance is used for identifying sample of odd element composition relative to the bulk of element compositions. The scheme is based on assuming that mineralization is not restricted to a few elements (pathfinders) rather than it is a multi-element affair. Principal Component Analysis is employed to determine the contribution of each element to the 'oddness' of the element composition of the anomalous sample. Hence the cause of a sample's abnormal element composition is revealed. Elements with a high contribution to the oddness provide clues about the type of abnormality and its exploration potential. Pearson correlation of samples composition is used for identifying similar samples. Samples of similar element composition share the same rock genesis and belong to the same lineage. Thus by plotting similar samples the spatial distribution of anomalies can be shown and it is used for the further evaluation of the target potential. The more reliable data set 4 acid is used to appraise the exploration potential of the Mt. Freegold sample area using MPAC. Fifteen exploration targets are identified. Not all of them are gold related.
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A method for automatic surface water extent mapping from Sentinel-1 SAR data for improved response to weather related hazardsTorrential rains, flooding, and storm surges are all considered meteorological and hydrological hazards. These hazards can quickly transition into disasters whenever they begin to effect human life or infrastructure. When these disasters occur, they can lead to devastating outcomes such as damage or complete loss of infrastructure, reduced crop yields and related impacts on food security, as well as risks to human life. For decades, these events have been monitored and tracked primarily from visible/infrared sensors. Unfortunately, flooding and storm surges often occur during extensive weather and cloud cover conditions, which can make monitoring these hazards across large spatial scales difficult if not impossible, especially in poorly developed regions. Synthetic Aperture Radar (SAR), with its capability to penetrate through clouds and monitor during both day and night cycles, may provide substantial improvements to flood hazard management, once robust techniques for the detection of surface water extent were developed. This thesis details the development of HYDRO30, an automatic algorithm to map surface water extent from Sentinel-1 SAR data. At its core the HYDRO30 approach automatically creates surface water extent maps by preforming adaptive thresholding on dual-polarized and radiometrically terrain corrected (RTC) SAR images. We use data from the Sentinel-1 C-band SAR constellation as input, as this constellation provides global access to free and open medium resolution SAR data that comes at a reliable sampling rate of six-to-twelve days. Such free-and-open, regularly sampled data is indispensable for hazard monitoring across regional to continental scales. In this thesis, I will show that the HYDRO30 algorithm achieves promising results in delivering robust and accurate surface water extent maps within an efficient timeline. The work presented in this thesis was developed as part of the HydroSAR project, a NASA-funded effort led by UAF to develop an automatic service for the monitoring of weather-related hazards in the Hindu Kush Himalaya. The thesis will also show an application of the HYDRO30 technology for the monitoring of flood hazards in northern Bangladesh during the 2020 south-Asian monsoon season.
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Mechanisms of magmatic degassing and eruption triggering at Alaska volcanoes: experimental controls and natural system analoguesUnderstanding the magmatic processes that drive volcanic eruptions is integral to monitoring volcanic unrest and mitigating the hazards that these systems pose on local communities, infrastructure, aviation, and maritime traffic. Variations in eruption style likely result from the complex interplay between bulk magma viscosity, magma ascent rate, and the efficiency of magma degassing/outgassing. The main goals of this dissertation will be to investigate parameters that influence eruption style and triggering through direct comparison of high pressure-temperature decompression experiments to natural system analogues, including well-studied systems in eastern California and a remote volcanic system in Alaska. The results of this study can be used to aid in more precise modeling of volcanic systems and assist in monitoring active volcanoes in Alaska, California, and worldwide. This thesis investigates eruption triggering dynamics by: 1) determining the extent to which crystals of varying size and shape influence degassing and outgassing kinetics in hydrous intermediate magmas from a purely experimental approach, 2) applying these results to analogue silicic lava domes in eastern California to investigate porosity-permeability relationships in some well-studied natural systems and use these results to form a first order model for post emplacement gas flux for these lava domes, and 3) investigating how magma mixing can trigger eruptions at Gareloi volcano, a frequently active yet poorly understood volcano in the western Aleutians, Alaska.
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Storminess in the Bering Sea: integrating instrumentation data with local and indigenous knowledge to support flood mitigation strategies in Goodnews Bay and St. Paul IslandExtratropical cyclones in the Bering Sea have the potential to cause widespread damage to the coastline of western Alaska, a threat that disproportionately affects Indigenous communities that inhabit these remote regions. A paucity of historical and instrumentation data in these regions, combined with the potential for increases in coastal hazards as a result of climate change, hinders coastal resilience at the local level. To address this problem, this study incorporates local and Indigenous Knowledge into a historical assessment of storm impacts in two communities in the Bering Sea, St. Paul Island and Goodnews Bay, to partially fill these gaps and improve coastal hazard mitigation and preparation. We conducted interviews with local and Indigenous Knowledge bearers in both communities, performed topographic field surveys of historical storm heights, and mapped flooding based on surface models generated from Unmanned Aircraft Systems and flood heights. Particularly impactful storms were described in storm histories, which detail information gathered from instrumentation, on-the-ground field visits, and Indigenous Knowledge interviews. Finally, an online Esri Storymap was designed as an outreach product to combine and visualize the various data products from this analysis with narrative on the experience of living through extreme storm events. This thesis integrates Western and Indigenous Knowledge into actionable, community-prioritized data products to support coastal resilience to climate changes.
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Exploring competing gold system models in the Valdez Creek region, Clearwater Mountains, AlaskaGold 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.
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Volcanic gas quantification under suboptimal conditionsVolcanic 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.
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The effects of summer snowfall on Arctic sea ice radiative forcingThe 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.
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The relationship between fracturing, asymmetric folding, and normal faulting in Lisburne Group carbonates: West Porcupine Lake Valley, Northeastern Brooks Range, AlaskaThe 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.
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Instability and retreat of a lake-calving terminus, Mendenhall Glacier, Southeast AlaskaMendenhall 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.
