Browsing by Subject "Glaciers"
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Item Acoustical characterization of glacierized fjords(2022-05-05) Zeh, Matthew Charles; Wilson, Preston S.; Ballard, Megan S; Deane, Grant B; Haberman, Michael R; Hamilton, Mark F; Pettit, Erin CThe rapidly changing cryosphere motivates a better understanding of the physical processes governing ice-ocean boundaries. These processes are no more pronounced than in glacierized fjords where massive glaciers meet the ocean. This underwater acoustic environment is significantly louder than other ice-covered environments. The abundant acoustic information, coupled with the difficulty performing measurements on or near glacier termini, encourage the use of passive acoustic monitoring to observe the system. While progress has been made towards improved understanding of sound in glacierized fjords, there remain considerable gaps in the community's understanding of the temporal variability of the acoustic field and the influence of the acoustic propagation environment. To address these deficiencies, three field experiments were conducted in three glacierized fjords: LeConte Bay at the terminus of LeConte Glacier near Petersburg, Alaska; Hornsund Fjord at the terminus of Hansbreen Glacier in Svalbard, an archipelago in the Arctic Ocean; and Disenchantment Bay at the termini of Hubbard and Turner Glaciers near Yakutat, Alaska. Acoustic data were collected between October 2016 and May 2017 from an underwater hydrophone array moored 500 m from LeConte Glacier. Ambient noise levels (ANL) from recordings were clustered, revealing relationships between ambient noise and the speed of icebergs above the mooring and with calving events. In particular, the local acoustic field demonstrated a uniquely consistent period between late February and early April 2017 where a single cluster dominated observations. The beginning and end of this period coincided with the formation and breakup of a dense pack of icebergs in the fjord. Characterization of the underside of a brash ice surface was obtained using an inference procedure and time difference of arrival and transmission loss data from an acoustic propagation experiment performed in Hornsund Fjord in September 2017. The inferred surface was incorporated into a forward simulation of the environment using BELLHOP, a ray tracing code. The measured data and simulated results were compared, providing insight to the shape and reflection characteristics of brash ice. Nearly continuous acoustic data was collected over fifty-two hours in June 2021 on two hydrophone arrays moored in Disenchantment Bay. The effect of recording duty cycle on sampling the spectral and temporal variability of the acoustic field was analyzed by comparing clustered spectral shapes and observations from full and reduced duty cycle recordings of varying length from 1% to 99% of the full 59-minute recordings. A relationship between duty cycle and relative error in hourly cluster observations was determined, which may inform the sampling procedure used in future deployments.Item And then, I wait(2022-08-16) Maguire, Kerry M.; Acha, Beverly; Lucas, Kristin; Stoney, John; McMaster, Richard Eric; Williamas, JeffThis report details the conceptual and material framework of my thesis artwork, Boundary Objects. I formulate an idea of ‘quotidian printmaking’ as a way of seeing fluctuations in the material world caused by climate change and human intervention. From the ‘quotidian print’ cascade four other contexts: the elemental, water, rumor, and drought. These five contexts are interrelated, but each can stand on its own. Using this lexicon, I define some possible frameworks for understanding my printmaking processes and my artwork.Item Drivers of change in East Antarctic ice shelves(2017-12) Greene, Chad Allen; Blankenship, Donald D.; Dickinson, Robert E.; Heimbach, Patrick; Jackson, Charles S.; Wilson, Clark R.; Young, Duncan A.Antarctica holds enough landlocked ice to raise the global sea level by nearly 60 m in the event of wholesale ice sheet collapse. In East Antarctica, the Aurora Subglacial Basin is drained by Totten Glacier and is one of the world’s largest and most rapidly-changing ice catchment systems. In recent decades, Totten Glacier has exhibited variability in its flow rate, mass balance, and ice thickness, each led by changes at the ice sheet margin. Totten Glacier dynamics are linked to processes in the Totten Ice Shelf, which buttresses the flow of grounded ice while being subjected to variable ocean forcing from below. Understanding the stability of the Aurora Subglacial Basin in a changing climate requires an understanding of how Totten Ice Shelf responds to changes in its environment. This dissertation investigates ice shelf processes on spatial scales of 1 km to 100 km, that act on sub-annual to decadal time scales. The independent roles of channelized basal melt and large-scale basal melt resulting from a variable supply of oceanic heat content are examined using surface elevation changes measured by airborne laser altimetry, satellite laser altimetry, and a new method of photometry applied to satellite images. A new method of satellite image template matching is also developed to understand ice shelf velocity response to several environmental forcing mechanisms. On the interannual time scale, Totten Ice Shelf is seen accelerating in response to nearby upwelling of warm circumpolar deep water that enhances basal melt rates. On the subannual time scale, Totten Ice Shelf exhibits winter slowdown as buttressing from seasonal landfast sea ice at the ice shelf front slows the flow of the glacier. These findings show that the Totten Glacier catchment is sensitive to changes in its environment, and may be susceptible to changes in the coastal wind stress projected for the 21st century.Item The impact of climate and tectonics on sedimentary and deformational processes, Gulf of Alaska(2012-12) Reece, Robert Sherman; Gulick, Sean P. S.Collision of the Yakutat Terrane with North America in southern Alaska has driven growth of the Chugach-St. Elias orogen. Glaciation of the St. Elias Range has periodically increased since the Miocene, but began dominating erosion and spurred enhanced exhumation since the mid-Pleistocene transition at ~1 Ma. Ice associated with this glacial intensification carved cross-shelf sea valleys that connect the St. Elias Range to the deep-sea Surveyor Fan. A newly increased terrigenous sediment flux into the fan triggered the formation and growth of the Surveyor Channel. The change in geomorphology observed throughout Fan sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathways from source to sink. Seismic data also reveal an isolated, large, short runout, mass-transport deposit (MTD) buried in the Surveyor Fan. The MTD geometry, size and location on a convergent margin lend support to recent studies suggesting seismic strengthening and infrequent sediment failure on active margins. This study provides insight into the magnitude and scope of events required to cause submarine mega-slides and overcome higher than normal sediment shear strength, including the influence of climate and sea level change. Beneath the Surveyor Fan, integrated geophysical data reveals massive intraplate shearing, and a lack of oceanic crust magnetic lineaments in regions of Pacific Plate crust. We argue that stress from the Yakutat-North America collision transferred outboard to the Pacific Plate is the major driver for the deformation causing these features. This stress would have resulted in significant strain in the NE corner of the Pacific Plate, creating pathways for sill formation in the crust and Surveyor Fan. The collision further intensified as the thickest Yakutat portion began to subduct during the Pleistocene, possibly providing the impetus for the creation of the Gulf of Alaska Shear Zone, a >200 km zone of shear extending out into the Pacific Plate. This study highlights the importance of farfield stress from complex tectonic regimes in consideration of large-scale oceanic intraplate deformation.Item Quaternary seismic stratigraphic investigations, Yakutat Bay region, Gulf of Alaska : subglacial drainage mechanics and glacial expanse(2008) Elmore, Christopher Ryan, 1984-; Gulick, Sean P. S.Quaternary tectonic and climate interactions have and continue to contribute to a substantial stratigraphic record that preserves the key regional events that result from the interplay of these dynamic processes. Near Yakutat Bay, Alaska, temperate glacial cover continuously manipulates and shapes the southern Alaskan margin and delivers substantial amounts of sediment annually. During cooler climatic periods, these glaciers, like most glaciers in Alaska, experience increases in volume and advance across the shelf. Using an integrated seismic data set, we investigate stratigraphic signatures buried along the shelf, between the present Yakutat and Alsek Sea Valleys, in order to understand the mechanics governing the regional glacial system during advance phases. Our investigations reveal four glacial unconformities, of which, two show preserved retreat sediment packages. The events are indicative of ice advance phases during the Little Ice Age (LIA), the Last Glacial Maxima (LGM), and two pre-LGM events. The events show dominance by ice expanse from the Malaspina and Alsek River districts. The LGM event transgresses the shelf and concentrates erosion in highly overdeepened troughs, somewhat analogous to ice stream behavior. In addition, associated with these regional events, we find a suite of large-scale channel forms, exhibiting widths between 0.6-4.2 km and depths between 49-353 m. The channels are highly eroded vertically relative to lateral extent; widths to thickness ratios of the buried channel deposits are 15.7 on average. The channels show good correlation with the interpreted erosional events and other stratigraphic signatures indicative of ice occupation, i.e. moraines, grounding lines, etc. The channels exhibit distinct facies and facies assemblages of variable thicknesses and occurrence and show common morphologic characteristics with one another, i.e. cross-cuts. The facies and assemblages appear dominated by glacio-proximal, glacio-fluvial and glacio-lacustrine/marine physical processes. The characteristic morphology of the channels implies they are subglacially derived, and facies suggest subsequent fill by subaerial/submarine processes after ice retreat. Based on morphologic interpretations of the channels and their associations with glacial stratigraphy and erosional events, we interpret them as tunnel valleys. Expanding on their predictable relationship with specific glacial stratigraphy, we conclude that the tunnel valleys are indicators of retreat following glacial advance periods, when significant amounts of ice and melt are available to initiate and generate large tunnel valley deposits. As such, we conclude that the tunnel valleys are useful paleoclimate indicatorsItem Surface boulder banding indicates martian debris-covered glaciers formed over multiple glaciations(2020) Levy, JosephGlacial landforms including lobate debris aprons are a globally distributed water ice reservoir on Mars preserving ice from past periods when high orbital obliquity permitted non-polar ice accumulation. Numerous studies have noted morphological similarities between lobate debris aprons and terrestrial debris-covered glaciers, an interpretation supported by radar observations. On both Earth and Mars, these landforms consist of a core of flowing ice covered by a rocky lag. Terrestrial debris-covered glaciers advance in response to climate forcing, driven by obliquity-paced changes to ice mass balance. However, on Mars, it is not known whether glacial landforms that were emplaced over the past 300-800 Ma formed during a single, long deposition event or during multiple glaciations. Here we show that boulders atop 45 lobate debris aprons exhibit no evidence of sequential comminution, but are clustered into bands that become more numerous with increasing latitude, debris apron length, and pole-facing flow orientation. Boulder bands are prominent at glacier headwalls, consistent with debris accumulation during the current martian interglacial. Terrestrial debris-covered glacier boulder bands occur near flow discontinuities caused by obliquity-driven hiatuses in ice accumulation that form internal debris layers. By analogy, we suggest that martian lobate debris aprons experienced multiple cycles of ice deposition, followed by destabilization of ice in the accumulation zone leading to boulder-dominated lenses, and subsequent ice deposition and continued flow. Correlation between latitude and boulder clustering suggests that ice mass balance works across global scales on Mars. Individual lobate debris aprons may preserve ice spanning multiple glacial/interglacial cycles.