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    Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System

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    Vore et al 2019 JGR - Jason ...
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    Author
    Vore, Margot E.
    Bartholomaus, Timothy, C.
    Winberry, J. Paul
    Walter, Jacob I.
    Amundson, Jason M.
    Keyword
    subglacial environment
    glacier dynamics
    conduit evolution
    glaciohydraulic
    subglacial
    polarization analysis
    Taku Glacier
    glacier dynamics
    seismic tremor
    conduit flow path
    subglacial hydrologic system
    subglacial discharge
    glacier beds
    melt‐water input
    tremor frequencies
    delta‐like flow
    gradients
    vertical ground motion
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    URI
    http://hdl.handle.net/11122/10936
    Abstract
    Subglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from single‐conduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3–7 days, while tremor produced by single‐conduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.
    Description
    ©2019. American Geophysical Union. All Rights Reserved.
    Date
    2019-02-09
    Source
    Research Article
    Publisher
    American Geophysical Union
    Type
    Article
    Peer-Reviewed
    Yes
    Citation
    Vore, M. E., Bartholomaus, T. C., Winberry, J. P., Walter, J. I., & Amundson, J. M. (2019). Seismic tremor reveals spatial organization and temporal changes of subglacial water system. Journal of Geophysical Research: Earth Surface, 124, 427–446. https://doi.org/10.1029/2018JF004819
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    Amundson, Jason M.

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      Vore, M.E.; Bartholomaus, T.C.; Winberry, J.P.; Walter, J.I.; Amundson, J.M. (American Geophysical Union, 2019-02-09)
      Subglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, hat is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from single‐conduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3–7 days, while tremor produced by single‐conduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.
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      Subglacial discharge at tidewater glaciers revealed by seismic tremor

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