• Active seismic studies in valley glacier settings: strategies and limitations

      Zechmann, Jenna M.; Booth, Adam D.; Truffer, Martin; Gusmeroli, Alessio; Amundson, Jason M.; Larsen, Christopher S. (International Glaciological Society, 2018-09-20)
      Subglacial tills play an important role in glacier dynamics but are difficult to characterize in situ. Amplitude Variation with Angle (AVA) analysis of seismic reflection data can distinguish between stiff tills and deformable tills. However, AVA analysis in mountain glacier environments can be problem- atic: reflections can be obscured by Rayleigh wave energy scattered from crevasses, and complex basal topography can impede the location of reflection points in 2-D acquisitions. We use a forward model to produce challenging synthetic seismic records in order to test the efficacy of AVA in crevassed and geo- metrically complex environments. We find that we can distinguish subglacial till types in moderately cre- vassed environments, where ‘moderate’ depends on crevasse spacing and orientation. The forward model serves as a planning tool, as it can predict AVA success or failure based on characteristics of the study glacier. Applying lessons from the forward model, we perform AVA on a seismic dataset col- lected from Taku Glacier in Southeast Alaska in March 2016. Taku Glacier is a valley glacier thought to overlay thick sediment deposits. A near-offset polarity reversal confirms that the tills are deformable.
    • Analysis of low-frequency seismic signals generated during a multiple-iceberg calving event at Jakobshavn Isbræ, Greenland

      Walter, Fabian; Amundson, Jason M.; O'Neel, Shad; Truffer, Martin; Fahnestock, Mark; Fricker, Helen A. (American Geophysical Union, 2012-03-27)
      We investigated seismic signals generated during a large-scale, multiple iceberg calving event that occurred at Jakobshavn Isbræ, Greenland, on 21 August 2009. The event was recorded by a high-rate time-lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus. During the event two full-glacier-thickness icebergs calved from the grounded (or nearly grounded) terminus and immediately capsized; the second iceberg to calve was two to three times smaller than the first. The individual calving and capsize events were well-correlated with the radiation of low-frequency seismic signals (<0.1 Hz) dominated by Love and Rayleigh waves. In agreement with regional records from previously published ‘glacial earthquakes’, these low-frequency seismic signals had maximum power and/or signal-to-noise ratios in the 0.05–0.1 Hz band. Similarly, full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus. The signals therefore appear to be local manifestations of glacial earthquakes, although the magnitudes of the signals (twice-time integrated force histories) were considerably smaller than previously reported glacial earthquakes. We thus speculate that such earthquakes may be a common, if not pervasive, feature of all full-glacier-thickness calving events from grounded termini. Finally, a key result from our study is that waveform inversions performed on low-frequency, calving-generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving. In particular, the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude. Accordingly, in our analysis, it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal.
    • Blocking a wave: frequency band gaps in ice shelves with periodic crevasses

      Freed-Brown, Julian; Amundson, Jason M.; MacAyeal, Douglas R.; Zhang, Wendy W. (International Glaciological Society, 2012)
      We assess how the propagation of high-frequency elastic-flexural waves through an ice shelf is modified by the presence of spatially periodic crevasses. Analysis of the normal modes supported by the ice shelf with and without crevasses reveals that a periodic crevasse distribution qualitatively changes the mechanical response. The normal modes of an ice shelf free of crevasses are evenly distributed as a function of frequency. In contrast, the normal modes of a crevasse-ridden ice shelf are distributed unevenly. There are ‘band gaps’, frequency ranges over which no eigenmodes exist. A model ice shelf that is 50 km in lateral extent and 300 m thick with crevasses spaced 500 m apart has a band gap from 0.2 to 0.38 Hz. This is a frequency range relevant for ocean-wave/ice-shelf interactions. When the outermost edge of the crevassed ice shelf is oscillated at a frequency within the band gap, the ice shelf responds very differently from a crevasse-free ice shelf. The flexural motion of the crevassed ice shelf is confined to a small region near the outermost edge of the ice shelf and effectively ‘blocked’ from reaching the interior.
    • Building Community: Synergy and Empowerment through Staff Development and Marketing in a Small Rural Academic Library

      Ward, Jennifer; Wilkes, Bethany (Collaborative Librarianship, 2016)
      This paper presents two collaborative programs at a small academic library that leverage the insights, engagement, and interests of our most important asset: our staff. Two new library committees, the Staff Training Advisory Group and the Marketing Team, extended planning, accountability, and partnerships to paraprofessional staff members. The onset and associated activities of these two committees yielded not only direct results in terms of staff training programs and marketing initiatives, but also resulted in creating a more collaborative culture and shared purpose in our library. This paper examines how the overlap of these two committees created a convergence that fostered excitement about the library, interest in improving library roles, and furthering library initiatives. By working together, and with our university community, we developed solid, popular programs in addition to cultivating a more intentional, thoughtful, and inclusive approach to our work and, ultimately, to supporting our university community.
    • Chancellor's Comments 2015-08-28

      Caulfield, Richard (University of Alaska Southeast, 2015-08-28)
    • Chancellor's Comments 2015-11-05

      Caulfield, Richard (University of Alaska Southeast, 2015-11-05)
    • Chancellor's Comments 2016-02-09

      Caulfield, Richard (University of Alaska Southeast, 2016-02-09)
    • Chancellor's Comments 2016-03-30

      Caulfield, Richard (University of Alaska Southeast, 2016-03-30)
    • Chancellor's Comments 2016-04-22

      Caulfield, Richard (University of Alaska Southeast, 2016-04-22)
    • Chancellor's Comments 2016-08-05

      Caulfield, Richard (University of Alaska Southeast, 2016-08-05)
    • Chancellor's Comments 2016-09-12

      Caulfield, Richard (University of Alaska Southeast, 2016-09-12)
    • Chancellor's Comments 2016-11-23

      Caulfield, Richard (University of Alaska Southeast, 2016-11-23)
    • Chancellor's Comments 2016-12-21

      Caulfield, Richard (University of Alaska Southeast, 2016-12-21)
    • Chancellor's Comments 2017-03-29

      Caulfield, Richard (University of Alaska Southeast, 2017-03-29)
    • Chancellor's Comments 2017-05-04

      Caulfield, Richard (University of Alaska Southeast, 2017-05-04)
    • Chancellor's Comments 2017-09-13

      Caulfield, Richard (University of Alaska Southeast, 2017-09-13)
    • Chancellor's Comments 2017-11-22

      Caulfield, Richard (University of Alaska, Southeast, 2017-11-22)
    • Chancellor's Comments 2018-02-28

      Caulfield, Richard (University of Alaska, Southeast, 2018-02-28)
    • Chancellor's Comments 2018-06-13

      Caulfield, Richard (University of Alaska, Southeast, 2018-06-13)
    • Chancellor's Comments 2018-07-27

      Caulfield, Richard (University of Alaska, Southeast, 2018-07-27)