Details:

Journal Title:
Proceedings of the National Academy of Science of the United States
Personal Author:
Burton, Justin C. ; Amundson, Jason M. ; Cassotto, Ryan ; Kuo, Chin-Chang ; Dennin, Michael
Burton, Justin C. ; Amundson, Jason M. ; Cassotto, Ryan ; Kuo, Chin-Chang ; Dennin, Michael Less -
NOAA Program & Office:
OAR (Oceanic and Atmospheric Research) ; CIRES (Cooperative Institute for Research in Environmental Sciences)
OAR (Oceanic and Atmospheric Research) ; CIRES (Cooperative Institute for Research in Environmental Sciences) Less -
Description:
Ice mélange, a granular collection of broken icebergs ranging from tens of meters to hundreds of meters in size, sits in front of many of the Earth’s most active tidewater glaciers. In addition to influencing heat and mass transport in the ocean, the jam-packed mélange provides a geophysical living laboratory to test principles developed for small-scale granular materials such as sand. By characterizing both flow and mechanical stress using field measurements, laboratory experiments, and numerical modeling, we show that ice mélange is a quasi-2D, creeping granular fluid which constantly jams and unjams as it advances through the fjord. Most importantly, our results show how ice mélange can act as a “granular ice shelf” which buttresses even the largest icebergs that calve into the ocean.Tidewater glacier fjords are often filled with a collection of calved icebergs, brash ice, and sea ice. For glaciers with high calving rates, this “mélange” of ice can be jam-packed, so that the flow of ice fragments is mostly determined by granular interactions. In the jammed state, ice mélange has been hypothesized to influence iceberg calving and capsize, dispersion and attenuation of ocean waves, injection of freshwater into fjords, and fjord circulation. However, detailed measurements of ice mélange are lacking due to difficulties in instrumenting remote, ice-choked fjords. Here we characterize the flow and associated stress in ice mélange, using a combination of terrestrial radar data, laboratory experiments, and numerical simulations. We find that, during periods of terminus quiescence, ice mélange experiences laminar flow over timescales of hours to days. The uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate. In addition, the average force per unit width that is transmitted to the glacier terminus, which can exceed 107 N/m, increases exponentially with the mélange length-to-width ratio. These “buttressing” forces are sufficiently high to inhibit the initiation of large-scale calving events, supporting the notion that ice mélange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini.
Source:
Proceedings of the National Academy of Sciences, 115(20), 5105-5110.
DOI:
https://doi.org/10.1073/pnas.1715136115
Document Type:
Journal Article
Rights Information:
Other
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Submitted
Main Document Checksum:
[+]
urn:sha256:b8efa2f2adb97603113351a2c7b20a9d9a5dde70c3535d8e597308ffecf6b8a0
Download URL:
https://repository.library.noaa.gov/view/noaa/20970/noaa_20970_DS1.pdf
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