Magnetic anisotropy and debris-dependent rheological heterogeneity within stratified basal ice

Nathan R. Hopkins, Edward B. Evenson, Dario Bilardello, Richard B. Alley, Claudio Berti, Kenneth P. Kodama

Research output: Contribution to journalArticle

Abstract

Basal ice of glaciers and ice sheets frequently contains a well-developed stratification of distinct, semi-continuous, alternating layers of debris-poor and debris-rich ice. Here, the nature and distribution of shear within stratified basal ice are assessed through the anisotropy of magnetic susceptibility (AMS) of samples collected from Matanuska Glacier, Alaska. Generally, the AMS reveals consistent moderate-to-strong fabrics reflecting simple shear in the direction of ice flow; however, AMS is also dependent upon debris content and morphology. While sample anisotropy is statistically similar throughout the sampled section, debris-rich basal ice composed of semi-continuous mm-scale layers (the stratified facies) possesses well-defined triaxial to oblate fabrics reflecting shear in the direction of ice flow, whereas debris-poor ice containing mm-scale star-shaped silt aggregates (the suspended facies) possesses nearly isotropic fabrics. Thus, deformation within the stratified basal ice appears concentrated in debris-rich layers, likely the result of decreased crystal size and greater availability of unfrozen water associated with high debris content. These results suggest that variations in debris-content over small spatial scales influence ice rheology and deformation in the basal zone.

Original languageEnglish (US)
Pages (from-to)770-779
Number of pages10
JournalJournal of Glaciology
Volume65
Issue number253
DOIs
StatePublished - Oct 1 2019

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Keywords

  • Basal ice
  • glacial rheology
  • ice rheology
  • subglacial processes

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