Magnetic fabric of sheared till: A strain indicator for evaluating the bed deformation model of glacier flow

dc.contributor.author Hooyer, Thomas
dc.contributor.author Iverson, Neal
dc.contributor.author Iverson, Neal
dc.contributor.author Lagroix, France
dc.contributor.author Thomason, Jason
dc.contributor.department Geological and Atmospheric Sciences
dc.date 2018-02-18T09:29:19.000
dc.date.accessioned 2020-06-30T04:03:24Z
dc.date.available 2020-06-30T04:03:24Z
dc.date.copyright Tue Jan 01 00:00:00 UTC 2008
dc.date.issued 2008-04-05
dc.description.abstract <p>[1] Wet-based portions of ice sheets may move primarily by shearing their till beds, resulting in high sediment fluxes and the development of subglacial landforms. This model of glacier movement, which requires high bed shear strains, can be tested using till microstructural characteristics that evolve during till deformation. Here we examine the development of magnetic fabric using a ring shear device to deform two Wisconsin-age basal tills to shear strains as high as 70. Hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility (AMS) develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller. At moderate shear strains (∼6–25), principal axes of maximum magnetic susceptibility develop a strong fabric (S1 eignevalues of 0.83–0.96), without further strengthening at higher strains. During deformation, directions of maximum susceptibility cluster strongly in the direction of shear and plunge “up-glacier,” consistent with the behavior of pebbles and sand particles studied in earlier experiments. In contrast, the magnitude of AMS does not vary systematically with strain and is small relative to its variability among samples; this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear. Although processes other than pervasive bed deformation may result in strong flow parallel fabrics, AMS fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model.</p>
dc.description.comments <p>This article is from <em>Journal of Geophysical Research: Earth Surface </em>113 (2008): F02002, doi:<a href="http://dx.doi.org/10.1029/2007JF000757" target="_blank">10.1029/2007JF000757</a>. Posted with permission.</p>
dc.format.mimetype application/pdf
dc.identifier archive/lib.dr.iastate.edu/ge_at_pubs/146/
dc.identifier.articleid 1141
dc.identifier.contextkey 10068932
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath ge_at_pubs/146
dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/38077
dc.language.iso en
dc.source.bitstream archive/lib.dr.iastate.edu/ge_at_pubs/146/2008_Iverson_MagneticFabric.pdf|||Fri Jan 14 20:23:10 UTC 2022
dc.source.uri 10.1029/2007JF000757
dc.subject.disciplines Geomorphology
dc.subject.disciplines Glaciology
dc.title Magnetic fabric of sheared till: A strain indicator for evaluating the bed deformation model of glacier flow
dc.type article
dc.type.genre article
dspace.entity.type Publication
relation.isAuthorOfPublication 8f9617fd-0ee4-4473-b7bb-ef722542e676
relation.isOrgUnitOfPublication 29272786-4c4a-4d63-98d6-e7b6d6730c45
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