Structures and Deformation in Glaciers and Ice Sheets

Abstract

The purpose of this review is to provide a comprehensive assessment of the state of knowledge concerning the manner in which macroscopic structures evolve within glaciers, and to evaluate their meaning in terms of understanding the flow of glaciers and ice sheets. Using concepts drawn from structural geology (e.g., Fossen, 2010;Hobbs et al., 1976;Ramsay, 1967;Ramsay & Huber, 1983), attention is drawn to the similarities between glacier ice and deformed rocks. The review emphasizes those structures that can be observed at the glacier surface and considers their three-dimensional (3-D) geometry. Structures in glaciers are commonly complex and challenging to interpret, especially where several phases of deformation over-print one another. Hence, to aid the reader in the field, many of the described structures and their cross-cutting relationships are illustrated in photographs, maps, and conceptual diagrams, with examples ranging from the Arctic, through mid-latitude mountain ranges, to the Antarctic.

Microstructure and Crystallographic Preferred Orientations of an Azimuthally Oriented Ice Core from a Lateral Shear Margin: Priestley Glacier, Antarctica

“…The changes in CPO orientation with depth (Figure 14) would require heterogeneity in the shear kinematics on the meter to 10 m scale. Such heterogeneity should be expected; it is commonplace in highly anisotropic rocks from shear zones (Berthe et al, 1979a;Platt and Vissers, 1980;Lister and Snoke, 1984;Goscombe and Passchier, 2003;Toy et al, 2012) and such complexity of structure has been described in glaciers (Kamb, 1959;Hambrey, 1977;Hooke and Hudleston, 1978;Hudleston, 2015;Jennings and Hambrey, 2021). Such heterogeneity may integrate over the scale of many tens of meters to approximate the broad kinematics of the shear margin.…”

“…The sub-parallel layers with isoclinal fold structures, anastomosing layer patterns and local low angle truncations are typical of planar structures in high strain zones in rocks (Berthe et al, 1979b;Lister and Snoke, 1984;Toy et al, 2012). High shear strain will cause planar features of a wide range of orientations to become sub-parallel (Ramsay, 1980) and in a high shear strain zone of a glacier; original sub-horizontal annual layering and ice filled fractures (veins) will all become sub-parallel (Hooke and Hudleston, 1978;Hudleston, 2015;Jennings and Hambrey, 2021) while non-planar original features may be strained to generate new sub-parallel planar layers (see Figure 14 in Hudleston, 2015). The sub-parallel vertical layers in the Priestley core are consistent with the location in the lateral shear margin, however the strike orientation of the layers is rotated clockwise of that expected.…”

Upscaling ground‐based structural glaciological investigations via satellite remote sensing to larger‐scale ice masses: Bylot Island, Canadian Arctic

“…[Color figure can be viewed at wileyonlinelibrary.com] geometry. Structural assessment procedures have been provided in review papers by Hambrey and Lawson (2000) and Jennings and Hambrey (2021).…”

“…Note that lateral measurements decrease after experiencing pure shear, whereas lateral measurements remain the same after experiencing simple shear. Modified fromJennings and Hambrey (2021). [Color figure can be viewed at wileyonlinelibrary.com] When layers within longitudinal foliation become grouped into individual pixels, structural information is inevitably lost.…”

Time‐lapse photogrammetry reveals hydrological controls of fine‐scale High‐Arctic glacier surface roughness evolution

“…Melting glacier bare-ice surface topography is complex and dynamic. This variability, at the local scale, is driven by spatially differing ablation caused by crystal anisotropy (e.g., Greuell & de Wildt, 1999); emergent ice structures (e.g., Hambrey & Lawson, 2000;Hudleston, 2015;Jennings & Hambrey, 2021); non-stationary impurities (including dust and cryoconite: e.g., Gribbon, 1979;Bøggild et al, 2010;Irvine-Fynn et al, 2011;Nield et al, 2013;Takeuchi et al, 2018); and incipient surface hydrology and 'micro-channels' (Bash & Moorman, 2020;Mantelli et al, 2015;Rippin et al, 2015).…”