Levels

7.4.1 Glacier Structures

An understanding of glacier structures or structural glaciology is vital to understanding how debris is distributed and transferred within a glacier (Box 7.1). These structures are principally the product of internal deformation, and are intimately associated with debris transport (Figure 7.12). Glacier ice is similar to any other type of geological material in that it comprises strata that progressively deform to produce a wide range of structures. Primary structures include sedimentary stratification derived from snow and superimposed ice, unconformities and regelation layering resulting from pressure melting and refreezing at the base of a glacier. Secondary structures are the result of deformation, and include both brittle features (crevasses, crevasse traces, faults and thrusts) and ductile features (foliation, folds, boudinage). Typically, a glacier will reveal a sequential development of structures over time and consequently ice at the glacier snout may record several phases of deformation. These phases of deformation reflect the passage of a 'parcel' of ice through the glacier from top to bottom. Ice high in the accumulation area will therefore be experiencing its first phase of deformation while ice at the snout may be experiencing its third or fourth phase.

Figure 7.11 Plan view showing a schematic configuration of the possible sediment transport mechanisms beneath a glacier. The glacier is flowing from the top towards the bottom of the page. [Modified from: Alley et al. (1997) Quaternary Science Reviews, 16, figure 2, p. 1031]

Figure 7.11 Plan view showing a schematic configuration of the possible sediment transport mechanisms beneath a glacier. The glacier is flowing from the top towards the bottom of the page. [Modified from: Alley et al. (1997) Quaternary Science Reviews, 16, figure 2, p. 1031]

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