Landsystem Model for Svalbard Glaciers

From observations of modern Svalbard glaciers and the published literature we suggest the following landsystem model (Fig. 4.10). A typical receding Svalbard glacier has three zones within its forefield:

1. an outer moraine ridge

2. a moraine-mound complex, often draped by supraglacial debris stripes

3. an inner zone comprising various quantities of foliation-parallel ridges, supraglacial debris stripes, geometrical ridge networks, streamlined ridges/flutes and minor moraine mounds.

Outer moraine ridges are arcuate ridges rising steeply from the surrounding topography to heights of up to 15—20 m. They are commonly ice-cored, and the degree of degradation depends greatly on their constituent sediments. Some may be the product of permafrost deformation, while others represent former englacial, or proglacial thrusts. Some glaciers (e.g. Midtre Lovénbreen, Kongsvegen) are also flanked by large ice-cored lateral moraines (see Fig.

Moraine-mound complexes commonly comprise arcuate belts of aligned hummocks or mounds of a wide variety of morphological types. They include linear ridges up to 100 m long, short-crested ridges several metres long, and near-conical mounds; all reaching elevations of several metres. Irrespective of size, they show ice-proximal rectilinear or curvilinear slopes with consistent angles of around 30°, irregular distal slopes that are commonly steeper, and are formed of stacked units of a variety of sedimentary facies. The rectilinear slopes and stacking indicate thrusting in proglacial, ice-marginal and englacial positions. There is a continuum of forms of moraine complex, based on displacement characteristics of the glacier bed or the décollement surface. Where friction at the décollement surface is high, then thrust-dominated moraine complexes form (e.g. Comfortlessbreen, Uvêrsbreen, Kronebreen). In permafrost areas, proglacial deformation may also occur, particularly during rapid advances into seasonally unfrozen sediments (Erikbreen, Usherbreen). Where friction at the glacier bed is very low, as when ice moves over saturated muddy sediments on the sea floor, the deformation in the sediment is represented by polyphase folding alone (Sefstrembreen). The application of these principles to Pleistocene moraine complexes will be of value in assessing the nature of terrain over which the glacier moved.

The inner zone is located between the moraine-mound complex and the modern glacier snout. Foliation-parallel ridges, supraglacially-derived stripes of debris, geometrical ridge networks and streamlined ridges/flutes are formed in variable quantities in this zone. Sedimentary facies are predominantly diamicton (previously deposited as basal till), preserved in the geometrical ridge networks and streamlined ridges and flutes, commonly undergoing reworking by proglacial streams.

Figure 4.10 A landsystem model for a typical terrestrial Svalbard polythermal glacier.

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