Conclusions

The landform-sediment assemblages associated with polythermal glaciers in Svalbard differ from those in temperate and cold-glacier systems. In particular, the deformation of glacier ice during debris entrainment and transport is a primary control on the nature of the Svalbard valley glacier landsystem. Debris entrainment and transport at Svalbard glaciers takes place by:

1. incorporation of angular rockfall material within the stratified sequence of snow/firn/superimposed ice. This debris takes an englacial path, becomes folded in zones of converging flow with axes parallel to ice flow, and is usually associated with the formation of an axial planar foliation. Near the glacier snout, the debris emerges at the surface along the hinges and limbs of the folds, producing medial moraines, which on deposition give rise to flow-parallel linear debris stripes.

2. entrainment of debris at the bed to form the basal ice layer, involving primarily regelation, bulk freezing-on, folding and shearing. These processes can result in a debris layer several metres thick within the glacier and a sheet of basal till on deposition.

3. incorporation of debris of basal character within longitudinal foliation. The foliation is the product of shearing or very tight folding within the ice. The resulting landforms, foliation-parallel ridges, have a low preservation potential.

4. thrusting, in which basal glacial sediments (including regelation ice) and subglacial sediments are uplifted into an englacial position, sometimes emerging at the ice surface. Thrusting is a dynamic process, and in polythermal glaciers may be linked mainly to the transition from sliding to frozen bed conditions. Thrusting may also be promoted by compressive flow against a reverse bedrock slope.

5. subglacial upright folding with transverse axes and faulting of sediment as a result of a glacier overriding a deformable bed.

6. reworking of thrust- or fold-derived glacifluvial material to produce longitudinal debris ridges within and on the ice. The resulting landforms are, however, ephemeral.

The most widespread deposit on the forefields of receding Svalbard polythermal valley glaciers is diamicton, which would typically be interpreted as a lodgement or melt-out till. Sediment release is controlled by the thermal regime of the glacier, the distribution of debris in the basal ice layer, and the nature of the bed beneath the glacier (deformable or non-deformable). Once released, glacifluvial processes rework much of this debris, although to a lesser extent than at temperate glaciers. The principal landforms in the Svalbard glacier landsystem resulting from ice-deformational processes are moraine-mound complexes (also referred to as thrust or push moraines where their genesis is known). The sediments in these complexes are highly variable and include diamicton of subglacial derivation, sand and gravel of glacifluvial origin, and mud with scattered gravel clasts and laminites of marine origin. Application of the Svalbard glacier landsystem to formerly glaciated areas is still at an early stage.

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