Development of Landform and Sediment Assemblages at Maritime High-Arctic Glaciers

Abstract

Detailed studies of sedimentary processes and landform development at modem glaciers are an essential pre-requisite for the interpretation of Quaternary glacial sediments and landforms. Recent work on polythermal glaciers in Svalbard has provided new insight concerning the processes responsible for glacial sediment/landform assemblages. Although the landforms associated with Svalbard glaciers are not in themselves unique, the particular assemblages and proportions of sedimentary facies differ markedly from those in temperate and cold glacier systems. The main conclusion is that deformation within glacier ice, as debris is entrained and subsequently transported, is the primary control on the nature of landform/sediment assemblages in the proglacial areas of Svalbard valley glaciers. The most important landform-creating modes of debris entrainment are: (1) Incorporation of angular rockfall material within the stratified sequence of snow, firn and superimposed ice, followed by folding with flow-parallel axes; the resulting medial moraines are preserved in the proglacial area as linear debris trains; (2) Entrainment of debris at the bed to form a several metre-thick basal ice layer, which is released as a sheet of basal till; (3) Incorporation of basal debris within longitudinal foliation, resulting in landforms referred to as foliation-parallel ridges; (4) Thrusting, whereby basal and subglacial sediments are uplifted towards the glacier surface, and ultimately released as individual mounds within a large end-moraine complex (often referred to as 'hummocky moraine'); (5) Subglacial upright folding with transverse axes and faulting also producing large end-moraine complexes; (6) Reworking of thrust- or fold-derived glaciofluvial material to produce longitudinal debris ridges in the ice, although their translation into landforms is poor. The principal sedimentary facies associated with these polythermal glaciers is diamicton of basal glacial origin, followed by sandy gravel of glaciofluvial origin. These facies, reworked by thrusting in glacier ice, dominate the end-moraine complexes. These observations and inferences have been applied to areas such as Britain, where glaciers no longer exist, in the interpretation of Pleistocene landforms and sediments.