Vanessa Brazier

15.1 INTRODUCTION

The concept of the glaciated valley landsystem was introduced by Boulton and Eyles (1979) and Eyles (1983b), to describe the characteristic sediments and landforms associated with valley glaciers in upland and mountain environments. By focusing on the scale of the whole depositional basin, the glaciated valley landsystem has a broader compass than most of the other landsystems explored in this book, which are specific to particular depositional environments. Indeed, glaciated valley landsystems may incorporate ice-marginal, supraglacial, subglacial, proglacial, periglacial and paraglacial landsystems, recording the juxtaposition and migration of very different depositional environments. Additionally, because glaciated valleys occur in every latitudinal environment from equatorial to polar regions, the dimensions of climate and glacial thermal regime add even more variability. Thus the 'glaciated valley landsystem' should be regarded as a family of landsystems, which exhibits considerably more variety than suggested by the original Boulton and Eyles model (Fig. 15.1).

Despite this variability, landsystems in glaciated valleys tend to have certain recurrent features, as a result of two main factors:

1. the strong influence of topography on glacier morphology, sediment transport paths and depositional basins

2. the importance of debris from supraglacial sources in the glacial sediment budget.

In this chapter, we emphasize the contrasts between glaciers with limited supraglacial debris ('clean glaciers') and glaciers with substantial debris covers in their ablation zones ('debris-covered glaciers'), although it should be recognized that intermediate forms occur between these end members. Before examining the landsystems of glaciated valleys, we begin by considering debris sources and transport pathways through valley glaciers, and the ways in which debris cover influences glacier dynamics.

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