Abstract
AbstractIce streams are integral components of an ice sheet's mass balance and directly impact on sea level. Their flow is governed by processes at the ice‐bed interface which create landforms that, in turn, modulate ice stream dynamics through their influence on bed topography and basal shear stresses. Thus, ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics. This paper reviews developments in our understanding of ice stream geomorphology from a historical perspective, with a focus on the extent to which studies of modern and palaeo‐ice streams have converged to take us from a position of near‐complete ignorance to a detailed understanding of their bed morphology. During the 1970s and 1980s, our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in Antarctica. Very few palaeo‐ice streams had been identified with any confidence. During the 1990s, however, glacial geomorphologists began to recognise their distinctive geomorphology, which included distinct patterns of highly elongated mega‐scale glacial lineations, ice stream shear margin moraines, and major sedimentary depocentres. However, studying relict features could say little about the time‐scales over which this geomorphology evolved and under what glaciological conditions. This began to be addressed in the early 2000s, through continued efforts to scrutinise modern ice stream beds at higher resolution, but our current understanding of how landforms relate to processes remains subject to large uncertainties, particularly in relation to the mechanisms and time‐scales of sediment erosion, transport and deposition, and how these lead to the growth and decay of subglacial bedforms. This represents the next key challenge and will require even closer cooperation between glaciology, glacial geomorphology, sedimentology, and numerical modelling, together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
An ice stream is defined as ―a region in a grounded ice sheet in which the ice flows much faster than in the regions on either side‖ (Paterson, 1994: p. 301)
In addition to the confirmation that bedforms were being created under the ice stream, King et al.‘s (2007) study was significant because it was the first to demonstrate a clear link between ice velocity and bedform elongation that had only been hypothesised from work on palaeo-ice stream beds, i.e. the drumlinised ribbed moraine were found under ice velocities of ~72 m a-1, whereas the more elongate drumlins were observed beneath ice flowing at ~125 m a-1
The mega-scale glacial lineations (MSGLs) observed under Rutford Ice Stream were largely indistinguishable from those observed on palaeo-ice stream beds (Fig. 15b) and this study provided the first conclusive evidence that MSGLs are diagnostic of ice stream flow, which had been postulated well over a decade earlier (Clark, 1993)
Summary
An ice stream is defined as ―a region in a grounded ice sheet in which the ice flows much faster than in the regions on either side‖ (Paterson, 1994: p. 301). The early descriptions and discussions of ice streams (Rink, 1877; Edgeworth, 1914; Swithinbank, 1954) emphasised that they have no exposed rock to define their lateral margins, thereby distinguishing them from outlet glaciers Adhering to such a strict definition is often deemed impractical (cf Bentley, 1987; Paterson, 1994), not least because the vast majority of ice streams sensu stricto become bordered by rock-walls in coastal regions, where they flow through deep fjords, or may lie within deep glacial valleys where rock walls lie just beneath the ice surface. I will refer to ice streams in the broadest sense and include fast flowing outlet glaciers that are topographically controlled (cf. McIntyre, 1985; Bentley, 1987; Paterson, 1994)
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