Ice streams are spatially restricted regions in a grounded ice sheet, which flow much faster than the surrounding ice (Fig. 9.1). They are known to be one of the main regulators of ice sheets because of their ability to rapidly drain large volumes of ice. The processes that promote fast flow and restrict it to well-defined arteries are still poorly known. In recent times, the focus of research has been on investigating Antarctic ice streams to try to elucidate their processes of operation (e.g. Bell et al., 1998). Meanwhile, researchers of Quaternary oceanography and palaeo-glaciology have discovered that ice streams were responsible for producing large-order ice sheet instabilities that were of great enough magnitude to force climate change on abrupt (millennial) timescales (Bond and Lotti, 1990). It follows that an understanding of ice stream operation is critical to both contemporary and palaeo-glaciology, and has implications for mechanisms of abrupt climate change.
The definition of ice streams as an artery of fast flow surrounded by slower flow, makes it relatively easy to identify contemporary examples from observed flow structures (e.g. Fig. 9.1) or velocity fields measured by satellite interferometry (Joughin et al., 1999). For palaeo examples, it is much harder and we have to rely on evidence left behind that is indicative of the existence of fast and spatially restricted flow. This chapter tackles this issue and builds a landsystem model of what we expect the geological and geomorphological products of ice streaming to look like. This expectation is driven by the characteristics of contemporary ice streams. Reasons for wishing to find and investigate palaeo-ice streams are outlined below.
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