Subglacial sediment transport also can occur by deformation of till at the glacier bed, and may be the LY300164 mode of transport under ice streams (Fig. 4B; Kristoffersen et al., 2000 and Bennett, 2003). Characteristic basal sediment thicknesses of less than 0.5 m have been measured beneath temperate Alaskan tidewater glaciers (e.g., Kamb et al., 1985 and Humphrey et al., 1993). The few observations of these deformable till layers from boreholes suggest they are no more than a few meters thick at most (Engelhardt et al., 1990 and Truffer et al., 1999). Transport also occurs by freezing to the sole of the glacier, resulting in thick zones of debris-rich basal ice where regelation and freeze-on from supercooled subglacial water is prevalent (Alley et al., 1997 and Creyts et al., 2013). Sediment fluxes associated with ice streams range from 102 to 103 m3 yr− 1 per meter ice width (Alley et al., 1987, Alley, 1989, Hooke and Elverh?i, 1996, Tulaczyk et al., 2001, Shipp et al., 2002, Dowdeswell et al., 2004, Anandakrishnan et al., 2007, Laberg et al., 2009 and Christoffersen et al., 2010). To generate and sustain such a large sediment flux, subglacial sediment transfer near the ice margins must be dominated by thick zones of deforming till (Alley et al., 1989, Anandakrishnan et al., 2007 and Livingstone et al., 2012) or debris-rich basal ice layers (Christoffersen et al., 2010).
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