Glacitectonic controls on subglacial to ice-marginal drainage : Sheringham to Weybourne

Abstract

Subglacial drainage systems have been shown to exert a strong control upon the processes operating within the beds of glaciers, sediment mobility and ultimately ice sheet dynamics (Kamb, 1987; Stokes and Clark, 2001; Breemer et al., 2002; Lowe and Anderson, 2003; Bell et al., 2007). The pathways followed by pressurised subglacial meltwater have been described as taking the form of either: (i) thin sheets or films developed along the ice‐bed interface (Weertman, 1972; Sharp et al., 1990; Hubbard and Sharp, 1993) potentially leading to the decoupling of the ice from its bed and rapid forward motion of the ice; (ii) intergranular flow, with meltwater flowing through pore spaces (Darcian flow) within subglacial sediments (Hubbard et al., 1995; Boulton et al., 1995) promoting soft‐sediment deformation of the bed (deforming beds); (iii) distributed flow through a network of linked cavities (Sharp et al., 1989) or braided canals (Shoemaker, 1986; Clark and Walder, 1994; Benn and Evans, 1996) between the ice and underlying bed; or (iv) discrete, highly efficient systems of drainage channels or tunnel valleys feeding meltwater to the margin of the glacier or ice sheet (Wingfield, 1990; Ó Cofaigh, 1996; Praeg, 2003; Longeran et al., 2006)