“…Furthermore, observations show that the style of subglacial drainage influences sliding speed (Kamb and others, 1985;Brugman, 1986;Raymond, 1987). There are generally thought to be two modes of drainage in subglacial hydrology: (1) concentrated channels such as Röthlisberger channels (R-channels) incised into the ice (Röthlisberger, 1972;Shreve, 1972;Weertman, 1972) or Nye channels eroded into hard bedrock (Weertman, 1972;Nye, 1973;Walder and Hallet, 1979), that operate at low water pressure relative to the overburden pressure of the overlying ice, (2) distributed water systems, including a network of linked cavities (Lliboutry, 1979;Anderson and others, 1982;Walder, 1986) or canals (Walder and Fowler, 1994;Fowler and Ng, 1996;Ng, 1998) connected by thin sheets of water at high pressure (Flowers and Clarke, 2002a;Creyts and Schoof, 2009;Hewitt, 2011).…”