Outlet glaciers and ice streams

The ice movement in an ice sheet can be divided into sheet flow in the central dome areas, and stream flow in outlet glaciers and ice streams, characterized by rapidly moving, channelled ice flow. Outlet glaciers draining plateau glaciers normally have the form of valley glaciers. The accumulation area may be difficult to delimit. The longest glacier in the world, the 700 km Lambert Glacier in Antarctica, and the world's fastest moving glacier, Jacobshavn Glacier in western Greenland, are both ice streams. Ice streams can be divided from surrounding ice by the presence of heavily crevassed zones along their margins, for example, on the ice streams of West Antarctica. The flow and morphology of ice streams are the result of conditions at the glacier bed. In particular, the presence of deformable sediments and high porewater pressure are considered to be important in maintaining rapid ice flow in ice streams. Outlet glaciers and ice streams terminating in the sea are responsible for most of the icebergs and ice-rafted debris reaching the world's oceans: The dynamics of ice streams are also considered to have been important for the stability and break-up of the great mid-latitude ice sheets (Hughes et al., 1985).

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