An ice stream is a region of an ice sheet that moves significantly faster than the surrounding ice. Ice streams are significant features of the Antarctic where they account for 10% of the volume of the ice. They are up to 50 km wide and 2 km thick. They stretch for hundreds of kilometres and account for most of the ice leaving the ice sheet, and entering the ice shelf.
The speed of the ice in the ice stream can be 1,000 meters per year, an order of magnitude faster than the surrounding ice. The shear forces at the edge of the ice stream causes deformation and recrystallization of the ice from hard glacial ice to a softer and more brittle form. Crevasses form particularly around the shear margins.
The causes of ice streams vary, though most are associated with sub-ice water streams, which lubricate the ice flow. The type of bedrock also is significant. Soft, plastic sediments result in the fastest flow.
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