Ice Streams in Antarctica
Although they account for only 10% of the volume of the ice sheet, ice streams are sizeable features, up to 50km wide, 2000m thick and hundreds of km long. Some flow at speeds of over 1000m per year and most of the ice leaving the ice sheet passes though them.
Ice streams generally form where water is present, but other factors also control their velocity, in particular whether the ice stream rests on hard rock or soft, deformable sediments. At the edges of ice streams deformation causes ice to recrystallise making it softer and concentrating the deformation into narrow bands or shear margins. Crevasses, cracks in the ice, result from rapid deformation and are common in shear margins.