Trail of Ice Stream in Antarctica
In this radar (ASAR) image, an ice stream appears as a bright white trail through the surrounding Antarctic terrain.
An ice stream is a region of an ice sheet that moves significantly faster than the surrounding ice. They are significant features of the Antarctic where they account for 10% of the volume of the ice. They are up to 50 km wide, 2 km thick, can stretch for hundreds of kilometres, and account for most of the ice leaving the ice sheet.
The speed of an ice stream can be over 1,000 meters per year, an order of magnitude faster than the surrounding ice. The shear forces at the edge of the ice stream cause deformation and recrystallization of the ice, making it softer, and concentrating the deformation in narrow bands or shear margins. Crevasses form, particularly around the shear margins.
Most ice streams have some water at their bases, which lubricates the flow. The type of bedrock also is significant. Soft, deformable sediments result in faster flow than hard rock.
It has been suggested that the Antarctic ice sheet is losing mass. The past and ongoing acceleration of ice streams and outlet glaciers is considered to be a significant, if not the dominant cause of this recent imbalance.