Formation of Glaciers (II)
After several years the lower part of the snow bank has been converted to firn. With increasing time the porosity of the ice is reduced to ~0% - glacial ice
When the ice reaches ~20 meters it begins to flow (plastic behavior) aided by gravity
The upper portion flows more rapidly than the base (due to friction and freezing at the base). Upper portion may behave as a brittle substance and fractures (crevasses) are common.