Ice caps presently cover much of Antarctica and Greenland. These icecaps lose ice primarily by calving of icebergs. Accumulation and melting of snow leads to annual layers.
Glaciers move by two main processes, internal deformation and basal sliding.
Water must be present at the base of the glacier for sliding to occur. Glaciers that are frozen to their beds move by ice deformation alone. Glaciers are capable of great erosion, if rock particles are embedded in the lower part of the ice by freezing and thawing of water. Smoothed, grooved and polished rocks are produced by glacial erosion. Glacial flow can produce streamlined landforms, such as drumlins , from unconsolidated sediments.