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.
These landforms show the extent of past glaciers. Water flowing beneath glaciers can deposit sediment, which is then left as ridges and hills after the ice melts. Glaciers also act as conveyor belts for sediment, dumping it in piles, or moraines , at the end of the glacier. Water flowing in streams from the margin of glaciers deposits sediment as outwash fans or trains . Glacial troughs carved below present sea level and now filled with sea water are called fjords .