Where rivers channel water from the surface of more temperate continents Antarctica is drained by vast systems of glaciers and ice streams. These glaciers occur around the edges of the ice sheet, where they finish on land, or more often they end directly into the ocean. At sea the glaciers from a floating extension from which icebergs calve.

There are two different ways who glaciers move: First, the whole glacier move, or second, there is a movement within the ice mass itself. The first way can only happen if there is a layer of water between the ice and bedrock to reduce friction. Either the glacier melt the layer next to the bedrock with his weight or near the sea, water filter in under the ice.

The second way is caused by the weight of the accumulated snow and ice. Under this pressure, the ice crystals form into layers which slide over each other. Gravity forces these layers to follow the slop within the ice mass, which is steepest at the surface and less steep close to the bedrock. So the glacier does not move as a solid block, rather, the ice moves fastest at the surface and slower near the bedrock.

          The moving ice is constantly being stretched and compressed. Where it is stretched by flowing over ridge in its bed, or as its speeds up downstream, it cracks open to form crevasses. Complex patterns of crevasses may be created, varying from a few millimetres to 30m wide, up to 40m deep and sometimes several kilometres long. Often snow will collect on each lip of a crevasse, building outwards until the opening is bridged. The crevasse may then become invisible.

          The Lambert Glacier, the worlds largest, drains an area of over 1 million km² of East Antarctica. The glacier is 400 km long and over 40 km wide, and the ice shelf adds another 300 km to its length. On average, 35 km³ of ice a year flows down the glacier and breaks off as icebergs from the ice front, which is 200 km wide where it meets the sea. Through the mountains, the glacier moves at about 230m a year, but by the time it reaches the floating ice shelf it has speeded up to around 1km a year.

Ice sheets

Ice shelves