Beautiful pastel colours of the sunset above Franz Josef Glacier photographed from Centennial Hut toward the Tasman Sea visible on a horizon. Tusk Rocks in a foreground, Chamberlin Snowfield right, Agassiz Glacier left - Westland National Park, West Coast, New Zealand

The most destructive and powerful hand of Mother Nature lies, arguably, in the cryosphere. We may not see it doing much immediate damage, but by observing the landscape we can see enormous changes in our environment caused by glaciers. One of the very typical and most visible footprints glaciers leave behind are our, often ice free, valleys. Entire mountainsides were remodeled by

glacial action leaving only steep valley walls behind. In the upper reaches of the Franz Josef Glacier there is massive pressure from the build up of up to 300m of ice and snow. Associated erosional forces combine to create a bowl shaped depression in the underlying rock called a Cirque, with the snow and ice field contained in the cirque being called the Neve. As gravity encourages ice down the valley the weight of the ice presses downwards and outwards scouring the valleys into a distinctive glaciated U-shape. These are much broader and flatter floored than the V-shaped valleys carved by rivers.

The ice flow of a glacier is divided into two types, internal deformation and basal sliding. Internal deformation is movement of parts of the glacier relative to itself. Throughout the descent of the glacier, the ice at the sides and bottom side of the glacier are subject to more friction from the valley floor and walls, and therefore forced to move at a slower rate than the ice in the centre of the glacier. As a result the ice deforms within itself. Basal sliding occurs as water, either rain or melt passes underneath the glacier and acts as a lubricant between the ice and the bedrock. This is the main source of terminal velocity of temperate glaciers.

The bottom layers of the glacier flow deform plastically under the pressure allowing the glacier as a whole to slide down the valley like a huge toffee. It is the upper layer of around 30metres where the glacier is more brittle, therefore the ice here cracks and breaks into crevasses and seracs in order to bend over uneven bedrock.