Ice+as+a+shaping+agent

Glaciers:

A glacier acts as a system with inputs (**accumulation**) and outputs (**ablation**).

Ice formation: The main input is snow. When snow falls it becomes compacted as more snow settles on top. Air is expelled and the individual snowflakes turn into granular ice crystals. The ice becomes denser and eventually turns into clear glacier ice. Another input is **avalanches** of snow and ice.

Losses of ice: Ablation mostly involves melting. This is likely to occur near the **snout** (end of the glacier) where the air temperature is higher, particularly in summer. Chunks of ice can break away from the end of the glacier and this is called **calving** and is another output. A final output os the loss of ice due to **evaporation** (water liquid to water vapour) and **sublimation** (water soild to water vapour).

Animations showing how different glacial processes and landforms work - []

BBC video explaining why the amount of ice changes - [] Changes in the amount of ice - [] The Franz Josef Glacier - Formation and flow - []
 * Inputs of ice || Outputs of ice ||
 * Snow || Melting ||
 * Avalanches || Calving ||
 * || Evaporation ||
 * || Sublimation ||

The glacier budget:

The glacier budget is the balance between the inputs and outputs. If accumulation exceeds ablation over several years, the glacier will advances. If ablation exceeds accumulation over several years, the glacier will retreat. In the glacial system accumulation mainly occurs near the top of the glacier with ablation mainly at the bottom.

The glacier budget varies between the seasons. In the winter, there will be a lot of accumulation with little ablation. In the summer, when it is wamrer, ablation will tend to dominate over accumulation.



Glacial processess: Glaciers have a huge effect on the landscapes they exist in. Freeze-thaw weathering: Freeze-thaw weathering Occurs in cold climates with temperature near or around freezing The exposed rock needs to contain many cracks Water enters the cracks during the warmer day and freezes during the colder night As the water turns to ice it expands and exerts pressure on the surrounding rock When temperatures rise, the ice melts and pressure is released Repeated freezing and thawing widens the cracks and causes pieces of rock to break off

Glacial erosion:

 The angular rock fragments produced by freeze-thaw weathering are vital tools for glacial erosion. They work their way under the ice, acting like sand on a sheet of sandpaper enabling the ice to grind away at the valley floor and sides. The scree fragments themsleves become shattered and pulverised by the weight of the ice, turning them into tiny pieces.

Glaciers only move very slowly but are still capable of tremendous amount of erosion.

Abrasion - when the material carried by a glacier rubs against, and, like sandpaper, wears away the sides and floors of the valley.



Plucking: as the glacier moves the bottom layers of ice stick to rock and the landscape. As the glacier moves it 'plucks' or rips the rocks out of the ground. Glacial movement:

In areas such as the Alps in Europe, melting ice in the summer produces a great deal of meltwater. This water helps lubricate the glacier, enabling it to slide downhill. This type of movement is called basal slip and it can simetimes cause sudden movements of a glacier. In winter, the glacier is frozen to the rocky surface. The weight of the ice and gravity cause the ice to deform and the glacier slowly moves down the slope.

Key terms:

Abrasion: a process of erosion involving the wearing away of the valley floor and sides (glaciers) and the shoreline (coastal zones)

Plucking: a process of glacial erosion where individual rocks are plucked from the valley floor or sides as water freezes to the glacier