Glacial Ice Formation

• These notes give basic details on Glaciation. You don't need to be able to write a 30-mark question on any landforms associated with these topics – you can pick either coastal or fluvial for this type of question

Glaciation

• Glaciation is the spread of large masses of ice over land and sea
• Glaciers are rivers of ice that move slowly
• They move downslope under the influence of gravity and the pressure of their own weight
• Form where rate of accumulation of snow and ice is greater than rate of melting

How Ice Moves

Basal Sliding

• Basal sliding occurs when meltwater at the base of a glacier reduces friction between the ice and the bedrock.
• The weight of the glacier and the friction it generates produces heat, which melts some of the ice to form a thin layer of water.
• This meltwater acts as a lubricant, allowing the glacier to slide downslope more easily.
• Basal sliding is most common on steep slopes with a smooth profile, where the ice can move quickly, and is especially active in summer when higher temperatures increase melting.
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Plastic Flow

• Plastic flow occurs in extremely cold regions, such as Greenland and Antarctica, where basal sliding cannot take place because the base of the glacier is frozen to the bedrock.
• Under these conditions, the immense weight of the overlying ice causes the ice crystals within the glacier to deform.
• The ice behaves like a slow-moving plastic, and horizontal layers of ice begin to creep past each other.
• The upper and middle layers of the glacier move faster than the layers near the base, which are slowed by friction with the valley floor.
• This allows the glacier to bend and flow over uneven surfaces, even without meltwater.
• Plastic flow is a much slower process than basal sliding and will only occur if the glacier is more than 50 metres thick, as this depth provides enough pressure for the ice to deform.