A-level Geography/AS OCR Geography/Cold environments

Types of cold environment

Glacial

Snow and ice all year round
Dry climate
Temperatures stay below 0 °C

Periglacial

Significant snow and ice cover but not all year round
Temperatures rise above freezing during summer
Low precipitation

Upland

Once covered in snow
Can be periglacial
Wet climate due to orographic rainfall

Processes

Plucking

The ripping of material from the bedrock of a glacier

It occurs when there is a large downwards pressure from the weight of glacier. As the glacier moves downwards, friction between the basal ice of the glacier and the rock below causes melting. This water freezes to obstacles, which are then 'plucked' from the bedrock.

Abrasion

The sandpaper effect

It occurs when there is material present at the base or sides of the glacier. This material is dragged along the rock, erasing it. This process may cause grooves called striations to be formed. The larger and more angular material causes the most erosion.

Freeze-thaw

The weathering of rock with water

It occurs when water, which has penetrated cracks or fractures in rock, freezes. Water expands approximately 9% when it freezes so this expansion puts pressure on the rock. Repeated freezing and thawing (over many years) can lead to fracturing. As this process relies on fluctuating temperatures, it is mainly seen in periglacial areas.

Chemical weathering

The weathering of carbonate rocks by carbonic acid

It occurs when CO₂ in the air dissolves into rainwater, forming a weak carbonic acid. CO₂ is more soluble at lower temperature, so therefore the water becomes more acidic. This acid then reacts with carbonate rocks, such as limestone, dissolving them.

Glaciers

Ice Formation

Snow is compressed by the weight of subsequent snowfalls. Compacted snow which has experienced a winters freezing and a summers melting is known as firn. For this to happen, the summer must have low temperatures.
As more snow builds onto of the firn, air is squeezed out, and ice is formed.
Ice accumulates as more snow falls.

When this ice flows downhill under its own weight and gravity, it's called a glacier.

Types

Ice sheets - largest glaciers (Antarctica)
Icefields/icecaps - miniature ice sheets (Uplands)
Valley glaciers - flow down mountainous regions (Alps)

Zones

Upper Glacier - Accumulation (input>output)
Lower Glacier - Ablation (input<output)
Zone of Equilibrium - Snow line (input=output)

The glacial budget is the difference between total accumulation and total ablation/year.