Glacial revision - Part 1

Some bits and bobs on glacial aspect of a-level geography

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Geography revision ­ Part 1
Cold Environments ­ Glacial
Features
Glacial environments contain snow and ice all year round, but are relatively dry. Temperatures on the
ice sheets vary from -60°C to -10°C at the coast. In the winter, -75°C to 25°C and summer
temperatures, -40°C to -2°C. There is considerable variation in the amount of precipitation in
Antarctica. The cold mountain winds (katabatic winds) go from out from the centre of Antarctica
towards the edges. They form as dense cold air over the central plateau drains into depression and
valleys.
Processes
Plucking ­ ripping out material from the bedrock. The downward pressure from the weight of the
glacier and the downhill drag is slow enough for the ice to melt onto obstacles; occurs at the
base of the glacier but also on the sides of the valleys.
Abrasion ­ the sandpaper effect. The material from plucking is used, the larger and more angular
the material, the greater the potential for erosion, leaves striations and shatter marks. The finer
material will smooth and `polish' the rock.
Freeze-thaw weathering ­ Meltwater from the glacier seeps into the cracks or joint in the rock.
When the water freezes it expands in the cracks and breaks the rock. This process continues and
the water continues to weaken the rock until it breaks into angular fragments.
Meltwater ­ Chemical weathering. CO2 is more soluble at low temperatures hence meltwater
have the capacity to hold more CO2. As streams become more acidic, they are able to weather
carbonate rocks more effectively.
Nivation - Rock or soil erosion beneath a snow bank or snow patch, freezing and thawing of the
thin snow.
Factors affecting rate of erosion
Local geology ­ areas with well-fractured, jointed bedrocks are easily plucked; for example,
carboniferous limestone of the Burren in County Clare, Ireland.
Velocity of the glacier ­ This is somewhat dependent on gradient ­ areas of fast-flowing ice lead
to increased erosion.
Amount and character of the load carried by ice ­ If the load is coarse, resistant and angular, it
will erode more than a load that is fine, weak and rounded.
Features
Cirque/Corrie/Cwm ­ Arm chair shaped hollow surrounded by knife-edged ridges called arêtes. Best
form in Britain on a north/east facing slope. They are heavily influenced by the joint pattern of rocks;
rocks need to be resistant enough to withstand complete destruction, but weak enough to be
heavily eroded or weathered.

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General formation ­ a snow covered hollow on the side of a slope is enlarged by freeze thaw
weathering. Further erosion means that ice can accumulate, and at a critical depth and weight of the
ice the ice begins to move out of the hollow by extrusion flow in a rotational manner. The rotational
movement of the ice helps to aid further plucking and abrasion which is where a true cirque is
formed.…read more

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Truncated spurs ­ a blunt ended rock ridge which descend from the steep sides of a u-shaped valley
or glacial trough.
Key Words
Striations ­ scratch marks on rocks caused by abrasion.
Chatter marks ­ discontinuous scratch marks on rocks caused by abrasion.
Extrusion flow ­ the movement of ice when it becomes too heavy or deep and therefore unstable.
Arête ­ are sharp, narrow mountain ridges.…read more

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