ice on the land

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  • Created on: 10-06-12 11:47
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Pleistocene and current ice coverage
A glacier is a mass of ice that moves very slowly downhill. They are found at high altitude across the globe, even on high
mountains close to the equator, and at lower altitude in high latitudes close to the North and South Poles. The formation of
glaciers and the process by which they shape the landscape around them is called glaciation.
Pleistocene
18,000 years ago ice covered about 30 per cent of the land in the world. In Britain, ice covered land as far as the
Bristol Channel. During the last ice age the temperature remained below 0°C which allowed the ice to remain on
the land all year.
The last ice age was between 10 000BP and 2,000,000 BP
(BP-before present)
The temperatures went up and down, a shift, fluctuated.
18,000 yers ago there was 4 ice sheets that existed in the northern hemisphere. These ice sheets included:
-Cordilleran ice sheet
-Laurentide ice sheet
-Scandinarian ice sheet
-Greenland ice sheet
The extent of the ice coverage in North America was that the Laurentide ice sheet covered most of Canada and the
Great Lake area, upto 40N
The Cordilleran ice sheet covered most of Alaska upto 50N
The current ice coverage
It has retreated to both poles, therefore the level of ice is less
Greenland is only the major block of ice in the northern hemisphere
The other piece of block ice Antarctica
Largest ice sheet is in Antarctica, this covers an area of 14 MILLION KM2 and holds 90% of all fresh water on the
earth's surface.
In places it is several kilometres thick
Ice is also on the mountain tops-Himalayas, Rockies, Andes
The colder it gets the further the ice will go
Temperature fluctuations and evidence of these
Ice Cores
The deeper down the ice you get- the older it is
That ice will store air bubbles-some of them air pockets could be at least 1000 years old
They can measure the amount of CO2 and other gases trapped in the pockets
The less CO2 the colder it is and vice versa
They also look for dust-more dust, less vegetation so therefore should've been colder.
Deep-sea sediments
They look at oxygen isotopes
If you have got 2 isotopes, O18 and O16
O16 evaporates more easily than O18
In colder periods O16 gets trapped in ice therefore less of it in the sea
Lots of O16 in ice then it means that it was warmer, because it evaporates turns into rain.
Measure amounts of oxygen in the sea sediments-
Lots of O18 then colder temperatures
Lots of O16 then warmer temperatures
Landforms
Direct evidence of glacial/erosion-tells you how far south the ice has gone
Glacial Budgets
Glacial budget-the balance between the inputs (accumulation) and the outputs (ablation) of a glacier
Accumulation-inputs to the glacier budget, such as snowfall and avalanches

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Ablation-outputs from the glacier budget, such as melting
Snout-the bottom of the glacier
Weathering and glacial erosion
Weathering
The valley sides above the glacier are affected by freeze-thaw.
The predominant process is freeze-thaw weathering.
Freeze-thaw describes the action of glacial meltwater on joints, cracks and hollows in rock.
When the temperature reaches freezing point, the water inside cracks freezes, expands and causes the cracks to
widen. When the temperature rises, the water thaws and contracts.
This eventually causes rocks to break up.…read more

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Distinctive landforms created by glacial
erosion
Corries, arêtes, pyramidal peaks, glacial trough, truncated spurs, hanging valleys and
ribbon lakes
Corries
Corries, are often the starting point of a glacier. The diagram below shows the formation of a corrie.
Snowflakes collect in a hollow. As more snow falls, the snow is compressed and the air is squeezed out to
become firn or neve.
With the pressure of more layers of snow, the firn will, over thousands of years, become glacier ice.…read more

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Snow acts plastic again-malleable.
Description
Steep back wall
Raised lip
Over-deepened hollow
Once ice has gone it leaves a lake-tarn
Arete
An arête is a knife-edge ridge.
It is formed when two neighbouring corries run back to back.
As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower, eg
Striding Edge found on Helvellyn in the Lake District.…read more

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Glacial Trough
Glaciers cut distinctive U-shaped valleys with a flat floor and steep sides.
The glacier widens, steepens, deepens and smoothes V-shaped river valleys, eg Great Langdale Valley in the Lake
District.
The images below show the difference between a U-shaped valley and a V-shaped valley.…read more

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They form in hollows where softer rock was eroded more than the surrounding hard rock
E.g. Windermere, Lake District
Can be caused by compressing flow (thickening ice resulting in greater potential erosion)
It can also be caused by an area of relatively less resistant rock.
Distinctive landforms created by glacial
transport and deposition
Moraine
Name given to the largely angular rock material transported and then deposited by the ice.…read more

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Drumlin
Drumlins are elongated hills of glacial deposits.
They can be 1 km long and 500 metres wide, often occurring in groups.
A group of drumlins is called a drumlin swarm or a basket of eggs, eg Vale of Eden.
These would have been part of the debris that was carried along and then accumulated under the ancient glacier.
The long axis of the drumlin indicates the direction in which the glacier was moving.…read more

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They usually form in groups
E.g. Vale of Eden, Cumbria
Avalanches
Loose snow avalanche
Lots of freshly fallen snow, powdery, not dense, not compressed.
Found on a STEEP slope
A slight change can cause the snow to move; then gathers snow as momentum picks upp.
Steep hill-gravitation will pull it down
Slab avalanche
An avalanche of consolidating snow (a slab) moving rapidly downhill, carrying rocks and trees with it.…read more

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Major temperature changes, rapid wind speed and man-made influences, such as the weight of two skiers, often
trigger avalanches before they would naturally occur.…read more

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Comments

harry.arnett

yo bro

that is awse it got a U

Iswariya

really helpful thanks

Mr A Gibson

Fabulous set of notes, one of the best I've seen on the site. Really detailed, well put together and well presented. A document you can't afford not print out for your notes!

lwood7

Great notes! Thanks :)

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