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The Global Distribution of Cold
The last ice age in Britain was 10,000 years ago. Glaciers retreated from
Britain and Ireland.
Today we can recognise the extent of the ice masses from Erosional and
depositional features which they left behind.
The polar climate which was experienced in Britain was replaced by the
temperate climate which we have today over thousands of years.
Ice Ages
Ice ages have been the result of global climatic changes, every 200 to
250 million years during the Earths history there appear to have been
major periods of glacial activity.
During the quaternary period (latest period in geological time spanning
last 2million years) ice began to spread from the polar ice caps, into
North America and northern Europe.
At its greatest extent the ice covered nearly a third of the Earth's surface
and 18,000 years ago the ice reached as far as Norfolk.…read more

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The Global Distribution of Cold
There Influences
are several interrelated factors which combine to help develop Glaciers in
the for the climatic
accumulation zone. fluctuations are though to include:
Changes in the Earth's position in space (orbit and tilt)
·At higher altitudes
Variations thereactivity
in sunspot is morechanging
precipitation, mainlyof
the amount insolar
the form of snow.
radiation on Earth
·New snow is highly reflective , absorbing less heat meaning they melt slower
Changes in the amount of volcanic dust, changing the amount of radiation
trapped winds at high
by the altitudes cause snow to be blown into hollows and
basins so that snow accumulates.
Trapping of carbon dioxide by the oceans reducing the total amount in the
·As temperatures are low, sublimination (the change from solid water to vapour)
atmosphere, cooling the planet
and other losses are low and melt-water is likely to refreeze.
Variations in oceans currents
InGlaciers as Systems
the ablation (process of wastage snow or ice, especially by melting) zone the
outputs exceed
Glaciers arethe inputs:
masses of ice which are continually changing.
They can be seen as an open system with inputs (snow and avalanches) which
addis to
thesnowfall and
mass, and temperatures
outputs are higher
(evaporation resulting in which
and melt-water) outputs in the the
of melting (surface, basal and within the glacier), sublimination, evaporation
Near the source of the glacier, inputs generally exceed outputs (zone of
The dividing line between the two zones is called the equilibrium line. Gravity
moves ice continually towards this line, replacing that lost at the snout by
ablation.…read more

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The Global Distribution of Cold
The difference between the total accumulation and total ablation for the
glacier over one year is called the glacial budget. This is calculated for the
balance year which runs from autumn to autumn (when summer will
have reduced the total ice mass to a minimum).
There is a positive winter balance and a negative summer balance (for
example, a typical Alpine glacier may lose ice at over 10m a year
through melting and is normally replenished by ice flowing from above).
When the amounts of accumulation and ablation are equal, the glacier is
in a steady state. The snout may not move by the ice is flowing through
it like a conveyor belt.
Glacial Surges
Glaciers may take many years to react to changes in accumulation or
ablation but where snowfall is exceptionally heavy, the glacier may
suddenly surge forward.
Rates of movement of flowing glaciers are extremely variable, fastest
parts can flow anything between 50m and 400m a year.…read more

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Glacier Size and Shape
Ice mass classifications can vary in detail. Here is a list (smallest to largest):
Niche Glaciers ­ small patches of glacier ice found on upland slopes, mostly north-facing
in the northern hemisphere. Little effect on topography.
Corrie Glaciers - small ice masses on mountain slopes, gradually erode arm-chair shaped
hollows. If they develop to be too large for the hollow, they spill over the lip to feed a valley
Valley Glaciers - are larger masses of ice the flow from ice-fields or a corrie and usually
follow pre-glacial river valleys, developing steep sides as they erode their course.
Piedmont Glaciers - large lobes of ice formed when glaciers spread out. They may
merge on reaching lowland areas and escape the confines of their valleys.
Ice Caps ­ are huge, flattened, dome shaped masses of ice that develop on high plateaus.
They are similar to an ice sheet, but are less than 50,000km in area, if they are over that
then they are known as ice sheets. An Antarctic ice sheet has a thickness of over 4000m.
Ice Shelves - are extensions of ice sheets that reach out over the sea. These shelves of
floating ice can be up to 1000m thick but diminish to around 500m on edge where icebergs
calve.…read more

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Glacier Size and Shape
Cold Based Glaciers ­ these are glaciers which occur in polar latitudes, where the temperature
of the snowfall is far below freezing and the glacier remains well below freezing point. Ice remains
frozen to the bed rock and as a result there is very little ice movement and thus limited erosion.
Warm Based Glaciers ­ these are most of the glaciers outside Antarctica and the northern
Greenland ice caps. Water is present throughout the glacier and acts as a lubricant. This allows for
movement of between 20m and 200m per year, which greatly increases the capacity of the glacier
to erode the bedrock.
How glaciers move
A key factor in determining the rate of ice movement is the temperature of the ice. Some ice is
warmer than other ice and this depends on the pressure melting point (PMP the temperature at
which ice melts).
The PMP is lower within the glacier because the ice is under pressure. Ice melts more easily when it is
under pressure, and all ice is under some pressure, especially towards the base of the glacier.
Internal flow ­ this is movement within the glacier ice resulting from the stresses applied by the
force of gravity. Where ice crystals orientate themselves in the direction of the glacier's overall
movement, they may slide past each other. Such movements often result in the formation of
crevasses within and at the surface of the ice
Basal Slippage - this is the sliding effect of a glacier over the bedrock by regelation slip / creep.
Regelation slip is most effective with small obstacles while creep is the process that overcomes
larger problems. On the up-glacier side of an obstacle, the increasing pressure causes melting
locally. The melt-water creates slipping of the ice over the obstacle then freezes again in lower-
pressure conditions on the down-glacier side of the obstacle. The thin layer of ice where this
happens is called regelation layer.
Creep may happen where there is little or no regelation slip. It refers to the plastic like movement of
the ice when it's course is impended with large obstacles. Larger obstacles greatly increase the stress
in the ice and cause it to become more plastic like in behaviour so that it flows around the obstacle.…read more

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Theo Styles

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