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lacierslaciersA glacier forms when winter snowfallin an area
exceeds summer melt andtherefore accumulates year after year.
Snow is compacted and converted toglacial ice, and when the ice
is about40 m thick, pressure causes it to flow.
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Glacier TypesGlacier Types 1. Valley (Alpine)
Found in mountainous areas
Smaller than ice sheets
Lengths greater than widthsOnly cover a small region
Transform V-shaped valleys into U-
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lpineGlaciers
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Glacier Types 2. Ice sheets (Continental glacier)
Large scale cover 10% of Earths
land
Found in polar regions
Greenland 1.7 million km2
Antarctica 13.9 million km2
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ContinentalGlaciers
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So where does glacial ice comefrom?
Ice that makes up glaciers originally fell on its surface as
snow. Tobecome ice, this snow underwent changes that caused it to
become more
compact and dense. Glacial ice has a density of about 850
kilograms per
cubic meter. After the snow falls, the crystals can be reduced
by the
effects of melting and sublimation. Scientists call this process
ablation.
For most glaciers, ablation is a takes place in the summer
months. Thesnow also undergoes compaction through melting and
refreezing.
At first, these processes cause the original snowflakes to
be
transformed into small round crystals. This partly melted,
compressed
snow is called nv.
Nv has a density exceeding 500 kilograms per cubic meter. If the
nvsurvives the ablation that occurs during the summer months it is
called
firn.
When this process happens year after year, a number of layers of
firn
can accumulate. Accumulation then causes a further increase in
density,
changing the firn into glacier ice, as the lower layers of firn
arecom ressed b the wei ht of the la ers above. On avera e, the
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he c on versi on o fresh ly fall en s nowo fi rn and sn
ow.ce
Firnis a partially-compacted type of snow
that has been left over
from past seasons and has
been recrystallised. It is
ice that is at anintermediate stage
between snow and glacial
ice. Firn has the
appearance of wet sugar,
but has a hardness that
makes it extremely
resistant to shovelling.
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Glaciers BudgetGlaciers Budget
In - Zone of accumulation Snow accumulates and forms ice
Outer limit of accumulation is called thesnowline
Out Zone of wastage ablation general term for loss of ice or
snow from a glacier
1.Sublimation (Process where ice changes into watervapour
without first becoming liquid)
2.Melting
3.Evaporation
4.Calving - icebergs
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Glacier as a system
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How a glacier changes inresponse to inputs and.wastage
Inputs=outputs=glacier remains
stationary
Inputs> outputs = glacier advances
Inputs< outputs = glacier retreats.
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