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The glacier system
- As climate deteriorates and becomes colder more
precipitation in winter falls as snow and summers are
shorter, leaving less time for snow to melt. May be permanent snow cover in upland areas.
- Lower edge of area of
permanent snow cover is known
as the snow line. The snow line
will be further down slope as
climate becomes colder.
- In Greenland snow line is at sea level. In
Northern Hemisphere the snow line found
higher on south facing slopes as south
facing sloes recieve more radiation from
sun.
- In Greenland snow line is at sea level. In
Northern Hemisphere the snow line found
higher on south facing slopes as south
facing sloes recieve more radiation from
sun.
- Lower edge of area of
permanent snow cover is known
as the snow line. The snow line
will be further down slope as
climate becomes colder.
- Formation of Ice
- Ice is derived from compacted snow
(also some sleet, hail, rain which
freezes on top/inside glacier)
- As climate gets colder more
snow - permanent snow line
forms as snow accumulates on
ground
- Formation of permanent
snow field first stage in
formation of glacier (at high
altitudes in mountains or high
latitudes where winter
accumulation exceeds
summer snow melt)
- Snow falls - traps air, low density 0.1gcm3
- Snow accumulates layer on
layer - compaction. Each
new layer compresses
below, forces air out
converting to ice -
diagenesis
- Snow experiencing a winter's
accumulation and survives
summer melting is compacted to
density of 0.5gcm3 and is known
as neve. Increased density due to
increased pressure. Some melting
within snow, water re-freezes
and fills gap between individual ice
crystals.
- Over time with increasing depth, density
increases forming glacial ice - density
0.9cm3 (colder climate - longer to form
glacial ice as meltwater speeds up
process). Where wet snow, e.g. Alaska -
glacial ice within 5 years. Antarctica
150-200 years.
- Overlying weight increases-
glacial ice deforms, moves
outwards to area of lower
pressure downhill and moves -
glacier.
- Overlying weight increases-
glacial ice deforms, moves
outwards to area of lower
pressure downhill and moves -
glacier.
- Over time with increasing depth, density
increases forming glacial ice - density
0.9cm3 (colder climate - longer to form
glacial ice as meltwater speeds up
process). Where wet snow, e.g. Alaska -
glacial ice within 5 years. Antarctica
150-200 years.
- Snow experiencing a winter's
accumulation and survives
summer melting is compacted to
density of 0.5gcm3 and is known
as neve. Increased density due to
increased pressure. Some melting
within snow, water re-freezes
and fills gap between individual ice
crystals.
- Snow accumulates layer on
layer - compaction. Each
new layer compresses
below, forces air out
converting to ice -
diagenesis
- Snow falls - traps air, low density 0.1gcm3
- Formation of permanent
snow field first stage in
formation of glacier (at high
altitudes in mountains or high
latitudes where winter
accumulation exceeds
summer snow melt)
- As climate gets colder more
snow - permanent snow line
forms as snow accumulates on
ground
- Ice is derived from compacted snow
(also some sleet, hail, rain which
freezes on top/inside glacier)
- Summary of the glacial system
- Inputs
- Energy (solar and kinetic)
- Precipitation
- Moraine
- Energy (solar and kinetic)
- Processes/transfers
- Ice movement
- Erosion (abrasion/plucking)
- Transportation
- Deposition
- Ice movement
- Outputs
- Ablation (melting)
- Sediment
- Calving (breaking
off of chunks of ice
at end of glacier)
- Ablation (melting)
- Inputs
- Change in position of a glacier over a year - advance and retreat
- Glacier system constantly adjusts to change in
balance between accumulation and ablation -
known as mass balance
- Accumulation - net
gain in an ice mass,
dominant in upper
parts of glacier
(accumulation zone)
Inputs leading to
accumulation - snow,
refreezing of
meltwater,
avalanches, rockfalls
- Ablation- net loss of water,
dominant in lower parts of
glacier - ablation zone.
Higher annual temperatures.
Outputs include melting
(formation of meltwater
streams), calving.
evaporation and sublimation
(ice straight to gas without
turning into liquid)
- Over the course of a year
glaciers expand and contract
as mass balance differs
according to season. Whether
a glacier advances or retreats
depends on average mass
balance over year: annual
budget or net balance.
- The balance year for calculating: time
taken from minimum mass of one year
to minimum mass next year (autumn to
autumn - end of summer ablation)
- Positive mass balance is
where accumulation> ablation.
Net gain of ice normally case in
winter, glacier advances.
- Negative mass balance: ablation>
accumulation Normally case in spring and
summer
- The balance year for calculating: time
taken from minimum mass of one year
to minimum mass next year (autumn to
autumn - end of summer ablation)
- Glacier system constantly adjusts to change in
balance between accumulation and ablation -
known as mass balance
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