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Mind Map by laura southwell, updated more than 1 year ago
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Glaciation
- Ice ages
- An Ice Age is a period of
time in which part of the
surface of the Earth is
covered in ice permanently.
- The last ice age was called the Pleistocene age (not plasticene!) and it began
approximately 2 million years ago. We are still (technically) in the
Pleistocene age. The pleistocene age's peak was around 18,000 years B.P.
(before present; actually means before the year 1950) and at this point, 30%
of the Earth's surface was covered in ice permeanently. During this time,
Earth's mean temperature fluctuated significantly between warm periods,
known as "interglacial periods" and cold periods, known as "glacial periods".
Fom both ice cores and deep sea sediment, we can tell that there have been
around 20 cold periods. During the Pleistocene age, the UK was covered in
2-3km of solid ice.
- An Ice Age is a period of
time in which part of the
surface of the Earth is
covered in ice permanently.
- The amount of ice on Earth depends on
the glacial budget; the glacial budget is
the net result of accumulation and
ablation. Accumulation is basically the
amount of precipitation and moraine are
inputted into the glacial system, and
ablation is how much is lost to global
warming, friction and other factors.
- Current global ice cover
- Ice now covers only
10% of Earth on a
permanent basis. This
ice is found in 2 main
areas, the first being
areas of high latitude
(above 66° south or
north) and the second
being areas of high
altitude (high in the
mountains).
- An ice sheet is an area of
ice with an area of 50,000
km² or over. There are just
two large ice sheets left on
Earth; the Greenland ice
sheet and the Antarctica ice
sheet. Both are declining in size.
- Valley glaciers are found
in the Alps (Europe), the
Himalayas (Asia), the
Andes (South America)
and also in New Zealand;
glaciers are found in all
of Earth's continents and
in 47 countries.
- The Antarctica ice sheet covers
14 million km² and conatins
90% of Earth's fresh water. It is
in places several kilometres
thick.
- The Greenland ice
sheet covers an area of
1.7 million km² (80% of
Greenland!)
- Ice now covers only
10% of Earth on a
permanent basis. This
ice is found in 2 main
areas, the first being
areas of high latitude
(above 66° south or
north) and the second
being areas of high
altitude (high in the
mountains).
- What is ice?
- Many people think of ice as frozen water, but in
glaciation, that is incorrect. In glaciation, ice is
supercompressed snow. The ice is formed by the
following process:
- When snow falls to the ground, there are pockets of air
between the crystals. Over time, as more snow falls every
year, the crystals become compressed under the weight of
the new snow and the crystals stick together to form a
form of granulated snow which is stuck together; this is
called firn. Once all air has been completely squeezed out
of the firn and there are no more air spaces left, this is ice.
- When snow falls to the ground, there are pockets of air
between the crystals. Over time, as more snow falls every
year, the crystals become compressed under the weight of
the new snow and the crystals stick together to form a
form of granulated snow which is stuck together; this is
called firn. Once all air has been completely squeezed out
of the firn and there are no more air spaces left, this is ice.
- Many people think of ice as frozen water, but in
glaciation, that is incorrect. In glaciation, ice is
supercompressed snow. The ice is formed by the
following process:
- Features of glacial erosion
- A diagram to show features of glacial erosion. A Pater noster lake is one of a series of glacial lakes
connected by a single stream or a braided stream system.
- Corries/Cwms/Cirques
- Snow accumulates in a nivation hollow. As more snow falls, gradually
the snow becomes compressed and the air is squeezed out to become
firn. Over thousands of years the firn becomes a glacier. Erosion and
weathering by abrasion, plucking and freeze-thaw action gradually
make the hollow bigger. Gravity can cause the ice trapped in the corrie
to move. This circular motion is known as rotational slip and can cause
the ice to pull away from the backwall creating a crevasse or
bergschrund. Plucked debris from the backwall causes further erosion
through abrasion which deepens the corrie. Some of this debris is
deposited at the edge of the corrie, building up the lip. These processes
create a characteristic rounded, armchair shaped hollow with a steep
back wall. When ice in a corrie melts, a circular lake is often formed at
the bottom of the hollow. This is known as a tarn.
- Snow accumulates in a nivation hollow. As more snow falls, gradually
the snow becomes compressed and the air is squeezed out to become
firn. Over thousands of years the firn becomes a glacier. Erosion and
weathering by abrasion, plucking and freeze-thaw action gradually
make the hollow bigger. Gravity can cause the ice trapped in the corrie
to move. This circular motion is known as rotational slip and can cause
the ice to pull away from the backwall creating a crevasse or
bergschrund. Plucked debris from the backwall causes further erosion
through abrasion which deepens the corrie. Some of this debris is
deposited at the edge of the corrie, building up the lip. These processes
create a characteristic rounded, armchair shaped hollow with a steep
back wall. When ice in a corrie melts, a circular lake is often formed at
the bottom of the hollow. This is known as a tarn.
- Arêtes and Pyramidal Peaks
- 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. A pyramidal peak is formed where three
or more corries and Arêtes meet. The glaciers have
carved away at the top of a mountain, creating a
sharply pointed summit.
- 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. A pyramidal peak is formed where three
or more corries and Arêtes meet. The glaciers have
carved away at the top of a mountain, creating a
sharply pointed summit.
- Glacial troughs, hanging valleys and truncated spurs
- Glaciers cut distinctive U-shaped valleys or troughs
with a flat floor and steep sides. The glacier widens,
steepens, deepens and smoothes V-shaped river
valleys. Glaciers also have tributaries. As the main
glacier erodes deeper into the valley, the tributary is
left higher up the steep sides of the glacier. These
U-shaped valleys ending with a water fall at the
cliff-face are called hanging valleys. When a river
erodes the landscape, ridges of land form in its
upper course which jut into the river. These are
called interlocking spurs. A glacier cuts through
these ridges leaving behind truncated spurs.
- Glaciers cut distinctive U-shaped valleys or troughs
with a flat floor and steep sides. The glacier widens,
steepens, deepens and smoothes V-shaped river
valleys. Glaciers also have tributaries. As the main
glacier erodes deeper into the valley, the tributary is
left higher up the steep sides of the glacier. These
U-shaped valleys ending with a water fall at the
cliff-face are called hanging valleys. When a river
erodes the landscape, ridges of land form in its
upper course which jut into the river. These are
called interlocking spurs. A glacier cuts through
these ridges leaving behind truncated spurs.
- Roche
Moutonnes
- Roche moutonnées often have steep,
jagged faces created by plucking on the far
(lee) side and a gradual incline which is
smoothed and polished by abrasion on the
other (stoss) end. It may have striations on
it indicating the direction of glacier
movement.
- Roche moutonnées often have steep,
jagged faces created by plucking on the far
(lee) side and a gradual incline which is
smoothed and polished by abrasion on the
other (stoss) end. It may have striations on
it indicating the direction of glacier
movement.
- A diagram to show features of glacial erosion. A Pater noster lake is one of a series of glacial lakes
connected by a single stream or a braided stream system.
- Valley glaciers
- A glacier is a system of inputs and outputs, as
well as stores and flows. The inputs mainly
occur in the zone of accumulaton in the form
of snow from precipitation and avalanches, as
well as moraine (sediment) from freeze-thaw
weathering The outputs mainly occur ikn the
zone of ablation, in the form of meltwater,
evaporation and moraine deposits.
- As with any system, the relationship between
the inputs and outputs alters the behaviour
of the glacier. We call the study of these
things the glacial budget. The budget or
balance of the glacier is usually a net gain or
a net loss over a 2-month period.
- If:
- Accumulation > ablation, snout of the glacier will advance (net gain)
- Accumulation = ablation, the snout of the glacier will remain in a state of equilibrium
- Accumulation < ablation, the snout of the glacier will retreat (net loss)
- Accumulation > ablation, snout of the glacier will advance (net gain)
- If:
- As with any system, the relationship between
the inputs and outputs alters the behaviour
of the glacier. We call the study of these
things the glacial budget. The budget or
balance of the glacier is usually a net gain or
a net loss over a 2-month period.
- A glacier is a system of inputs and outputs, as
well as stores and flows. The inputs mainly
occur in the zone of accumulaton in the form
of snow from precipitation and avalanches, as
well as moraine (sediment) from freeze-thaw
weathering The outputs mainly occur ikn the
zone of ablation, in the form of meltwater,
evaporation and moraine deposits.
- Glacial processes
- Abrasion
- Abrasion - rocks stuck in the ice grind away
the bedrock under the glacier
- Abrasion - rocks stuck in the ice grind away
the bedrock under the glacier
- Plucking
- Plucking - the base of glacier ice melts
due to pressure and friction. This allows
water to freeze into cracks in rocks, and
when the glacier moves it pulls out
chunks to leave a jagged surface. This
provides material for abrasion
- Plucking - the base of glacier ice melts
due to pressure and friction. This allows
water to freeze into cracks in rocks, and
when the glacier moves it pulls out
chunks to leave a jagged surface. This
provides material for abrasion
- Freeze-thaw weathering
- Freeze Thaw - water in cracks in the rock freezes
and expands forcing open the gap. When the ice
melts more water can get into the crack and
freeze again. After many cycles of freezing and
thawing lumps of rock are broken off the
surface.
- Freeze Thaw - water in cracks in the rock freezes
and expands forcing open the gap. When the ice
melts more water can get into the crack and
freeze again. After many cycles of freezing and
thawing lumps of rock are broken off the
surface.
- Abrasion
- Moraines
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