Lecture 4
GLACIAL AND ARID LANDSCAPES
Glacial
Landscapes
Glaciers are thick ice
masses that form over hundreds or thousands of years. The originate on land
from the accumulation, compaction and recrystallization of snow.
1.
1.
Alpine glaciers or valley glaciers, which are rivers of ice flowing
downhill in narrow ribbons. They start as snow fields in the high slopes of
mountains.
2.
2.
Ice sheets are enormous thick sheets of glacial ice that cover large
land mass. These glaciers are not confined to a channel/valley and flow out in
all directions.
o
o
Ice on slopes build to a great enough thickness; the ice begins to move.
o
o
Ice flows in two ways:
1.
1.
Plastic movement within the ice, occurs in the body of the ice above the
lowest portion of the glacier. Here the pressure over of the overlying ice is
such that the pressure causes plastic flow.
2.
2.
The ice mass slips along the ground, which is the lowest portion of the
glacier.
o
o
The uppermost 50 meters of glacier is referred to the zone of fracture,
because the ice is brittle (there is not enough overlying ice above to cause
plastic flow).
o
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Zone of Wastage is where net loss of the glacier occurs.
o
o
Zone of Accumulation is where snow accumulates and ice forms.
o
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Glaciers erode by plucking and abrasion.
o
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Plucking loosens and lifts blocks of rock.
o
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Abrasion grinds rock up producing rock flour and grooves in the rocks
called glacial
striations.
Some features of valley glaciers are: (Look these
terms up in the text or Internet)
o
o
Glacial troughs;
o
o
Hanging valleys;
o
o
Cirque;
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o
Aretes;
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o
Horns;
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Fiords.
Glacial Deposits
Drift is an all embracing term for sediments of
glacial origin.
There are two types of drift: 1) stratified
drift, which is sediment laid down by glacial melt water, usually well sorted,
and 2) till, which is sediment deposited directly by the glacier, usually
poorly sorted.
Glacier erratics are when boulders are found in
the till or lying free on the surface, if they are different from the bedrock
below.
Glacial
depositional features: when you
enter the glacial depositional features site scroll to Glacial Landforms.
Moraines
(lateral, medial and end moraines);
Outwash plain;
Valley train;
Kettle;
Drumlins;
Eskers;
Kames.
Arid Landscapes
Desert means deserted
or unoccupied.
o
o
Deserts can be found in lower latitudes between the Tropics of Cancer and
Capricorn.
o
o
Deserts can be found in areas of subtropical high (zones of high air
pressure).
o
o
Rain shadow areas are places that deserts can be found. The leeward
sides of mountains are much drier because air reaching the leeward side has
lost its moisture and clouds are less likely to form.
Water in the desert
o
o
Streams are ephemeral that is they carry water only in responses to
specific episodes of rainfall, usually flow for a few days or hours after a
rainfall episode.
o
o
Deserts lack an extensive system of tributaries and streams will die out
before reaching the sea.
Some desert features
are:
Wind erosion occurs
in the following manner.
o
o
Moving air is turbulent and is able to pick up loose debris and
transport it to other locations.
o
o
The velocity of the wind increases with the height of the above the surface.
o
o
The wind carries sediment in suspension and as bed load, similar to a
stream.
o
o
The wind erodes by deflation, that is, the lifting and removal of loose
material.
Wind deposits
Types of deserts: there are various
types of deserts throughout the
world. Each desert is different
in terms of geology, biology, and processes.
Click on the link: types
of deserts for more information.