ES 4.5 PPT
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Transcript of ES 4.5 PPT
4.5GLACIER
S
Glaciers – Rivers of Ice
•A glacier is a large mass of moving ice.
▫Capable of eroding, moving, and depositing large amounts of material. Form in very cold regions where snow is
on the ground year-round.
▫Two main types of glaciers: Alpine Continental
Alpine Glaciers• An alpine glacier is a narrow,
wedge-shaped mass of ice forming in a mountainous regions and is confined to a small area by surrounding topography.▫ Examples are located in Alaska,
the Himalaya Mountains, the Andes Mountains, the Alps, and New Zealand. Form in valleys created by stream
erosion. Widen and straighten the valleys
into U-shaped, rather than V-shaped.
Continental Glaciers
• Continental glaciers are massive sheets of ice that may cover million of square kilometers, can be thousands of meters thick, and are not confined by surrounding topography.▫Also called ice sheets.
Exist only in Greenland an Antarctica.
Glacial Movement
•Move by two basic processes:
▫Basal Slip – the process causing the ice at the base of a glacier to melt and the glacier to slide.
▫Internal Plastic Flow – the process by which glaciers flow slowly as grains of ice deform under pressure and slide over each other.
Features of Glaciers
• An area where an ice sheet is resting on open water is called an ice shelf.▫ When pieces of the ice shelf break off, they are called
icebergs.
Glacial Erosion• Like rivers, glaciers are agents of erosion.
▫The glacial processes that change the shape of mountains begin in the upper end of the valley where an alpine glacier forms. Cirque – bowl-shaped depression where glacial ice cuts
back into the mountain walls. Horn – sharp, pyramid-like peaks forming due to the
erosion of cirques.
Arete – jagged ridges forming between cirques.
Glacial Erosion• A stream or river forms the V-
shape of a valley.
▫ As a glacier scrapes away a valley’s walls and floor, the original V-shape changes. U-shaped Valley – valley formed
when a glacier erodes a river valley from its original V shape to U shape.
Hanging Valley – smaller glacial valley joining the deeper main valley when the ice melts; when a stream flows from a hanging valley, a waterfall forms.
Glacial Deposition• Glaciers are also agents of
deposition.▫ Large rocks transported from a
distant source by a glacier are known as erratics.
• The general term for all rock material that is carried and deposited by a glacier is known as glacial drift.▫ Unsorted glacial drift deposited
directly by a melting glacier is called till.
▫ A glacial deposit sorted into layers based on the size of the material within it is called stratified drift.
Glacial Deposition• Landforms resulting from a glacier depositing till are
called moraines. Lateral moraine: deposited along the sides of an alpine
glacier, usually as a long ridge. Medial moraine: form when the lateral moraines of
alpine glaciers meet. Ground moraine: unsorted materials left beneath the
glacier when the ice melts. Terminal moraine: small ridges of till deposited at the
leading edge of a melting glacier. Drumlin: long, low, tear-shaped mounds of till.
Outwash• An outwash plain is a deposit of
stratified drift that lie in front of a terminal moraine.▫ Sometimes, a block of ice is left in the
outwash plain when a glacier retreats. As the ice melts, sediment will build
up around the block of ice, and a depression in the glacial drift deposit called a kettle forms. Commonly fill with water to form
kettle lakes.
• When continental glaciers recede, eskers – long, winding ridges of gravel and sand – may be left behind.
Kettle Lake in Dundee, Wisconsin
Esker in NW Manitoba, Canada