4.5GLACIER

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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