GLACIERS

GLACIERS

• Just 15,000 years ago, up to 30% of Earth’s land was covered by glacial ice.

GLACIERS

• During this time period, the earth was just coming out of an ice age.

• This is simply a period of time when much of earth’s land is covered with ice.

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• Sheets of ice that were thousands of meters thick carved out places like Long Island, Cape Cod and The Great Lakes.

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• Today, glaciers still cover about 10% of the earth’s land area.

• In these areas they are still sculpting the landscape.

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• Glaciers are formed in areas where more snow falls in the winter than melts in the summer.

• The snowline is the lowest elevation that remains covered with snow all year.

GLACIERS• At the poles, this is at sea level, but at places

near the equator, it is at or near the peaks of mountains.

• The more snow that is packed on the top of old layers, the more pressure on those lowest layers.

• The lowest layers recrystallize into large ice crystals.

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• Gravity pulls glaciers downhill and as they do, they accumulate, transport, and deposit sediment.

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• Valley glaciers are one type of glacier.• This is a stream of ice that flows between

steep rock walls from a place near the top of the mountain valley.

• Basically put, they flow through a river valley.

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• Another type of glacier is called an ice sheet.• They flow in all directions from one or more

centers and they cover all but the highest land.

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• Ice sheets are sometimes called continental ice sheets because of the large amount of land they occupy.

• They are gigantic compared to valley glaciers.

GLACIERS• Today, there are two remaining ice sheets in

the world today.• Combined, they cover about 10% of Earth’s

land area.• One covers about 80% of Greenland.• The other covers Antarctica, in some places

4300 meters thick!• That’s nearly ten Empire State Buildings

stacked up!

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• The Antarctic Glacier counts for about 80% of the world’s ice, and holds nearly 2/3 of the Earth’s fresh water.

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• The movement of glaciers is referred to as glacial flow. There are two types of this…– Plastic Flow– Basal Slip

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• Plastic flow is when the entire glacier begins to distort or change shape.

• It does this because of the enormous pressure.

• This usually begins about 50 meters below the ice surface

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• Basal slip is when a glacier simply slides along using its own melt to make it slippery.

GLACIERS• Different glaciers move at different speeds.• Some move so slowly that trees and other

vegetation can grow on them!• Some can advance several hundred meters

per day!• Some alternate between rapid movement and

no movement.

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• Glaciers are constantly gaining and losing ice.• The zone of accumulation at the head of a

glacier is above the snow line.• The zone of wastage is below the snow line

and any ice or snow here is lost to melting.

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• The glacial budget is the balance or lack of balance between the accumulation and wastage.

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• Glaciers cause glacial erosion as you well know!!!

• What are glacial erratics?

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• There are many types of glacial erosion.• One type is called plucking.• This is when rock and other sediment is pulled

up by glaciers and carried to another place.

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• Another type of glacial erosion is called glacial abrasion.

• This simply scrapes the land smooth as it slides along…much like sandpaper!

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• The rate of glacial erosion is highly variable.• Factors that effect it are…– Rate of Glacial Movement– Thickness of Ice– Shape, Abundance and Hardness of Affected Rock– Type of Surface below Glacier

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• Glacial Troughs are the U-shaped valleys created by moving glaciers.

• Cirques are bowl-shaped depressions at the head of a glacial valley that is surrounded on three sides by steep rock walls.

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• Arêtes are peaks that are made when two cirques are very close creating a sharp ridge.

• Horns are when several cirques surround a large mountain.

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• A new term we have for glacial erratics is glacial drift.

• There are two types this…– Till– Stratified Drift

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• Till is when an object is simply dropped when a glacier melts.

• Stratified drift is when a layer is laid down over a long span of land.

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• Glaciers are responsible for a large number of depositional features. These include…– Moraines– Outwash Plains– Kettles– Drumlins – Eskers

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• Moraines are the layers or ridges of till left by glaciers.

• Outwash Plains are sediment ramps that result from an ice sheet.

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• Kettles are when blocks of stagnant ice melt leaving a pit filled with water.

• Drumlins and Eskers are hills made entirely of till.