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.
GLACIERS
• Today, glaciers still cover about 10% of the
earth’s land area.
• In these areas they are still sculpting the
landscape.
GLACIERS
• 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.
GLACIERS
• 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.
GLACIERS
• 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!
GLACIERS
• The Antarctic Glacier counts for about 80% of
the world’s ice, and holds nearly 2/3 of the
Earth’s fresh water.
GLACIERS
• The movement of glaciers is referred to as
glacial flow. There are two types of this…
– Plastic Flow
– Basal Slip
GLACIERS
• 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
GLACIERS
• 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.
GLACIERS
• 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.
GLACIERS
• The glacial budget is the balance or lack of
balance between the accumulation and
wastage.
GLACIERS
• 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
GLACIERS
• Moraines are the layers or ridges of till left by
glaciers.
• Outwash Plains are sediment ramps that
result from an ice sheet.
GLACIERS
• Kettles are when blocks of stagnant ice melt
leaving a pit filled with water.
• Drumlins and Eskers are hills made entirely of
till.