The Illustrated History of GLACIAL EROSION

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The Illustrated History ofGLACIAL EROSION
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This is a glacier. Actually its several glaciers
coming together to form a larger one.
The glaciers are hundreds of feet thick. They
have enormous mass. They flow downhill due to the
FORCE OF GRAVITY.
These are VALLEY or ALPINE glaciers. They flow in
valleys between mountains. They are small when
compared with CONTINENTAL glaciers which cover
entire continents. Antarctica is covered by a
continental ice sheet.
The dark bands in the glacier are rocks ripped
from the sides of the mountains as the glaciers
flow. The dark bands are called MORAINES. The
rock will be carried to the point where the
glacier melts and then it will be deposited. A
glacier is a rock conveyor belt.
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Heres another view of a glacier showing the
Terminal Moraine. It forms at the point at which
the rate of melting is equal to the flow of ice.
You can also see a Medial Moraine in the middle
of the glacier.
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The V-shaped valley seen to the right is typical
of stream or water erosion. As the stream flows,
its cutting tools which are the rocks and
stones it carries, cut deeper and deeper into the
streambed forming a V-shape. If the climate gets
colder and the valley fills with ice the glacier
will rip rocks from the sides as well as the
bottom of the valley. This will widen the valley
and change its shape.
To the left is a wide U-shaped valley which is
typical of glacial erosion. V-shaped
streams U-shaped glaciers
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Another view of a typical U-shaped glacial valley.
And another...........................
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The power of glaciers can be seen in this photo
of 'El Capitan' aka Half Dome mountain in
Yosemite Valley in California. As glaciers moved
through this valley they sliced this solid
granite mountain in two and scooped out
the U-shaped valley to the left.
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As glaciers flow, the rocks embedded in the ice
cut deep PARALLEL GROOVES in the bedrock beneath.
When the glaciers melt these parallel grooves
remain as evidence that the glaciers were
there. The picture to the right shows
bedrock exposed at the Bronx Zoo.
Above more parallel grooves and scratches in
exposed bedrock.
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Sometimes the grooves are very deep and dramatic
such as these from the Peruvian Andes
(left).........
or these (right) known as Kelleys Grooves found
on Kelleys Island, Ohio.
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These rocks were embedded in the ice at the
bottom of a glacier. As the glacier moved over
bedrock it was rocks like these that cut the
parallel grooves. In the process these rocks
tumbled and rolled becoming SCRATCHED
and POLISHED.
SCRATCHED and POLISHED boulders are evidence of
glacial erosion.
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Unlike streams or rivers glaciers can carry
enormous blocks of stone for many, miles. When
the glaciers melt these rock are left stranded
far from their origins. Such rocks are called
ERRATICS. An erratic is a boulder that was
transported to its present location and
is generally unrelated to the underlying bedrock.
The ERRATIC on the left was deposited in Central
Park.
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Some erratics come to rest in strange places.
Some are deposited closer to home like this
boulder in Eastport.
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This is a satellite view of the Finger
Lakes region of New York State. The finger lakes
are very deep and narrow parallel lakes scooped
out during the last ices age. The glaciers
movement from north to south accounts for the
N-S orientation of these bodies of water. Lakes
like these are found all over the world
wherever the last continental ice sheet scraped
and scarred the land.
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If the U-shaped depression carved by the glaciers
reaches all the way to the sea it is often
referred to as a fjord. A fjord is a long,
narrow salt water bay carved by glaciers and they
are found in many countries all over the
world. The photo was taken at Misty Fjords in
Alaska.
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The material transported by a glacier is called
TILL. When the glacier melts the till is
deposited in a pile. There is no sorting as
occurs when a stream slows. UNSORTED SEDIMENTS is
good evidence of glacial deposition.
Above and to the right are pictures of unsorted
glacial till. Material from fine silt to large
boulders are mixed together randomly. You live
on unsorted glacial till since Long Island is
composed completely of glacial material.
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Sometimes the glacial till is deposited in mounds
or hills. These are called DRUMLINS. The
drumlins above are found in Scotland but similar
features are found all over the northern
hemisphere. Often drumlins are so large that they
cannot be appreciated for what they are except
when photographed from high altitudes.
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A drumlin in the midwest.
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As glaciers retreat (melt) huge blocks of ice may
remain buried in the earth. As these blocks
gradually melt they leave deep depressions which
fill in with water forming "KETTLE LAKES" such as
those seen above. Kettle lakes represent more
evidence that a region has undergone glaciation.
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A summary of glacial features
1) U-shaped valleys 2) Parallel grooves in
bedrock 3) Scratched and polished boulders 4)
Erratics 5) Long, deep, glacial lakes 6) Unsorted
sediments 7) Drumlins 8) Kettle lakes
Learn these terms. Whenever you see one on a test
or on the regents the answer is always "GLACIERS".
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Glaciers are an endangered species. This is the
Muir glacier in Glacier Bay, Alaska photographed
in 2007.
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The Muir Glacier is retreating rapidly. Ice is
melting faster than new ice can replace it. The
arrows show where the glacier was just a few
years ago. As it melts it exposes rock that
appears lighter because it hasnt had time
to weather.
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These views show how the Muir Glacier has changed
in just over half a century. In that time it has
retreated over 20 km and it continues to get
smaller every year. People may debate the causes
of global warming but the evidence is clear. The
Earth IS warming.
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This is the Mendenhall Glacier in Juno, Alaska.
The picture was taken in 2007. If these people
had been standing here in 1987 they would have
been under 65 feet of ice.
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Lastly, a very quick review of essential terms
that are likely to appear on the
regents..............
What kind of sediments do glaciers produce?
UNSORTED
What kind of valleys are associated with glaciers?
U-SHAPED
What term applies to a boulder deposited by a
glacier?
ERRATIC
What do glaciers do to the rocks they pass over?
They cut LONG,PARALLEL GROOVES
What evidence indicates that a rock was
transported by a glacier?
It may be SCRATCHED and POLISHED