Glaciers - Features

7/27/2019 Glaciers - Features

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The Illustrated History of

GLACIAL 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 calledMORAINES. 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 deeperand 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 asthe 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. Inthe process these rocks tumbled and

rolled becoming SCRATCHEDand

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 theirorigins.

Such rocks are called

ERRATICS. An erratic is a

boulder that was transported

to its present location and is

generally unrelated to theunderlying bedrock.

The ERRATIC on the left was depositedin Central Park.


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Some erratics come to rest

in strange places.

Some are deposited closer to homelike 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 verydeep and narrow parallel

lakes scooped out during

the last ices age.

The glaciers movement

from north to south

accounts for theN-S orientation of these

bodies of water.

Lakes like these are found

all over the world wherever

the last continental icesheet scraped and

scarred the land.


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If the U-shaped

depression

carved by the glaciers

reaches all the way tothe sea it is often

referred to as a fjord.

A fjord is a long, narrow

salt water bay carved by

glaciers and they arefound 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 theyleave 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 valleys2) Parallel grooves in bedrock

3) Scratched and polished boulders

4) Erratics5) Long, deep, glacial lakes

6) Unsorted sediments

7) Drumlins

8) Kettle lakes

Learn these terms. Whenever you see one on a test o r

on th e 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 fasterthan 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 justover half a century.

In that time it has

retreated over 20

km and it continuesto get smaller every

year.

People may debate

the causes ofglobal 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

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Glaciers - Features