Download The Illustrated History of GLACIAL EROSION

The Illustrated History of
GLACIAL EROSION
This is a glacier. Actually
it’s 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.
Here’s 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.
The V-shaped valley seen to the
right is typical of stream or water
erosion. As the stream flows, it’s
‘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 it’s
shape.
To the left is a wide
U-shaped valley which
is typical of glacial
erosion.
V-shaped = streams
U-shaped = glaciers
Another view of a typical
U-shaped glacial valley.
And another...........................
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.
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.
Sometimes the grooves are
very deep and dramatic such
as these from the Peruvian
Andes (left).........
or these (right) known as Kelley’s
Grooves found on Kelley’s Island,
Ohio.
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.
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.
Some erratics come to rest
in strange places.
Some are deposited closer to home
like this boulder in Eastport.
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.
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.
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.
Long Island New York is
composed completely of
glacial material.
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.
A drumlin in the midwest.
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.
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
This is the Muir glacier in Glacier Bay, Alaska
photographed in 2007.
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 hasn’t had time to
weather.
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.
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.
Lastly, a very quick review of essential terms.
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