Transcript glacier_presentation_2004

Glaciers
We wouldn’t be here without them.
What are glaciers?
A Glacier is an accumulation of snow that is large enough to
survive the summer melt.
How do these large masses of ice move?
These large ice masses begin to move
down hill by gravity. It can move several
centimeters to several meters a year
depending on its size. The steeper the
slope or the warmer the temperatures the
faster the rate.
These glaciers will settle into lower lying
areas as they move.
The two types of glaciers we will talk about
are alpine glaciers and continental glaciers.
Alpine glaciers :
• Are found at high
elevations
• Are found at high
latitudes. (North or
South Pole)
• Move downhill into
valleys
• Carve out U-shaped
valleys
Why would high mountain tops be a good
place to find a glacier? What side of a
mountain in the northern hemisphere is more
likely to have the glacier?
• It is colder at the top of a mountain.
• The north side is in the shade all day.
Why is this glacier dirty?
It picks up the dark sediment as it moves over the landscape.
What will happen when a glacier rubs
against the side of the valley?
Material will be removed from the side
causing a lateral moraine.
Because there is friction on the sides of the
glacier, the middle is the fastest, just like a
river.
What happens when two alpine
glaciers meet into one valley?
• One large glacier will
form
• A section of unsorted
material will form in
the middle called a
medial moraine.
Medial moraines
What type of valley is formed from
an alpine glacier?
The U-shaped valley starts as a Vshaped river valley.
The glacier moves in.
When the ice melts, a U-shaped
valley is left behind.
U-Shaped Valley
What happens when glaciers meet water?
Icebergs are large pieces of glacier that break off into the
water.
Continental Glaciers are also known as ice sheets. These large
sheets can cover thousands of square miles and are
responsible for most of the features we see in New York State
and Long Island.
They are different than alpine glaciers
because they do not need to be at high
altitudes or on the north side of a
mountain
When continental glaciers move across the
landscape they pick up a lot of material and
move forward. This is called advancing.
When the glacier stops moving forward, they
will melt, this is called retreating.
The material left behind will be left in
unsorted piles called terminal moraines
Long Island was formed in this manner
Most continental glaciers have advanced
and retreated many times.
How was Long Island formed?
Unsorted piles of sediment called moraines were deposited
when the glaciers started to melt or retreat.
When a glacier moves it carries the
material from one place to another.
• This is called transported soil
Once any type of glacier moves over the landscape,
it leaves behind a path of deeply scratches rocks.
These scratches called striations are caused by rocks
already suspended in the glacier scratching the
ground rock by abrasion.
Striations
What causes these scratches or straitions in the rock?
Material trapped in the glacier is dragged over the
surface and scratches it.
Glaciers also drop unsorted material called till
into piles. Then the glacier advances over them.
These piles are called drumlins.
Drumlins
These piles are unsorted and unlayered
Deeper and steeper on the side the glacier came from,
usually they come from the north and move south.
As the ice passes it rips out large portions
of the ground. When the ice melts, these
holes fill with water. This other glacial
feature is called a Kettle Lake.
Lake Ronkonkoma is a kettle lake.
The ice sheet advanced to the where the middle of Long
Island is today.
The middle of Long Island is where you will find the
moraines. All areas south are called outwash plains
(flood plains), where the meltwater flowed.
These are areas where the landscape is flat and the area
is fine sediment. There are very few natural, large
boulders.
This sandy, silty, milky looking water is called outwash.
This material formed the land we live on today.
Outwash Plain
Remember we said the glaciers deposit material in
unsorted piles. This is because all different size
particles can be carried by a glacier.
Every once in a while we find large boulders that
don’t fit in with the surrounding material. These are
called Erratics.
Glacial erratics do not match the surrounding bedrock.
Here is the whole picture all together.
Why can’t you find any glaciers in New York State today?
The ice and snow all melts during the summer.
What is the difference between transported soil and
residual soil?
Transported soil was deposited by an agent of erosion.
What is a glacial erratic and why are they not found
around here?
A glacial erratic is a larger boulder left behind by a
glacier that does not match the surrounding bedrock.
You don’t find them around here because we are
located on an outwash plain and the meltwater was
not strong enough the carry the large rocks.