1
Unit 5 Chapter 17
Glaciers
Section 1 Glaciers: Moving Ice
Glacier - __________________________________________________
_____________________________________________________
Formation of a Glacier
Snow line:
A snow line ____________________________________________.
This means that in higher latitudes, the snow line can be at sea level, but at
the equator, the snow line will be on a mountaintop. A mountain that gets
covered in snow during the winter, but melts all the way down in the
summer, does not have a snow line.
Example:
1.
The mountains we ski on in the winter (_______________________),
they offer summer sports like hiking and other things.
2.
The mountains of Colorado have a high snow line they have snow
even in summer.
2
How glaciers form:
In order for a glacier to form you need
1. Cold temperatures year round
2. More snow precipitating than snow that melts
3. Buried snow becomes more & more compact
4. It starts to re-crystallized into rough granular ice know as firn.
5. The weight of the material on top compresses more & more turning
the firn into solid ice.
6. The weight of the snow & firn causes the ice to move with gravity,
downward & outward.
Types of Glaciers
Valley (Alpine) Glacier - a glacier that covers a mountain valley (very big)
They occur in all parts of the world where mountains reach above the
snow line; except in Australia. The smallest glacier can be approximately 2
kilometers long. The largest ones are in Alaska one of them is Muldrow
Glacier in Denali National Park. It is approx. 56 kilometers long. The
Himalayas have very large valley glaciers also.
Continental Glacier – __________________________________
They are roughly circular or oval in shape. They occur in areas where
all of the precipitation that falls in snow. Summer is not warm enough to
melt it either. This forms landmasses almost entirely covered with ice and
snow except for the highest mountain peaks, known as Nunatak.
___________________ – approx. 1.7 million Km2, approx 3 Km2 thick
3
_____________ – approx 13.7 million Km2, approx 5 Km2 thick, (the ice may
descend more than 2 Km below sea level at the coast.)
Movement of Glaciers
1.
2.
3.
4.
5.
6.
They always move forward, never backward
Heavy winters with little melting will cause them to move fast
Warm summers cause then to recede (rate of melting is more rapid).
They move like a bulldozer by grabbing and pushing everything in its way.
They can move a few centimeters or thousands of centimeters in a day.
The speed is rapid at the surface, but faster in the center due to the
friction
4
Basal Slip
Basal Slip –
__________________________________________________________.
This creates a slushy layer allowing the glacier to move at the base. It
also moves in smaller areas by melting and then refreezing.
Internal Plastic Flow
________________ – Occurs when the pressure of the ice & snow, the
grains change shape and become flat. This flatter shape makes the
glacier “flow” forward.
Features of Glaciers
Crevasses – _________________________________________________
__________________________________________.
Ice Front – _____________________________. The place where it moves
as fast as it melts. If the glaciers rate of melting is more than its rate of
movement, the ice front recedes.
Calving – when part of the glacier reaches the coast, it breaks off and
becomes an ______________________.
Ice Shelves – when the ice front overhangs into the water. The largest one
is the Ross Ice Shelf, off the coast of Antarctica. It is 100’s of
5
kilometers wide.
In 2000 an iceberg broke off the size of
___________________ (approx 295 kilometers long and 37
kilometers wide).
Section 2 Glacial Erosion and Deposition
Many of the landforms and features of areas in Canada and Northern
America were created by erosion and deposition from glaciers.
Glacial Erosion:
Material movement – ____________________________________
Striation is the parallel scratches left on rocks after a glacier passes. It
shows the general direction of the movement of the ice.
Glaciers leave different kinds of features due to the way they move, melt and
deposit. Rivers and lakes can be formed by them.
Landforms Created by Glacial Erosion
_________________ – a semi-circular basin at the head of a glacial valley
where the valley glacier began.
6
_______________– when three or more cirques cut the same peak it forms
a pyramid-shaped peak (the Matter horn in Switzerland & Italy).
____________- sharp pointed mountain peak formed by multiple cirques
___________________ – the glacier smoothes the side of an outcrop and
leaves the other side rough.
7
_______________________
Areas in the US like the Rocky Mountains & the Sierra Nevada of California
have valley glaciers. These glaciers produce sharp mountain peaks.
Glacial trough – _____________________, the glacier removes the valley
and the walls.
_______________ – when a cirque fills in with water (Lake Louise in the
Canadian Rockies)
Hanging Valleys – a valley carved out by tributary glaciers. A river that flows
from these valleys are called hanging waterfalls. Yosemite
Falls in California.
Erosion by Continental Glaciers
Continental Glaciers
Unlike valley glaciers, continental glaciers grind down mountain peaks. The
are very familiar in the Northeast US, Canada, Iceland and the
Antarctic.
8
Nunatak
Glacial Deposits
Rock Flour – ____________________________________.
Glacial drift – a name for any glacial deposit
Stratified drift – is material that has been sorted and deposited inlayers by
steams flowing from the melting ice.
Till – unsorted rock material that is left by the glaciers movement
Erratic – large glacial boulders transported from somewhere else
9
Ventifact – wind and sand smooth rocks
Drumlins – canoe shaped hills formed when a glacier moves over earlier
glacial moraines; shows direction of the movement (Eastern Wisconsin
and West & Central New York)
Kames – small cone shaped hills of layered sand and gravel
Till Deposits
Moraine – is the accumulation of glacial till; glacial garbage
Terminal Moraine – a pile of material left at the ice front. Long Island has
two terminal moraines. The terminal moraines mark the furthest
advance of a glacier.
10
Lateral- forms along the sides of the glacier, runs the same direction as the
flow
Medial – when two or more glaciers combine, the combined lateral moraines
form this
Recessional – when other end moraines form behind the end moraine.
Outwash Plains
Outwash – sand deposits made from glacial streams (melted ice)
11
Outwash plains – Glacial Alluvial Fans that overlap each other.
Most
of Long Island is an outwash plain. We have
_______________________________________________.
Kettles
Kettle Holes – circular holes in the ground at terminal moraines
Step 1 – Large blocks of ice break off of the front of a glacier. As it
moves it gets buried.
Step 2 – the ice melts and leaves a hole. Water may re-fill the hole
making it a kettle lake (Lake Ronkonkoma, Wildwood Lake,
Scuttle hole road)
the
12
Esker
Esker – long winding glacial deposit formed from internal glacial streams
Glacial Lakes
Finger Lakes – Long narrow deposits formed by glacial erosion and
deposition
Lake George – Moraine damned lake
Kettle Lakes – found in Minnesota (land of 1000 lakes), Michigan,
Wisconsin, NY and New England.
Formation of Salt Lakes
The Great Salt Lakes in Utah formed because of the streams were cut off by
the deposition of glacial material. These streams became lakes which than
evaporated some of the water leaving large salt mineral deposits behind.
They now are considered some of the saltiest lakes around.
History of the Great Lakes
13
Section 3 Ice Ages
Ice Age – a long period of climate cooling during which the continents are
glaciated repeatedly.
Earliest – _____________________________________
Latest – ______________________________________
Glacial and Interglacial Periods
Glacial period is when glaciers advance
Interglacial periods are when glaciers have retreated. We are in
this period of retreat.
Glaciation in North America
How the Glacier Formed Long Island.
About 1,000,000 years ago
1. The temperature was very cold
2. Ice Sheets formed over Central and Eastern Canada and Northern
Scandinavia. In North America they formed over the area where the
Mississippi River and Ohio River meets and eastward to Long Island.
3. There is evidence that the glacier advanced and receded about 4 times.
We have evidence that on Long Island it occurred 2 times:
1.
The first one extends from Brooklyn to Montauk (225kms)
2.
The second is from Nassau County to the North Shore
14
Glaciation in Eurasia and the southern hemisphere
Ice sheets centered in the Baltic Sea which spread over Germany, Belgium
and the Netherlands, west over to Great Britain and Ireland; Eastward to
Poland and Russia; to the Alps and the Himalayas.
Causes of Glaciation
Glacial Causes:
The last time glaciers retreated was about 11, 000 years ago.
Causes:
1. Change in the position of the land on the earth’s crust (former position of
the continents)
2. Change in weather patterns (climate)
3. Change in the amount Carbon Dioxide in the atmosphere
15
4. Change in the amount of solar energy being absorbed by the land and
reflected by the atmosphere.
5. Mountain building may have caused more land area above the snowline.