Glaciers (Ch. 15)
Glaciers (Ch. 15)
What you should know:
Ch. 15.1: glacier, snow line, firn, valley glacier,
continental glacier, ice cap, ice sheet
Ch. 15.2: Crevasse, ice front, calving, till, moraine,
striations, glacial valley
Ch. 15.3: outwash, drumlins, erratics, outwash plain,
esker, kame, kettle lake
Ch. 15.4: Evidence for ice ages
And relating it all to Minnesota’s glacial past
• Only 3% of earth’s water is fresh. Of that, 68.7%
(about 2/3) is frozen in icecaps and glaciers.
• That means that about 2% of earth’s water is
frozen.
Image from USGS http://ga.water.usgs.gov/edu/earthwherewater.html
Glaciers – How they form.
How do glaciers form?
• Glaciers can form anywhere on earth where air
temperatures are cold enough to have permanent snow
cover – or in other words these areas are above the
“snow line”
•To the right is a graph of
snow line elevation vs.
latitude. Is modern day
Minnesota above or below
the snow line?
•What would our elevation
have to be for us to be
above the snow line?
Irondale
Image from your textbook
Glaciers – How they form
• Buried snow becomes compressed and turns
into granular ice material (kind of like a snow
cone) – called “firn”
• If enough firn accumulates it can turn into a
valley glacier (in mountains) or continental
glacier (over vast inland areas)
• A glacier of less than 50,000 km2 is called an
ice cap
• Greenland and Antarctica are examples of
places currently with continental glaciers (the
background picture is a photo of Greenland)
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Glaciers (Ch. 15)
An Alaskan valley glacier (photo by USGS)
Glaciers – How they move.
• The ground up material the glacier creates is
called “till” (most of MN is covered in till!)
• When the glacier stops, it leaves a ridge of
till at the ice front, called a “moraine”
• To us, a moraine looks like a long ridge of
till
• As the glacier moves past bedrock, it leaves
scratches called “striations”. These
scratches point in the direction the glacier
was flowing
Glaciers – How they move.
When glaciers move…
• Glaciers can move by flowing like silly putty (due
to their own weight and gravity) – this is called
“plastic flow”
• Glaciers can also move by sliding along their base
– this is called “basal slip”. Basal slip can be sped
up by liquid water forming along the base.
• The forward edge of the glacier is called the “ice
front”
• The ice front plows up rock and sediment as it
moves, like a bulldozer
Glacial Deposits
• Discuss vocabulary
pictured here
Left: image from ND Geol. Survey (Dahlen, ND)
Below: image from your textbook
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Glacial Deposits
• Discuss
vocabulary
pictured here
Aerial view of drumlin
field, Wadena, MN
Esker – formed
by stream
under glacier
Left: images from
http://www.winona.edu/geology/MRW/Qu
aternary.htm
Below: image from your textbook
Narrow end of
drumlin points
in direction of
movement of
glacier
Earth 20,000 Years Ago
Glaciers – Ice Ages
•Minnesota has experienced several glaciations, the last
of which ended about 11,000 years ago
•Map to the right shows maximum extent of the last ice
age (14,000 yrs ago), covering nearly all of Canada, and
large parts of many northern states. (MN Geol. Survey)
An ice age is an long
period of extensive
glaciation.
Glaciers – Ice Ages
•Causes of ice ages (See your text – page 331-332)
•Changes in position of the Earth relative to the
sun
•Changes in atmospheric carbon dioxide levels
•Changes in the positions of Earth’s landmasses
•Changes in the amount of solar energy reaching
the earth’s surface
•A combination of the above
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Glaciers in Minnesota
Farthest extent of the last glaciation of Minnesota is pictured below/right – 14,000
years ago. (MN Geol. Survey)
Satellite view shows the how these influenced the topography of Minnesota
Glaciers in Minnesota
By 11,000 years ago the glaciers had retreated into Canada, leaving behind
massive lakes. (image to the right from MN Geol. Survey)
• Can you match the
pattern of the
glacial lakes and
current topography?
• Can you match the
pattern of the ice lobes
and current
topography?
Glacial Deposits
• Old River Valleys in the Twin Cities
Can you match the patterns in the map on the left
with the location of lakes on the right?
Glacial Deposits
• Many of you live on a glacial outwash plain – the
Anoka Sandplain
• See maps below
• Fun fact: Around 4,000-8,000 years ago sand dunes
formed in places on the Anoka Sandplain
Image above from Google Earth
Image above from Minnesota’s Geology, Ojakangas and Matsch
Images from http://www.anokanaturalresources.com/
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Glacial Deposits
• We live only a few miles from a kame – the big hill in
the Army Ammunition Plant (Arden Hills)
Anoka Sandplain
Arsenal Kame
Animations
• McGraw Hill Glacier Animations
Cross-section of an Ice Sheet, Glacier Basics, Ice Flow in a Glacier, Crevasses on a Glacier
• Bering Land Bridge
• Formation of the Great Lakes
• Seasonal Migration of Snow Cover
Long Lake
Images from USGS
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