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Glaciers
Chapter 17
Vocabulary
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Glacier
Snowfield
Firn
Alpine glacier
Continental glacier
Basal slip
Internal plastic flow
Crevasses
Glacial grooves
Ice shelves
Icebergs
Cirque
Arête
Horn
Erratic
Glacial drift
17. Till
18. Moraine
19. Lateral moraine
20. Medial moraine
21. Ground moraine
22. Terminal moraine
23. Drumlin
24. Outwash plain
25. Kettle
26. Esker
27. Finger lakes
28. Ice age
29. Glacial period
30. Interglacial period
31. Milankovitch theory
I.Glaciers: Moving Ice
A. Formation of Glaciers
1. Glacier: large mass of
moving ice
2. Cycles of partial melting &
refreezing change the snow
into a grainy ice called firn
3. Pressure on deep layers of
snow & firn compresses the
ice grains
4. As this material continues to
build up, a glacier is formed
5. Glaciers move downslope or
outward under their own
weight
6. Size of a glacier depends on
the amount of snowfall
received & the amount of ice
lost
a. Several factors can affect
these amounts:
i. Differences in average
annual temperatures
ii. Varying amounts of
snowfall
b. Glaciers will get bigger
when snowfall > ice melt,
and smaller when snowfall
< ice melt
B. Types of Glaciers
1. Alpine glacier: narrow, wedge-shaped mass of ice that forms in a
mountainous region
a. Confined to a small area by surrounding topography
b. Exist in Alaska, Himalayas, Andes, Alps, New Zealand
2. Continental glacier: massive sheet of ice
a. May cover millions of square kilometers & be thousands of meters
thick
b. Not confined by surrounding topography -- free-moving
c. Currently only exist in Greenland & Argentina
C. Movement of Glaciers
1. Glaciers, like rivers, flow according to gravity -- downward!
a. Cannot move as quickly or move around obstacles like water can
b. Rates of glacial movement vary; in a year, some glaciers travel a few
centimeters, while others can move a kilometer or more
2. There are two processes of glacial movement…
a. Basal slip: process causing the ice at the base of a glacier to melt and
the glacier to slide
i. Weight of the ice in a glacier applies pressure that lowers the
melting point of ice
ii. Causes ice to melt where the glacier touches the ground
iii. Water mixes with sediment at the base of the glacier; acts as a
lubricant between the ice & ground
iv. Allows glacier to slide along the water-sediment mixture layer
b. Internal Plastic Flow: process by which glaciers flow slowly as grains of
ice deform under pressure and slide over each other
i. Rate varies for different parts of a glacier
ii. Rate is determined by the slope of the ground & the thickness and
temperature of the ice
iii. Edges of a glacier move more slowly than the center because of
friction with underlying rock
D. Features of Glaciers
1. Glaciers flow unevenly beneath the surface, causing regions of tension &
compression under brittle surface
a. This results in large cracks, crevasses, that form on the surface
2. Some parts of the ice sheets may move out over the ocean & form ice
shelves.
a. When tides rise and fall, large blocks of ice, icebergs, may break from
the ice shelves & drift into the ocean
II.Glacial Erosion & Deposition
**See Directed Reading Packet**
III. Ice Ages
A. Glacial & Interglacial Periods
1. Ice age: long period of climatic cooling during which continents are
glaciated repeatedly
a. There have been several ice ages in Earth’s history; most recent began
about 4 mya
2. An ice age consists of several glacial & interglacial periods
a. In a glacial period, climate is cooler & glaciers advance
i. In the most recent glacial period, ⅓ of Earth’s surface was glaciated
b. In an interglacial period, climate warms & glaciers retreat
i. We are currently in an interglacial period of the most recent ice
age
3. Glaciation in North America
a. Canada & mountainous parts
of Alaska were covered
b. Mountains in western US had
numerous small alpine
glaciers which combined to
form larger glaciers
c. Continental ice sheet covered
Hudson Bay region of Canada
down to the Missouri & Ohio
rivers
4. Glaciation in Eurasia & the
Southern Hemisphere
a. Continental ice sheet over
Germany, Belgium, the
Netherlands, Great Britain,
Ireland, Poland, & Russia
b. Alpine glaciers in Alps &
Himalayas
c. Continental ice sheet in
Siberia
d. Andes mountains & New
Zealand covered in
mountainous ice fields &
alpine glaciers
B. Causes of Glaciation
1. Milankovitch theory: over thousands of years, cyclical changes in Earth’s
orbit & the tilt of Earth’s axis occur; this causes changes in solar energy
reaching Earth’s surface, causing climatic changes
2. Periodic changes include:
a. Eccentricity: shape of Earth’s orbit; changes from nearly circular to
elliptical and back to circular every 100,000 years
b. Tilt of Earth’s axis varies between 22.2° and 24.5° every 41,000 years
c. Precession: circular motion of Earth’s axis; causes axis to change its
position in a “wobble”, completes a circle every 25,700 years
3. Biological Evidence of Glaciation
a. Shells of marine animal fossils
i. Amount of dissolved oxygen in shells
ii. Temp > 8° C – shells coil to right
iii.Temp < 8° C – shells coil to left
4. Other Explanations for Glaciation
a. Changes in solar energy caused by varying amounts of energy produced
by the sun
b. Changes in solar energy caused by volcanic dust blocking sun’s rays