glaciers october 21st, 2009. pre - activity knowledge check on the note sheet provided, answer the...
TRANSCRIPT
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GlaciersOctober 21st, 2009
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Pre - Activity Knowledge Check
on the note sheet provided, answer the true or false questions
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Glacial Power
http://www.youtube.com/watch?v=cIBFAke90SI
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Glaciation of Canada
at one time, ice sheets covered much of North America
the last ice age ended approximately 10, 000 years ago, at which time 30% of the land was covered and glaciers were up to 1000 km wide (about the distance from Montreal to Windsor) and 100m thick
today only about 10% (mostly Antarctica) of the earth is covered by ice sheets
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What is a glacier?
a large mass of ice and snow that moves over the earth's landscapes
generally formed by the continual accumulation (continuously building up) of snow that compacts into ice
formed in areas where temperatures are so low that snowfall does not melt entirely during the summer
today, such conditions are found only at high latitudes (North / South poles) or high altitudes (the Alps, Rockies, Himalayas)
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Konkordia, Switzerland
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
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Types of Glaciers
Continental glaciers (high latitudes)
cover large areas of land
found in areas of high latitude (North / South poles)
in their most extensive form are referred to as ice sheets
example: Greenland
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Alpine glaciers (high altitude)
found in he mountainous regions (high altitudes)
located in bowl-shaped hollows or valleys on the mountains
continually grow from a collection of snow (snowfield) near the top
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Movement
glaciers are constantly advancing and retreating, despite the movement not always being visible to the naked eye
glaciers shape land through scraping and depositing material (deposition)
as the snow and ice buildup continues, glaciers move
thicker continental glaciers move outward from the centers of accumulation (think of a mound of play-doh being squished down)
smaller alpine glaciers aided by gravity, move downhill
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Glacier Advance / Retreat Model
http://www.uky.edu/AS/Geology/howell/goodies/elearning/module13swf.swf
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There are 3 main mechanisms by which glaciers are thought to move:
Creep
Basal Slip
Shearing
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Creep
the pressure of the overlaying ice causes the crystals to be crushed and produced and an outward or downward movement under the influence of gravity
creep occurs very gradually and seldom amounts to more than a few centimeters per day
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Basal Slip
occurs when there is a thin film (layer) of water between the ice and rock
movement is more rapid than creep (up to 1 meter per day)
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Shearing
process is similar to faulting
usually occurs when glaciers are moving down slope
sometimes ice in glaciers cannot adjust to the pressures produced by creep and basal slip
so the ice shears as it moves forward, producing deep cracks in the ice called crevasses
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Shearing / Crevasse Model
http://highered.mcgraw-hill.com/sites/0072402466/student_view0/chapter12/animations_andmovies.html#
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True / False
answer the same true / false questions on the note sheet from the beginning of the lesson
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Glaciers and Climate Change
www.youtube.com/watch?v=M3g1iZn95sc
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Exit Card
pull out a sheet of lined paper
on that sheet of paper, WRITE DOWN AS MUCH AS YOU KNOW ABOUT GLACIERS
you have 2 minutes
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Homework
use your textbook pages 118 - 125 for this work (you can also use an atlas)
do questions 1, 2, 4, 5, 7 and 8