Chapter 7: Erosion
and Deposition
7.1: Forces wear down and build up Earth’s surface
7.2: Moving water shapes land
7.3: Waves and wind shape land
7.4: Glaciers carve land and move sediments
7.4 Glaciers carve land and move sediments
Before, you learned:
Running water shapes landscapes
Wind changes landforms
Now, you will learn:
How moving ice erodes land
How moving ice deposits sediment and
changes landforms
Glaciers are moving bodies of ice
 Glacier: a large mass of ice that moves over
land
Forms in a cold region where more snow falls than melts
per year
 The weight of each following year’s snow compresses the
snow below  ice
On a mountains: becomes a heavy mass and can flow
On flatter land: can spread out as ice sheets
http://academic.brooklyn.cuny.edu/geology/leveson/core
/graphics/nyc_mins2/glac2_rollover.html
Extent of Glaciers
 Must be cold enough for water to remain ice
year round
 Mountains (high elevation/altitude) and land
regions near the poles (high latitude)
= COLD!
 Currently cover ~10% of the Earth’s land surface
Ice Ages
~30,000 years ago (ya) glaciers covered 30%
 “Last Glacial Maximum” ~17,000 ya
 Lasting until ~13 to 10,000 ya
Two Types of Glaciers: (1) Alpine
 Aka “valley glaciers”
 Form in mountains and flow down
through valleys
 Cause erosion (and deposition)
 Can change a “V-shaped” mountain valley
into a “U-shaped” valley overtime
 Melting can occur at the base
Carries sediment
Can break off into the ocean: icebergs
Two Types of Glaciers: (2) Continental
Aka “ice sheets”
Larger than alpine glaciers
Can cover entire continents
One covered North America until about
10,000 years ago
 Still cover most of Greenland and Antarctica
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 As much as 4500 meters (15,000 ft) thick!
Glacial Movement
Gravity causes glacial ice to move downhill:
Flowing: ice near the surface is brittle and cracks
often form in it, but pressure deep inside does not
Inside ice flows like toothpaste tube being squeezed
Sliding: weight of a glacial and heat from Earth
cause melting
Layer of water forms under the glaicer - sliding
Interesting
 During the last glaciation (~26 to 13,000 ya), woolly mammoths and
saber-toothed cats roamed just south of the glaciers
 At the end of the last ice age ~10,000 ya, these large mammals
became extinct
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Why?
Hunting?
Climate?
Diseases from humans?
Glaciers deposit large
amounts of sediment
 As glaciers melt and
treat: shape
landscape
 As glaciers move and
expand: transport
sediment (boulders,
rocks, sand, clay)
Scratches and scrapes
rock: abrasion
Glaciers deposit large amounts of
sediment
 Moraines
Glaciers push sediment to their sides and front
These sediment deposits remain after glacial retreat
Till: the sediment left directly on the ground surface by a
retreating glacier
Moraine: a deposit of till left behind by a retreating
glacier
Lateral moraine: till at sides of glacier
End moraine: till at farthest advance of glacier
Ground moraine: blanket of till along the ground
Till is different than the rocks from the area
Glaciers deposit
large amounts
of sediment
 Lakes
 Melting glaciers leave
behind depressions
than can become lakes
 Kettle lakes: bowlshaped depression that
was formed by a block
of ice from a glacier
Great Lakes Formation
 Glaciers in valleys
melted and left behind
moraines
 A million years ago, the
Great Lake region had
many river valleys
 Ice sheets gouged out
large depressions and
left piles of rock and
debris
 Prevented water from
draining out
 Weight of glacier caused
the land to sink as much
as one kilometer