Transcript Glaciers and Erosion

Chapter 7 Section 1
Glaciers Natural Forces compact snow
to create an enormous mass
of moving ice.
GLACIERS ARE
POWERFUL AGENTS OF
EROSION!
Forming Glaciers
 Glaciers form at High
Elevations or Polar
Regions where the snow
remains all year
 http://www.youtube.co
m/watch?v=MQhtlddsk
Ds
Snowfield or Icefield
 An almost motionless
mass of permanent snow
and ice formed by
accumulation above the
snowline.
 Covers most land near
poles and some
mountain tops.
Required Conditions
 Avg. temperatures
remain at or near
freezing
 This causes partial
melting and refreezing
changing the snow into
grainy ice crystals called
firn.
 Snow accumulates
squeezing air out and
flattening it.
 After the firn is flattened and the air squeezed
out, it becomes a steel-blue color
Is it a glacier yet?
 A Glacier is not
formed until the
snow and ice is thick
enough to move due
to GRAVITY.
 Glacial formation is
greatest in regions
where temperatures
are LOW and
snowfall is HIGH
How Does a Glacier Grow?
 Growth depends on how
much snow is received
and how much ice is
lost(evaporation and
melt).
 Increase – New snow is
added faster than it
melts, evaporates, or
breaks off into the sea as
an ICEBERG
 Decrease – Ice
disappears faster than
the snowfalls
Types of Glaciers
Valley Glacier in the Swiss Alps
 Valley Glacier
 Long, narrow, wedgeshaped masses of ice
 Found in high mountain
regions
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Alps
Himalayas
Andes
Alaska
New Zealand
Continental Ice Sheet
 Occupies millions of
square kilometers
 Greenland
 90% buried
 3000m at its thickest
 Antarctica
 Largest in the World
 Some areas up to 4000m
thick!
 Worldwide sea-levels
would rise by more than
60 meters if they both
melted.
 http://www.foxnews.co
m/story/0,2933,554123,0
0.html
Glacier Movement ~100m per year
 Basal Slip
 Water on the
bottom of glacier
acts a lubricant
between the
ground/rock and ice
because the
pressure causes it to
melt.
Movement continued
 Internal Plastic Flow
 Solid ice crystals slip
over each other causing
a slow forward motion
 Rate affected by



Slope
Thickness
And Temperature
 Faster at surface than
bottom
 Friction
 Calving
Glacial Features
 Crevasses – large cracks
in the surface
 Can be greater than 30m
deep
 Can be covered by snow
Ice Shelves
 Ice sheet that has moved
out over the ocean
 Ross Ice Shelf,
Antarctica
 Icebergs – large blocks
of ice that break off and
drift in the ocean
Largest ice calving on camera
 http://www.youtube.co
m/embed/hC3VTgIPoG
U?rel=0
Landforms Created by Glaciers
 Cirque – bowl shaped
depression
arête
 Spiney, sharp, jagged
ridges between cirques.
Horn
 Aretes join together
forming sharp, pyramid
peakes
Roches moutonnees (sheep rocks)
 Solid rock can be
polished, scraped, and
scratched by glaciers.
Large projectiles are
rounded
 Side facing glacier is
smooth
 Side opposite is steep
and jagged from rock
being pulled away by ice
U-Shaped Valleys
 Can only be created by
glacial erosion –
glaciated valley
 (v-shaped valleys are
from running water)
Hanging Valley
 Small tributary glaciers
flow into main valley
glaciers
 Smaller tributary glacial
valleys are left above
main valley floor
Glacial Deposition
 Material (rocks and dirt)
are trapped in glacial ice.
 When the glacial ice
melts – the rocks and
dirt are deposited
Types of Glacial Deposit Materials
 Erratics – large boulders
 Glacial drift – gen. term
for all sediments deposited
by glaciers.
 Till – unsorted sediment
that has been scraped off
by base of glacier
 Stratified drift – sorted
material that is deposited
by streams flowing from
melting glacial ice (melt
water)
Till Deposits
 Moraine – landform
made by glacier till
deposits.
 Lateral Moraine –
side of valley/long ridge
 Medial Moraine – 2
valley glaciers meet and
their lateral moraines
meet creating a dark
strip of deposits
Till Deposits continued
Ground Moraine – unsorted
material left behind when a
glacier melts.
 Landscape of Ohio,
Montana, and Canada
Drumlins – tear shaped
mounds of till usually found
in clusters parallel to the
direction of glacier
movement.
 Bunker Hill Revolutionary
War Battle actually took
place in neighboring drumlin
called Breed’s Hill
Ice Ages
 Milankovitch Theory – small regular changes in the
earth’s orbit and tilt of the earth’s axis causes ice ages
 41,00o years the earth’s tilt goes between 21.5 degrees
and 24.5 degrees