Transcript How Do Glaciers Shape the Land

What causes
Glaciers?
Glaciers –masses of ice on land
Continental
 Ice sheets on land
Valley
 Rivers of ice moving through
mountains
 They move like rivers (faster
in the center) only much
slower
How glaciers form?
 Glaciers occur where the temperature is
such that there is an accumulation of snow.
 Current Glaciers form at high latitudes
(poles) and high elevations (Mountain
peaks)
 Glacial sheets of the past formed during ice
ages. These sheets covered the northern
section of the United States.
Pleistocene Epoch:
the Great Ice Ages
 2.0 Ma to 10,000 years
ago
 Four (or more) distinct
episodes expansion
and melting of ice
sheets (continental
glaciers)
Why did the climate change so
drastically and repeadedly?
 Past hypotheses:
 Climate change and variations in
Earth’s orbit
 Earth was further from the sun at
certain points
 “Wobble” – Earth tilt was larger
 If we were tilted more we would
have colder winters and warmer
summers
Effects of Pollution
 Variations affect amount
and distribution of solar
energy received by Earth
 Pollution could block
sunlight from reaching the
earth, creating colder
temps
 Meteor and volcanic dust
could have blocked
sunlight in the past
creating the ice age that
killed off the dinosaurs.
What Makes a Glacier Move?
 The weight of overlying layers compact
the snow
 The friction with the underlying rocks
creates heat and melts the bottom and
sides that are scratching against rock
layers.
 It slips and slides downhill under the
pressure of its own weight and gravity
pulls it down slope
Advance and Retreat of Glaciers
Advance: Glaciers grow
and appear to move
forward as snow
accumulates due to
colder weather.
Retreat: Glaciers “appear”
to move backwards as they
melt. **The glaciers are not
moving backwards the front
edge is just melting as the
temperature increases.***
melting glacier national
park
Valley Glaciers move like rivers
Glaciers are
moving fastest
in the center of
the valley b/c
there is less
friction there
Erosional Marks Left by Glaciers
 1. U shape Valley
2. Striations
 Deep scratches in rocks.
As Glaciers move they
are carrying a mix of
large and small
sediments. The larger
sediments scratch the
underlying rocks.
 These scratches could
help determine the
direction the glacier
came from.
3. Polish
 Smooth surfaces on large
rocks created as small
sediments in glaciers
sand down the rough
surfaces.
3. Kettle Lakes
 Block of ice is
deposited and
creates a lake as the
water wears out a
hole in the land.
Glacial Deposits - Drift
Outwash
Till
 Deposits left
 Deposits left by the
directly by the ICE
 Unsorted and not
layered
melting water of a
glacier
 Sorted and layered
Depositional Marks Left by
Glaciers
 1. Erratics- large
Boulders left behind by
glaciers
2. Moraines
 Pile of unsorted
sediments at the edges of
glaciers
 Lateral moraines – side
edges of glaciers
 Terminal moraines –
front edge of glaciers.
 *** mark where a glacier
stopped advancing
Terminal Moraine
Long Island – was created by
terminal glacial moraines
Eskers – winding ridge of
sediments deposited in a
tunnel under glacier
Drumlins- long narrow hills of
glacial till- trails off to south
Gentle sloping
side is the
direction the
ice was moving
Kames- fan shape deposits left at the
edge of valley glaciers *** like a delta
only created by glacier instead of river