8.3 Glaciers
Types of glaciers
Alpine
Small glaciers that form valleys
Ice sheets
Enormous glaciers that can cover entire
continents
Glacier Formation
Describe the steps
Firn: Thick, dense compacted snow
Glacial ice: Firn compacts into glacial ice
Advancing: A glacier growing faster than it is melting
Retreating: A glacier melting (receding) at the leading
edge faster than its growing. It’s NOT
traveling backwards.
Glacier Movements
Plastic Flow
Describe: Deep within, there is a huge amount of
pressure due to weight of ice pressing down.
50 meters thick of ice creates enough
pressure to cause ice to flow through the
center of a glacier very slowly.
Glacier Movements
Basal Slip
Describe: Water beneath glacier acts as a lubricant, so
entire glacier can slide. This movement can
cause a large crevasse (crack), to form.
Rate of movement:
Typically a few meters/ day, but can have faster surges.
Glacial structures from erosion
Striation
Long scratch marks found in rocks due
Describe: abrasion caused by rocks & gravel dragged by
glacial movement.
U-Shaped Valleys
Describe: V-shaped valleys that are widened by glaciers.
Glacial structures from erosion
Horn peaks
Describe: When several cirques converge, the part that
is not cut out looks like a horn sticking out of
the ground.
Cirques
Describe: Valleys that look like giant armchairs because
they have 3 steep sides & one open side.
Glacial structures from erosion
Fjords
Describe: Very steep inlets to the ocean.
Roche moutonnees
Landforms
w/
1
rough
side
&
1
side
that
has
Describe:
been abraded smooth.
Glacial Drift
Describe:
The coarsely graded sediment deposited by glaciers
Till
Describe:
Unsorted glacial sediment
Structures Formed
Glacial Erratics
Describe: Big rocks deposited by a glacier into an area
w/ a different type of rock.
Morraines
Describe: Piles of boulders, rocks, pebbles, & clay left
behind by a glacier.
Structures Formed
Terminal Moraines
Describe: form at the edge of glaciers.
Drumlins
Describe: Smooth, egg-shaped hills left behind by
continental ice sheets.
Stratified Drift
Define: Deposits left by melted water coming off a glacier.
Structures Formed:
kettles
Describe: When large blocks of ice get trapped under
stratified drift, the ice melts and leaves large
holes.
Eskers
Describe: Winding ridges of sand & gravel left behind by
receding glaciers.
Earth’s Orbit
Effects: Change in Earth’s orbit around the sun cause
slight temperature variations.
Precession
Effects:
The tilt of Earth’s axis changes over time & can
affect the amount of sunlight reaching different
parts of earth.
Current ice age theory
Explain: Changes in the Earth’s axis of rotation can work
together to alter the temperatures. This is
thought to lead to the formation of large
glaciers & put Earth into ice ages.
Last ice age
2 million years ago, & peaked 20,000 years ago.