Glaciers
Erosive forces
Glacier
• persistent body of dense ice that is constantly
moving under its own weight.
• It forms where the accumulation of snow exceeds
its ablation (melting and sublimation) over many
years.
Glacier formation
Snowfall
• Glaciers form where the accumulation of snow and ice
exceeds ablation.
o This snow collects and is compacted by the weight of the snow falling above it,
crushing the individual snowflakes and squeezing the air from the snow
Firn
• left over from past seasons and has been recrystallized into a
denser substance
• snow repeatedly freezes and thaws, changing into granular
ice
Glacial Ice
• Once all air has been squeezed from it, the snow is turned
into extremely dense glacial ice
• When the mass of snow and ice is sufficiently thick, it begins
to move due to a combination of surface slope, gravity and
pressure.
Explain what the growth
of a glacier depends on
• The balance between snow fall received and the
amount of ice lost be melting and
sublimation(evaporation)
Advance v. Retreat
• Advance
o Snow accumulation is greater than ablation
• Retreat
o Ablation is greater than snow accumulation
Glacier Types
Alpine (Valley)
Continental
• Long, narrow wedge
shaped
• Wide, very large millions
of km2
• form on the crests and
slopes of mountains.
• Polar regions
o Ex. Alaska, Himalayas, Alps,
Andes
o Only found in two places
• Greenland and
Antarctica
Glacial Movement
Basal Slip
• glacier slides over the
terrain on which it sits,
lubricated by the
presence of liquid
water.
o Refreezes as pressure removed
Internal Plastic Flow
• Solid ice crystals slip
over each other,
causing slow forward
motion.
o Slope
o Thickness
o Temperature (of Ice)
• Surface faster
o Friction
Erosion
• Plucking/ Ice wedging :
Plucking: “pluck” material from V sides
makes a U shaped valley
Ice wedging: water seeps into cracks and
expands leaving larger cracks.
Erosion
• Abrasion:
o Mechanical erosion of rocks (think
sand paper) as glacier scrapes over
the landscape/ bedrock below
Features caused by
• Cirques:
Erosion
o start of a classic valley glacier is a bowl-shaped
• Horns:
o 3 or more cirques or Arêtes that encircle a single mountain
(looks like a pyramid)
• Arêtes:
o Two glacial cirques may form back to back and erode their
back walls until only a narrow ridge or “spine” is formed
• U-shaped valley:
o widened, deepened, and smoothed, by a glacier forming a "U"shaped glacial valley
Features caused by
Erosion
• Hanging valleys:
o when glaciers recede, the valleys of the tributary glaciers
remain above the main glacier's depression ( water falls
often)
• Striations:
o Grooves from plucking/ and abrasion
• Kettle lake
o shallow, sediment-filled body of water formed by retreating
glaciers or draining floodwaters.
Deposition
• Drumlins:
o elongated hill in the shape of an inverted spoon
or half-buried egg formed by glacial ice acting
on underlying unconsolidated till or ground
moraine.
Deposition
• Eskers:
o An esker is a long, winding ridge of stratified sand
and gravel.
Deposition
• Kames:
o an irregularly shaped hill composed of sand,
gravel and till that accumulates in a depression
on a retreating glacier.
Deposition
• Moraines:
o are accumulations of dirt and rocks that have
fallen onto the glacier surface or have been
pushed along by the glacier as it moves.
o End/recessional: between glacier and last
moraine
o Terminal= farthest
forward motion
o Lateral: side (parallel)
Glacial sediment
• Erratics:
o are stones and rocks that were
transported by a glacier, and then left
behind after the glacier melted.
Glacial sediment
• till:
o Glacial till is unsorted sediment deposited
directly by glacial ice.
Glacial sediment
• Outwash:
o Glacial outwash is sand and gravel
deposited by running water from the
melting ice of a glacier.
Michigan’s Glacial
History
Big idea Great lakes
Each of the Great Lakes began as a
river.
As the climate cooled…
• The rivers froze.
• Glaciers moved
through them –
widening and
deepening them to
form today’s “U”
shaped lake bottoms.
Why do scientists believe that
glaciers once covered Michigan?
• The unsorted moraine deposits follow the
outline of Great Lakes.
• Other depositional features such as
drumlins and kettle lakes are found
throughout Michigan.
• Erosional features like striations are found
in Michigan as well.
Explain what happens to Earth’s
crust when a glacier is removed.
• Isostatic Rebound
– The upward movement of the Earth’s crust