23.4 Glaciers and Wind
This valley glacier
has bands that
look like ripples.
The dark bands,
which include rock
debris, show the
glacier’s slower
growth in summer.
The light bands
form in the winter.
Red Sea
23.4 Glaciers and Wind
How Glaciers Form and Move
How do glaciers form?
Glaciers form in places where more snow
falls than melts or sublimates.
23.4 Glaciers and Wind
How Glaciers Form and Move
As the layers of snow pile up, the weight on
the underlying snow increases, and glacial ice
is formed.
The force of gravity pulls the ice downhill.
Like a river, a glacier flows fastest in the
middle and slowest along the sides.
23.4 Glaciers and Wind
How Glaciers Form and Move
There are two types of glaciers.
• A continental glacier is a thick sheet of ice that
covers a huge area, such as a continent or large
island.
• A glacier that occurs in a high mountain valley is
called a valley glacier.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
What landscape features are created by
glacial erosion and deposition?
Glaciers cause many distinctive features in
the landscape, including cirques, horns, Ushaped valleys, and glacial lakes.
When a glacier melts, it deposits its load of
sediment, creating a variety of landforms.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Though glaciers move much more slowly than
rivers, they are very effective at eroding and
depositing sediment. Glaciers erode rock
through abrasion and plucking.
• In plucking, glacial ice widens cracks in
bedrock beneath the glacier. Pieces of loosened
rock are then frozen to the bottom of the glacier,
which carries them away.
• The pieces of rock that are stuck to the bottom
and sides of the glacier act like sandpaper,
scraping the bedrock and soil under it and along
its sides.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
As a glacier
moves downhill, it
loosens and lifts
pieces of rock
from the ground
underneath.
Glacial ice
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Features Formed by Glacial Erosion
A glacier can carve large bowl-shaped valleys,
called cirques, out of a mountainside.
• If several cirques form close together, a ridge may be
left between them.
• If several ridges connect to form a pyramid-shaped
peak, the peak is called a horn.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
The distinctive
landscape near
Mount Robson in
British Columbia,
Canada, was
formed by
glaciers.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Glaciers also widen and deepen the valleys
through which they flow.
• When glaciers flow through V-shaped valleys,
they widen them into U-shaped valleys.
• Glacial valleys are U-shaped because the
moving ice scours the entire valley.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Glaciers can
carve out large
U-shaped
valleys, such
as this one in
Glacier
National Park,
Montana.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Unlike valley glaciers, continental glaciers
tend to level large surface areas through the
scraping and grinding of thick ice.
• Continental glaciers can enlarge and deepen
natural depressions in the surface.
• These depressions then fill with water when the
glaciers retreat.
23.4 Glaciers and Wind
Glacial Erosion and Deposition
Features Formed by Glacial Deposition
Glacial sediment is called till. Till is an unsorted
mixture of sediment containing fragments of many
sizes.
• Glaciers deposit till as they melt.
• The till forms moraines, mounds of sediment at the
downhill end of the glacier and along its sides.
23.4 Glaciers and Wind
Wind Erosion and Deposition
What are the effects of wind erosion and
deposition?
Wind erodes the land by deflation and
abrasion.
Features deposited by wind include sand
dunes and loess deposits.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Wind can also cause erosion and deposition.
• The speed of the wind determines the size of
the materials it carries.
• A constant, strong wind can produce a large
cloud of dust or sand.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Most wind erosion occurs in dry areas, such
as deserts.
Wind erosion also occurs in areas where
drought has caused the ground to dry out and
the soil is not held in place by plants.
23.4 Glaciers and Wind
Wind Erosion and Deposition
How Wind Causes Erosion
The wind moves small particles such as sand
grains in a series of leaps called saltation.
• Wind lifts sand grains a short distance into the air.
• Gravity pulls the grains back down to the ground,
where they collide with and loosen other grains.
• The result is that the sand grains leap-frog along.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Wind erosion moves particles of different sizes.
Direction of Wind
Large particles
pushed by wind
Sand grains moving
by saltation Dust particles
suspended in
wind
23.4 Glaciers and Wind
Wind Erosion and Deposition
The process of deflation occurs when wind
picks up and carries away loose surface
material.
• Over time, the surface of the ground is lowered.
• Larger rocks are left behind, forming a rocky
surface that covers much of the land in dry
regions.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Abrasion by wind occurs in much the same
way as abrasion by flowing water.
Wind blows sand against other rocks, slowly
sandblasting them away and removing the
weathered particles.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Wind deposits sand in the form of dunes.
These large sand dunes are found in the
Namib Desert in Africa.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Effects of Wind Deposition
When wind slows down, it drops the sediment it is
carrying. Deposits formed from windblown sand
are called dunes.
• Over time, sand dunes can move great distances, as
the wind picks up sand from the back of the dune and
blows it to the front.
• Sand dunes can take many different forms,
depending on wind direction and how much sand is
available.
23.4 Glaciers and Wind
Wind Erosion and Deposition
Deposits formed from windblown dust are
called loess.
• Loess consists mainly of finely ground particles.
• The two major sources of loess are deserts and
glacial deposits.
A dust storm can transport tons of dust for
long distances. Dust from the Sahara Desert
in Africa regularly blows across the Atlantic
Ocean.
23.4 Glaciers and Wind
Wind Erosion and Deposition
This large dust storm blew through downtown
Phoenix, Arizona, in 1999.
23.4 Glaciers and Wind
Assessment Questions
1. Large, bowl-shaped valleys carved by glaciers are
called
a.
b.
c.
d.
cirques.
horns.
moraines.
loess.
23.4 Glaciers and Wind
Assessment Questions
1. Large, bowl-shaped valleys carved by glaciers are
called
a.
b.
c.
d.
cirques.
horns.
moraines.
loess.
ANS: A
23.4 Glaciers and Wind
Assessment Questions
2. How does wind erode land?
a.
b.
c.
d.
plucking and abrasion
abrasion and slumping
deflation and abrasion
deflation and frost wedging
23.4 Glaciers and Wind
Assessment Questions
2. How does wind erode land?
a.
b.
c.
d.
plucking and abrasion
abrasion and slumping
deflation and abrasion
deflation and frost wedging
ANS:
C