EARTH SCIENCE
Geology, the Environment and the Universe
Chapter 8: Mass Movements, Wind,
and Glaciers
CHAPTER
8
Table Of Contents
Section 8.1
Mass Movements
Section 8.2
Wind
Section 8.3
Glaciers
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SECTION
8.1
Mass Movements
Essential Questions
• What is the relationship between gravity and
mass movements?
• What factors affect mass movements?
• What are the different types of mass movements
and how are they described?
• How do mass movements affect people?
SECTION
8.1
Mass Movements
• Mass movements alter Earth’s surface over time
due to gravity moving sediment and rocks
downslope.
Review Vocabulary
• gravity: the force every object exerts on every
other object due to their masses
SECTION
8.1
Mass Movements
New Vocabulary
mass movement
creep
mudflow
landslide
slump
avalanche
SECTION
8.1
Mass Movements
Mass Movements
• The downslope movement of soil and weathered
rock resulting from the force of gravity is called
mass movement.
• Because climate has a major effect on the
weathering activities that occur in a particular
area, climatic conditions determine the extent of
mass movement.
SECTION
8.1
Mass Movements
Mass Movements
• All mass movements occur on slopes. Because
few places on Earth are completely flat, almost all
of Earth’s surface undergoes some degree of
mass movement.
SECTION
8.1
Mass Movements
Factors that Influence Mass Movements
• Several factors influence the mass movements of
Earth’s material: the material’s weight, the
material’s resistance to sliding or flowing, triggers
that shake material loose, and the presence of
water.
SECTION
Mass Movements
8.1
Types of Mass Movements
Creep
• The slow, steady, downhill flow of loose,
weathered Earth materials, especially soils, is
called creep.
• The effects of creep are usually noticeable only
over long periods of time.
SECTION
Mass Movements
8.1
Types of Mass Movements
Creep
• One way to way to tell
whether creep has
occurred is to observe
the positions of
structures and objects.
SECTION
Mass Movements
8.1
Types of Mass Movements
Flows
• Earth flows are moderately slow movements of
soils, whereas mudflows are swiftly moving
mixtures of mud and water.
SECTION
8.1
Mass Movements
Types of Mass Movements
Mudflows
SECTION
8.1
Mass Movements
Types of Mass Movements Mudflows
SECTION
8.1
Mass Movements
Types of Mass Movements Mudflows
SECTION
Mass Movements
8.1
Types of Mass Movements
Flows
• Mudflows are also common in sloped, semi-arid
regions that experience intense, short-lived
rainstorms.
SECTION
Mass Movements
8.1
Types of Mass Movements
Flows
• Mudflows can be triggered by earthquakes or
similar vibrations.
• Lahars are mudflows that occur in volcanic
regions where the heat from a volcano melts
snow on nearby slopes that have fine sediment
and little vegetation.
SECTION
8.1
Mass Movements
Types of Mass Movements
Lahar - Flows
SECTION
8.1
Mass Movements
Types of Mass Movements
Lahar - Flows
SECTION
8.1
Mass Movements
Types of Mass Movements
Lahar - Flows
SECTION
8.1
Mass Movements
Types of Mass Movements
Lahar - Flows
SECTION
Mass Movements
8.1
Types of Mass Movements
Slides
• A rapid, downslope movement of Earth
materials that occurs when a relatively thin block
of soil, rock, and debris separates from the
underlying bedrock is called a landslide.
SECTION
Mass Movements
8.1
Types of Mass Movements
Slides
• Landslides are common on steep slopes,
especially when soils and weathered bedrock
are fully saturated by water.
• A rockslide is a type of landslide that occurs
when a sheet of rock moves downhill on a
sliding surface. Rockslides are often triggered
by earthquakes.
SECTION
8.1
Mass Movements
Types of Mass
Movements
Slides
• Landslides
SECTION
8.1
Mass Movements
Types of Mass
Movements
Slides
• Landslides
SECTION
8.1
Mass Movements
Types of Mass
Movements
Slides
• rockslides
SECTION
8.1
Mass Movements
Types of Mass
Movements
Slides
• rockslides
SECTION
Mass Movements
8.1
Types of Mass Movements
Slides
• When the mass of material in a landslide moves
along a curved surface, a slump results.
• Material at the top of the slump moves downhill,
and slightly inward, while the material at the
bottom of the slump moves outward.
SECTION
8.1
Mass Movements
Please click the image above to view the video.
SECTION
Mass Movements
8.1
slump
Stop here
SECTION
Mass Movements
8.1
Types of Mass Movements
Slides
• Landslides that occur in mountainous areas
with thick accumulations of snow are called
avalanches.
• Avalanches occur when snow that falls on an
icy crust builds up, becomes heavy, slips off,
and slides downslope.
SECTION
Mass Movements
8.1
Types of Mass Movements
Rockfalls
• On high cliffs, rocks that are loosened by
physical weathering processes or by plant
growth can break up and fall directly downward.
Rockfalls commonly occur at high elevations, in
steep road cuts, and on rocky shorelines.
SECTION
8.1
Mass Movements
Mass Movements Affect People
• Human activities such as construction of
buildings, roads, and other structures can make
slopes unstable, contributing to the factors that
cause mass movements.
SECTION
8.1
Mass Movements
Mass Movements Affect People
Reducing the risks
• The best way to reduce the number of disasters
related to mass movements is to educate
people about the problems of building on steep
slopes.
SECTION
Section Check
8.1
By adhering to sediment grains and
rock layers, water reduces the risk of
landslides.
a. true
b. false
SECTION
Section Check
8.1
The effects of gravity increase with the
steepness of the slope.
a. true
b. false
SECTION
Section Check
8.1
In which type of mass movement does a
section of rock or sediment move downhill
along a curved surface?
a. rockslide
b. rockfall
c. slump
d. mudflow
SECTION
8.2
Wind
Essential Questions
• What are the conditions that contribute to the
likelihood that an area will experience wind
erosion ?
• What features are characteristic of wind erosion
and deposition ?
• How do dunes form and migrate ?
SECTION
8.2
Wind
• Wind modifies landscapes in all areas of the world
by transporting sediment.
Review Vocabulary
• velocity: the speed of an object and its direction
of motion
SECTION
8.2
Wind
New Vocabulary
deflation
abrasion
ventifact
dune
loess
SECTION
8.2
Wind
Wind Erosion and Transport
• Limited precipitation leads to an increase in the
amount of wind erosion because precipitation
holds down sediments and allows plants to grow.
SECTION
8.2
Wind
Wind Erosion and Transport
• Wind transport and
erosion primarily
occur in areas with
little vegetative cover,
such as deserts,
semiarid areas,
seashores, and some
lakeshores.
SECTION
Wind
8.2
Wind Erosion and Transport
Deflation
• The lowering of the land surface that results
from the wind’s removal of surface particles is
called deflation.
SECTION
Wind
8.2
Wind Erosion and Transport
Deflation
• During the 1930s, portions of the Great Plains
region experienced severe drought. Because
large areas of natural vegetation had been
removed, strong winds readily picked up the dry
surface particles. The region became known as
the Dust Bowl.
SECTION
Wind
8.2
Wind Erosion and Transport
Abrasion
• Another process of erosion, called abrasion,
occurs when particles such as sand rub against
the surface of rocks or other materials.
SECTION
Wind
8.2
Wind Erosion and Transport
Abrasion
• Because sand is often made of quartz, a hard
mineral, wind abrasion can be an effective
agent of erosion—windblown sand particles
eventually wear away rocks.
SECTION
Wind
8.2
Wind Erosion and Transport
Abrasion
• Rocks shaped by windblown sediments are
called ventifacts.
SECTION
Wind
8.2
Wind Deposition
Dunes
• In windblown environments, sand particles tend
to accumulate where an object, such as a rock,
landform, or piece of vegetation, blocks the
forward movement of the particles. Over time,
the pile of windblown sand develops into a
dune.
SECTION
Wind
8.2
Wind Deposition
Dunes
• The conditions under which a dune forms
determine its shape and include the availability
of sand, wind velocity, wind direction, and the
amount of vegetation present.
SECTION
Wind
8.2
Wind Deposition
Dunes
• Dune migration is caused when prevailing winds
continue to move sand from the windward side
of a dune to its leeward side, causing the dune
to move slowly over time.
SECTION
8.2
Wind
Please click the image above to view the interactive table.
SECTION
Wind
8.2
Wind Deposition
Loess
• Thick, windblown silt deposits are known as
loess.
• Loess soils are some of the most fertile soils
because they contain abundant minerals and
nutrients.
SECTION
Wind
8.2
Wind Deposition
Loess
• This map shows the
location of loess
deposits in the
continental United
States.
SECTION
Section Check
8.2
Most of the sand that is blown by wind
moves along the ground with a bouncing
motion.
a. true
b. false
SECTION
Section Check
8.2
Which feature forms as a result of
deflation?
a. dunes
b. blowouts
c. ventifacts
d. pillars
SECTION
8.2
Section Check
How do sand dunes migrate?
Possible answer: Sand that is blown by wind
from the windward side of the dune accumulates
at the crest until it is carried down the leeward
side. As long as the wind blows, this process
continues, moving sand from one side of the dune
to the other and causing the dune to advance.
SECTION
8.3
Glaciers
Essential Questions
• How do glaciers form?
• What are the similarities and differences between
valley glaciers and continental glaciers?
• How do glaciers modify landscapes?
• What features are characteristic of glacial erosion
and deposition?
SECTION
8.3
Glaciers
• Glaciers modify landscapes by eroding and
depositing rocks.
Review Vocabulary
• latitude: distance in degrees north and south of
the equator
SECTION
8.3
Glaciers
New Vocabulary
glacier
valley glacier
continental glacier
cirque
moraine
outwash plain
drumlin
esker
kame
kettle
SECTION
8.3
Glaciers
Moving Masses of Ice
• A large mass of
moving ice is called a
glacier.
• Glaciers form near
Earth’s poles and in
mountainous areas
at high elevations.
They cover about 10
percent of Earth’s
surface.
SECTION
Glaciers
8.3
Moving Masses of Ice
Valley glaciers
• Glaciers that form in valleys in high,
mountainous areas are called valley glaciers.
• As valley glaciers flow downslope, they carve
V-shaped stream valleys into U-shaped glacial
valleys.
Valley Glaciers
Bylot Island, Canada
SECTION
Glaciers
8.3
Moving Masses of Ice
Continental glaciers
• Glaciers that cover broad, continent-sized areas
are called continental glaciers.
• These glaciers form in cold climates where
snow accumulates over many years.
SECTION
Glaciers
8.3
Moving Masses of Ice
Glacial movement
• Both valley glaciers and continental glaciers
move outward when snow gathers at the zone
of accumulation, a location in which more snow
falls than melts, evaporates, or sublimates.
SECTION
8.3
Glaciers
Glacial Erosion
• Of all the erosional agents, glaciers are the most
powerful because of their great size and weight.
SECTION
8.3
Glaciers
Glacial Erosion
• When a valley glacier moves, it breaks off pieces
of rock through a process called plucking.
• When glaciers with embedded rocks move over
bedrock, they act like grains on a piece of
sandpaper, grinding parallel scratches into the
bedrock.
SECTION
8.3
Glaciers
Glacial Erosion
• At the high elevations where snow accumulates,
valley glaciers scoop out deep, bowl-shaped
depressions, called cirques.
SECTION
8.3
Glaciers
Glacial Erosion
• When there are glaciers on three or more sides of
a mountaintop, the carving action creates a steep,
pyramid-shaped peak, called a horn.
SECTION
8.3
Glaciers
Glacial Erosion
• Hanging valleys are formed by valley glaciers
when higher tributary glaciers converge with the
lower primary glaciers and later retreat. A valley is
left hanging high above the primary valley floor.
SECTION
8.3
Glaciers
Glacial Deposition
• Glacial till is the unsorted rock, gravel, sand, and
clay that glaciers carry embedded in their ice and
on their tops, sides, and front edges.
• Glaciers deposit unsorted ridges of till called
moraines when the glacier retreats.
SECTION
Glaciers
8.3
Glacial Deposition
Outwash
• When the farthest ends of a glacier melt,
meltwater floods the valley below. Outwash is
the gravel, sand, and fine silt sediment that is
deposited by meltwater carried away from the
glacier.
SECTION
Glaciers
8.3
Glacial Deposition
Outwash
• The area at the leading edge of a glacier where
meltwater flows and deposits outwash is called
an outwash plain.
SECTION
Glaciers
8.3
Glacial Deposition
Drumlins, eskers, and kames
• Continental glaciers that move over older
moraines form the material into elongated
landforms called drumlins.
SECTION
Glaciers
8.3
Glacial Deposition
Drumlins, eskers, and kames
• Streams flowing under melting glaciers leave
long, winding ridges of layered sediments called
eskers.
• A kame is a mound of layered sediment that
forms when till gets washed into depressions or
openings in the melting ice.
SECTION
8.3
Glaciers
Visualizing Continental Glacial Features
• Continental glaciers carve out vast regions of
landscape, leaving behind distinctive features
such as kames, eskers, drumlins, and moraines.
SECTION
8.3
Glaciers
Please click the image above to view the video.
SECTION
Glaciers
8.3
Glacial Deposition
Glacial lakes
• Kettles, or kettle lakes, form when water from
runoff or precipitation fills a hole that formed
when a large block of ice broke off a continental
glacier and melted.
SECTION
Glaciers
8.3
Glacial Deposition
Glacial lakes
• With valley glaciers, cirques can also fill with
water and become cirque lakes.
• When a terminal moraine blocks off a valley, the
valley fills with water to form a moraine-dammed
lake.
SECTION
Section Check
8.3
About how much of Earth’s surface
is currently covered by glaciers ?
a. 10 percent
b. 20 percent
c. 30 percent
d. 40 percent
SECTION
Section Check
8.3
Which glacial feature forms from
sediments deposited by a stream flowing
beneath a glacier?
a. esker
b. cirque
c. kettle
d. moraine
SECTION
Section Check
8.3
Which glacial feature forms as a result of
deposition of sediment?
a. horn
b. arête
c. cirque
d. moraine
CHAPTER
8
Mass Movements, Wind, and Glaciers
Resources
Earth Science Online
Study Guide
Chapter Assessment Questions
Standardized Test Practice
Click on a hyperlink to view the corresponding feature.
SECTION
Mass Movements
8.1
Study Guide
• Mass movements alter Earth’s surface over time
due to gravity moving sediment and rocks
downslope.
• Mass movements are classified in part by how
rapidly they occur.
SECTION
Mass Movements
8.1
Study Guide
• Factors involved in the mass movement of Earth
materials include the material’s weight, its
resistance to sliding, the trigger, and the presence
of water.
• Mass movements are natural processes that can
affect human life and activities.
• Human activities can increase the potential for the
occurrence of mass movements.
SECTION
Wind
8.2
Study Guide
• Wind modifies landscapes in all areas of the world
by transporting sediment.
• Wind is a powerful agent of erosion.
• Wind can transport sediment in several ways,
including suspension and saltation.
SECTION
Wind
8.2
Study Guide
• Dunes form when wind velocity slows down and
windblown sand is deposited.
• Dunes migrate as long as winds continue to blow.
SECTION
Glaciers
8.3
Study Guide
• Glaciers modify landscapes by eroding and
depositing rocks.
• Glaciers are large moving masses of ice that form
near Earth’s poles and in mountain areas.
• Glaciers can be classified as valley glaciers or
continental glaciers.
SECTION
Glaciers
8.3
Study Guide
• Glaciers modify the landscape by erosion and
deposition.
• Features formed by glaciers include U-shaped
valleys, hanging valleys, moraines, drumlins, and
kettles.
CHAPTER
8
Mass Movements, Wind, and Glaciers
Chapter Assessment
Which sediment grain size is most abundant in
loess?
a. clay
b. silt
c. sand
d. gravel
CHAPTER
8
Mass Movements, Wind, and Glaciers
Chapter Assessment
Which observation provides evidence that
material has moved by the process of creep?
a. scattered large boulders
b. steep scarps in hills
c. tilted trees or posts
d. piles of rock talus
CHAPTER
8
Mass Movements, Wind, and Glaciers
Chapter Assessment
By what agent is glacial outwash deposited?
a. ice
b. wind
c. water
d. gravity
CHAPTER
8
Mass Movements, Wind, and Glaciers
Chapter Assessment
What is a lahar?
Answer: A lahar is a mudflow that forms on a
volcano, often just after an eruption. The presence
of loose volcanic ash and snow that can melt
rapidly contributes to conditions favorable for the
formation of lahars.
CHAPTER
8
Mass Movements, Wind, and Glaciers
Chapter Assessment
How do valley glaciers and continental glaciers
differ?
Possible answer: Valley glaciers form in
mountains at high altitudes and are comparatively
small. Continental glaciers are much larger and
form at high latitudes. Continental glaciers have,
however, extended into midlatitudes during ice
ages.
CHAPTER
8
Mass Movements, Wind, and Glaciers
Standardized Test Practice
Which landmass has the most glacier ice?
a. Greenland
b. North America
c. South America
d. Antarctica
CHAPTER
8
Mass Movements, Wind, and Glaciers
Standardized Test Practice
Which type of sand dune has a horseshoe shape
with arms that point downwind?
a. transverse
b. barchan
c. parabolic
d. longitudinal
CHAPTER
8
Mass Movements, Wind, and Glaciers
Standardized Test Practice
By which process does a ventifact form?
a. abrasion by windblown sand
b. erosion of kame gravel
c. tumbling in a landslide
d. scraping beneath a glacier
CHAPTER
8
Mass Movements, Wind, and Glaciers
Standardized Test Practice
How does a kettle lake form?
Answer: As a glacier recedes, blocks of glacier
ice are sometimes left in front of the receding ice
margin. When an ice block melts, a depression
remains. A kettle lake forms if the depression
remains filled with water.
CHAPTER
8
Mass Movements, Wind, and Glaciers
Standardized Test Practice
Flows and slides are basic types of mass
movements. How is a flow different from a slide?
Possible answer: A flow moves like a liquid.
Some flows are stiff and move relatively slowly;
others are thin and flow like water. A slide is a
mass of rock or sediment that rapidly slides over
a surface of weakness. The mass sometimes
breaks apart as it moves downhill.