Transcript Chp 8 ppt
EARTH SCIENCE
Geology, the Environment and the Universe
Chapter 8: Mass Movements, Wind, and Glaciers
CHAPTER 8
Table Of Contents
Section 8.1
Section 8.2
Section 8.3
Mass Movements
Wind
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 8.1
Mass Movements
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 8.1
Mass Movements
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 8.1
Mass Movements
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 8.1
Mass Movements
Types of Mass Movements Flows
• Mudflows are also common in sloped, semi-arid regions that experience intense, short-lived rainstorms.
SECTION 8.1
Mass Movements
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 8.1
Mass Movements
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 8.1
Mass Movements
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 8.1
Mass Movements
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
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SECTION 8.1
Mass Movements
slump Stop here
SECTION 8.1
Mass Movements
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 8.1
Mass Movements
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 8.1
Section Check
By adhering to sediment grains and rock layers, water reduces the risk of landslides.
a.
true
b.
false
SECTION 8.1
Section Check
The effects of gravity increase with the steepness of the slope.
a.
true
b.
false
SECTION 8.1
Section Check
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
New Vocabulary
deflation abrasion ventifact dune loess
Wind
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 8.2
Wind
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 8.2
Wind
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 8.2
Wind
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 8.2
Wind
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 8.2
Wind
Wind Erosion and Transport Abrasion
• Rocks shaped by windblown sediments are called
ventifacts
.
SECTION 8.2
Wind
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 8.2
Wind
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 8.2
Wind
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 8.2
Wind
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 8.2
Wind Deposition Loess
• This map shows the location of loess deposits in the continental United States.
Wind
SECTION 8.2
Section Check
Most of the sand that is blown by wind moves along the ground with a bouncing motion.
a.
true
b.
false
SECTION 8.2
Section Check
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
New Vocabulary
glacier valley glacier continental glacier cirque moraine
Glaciers
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 8.3
Glaciers
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 8.3
Glaciers
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 8.3
Glaciers
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 8.3
Glaciers
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 8.3
Glaciers
Glacial Deposition Outwash
• The area at the leading edge of a glacier where meltwater flows and deposits outwash is called an
outwash plain
.
SECTION 8.3
Glaciers
Glacial Deposition Drumlins, eskers, and kames
• Continental glaciers that move over older moraines form the material into elongated landforms called
drumlins
.
SECTION 8.3
Glaciers
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 8.3
Glaciers
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 8.3
Glaciers
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 8.3
Section Check
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 8.3
Section Check
Which glacial feature forms from sediments deposited by a stream flowing beneath a glacier? a.
esker
b.
cirque
c.
kettle
d.
moraine
SECTION 8.3
Section Check
Which glacial feature forms as a result of deposition of sediment?
a.
b.
horn 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 8.1
Study Guide
Mass Movements
• 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 8.1
Study Guide
Mass Movements
• 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 8.2
Study Guide
Wind
• 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 8.2
Study Guide
Wind
• Dunes form when wind velocity slows down and windblown sand is deposited.
• Dunes migrate as long as winds continue to blow.
SECTION 8.3
Study Guide
Glaciers
• 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 8.3
Glaciers
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.