objectives - winston-salem/forsyth county schools / … • identify factors that affect mass...

Objectives

• Identify factors that affect mass movements.

Mass Movements, Wind, and Glaciers

• Relate how mass movements affect people.

• Analyze the relationship between gravity and mass movements

– mass movement

– creep

– mudflow

– landslide

Vocabulary

– slump

– avalanche

http://www.earthgeu.com/

• Climatic conditions determine which materials and how much of each will be made available for mass movement.

• All mass movements occur on slopes and range from extremely slow motions to sudden slides, falls, and flows.

Mass Movements

• Mass movement is the downslope movement of loose sediments and weathered rock resulting from the force of gravity.

Mass Movements at Earth’s Surface


– The material’s weight resulting from gravity, which works to pull the material down a slope

– The material’s resistance to sliding or flowing

– A trigger, such as an earthquake, that works to shake material loose from a slope

Variables That Influence Mass Movements

• Variables that influence the mass movements of Earth’s material include:


• Mass movement occurs when the forces working to pull material down a slope are stronger than the material’s resistance to sliding, flowing, or falling.



• Some common types of mass movement include:




Water


– On a slope, too little water may prevent sediment grains from holding together at all, thereby increasing the material’s potential for movement.

– The addition of water to sediments on a slope helps to hold the grains together and makes the material more stable.

– Too much water can make a slope unstable.

– Water is very important to the process of mass movement, but it is not involved as a transport agent.



Water



Types of Mass Movements

Creep


– Creep is the slow, steady, downhill flow of loose, weathered Earth materials, especially soils.

– The effects of creep usually are noticeable only over long periods of time.

– Loose materials on almost all slopes undergo creep.

– Soil creep moves huge amounts of surface material each year.



Flows


– In some mass movements, Earth materials flow as if they were a thick liquid.

– Earth flows are moderately slow movements of soils.

– Mudflows are swiftly moving mixtures of mud and water.

– Mudflows can be triggered by earthquakes or similar vibrations and are common in volcanic regions.

– Mudflows are also common in sloped, semi-arid regions that experience intense, short-lived rainstorms.



Slides


– A landslide is a rapid, downslope movement of Earth materials that occurs when a relatively thin block of loose soil, rock, and debris separates from the underlying bedrock.

– The material rapidly slides downslope as one block, with little internal mixing.

– Landslides are common on steep slopes, especially when soils and weathered bedrock are fully saturated by water.



Slides


– A rock slide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface.

– During a rock slide, relatively thin blocks of rock are broken into smaller blocks as they move downslope.



Slumps


– A slump results when the mass of material in a landslide rotates and slides along a curved surface.

– Slumps may occur in areas that have thick soils on moderate-to-steep slopes.

– Slumps are common after rains and leave crescent-shaped scars on slopes.



Avalanches


– Avalanches are landslides that occur in mountainous areas, usually on slopes of at least 35°, with thick accumulations of snow.

– Avalanches usually occur when snow has melted, either due to radiation from the Sun or warmth from the ground, and then refrozen into an icy layer.

– Snow that falls on top of this crust can eventually build up, become heavy, slip off, and slide down a slope as an avalanche.

– A vibrating trigger, even from a single skier, can send such an unstable layer sliding down a mountainside.



Rock Falls


– Rock falls commonly occur at high elevations, in steep road cuts, and on rocky shorelines.

– Rocks loosened by physical weathering processes may fall directly downward or bounce and roll, ultimately producing a cone-shaped pile of coarse debris, called talus, at the base of the slope.


Mass Movements Affect People

• Human activities often contribute to the factors that cause mass movements.


• Activities such as constructing heavy buildings, roads, and other structures can make slope materials unstable.


Mass Movements Affect People

Dangerous Mudflows


– Human lives are in danger when people live on steep terrain or in the path of unstable slope materials.

– In December of 1999, northern Venezuela experienced severe mudflows and landslides in which tens of thousands of people died and more than 114 000 people were left homeless.


Reducing the Risks

• Catastrophic mass movements are most common on slopes greater than 25° that experience annual rainfall of over 90 cm.


• The best way to minimize the destruction caused by mass movements is to avoid building structures on such steep and unstable slopes.


Reducing the Risks

Preventative Actions


– Some actions can help to avoid the potential hazards of landslides.

– Most of the efforts at slope stabilization and prevention of mass movements, however, are generally successful only in the short run.


Section Assessment

1. Match the following terms with their definitions.

___ creep

___ landslide

___ slump

___ avalanche


A. a rapid downslope movement of Earth materials

B. landslides that occur in mountainous areas with thick accumulations of snow

C. the slow, steady, downhill flow of loose, weathered Earth materials

D. when the mass of material in a landslide rotates and slides along a curved surface

C

A

D

B


Section Assessment

2. What are four variables that influence mass movements?


Four variables that influence mass movements are the material’s weight resulting from gravity, the material’s resistance to sliding or flowing, a trigger, and quantity of water in the material.


________ All mass movements occur on slopes.

________ Creep is a rare occurrence, limited to areas of steep slope.

________ Mudflows can travel at speeds greater than 30 km/h.

________ About 2,000 avalanches occur each year in the western United States.

________ Landslides cause almost $2 billion in damages per year in the United States.

Section Assessment

3. Identify whether the following statements are true or false.


true

false

true

false

true


End of Section 1

Objectives

• Describe conditions that contribute to the likelihood that an area will experience wind erosion.

• Identify wind-formed landscape features.

• Describe how dunes form and migrate.

• Explain the effects of wind erosion on human activities.

– deflation

– abrasion

– ventifact

– dune

– loess

Vocabulary

Wind


Wind

• Moving air can pick up and transport Earth materials in the process of erosion.

Wind

• Unlike water, wind can transport sediments uphill as well as downhill.

• As an erosional agent, wind can modify and change landscapes in arid and coastal areas.


Wind Erosion and Transport

Wind



• Wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semi-arid areas, seashores, and some lakeshores.

Wind

• Wind erosion is a problem in many parts of the United States.



Wind



• Deflation is the lowering of the land surface that results from the wind’s removal of surface particles.

Wind

• In areas of intense wind erosion, coarse gravel and pebbles are usually left behind as the finer surface material is removed by winds.

• The coarse surface left behind is called desert pavement.



• Abrasion is a process of erosion that occurs when particles, such as sand, rub against the surface of rocks or other materials.

Wind

• In wind abrasion, wind picks up materials such as sand particles and blows them against rocks and other objects.

• Because sand is often made of quartz, a very hard mineral, wind abrasion can be a very effective agent of erosion.



• Windblown sand causes rocks to become pitted and grooved.

Wind

• Ventifacts are rocks shaped by wind-blown sediments.


Wind Deposition

• Wind deposition occurs in areas where there are changes in wind velocity.

Wind

• As wind velocity decreases, some of the wind-blown sand and other materials can no longer stay airborne, and they drop out of the airstream to form a deposit on the ground.


Wind Deposition

Formation of Dunes

Wind

– In wind-blown environments, sand particles tend to accumulate where an object blocks the particles’ forward movement.

– A dune is a pile of wind-blown sand that develops over time.

– Conditions, including the availability of sand, wind velocity, wind direction, and the amount of vegetation present under which a dune forms, determine its particular shape.


Wind Deposition

Formation of Dunes

Wind

– The velocity of the wind above the ground surface determines the height of a dune.

– Although quartz sand is the most common component of dunes, any dry, granular material can be formed into a dune.


Wind Deposition

Types of Dunes

Wind

– Barchan dunes are solitary, crescent-shaped dunes that form in flat areas where there is little sand or vegetation.

– Transverse dunes form where there is plenty of sand, little or no vegetation, and steady, prevailing winds.

– Transverse dunes form in a series of long ridges that are perpendicular to the direction of the wind.

– U-shaped parabolic dunes form between clumps of plants.

– Longitudinal dunes form where there is limited sand available and strong prevailing winds.


Wind Deposition

Wind


Wind Deposition

Types of Dunes

Wind

– On offshore islands and on lakeshores, dunes are formed by winds blowing off the water toward the shore.

– Coastal dunes protect against beach and coastal erosion by reducing the direct action of wind on beach sand.

– They also act as buffers against the action of waves and provide shelter for vegetation.

– Dune migration is caused when prevailing winds continue to move sand from the windward side of a dune to its leeward side.


Wind Deposition

Types of Dunes

Wind


Wind Deposition

Loess

Wind

– Wind can carry fine, lightweight particles such as silt and clay in great quantities and for long distances.

– Many parts of Earth’s surface are covered by thick layers of windblown silt known as loess.

– Where precipitation is adequate, loess soils are some of the most fertile soils on Earth because they contain abundant minerals and nutrients.


Wind Deposition

Wind


Section Assessment


___ deflation

___ abrasion

___ ventifact

___ loess

Wind

A. a process in which particles such as sand rub against the surface of rocks or other materials

B. the lowering of land surface that results from the wind’s removal of surface particles

C. rocks shaped by wind-blown sediments

D. thick, wind-blown silt deposits

B

A

C

D


Section Assessment

Wind

2. Match the description of how the dune forms to its type.

___ Most common dune, generally forms in areasof constant wind direction

___ Form in areas with high, somewhat variable winds and little sand

___ Form in areas with moderate winds and some vegetation

___ Form in areas with strong winds and abundant sand

A. Barchan

B. Transverse

C. Parabolic

D. Longitudinal

A

D

C

B


Section Assessment

3. How do dunes migrate?

Wind

Wind blows sand particles up the windward side of the dune, depositing it on the leeward side. Over time, as sand is moved from the windward side to the leeward side, the dune shifts toward the leeward side.


End of Section 2

– glacier

– valley glacier

– continental glacier

– cirque

Objectives

• Explain how glaciers form.

• Compare and contrast the conditions that produce valley glaciers and those that produce continental glaciers.

• Describe how glaciers modify the landscape.

• Recognize glacial landscape features.

Vocabulary

Glaciers

– moraine

– outwash plain

– drumlin

– esker


Glaciers

• Glaciers formed much of the landscape that exists presently in the northern United States and elsewhere in the world.

Glaciers

• Today, scientists measure the movements of glaciers and changes in their sizes to track climatic changes.

• Air bubbles trapped deep in glacial ice can provide data about the composition of Earth’s atmosphere at the time when the ice layers were formed.


Moving Masses of Ice

• A glacier is a large, moving mass of ice.

Glaciers

• Glaciers form near Earth’s poles and in mountainous areas at high elevations.

• Cold temperatures year-round keep fallen snow from completely melting, and allow it to accumulate in an area called a snowfield.

• The weight of the top layers exerts downward pressure that forces the accumulated snow below to recrystallize into ice.

• Glaciers currently cover only about 10 percent of Earth’s surface.



Glaciers



Valley Glaciers

Glaciers

– Glaciers can be classified as one of two types: valley glaciers or continental glaciers.

– Valley glaciers are glaciers that form in valleys in high, mountainous areas.

– As a valley glacier moves down the valley, deep cracks in the surface of the ice, called crevasses, can form.

– As valley glaciers flow downslope, their powerful carving action widens V-shaped stream valleys into U-shaped glacial valleys.



Continental Glaciers

Glaciers

– Continental glaciers, also called ice sheets, are glaciers that cover broad, continent-sized areas.

– A continental glacier is thickest at its center.

– The weight of this thicker central region forces the rest of the glacier to flatten out in all directions.

– Continental glaciers are confined to Greenland, northern Canada, and Antarctica.


Glacial Erosion

• Glaciers are the most powerful erosional agent because of their great size, weight, and density.

Glaciers

• When glaciers with embedded rocks move over bedrock valley walls, they grind out parallel scratches into the bedrock.

• Small scratches are called striations, and the larger ones are called grooves.

• Scratches and grooves provide evidence of a glacier’s history and establish its direction of movement.


Glacial Erosion

• Glacial erosion can create certain features.

Glaciers

– Cirques are deep depressions scooped out by valley glaciers.

– An arete is a sharp, steep ridge where two cirques on opposite sides of a valley meet.

– A horn is a steep, pyramid-shaped peak formed by glaciers on three or more sides of a mountaintop.

– A hanging valley is a tributary valley that enters a U-shaped valley from high up a mountain side.


Glacial Erosion

Glaciers


Glacial Deposition

• Glacial till is the mixed debris that glaciers carry embedded in their ice and on their tops, sides, and front edges.

Glaciers

• Moraines are ridges consisting of till deposited by glaciers.

– Those at the foot of a large glacier are called terminal moraines and those at its sides are called lateral moraines.

– Where two glaciers join together, their lateral moraines combine to form a medial moraine.


Glacial Deposition

Outwash

Glaciers

– When a glacier melts and begins to recede, meltwater floods the valley below.

– Outwash is gravel, sand, and fine silt formed from the grinding action of the glacier on underlying rock that is deposited by meltwater.

– An outwash plain is the area at the leading edge of the glacier, where the meltwater streams flow and deposit outwash.


Glacial Deposition

Drumlins and Eskers

Glaciers

– Drumlins are elongated landforms that are formed when glaciers move over older moraines.

– Eskers are long, winding ridges of layered sediments that are deposited by streams flowing under a melting glacier.


Glacial Deposition

Glacial Lakes

Glaciers

– Sometimes, a large block of ice breaks off a glacier and is later covered by sediment.

– When the ice block melts, it leaves behind a depression called a kettle hole.

– After the ice block melts, the kettle hole fills with water from precipitation and runoff to form a kettle lake.

– Cirques also can fill with water, becoming cirque lakes.

– When a terminal moraine blocks off a valley, the valley fills with water to form a lake.


Section Assessment


___ cirques

___ moraines

___ drumlins

___ eskers

Glaciers

A. long, winding ridges of layered sediments that are deposited by streams flowing under a melting glacier

B. deep depressions scoopedout by valley glaciers

C. elongated landforms that are formed when glaciers move over older moraines

D. ridges consisting of till deposited by glaciers

D

B

C

A


Section Assessment

2. What causes a continental glacier to move?

Glaciers

A continental glacier is thickest at its center. The weight of this thicker central region forces the rest of the glacier to flatten out in all directions.


Section Assessment

Glaciers

3. What are striations and why are they significant?

Striations are small scratches left in bedrock from rocks embedded in a glacier as they passed. They provide evidence of a glacier’s history and establish its direction of movement.


End of Section 3

Chapter Resources Menu

Study Guide

Section 8.1

Section 8.2

Section 8.3

Chapter Assessment

Image Bank

Section 8.1 Main Ideas

• Mass movement is the movement of Earth materials downslope as the result of the force of gravity. Almost all of Earth’s surface undergoes mass movement.

• Mass movements may occur very slowly and become noticeable only over long periods of time. Creep is a form of slow mass movement. Rapid mass movements are noticeable.

• Variables involved in the mass movement of Earth materials include the material’s weight, its resistance to sliding, and sometimes a trigger such as an earthquake. Water is important to the process of mass movement.

• Mass movements can cause great damage and loss of lives. Human activities may increase the potential for the occurrence of mass movements.

Section 8.1 Study Guide


• Arid, semi-arid, and seashore environments are likely to experience wind erosion. Limited amounts of precipitation and protective vegetation commonly contribute to wind erosion in an area.

• Wind-carried sediments can cause abrasive action. Rocks exposed to continual wind abrasion often exhibit angular shapes with polished, smooth sides on the windward side. Features formed in wind-affected areas include deflation blowouts, dunes, and desert pavement. Dunes are classified by shape.

• The transport of Earth materials by wind can create problems for humans. Migrating dunes can block highways and cover structures.

• Loess soils deposited by wind are fertile soils because they contain minerals and nutrients.



• Glaciers are large, moving masses of ice that form near Earth’s poles and in mountainous areas at high elevations.

• Valley glaciers are formed in mountains, and continental glaciers are formed over broad regions of land. Valley glaciers move down mountainsides and form unique glacial features. Continental glaciers usually spread out from their centers.

• Features formed by glaciers include U-shaped valleys, hanging valleys and waterfalls in the mountains, moraines, drumlins, kettle holes along outwash plains, and several types of lakes.


1. Catastrophic mass movements are most common on slopes greater than ____.

a. 10º c. 20º

b. 15º d. 25º

Multiple Choice

Chapter Assessment

A slope that is high risk for a catastrophic mass movement also experiences over 90 cm of annual rainfall.

2. What accounts for most sand transport by wind?

a. suspension c. deflation

b. saltation d. abrasion

More material is moved by saltation than by suspension. Deflation and abrasion are possible results of wind erosion or transport, but not methods of transport themselves.

Multiple Choice

Chapter Assessment

Multiple Choice

3. Which of the following features provides evidence of a glacier and establish its direction of movement?

a. grooves c. kettle holes

b. aretes d. eskers

Chapter Assessment

Grooves and striations are scratches in bedrock resulting from glacial movement dragging rocks across its surface. All of the other answers are evidence of a glacier, but they do not establish direction of movement by themselves.

Multiple Choice

4. Which type of dune would you expect to see in a coastal area with some vegetation?

a. barchan c. parabolic

b. transverse d. longitudinal

Chapter Assessment

The key is vegetation. Parabolic dunes form in U-shapes between clumps of plants. The other three dune types are more common in areas with little or no vegetation.

Multiple Choice

5. In which state are you most likely to find a loess deposit?

a. North Dakota c. Illinois

b. Texas d. Florida

Chapter Assessment

More than half of the state of Illinois has loess soil. With adequate precipitation, such as in Illinois, loess soils are some of the most fertile soils on Earth because they contain abundant minerals and nutrients.

Short Answer

6. What differentiates a slump from a landslide?

Chapter Assessment

In a landslide, a thin block of loose soil, rock, and debris separates from the underlying bedrock. The material rapidly slides downslope as one block, with little internal mixing. When a slump occurs, the material in a landslide rotates and slides along a curved surface.

Short Answer

7. How does the distribution of valley and continental glaciers on Earth’s surface differ?

Chapter Assessment

Valley and continental glaciers need the same environmental conditions to exist. Perpetually cold conditions only exist on a large scale near the polar regions, limiting continental glaciers to Antarctica, Greenland, and northern Canada. Valley glaciers, being much smaller, can exist anywhere in the world that has the cold conditions. They are found high in mountainous areas from the arctic to the equator.

True or False

8. Identify whether the following statements are true or false.

______ More material is moved by creep than by other means of mass movements.

______ Rock falls are less likely to occur in dry regions.

______ The Great Plains are characterized by the effects of deflation.

______ Moraines are the effect of glacial straition.

______ Glaciers cover about 17 percent of Earth’s surface.

Chapter Assessment

true

false

true

false

false

Image Bank

Chapter 8 Images

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