Objectives

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Objectives
Glaciers

• 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

• glacier
• valley glacier
• continental glacier
• cirque

• moraine
• outwash plain
• drumlin
• esker

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Glaciers
Glaciers

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

• 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 Earths
  atmosphere at the time when the ice layers were
  formed.

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Moving Masses of Ice
Glaciers

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

• Glaciers form near Earths 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 Earths surface.

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Moving Masses of Ice
Glaciers
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Moving Masses of Ice
Glaciers

• Valley 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.

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Moving Masses of Ice
Glaciers

• Continental 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.

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Glacial Erosion
Glaciers

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

• 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
  glaciers history and establish its direction of
  movement.

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Glacial Erosion
Glaciers

• Glacial erosion can create certain features.

• 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.

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Glacial Erosion
Glaciers
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Glacial Deposition
Glaciers

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

• 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.

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Glacial Deposition
Glaciers

• Outwash

• 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.

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Glacial Deposition
Glaciers

• Drumlins and Eskers

• 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.

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Glacial Deposition
Glaciers

• Glacial Lakes

• 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.

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Section Assessment
Glaciers

• 1. Match the following terms with their
  definitions.
• ___ cirques
• ___ moraines
• ___ drumlins
• ___ eskers

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
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Section Assessment
Glaciers

• 2. What causes a continental glacier to move?

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.
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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 glaciers history and
establish its direction of movement.
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End of Section 3
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Chapter Resources Menu
Chapter Resources Menu

• Study Guide
• Section 8.1
• Section 8.2
• Section 8.3
• Chapter Assessment
• Image Bank

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Section 8.1 Main Ideas
Section 8.1 Study Guide

• Mass movement is the movement of Earth materials
  downslope as the result of the force of gravity.
  Almost all of Earths 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 materials 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.

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Section 8.2 Main Ideas
Section 8.2 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.

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Section 8.3 Main Ideas
Section 8.3 Study Guide

• Glaciers are large, moving masses of ice that
  form near Earths 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.

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Multiple Choice
Chapter Assessment

• 1. Catastrophic mass movements are most common on
  slopes greater than ____.
• a. 10º c. 20º
• b. 15º d. 25º

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

• 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.
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Multiple Choice
Chapter Assessment

• 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

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.
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Multiple Choice
Chapter Assessment

• 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

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.
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Multiple Choice
Chapter Assessment

• 5. In which state are you most likely to find a
  loess deposit?
• a. North Dakota c. Illinois
• b. Texas d. Florida

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.
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Short Answer
Chapter Assessment

• 6. What differentiates a slump from a landslide?

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.
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Short Answer
Chapter Assessment

• 7. How does the distribution of valley and
  continental glaciers on Earths surface differ?

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.
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True or False
Chapter Assessment

• 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
  Earths surface.

true false true false false
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Chapter 8 Images
Image Bank
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Chapter 8 Images
Image Bank
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Chapter 8 Images
Image Bank
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Chapter 8 Images
Image Bank
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