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Lesson 1: Interaction at Plate Boundaries

Lesson 2: California Geology

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fracture

fault

divergent plate boundary

continental rifting

5.1 Interactions at Plate Boundaries

rift valley

convergent plate boundary

subduction

transform plate boundary

Stress and Deformation

• Earth’s lithosphere is made up of crust and upper mantle that are broken into plates.

5.1 Interactions at Plate Boundaries

• Each plate travels at different speeds and in different directions.

• Collisions between plates causes stress at plate boundaries, resulting in deformation.

Stress and Deformation (cont.)

5.1 Interactions at Plate Boundaries

Deforming Rocks• Plastic deformation occurs when rocks change shape

by folding under high temperatures and pressure.

• Elastic deformation occurs when rocks resume their original shapes after the stress is removed.

5.1 Interactions at Plate Boundaries

Deforming Rocks (cont.)

• A fracture is a break or crack in rock.

• If rock on side of a fracture has moved relative to the other side it is called a fault.

5.1 Interactions at Plate Boundaries

Types of Stress

• Three main types of stress:

– Tension: rocks are stretched

– Compression: rocks are squeezed

– Shear: rocks slide horizontal in opposite directions

5.1 Interactions at Plate Boundaries

Types of Stress (cont.)

5.1 Interactions at Plate Boundaries

Types of Faults

• Three main types of faults:

– Normal faults

– Reverse faults

– Strike-slip faults

5.1 Interactions at Plate Boundaries

Normal Faults• Normal faults result from tension stress and slope at

an angle.

5.1 Interactions at Plate Boundaries

Reverse Faults• Reverse faults result from compression stress and slope

at an angle.

5.1 Interactions at Plate Boundaries

Strike-Slip Faults• Strike-slip faults result from shearing stress and are often

vertical.

5.1 Interactions at Plate Boundaries

Types of Plate Boundaries• Divergent plate boundary occurs when two

lithospheric plates move apart.

• Convergent plate boundaries form when two lithospheric plates move toward each other.

5.1 Interactions at Plate Boundaries

Divergent Plate Boundaries• Mid-ocean ridges occur along divergent plate

boundaries.

5.1 Interactions at Plate Boundaries

Divergent Plate Boundaries (cont.)

• Continental rifting occurs when two continental plates are being pulled apart.

– East African Rift

– Gulf of California

5.1 Interactions at Plate Boundaries

Convergent Plate Boundaries

• Three possible interactions:

– Ocean-to-ocean: two oceanic plates move towards each other—subduction occurs as one plate is forced down into the mantle beneath another plate

– Ocean-to-continent: oceanic plate subducts beneath continental plate

– Continent-to-continent: compression stresses force crust to rise up, thicken, and shorten

5.1 Interactions at Plate Boundaries

Convergent Plate Boundaries (cont.)

5.1 Interactions at Plate Boundaries

Transform Plate Boundaries• A transform plate boundary exists when

two plates slide horizontally past one another.

5.1 Interactions at Plate Boundaries

Transform Plate Boundaries (cont.)

• Oceanic transform plate boundaries connect pieces of the mid-ocean ridges.

• Transform plate boundaries can slice through continental lithosphere as strike-slip faults.

• Large earthquakes can occur on these faults and can be very destructive.

5.1 Interactions at Plate Boundaries

Where do most earthquake epicenters and volcanoes occur?

Lesson 1 Review

What type of deformation results from tension?

A thickening of the lithosphere

B compression of the lithosphere

C thinning of the lithosphere

D movement of rocks past each other

5.1 Interactions at Plate Boundaries

A B C D

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1. A

2. B

3. C

4. D

Lesson 1 Review

Subduction results from _____.

A one oceanic plate being forced into the mantle beneath another plate

B two plates moving away from each other

C two continental plates colliding with each other

D two continental plates sliding horizontally past each other

5.1 Interactions at Plate Boundaries

A B C D

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1. A

2. B

3. C

4. D

Lesson 1 Review

What type of plate boundary separates the North American and Pacific Plates in California?

A convergent

B rift

C transform

D divergent

5.1 Interactions at Plate Boundaries

A B C D

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2. B

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End of Lesson 1

San Andreas Fault

5.2 California Geology

Plate Tectonics in California

• A convergent plate boundary resides off the northern shore of California.

• This active plate tectonic setting produces earthquakes, volcanoes, and mountains.

• A continental transform plate boundary cuts across California.

5.2 California Geology

80 Million Years Ago

5.2 California Geology

Transform Plate Boundary• The San Andreas Fault is a transform

plate boundary between the North American and Pacific Plates.

• This boundary switches to an oceanic transform boundary when it goes out to sea.

5.2 California Geology

Convergent Plate Boundaries• Two small oceanic plates are being

subducted in the Cascadia Subduction Zone.

• This subduction zone forms a convergent plate boundary.

5.2 California Geology

California’s Mountains• California’s mountains often formed

from interactions at several plate boundaries.

5.2 California Geology

Subduction• The Klamath Mountains, Costal Ranges, peninsulas, and Sierra Nevada all

contain igneous and metamorphic rocks formed below the surface.

• These rocks were formed when an ancient oceanic plate subducted beneath the North American Plate.

5.2 California Geology

Rifting• Some mountains in California have formed from

tension stress.

• The Panamint Range is rising up as the crust in eastern California stretches.

5.2 California Geology

Lesson 2 Review

Convergent plate boundaries in California are important in _____.

A the development of California’s rift valleys

B the formation of California’s mountains

C movement along the San Andreas Fault

D the existence of the Gulf of California

5.2 California Geology

A B C D

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1. A

2. B

3. C

4. D

Lesson 2 Review

The San Andreas Fault is a transform plate boundary; this also makes it a _____.

A subduction zone

B convergent plate boundary

C rift valley

D strike-slip fault

5.2 California Geology

A B C D

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2. B

3. C

4. D

Lesson 2 Review

Which of the following are active California volcanoes?

A Lassen Peak and San Andreas

B Sierra Nevada and Mount Shasta

C Lassen Peak and Mount Shasta

D Panamint Range and Mount Shasta

5.2 California Geology

A B C D

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2. B

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End of Lesson 2

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Chapter Assessment

California Standards Practice

Image Bank

Science Online

Interactive Table

Virtual Lab

What does shearing stress produce when plates slide past each other?

A subduction zones

B strike-slip faults

C divergent plate boundaries

D rift valleys

Chapter Assessment 1

A B C D

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2. B

3. C

4. D

Where do mid-ocean ridges usually occur?

A convergent plate boundaries

B strike-slip faults

C divergent plate boundaries

D normal faults

Chapter Assessment 2

A B C D

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2. B

3. C

4. D

In what areas of the Earth does present-day continental rifting occur?

A eastern Africa and western South America

B the Gulf of California andeastern South America

C Gulf of California and the Himalayas

D eastern Africa and the Gulf of California

Chapter Assessment 3

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2. B

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Which two oceanic plates are being subducted in the Cascadia Subduction Zone?

A San Andreas and Juan de Fuca

B Juan de Fuca and Gorda

C Gorda and San Andreas

D San Andreas and Pacific

Chapter Assessment 4

A B C D

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2. B

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The San Andreas Fault is a(n) _____.

A strike-slip fault

B oceanic transform plate boundary

C subduction zone

D rift valley

Chapter Assessment 5

A B C D

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2. B

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Northern California is located _____.

A above a subduction zone

B below a subduction zone

C above a rift valley

D below a rift valley

CA Standards Practice 1

SCI 1.f

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2. B

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4. D

Which of the following scenarios would most likely result in the development of mountains?

A two oceanic plates pulling apart

B two continental plates colliding

C one oceanic and one continental plate colliding

D erosion by wind and water

CA Standards Practice 2

SCI 1.e

A B C D

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2. B

3. C

4. D

The Pacific Plate moves about 3.4 cm/year relative to the ____.

A Atlantic Plate

B San Andreas Plate

C North American Plate

D Gorda Plate

CA Standards Practice 3

SCI 7.g

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1. A

2. B

3. C

4. D

What is subduction?

A the process in which one plate is forced down into the mantle beneath the other plate

B the result of two plates moving away each other

C the process of two continental plates colliding

D the result of two plates sliding sideways past each other

CA Standards Practice 4

SCI 1.e

A B C D

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2. B

3. C

4. D

Deformation that results from compression stress is _____.

A the thickening of the lithosphere

B the melting of the rocks

C the thinning of the lithosphere

D always minimal

CA Standards Practice 5

SCI 1.e

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2. B

3. C

4. D

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