Section 4 Deforming the Earth’s Crust

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Section 4 Deforming the Earth’s Crust

Bellringer

Compare the mountains in the photographs. Write a description of each mountain, and suggest how it might have formed.

Do you know where these various types of mountains are found in the world? Have you ever visited any of them? Would it ever be dangerous to study them?

Chapter F4



Objectives• Describe the types of stress that deform rocks

and the major types of folds and faults.• • Identify the most common types of mountains and

explain the difference between uplift and subsidence.

Section 4 Deforming the Earth’s CrustChapter F4



Agenda• Day 1• Today we will:

• Do a do now.• Complete a start up activity.• Learn about mountains.

• Day 2• Today we will:




Objectives• compression• tension• folding

• syncline• anticline

• fault• uplift• subsidence




Deformation• Whether a material bends or breaks depends on the how much stress is applied to the material.

• Stress is the amount of force per unit area on a given material.

• Different things happen to rock when different types of stress are applied.




Deformation, continued• The process by which the shape of a rock changes because of stress is called deformation.

• Rock layers bend when stress is placed on them.

• When enough stress is placed on rocks, they can reach their elastic limit and break.




Deformation, continued• The type of stress that occurs when an object is squeezed, such as when two tectonic plates collide, is called compression.

• When compression occurs at a convergent boundary, large mountain ranges can form.




Deformation, continued• Tension is stress that occurs when forces act to stretch an object.

• Tension occurs at divergent plate boundaries, such as mid-ocean ridges, when two tectonic plates pull away from each other.




Folding• The bending of rock layers because of stress in the Earth’s crust is called folding.

• Types of Folds Depending on how rock layers deform, different types of folds are made.

• The major types of folds are anticlines, synclines, and monoclines.




Folding, continued• Anticlines are upward-arching folds.

• Synclines are downward, troughlike folds.




Folding, continued• In a monocline, rock layers are folded so that both ends of the fold are horizontal.




Faulting• Some rock layers break when stress is applied. The surface along which rocks break and slide past each other is called a fault.

• The blocks of crust on each side of the fault are called fault blocks.




Faulting, continued• When a fault is not vertical, its two sides are either a hanging wall or a footwall.




Faulting, continued• The type of fault depends on how the hanging wall and footwall move in relationship to each other.

Section 4 Deforming the Earth’s Crust

•When a normal fault moves, it causes the hanging wall to move down relative to the footwall.

Chapter F4



Faulting, continued• When a reverse fault moves, it causes the hanging wall to move up relative to the footwall.




Faulting, continued• A third major type of fault is a strike-slip fault. These faults form when opposing forces cause rock to break and move horizontally.




Plate Tectonics and Mountain Building

• When tectonic plates collide, land features that start as folds and faults can eventually become large mountain ranges.

• When tectonic plates undergo compressions or tension, they can form mountains in several ways.




Mountain Building, continued• Folded Mountains form when rock layers are squeezed together and pushed upward.

• Fault-Block Mountains form when large blocks of the Earth’s crust drop down relative to other blocks.

• Volcanic Mountains form when magma rises to the Earth’s surface and erupts.




Uplift and Subsidence• Vertical movements in the crust are divided into two types—uplift and subsidence.

• Uplift is the rising of regions of the Earth’s crust to higher elevations.

• Subsidence is the sinking of regions of the Earth’s crust to lower elevations.




Uplift and Subsidence, continued• Uplifting of Depressed Rocks Uplift can occur when large areas of land rise without deforming.

• One way areas rise without deforming is process known as rebound. When the crust rebounds, it slowly springs back to its previous elevation.




Uplift and Subsidence, continued• Subsidence of Cooler Rocks Rocks that are hot take up more space than cooler rocks.

• The lithosphere is relatively hot at mid-ocean ridges, but cools as it moves farther from the ridge.

• As it cools, the oceanic lithosphere takes up less volume and the ocean floor subsides.




Uplift and Subsidence, continued

• Tectonic Letdown Subsidence can also occur when the lithosphere becomes stretched in rift zones.

• A rift zone is a set of deep cracks that forms between two tectonic plates that are pulling away from each other.

• As tectonic plates pull apart, stress between the plates causes a series of faults to form along the rift zone.




Exit Ticket

• What are mountains? Explain at least 2 ways in which they form.



Plate Tectonics

Concept MapUse the terms below to complete the concept map on the next slide.

transform boundaries

tectonic plates

divergent boundaries

converge

diverge

Chapter F4



Plate TectonicsChapter F4



End of Chapter F4 Show

Chapter F4



Reading

Read each of the passages. Then, answer the questions that follow each passage.

Standardized Test PreparationChapter F4



Passage 1 The Deep Sea Drilling Project was a program to retrieve and research rocks below the ocean to test the hypothesis of sea-floor spreading. For 15 years, scientists studying sea-floor spreading conducted research aboard the ship Glomar Challenger. Holes were drilled in the sea floor from the ship.

Continued on the next slide




Passage 1, continued Long, cylindrical lengths of rock, called cores, were obtained from the drill holes. By examining fossils in the cores, scientists discovered that rock closest to mid-ocean ridges was the youngest. The farther from the ridge the holes were drilled, the older the rock in the cores was. This evidence supported the idea that sea-floor spreading creates new lithosphere at mid-ocean ridges.




1. In the passage, what does conducted mean?

A directed

B led

C carried on

D guided




2. Why were cores drilled in the sea floor from the Glomar Challenger?

F to determine the depth of the crust

G to find minerals in the sea-floor rock

H to examine fossils in the sea-floor rock

I to find oil and gas in the sea-floor rock




3. Which of the following statements is a fact according to the passage?

A Rock closest to mid-ocean ridges is older than rock at a distance from mid-ocean ridges.

B One purpose of scientific research on the Glomar Challenger was to gather evidence for sea-floor spreading.

C Fossils examined by scientists came directly from the sea floor.

D Evidence gathered by scientists did not support sea-floor spreading.




Passage 2 The Himalayas are a range of mountains that is 2,400 km long and that arcs across Pakistan, India, Tibet, Nepal, Sikkim, and Bhutan. The Himalayas are the highest mountains on Earth. Nine mountains, including Mount Everest, the highest mountain on Earth, are more than 8,000 m tall.

Continued on the next slide




Passage 2, continued The formation of the Himalaya Mountains began about 80 million years ago. A tectonic plate carrying the Indian subcontinent collided with the Eurasian plate. The Indian plate was driven beneath the Eurasian plate. This collision caused the uplift of the Eurasian plate and the formation of the Himalayas. This process is continuing today.




1. In the passage, what does the word arcs mean?

A forms a circle

B forms a plane

C forms a curve

D forms a straight line




2. According to the passage, which geologic process formed the Himalaya Mountains?

F divergence

G subsidence

H strike-slip faulting

I convergence




3. Which of the following statements is a fact according to the passage?

A The nine tallest mountains on Earth are located in the Himalaya Mountains.

B The Himalaya Mountains are located within six countries.

C The Himalaya Mountains are the longest mountain range on Earth.

D The Himalaya Mountains formed more than 80 million years ago.




Interpreting GraphicsThis illustration shows the relative velocities (in centimeters per year) and directions in which tectonic plates are separating and colliding. Arrows that point away from one another indicate plate separation. Arrows that point toward one another indicate plate collision.




1. Between which two tectonic plates does spreading appear to be the fastest?

A the Australian and the Pacific

B the Antarctic and the Pacific

C the Nazca and the Pacific

D the Cocos and the Pacific




2. Where do you think mountain building is taking place?

F between the African and South American plates

G between the Nazca and South American plates

H between the North American and Eurasian plates

I between the African and North American plates




Math

Read each question, and choose the best answer.




1. The mesosphere is 2,550 km thick, and the asthenosphere is 250 km thick. If you assume that the lithosphere is 150 km thick and that the crust is 50 km thick, how thick is the mantle?

A 2,950 km

B 2,900 km

C 2,800 km

D 2,550 km




2. If a seismic wave travels through the mantle at an average velocity of 8 km/s, how many seconds will the wave take to travel through the mantle?

F 318.75 s

G 350.0 s

H 362.5 s

I 368.75 s




3. If the crust in a certain area is subsiding at the rate of 2 cm per year and has an elevation of 1,000 m, what elevation will the crust have in 10,000 years?

A 500 m

B 800 m

C 1,200 m

D 2,000 m




4. A very small oceanic plate is located between a mid-ocean ridge and a subduction zone. At the ridge, the plate is growing at a rate of 5 km every 1 million years. At the subduction zone, the plate is being destroyed at a rate of 10 km every 1 million years. If the oceanic plate is 100 km across, how long will it take the plate to disappear?

F 100 million years

G 50 million years

H 20 million years

I 5 million years




Section 1 Inside the EarthChapter F4



Section 2 Restless ContinentsChapter F4



Section 3 The Theory of Plate TectonicsChapter F4

Section 4 Deforming the Earth’s Crust

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Transcript of Section 4 Deforming the Earth’s Crust