unit 4 lesson 7 mountain building - greenfield-central...

Unit 4 Lesson 7 Mountain Building

Indiana Standards

Copyright © Houghton Mifflin Harcourt Publishing Company

• 7.2.4 Explain how convection currents in the mantle cause lithospheric plates to move causing fast changes like earthquakes and volcanic eruptions, and slow changes like creation of mountains and formation of new ocean floor.

• That means that when the earths crust changes

quickly, it is usually caused by earthquakes and

volcanoes and s l o w changes to earths crust result

in mountain building and new ocean floor.

Stressed Out


How can tectonic plate motion cause deformation?

• The movement of tectonic plates causes stress on rock structures.

• Stress is the amount of force per unit area that is placed on an object.

• When a rock is placed under stress, it deforms, or changes shape, in a process called deformation.

• Deformation can cause rock to bend or break.


What are two kinds of folds?

• Folding occurs when rock layers bend under stress.

• Rock layers start out as horizontal layers deposited over time.

• A fold, or bend, in the rock layers means that deformation has happened.

• Two common types of folds are synclines and anticlines.



Two Types of Folds



• Syncline, the youngest layers of rock are at the core of the fold and the oldest are found on the outside.

• Anticline, the oldest layers of rock are at the core of the fold and the youngest are found on the outside.

Faulted


What are the three kinds of faults?

• Sometimes rock is under so much stress that it breaks.

• A crack called a fault forms when large blocks of rock break and move past each other.

• The three main kinds of faults are strike-slip faults, normal faults, and reverse faults.



• Faults are classified based on how the fault blocks move.

• The fault plane is the location where two fault blocks meet.

• The fault block that tilts over the fault plane is called the hanging wall.

• The fault block below the hanging wall is called the footwall.




• In a strike-slip fault, the fault blocks move past each other horizontally.

• Strike-slip faults form when rock is under shear stress, or stress that results from the sliding of rock structures in parallel but opposite directions.




• In a normal fault, the hanging wall moves down relative to the footwall.

• Normal faults form when rock is under tension, which is stress that stretches or pulls rock apart.




• In a reverse fault, the hanging wall moves up relative to the footwall.

• Reverse faults form when rocks undergo compression, which is stress that squeezes or pushes rock together.



Moving on Up


What are the three kinds of mountains?

• Mountains can form through folding, volcanism, and faulting.

• The process by which land rises or mountains form is called uplift.

• Because tectonic plates are always in motion, some mountains are constantly uplifting.



• Folded mountains form when rock layers are squeezed together and pushed upward.

• Most folded mountains form at convergent boundaries.




• Volcanic mountains form when melted rock erupts onto Earth’s surface.

• Most volcanic mountains form at convergent boundaries.




• Fault-block mountains form when tension makes the lithosphere break into many normal faults.

• Pieces of the lithosphere sink, and the blocks left standing are the mountains.



unit 4 lesson 7 mountain building - greenfield-central...

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