Transcript
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Stress, Faulting, Folding, Mountain BuildingInside Earth:

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•Have you ever tried to bend something, only to have it break?

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How can material bend at one time and break at another?• The answer is that the stress you put on the material was different each time.

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

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This same principle applies to the rocks in the Earth’s crust• Different things happen to rock when different

types of stress are applied.

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Deformation• Deformation is the process

by which a rock changes because of stress.

• Rock layers bend when stress is placed on them.

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

• There are two kinds of stress:• Compression• Tension

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Compression• This type of stress

occurs when an object is squeezed.• Tectonic plates collide

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

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Tension• Another form of

stress is tension.• Tension is the stress

that occurs when forces stretch an object.

• They occur at divergent boundaries.•Mid Ocean ridges

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Folding• The bending of rock layers because of stress in

the Earth’s crust is called folding.

• Scientists assume that all rock layers started as horizontal layers.

• When they see folding, they know that deformation has occurred

• There are three types of folding: anticlines, synclines and monoclines

• http://www.youtube.com/watch?v=jVyBsUgD7Gk&safety_mode=true&persist_safety_mode=1

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Anticlines• Upward arching

folds

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Synclines• Down-ward, trough-

like folds

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Monoclines• Rock layers are

folded so that both ends of the fold are horizontal.

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Faulting• Some rock layers break when stress is

applied to them.• The surface along which rocks break and

slide past each other is called a fault.• The blocks of crust one each side of the

fault is called a fault-block.

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Not all faults are vertical…• And understanding the

difference between it’s two sides, called hanging walls and foot walls is useful.

• The type of fault that forms depends on how the hanging wall and foot wall move in relationship to each other.

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Normal Faults• When a normal

fault moves, it causes the hanging wall to move down relative to the footwall.

• Normal faults usually occur when tectonic forces cause tension that pull rocks apart

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Reverse Faults• When a reverse

fault moves, it cause the hanging wall to move up relative to the footwall.

• Usually happen when tectonic forces cause compression that pushes rocks together

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Strike-Slip Faults• The third type of

fault is called a strike-slip fault

• These form when opposing forces cause rock to break and move horizontally.

• The San Andreas fault is a strike-slip fault

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Plate Tectonics and Mountain Building• http://www.youtube.com/watch?v=jqEo6nnSvhM&safety_mode=true&persist_safety_mode=1

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

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Mountains exist because tectonic plates are constantly moving around• As a result of this movement, they collide with

each other.

• Mountains, such as the Andes Mountains in South America, form in the subduction zone where two tectonic plates converge.

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Mountains are formed in several ways• The three most common types of

mountains are classified by the way they were formed

•Folded Mountains

•Fault-Block Mountains

•Volcanic Mountains

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Folded Mountains• Formed at the

convergent boundaries where the continents have collided.

• Formed when rock layers are squeezed together and pushed upward.

• The highest mountain ranges in the world• Appalachians• Himalayas

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Fault-Block Mountains• Form when tension

pulls on large blocks of the Earth’s crust to drop down relative to other blocks.

• Sharp, jagged peaks

• Grand Tetons in Wyoming

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Volcanic Mountains• Most of the world’s major

volcanic mountains are located at convergent boundaries.• Ring of Fire!

• They form when magma rises to the Earth’s surface and erupts, forming a volcanic mountains.

• Can also be found underwater

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Uplift and Subsidence• Vertical movements in the Earth’s crust are

divided into two types.

• Uplift: created by the rising of the Earth’s crust to higher elevations

• Subsidence: The sinking of the Earth’s crust to low.er elevations

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Compression Th


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