MOUNTAIN BUILDING

Layers of the Earth

Plate Boundaries

• 3 Kinds of Plate Boundaries
• Divergent
• Convergent
• Transform

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• Are the result of “pulling” forces
• Have small earthquakes
• Create many normal faults
• Are usually on the opposite side of the plate from a convergent boundary

• Collision of two plates
• Have all the large earthquakes
• 90% of all earthquakes happen here
• Ocean-continent collisions = subduction
• Explosive volcanoes
• Reverse faults

• Are the result of parallel and opposite forces
• Have small to medium earthquakes
• Create strike-slip faults
• Can cause streams to turn at right angles

Stress

Due mostly to plate movements, the earth’s crust is under a lot of stress. There are 3 types, shown at the right

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• “A” occurs where plates pull apart, divergent boundaries, and is called tension

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• “B” occurs where plates converge, and is called compression

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• “C” occurs where plates move past each other, at transform fault boundaries and is called shearing

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Strain

• Stress leads to strain on the crust which bends it.

If it is warm, under the

ground, it can bend.

The features are called

folds.

• Upturned folds are anticlines while downturned folds are synclines.
• Or the rock may break, if it is brittle. This causes faults –breaks of the earth.

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anticline

syncline

A fold above and

a fault below

Different faults

Faults move in different ways, depending on the type of stress on them. Remember “3” types form.

1. Normal fault
2. Strike slip fault
3. Reverse fault

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Can you match the stress and strain?

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Plate Tectonic and Mountain Formation

• The most common types of mountains:
1. Folded Mountains: from when rock layers are squeezed together and pushed upward –Ural Mountains (Russian)

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• Fault-Block Mountains: form when tension causes land to drop down – Teton Range (USA)

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• Volcanic Mountains: molten material rises to the Earth’s surface and erupts on the surface - Mount Kilimanjaro (Tanzania)

Mountain Formation

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Mountains can be a result of:

1. Continental Collisions (Himalayan Mountains; Alps in Europe)
2. Subduction Zones (Andes Mountains)
3. Fault Block Mountains (Grand Tetons, Wasatch Range)
4. Volcanic Eruptions (Mount Kilimanjaro-Africa; Parícutin-Mexico)
5. Hot Spots (Mauna Kea- Hawaiian Islands)
6. Sea-floor Spreading (Mt. Oraefajokull -Iceland: Mid-Atlantic Ridge)

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Continent-Continent Collision

• When two (2) continental plates come together.
• The plates push up and form mountains

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• (Example: Himalayas)

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• When continental crust pushes against continental crust both sides of the convergent boundary have the same properties.

• Neither side of the boundary wants to sink beneath the other side, and as a result the two plates push against each other and the crust buckles and cracks, pushing up (and down into the mantle), forming high mountain ranges.

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• Examples:
• The European Alps
• Himalayan Mountains

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Alps in Europe

Collision of Africa and Eurasia

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COLLISION MOUNTAINS

Where two continental plates collide the plates will buckle and compress or one will be pushed under the other.

Today the Indian Plate is being pushed under the Eurasian Plate creating the Himalayan Mountain Range and the Tibetan Plateau.

Mt. Everest

Himalayas�

Subduction Zones

Andes Mountains in South America

• SUBDUCTION
• Nazca Plate dives under the South American Plate

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Andes formed along the coast of South America

ONE TYPE OF MOUNTAIN BUILDING IS CALLED: SUBDUCTION VOLCANOES�

• Far beneath the mountains, the descending plate has carried seawater down with it.
• As the plate heats up from friction and from exposure to the hot mantle, the water is expelled, and magma begins to form.
• The magma rises up into the plate above melting and incorporating bits of the continent and becoming more and more silica-rich.

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Energy Source:

Friction & Heat from Earth’s interior

Subduction Volcano

EXAMPLES OF SUBDUCTION VOLCANOES IN WASHINGTON STATE

Mt. Rainier

Mt St. Helens

WHAT ABOUT THE ROCKY MOUNTAINS?

The Rocky Mountains were built very slowly between 70 and 30 million years ago during the Laramide Orogeny. During this time there was a unusually shallow subduction zone that allow mountain building much further inland than would be expected.

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• Normal Subduction Zone Unusual Subduction Zone
• Steep Shallow

Convergent: Ocean/ocean Japanese Islands�

Volcanoes in Japan

Fault Block Mountains

• The result of the tension stress pulling apart at a fault line (or plate boundary) this is also called rifting as it leads to a valley with a steep wall.
• Two types of Fault Block Mountains
• Lifted Block Mountains
• Tilted Block Mountains

Lifted Block Mountains

• This happens when multiple faults form from the same stress. This leads to the formation of two rift valleys with a raised section in the middle.
• The Horst in the middle can take various shapes and those shapes are used to describe the different types.

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Tilted Block Mountains

• With tilted Block Mountains it forms one large fault and then as it lifts up you get mountains with a steep face and then a slopping back
• Teton Range in Idaho and the Wasatch Range in Utah

Volcanic Mountains

• A recent witnessed example of a volcano being born was the spectacular event that began on February 20, 1943, when a farmer's cornfield in Mexico suddenly began to erupt. By the second day, the cone had risen to 100 feet (30.5 m.). By two weeks it was 450 feet high (137 m.), and when the eruptions finally ceased in 1952 the cone had risen to 1,350 feet (411 m.).

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Volcán de Parícutin

Mountain Formation

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Mountains can be a result of:

1. Continental Collisions (Himalayan Mountains; Alps in Europe)
2. Subduction Zones (Andes Mountains)
3. Volcanic Eruptions (Mount Kilimanjaro-Africa; Parícutin-Mexico)
4. Hot Spots (Mauna Kea- Hawaiian Islands)
5. Sea-floor Spreading (Mt. Oraefajokull -Iceland: Mid-Atlantic Ridge)

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