Plate Boundaries

Both Hess’s discovery and Wegner’s continental drift theory combined into what scientists now call the Plate Tectonic Theory

Theory of Plate Tectonics: • The Earth’s crust and part of the

upper mantle are broken into sections, called plates which move on a plastic-like layer of the mantle

Plate Tectonic Theory

Effects of Plate TectonicsThere are several geological processes that occur where plates meet:

1. Volcanoes - tend to erupt at plate margins as a result of a process called subduction

2. Earthquakes - occur where plates grind against or over one other

3. Mountain building - occurs as one plate is pushed over another

4. Seafloor spreading - occurs where two oceanic plates pull apart

Plate BoundariesThe earth’s tectonic plates continue to gradually move even today. The plates interact. Where one plate meets another, it is called a boundary.

Divergent: Boundary between two plates that are moving apart

Convergent: Boundary between two plates that are pushing together.

Subduction Zone: The area where one plate pushes down under another. Volcanoes are often created by this.

Transform (Strike-slip): Boundary between two plates that are sliding past one another.

The 3 Types of Plate Boundaries

Convergent BoundariesDescription: two plates that are pushing together

Land Features Formed: island arcs, trenches, volcanoes

Actual Examples: Himalayas, Mariana Trench, Hawaiian Islands

Picture of Motion:

“Convergent, means to come together.”

convergent boundary animation

Convergent Boundaries

What can convergent boundaries create? earthquakes island formation mountain forming volcanoes

Oceanic-Continental

Oceanic-Oceanic

Continental-Continental

ocean floor plate collides with a less dense continental plate

ocean floor plate collides with another ocean floor plate

continental plate collideswith another continental plate

Types of Convergent Boundaries

Convergent Boundaries

Oceanic/oceanic Subduction occurs

Oceanic/continental Oceanic plate sinks

Continental/continental Mountain ranges form

When two plates collide (converge) one plate moves under the other. This process is called “subduction.”

Convergent boundary of two oceanic plates.

Creates an ________ and a _____. Example: _____island arc trench Japan

Trench FormationSUBDUCTIONWhen two plates collide (converge) one plate moves under the other

Mariana Trench

Convergent boundary of an oceanic plate and a continental plate. Forms a _______ mountain range and a ______. Examples: _______ or _______ Mts

volcanictrench Cascades Andes

Convergent boundary of two continental plates. Forms a ______ mountain range. Examples: ___________, Alps, ______________

folded HimalayasAppalachians

The convergent boundary of the Eurasian and Indian Plates has resulted in the formation of the highest mountain range in the world – The Himalayas

This illustration shows the movement of the

land mass known as

India today. As it moved

on the Indian plate through

time, over millions of years,

it finally collided with the

Eurasian plate forming the

Himalayan Mountains

Mount Everest is the tallest mountain in the world, at over 29,000 ft. and is part of the Himalayas. This is a result of the Eurasian and Indian Plates colliding and it is still getting higher as these two plates continue to collide.

This map shows the large Himalayan Mountain range that has resulted from the collision of these two continental plates; which continues today.

Indian Plate

Eurasian Plate

Convergent Boundary – Indian and Eurasian Plates

Divergent BoundariesDescription: two plates that are diverging, or moving away from each other

Land Features Formed: earthquakes, rift valleys, and volcanoes

Actual Examples: African rift valley, mid-Atlantic ridge

Picture of Motion:

“Convergent means to spread apart.”

divergent boundary - seafloor

Divergent BoundariesDivergent Boundaries are the boundaries between two plates that are diverging, or moving away from each other.

divergent boundary - rift valley

When plates are spreading apart from one another there is a lot of geological activity. Earthquakes, and volcanoes occur here.

• In some places like East Africa, a rift valley can form that is hundreds of feet deep.

Divergent Boundary – Arabian and African Plates

Arabian Plate

African PlateRed Sea

Divergent boundary of two continental plates

East African Rift Zone

The Mid-Atlantic Ridge is one of the world’s largest divergent plates, running North to South in just about the center of the Atlantic Ocean. All along this ridge, volcanic activity takes place and the sea floor is spreading East and West at a rate of 1.25 cm per year. The divergent plate in Iceland is part of the Mid-Atlantic Ridge.

This map shows a divergent plate in Iceland. You can tell from the arrows that the Eurasian Plate and the North American Plate are spreading apart from one another

Transform BoundariesDescription: two plates that are sliding past one another

Land Features Formed: earthquakes

Actual Examples: San Andreas Fault

Picture of Motion:

“Transform means slide past one another.”

Transform Boundary

Transform Fault Boundaries

Transform Boundaries are the boundaries between two plates that are sliding horizontally past one another.

Plates Move Side by SideTransform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.

Earthquakes in Austin

Transform-fault boundary where the North American and Pacific plates are moving ____ each other.

Example: ________________ in California

past

San Andreas Fault

The San Andreas Fault, seen

here, is the result of the Pacific

Plate sliding past the North

American Plate. This is the site

of many of the earthquakes that

occur in the United States.

Changing Earth’s Surface

Plate movement can alter Earth systems and produce changes in Earth’s surface

Deformation of the crustFaultsMountain buildingLand subsidenceVolcanoes

Mechanism for Plate Tectonics

Why do the plates move?

• Due to tremendous heat, rock in the asthenosphere is like hot taffy

• This allows plates to ride on top of hot, flowing rock

• Plates move because heat is being released from deep inside the earth

• Convection currents cause hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge)

Plates are “pushed” and “pulled” over the surface of the Earth due to unbalanced forces.

When convection currents reach the surface, plates are pushed apart

As the plates move away from each other, part of them are pulled into the Earth’s mantle

Convection Currents

Because temperature increases with depth, the inside of the earth is very hot. Rock near the core is heated and becomes less dense. It slowly rises while cooler rock nearer the surface is more dense and sinks. This forms convection currents just like those in our atmosphere.

As these convection currents in the mantle circulate, they cause the continents above them to move. What Wegener had no way of knowing is that the force that is driving plate tectonics is convection currents in the mantle.

Con

vect

ion

Cur

rent

s

Another way to relate to

convection currents is like

when you boil soup. As the

soup heats up, it rises to the

top of the container where it

begins to cool and sinks,

causing convection currents

to form, re-creating the same

process that takes place in

our Earth.

As two continental plates move toward each other, what landforms would you expect to see?a. Volcanoes

b. Cliffs

c. New Land

d. Mountains

No - These form at edges of plates or over hot spots

No - Forms when plates move apart

No - These are erosional landforms or minor uplift areas

Yes - because 2 continental masses will push into each other and “crumple” the edges to form mountains

Where would you find the newest land on Earth?a. In areas of continental convergence

b. In areas where two ocean plates come together

c. In areas where plates are moving apart

d. In areas where two plates are sliding past each other

No - Mountains would form here from existing land.

No - You would find land movement but not new land being formed

No - You would find trenches in this area.

Yes - When plates move apart it is due to magma reaching the surface. When magma cools new land is formed.