Download Plate Boundaries

Plate Tectonic Theory
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
Effects of Plate Tectonics
There 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 Boundaries
The 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, means to come together.”
Convergent Boundaries
Description: two plates that are pushing
together
Land Features Formed: island arcs,
trenches, volcanoes
Actual Examples: Himalayas, Mariana
Trench, Hawaiian Islands
Picture of Motion:

convergent boundary animation
Convergent Boundaries
What can convergent boundaries create?

earthquakes

island formation

mountain forming

volcanoes
Types of Convergent Boundaries
 Oceanic-Continental
ocean floor plate collides with a
less dense continental plate
Oceanic-Oceanic 
ocean floor plate collides with
another ocean floor plate
 Continental-Continental
continental plate collides
with another continental plate
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.”
Trench Formation
SUBDUCTION
When two
plates collide
(converge) one
plate moves
under the other
Convergent boundary of two oceanic plates.
island arc and a _____.
trench Example: _____
Japan
Creates an ________
Mariana Trench
Convergent boundary of an oceanic plate and a
continental plate. Forms a _______
volcanic mountain range
trench Examples: Cascades
Andes Mts
and a ______.
_______ or _______
Convergent boundary of two continental plates. Forms
folded mountain range. Examples: ___________,
Himalayas
a ______
Appalachians
Alps, ______________
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.
Convergent Boundary –
Indian and Eurasian Plates
“Convergent means to spread apart.”
Divergent Boundaries
Description: two plates that are diverging,
or moving away from each other
Land Features Formed: earthquakes, rift
valleys, and volcanoes
Actual Examples: African rift valley, midAtlantic ridge
Picture of Motion:

divergent boundary - seafloor
Divergent Boundaries
Divergent 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
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 means slide past one another.”
Transform Boundaries
Description: two plates that are sliding
past one another
Land Features Formed: earthquakes
Actual Examples: San Andreas Fault
Picture of Motion:
Transform Boundary
Transform Fault Boundaries
Transform Boundaries are the boundaries
between two plates that are sliding
horizontally past one another.
Plates Move Side by Side
Transform 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
past each other.
and Pacific plates are moving ____
San Andreas Fault in California
Example: ________________
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 crust
Faults
Mountain building
Land subsidence
Volcanoes
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)
Convection Currents
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.
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
No - These form at edges of plates or over hot spots
No - These are erosional landforms or minor uplift areas
c. New Land
d. Mountains
No - Forms when plates move apart
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
No - Mountains would form here from existing land.
b. In areas where two ocean plates come together
No - You would find trenches in this area.
c. In areas where plates are moving apart
Yes - When plates move apart it is due to magma reaching the surface. When magma cools
new land is formed.
d. In areas where two plates are sliding past each other
No - You would find land movement but not new land being formed