Plate Tectonics
Types of Plate Movement
Tectonic Plates
• The lithosphere of the earth is broken up into
small pieces.
• These small pieces are called tectonic plates.
• The tectonic plates move as the convection
currents in the mantle turn and add new
seafloor at divergent boundaries, and recycle
old seafloor at convergent boundaries.
Tectonic Plates
Tectonic Plates
• The location where two plates meet is called a
plate boundary
• Plates can move in three directions at plate
boundaries: toward each other, away, or slide
past
Plate Boundary
• As the plates move relative to each other, a
few things can happen
• We are going to explore what happens at
each of the boundaries
Transform Boundary
plates slide past
Transform boundary
• Plates slip past each other, moving in opposite
directions called a fault
• are breaks in earth’s crust where rocks have
slipped past each other
• Earthquakes occur
Transform Boundary- plates slip
past each other
Transform - occur at a fault
Transform - cause earthquakes to
occur
Divergent Boundary
plates move away from each other
Divergent Boundary
• Plates move apart from each other
• Creates sea floor ridges in the ocean
• Most occur along the mid-ocean ridges (new
crust is added during sea-floor spreading)
• Rift Valley is where several pieces of Earth’s
crust have diverged on land
Divergent - plates move away from
each other
Divergent - new sea floor is added
at mid ocean ridges (in the ocean)
Two Oceanic plates that diverge
form a mid ocean ridge
Divergent- a rift valley forms when
2 pieces of continental crust
diverge on land
Two continental plates that
diverge form a rift valley
Convergent Boundary
plates move toward
Convergent Boundary
• Plates come together
• Creates sea floor trenches when oceanic crust and
continetal crust come together
• The plate that is more dense sinks under the less
dense plate
• Oceanic crust is more dense than continental crust
so it sinks underneath the continental crust. This
process is called subduction - where old oceanic
crust is recycled
• Mountains occur on land
Convergent - Trench: old oceanic crust sinks beneath
continental crust in a process called subduction
Convergent - when 2 continental
crusts collide, it creates a
mountain
Recap
Self Assessment
Click through the following slides and ask
yourselves the question that is there. Once you
have mentally answered the question, click next
to reveal the correct answer.
#1 Great African Rift Valley
What kind of boundary caused the
african rift valley?
A) Transform
B) Divergent
C) Convergent
Answer: Divergent
When 2 continental plates diverge on land, it is
called a rift valley
#2 The Himalayas
What kind of boundary caused the
Himalayas?
A) Transform
B) Divergent
C) Convergent
Answer: Convergent
When 2 continental plates converge on land, it
forms mountains
#3 San Andreas
Fault
What kind of boundary caused the
San Andreas Fault?
A) Transform
B) Divergent
C) Convergent
Answer: Transform
When 2 continental plates slide past each other,
it forms a fault.
Earthquakes typically occur at a fault. This is
why there are so many earthquakes in
California.
#4 Mariana Trench
What kind of boundary caused the
Mariana Trench?
A) Transform
B) Divergent
C) Convergent
Answer: Convergent
When an oceanic crust and continental crust
converge, it is called a trench.
What is happening at the trench
A) oceanic crust sinks beneath the continental
because it is more dense
B) continental crust sinks beneath of the
oceanic crust because it is more dense
C) new sea floor is added
D) old sea floor is recycled
E) both A & D
F) both B & C
Answer: E
When a continental crust and oceanic crust
converge, it forms a trench.
At the trench, the oceanic crust sinks beneath
the continental crust because it is more dense
This process causes old seafloor to be recycled
back into the mantle
What is the name of the process
that occurs at the trench
A) Sea Floor Spreading
B) Subduction
Answer B: Subduction
When old sea floor is recycled back into the
mantle as the oceanic crust sinks beneath the
continental crust, the process is called
subduction.
#5 Mid Atlantic Ridge, Iceland
What kind of boundary caused the
Mid Ocean Ridge ?
A) Transform
B) Divergent
C) Convergent
Answer: A Divergent
when 2 oceanic plates move away from each
other in different directions at a divergent
boundary, it is called a mid ocean ridge
What is happening at the mid
ocean ridge
A) oceanic crust sinks beneath the continental
because it is more dense
B) continental crust sinks beneath of the
oceanic crust because it is more dense
C) new sea floor is added
D) old sea floor is recycled
E) both A & D
F) both B & C
Answer C
At a mid ocean ridge, as 2 oceanic plates move
away from each other, new sea floor bubbles up
from the mantle. This is why the age of the
seafloor is brand new along mid ocean ridges.
As new seafloor is added old sea floor gets
pushed toward the trench where it will get
recycled in the mantle.
What is the name of the process
that occurs at the mid ocean ridge
A) Sea Floor Spreading
B) Subduction
Answer: A Sea Floor Spreading
The process of adding new sea floor as two
oceanic plates move away from each other or
diverge is called sea floor spreading
Map of Tectonic Plates
Use the arrows in the map to
determine where you see a
divergent, convergent, or
transform boundary
Example: What kind of boundary
exists between the Antarctic Plate
and Pacific Plate?
Answer: Divergent
most likely, we would find a mid ocean ridge
here because the plates diverge in the ocean