Plate Tectonics refers to the movements
of plates (large segments of continents
and ocean) around the Earth’s surface.
 These land masses are seen as a giant
jigsaw puzzle, and any one mass can’t
move without creating gaps between or
overlaps with other pieces
 They move on the Lithospheric plates on
the Liquid Mantle and move along by
convection currents in the magma.

There are 7 major plates and 5 minor
plates – 12 plates total.
 It is on the edges of the plates – near the
borders of plates where all the action is!
(earthquakes, volcanoes, mountain
building!)
 These edges of the plates are called
PLATE BOUNDARIES

These tectonic plates move
approximately 1 inch per year due to
CONTINENTAL DRIFT!!!
 So in 100 million years, there will be 1250
miles of movement!!

 The
ring of Fire is a Ring around the
Pacific ocean (on the edges of the
Pacific tectonic plate) where there are
numerous volcanoes and
Earthquakes.
 Why???...There are 7 other plates that
meet the edges of the Pacific plate
there– so there is lots of jostling,
smashing, and moving where all the
edges meet.
At the edges of the plates is where all the
action occurs because of all the jostling
that takes place
 When Plates move – there are
only 3 choices they have…
 1) crash directly into each other and one
goes under the other
 2) separate from each other
 3)slide past/along one another

1) DIVERGENT boundaries
 2 plates move away from each other
opening a gap called a spreading
center
 Sometimes, molten rock rises to the
Earth’s surface in the trench and this area
is called a
HOT SPOT
As molten rock comes up through the
trench created by the diverging plates, it
pushes the old crust aside causing it to
buckle.
 This process is called RIDGE PUSH

This is the symbol on a map for
divergent boundaries
RIDGE PUSH
Ridge
 When
tectonic plates diverge, pull
part, over water, the spreading center
is called spreading ridge or oceanic
ridge.
 Because the magma rising up through
the trench and pushes the old crust
aside, new sea floor is created
 This is called SEA FLOOR SPREADING
It is an area in the
middle of the
Atlantic ocean that
is forming an ocean
ridge
 Sea floor spreading

When tectonic plates diverge, pull apart,
under land, the spreading center is
called a rift valley.
 This is less common than spreading
under water


Diverging
plates in
eastern
Africa are
slowly
breaking
Africa into
pieces
creating rift
valleys at
the
spreading
centers
2) CONVERGENT Boundaries
 When 2 plates move toward each-other
 When they collide, they push on each
other and one plate dives under the
other. The one that dives under is the
more dense (heavier) plate.
 The process of one plate diving under
the other is called SUBDUCTION.
 Places where you find subduction are
called Subduction zones.
When Subduction occurs – the edge of the
plate subducts deep into the mantle and
starts to melt creating magma. That
magma can make it’s way up through
cracks in the crust and form volcanoes.
 When the plate subducts, it “pulls” the rest
of the plate with it - This is called Slab pull (
the whole slab is pulled under the other
slab)
 This slab pull helps keep the tectonic plates
in motion.






When a dense (heavier) oceanic plate
collides with a less-dense (lighter) continental
plate, the oceanic plate subducts.
This creates a deep underwater valley called
a trench.
As the subducting plate moves deeper, it starts
to melt and magma can work it’s way to the
surface forming cone-shaped Volcanoes
A chain of volcanoes = Volcanic belt
This force of collision between the 2 plates
creates mountain ranges as the continental
rock crumbles and folds
Symbol for converging plates
Subduction occurs when 2 oceanic
plates converge/collide.
 The denser plate subducts under the
other, a deep ocean trench is formed,
and the subducting plate sinks deep into
the mantle
 This interaction may produce a long
chain of volcanic islands known as a
Volcanic island arc ( ie. Japan islands)

When continental plates collide, subduction
DOES NOT occur because the plates are the
same density.
 Instead, the plates hit head on and their
edges crumple and fold forming great
Mountain ranges ( ie. The Himalayas)
 The Himalayas are the highest and
youngest mountain range and are
increasing in height several cm a year due
to continuous convergence of the plates!

3) Transformation boundaries
 2 plates slide past one another
 Because they are sliding horizontally
past each other –
no mountains or
volcanoes are formed
 Faults (breaks in rock
layers due to
movement on either
side) forms.
 San Andreas Fault
DIVERGENT
CONVERGENT
TRANSFORM