Plate Tectonics Rock!!!
Theory of Plate Tectonics
A rigid slab of solid rock is called a plate.
Tectonics is a Greek word meaning “to build”.
The theory of plate tectonics states that the lithosphere is
broken into several plates that are moving relative to one
another as they ride on top of hotter, more mobile
material known as the asthenosphere.
How Does Plate Tectonics Work?
• The plates ride on top of the asthenosphere due to the
fact that the elements of the rock in the lithosphere are
less dense than the elements of the rock in the ductile
• These plates have different types of boundaries with
each other and each type of boundary has different
Divergent Plate Boundaries
• The first type of boundary is known as a
divergent plate boundary.
• Divergent boundaries occur along
spreading centers where plates are
moving apart and new crust is created by
magma pushing up from the mantle.
• Divergent boundaries create mid-ocean
ridges, which are underwater mountain
ranges formed as new crust is created
from magma rising from the mantle. The
most famous mid-ocean ridge is called
the Mid-Atlantic Ridge located between
Europe and North America which is
currently ripping apart Iceland.
• Divergent boundaries also create rift
valleys. Rift valleys are valleys formed
when lithospheric plates are pulled apart.
This is currently occurring in Africa and is
known as the The Great Rift Valley.
Volcanoes are often created at these
sites due to the magma rising up from the
Convergent Plate Boundaries
• Convergent boundaries, the next type of plate
boundary, is where crust destruction occurs.
This is where two plates collide together.
• There are three different types of convergent
boundaries. They are called oceanic-continental
convergence, oceanic-oceanic convergence and
continental-continental convergence. Different
processes occur at each of these convergent
• Oceanic-Continental convergence
occurs when a oceanic plate
collides with a continental plate.
Due to the differences in density
between the two plates, the
oceanic plate subducts, or goes
under the continental plate,
creating trenches at the subduction
zone. The continental plate often
rises at this same point creating
mountains and volcanoes like that
seen on the West Coast of South
America and the Northwestern
Coast of the United States.
• Oceanic-oceanic convergence
occurs when two oceanic plates
collide and one subducts under
the other. This causes deep
trenches in the sea floor. The
most famous trench caused by
this type of convergence is called
The Marianas Trench. This trench
is deeper than the tallest mountain
in the world, Mt. Everest. It is over
2000 meters deeper than Mt.
Everest is tall.
• Volcanoes are also formed at
oceanic-oceanic convergent sites.
These volcanoes create island
arcs which is how many of the
world’s islands formed.
• The final type of convergence,
convergence, is how our
largest mountains are formed.
• Because continental crust is
relatively low in density, when
two continental plates collide,
they resist downward motion
and instead push each other
up, building tall mountains.
The most famous mountain
range created by this are The
Himalayas located in Asia.
Transform Plate Boundaries
• A transform boundary occurs
when two plates are sliding
horizontally past each other.
• Also known as fracture zones,
they are thought to be
spreading centers and most
occur underneath the ocean.
• The most famous transform
boundary is known as The San
Andreas Fault that runs
through the length of
California. This one happens
to occur on land and not
underneath the ocean.
• Earthquakes occur only in
the lithosphere layer of the
Earth along faults.
• Earthquakes typically occur
at plate boundaries. This
includes all three
convergent, and transform.
• Which boundary creates the
biggest earthquakes and