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Plate Tectonics
the movement of Earth
Tectonic Plates
• Earth’s lithosphere is broken into about 19
pieces
• These plates move on top of the
asthenosphere
Plate Boundaries
• Places where the plates meet
Types of Plate Boundaries
• Transform Fault Boundaries –(Sliding)
• Divergent
– Moving apart / Rifting
• Convergent
– Colliding / Sub-duction
Transform Fault Boundaries
• Faults form when plates slide past each other
• A fault is a large crack in rocks that can break
• EARTHQUAKES can happen along fault lines
San Andreas Fault, CA
Divergent Boundaries
• Boundary between two plates that are
moving apart or rifting

• RIFTING causes SEAFLOOR
SPREADING
Divergent Plate Movement: Seafloor
Spreading
• the movement of two oceanic plates away
from each other (at a divergent plate
boundary), which results in the formation
of new oceanic crust (from magma that
comes from within the Earth's mantle)
along a mid-ocean ridge.
• Ocean floor spreading was first suggested
by Harry Hess and Robert Dietz in the
1960's.
Features of Divergent
Boundaries
• Mid-ocean ridges
Features of Divergent
Boundaries
• Rift valleys
Quilotoa, Ecuador
Features of Divergent
Boundaries
• Fissure volcanoes
Hawaii, USA
Convergent Boundaries
• Boundaries between two plates that
are colliding
 
• Different things can happen,
depending on the density of the
plates involved.
• There are 3 types…
Oceanic-Continental
• Ocean plate colliding with a
less dense continental plate
• Subduction Zone: where the
less dense plate slides under
the more dense plate
• VOLCANOES occur at
subduction zones
Andes Mountains,
South America
Oceanic-Oceanic
• Ocean plate colliding with
another ocean plate
• The less dense plate slides
under the more dense plate
creating a subduction zone
called a TRENCH
•Two Oceanic Plates - When two oceanic plates
collide, one may be pushed under the other and
magma from the mantle rises, forming volcanoes
in the vicinity
Aleutian Islands, Alaska
Continental-Continental
• A continental plate colliding
with another continental plate
• Have Collision Zones:
–a place where folded and thrust
faulted mountains form.
• Two Continental Plates - When two
continental plates collide, mountain ranges
are created as the colliding crust is
compressed and pushed upwards.
Fold: When rocks bend
• Anticline (Upward)
• Syncline (Downward)
Causes of Plate
Tectonics
Convection Currents
• Hot magma in the Earth moves
toward the surface, cools, then sinks
again.
• This circulation of heat creates
convection currents.
• Convection currents beneath the
plates cause the plates to move.