Plate tectonics theory explains that the Earth's crust is divided into plates that move over time. There are three main types of plate boundaries: convergent boundaries where plates collide, divergent boundaries where they move apart, and transform boundaries where they slide past each other. Convergent boundaries can be continent-continent, ocean-ocean, or continent-ocean, and result in mountain building or subduction zones with volcanoes and earthquakes. Divergent boundaries cause rift valleys and seafloor spreading with volcanoes and quakes. Transform boundaries, like the San Andreas Fault, cause strike-slip earthquakes.

1. Plate
Boundaries
Lesson 6

2. At the end of the lesson, the learners will be able to:
• identify the different types of plate boundaries
• explain the presence of active volcanoes and mountain ranges
along plate boundaries
• explain the relationship between the locations of the epicenter
and the type of plate boundary
Objective:

3. • Aside from the Continental Drift Theory, the Seafloor Spreading Theory
played a crucial role in providing a conceptual base for the development of
the plate tectonics.
• The Seafloor Spreading Theory was first proposed by an American geologist,
professor and military officer Harry Hess in the 1960s.
• The term seafloor spreading was first coined by Robert S. Dietz, a scientist
with the US Coast and Geodetic Survey in 1961.
• Seafloor spreading and continental drift are inseparable concepts in geology.
• Tectonic plates constantly move around the planet.
• The border between two tectonic plate is called boundary.
• The movement of plates varies.

4. Boundary where plates
come together .
ex: Himalayan
mountains, Alps
Divergent—Boundary
where plates move
apart.
ex: Great Rift Valley—
Africa; Mid ocean
Ridges
Boundary where two
plates slide along side
each other.
ex: San Andreas
Fault—San Francisco
Types of Plate Boundaries
Convergent
Boundary
Divergent
Boundary
Transform
Boundary

5. form when two tectonic plates come
towards each other.
There are three types of convergent
boundaries or destructive boundaries.
• continent – continent
• ocean – ocean
• continent – ocean

6. Mountains form and
earthquakes occur when
continental plates run into each
other and fold upwards.
Ex: Himalayas and Alps
Continent-Continent

7. A continental plate colliding with another continental plate have
Collision Zones:
A place where folded and thrust faulted mountains form.

8. Volcanic island arcs, trenches &
earthquakes occur when older
ocean plate subducts under a
younger ocean plate.
Ex: Japan, Aleutian Islands-off
Alaska, Philippines, Tonga Islands,
Marianas Trench
Ocean Plate-
Ocean Plate

9. • Ocean plate colliding with another ocean plate
• The less dense plate slides under the more dense plate creating a
subduction zone called a TRENCH

10. Mountains, volcanoes and
earthquakes occur as an ocean plate
subducts under a continental plate.
The Oceanic plate melts; less dense-
magma rises to form volcanoes.
Ex: Andes, Cascade Range, Sierra
Nevada
Ocean Plate-
Continent Plate

11. • Ocean plate colliding with a less dense continental plate
• Subduction Zone: The process by which oceanic crust sinks
beneath a deep-ocean trench and back into the mantle at a
convergent plate boundary.

12. VOLCANOES occur at
subduction zones
What else happened
at Convergent
Boundary?

13. Boundaries between two plates that
are colliding
This stress is called COMPRESSION
How is the rock
pushed at Convergent
Boundary?

14. • A REVERSE FAULT
• Rock is forced upward as it
is squeezed.
What happens when the rock is squeezed
from the Stress of Compression?

15. Take note:
• Rock goes crunches up to make
folded mountains.
• Rock goes down “under” at
subduction zone.

16. When two plates move apart.
Features:
• In continents:
Rift Valley, Volcanoes, Earthquakes
• In oceans:
Mid-Ocean Ridge, Volcanoes,
Earthquakes

17. • Great Rift Valley, Africa
• Mid-Atlantic Ridge, Atlantic Ocean
Examples

18. Rock gets THIN in the middle as it is
pulled apart.
This STRESS is called
How is the rock
pulled at Divergent
Boundary?

19. • A Normal Fault (fault is a
break in Earth’s crust)
• Rock drops down as it
breaks
What will happen when the rock snaps
from the stress of tension?

20. A geologic feature or event…
• May form RIFT VALLEYS on
continents
• SEA-FLOOR SPREADING in
the ocean
What happen next at
Divergent Boundary?

21. Take note:
• If you pull warm bubble gum or silly
putty, it will thin in the middle until
it is stressed so much that it breaks.
• Happens on land & under H2O

22. occur where two plates slide along side each
other. Earthquakes occur in these areas.
Ex: San Andreas Fault in California

23. Rock is pushed in two opposite
directions (or sideways, but no rock
is lost)
This stress is called SHEARING.
How is the rock
broken in Transform
Boundaries?

24. • May cause Earthquakes when
the rock snaps from the
pressure.
• A famous fault at a Transform
Boundary is the San Andreas
Fault in California.
What happen next at
Transform Boundary?

25. • A STRIKE-SLIP FAULT
• Rocks on each side of the
fault slip past each other as
they break.
What happen when the rock is sheared (or
“cut”) from the Stress of Shearing?

26. Take note:
• Transform boundaries run like trains
going past each other in different
directions & they shake the ground!