1. Types of
Plate Boundaries

2. Divergent Boundaries
Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed crust away from the ridge crest.

3. Divergent Boundaries Mid-Atlantic Ridge
The rate of spreading along the Mid-
Atlantic Ridge averages about
2.5 centimeters per year, or 25 km
in a million years.
Seafloor spreading
over the past million years
has caused the Atlantic Ocean to
grow from a tiny inlet of water
between the continents of Europe,
Africa, and the Americas into the
vast ocean that exists today.

4. Divergent Boundaries
They also cause volcanoes to occur. An example of this is in Iceland The island of Iceland is actually being pulled apart, and the result are lava fountains, like Krafla Volcano.
Krafla

5. Divergent Boundaries African Rift Valley Rifting A 6,000-mile crack in
the earth's crust, stretching
from Lebanon to
Mozambique is known as the African Rift Valley. The force of the plates pulling apart caused huge chunks of the crust to sink and force up molten rock in volcanic eruptions.
Rifting
This process, called rifting, is still in progress comes in the many active and semi-active volcanoes located along the Rift (designated by red triangles on the map). Further evidence of volcanic activity along the rift is provided by the presence of numerous boiling hot springs.

6. Divergent Boundaries
The Red Sea (just off the east coast of Africa) is spreading. The land to either side is actually pulling away! The Red Sea continues to get bigger each year.

7. Convergent Boundaries
Convergent boundaries exist where one plate is
subducted underneath another plate.
Subduction - one plate sinks underneath another plate
Where convergent plates exist, the earth’s crust is being
destroyed as it slowly moves underneath another section
of crust and melts into the mantle.

8. Convergent Boundaries
Ocean-Continent Collision:
Underneath the ocean water there are a number of long, narrow, curving trenches thousands of kilometers long and 8 to 10 km deep cutting into the ocean floor. Trenches are the deepest parts of the ocean floor and are created by subduction.

9. Ocean-Continent Collision:
Andes Mountains
Ocean-Continent Collision:
Off the coast of South America, the oceanic Nazca Plate is pushing into and being subducted under the continental part of the South American Plate. At the same time, the South American Plate is being lifted up, creating the Andes Mountains.
Strong, destructive earthquakes and the rapid uplift of mountain ranges are common in this region. Such earthquakes have been known to jolt the land up several meters.

10. Ocean-Ocean Collision:
When two oceanic plate collide, it can result in the formation of volcanoes, too. One oceanic plate sink beneath the other, and over millions of years, the erupted lava and volcanic debris pile up on the ocean floor. Finally, a volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs.
This is how the Aleutian Islands have formed and why they experience numerous strong earthquakes.

11. Continent-Continent Collision:
The Himalayan Mountains were created when two continental plates met head-on,and neither was subducted. Continental rocks are relatively light and, like two colliding icebergs,
resist downward
motion. Instead,
the crust buckled
and was pushed
upward and
sideways. Viola!
Mountains!

12. Continent-Continent Collision:
India collided into Asia 50 million years ago, causing the Eurasian Plate to crumple up and override the Indian Plate.
After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights.
The Himalayas, towering as high as 8,854 m above sea level, are the highest continental mountains in the world.

13. Transform Boundaries
Most transform boundaries are found on the ocean floor. A few occur on land, an example is the San Andreas fault in California. Transform boundaries are the result of two plates sliding past each other.

14. The San Andreas Fault
• Stretches about 1,300 km long and in some places tens of kilometers wide.
• Slices through two thirds of the length of California.
• The Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr.
• Land on the west side of the
fault (on the Pacific Plate) is
moving in a northwesterly
direction relative to the land
on the east side of the fault
zone (on the North American
Plate).

15. Remember... all boundaries can cause
EARTHQUAKES!
Why???

17. So what will the earth look like in the future? We can only guess…

26. Let’s take a closer look…
All of this movement on the earth’s surface…
What does it cause?
Let’s take a closer look…
Cross Section of a Milky Way…
What does each ingredient represent?

27. Carefully unwrap your Milky Way candy bars.
With someone at your table, attach the two pieces of candy so that one side touches.
Slowly slide the two “plates” (candy) past each other and watch what happens.
What kind of plate boundary are you demonstrating?
Draw it next to the term on your web!

28. Carefully unwrap your two Milky Way candy bars.
Attach the two pieces of candy so that one side touches.
Slowly slide the two “plates” (candy) past each other and watch what happens.
What kind of plate boundary are you demonstrating?
Draw it next to the term on your web!
Transform!

29. Now split the next two plate boundaries so that you only demonstrate one more… Your candy can only withstand one more demonstration before this gets too messy!
Watch as two people at your table…
- Start with the candy pieces touching
- Slowly apply compression force (push them together)
What forms?
What kind of plate boundary is this?
Draw it next to the term on your web!

30. Now split the next two plate boundaries so that you only demonstrate one more… Your candy can only withstand one more demonstration before this gets too messy!
Watch as one person at your table…
- Starts with the candy pieces touching
- Slowly apply compression force (push them together)
What forms?
What kind of plate boundary is this?
Draw it next to the term on your web!
Convergent!

31. So you probably know what is next…
Have another two people carefully bite off one sliver from a side of the chocolate on each piece of candy.
Attach the two “exposed” sides.
Carefully pull them apart.
What is exposed from the candy?
What kind of plate boundary is this?
Draw it next to the term on your web!

32. Divergent! So you probably know what is next…
Have another person carefully bite off one sliver from a side of the chocolate on each piece of candy (don’t do anything for the Starburst).
Attach the two “exposed” sides.
Carefully pull them apart.
What is exposed from the candy?
What kind of plate boundary is this?
Draw it!
Divergent!

33. Think…
• What kind of boundary is at the uplift zone?
• What kind of boundary is at the spreading center?
• What kind of boundary is at the subduction zone?

34. Think… • What kind of boundary is at the uplift zone? CONVERGENT
• What kind of boundary is at the spreading center?
DIVERGENT
• What kind of boundary is at the subduction zone?