1. Plate Tectonics Sec 3 IHE GE 2014/Chan ML
Sec 3 IHE GE 2014/Chan ML

2. Why do Plates Move? Convection Currents
Rising, spreading convection currents = pull plates apart
Sinking convection currents = drag plates together

3. Divergent Plates (Constructive Boundaries)
Cause:
Plates move in opposite direction due to the convection movement.
Effects/Landforms
new crust is created (oceanic ridges)
Oceans are born and grow wider
When a diverging boundary occurs on land a 'rift', or separation will arise and over time that mass of land will break apart into distinct land masses and the surrounding water will fill the space between them.
Earthquakes
Volcanoes

4. Oceanic-Oceanic
The divergent Mid-Atlantic Ridge rises above sea level at Thingvellir, with the North American plate to the west and the Eurasian plate to the east.

5. Formation of Oceanic Ridge (answer)
As the N. American and Eurasian plates move apart (divergent movement) in a constructive boundary due to convection currents
Tensional stresses cause fractures in the lithosphere to occur
The zone where the plates separate is the spreading centre,
Allowing basaltic magma to well up, cool and solidify; thus becoming / forming new sea floor (this process is called sea floor spreading)
As the plates continue to move apart, more basaltic magma piles up, cool and solidify; and new mountains are formed
The mountains closest to the spreading zone are the youngest
The rows of mountains rise from 2,000 to 4,000m from the ocean floor – these are the mid-oceanic ridges
Eg: Mid-Atlantic Ridge

6. Continental-Continental
As the Nubian and Somalian plates move apart,
They are stretched and fractures are created
The land in between sinks, creating a linear depression, known as a rift valley
As a result, earthquakes are experienced in the region
Magma may also rise to the surface creating volcanoes
Eg: the East African Rift Valley

7. Convergent Plates (Destructive Boundaries)
3 types:
Oceanic – oceanic
Oceanic – continent
Continent - continent

8. Oceanic-Oceanic
The Japanese Islands are examples of volcanic island arcs formed by the convergence of two oceanic plates.

9. Cause:
2 oceanic plates collide
One plate sinks beneath the other
Subduction zone
Effects/Landforms:
Trench
Volcanoes
Earthquake

10. Formation of Trench and volcanoes (answer)
Trench in a convergence between Oceanic and Continental Plate (destructive boundary)
When a thinner and denser oceanic plate converges with a thicker and lighter continental plate
The oceanic plate descends beneath the continental
This descent is called subduction
The old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magma
A long narrow and deep oceanic trench is formed where the plate dips into the mantle
Eg: Peru-Chile Trench, Java Trench
Name of plates

11. The movement of the plates cause faults to occur
Rocks break and are displaced relative to each other,
the melting of the subducting oceanic plate produces silica-rich magma
Being less dense than the mantle, the magma moves up any break or fractures
When it escapes through vents to the land surface, it forms subduction volcanoes
Eg: Mt. St. Helens, Mt Pinatubo

12. Oceanic-Continental Cause:
Oceanic plate collides with thinner & lighter continental plate
Subduction occurs
Effects/Landforms
Descending plate is destroyed
Trenches are formed
Volcanoes
Earthquakes

13. Formation of Fold Mountains (answer)
When two continental masses collide, one is pushed under the other for a short distance
When a thinner and denser oceanic plate converges with a thicker and lighter continental plate
The oceanic plate descends beneath the continental
This descent is called subduction
The old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magma
The edges of these plates are also contorted and buckled up, creating a great uplift, forming fold mountains
Since sediments from the ocean floor are contorted and uplifted, marine fossils were found at the summit of fold mountains!!!
Eg: Rocky Mountains (N. America), Andes Mountains (South America)
Name of plates

14. Continental-Continental
Cause:
2 continental plates collide
No subduction
Effects/Landforms
Great uplift
Rocks are contorted
Earthquakes
                                              Earthquakes are shown as yellow squares.

15. Formation of Fold Mountains (answer)
When two continental masses collide, the Indian plate is pushed under the Eurasian plate for a short distance
However, there is NO subduction
Because both are light and buoyant
This process produces a great uplift as the rocks at the edges of these two plates are contorted and buckled up
Due to the absence of magma supply, there are no volcanoes in this area
Eg: the Himalayan Mountains

16.                                                                                  
Transform Boundaries
occur in a few places to accommodate lateral motion, in which plates slide past one another.
very rare on continents, but they are dramatic where they do occur. Example: the San Andreas Fault (USA) and The Alpine Fault (New Zealand).
Most transform
boundaries occur in short
segments along
mid-oceanic ridges

17. Sit back and relax… well… can’t be too relaxed…
Here’s a summary… don’t fall asleep

18. References Chong, Marianne (2001) Aspects of Physical Geography
Waugh, David (2009) Geography: An Integrated approach