http://science.nationalgeographic.com/science/earth/the-dynamic-earth/plate-tectonics-article.html

Plate Tectonics

Sec 3 IHE GE 2014/Chan ML

Convection CurrentsRising, spreading convection currents = pull plates apartSinking convection currents = drag plates together

Why doPlatesMove?

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

http://www.platetectonics.com/book/images/Divergent1.gif

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.

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

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

Convergent Plates(Destructive Boundaries)

3 types:• Oceanic – oceanic• Oceanic – continent• Continent - continent

http://www.scienceclarified.com/images/uesc_08_img0459.jpg

Oceanic-Oceanic

The Japanese Islands are examples of volcanic island arcs formed by the convergence of two oceanic plates.http://www.lee.edu/~cguldenzopf/Images/Historical/Historicalmw45.jpg

Cause:• 2 oceanic plates collide• One plate sinks beneath the other• Subduction zone

Effects/Landforms:• Trench• Volcanoes• Earthquake

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

• 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

Oceanic-ContinentalCause:• Oceanic plate collides with thinner & lighter

continental plate• Subduction occurs

Effects/Landforms• Descending plate is destroyed• Trenches are formed• Volcanoes• Earthquakes

http://www.revisionworld.com/files/oceaniccont.jpg

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

Continental-ContinentalCause:• 2 continental plates collide• No subduction

Effects/Landforms• Great uplift• Rocks are contorted• Earthquakes

                                              Earthquakes are shown as yellow squares.

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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

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

                                                                         

        

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https://www.youtube.com/watch?v=0mWQs1_L3fA

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

References

• Chong, Marianne (2001) Aspects of Physical Geography

• Waugh, David (2009) Geography: An Integrated approach