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Plate Tectonics



Plate Tectonics:  Investigating Plate Movement and Faults.

In this lesson, students will use models to simulate plates that seperate, collide, and slide past each other.  Students will discover that landforms such as mid-ocean ridges, mountains, and trenches, are among the constructive results of plate interactions.



Scientists and engineers construct models to help them understand how complex systems behave.

Lithospheric plates on the surface of the earth slide past one another, collide, and separate at the rate of 2 to 20 cm per year.

Landforms – mid-ocean ridges, trenches, and mountains – form as a result of plate movement.

Rock responds to the forces caused by plate movement by either folding (bending) or fracturing (breaking).

Faults aere fractures in the earth’s crust and upper mantle along which measurable movement of rock has occurred.

Earthquakes occur along faults and are common along plate boundaries.



1.  Tectonic Plate Theory

The theory that earth’s lithosphere is broken up into tectonic plates that collide, divide, and slide past one another driven by convection in the mantle and gravity.  Movement at plate boundaries causes seismic (earthquake) activity.


2.  Plate Boundaries

Convergent:  two plates colliding into one another

oceanic-oceanic convergent:

oceanic-continental convergent:

continental-continental convergent:


Divergent:  two plates moving apart


Transform:  two plates sliding past one another


3.  Mountains, Volcanoes, and Trenches

Mountains are formed by the collision (convergent boundary) of two continental plates.  When two continental plates collide, the edges of the continents fold upward to form large mountain ranges. (The Himalayas)

Volcanoes are formed by the collision of an oceanic plate and a continental plate OR by the collision two oceanic plates.  When an oceanic plate collides with a continental plate, the oceanic plate is subducted under the continental plate forming a trench.  Subduction pushes upward on the edge of the continental plate causing mountains to form.  The subducting oceanic plate melts in the earths mantle and molten rock rises to form volcanoes. (i.e.: The Pacific NW / Mount Rainier)

When two oceanic plates collide, the older denser plate is subducted under the younger less dense plate.  The subducted plate melts and molten rock rises and breaks through the sea-floor producing a string of undersea volcanoes that may, in time, rise above the oceans surface. (Japan)


4.  Sea-floor Spreading
In the process of sea-floor spreading, ocean floor moves away from the mid-ocean ridge and lava erupts onto the ocean floor to make new crust.  Sea-floor spreading occurs at divergent boundaries.


5.  Evidence for Plate Tectonic Theory

Fossils:  same fossils found on continents separated by wide oceans.

Rocks:  mountains of the same age and rock type found on continents separated by wide oceans.

Pangaea:  the continents seem to fit together like puzzle pieces forming the ancient supercontinent Pangaea.



Tectonic Plate:  a piece of the earth’s lithosphere that rides on the asthenosphere and causes the formation of mountains, volcanoes, mid-ocean ridges, and trenches.

Fault:  a crack in the earth’s lithosphere, mainly along plate boundaries.  This is where earthquake foci are located.

Subduction:   to be carried under the edge of an adjoining continental or oceanic plate, causing tensions in the Earth’s crust that can produce earthquakes or volcanic eruptions

Trench:  a deep V-shaped valley that lies along the bottom of the ocean and is formed by the process of subduction.

Mid-Ocean Ridge:  underwater mountain chains associated with sea-floor spreading.

Rift Valley:  a valley of new continental crust formed at the center of a divergent boundary between two continental plates.

Mountain:  the folding or pushing up (upwelling) of continental plates at a convergent boundary.

Volcano:  An opening in the earth’s lithosphere through which molten lava, ash, and gases are ejected.

Volcanic Island Arc:  a curved chain of volcanic islands formed by the subduction of an oceanic plate at a convergent boundary.


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