Notes

DIVERGENT PLATE MOVEMENT
When plates move apart, magma wells up from Earth's mantle to form a new ocean floor with mid-oceanic ridges.
It is a constructive plate boundary because new land crust is being created.

O & O (Oceanic and Oceanic)
Oceanic Ridges and Submarine volcanoes are formed. Shallow earthquakes may occur and there may be volcanic activity.

Magma from the deeper mantle wells up into the gap formed when two oceanic plates move away from each other, and some of it melts and is erupted on the surface as lava, while others are injected near the surface to crystallize as other igneous rocks.

The seafloor may also spread, and magma rises to the floor and solidify, forming new crust. Therefore it is a constructive plate boundary as new crust is formed and added to the ocean floor. An example of the resulting landforms would be the Mid-Atlantic Ridge.

C & C (Continental and Continental)
When two continental plates move away from each other, a sea is formed. E.g. Red Sea.


CONVERGENT PLATE MOVEMENT
When plates move towards each other, they may collide.
When 2 oceanic plates collide, plate edges are bent into a deep trench called the subduction zone. It is a destructive plate boundary because the subducted plate is destroyed in the process.

O & O
Subduction takes place, and the over-riding plate (the plate above) folds and form islands, whilst the heavier plate sinks into the mantle of the Earth and is melted away by the magma. The magma rises and forms volcanoes. E.g. Japan.

C & O
When an oceanic plate collide with a continental plate, the oceanic plate sinks as it has a larger density. Lithosphere materials from the oceanic crust are subducted in the trench whilst the continental border is fractured, folded and uplifted. Magma rises and a mountain accompanied by volcanic activity are formed.
E.g. Andes Mountains.

C & C
When two continental plates collide, neither sinks because they have similar densities. The continental lithosphere buckles and is uplifted instead, forming fold mountains. Little volcanic activity occur as rocks from the lithosphere do not sink deep into the asthenosphere (upper mantle zone) Earthquakes, faulting and folding however, are common.
E.g. Himalayas.

TRANSFORM PLATE MOVEMENT
Occurs when two plates slip past each other. Tear faults form, accompanied by earthquakes due to great amount of stress built up in these areas, but there is little volcanic activity and little crustal material is destroyed.