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lithosphere
The lithosphere is broken up into a number of rigid large sections called plates
There are 7 major plates and several minor plates.
convection currents
plates move due to forceful convection currents in the earth’s mantle
As a result of plate movements, volcanoes occur.
The type of boundary and type of crust involved will determine where the volcanoes will form.
plate boundary
plates meet at a plate boundary.
Volcanoes occur at destructive (convergent) and constructive (divergent) plate boundaries.
divergent plate boundaries
occur when two plates pull apart
convection currents moving in opposite directions in the mantle cause plates to separate creating a fissure.
This fissure or crack allows magma to erupt onto the surface.
This process creates volcanic activity - most commonly associated with the formation of shield volcanoes
seafloor spreading
formed when magma cools and solfidifes on the sea bed
overtime volcanic mountains or mid ocean ridges occur in these areas
with further eruptions these volcanic mountains appear above water and are known as volcanic islands e.g Iceland
east african rift
plates separate on land, east african rift occurs
divergent plate boundaries create volcanic activity
runs through east of africa where Nubian and Somalian plates are moving away from each other creating rift and rift valleys
subduction
convergent plate boundaries are where to plates collide and rock is changedd or destroyed
subduction occurs - the older heavier palte, sinks beneath the younger lighter plate
volcanic acitivty
occurs at boundary of two colliding oceanic plates
magma from the descending melting plate rises up on the ocean floor and forms islands known as island arcs.
These can be active volcanoes e.g Japan - Pacific and Eurasian plates collide
subduction - oceanic and continental
can cause volcanic activity
e.g Andes mountains when Nazca plate collides with the South American plate - creating 200 active volcanoes along the Andes range
e.g Mount Aconcagua
transform boundaries
e.g San Andreas Fault in California
plates slide past each other - no formation or destruction of crust
volcanic activty due to release of pressure and movement of magma