tectonic cycle and distribution volcanoes Flashcards
what is the tectonic cycle
the constant formation and destruction of the earth’s crust
what does plate tectonic theory describe
how the earths crust/lithosphere is split into large slabs called plates
why do the plates move
heat from the earth core cause the upper mantle to low in huge slow moving convection currents in the upper mantle
what does this form
destructive and constructive plate boundaries
1.volcanoes at constructive plate boundaries e.g
mount hekla, Iceland
where are most constructive boundaries found
under the ocean
what happens at constructive plate boundaries
mantle currents pull the earths plates apart e.g. the eurasian plate is pulled away from the North American plate
what does the sepration of plates form
a long split in the crust called a rift valley
why does magma rise
to fill the gap created by the rift
what happens when the magma reaches the surface
cools and forms a long ridge of volcanic mountains called mid ocean ridges
example
Iceland is part of the mid Atlantic ridge
2.volcanoes at destructive plate boundaries e.g
Mount Fuji, Japan
where do volcanos occur
two oceanic plates collide e.g. the pacific plate collides with the philippine plate
what happens here
one plate sinks beneath the other and is absorbed back into the mantle
what is this process called
subduction
what is the melted oceanic crust
less dense than the mantle and the recycled material rises through the cracks in the crust unit it reaches the surface through a vent to form a volcano island arcs
what are these
curved chains of volcanic islands which mark the subduction zone
what Is the magma at these destructive plate boundaries
very cidic and tends o form steep sided volcanic cones
example
mount pinatubo in the philippine islands
3.volcanpes at hotspots e.g.
the Hawaiian islands of the pacific
what is magma sometimes able to do
reach the surface of the earth in the middle of a plate
what is this location called
hotspot
why do hotspots occur
a large fountain or plume of magma rises to the surface and forces its way through the crust to form volcanoes
what do mantle plumes generally contain
very basic madam (less than 55% silica) which is not very gaseous and can flow for many kilometres
what are the volcanic mountains that result
gently sloping and have very wide bases (shield volcanoes)
what happens as the plates move over the mantle plume
new volcanoes form
what happens to the existng one
gradually become less active and eventually extinct as plates move away from the plume
example
Hawaii islands
diagram
