Download Causes of Volcanoes

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Subduction volcanoes occur where plates move
towards each other and collide.
One plate, usually the one that is heavier or more
dense, is forced to dive (subduct) beneath the other
into the mantle, causing it to heat up and melt.
This melted material pushes its way back to the
earth’s surface under great pressure, and often erupts
explosively.
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Some volcanoes are found away
from the edges of the plates.
They are formed where rising
plumes of magma force their way
to the surface from deep within
the mantle, a ‘hot spot’.
As the plate moves, the existing
volcano is carried away from the
hot spot and becomes extinct. The
next time the pressure builds up,
new magma erupts to form
another volcano in its place.
The best-known hot-spot
volcanoes are in the Hawaiian
Islands.
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Where plates are moving apart, magma rises
through the gap between the separating plates and
creates new rock.
Here the volcanoes are known as rift volcanoes.
There are more rift volcanoes than subduction
volcanoes
Most of them are hidden from view on the ocean
floor, and they do not often threaten human life or
property.
They erupt more gently than
other types of volcano, with
lava that oozes rather than
explodes from inside them.