How is a volcano formed?
There are four types of plate boundaries – ___________ (when two
plates move away from each other), ___________ (when an oceanic
and continental plate move towards each other), ___________
(when two plates slide past each other) and ___________ (when two
continental plates crash into each other). Although ___________
happen at all of the plate boundaries, volcanoes only happen at
destructive and constructive plate boundaries.
Destructive plate boundaries
Firstly, the continental crust and __________ crust move towards each other. As the
oceanic crust is _______ _______or SUBDUCTED beneath the continental crust the
pressure is increased. As well as pressure increasing, friction also increases. This means
that the ___________ of the rock goes up. As the crust continues down it heats up even
more and begins to _________. The molten rock collects in a _________ chamber. As the
pressure increases the molten rock begins to force its way upwards through the _______
___________. Eventually it breaks through the crust and a volcano __________ at the
surface.
As time goes on, more eruptions happen and the volcano builds up __________ of rock. This
is repeated for millions of years and so a volcano is __________.
Constructive plate boundary
Volcanoes happen at this type of plate boundary because two plates move ___________
from each other. As they separate, molten rock (magma) rises from the __________ to fill
the gap between the two plates. This forms a mid-___________ ridge. A good example of
a constructive plate boundary can be found where the North American plate is moving away
from the Eurasian plate. This has caused the Mid-___________ ridge to form and has
created Iceland through volcanic activity. These volcanoes tend to be more
_____________ eruptions than those that happen at the destructive plate boundaries.
What are the different types of volcano?
A volcano is called __________ if it has not erupted for thousands of years, and its shape
has been worn away by the wind and rain. If it has not erupted for years, or even centuries,
but still seeps gas sometimes, it is known as a ___________ (sleeping) volcano. However,
the ones we need to worry about are the __________ volcanoes because these have erupted
recently and are likely to do so again soon.