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Volcanic Activity
Volcanoes
• In the last section we learned that the outer
layer of the earth is called the Crust.
• We also learned that the crust is broken into
many different pieces called Plates.
• The plates are constantly moving because of
Continental Drift.
• This movement causes the plates to push
together, pull apart, or slide past one another.
How do Volcanoes Occur?
• Volcanoes occur when two of the earth’s plates pull
apart.
• Remember, beneath the crust the mantle is made
from semi-molten (melted) rocks called magma.
• So when a gap occurs in the crust (which happens
when two plates pull apart) the magma spills out
through the gap.
Lava
• When the magma
reaches the
surface of the
earth it is called
lava. This is the
reddish liquid you
see coming out of a
volcano.
The effects of Volcanoes
•
When the lava comes out of a volcano it
cools and forms into solid rock.
This can result in the formation of,
1. Mid Ocean Ridges
2. Volcanic Islands
3. Volcanic Mountains
Mid-Ocean Ridge
• Sometimes volcanoes occur
under the sea.
• If two plates pull apart under
the sea the lava rises up to
the ocean floor.
• It cools quickly into solid rock
as it touches the cold sea
water.
• After many eruptions these
layers of new rock build up to
form mountains under the
water.
• A long chain of volcanic
mountains under the sea is
called a Mid-Ocean Ridge.
The Mid-Atlantic Ridge
• Under the Atlantic Ocean
the American plate is
pulling apart from the
Eurasian and African
Plate.
• This is causing
underwater volcanic
eruptions which has
created a long chain of
underwater mountains.
• These mountains make up
the Mid-Atlantic Ridge.
• Some of the mountains in
the chain are so high they
stick out of the water and
form volcanic islands.
The Mid-Atlantic Ridge
The Mid-Atlantic Ridge
Volcanic Islands
Volcanic Islands
• When
underwater
volcanoes
continually erupt
eventually they
may grow big
enough to stick
out of the water.
• They form
volcanic islands.
Iceland is an
example of a
volcanic island.
Iceland: A Volcanic Island
• Iceland is a
volcanic island
which has
been formed
as a result of
underwater
volcanic
eruptions.
Iceland: A Volcanic Island
Volcanic Mountains
• When two plates pull
apart a gap is created.
This gap provides a
hole which the magma
can escape from the
mantle. It is called a
Vent.
• When the magma
cools, along with other
materials from the
volcano such as mud
and ash, they usually
form a cone shaped
mountain
Volcanoes
Stages in volcanoes
• Volcanoes can be in one of 3
stages,
1. Active
2. Dormant
3. Extinct
Stages in volcanoes
Active Volcanoes - The volcano is still
erupting quite regularly. E.g. Mount
Etna, Italy.
Dormant Volcanoes - The volcano has
not erupted for a long time but may
erupt in the future.
Extinct Volcanoes – The volcano has
not erupted in historic times and will
not erupt again.
The Pacific Ring of Fire
• Many of the world’s
major earthquakes and
many of the world’s
active volcanoes occur
in a zone that encircles
the Pacific Ocean.
•
This is because many of
the world’s major plates
meet here. Therefore, at
this place the plates are
pulling apart, pushing
together and sliding
past one another.
•
This causes
earthquakes and
volcanoes to occur.
The Pacific Ring of Fire
The Pacific Ring of Fire