Transcript Volcanic Activity - St Angela`s College Geography

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
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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
Dormant
Extinct
2.
3.
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