Volcanic Activity
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Transcript of Volcanic Activity
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Volcanic Activity
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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.
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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.
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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.
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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 Ridges2. Volcanic Islands3. Volcanic Mountains
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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.
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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.
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The Mid-Atlantic Ridge
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The Mid-Atlantic Ridge
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Volcanic Islands
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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.
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Iceland: A Volcanic Island
• Iceland is a volcanic island which has been formed as a result of underwater volcanic eruptions.
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Iceland: A Volcanic Island
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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
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Volcanoes
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Stages in volcanoes
• Volcanoes can be in one of 3 stages,
1. Active2. Dormant3. Extinct
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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.
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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.
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The Pacific Ring of Fire
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The Pacific Ring of Fire