1. Volcanic Activity

2. 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.

3. 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.

4. 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.

5. 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,
Mid Ocean Ridges
Volcanic Islands
Volcanic Mountains

6. 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.

7. 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.

8. The Mid-Atlantic Ridge

9. The Mid-Atlantic Ridge

10. Volcanic Islands

11. 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.

12. Iceland: A Volcanic Island
Iceland is a volcanic island which has been formed as a result of underwater volcanic eruptions.

13. Iceland: A Volcanic Island

14. 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

15. Volcanoes

18. Stages in volcanoes Volcanoes can be in one of 3 stages, Active
Dormant
Extinct

19. 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.

20. 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.

21. The Pacific Ring of Fire

22. The Pacific Ring of Fire