Volcanic Activity Volcanoes In the last section we

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. 2. 3. Active Dormant 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