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Extrusive Volcanism

t’sThe word extrusive means exterior. this means it is something on the outside. That is why extrusive volcanism is when volcanic activity takes place above the ground. It is outside the Earth instead of inside it. The hot magma escapes the Earth’s crust. Once the magma has reached the surface, it is then called lava.

An image of a volcano erupting; extrusive volcanism.

This is a form of extrusive volcanism.

Lava Extrusion

When the lava comes out of the volcano it’s known as a lava flow. Lava is extremely hot and very dangerous! Many lava flows move very slowly. Some are much more explosive. Lava flows can move over and over again down a volcano, creating new terrain. 

An image of an erupting volcano.

The volcanoes in Hawaii often erupt.

Lava Can Build…

Each time the volcano erupts, the lava flow creates new terrain for the volcano. The new flow builds on what the last one left behind. What shape it makes depends on what type of volcano it is. Each type of volcano has a different type of lava flow. This changes how the volcano forms. The three different types of volcanoes are:
 This type of volcano forms a high cone that holds up well.
 This type of volcano forms a tall sharp peak that can fall in on itself. That is because it’s made of softer rock.

This type of volcano forms a big short volcano that is lower to the ground than the others.


…It Can Also Be Destructive

However, volcanoes do not always follow this process over and over. Some can erupt with a lot of power and force that can send lava, rock, and hot ash flying out. This is pyroclastic material. It can be sent flying hundreds of miles. Sometimes, a cloud of dust and ash makes it all the way around the world from one of these explosions!

The Krakatoa Eruption

The island of Krakatoa’s volcano is an example of this. In 1883, the volcano erupted and caused a lot of damage to the island. Only the ocean was left behind! People as far as 1,500 miles away were able to hear the explosion, and lots of dust filled the sky all over the world! 

An image of the Krakatoa volcano erupting.

The volcano on the island of Krakatoa’s eruption destroyed a whole town, as well as sent dust all over the world!

For more information on extrusive volcanism, watch this video: