If rocks, ash, and gas into the air.

If you have ever wondered why volcanoes erupt, this lesson is for you! You will learn about some of the events that lead to a volcanic eruption. As you will see, not all eruptions are alike.

Volcanic Eruptions

Imagine that your best friend plays a prank on you and shakes up your soda can when you’re not looking. What happens when you open that can? Boom! Soda everywhere! This happens because gas is dissolved in the soda and kept under pressure. When you open the can, the pressure is released, and gas bubbles rush out of the can, pushing the soda out with it.

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No wonder it makes a mess!Volcanic eruptions work in pretty much the same way. Nobody picks up the volcano and shakes it, but the process still depends on pressure buildup inside a liquid. In this case, the liquid is molten rock, also called magma.As magma rises through surrounding rock, gas bubbles form and expand, causing lots of pressure.

This pressure pushes the magma through weak spots in the earth’s surface, or crust, causing it to flow out as lava. Lava is the name given to magma once it exits the earth’s crust. This can happen slowly or in a huge explosion.

Types of Eruptions

Why do some volcanoes ooze lava, while others shoot rocks, gases, and ash high into the air? It all depends on how many bubbles form in the magma. If a lot of bubbles form as the magma rises to the surface, then enough pressure will build to cause a huge explosion. These types of eruptions often send rock, mud, and ash down the side of the volcano.

This mess can travel many miles. These eruptions also release dangerous gases that can harm living things in the area.If few or no bubbles form, then you see a calmer lava flow. This type of eruption can still be dangerous, but it gives people more time to get out of the way.

Do Volcanoes Always Erupt?

Some volcanoes go thousands of years without erupting. It takes a long time for enough pressure to build up and push the magma out.

Other volcanoes erupt more often. If the magma is slowly bubbling to the surface, they may erupt almost constantly. One famous Hawaiian volcano, called Kilauea, has been erupting for over 30 years!

Lesson Summary

Volcanic eruptions happen when gas bubbles inside magma, or hot liquid rock, expand and cause pressure to build up. This pressure pushes on weak spots in the earth’s surface, or crust, causing magma to exit the volcano.

Smaller eruptions cause lava, or magma that has left the earth’s crust, to flow out of the volcano, while larger eruptions can cause violent explosions that send rocks, ash, and gas into the air.


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