Volcanic eruption explained Ted Ed

The Earth’s upper mantle melts and forms magma when water is present and lowers the melting point of mantle rocks. How does water get into the upper mantle?

• Great underground rivers bring water deep into the Earth where they can interact with the mantle.

• Water first hydrates minerals on the floor of the ocean, which are then subducted to the mantle.

• As you go deeper into the Earth, the amount of water increases, so there is more water in the Earth’s mantle and core than at the surface.

• There are great cracks that allow water to flow to the mantle from the oceans.

Which of the following would be an example of decreasing the lithostatic pressure under a volcano?

• Lava flows stacking on top of one another to make a taller volcano.

• Volcanic gas interacting with the rocks to make them weaker.

• Violent shaking of the volcano due to large earthquakes.

• A landslide that removes the top of a volcano.

Imagine that a volcano starts to emit a lot of gas and has an increase in shallow earthquakes, indicating that magma may be rising towards the surface. A couple of days later the activity ceases before an eruption occurs. Which of the following could explain why the activity shut off?

• The rising magma encountered a very strong rock layer.

• There was probably a large landslide on the volcano that increased the lithostatic pressure?

• The number of bubbles in the magma increased and stopped the magma from rising.

• The magma encountered water which made it stop erupting.

If a volcanic eruption made a volcano taller, the next eruption would

• Be more likely because less lithostatic pressure is present

• Be less likely because more lithostatic pressure is present.

• The height of a volcano has no effect on the likelihood of eruption

• Eruptions do not make volcanoes taller.

How do gases cause volcanic eruption?

• They decrease the amount of lithostatic pressure present on a volcano.

• They weaken the overlying rock by breaking down minerals.

• They make the magma buoyant.

• Answers a and b

• Answers b and c