8.1 Volcanoes

Do you think volcanoes are cool?

Active volcanoes are found on all continents except Australia. Volcanoes even erupt under the ice on Antarctica! Do you live near a volcano? What are the chances that it will erupt in your lifetime? If you don't live near one, could a volcanic eruption elsewhere cloud the skies above where you live?

Volcanoes

A volcano is a vent from which the material from a magma chamber escapes. Volcanic eruptions can come from peaky volcanic cones, fractured domes, a vent in the ground, or many other types of structures.

Where They Are

Volcanoes are a vibrant manifestation of plate tectonics processes. Volcanoes are common along convergent and divergent plate boundaries. Volcanoes are also found within lithospheric plates away from plate boundaries. Wherever mantle is able to melt, volcanoes may be the result.

What is the geological reason for the locations of all the volcanoes in the figure? Does it resemble the map of earthquake epicenters? Are all of the volcanoes located along plate boundaries? Why are the Hawaiian volcanoes located away from any plate boundaries?

Creating Magma

Volcanoes erupt because mantle rock melts. This is the first stage in creating a volcano. Remember from the chapter Materials of Earth's Crust that mantle may melt if temperature rises, pressure lowers, or water is added. Be sure to think about how and why melting occurs in the settings where there is volcanism mentioned in the next few concepts.

Stages

Of all the volcanoes in the world, very few are erupting at any given time. Scientists question whether a volcano that is not erupting will ever erupt again and then describe it as active, dormant, or extinct.

• Active: currently erupting or showing signs of erupting soon.
• Dormant: no current activity, but has erupted recently.
• Extinct: no activity for some time; will probably not erupt again.

Summary

• Volcanoes are located along convergent and divergent plate boundaries.
• Magma can be created when temperature rises, pressure lowers, or water is added.
• Volcanoes may be active, dormant, or extinct depending on whether there is the possibility of magma in their magma chambers.

Review

1. Where do most volcanoes occur? Why?
2. What is needed for magma to form?
3. If a volcano is dormant, can it become active? Can it become extinct?

Explore More

Use this resource to answer the questions that follow. 

1. Where do volcanoes mostly occur?
2. Why does magma come out of a volcano?
3. What is magma that reaches the surface called? What happens when it cools?
4. What does magma collect in beneath the volcano? How does it go onto the surface?
5. When does an eruption occur?
6. How are fast-moving mudflows created?
7. How are volcanoes essential for life on our planet?
8. When will an extinct volcano erupt next?