- Divergent plate boundaries produce huge mountain ranges under water in every ocean
basin. - Volcanoes like those that form the islands of Hawaii, form over areas called hot spots.
Review Questions
- What is the difference between magma and lava?
- Explain how volcanoes are formed.
- Why are there volcanoes along the west coast of the United States?
- Why do volcanoes occur where tectonic plates pull apart or diverge?
- Explain how the Pacific Ring of Fire got its name.
- What is a mantle plume?
- Suppose a new volcano suddenly formed in the middle of the United States. How might
you explain what caused this volcano? - Volcanoes have been found on Venus, Mars, and even Jupiter’s moon Io. What do you
think this indicates to planetary geologists?
Vocabulary
fissures A long crack into the Earth’s surface, from which lava erupts onto the surface.
hot spot A fixed region of hot magma that rises through the mantle and creates volcanoes
on the Earth’s surface. A hot spot is above a mantle plume.
lava Molten rock that has been erupted onto the Earth’s surface. Magma becomes lava
once it emerges on the surface.
magma Molten rock found under the Earth’s surface.
mantle plume Acolumnofveryhotrockthatrisesupthroughthemantle. Mantleplumes
will form hot spots if they make it all the way up to the surface of the Earth’s crust.
Points to Consider
- When you look at the map of tectonic plates (Figure 3), what areas besides the Pacific
Ring of Fire would you expect to have volcanic activity? - Some volcanoes are extinct; they are no longer active and will probably never be again.
What do you think causes a volcano to become extinct? - Hot spots are still poorly understood by earth scientists. Given your understanding of
the Earth’s interior, why do you think it’s hard to study hot spots?