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Simile • Literal
Author’s Purpose • Critical
Author's Purpose 
MODEL Until now, I've been reading about what volcanoes are and what causes them, but until I got to p. 391, I didn't know how much damage one could do. I had no idea the top of an entire mountain could be blown away, or that entire cities could be buried! The author must have included the examples to show how powerful and destructive volcanoes can be.
Student Edition
Unit 3, pp. 384–393
Expository nonfiction gives facts and information. Look for facts about volcanoes as you read.
Earth is constantly moving. Volcanoes quietly erupt each day somewhere and prove there is activity inside our planet.
Earth is like a giant ball with four layers. We live on top, on the miles-deep crust. But the crust is really many huge pieces that almost fit together. Where the pieces don't exactly meet is where most volcanoes and even earthquakes happen.
The pieces that form Earth's crust are called plates. They rest on the layer beneath, called the mantle. In the mantle it is so hot that rocks can melt into sticky magma. When a big volcano erupts, magma can shoot up as red-hot lava—nature's incredible fireworks. Buried deeper still is Earth's core. The outer core is so hot that iron melts into liquid. At the very center is Earth's solid inner core.
Volcanoes erupt when fiery hot magma finds a weak spot and bubbles up. They can occur on the ocean floor. Some erupt up a chimney-like cone. Then lava cools back into rock, and they erupt again. This can happen over and over for thousands of years, until mountains are created. (The islands of Hawaii are really volcanoes.)
Or a volcano can erupt in an old volcanic mountain that looks peaceful and quiet. Mount St. Helens in the United States suddenly exploded in 1980 with tremendous force.
Most volcanoes don't make the news. They have been occurring for millions of years. Yet a very big one happened almost 2,000 years ago in Italy. Mount Vesuvius erupted and buried two cities and all their people and animals.
When magma rubs against the bottom of a plate, rocks can move and the earth trembles. Plates bump into each other so often around the Pacific Ocean that the vast area is called the Ring of Fire. Some of Earth's most serious eruptions and earthquakes have happened there.
Scientists study volcanoes so they can learn more about these powerful natural giants. They also want to be able to predict the next big blow-up.
Text copyright © 2002 by David L. Harrison, from Volcanoes: Nature's Incredible Fireworks by David L. Harrison. Published by Boyds Mill Press, Inc. Reprinted by permission.
Copyright © Pearson Education.
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 Context Clues Have students use context clues to figure out the meaning of collide on p. 391. They may need to look back at p. 390 for clues to its meaning. (Two plates meet with force, sometimes bending or even breaking, causing earthquakes. To collide means to meet with force.)
Changes in Landforms
The area around the Pacific Ocean is one of the most
explosive in the world. Known as the Ring of Fire, it is the area where most of the world's volcanoes are found. It is also where the strongest earthquakes occur. Many of the islands, mountain ranges, and oceanic trenches in the Pacific Ocean are the result of frequent volcanic activity. The Hawaiian and Aleutian islands, the Cascade Mountains of North America, the countries of Japan, Indonesia, and the Philippines, to name just a few, all formed because of volcanoes along the Ring of Fire. And the earth hasn't finished yet. All along the ring are active volcanoes and frequent, strong earthquakes. The residents of the Hawaiian Islands also have to deal with tsunamis, or tidal waves, the result of earthquakes. |
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Volcanoes: Nature’s Incredible Fireworks. See 
