Did you know that there are more than 600 active volcanoes on Earth? To explain their origins, it helps to hold up an apple: If our planet were the size of the apple, its crust would be about the same thickness as the apple´s skin. Below Earth´s thin, hard crust comes the mantle, which—just like the white flesh of the apple—surrounds the core. Earth´s mantle is made up of thick, hot rock in liquid form, called magma. The molten magma layer is under intense pressure. When magma seeps or rises through a crack in Earth´s hard crust, it forms a volcano. What happens as pressure builds up?

The earth's hard crust isn't solid rock. It is seven major tectonic plates that glide and collide atop magma. To demonstrate the movement of the earth's crust, trim a sheet of brown craft foam to fit the bottom of a large baking pan. Cut the foam into seven pieces to represent the plates. Have students trickle red-tinted water down the sides of the pan. When the “plates” are floating on an inch of “magma,” slowly tilt the dish side to side. What happens? Next, have a child gently press down on two adjoining plates and release. Invite students to share their observations about the magma. Explain that when pressure on the plates allows hot magma to seep or squeeze through the earth's crust, a volcano is formed.

Nearly half of the earth's volcanoes exist along the edges of the Pacific Plate. This region of volcanic activity encircles the Pacific Ocean and is known as the Ring of Fire. Help students locate several volcanoes found within this region—such as Mt. Pinatubo in the Philippines, Mt. Fuji in Japan, and Mt. Saint Helens in the U.S.—on a map. Then ask them to select one of these volcanoes to research. When students have learned all they can about their volcanoes, have them write an imagined, eyewitness account of one of its eruptions. Encourage them to use volcano-related vocabulary as they write from their own perspectives, or take the perspective of animals, trees, or even rocks found near the volcano. Then have them illustrate their accounts. Finally, invite students to share their work with the class.

Below Earth´s surface, a red-hot storm is brewing, and it´s on the move! Magma traveling through the crust collects in magma chambers. The molten rock expels gases, which pressure the crust above and cause it to swell and rise. Eventually the crust cracks and magma spews out, resulting in a volcano. Invite students, working in small groups, to conduct the following experiment to simulate magma´s effect. First, create a magma chamber by pouring a cup of vinegar into a small, clear plastic soda bottle. Add a few drops of food coloring. Insert a small funnel into a 7-inch balloon. Pour a teaspoon of baking soda into the balloon. Next, Stretch the balloon over the mouth of the bottle, being careful not to spill baking soda into the bottle. The balloon represents the earth´s crust.Then when ready, carefully empty the contents of the balloon into the bottle and observe. The magma mixture expels gases, which put pressure on the earth´s crust above and cause it to swell and rise—similar to an actual volcano!

When magma reaches the earth's surface, it cools and turns into lava. As lava flows, it eventually stiffens, solidifies, and then stops. Invite students to simulate this cooling effect: 1. Mark lines on the bottom of a clear loaf pan, then tape a thermometer inside it at one end. 2. Make thick lava by adding water (and red food coloring, if desired) to quick-cooking oatmeal. Microwave briefly, then pour into the pan. 3. Using a potholder, tilt the pan so the lava is at one end. Start a stopwatch as that end of the pan is propped up about 3 inches. Stop timing when most of the flow crosses the center. Lower pan, stir the mixture, then have students record the temperature and time. 4. Repeat step 3 every five minutes. Have students plot times and temperatures on a line graph. Discuss: What do they think will happen to the temperature and lava flow after another hour? Several hours? A day?

Making the Dough
First, gradually stir brown craft paint into a large cup of water. Then mix the watery paint with 2 cups of flour and 1 cup of salt. Finally, knead into smooth dough, adding flour or water as needed.
 
Building the Volcano
Flatten a ball of the modeling dough into a large, flat patty. Next, cut out the entire bottom piece of a Styrofoam cup.Then, using the cup as a cutter, make a hole in the center of the patty. Turn both the cup and the dough patty upside down and spread the dough down around the cup to form a volcano. Finally, insert a small medicine cup in the top of the volcano, using extra dough to anchor it in place.
 
Erupting the Volcano
Mix a tablespoon of Plaster of Paris, a tablespoon of water, a few drops of dish soap, and red food coloring. To start the eruption, stir in a teaspoon of baking soda. After the mixture settles, try this step again!
Safety Tip: Remember to wear goggles and gloves when erupting your volcano!

Volcanoes, although dangerous and destructive, can also be helpful to life on earth. Challenge students to name reasons why this might be true. (Volcanoes fertilize soil, produce rock, provide energy and mineral resources, and more.) A key benefit is that volcanoes build new land, counteracting the force of erosion. After sharing this with students, have small groups collaborate to create landscape models out of layers of pea gravel, potting oil, and sand. Invite them to simulate the effects of wind, wear, and rain by blowing air on their models, “galloping” their fingers across (as a running animal would), and spraying on a bit of water. Finally, have students compare their landscapes to their lava-layered volcanoes. How are they different?

Invite students to learn about some key U.S. volcanoes—and practice chart-reading and critical-thinking skills at the same time—with the Top Ten U.S. Volcanoes Reproducible, below. Have students read through all the information on the chart. Then challenge them to answer the questions in complete sentences, using the chart as a guide.

Mackie Rhodes is an education writer based in Greensboro, NC. Her most recent professional books are Teaching with Favorite Back-to-School Books (Scholastic, 2004) and Teaching about Winter Holidays with Favorite Picture Books (Scholastic, 2003). This article was originally published in the March 2004 issue of Instructor.

Download the Top Ten U.S. Volcanoes Reproducible. To open the Reproducible, you will need Adobe Acrobat Reader software. If you do not have this software already installed, click here to download it FREE.