VOLCANOES Mountains of Fire

Transcription

1 VOLCANOES Mountains of Fire Educational Video 24 Minutes Copyright, MCMXCV, Rainbow Educational Media, Inc. Distributed by: United Learning 1560 Sherman Ave., Suite 100 Evanston, IL

2 PRINCIPLE CREDITS Producer, Writer and Director: Consultants: Peter Matulavich Jim Mod, Ph.D. Scientist in Charge United States Geological Survey Michael Worosz, M.A. Curriculum Consultant Associate Producer: Videography & Animation: Production Manager: Special Thanks to: Diann Fried Peter Matulavich Roxanne Hall United States Geological Survey National Geophysical Data Center KTVU Volcano National Park Stephen Harris, Ph.D. Cascade Volcano Observatory Mt. Rainier National Park Video and Teacher's Guide produced for Rainbow Educational Media by Peter Matulavich Productions San Dimas, California

3 TABLE OF CONTENTS Introduction 2 Objectives 3 Summary 4 Review Questions 7 Discussion Questions 10 Activities 13 Glossary 14 Bibliography 16 Script 19

4 INTRODUCTION This video is designed to introduce students to the subject of volcanoes, their causes and their effects. Few natural forces are so destructive or instill such awe as volcanoes, yet it has been only in recent years that scientists have determined the mechanism behind volcanoes: the movement of tectonic plates which compose our planet's shell. Students will learn through full-motion animation and exciting volcano footage that the world's most destructive volcanoes occur near one type of plate boundary, a subduction zone. This is where two plates collide and one dives beneath the other. As the leading edge of the diving plate is consumed back into the earth's mantle, it causes solid rock to liquefy and the molten rock rises through fractures in the crust, erupting on the earth's surface. Also featured are "hot spot" volcanoes, which occur far from plate boundaries. They are formed by magma rising from the mantle through thin or weak spots in the crust. The volcanoes which make up the Hawaiian islands are examples of hot spot volcanoes. The three types of volcanoes are highlighted and examples are given for each. The Hawaiian volcanoes are typical of shield volcanoes. Many of the volcanoes of the Pacific Northwest, such as Mt. St. Helens, are typical of composite volcanoes. Smaller, lesser known volcanoes generally make up cinder cone volcanoes. Students will learn that volcanoes are not only exciting to watch, but they contribute to the continuing regeneration of the earth's crust.

5 OBJECTIVES After viewing this video students should know: that many mountains are actually volcanoes the names of the earth's interior layers the concepts of continental drift and plate tectonics the cause of plate movement the location and importance of the mid-ocean ridge the location and importance of subduction zones the location of the Ring of Fire that volcanic eruptions are among the dramatic effects of plate movement where the world's most destructive volcanoes are located the three types of volcanoes that volcanic activity contributes to the regeneration of the earth's crust

6 SUMMARY The video opens with dramatic scenes of volcanoes erupting of the island of Hawaii. We see how Hawaiian volcanoes erupt in towering "fountains" spewing lava high into the air. Then we see how the lava proceeds downhill in "rivers of fire" before it reaches the ocean where it sizzles and splatters and hardens into rock. Students learn that all of the Hawaiian Islands were formed in this way. The video explains that volcanoes are mountains, and when they are not erupting, volcanoes resemble other mountains; but while they may resemble other mountains, they are different in how they are formed. The narrator explains that to understand more about volcanoes we have to look deep inside the earth. Next, though the use of animation, we see that the earth's interior consists of several layers: the inner core; the outer core; the mantle; and the earth's outer shell, the lithosphere, which consists of the crust and the rigid, outer portion of the mantle. Students learn that the earth's shell is cracked into more than a dozen pieces called plates, and that each plate carries a continent, or an ocean basin, or sometimes both. The positions of these plates are only temporary. They are moving at an average rate of one to four inches a year in a variety of directions, carrying continents and ocean basins with them. Animation reveals what the continents looked like millions of years ago and how they slowly reached their present-day positions. Animation also shows what the world will look like millions of years in the future as the continents continue their slow dance around the globe.

7 The video then discusses what causes the plates to move: the circulating movement of magma within the earth's mantle. Students learn that in some places, plates carrying ocean basins are moving apart, and as they do, magma rises from the mantle to fill the gap. This process is referred to as sea floor spreading, and the area where magma rises is known as a mid-ocean ridge. The midocean ridge circles the globe, generating new plate material along its length. The mid-ocean ridge is where plate material is created. Subduction zones are where plate material is destroyed. In these areas, a plate carrying an ocean basin presses against a plate carrying a continent. The plate carrying the ocean basin, because it is heavier, dives beneath the plate carrying the continent, in a process called subduction. This process, creates tremendous heat and pressure and causes solid rock to liquefy into magma. The magma rises between fractures in the plate carrying the continent into a volcano that has been gradually built up over thousands of years from repeated magma uprisings. Magma builds up within the volcano creating tremendous stress until the volcano erupts. The world's most destructive volcanoes are located near subduction zones. Mt. St. Helens is such a volcano and the video includes clips showing the devastation that occurred there during its eruption in The video explains that most of the world's active volcanoes are a result of the subduction process, and one region of the world is referred to as the Ring of Fire because of the circular pattern formed by the locations of volcanoes there. Next, the video segues to volcanoes which occur far from subduction zones, "hot spot" volcanoes like those in Hawaii. Hot spots are areas where magma has found its way through weak or thin areas in the earth's crust, emerging on the ocean floor, where it hardens into rock.

8 More magma follows, adding to the formation of an underwater volcanic dome. After thousands of years, the dome may rise above sea level. Every island in the Hawaiian chain was formed in this way. The Hawaiian islands form a long chain due to the fact that the pacific plate continues to move over the stationary hot spot. Students will learn that hot spot volcanoes seldom erupt with the explosive force of volcanoes like Mt. St. Helens, but what they lack in explosive impact, they make up for in showy displays. The video then presents exciting scenes from several Hawaiian eruptions. Featured are fire curtains, lava lakes, lava tubes, windows, and lava rivers. While Hawaiian volcanoes are not explosive, they are nonetheless destructive, and the video shows roads, vehicles and houses destroyed by the relentless flow of lava. Sometimes lava reaches the sea and the video shows what happens as the lava enters the ocean, sizzling and splattering as it hardens into rock with new shorelines forming under clouds of hissing steam. Next the video discusses the three types of volcanoes: shield, cinder cone and composite. Hawaiian volcanoes are examples of shield volcanoes. Their gently sloping sides were formed by lava flows. The shapes of Hawaiian volcanoes resemble warrior shields. Cinder cone volcanoes have steeper sides and composite volcanoes have characteristics of both shield and cinder cone volcanoes. The world's most destructive volcanoes, such as Mt. St. Helens, are composite volcanoes. The video concludes with the observation that while we may be impressed with the explosive nature of volcanoes and their fiery displays, we should remember that volcanoes help contribute to the regeneration of our planet.

9 REVIEW QUESTIONS 1. Name the earth's interior layers. The earth's interior layers are the inner core, the outer core, the mantle and the lithosphere or shell. 2. What composes the lithosphere? The lithosphere is composed of the crust and upper portion of the mantle. 3. The lithosphere is broken into more than a dozen pieces. What are these pieces called? They are tectonic plates. 4. What causes the earth's tectonic plates to move? The movement of magma within the mantle causes the plates to move. 5. What is the difference between magma and lava? Lava is the name for magma after it erupts from volcanoes. 6. What is the mid-ocean ridge? It is an area where two plates move apart, allowing magma to rise and fill the gap.

10 7. What are subduction zones? They are areas where one plate dives beneath another, becoming consumed back into the earth's mantle. 8. Where do the world's most destructive volcanoes occur? They occur near subduction zones. 9. What is the Ring of Fire? It is the circular pattern created by connecting the locations of hundreds of subduction zone volcanoes. 10. Name the area where plate material is created? It is the mid-ocean ridge. 11. Name the areas where plate material is destroyed. They are subduction zones. 12. How do volcanoes form near subduction zones? As one plate dives beneath another, its leading edge is consumed back into earth's mantle. Under the tremendous heat and pressure, solid rock liquefies into magma which rises to the surface, creating volcanoes.

11 13. How do volcanoes form above hot spots? Magma rises through thin or weak areas of the crust, emerging on the ocean floor, creating a volcanic dome. Over thousands of years, the dome increases in size and may eventually rise above sea level. 14. Why do the Hawaiian Islands form a chain? As the earth's crust moves in relation to the hot spot, the islands form a chain. 15. What are the characteristics of shield volcanoes? They have gentle slopes and resemble warriors' shields. 16. What are the characteristics of cinder cone volcanoes? They have steep slopes and resemble cones. 17. What are the characteristics of composite volcanoes? They have gentle slopes near their bottom and steeper slopes near their top.

12 DISCUSSION QUESTIONS These questions are designed to encourage classroom discussion 1. While it is not discussed in the video, ancient people attributed volcanic eruptions to a variety of supernatural and unscientific causes. Explain the occurrence of volcanic eruptions as they might have been explained by ancient peoples. Answers include eruptions' being attributed to angry gods venting their anger, warring giants, and various supernatural explanations. 2. The video discusses why volcanoes occur in some areas but not in others. What is the likelihood of a volcano erupting in the area in which you live? Answers, of course, vary with each locality, but in the United States, volcanic activity is limited to Hawaii, Alaska and some western states. 3. The video discusses how plate tectonics is the mechanism behind volcanoes. What other natural phenomena can be explained by plate tectonics? Continental drift, earthquakes, and mountain building can all be explained by plate tectonics. 10

13 4. Volcanoes erupt throughout the world. Ask students to recall and discuss volcanic eruptions they've heard about. Answers include: Kilauea (Hawaii), presently erupting; Mt. St. Helens (Washington) 1980; Ml. Pelee (Martinique) 1902; Krakatoa (Java) 1883; Mt. Vesuvius (Italy) 79 A.D.; and many others. 5. While not discussed in the video, hot spots occur below continents as well as oceans. Yellowstone National Park is situated directly above a hot spot. What type of volcanic activity occurs in Yellowstone? Numerous geysers and hot springs occur. 6. Sixty-two people were killed in the eruption of Mt. St. Helens. Tens of thousands have been killed in other eruptions. In what ways do volcanoes kill? Death occurs through blast effects, heat and suffocation. 7. While not discussed in the video, entire villages have been wiped out during some eruptions. If your town were located near an active volcano, would you stay or move away? Give your reasons. 11

14 There is no right or wrong answer of course. While some people wouldn't want to take the risk, others feel the risk is very small. Many people who live in the shadows of active volcanoes believe there will be ample warning for them to evacuate the area before an eruption. 8. The video shows tons of ash pouring out of Mt. St. Helens. How might volcanic eruptions affect worldwide weather? Large eruptions can spew enormous amounts of ash and debris into the atmosphere were it can circle the globe, block out the sun, and lower temperatures worldwide. 9. The video discusses how magma rises to the earth's surface in a continuing process of regeneration. What might the earth be like if magma didn't rise to the surface. The earth's surface would likely be flat, as the mountains would have eroded millions of years ago. 12

15 ACTIVITIES These activities are designed to encourage students to learn more about some of the things covered in the video. 1. The video features several volcanic eruptions. Activity: Students can make their own erupting volcanoes. First, construct a volcano out of papiermache, clay, or other material, making sure to include a vent. Next, pour about 1/4 cup of baking soda into the vent, followed by a similar amount of vinegar. The baking soda reacts with the vinegar, producing a foam which simulates lava during a volcanic eruption. 2. The video features eruptions on Kilauea and Mt. St. Helens, but there have been many other famous eruptions. Activity: Have students research and report on a famous volcanic eruption. 3. The video shows how magma chambers can fill with magma, causing a volcano to bulge. Activity: This can be simulated by having students lay a deflated balloon near the edge of a table top and then covering it with dirt. When the balloon is inflated it causes the dirt to rise. 4. The video highlights the Ring of Fire. Activity: Have students draw a map of the world marking the locations of active volcanoes. Have them highlight the Ring of Fire. 13

16 GLOSSARY aa lava: lava that has a crusty and blocky texture cinder cone: type of volcano characterized by steep sides composite volcano: type of volcano characterized by gentle slopes near the bottom and steeper slopes near the top consume: destroy; use up crater: depression at the top of a volcano crust: thin outermost layer of the earth decimated: having been destroyed destructive: causing much damage emerge: rise or come forth eruption: violent outburst hot spot: area of the crust far from plate boundaries where magma has surfaced inner core: solid innermost layer of the earth lava: molten rock that erupts from the earth lava tube: type of lava flow in which a hard, outer portion surrounds a hot, liquid interior liquefy: become liquid lithosphere: outermost layer of the earth including the crust and outermost portion of the mantle 14

17 magma: name for lava before it reaches the earth's surface magma chamber: reservoir of magma located in the earth's crust mantle: mostly molten layer of the earth located below the crust mid-ocean ridge: undersea mountainous ridge and divergent plate boundary that circles the earth molten: liquefied by heat outer core: molten layer of the earth located below the mantle pahoehoe lava: lava that has a smooth liquid texture pillow lava: pillowy-shaped lava hardened by contact with water plates: rigid moveable sections of the lithosphere Ring of Fire: circular pattern created by connecting the locations of hundreds of subduction zone volcanoes in the Pacific shell: informal name for the lithosphere shield volcano: type of volcano characterized by gentle slopes and resembling a warrior's shield subduction zone: area where one tectonic plate descends beneath another window: opening in a lava tube 15

18 BIBLIOGRAPHY Ballard, Robert D. Exploring Our Living Planet. National Geographic Society, Washington, D.C Bernstein, Leonard and Wong, Harry K. Earth Science. 2nd ed. Globe Book Co., New Jersey, Calder, Nigel. The Restless Earth. The Viking Press, Cattermole, Peter and Moore, Patrick. The Story of the Earth. Cambridge Univ. Press, Clark, John. Earthquakes to Volcanoes. Gloucester Press, New York, Editors of Time-Life Books. Volcano. Time-Life Books, Alexandria, VA, Erickson, Jon. Rock Formations and Unusual Geologic Structures. Facts on File, Inc., New York. Erickson, Jon. Volcanoes and Earthquakes. Tab Books, Inc., 1988 Frances, Peter and Jones, Pat. Images of Earth. Prentice Hall, Inc., New Jersey, Harris, Stephen L. Fire and Ice. Pacific Search Press,

19 Harris, Stephen L. Agent of Chaos. Mountain Press Publishing Co., Missoula, Montana, Kaye, Glen. Hawaii Volcanoes. KC Publications, Lutgens, Frederick and Tarbuck, Edward. Essentials of Geology, 4th ed. Macmillan Co., New York, Marvin, Ursula. Continental Drift. Smithsonian Institution Press, Mather, Kirtley F. The Earth Beneath Us. Random House, New York, Miller, Russell. Continents in Collision. Time-Life Books, Alexandria, VA., Redfern, Ron. The Making of a Continent. Times Books, New York, Simpson, Brian. Minerals and Rocks. Galahad Books, New York, VanCleave, Janice. Earthquakes, Spectacular Science Projects. John Wiley & Sons, New York, VanCleave, Janice. Volcanoes, Spectacular Science Projects. John Wiley & Sons, New York, Van Rose, Susanna and Marcer, Ian F. Volcanoes. British Museum, Van Rose, Susanna. Volcano & Earthquake, Alfred A. Knopf, Walker, Bryce. Earthquake. Time-Life Books, Alexandria, VA.,

20 Weiner, Jonathan. Planet Earth. Bantam Books, New York, Wright, Thomas and Takahashi, Taeko and Griegs, J.D. Hawaii Volcano Watch. Univ. of Hawaii Press, Zike, Dinah. The Earth Science Book. John Wiley & Sons, Inc

21 SCRIPT Every few years on the island of Hawaii, nature puts on a dazzling show. Red hot lava erupts from deep within the earth, exploding high into the sky in fiery displays; and then it rushes downhill in rivers of fire. When it reaches the ocean, the lava cools immediately, sizzling and splattering, exploding, before it hardens into rock, becoming new land. All of the Hawaiian Islands were formed in this way. Of all of earth's forces, none are quite so spectacular, or so important to the regeneration of our planet, as volcanoes. Volcanoes are mountains; types of mountains. When they're not erupting, volcanoes look pretty much like any other mountain, as does this volcano, Mt. Rainier, in Washington State, or this one, Mt. Shasta in California. But volcanoes differ from other types of mountains in two very important ways: how they are created, and what they do. To understand more about volcanoes, we have to look deep inside the earth. The earth's interior consists of several different layers: the inner core which is believed to be solid iron and which is very hot; the outer core which is believed to consist of rocky material so hot and under such great pressure that it is a liquid; the mantle which is not quite so hot as the outer core and not so liquid. The mantle's outermost portion is solid. This is the solid outer portion of the mantle. Above this is the outermost layer of the earth, the crust. 19

22 Together, the crust and the solid outer portion of the mantle form the earth's outer shell. They are referred to as the lithosphere. It's not always easy to see the earth's crust. It is covered by vegetation and oceans. But if you could drain the earth's oceans and strip away our planet's vegetation, the earth might look something like this. Now we can see the earth's hard outer shell. And if you look closely, you can also see where the shell is cracked. The red glowing lines mark the places where the earth's shell is broken into small and large pieces called tectonic plates. Each plate carries a continent, or an ocean basin, or sometimes both. The plates are moving one to two inches a year in different directions, carrying continents and ocean basins with them. Millions of years ago, the earth looked something like this, every continent in a different position. They were so close together, they formed a single, supercontinent, called Pangaea. Even then, the plates were moving, a few inches a year, and kept moving, until they reached their present-day positions. The theory that continents move is called continental drift. When you look at a globe today, you are looking at only a moment in time, because the continents are still moving, inches a year, too slow to see, as they move farther and farther apart. Then the continents will stop moving apart. They will change directions, coming together once again. Millions of years from now, scientists expect the world to look entirely different, every continent in a new position, carried there by the moving plates. 20

23 While we can't see this movement occurring, we can see the effects. Volcanic eruptions are just one of several dramatic effects of plate movement. Here's why the plates are moving. Scientists believe material in the mantle is circulating much as it is doing here. The movement may be caused by heat within the mantle. You can get an idea of how heat can cause a circulating movement by watching rice as it boils. What you see happening within this beaker is similar to what's happening within the earth's mantle. As mantle material moves, perhaps only inches a year, it causes the plates above it to move as well. In some places, plates are moving in opposite directions. They are moving apart. The area where two plates are moving apart is called a divergent boundary. In some places, plates move past each other. The area where two plates move past each other is called a transform boundary. In other places, plates are colliding. The area where two plates are colliding is called a convergent boundary. The red glowing lines on this globe mark convergent boundaries. These are the places where plates push against each other. Sometimes both plates pushing against each other are carrying continents. In this cross-section, two plates carrying continents are colliding. As they squeeze against each other, the earth's crust is compressed and folded, rising high into the air. These raised layers of earth are what we call mountains. 21

24 Some of the world's highest mountains are a result of two plates' pushing against each other, along convergent boundaries. But sometimes plates pushing against each other are not both continents. At this convergent boundary, a plate carrying an ocean basin is colliding with a plate carrying a continent. Here's what happens. Because it is heavier, the plate carrying the ocean basin, shown here on the left, dives beneath the plate carrying the continent, in a process called subduction. As the plate dives, tremendous heat is created, causing solid rock to liquefy into a material called magma. The magma rises in large globs into the plate carrying the continent. Eventually, the magma stops rising. Some of the globs may form a magma chamber. As more and more magma adds to the chamber, pressures build, some of the magma finds its way to the surface, where it can erupt. The eruption of Mt. St. Helens in Washington State in 1980 occurred in much this same way. In a matter of seconds, much of Mt. St. Helens was blown away, the mountain literally losing its top. Dense clouds of volcanic ash and debris poured out of a newly formed crater for days on end. Carried by the wind, the ash was blown hundreds of miles, burying towns and cities, turning day into night. The shots you are now looking at were photographed in mid-afternoon. The eruption leaves a ghostly wasteland. Trees toppled like match sticks. Vehicles tossed about like toys. 22

25 Crews were brought in to search for the dead and injured. All told, 62 people were killed. Forests and animal life were decimated, and at the mountain's summit, a new crater, nearly 2,000 feet across and 500 feet deep. Mt. St. Helens is a result of the subduction process where one plate dives beneath another. The area where one plate dives beneath another is called a subduction zone, and the world's most destructive volcanoes are found in these zones. These symbols mark the locations of active volcanoes. Most of them are located near subduction zones. One region of the world, because of the great number of volcanoes and the circular pattern they form, is referred to as the Ring of Fire. Most of the world's active volcanoes are located in this ring. But some volcanoes occur far from plate boundaries. The Hawaiian Islands are thousands of miles away from the nearest plate boundary, yet this area is among the most volcanically active areas in the world. Scientists believe a hot spot exists in the earth's mantle below Hawaii. Hot spots are areas where magma has found its way through the earth's crust, emerging on the ocean floor, where it becomes hardened by the cold ocean water. More magma follows, adding to the formation of an underwater volcanic dome. The dome becomes larger and larger with each eruption and may, after thousands of years, rise above sea level. Every island in the Hawaiian chain, as well as many others around the world were formed in this way. 23

26 Hot spots are stationary. The one beneath Hawaii has existed here for over 70 million years. But as we have seen, the earth's plates are not stationary. As this plate moves, it carries the newly formed island with it. As more magma rises, it starts to build another dome all over. This arrow shows the direction of movement of the plate carrying the Hawaiian Islands. The area glowing in red is the hot spot. The islands farthest away from the hot spot are the oldest. It is the island directly above the hot spot, the so-called Big Island, which is the youngest and most active. Eruptions on the Big Island occur every few years and can last for months, even years. This is what happens during a typical Hawaiian eruption. Magma rises up through the crust into the volcano's magma chamber. The chamber swells. Magma fills channels that lead toward the surface. The magma is held back by rock and sediment blocking the openings. More magma rises. Pressures build. The ground may bulge, causing small localized earthquakes. An eruption can occur at the end of any one or more of several channels or conduits. Seldom do hot spot volcanoes erupt with the explosive force of volcanoes like Mt. St. Helens. But what they lack in explosive impact, they make up for in showy displays. Lava fountains are typical of these kinds of volcanoes. Lava can shoot hundreds of feet into the sky, for days on end. 24

27 Lava can also erupt through cracks in the ground, creating walls of fire, sometimes called curtains. A lava curtain can sometimes be more than a mile long and reach heights of over 150 feet. Lava lakes are formed when lava fills a depression. The edges of these lakes resemble ocean shorelines. But these are lakes in which you wouldn't want to swim. Temperatures exceed 2,000 degrees Fahrenheit. Lava spattering is common in these lakes, and sometimes the spattering moves eerily across the surface as if some creature were thrashing about below. Sometimes, the lake's surface resembles the plates of our planet, but in miniature; folding, bending, subducting. Lava domes will occasionally form on the lake and may last for hours. When the lake becomes too full, it overflows. Lava rushes down the volcano's slopes in rivers. In some places, the rivers run fast. In others, they slow to a crawl. When a flow begins to slow down, the surface will cool and harden, sometimes encasing flowing lava beneath it, creating a lava tube. Holes in lava tubes are called windows or skylights and provide glimpses of the rushing lava below. Lava tubes are good insulators, and the lava flowing in them will remain hot and fluid much longer than it does in surface flows. 25

28 When flows exit tubes, they will often broaden, burning their way through forests, crossing roads, engulfing vehicles and homes. Lava is slow-moving and people have time to escape with a few possessions and pets. Some try to save their homes. Water is sometimes used in an attempt to stop lava in its tracks. Using just two garden hoses, two men were able to divert a lava flow around this house, and it worked, for a few days, but as is often the case, the home would eventually go up in flames. There are different types of lava. One is very fluid. It has the consistency of thick cream. It is called pahoehoe lava. Another lava type is thick and chunky, and usually slowmoving. It is called aa lava. In some places, the lava slows to a stop, hardening into black rock as it cools. In other places, the lava doesn't stop, reaching the ocean. Here, you sense a battle, as fire meets water. Steam explosions are common, as the lava explodes as it hardens. This unusual lava flow is called fire hose lava. At night, the explosions take on an eerie quality. Beneath the water, lava quickly crusts over and then cracks open again, like the egg of an alien creature. 26

29 This kind of lava is known as pillow lava because of its pillowy shape, and has seldom been photographed. Back on the surface, new shorelines form under clouds of hissing steam. What has been destruction, now becomes construction as new land is formed and the Big Island of Hawaii is now a little bit bigger. Hawaii's volcanoes are referred to as shield volcanoes; their shapes resembling warriors' shields. Shield volcanoes have gentle slopes, seldom explode and are not considered particularly destructive. Other volcanoes have steeper sides and resemble cones. They are called cinder cone volcanoes. This is an example of a cinder cone volcano. Notice the steep slopes. The third type of volcano has features of both shield, and cinder cone volcanoes. They are called composite volcanoes. The bases of composite volcanoes usually have gentle slopes, but the slopes at the top are usually steeper. This is an example of a composite volcano, Mt. Shasta in California. Again, notice how the slopes are steeper near the top. Most of the world's destructive volcanoes, such as Mt. St. Helens, are composite volcanoes. Composite volcanoes can be dangerous and that's why scientists study them, in the hope of learning more about them and our ever-changing planet. 27

30 In this program, we have seen that volcanoes are a type of mountain. Volcanoes are created in several ways. One way is when one plate subducts or dives beneath another, causing magma to rise to the earth's surface, and erupt. Another way is when magma rises through the earth's crust above hot spots. We have seen how most volcanoes are located near subduction zones, and that most of the world's active volcanoes are located in an area known as the Ring of Fire. Finally, we've seen that there are three different types of volcanoes: shield volcanoes, cinder cone volcanoes, and composite volcanoes. While we are impressed by the explosive nature of volcanoes, and their fiery displays, we should remember that volcanoes and volcanic activity help contribute to the continuing regeneration of our planet. 28

31 CLOZE EVALUATION QUESTIONS VOLCANOES: MOUNTAINS OF FIRE NAME DIRECTIONS: Select the answer, from the four choices given, by circling the correct letter. 1. Our earth is an ever-changing place on which we live. Some sources of this change are. These structures are considered nature's "fire works display". When they erupt they can certainly be dazzling as well as devastating. 2. In order to understand how volcanoes form and erupt, we need to look inside the earth. The earth is made up of several different layers. The center layer is called the inner core. Next is the outer core, followed by the, which is not as hot as these cores. 3. The uppermost layer of the earth is the region we live on. The is this layer which is affected by what is happening beneath rt. The many geologic formations like volcanoes and mountains were really formed by forces acting beneath this upper layer of the earth. 4. The crust would look quite different if we could strip away the oceans and plant life. In many places the crust is cracked. These large pieces of the crust are called. The continents rest upon these pieces and have actually moved over millions of years. 5. The earth's huge plates have been moving very, very slowly. The movement is so slight that one cannot see it happening. Scientists believe that this process of movement, called, is a major cause of geologic changes on the planet. 6. One of the dramatic side effects of the movement of the earth's plates is the formation of volcanoes. In fact, scientists believe that volcanoes can be traced along a or area where they are very active. Most of the world's active volcanoes are found here. 7. The destructive effect of a volcanic eruption was evident in the state of Washington in When erupted, dense clouds of ash and dust covered the landscape. On the sides of this volcano trees were toppled like match sticks. The entire forest and animals within it were destroyed. 8. Scientists can classify volcanoes by their shape. One type of volcano is called a volcano because of its gently sloping sides. Examples of this type are found in the Hawaiian Islands. In fact, the shape looks like a circular protector that warriors carried into battle in ancient Greece and Rome. 9. The next type of volcano has steeper sides. It can also be very destructive when it erupts. This steep-sided volcano is called a type. In fact, its shape gives it the distinctive name. 10. The last type of volcano looks like a combination of the two other types. The has gentle slopes at the bottom, but gets much steeper near the top. In fact, Mt. St. Helens is an example of this type of destructive volcano. 1. A. geysers B. earthquakes C. hurricanes D. volcanoes 2. A. crust B. mantle C. magma core D. middle core 3. A. surface B. mantle C. crust D. outside core 4. A. plates B. landforms C. land masses D. countries 5. A. transformation B. subduction C. volcanism D. continental drift 6. A. river of fire B. hot spot C. Ring of Fire D. region of explosion 7. A. Kilauea B. Mt. St. Helens C. Mt. Vesuvius D. Mt. Pelee 8. A. shield B. composite C. cinder cone D. funnel shape 9. A. shield B. composite C. cinder cone D. funnel 10. A. cinder cone B. shield C. funnel type D. composite This form may be reproduced without permission from Rainbow Educational Media.