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VOLCANOES
Mountains of Fire
Educational Video
24 Minutes
Copyright, MCMXCV, Rainbow Educational Media, Inc.
Distributed by:
United Learning
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Evanston, IL. 60201
1-800-323-9084
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PRINCIPLE CREDITS
Producer, Writer and Director:
Peter Matulavich
Consultants:
Jim Mod, Ph.D. Scientist
in Charge United States
Geological Survey
Michael Worosz, M.A.
Curriculum Consultant
Diann Fried
Associate Producer:
Videography & Animation:
Production Manager:
Special Thanks to:
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
TABLE OF CONTENTS
Introduction
2
Objectives
3
Summary
4
Review Questions
7
Discussion Questions
10
Activities
13
Glossary
14
Bibliography
16
Script
19
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.
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
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.
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 1980.
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.
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.
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.
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.
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.
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
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
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
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
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
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
BIBLIOGRAPHY
Ballard, Robert D. Exploring Our Living Planet.
National Geographic Society, Washington, D.C.
1983.
Bernstein, Leonard and Wong, Harry K. Earth Science. 2nd
ed. Globe Book Co., New Jersey, 1979.
Calder, Nigel. The Restless Earth. The Viking Press,
1972.
Cattermole, Peter and Moore, Patrick. The Story of the Earth.
Cambridge Univ. Press, 1985.
Clark, John. Earthquakes to Volcanoes. Gloucester Press,
New York, 1992.
Editors of Time-Life Books. Volcano. Time-Life Books,
Alexandria, VA, 1982.
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, 1984.
Harris, Stephen L. Fire and Ice. Pacific Search Press, 1980.
16
Harris, Stephen L. Agent of Chaos. Mountain Press
Publishing Co., Missoula, Montana, 1990.
Kaye, Glen. Hawaii Volcanoes. KC Publications, 1976.
Lutgens, Frederick and Tarbuck, Edward. Essentials of
Geology, 4th ed. Macmillan Co., New York, 1989.
Marvin, Ursula. Continental Drift. Smithsonian Institution
Press, 1973.
Mather, Kirtley F. The Earth Beneath Us. Random
House, New York, 1964.
Miller, Russell. Continents in Collision. Time-Life
Books, Alexandria, VA., 1983.
Redfern, Ron. The Making of a Continent. Times Books,
New York, 1986.
Simpson, Brian. Minerals and Rocks. Galahad Books, New
York, 1974.
VanCleave, Janice. Earthquakes, Spectacular Science
Projects. John Wiley & Sons, New York, 1993.
VanCleave, Janice. Volcanoes, Spectacular Science
Projects. John Wiley & Sons, New York, 1994.
Van Rose, Susanna and Marcer, Ian F. Volcanoes. British
Museum, 1991.
Van Rose, Susanna. Volcano & Earthquake, Alfred A.
Knopf, 1992.
Walker, Bryce. Earthquake. Time-Life Books,
Alexandria, VA., 1982.
17
Weiner, Jonathan. Planet Earth. Bantam Books, New
York, 1986.
Wright, Thomas and Takahashi, Taeko and Griegs, J.D.
Hawaii Volcano Watch. Univ. of Hawaii Press,
1992.
Zike, Dinah. The Earth Science Book. John Wiley &
Sons, Inc. 1993.
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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
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
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
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
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
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
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
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
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
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
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.
1.
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.
A.
B.
C.
D.
geysers
earthquakes
hurricanes
volcanoes
2.
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.
A.
B.
C.
D.
crust
mantle
magma core
middle core
3.
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.
A.
B.
C.
D.
surface
mantle
crust
outside core
4.
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.
A.
B.
C.
D.
plates
landforms
land masses
countries
5.
A.
B.
C.
D.
transformation
subduction
volcanism
continental drift
6.
A.
B.
C.
D.
river of fire
hot spot
Ring of Fire
region of explosion
7.
A.
B.
C.
D.
Kilauea
Mt. St. Helens
Mt. Vesuvius
Mt. Pelee
8.
A.
B.
C.
D.
shield
composite
cinder cone
funnel shape
9.
A.
B.
C.
D.
shield
composite
cinder cone
funnel
10. A.
B.
C.
D.
cinder cone
shield
funnel type
composite
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 1980. 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.
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