Download EQ-16_Global_Plates - Environmental Volunteers

EQ-16 GLOBAL PLATES
MATERIALS:
• "TREMOR TALES — THE TURTLE STORY" and "QUAKE MYTHS"
• PLATE GLOBE
• PLATE PUZZLE MAP (EQ-03)
• WORLD SEISMICITY MAP & MODEL
• CALIFORNIA RELIEF MAP
• One container of SILLY PUTTY
© Environmental Volunteers
Global Plates
E. Q. 16
page 1
GLOBAL PLATES
E.Q. 16
OBJECTIVES:
The crust of the Earth is divided into separate plates that "float" on a mantle layer. By examining the shape,
size and boundaries of these plates, we can begin to see where earthquake action is most likely to occur — at
the active edges of global plates.
SCIENCE THEMES:
Systems and interactions, energy
PROCESS SKILLS:
Observing, inferring, applying
GRADE LEVELS:
4–6
FOCUS WORDS:
Pangea, Plate tectonics, plate action, core, mantle, crust, magma, subduction, transverse zone, divergent zone,
convergent zone
BACKGROUND INFORMATION:
Geologists believe that twelve major and many minor plates are "floating" on a plastic layer in the Earth's
upper mantle. Most plates carry both continental and ocean floor crust on their "backs." Like giant
icebergs, jostling and colliding in a spring thaw, the crustal plates are in constant motion.
Where plates meet, they can spread apart, with new crust forming in the gap. One plate may slide down
under and there, they may grind slowly past each other, or they may collide with mountain build-up the
result.
The speed of plate movement is extremely slow, from 1/2 to 4 inches per year, and the movement is
seldom smooth. Blocks of locked crustal rocks bend and strain under enormous pressures, fracture and
move suddenly, causing earthquakes. Then they lock again, building up strain for the next round. Most
of the quakes caused by this sudden movement are small and are not usually felt by anyone. Some,
though, are strong enough to register on seismographs all over the world — these "superquakes" can
cause major destruction.
As the earth's global plates continue to move at their "turtle's pace," earthquakes will continue to occur
— the "growing pains" of an evolving Earth.
ACTIVITIES:
TIME: 10 - 15 minute activity
LESSONS:
1. The crust of the Earth is divided into a dozen major global plates.
2. These plates "float on the surface of a plastic, upper mantle layer and are constantly moving.
3. Plate movement causes earthquakes, especially on or near plate boundaries.
4. The San Andreas Fault in California is actually a plate boundary.
© Environmental Volunteers
Global Plates
E. Q. 16
page 2
PREPARE:
Set up PLATE GLOBE, PLATE PUZZLE MAP, CALIFORNIA RELIEF and FAULT MAPS, and MODEL
for easy viewing. Remove all the plates from the PLATE GLOBE and the PLATE PUZZLE MAP, so they
can be assembled later. Have container of SILLY PUTTY ready.
AUDIENCE:
Younger children — Point out the Indian "Turtle Story" as one way people have tried to explain earthquakes,
and the "plate theory" is the way that scientists now explain why they occur. Spend most of the time
manipulating the PLATE GLOBE and the PUZZLE MAP.
Older children — Focus on the plate boundaries, where they occur on the globe, and how the plates move.
Give special attention to the San Andreas Fault system and its relation to plate movements around the globe.
Adults — Emphasize the inevitability of earthquakes due to plate movement in California and other places
around the world.
ASK: What happens to the Earth in an earthquake?
ASK: Why does the Earth move?
RESPONSE: Lead to "the Earth moves." Encourage a variety of responses as to
why.
EXPLAIN:
There have been many explanations for why the earth moves. Here
is one from the California Indians.
DO: Read TREMOR TALES: THE TURTLE STORY" (included in this folder)
EXPLAIN:
There are many other earthquake myths or stories from other cultures
("geomythology") that can be used here (see "TREMOR TALES — QUAKE MYTHS" and
REFERENCE 29).
EXPLAIN:
After reading the Turtle Story, explain: Scientists now have a different
"story" for why the Earth moves. Review: "CRUST," "MANTLE," and "CORE" using the
globe model of the Earth.
REVIEW:
You may want to review EARTH'S INTERIOR. Focus on the crustal
plates "floating" on a plastic, flowing mantle layer.
DO: Have a few people put the plates in the proper places on both the PLATE
GLOBE and the PLATE PUZZLE MAP.
DO: If there is time have more than one group assemble the GLOBE and PUZZLE
MAP.
ASK: When one plate moves, what happens to the others?
ASK: What happens at the plate edges or boundaries?
EXPLAIN:
Plate interaction causes "the other plate to move." Using your two
hands as plates explain: They either spread apart; one goes under another; they grind past each
other; or they collide, forming mountains.
ASK: What else happens around plate boundaries? Display the WORLD
SEISMICITY MAP & MODEL.
DO: Point out that most of the world's earthquakes happen on or near plate
boundaries.
ASK: What is happening in California as a result of plate movement? Does anyone
know what the plate boundary that cuts through California is called?
REPLY: California is divided by a transform fault type of plate boundary (one plate
grinding past another), known as the San Andreas Fault.
DO: Have students trace the line of the San Andreas Fault on the CALIFORNIA
RELIEF and FAULT MAPS.
EXPLAIN:
The land west of the fault is on the Pacific Plate and land east of the
fault is on the North American Plate.
© Environmental Volunteers
Global Plates
E. Q. 16
page 3
DO: Point out places along the fault that are familiar to the audience, especially their
own town or city.
ASK: Why do earthquakes occur on the San Andreas Fault and all the branch faults
related to it?
EXPLAIN:
The Pacific Plate is moving in a northwesterly direction at a rate of
about 2 inches a year. As it grinds past the North American Plate, the rocks strain and bend
below the surface. Stress builds all along the San Andreas and its branch faults, and is
released from time to time by earthquake action.
DO: Pull off the Pacific and North American Plates from the PLATE GLOBE
and demonstrate the kind of movement that is happening.
DO: Facing the audience, display the Pacific Plate in your right hand, and the North
American Plate in your left. Move the Pacific Plate up and to your right while holding the
North American Plate fixed.
DO: With both hands, pull the Silly Putty slowly at first, then rapidly, snapping it in
two.
EXPLAIN:
That is how crustal rocks bend, snap, and cause earthquakes.
Other stress/release activities will be demonstrated in later activities.
FOLLOW-UPS:
Read myths and stories about earthquakes and other natural phenomena from other countries around the
world. Create and illustrate your own earthquake myth.
Draw a map of the section of California in which you live. Mark the San Andreas Fault and the Pacific
and North American Plates on the map. Note which plate you live on and how close you are to the fault.
Make a puzzle of your own based on the PLATE PUZZLE MAP. (See PLATE PUZZLES Activity.)
REFERENCES:
Geological Museum. The Story of the Earth. North American Edition,
pp. 13 - 14
Vitaliano, Dorothy B. Legends of the Earth. Their Geological Origins,
pp. 81 - 103
"This Changing Earth," National Geographic, January 1973,
pp. 1 - 37.
CULTURE:
EARTHQUAKE EXPLANATIONS
JAPANESE:
An "earthquake insect" a sort of scale-covered spider ("jushin
mushi")
causes the Earth to shake when it stirs, or a giant catfish ("namazu") which is curled under the sea and on whose
back
rest the
islands of Japan, causes quakes each time it stirs.
EARLY HINDU:
The earth is supported by elephants standing on a turtle that stands on a
cobra. When any of these overburdened animals move, an
earthquake occurs.
EARLY SCANDINAVIAN:
The god Loki, having killed his brother, is bound to a rock in a deep cave
where a serpent slowly drips poison on his upturned face.
Loki's wife catches most of the poison in a dish,
but when it is full,
she has to go away to empty it. The poison falls on Loki's face,
causing
him to writhe and shake the Earth.
MAORI OF NEW ZEALAND: God Ru, inside the womb of his
parent,
Mother of Earth, is a restless offspring; when he stirs, the
Earth trembles.
© Environmental Volunteers
Global Plates
E. Q. 16
page 4
MAYAN:
The Earth is cube-shaped and supported at the corners by four
gods,
the Vashakmen, who, whenever they believe the world is
overpopulated, tip it to get rid of surplus people.
SIBERIAN KAMCHA:
A god named Tuli drives an earth-laden sledge pulled by fleainfested
dogs. When the dogs stop to scratch, the Earth shakes.
RUMANIAN:
The world is resting on the divine pillars of Faith, Hope, and
Charity.
When one falters, the earth shakes.
WEST AFRICAN:
One side of the Earth's disk rests on a mountain, while the other is held up
by a giant whose wife holds up the sky. When the giant embraces his wife, the Earth trembles.
KUKI OF ASSAM:
A race of people living inside the Earth shakes the Earth to find
out if
anyone still lives on the surface. When the Kukis feel a quake, they shout "Alive, alive!" to assure the people
within that someone is
still here.
© Environmental Volunteers
Global Plates
E. Q. 16
page 5
This is a story that the Gabrielino Indians used to tell. These Indians once lived in the San Gabriel Valley in
Southern California, where earthquakes are common. They told this story to explain the cause of earthquakes
and how California was made:
Long, long ago, before there were people, there was hardly anything in the world but water. One day, Great
Spirit looked down from heaven. He decided to make a beautiful land. But where could he begin? All he saw
was water. Then he spotted a giant turtle. The turtle was as big as an island. Great Spirit decided to make the
beautiful land on the turtle's back.
One turtle was not big enough. The land Great Spirit wanted to make was very large. So he called out, "Turtle,
hurry and find your six brothers!"
Turtle swam to find them. It took him a whole day to find the first. It took another day to find the next. After six
days, turtle had found his six brothers. "Come," he said, "Great Spirit wants us."
Great Spirit called down, "Turtles! Form a line, head to tail, north to south. Umm, you to the south, please move
a little to the east. Hmmm. There, that's just right. What a beautiful land you will make!" Then the Great Spirit
reminded them, "It is a great honor to carry this land on your backs. So you must not move!"
The turtles stayed very still. Great Spirit took some straw from his supply in the sky. He put it on the turtles'
backs. Then he took some soil and patted it down on top of the straw.
Great spirit cleaned his hands on a fluffy white cloud. "I'll use these clouds to make mountains," he said
Then Great Spirit made trees and lakes and rivers. When he was finished, he looked at the beautiful land he had
made. Great Spirit was very pleased. But soon trouble came. The giant turtles grew restless. They wanted to
leave.
"I want to swim east" said one. "This beast goes EAST!"
"WEST is best; I'll swim toward the setting sun," said another.
The turtles began to argue. They could not agree. One day, four of the turtles began to swim east. Three turtles
began to swim west. The Earth shook! It cracked with a loud noise! But after a minute, the shaking stopped.
The turtles had to stop because the land on their backs was so heavy. They had only been able to swim a little
way from each other. When they saw that they could not swim away, they stopped arguing and made up.
But every once in a while the turtles that hold up California argue again. Each time they do, the Earth shakes
© Environmental Volunteers
Global Plates
E. Q. 16
page 6
© Environmental Volunteers
Global Plates
E. Q. 16
page 7