Title: What are Earthquakes?
Authors: Leslie Bucar, 7-12 Science Teacher, Fond du Lac Ojibwe School, B.S.
Biology, B.A.S. Teaching Biology, B.A.S. equiv Teaching Chemistry
Dan Johnson, 7-12 Math Teacher, Fond du Lac Ojibwe School, B.A.S.
Teaching Math
Objectives:
Compare and contrast different types of plate boundaries.
Grade Level: Middle School
Time: 30 Minutes- 1 Hour
Materials:
1 graham cracker per student
1 piece of Styrofoam per student
1 cup of water per student
Frosting
Wax paper
Plastic knife or spoon
Content Standards:
National:
Structure of the Earth System
Minnesota State:
History and Nature of Science 7-Scientific World View
History and Nature of Science 8- Scientific World View
History and Nature of Science 7-Scientific Inquiry
History and Nature of Science 8- Scientific Inquiry
Earth and Space Science 8-Earth Structure and Processes
Problem: In this lab, we will be modeling how crustal plates move. What ways can
you think of?
Vocabulary:
Faults, earthquake, normal fault, reverse fault, strike-slip fault, plate tectonics, plates,
lithosphere, asthenosphere, convection current, boundaries, divergent boundaries,
convergent boundaries, transform boundaries
Introduction:
If you imagine the earth like an apple, there are three main parts. There is the
core, the mantle (the “white” part of the apple), and the crust (the skin of the apple).
Earth’s rigid outer shell, the lithosphere, is made up of the crust and the top part of the
mantle. The asthenosphere is the plastic-like layer below the lithosphere. According to
the plate tectonic model, the lithosphere is broken into vast slabs called plates.
Plate tectonics is the idea that the Earth’s outer shell consists of individual plates,
which interact in various ways and thereby produce earthquakes, volcanoes, mountains,
and the crust itself.
These plates are slowly and continually moving. This movement is caused by hot
material moving up from deep within the Earth unevenly and spreading over the
asthenosphere, setting the plates in motion. This is called a convection current.
When plates move, they can interact in several ways. Because each plate moves
as a distinct unit, all interaction among individual plates occurs along their boundaries.
Divergent boundaries are where plates move apart, leaving a gap between them. The gap
then fills with the asthenosphere from below, and cools, forming new crust. Convergent
boundaries are where plates move together, forcing one of the slabs of lithosphere to
descend beneath the other or both get pushed up. Transform boundaries are where plates
grind past each other, scraping and deforming as they pass.
When the plates move, it puts stress on the rocks near the plate edges. To relieve
this stress, the rocks tend to bend, compress, or stretch. This stress often builds up over
time, as the plates move relative to each other and the stress is built up along the edges.
When the built-up stresses become large enough, the plates will break and move. An
earthquake is the vibrations produced by the breaking of rock. The location where the
plates break or move is called a fault. Faults interrupt rock layers by moving them out of
place.
There are three kinds of faults. One kind pushes the rocks together, one pushes
them apart, and in one, the rocks slide past each other. In a normal fault, there is a pullapart force. In a normal fault, rock above the fault surface moves downward in relation
to rock below the fault surface. In a reverse fault, the rock gets squeezed and the rock is
forced over and up. In a slip-strike fault, rocks on either side of the fault are moving past
each other without much upward or downward movement. The San Andreas fault in
California is a slip-strike fault.
Hypothesis: Write your hypothesis using the problem here.
Procedure:
PART 1 DIVERGENT PLATE BOUNDARIES ( Oceanic and Oceanic Plates )
1. Break a whole graham cracker in half following the perforations on the cracker. You
should have two graham cracker squares.
2. Using a plastic knife/spoon, spread a thin (about the thickness of a playing card) layer
of frosting on the center of the wax paper.
3. Lay the two pieces of graham cracker on the frosting and gently pressing down push
them together. Now you are ready to begin modeling a divergent plate boundary.
4. To imitate the result of diverging oceanic plates, press down lightly on the crackers as
you slowly push them apart. Do not push the crackers more than one centimeter.
5. Make observations and answer questions for Part 1.
PART 2 CONVERGENT PLATE BOUNDARIES (Continental and Oceanic Plates)
1. Remove one of the graham crackers from the frosting.
2. Lay a graham cracker and the styrofoam piece end to end (against each other) on top of
the frosting. The graham cracker represents the thin but dense oceanic plate and the
styrofoam represents the thicker but less dense continental plate. Now you are ready to
model a convergent plate boundary.
3. Slowly push the graham cracker and styrofoam toward each other. Gently push the
graham cracker under the styrofoam. This models what occurs on Earth’s surface as an
oceanic plate is subducted under a continental plate.
4. Make observations and answer questions for part 2.
PART 3 CONVERGENT PLATE BLOUNDARIES (Continental and Continental
Plates)
1. Reuse the two graham cracker squares used in Part 1 and Part 2.
2. Break the graham cracker into four rectangles following the perforations. Set aside two
graham cracker pieces for Part 4.
3. Using two graham cracker rectangles, dip one end of both graham crackers about 2
centimeters into a cup of water. Immediately remove the crackers and lay them end to
end on the frosting with the wet edges nearly touching. Now you are ready to model a
convergent plate boundary.
4. Slowly push the two graham crackers together, modeling the convergence between two
continental plates. The wet end of the graham crackers will curl and fold upwards as the
graham crackers are pushed together.
5. Make observations and answer questions for part 3.
PART 4 TRANSFORM PLATE BOUNDARIES
1. Use the last two graham cracker pieces for this part of the lab.
2. Fit the two pieces together end to end on top of the frosting on the wax paper. Now
you are ready to model a transform plate boundary.
3. Place one hand on each of the graham crackers and push them together by applying
steady, moderate pressure. At the same time, also push one of the pieces away from you
while pulling the other toward you. If you do this part correctly, the graham cracker
should hold while you increase the push-pull pressure, but will finally break form the
opposite forces.
4. Make observations and answer questions for part 4.
Collecting and Analyzing Data:
Part 1 Divergent Plate Boundaries
1. What happens to the frosting between the graham crackers, how does it look?
2. What do each of the graham crackers represent?
3. What does the frosting represent?
Part 2 Convergent Plate Boundaries
1. What type of plate does the styrofoam represent?
2. What type of plate does the graham cracker represent?
3. What happens when a piece of crust goes under another piece of crust (called
subduction)?
Part 3 Convergent Plate Boundaries
1. What does the graham cracker represent?
2. In what way are the wet graham crackers more like the real crustal plates than are the
dry graham crackers?
3. What feature is represented where curling and folding occurred at the ends of the wet
graham cracker?
Part 4 Transform Plate Boundaries
1. Why is this movement often described as “horizontal sliding?”
2. What famous fault is associated with this type of movement?
3. As you modeled this type of fault, nothing happened at the beginning, but as the
pressure increased, the graham crackers finally broke. How is this similar to the situation
in California?
Conclusion:
1. What is an earthquake?
2. Why do you think it is easier to predict where an earthquake will occur than it is
to predict when it will occur?
Teacher Lesson Guide and Key: What are Earthquakes?
Collecting and Analyzing Data Key:
Part 1 Divergent Plate Boundaries
1. What happens to the frosting between the graham crackers, how does it look?
The frosting is forced up between the graham crackers, answers will vary
2. What do each of the graham crackers represent?
Crustal plates/lithosphere
3. What does the frosting represent?
asthenosphere
Part 2 Convergent Plate Boundaries
1. What type of plate does the styrofoam represent?
Continental plate
2. What type of plate does the graham cracker represent?
Oceanic plate
3. What happens when a piece of crust goes under another piece of crust (called
subduction)?
It melts
Part 3 Convergent Plate Boundaries
1. What does the graham cracker represent?
Crustal plates/lithosphere
2. In what way are the wet graham crackers more like the real crustal plates than are the
dry graham crackers?
They are able to bend
3. What feature is represented where curling and folding occurred at the ends of the wet
graham cracker?
Mountains
Part 4 Transform Plate Boundaries
1. Why is this movement often described as “horizontal sliding?”
The plates move past each other horizontally with neither crustal plate moving up or
down
2. What famous fault is associated with this type of movement? The San Andreas Fault
3. As you modeled this type of fault, nothing happened at the beginning, but as the
pressure increased, the graham crackers finally broke. How is this similar to the situation
in California?
The pressure is building up, until there is a release, resulting in an earthquake
Conclusion Key:
3. What is an earthquake?
A vibration produced by the breaking of rock.
4. Why do you think it is easier to predict where an earthquake will occur than it is
to predict when it will occur?
Scientists know that most earthquakes occur near plate boundaries, but they
cannot predict when rocks in the crust will break in response to the forces acting
on them.
Bibliography:
Feather, R., Snyder, S., and Zike, D. 2002. Earth Science. Glencoe McGraw-Hill, New
York, NY.
Lutgens, F. and Tarbuck, E. 1998. Essentials of Geology. Prentice Hall, New Jersey.
Marshall, R. and Rosskopf, A. 1992. Earth Science. Media Materials Publishing,
Maryland.
http://www.inghamisd.org/~goals2k/lessons/sciencelesson/tippin3.html
http://www.atropos.as.arizona.edu/aiz/teaching/nats102/images/faults.gif