LESSON 15

INVESTIGATING PLATE MOVEMENT AND FAULTS

INTRODUCTION

What does the word “model” mean to you?

Miniature version

Used for study

Something’s too large to view

OBJECTIVES

Describe what a model is and distinguish models from real objects or events. A representation of an object or event that is too large, too small or complicated to be viewed or studied

Classify materials as either brittle or ductile.

Investigate the effects of applying a force to a model of a fault.

Let’s view the video to answer the questions:

Record the following in your notebooks:

A. What occurs at a Transform fault?

B. How does plate movement cause earthquakes at a transform fault?

MODELSA. How are the map and computer images used in this lesson like the real earth? How are they different?The map and computer images are models of the earth.B. What are some examples of models?Globe, map, tornado in a bottleC. Write a working definition for the word “model”..Let’s look at the models we’ll use for this lesson.

Inquiry 15.1Using a Simple Model of

Plate MovementLook at the blue and green foam pads used in this activity and record their properties.

Density, appearance, thickness, weight, and size.

Predict

How would each pad respond if we did the following:

Pulled on the pad from opposite ends

Pushed on the pad at opposite ends

Slid two pads past one another

Collided two pads by pushing them together

Test and Record

As each foam pad is demonstrated, record in your notebook what happens. Use a table to record your observations.

pull push slide collide

Blue

Green

REFLECTIONS 15.1

A. How did the pads behave when pulled from opposite ends?

The pads were stretched thin. The blue pad was more “stretchy”.

B. How did the pads behave when compressed?

The pads folded—resembling mountains

C. If oceanic plates are colder, denser, and thinner than continental plates are, which pad do you think represented oceanic plates? Which pad represented continental plates?The thin, blue, dense pads represented oceanic plates. The thick green pads represented continental plates.D. How did the density of the pads affect the way they behaved when you made them collide?The dense blue pads always moved beneath the less dense green pads.

E. When do colliding plates on the earth form mountains?

Mountains form when two continental plates of a similar density collide.

F. When do colliding plates form trenches?

Trenches form when a dense oceanic plate collides with a less dense continental plate.

G. Why would a more dense oceanic plate slide under a less dense continental plate?

Something more dense usually moves beneath something less dense.

H. Can plates ever move without forming new land? If so, when?

No new land forms when plates slide past one another.

I. How do you think colliding plates on the earth cause earthquakes?

Colliding plates either bend or fracture the land; earthquakes can form when rock fractures.

Read pgs. 174, 175

Colliding, Sliding, and Separating Plates

INQUIRY 15.2Using the Moving Plates

Model

Turn to page 176 in your Catastrophic Events book and follow the procedure listed as it’s demonstrated for you.

REFLECTIONS 15.2A. How do you think the Moving Plates Model shows what happens on the earth when two plates separate?

It shows the form they took as they moved.

B. What causes the ocean floor to separate and grow?

Newly melted rock rises and pushes aside the old rock.

C. Think about what happened to the black belt as it reached the edges of the model’s lid. What landform is created when the ocean floor sinks back into the earth?

A trench forms

D. What patterns did you observe in the shapes of Africa and South America?

They fit together like puzzle pieces.

E. How did the shapes of these continents compare with the shape of the Mid-Atlantic Ridge?The MAR has the same shape as the coastlines of these continents, which border the Atlantic. This is because the continents broke apart as the ridge formed.F. What landform is created when plates separate? Give an example.A ridge forms. Ex: The Mid-Atlantic Ridge.

G. What landform is created when two continental plates collide? Give an example.

A mountain forms. Ex: The Appalachian Mountains (North Amer)

INQUIRY 15.3Investigating Faults With

Models

Turn to page 179, 181 in your Catastrophic Events book and follow the procedure listed on these pages.

REFLECTIONS 15.3

A. How did the amount of friction along the fault affect the amount of force needed to rupture the fault? Use data to support your answer.

The greater the friction, the more force is needed to rupture the fault. The hooks and loops of the Velcro act like protrusions that connect the rock across the rock.

B. Under what conditions did the blocks rupture more abruptly?The greater the force applied to the block, the more abrupt the rupture.

C. Under what conditions did the block slip (more slowly) but not rupture?When two strips of loop Velcro are side by side, the friction along the fault was at its lowest. When resistance along a fault is low, blocks of rock can slip without faulting.

D. Think about what happened with the masking tape. Is there any sign on the earth’s surface that the earth is moving slowly beneath the crust?

Wrinkles in a sidewalk or on a road are signs that pressure is building up along a fault. This is called “creep.”