1. 8.3 Causes of Plate Movement
Objectives:
Explain the “mantle convection hypothesis”.
Compare and contrast ridge push and slab pull.

2. Introduction 3 major hypotheses describe how tectonic plates move
Mantle convection
Ridge push
Slab pull
Asthenosphere
Provides the plates with a surface on which they can move
Pliable
Rock materials are hotter than those in the lithosphere

3. Mantle Convection
The mantle may be moving the plates along with it as it convects
Magma that is hotter and less dense than its surroundings rises upward at a mid-ocean ridge
It drags the lithospheric plate with it as the current moves away from the mid- ocean ridge
Cooler, denser rocks of the lithospheric plate sink down at a subduction boundary

4. Ridge Push “Gravitational Sliding”
Molten magma rises at the mid- ocean ridge
Heats the rock around it
Surrounding rock is heated to expand and elevate
Creates a slope
New rocks are less dense and more buoyant
Becomes denser as it cools
Gravity causes older, denser rock to slide away from the ridge down the slope
New molten magma wells up (etc.)

5. Slab Pull
The edge of the subducting plate is much colder and heavier than the mantle
It continues to sink, pulling the rest of the plate along with it
Definition: the force that the sinking edge of the plate exerts on the rest of the plate
Scientists think this is a stronger factor than ridge push or mantle convection in driving plate movements

6. 8.3 Exit Ticket Answer the following questions.
Use complete sentences.
You may NOT use your book. You MAY use your notes.
This is a quiz grade
What is the “mantle convection hypothesis”?
Compare and contrast ridge push and slab pull. (use a Venn diagram)