2 - Plate Tectonics


You now have an introduction to the internal structure of the Earth. Now we will concentrate on details of the rocky, silicate-rich outer part of the planet. We will use the old word "crust", although the rocky shell of the planet actually includes the crust and the upper bit of the mantle and is now called the lithosphere. Most of you already have a basic understanding of plate tectonics so some of this chapter will be a review but we will get into much more detail. This is important because plate boundaries are where many geologic disasters originate but different processes are active at different types of plate boundaries and some disasters are not associated with any kind of plate boundary at all. We will discuss the processes and rocks at each type of plate boundary and briefly talk about the different types of geological disasters that occur in each environment.

The majority of large physiographic features on Earth are the result of plate movement. These include the ocean basins and all the features they contain as well as the continental masses and their mountain chains. Earthquakes are one of the physical expressions of plate movement and although a single event may only move the surface of the Earth a few centimeters (or in a big earthquake a few metres), over millions of years these movements cause continents to break apart, crash together and give rise, for instance, to the large mountain chains we see at the Earth's surface.

Learning Objectives

Upon completion of this unit you should be able to:

1. Identify the predominant mineral and rock composition of continental crust.
2. Explain why continental crust tends to be older than oceanic crust.
3. Describe the processes occurring in the upper mantle that result in plate movement.
4. Explain how slab pull and ridge push occur.
5. List and Describe the stages of the “Wilson Cycle.”
6. Identify what hot-spots are and where they occur.
7. Say what convergent, divergent, and transform boundaries are and the processes and events associated with each.
8. Explain why large mountain ranges are formed at continent-continent convergent boundaries.
9. Describe how movement at transform boundaries can result in dangerous earthquakes.
10. Explain how plate tectonics drive the rock cycle.

Required Readings

Abbott, P.L., 2014. Natural Disasters, Ninth Edition: Readings From the Old Book

Abbott, P.L., 2012.  Natural Disasters, Eighth Edition:

Glossary Terms

Arkose Radiogenic
Convection Radiometric Age Dating
Fauna Ridge Push
Feldspar Rift
Gneiss Shield Volcano
Granite Slab Pull
Hot-Spot Strato-volcano
Island Arc Subduction Zone
Mantle Plume Supercontinent
Plutonic Igneous Rock Tethys Sea
Quartz Tsunami