PLATE TECTONICS
The Principal Tectonic Plates The earth’s crust is divided into seven large plates and about a dozen smaller plates. The principal plates are shown in Figure 6. Memorise the names and approximate positions of the principal plates.
Plate Boundaries The place where two plates touch each other is called a plate boundary. Figure 7 shows
that there are three main types of plate boundary. You will learn on the following pages that each type of boundary affects the earth’s surface in a different way.
The earth’s crustal plates. (a) In which plate is each of the following countries
situated? Ireland India South Africa
(b) At which type of plate boundary is each of the
following areas situated? Northern India The Mediterranean Sea The Mid-Atlantic area The west coast of the USA
6 North
American Plate
1
Pacific Plate
South
Nazca Plate
American Plate
2 plate boundary
direction of plate movement
Antarctic Plate 3 Indo-Australian Plate
African Plate
Pacific Plate
Eurasian Plate
1
2
3
Types of plate boundary
7
Conservative boundary
Conservative plate boundaries occur where two plates slide past each other. These boundaries are also called passive or transverse boundaries
Convergent boundary
Convergent plate boundaries occur where plates collide with each other. These boundaries are also called destructive boundaries because parts of the earth’s crust are destroyed where they occur.
Divergent boundary
Divergent plate boundaries occur where plates separate from each other. These boundaries are also called constructive boundaries because new crust is constructed (grows) where they occur.
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