Page 143 - Science Course 2 (Book 2)

Mo11-L3a: Types of Plate Boundaries

The lithosphere is thin below mid-ocean ridges and A transform plate boundary forms where two plates
thick below continents. slide past each other.

Earth’s tectonic plates are large pieces of the As they move past one another, the plates can get
lithosphere that f t together like the pieces of a giant stuck and stop moving.
jigsaw puzzle.
Stress builds up where the plates are stuck until they
The layer of Earth below the lithosphere, called the eventually break and suddenly move apart, resulting
asthenosphere, is so hot that it behaves like a plastic in a rapid release of energy as earthquakes.
material and enables Earth’s plates to move.

Lithosphere
Asthenosphere Transform Plate Boundary

Two plates slide horizontally past one another
along a transform plate boundary Earthquakes
are common along this type of plate boundary.
The San Andreas Fault, shown below, is part of the
Plate Boundaries transform plate boundary that extends along the
coast of California.
A divergent plate boundary forms where two plates
separate.

When the seaf oor spreads at a mid-ocean ridge,
lava erupts, cools, and forms new oceanic crust.
Divergent plate boundaries can also exist in the
middle of a continent, where they pull continents
apart and form rift valleys.

Mid-Ocean Ridge

Divergent Plate Boundary Convergent plate boundaries form where two
When two plates separate and create new oceanic plates collide.
crust, a divergent plate boundary forms.
The denser plate sinks below the more buoyant plate
This process occurs where the seaf oor spreads in a process called subduction.
along a mid-ocean ridge, as shown to the right.
The area where a denser plate descends into Earth
This process can also occur in the the middle of along a convergent plate boundary is called a
continents and is referred to as a continental rifting. subduction zone.

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