UNIT
7
The Earth’s dynamics
PLATE BOUNDARY ACTIVITY
Natural Science 2. Secondary Education
UNIT
7
Plate boundary activity
Lithospheric plates move
• As we saw in unit 6, there are convection currents in the mantle.
• These currents cause the lithospheric plates to move and
sometimes grow larger or smaller.
• Lithospheric plate boundaries are especially active. There are
three types:
• Convergent boundaries
• Divergent boundaries
• Transform fault boundaries
Natural Science 2. Secondary Education
UNIT
7
Plate boundary activity
Convergent boundaries
• These are the edges between two plates moving towards each other.
Usually, one plate
sinks inside the
mantle, destroying part
of the lithosphere and
shrinking in size.
There are usually
deep trenches
where the two
plates meet.
Natural Science 2. Secondary Education
The other plate
gets pushed up,
forming a mountain
range.
As the sinking plate
melts, it generates
magma, which results
in intense volcanic
activity in these areas.
UNIT
7
Plate boundary activity
Divergent boundaries
• These are the edges between two plates moving away from each other.
• They usually coincide with oceanic ridges.
A rift forms between the two
plates. Molten material from
the mantle rises up through
these rifts, forming new
lithosphere.
Natural Science 2. Secondary Education
As new lithosphere is
formed, both plates
grow in size.
UNIT
7
Plate boundary activity
Transform fault boundaries
• Also called conservative boundaries, these occur when two plates touch
as they move parallel to one another in opposite directions.
Because the plates slide past
each other, no lithosphere is
created or destroyed and so
the plates stay the same size.
Natural Science 2. Secondary Education
Although volcanic activity is
usually not present, transform
fault boundaries are sites of
intense seismic activity.
UNIT
7
Plate boundary activity
The world’s plate boundaries
• As you might expect, this map shows that plate boundaries coincide with
significant geographical features and areas with intense seismic and
volcanic activity.
Natural Science 2. Secondary Education