Environmental Engineering Reference
In-Depth Information
Spreading
center
Ocean
trench
t
Subduction
zone
Oceanic crust
Oceanic crust
Continental
crust
Continental
crust
Cold dense
material falls
back through
mantle
Material cools
as it reaches
the outer mantle
Hot material
rising
through
the mantle
Mantle
convection
cell
Two plates move
towards each other.
One is subducted
back into the mantle
on falling convection
current.
Mantle
Hot outer
core
Inner
core
Active Figure 12-3
Natural capital:
the earth's crust is made up of a series of rigid plates, called
tectonic
plates,
which move around in response to forces in the mantle.
See an animation based on this figure and
take a short quiz on the concept.
with a continental plate, the continental plate usually
rides up over the denser oceanic plate and pushes it
down into the mantle in a process called
subduction.
The area where this collision and subduction takes
place is called a
subduction zone.
Over time, the sub-
ducted plate melts and then rises again to the earth's
surface as molten rock or magma. A
trench
ordinarily
forms at the boundary between the two converging
plates. Stresses in the plate undergoing subduction
cause earthquakes at convergent plate boundaries.
The third type of boundary is a
transform fault,
where plates slide and grind past one another along a
Science: Types of Boundaries
between the Earth's Plates
The earth's tectonic plates move apart, push together,
and slide past one another.
Lithospheric plates have three types of boundaries.
The first type is a
divergent plate boundary,
where
plates move apart in opposite directions (Figure 12-5,
top, p. 274).
The second type is a
convergent plate boundary,
where plates are pushed together by internal forces
(Figure 12-5, middle). When an oceanic plate collides
