Environmental Engineering Reference
In-Depth Information
Arabian Plate
Caribbean Plate
Cocos Plate
Juan de Fuca Plate
Nazea Plate
Philippine Plate
Scotia Plate
The plates literally ride on the asthenosphere , which is the ductile, soft, plastic-
like zone in the upper mantle. Crustal plates move in relation to one another at one of
three types of plate boundaries: convergent (collision) boundaries, divergent (spread-
ing) boundaries, and transform boundaries. These boundaries between plates are
typically associated with deep-sea trenches, large faults, fold mountain ranges, and
mid-oceanic ridges.
Convergent Boundaries
Convergent boundaries (or active margins) develop where two plates slide toward
each other, commonly forming either a subduction zone (if one plate subducts or
moves underneath the other) or a continental collision (if the two plates contain con-
tinental crust). To relieve the stress created by the colliding plates, one plate deforms
and slips below the other.
Divergent Boundaries
Divergent boundaries occur where two plates slide apart from each other. Oceanic
ridges, which are examples of divergent boundaries, occur where new oceanic,
melted lithosphere materials well up, resulting in basaltic magmas, which intrude
and erupt at the oceanic ridge, in turn creating new oceanic lithosphere and crust
(new ocean floor). Along with volcanic activity, the mid-oceanic ridges are also areas
of seismic activity.
Transform Boundaries
Transform boundaries do not separate or collide; rather, they slide past each other
in a horizontal manner with a shearing motion. Most transform boundaries occur
where oceanic ridges are offset on the sea floor. The San Andreas Fault in California
is an example of a transform fault.
DID YOU KNOW?
Plates are in constant motion (several centimeters per year). When collision or
grinding occurs, it can create mountains, volcanoes, geysers, and earthquakes.
Near the junction of these plates is where heat travels rapidly from the interior
of the planet.
 
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