 The
variety of plates that are moving across the surface of Earth manifest
amazing effects at the zones of interaction or boundaries as they are
called. Volcanoes and earthquakes are such manifestations.
There are four types of plate boundaries:
- Divergent boundaries -- new crust
is generated as the plates pull away from each other.
- Convergent boundaries --
crust is destroyed as one plate dives under another.
- Transform boundaries --
crust is neither produced nor destroyed as the plates slide horizontally
past each other.
- Plate boundary zones --
broad belts in which boundaries are not well defined and the effects of
plate interaction are unclear.
Rates of Motion
> measuring distance and estimating time between boundary edges of plates
can yield motion speed estimates
> using magnetic striping of ocean floor
minerals the flip flop time of Earth's magnetic field can produce evidence
for historic rates of flow
> satellites can now measure these movements accurately
> the Arctic Ridge has the slowest rate (less than
2.5 cm/yr)
> the East Pacific Rise near Easter Island, in the
South Pacific about 3,400 km west of Chile, has the fastest rate (more
than 15 cm/yr).
> GPS monitors can now accurately track plate movement of shorter periods
of time |