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Characteristics of Lithospheric Plate Boundaries
Plate Boundary Plate Composition
Plate Motion(s)
What Happens to the Sea Floor Events Observed
Example Locations
Divergent
ocean/ocean
apart
Upwelling magma forms new
rock at ridge
Ridge forms at spreading center
Ocean basin expands
Plate area increases
Many small volcanoes
Shallow focus earthquakes
Mid-Atlantic Ridge
Divergent
continent/continent
apart
New seafloor may form
Continent spreads
Central rift collapses
Ocean may intrude
East-Africa Rift Valley
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Convergent
ocean/ocean
toward
Subduction trench forms
Dense, cold, oceanic
lithosphere plunges beneath
less dense, oceanic lithosphere.
Strong earthquakes
(shallow, int. and deep foci) trace
path of subducting slab. Heat from
friction melts part of both plates
forming magma which rises, forming
Island Arc of volcanoes.
Japan, Philippine &
Aleutian Island arcs
Convergent
continent/continent
toward
Subduction trench forms
Dense, cold, oceanic
lithosphere plunges beneath
less dense, warmer continental
lithosphere. Strong earthquakes
(shallow, int. and deep foci) trace
path of subducting slab. Heat from
friction melts part of both plates
forming magma which rises, forming
Volcanic Arc of volcanoes.
Cascades & Andes Mtns.
Convergent
continent/continent
toward
Old sea floor is gone
Masses of low density, relatively
warm continental lithosphere collide.
Neither subducts, plate edges are
compressed, folded, uplifted.
Alps & Himalayan Mtns.
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Transform
can be either
composition
past each other
in opposite directions
Plates move past each other in
opposite directions. Shallow earthquakes.
San Andreas Fault
system, California