Download 2.13 Divergent Plate Boundaries

Where Things Come Apart
Oceanic Spreading Centers

 At divergent plate boundaries, plates move away
from each other .
 Many of these boundaries occur along the oceanic
ridge system and are referred to as oceanic spreading
centers.
 They are the sites where the seafloor spreads
 As two oceanic plates move apart, the lithosphere is being
extended, thinned and fractured.
 Magma form the asthenosphere upwells into the rift valley.

 Magma solidifies to form basalt, new material which is added
to the plate.
 This type of boundary is referred to as a constructive plate
boundary
 The new material is hotter and less dense than the
surrounding lithosphere causing the resultant midoceanic ridge to rise 2-3 km above the ocean floor.

 In Iceland the ridge rises above sea level
 Mid-ocean ridges encircle the Earth like a seam on a
baseball.
 These ridges form the longest and widest mountain
chain in the world.

 65,000 km long
 And up to 1500 km wide
 The topography of a ridge is very rugged.
 Split down the middle by a rift valley, which extrudes
lava
 The Bay of Fundy began as a divergent plate
boundary that never completely developed into an
ocean
Continental Rifting

 Divergent plate boundaries can also occur on
continents where continental crust is moved apart
forming a rift between the plates.
 This is know as continental rifting.
 If water flows into the rift from an adjoining ocean, a
new ocean is born.
 The Read Sea was formed in this manner.



 Geological activity associated with divergence
includes:
 Volcanism
 And earthquake activity
 Neither of these poses much of a threat to people as
the activity generally occurs on the ocean floor
Links of Interest

http://geology.com/plate-tectonics.shtml