Where Things Come Apart

  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 Oceanic Spreading Centers

  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 mid- oceanic 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

  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. 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.

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  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

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