JC Separating Plate Boundaries

Separating plate boundaries are places where two plates pull apart or separate from each other. The Mid-Atlantic Ridge Rift is an example of a separating plate boundary.  They are also called constructive plate boundaries because new rock is added to the oceanic crust at these boundaries as if the oceanic plate is being constructed (built).

When convection currents move in the Transition Zone, they put pressure on the ridge-rift between the two plates.  This forces the rift open.  Magma rises up through the rift.  When it meets the sea water, it cools rapidly to form a basaltic rock. In this way, new rock is added to the ridge making it higher. At the same time, the convection currents exert a drag effect on the underneath of the oceanic crust.  This helps pull the ridge-rift apart and allows magma to rise up through the rift.  In this way, the ridge get higher and the oceanic plate spreads and gets wider. In Atlantic Ocean is spreading at about 2.5 cm each year.


Iceland is a country in the middle of the North Atlantic Ocean.  It is located on top of the Mid-Atlantic Ridge-Rift.  One half of Iceland is being pulled westward by convection currents in the Mantle.  The other half is being pulled eastward. Running down the middle of Iceland is a giant fault line – the Mid-Atlantic Ridge.  Iceland also has lots of volcanoes. When the convection currents cause the Mid-Atlantic Ridge to open, magma rises out of the ground in Iceland and builds up to form volcanoes. Many of these are covered in snow and ice.  When they erupt, they can be quiet spectacular.  In 1973, a volcano erupted under the ocean just south of Iceland. After one week, a whole new island grew up over the level of the water.  This new island was called Surtsey.