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What causes the magma to harden?
Cool ocean water causes the magma to harden after the magma comes out through the middle of two plates.
What causes the plates to seperate at this plate boundary?
The force of the Magma coming from between the two plates pushes the plates away from eachother at a Divergent Plate Boundary.
What is the Rift Zone?
The highest part of the Mid-Ocean Ridge is a narrow trench called the Rift Zone. (Usually formed when Divergent Plates seperate and move apart.)