How Magma Is Made

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Magma is created within the lithosphere, which is divided into 16 major plates. When these plates shift mantle pockets are disrupted which causes steam and gases in the mantle to become magma called hotspots. The shifting plates are lubricated by the soft layer called the athenosphere.

Spreading Center Volcanism
When the plates shift away from each other an ocean ridge or continental ridge is formed. As two plates separate mantle rock from the athenosphere flows up into into the crack. Due to the change in pressure the mantle rock will melt and form magma. When the magma flows out it cools and hardens to become a new crust.

Subduction Zone Volcanism
This is where two plates collide and one is pushed under the other plate into the mantle. Magma is formed when the heat and the pressure forces the water out of the plate and into the mantle layer. The increased water content lowers the melting point of the mantle rock in the wedge causing it to melt into magma.