As the oceanic plate sinks, fluid (shown in purple) is squeezed out of it. The fluid flows up into the mantle rock above and changes its chemistry, causing it to melt. This forms magma (molten rock). ... If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption.
Answer:
As the oceanic plate sinks, fluid is squeezed out of it. The fluid flows up into the mantle rock above and changes its chemistry, causing it to melt. This forms magma (molten rock). If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption.
