Please clarify sentence.
 

Source: Bajwa book, chp4: volcanism.
''The magma in the interior of the earth is subjected to great pressure which doesn't allow the magma to melt.''


not getting this sentence. I think Great pressure allow the magma to melt rapidly, while here they wrote opposite.



Thanks in advance for your concern.

I hope it will solve your problem.
Very high pressures in mantle rocks prevent atoms within minerals from breaking chemical bonds and moving freely from one another to form a magma. Therefore, most rocks within the mantle do not melt even though their temperature may be greater than that necessary to melt the same rocks at the lower pressures of the Earth's surface. However, if pressure on mantle rock is decreased the atoms may move freely from one another, resulting in partial melting of the rock. This process is called pressure-release melting.