12. If temperature inside the Earth is steady and is not the main reason for the creation of magma, what does change inside the Earth to cause rocks to partially melt?

The pressure changes within the earth so that the rocks partially melt

Explanation:

The temperature inside the earth is always high and constant, that is, it does not vary. However the pressure in this environment is fickle and can vary quickly and influence the activity of volcanism and the melting of rocks.

Generally, the internal part of the earth remains under normal pressure conditions. However, when the pressure drops considerably and interacts with the temperature of the interior of the earth, it can cause the partial melting of the rocks, creating magma and often causing the magma to overflow to the surface.