* Pressure decreases: Rocks deep within the Earth are under immense pressure.

* Mantle rises: When the mantle (the layer beneath the Earth's crust) rises, the pressure on the rocks decreases.

* Melting point lowers: This decrease in pressure lowers the melting point of the rocks. Since the mantle is already very hot, this lowering of the melting point is enough to cause some of the rock to melt, forming magma.

This process is often associated with plate tectonics, specifically at divergent plate boundaries where plates are moving apart, and at hotspots where plumes of hot mantle material rise to the surface.