Here's a breakdown:

* Melting occurs when existing rocks are heated to a point where they become liquid. This happens deep within the Earth's crust and mantle.

* Heat sources for melting:

* Geothermal Gradient: The natural increase in temperature with depth within the Earth.

* Magma Intrusions: When existing magma rises and heats surrounding rocks.

* Plate Tectonics: Friction and pressure at plate boundaries can generate heat.

* Radioactive Decay: Radioactive elements within the Earth release heat.

Once the rocks melt, the molten material is called magma. This magma can then rise to the surface through volcanic eruptions or solidify underground to form igneous rocks.