Magmatism

thumb|300px|Geological map showing the [[Gangdese batholith, which is a product of magmatic activity about 100 million years ago.]] Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of magma or lava. Volcanism is the surface expression of magmatism.