• (n.) Volcanism.
Vul'can·ism noun Volcanism. 
volcanism, vulcanism 1. The processes by which magma and its associated gases rise up into the crust and are extruded onto the earth's surface and into the atmosphere. 2. Volcanic power or action; volcanicity. The term ordinarily includes all natural processes resulting in forming volcanoes, lava fields, laccoliths, dikes, etc.
term given to processes whereby magma is extruded on to the earth's surface.