The answer is tectonic plates. The central plateau and the western side of Mexico is part of the Pacific ring of fire due to the subduction below the western side of North and South America where the oceanic crust is melted as it becomes submerged below the continental crust and then some of the resulting magma flows out or is ejected onto the surface as volcanoes such as the ones in the central plateau of Mexico. Volcanoes occur in this ring of fire from Alaska to Canada to the western US, to Mexico, Central America and South America on the west.
