Why is western mexico subject to volcanic eruptions?

Because of the ring of fire, that produces "the phenomenon of subduction" is the name given to this movement of the continental plates. The center of the Pacific is where the tectonic plates are born and it is at the edge of the continents where these earthquakes are felt because one gets under another . Subduction produces two things: seismic and volcanic activity. Almost 90% of earthquakes and volcano eruptions occurring in the world occur in the Pacific Ring of Fire. This phenomenon is caused by the violent release of energy that unties the friction of tectonic plates. In the case of Mexico, there are up to three plates that coincide (the Caribbean, the Cocos and the North American).