When we arrived with our six children to study Spanish in Mexico in January 1985 we knew nothing about the tectonic plate under the Pacific Ocean that was grinding against the one on which we intended to set up home. Moving at the speed at which a fingernail grows, the Cocos Plate, named after the protruding island, had long engaged the less dense North American Plate, subducting beneath it and lifting it to form the plateau in the middle of Mexico on whose southern slopes we had rented a house. We were interested in the nearby, snow-capped peak of the…