Popocatépetl

The snow-covered Popocatepetl volcano spews a cloud of steam into the air in Puebla July 9, 2013. (Photo by Imelda Medina/Reuters)

Smoke rises from the Popocatepetl as it spews incandescent volcanic material on the outskirts of Puebla July 4, 2013. (Photo by Imelda Medina/Reuters)

A rainbow forms over the town of Santiago Xalizintla where the Popocatepetl volcano, behind center, is covered by clouds in Mexico, Monday, July 8, 2013. The Environment Ministry has urged residents to take preventive measures to deal with the ash, including wearing dust masks, covering water supplies and staying indoors as needed. (Photo by Marco Ugarte/AP Photo)