Mexico

Smoke rises from the Popocatepetl as it spews incandescent volcanic material on the outskirts of Puebla July 4, 2013. The 5,450-metre (17,900 ft) Popocatepetl volcano has been kept on yellow phase two alert, the second-highest warning on the center's seven-step scale, according to local media.

melda Medina/Reuters

Smoke rises from the Popocatépetl volcano as it spews incandescent volcanic material on the outskirts of Puebla, Mexico on Thursday.

Lightning flashes during a thunderstorm over Monterrey

Daniel Becerril /Reuters

Lightning flashes during a thunderstorm over Monterrey, Mexico

Backdropped by Popocatepetl Volcano, Mexico's second highest peak just 55 km southeast of Mexico City, a farner plows the land in San Nicolas de los Ranchos, in the state of Puebla, on May 14, 2013. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three" as the Popocatepetl continues to spew ash and smoke.

Ronaldo Schemidt/AFP

A farmer ploughs the land in San Nicolas de los Ranchos, in the state of Puebla, with the Popocatepetl volcano, Mexico’s second-highest peak, 55km southeast of Mexico City, in the background. The National Disaster Prevention Centre raised the alert level to ‘yellow phase three’, as the Popocatepetl continues to spew ash and smoke.

Burned cars are pictured in a highway in Ecatepec near Mexico city, on May 7, 2013. A gas tanker exploded in a Mexico City suburb on Tuesday, killing at least 18 people and damaging several homes and cars, an official said. AFP PHOTO/Victor RojasVICTOR ROJAS/AFP/Getty Images

Victor Rojas/Getty Images

Burning cars are pictured in a highway in Ecatepec near Mexico city, on Tuesday. A gas tanker exploded in a Mexico City suburb on Tuesday, killing at least 18 people and damaging several homes and cars

U.S. President Obama delivers speech in Mexico City...U.S. President Barack Obama delivers a speech at the Anthropology Museum during his visit to Mexico City May 3, 2013.   REUTERS/Kevin Lamarque   (MEXICO - Tags: POLITICS)

Kevin Lamarque/Reuters

US President Barack Obama delivers a speech at the Anthropology Museum during his visit to Mexico City on Friday.