POPOCATÉPETL VOLCANO, Mexico — In the predawn darkness, a team of scientists climbs the slope of Mexico's Popocatépetl volcano, one of the world's most active and whose eruption could affect millions ...

Popocatépetl Volcano, Mexico — In the predawn darkness, a team of scientists climbs the slope of Mexico's Popocatépetl volcano, one of the world’s most active and whose eruption could affect millions ...