XALITZINTLA, Mexico - The white-capped volcano that looms over Mexico City emitted a terrifying low-pitched roar Friday and spewed roiling towers of ash and steam as it vented the pressure built up by a massive chamber of magma beneath its slopes. Authorities prepared evacuation routes, ambulances and shelters in the event of a bigger explosion. Even a large eruption of the 17,886-foot (5,450-meter) cone of Popocatepetl is unlikely to do more than dump ash on one of the world's largest metropolitan areas. But the grit could play...

XALITZINTLA, Mexico - The white-capped volcano that looms over Mexico City emitted a terrifying low-pitched roar Friday and spewed roiling towers of ash and steam as it vented the pressure built up by a massive chamber of magma beneath its slopes. Authorities prepared evacuation routes, ambulances and shelters in the event of a bigger explosion. Even a large eruption of the 17,886-foot (5,450-meter) cone of Popocatepetl is unlikely to do more than dump ash on one of the world's largest metropolitan areas. But the grit could play...