A cloud of ash from the 17,886-foot (5,450-meter) Popocatépetl volcano caused the suspension Thursday morning of flights to and from Puebla, a major city southeast of Mexico City.

Local authorities ordered the closure of the airport as a safety precaution, which delayed flight to cities such as Monterrey and Houston, Texas, a local news report stated.

The alert level for the volcano was raised last month after the volcano began to pump out red-hot ash and 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 Popocatépetl is unlikely to do more than dump ash on one of the world's largest metropolitan areas. But the grit could play havoc with Mexico City's busy airport and force the evacuation of tens of thousands of people in the farming villages on its flanks.

Popo, as it's commonly known, has put out small eruptions of ash almost daily since a round of eruptions began in 1994. A week ago, the eruptions started growing larger and authorities slightly elevated the alert level for people living nearby. Before dawn on Friday, the mountain moved into what appeared to be a new level of activity, spitting out dozens of ash and shot fragments of glowing rock down its slopes and frightening the residents of surrounding villages with deep roaring not heard in a decade.

A 35 million cubic foot (1 million cubic meter) chamber of magma is seething about six miles (8 to 10 kilometers) beneath Popocatépetl, a mountain named for a legendary indigenous warrior, Roberto Quaas, director of the disaster prevention center, told a press conference laying out emergency preparations.

Scientists have no way of predicting whether the molten rock in the chamber will be slowly released, or erupt in a powerful explosion like one on Dec. 18, 2000 that sent up a plume of red-hot rock and forced the evacuation of thousands of people who live at the volcano's base.

An iconic backdrop to Mexico City's skyline on clear days, Popocatépetl sits roughly halfway between Mexico City and the city Puebla — meaning some 25 million people live within a 60-mile radius of the volcano, Quaas said.

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