The 17,886-foot volcano spat hot rocks half a mile from its crater and gritty ash showered nearby towns, including Puebla, a city of 1.2 million people 25 miles east of the crater. More ominous was a small mudslide of volcanic ash down the Huiloac canyon that leads to the town of Santiago Xalitzintla.
Officials consider mudslides of built-up ash one of the gravest dangers posed by the volcano.
The National Center for the Prevention of Disasters said the slide Monday was probably caused by flows of hot ash from the crater melting part of a glacier near the summit. The slide stopped five miles short of the town. Though the volcano is only 40 miles southeast of Mexico City, experts say it poses little danger beyond a possible sprinkling of ash on North America's largest city. On Dec. 18, the volcano staged its most violent eruption in 1,200 years, spewing red-hot rock like a Roman candle and convincing thousands who live at its base to flee to shelters set up in safe areas. The villagers were allowed to return Dec. 27.