A plume of ash rises from the crater of the Popocatepetl volcano seen from the town of San Nicolas de los Ranchos, Mexico, Friday April 20, 2012.  Authorities prepared evacuation routes, ambulances and shelters in the event of a bigger explosion after the volcano that looms over Mexico City emitted a low-pitched roar early Friday morning and spewed ash and steam. (AP Photo/Joel Merino)
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