Rumbling Mexican volcano keeps residents on alert - 4/23/12



Mexico's famed Popocatepetl continued to spew columns of ash and gas into the air on Monday.
Mexico's National Center for Disaster Prevention raised the alert level for Popocatepetl to yellow phase three from yellow phase two last week, indicating possible magma expulsion and explosions of increasing intensity. It is the third-highest warning on the center's seven-step scale.
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