In this July 23, 2013 photo, Gilberto Castelan, director of instrumentation at Mexico’s National Disaster Prevention Center laboratory, shows a seismic graph from Dec. 18, 2000 when a large eruption... more 
In this July 23, 2013 photo, Gilberto Castelan, director of instrumentation at Mexico’s National Disaster Prevention Center laboratory, shows a seismic graph from Dec. 18, 2000 when a large eruption was recorded at the Popocatepetl volcano in Mexico City. Sensors feed data to the constantly scrolling seismographs as the crew and volcanologists analyze the concentration of gases and changes in the shape of the mountain. (AP Photo/Marco Ugarte) less 
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Associated Press | Photo By Marco Ugarte
Wed, Jul 31, 2013 6:57 AM EDT