May 15, 2012 07:43 AM EDT
Earth Observatory: Activity at Popocatépetl
During the first week of May, 2012, Mexico's Popocatépetl Volcano maintained a high level of activity. Nearby seismographs recorded periods of harmonic tremor (long lasting, low frequency earthquakes that occur during some volcanic eruptions), along with occasional bursts of spasmodic tremor (sho...