CENAPRED reported that eruptive activity continued at Popocatépetl during 14-21 May. The seismic network recorded long-period events totaling 30-85 per day that were sometimes accompanies by steam-and-gas emissions; steam, gas, and ash emissions were visible during 18-19 May. The seismic network also recorded 98 minutes to more than 8.5 hours of tremor each day and a few volcano-tectonic earthquakes. According to the Washington VAAC daily ash plumes visible in webcam and satellite images rose to 5.5-6.1 km (18,000-20,000 ft) a.s.l. (or as high as 700 m above the crater rim) and drifted SW, SW, and WSW. Thermal anomalies in the crater were detected during 16-17 May. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

Geological Summary. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Sources: Centro Nacional de Prevencion de Desastres (CENAPRED), Washington Volcanic Ash Advisory Center (VAAC)