The Centro Nacional de Prevención de Desastres (CENAPRED) reported that eruptive activity continued at Popocatépetl during 28 January-4 February. The seismic network recorded 41-170 long-period events per day that were accompanied by steam-and-gas emissions sometimes containing minor amounts of ash. The seismic network also recorded daily tremor, sometimes characterized as very-low amplitude, with periods lasting 14 minutes to as long as four hours and 24 minutes. During 30-31 January a period of emissions lasted 170 min based on seismic data. One volcano-tectonic per day was detected during 31 January-4 February. According to the Washington VAAC ash plumes were visible in webcam and satellite images during 31 January-4 February rising 5.8-7 km (19,000-23,000 ft) a.s.l. (as high as 1.6 km above the summit) and drifting N and NE. 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)