The Centro Nacional de Prevención de Desastres (CENAPRED) reported that eruptive activity continued at Popocatépetl during 16-23 September. The seismic network recorded 32-80 long-period events per day, accompanied by steam-and-gas emissions with occasional minor ash content. In addition, the seismic network recorded daily periods of low-amplitude tremor, characterized by harmonic tremor and high-frequency signals, lasting from two hours and 52 minutes to 7 hours and 42 minutes. A minor explosion was recorded at 0148 on 22 September. A webcam image from 0149 showed a small amount of incandescent material on the upper flanks. An explosion at 0049 on 23 September also ejected incandescent material a short distance onto the upper flank. According to the Washington VAAC ash plumes visible in webcam and/or satellite images during 16-18 and 20-22 September rose 5.8-6.7 km (20,000-22,000 ft) a.s.l. (about 400-1,300 m above the crater rim) and drifted as far as 46 km W, WSW, and SW. 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)