CENAPRED reported that during 31 July-6 August seismicity at Popocatépetl indicated continuing gas-and-steam emissions that sometimes contained ash; cloud cover often prevented visual confirmation. Incandescence from the crater was occasionally observed. On 31 July a clear decrease in the size of the water vapor and gas plumes was observed; plumes were pushed by winds down the NW flank and rose only 100 m above the crater rim. An explosion was detected at 2312 on 1 August, but cloud cover prevented confirmation of any ejecta. On 2 August minor amounts of ash fell in the Tepetlixpa, Atlautla, Ecatzingo, and Ozumba municipalities of Mexico State. On 4 August emissions of gas, steam, and ash drifted NW. During 5-6 August a few observed plumes rose 1-2 km and drifted WNW, W, and WSW. The Alert Level remained at to Yellow, Phase Two.

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.

Source: Centro Nacional de Prevencion de Desastres (CENAPRED)