Centro Nacional de Prevención de Desastres (CENAPRED) reported that eruptive activity continued at Popocatépetl during 30 July-6 August. Daily activity consisted of 30-90 long-period (LP) events that were accompanied by emissions of gas, steam, and sometimes small quantities of ash. A total of 16 minutes of high-frequency, very low-amplitude tremor was registered during 30-31 July, and 169 minutes (approximately 2.8 hours) of harmonic, very low-amplitude tremor was recorded during 30 July-5 August. Additionally, a M1.4 volcano-tectonic (VT) earthquake was registered on 30 July at 2108. On 4 August at 0939, a plume with low ash content reached 800 m above the summit and drifted W; the Washington Volcanic Ash Advisory Center (VAAC) reported that satellite images showed that the ash had dissipated by 2146 later that night. Continuous gas-and-steam emissions were observed on some mornings; plumes dispersed toward the NW, WNW, and W. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay at least 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)