Each day during 12-19 September CENAPRED reported 141-299 steam and gas emissions from Popocatépetl. Cloud cover often prevented observations, though gas-and-steam plumes were visible daily. During 12-13 September there were 22 explosions detected, four of which generated emissions with minor amounts of ash and ejected incandescent tephra. An explosion was detected at 1820 on 14 September. On 19 September a plume with low ash content rose 1 km. CENAPRED stated that there was no significant increase in activity at Popocatépetl related to the M 7.1 earthquake, centered beneath Puebla (45 km E), that occurred at 1314. The Alert Level remained at 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)