Volcanic activity at Popocatépetl decreased in comparison to last week. The Washington VAAC reported that during 21 to 25 December there were intermittent emissions of mostly steam. In addition, several small-to-moderate explosive events occurred during the week; at 1555 on 24 December ash was erupted to ~9 km a.s.l. and then blown to the E; at 1045 on 25 December ash was erupted to between 5.5 and 7.6 km a.s.l., blown to the NE, and deposited less than 5 km from the summit; and moderate exhalations occurred at 0111 and 0631 on 27 December that sent ash up to 7.6 and 9.8 km, respectively. On 26 December CENAPRED reported that beginning on 24 December the volcano entered a new phase of activity. Moderate explosions were expected to continue for several days or weeks until the lava dome in the summit crater is destroyed. CENAPRED scientists determined that there was decreased likelihood of a large eruption. Most of the 41,000 residents near the volcano, who were evacuated beginning on 15 December, were permitted to return to their homes. The evacuees were warned to remain alert for further activity. The director of CENAPRED, Robert Quaas, told journalists at a press conference on 26 December that, "The volcano could continue to launch incandescent fragments as far as 5 km and could provoke a moderate rain of cooled fragments as far away as 10 km, because of events related to the destruction of the lava dome." The volcano remained at Alert Level Yellow Phase III, but the restricted area was reduced from 13 to 12 km. For more information about the present state of the volcano and the return of evacuees to their homes refer to CENAPRED's 26 December Bulletin.

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), Associated Press, Notimex, Reuters