CENAPRED reported that eruptive activity continued at Popocatépetl during 12-18 July. Long-period events totaling 25-108 per day were accompanied by steam-and-gas plumes that sometimes contained minor amounts of ash. Seismic activity also included variable-amplitude volcanic tremors (16 hours 20 minutes), harmonic tremor (10 minutes), explosions, and volcano-tectonic earthquakes (maximum magnitude 2.1 at 0044 on 13 July). Ash plumes identified in webcam and satellite images were described in daily aviation notices issued by the Washington VAAC; some plumes rose as high as 1.6 km above the summit and drifted SW, W, or NW. Minor explosions occurred at 1739 on 11 July. Moderate explosions were recorded at 2154 and 2345 on 11 July and at 0316 and 0343 on 12 July. During 11-12 July ashfall was reported in the municipalities of Atlautla (10 km W), Tepetlixpa (23 km W), Calimaya (108 km W), Ayapango (24 km WNW), Tenango del Aire (29 km WNW), Juchitepec (30 km WNW), Chapultepec (100 km WNW), Amecameca (15 km NW), Temamatla (33 km NW), Cocotitlán (34 km NW), Valle de Chalco (44 km NW), La Paz (51 km NW), Nezahualcóyotl (60 km NW), Ixtapaluca (60 km NNW) in the state of Mexico. In Mexico City, ashfall was reported in Milpa Alta (46 km WNW), Tlalpan (67 km WNW), Tláhuac (49 km NW), Iztapalapa (59 km NW). During 12-13 July ashfall was reported in Valle de Chalco, Ixtapaluca, La Paz, Nezahualcóyotl, Amecameca, Atlautla, Ayapango, Cocotitlán, Temamatla, Tepetlixpa, Tenango del Aire, Juchitepec, Chapultepec and Calimaya, as well as in the municipalities of Milpa Alta, Tláhuac, Iztapalapa and Tlalpan of Mexico City. During 13-14 ashfall was reported in Valle de Chalco, Amecameca, Ayapango, Atlautla and Tenango del Aire. 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), Secretaría de Gestión Integral de Riesgos y Protección Civil (SGIRPC)