CENAPRED reported that ongoing activity at Popocatépetl during 27 June-4 July included 29-72 daily steam-and-gas emissions, sometimes containing minor amounts of ash. Seismic activity was characterized as daily periods of high-frequency events and variable amplitude tremors, harmonic tremor, and both minor and moderate explosions. During 27-28 June there were three major and two minor explosions, along with emissions of steam, gas, and ash that rose 1 km above the crater and drifted to the WNW and NW; minor ashfall was reported over that time in Ixtapaluca (42 km NW), Valle de Chalco (44 km NW), and Nezahualcóyotl (54 km NW) in the State of Mexico. Two moderate explosions were recorded during 28-29 June; plumes of steam, gas, and ash rose as high as 1.6 km above the crater and drifted to the W, WNW, and NW, causing minor ashfall in Amecameca de Juárez (18 km NW), Ozumba (18 km W), Temamatla (32 km NW) and moderate ashfall in Tenango del Aire (29 km NW) in the State of Mexico. During 30 June-1 July emissions of steam, gas and ash rose 1 km above the crater and drifted to the NW, and ashfall was reported in Atlautla (16 km W), Chalco and Tlalmanalco (27 km NW), and moderate in Amecameca and Cocotitlan (34 km NW) in the state of Mexico.

Two moderate explosions were again recorded during 1-2 July, and emissions of steam, gas, and ash rose as high as 1.6 km and drifted to the SSW, SW, WSW, and NW. Minor ashfall was reported in Atlautla, Ecatzingo (15 km SW), Yecapixtla (30 km SW), Ocuituco (23 km SW), Tetela del Volcán (18 km SSW), Hueyapan (17 km SW), Cuautla (43 km SW), and Ayala (48 km SW) in the state of Morelos. During 2-3 July emissions of steam, gas, and ash rose 1.3 km above the crater and drifted to the SW 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 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)