During 21-28 May, Popocatépetl emitted small clouds of steam, gas, and generally minor amounts of ash. In addition, episodes of harmonic tremor were recorded. On 21 May at 1330 a small explosion occurred that was followed by 15 minutes of high-frequency tremor. According to a news report, a small amount of ash fell on communities neighboring the volcano on 22 May.

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), Associated Press