INSIVUMEH reported that on 20 July Strombolian explosions from Pacaya's MacKenney cone ejected ash that fell in neighboring areas. During 20-21 July there were 90 explosions recorded by the seismic network. Based on information from INSIVUMEH, the Washington VAAC reported that on 22 July a plume rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted N. A weak thermal anomaly was seen in subsequent images. The next day, ash plumes drifted N at an altitude of 4.1 km (13,500 ft) a.s.l. and produced ashfall in areas within 10 km. On 25 July, INSIVUMEH noted that Strombolian explosions ejected tephra 100 m above the crater, and generated ash plumes that rose 300 m above the crater and drifted 10 km SW. Ejected blocks fell onto the flanks.

Geological Summary. Eruptions from Pacaya are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the older Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1,500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate scarp inside which the modern Pacaya volcano (Mackenney cone) grew. The NW-flank Cerro Chino crater was last active in the 19th century. During the past several decades, activity has consisted of frequent Strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and covered the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit.

Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC)