INSIVUMEH reported that during 10-11 September explosions at Pacaya generated diffuse ash plumes that rose 150 m and drifted 150 m NW. There were no direct visual observations during 11-12 September, though the seismic network recorded tremor and small explosions. Explosions during 12-13 September ejected material 50-100 m high. White and blue plumes rose 300 m and drifted N. In a special notice on 13 September INSIVUMEH noted that the cone in MacKenney Crater had already grown above the crater rim; incandescence from the cone was visible from many areas around the volcano, including the capital.

Weak-to-moderate explosions generated rumbling during 14-15 September. An increased number of explosions were detected during 15-16 September. Material was ejected above the crater and ash plumes drifted 3 km W and SW. The seismic network recorded tremor and explosions that occurred about every 5 minutes.

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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)