After a month of increasing steam emission, a 1-day series of ash eruptions occurred on 27 August from MacKenney Crater, the active vent of the 1965-75 eruption. Although the eruptions were conspicuous, the amount of ash ejected was not large, and was carried W by the wind. Small eruptions were also reported 19 August (black ash) and 20 August, accompanied by a strong sulfur odor near the volcano.

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.

Information Contacts: S. Bonis, IGN; R. Stoiber, Dartmouth College; P. Newton, Antigua.