Geologists from Michigan Tech. Univ. and the Instituto Geográfico Militar (IGM) visited the volcano 13 and 16 November. Cloudy weather on the 13th allowed only brief glimpses of the crater; activity appeared to be weak but some spattering may have been occurring. On 16 November, the geologists noted that the active cone, centered on the S edge of MacKenney Crater, had grown to more than 100 m in height and filled 1/3-1/2 of the crater. Several Strombolian bursts per minute occurred from a vent at the top of the cone, ejecting spatter to 20 m height. Bombs reached 30 cm in maximum dimension. Aa lava emerged from below the base of the active cone, flowed down the crater's NW flank, and was beginning to pond in the saddle between MacKenney Crater and an older cone (Cerro Chino).

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. Halsor, Michigan Tech. Univ.