Two cones have been growing within MacKenney Crater in October and November. On 18 and 23 November, explosions alternated at about 30-60-second intervals from the two cones, 3 and 5 m high and about 10 m apart. Ejecta from the new cones fell on the outer flanks of MacKenney Cone on 23 November. Narrow lava flows on the W flank of MacKenney Cone were observed on 16 November. The highest vent feeding the flows was about 300 m below the summit. Lava extended as much as 500 vertical meters downslope.

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: A. MacKenney, Guatemala City; R. Stoiber, R. Pool, D. Barnett, and other geologists, Dartmouth College.