Report on Pacaya (Guatemala) — 9 December-15 December 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 December-15 December 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Pacaya (Guatemala). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 9 December-15 December 2020. Smithsonian Institution and US Geological Survey.
14.382°N, 90.601°W; summit elev. 2569 m
All times are local (unless otherwise noted)
INSIVUMEH reported that on 9 December a new lava flow emerged from a vent S of Cerro Chino, NNW of Pacaya’s summit, and traveled as far as 250 m WSW. The branched lava flow which had opened in October on the WSW flank was active, with lengths between 400 and 600 m. Avalanches of material from the new flow and the SW-flank lava flows descended 100 m. Strombolian explosions from the cone in Mackenney Crater were visible on most days during 9-15 December and ejected material as high as 150 m above the vent. Gray ash plumes were occasionally visible drifting S, SW, and W at generally low altitudes. On 12 December strong winds picked up ash deposits and created ash curtains that drifted 1.5 km away and dispersed. Lava flows on the SW flank varied in length between 500 m and 1,000 m. The NW-flank lava flow ceased effusing by 13 December.
Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, 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 ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and 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 armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.