Report on Pacaya (Guatemala) — 4 August-10 August 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
4 August-10 August 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Pacaya (Guatemala). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 4 August-10 August 2021. 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 explosions at Pacaya were recorded at 0905, 1340, and 1421 on 4 August, a departure from the low levels of activity observed during the previous four months. The explosions produced ash plumes that rose about 1 km above the summit and drifted 12 km N, causing ashfall in Mesías Altas, Mesías Bajas, and Villa Canales. The report noted that the cinder cone in Mackenney Crater had been destroyed during the previous eruption phase and the crater was about 100 m deep. Cracks were seen around the crater indicating areas of instability at the summit. Steam-and-gas plumes rose as high as 1 km above the summit and drifted as far as 3 km in multiple directions during 5-10 August. No explosions were heard or visually observed, though the seismic network recorded weak explosion signals during 6-7 August.
Geological Summary. 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.