Report on Pacaya (Guatemala) — 10 March-16 March 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
10 March-16 March 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, 10 March-16 March 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 and CONRED reported that pulses of moderate-to-strong Strombolian explosions at Pacaya’s Mackenney Crater were commonly recorded during 9-16 March. Frequent ash plumes rose as high as 2 km and drifted as far as 30 km W, SW, and S. On 10 March lapilli (2 mm to 6 cm in length) fell in El Caracol (3 km SW), and ash fell in El Patrocinio (about 5 km W) and likely in other areas downwind. Ash plumes caused daily ashfall in variable places during 11-16 March, including El Patrocinio, San José El Rodeo, the municipality of San Vicente Pacaya (5 km NW), San Francisco de Sales (5 km N), San José el Bejucal (4 km N), San Antonio el Pepinal (7 km N), Concepción El Cedro (9 km NNW), San José Calderas, and the municipalities of Amatitlán (12 km N), Villa Nueva (16 km N), and Mixco (30 km N). Lapilli as long as 2 cm fell in El Patrocinio, San José El Rodeo and Concepción El Cedro on 16 March.
Strombolian explosions and periodic lava fountaining ejected incandescent material as high as 800 m above the summit; tephra fell within a 500 m radius of Mackenney Crater. Explosions and ash emissions also rose from fissures on the S flank, 300 m below Mackenney Crater. The lava flow on the S flank had two branches and was 1 km on 10 March, but had lengthened to 1.8 km by 16 March. Block avalanches from the summit traveled down the S flank.
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.