Report on Pacaya (Guatemala) — 24 July-30 July 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 July-30 July 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Pacaya (Guatemala). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 July-30 July 2013. Smithsonian Institution and US Geological Survey.
14.382°N, 90.601°W; summit elev. 2569 m
All times are local (unless otherwise noted)
In a special bulletin on 24 July, INSIVUMEH noted that the eruption at Pacaya had been changing during the previous few days, especially the seismic pattern. Seismic signals indicating explosions and ejections of material lasted up to seven minutes; the events were low frequency and long duration. The cone continued to grow and was 30 m high earlier in the week. By 24 July the cone was 4 m above the MacKenney crater rim. Seismicity again increased. On 25 July weak explosions and incandescence from the cone were observed at night. Rumbling was heard. On 29 July incandescence from the crater was observed for a few hours in the morning, and a plume rose at most 100 m and drifted S. An eruption on 30 July included a high-energy phase that lasted for four hours and incandescent material that was ejected 250 m above the cone. A diffuse ash plume drifted 2 km N, causing ashfall in areas downwind, and another ash plume drifted 5 km S. Activity then declined considerably; explosions were not observed and seismicity decreased, although signals indicating fluid movement continued to be detected.
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.