Report on Fuego (Guatemala) — December 1978
Scientific Event Alert Network Bulletin, vol. 3, no. 12 (December 1978)
Managing Editor: David Squires.
Fuego (Guatemala) Lava flow stops, but intermittent fountaining and ash emission persist
Please cite this report as:
Global Volcanism Program, 1978. Report on Fuego (Guatemala) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 3:12. Smithsonian Institution.
14.473°N, 90.88°W; summit elev. 3763 m
All times are local (unless otherwise noted)
Information for the period 23 November through 5 December is from Don Willever and Paulino Alquijay, compiled by Paul Newton. Observations from 6 through 18 December are by Paul Newton. Clouds frequently obscured the volcano, permitting only brief views of the summit area on many days.
After the moderate Vulcanian eruption of 21 November, activity had declined to occasional explosions and intermittent ejection of small amounts of incandescent material by the night of 22 November. No activity was visible when clouds briefly dissipated on 23 November. Between 24 November and the evening of 2 December, steam and ash clouds, usually white or gray but occasionally black, were ejected intermittently from the main crater, and steam was emitted from the N-S-trending fissure extending northwards from the summit. The steam and ash clouds usually rose only a few hundred meters, but an 1,100-m column was seen early on 28 November. A weak glow could be seen over the crater at night, but no lava fountaining or flows were reported.
Lava fountaining from the summit crater was observed after sunset on 2 December. The next night, incandescent material was visible in Barranca Honda, the principal lava flow channel on Fuego's E flank. Intermittent steam and ash emission, similar to the 24 November-2 December activity, was reported on 4-5 December. Clouds prevented observations on the 6th, but lava was seen in Barranca Honda on the morning of 7 December. Only weak steaming occurred on 8 December. Cloudiness obscured the volcano until after sunset on the 10th, when incandescent material rose a short distance above the summit. Low but voluminous black clouds were ejected the next day, then weather clouds prevented observations on 12 December. Activity was weak during the morning of the 13th, but frequent bursts of incandescent ejecta were thrown more than 500 m above the crater after sunset. Ejection of incandescent material was visible each night through 18 December, the last day of observations. Dense gray ash clouds rose about 700 m above the summit. Block avalanches, or rising dust produced by them, were seen in Barranca Honda on 15 and 16 December.
The following is from a report by Dennis Martin. "By 16 December, the summit mound seemed to have grown markedly, perhaps more than 100 m in height since 21 November. Between 11 and 16 December, ash-laden clouds were ejected at intervals of a few seconds to a few minutes, to a maximum height of approximately 1 km. Most clouds rose only a few hundred meters and were blown away by predominantly westerly winds. The duration of explosive intervals varied from 1 second to 2 minutes. At night, fountains of molten lava thrusting up to a maximum of 750 m could be seen within the ash-laden gray clouds. These incandescent blocks cascaded in a spectacular display from 100 to 1,000 m down the flank. However, the incandescent lava flow and resulting block avalanche down Barranca Honda were no longer visible. A walk up the Barranca Honda on 13 December confirmed that the block avalanche had stopped at approximately 2,600 m elevation. The new lava is a vesicular, olivine-bearing basalt like previous Fuego magmas."
Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.
Information Contacts: P. Newton, P. Alquijay, and D. Willever, Antigua; D. Martin, Michigan Tech. Univ.