Report on Fuego (Guatemala) — August 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 8 (August 1979)
Managing Editor: David Squires.
Fuego (Guatemala) Activity declines to weak fumarolic emission
Please cite this report as:
Global Volcanism Program, 1979. Report on Fuego (Guatemala). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 4:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197908-342090.
14.473°N, 90.88°W; summit elev. 3763 m
All times are local (unless otherwise noted)
The intensity and frequency of ash emission at Fuego began to decline in late July. By mid-August only weak steam emission was visible, a condition that continued through 21 August.
On 25 July, four small explosions in a 45-minute period produced dark gray ash clouds that rose less than 0.6 km, after 1 hour of inactivity earlier that morning. A similar pattern of activity was observed on 26 and 27 July, but ash clouds were more voluminous, and reached 0.8 km on the 27th. Only steaming took place on 28 July until late afternoon, when 3-4-minute bursts of gray ejecta, rising to more than 1 km above the summit, occurred at intervals of 10-30 minutes. The next day, long periods of quiescence separated voluminous, but ash-poor emissions lasting 2-4 minutes each. The volcano was inactive on 30 July and only weakly active the following morning, but at 1330 on 31 July, the largest explosion of the reporting period took place, producing a cloud that rapidly rose to more than 2 km. Weak steam and ash emission followed this explosion, and similar activity was visible on 2 and 3 August (after a cloudy day on 1 August).
From 4-7 August, steam and ash emission was very weak, and by 8 August was interspersed with periods of complete inactivity. No activity was occurring during 1-hour breaks in cloud cover early on 9 and 10 August. Clouds obscured the volcano 11-12 August, but clear visibility 13-15 August revealed no activity. Fumarolic emission from a subsidiary vent near the summit resumed on 16 August and was continuing on 21 August, the last day of observations reported here.
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, Antigua.