Report on Fuego (Guatemala) — January 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 1 (January 1979)
Managing Editor: David Squires.
Fuego (Guatemala) New lava flow and block avalanches
Please cite this report as:
Global Volcanism Program, 1979. Report on Fuego (Guatemala). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 4:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197901-342090.
14.473°N, 90.88°W; summit elev. 3763 m
All times are local (unless otherwise noted)
Sporadic ejection of ash clouds, sometimes accompanied by incandescent material, continued through early January. Lava flows and block avalanches moved down the E flank 6-8 January, then a pattern of intermittent ash emission and occasional fountaining resumed, continuing through 21 January. Fuego's summit was only briefly visible through clouds on many days of the 19 December-21 January observation period, but was totally obscured only on 3-4 and 12 January.
A thin ash column rose more than 1,300 m during the late afternoon of 19 December and a small ash flow moved down Barranca Honda the next morning. Low incandescent ejections were visible during the night of 21-22 December, but ash rose only about 0.5 km the next day. On the 23rd, voluminous ash clouds were ejected to about 1 km above the summit and there was a slight ashfall in Antigua. That night incandescent ejecta was again visible, and ash and small blocks flowed about 500 m down Barranca Honda. Ash clouds as high as 1,600 m were emitted on 24 December, but activity declined to minor steaming between the 25th and 31st. Ejection of incandescent material after sunset on 31 December and 1 January was succeeded by weak steaming through 5 January.
Before dawn on 6 January, lava began to flow down Fuego's E flank, dividing into separate streams that moved down Barranca Honda and several other canyons with a rolling, tumbling motion (see the description of lava cascades at Fuego in 3:11). Large blocks fell away from the main body of the flow, and a persistent brighter red area could be seen about 200 m below its source. On the 7th, a dense dust cloud rose from Barranca Honda and remained above it through evening, as lava continued to flow down the E flank. At 0400 on 8 January, a loud explosion was heard in Antigua and bursts of incandescent ejecta were thrown about 0.5 km above the crater. After dawn, ash clouds could be seen rising 2 km. Some of the ash was ejected from the base of the summit mound at an angle of about 30° from the vertical. Nuées ardentes flowed down the E flank. By late morning, the height of the ash columns was decreasing and ash emission had ended by late afternoon.
Several streams of lava continued to flow down the E flank through the 8th and block avalanching was prominent that night. However, only weak steaming was observed from 9 January until the night of 14 January, when small bursts of incandescent material were ejected from the summit crater and red glow in Barranca Honda was barely visible through dense haze. Weak ash emission on the 15th was succeeded by low but more voluminous ash clouds on the 16th, accompanied by a brown dust cloud that was present over the entire visible length of Barranca Honda. That evening, low but dense black clouds dropped ash onto the NW flank and brilliant bursts of lava and blocks were ejected nearly vertically from the foot of the summit mound to a height of about 0.3 km. A block avalanche descended Barranca Honda, then clouds prevented further observations. Similar but slightly stronger activity was seen on 17 January. Only weak steaming was visible during the day on the 18th, but at night bursts of lava fed block avalanches that traveled almost 1 km down Barranca Honda. Intermittent dark gray to black ash columns rose more than 1,100 m on 19 January. A light fall of fine ash on Antigua obscured the volcano from view on 20 January. The next morning, low lava fountaining was visible before dawn. Ash clouds rose more than 2 km by the evening of the 21st, accompanied by moderate ash emission from the base of the summit mound, at an angle of 40° from the vertical.
One large and several small earthquakes were felt in Antigua during the observation period. The largest was a magnitude 5.5 event centered 67 km SE of Fuego on 12 January.
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.