More prominent Vulcanian activity 28-31 January was followed in February by a lava flow, uncommon in Fuego's history. Since Fuego's first recorded event, in 1524, less than one in four eruptions have been accompanied by a lava flow.

The following information, provided by Paul Newton, supplements the report last month. Weak glow in Fuego's summit crater was observed at 1800 on 28 January, beginning 3 days of strong explosive activity. By 2000, bright orange-red incandescent material could be seen in the crater and glowing avalanches flowed down the flanks, accompanied by large incandescent blocks. The next day, black to gray-black ash was emitted steadily to several hundred meters above the crater. Strong, low-pitched rumbling was heard and a few weak felt shocks occurred. At night, glowing avalanches were again visible and incandescent material rose a short distance above the crater rim. On 30 January, frequent strong rumbling accompanied emission of black to gray-black ash to an estimated height of 2,300 m above the crater. After sunset, incandescent ejecta including large light orange to bright red blocks rose as much as 250 m above the crater and large glowing avalanches flowed down the flanks. The eruption began to weaken after dawn on the 31st. Ash ejection had become intermittent by 1630 and had stopped by 2200. Crater glow had dimmed to a dull red. The next morning, activity was limited to emission of a small brown-white to white plume.

The following is a report by William I. Rose, Jr. "Throughout February, Fuego has been repeatedly visited by a plume-sampling aircraft from NCAR. Lava flows were first observed on 9 February in two 30 m-diameter craters 0.1 km SW of Fuego's summit. The flows had advanced 0.5 km down the SW flank of the cone by 11 February and the lava craters showed continuous incandescence. Hot debris slides from the toes of the two flows had cascaded more than 3 km down the valley of the Río Taniluya by 22 February. Small (100-500 m-high) ash eruptions (3-15/hr) occurred from the summit crater as the lava flow activity continued. On 24 February the three vents were observed in simultaneous activity. The summit crater was erupting a continuous stream of gas and fine ash, while the two lava vents exhibited lava fountaining interspersed with dark ash explosions. The rate of lava flow extrusion appeared to be increasing."

Further Reference. Rose, W.I., Jr., Chuan, R.L., Cadle, R.D., and Woods, D.C., 1980, Small Particles in Volcanic Eruption Clouds; American Journal of Science, v. 280, p. 671-696.

Geological Summary. 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: W. Rose, Jr., Michigan Tech. Univ.; P. Newton, Antigua.