Activity observed at Fuego during the 26 April-24 May reporting period was limited to intermittent and usually weak ash ejection. All of the ash appeared to originate from the summit cone fissure, but Newton suggests that significant quantities may also be ejected from vents on the W side of the summit area, not visible from his vantage point. Clouds prevented any observations on 25, 27, and 28 April and 2, 5, and 19-23 May, as well as limiting visibility to brief glimpses on many other days.

From 26 April through 9 May, Fuego's eruption column was gray to black, usually rising 0.5 km or less. Ash ejection was often intermittent, as on 3 May when low but voluminous ash clouds were emitted for 4- to 7-minute periods, separated by 5-8 minutes of quiescence. Windless conditions allowed the ash column to rise an estimated 1.4 km on 6 May and 1.6 km on 9 May. Fine ash fell on Antigua, 17 km NE of Fuego, on 1, 7, and 8 May. A hot avalanche appeared to descend about 0.5 km down an E flank canyon on 30 April.

A small earthquake, lasting less than 2 seconds, was felt in Antigua at 1700 on 9 May. Rumbles were heard there the next morning, at 0300, 0400, 0600, and 0630, the last of which was quite loud. After dawn, thick and voluminous ash clouds were ejected to about 0.5 km above the crater. By midmorning the plume was white, rising a maximum of 1.4 km in still air. That night, the only incandescent material observed during the reporting period was ejected to a short distance above the summit.

Activity similar to that of 26 April-9 May resumed on 11 May. Intermittent bursts of black ejecta rose about 0.5 km, accompanied by steady steaming. Larger ash clouds were ejected on the 15th (to 1.6 km) and 16th (more than 2 km), then activity declined on 17 May to mild steaming and a single burst of gray ash to about 0.5 km above the crater. During the 2 hours of visibility the next day, no activity was observed. What appeared to be dense white gas was twice seen flowing down an E flank canyon during this period, on 14 and 17 May.

Clouds obscured the volcano 19-23 May. A mild, 4-second earthquake was felt in Antigua at 0300 on the 20th and a single sharp shock at 2315 on the 21st. Residents of Alotenango, at the base of Fuego, had reported numerous rumblings and earthquakes during a 15-day period prior to 17 May.

Although fine ash fell on Antigua on 22 and 23 May, only a very small plume, rising less than 0.3 km, was seen on 24 May, the last day of observations reported here.

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: P. Newton, Antigua.