Fuego's pattern of frequent ash emission and occasional extrusion of block lava continued through late April. Cloudiness obscured the volcano frequently during this period, as Guatemala's rainy season approached.

The strong explosive activity observed on 22 March had declined somewhat by the following morning, but ash emission remained voluminous for the next several days. Dense black ash rose as much as 0.7 km and vapor reached a height of 1.3 km. Ash fell on Antigua on 23 and 25 March.

Activity intensified on 29 March. During the early morning, a black eruption column was ejected to more than 1 km over the summit. By late afternoon (when cloud conditions again permitted observations) the height of the eruption column had decreased but heavy ashfall was occurring on the flanks. Sporadic ejection of incandescent tephra was visible after sunset, and a glowing avalanche traveled down the E flank. Block lava extrusion began the next day, probably by morning, when dust could be seen rising from Barranca Honda. By evening, slow-moving lava had flowed more than 0.5 km down the canyon, and some large blocks had tumbled from its upper end. Small amounts of incandescent tephra could be seen emerging from a vent W of the summit cone.

Clouds obscured the volcano for most of the period 31 March-5 April. A dark gray eruption column, about 0.5 km high, was briefly visible on 31 March, and mild to moderate steam emission could sometimes be seen in the mornings during the cloudy period. On 6 April, a glowing avalanche descended Barranca Honda, and steam and ash were sporadically ejected from the summit. Stronger ash emission occurred the next day, causing heavy ashfall near the summit. Vapor clouds rose higher than the ash, to 1.1-1.7 km. The fissure on the summit cone had been substantially filled by ash.

Small bursts of incandescent tephra, separated by 5-18-minute periods of quiescence, were seen during the evening of 7 April. Activity was limited to mild steaming during the day on the 8th, but low, sporadic ejection of incandescent tephra could be seen after sunset. A 4-5-second, very low-pitched rumble was heard in Antigua just before midnight. Ash fell on Antigua during each of the next 3 days, while the volcano was hidden by clouds. Between 12 and 14 April, gray ash and vapor were intermittently ejected, rising as much as 750 m. Ash content of the eruption clouds increased on 15 April. A new fissure that had formed in the top of the summit cone was the source of low emission of black ash.

At 0820 on 16 April, deep rumbling was followed by an explosion that produced a 2.1-km-high ash cloud. Poor weather prevented further observations on the 16th, but by the next morning, maximum ash cloud heights had declined to about 0.5 km. Some incandescent tephra was visible, falling a few hundred meters from the summit cone.

Although clouds obscured the volcano from 18-20 April, ashfalls in Antigua on each of these 3 days indicated continuing activity. When visible through clouds 21-23 April, ash emission was moderate, rising about 0.5-1 km. Better visibility on 24 April revealed ash ejection from the fissure at the top of the summit cone; ash rose about 0.5 km and white vapor as much as 2 km. Ash again fell in Antigua on 23-24 April, the last days 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.