Activity at Fuego increased during July. Voluminous ash clouds frequently rose more than 1 km above the summit, and incandescent tephra was seen on several occasions, but no new lava flows were reported.

During the afternoon of 29 June, an explosion projected a black eruption cloud to about 2.5 km height, but activity quickly declined to intermittent gray steam and ash emission. When the volcano was next visible, on 3 July, occasional low-velocity bursts of brown to black tephra rose about 0.7 km. Tephra rose only about 0.5 km the next day, but incandescent material was ejected a short distance above the summit that night. After Fuego was obscured by 2 days of clouds, ash emission was voluminous and steady early on 7 July, rising to about 1.5 km. Shortly after sunset, incandescent tephra rose about 0.3 km, and large blocks fell on the flank. This activity intensified 45 minutes later, some tephra reaching an estimated 1.8 km above the summit, then subsided after about 10 minutes. The next day a brief explosion produced a 2-km-high voluminous gray-black cloud, but otherwise only weak steaming was visible. During the early evening three loud explosions were heard from Antigua but the volcano could not be seen through clouds. Several explosions, similar to the one observed on 8 July, took place on the 9th, with clouds reaching maximum heights of 1.5 km. Ash fell on the flanks of Fuego and adjacent Acatenango. The S end of the summit fissure could be seen to have widened.

Activity ceased the evening of 9 July, and only weak steam emission was seen 10-13 July. A single explosion produced a 0.75-km-high gray cloud on the 14th. Clouds obscured the volcano the next day. On 16 July, weak steaming during the day was succeeded by 15 minutes of thick intermittent bursts of black ejecta, rising about 0.5 km. Two small incandescent ejections were seen after nightfall.

Clouds prevented observations 17-18 July. Brown eruption columns were seen above the clouds on three occasions 19 July, rising an estimated 1.5-2 km. After another cloudy day on the 20th, a 0.6-km black ash column was seen in a brief clear period on the 21st. On 22 July, sporadic bursts of brown tephra produced dense clouds that rose 1-2 km. Eruption cloud densities declined 23-24 July, and reached heights of 1 km or less.

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.