Between 1 and 6 June, activity was confined to weak steam and ash emission from the summit crater and vapor emission from a small subsidiary vent near the summit. During the late afternoon of 7 June, steam and ash clouds rose 1,100 m, and after sunset loud rumbling was heard for several hours. Activity was very weak on 8 June and clouds obscured the volcano on the 9th.

Several incandescent avalanches were observed flowing down a canyon on Fuego's E flank before dawn 10 June, and that evening more incandescent material was seen in the same canyon, as much as 725 m below the summit. Similar activity was observed 11-12 June, but during the morning of the 13th, only weak steaming was visible.

A lava flow moved slowly down the E flank canyon after sunset on the 13th, to about 550 m below the summit. The volcano was obscured by clouds on the 14th and much of the 15th, but lava was visible during the evening of the 15th. Activity intensified on 16 June. At 0700, three lava flows were moving down the E and NE flanks, and at 1100 a hot avalanche traveled several kilometers down the NE flank as ash rose 1,900 m from the summit crater. Felt earthquakes accompanied by loud rumbling occurred at 1400, followed by a 2,300-m ash cloud and hot avalanches at 1600. Throughout the evening, several streams of lava could be seen descending the E and NE flanks. Lava extrusion had ended by the next morning, but a few hot avalanches were observed.

Activity between 18 and 25 June consisted primarily of weak steam and ash emission, but some incandescence was seen above the summit on 19, 21, 24, and 25 June. A hot avalanche was observed early on 26 June accompanied by 1,200-m ash clouds. Incandescent material, possibly another lava flow, reached a level more than 1,000 m below the summit in 4 hours of evening activity. Incandescent ash rose about 800 m above the summit and loud rumbling was heard. Similar activity continued through the end of June, with frequent hot avalanches and accompanying vertical emissions rising as much as 2,200 m.

Powerful explosions were heard at 2230 on 30 June and at 0215, 0700, and 2300 on 1 July. The 3rd explosion produced a 2,200-m ash cloud; the 4th caused a strong air shock at the base of the volcano, and yellow to red ejecta including large blocks rose a short distance above the crater.

Poor weather conditions prevented observation of Fuego during much of July. The volcano was inactive during brief periods of visibility on 4 and 5 July, but incandescence was observed above the crater on the 6th and a glowing avalanche moved down the NE flank. Some incandescence was visible above the crater on 8 July. Activity was limited to weak steaming and a few ash puffs between 12 and 19 July. A hot avalanche flowed about 800 m down an E flank canyon on 21 July and ash rose about 1,000 m on the 21st and 22nd. On 23 July, the last day of observations reported here, only weak ash emission was observed.

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, P. Alquijay, D. Willever, Antigua.