Fuego's eruption declined substantially in October. The summit dome noted last month continued to grow. Fuego was steaming weakly on 23 September and a brief break in the clouds on the 24th revealed no activity. Voluminous steaming had begun by the morning of the 25th. That night, a glowing avalanche traveled about 550 m down a canyon on the E flank. After dawn on 26 September, steam rose slowly to about 1,100 m, then clouds prevented further observation. Weak steaming was seen after dawn the next day. Beginning before dawn on 28 September and continuing through the evening, nuées ardentes moved down the E flank canyon. Red glow and some small incandescent eruptions were visible at night. Heavy cloudiness prevented observations on 29 September, but brief glimpses of the volcano on 30 September and during the day on 1 October showed no explosive activity. Weak ejections of incandescent material after sunset on 1 October were separated by long periods of quiescence. After 1 October, no ash or incandescence was seen. Although the summit dome was clearly growing, other activity was confined to weak or moderate steaming from the summit crater, and occasionally from two smaller vents near the summit. The maximum steam plume height during the period was about 1,000 m. Small earthquakes were felt in Antigua at 1209 on 4 October and at about 0245 on 22 October.

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.