Intermittent emission of ash and some hot avalanches persisted through September. Ash clouds reached a maximum observed height of 5,500 m, on 3 September.

The weak activity of 22-23 August continued on the 24th. Activity strengthened on 25 August, and between the 25th and 28th varied from emission of thin grayish clouds about 1,000 m high, to ejection of larger, more ash-saturated clouds about 1,500 m high. On 29 August, intermittent bursts of dense black ejecta were thrown slightly above the crater rim during the morning, and incandescent ejecta rising to about 550 m were seen after sunset. Weak ash emission was briefly visible through clouds the next day, then clouds and rain obscured the volcano until 2 September. That evening, incandescent material, including large blocks, was thrown to about 550 m. An avalanche of yellow-orange to red material, originating from the toe of what appeared to be a short lava flow just below the crater rim, traveled down a canyon on the E flank. After midnight, a nuée ardente traveled down the same E flank canyon to the foot of the volcano. Between 0630 and 0930 on 3 September, a cauliflower-shaped eruption cloud rose to 5,500 m above the crater and nuées ardentes flowed down the E flank canyon. Ashfall was confined to Fuego's flanks. Rumbling and felt seismicity accompanied the activity during the night of 2-3 September and the morning of the 3rd. Clouds obscured the volcano for much of 3 September, but a 2,200-m eruption cloud and a large red glow were visible above the crater in the early evening.

Activity had declined to weak steam and ash emission early on 4 September, although incandescence was seen through clouds that night. From 4 to 14 September, clouds of varying ash contents reached a maximum observed height of 1,100 m (on the 8th) but most rose only a few hundred meters and there were periods of quiescence. A small earthquake was felt for about 3 seconds in Antigua at 1305 on 7 September, and a much larger, magnitude 5.5 (m_b) event, 67 km WNW of Fuego, was felt there at 1724 on 10 September, continuing for nearly 1 minute. A rounded dome or cone could be seen protruding over the top of the crater rim.

Glow was seen over the crater after sunset on 14 September and intermittent incandescent activity occurred the next night. On 16 September, voluminous dark gray ash clouds were emitted to 1,100 m and a thunderstorm generated large lightning bolts that struck Fuego's crater just before sunset. Similar ash ejection occurred on 17 September. Incandescence was seen above the crater that night, as hot avalanches traveled down a canyon on the E flank. Black and gray ash rose as much as 2,000 m on the 18th and intermittent incandescence was visible at night. Rain and clouds prevented further September observations.

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.