Explosive and effusive activity, last reported through January 2003 (BGVN 28:01) has continued through October 2003. Plumes identified on satellite imagery between April and September 2003 were described in aviation advisories issued by the Washington Volcanic Ash Advisory Center (VAAC). Regular reports of daily activity provided by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH) on their website have been summarized for many days in the second half of October.

Activity during April-September 2003. The Washington VAAC reported that on 28 April 2003 Fuego generated intermittent ash eruptions. One cloud was observed at ~ 7 km altitude moving SW at 19-29 km/hour. On 2 May the VAAC reported possible ash around the summit, but as of 1515, none was visible. INSIVUMEH indicated that although Fuego was active with explosions, most ash was confined to near the summit.

On 29 June INSIVUMEH reported a moderate eruption during 1745-2200 that consisted mainly of lava effusion. Lava flows were observed on the E flank, in the Lajas, Jute, and Barranca Honda ravines. Avalanches generated sounds similar to a locomotive, with strong rumblings and acoustic waves. Fuego's Observatory 2, on the SW flank, reported 2 cm of ashfall. Ashfall also occurred in San Pedro Yepocapa, Patulul Suchitepequez, Cocales, and villages W and SW of the volcano. At about 2335 there was a reduction in seismic activity at the Fuego 3 station.

INSIVUMEH reported on 1 July that explosive activity continued with weak to sometimes strong explosions ejecting grayish ash up to 900 m above the crater, with occasional degassing sounds and rumblings. Pyroclastic-flow material moved into the W-flank Seca and Santa Teresa valleys, 1.5 km from the village of Sangre de Cristo. A pyroclastic flow was reported by the Washington VAAC at 1130 on 9 July. INSIVUMEH reported strong explosions with ash to 2 km above the summit, a plume extending 5-7 km W, and ashfall to the W and SW. GOES-12 imagery showed a 3.7-km-wide plume extending ~ 11 km W.

The Washington VAAC reported on 7 August that a brief puff of ash was ejected at about 1600; the small plume moved to the NW and dissipated by 1745. On 28 September the Washington VAAC, based on visible and multi-spectral IR techniques, reported an ash eruption at about 1100. This plume, which was ~ 5 x 5 km, moved S toward the coast and was no longer discernable on imagery by 1400. A second ash emission between 1415 and 1432, with an approximate altitude of 6 km, was partially obscured by clouds.

Activity during 15-30 October 2003. On 15 October INSIVUMEH reported the continuation of eruptive activity, with degassing and small rumbling sounds. Incandescence was seen above the crater at night. The ejected ash was dispersed around the volcanic edifice. A small eruption that began at 0007 on 17 October ended at 0040 after five moderate explosive pulses, each 2-3 minutes in duration, generated thick columns of grayish ash ~ 1,500 m high. Before and after this eruptive event moderate and strong explosions caused rumbling and shock waves felt at the OVFGO and FG2 observatories. Small incandescent avalanches moved towards the Santa Teresa valley.

Harmonic tremor was registered at the FG3 station at 1630 on 20 October. On 21 October, INSIVUMEH reported explosions after 0350. The majority were strong, expelling abundant incandescent material. Ash columns caused small and moderate avalanches, mainly in the Santa Teresa and Trinidad valleys, and occasionally in the Taniluyá. Shock waves were felt by communities around the volcano. Slight ashfall occurred in the Morelia and Santa Lucia villages located 7 and 10 km, respectively, SSW of the active crater.

On 23 October, INSIVUMEH reported moderate, weak and occasionally strong explosions producing grayish and blackish plumes up to one km high. Moderate and strong explosions generated rumbling and lava flows that traveled toward the Santa Teresa and Trinidad valleys. Ashfall occurred in the upper portion of the Fuego-Acatenango complex. At 0945 a strong explosion, lasting 1.5 minutes, produced a thick ash cloud that reached a height of ~ 1 km and dispersed to the SW. Two short pulses lasting 45-60 minutes between 1200-1300 and 1800-1900 on 23 October generated a series of 7-9 moderate explosions that produced a grayish column to ~ 1 km over the central crater.

A strong explosion at 0910 on 27 October was preceded by five moderate explosions at intervals of 3-7 minutes that produced gas clouds and ash 700 m high. The first event produced a heavy ash column of a height of ~ 1 km which dispersed to the SW. An explosion at 0625 caused a pyroclastic flow toward the Trinidad and Santa Teresa valleys, and produced light ashfall in the village of Sangre de Cristo. On 29 October INSIVUMEH reported predominantly weak and moderate explosions 1-3.5 minutes long with gas-and-ash columns up to 1 km high. The last of these produced ashfall, shock waves felt at OVFGO, and avalanches of incandescent material toward the Santa Teresa and Trinidad valleys.

On 30 October an effusive eruption during 2300-0600 produced incandescent lava fountains 75-100 m high with pulses of 5-6 minutes, changing to fountains ~ 50 m high and 15-20 minutes long. A short lava flow descended SW from the crater rim, reaching ~ 250 m in length and splitting into three short branches. Short avalanches and pyroclastic flows descended to the top of the Santa Teresa valley. The eruption produced moderate to weak sounds lasting ~ 2 minutes. At dawn, a thick fumarolic plume was observed blowing NW. There was no ash emission during this activity, but at 0625 hours a small explosion sent a column of gas and ash ~ 400 m high. The seismic station at FG3 registered harmonic tremor (2-4 mm amplitude).

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: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Ministero de Communicaciones, Transporto, Obras Públicas y Vivienda, 7a. Av. 14-57, zona 13, Guatemala City 01013, Guatemala (URL: http://www.insivumeh.gob.gt/).