INSIVUMEH reported that during the night of 21-22 September a possible lava flow had traveled 400 m down Fuego’s Ceniza drainage on the SSW flank. Ash rose along the flow forming a curtain that extended above the summit; ash fell in communities to the W and SW. Explosions at a rate of 6-11 per hour produced ash plumes that rose as high as 800 m above the summit and drifted W and SW.

INSIVUMEH and CONRED reported that activity significantly increased on 23 September. Seismic activity intensified during the early morning and Strombolian activity at the summit was visible. Incandescent material was ejected 100-300 m high. Lava flows traveled 1 km down the Ceniza (SSW) and Trinidad (S) drainages, and sent block-and-ash flows down the Ceniza, Trinidad, Taniluyá, Las Lajas, and Santa Teresa (W) drainages to vegetated areas. Shock waves were detected within a 10 km radius. At 0540 a pyroclastic flow traveled 4-6 km down the Ceniza drainage, reaching the base of the volcano. According to CONRED a pyroclastic flow descended the Ceniza and Trinidad drainages 2-4 km. Explosions generated ash plumes that rose as high as 2.3 km above the summit and drifted 30 km W and SW. The activity began to decline around noon the next day, based on seismicity, acoustic data, and field observations. A few hours later RSAM data suggested that the period of elevated activity had ended after about 32 hours from the onset. Lava flows were no longer active by 25 September.

During 24-28 September there were that 6-12 explosions per hour generating ash plumes as high as 1.1 km above the crater rim and shock waves that often rattled buildings within 10 km of the volcano. Ash plumes mostly drifted as far as 15 km W and SW, causing daily ashfall in several areas downwind, including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Finca Palo Verde, and San Pedro Yepocapa (8 km NW). Block avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Las Lajas (SE), and Honda drainages, often reaching vegetated areas. Explosions ejected incandescent material 100-300 m above the summit on most days.

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.

Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Coordinadora Nacional para la Reducción de Desastres (CONRED)