INSIVUMEH reported that on 10 July lahars traveled SE down Fuego's Las Lajas and El Jute drainages carrying blocks 1-1.5 m in diameter. The lahar in Las Lajas was hot and had a sulfur odor. During 10-12 July explosions from Fuego produced ash plumes that rose 150-800 m above the crater and drifted W. On 11 July ashfall was reported in Sangre de Cristo (8 km WSW) and surrounding areas. Tephra avalanches descended the Ceniza (SSW) drainage. During 16-17 July explosions generated ash plumes that rose 200-600 m above the crater and drifted 10 km S and SW. Incandescence emanated from the crater and avalanches descended the Taniluyá (SW) and Ceniza (SSW) drainages.

In a special bulletin on 17 July, INSIVUMEH reported that seismic patterns indicated the beginning of a new phase of activity; avalanches on the S and SW flanks were constantly active, and a new lava flow emerged on the SW flank that traveled 200 m and produced blocks that rolled SW down the Taniluya drainage.

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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)