Fuego & Acatenango Volcanoes

Fuego volcano is located 13km W of Antigua, the former capital and touristic center of Guatemala. The volcano is frequently active, displaying explosive strombolian and vulcanian activity. This can be accompanied by lava flows and pyroclastic flows. Fuego forms part of a large volcanic complex which includes Yepocapa (3880m), Acatenango (3976m), Meseta (3600m) and Fuego (3763m). Yepocapa itself nests on the remains of Acatenango Antiguo. Whilst Fuego and Meseta share a common magma source, Acatenango and Yepocapa are fed by a distinct system and thus represent a distinct volcanic unit. Nevertheless, due to their geographic proximity, both are dealt with together here.

Fuego (erupting), Meseta, Acatenango (highest peak), Yepocapa (on right)	Strong explosive eruption of Fuego with associated rockfalls, Dec. 2007	Fuego and Acatenango complexes seen from Antigua bus station

The structure of the Fuego-Acatenango Massif was shaped not only by progressive dome growth but also by at least two catastrophic failures of different parts of the edifice. It is thought that construction of the massif began about 230000 years ago with effusive activity around the site of the Meseta vent. Activity at Meseta is thought to have terminated after a large portion of its edifice collapsed leading to the Escuintla debris avalanche. Around 9 cubic km of material appear to have been mobilized with a runout distance of 27km to the SSE. Following this event it is thought that the Meseta conduit became plugged and that magma from the same underlying system migrated to a new vent underlying present day Fuego volcano. Primarily effusive activity at Acatenango Antiguo occurred over a period starting no earlier than 85000 years ago and is thought to have terminated about 43000 years ago following a large debris avalanche (La Democracia deposit). Between then and about 5000 years ago, Yepocapa cone has been growing on its remains. Pico Mayor de Acatenango (or simply Acatenango) started to grow about 20000 years ago.

Yepocapa summit viewed from flank of Acatenango. On right is crater from 1972 phreatic eruption.	Flank of Acatenango seen from Yepocapa. Note craters from 1924-1927 phreatic eruptions	Summit of Acatenango volcano. Often used for camping but exposed during storms.

Summit and E flank of Fuego with forest-covered Meseta in foreground	Summit of Fuego seen at night. Weak incandescence is visible.

Volcanism at Acatenango is primarily of an explosive andesitic type. Eruptions about 1900 years ago from Pico Mayor and 5000 years ago from Yepocapa produced widespread ash and pyroclastic flow deposits. However, since then only minor explosive phreatic activity has been documented at sites between the two summits in 1924-1927 and 1972.

Volcanism at Fuego has been primarily basaltic in historical times. This is thought to result from high input rates of mafic (<55% silica) magmas into the subvolcanic magma chamber. Studies on strata from the Meseta collapse scar and comparison thereof with young Fuego eruptates have revealed several interesting trends in activiity at the volcano (Chesner and Halsor (1997), J. Volc. Goetherm. Res. 78, p.221-237). As Meseta grew in size, deposits initially became more silicic. This is apparently common in basalt-andesite composite volcanoes and may result from the increasing difficulty to erupt material from a large cone, resulting in longer rest periods and consequent increased time for magma fractionation (associated with higher silica levels) between eruptions. However, towards the end of Meseta's growth this trend was reversed. It is suggested that increased influx of mafic magma into the system resulted in progressively more mafic lavas. It is possible that increased magma input into the N-S trending dyke system thought to connect the underlying magma chamber with the vent played a role in triggering failure of the E flank resulting in the Escuintla debris avalanche. Magma pressure in a N-W oriented dyke will push E and W flanks apart. It is interesting that the basaltic lavas presently erupted from Fuego are similar in composition to the last eruptives from Meseta. Further, Fuego's E flank is hydrothermally weakened and steep, suggesting that it may be prone to failure.

Daytime ash-rich strombolian eruption from Fuego, Dec. 2007	Nighttime strombolian eruption of Fuego.

More than 60 eruptions have been documented from Fuego since 1524. Most were short-lived vulcanian explosive eruptions accompanied by ashfall, pyroclastic flows and later lahars. About 25% of these eruptions are reported to have involved lava flows. Clusters of historic eruptions lasting 20-70 years, seperated by relatively quiet periods of 80-170 years have been defined (Chesner and Rose (1984) J. Volc. Geotherm. Res. 21, p.25-44). These may coincide with the arrival of batches of magma into the shallow magma chamber from a far deeper source. The last "major" eruption occurred in 1974 when 0.1 cubic km of magma was erupted in essentially 4 main bursts. On 14, 17, 15 and 23 October, a series of powerful blasts produced up to 10km high ash columns and pyroclastic flows in 6 drainages to the E, W and SW. The longest flows reached over 10km from the summit but were fortunately restrained in uninhabited valleys. A 30cm layer of ash was deposited 10km to the W by the first burst, the second was even more powerful. Many thousands temporarily abandoned their homes due to the eruption. Roofs collapsed under the weight of the ash and crops and grazing areas were destroyed over a wide area extending up to 100km downwind. Many who initially stayed to sweep their roofs left after larger ballistics fell (10cm long ballistics were thrown over 5km from the crater).

Further smaller eruptions occurred in subsequent years. Fuego was then essentially quiet from 1987 to 1999. Since then, the volcano has once again been in a period of heightened activity. Most commonly, sporadic small strombolian or vulcanian eruptions can be witnessed producing ash clouds. Events may be anything from minutes to days apart. Lava flows have also been seen in recent years. These tend to break up easily on the steep flanks causing incandescent rockfalls and small pyroclastic flows. At night, incandescence can often be observed in the base of eruption columns. The eruption photos in the present report were taken in Dec. 07 and Jan. 08 and reflect a period of sporadic yet slightly above average activity. Unusually harsh weather conditions unfortunately hampered observation somewhat.

Steam column followed by small ash eruption, Dec. 2007.	Ash cloud taking the form of a kissing couple. Cloud was driven sideways by 80kmh wind.	Clouds partially obscuring Fuego during strong ash eruption.

Fuego volcano can be seen from Antigua although cloud and haze often limit visibility. Alternatively, weather permitting, it is possible to climb Acatenango and observe Fuego from its summit. The climb is however long and robberies have been reported on the route. Altitude sickness can also be a problem. For other volcanoes in Guatemala see sections on Santiaguito/Santa Maria and Pacaya.

Fuego ash eruption, Dec. 2007	Fuego ash eruption animation, Dec. 2007	Fuego ash eruption, Dec. 2007

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