Vertical eruption cloud from Fuego, seen from the NW on August 12, 1966. The prevailing winds during this eruption were from the east (left in the picture). At the top of the photo is the tropopause at about 12 km, where diffusion rings can be seen. Fuego's eruptions are typically energetic vertical explosions of relatively short (a few hours) duration. Photo by Bill Rose.

Fuego is one of the world's most active volcanoes, with more than 60 historic eruptions over the course of 500 recorded years. There is a tendency for eruptions to occur in clusters, and the probablility of eruption declines from 0.02 to 0.01 after 6 years of repose (Rose et al., 1978). Eruption clusters happen at intervals of 80-170 years and last 20-70 years. The most recent of those began in 1932 and has continued until the present, consisiting of more than 30 individual events. Martin and Rose (1981) has suggested that Fuego is a "Bell-Weather" volcano, with its activity pattern in sympathy with the combined record of other volcanoes in the same arc. The specific timing of eruptions is influenced by earth tides (Martin and Rose, 1981) and plagioclase crystal in Fuego lavas have patterns of oscillatory zoning which reflect earth tides (Anderson, 1984). Most of Fuego's historic eruptions have occurred in or near February or September. We do not know the reason for this.
Eruption probability plot for Fuego. The slope of No. of repose periods (upper graph) does not change as N decreases beyond the right margin of the graph.
(Rose et al., 1978)

Fuego eruptions are vertical explosions from its summit crater. No lateral vents are well defined, and no record of historic lateral vent activity exists. The eruptions are usually ranked as VEI of 2 or 3 (Simkin et al., 1981), and usually include glowing avalanches which descend the barrancas surrounding the cone. The larger vertical explosions result in widespread ashfall blankets. Larger eruptions last only hours, a shorter period than smaller eruptions, which can continue for days.
(Rose et al., ????)

In 1974 Fuego recorded its most voluminous eruption since at least 1932 (Deger, 1932), and began at 4:00 a.m. on October 10, with small ash eruptions from the summit crater (Bonis, 1974). Four distinct episodes of basaltic airfall and ashflow activity followed. After October 23 the eruption diminished greatly in intensity and by December 4 the plume from the central crater was less than 1.5 km in height and contained almost no ash (Crafford, 1977). The 1974 eruption produced a substantial increase in stratospheric particulate matter in the northern hemisphere (Meinel and Meinel, 1975; Volz, 1975) and probably in the southern hemisphere as well (Hoffman and Rosen, 1976).

Fuego eruption of 14 October 1974, as viewed from the Finca Capetillo, 8 km ENE of the summit. The vertical eruption column reached stratospheric levels, and numerous block and ash flows descended from the column into barrancas on all flanks of the cone. Photo by W.C. Buell.

A maximum average rate of extrusion of void-free magma during the eruption is 4x10^9 cm³/s. The ash blanket produced in the most intense pulse amounted to about 0.04 km³ and was generated in less than three hours.

The commencement of 1974 activity at Fuego coincided with minima in the luni-solar tidal acceleration. The first major pulse of the eruptive sequence commenced during the fortnightly maximum in the range of tidal acceleration and coincided with a minimum in the luni-slar tidal acceleartion. Each of the other principal pulses of the eruption also began within two hours of a tidal minimum.

(Rose et al., 1978)

From September, 1977, until mid-1979, Fuego was in an extraordinary state of persistent, relatively low-level activity consisting of almost daily emission of ash-laden steam clouds. In contrast, Fuego has had more than 25 discrete, short-lived (hours to days in length) vulcanian eruption since 1944. The vulcanian eruptions are characterized by the explosive ejection of fragments of new lava, commonly incandescent at the vent by but too viscous to round during flight. Large volumes of ash (up to 10^8 m³ per event) are produced during the vulcanian activity and by acompanying ash flows. Fuego has probably projected the ash into the stratosphere 8 times since 1880.

Martin and Rose propose that there are at least five states of eruptive activity at Fuego: (1) long repose such as the 52 years before the 1932 eruption; (2) major eruption such as the October, 1974, activity; (3) intermediate repose within a cluster of activity such as the four years prior to the September, 1971, eruption; (4) intermediate-intensity eruption such as the November 21, 1978, eruption; and (5) low-level, persistent activity such as September, 1977 to mid-1979. The states of activity are not presented in an implied order of occurrence, and the transition from one state to another is not yet predictable.

(Martin and Rose, 1981)

Historic activity of Fuego Volcano. Data from Mooser et al. (1958).

Fuego's historic activity up to 1957 is given in Meyer-Abich (1956) and Mooser et al. (1958).