AGE OF THE VOLCANISM

Small-scale vertical eruptions from Fuego's summit crater, viewed from the NE. Photo by Bill Rose, November 1978.

Assuming the maximum time of 170 years between clusters of historic activity to represent the time between batch arrivals throughout Fuego's history (Martin and Rose, 1981), an age for the complex can be estimated. Considering the Meseta vent first, the explosed section represents approximately 25% of its history. Selecting 4 lava flows as an average for each batch and counting ~50 lava flows in the exposed section, an age estimate of approximately 8500 years is calculated for Meseta. Fuego appears to have a similar volume to that which Meseta had and would also be about 8500 years old. Combining these ages, the Fuego complex might be about 17,000 years old. If Fuego has a shorter batching period than Meseta due to different rates of magma generation, Meseta could represent a longer time period. If this is so, 17,000 years is a minimum age for the complex.

Martin and Rose (1981) calculated the age of Fuego in a slightly different manner. They assumed an overall eruption rate, and determined that at that rate it would take 13,000 years to produce the observed volume of the Fuego complex. Rose et al. (1977) estimated an age of 30,000 years for Santa Maria volcano based upon paleomagnetic correlations. Ashes from Agua have been found interbedded with the Pinos Altos tephra in southeastern Guatemala. This tephra has been dated by C14 methods at 23,000 years Peterson, 1980). Therefore, the proposed minimum age of 17,000 years for the Fuego complex does not seem unreasonable. (Chesner and Rose, 1984).