Type of Edifice

Izalco volcano seen from Santa Ana volcano.

Izalco is an asymmetrical strombolian stratovolcano. According to Stoiber, Rose, Lange, and Birnie (1975, pp. B-2-B-4), it has "a small composite cone, representing a total volume of about 2 km3. It is composed of basalt of rather uniform compostition (Rose and Stoiber, 1969, p. 3124). The summit crater has been of interest to the authors because of the existence of several high temperature volcanic fumaroles. These fumaroles have been thoroughly studied geochemically mainly by the sampling of gas condensates (Stoiber and Rose, 1970), and mineral incrustations around the fumarole openings (Stoiber and Rose, 1974). Part of the interest of these geochemical studies has been the examination of variations with time, since for many years it ahs been apparent that the crater was cooling. In general, as the temperatures have decreased the geochemistry of the gaseous emanations have become more and more nearly completely dominated by H2O, finally containing barely detectable concentrations of acid gases. During the same period the variety of incrustations depositing around the fumaroles have decerased markedly also."