Stoiber and Rose (1974, p.2891) note that " there have been many investigations of the chemistry of the gaseous constituents emitted by volcanoes. Analyses have been make of gas samples (Elskens and others, 1969, p. 523-542); of fume from active vents (Cadle and others, 1969); of fumarolic sublimates (Naboko, 1964); and of condensed gas from fumaroles. All data refer to a specific time and place at a specific volcano. It is, therefore, pertinent to inquire how the kind and amount of components of the gas are related to the specific volcano, to the chemistry of its eruptive products, to the fumarole's location relative to volcanic features such as vents or flows, and how the chemical data and time of collection relate to the eruptive cycle of the volcano."
The fumarolic activity at Izalco volcano, according to Stoiber and Rose (1974, p.2894) "is confined to the crater, which is some 20 to 40 m deep and almost 200
m in diameter. There are two areas of hot (>150 degrees C) fumaroles on opposite sides of the crater. Condensates have been repeatedly collected over a period of 5 years from three of the hottest fumaroles in one area (L,U,W; Table 3 - E
, F,G) and from the hottest fumarole in the other area (Y; Table 3 - H). All four fumaroles have remained undisturbed by volcanic activity, so samples were taken from identical locations. From this crater, 73 condensate samples have been obtained."