Symonds, Rose, Bluth, Gerlach (1994) have reported on the concentrations of various gases present in volcanic emanations for three volcanoes: Kilauea, Erta` Ale, and Momotombo. These gases typically include water vapor (H20), and, in order of their occurrence by volume, carbon dioxide (C02) and sulfur dioxide (S02). In addition, volcanoes are also known to release small amounts of several other gases, among them hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He). The United States Geological Survey, in a web site describing volcanic gases (2006), includes some of the data provided by…