Between 1992 and 1998, we sampled gas discharges from =173?C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. For each site, we collected and analyzed samples to characterize the chemical (H2O, CO2, H2S, N2, CH4, H2, HCl, HF, NH3, Ar, O2, He) and isotopic (a13C of CO2, 3He/4He, 40Ar/36Ar, a34S, a13C of CH4, a15N, and aD and a18O of water) compositions of the gas discharges, and to create baseline data for comparison during future unrest. The chemical and isotopic data show...
