Samples from outside the crater lake were analyzed for their sulfur isotopic composition. Samples of sulfate alteration and native sulfur from the Kīlauea summit, Halema’uma’u crater (HMM), and the Lower East Rift Zone (LERZ) were ground, weighed into tin capsules, and analyzed by conversion to sulfur dioxide with an elemental analyzer. Samples were subsequently analyzed with a continuous flow isotope ratio mass spectrometer (Brenna, 1997). Water samples from the NSF well on Kīlauea summit and samples of ash leachate from the 2018 eruption of Kīlauea were processed by precipitating dissolved sulfate as barium sulfate, using the methods described in Carmody and others (1997), and then analyzed as described above. Samples are analyzed simultaneously with BaSO4 isotopic reference materials. No correction for oxygen isotopic composition is made to the reported sulfur isotope data. For oxygen isotope ratio measurements, BaSO4 is converted into CO with a Thermo-Finnigan Thermo-Chemical Elemental Analyzer at 1325°C. The CO is analyzed for oxygen isotopic composition using a continuous flow isotope ratio mass spectrometer analyzing (Böhlke and others, 2003; Brand and others, 2009). The 2-sigma uncertainty of both sulfur and oxygen isotope ratio determinations is 0.4 per mil, and reported relative to VCDT and VSMOW respectively. References Böhlke, J.K., Mroczkowski, S. J., and Coplen, T. B., 2003, Oxygen isotopes in nitrate: New reference materials for 18O:17O:16O measurements and observations on nitrate-water equilibration: Rapid Communications in Mass Spectrometry, v. 17, p. 1835-1846. Brenna, J. T., Corso, T. N., Tobias, H. J., and Caimi, R. J., 1997, High-precision continuous-flow isotope ratio mass spectrometry: Mass Spectrometry Reviews, v. 16, p. 227-258. Carmody, R. W., Plummer, L. N., Busenberg, E., and Coplen, T. B., 1997. Methods for collection of dissolved sulfate and sulfide and analysis of their sulfur isotopic composition, U.S. Geological Survey Open-File Report 97-234, 91 pp.