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SIR 2020-5043: Chemical Evaluation of Water and Gases Collected from Hydrothermal Systems Located in the Central Aleutian Arc, A

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Chemical Evaluation of Water and Gases Collected from Hydrothermal Systems Located in the Central Aleutian Arc, August 2015 Scientific Investigations Report 2020–5043 U.S. Department of the Interior U.S. Geological Survey Cover. Photograph of Christoph Kern (U.S. Geological Survey) taking gas measurements between large gas plumes on Geyser Bight, Umnak Island, Alaska. Photograph by Cynthia Werner. Back cover. Photograph of the northern interior of Fisher Caldera on Unimak Island, Alaska. The view is from mount Finch looking west-southwest. Photograph by Cynthia Werner. Chemical Evaluation of Water and Gases Collected from Hydrothermal Systems Located in the Central Aleutian Arc, August 2015 By Cynthia Werner, Christoph Kern, and Peter Kelly Scientific Investigations Report 2020–5043 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia: 2020 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS (1–888–275–8747). For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Werner, C., Kern, C., and Kelly, P. K., 2020, Chemical evaluation of water and gases collected from hydrothermal systems located in the central Aleutian arc, August 2015: U.S. Geological Survey Scientific Investigations Report 2020–5043, 35 p., https://doi.org/10.3133/sir20205043. ISSN 2328-0328 (online) iii Acknowledgments The authors gratefully acknowledge the contributions from John Power, Deb Bergfeld, Laura Clor, Pete Stelling, and Bill Evans for their help with project planning and funding negotiations, field work preparations, analytical support, and for reviewing this report. We also gratefully acknowledge the careful review by Taryn Lopez and Phil Frederick. The authors would also like to thank JoJo Mangano for his skill in redrafting the map figures. The work would not have been possible without the field logistical support provided by Maritime Helicopters, Homer, Alaska. Funding was provided by the Alaska Volcano Observatory, the Deep Carbon Observatory, and the National Science Foundation (Grant # EAR-1456939 to Diana Roman, Erik Hauri, and Terry Plank). The science team are very grateful for the support received from Maritime Helicopter’s research vessel Maritime Maid and crew, and the Bell 407 helicopter, skillfully piloted by Dan Leary. Contents Acknowledgments ........................................................................................................................................iii Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Methods...........................................................................................................................................................1 Water Sampling .....................................................................................................................................1 Gas Sampling .........................................................................................................................................2 Chemical Analyses ...............................................................................................................................3 Additional Measurements on Site—MultiGAS ................................................................................3 Makushin Volcano .........................................................................................................................................4 Makushin Valley ....................................................................................................................................5 Glacial Valley .........................................................................................................................................6 Water Chemistry Summary .................................................................................................................6 Gas Chemistry Summary......................................................................................................................8 Carbon and Helium Isotopes ......................................................................................................9 Gas Geothermometry ................................................................................................................10 Apparent Decline in Hydrothermal Activity at Makushin Volcano since the 1980s .......10 Future Study Recommendations ......................................................................................................10 Akutan Volcano ............................................................................................................................................11 Water Chemistry Summary ...............................................................................................................12 Fluid Geothermometry ...............................................................................................................12 Gas Chemistry Summary....................................................................................................................14 Carbon and Helium Isotopes ....................................................................................................17 Gas Geothermometry ................................................................................................................17 Future Study Recommendations ......................................................................................................17 Tana Volcano ................................................................................................................................................17 Water Chemistry Summary ...............................................................................................................18 Gas Chemistry Summary....................................................................................................................20 Carbon and Helium Isotopes ....................................................................................................20 Gas Geothermometry ................................................................................................................20 Future Study Recommendations ......................................................................................................20 Fisher Caldera...............................................................................................................................................22 Mount Finch and Caldera Sampling ................................................................................................23 iv Water Chemistry Summary ...............................................................................................................24 Gas Chemistry Summary....................................................................................................................26 Carbon and Helium Isotopes ....................................................................................................26 Gas Geothermometry ................................................................................................................26 Future Study Recommendations ......................................................................................................27 Geyser Bight Hydrothermal Area ..............................................................................................................27 Water Chemistry Summary ...............................................................................................................29 Fluid Geothermometry ...............................................................................................................31 Gas Chemistry Summary....................................................................................................................31 Carbon and Helium Isotopes ....................................................................................................32 Future Study Recommendations ......................................................................................................32 Conclusions...................................................................................................................................................32 References Cited..........................................................................................................................................33 Figures 1. Map showing the central Aleutian Islands and general sample locations from this study ................................................................................................................................................2
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