Aleutian Arc Geothermal Fluids: Chemical Analyses of Water and Gas Samples Collected During Volcano Hazards Investigations

As part of ongoing efforts by the Alaska Volcano Observatory (AVO) to study and monitor volcanoes of the Aleutian Arc, samples of water and gas are occasionally collected from thermal springs, fumaroles, gas vents, and other features. These samples are analyzed in one or more laboratories at the U.S. Geological Survey (USGS). Some of the analytical results are eventually included in publications that summarize the field work or present major conclusions, but some data remains unpublished, especially results from single "grab" samples that are collected during the performance of other work. Such data could be useful for purposes such as constraining the strength of magmatic degassing, evaluating geothermal resources, or simply establishing baseline hydrologic conditions at remote volcanoes that are seldom visited. This report contains the chemical and isotopic data from thermal waters and gases collected from the Aleutian Arc (Figure 1) over the past 20 years, where such data remain unpublished or only published in part. We discuss some interesting features in the data, and offer brief overviews on what the data indicate about subsurface conditions. We emphasize however, that the datasets are small and the inferences drawn from them are preliminary and should not be considered as peer reviewed. One main goal in providing these overviews is to stimulate future research.\r\n\r\nFor completeness, this report also summarizes the focused investigations of thermal fluids and gases carried out in the past 20 years at Aleutian Arc volcanoes where the data have already been published (e.g., Chiginagak, Akutan, Ukinrek Maars). Results from ongoing investigations focused on the Katmai area (Lopez and others, in prep.) are not included. Brief statements about the volcanoes and their recent eruptive histories are mostly taken from the Alaska Volcano Observatory website (AVO, 2015) as of 1 April 2015, but derive in many cases from Miller and others (1998) or Wood and Kienle (1990).