Geology and geochemistry of the Geyser Bight Geothermal Area, Umnak Island, Aleutian Islands, Alaska

• Main Authors: Nye, C.J. . Geophysical Inst. Alaska Dept. of Natural Resources, Fairbanks, AK . Div. of Geological and Geophysical Surveys), Motyka, R.J. . Div. of Geological and Geophysical Surveys), Turner, D.L. . Geophysical Inst.), Liss, S.A. (Alaska Dept. of Natural Resources, Fairba
• Language: unknown
• Published: 2014
• Subjects: 15 GEOTHERMAL ENERGY; GEYSERS GEOTHERMAL FIELD; GEOCHEMISTRY; GEOLOGY; GEOTHERMAL FLUIDS; HEAT FLOW; PLUTONIC ROCKS; PROGRESS REPORT; VOLCANIC ROCKS; WATER CHEMISTRY; CHEMISTRY; DOCUMENT TYPES; FLUIDS; GEOTHERMAL FIELDS; IGNEOUS ROCKS; ROCKS; Alaska; Aleutian Islands
• Online Access: http://www.osti.gov/servlets/purl/6193109; https://www.osti.gov/biblio/6193109; https://doi.org/10.2172/6193109

The Geyser Bight geothermal area is located on Umnak Island in the central Aleutian Islands. It contains one of the hottest and most extensive areas of thermal springs and fumaroles in Alaska, and is only documented site in Alaska with geysers. The zone of hot springs and fumaroles lies at the head of Geyser Creek, 5 km up a broad, flat, alluvial valley from Geyser Bight. At present central Umnak is remote and undeveloped. This report describes results of a combined program of geologic mapping, K-Ar dating, detailed description of hot springs, petrology and geochemistry of volcanic and plutonic rock units, and chemistry of geothermal fluids. Our mapping documents the presence of plutonic rock much closer to the area of hotsprings and fumaroles than previously known, thus increasing the probability that plutonic rock may host the geothermal system. K-Ar dating of 23 samples provides a time framework for the eruptive history of volcanic rocks as well as a plutonic cooling age.