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Winer, G.S., 2001

St. Paul Island, Pribilof Islands, Alaska: geology, volcanic evolution, and volcanic hazards

Bibliographic Reference

Winer, G.S., 2001, St. Paul Island, Pribilof Islands, Alaska: geology, volcanic evolution, and volcanic hazards: Bozeman, Montana, Montana State University, M.S. thesis, 169 p., illust., maps.


St. Paul Island, Alaska, is a potentially active Pleistocene to Holocene volcanic center in the Bering Sea about 400 km north of the Aleutian arc front. Previous geologic mapping and studies of the geology of St. Paul Island have been only reconnaissance in nature. This study has been undertaken to make the first detailed geologic map of the island, to reconstruct its eruptive history and volcanic evolution, and to assess volcanic hazards that may be associated with future eruptions. New geologic mapping covers the entire island at a scale of 1:28,000 and includes 17 volcanic units. Eruptive styles on St. Paul Island have evolved from early, mostly effusive eruptions of primitive lavas that form the platform of the island, to more explosive monogenetic cinder cones emplaced upon the platform, to the polygenetic centers that are forming large shields from repeated eruptions of evolved low-viscosity lavas. Lavas erupted are mainly basalts, basanites, and tephrites with MgO contents ranging from 14 to 4 wt% and phenocryst assemblages of olivine +/- clinopyroxene and plagioclase. St. Paul's volcanic system as a whole is trending toward the progressive development of shallow crustal magma chambers where cooling and differentiation are occurring. A new 14C date of 3,230 ybp has been obtained on the youngest lava flow on St. Paul. Volcanic hazards associated with a future eruption on St. Paul Island are similar to those from dominantly Strombolian style eruptions at other basaltic lava fields. However, because of St. Paul's unique human and wildlife populations, isolated location, and extreme weather conditions in the Bering Sea, volcanic risks may be exacerbated. Assuming a predictable eruption recurrence interval of 7,400 years, the probability of an eruption on St Paul Island in future decades is estimated to be extremely small.

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