Geology and eruptive history of Bogoslof volcano

Abstract

Bogoslof volcano is a shallow submarine/subaerial volcano in the southern Bering Sea about 100 km west of the community of Dutch Harbor, Alaska. The subaerial parts of the volcano consist of two small islands, Bogoslof Island and Fire Island, that together have a total area of about 1.6 km2. Bogoslof was first depicted on a Russian map in 1772 and since then has been observed and visited occasionally. The volcano has had at least nine periods of eruptive activity since 1796 and all of its historical eruptions have been similar in style. Historical Bogoslof eruptions involved the effusion of basalt, trachybasalt, basaltic trachyandesite, and trachyandesite lava domes with above sea level relief of 100–200 m. Many of the eruptions are accompanied by the formation of tuff rings and ejection of ballistic particles. Historical observations suggest that eruption clouds are relatively ash-poor. Minor ash fallout has typically occurred within about 100 km of the volcano. Many of the historical eruptions began at vents that were below sea level, and thus, seawater has played an important role in the style of eruptive activity exhibited by the volcano. At times, eruptive activity has been characterized by Surtseyan style eruptions and magma interaction with wet vent-fill deposits. At other times, the eruptive style has been more magmatically driven and has resulted in the formation of pyroclastic flows and small ash clouds. Preliminary studies of the deposits produced during the 2016–2017 eruption indicate vertical sequences of coarse-grained, horizontally bedded pyroclastic flow and fall deposits with numerous blocks, bombs, and lapilli of dense juvenile and accidental lithic material. These deposits were emplaced by near-vent pyroclastic flows, surges, and explosions some of which originated from shallow, highly crystalline cryptodomes.