Geological and Seismological Evidence of Increased Explosivity during the 1986 Eruptions of Pavlof Volcano, Alaska

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Initial Phase, Historic Time, Temporal Pattern, Tephra, Sedimentology

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We present results of study of the best-documented eruptions of Pavlof volcano in historic time. The 1986 eruptions were mostly Strombolian in character; a strong initial phase may have been Vulcanian. The 1986 activity erupted at least 8×106 m3 of feldspar-phyric basaltic andesite lava (SiO2=53–54%), and a comparable volume of wind-borne tephra. During the course of the eruption, 5300 explosion earthquakes occurred, the largest of which was equivalent to an M L =2.5 earthquake. Volcanic tremor was recorded for 2600 hours, and the strongest tremor was recorded out to a distance of 160 km and had an amplitude of at least 54 cm2 reduced displacement. The 1986 eruptions modified the structure of the vent area for the first time in over two decades. A possible pyroclastic flow was observed on 19 June 1986, the first time such a phenomenon has been observed at the volcano. Overall, the 1986 eruptions were the strongest and longest duration eruptions in historic time, and changed a temporal pattern of activity that had persisted from 1973–1984.

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Bulletin of Volcanology, v. 53, issue 2, p. 86-98