Seismic activity at Pavlof, characterized by [50-1,000] events/day August-November 1976, had declined to 10-15 events/day during a 2-day period in mid-December. During periods of high seismic activity, individual events frequently blended together, producing an effect similar, but not identical, to harmonic tremor (one frequency dominant). Approximately one earthquake/week (probably tectonic in origin) is locatable.

Due to poor weather conditions, visual observations of Pavlof were impossible during January. When visited on 21 December, Pavlof was emitting very small amounts of steam.

Geological Summary. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Information Contacts: J. Davies, LDGO; R. Dean, USAF, Cold Bay.