Report on Pavlof (United States) — December 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 12 (December 1986)
Managing Editor: Lindsay McClelland.
Pavlof (United States) Strong tremor accompanied early December lava flows; steaming from summit and flank fissures
Please cite this report as:
Global Volcanism Program, 1986. Report on Pavlof (United States). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 11:12. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198612-312030.
55.417°N, 161.894°W; summit elev. 2493 m
All times are local (unless otherwise noted)
John Taber reported that from 1 to 6 December, 140-200 volcanic events/day were recorded; 30-60 were explosions with a distinct airwave arrival. On 8 and 9 December the number of individual events gradually decreased until replaced by low-amplitude harmonic tremor. Tremor amplitude gradually increased until the record suddenly became saturated on 9 December at 2310, remaining saturated until 13 December at about 1400. Tremor continued to decrease until discrete events were again visible by about 0100 the next morning.
Airplane pilots had observed steam and ash emissions from summit area vents in early December, saw glow on 10 December, and new SSE flank lava flows the next day (SEAN 11:11). Closer examination by Harold Black, James Fredenhagen, and Donald Munson (Reeve Aleutian Airways) revealed that the narrow lava flow that appeared to have reached the ocean on 11 December had in fact stopped in a stream bed about 600 m short of Pavlof Bay. The flow was black and emitting no steam when Fredenhagen observed it on 20 December.
On 18 December, Fredenhagen observed that a fissure, emitting steam plumes to as much as 60 m height at intervals of 6-15 m, extended from the SE summit vent, active in the November eruption (SEAN 11:10-11), to about halfway down the SE flank. There it split at about a 90° angle, with both segments continuing for another 300 m downslope; steam issued from both segments for at least 150 m. On 23 December, he also observed small puffs of steam emerging from the old NE summit vent. During clear weather on 27-28 December, Marcia Brown (FAA, Cold Bay) saw steam issuing from the NE summit vent and moving about 300 m down the NE flank. On the 29th, the plume was blowing horizontally about 300 m to the E. The volcano was snow-covered with no detectable ash deposits. Poor weather prevented further observations.
Geologic Background. 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. Reeder, ADGGS; J. Taber, LDGO.