Report on Pavlof (United States) — May 1987

Scientific Event Alert Network Bulletin, vol. 12, no. 5 (May 1987)
Managing Editor: Lindsay McClelland

Pavlof (United States) Ash emission; flow; seismic amplitudes increase

Please cite this report as:

Global Volcanism Program, 1987. Report on Pavlof (United States). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 12:5. Smithsonian Institution.

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United States

55.417°N, 161.894°W; summit elev. 2493 m

All times are local (unless otherwise noted)

The 15-month eruption continued in May. The summit was visible on several days from the end of May until 9 June. On about 22 May, Warren Johnson (Kenai Float Plane Air Service) observed a small lava flow and minor ash emission from a vent on the NE flank near the summit. On 28 May at 0627, Marsha Brown (FAA, Cold Bay) observed emission of black ash puffs at 5-minute intervals from 2 vents on the NE flank, one near the summit and the other halfway down the flank. The near-summit vent was emitting more ash. Ash from both vents rose about 800 m above the volcano and drifted about 10 km SE. Ash deposits covered the NE flank. At 1200 that day Lee Goch (Reeve Aleutian Airways) saw only minor steam emission.

On 30 May, Edward Livingston (Reeve Aleutian Airways) observed fairly steady black ash emission from the near-summit vent rising to ~300 m above the summit and drifting 24 km SSE. The SE flank was blackened by ash while the rest of the volcano was snow-covered. Ash emission was continuing at 1956 when a Peninsula Airways aircraft passed.

On 2 June at 1615 Pavlof was again visible and James Gibson (Reeve Aleutian Airways) observed, from more than 25 km away, a black steaming lava or debris flow on the NE slope that originated from the near-summit vent. The flow extended into the saddle between Pavlof and Pavlof Sister, then turned NW. Ash rose about 600 m above the near-summit vent and to about summit altitude from a source in the flow about 1/3 of the way down the NE flank.

On 6 June at 1601, the pilot of a small aircraft saw an ash plume rising to 600 m above the summit and drifting S. The 2 June flow had descended to 120 m elevation and steam was rising where the flow touched snow. On 9 June only steam emission from the upper NE vent was seen but the entire summit area was covered with ash.

Volcanic earthquake amplitudes and tremor were greatly increased from about 5 to 10 June and were much higher than during most eruptions.

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; T. Miller, USGS Anchorage.