Report on Pavlof (United States) — March 1986

Scientific Event Alert Network Bulletin, vol. 11, no. 3 (March 1986)
Managing Editor: Lindsay McClelland

Pavlof (United States) Ash cloud to 4 km after 10 days of increasing seismicity

Please cite this report as:

Global Volcanism Program, 1986. Report on Pavlof (United States). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 11:3. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198603-312030.

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Pavlof

United States

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

All times are local (unless otherwise noted)


On 16 April at about 1100, a Reeve Aleutian Airways pilot saw an ash and vapor plume rising from Pavlof to ~4 km asl [see also 11:5]. About 30 minutes later, another pilot reported relatively steady ash emission to ~4.5 km altitude. Similar activity was observed around 1900.

A large eruption column that rose through low weather clouds to 14.5-16 km altitude was observed by airline pilots on 18 April at about 1620. That evening, ~0.3 cm of ash fell on Cold Bay, 55 km WSW. Minor ash emission was seen the next day, but weather conditions limited observations. Increased flow was reported in the Cathedral River, which drains Pavlof's NW flank.

Seismographs recorded a gradual increase in small volcanic events starting on 6 April, and a more rapid increase in seismicity 10-12 April. On 12 and 13 April, frequent discrete volcanic events were accompanied by brief (6-7 minutes or less) episodes of tremor. Preliminary inspection of later records indicated that vigorous seismicity was continuing as of 17 April, and instruments were saturated by events associated with the strong explosive activity on 18 April.

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: M.E. Yount, USGS Anchorage; J. Taber, Lamont-Doherty Geological Observatory (LDGO).