AVO reported that at about 1035 on 13 May seismic activity at Pavlof increased to levels typically associated with low-level eruptive activity; cloud cover prevented visual observations of the volcano though no thermal signals or ash emissions were evident through the cloud deck. AVO raised the Aviation Color Code to Orange and the Volcano Alert Level to Watch due to the possibility of an eruption in progress. On 14 May seismicity remained above background levels. Clear satellite and webcam views revealed no evidence for an eruption, and no ash emissions or thermal anomalies at the summit were observed. During 1927-2107 on 14 May ash emissions were evident in webcam views and reported by local observers. A diffuse ash plume rose to altitudes of 4.6-5.5 km (15,000-18,000 ft) a.s.l. and remained in the vicinity of the volcano. Elevated surface temperatures were detected in satellite data at 0850 on 15 May. Periods of elevated volcanic tremor and a small explosion associated with minor ash emissions began at 0445 on 17 May; observers in Cold Bay (60 km SE) and Sand Point (90 km E) reported ash emissions interspersed with steam emissions. A National Weather Service SIGMET noted that ash was below an altitude of 4.6 km (15,000 ft) a.s.l.

Geological Summary. The most active volcano of the Aleutian arc, Pavlof is a Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and Pavlof Sister to the NE form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that overlook Pavlof and Volcano bays. Little Pavlof is a smaller cone on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, eruptions have frequently been reported from Pavlof, typically 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 recorded 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.

Source: US Geological Survey Alaska Volcano Observatory (AVO)