Description: From Dixon and others (2015): "Pavlof Volcano erupted in May 2013 and was characterized by Strombolian explosions and periods of continuous tremor. Eruption plumes deposited trace amounts of ash in nearby communities during the first 2 weeks of the eruption and again in early June. Activity and observations are summarized in table 7 [in original text]. Pavlof was upgraded from the Aviation Color Code and Volcano Alert Level of GREEN/NORMAL to ORANGE/WARNING on May 13, remaining at ORANGE/WARNING for 17 days during the 3-week-long eruption, with remainder of the time at YELLOW/ADVISORY. On August 8, the Aviation Color Code and Volcano Alert Level were downgraded to GREEN/NORMAL, where it remained for the rest of the year.
"The 2013 eruption of Pavlof Volcano began on the morning of May 13, 2013, following a 6-year period of repose. Eruption onset was characterized by subtle, low-level seismicity beginning about 16:00 UTC (08:00 AKDT) and continuing for the first 24-48 hours of the eruption. A strong, persistent thermal signal from the Pavlof summit area was first observed in mid-infrared AVHRR satellite imagery at 15:17 UTC (07:17 AKDT) on May 13, and AVO upgraded the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH, stating that an eruption was likely to progress. A pilot report at 03:00 UTC on May 13 (19:00 AKDT, May 14) confirmed the eruption, with numerous dark streaks on the upper northern flank of the volcano that appeared to be a lava flow and lahars initiated by melting of snow and ice in the summit area (fig. 28 in original text). Similar flows also were observed farther down the northern flank and that were initiated by the ejection of hot debris onto snow and ice. Residents of Sand Point, 85 km (53 mi) east of the volcano, reported seeing a distinctive glow at the summit of Pavlof during the evening of May 13, indicating likely lava fountaining. By the next day, satellite observations showed that a lava flow extending down the northern flank well beyond the summit vent. The flow was estimated to be about 600 m (2,000 ft) long and 30 m (100 ft) wide, and originated from a vent within a small crater just north of the summit.
"AVO received numerous observations on May 14 confirming eruptive activity underway at Pavlof Volcano. Pilot reports and Web camera views of the volcano indicated that ash emissions as high as about 4 km (13,000 ft) ASL were occurring intermittently. Views of Pavlof, such as that in figure 29 [in original text], indicated several light-colored plumes rising off the lower northern flank, suggesting flowage of hot debris over ice and snow. Throughout the day on May 14, numerous strong bursts of tremor coincided with similar observations of large steam plumes rising off the northern flank of the volcano. Light-colored plumes from some of these events reached as high as 6 km (20,000 ft) ASL. Incandescence associated with strong lava fountaining at the summit also was observed throughout the evening of May 14. The lava fountaining was robust enough that relatively continuous infrasonic tremor was produced and recorded on infrasound arrays on Akutan Island (290 km [180 mi] southwest of Pavlof) and Okmok (460 km [285 mi] southwest of Pavlof) Volcanoes and at Dillingham (455 km [283 mi] northeast of Pavlof).
"Noticeable fallout of fine ash occurred as far as 80 km (50 mi) downwind of the volcano on May 14, 15, and 18, and was reported to AVO. During May 15-20, sulfur dioxide (SO2) from Pavlof was detected in OMI satellite data; the estimated SO2 mass during May 15-16 was 1,000-2,000 metric tons and at least 4,000 metric tons on May 18-20 (Simon Carn, written commun., 2013). Sulfur dioxide also was detected on multiple days by the GOME-2 (Global Ozone Monitoring Experiment-2) and IASI (Infrared Atmospheric Sounding Interferometer) instruments.
"From May 15 to 21, the eruption was characterized by nearly continuous tremor and explosions. A relatively continuous ash plume was apparent in AVHRR and MODIS satellite images and also was observed by pilots. Ash emissions during this period reached as high as 7 km (23,000 ft) ASL and extended about 400-500 km (250-310 mi) southeast of the volcano on May 18 (fig. 30 in original text). On May 19, trace amounts of ash fall occurred on the communities of Sand Point and Nelson Lagoon, 90 km (56 mi) southwest and northeast of Pavlof, respectively. AVO scientists examined an ash sample collected in Sand Point that consisted almost entirely of dark angular glass shards. A single electron microprobe analysis of the glass indicated that it is compositionally andesite (58 percent silicon dioxide, SiO2) and similar to ash deposits associated with previous historical eruptions (K. Wallace, USGS-AVO unpub. data; microprobe analyses by L. Hayden, USGS).
"From May 22 to June 4, the volcano was relatively quiet, and the seismicity during this period was characterized by episodic, discrete bursts of tremor lasting from 30 seconds to approximately 1 minute. During May 22-23, the Pavlof seismic network detected distinct ground-coupled airwaves. Infrasonic arrays at Dillingham and Okmok Volcano also recorded these probable explosion signals as impulsive infrasonic waves.
"From May 27 to June 4, seismic tremor and small discrete explosions were no longer detected in seismic and infrasound data. Satellite observations during this period showed no evidence of elevated surface temperatures, volcanic gas (SO2) or ash emissions. During periods of clear weather, no visual observations of ash emissions and Web camera views of the volcano were noted, indicating eruptive activity had paused. These observations prompted AVO to downgrade the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY at 20:50 UTC (12:50 AKDT) on May 27.
"On June 4, 2013, AVHRR, MODIS, and GOES satellite data detected ash emission from Pavlof; passing pilots reported ash plumes as high as 5.7 km (18,700 ft) ASL. Slightly elevated levels of seismic tremor also were observed by midday (local) on June 4, roughly coincident with the observations of ash emissions, prompting an upgrade to ORANGE/WATCH at 12:15 UTC (20:15 AKDT). From June 14 to 19, seismic activity was characterized by periods of intermittent volcanic tremor and slightly more robust and more frequent explosions compared to the character of the seismicity from May 13 to 24. During this period, ash plumes generally were smaller and did not extend more than about 50 km (30 mi) downwind of the volcano. The maximum plume height reported by pilots was approximately 6 km (29,000 ft) ASL on June 10. Residents of Cold Bay reported barely perceptible trace ash fall during June 6-7.
"From June 20 to 24, the Pavlof seismic network recorded moderate levels of relatively continuous tremor and small explosions. Several low-level ash plumes (generally less than 3.5 km or 11,500 ft) ASL were generated, although cloud cover occasionally inhibited observations.
"Beginning around 07:00 UTC on June 25 (23:00 AKDT on June 24), tremor amplitudes at the volcano increased significantly and were characterized by high levels of continuous tremor and frequent explosions associated with robust episodes of lava fountaining and ash emission. The level of seismicity on June 25 was the strongest detected during the entire eruption. Observers in Sand Point reported incandescence and ash plumes as high as 6 km (20,000 ft) ASL on the morning of June 25, and around midnight on June 25, ash fall was reported in King Cove 50 km (30 mi) southwest of the volcano. Analysis of satellite images and pilot reports confirmed ash plumes as high as 7-8 km (23,000-26,000 ft) ASL. Sulfur dioxide emissions from Pavlof were detected by the Joint Polar Satellite System Ozone Monitoring Profiler Suite from 01:00 to 23:10 UTC on June 25. Automated analysis of this data indicated a mass of SO2 of 6,000-7,000 metric tons near the volcano.
"Between June 25 and 27, intermittent ash plumes rose to 6 km (20,000 ft) ASL. After June 27, the seismicity became less energetic, and occasional low-frequency events and low levels of increasing discontinuous tremor characterized the seismicity. Pilot reports on June 28 indicated no activity at the volcano, and over the next several days, seismic tremor and small discrete explosions were no longer detected in seismic and infrasound data. Satellite observations after July 1 showed no evidence of elevated surface temperatures, volcanic gas, or ash emissions. On July 2, AVO downgraded the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY, where it remained until August 8 when the volcano returned to its normal background state and the Aviation Color Code and Volcano Alert Level were downgraded to GREEN/NORMAL.
"The lahars and ash plumes generated during the eruption did not pose any serious hazards for the area. However, numerous local airline flights were cancelled or rerouted, and trace amounts of ash fall occurred at all local communities surrounding the volcano, including Cold Bay, Nelson Lagoon, Sand Point, and King Cove. Observations by AVO scientists during July 16-17 indicated that only the upper part of the Cathedral River drainage (fig. 31 in original text) had been inundated by lahars. However, a fountain-fed lava flow, about 5.8 km (3.6 mi) in length, covering an area of about 730,000 m2 (180 acres) on the northern flank of the volcano was observed (fig. 32 in original text). It was only possible to collect a few samples of the lava. These samples have not yet been analyzed (as of July 2015), but appeared similar to other andesitic lava flows produced by historical eruptions of Pavlof."