Description: From Cameron and others (2020): "Pavlof Volcano erupted on March 27, 2016, about 500 days after the end of the previous eruption in 2014 (table 5). The March 27-28 eruption was a brief but intense eruptive event lasting about one day (fig. 16). This event generated minor ashfall at Nelson Lagoon 77 km (48 mi) northeast of Pavlof Volcano and trace ashfall at Port Heiden and Dillingham 263 km (164 mi) and 453 km (281 mi) northeast of Pavlof, respectively. More than a hundred flights were cancelled between March 27 and March 29 because of ash from the eruption. Two additional eruptive periods occurred in May and July 2016, but these events produced only small ash clouds and minor ash fallout confined to the upper flanks of the volcano. The March 28 eruption generated significant ash clouds reaching as high as 12.5 km (41,000 ft) ASL, and pyroclastic flows and lahars on the flanks of the volcano, one of which destroyed seismic station PV6 on the north flank of the volcano.
"The first indication of unrest in 2016 began with a late morning telephone call on March 25 from National Weather Service personnel in Cold Bay, Alaska, who reported a steam plume rising from the summit of Pavlof Volcano (fig. 17). Although steam plumes at Pavlof are common, this particular plume was reported as more robust than usual. A review of web camera images from a Federal Aviation Administration (FAA) web camera in Cold Bay showed a prominent steam plume visible from 17:47 until 19:57 UTC (9:47 to 11:57 AKDT), when it became obscured by clouds. No unusual seismic activity was noted on March 25 or the following day on March 26.
"The volcano remained quiet throughout most of the day on Sunday, March 27, and a relatively clear satellite view of the volcano summit above the cloud deck at 22:33:15 UTC (14:33 AKDT) showed no evidence of any unrest. At 00:18 UTC, March 28 (16:18 AKDT), an ash cloud reaching about 6 km (20,000 ft) ASL and moving north was reported by a nearby pilot. At about 01:33 UTC March 28 (17:33 AKDT March 27), AVO received a pilot report of ash emissions from Pavlof Volcano reaching an altitude of about 9.1 km (30,000 ft) ASL and observations of lava at the surface. Retrospective analysis of seismic data indicated that seismicity began to increase from background levels at about 23:53 UTC (15:53 AKDT) denoted by an abrupt increase in real-time seismic amplitude measurement (RSAM) levels and the appearance of continuous tremor on all operating stations of the Pavlof Volcano network. The tremor and RSAM levels observed on station PS4A illustrate seismicity during the eruption (fig. 18). At about 00:00 UTC March 28 (16:00 AKDT) tremor and RSAM levels continued to increase until about 06:38 UTC March 28(22:38 AKDT) after which the RSAM values leveled off but continued to fluctuate. At approximately 09:46 UTC March 28 (01:46 AKDT) they increased toward a peak value of 3200 and then began to decline in a saw tooth pattern until 20:40 UTC (12:40 AKDT) when the values fell to about pre-eruption levels (fig. 18).
"The abrupt increase in RSAM and tremor observed around 00:00 UTC March 28 (16:00 AKDT March 27) prompted AVO to raise the Aviation Color Code and the Volcano Alert Level to RED and WARNING at 01:12 UTC March 28 (17:12 AKDT), respectively. The rapid increase in seismicity is characteristic of several recent Pavlof Volcano eruptions, and it is not uncommon for the Aviation Color Code and the Volcano Alert Level to move from background status to the highest level with minimal precursory seismic activity.
"At 04:05 UTC March 28 (20:05 AKDT March 27), AVO received a pilot report of lava fountaining near the summit and a flowage feature on the north flank of the volcano. According to the pilot, the flowage feature had apparently reached the Bering Sea coast. The pilot referred to the feature as a pyroclastic flow, and it is possible that pyroclastic flows produced by collapse of the eruption column formed during the eruption. It is also possible that meltwater generated by the interaction of pyroclastic flows with snow and ice may have flowed well beyond the volcano to the north as lahars. The specific drainage containing the flow was not identified by the pilot, but lahars from previous historical eruptions have inundated both the Leontovich and Caribou River drainages on the north side of Pavlof Volcano.
"Pyroclastic flows or hot granular mass flows associated with collapse of spatter accumulations on the upper part of the edifice likely destroyed seismic station PV6 on the lower north flank of the volcano (fig. 19). Flowage signals were evident at PV6 starting about 01:06 UTC March 28 (17:06 AKDT March 27), and the station stopped transmitting 12 minutes later at 01:18 UTC March 28 (17:18 AKDT March 27).
"Satellite observations from 04:15 UTC March 28 (20:15 AKDT March 27) indicated that the ash cloud from the eruption extended 180 km (108 mi) northeast beyond the volcano over the Bering Sea (fig. 20). Ash cloud heights from pilot reports indicated a maximum altitude of about 9.1 km ASL (30,000 ft). By 15:10 UTC March 28 (07:10 AKDT), the Pavlof Volcano ash cloud formed a narrow, continuous plume that extended for about 885 km (550 mi) from the volcano over interior Alaska as detected in a Himawari-8 false color image (fig. 21).
"Ash fallout on March 27–28 was reported in several communities northeast of Pavlof Volcano, including Nelson Lagoon, Port Heiden, and Dillingham, Alaska. In Nelson Lagoon 77 km (48 mi) northeast of Pavlof, 3–17 millimeters (mm; 0.125–0.66 inches) of dark ash fell, covering roofs and surfaces (fig. 22). Trace amounts of ash (<0.8 mm) were reported in Port Heiden and in Dillingham 263 km (164 mi) 453 km (281 mi) northeast of Pavlof Volcano, respectively.
"The March 27-28 ash plume caused the cancellation of 41 Alaska Airlines flights to and from Barrow, Bethel, Anchorage, Fairbanks, Kotzebue, Nome, and Prudhoe Bay, Alaska, on Monday, March 28, 2016. Regional flights operated by Bering Air were cancelled on the morning of March 28, PenAir suspended service to Dutch Harbor, Alaska, in the afternoon, and Ravn reported numerous flight cancellations (FOX59, 2016). Flight cancellations continued on Tuesday, March 29, and Alaska Airlines reported 28 cancelled flights to Barrow, Bethel, Kotzebue, Nome, and Prudhoe Bay, representing about 57 percent of Alaska’s flights to the most northern region it serves. Alaska Airlines additionally reported more than 6,200 travelers were affected on March 28 and 29 (Alaska Airlines, 2016).
"Lightning in the vicinity of Pavlof Volcano was reported by the WWLLN, which consisted of 16 lightning flashes detected over a 6-hour period between 13:10-19:13 UTC (05:10–11:13 AKDT) on March 28. Sulfur dioxide (SO2) emissions were detected by Infrared Atmospheric Sounding Interferometer (IASI) satellite sensors on the European Space Agency MetOp series of polar orbiting satellites on March 28 and 29. The SO2 cloud extended over interior Alaska and northwestern Canada (fig. 23) and eventually reached the southern Hudson Bay area of central Canada. The cumulative SO2 mass determined from the Ozone Mapping Profiler Suite (OMPS) satellite data obtained on 28 March was on the order of 20–30 kilotons (Simon Carn, Michigan Technological University, written commun., 2016).
"The March 28 Pavlof eruption was clearly recorded by infrasound instruments 453 km (281 mi) to the northeast at Dillingham (fig. 18). An infrasound signal was first evident at about 02:00 UTC March 28 (18:00 AKDT March 27), which corresponds to an emission time at the vent of about 01:40 UTC March 28 (17:40 AKDT March 27). The magnitude of the infrasound signals gradually rose until about 04:30 UTC March 28 (20:30 AKDT March 27) and then stabilized at high levels for several hours before declining significantly with no clear signals detected at Dillingham after about 21:00 UTC (13:00 AKDT) March 28 (David Fee, University of Alaska Fairbanks Geophysical Institute, written commun., 2016).
"By 20:40 UTC (12:40 AKDT) March 28, ash emissions were no longer evident in satellite data, and seismic activity had declined to nearly pre-eruption levels. AVO lowered the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH at 02:01 UTC (18:01 AKDT) March 29 because of the decline in robust eruptive activity.
"After March 28, 2016, unrest at Pavlof Volcano gradually declined. By April 6, 2016, ash emissions were no longer detected, and only weakly elevated surface temperatures associated with cooling deposits were observed in satellite data. At this point, AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. Unrest continued to decline throughout the month of April 2016, and on April 22 AVO lowered the Aviation Color Code to GREEN and the Volcano Alert Level to NORMAL.
"Pavlof Volcano remained at background levels of unrest until May 13, 2016. At about 18:35 UTC (10:35 AKDT) May 13, seismic activity increased to levels commonly associated with low-level eruptive activity, suggesting that an eruption may have started. AVO responded by raising the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH at 20:04 UTC (12:04 AKDT) May 13. No volcanic activity was observed in satellite data or in web-camera views of the volcano on May 13. Minor ash emissions reaching as high as 6 km (20,000 ft) ASL were observed in images from the Cold Bay FAA web camera beginning around 03:46 UTC May 15 (19:46 AKDT May 14). Elevated surface temperatures were observed in satellite data on May 15, and SO2 emissions were detected in Ozone Monitoring Instrument (OMI) satellite data at 23:28 UTC (15:28 AKDT) May 17. AVO received several pilot reports of ash clouds rising to about 4.6 km (15,000 ft) ASL on May 17. This brief period of low-level eruptive activity lasted only a few days, and on May 20 AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. After a few more weeks of no activity, AVO moved the Aviation Color Code to GREEN and Volcano Alert Level to NORMAL on June 17.
"The volcano remained quiet until July 1, 2016, when seismicity at the volcano began to increase, and minor steam emissions were observed in web-camera images. The increase in unrest prompted AVO to raise the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY.
"Beginning around 21:00 UTC (13:00 AKDT) July 12 web-camera images showed minor ash emissions rising just above the roughly 2.6 km (8,500 ft) high summit vent and extending a few miles to the southwest. Clear satellite views of the volcano from about this same time showed no evidence of ash emissions or elevated surface temperatures, and there was no anomalous seismicity associated with this low-level activity. After July 12, Pavlof Volcano remained in a state of low-level unrest with occasional slightly elevated surface temperatures and minor steam and diffuse ash clouds observed. The Aviation Color Code remained YELLOW and the Volcanic Alert Level ADVISORY.
"On July 28, minor eruptive activity was observed in web-camera and satellite images of Pavlof Volcano and was characterized by vigorous, steam-rich degassing and minor ash emissions. Pilots also reported seeing ash emissions as high as 2.7–3.6 km (9,000–12,000 ft) ASL. These observations coincided with a minor increase in seismicity to levels high enough to warrant raising the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH at 19:55 UTC (11:55 AKDT) on July 28. Observations of minor steam and ash emissions as high as 2.4 km (8,000 ft) ASL were made by pilots on July 31. Only weakly elevated surface temperatures were observed on August 2, and by August 4 there was no further evidence of unrest at Pavlof Volcano. Thus, AVO reduced the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY.
"Unrest at Pavlof Volcano remained slightly above background levels for about six months after early August 2016. Throughout this period, low-level steam and gas plumes from the summit and weakly elevated surface temperatures were observed occasionally when viewing conditions were favorable. The elevated surface temperatures were likely associated with still cooling pyroclastic deposits on the north flank of the volcano. By February 2017, unrest had declined to background levels although occasional, small, low-frequency events were observed in seismic data, consistent with an open, degassing system. AVO lowered the Aviation Color Code to GREEN and the Alert Level to NORMAL on February 2, 2017."