Pavlof

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  • United States
  • Alaska
  • Stratovolcano
  • 2014 CE
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  • Last Known Eruption
  • 55.417°N
  • 161.894°W

  • 2493 m
    8177 ft

  • 312030
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Most Recent Weekly Report: 19 November-25 November 2014


AVO reported that seismic activity at Pavlof decreased during 21-22 November but continued to remain above background levels. Weakly elevated surface temperatures during 22 and 24-25 November, consistent with the cooling lava flow on the NW flank, were observed in satellite images. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory on 25 November; AVO noted that seismicity was at low levels during the previous week, and satellite observations show no evidence for continuing eruptive activity.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Most Recent Bulletin Report: May 2013 (BGVN 38:05)


Eruption in May-June 2013 with lava flows and ash emissions to ~8.5 km a.s.l.

Pavlof, the most active volcano in the Aleutian arc, erupted on 13 May 2013. Before this, it had most recently erupted on 15 August 2007, following an 11-year period of quiescence. The eruption that began in May 2013 continued through June before slowly subsiding to background levels by 8 August. Pavlof generated several ash plumes during the six-week eruption that disrupted aviation, including an 8-km high plume on 24 June. As in past Pavlof eruptions, the recent eruptions fluctuated in intensity. This report briefly discusses earthquake data during 2007-2011 and, in greater detail, the series of eruptions during May and June 2013.

According to Mangan and others (2009), Pavlof has discharged more than 40 recorded eruptions within the previous 200 years, producing mostly basaltic andesite to andesite products. That work, discussed in a separate subsection near the end of this report, also discusses the adjacent 12x19 km Emmons Lake caldera (a chain of nested calderas) on Pavlof's SW flank (figure 5). The Emmons Lake Volcanic Center (ELCV) is used to collectively describe the entire complex, including the nested caldera, intra-caldera stratovolcanoes, and the adjacent stratovolcanoes (including Pavlof) to the NE.

Figure 5. Maps showing both the location of Pavlof on the lower Alaska Peninsula (upper left) and showing more details of the complex, including the elongate Emmons Lake caldera and six stratovolcanoes. The lake occupies but a small volume of the caldera, which is breached to the SE. Taken from Mangan and others (2009).

According to the Alaska Volcano Observatory (AVO), 48 earthquakes were located beneath Pavlof in 2007, the year of the previous eruption. During the following non-eruptive years, AVO reported 9 earthquakes centered at Pavlof in 2008, 7 earthquakes in 2009, 19 in 2010, and 13 in 2011. As of this writing, AVO has not yet published 2012 earthquake data.

Eruption in May 2013. On 13 May 2013, seismicity increased at 0800 and an intense thermal anomaly was observed at the summit in satellite imagery. Several spikes in seismicity occurred between 0900 and 1000. AVO noted that similar patterns of seismicity and elevated surface temperatures in previous cases had signaled the onset of eruptive activity at Pavlof. The Volcanic Alert Level was increased to Watch (the second highest category of four) and the Aviation Color Code was increased to Orange (the second highest category of four).

On 14 May 2013, pilot reports and satellite images indicated a spatter-fed lava flow that had advanced about 0.5 km down the N flank. The advancing lava had also generated debris-laden deposits, presumably from the interaction of hot lava with snow and ice on the flank. According to AVO, a diffuse ash plume drifted about 160 km NE at an altitude of 4.6 km before dissipating. Minor ashfall was reported the evening of 14 May in a mining camp 80 km NE of the volcano. No other nearby communities reported ashfall. Minor steam-and-ash emissions from the summit were visible from Cold Bay (~58 km SW).

During 14-15 May 2013, elevated seismicity persisted. Steam-and-ash clouds observed with a web camera at Cold Bay (55 km W of the volcano) occasionally rose to an altitude of 6.1 km. Residents in Cold Bay observed incandescence from the summit during the night. On 15 May a pilot reported a dark ash cloud drifting ENE at an altitude of 6.1 km.

On 16 May, AVO observed lava fountaining at the summit and a continuous ash, steam, and gas cloud extending 50-100 km downwind at an altitude of about 6.1 km. Satellite images showed persistent elevated surface temperatures at the summit and on the NW flank, consistent with lava fountaining at the summit and the resulting lava flow.

During 18-19 May 2013, reports noted that a narrow plume of steam, ash, and gas occasionally rising up to an altitude of 6.7 km and drifting SE was visible in satellite and pilot images (figures 6 and 7). Pilots noted that lava fountaining and ash emission continued. Overnight, trace amounts of ash fell on the community of Sand Point (88 km E). During the afternoon on 19 May, pilots reported that ash plumes rose to altitudes of 4.6-6.7 km. Trace amounts of ash fell in Nelson Lagoon (78 km NNE) during 19-20 May.

Figure 6. Photograph of Pavlof taken on 18 May 2013 by astronauts aboard the International Space Station. The space station was ~770 km away and S-SE of the volcano when the photograph was taken. The volcanic plume extended SE over the North Pacific Ocean. Residing next to Pavlof is the white, seemingly ash free stratovolcano Pavlof Sister. Courtesy of NASA Earth Observatory with credit for caption and processing to Robert Simmon, (NASA Earth Observatory) and G. M. Gentry (DB Consulting Group at NASA-JSC).
Figure 7. Photo of Pavlof eruption taken by a commercial pilot on 18 May 2013. Plume direction was not identified, but based on the NASA photo taken the same day (figure 6), the plume is drifting SE and the volcano in the foreground is Pavlof Sister (NE of Pavlof). Courtesy of Brandon Wilson (PenAir) and provided by AVO/Alaska Division of Geological & Geophysical Surveys.

News articles (Associated Press, PRNewswire, Alaska Dispatch) stated that during 19-21 May 2013 two regional airlines canceled flights to several remote communities and delayed or re-routed other flights. On 21 May AVO reported that a low-level plume of steam, gas, and ash occasionally rose to an altitude of 6.1 km and drifted NNE. Trace amounts of ash again fell in Nelson Lagoon.

AVO reported that seismic tremor markedly declined around 1100 on 21 May 2013 and was followed through 23 May by the detection of small discrete events, likely indicative of small explosions, by an infrasonic pressure sensor (Chaparral model 2.5 at site PN7). Although cloud cover prevented satellite observations, elevated surface temperatures at the vent were detected. On 22 May a pilot report and photographs indicated weak steam-and-gas emissions containing little to no ash.

The eruption continued at a lower level during 24-26 May. Neither evidence of elevated surface temperatures nor a plume were observed in partly clear satellite images during 24-25 and 27 May. Clouds obscured views on 26 May. The Volcanic Alert Level was lowered to Advisory and the Aviation Color Code was lowered to Yellow on 28 May.

According to AVO, Pavlof emitted ash on 4 June at about 1100, as observed in satellite images and by pilots. Satellite images showed an ash cloud drifting SE, and pilots estimated that the cloud was at an altitude of 5.8 km. Weak seismicity that began at 1057 accompanied the emissions, and then continued. AVO increased the Volcanic Alert Level to Watch and increased the Aviation Color Code to Orange.

AVO reported that ash emissions continued during 5-11 June 2013, accompanied by tremor and explosion signals. Overnight during 4-8 June, satellite images detected elevated surface temperatures near the vent consistent with lava effusion and fountaining. Elevated surface temperatures persisted until 14 June. On 5 and 6 June, an ash plume drifted 40-45 km W and SW at altitudes of 4.3-5.5 km based on pilot estimates. During 8-10 June, an ash plume drifted 20-53 km SE. During 12-14 June, ash emissions were intermittent and minor; ash plumes remained below an altitude of 6.1 km and mostly drifted SE.

During 14-15 June 2013, seismicity decreased. Minor emissions probably ceased, but web-camera views were partially obscured by clouds. On 17 June no plumes were visible in satellite images, and web camera views showed mostly cloudy conditions.

During 17-18 June, tremor amplitude increased slightly, and elevated surface temperatures were again detected in satellite images. A small ash plume rose from the crater. The eruption continued during 19-25 June, with tremor and occasional explosions. Cloud cover prevented web camera views. Elevated surface temperatures continued to be detected during 19-20 and 24 June. A small ash plume from the summit vent was also detected in a satellite image on 19 June, and possibly during 20-22 June.

On 24 June, seismicity increased to the strongest level to date during 2013 and included continuous intense tremor and frequent small explosions likely associated with lava fountaining and ash production. Seismicity remained high on 25 June. Satellite images and pilot observations indicated that a plume drifted W at altitudes as high as 8.2-8.5 km. Satellite images also detected a strong thermal anomaly at the summit. Trace amounts of ash fell in King Cove (48 km SW). According to a news report (Reuters), regional air traffic was again cancelled or re-routed.

According to AVO, seismicity declined during 25-26 June and consisted of intermittent bursts of tremor and occasional small explosions. Satellite images showed a plume containing small amounts of ash drifting NW, and strong thermal anomalies at the summit. Pilot reports on 26 June indicated that plumes rose to altitudes between 6.1-7.6 km during the morning and then to heights just above the summit later that day. Seismicity during 26 June-1 July continued at low levels and consisted primarily of intervals of continuous, low-level tremor. Thermal anomalies at the summit detected in satellite images were strong during 26-29 June and weak during 30 June-1 July.

AVO reported that activity further declined during 1-2 July; tremor and explosions were no longer detected in seismic and pressure sensor data. Satellite images did not detect elevated surface temperatures, volcanic gas, or ash emissions, and there were no visual observations from pilots or from webcam images of any eruptive activity since 26 June. Consequently, AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory.

On 8 August, AVO reported that no lava or ash emissions had been observed at Pavlof since 26 June and the volcano had exhibited gradually declining levels of unrest. Seismicity was at background levels. Thus, AVO lowered the Aviation Color Code to Green and the Volcano Alert Level to Normal.

Mangan and others (2009) discussion. Mangan and others (2009) cite Power and others (2004) as stating that background (non-eruptive) seismicity at Pavlof occurs as infrequent long-period earthquakes at focal depths between 20-40 km. Mangan and others contend that while only a few of these events at most occur annually, they are a stable feature attributed to quasi-steady fluxing of basaltic magma and exsolved CO2 in a deep dike and sill complex. According to the article, the seismic network at Pavlof is poorly situated to detect deep seismicity under the Emmons Lake caldera.

Mangan and others state, "All witnessed [Emmons Lake Volcanic Center] ELVC eruptions have occurred outside the caldera [,specifically] at Pavlof, the most active volcano in the entire arc. Pavlof's slopes are extensively mantled with tephra and pyroclastic debris produced during [its] historical strombolian, vulcanian, and lava fountain events (Miller et al., 1998). Limited precursory seismicity herald Pavlof eruptions (McNutt, 1989) and, to the extent studied, negligible precursory ground deformation (Lu et al., 2003; Z. Lu personal communication 2008). Of the 20 eruptions occurring since the installation of Pavlof's seismic network (1973), 13 eruptions have occurred with less than 24 h of warning. Pavlof is essentially an "open vent" volcano with magma rising aseismically through a thermally well-groomed conduit. High-frequency volcano-tectonic earthquakes, characteristic of magma rise through brittle crust, are virtually absent."

Figure 8 presents Mangan and others (2009) conceptualization of the plumbing beneath the ELVC, which includes Pavlof.

Figure 8. Conceptual cross-section through the Emmons Lake Volcanic Center looking at a vertical plane parallel to the volcanic axis. The drawing shows two distinct plumbing systems drawing from a common magmatic source at more than 20 km depth. Courtesy of Mangan and others (2009).

The other volcano of the ELVC considered to have high likelihood of eruption is Mt. Hague (Waythomas and others, 2006). That study also presents a set of hazard maps for the complex.

References. Mangan, M., Miller, T., Waythomas, C., Trusdell, F., Calvert, A., and Layer, P., 2009, Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc, Earth and Planetary Science Letters, Vol. 287, pp. 363-372.

Waythomas, CF; Miller, TP, and Mangan, MT, 2006, Preliminary Volcano Hazard Assessment for the Emmons Lake Volcanic Center, Alaska, U.S. Geological Survey Scientific Investigations Report 2006-5248 (URL: http://pubs.usgs.gov/sir/2006/5248/).

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Associated Press (URL: http://www.ap.org/); PRNewswire (URL: http://www.prnewswire.com); Alaska Dispatch (URL: http://www.alaskadispatch.com/); and Reuters (URL: http://www.reuters.com/).

Index of Weekly Reports


2014: May | June | November
2013: May | June | August
2007: August | September

Weekly Reports


19 November-25 November 2014

AVO reported that seismic activity at Pavlof decreased during 21-22 November but continued to remain above background levels. Weakly elevated surface temperatures during 22 and 24-25 November, consistent with the cooling lava flow on the NW flank, were observed in satellite images. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory on 25 November; AVO noted that seismicity was at low levels during the previous week, and satellite observations show no evidence for continuing eruptive activity.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 November-18 November 2014

On 12 November AVO raised the Aviation Color Code for Pavlov to Orange and the Volcano Alert Level to Watch, citing the beginning of a new phase of eruptive activity at about 1500. An observer in Cold Bay (52 km SW) reported that ash emissions rose slightly above the summit; minor ash emissions were also recorded by an FAA-operated webcam in Cold Bay beginning at 1650. Seismicity increased and remained elevated. Lava fountaining occurred from a vent just N of the summit and flows of rock debris and ash descended the N flank. A thermal anomaly appeared in satellite images at 1740. The eruption continued on 14 November. A narrow ash plume observed in satellite images drifted 200 km at an altitude of 4.8 km (16,000 ft) a.s.l.

The eruption intensified on 15 November prompting AVO to raise the Aviation Color Code to Red and the Volcano Alert Level to Warning. Ash plumes rose to an altitude of 7.6 km (25,000 ft) a.s.l. and drifted 200 km NW. The intensity of seismic tremor had increased significantly. Pilot reports through 1230 indicated that the ash plume had risen to an altitude of 9.1 km (30,000 ft) a.s.l. At about 1900 seismicity abruptly decreased and remained low. Satellite observations confirmed a significant decrease in ash emissions; discrete seismic events possibly indicated minor ash emissions that were not detected in satellite images. The Aviation Color Code was lowered to Orange and the Volcano Alert Level was lowered to Watch. Pilot reports on 16 November indicated no eruptive activity, and satellite images showed diminished temperatures in the summit crater. During 17-18 November seismic activity remained at low levels and elevated surface temperatures on the upper NW flank were observed, consistent with a flow of lava and/or hot debris.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 June-24 June 2014

AVO reported that seismicity at Pavlof continued steadily with intermittent seismic events during 18-23 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 June-17 June 2014

AVO reported that the eruption at Pavlof continued during 11-16 June. Seismic activity was steady and characterized by intermittent events. Weakly elevated surface temperatures were occasionally observed in mostly cloudy satellite images.The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 June-10 June 2014

AVO reported that the Strombolian eruption at Pavlof continued during 3-10 June. On 3 June the FAA webcam showed a high steam plume rising above a vent on the NE flank and lower-level ash from pyroclastic flows on the N flank. During 3-4 June seismicity remained unchanged and persistent elevated surface temperatures were detected in satellite images. A steam plume with minor amounts of ash but rich in sulfur dioxide drifted 100 km W. Incandescence from lava fountaining was visible in webcam images on 4 June. According to a news article, flights in and out of Cold Bay and Unalaska were canceled on 4 June, affecting about 200 people.

Two strong explosions were detected by the seismic network at 0205 and 0245 on 5 June. Lightning was detected by the World Wide Lightning Location Network indicating the presence of ash; satellite images did not detected ash above the meteorological cloud tops at about 8.5 km (28,000 ft) a.s.l. A third event was detected at 0844. The level of activity declined during 5-6 June; ash emissions appeared to be greatly reduced although cloud cover continued to obscure satellite views. Elevated surface temperatures were observed in mostly cloudy satellite images during 8-9 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Sources: US Geological Survey Alaska Volcano Observatory (AVO); Alaska Public Media


28 May-3 June 2014

AVO reported that on 31 May elevated surface temperatures were detected over Pavlof in satellite images, suggesting a low-level eruption with lava. Observers camping near the volcano confirmed lava and noted that flows were originating from a vent on the NE flank. A low-level steam plume was visible in satellite images and recorded by the FAA web-cam located in Cold Bay. Several pilots observed a gas-and-ash plume drifting N at altitudes of 2.1-2.4 km (7,000-8,000 ft) a.s.l. The Aviation Color Code was raised to Orange and the Volcano Alert Level was raised to Watch. Small explosion signals were detected by a distant infrasound sensor. Later that night weak incandescence from the summit was observed in the webcam. On 1 June clouds obscured web-cam views and ash plumes were not detected in satellite images. The seismic network detected weak activity.

Activity escalated on 2 June, prompting AVO to raise the Aviation Color Code to Red and the Volcano Alert Level to Warning. Seismic tremor increased at 1500 and pilots observed ash plumes at altitudes of 6.7 km (22,000 ft) a.s.l. Satellite images showed a plume drifting more than 80 km E. Seismicity started to decrease at 2300. The web cam recorded intense lava fountaining at the summit and incandescence from a spatter-fed lava flow on the N flank. On 3 June seismicity again increased and pilots observed ash-and-steam plumes at altitudes of 7.3 km (24,000 ft) a.s.l. that drifted SSW. Later that day AVO lowered the Aviation Color Code to Orange and the Volcano Alert Level to Watch due to a decrease and stabilization of volcanic tremor. Satellite and webcam images showed two distinct parts of the plume: gas and steam with minor amounts of ash rose high above the volcano and drifted S, while pyroclastic flows on the N flank produced diffuse ash that caused hazy air and variable concentrations of ash below 3 km (10,000 ft) a.s.l. Winds were likely to push ash at lower altitudes WSW.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 August-13 August 2013

On 8 August AVO reported that no lava or ash emissions had been observed at Pavlof since 26 June and the volcano exhibited gradually declining levels of unrest. Seismicity was at background levels. AVO lowered the Aviation Color Code to Green and the Volcano Alert Level to Normal.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 June-2 July 2013

According to news articles, ash plumes from Pavlof caused airlines to cancel one flight and reroute six more on 25 June. AVO reported that during 25-26 June seismicity declined, and consisted of intermittent bursts of tremor and occasional small explosions. Satellite images showed a plume containing small amounts of ash drifting NW, and strong thermal anomalies at the summit. Pilot reports on 26 June indicated that plumes rose to altitudes between 6.1-7.6 km (20,000 to 25,000 ft) a.s.l., and then to heights just above the summit later that day. Seismicity during 26 June-1 July continued at low levels and consisted primarily of periodically continuous, low-level tremor. Thermal anomalies at the summit detected in satellite images were strong during 26-29 June and weak during 30 June-1 July.

Activity further declined during 1-2 July; tremor and explosions were no longer detected in seismic and pressure sensor data. Satellite images did not detect elevated surface temperatures, volcanic gas, or ash emissions, and there were no visual observations from pilots or from webcam images of any eruptive activity since 26 June. AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 June-25 June 2013

AVO reported that during 19-25 June the eruption at Pavlov continued; seismic tremor and occasional explosions were detected. Cloud cover prevented web camera views. During 19-20 and 24 June elevated surface temperatures detected in satellite images were consistent with lava effusion. A small ash plume from the summit vent was also detected in satellite image on 19 June, and possibly detected during 20-22 June.

At 2250 on 24 June seismicity increased and became the strongest seismic activity detected so far during 2013. The seismicity was characterized by continuous intense tremor and frequent small explosions likely associated with lava fountaining and ash production. Seismicity remained high on 25 June. Satellite images and pilot observations indicated that a plume drifted W at altitudes as high as 8.2-8.5 km (27,000-28,000 ft) a.s.l. Satellite images also detected a strong thermal anomaly at the summit. Trace amounts of ash fell in King Cove, 48 km SW. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 June-18 June 2013

AVO reported that ash emissions from Pavlof were intermittent and minor during 12-14 June; ash plumes below an altitude of 6.1 km (20,000 ft) a.s.l. mostly drifted SE. Elevated surface temperatures consistent with lava effusion persisted until 1620 on 14 June. Seismicity decreased during 14-15 June. Minor emissions likely stopped, but web-camera views were cloudy. On 17 June no plumes were visible in satellite images, and web camera views showed mostly cloudy conditions. During 17-18 June seismic tremor amplitude increased slightly, and elevated surface temperatures consistent with lava effusion were detected in satellite images. A small ash plume rose from the crater. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 June-11 June 2013

AVO reported that ash emissions from Pavlof that began on 4 June continued during 5-11 June, and were accompanied by seismic tremor and explosion signals. Overnight during 4-8 June satellite images detected elevated surface temperatures near the vent consistent with lava effusion and fountaining. On 5 and 6 June an ash plume observed in images drifted 40-45 km W and SW, at altitudes of 4.3-5.5 km (14,000-18,000 ft) a.s.l., based on pilot estimates. During 8-10 June images showed an ash plume drifting 20-53 km SE. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 May-4 June 2013

AVO reported that ash emissions at Pavlof began at approximately 1100 on 4 June as observed in satellite images and by pilots. Satellite images showed an ash cloud drifting SE, and pilots estimated that the cloud was at an altitude of 5.8 km (19,000 ft) a.s.l. Weak seismicity that began at 1057 accompanied the emissions, and then continued. The Volcanic Alert Level was increased to Watch and the Aviation Color Code was increased Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 May-28 May 2013

AVO reported that seismic tremor at Pavlof markedly declined around 1100 on 21 May, and was followed through 23 May by the detection of small discrete events, likely indicative of small explosions, by pressure sensors. Although cloud cover prevented satellite observations, elevated surface temperatures at the vent were detected. On 22 May both a pilot report and photographs indicated weak steam-and-gas emissions containing little to no ash.

The eruption continued but at a lower level during 24-26 May. Neither evidence of elevated surface temperatures nor a plume were observed in partly clear satellite images during 24-25 and 27 May. Clouds obscured views on 26 May. The Volcanic Alert Level was lowered to Advisory and the Aviation Color Code was lowered to Yellow on 28 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 May-21 May 2013

AVO reported that on 14 May a diffuse ash plume from Pavlof drifted about 160 km NE at an altitude of 4.6 km (15,000 ft) a.s.l. before dissipating. Pilot reports and photographs indicated that the lava flow extending down the NW flank was still active and generated debris-laden flow deposits, presumably from the interaction of hot lava with the snow and ice on the flank. Light ashfall was reported the evening of 14 May in a mining camp 80 km NE of the volcano. No other nearby communities had reported ash fall. During 14-15 May elevated seismicity persisted and steam-and-ash clouds observed with a web camera occasionally rose up to 6.1 km (20,000 ft) a.s.l. Residents in Cold Bay (37 km SW) observed incandescence from the summit during the night. On 15 May a pilot reported a dark ash cloud drifting ENE at an altitude of 6.1 km (20,000 ft) a.s.l.

On 16 May lava fountaining at the summit was observed and photographed, and a continuous ash, steam, and gas cloud extended downwind 50-100 km at an altitude of about 6.1 km (20,000 ft) a.s.l. Satellite images showed persistent elevated surface temperatures at the summit and on the NW flank, commensurate with the summit lava fountaining and resulting lava flow.

During 18-19 May a narrow plume of steam, ash, and gas, occasionally rising up to 6.7 km (22,000 ft) a.s.l., and drifting southeast, was visible in satellite images. Pilot reports indicated that lava fountaining and ash emission continued. Overnight, trace amounts of ash fell on the community of Sand Point. During the afternoon on 19 May pilots reported that ash plumes rose to altitudes of 4.6-6.7 km (15,000-22,000 ft) a.s.l. Trace amounts of ash fell in Nelson Lagoon, 78 km NNE, during 19-20 May. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

A news article stated that on 20 May a regional airline canceled about a dozen flights to several remote communities, including Sand Point. Another regional airline canceled a few flights, but mostly re-routed flights. On 21 May AVO reported that a low-level plume of steam, gas, and ash occasionally rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted NNE. Trace amounts of ash again fell in Nelson Lagoon.

Sources: US Geological Survey Alaska Volcano Observatory (AVO); Associated Press


8 May-14 May 2013

AVO reported that on 13 May seismicity at Pavlof increased at 0800 commensurate with the presence of an intense thermal anomaly at the summit observed in satellite imagery. Several spikes in seismicity occurred between 0900 and 1000. AVO noted that similar patterns of seismicity and elevated surface temperatures have previously signaled the onset of eruptive activity at Pavlof. Although not yet visually confirmed at the time of the report, a low-level eruption of lava had likely begun from a summit vent. No ash clouds were detected. The Volcanic Alert Level was increased Watch and the Aviation Color Code was increased Orange. On 14 May pilot reports and satellite images confirmed activity; a spatter-fed lava flow advanced about 0.5 km down the N flank. Minor steam-and-ash emissions from the summit were visible from Cold Bay (60 km SW).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 September-25 September 2007

On 19 September, a field crew confirmed that all eruptive activity from Pavlof ceased. AVO decreased the Volcanic Alert Level to Advisory and the Aviation Color Code to Yellow on 20 September due to a significant decrease of seismic activity during the previous week.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 September-18 September 2007

AVO reported that seismic activity at Pavlof declined markedly during 8-18 September, compared to levels recorded during the first week of September. Seismicity was characterized by volcanic tremor, and signals interpreted as small explosions. Based on observations of satellite imagery, a steam plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. on 12 September and multiple thermal anomalies were present during 12-14 September. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 September-11 September 2007

Seismic activity at Pavlof fluctuated, but generally remained elevated during 5-11 September. Seismicity was characterized by volcanic tremor, and signals interpreted as frequent explosions and debris flows. During the reporting period, satellite imagery revealed strong thermal anomalies at the summit. On 8 September, a possible steam plume was visible on satellite imagery and a pilot reported that a steam-and-ash plume drifted from the summit. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 August-4 September 2007

Seismic activity at Pavlof fluctuated, but generally remained elevated during 29 August-4 September. A strong thermal anomaly was present at the summit on satellite imagery during 29 August-2 September; clouds inhibited observations on 3 and 4 September. Based on pilot reports and observations of satellite imagery, ash plumes rose to altitudes of 2.4-4.9 km (8,000-16,000 ft) a.s.l. during 28-30 August and drifted SSE and SE. On 30 August, National Weather Service observers in Cold Bay (about 60 km SW) reported that a plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. and produced lightning. Based on satellite imagery, AVO reported that steam-and-ash plumes rose to altitudes of 6.1 km (20,000 ft) a.s.l. on 31 August. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 August-28 August 2007

Seismic activity at Pavlof remained elevated during 22-28 August. A strong thermal anomaly was present at the summit on satellite imagery on 22, 24, 25, and 28 August; clouds inhibited observations on other days. Based on pilot reports and calculations using satellite imagery, a steam-and-ash plume rose to an altitude between 3-5.5 km (10,000-18,000 ft) a.s.l. On 25 August, seismic events and explosions were more energetic and a signal suggesting a large lahar was noted. Plume altitudes from previous days and seismic interpretation indicated that an ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. on 26 and 28 August. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 August-21 August 2007

AVO raised the Volcanic Alert Level to Advisory and the Aviation Color Code to Yellow for Pavlof on 14 August due to an abrupt increase in seismicity. During 14-15 August, a strong thermal anomaly was detected in the crater and prompted AVO to again raise the Volcanic Alert Level/ Aviation Color Code, to Watch/Orange. According to eye witnesses aboard a ship on 15 August, incandescent blocks rolled down the ESE flank and lava-fountaining occurred on the SE flank. The presence of lava was confirmed using satellite imagery. Pilots reported that the flanks were covered with ash and that an ash plume rose to an altitude of 2.6 km (8,400 ft) a.s.l. and drifted SW.

On 16 August, residents of Cold Bay, about 60 km SW, and of Sand Point, about 97 km ESE, saw incandescence at the summit. A strong thermal anomaly was present at the summit on satellite imagery. Seismicity increased in intensity and possibly indicated a lahar on the SE flank.

During 17-20 August, seismicity continued at high levels. Explosions were recorded and seismic signals possibly indicated flow events such as lahars. A strong thermal anomaly continued to be present at the summit. Aerial and ground observations revealed a vigorous eruption of lava during 18-20 August. Members of an AVO field party saw a lahar on the SE flank on 20 August.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Index of Bulletin Reports


Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

11/1973 (CSLP 144-73) Harmonic tremor coincides with report of observed lava flow

10/1975 (NSEB 01:01) Columns of "smoke" to 2,400 m

12/1975 (NSEB 01:03) Ash eruptions, lava emission, and orange glow

01/1976 (NSEB 01:04) Intermittent steam and ash emissions

02/1976 (NSEB 01:05) Ash eruptions and lava flows during 21-24 February

03/1976 (NSEB 01:06) Activity remains low in March

04/1976 (NSEB 01:07) Steam-and-ash emissions; ashfall seen on flanks

05/1976 (NSEB 01:08) Ash emissions in mid-May

06/1976 (NSEB 01:09) Steam-and-ash emissions continue; ashfall on cone

07/1976 (NSEB 01:10) Ash on N slope; heavy steaming

08/1976 (NSEB 01:11) Light steam plume seen on one day in August

10/1976 (NSEB 01:13) Ash covering upper slopes and the cone

11/1976 (NSEB 01:14) Continued steam-and-ash emissions

01/1977 (NSEB 02:01) Decreased seismicity; small steam emissions

03/1977 (NSEB 02:03) Some steaming and ash near the summit

04/1977 (NSEB 02:04) Ashfall darkens snow near the summit on 22 March

07/1980 (SEAN 05:07) Steam and a little ash

11/1980 (SEAN 05:11) Lava fountaining and ash emission; possible lava flow

09/1981 (SEAN 06:09) Ash clouds; lava flow; seismicity

10/1983 (SEAN 08:10) Large eruption column; tremor

11/1983 (SEAN 08:11) Ash emission; vapor plume; volcanic tremor

12/1983 (SEAN 08:12) Brief ash emission episodes

01/1984 (SEAN 09:01) Plumes on satellite imagery; harmonic tremor

03/1984 (SEAN 09:03) Vapor plume to 6 km altitude

03/1986 (SEAN 11:03) Ash cloud to 4 km after 10 days of increasing seismicity

04/1986 (SEAN 11:04) Strong tremor accompanied large 18 April plume

05/1986 (SEAN 11:05) Strombolian activity feeds lava flow; seismicity increases

06/1986 (SEAN 11:06) Strombolian activity feeds lava flow; strong seismicity

07/1986 (SEAN 11:07) Continued Strombolian activity and vigorous seismicity

08/1986 (SEAN 11:08) Strombolian activity and ash emission ends

10/1986 (SEAN 11:10) Ash emission and lava fountaining

11/1986 (SEAN 11:11) Eruption continues; lava flow reaches ocean

12/1986 (SEAN 11:12) Strong tremor accompanied early December lava flows; steaming from summit and flank fissures

01/1987 (SEAN 12:01) Steam emission from two near-summit vents

03/1987 (SEAN 12:03) Fresh ash on summit

05/1987 (SEAN 12:05) Ash emission; flow; seismic amplitudes increase

06/1987 (SEAN 12:06) Incandescent flow; summit glow; ash emission continues

07/1987 (SEAN 12:07) Activity decreases; steam and ash emission

08/1987 (SEAN 12:08) Continued ash emission

09/1987 (SEAN 12:09) New ash deposit

10/1987 (SEAN 12:10) Ash-rich explosions; blocks and spatter form flow

11/1987 (SEAN 12:11) Dark ash plumes from near-summit vent

02/1988 (SEAN 13:02) Weak steam and ash emission

07/1988 (SEAN 13:07) Fresh ash on upper flanks

08/1988 (SEAN 13:08) New ash deposit on summit

08/1996 (BGVN 21:08) Vigorous seismicity and intermittent eruptive activity

09/1996 (BGVN 21:09) Increasing seismicity corresponds to stronger eruptive activity

10/1996 (BGVN 21:10) Eruptions that began on 15 September persist during November

12/1996 (BGVN 21:12) Intermittent eruptions from 15 September through [3] January

01/1997 (BGVN 22:01) Pause in eruptive activity, but continued small intermittent steam plumes

09/1997 (BGVN 22:09) Steam plume in June; ash covering ice near summit seen in July

08/2007 (BGVN 32:08) Thermal and seismic data presage August 2007 eruption

05/2013 (BGVN 38:05) Eruption in May-June 2013 with lava flows and ash emissions to ~8.5 km a.s.l.




Bulletin Reports

All information contained in these reports is preliminary and subject to change.


11/1973 (CSLP 144-73) Harmonic tremor coincides with report of observed lava flow

Card 1744 (14 November 1973) Harmonic tremor coincides with report of observed lava flow

The following was received by cable from D.B. Stone. "Eruptive activity was observed about 10:00 p.m. Alaska Standard Time from a point 33 km NW of the summit of Pavlof. Reported as 'shooting flames' intermittently with a possible lava flow on the NW flank. A seismometer 7 km SE of the summit recorded increased microearthquake activity at about that time. Seismic records showed onset of harmonic tremor on November 13, 07:00 AST, coincident with reported eruption of lava."

Information Contacts: D.B. Stone and J. Kienle, Geophysical Institute, University of Alaska, Fairbanks AK; J.N. Davies, c/o White Alice Como Site, Cold Bay AK.

10/1975 (NSEB 01:01) Columns of "smoke" to 2,400 m

For the past several weeks Pavlof has been producing columns 2,100-2,400 m high, carried NE up the Alaska Peninsula. Weather conditions commonly prevent observation of the volcano, but on 26 October it was active for 30 minutes of the hour that it was visible. On 31 October, for 1.5 hours, "lava" was reported streaming down the N side of the cone; this may have been a mud flow.

Information Contacts: P. Sventek, USAF, Cold Bay.
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12/1975 (NSEB 01:03) Ash eruptions, lava emission, and orange glow

10 December, 0100-0800: black ash and numerous sporadic orange mud/lava bursts. 18 December, 1300: white steam. 19 December, 1000: grey smoke. 23 December, 1000: white steam; fresh snow on N slope was darkened from the ashfall. 23 December, 1900: 10-second orange glow. 27 December, 1000: white steam; snow was white except for ash on N slope. 28 December, 0815: Tephra ejection like "a blowtorch" visible (in daylight) for 30 seconds; 1300: grey smoke. 30 December, 1755-1810: energetically emitted surges of glowing red-hot ejecta. In contrast to the sporadic 10 December activity, this emission was of a continuous pulsing nature and surges rose at least 150 m above the summit. This was the most energetic activity observed during the last several months. For the next five hours Pavlof was visible but quiet.

Information Contacts: P. Sventek, USAF, Cold Bay.
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01/1976 (NSEB 01:04) Intermittent steam and ash emissions

3-4 January: intermittent steam, grey smoke, and black ash. 5 January: black ash. 11-12 January: steam. At 2130 on 11 January a pilot reported the volcano erupting red-hot mud/lava up to 300 meters above the cone. 17 January: grey smoke. 22 January: steam. 24-25 January: grey smoke and steam. 29-30 January: constant steam. 31 January: very intermittent steam.

Information Contacts: P. Sventek, USAF, Cold Bay.
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02/1976 (NSEB 01:05) Ash eruptions and lava flows during 21-24 February

At approximately 1400 on 20 February, Pavlof was seen to eject ash clouds at about 3-minute intervals. The ash clouds moved S and dissipated into a layer near the 3,000 m level. After sunset, lava emissions became visible, but were not as energetic as those observed on 31 December.

At 2230 22 February, a USAF pilot flying at 12.5 km reported that lava was visible trailing as a rivulet down the entire NW flank. The volcano continuously emitted lava during the 45-minute pilot observation. On 23 February at 1530 a pilot reported that the activity was basically the same as on the 22nd. On 24 February at 1115 another pilot reported that the lava activity appeared to have ceased, but that strong winds were driving ash, smoke and steam down the S side of the volcano.

Information Contacts: P. Sventek, USAF, Cold Bay.
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03/1976 (NSEB 01:06) Activity remains low in March

Activity during March remained low. 3 March, 1200-1400: steaming continuously. 10 March, 1800: inactive; snow on the W flank was white. 12 March, 1400-1600: steaming quietly; 1730 snow umblemished on all sides of cone visible on fly-by. 19 March, 1600: steaming; snow umblemished on all sides of cone visible on fly-by. 22 March, 1200: steaming, W flank umblemished. 23 March, 1900: steaming weakly. 25 March, 1730: several radial ash sprays visible on N flank. 28 March, 1500-1700: inactive, with ash still visible on N flank.

Information Contacts: P. Sventek, USAF, Cold Bay.
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04/1976 (NSEB 01:07) Steam-and-ash emissions; ashfall seen on flanks

6 April, 1118: pilot reported ash extensively covering entire expanse of Pavlof's SE flank. Black smoke and intermittent steam were observed. 14 April, 0900-1900: steaming intermittently; 2 ash sprays visible on NW flank. 15 April, 0600-0700; 25 April 2300; and 27 April 1200-1900: steam emissions. 29 April, 1500: a pilot reported the volcano steaming. The entire E flank was reported to be ash-covered and very black. 30 April, 1200-1900: Although difficult to differentiate between ash and exposed rock (when viewed from Cold Bay, 60 km to the W) there appeared to be ash over the upper 100 m of the cone and along several radial areas along the near (SW) flank. Pavlof apparently produced extensive ash during the last few days of the month.

Information Contacts: P. Sventek, USAF, Cold Bay.
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05/1976 (NSEB 01:08) Ash emissions in mid-May

7 May, 1200: all flanks of volcano snow-covered. 14 May, 1500: dark ash visible on cone. 16 May, 2100: dark ash and steam emission visible. 20 May: upper 100 m of cone irregularly darkened, apparently from ash. Steam issuing from cone. At 2000, a thin layer of ash at the 3,000-m level was carried S for at least 25 km. At 2045, light grey material was ejected a few hundred meters. 21 May, 0900-0930: steaming. 31 May, 1200-1500: quiet. No longer possible to distinguish (at distance) between new ash darkening snow and dark bedrock exposed by melting snow.

Information Contacts: P. Sventek, USAF, Cold Bay.
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06/1976 (NSEB 01:09) Steam-and-ash emissions continue; ashfall on cone

2 June, 1450: pilot reported volcano steaming, extensive ash deposits visible on top and E flank of cone. 3 June, 1200-1800: volcano quiet, cone darkened by ash, or exposed rock due to melted snow. 4 June, 0900-2100: steamed continuously; occasionally ejected a light tan ash that settled into a thin layer at the 2500-m level and moved NE up the Alaska Peninsula. 5 June, 1500-2200: no activity noted. 6 June 1810-1830: no activity noted.

10 June, 2100: black smoke and ash emitted. Flanks extensively darkened by ash. 11 June, 1500: pilot reported volcano steaming. 12 June, 0900-2100: no activity apparent. 15 June, 0600-0700, 2200: steaming constantly. 19 June, 1630: steaming and emitting grey smoke. 26 June, 1400-2100: vertical steam column reached 300-500 m above cone. 27 June, 1200-1500: intermittent steam and ash emissions formed a thin layer stretching NE at the 2500-m level. 28 June, 1300-2200: ash layer extended NE at the 2,500-m level.

Information Contacts: P. Sventek, USAF, Cold Bay.
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07/1976 (NSEB 01:10) Ash on N slope; heavy steaming

4 July, 0600-2200: black ash noted on the N slope. 15 July, 2000-2300: heavy steam blown down the W slope. 18 July, 1600-2300: heavy steam emitted. 23 July, 2100-2200: no activity.

Information Contacts: R. Dean, USAF, Cold Bay.
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08/1976 (NSEB 01:11) Light steam plume seen on one day in August

31 July, 1730-2130: no activity. 3 August, 2200-2232: plume of light steam. 12 August, 1845-1900: no activity. 22 August, 1010-23 August, 1807: no activity.

Information Contacts: R. Dean, USAF, Cold Bay.
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10/1976 (NSEB 01:13) Ash covering upper slopes and the cone

10 September, 1520-1523: "smoke" emission with some intermixed ash. Ash deposits were noted on the SE slope. 22 September, 0745-1200: no activity. Lower slopes were snow-covered, the upper slopes were "dark," and the cone was black. 28 September, 0750-0843: a steady 150-m steam plume was observed. The cone was ash-covered, but snow blanketed the rest of the mountain.

Information Contacts: R. Dean, USAF, Cold Bay.
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11/1976 (NSEB 01:14) Continued steam-and-ash emissions

7 October, 1852: no activity. Ash covered the top 100 m of the cone. 9 October, 0930-1110: heavy steam emission was visible on a rare windless day. The cone was covered with ash. 28 October, 1430: a steady "smoke" plume and occasional small ash clouds issued from the vent.

6 November, 0330-0500: an eruption was reported by fishermen working in the Bering Sea off Cold Bay. 17 November, 1240: "smoking." 18 November, 1510, 1715: heavy "smoke" rose about 200 m above the vent. 19 November, 0915: steam and ash emission. Ashfall had darkened the cone. 1530: steam emission.

Information Contacts: R. Dean, USAF, Cold Bay.
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01/1977 (NSEB 02:01) Decreased seismicity; small steam emissions

Seismic activity at Pavlof, characterized by [50-1,000] events/day August-November 1976, had declined to 10-15 events/day during a 2-day period in mid-December. During periods of high seismic activity, individual events frequently blended together, producing an effect similar, but not identical, to harmonic tremor (one frequency dominant). Approximately one earthquake/week (probably tectonic in origin) is locatable.

Due to poor weather conditions, visual observations of Pavlof were impossible during January. When visited on 21 December, Pavlof was emitting very small amounts of steam.

Information Contacts: J. Davies, LDGO; R. Dean, USAF, Cold Bay.
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03/1977 (NSEB 02:03) Some steaming and ash near the summit

10 February, 1010-1640: no activity. Entire volcano covered with snow. 12 February, 1105-1355: steaming lightly. Part of cone covered with ash. 22 February, 0917-1625: no activity. Entire volcano covered with snow. 23 February, 0935-1710: no activity. 13 March, 1525: no activity. 16 March, 1530: overflight in private aircraft piloted by Capt. Young (USAF); steam was issuing from about 20 small vents in an ash-covered area approximately 50 m in diameter, l0 m below the base of the cone on the W slope. An older 30-m-diameter crater, partially filled with snow, was about 20 m below the base of the cone on the N slope.

Information Contacts: R. Dean, USAF, Cold Bay.
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04/1977 (NSEB 02:04) Ashfall darkens snow near the summit on 22 March

22 March, 1915: light "smoke" plume. Ash darkened the top 100 m of the cone; 2305: steaming.

Information Contacts: R. Dean, USAF, Cold Bay.
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07/1980 (SEAN 05:07) Steam and a little ash

Pavlof was emitting steam when viewed by J. Davies on 3 July. A few days later, according to second-hand reports, ash was present in the steam column.

Information Contacts: J. Davies and S. McNutt, LDGO.
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11/1980 (SEAN 05:11) Lava fountaining and ash emission; possible lava flow

An eruption from Pavlof 11-12 November ejected large lava fountains and ash clouds that reached 11 km altitude, and may have produced lava flows.

A seismic station [8.5 km SE] of Pavlof registered a 2.5-minute burst of low-amplitude harmonic tremor beginning 5 November at 1351. Emission of steam, ash, and some blocks from a vent high on the NE flank started 8 November at 1047 and lasted about 5 minutes, without accompanying seismicity. A second burst of low-amplitude tremor occurred between 0536 and 0541 on 9 November.

In contrast to the pattern observed before eruptions in 1973, 1974, 1975, and 1976, virtually no additional seismic activity was recorded until a group of 7 low-frequency volcanic earthquakes occurred at about 2300 on 10 November. After an explosion event appeared on seismic records at 0243 on 11 November, 10 more low-frequency volcanic earthquakes were recorded between 0300 and 0400. Continuous harmonic tremor, of fairly low amplitude, began at 0608, but amplitude intensified around 0900.

Reeve Aleutian Airways pilot Everett Skinner saw rocks up to 1 m in diameter rising 10-30 m at 1315 on the 11th. An observer in Cold Bay, 60 km to the W, noted an increase in activity about 1600. Skinner returned to the vicinity between 1630 and 1700, reporting lava fountaining from the summit, a black cloud hugging the upper N flank, and an eruption column reaching an estimated 6 km altitude. Between 1800 and 2000, various witnesses reported lava fountaining to a maximum height of 300 m, and incandescent material moving down the N flank. A satellite image returned at 1958 shows a nearly circular plume, 15 km in diameter, N of the volcano. Activity was visible through the night from Cold Bay and the Sand Point area (50-65 km to the ENE).

The next morning, at 0946, a satellite image revealed a plume 160 km long and almost as wide spreading N of Pavlof. Spectral analysis and weather balloon data indicated that the plume reached 8-9 km above sea level. Pilot reports on 12 November placed the top of the eruption cloud at 9 km at 1000, 6 km at 1100, and 11 km at 1400. The eruption clouds were described as varying from ash-rich to ash-poor. A helicopter crew from KENI television, Anchorage, videotaped pulses and bursts of lava fountaining, rising 150-300 m between 1600 and 1700. The fountains emerged from a pre-existing vent high on the NE flank, the only vent confirmed active during the eruption.

Very high-amplitude harmonic tremor accompanied the eruption, reaching its strongest levels between 2000 on 11 November and 0700 on 12 November. Tremor ceased at 1835 on the 12th, when many B-type earthquakes began to be recorded.

By the morning of 13 November, the eruption had ended. Several hundred B-type events per day were recorded 14-15 November. Renewed high-amplitude tremor began 15 November at 1306, lasting until 1711. B-type earthquakes continued 16-19 November, but fewer than 100/day were recorded.

Information Contacts: S. McNutt and J. Davies, LDGO; A. Till, USGS, Anchorage; J. Kienle, Univ. of Alaska; G. Roberts, Cold Bay Weather Station; Cmdr. J. Hair, Marine Environmental Branch, Juneau.
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09/1981 (SEAN 06:09) Ash clouds; lava flow; seismicity

NOAA weather satellite images revealed an eruption plume emerging from Pavlof at 1030 on 25 September. On the image at 1415, when weather clouds next permitted a clear view of the area, both Pavlof and Shishaldin (about 150 km to the SW) were emitting plumes. At 1545, data from infrared imagery indicated that the temperature at the top of Pavlof's cloud was -55°C, corresponding to an altitude of about 9 km. This cloud drifted nearly due E and was still visible at 1945 when imagery showed a new plume originating from Pavlof. By 2215, the new plume had reached 9-10.5 km altitude and feeding from Pavlof appeared to be continuing. By 0415 the next morning, the bulk of this plume had drifted SE and appeared to be largely disconnected from its source, although faint traces of plume may have extended back to Pavlof.

Fishermen in Pavlof Bay reported that activity continued through the night, dropping nearly 4 cm of ash on one boat. An ash sample from one of the boats was sent to the USGS in Anchorage. No certain activity could be distinguished on the satellite image returned at 0615, but there were unconfirmed reports of a renewed eruption by about 0700 and by 0930 the imagery again showed plumes from both Pavlof and Shishaldin. From infrared imagery, a temperature of -28°C was determined for the top of Pavlof's plume, indicating that its altitude was approximately 7.5 km. A Reeve Aleutian Airways pilot flying near Pavlof at 1000 observed a black eruption column and estimated the altitude of its top at roughly 6-7 km. He also reported incandescent material on the W flank. A faint plume extended ESE and was still connected to Pavlof on the satellite image at 1415. No eruption clouds have been observed on the imagery since then, and there have been no reports from pilots of renewed activity.

A visit to the volcano 2-3 October by Egill Hauksson and Lazlo Skinta revealed that lava had been extruded from a vent about 100 m below the summit and had flowed down the NNW flank to about the 600 m level. The lava covered an area of roughly 3 km2, and was 6-7 m thick at the thickest portion of the flow front, which was not advancing. A sample of the lava was sent to the Lamont-Doherty Geological Observatory. No ashfall thicknesses could be determined because of redistribution by very strong winds.

A Lamont-Doherty seismic monitoring station [8.5] km SE of the summit recorded occasional periods of harmonic tremor and an increase in the size of B-type events beginning about 2 weeks before the eruption. However, a few days before the eruption began both the number and size of events decreased; only five discrete shocks were recorded between 1500 on 22 September and 1500 on the 23rd, and only two during the next 24 hours, as compared to an average background level of 15-25/day. On 25 September, the day Pavlof's eruption was first observed on satellite imagery, the seismographs recorded a few more discrete events and intermittent, very low-amplitude harmonic tremor. Between 2000 on 25 September and 0300 on 26 September tremor amplitude increased gradually, and by about 0330 tremor was saturating the instruments. The strongest tremor was recorded between 0500 and 0900, then amplitudes began to decrease. However, tremor remained strong and continuous until 1220 on 27 September, when it declined to several-minute bursts, between which discrete events could be observed. About 100 discrete events and lower amplitude bursts of tremor were recorded during the 24-hour period ending at 1500 on 28 September. As of 5 October, B-type events and bursts of harmonic tremor were continuing.

Both the 1980 and the 1981 eruptions occurred from vents high on the N flank, but it was not certain whether these were the same vents.

Information Contacts: T. Miller and J. Riehle, USGS, Anchorage; S. McNutt and E. Hauksson, LDGO; W. Younker, NOAA/NESS, Anchorage.
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10/1983 (SEAN 08:10) Large eruption column; tremor

Strong tremor started to appear on local seismic records on 14 November at about 1500 and by 1800 was saturating the instruments. The mayor of Sand Point, about 90 km E of Pavlof, saw glow over the volcano at 2330 that night. At 1220 the next day, an airline pilot reported an eruption column rising to about 5.5 km altitude through weather clouds that covered the summit and obscured the vent area. Twenty minutes later, the column had reached 7.5 km altitude. Tephra emission was continuing at 1300. The plume blew S and SE, and spread to about 50 km width, 50 km S of the volcano. Aircraft were diverted from the area. Tremor continued to saturate the seismic instruments through the afternoon.

Information Contacts: T. Miller, USGS, Anchorage; S. McNutt, LDGO.
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11/1983 (SEAN 08:11) Ash emission; vapor plume; volcanic tremor

On 19 November a small vapor cloud rose approximately 100 m above the vent. Bad weather prevented observations until 26 November when Pavlof was visible until mid-afternoon from Cold Bay. During the morning, a vapor plume containing a little ash rose to 4.5 km altitude. At intervals of approximately 30 minutes, puffs of dark ash were emitted. The intervals became shorter, and by 1500 ash emission was nearly continuous.

Through October and early November, a Lamont-Doherty seismic monitoring station near the volcano recorded background levels of 0-40 (usually 0-30) small low-frequency events per day. A 30-minute burst of volcanic tremor began at 2000 on 4 November, and a 6-minute burst at 1757 on 9 November. Between 1430 on 11 November and 1100 on 13 November, 15 explosions were recorded. Several 1-2 minute bursts of tremor occurred between 1700 and 1900, when continuous tremor started. Its amplitude gradually increased, and tremor began to saturate the seismograph at 1100 on 14 November. Tremor was strongest between midnight and 1200 on 15 November, and continued to saturate the seismograph until 2100 on 15 November when its amplitude began to decrease. Tremor remained continuous but at low amplitude between 1300 on 16 November and 1200 on 18 November. Intermittent low-amplitude tremor and numerous low-frequency (B-type) events recorded after 1200 on 18 November were continuing on 21 November.

An increase in seismic activity had also been recorded in mid-July. Seismicity remained at background levels until 11 July. During the 24-hours beginning at 1500 on the 11th, 6 explosions were recorded at a Lamont-Doherty seismic monitoring station near the volcano. The number of recorded events increased to 55 for the same period on 12-13 July, and to 150 on 13-14 and 14-15 July, then decreased to 120 on the 15-16th, 38 on the 16-17th, and 19 on the 17-18th, returning to back-ground after 1500 on 18 July. During the period of increased seismicity, approximately half of the recorded events were explosions and half low-frequency events.

At 1549 on 15 July, a thermal infrared image from the NOAA 7 polar orbiting satellite showed a bright spot over Pavlof and an elongate plume extending approximately 150 km to the E. This plume was distinctly colder (at higher altitude) than the layer of low clouds that covered the area. No activity was visible on other NOAA 7 images returned approximately every 12 hours 11-18 July.

Information Contacts: S. McNutt, LDGO; T. Miller and M. E. Yount, USGS, Anchorage; M. Matson, NOAA/NESDIS.
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12/1983 (SEAN 08:12) Brief ash emission episodes

Activity continued through December. At 1400 on 15 December, an airline pilot observed a burst of ash from the volcano, producing a plume that drifted NW. Brief periods of ash emission separated by longer quiescent periods were continuing as of 28 December. These short eruptions produced plumes that dissipated after a few hours.

Information Contacts: M. E. Yount and T. Miller, USGS, Anchorage.
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01/1984 (SEAN 09:01) Plumes on satellite imagery; harmonic tremor

Six explosions were recorded between 1600 and 2000 on 15 December by Lamont-Doherty's 5-station seismic net 4.5-10 km from the volcano. One station, about [8.5] km from Pavlof, detected bursts of harmonic tremor 17 December, 1100-18 December, 0330; 18 December, 0530-0615 and 1040-1110; 20 December, 2200-2245; and 21 December, 2035-2048. Seismicity then decreased to the background level of several tens of events per day and remained at that level as of 26 January.

Eruption plumes were observed on three images returned 15-17 December from the NOAA 8 polar orbiting satellite. The images at 2101 on the 15th and 1031 on the 17th showed well-defined, relatively dense plumes extending 225 km E and 400 km NE from Pavlof above the weather cloud layer. A diffuse plume was observed on the image at 2018 on 18 December. No volcanic plumes were observed on other images 15-21 December, but heavy weather clouds obscured the area. There have been no eyewitness reports of eruptive activity since airline pilots last reported eruption clouds from Pavlof at 1400 on 15 December.

Information Contacts: S. McNutt, LDGO; M. E. Yount, USGS, Anchorage; M. Matson and W. Gould, NOAA/NESDIS.
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03/1984 (SEAN 09:03) Vapor plume to 6 km altitude

At 1225 on 16 March, the pilot of Air Pacific flight S27 observed a white vapor plume rising to 6 km altitude from the volcano and drifting NW. There had been no eyewitness reports of activity at Pavlof since 15 December 1983 (8:12). After an increase on 17-21 December, seismicity decreased to the background level of several tens of events per day and remained at that level as of 2 April.

Information Contacts: M. E. Yount, USGS, Anchorage; S. McNutt, LDGO.
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03/1986 (SEAN 11:03) Ash cloud to 4 km after 10 days of increasing seismicity

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.

Information Contacts: M.E. Yount, USGS Anchorage; J. Taber, Lamont-Doherty Geological Observatory (LDGO).
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04/1986 (SEAN 11:04) Strong tremor accompanied large 18 April plume

No other reports of activity had been received as of early May [but see 11:05], and no information was available about changes that might have occurred to the active crater.

John Taber provided the following information from seismic stations operated by LDGO. "The number of volcanic events increased from a slightly above normal 20 events on 6 April, to 370 events on 11 April and 750 events on 13 April. The rate of seismicity then stayed relatively constant until the main eruption on 18 April. Continuous tremor began at around 1440 and intensified around 1610, when it was visible at stations 100 km away. The strong tremor continued until 1800 then gradually subsided, ending around 2100. The number and duration of volcanic events dropped abruptly after the tremor ended and continued to decrease until background levels were reached by 26 April."

Information Contacts: J. Taber, LDGO.
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05/1986 (SEAN 11:05) Strombolian activity feeds lava flow; seismicity increases

Airplane pilots reported occasional ash emission through early June. Seismicity had decreased to background levels by 26 April but began to increase again in late May and remained vigorous as of mid-June. On 14-15 June, T. Miller observed Strombolian activity feeding a lava flow from a new vent on the E side of the cone.

J. Reeder provided additional observations of the 16-18 April eruption clouds and reports of continuing minor ash emission. On 16 April at 1117, Reeve Aleutian Airways Captain Edward Livingston noted a white steam plume rising to 4.6 km altitude over Pavlof. About noon the next day, MarkAir Captain Ray Wells reported a dark gray plume over Pavlof that rose to 4.9 km altitude and drifted SW over the Pacific Ocean. On 18 April at about 1130, Reeve Aleutian Captain Lee Goch saw a plume at 3 km altitude that was again drifting over the Pacific Ocean. At 1743, a jetliner crew reported to FAA Flight Control that a plume at 15.2 km altitude was drifting NE.

Weather prevented further observations of the volcano until 6 May, when Goch saw a white steam plume, containing some minor swirls and streaks of gray ash, that reached 2.9 km altitude. The plume drifted NW for 1.5 km, but traces of ash could be detected several kilometers further downwind. A minor ash deposit was visible on the S flank of the volcano. At about noon on 10 May, Reeve Aleutian Flight Engineer George Wooliver observed ash on the N and NW flanks of Pavlof and the SW upper flank of Pavlof Sister, about 4.5 km NE. Pavlof was steaming weakly, emitting a white plume that rose no more than 100 m above the summit.

The USGS received reports from several airplane pilots of renewed activity on 30 May. At 1135, MarkAir and Reeve Aleutian pilots observed an eruption cloud rising to 4.5-5 km and drifting to the west. At 1523, an ash cloud reached about 3.5 km altitude and extended NE over Pavlof Bay. At 1604, the crew of another airliner reported "heavy smoke" that rose to about 6 km altitude and drifted NE. At 1723, white steam was being emitted to <3 km altitude.

John Reeder reports that on 4 June at about 1230, Goch and MarkAir Captain Clint Schoenleber observed a white plume with no visible ash that rose to 4.9 km and drifted N. On 9 June at 1200, Captain Livingston and co-pilot Don Munson saw a gray steam and ash plume drifting 40 km to the NE. Reeder noted that Livingston's 9 June photograph suggested that a pyroclastic flow had just moved down the ESE side of the volcano and that previous pyroclastic flows had advanced down the same flank. Goch's 6 May photograph and other observations suggested to Reeder that April eruptive activity had been confined to N and NE parts of the summit [see below], depositing tephra on the NE, N, and NW sides of the volcano. Goch observed only minor steaming on 10 June.

John Taber reported that seismicity began a gradual increase about 23 May, reached high levels by 28 May, remained vigorous through 15 June, then declined slightly.

During fieldwork near Pavlof 14-15 June, T. Miller observed vigorous Strombolian activity from a new upper E flank vent ~150 m below the summit. Spatter rose 200-250 m above the vent, feeding an E flank lava flow that was ~100 m wide and reached ~1,000 m elevation [see also 11:6]. The activity produced a small ash-poor plume fed at 5-10-second intervals. Adjacent to the new vent, the old crater was emitting steam and had enlarged somewhat since 1983.

While flying past the volcano on 16 June, James Dickson observed a 600-m ash and steam plume that was drifting toward the N. Reddish-brown ash fell from the plume.

Information Contacts: J. Reeder, ADGGS; T. Miller and M.E. Yount, USGS Anchorage; J. Taber, LDGO.
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06/1986 (SEAN 11:06) Strombolian activity feeds lava flow; strong seismicity

USGS personnel observed Strombolian activity from a new vent E of and ~100 m below the summit during fieldwork in the area 10 June-1 July. Activity was similar on each of seven occasions when the volcano was clearly visible. Spatter from the vent fell on the upper E flank, feeding a flow [see 11:4] that had reached ~1,100 m altitude by 15 June and had advanced to ~600 m altitude two weeks later. On 29 June, the flow was ~100 m wide at 750 m altitude. Some mudflow activity (2-3 lobes) was associated with the [spatter-fed] flow. Occasional moderate ash emission occurred but the largest ash columns rose only several hundred meters above the vent. On the NNE side of the summit, the vent that had been active for the past 15 years had enlarged, probably during the April eruption, but was only steaming in June. A flow fed by spatter from the old vent, probably in April, was snow-covered [see 11:7]. Thick April ashfalls were sampled NW of the volcano, and large April mudflows and significant flooding were evident.

When John Reeder flew past Pavlof on 8 July at 1500, ash ejection fed a plume that reached about 3900 m altitude and drifted approximately 15 km WSW. Flows were seen on the SE and N sides, and black ash covered the summit area.

Seismicity declined slightly 17 June, but was still strong as of 4 July. No harmonic tremor was recorded. Seismicity was stronger on GMT days 28 June and 1 July than other days between 17 June and 4 July, but USGS personnel did not observe significant fluctuations in eruptive activity.

Information Contacts: T. Miller, USGS Anchorage; J. Taber, LDGO; J. Reeder, ADGGS.
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07/1986 (SEAN 11:07) Continued Strombolian activity and vigorous seismicity

Eruptive activity accompanied by strong seismicity continued through early August. Poor weather usually obscured the volcano, but seismicity remained high with only slight day-to-day variations. A thin ash plume was visible during the late evening of 18 July and reached ~5.5 km altitude the next day. Little activity was evident on 20 July, but several explosions were heard 23 July. No changes in seismicity could be correlated with these observations.

Seismicity increased substantially on 31 July at 1845, and an airline pilot reported explosions an hour later. Pulses of seismicity that varied in amplitude from 5-6 mm to about 40 mm saturated instruments for about 20 hours, and were recorded by stations as far as 60 km from the volcano. Seismic activity declined somewhat on 2 August, remaining vigorous but detected only on the instrument 7.5 km from the summit. As of 5 August, discrete high-amplitude volcanic events averaging 30-40 seconds long continued to be recorded.

When visited by geologists on 7 August, snowfields at 800 m altitude about 4 km N of the summit were covered by 2.5-7.5 cm of pea-sized to fist-sized tephra. At a location 10-12 km WNW of the summit, 15 cm of ash had fallen since the previous visit 2 years earlier. Some ash was clearly fresh, as it was visible on top of snowfields in nearby ravines, but geologists were unable to sample or measure the thickness of ash deposits on the snow. Several booming explosions were heard during ½ hour at this site, and several more explosions were heard later that day from S of the summit. Airline pilots continued to report emission of vapor and ash through early August (table 1).

Table 1. Summary of reports describing activity at Pavlof, 14 June-15 September 1986, compiled by John Reeder. Observers (initials in brackets): FWS; Jean Shaul, Marcia Brown, and Clayton Brown, Cold Bay; Reeve Aleutian Airways; MarkAir; Peninsula Airways; Sand Point Air; NOAA aircraft; Clint Schoenleber and Jerry Chisum, Markair; John Reeder; Mike Whelan; Lee Goch, Don Munson, George Wooliver, Harold Black, Andy Livingston, and Edward Livingston, Reeve Aleutian Airways; Mary Maurer; Adrian Brown; Robert Adams; Steve Hakala; Guy Morgan; Chris Dan; John Sarnis; Mike and Peggy Blenden; Jeff Wilson; Jeff Backlund; Federal Aviation Administration; Wayne Russell; British sailors on the Ashley St. Mary; Theresa Dubber and Robert Senimore, FAA, Cold Bay; Steve Hakala, Sand Point.

    Date     Time    Activity Reported [Observers]

    14 Jun   1710    New vent on Se summit ejected blocks and magma to 35 m,
                       lava flow to ESE, ash plume towards SW.
    15 Jun   1200-   Incandescent blocks and lava fountains 30-60 m from new
              2000     SE vent, lava flow on SE flank, ash and steam from four
                       vents on SE summit, 3,300 m ash-and-steam plume 30 km
                       to NNW.
    16 Jun   1211    3,600-m ash plume 40 km to N.
    17 Jun   1325    3,300-m steam and light ash plume 8 km to NNE.
    18 Jun   1142-   3,000-4,600-m ash-and-steam plumes extending 80-120 km to
              1619     the NE and NNE.
    19 Jun           3,500-m steam plume with no detectable ash to NE.
    21 Jun   1330    4,200-m steam plume with streaks of ash 40 km to SW.
    22 Jun   1127    3,000-m steam plume with blue/brown haze 40 km to SW.
    23 Jun   1200    3,000-m light ash plume drifting E.
    24 Jun   1712    Wind-blown ash to 300 m above ground surface 9 km S of
                       summit.
    27 Jun   1045    3,300-m dark ash plume extending 40 km to SW.
    08 Jul   1500    3,950-m steam-and-ash plume 40 km to WSW.
    06-12 Jul        Explosions were heard and felt at canoe Bay, 45 km ENE of
                       Pavlof by U.S. Fish and Wildlife personnel working in
                       the area.
    13 Jul   1145    3,600-m ash plume 30 km to ENE.
    13-19 Jul        Almost continuous rumblings, 4-5 second intervals,
                       earthquakes and ground vibrations strong enough to
                       rattle windows, shake shelf items, and prevent sleep;
                       some ashfall at USF&W camp, 45 km ENE.
    16 Jul   1300    Extensive ash deposits in Cathedral Peaks region, 17.6 km
                       W of summit, Pavlof and Pavlof's Sister covered with
                       ash, SE vent ejected steam with dark vertical plume of
                       ash at 3-5-minute intervals, N vent quiet.
    17 Jul   1315    3,600-m ash plume to 30 km ENE.
    18 Jul           SE summit vent eruptions at several-minute intervals
                       caused pulsating plume and incandescent lava flowing
                       down SE flank that did not reach the ocean.
    19 Jul   1320    3,300-m ash plume extending 24 km to ENE.
    20 Jul           Several vents observed at SE summit, none with active
                       lava flows, one ejecting rocks and lava bombs tens of
                       meters high, three separate SE-flank flows, one still
                       steaming; none had entered the ocean.
    22 Jul   1200    3,600-m dark ash plume extending to ENE.
    29 Jul   1200    3,600-m steam-and-ash plume toward WSW.
    20-30 Jul        Very little rumbling and ground vibrations at USF&W camp.
    31 Jul   1217    Small puffs of ash and steam to 150 m from SE vent.
             1836    Active 600-m-long lava flow down E slope from SE vent
                       located 120 m below summit.
    01-03 Aug        Explosions heard from 55 km NE of Pavlof, 3-5-minute
                       intervals, heavy ash detected in streams and rivers in
                       Aghileen Pinnacles and Cathedral Valley areas, 17.5 to
                       W and NW of Pavlof.
    02 Aug   1240    3,000-m steam-and-ash plume extending to NE.
    05 Aug           4,500-m steam-and-ash pluem to E.
    08 Aug   1300    Dark ash clouds from N summit vent to 30-50 m at several-
                       minute intervals, SE near-summit vents emitting traces
                       of steam.
    13 Aug   evening Summit lava fountaining. [ASM]
    14 Aug   midday  Large white steam plume. [GW]
    18 Aug   0850    Dark ash to 3,600 m, drifting 80 km SE. [PA]
             1047    Steam-and-ash plume to 4,000 m, drifting 55 km ESE. [SP]
    20 Aug   1556    Ash plume to 3,600 m, drifting SE. [NOAA]
                     Sound heard just before emission of large ash puff. [JS]
    21 Aug   0900    Plume alternating steam and ash at 3-minute intervals to
                       3,000 m; visible for 15 minutes, then obscured by
                       weather. [TD & RS]
    22 Aug   1152    Ash plume to 3,600 m, drifting at least 16 km ESE. [RA]
             1241    Occasional steam plumes. [RA]
    05 Sep           300-m dark nearly vertical column, drifting slightly NE.
                       [SH]
    10 Sep   1155    Ash and steam to 3,000 m, drifting NE for 8 km. [HB & AL]
    12 Sep   1100    Minor steam emission from 100-m region near summit. [JC]
    15 Sep   1430    White steam from old N vent did not rise above summit.
                       [MB & CB]

The active spatter-fed flow on the E flank and an inactive flow probably associated with April explosions were composed of individual tephra fragments, and moved downslope as debris flows. Airline pilots reported that the flow front on the E flank remained at about 600 m altitude as of 31 July.

On 8 August personnel aboard a Reeve Aleutian Airways plane reported that they sighted what may be a large bulge on the W side of the volcano about 2/3 of the way upslope. It appeared to have a diameter of about 300 m.

Information Contacts: T. Miller, USGS Anchorage; J. Taber, LDGO; J. Reeder, ADGGS.
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08/1986 (SEAN 11:08) Strombolian activity and ash emission ends

Airplane pilots frequently reported vapor and ash rising to 3.5-4 km altitude from Pavlof through 22 August (table 1). Sailors observed lava fountaining during the evening of 13 August, but airplane pilots generally do not fly close enough to the volcano to observe Strombolian explosions and most flights are in daylight when eruptive glow is unlikely to be evident. No pilot reports of activity were received between 22 August and 8 September, although there was some clear weather during that period. On 8 September, vigorous vapor emission was observed from Sand Point, 90 km E. During an overflight on 12 September, only minor steaming was observed.

Information Contacts: T. Miller, USGS Anchorage; J. Taber, LDGO; J. Reeder, ADGGS.
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10/1986 (SEAN 11:10) Ash emission and lava fountaining

Airplane pilots reported that ash emissions and lava fountaining resumed in early November. No activity had been reported since mid-September. Observers named below are Reeve Aleutian Airways pilots; other reports are from the FAA.

The start time of the eruption is not known, but on 30 October a clear view of the snow-covered volcano showed that it remained inactive, without vapor emissions. No other observations of Pavlof are known until 1100 on 6 November when activity was first reported. At 1130 Lee Goch and Don Munson observed a 2750 m-high plume of dark ash and white vapor drifting more than 40 km to the NE. An incandescent lava fountain (about 10 m high) emerged from a vent just SE of the summit. Two fresh-looking, gray-black, linear, flow-like features, 120 m and 50 m wide, extended about 1/3 of the way down the SE and NW flanks. Neither feature emitted any steam, and both were free of snow. The rest of the volcano remained covered with white snow. At 2045 a pilot reported that lava fountaining was continuing at the SE summit vent.

On 10 November at 1135 James Fredenhagen and Ken Gendron observed bubbling incandescent lava and a 10-m-high, 6-m-wide fountain in a crater on the upper SE flank, ~120 m below the summit. A vertical ash and steam plume rose to ~300 m above the vent.

Fredenhagen did not see incandescent lava during a 12 November flight at 1140, but vapor and ash were released from the SE summit-area vent and drifted eastward. Earlier that day he passed through a haze layer at 1,500-1,800 m altitude during his approach to Sand Point, 90 km to the east. A fissure-like feature extending from the summit to at least halfway down the SE flank appeared to be emitting black ash and depositing it nearby. No incandescent material or vapor was visible in the fissure.

On [13] November Edward Livingston reported that grayish-black ash deposits covered the entire SE side of the volcano. At 1200 on 17 November a 3,600-3,900-m-high plume issued from the vent below the SE crater. Black ash pulses occurred at 5-8-minute intervals and winds blew the ash SE in a 70-km-long cloud. By afternoon (around 1400-1630) the FAA reported that the plume had grown to 4,500 m height.

On 18 November the FAA reported that the semi-continuous plume was 4200 m high between 1000 and 1030. At 1512 an image from the NOAA 9 polar orbiting satellite recorded a weak plume extending 50-60 km N. The FAA has warned pilots in the area not to go below 3750 m and to avoid the vicinity of the volcano.

Information Contacts: J. Reeder, ADGGS; M.E. Yount, USGS Anchorage.
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11/1986 (SEAN 11:11) Eruption continues; lava flow reaches ocean

The eruption continued into December with steam plumes from the N-summit vent and ash emissions from a SE flank vent 200-300 m below the summit (table 2). Steam and ash emissions were continuing at 1840 on 10 December when pilots saw an orange-red glow in a cloud above the summit. They did not observe any material moving through the clouds. The next day at 1324, airplane pilots reported that 3-4 lava flows had moved down the SSE flank and that one had reached the Pacific Ocean at Pavlof Bay, 10 km from the summit [but see 11:12]; a 300-m-high steam column rose where the flow entered the water.

Table 2. Summary of reports describing activity at Pavlof, 17 November-16 December 1986, collected by John Reeder. Observers (initials in brackets): Edward Livingston, Lee Goch, James Fredenhagen, Don Munson, and Harold Black (Reeve Aleutian Airways); Clayton Brown (Alaska Fish and Game); Jerry Chisum (MarkAir); Marsha Brown (FAA, Cold Bay); unnamed observers from Reeve Aleutian Airways (RA), MarkAir (MA), Peninsula Airways (PA), and a private plane (Cessna).

    Date     Time    Activity Reported [Observers]

    17 Nov   1006-   Constant steaming from N vent; black ash pulsed (every 5-
              1600     8 minutes at 1200) from SE vent, feeding a plume to
                       3,600-4,200 m altitude that drifted 25-30 km S; ash
                       covered the entire SE flank. [CB, EL, JC, MA]
    18 Nov   1200-   Steam emission from N vent; ash emission from SE vent,
              1652     drifting SW. [JC, JF, CB]

    19 Nov   1030    Ash plumes to 3,000-3,300 m altitude emitted at 5-minute
                       intervals from SE vent. [EL]
             1600    No eruption apparent despite clear visibility. [RA]
    21 Nov   1522    Small amounts of ash formed 1.5-km-long plume. [PA]
    23 Nov   1545    Plume rose to 3,000 m altitude; drifted NE. [Cessna]
    26 Nov   1130    Dark gray ash pume rose 90-150 m above summit from SE
                       vent and drifted 8 km SE. [LG & DM]
    02 Dec   1045    Ash column from SE vent rose to 3,000 m, drifted E. [MB]
             1359    60-m-high brown ash cloud from SE vent. [JC & MB]
    10 Dec   1840    Pilots at 3,600 m altitude observed an orange-red glow in
                       a thin cloud horizon at 2,500 m altitude (just above
                       the summit). [LG & DM]
    11 Dec   1324    SE-vent ash plume reached 4,500-5,400 m altitude and
                       drifted WSW for 32 km; three to four narrow lava flows
                       had moved down the SSE flank. [HB & DM]
    16 Dec   1140    60-m-high steam plume from the SE vent; no other activity
                       was observed. [LG]

Seismicity in early November reached more than 150 events/day, all apparently explosion shocks. Individual events had similar durations but variable amplitudes. Only a few hours of tremor were recorded.

Information Contacts: J. Reeder, ADGGS; J. Taber, LDGO.
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12/1986 (SEAN 11:12) Strong tremor accompanied early December lava flows; steaming from summit and flank fissures

John Taber reported that from 1 to 6 December, 140-200 volcanic events/day were recorded; 30-60 were explosions with a distinct airwave arrival. On 8 and 9 December the number of individual events gradually decreased until replaced by low-amplitude harmonic tremor. Tremor amplitude gradually increased until the record suddenly became saturated on 9 December at 2310, remaining saturated until 13 December at about 1400. Tremor continued to decrease until discrete events were again visible by about 0100 the next morning.

Airplane pilots had observed steam and ash emissions from summit area vents in early December, saw glow on 10 December, and new SSE flank lava flows the next day (SEAN 11:11). Closer examination by Harold Black, James Fredenhagen, and Donald Munson (Reeve Aleutian Airways) revealed that the narrow lava flow that appeared to have reached the ocean on 11 December had in fact stopped in a stream bed about 600 m short of Pavlof Bay. The flow was black and emitting no steam when Fredenhagen observed it on 20 December.

On 18 December, Fredenhagen observed that a fissure, emitting steam plumes to as much as 60 m height at intervals of 6-15 m, extended from the SE summit vent, active in the November eruption (SEAN 11:10-11), to about halfway down the SE flank. There it split at about a 90° angle, with both segments continuing for another 300 m downslope; steam issued from both segments for at least 150 m. On 23 December, he also observed small puffs of steam emerging from the old NE summit vent. During clear weather on 27-28 December, Marcia Brown (FAA, Cold Bay) saw steam issuing from the NE summit vent and moving about 300 m down the NE flank. On the 29th, the plume was blowing horizontally about 300 m to the E. The volcano was snow-covered with no detectable ash deposits. Poor weather prevented further observations.

Information Contacts: J. Reeder, ADGGS; J. Taber, LDGO.
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01/1987 (SEAN 12:01) Steam emission from two near-summit vents

Satellite images at 0514 and 1041 on 9 January show plumes drifting 150 and 100 km ESE from Pavlof. Between 17 January and 11 February, airplane crewmembers and observers at Cold Bay reported steaming from two near-summit vents (table 3).

Table 3. Summary of observations describing activity at Pavlof, 17 January-11 February 1987, collected by John Reeder.Observers (initials in brackets): Marsha Brown and Theresa Dubber, FAA, Cold Bay; Lee Goch, Don Munson, Janice Reeve Ogle, and James Fredenhagen, Reeve Aleutian Airways; Guy Morgan, Peninsula Airways.

    Date     Time    Activity Reported [Observers]

    17 Jan   1546    Continuous steam emission from an upper NE-flank vent.
                       [MB]
    22 Jan   0953    Continuous steam emission from an upper NE-flank vent.
                       [MB]
    23 Jan           Steam emission on SE flank. [TD]
    26 Jan   1011    Steam emission from the NE vent. [MB]
    31 Jan   1400    250-m steam plume from a upper SE-flank vent drifted
                       about 5.5 km NW. [LG, DM, JO]
    02 Feb   1300    150-m-high steam column from the SE vent. [LG & JF]
    03 Feb   1400    150-m-high steam column from the NE vent drifted NE. [MB]
    05 Feb   1000    Ash plume from summit drifted about 20 km WSW; several
                       black flows (lava or debris) had extended at least
                       600 m down the NW slope. [MB]
    11 Feb   1500    30-m steam plume from the NE vent; the summit was coverd
                       with fresh snow. [MB]

Information Contacts: J. Reeder, ADGGS; Steve Shivers, USGS Anchorage.
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03/1987 (SEAN 12:03) Fresh ash on summit

At 1105 on 22 March Marsha Brown (FAA, Cold Bay) saw a steam plume emerging from the upper NE flank vent and drifting NE. The summit appeared to be covered with a thick layer of fresh ash. Minor steam emission occurred at other times during the month.

Information Contacts: J. Reeder, ADGGS.
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05/1987 (SEAN 12:05) Ash emission; flow; seismic amplitudes increase

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.

Information Contacts: J. Reeder, ADGGS; J. Taber, LDGO; T. Miller, USGS Anchorage.
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06/1987 (SEAN 12:06) Incandescent flow; summit glow; ash emission continues

The eruption . . . continued in June. On 7 June at 1601 pilot Richard Williams (Peninsula Airways) saw an incandescent flow (probably lava) that had descended to 1,200 m elevation on the NNE flank. Ash was rising to 600 m above the volcano from the NE near-summit vent, drifting S. Forty minutes later the ash plume reached 760 m. Residents of Nelson Lagoon, 80 km NE, reported a bright red glow from the summit throughout the night. On 9 June at 1153 a pilot reported only steam emission from the NE near-summit vent.

The following day at 1419 the U.S. Coast Guard reported that gray ash was being emitted from the active vent and 7 hours later pilot Harold Wilson (Peninsula Airways) saw (and photographed) gray then black-gray ash emission. A plume rose to 760 m above the NE vent and drifted 2 km W. The black-gray ash emission was intermittent and lasted for about 15 minutes. Only minor steam emission was reported on 11 June but dark ash emission had resumed on 12 June at 1602 when Chuck Nickerson and George Wooliver (Reeve Aleutian Airways) passed the volcano.

A lava or debris flow seen from 25 km away during the afternoon of 2 June was reported in 12:5. That evening from 2130 to 2200 Marsha Brown (FAA, Cold Bay) saw an incandescent flow move down the NNE flank. Richard Williams observed the incandescent flow from Nelson Lagoon (80 km NE) and estimated that it extended almost 1/3 of the way down the volcano.

Information Contacts: J. Reeder, ADGGS.
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07/1987 (SEAN 12:07) Activity decreases; steam and ash emission

Activity appeared to decrease during July. A 460-m-high steam plume was sighted on 6 July by R. Williams (Peninsula Airways) from Nelson Lagoon, and a small amount of what appeared to be ash on the summit and N flank was reported on 11 July by Marsha Brown (FAA, Cold Bay). The weather was generally poor for the rest of the month but numerous pilots reported that no eruptive activity was occurring on 26 and 28 July.

Information Contacts: J. Reeder, ADGGS.
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08/1987 (SEAN 12:08) Continued ash emission

Eruptive activity was continuing in late August. At about 1130 on 29 August, pilot Chuck Nickerson (Reeve Aleutian Airways) observed a thick dark ash horizon at 1200-1800 m altitude extending 50 km SSW from Pavlof. The ash appeared to originate from a SE flank vent. Below that vent, white steam was rising along a 100 m, narrow, flow-like, feature or crack. At 1550 pilots Andy Livingston and James Fredenhagen (Reeve Aleutian Airways) observed from Sand Point (88 km E), a diffuse ash layer at 1200-1800 m altitude that extended at least 15 km SW. Ben and Lorie Kirker reported that no ash reached King Cove, about 40 km SW. On 30 August at 1400 Theresa Dubber (FAA) saw no ash being emitted during a clear view of the volcano from Cold Bay.

Information Contacts: J. Reeder, ADGGS.
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09/1987 (SEAN 12:09) New ash deposit

Marsha Brown (FAA, Cold Bay) observed "fairly extensive" black ash deposits on Pavlof's flanks during a flight on 4 September. Both the NE and SE summit-area vents were emitting steam. The ash deposits had not been visible when the volcano was observed on 30 August. On 20 September the volcano was inactive and fresh snow covered the flanks.

Information Contacts: J. Reeder, ADGGS.
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10/1987 (SEAN 12:10) Ash-rich explosions; blocks and spatter form flow

Activity increased 17 October when ash-rich explosions from the NW summit vent occurred every 30 seconds to several minutes. Ash plumes, reported through 9 November attained a maximum altitude of 4500-5800 m on 30 October (table 4). Plumes stretched E as much as 200 km and tephra fell at Canoe Bay, 45 km ENE, on 19 October. Blocks and spatter ejected to 30 m from the near-summit vent formed a short spatter flow. Night glow from the summit was visible on several evenings in mid-October. Incandescent rocks and spatter were reportedly continuing in early November. Ash deposits were last reported on 4 September (SEAN 12:09).

Table 4. Reports of activity at Pavlof, 16 October-27 November 1987, compiled by John Reeder and M.E. Yount from the following observers (initials in brackets): Steve Hakala (Canoe Bay); Dan Coy (Sand Point Air); Scotty Gibbens and John Sarvis (USFWS); Deedee and Tom O'Malia (Cold Bay); Marsha Brown, Theresa Dubber, Chuck Taylor, Jim Yakal (FAA Flight Service, Cold Bay); Steve Shivers (USGS, Anchorage); James Gibson, George Wooliver, Chuck Nickerson, Gary Lintner, Harding (Reeve Aleutian Airways); Guy Morgan, Bryan Carricaburu, Doug Ruberg (Peninsula Airways); Harold Johnson Sr. (Nelson Lagoon); Will Gould (NOAA/NESDIS); John Sarvis (USFWS); Sand Point Air pilot; James Fredenhagen (Reeve Aleutian Airways);Coast Guard pilot. Unattributed reports were compiled by M.E. Yount.

    Date     Time    Activity Reported [Observers]

    16 Oct   1646    Thin gaseous plume on NOAA 9 satellite image.
    17 Oct   1130    Loud explosions (continued through the night);
                       incandescent flow feature on NE flank. [SH]
    18 Oct   0800    Incandescent material flowed 800 m from vent. [SH]
             0950    Ash to 3,200 m altitude, drifting 16 km NW; lava spatter
                       to 30 m above vent. [DC]
        afternoon    Rain, very black with ash near volcano. [SG]
        1200-1600    Nearly continuous black ash emission to 3,050 m altitude,
                       then clouds obscure volcano. [DO & TO]
             1830    Volcano still very active. [SH]
    19 Oct   1101    Plume on NOAA 10 satellite image drifting 200 km E.
                       [SS & WG]
             1138    Ash rising to 3,000 m altitude, drifting ESE. [JG & GW]
          morning    Coarse black tephra fell at Canoe Bay. [SH]
             1210    Ash to 4,250 m altitude, drifting E at least 90 km; ash
                       pulses every 30 seconds and rocks (some incandescent)
                       ejected to 180 m above the vent, landing about 800 m
                       down the flank. [BC]
             1300    Plume to over 3,350 m, extended at least 100 km E. [GM]
        afternoon    Black, steaming, flow feature on NE flank, melted snow;
                       incandescent material ejected. [BC]
             1600    Nearly continuous ash emission formed a plume, drifted
                       SE. [FAA]
             1700    Mushroom-shaped plume rose to 1,220 m above summit. [FAA]
             2000    Ejection of incandescent material. [JY & CT]
          evening    Incandescent glow from summit. [HJ]
    25 Oct           Red glow from vent; ash to 900 m above vent, drifting NE;
                       incandescent rocks ejected. [MB]
    26 Oct   1828    Ash to 460 m above volcano. [CN, GL, H]
             1907    Incandescent material ejected 30 m; ash to 300 m above
                       volcano, drifting E. [JS]
             1940    Ash to 4,600 m altitude, drifting SSE; incandescent
                       material ejected. [DR]
    27 Oct  morn.    Ash to 60 m above volcano, drifting NE. [SH]
    29 Oct   1608    Ash to 30 m above volcano, drifting ESE. [CT]
             1742    Plume to 4,600 m altitude, driftin ESE; ash fell from
                       plume 1 km from vent. [CT]
    30 Oct           Ash plumes reached 4,500-5,800 m altitude.
    01 Nov           Volcano obscured.
    05 Nov   0921    Dark ash rose about 250 m above summit, drifting NE. [JS]
    06 Nov   1657    Dark ash was blown down SE flank, then drifted 20-25 km
                       WNW. [JF].
    07 Nov   1238    Dark ash rose 150-300 m above summit. [TD]
             1450    Ash plume rose to 3.6 km altitude; some ash drifted
                       20-25 km WNW. [JF]
             1600    Dark ash to 3.6 km altitude, drifted 35 km NW. [JF]
    09 Nov   0900    Ash plume rose to a maximum of 3.6 km altitude. [TD]
             1000    Ash blown down S flank. [MB]
             1210    No eruptive activity. [CG]
    10-16 Nov        Poor visibility.
    16 Nov   0931    White steam rose to summit. [MB]
    27 Nov   0934    Steam rose 60 m above the summit. [JY]

Information Contacts: J. Reeder, ADGGS; M.E. Yount, USGS Anchorage.
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11/1987 (SEAN 12:11) Dark ash plumes from near-summit vent

The volcano had apparently been quiet for several weeks after new flank ash deposits were seen 4 September; it was inactive and covered with fresh snow on 20 September. A NOAA 9 satellite image on 30 September at 0525 showed a plume extending about 20 km S from Pavlof. Weather clouds obscured later activity.

Eruptions began again in mid-October and continued in November (table 4). Dark ash was steadily emitted to 250 m above the summit on the morning of 5 November. The next day wind blew ash down the SE flank for 120 m; the plume trailed about 30 km SE. Continued ash emission was observed on 6, 7, and 9 November. Plumes reached to 3.6 km altitude (~1 km above the summit) and drifted a maximum of 35 km from the volcano. During observations on 16 and 27 November only white steam was emitted.

Information Contacts: J. Reeder, ADGGS; M. Matson, NOAA/NESDIS.
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02/1988 (SEAN 13:02) Weak steam and ash emission

During observations that were limited by poor weather December-February, only weak steam and ash emission was reported (table 5).

Table 5. Reports of activity at Pavlof, 9 January-2 March 1988, compiled by John Reeder from the following observers (initials in brackets): Theresa Dubber, James Yakal, and Marsha Brown (FAA, Cold Bay); Guy Morgan (Peninsula Airways).

    Date     Time    Activity Reported [Observers]

    09 Jan   1530    150-m steam plume with some ash from NE summit vent. [TD]
    28 Feb   0845    Black plume several hundred meters high from NE summit
                       vent; 15 minutes later, a steam-and-ash plume was
                       rising 600 m and drifting a short distance E. [JY & MB]
    02 Mar   1200    Gray steam-and-ash plume rising 300-450 m from NE summit
                       vent and drifting E. Only white steam was visible by
                       1630 and there were no emissions by 1819. The volcano
                       was snow-covered except for snow-free areas around the
                       summit and NE vents. [GM & MB]

Information Contacts: J. Reeder, ADGGS.
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07/1988 (SEAN 13:07) Fresh ash on upper flanks

At 1800 on 20 July, Marsha Brown observed light steam emission from Pavlof's NE summit vent. The volcano's upper flanks appeared black with fresh ash, with more on the N than on the S slope. Six days earlier, at 1519 on 14 July, this ash had not yet been emitted and no steam was evident.

Information Contacts: J. Reeder, ADGGS.
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08/1988 (SEAN 13:08) New ash deposit on summit

At 1000 on 13 August, M. Brown (FAA) observed fairly extensive ash deposits on Pavlof's flanks. From Cold Bay ~20% of the visible edifice appeared dark gray and the remainder was black. The ash had been deposited since the volcano was last observed on 7 August. A wispy dark plume rose <300 m from the NE summit vent. The next day at 0740, Peninsula Airways pilot Gary Joseph reported that the volcano was covered with white snow and no ash or steam was being emitted.

Information Contacts: J. Reeder, ADGGS.
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08/1996 (BGVN 21:08) Vigorous seismicity and intermittent eruptive activity

Residents of the Alaska Peninsula first noticed small glowing plumes from Pavlof on 15 September. During the following week, seismicity was vigorous and eruptions were intermittent. Poor weather in the first week inhibited visual observations.

On the morning of 16 September, AVO received a report from residents of Cold Bay about an unusual plume emanating from the N flank of the volcano. Local pilots reported glow near the summit and large "car-sized" fragments being ejected from the summit vent. Satellite imagery showed a hot spot in the vicinity of the cone. Seismic data from stations on and near the volcano suggested a low-level eruption. By that afternoon eruptive activity had declined somewhat, although seismicity indicative of eruption remained sporadic.

Persistent seismic activity suggested that an episodic, low-level eruption continued during 17-22 September. The summit hot spot was not seen on images obtained on the early morning of 17 September. Several periods of increased seismicity from the afternoon of 17 September to the morning of 18 September suggested that the eruption was episodic in character with ejection of ash and bombs up to 300 m above the summit of the cone.

Intermittent low-level ash clouds were detected on satellite imagery on 18 September, although imagery from that afternoon to the next morning showed no ash cloud. Pilot reports on 18 September confirmed that there was no significant ash venting above the cloud tops at 3,000 m altitude. Satellite imagery from the afternoon of 19 September to the morning of 20 September also detected no ash cloud.

From the afternoon of 20 September to the afternoon of 22 September several periods of increased seismicity were observed and intermittent low-level ash clouds were detected on satellite imagery. On 23 September local observers confirmed Strombolian fountaining 150-200 m above the summit. There were no major explosions.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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09/1996 (BGVN 21:09) Increasing seismicity corresponds to stronger eruptive activity

Residents of the Alaska Peninsula observed small glowing plumes from Pavlof on 15 September. During the next week, seismicity was vigorous and eruptions were intermittent (BGVN 21:08). At 1328 on 24 September seismicity began to increase, suggesting stronger eruptive activity. This increased level of seismicity persisted through the first half of October. Visual observations and satellite imagery verified that increased seismicity correlated with eruptions of ash and bombs up to 1,200 m above the summit.

On 26 September satellite imagery showed a small steam-and-ash plume extending ~45 km SE. A pilot subsequently reported a steam plume to an estimated altitude of 3,700 m. AVO staff doing airborne observations during 27-30 September reported low-level fountaining and occasional small explosions of incandescent material in the summit crater. The small explosions produced sporadic steam-and-ash plumes to 610 m above the vent. The largest plume drifted S for ~110 km and appeared faintly on satellite images. Incandescent spatter was deposited on the NW summit slope or moved down a deep gully on the NW side of the volcano.

During 4-11 October lava fountaining from two vents continued to heights of a few hundred meters above the summit. Incandescent spatter-fed lava flows moved down the steep, snow- and ice-covered slope, widening at the base and extending NW. Occasional water-rich slurries of ash and mud descended the N flank. Diffuse plumes of steam, gas, and ash rose to as high as 6 km above sea level and drifted 160 km downwind. On 15 October eruptive activity increased and seismicity reached the highest levels yet observed. Satellite imagery and pilot reports showed ongoing lava fountaining from two vents near the summit. Pilot reports indicated that diffuse ash layers reached 7,300-m altitude and extended perhaps as far as 50 km SE.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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10/1996 (BGVN 21:10) Eruptions that began on 15 September persist during November

The current episode of eruptive activity, which began on 15 September (BGVN 21:08-21:09), persisted during 15 October-29 November. Seismicity, satellite imagery, and visual observations indicated ongoing lava fountaining from two vents near the summit. Two lava flows advanced down the flanks of the volcano. Intermittent bursts of lava to heights of <300 m above the crater continued. These bursts formed diffuse ash layers that pilots reported to be typically below an altitude of 6,100 m.

From 2200 on 18 October intense seismicity was recorded, but it ceased the next morning (19 October). This increased seismic activity indicated that the eruption strengthened considerably. On 22 October, seismicity showed a short-lived burst at about 1300, and at 1330 pilots reported an ash plume rising to an altitude of 7,600 m. At 1450 satellite observations showed a narrow ash cloud 90 km long drifting NE up the peninsula. During 26 October-1 November, intermittent narrow plumes, extending up to several hundred kilometers downwind, were visible on satellite images. Light ashfall was observed at Nelson Lagoon on the morning of 28 October.

On 4 November, seismicity significantly increased at 0800 and declined several hours later. This seismic increase was followed by an increase in eruptive activity. Satellite imagery showed a plume extending 250 km to the NE. Pilots reported the cloud top at 5,800-m altitude. During 9-15 November, diffuse ash layers occasionally reached altitudes of 7,000-7,300 m. Observers in Sand Point, Nelson Lagoon, and Cold Bay reported a steam-and-ash plume, rising from low on the N flank, to altitudes as high as the plume issuing from the summit vents. Although the source of the plume was not directly observed, the presence of ash suggested the possibility of a new vent low on the N flank. Two half-hour periods of intense seismicity, beginning at 1130 on 22 November and at 0430 on 23 November, resulted in steam-and-ash emissions. The plumes reached altitudes of 9,100 m and extended downwind. A small ash plume from the 23 November event was detected moving several hundred kilometers to the NW. However, no ashfall was reported from local communities.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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12/1996 (BGVN 21:12) Intermittent eruptions from 15 September through [3] January

The current episode of eruptive activity, which began on 15 September (BGVN 21:08-21:10), persisted [through 3 January]. On 2 December, infrared video taken by the Alaska State Troopers confirmed that the E summit vent was more active than the W vent. The source of intense steaming low on the N flank, which had been intermittently visible to aerial and ground observers for several weeks, was not a new flank vent, but simply a site where lava was in contact with ice or meltwater. Meltwater channels extended down to the low pass between Pavlof and Pavlof Sister, then to the NW into the Cathedral River drainage. On the early morning of 4 December, seismic activity abruptly declined to about background, the lowest level after the onset of the eruption. The substantial decrease in seismicity implied that eruptive activity probably abated.

After a few days of quiescence, seismicity sharply increased on 10 December, accompanying intense long eruption pulses. Steam plumes reached an altitude of 8,500 m, and ash plumes rose to 7,700 m. On 11 December, pilots reported a steam plume at 8,700 m altitude and an ash cloud at 5,200 m. Satellite imagery indicated that a thick 20-km-wide plume extended as far as 160 km SE and a thinner, more diffuse part of the plume then turned E, extending 105 km. Seismicity declined on 12 December. However, lava fountaining from the summit vents and intermittent bursts of steam and ash to below 6,100 m continued; two lava flows were still active on the N flank. Seismicity decreased to about background levels on the evening of 13 December, but observers in Cold Bay, 60 km SW, reported lava fountaining prior to the seismic decrease. There was no steam or ash visible on the morning of 15 December.

Seismic activity began to build again around midnight on 25 December. In the early morning of 27 December seismicity quickly and steadily increased, reaching the highest level to date in this eruption episode. Early morning satellite images and pilot observations showed a summit hot spot, an active lava flow, and an ash plume extending tens of kilometers downwind (NW). That afternoon observers reported discontinuous bursts of ash and steam rising several hundred meters above the summit. Ground observers in Nelson Lagoon, 80 km NE, reported vigorous fire fountaining and a lava flow visible at night. On 28 December, visual reports in the afternoon from pilots and ground observers in Cold Bay indicated plumes reaching altitudes of 3,700-4,900 m and extending for up to 32 km WNW.

Seismicity started to decline in the afternoon, and the volcano was quiet during the night. On the morning of 29 December, pilots and ground observers in Cold Bay reported no eruptive activity. On 2 January, a pilot report indicated steam and ash drifting S from the summit. On the morning of 3 January, an observer in Cold Bay spotted a small burst of ash rising just above the summit. The eruptive pause continued during the week of 11-17 January with very low levels of seismicity.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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01/1997 (BGVN 22:01) Pause in eruptive activity, but continued small intermittent steam plumes

The latest eruption began on 15 September and continued intermittently through 3 January, when a small ash burst was observed just above the summit (BGVN 21:08-21:12). On the morning of 24 January a pilot reported weak emission of steam and possibly minor ash rising to ~4.2 km altitude, mixing with a cloud layer, and drifting SE. Very low levels of seismicity were recorded from early January through late February.

A ground observer who glimpsed the volcano on 4 February reported that the summit vent area, which had been snow-covered the previous week, was now bare. On 6 February the same observer saw a small steam plume rising from the vent area to the level of the summit. U.S. National Weather Service observers in Cold Bay (60 km SW) reported another small steam plume up to 300 m above the summit vents during 15-16 February. A similar steam plume to 600-900 m above the vents was reported by pilots on 19 February.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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09/1997 (BGVN 22:09) Steam plume in June; ash covering ice near summit seen in July

The latest eruption began on 15 September 1996 and continued intermittently through 3 January 1997, when a small ash burst rose just above the summit (BGVN 21:08-21:12). On the morning of 24 January a pilot reported steam and possibly minor ash emissions. A ground observer reported on 4 February that the summit vent area, which had been snow-covered the previous week, was bare. Small steam plumes, varying in height up to 900 m above the summit, were reported on 6, 15-16, and 19 February (BGVN 22:01).

Observers in Cold Bay (60 km SW) reported snow-free conditions at the summit during 8-21 March. Satellite images at the time did not show any thermal anomalies. By 4 April seismicity had returned to a near-background level, after fourteen weeks of eruptive quiescence, and the alert status was lowered from Yellow to Green. A slight increase in the level of seismicity began on 1 June and continued through the 6th. On the afternoon of 2 June U.S. National Weather Service observers in Cold Bay saw a steam plume rising and increasing in vigor to 900 m above the summit. This event prompted an increase in the alert status to Code Yellow. Satellite images recorded a moderate thermal anomaly on 3 June. Seismic activity declined during 7-13 June. Although fluctuations continued, the level was near background, so on 13 June the status returned to Code Green. Clouds obscured the volcano during 4-13 June.

During fieldwork on 8 July, Alaska Volcano Observatory (AVO) scientists had a clear aerial view of the volcano. They circled the volcano in an upward spiral, observing that most of the glacial ice was still intact. At a distance, the Pavlof cone appeared black, which had led to the belief that the glacial ice had been melted by volcanic heat. Closer inspection showed that the dark coloring was due to ash covering the snow; bright blue glacial ice could be seen in crevasses. The adjacent peak of Pavlof Sister showed an ash concentration gradient; higher concentrations made it appear darker towards its base. The only parts where the ice seemed to be missing corresponded to a rust-red region where lava had recently flowed. Approaching the summit of Pavlof, the scientists observed sulfur deposits within and around the perimeter of the jagged crater walls. The crater was filled in with debris and tephra; only remnant steam remained around the crater, and no active degassing could be seen around the buried vent.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.
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08/2007 (BGVN 32:08) Thermal and seismic data presage August 2007 eruption

The Alaska Volcano Observatory (AVO) reported that Pavlof (figure 1) erupted on 15 August 2007 for the first time since 15 September 1996 (BGVN 22:09 and Waythomas, Miller, and Mangan, 2006) . Thermal anomalies and seismic activity just prior to the eruption prompted scientists at AVO to issue a warning. This report covers events reported through 3 October 2007.

Figure 1. Index map showing the location of Pavlof and other Alaska Peninsula volcanoes. Courtesy of AVO and Alaska Division of Geological & Geophysical Surveys.

According to AVO, an abrupt increase in earthquake activity began at Pavlof early on the morning of 14 August 2007. Based on patterns of unrest leading to past eruptions at Pavlof, AVO elevated the alert level and color code to 'Advisory/Yellow.' Observers from the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) in Cold Bay, Alaska, were able to see the volcano on the morning of 14 August and reported no anomalous steaming or other activity; satellite imagery from this morning also showed no obvious signs of surface activity or ash emission.

[AVO detected a strong thermal anomaly at the volcano overnight 14-15 September, and seismic activity continued to increase in both the number of events per hour and duration of individual events. Eyewitnesses aboard a ship reported incandescent blocks tumbling down the ESE flank of the volcano beginning at midnight 14 September (the night of 14-15 September). Satellite data confirmed the presence of lava. Pilot reports indicated that a weak ash plume extended 8 km SW of the summit at a height of ~ 2.6 km. Seismic activity continued at a high level. On 15 August AVO raised the aviation color code from Yellow to Orange and the Alert Level from Advisory to Watch.]

Earthquake intensity continued to increase slowly from 15 to 16 August. Strong signals at a single station SE of the summit suggested local flow activity, probably lahars (or mudflows) on that flank. Satellite images of the volcano overnight and during the morning of 16 August continued to show a strong thermal feature (figure 2). Residents of both Cold Bay and Sand Point, Alaska (105 km and 70 km, respectively, from Pavlof), observed incandescence at the summit during the night.

Figure 2. NOAA Advanced Very High Resolution Radiometer (AVHRR) satellite image showing a strong thermal anomaly at the summit of Pavlof on 16 August 2007 at 0750 local time (1550 UTC). In this image, white represents hot temperatures. Courtesy of the AVO/U.S. Geological Survey (USGS).

Persistent earthquake activity and flow events, probably lahars (mudflows), continued on 17 August 2007. Several discrete explosion earthquakes were also recorded. Though clouds obscured the volcano in most satellite images, one GOES (Geostationary Observational Environmental Satellite) image documented a large thermal feature at the summit, interpreted to be lava at the surface.

Activity at Pavlof continued to increase during 17-24 August 2007, with reports that the steam-and-ash plume sometimes exceeded 3 km altitude. For example, a pilot reported the top of the plume to be 5.5 km in the late afternoon of 23 August, and a plume height of 4 km was estimated using satellite data from 1410 that day. Seismic activity remained elevated, with moderate levels of tremor occurring almost continuously and with occasional bursts of higher amplitude. The average seismic amplitude increased slowly throughout the week of 17-24 August. Many small-to-moderate explosions were recorded in the seismic record, as were events from lahars flowing down the SE flank. [Note: Pilot Jeff Linscott of JL Aviation filmed a lahar front on Pavlof's lower flanks before it hit the ocean on 18 August 2007; the film is available on the AVO website, which is listed in under Information Contacts below.] Satellite data showed strong thermal anomalies at the summit, as well as occasional ash clouds, throughout this week.

An AVO field crew visited Pavlof on 18-19 August to make FLIR (forward looking infrared) thermal observations of the ongoing eruption. These observations confirmed the existence of a new vent ~ 200 m below the summit on the SE flank. The vent, ~ 50 m across, fed a lava flow that, on 18 August, was more than 0.5 km long and ~ 25 m across. The crew also observed a lahar reaching the Pacific coast, incandescent lava, and explosions at the vent that sent 5-m-long blocks flying 50 m through the air. Figure 3 shows the plume from Pavlof on 23 August, and figure 4 shows the plume on 30 August 2007.

Figure 3. An Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite image on 23 August 2007 at 2210 UTC showing Pavlof with a small steam-and-ash plume emitting from the crater on the SE side of the summit. The plume in this image (having a resolution of 15 m/pixel) reached an altitude of ~ 4.0 km based on the plume's temperature. Courtesy of the AVO/USGS.
Figure 4. Pavlof volcano and eruption plume on evening of 30 August at 2120 local time. View is to the S, out of the right side of a PenAir Metro Airline plane en route to Anchorage from Cold Bay; plume height was approximately 5.2-5.5 km. Courtesy of Chris Waythomas and AVO/USGS.

At about 2130 local time on 31 August, NOAA/NWS observers in Cold Bay reported a substantial plume emanating from Pavlof, along with associated lightning. The plume, which rose to an altitude of ~ 6 km, was also visible in images from the Pavlof web camera located in Cold Bay. However, there were no indications in satellite data or ground reports of an ash plume. Seismic activity remained elevated through 31 August.

During 1-19 September 2007 the eruption continued; however, seismicity after 10 September declined markedly from levels recorded earlier. AVO pointed out that typical eruptions at Pavlof were characterized by periods of diminished activity interspersed with periods of renewed eruptive activity. Satellite observations continued to show thermal anomalies even through the clouds, as well as steam plumes up to as high as 6.1 km altitude. Table 6 shows thermal anomalies from the beginning of 2007 through 3 October measured by MODIS satellite infrared detectors and processed by the Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System called MODVOLC. Anomalies measured during 2007 began on 15 August and continued through 11 September, after which none have been reported to present (3 October). Satellite thermal anomalies are frequently masked by cloud cover.

Table 6. MODIS/MODVOLC thermal anomalies measured at Pavlof for 2007 through 3 October. Courtesy of the HIGP Thermal Alerts System.

    Date (2007)      Time      Number of    Satellite
                     (UTC)      Pixels

    01 Jan-14 Aug     --           0           --
    15 Aug           0750          2          Terra
                     1330          2          Aqua
    16 Aug           0839          3          Terra
                     1235          1          Aqua
    18 Aug           2150          1          Terra
    19 Aug           0725          1          Terra
                     1350          2          Aqua
    20 Aug           0810          2          Terra
                     1210          3          Aqua
                     1350          1          Aqua
    23 Aug           2210          1          Terra
                     2220          1          Aqua
    24 Aug           0745          7          Terra
                     1325          5          Aqua
    25 Aug           1230          7          Aqua
    28 Aug           1300          4          Aqua
    29 Aug           0800          4          Terra
    30 Aug           0705          2          Terra
                     0845          4          Terra
                     1250          3          Aqua
    31 Aug           0750          3          Terra
                     1155          2          Aqua
                     1330          3          Aqua
    01 Sep           0830          3          Terra
                     1235          1          Aqua
    02 Sep           0735          1          Terra
                     0915          4          Terra
                     1320          4          Aqua
    04 Sep           2230          2          Terra
    05 Sep           1210          4          Aqua
                     2135          2          Terra
    06 Sep           0715        1 or 2       Terra
                     0850          8          Terra
                     1255          5          Aqua
    07 Sep           0755          4          Terra
                     1200          6          Aqua
                     1335          4          Aqua
    08 Sep           0840          1          Terra
    09 Sep           0745          2          Terra
                     2115          1          Terra
                     2250          1          Terra
                     2300          2          Aqua
    10 Sep           0825          8          Terra
                     1230          2          Aqua
    11 Sep           0910          2          Terra
                     1315          2          Aqua
                     2100          2          Terra
    12 Sep-03 Oct    none (possible cloud cover)

A status report on 3 October 2007 stated that "A pause in eruptive activity at Pavlof continues. Seismicity remains at low levels and has been relatively unchanged since about September 13. No sign of renewed volcanic activity was noted in clear satellite and web camera views today." [By 5 October the alert levels were returned to Green and Normal for aviation after more than three weeks without eruptive activity; the eruption was determined to have ended on 13 September 2007.]

References. Waythomas, C.F., Miller, T.P., and Mangan, M.T., 2006, Preliminary Volcano Hazard Assessment for the Emmons Lake Volcanic Center, Alaska: Anchorage, Alaska, U.S. Geological Survey, Scientific Investigations Report 2006-5248, 33 p., 1 sheet (available online at http://www.avo.alaska.edu/pdfs/SIR2006-5248.pdf ).

Linscott, J., 2007, Film of Pavlof lahar front, 18 August 2007 [on AVO website, URL: http://www.avo.alaska.edu/volcanoes/volcimage.php?volcname=Pavlof ).

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA; Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA; and Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.avo.alaska.edu/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/); Jeff Linscott, JL Aviation Helicopter Service, 8015 NE Airport Way, Portland, OR 97218 USA.
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05/2013 (BGVN 38:05) Eruption in May-June 2013 with lava flows and ash emissions to ~8.5 km a.s.l.

Pavlof, the most active volcano in the Aleutian arc, erupted on 13 May 2013. Before this, it had most recently erupted on 15 August 2007, following an 11-year period of quiescence. The eruption that began in May 2013 continued through June before slowly subsiding to background levels by 8 August. Pavlof generated several ash plumes during the six-week eruption that disrupted aviation, including an 8-km high plume on 24 June. As in past Pavlof eruptions, the recent eruptions fluctuated in intensity. This report briefly discusses earthquake data during 2007-2011 and, in greater detail, the series of eruptions during May and June 2013.

According to Mangan and others (2009), Pavlof has discharged more than 40 recorded eruptions within the previous 200 years, producing mostly basaltic andesite to andesite products. That work, discussed in a separate subsection near the end of this report, also discusses the adjacent 12x19 km Emmons Lake caldera (a chain of nested calderas) on Pavlof's SW flank (figure 5). The Emmons Lake Volcanic Center (ELCV) is used to collectively describe the entire complex, including the nested caldera, intra-caldera stratovolcanoes, and the adjacent stratovolcanoes (including Pavlof) to the NE.

Figure 5. Maps showing both the location of Pavlof on the lower Alaska Peninsula (upper left) and showing more details of the complex, including the elongate Emmons Lake caldera and six stratovolcanoes. The lake occupies but a small volume of the caldera, which is breached to the SE. Taken from Mangan and others (2009).

According to the Alaska Volcano Observatory (AVO), 48 earthquakes were located beneath Pavlof in 2007, the year of the previous eruption. During the following non-eruptive years, AVO reported 9 earthquakes centered at Pavlof in 2008, 7 earthquakes in 2009, 19 in 2010, and 13 in 2011. As of this writing, AVO has not yet published 2012 earthquake data.

Eruption in May 2013. On 13 May 2013, seismicity increased at 0800 and an intense thermal anomaly was observed at the summit in satellite imagery. Several spikes in seismicity occurred between 0900 and 1000. AVO noted that similar patterns of seismicity and elevated surface temperatures in previous cases had signaled the onset of eruptive activity at Pavlof. The Volcanic Alert Level was increased to Watch (the second highest category of four) and the Aviation Color Code was increased to Orange (the second highest category of four).

On 14 May 2013, pilot reports and satellite images indicated a spatter-fed lava flow that had advanced about 0.5 km down the N flank. The advancing lava had also generated debris-laden deposits, presumably from the interaction of hot lava with snow and ice on the flank. According to AVO, a diffuse ash plume drifted about 160 km NE at an altitude of 4.6 km before dissipating. Minor ashfall was reported the evening of 14 May in a mining camp 80 km NE of the volcano. No other nearby communities reported ashfall. Minor steam-and-ash emissions from the summit were visible from Cold Bay (~58 km SW).

During 14-15 May 2013, elevated seismicity persisted. Steam-and-ash clouds observed with a web camera at Cold Bay (55 km W of the volcano) occasionally rose to an altitude of 6.1 km. Residents in Cold Bay observed incandescence from the summit during the night. On 15 May a pilot reported a dark ash cloud drifting ENE at an altitude of 6.1 km.

On 16 May, AVO observed lava fountaining at the summit and a continuous ash, steam, and gas cloud extending 50-100 km downwind at an altitude of about 6.1 km. Satellite images showed persistent elevated surface temperatures at the summit and on the NW flank, consistent with lava fountaining at the summit and the resulting lava flow.

During 18-19 May 2013, reports noted that a narrow plume of steam, ash, and gas occasionally rising up to an altitude of 6.7 km and drifting SE was visible in satellite and pilot images (figures 6 and 7). Pilots noted that lava fountaining and ash emission continued. Overnight, trace amounts of ash fell on the community of Sand Point (88 km E). During the afternoon on 19 May, pilots reported that ash plumes rose to altitudes of 4.6-6.7 km. Trace amounts of ash fell in Nelson Lagoon (78 km NNE) during 19-20 May.

Figure 6. Photograph of Pavlof taken on 18 May 2013 by astronauts aboard the International Space Station. The space station was ~770 km away and S-SE of the volcano when the photograph was taken. The volcanic plume extended SE over the North Pacific Ocean. Residing next to Pavlof is the white, seemingly ash free stratovolcano Pavlof Sister. Courtesy of NASA Earth Observatory with credit for caption and processing to Robert Simmon, (NASA Earth Observatory) and G. M. Gentry (DB Consulting Group at NASA-JSC).
Figure 7. Photo of Pavlof eruption taken by a commercial pilot on 18 May 2013. Plume direction was not identified, but based on the NASA photo taken the same day (figure 6), the plume is drifting SE and the volcano in the foreground is Pavlof Sister (NE of Pavlof). Courtesy of Brandon Wilson (PenAir) and provided by AVO/Alaska Division of Geological & Geophysical Surveys.

News articles (Associated Press, PRNewswire, Alaska Dispatch) stated that during 19-21 May 2013 two regional airlines canceled flights to several remote communities and delayed or re-routed other flights. On 21 May AVO reported that a low-level plume of steam, gas, and ash occasionally rose to an altitude of 6.1 km and drifted NNE. Trace amounts of ash again fell in Nelson Lagoon.

AVO reported that seismic tremor markedly declined around 1100 on 21 May 2013 and was followed through 23 May by the detection of small discrete events, likely indicative of small explosions, by an infrasonic pressure sensor (Chaparral model 2.5 at site PN7). Although cloud cover prevented satellite observations, elevated surface temperatures at the vent were detected. On 22 May a pilot report and photographs indicated weak steam-and-gas emissions containing little to no ash.

The eruption continued at a lower level during 24-26 May. Neither evidence of elevated surface temperatures nor a plume were observed in partly clear satellite images during 24-25 and 27 May. Clouds obscured views on 26 May. The Volcanic Alert Level was lowered to Advisory and the Aviation Color Code was lowered to Yellow on 28 May.

According to AVO, Pavlof emitted ash on 4 June at about 1100, as observed in satellite images and by pilots. Satellite images showed an ash cloud drifting SE, and pilots estimated that the cloud was at an altitude of 5.8 km. Weak seismicity that began at 1057 accompanied the emissions, and then continued. AVO increased the Volcanic Alert Level to Watch and increased the Aviation Color Code to Orange.

AVO reported that ash emissions continued during 5-11 June 2013, accompanied by tremor and explosion signals. Overnight during 4-8 June, satellite images detected elevated surface temperatures near the vent consistent with lava effusion and fountaining. Elevated surface temperatures persisted until 14 June. On 5 and 6 June, an ash plume drifted 40-45 km W and SW at altitudes of 4.3-5.5 km based on pilot estimates. During 8-10 June, an ash plume drifted 20-53 km SE. During 12-14 June, ash emissions were intermittent and minor; ash plumes remained below an altitude of 6.1 km and mostly drifted SE.

During 14-15 June 2013, seismicity decreased. Minor emissions probably ceased, but web-camera views were partially obscured by clouds. On 17 June no plumes were visible in satellite images, and web camera views showed mostly cloudy conditions.

During 17-18 June, tremor amplitude increased slightly, and elevated surface temperatures were again detected in satellite images. A small ash plume rose from the crater. The eruption continued during 19-25 June, with tremor and occasional explosions. Cloud cover prevented web camera views. Elevated surface temperatures continued to be detected during 19-20 and 24 June. A small ash plume from the summit vent was also detected in a satellite image on 19 June, and possibly during 20-22 June.

On 24 June, seismicity increased to the strongest level to date during 2013 and included continuous intense tremor and frequent small explosions likely associated with lava fountaining and ash production. Seismicity remained high on 25 June. Satellite images and pilot observations indicated that a plume drifted W at altitudes as high as 8.2-8.5 km. Satellite images also detected a strong thermal anomaly at the summit. Trace amounts of ash fell in King Cove (48 km SW). According to a news report (Reuters), regional air traffic was again cancelled or re-routed.

According to AVO, seismicity declined during 25-26 June and consisted of intermittent bursts of tremor and occasional small explosions. Satellite images showed a plume containing small amounts of ash drifting NW, and strong thermal anomalies at the summit. Pilot reports on 26 June indicated that plumes rose to altitudes between 6.1-7.6 km during the morning and then to heights just above the summit later that day. Seismicity during 26 June-1 July continued at low levels and consisted primarily of intervals of continuous, low-level tremor. Thermal anomalies at the summit detected in satellite images were strong during 26-29 June and weak during 30 June-1 July.

AVO reported that activity further declined during 1-2 July; tremor and explosions were no longer detected in seismic and pressure sensor data. Satellite images did not detect elevated surface temperatures, volcanic gas, or ash emissions, and there were no visual observations from pilots or from webcam images of any eruptive activity since 26 June. Consequently, AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory.

On 8 August, AVO reported that no lava or ash emissions had been observed at Pavlof since 26 June and the volcano had exhibited gradually declining levels of unrest. Seismicity was at background levels. Thus, AVO lowered the Aviation Color Code to Green and the Volcano Alert Level to Normal.

Mangan and others (2009) discussion. Mangan and others (2009) cite Power and others (2004) as stating that background (non-eruptive) seismicity at Pavlof occurs as infrequent long-period earthquakes at focal depths between 20-40 km. Mangan and others contend that while only a few of these events at most occur annually, they are a stable feature attributed to quasi-steady fluxing of basaltic magma and exsolved CO2 in a deep dike and sill complex. According to the article, the seismic network at Pavlof is poorly situated to detect deep seismicity under the Emmons Lake caldera.

Mangan and others state, "All witnessed [Emmons Lake Volcanic Center] ELVC eruptions have occurred outside the caldera [,specifically] at Pavlof, the most active volcano in the entire arc. Pavlof's slopes are extensively mantled with tephra and pyroclastic debris produced during [its] historical strombolian, vulcanian, and lava fountain events (Miller et al., 1998). Limited precursory seismicity herald Pavlof eruptions (McNutt, 1989) and, to the extent studied, negligible precursory ground deformation (Lu et al., 2003; Z. Lu personal communication 2008). Of the 20 eruptions occurring since the installation of Pavlof's seismic network (1973), 13 eruptions have occurred with less than 24 h of warning. Pavlof is essentially an "open vent" volcano with magma rising aseismically through a thermally well-groomed conduit. High-frequency volcano-tectonic earthquakes, characteristic of magma rise through brittle crust, are virtually absent."

Figure 8 presents Mangan and others (2009) conceptualization of the plumbing beneath the ELVC, which includes Pavlof.

Figure 8. Conceptual cross-section through the Emmons Lake Volcanic Center looking at a vertical plane parallel to the volcanic axis. The drawing shows two distinct plumbing systems drawing from a common magmatic source at more than 20 km depth. Courtesy of Mangan and others (2009).

The other volcano of the ELVC considered to have high likelihood of eruption is Mt. Hague (Waythomas and others, 2006). That study also presents a set of hazard maps for the complex.

References. Mangan, M., Miller, T., Waythomas, C., Trusdell, F., Calvert, A., and Layer, P., 2009, Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc, Earth and Planetary Science Letters, Vol. 287, pp. 363-372.

Waythomas, CF; Miller, TP, and Mangan, MT, 2006, Preliminary Volcano Hazard Assessment for the Emmons Lake Volcanic Center, Alaska, U.S. Geological Survey Scientific Investigations Report 2006-5248 (URL: http://pubs.usgs.gov/sir/2006/5248/).

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Associated Press (URL: http://www.ap.org/); PRNewswire (URL: http://www.prnewswire.com); Alaska Dispatch (URL: http://www.alaskadispatch.com/); and Reuters (URL: http://www.reuters.com/).
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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.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2014 Nov 12 2014 Nov 18 (continuing) Confirmed 1 Historical Observations
2014 May 31 2014 Jun 23 (continuing) Confirmed 3 Historical Observations NE flank
2013 May 13 2013 Jun 26 Confirmed 3 Historical Observations Summit
2007 Aug 15 2007 Sep 13 Confirmed 2 Historical Observations
[ 2001 Jun 5 ± 4 days ] [ Unknown ] Uncertain 1  
1996 Sep 11 1997 Jan 3 (?) Confirmed 2 Historical Observations
1990 Mar 5 1990 Mar 5 Confirmed 2 Historical Observations
1986 Apr 16 1988 Aug 13 Confirmed 3 Historical Observations NNE & SE summit vents, NE & SE flanks
1983 Nov 11 1983 Dec 18 Confirmed 3 Historical Observations Upper NNE flank
1983 Jul 11 1983 Jul 18 Confirmed 2 Historical Observations
[ 1982 Jul 15 ± 45 days ] [ Unknown ] Uncertain 1  
1981 Sep 25 1981 Sep 27 Confirmed 3 Historical Observations Upper NNE flank (100 m below summit)
1981 Mar 30 (in or before) 1981 May 28 Confirmed 1 Historical Observations
1980 Nov 8 1980 Nov 13 Confirmed 3 Historical Observations Upper NNE flank
1980 Jul 6 ± 1 days Unknown Confirmed 1 Historical Observations
1975 Sep 13 1977 Mar (in or after) Confirmed 2 Historical Observations
1974 Sep 1 (in or before) 1975 Jan 13 Confirmed 3 Historical Observations
1974 Mar 12 1974 Mar 24 (?) Confirmed 1 Historical Observations
1973 Nov 12 1973 Nov 13 Confirmed 2 Historical Observations Upper NE flank
1966 Mar 15 Unknown Confirmed 2 Historical Observations Upper NE or NNE flank
1960 (?) 1963 Jun (?) Confirmed 2 Historical Observations Upper NE or NNE flank
1958 May 17 1958 Aug 28 Confirmed 2 Historical Observations Upper NNE flank
1953 Nov 25 1954 Aug Confirmed 1 Historical Observations Upper NE or NNE flank
1951 Oct 1952 Feb (?) Confirmed 2 Historical Observations Upper NE or NNE flank
1950 Jul 31 1951 May Confirmed 2 Historical Observations Upper NE or NNE flank
1936 1948 May (?) Confirmed 3 Historical Observations
1929 Mar 1931 Aug Confirmed 2 Historical Observations
1924 Jan 17 Unknown Confirmed 2 Historical Observations
1922 Dec 24 1923 Feb 28 ± 60 days Confirmed 2 Historical Observations
1917 Oct Unknown Confirmed 2 Historical Observations
1914 Jul 6 Unknown Confirmed 2 Historical Observations
1906 1911 Dec 7 (?) Confirmed 3 Historical Observations Summit and north flank fissure
1901 Unknown Confirmed 2 Historical Observations
1894 Unknown Confirmed 2 Historical Observations
1892 Unknown Confirmed 2 Historical Observations
1886 Unknown Confirmed 2 Historical Observations
1880 Unknown Confirmed 1 Historical Observations
1866 Mar 14 Unknown Confirmed 2 Historical Observations
[ 1852 ] [ Unknown ] Uncertain 1   Upper north flank
1846 Aug 1846 Aug Confirmed 2 Historical Observations
1845 Aug 12 Unknown Confirmed 2 Historical Observations
1838 Unknown Confirmed 1 Historical Observations
1825 Unknown Confirmed 2 Historical Observations
1817 Unknown Confirmed 2 Historical Observations
1790 Unknown Confirmed 2 Historical Observations
1762 1786 Confirmed 4 Unknown Volcano Uncertain

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.


Synonyms

Paulowsky

Cones

Feature Name Feature Type Elevation Latitude Longitude
Little Pavlof Cone
An ash plume trails to the south in mid-July 1986, 3 months after the start of an eruption of Pavlof that lasted nearly 2 1/2 years. This photo was taken from the west on a fishing boat in Pavlof Bay, with Pavlof Sister to the right. The 1986-88 eruption produced intermittent ashfalls and lava flows from two vents near the summit, one halfway down the SE flank, and another 600 m below the summit on the NE flank. Lava flows traveled to the north, NE, SE, ESE, and SSE, the latter to within 600 m of the Pavlof Bay shoreline.

Photo by Richard Mack, 1986.
The twin volcanoes of Pavlof (left) and Pavlof Sister (right) rise to 2519 m and 2142 m, respectively. This January 20, 1987, view from the SW shows steam clouds rising along the length of a lava flow descending a prominent gully on the SE (right-hand) flank of Pavlof volcano. Recent snowfall covers ashfall that frequently dusted its slopes. This eruption began with explosive activity on April 16, 1986, and continued until August 13, 1988. Lava flows traveled down the north, NE, SE, ESE, and SSE flanks, the latter reaching to within 600 m of Pavlof Bay.

Photo by Jerry Chisum (Mark Air), 1987 (courtesy of John Reeder, Alaska Div. Geology Geophysical Surveys).
An ash plume rises from vents near the summit of Pavlof volcano on June 10, 1987, in this aerial view from the NNE. Intermittent explosive eruptions took place from vents at the summit and flanks of the volcano from April 1986 until August 1988, and lava flows descended the flanks in several direction. One lava flow reached to within 600 m of Pavlof Bay and another descended to the saddle between Pavlof and Pavlof Sister volcano.

Photo by Harold Wilson, 1987 (Peninsula Airways).
The entire upper flanks of Pavlof volcano are darkened by ash in this November 1973 photo taken after a November 12-13 explosive eruption. Small steam plumes rise from the crater on the uppermost NE flank just below the normally snow-covered summit.

Photo by Tom Miller, 1973 (U.S. Geological Survey).
The summits of the twin volcanoes of Pavlof Sister (left) and Pavlof (right) rise to 2142 m and 2519 m, respectively, above a low, roughly 1100-m-high saddle. They are viewed here in 1975 from lowlands to the NW. The somewhat less eroded Pavlof volcano, its slopes darkened by recent ashfalls, has been the source of frequent eruptions in historical time. Little Pavlof, a small satellitic volcano on the right flank of Pavlof, was also constructed along a line of vents trending NE from Emmons Lake caldera.

Photo by Tom Miller, 1975 (U.S. Geological Survey, Alaska Volcano Observatory).
Pavlof volcano, rising above low plains to its NW, is one of Alaska's most active volcanoes. It is part of a NNE-SSW-trending line of volcanoes near the tip of the Alaskan Peninsula. The knob on the middle right horizon is Little Pavlof, a subsidiary peak of Pavlof. The low saddle at the left separates Pavlof from Pavlof Sister, whose lower flanks are seen at the extreme left.

Photo by Steve McNutt, 1979 (University of Alaska, Alaska Volcano Observatory).
Ash surrounds a mall crater on the NE side of the summit in 1942. Pavlof was in a period of almost continuous minor explosive activity from 1936 to 1948. Significant eruptions took place in 1936, July 1937 and 1942. By 1942 eruptions had healed the fissure formed during the 1911 eruption. A lava flow may have been extruded in May 1948.

Photo by U.S. Army Air Force, 1942.
An ash-and-steam plume rises above Pavlof volcano on November 13, 1996, as seen from Nelson Lagoon, about 70 km NE of the volcano. Intermittent small ash and strombolian eruptions began on September 15, 1996. Lava fountains fed a lava flow. The last ash eruption was reported on January 3, 1997. On October 18, 1996 the eruption plumes reached 6.7 km; on November 4, 7.3 km, on November 23, 9.2 km; on December 11, 8.7 km.

Photo by Elgin Cook, 1996 (U.S. Geological Survey, Alaska Volcano Observatory).
A small puff of dark ash rises from the summit crater of Pavlof volcano on May 28, 1960, as the detached plume from an earlier explosion drifts away to the east. Ash blankets the slopes of Pavlof in this view from the north. Mild ash eruptions took place from Pavlof from about 1960 to 1963, especially during July 1962 to June 1963. The sharp-topped peak at the left is snow-covered Pavlof Sister volcano, and Little Pavlof forms the smaller peak to the right of Pavlof.

Photo by Ken Morin, 1960 (courtesy of Bill Rose, Michigan Technological University).
Ash clouds rise above the surface of a pyroclastic flow descending the flanks of Pavlof volcano on the Alaska Peninsula in 1975. Incandescent lava can be seen on the upper cone. Intermittent phreatomagmatic to magmatic eruptions began September 13, 1975 and continued until at least March 1977. Possible lava flows or lahars were reported in October 1975 and December 1976.

Photo by U.S. Geological Survey, 1975.
A steam cloud (bottom center) rises from the toe of a lava flow descending the flank of Pavlof volcano on September 23, 1996. The eruption had begun on September 15 with lava fountains that fed the lava flow.

Photo by Susan Schulmeister, 1996 (U.S. Fish and Wildlife Service).
Pavlof volcano and eruption plume on evening of 30 August at 2120 local time. View is to the S, out of the right side of a PenAir Metro Airline plane en route to Anchorage from Cold Bay; plume height was approximately 5.2-5.5 km. Courtesy of Chris Waythomas and AVO/USGS.

Photo by Chris Waythomas, 2007 (Alaska Volcano Observatory, U.S. Geological Survey).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.

Henning R A, Rosenthal C H, Olds B, Reading E (eds), 1976. Alaska's volcanoes, northern link in the ring of fire. Alaska Geog, 4: 1-88.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Kennedy G C, Waldron H H, 1955. Geology of Pavlof volcano and vicinity Alaska. U S Geol Surv Bull, 1028-A: 1-18.

McNutt S R, 1987. Eruption characteristics and cycles at Pavlof volcano, Alaska, and their relation to regional earthquake activity. J Volc Geotherm Res, 31: 239-267.

McNutt S R, Miller T P, Taber J J, 1991. Geological and seismological evidence of increased explosivity during the 1986 eruptions of Pavlof volcano, Alaska. Bull Volc, 53: 86-98.

Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.

Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.

Roach A L, Benoit J P, Dean K G, McNutt S R, 2001. The combined use of satellite and seismic monitoring during the 1996 eruption of Pavlof volcano, Alaska. Bull Volc, 62: 385-399.

Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.

Waythomas C F, Miller T P, Mangan M T, 2006. Preliminary volcano hazard assessment for the Emmons Lake volcanic center, Alaska. U S Geol Surv, Sci Invest Rpt, 2006-5248: 1-33.

Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.

Volcano Types

Stratovolcano
Pyroclastic cone(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Andesite / Basaltic Andesite
Basalt / Picro-Basalt

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
0
0
0
3,002

Affiliated Databases

Large Eruptions of Pavlof Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.