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Semisopochnoi

Photo of this volcano
  • Country
  • Primary Volcano Type
  • Last Known Eruption
  •  
  • 51.93°N
  • 179.58°E

  • 1221 m
    4006 ft

  • 311060
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number
Most Recent Weekly Report: 2 August-8 August 2023 Citation IconCite this Report

AVO reported that the last time possible explosions were detected at Semisopochnoi’s Mount Young in monitoring data was 25 April and the last ash emission occurred on 5 May. Since then, earthquake activity has been low and steaming from the N crater continued. On 3 August the Volcano Alert Level was lowered to Normal (the lowest level on a four-level scale) and the Aviation Color Code was lowered to Green (the lowest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Most Recent Bulletin Report: December 2022 (BGVN 47:12) Citation IconCite this Report

Intermittent explosions and ash emissions during June-November 2022

Semisopochnoi is the largest subaerial volcano in the western Aleutians. It is 20-km-wide at sea level and contains an 8-km wide caldera. The three-peaked Mount Cerberus was constructed within the caldera during the Holocene. Each of these peaks contains a summit crater; the lava flows on the N flank appear younger than those on the S side. The current eruption period began in early February 2021 and has recently consisted of numerous weak ash explosions, ash plumes, ashfall, elevated surface temperatures, and sulfur dioxide emissions (BGVN 47:06). This report covers activity during June through November 2022 using daily, weekly, and special reports from the Alaska Volcano Observatory (AVO) and satellite data. AVO monitors the volcano using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

AVO reported low-level activity during June that consisted of elevated seismicity with intermittent tremor and explosions, and frequent gas-and-steam emissions that mostly consisted of sulfur dioxide, that rose above the N crater of Cerberus; weather clouds often obscured satellite and webcam views. Minor ash emissions were visible in webcam images rising to low heights during 6-9 and 11-12 June and extended as far as 40 km from the vent. Similar low-level activity during July prompted AVO to reduce the Aviation Color Code (ACC) and Volcano Alert Level (VAL) to Yellow and Advisory, respectively on 7 July. Low levels of seismicity and elevated surface temperatures were reported. Satellite and webcam images were mostly obscured due to weather clouds, though gas-and-steam emissions were visible from the active crater during 6-7 and 12-14 July.

During August, seismicity consisted of occasional small earthquakes and seismic tremor. Elevated surface temperatures were also recorded. Webcam images, when not obscured by weather clouds, showed gas-and-steam emissions rising from the N crater of Mount Cerberus. A short-lived explosion was detected at 1347 on 21 August, based on observations from local webcams. A low-level ash cloud was observed in webcam data and recorded in seismic and infrasound data that rose no higher than 6 km altitude; specific altitudes were not determined due to weather clouds (figure 23). As a result, the ACC and VAL were raised to Orange and Watch, respectively. Gas-and-steam emissions possibly containing minor amounts of ash were observed in clear satellite images after the explosion.

Figure (see Caption) Figure 23. Photo of a dense ash plume rising above the N active crater at Mount Cerberus at Semisopochnoi nine minutes after the start of an eruption event on 21 August 2022. Photo by Matt Loewen, courtesy of AVO.

Gas-and-steam emissions, and seismicity including volcanic tremor, continued during September and October. Several small ash eruptions from the active crater were visible in webcam images and detected in seismic and infrasound data during 2-3 September. During 13-15 September explosions generated ash emissions that rose no higher than 1.2 km altitude and drifted up to 8 km SE. Some local ashfall was observed in cloudy webcam images during 16-17 September. On 3 October an explosion was detected in infrasound data, though no accompanying ash emission was reported. Another small explosion was detected in geophysical data on 31 October.

The active crater continued to emit gas-and-steam emissions during November, and volcanic tremor and small earthquakes persisted, based on geophysical data, since weather clouds often obscured clear views. Small explosions were detected in geophysical data during 7 November; however, ash emissions were not visible in satellite or webcam images. After 7 November seismicity decreased and no explosive activity or ash emissions were observed.

Sentinel-2 satellite imagery showed occasional white gas-and-steam plumes rising above the crater, which sometimes contained ash (figure 24). The plumes drifted in different directions. A small thermal anomaly was detected in the crater on 6 October due to clear weather.

Figure (see Caption) Figure 24. Sentinel-2 satellite imagery showed gas-and-steam plumes rising above the active N crater of Mount Cerberus at Semisopochnoi on 6 June 2022 (top left), 13 July 2022 (top right), and 13 November 2022 (bottom right). A weak thermal anomaly was visible in the active crater on 6 October 2022 (bottom left). Plumes drifted NW and S in these images. Images using “Natural color” (bands 4, 3, 2) and “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Weekly Reports - Index


2023: January | February | March | April | May | August
2022: January | February | March | April | May | June | July | August | September | November | December
2021: February | March | April | May | June | July | August | September | October | November | December
2020: January | February | March | April | November
2019: July | August | September | December
2018: September | October | November
2015: April | May
2014: June


2 August-8 August 2023 Citation IconCite this Report

AVO reported that the last time possible explosions were detected at Semisopochnoi’s Mount Young in monitoring data was 25 April and the last ash emission occurred on 5 May. Since then, earthquake activity has been low and steaming from the N crater continued. On 3 August the Volcano Alert Level was lowered to Normal (the lowest level on a four-level scale) and the Aviation Color Code was lowered to Green (the lowest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 May-6 June 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 30 May-6 June. Seismicity remained low and few earthquakes were detected. Minor steam emissions were occasionally visible in webcam images on 31 May and 2 and 4 June. The Volcano Alert Level remained at Advisory (the second highest on a four-level scale) and the Aviation Color Code remained at Yellow (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 May-23 May 2023 Citation IconCite this Report

On 17 May AVO reported that eruptive activity at Semisopochnoi had declined during the previous week, though seismicity remained slightly elevated and low-level steaming continued from Mount Young. Ash emissions had last occurred on 5 May leaving minor deposits on the NW flank of Mount Young’s N crater. The Aviation Color Code was lowered to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level was lowered to Advisory (the second highest level on a four-level scale). Intense gas emissions were periodically visible in webcam images during 17-18 and 20-21 May. On 22 May a weak sulfur dioxide signal was detected, suggestive of low-level degassing.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


10 May-16 May 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 9-16 May. Weather clouds mostly obscured satellite and webcam views. Volcanic tremor was detected during 9-10 May; there was no evidence of explosive or earthquake activity in the geophysics data during the rest of the week. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


3 May-9 May 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 2-9 May, though it was seismically quiet for the most part, with only occasional small earthquakes. Cloudy weather often obscured satellite views. Steam emissions from the N crater of Mount Young were visible in partially clear webcam images during 3-6 May. A new NW-flank ash deposit was present on fresh snow; no signs of explosive activity were seen in geophysical data. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 April-2 May 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 26 April-2 May. Seismicity was at low levels, and a few small local earthquakes were recorded during 28-29 April. Daily minor steam emissions were seen rising from Mount Young, though cloudy weather sometimes prevented webcam and satellite views. Ash deposits near the crater rim were visible during 27-28 April, though it was unclear if they were recent. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 April-25 April 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 18-25 April. Daily periods or bursts of tremor and occasional low-frequency earthquakes were detected during the week. Small explosions were detected in seismic and infrasound data during 18-19 and 24-25 April. Cloudy weather prevented webcam and satellite views on most days. Possible recent ash deposits on Mount Young’s crater rim were visible in clear webcam images during 22-23 April, and steam emissions from the active N crater were visible during 22-25 April. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 April-18 April 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 12-18 April. No eruptive activity was observed, though some weak seismicity was recorded. Cloudy weather often prevented webcam and satellite views during most of the week. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 April-11 April 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 5-11 April. An extensive low-altitude steam plume drifted more than 400 km during 4-6 April and was likely related to volcanic emissions but did not appear to contain ash. Several small explosions were detected on 5 April, and periods of seismic tremor and local earthquakes were recorded during 5-6 April, but seismicity was quiet during the rest of the week. Clouds obscured webcam and satellite views during 7-10 April. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 March-4 April 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 28 March-4 April. Steam emissions from the N crater of Mount Young were visible in webcam images during 29-30 March; weather clouds obscured webcam and satellite views during most of the week. Minor seismic and infrasound signals were recorded during 31 March-1 April that may or may not have been related to activity at N crater. Local earthquakes and periods of tremor occurred during 1-2 April. A 200-km-long gas-and-steam emission was visible at low altitudes during the night of 3 April; no ash signatures were detected in the cloud. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 March-28 March 2023 Citation IconCite this Report

AVO reported that low-level unrest continued at Semisopochnoi during 22-28 March. Steam emissions from the N crater of Mount Young were visible during 22 and 26-27 March. No explosive activity was detected in seismic or infrasound data. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 March-21 March 2023 Citation IconCite this Report

AVO reported that low-level ash emissions from the N crater of Semisopochnoi’s Mount Young were observed in several web camera images during 18-19 March. Small explosions and volcanic tremor had also resumed. Ash emissions were not detected in satellite images, though on 18 March a robust steam-and-gas plume was visible drifting 150 km from the N crater. AVO raised the Volcano Alert Level to Watch (the second highest level on a four-level scale) and the Aviation Color Code to Orange (the second highest color on a four-color scale) on 19 March. Low-level seismicity continued during 20-21 March and one small explosion was detected in seismic and infrasound data. Clouds obscured webcam and satellite views.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 February-21 February 2023 Citation IconCite this Report

AVO reported that seismicity at Semisopochnoi’s Mount Young was low during 14-21 February, and steam emissions were visible in webcam images almost daily. On 22 February the Aviation Color Code was lowered to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level was lowered to Advisory (the second highest level on a four-level scale). AVO noted that no significant tremor, ash emissions, or explosive activity had been recorded since late January.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 February-14 February 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young continued during 7-14 February. Seismicity was low, and a few local earthquakes were recorded during 7-8 February. Steam emissions were visible in webcam images almost daily though views were often cloudy. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 February-7 February 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young continued during 1-7 February. Seismicity was elevated and daily weak tremor was recorded. Minor steam emissions were visible in webcam images during 3-7 February. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


25 January-31 January 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young was ongoing during 24-31 January. Seismicity was elevated and daily weak tremor was recorded. Minor steam emissions were visible in webcam images on 24 January and 29-30 January. Discolored snow observed at the summit in webcam images during 28-29 January possibly indicated minor, low-level explosive activity at the vent. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 January-24 January 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young was ongoing during 17-24 January. Seismicity was elevated with daily small local earthquakes and occasional weak tremor. Minor steam emissions were visible in webcam images during 17-19 January; no activity was identified in cloudy satellite views during the rest of the week. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 January-17 January 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young was ongoing during 10-17 January. Seismicity was elevated with small local earthquakes and weak tremor. Minor steam emissions were visible in webcam images during 11 and 16-17 January. Several small explosion signals were detected by local seismic and infrasound sensors during 16-17 January; no activity was identified in cloudy satellite views. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 January-10 January 2023 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi’s Mount Young, formerly Mount Cerberus, was ongoing during 4-10 January. Daily minor steam emissions were visible in webcam views. Seismicity was above background levels; low-level explosive activity was detected in geophysical data during 4-5 January with elevated seismicity and infrasound signals observed on local stations. Volcanic tremor was detected during 7-9 January, and very weak explosive activity was detected in seismic and infrasound data on 9 January. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


28 December-3 January 2023 Citation IconCite this Report

AVO reported that fresh ash deposits on the flanks of Semisopochnoi’s Mount Cerberus were visible in webcam images during 27-28 December, indicating that activity at the N crater had resumed on 27 December. The deposits extended about 1 km from the vent. Ash plumes were not visible in satellite and webcam images, though a persistent steam plume rising as high as 2.5 km (5,000 ft) a.s.l. may have been carrying minor amounts of ash. Increased seismicity, including seismic tremor, had been recorded during the previous week. AVO raised the Aviation Color Code to Orange (the second highest level on a four-color scale) and the Volcano Alert Level to Watch (the second highest level on a four-level scale).

Seismic tremor and explosions were recorded during 30-31 December. Satellite and webcam images were obscured by clouds; no plumes were observed above the meteorological cloud deck around 4.7 km (15,000 ft) a.s.l., so any ash emissions would have been at low altitudes. Possible explosions were detected during 31 December 2022-1 January 2023. A small ash deposit extending around 2 km SSW of the N crater were visible in satellite and webcam images. A likely explosion occurred during 1-2 January based on elevated seismicity recorded on local seismometers and an infrasound signal recorded minutes later by an array at Adak. Minor steam-and-gas emissions were visible in partly cloudy satellite images. Low-level explosive activity persisted during 2-3 January, with minor steam emissions and a new ash deposit visible in webcam images.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


23 November-29 November 2022 Citation IconCite this Report

On 23 November AVO lowered the Aviation Color Code for Semisopochnoi to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) noting that no ash emissions or explosive activity had been detected since 7 November. Seismicity had decreased, though remained at elevated levels. Steam emissions from the active vent in the N crater of Mount Cerberus persisted.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


16 November-22 November 2022 Citation IconCite this Report

AVO reported ongoing low-level seismicity at Semisopochnoi characterized by intermittent seismic tremor and occasional low-frequency earthquakes during 16-22 November. Satellite and webcam views were mostly obscured by weather clouds, though during clear views continuous gas-and-steam emissions from the N crater of Mount Cerberus were visible. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


2 November-8 November 2022 Citation IconCite this Report

On 7 November AVO stated that small explosions at the N crater of Mount Cerberus at Semisopochnoi had been detected in geophysical data during the previous week and volcanic tremor simultaneously resumed. Though ash emissions were not visually observed, the type of unrest was similar to previous periods associated with ash emissions below 3 km (10,000 ft) a.s.l.; the Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and the Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). Seismicity was low during 7-8 November, and clouds prevented webcam and satellite images.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


28 September-4 October 2022 Citation IconCite this Report

On 29 September AVO lowered the Aviation Color Code for Semisopochnoi to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) noting that no ash emissions or explosive activity had been detected since 14 September. Seismicity had decreased, though remained at elevated levels. Steam emissions from the active vent in the N crater of Mount Cerberus persisted. Seismic tremor and a small explosion were detected in seismic and infrasound data during 3-4 October.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


21 September-27 September 2022 Citation IconCite this Report

AVO reported that the eruption at Semisopochnoi was ongoing during 13-20 September. Seismicity remained elevated with intermittent periods of low-amplitude tremor. Steam emissions from the active vent in the N crater of Mount Cerebus were visible in webcam views on most days. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


14 September-20 September 2022 Citation IconCite this Report

AVO reported that the eruption at Semisopochnoi was ongoing during 13-20 September. Seismicity remained elevated and characterized by intermittent tremor. Low-level ash emissions from the N crater of Mount Cerberus were occasionally visible in mostly cloudy webcam views during 13-15 September. Possible fresh local ashfall was seen in webcam images during 16-17 September. Steam emissions were visible in webcam views during 19-20 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 September-13 September 2022 Citation IconCite this Report

AVO reported ongoing low-level seismicity and occasional steam emissions at Semisopochnoi during 6-13 September. Satellite and webcam views were mostly obscured by weather clouds. Explosions were recorded during 12-13 September and ash emissions drifting 8 km SE at an altitude of 1.2 km (4,000 ft) a.s.l. were visible in satellite and webcam images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 August-6 September 2022 Citation IconCite this Report

AVO reported ongoing low-level seismicity and steam emissions at Semisopochnoi during 30 August-6 September. Weakly elevated surface temperatures were identified in satellite images during 1-2 September. Several small ash eruptions from the N crater of Mount Cerberus were visible in webcam images during 2-3 September and detected in seismic and infrasound data. Satellite and webcam views were cloudy during 4-5 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


24 August-30 August 2022 Citation IconCite this Report

AVO reported ongoing low-level seismicity and steam emissions at Semisopochnoi during 23-30 August. Satellite images were mostly cloudy; steam emissions were seen almost daily in webcam images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 August-23 August 2022 Citation IconCite this Report

AVO reported that at 1347 on 21 August a short-lived explosion at Semisopochnoi's North Cerberus cone produced an ash emission that was visible in webcam images. The ash emission was not visible in satellite images due to weather clouds, indicating that they did not rise above 6 km (20,000 ft) a.s.l. This was the first explosion detected since 12 June. The Aviation Color Code was raised to Orange and the Volcano Alert Level was raised to Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


6 July-12 July 2022 Citation IconCite this Report

AVO reported ongoing low-level seismicity, steam emissions, and sulfur dioxide emissions at Semisopochnoi, though no explosive activity had been detected since 12 June. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory on 7 July.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 June-5 July 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone likely continued during 29 June-5 July. Seismicity was quiet. Weather clouds often prevented satellite and webcam views; sulfur dioxide emissions were detected in satellite images on 28 and 30 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 June-28 June 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 21-27 June. Periods of low-amplitude tremor and a few small low-frequency earthquakes were recorded by the seismic network. Weather clouds often prevented satellite and webcam views; sulfur dioxide emissions were detected in satellite images during 23-24 June and a robust steam plume was visible in webcam images during 25-26 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 June-21 June 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 14-21 June. Periods of weak tremor were recorded by the seismic network. Weather clouds often prevented satellite and webcam views; minor steam emissions were visible in one clear webcam image on 17 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 June-14 June 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 7-14 June. Seismicity remained elevated with intermittent tremor and occasional explosions. Minor ash emissions rising to low altitudes (less than 1.5 km (5,000 ft) a.s.l.) were visible in webcam images on most days; weather clouds sometimes prevented satellite and webcam views. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 June-7 June 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 31 May-6 June. Seismicity remained elevated with intermittent tremor; one explosion was recorded during 31 May-1 June and multiple small explosions were recorded during 4-6 June. Weather clouds mostly prevented satellite and webcam views. Minor ash emissions rising to low heights were visible in webcam images during 6-7 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


25 May-31 May 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 24-31 May. Seismicity continued to be elevated with intermittent tremor and several daily explosions recorded by infrasound and seismic instruments. Weather clouds often prevented satellite and webcam views; sporadic ash emissions were visible during 27-28 May and likely occurred on other days as well. Sulfur dioxide emissions were detected during 27-29 May, and elevated surface temperatures were identified during 28-29 May. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 May-24 May 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 17-24 May. Seismicity continued to be elevated with intermittent tremor and several daily explosions recorded by infrasound and seismic instruments. Low-level ash emissions were visible in clear satellite images and webcam views; clouds sometimes obscured views towards the end of the week. A sulfur dioxide plume drifted 240 km N during 17-18 May, and sulfur dioxide emissions were detected during 23-24 May. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 May-17 May 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 10-17 May. Seismicity continued to be elevated with intermittent tremor detected by the seismic network. Several daily explosions were recorded in infrasound and seismic data. Daily low-level ash emissions were visible in clear satellite images and webcam views. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 May-10 May 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 3-10 May. Seismicity continued to be elevated with intermittent tremor detected by the seismic network. Several daily explosions were recorded during 8-10 May. Weather clouds obscured views of the volcano, though daily minor, low-level ash emissions were seen in webcam views. A pilot reported a low-level eruption cloud on 9 May. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


27 April-3 May 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 26 April-3 May. Tremor continued to be detected by the seismic network. Weather clouds obscured views of the volcano on most days, though occasional views during 27-29 May revealed new ash deposits on the flanks. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


20 April-26 April 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 19-26 April. Periods of seismic tremor were occasionally detected and small explosions were recorded in seismic data during 19-20 April. Minor, low-level, plumes with low ash content were visible in webcam images through each day during 19-20 April, with occasional more energetic ash plumes. Weather cloud cover often hindered webcam and satellite views during the rest of the week. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


13 April-19 April 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 12-19 April. Periods of seismic tremor were detected daily and occasional small explosions were recorded in seismic and regional infrasound data on most days. Weather cloud cover often hindered webcam and satellite views; minor, low-level ash plumes were visible in webcam images during 16-19 April. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


6 April-12 April 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 6-12 April. Periods of seismic tremor were detected daily and occasional small explosions were recorded on most days in seismic and regional infrasound data. Partly-to-mostly-cloudy webcam views and occasional satellite images showed daily short-lived ash bursts and more continuous steam emissions. Steam plumes drifted as far as 70 km SW during 6-7 April. A low-level steam plume drifted more than 100 km at altitudes less than 1.5 km (5,000 ft) a.s.l. during 7-8 April. A low-level ash plume drifted up to 80 km WNW on 8 April. Local ash deposits were occasionally visible. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


30 March-5 April 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 30 March-4 April. Periods of seismic tremor and occasional small explosions were detected daily in seismic and regional infrasound data. Daily minor ash emissions rose no higher than 3 km (10,000 ft) a.s.l. and occasional steam emissions were visible in webcam and satellite images; clouds sometimes prevented satellite views. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


23 March-29 March 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 22-29 March. Periods of seismic tremor and occasional small explosions were detected daily in seismic and regional infrasound data. Daily minor ash emissions and occasional steam emissions were visible in webcam and satellite images; clouds sometimes prevented satellite views. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


16 March-22 March 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 15-22 March. Periods of seismic tremor and occasional small explosions were detected daily in seismic and regional infrasound data. Daily minor ash emissions and occasional steam emissions were visible in webcam images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


9 March-15 March 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 8-15 March. Seismic tremor and sometimes numerous daily explosions were detected in seismic and regional infrasound data. Minor ash emissions were visible in webcam images during 8-9 and 14-15 March; likely plumes on other days may have been hidden due to clouds. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


2 March-8 March 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 1-8 March. Local seismic and infrasound instruments recorded daily small explosions. Weather clouds often prevented satellite and webcam views of the volcano, though explosions likely produced low ash clouds from the summit and they were visually confirmed during 4-8 March. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


23 February-1 March 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 23 February-1 March. Seismicity was elevated with low-level tremor and daily small explosions. Weather clouds sometimes prevented satellite and webcam views of the volcano, though low ash clouds from the summit were visible on most days. Ash deposits on the N flank were visible in a few webcam images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


16 February-22 February 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 16-22 February. Seismicity was elevated with low-level tremor, and occasional explosions, detected almost daily in both seismic and infrasound data. Weather clouds prevented satellite and webcam views of the volcano. Low-level ash clouds from the summit were observed in webcam images drifting N during 21-22 February. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


9 February-15 February 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 9-15 February. Seismicity was elevated with low-level tremor, and several small explosions were detected daily in both seismic and infrasound data, through 13 February. Steam and low-level ash emissions likely occurred daily, though due to weather clouds they were not confirmed in satellite and webcam images during 13-14 February. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


2 February-8 February 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 1-8 February. Seismicity was elevated, and explosions were occasionally detected in both seismic and infrasound data during 4-8 February. Steam and low-level ash emissions likely occurred daily, though due to weather clouds they were only confirmed in satellite and webcam images during 1-2 and 5-8 February. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 January-1 February 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 25 January-1 February. Seismicity was elevated, characterized by periods of tremor and small earthquakes. Steam and low-level ash emissions likely occurred daily, though due to weather clouds they were only confirmed in webcam images during 25-26 and 29-31 January and 1 February. Numerous small explosions were recorded by local seismic and infrasound sensors during 29 January-1 February. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 January-25 January 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 18-25 January. Seismicity was elevated, characterized by periods of tremor and low-frequency earthquakes. Steam emissions were periodically visible in webcam images during 18-19 January and minor explosions were recorded by local seismic and infrasound sensors on 19 January. Steam and low-level ash emissions were visible in webcam and satellite images during 20-25 January. Daily explosions were recorded during 21-25 January, and elevated surface temperatures were identified in satellite data during 22-23 January. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 January-18 January 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus cone continued during 12-18 January. A small explosion was recorded by local seismic and infrasound sensors during 12-13 January. The weather was mostly cloudy, though low-level ash clouds were occasionally visible in webcam images during 12-15 January. Steam emissions were visible in 15-16 January webcam images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 January-11 January 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 4-11 January. Almost daily explosions (one per day during 4-8 January and a few during 10-11 January) were recorded by the local seismic network. The weather was mostly cloudy, though ash and/or steam plumes were occasionally visible in webcam images. Low-level ash clouds were visible in webcam images during 10-11 January. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 December-4 January 2022 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 29 December 2021 to 4 January 2022. Minor ash-and-steam emissions were visible in webcam images during 28-29 December. Ash plumes observed in webcam and satellite images on 31 December rose to 1.5 km (5,000 ft) a.s.l. and drifted as far as 100 km NE. Ash emissions observed in webcam images during daylight hours on 1 and 2 January were being blown down the flank by high winds. Small explosions were detected in seismic data during 2-4 January, though cloud cover obscured views. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 December-28 December 2021 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 22-28 December. Small explosions were detected almost daily in seismic and infrasound data. Low-level ash-and-steam emissions were observed by webcams and in satellite images during 22-25 December, when weather conditions were clear. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 December-21 December 2021 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 15-21 December. Small daily explosions were detected in seismic and infrasound data. Low-level ash-and-steam emissions were observed daily by webcams and were occasionally identified in satellite images when weather conditions permitted. Elevated surface temperatures were also identified in satellite data during 15-17 and 19-20 December. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 December-14 December 2021 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 8-14 December. Several daily explosions were detected in seismic and infrasound data. Small ash clouds drifting at least 185 km SE were identified in satellite images during 8-9 December. Persistent steam emissions occasionally punctuated by ash emissions were visible in webcam views during 10-11 December, and ash emissions were visible the next day even though conditions were mostly cloudy. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 December-7 December 2021 Citation IconCite this Report

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 1-7 December. Several daily explosions were detected in seismic and infrasound data. Weather clouds sometimes obscured satellite and webcam views of the volcano, though on most days low-level ash-and-steam plumes rising no higher than 1.5 km (5,000 ft) a.s.l. were visible mostly in webcam images. During 3-4 December a diffuse ash plume was identified in a satellite image drifting about 100 km E. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


24 November-30 November 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 24-30 November. Daily minor explosions were detected in seismic and infrasound data. Weather clouds obscured satellite and webcam views of the volcano on most days; small ash plumes rising no higher than 3 km (10,000 ft) a.s.l. were sometimes visible during breaks in the cloud cover but were likely emitted daily. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 November-23 November 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 17-23 November. Daily minor explosions were detected in seismic and infrasound data. Small ash plumes rising no higher than 3 km (10,000 ft) a.s.l. likely continued to be emitted, though weather clouds obscured satellite and webcam views of the volcano on most days. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


10 November-16 November 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 10-16 November. Daily minor explosions were detected in seismic and infrasound data. Daily ash plumes were visible in webcam and satellite data rising to 1.5-3.7 (5,000-12,000 ft) a.s.l., drifting NE, E, SE, and S, and dissipated quickly. Weather clouds sometimes obscured views. Ash plumes were typically dissipating within 50 km of the volcano. Minor ashfall on the island was sometimes visible. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


3 November-9 November 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 2-9 November. Daily tremor and minor explosions were detected in seismic and infrasound data. Several small low-level ash plumes were visible in webcam data rising to an estimated altitude of 1.5 (5,000 ft) a.s.l. during 2-3 November. Weather clouds obscured views during 4-7 November with the top of the cloud deck varying at altitudes of 3-6.1 km (10,000-20,000 ft) a.s.l.; ash plumes likely continued to be emitted though none rose above the cloud deck. Ash plumes were typically dissipating within 50 km of the volcano. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


27 October-2 November 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 26 October-2 November. Daily tremor and minor explosions were detected in seismic and infrasound data. Although weather clouds often prevented webcam and satellite views, intermittent, low-level ash emissions were visible during clear views, rising as high as 3.7 km (12,000 ft) a.s.l. and dissipating quickly. Sulfur dioxide emissions were detected during 26-27 and 30-31 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


20 October-26 October 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 19-26 October. Tremor and multiple minor explosions were detected daily in seismic and infrasound data. Although weather clouds often prevented webcam and satellite views, intermittent, low-level ash emissions were visible during clear weather rising to altitudes up to 3 km (10,000 ft a.s.l.); the farthest plume drifted 250 km on 19 October. Sulfur dioxide emissions were detected during 25-26 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


13 October-19 October 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 13-19 October. Seismicity remained elevated and daily minor explosions were detected in infrasound data. Although weather clouds often prevented webcam and satellite views, intermittent, low-level ash emissions were visible rising to altitudes up to 3 km (10,000 ft a.s.l.) and drifting E on 13 October. Ash plumes rose as high as 1.5 km (5,000 ft) a.s.l. on 18 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


6 October-12 October 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 6-12 October. Seismicity remained elevated and a few explosions per day were detected in infrasound data. Although weather clouds often prevented webcam and satellite views, discontinuous, low-level ash emissions were visible rising to altitudes up to 3 km (10,000 ft a.s.l.) and drifting E during 8-9 October. Low-level ash emissions were also visible in webcam images during 9-12 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 September-5 October 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 29 September-5 October. Seismicity remained elevated with intermittent explosion signals or bursts of activity likely from explosions. A few explosions were also detected in regional infrasound data during 2-5 October. Small ash clouds were observed almost daily in either webcam or satellite images rising to altitudes below 3 km (10,000 ft) a.s.l.; plumes drifted ENE on 2 October, then N and NW on 3 October. Sulfur dioxide plumes were possibly observed on a few days, though definitely on 3 October. Webcams located 5-6 km from the active vent recorded ashfall during 4-5 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 September-28 September 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 22-28 September. Seismicity remained elevated; daily explosions were recorded by seismic and infrasound networks. The frequency and intensity of ash emissions decreased during 21-22 September with occasional discrete ash clouds drifted W at altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. Sulfur dioxide plumes also drifted W. Occasional low-level ash emissions drifted NW, W, and SE during 22-26 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 September-21 September 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 15-21 September. Weather clouds obscured views of the volcano on most days. Several small daily explosions were recorded by local seismic stations; ash plumes were not visible in satellite images suggesting that they remained below 3 km (10,000 ft) a.s.l. and did not rise above the cloud deck. Overnight during 18-19 September small, discontinuous, low-level ash plumes were visible drifting 100 km SE. Ash emissions increased in frequency and intensity on 19 September. Ash clouds rose as high as 4.6 km (15,000 ft) a.s.l. and continued to drift 100 km SE. Sulfur dioxide emissions increased in the afternoon. AVO raised the Aviation Color Code to Red and the Volcano Alert Level to Warning at 2158. Explosions continued overnight and the next day, and ash plumes rose up to 4.6 km a.s.l. Plumes drifted 100 km NW. At 2012 on 20 September AVO lowered the Aviation Color Code to Orange noting the frequency of discrete explosions had decreased to a rate of about one per hour, though ash plumes from these events were still rising to 4.6 km a.s.l. and drifting NW. Sulfur dioxide plumes drifted N during 20-21 September.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 September-14 September 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 7-14 September. Seismicity was elevated and characterized by periods of continuous tremor. Short-lived explosions lasting several minutes were detected daily in infrasound data. Small ash clouds from the explosions rose 3-4.6 km (10,000-15,000 ft) and dissipated within two hours. Sulfur dioxide emissions were detected in satellite images at altitudes less than 3 km (10,000 ft) a.s.l., sometimes extending downwind for hundreds of kilometers. During 7-9 September periods of lower-altitude ash emissions interspersed with voluminous steam plumes were observed in web camera images moving horizontally by the wind and rising no higher than 1.5 km (5,000 ft) a.s.l. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 September-7 September 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 31 August-7 September. Multiple daily explosions were detected by seismic and infrasound networks. Ash-and-steam plumes from the explosions were sometimes confirmed in satellite and webcam images rising to altitudes lower than 3 km (10,000 ft) a.s.l., though during 6-7 September ash plumes rose as high as 4.6 km (15,000 ft) a.s.l. Local ashfall on the island was visible in satellite data. Sulfur dioxide emissions were detected in satellite images during 31 August-2 September and on 6 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


25 August-31 August 2021 Citation IconCite this Report

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 25-31 August. Multiple daily explosions were detected by seismic and infrasound networks. Ash-and-steam plumes from the explosions were sometimes confirmed in webcam images, in satellite data, and by nearby observers; plumes rose no higher than 3 km (10,000 ft) a.s.l. and produced local ashfall on the island. Daily sulfur dioxide emissions were identified in satellite images, drifting as far as 300 km NW during 29-31 August. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 August-24 August 2021 Citation IconCite this Report

AVO reported that multiple explosions and seismicity at Semisopochnoi's North Cerberus crater continued during 18-24 August. Low-level gas-and-ash emissions, including occasional sulfur dioxide emissions were detected in satellite and webcam data during 18-24 August and rose no higher than 3 km (10,000 ft) a.s.l.; views were often obscured due to weather. On 20 August minor ashfall deposits were reported; ashfall may have continued following explosive events during the rest of the week. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 August-17 August 2021 Citation IconCite this Report

AVO reported that an eruption at Semisopochnoi’s North Cerberus crater was ongoing during 11-17 August, characterized by daily explosions, ash plumes, and occasional sulfur dioxide emissions identified in satellite images. Multiple energetic explosions were detected daily in seismic and infrasound data, and strong seismic tremor was occasionally recorded. Daily steam-and-ash plumes identified in webcam and satellite data rose no higher than 3 km (10,000 ft) a.s.l. and drifted 200-300 km W. Daily ashfall likely occurred on the island. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 August-10 August 2021 Citation IconCite this Report

AVO reported that an eruption at Semisopochnoi’s North Cerberus crater was ongoing during 4-10 August, characterized by daily explosions, ash plumes, and sulfur dioxide emissions identified in satellite images. Multiple energetic explosions were detected almost daily in seismic and infrasound data. An ash cloud rose to 1.5-3 km (5,000-10,000 ft) a.s.l. and drifted 33 km NE during 3-4 August. Ash emissions were also visible in webcam images and photographed by an observer S of the island. An ash cloud was generated at 2123 on 4 August and was visible in satellite data until 0250 on 5 August, drifting 180 km SE over Gareloi and southern Tanaga Island. A small ash cloud at 2040 on 6 August drifted 50 km beyond the N crater vent and quickly dissipated. Another small ash cloud at 2103 caused ashfall on the webcam located 5 km NE about 30 minutes later. Ash-and-steam emissions were visible in webcam images until 2333. A large infrasound signal was recorded at 0653 on 8 August, though weather conditions prevented visual confirmation of emissions. A possible small ash cloud was visible in a satellite image at 0700. At least three separate explosions were recorded at 1714 on 8 August and 0339 and 0417 on 9 August. A small ash cloud at 900 m (3,000 ft) a.s.l. was visible in satellite images on the morning of 9 August. There were 10 explosions recorded during 9-10 August; small ash-and-steam emissions were visible in the webcam and small low-level plumes were occasionally identified in satellite data. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


28 July-3 August 2021 Citation IconCite this Report

AVO reported that seismicity at Semisopochnoi had increased in recent days. A notable increase at 0200 on 31 July prompted AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch a few hours later. Additionally, increased infrasound recorded by local stations suggested low-level emissions. Weather clouds obscured satellite views, though a possible sulfur dioxide plume was detected. Steaming was visible in webcam images. Increased seismicity and elevated activity in infrasound data were recorded during 31 July-1 August, and multiple, discrete, energetic explosions were detected during 1-3 August. Weather clouds again obscured satellite views; steaming was visible in webcam views. Beginning at 1015 on 2 August the local networks recorded an explosion and an intense burst of seismic and acoustic tremor that lasted for about 15 minutes. A small ash cloud was visible in satellite images drifting 60 km N at altitudes of 1.5-3 km (5,000-10,000 ft) a.s.l. Ash emissions from the active vent in North Crater were visible in webcam views on the morning of 3 August.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


21 July-27 July 2021 Citation IconCite this Report

AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory for Semisopochnoi on 22 July, noting that explosive activity had not been detected since 12 July. Seismicity continued to be elevated during 23-27 July. Robust steam emissions were visible in webcam views during 22-24 July and sulfur dioxide plumes were identified in satellite images on 23 July. Weather clouds obscured views during 24-27 July.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


14 July-20 July 2021 Citation IconCite this Report

AVO reported that unrest continued at Semisopochnoi during 13-20 July. Periods of low-level tremor and steam plumes from Mount Cerberus were occasionally recorded. Elevated surface temperatures at the N cone of Mount Cerberus were identified in satellite images during 13-14 July and robust steam-and-gas emissions were seen in webcam images. A plume with low amounts of sulfur dioxide drifting about 200 km N was identified in satellite data on 17 July. Sulfur dioxide emissions were also detected the next day. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 July-13 July 2021 Citation IconCite this Report

AVO reported that continuous volcanic tremor at Semisopochnoi began at 1200 on 12 July and explosive activity was recorded by the infrasound network. Emissions began at 1300 and lasted tens of minutes; a sulfur dioxide gas plume possibly containing ash was identified in satellite images drifting S at an altitude less than 1.5 km (5,000 ft) a.s.l. The Aviation Color Code was raised to Orange and the Volcano Alert Level was raised to Watch. Volcanic tremor decreased to low levels after several hours.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


16 June-22 June 2021 Citation IconCite this Report

AVO lowered Semisopochnoi’s Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 16 June, reporting that no explosions or ash emissions had been detected since 30 May and seismicity was relatively low. The report noted that elevated surface temperatures and sulfur dioxide emissions were recorded on several occasions during the previous few weeks, indicating continued volcanic unrest.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


9 June-15 June 2021 Citation IconCite this Report

AVO reported that seismic activity at Semisopochnoi was low during 9-15 June and no eruptive activity was detected in infrasound or satellite data. Elevated surface temperatures and steaming from the active vent were occasionally identified in satellite images. Sulfur dioxide emissions were visible in satellite data during 11-13 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


2 June-8 June 2021 Citation IconCite this Report

AVO reported that low-level unrest at Semisopochnoi continued during 2-8 June with seismicity occasionally above background levels. Steaming from Mount Cerberus was sometimes observed by field crews. Slightly elevated surface temperatures were identified in a few satellite infrared images during 4-7 June. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 May-1 June 2021 Citation IconCite this Report

AVO reported that an eruption at Semisopochnoi continued during 25 May-1 June. Steaming from the N crater at Mount Cerberus was visible in satellite images on 25 May. Radar data acquired between 15 and 27 May showed no morphological changes to the active vent. Tremor began to be recorded after AVO field engineers restored the satellite uplink to the seismic stations on 26 May. Field crews on 29 May observed low-level ash plumes rising to 2.4-3 km (8,000-10,000 ft) a.s.l., and small ash clouds drifting SW were visible in satellite images at around 0810 and 0920. Diffuse ash emissions were visible in satellite imagery at 1110. Strongly elevated surface temperatures were also identified in satellite data. Increased seismic tremor and accompanying low-level ash emissions began at 0945 on 30 May, with ash plumes drifting S at an altitude of 1.5 km (5,000 ft) a.s.l. at least through 1250. Elevated surface temperatures were detected during 30-31 May, likely from hot material on the crater floor. Seismic data showed low-level continuous tremor and occasional small discrete events. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 May-25 May 2021 Citation IconCite this Report

AVO reported that sulfur dioxide and steam plumes from Semisopochnoi were possibly visible in satellite images during 19-20 May. Satellite images on 21 May showed a sulfur dioxide gas plume drifting 160 km SE. Steam plumes rose from Cerberus on 24 May. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 May-18 May 2021 Citation IconCite this Report

AVO reported that weakly elevated surface temperatures and sulfur dioxide gas emissions at Semisopochnoi were identified in satellite images during 16-17 May. Several small explosions were recorded in infrasound data during 17-18 May; a small ash cloud was observed in a satellite image from 1521. Sulfur dioxide gas emissions and steaming from the active vents were identified in satellite data. The Aviation Color Code was raised to Orange and the Volcano Alert Level was raised to Watch on 18 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 May-11 May 2021 Citation IconCite this Report

AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory for Semisopochnoi on 7 May, noting that no ash emissions had been observed nor explosions recorded since 26 April. Sulfur dioxide emissions were recorded on 1 and 5 May, signifying continued unrest. Steam plumes were visible rising from the N crater of Mt. Cerberus on 7 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


21 April-27 April 2021 Citation IconCite this Report

Eruptive activity at Semisopochnoi gradually increased during 21-22 April based on satellite and infrasound data; ash emissions were first seen in satellite images at 1800 on 21 April and were continuous at least through 1348 on 22 April. Plumes rose to 2.4 km (8,000 ft) a.s.l. and drifted 80 km S. Sulfur dioxide emissions were also detected in satellite images on 22 April. Cloud cover mostly obscured views during 23-24 April, though possible minor ash emissions were sometimes visible. Low-level ash plumes drifting S were occasionally identified in satellite images during 24-26 April. Dense weather clouds prevented views for most of 26 April and the next day. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


14 April-20 April 2021 Citation IconCite this Report

AVO reported that an eruption at Semisopochnoi continued during 14-20 April. Sulfur dioxide emissions were identified in satellite images during 13-14 April. An explosion was recorded by the regional infrasound network at 0417 on 14 April, though weather cloud cover as high as 4 km (13,000 ft) a.s.l. prevented satellite confirmation of an ash plume. Ash emissions began during the morning of 15 April and continued through the day, drifting more than 350 km SE at altitudes as high as 6 km (20,000 ft) a.s.l. They did not decrease in intensity, so at 1915 AVO raised the Aviation Color Code to Red and the Volcano Alert Level to Warning. Sustained ash emissions continued on 16 April, though the plume rose as high as 3 km (10,000 ft) a.s.l. and winds pushed it N. Explosions were detected through the night and early in the morning. Minor ash deposits around the volcano were visible. Eruptive activity declined during 16-17 April; one clear satellite view suggested that activity had declined or ceased. At 1249 on 17 April AVO lowered the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Several explosions were recorded during 17-19 April though weather clouds obscured views. Volcanic plumes were visible just above the weather cloud deck (situated at 3 km (10,000 ft) a.s.l.) and drifted S during 19-20 April. A few darker (possibly ash rich) plumes were visible in satellite data at 0700 and 1150 on 19 April and on 20 April.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 April-13 April 2021 Citation IconCite this Report

AVO reported that low-level ash emissions from Semisopochnoi were visible in satellite images on 12 April along with a steam plume drifting E beyond the island. Additionally, new ash deposits extending SE at least to the coastline were also visible. The event was recorded by the regional infrasound network. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 March-6 April 2021 Citation IconCite this Report

AVO reported that a small plume from Semisopochnoi’s North Cerberus crater was visible in a satellite image on 31 March. Steam obscured the crater during the first part of 1 April. Later that day an ash plume was visible, and was followed by a sulfur dioxide plume an hour later. At 2200 a plume rose to an altitude below 3 km (10,000 ft) a.s.l. No activity was identified in partly cloudy images during 2-6 April. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


24 March-30 March 2021 Citation IconCite this Report

AVO reported that satellite data showed minor ash deposits on Semisopochnoi's flanks. Three explosions on 25 March (at 0142, 0330, and 0645) were recorded by regional infrasound sensors. Two more explosions were detected at 2130 on 26 March and at 0030 on 27 March; high weather cloud cover at 9.1 km (30,000 ft) a.s.l. prevented satellite confirmation; no ash was visible above the cloud deck during 25-27 March. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 March-23 March 2021 Citation IconCite this Report

AVO reported that satellite data showed minor ash deposits on Semisopochnoi’s flanks and a possible gas cloud on 14 March. Two small explosions on 19 March, at 0350 and 0534, were recorded by regional infrasound sensors and prompted AVO to raise the Aviation Color Code and the Volcano Alert Level to Orange and Watch, respectively. A small explosion at 0230 on 21 March was followed by a series of smaller explosions. A volcanic gas cloud was visible in satellite data during the previous day. Three small explosions were detected during 22-23 March, though high weather cloud cover, at 9.1 km (30,000 ft) a.s.l., prevented satellite confirmation; no ash was visible above the cloud deck.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


10 March-16 March 2021 Citation IconCite this Report

On 12 March AVO reported that although no ash plumes were observed at Semisopochnoi and nothing was detected in regional infrasound data during the previous week, ash deposits within Mount Cerberus’s N crater and extending 1.5 km on the flank were identified in satellite data. The Aviation Color Code and the Volcano Alert Level remained at Yellow/Advisory, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 February-23 February 2021 Citation IconCite this Report

AVO reported that no significant activity at Semisopochnoi was recorded after several ash deposits were visible in satellite images during 6-7 February. On 19 February the Aviation Color Code and the Volcano Alert Level were lowered to Yellow/Advisory, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


3 February-9 February 2021 Citation IconCite this Report

AVO reported that a 6 February satellite image of Semisopochnoi showed small ash deposits extending in a narrow strip less than 3 km N of North Cerberus Crater. The deposits were likely the result of a small explosions that occurred during the previous week. Steam emission obscured view of the summit crater. The Aviation Color Code and the Volcano Alert Level were raised to Yellow/Advisory. A second ash deposit, similar to the first, was visible in a satellite image on 7 February. This deposit extended at least 3 km NE of North Cerberus Crater. Weather clouds obscured views of the S side of the volcano. The report noted that the ash plumes associated with the deposits had not been observed; they likely rose less than 3 km (10,000 ft) a.s.l. and were short lived. The Aviation Color Code and the Volcano Alert Level were raised to Orange/Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 November-24 November 2020 Citation IconCite this Report

AVO reported that no signs of eruptive activity at Semisopochnoi had been recorded since mid-June. Seismicity had been elevated above background levels but declined to very low levels before 11 November, when the satellite the link to transmit the data failed. Both the Aviation Color Code and the Volcano Alert Level were lowered to Unassigned, reflecting the lack of available seismic data to detect unrest.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 April-7 April 2020 Citation IconCite this Report

On 1 April AVO reported that seismic, infrasound, and satellite data collected during the previous two weeks indicated no signs of eruptive activity at Semisopochnoi; the Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory. A crater lake and robust steam plume were both identified in recent satellite images.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


25 March-31 March 2020 Citation IconCite this Report

AVO reported that seismicity at Semisopochnoi remained elevated during 25-31 March and no surface activity was observed on most days, though weather clouds often prevented visual confirmation. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 March-24 March 2020 Citation IconCite this Report

AVO reported that activity at Semisopochnoi had decreased compared to the previous week. Seismicity remained elevated during 19-24 March and no surface activity was observed on most days, though weather clouds often prevented visual confirmation. A steam plume was visible in a satellite image on 21 March and weakly elevated surface temperatures were identified in one satellite image during 21-22 March. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 March-17 March 2020 Citation IconCite this Report

Seismicity at Semisopochnoi increased over a period of a few days and by 15 March was characterized by nearly continuous tremor and frequent signals indicating small explosions. The unrest prompted AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch on 15 March. A robust steam plume rising from the N cone of Mount Cerberus and minor ash deposits around the crater rim were visible in a clear satellite image acquired on 16 March.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 February-3 March 2020 Citation IconCite this Report

No signs of eruptive activity at Semisopochnoi were detected in infrasound and satellite data over the previous several weeks, prompting AVO to lower the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 26 February. A robust steam plume rose from the main vent that same day. Short bursts of tremor and earthquakes persisted during 26 February-3 March.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 February-25 February 2020 Citation IconCite this Report

AVO reported that intermittent, low-level tremor was detected at Semisopochnoi during 19-25 February. Brief periods of elevated tremor were recorded during 19-20 February. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 February-18 February 2020 Citation IconCite this Report

A series of explosions and tremor bursts at Semisopochnoi were detected by the seismic network beginning on 14 February, prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Tremor bursts lasting from three to twelve minutes every few hours were recorded the next day. Ash plumes were not visible, though a weather cloud deck persisted between 1.5 and 4.6 km (5,000 and 15,000 ft) a.s.l. Seismic data continued to record small explosions and tremor bursts lasting from six to ten minutes every few hours on 16 February, but by 17 February there were almost no events recorded. Weather clouds continued to obscure views of the volcano.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 January-14 January 2020 Citation IconCite this Report

On 9 January AVO lowered the Aviation Color Code for Semisopochnoi to Yellow and the Volcano Alert Level to Advisory, noting that explosions had not been detected since 19 December 2019. In addition, seismic tremor had last been recorded on 29 December 2019; seismicity subsequently declined but remained above background levels.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 December-24 December 2019 Citation IconCite this Report

AVO reported that ash plumes below 1.5 km (5,000 ft) a.s.l. from Semisopochnoi were identified in satellite images on 14 and 17 December; ash plumes on 17 December drifted about 15 km SE. During 17-20 December seismicity was characterized by tremor bursts and small explosions, though cloudy weather conditions prevented visual confirmation. Elevated seismicity was recorded on 21 December. Nothing significant was detected during 22-24 December. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 December-17 December 2019 Citation IconCite this Report

AVO reported that during 10-17 December activity at Semisopochnoi remained elevated, with bursts of tremor and small explosions detected in both seismic and infrasound data. An 80-km-long gas-and-steam plume possibly containing ash was visible in satellite images during 11-12 December. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 December-10 December 2019 Citation IconCite this Report

Strong tremor at Semisopochnoi was recorded by local seismic and regional infrasound networks beginning at 0026 on 7 December, heralding the start of an eruption and prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. The meteorological cloud deck over the volcano was at around 3 km (10,000 ft) a.s.l.; no ash signals were detected above this altitude. A period of intermittent explosions was detected, and afterwards seismicity remained elevated at least through 9 December.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 September-24 September 2019 Citation IconCite this Report

AVO lowered the Volcano Alert Level for Semisopochnoi to Advisory and the Aviation Color Code to Yellow on 18 September noting a decrease in seismic activity over the past few weeks and an absence of tremor since 15 September. Low-levels sulfur dioxide emissions persisted, and the crater lake continued to fill with water.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


4 September-10 September 2019 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi possibly continued during 4-10 September. Seismic activity was relatively minor and characterized by intermittent low-frequency earthquakes. Satellite images were mostly cloudy, though a low-altitude steam plume drifting 50 km S was visible on 8 September. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


28 August-3 September 2019 Citation IconCite this Report

AVO reported that low-level eruptive activity at Semisopochnoi possibly continued during 28 August-3 September. Seismic activity was relatively minor and characterized by intermittent low-frequency earthquakes. Minor tremor was detected until 30 August. Satellite images were obscured by clouds. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


21 August-27 August 2019 Citation IconCite this Report

AVO reported that during 17-23 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes; seismic data went offline starting sometime on 17 August, though was available by around 22 August. Ground-coupled airwaves, indicative of explosive activity, were sometimes recorded in seismic data; an infrasound signal was recorded during 23-24 August. Cloudy weather often prevented satellite views of the volcano, though a steam plume was visible on 18 August and sulfur dioxide emissions were detected during 21-22 August. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


14 August-20 August 2019 Citation IconCite this Report

AVO reported that during 14-17 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes; seismic data became unavailable starting sometime on 17 August. Cloudy weather often prevented satellite views of the volcano, however some recent clear views indicated that the N cone crater had a smooth featureless area, indicating water or tephra at an elevation several meters below the previous floor. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 August-13 August 2019 Citation IconCite this Report

AVO reported that during 7-13 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes. No unusual activity was observed in satellite images, though views were often cloudy. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 July-6 August 2019 Citation IconCite this Report

AVO reported that during 31 July-6 August seismicity at Semisopochnoi remained elevated and was characterized by periods of weak, continuous tremor and discrete low-frequency earthquakes. Satellite images were mostly cloudy, though a possible steam plume was visible during 5-6 August. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


24 July-30 July 2019 Citation IconCite this Report

On 24 July AVO reported that satellite data from the previous week indicated that the 100-m-wide crater lake in the N cone of Semisopochnoi’s Cerberus three-cone cluster was gone, and a new shallow inner crater about 80 m in diameter had formed on the crater floor. The lake had persisted since January 2019. Seismicity during 25-30 July was characterized by periods of continuous tremor, low-frequency earthquakes, and small explosion signals. Small steam plumes were visible in periodic, cloud-free satellite images, along with minor sulfur dioxide emissions.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


17 July-23 July 2019 Citation IconCite this Report

AVO reported that data from local seismic and infrasound sensors likely detected a small explosion at Semisopochnoi on 16 July. No ash was visible in cloudy satellite images although none was expected from an explosion of its size. A small plume drifted 18 km from the vent but had no indication of ash. A strong tremor signal was recorded at 2339 on 17 July and an infrasound signal was detected from an array located 260 km E on Adak Island. The event likely produced ash emissions, though none were visible above the cloud deck at 3 km (10,000 ft) a.s.l. Seismic activity continued to increase. On 18 July a short-lived, low-level eruption prompted AVO to raise the Aviation Color Code to Orange (the second highest level on a four-color scale) and the Volcano Alert Level to Watch (the second highest level on a four-level scale). A low-level plume was visible in occasional cloud-free satellite images. Seismic activity decreased abruptly that night and ground-coupled airwaves stopped being detected on adjacent islands, suggesting that the eruption had paused or ended. Seismic activity remained low at least through 21 July.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


3 July-9 July 2019 Citation IconCite this Report

An increase in seismicity above background levels on 4 July at Semisopochnoi prompted AVO to raise the Aviation Color Code to Orange (the second highest level on a four-color scale) and the Volcano Alert Level to Watch (the second highest level on a four-level scale). Elevated seismicity continued through at least 9 July. No eruptive activity was detected in regional infrasound data, and cloudy conditions obscured satellite views of the volcano. [Correction: the Aviation Color Code was raised to Yellow and the Volcano Alert Level was raised to Advisory.]

Source: US Geological Survey Alaska Volcano Observatory (AVO)


21 November-27 November 2018 Citation IconCite this Report

AVO reported that no evidence of activity at Semisopochnoi had been detected since an explosion was recorded in infrasound data on 31 October. The satellite link for transmitting seismic data failed on 1 November, though no activity was observed in satellite or infrasound data since then. As a result, the Aviation Color Code was lowered to Yellow and Volcano Alert Level was lowered to Advisory (both are the second lowest levels on four-level scales) on 21 November.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


7 November-13 November 2018 Citation IconCite this Report

AVO reported that three possible small explosions at Semisopochnoi were detected in infrasound data between 1951 and 2004 on 9 November. No associated ash clouds were observed in partly cloudy satellite images, and no other activity was noted during 7-11 November also in partly cloudy images. Images were cloudy during 12-13 November. The Aviation Color Code remained at Orange and Volcano Alert Level remained at Watch (both are the second highest levels on four-level scales).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 October-6 November 2018 Citation IconCite this Report

AVO reported that two small explosions at Semisopochnoi were detected in seismic and infrasound data on 31 October. Intermittent seismic tremor was recorded on 1 November but later that day the satellite link that transmits seismic data failed. Weather clouds obscured views of the volcano during 31 October-4 November. Nothing was observed in satellite data during 5-6 November. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


24 October-30 October 2018 Citation IconCite this Report

AVO reported that an eruptive event at Semisopochnoi began at 2047 on 25 October based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island (260 km SE). The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km (10,000 ft) a.s.l.; a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


10 October-16 October 2018 Citation IconCite this Report

On 11 October AVO reported that satellite data of Semisopochnoi indicated partial erosion of a tephra cone in the crater of Cerberus’s N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


3 October-9 October 2018 Citation IconCite this Report

AVO reported that during 3-9 October seismicity at Semisopochnoi remained elevated, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. The Aviation Color Code (ACC) remained at Yellow and Volcano Alert Level (VAL) remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 September-2 October 2018 Citation IconCite this Report

AVO reported that during 19-25 September seismicity at Semisopochnoi remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity. The Aviation Color Code (ACC) remained at Yellow and Volcano Alert Level (VAL) remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 September-25 September 2018 Citation IconCite this Report

AVO reported that during 19-25 September seismicity at Semisopochnoi remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity. The Aviation Color Code (ACC) remained at Yellow and Volcano Alert Level (VAL) remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 September-18 September 2018 Citation IconCite this Report

On 16 September AVO raised the Aviation Color Code (ACC) for Semisopochnoi to Yellow and Volcano Alert Level (VAL) to Advisory after increased seismicity was detected at 0831. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September. This new information coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September prompted AVO to raise the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor being recorded by local sensors.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


27 May-2 June 2015 Citation IconCite this Report

A decline in seismicity at Semisopochnoi over the previous few months, and no activity observed in satellite images, prompted AVO to lower the Aviation Color Code and the Volcano Alert Level to Unassigned on 28 May. Increased seismicity had been detected in January.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 April-7 April 2015 Citation IconCite this Report

On 25 March AVO reported that seismicity at Semisopochnoi that had begun in January continued and had increased over the previous few days. Brief periods of tremor were also detected. AVO raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. The elevated seismicity, characterized by discrete fairly small earthquakes beneath the center of the island, continued to be detected through 7 April.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


18 June-24 June 2014 Citation IconCite this Report

AVO reported that the earthquake swarm that had started at Semisopochnoi on 9 June continued until 23 June. No eruptive activity was indicated. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


11 June-17 June 2014 Citation IconCite this Report

AVO reported that an earthquake swarm at Semisopochnoi started at 1000 on 9 June and escalated at 1200 on 12 June. The continuation of the anomalous activity prompted AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 13 June. The earthquake swarm was continuing as of 17 June. Five of the six seismic stations on the volcano were operational.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Bulletin Reports - Index

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.

04/1987 (SEAN 12:04) Plume; possible ash deposits

02/2019 (BGVN 44:02) Minor ash explosions during September and October 2018

09/2019 (BGVN 44:09) Small explosions detected between 16 July and 24 August 2019

04/2020 (BGVN 45:04) Intermittent small explosions detected in December 2019 through mid-March 2020

06/2021 (BGVN 46:06) Ash emissions in June 2020 and during February-May 2021

12/2021 (BGVN 46:12) Intermittent explosions, ash plumes, and sulfur dioxide emissions during June-November 2021

06/2022 (BGVN 47:06) Numerous weak ash explosions during December 2021-May 2022

12/2022 (BGVN 47:12) Intermittent explosions and ash emissions during June-November 2022




Information is preliminary and subject to change. All times are local (unless otherwise noted)


April 1987 (SEAN 12:04) Citation IconCite this Report

Plume; possible ash deposits

A plume originating at about 52°N, 180° and extending 90 km ENE was noted by Steven Shivers from a NOAA 9 satellite image returned 13 April at 1731. On an image at 2135 the same day, the plume extended only 15 km ENE. On 24 April, pilot Harold Wilson (Peninsula Airways), flying 50 km SE of Semisopochnoi, noted a very dark-colored peak (perhaps Sugarloaf) among other snow-covered mountains on the island. Plumes from Semisopochnoi were reported several times in the 18th and 19th centuries.

Information Contacts: J. Reeder, ADGGS; T. Miller, USGS, Anchorage; W. Gould, NOAA/NESDIS.


February 2019 (BGVN 44:02) Citation IconCite this Report

Minor ash explosions during September and October 2018

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure (see Caption) Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/).


September 2019 (BGVN 44:09) Citation IconCite this Report

Small explosions detected between 16 July and 24 August 2019

The remote island of Semisopochnoi in the western Aleutians is dominated by a caldera measuring 8 km in diameter that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. A small (100 m diameter) crater lake in the N cone of Semisopochnoi's Cerberus three-cone cluster has persisted since January 2019. An eruption at Sugarloaf Peak in 1987 included an ash plume (SEAN 12:04). Activity during September-October 2018 included increased seismicity and small explosions (BGVN 44:02). The primary source of information for this reporting period of July-August 2019 comes from the Alaska Volcano Observatory (AVO), when there were two low-level eruptions.

Seismicity rose above background levels on 5 July 2019. AVO reported that data from local seismic and infrasound sensors likely detected a small explosion on 16 July. A strong tremor on 17 July generated airwaves that were detected on an infrasound array 260 km E on Adak Island. In addition to this, a small plume extended 18 km WSW from the Cerberus vent, but no ash signals were detected in satellite data. Seismicity decreased abruptly on 18 July after a short-lived eruption. Seismicity increased slightly on 23 July and remained elevated through August.

On 24 July 2019 AVO reported that satellite data showed that the crater lake was gone and a new, shallow inner crater measuring 80 m in diameter had formed on the crater floor, though no lava was identified. Satellite imagery indicated that the crater of the Cerberus N cone had been replaced by a smooth, featureless area of either tephra or water at a level several meters below the previous floor. Satellite imagery detected faint steam plumes rising to 5-10 km altitude and minor SO2 emissions on 27 July. Satellite data showed a steam plume rising from Semisopochnoi on 18 August and SO2 emissions on 21-22 August. Ground-coupled airwaves identified in seismic data on 23-24 August was indicative of additional explosive activity.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/).


April 2020 (BGVN 45:04) Citation IconCite this Report

Intermittent small explosions detected in December 2019 through mid-March 2020

Semisopochnoi is a remote stratovolcano located in the western Aleutians dominated by an 8 km-wide caldera containing the small (100 m diameter) Fenner Lake and a three-cone cluster: a northern cone known as the North cone of Mount Cerberus, an eastern cone known as the East cone of Mount Cerberus, and a southern cone known as the South cone of Mount Cerberus. Previous volcanism has included small explosions, ash deposits, and gas-and-steam emissions. This report updates activity during September 2019 through March 2020 using information from the Alaska Volcano Observatory (AVO). A new eruptive period began on 7 December 2019 and continued until mid-March 2020 with activity primarily focused in the North cone of Mount Cerberus.

During September-November 2019, low levels of unrest were characterized by intermittent weeks of elevated seismicity and gas-and-steam plumes visible on 8 September, 7-8 October, and 24 November. On 6 October an SO2 plume was visible in satellite imagery, according to AVO.

Seismicity increased on 5 December and was described as a strong tremor through 7 December. This tremor was associated with a small eruption on 7 December; intermittent explosions occurred and continued into the night. Increased seismicity was recorded throughout the rest of the month while AVO registered small explosions during 11-19 December. On 11-12 December, a gas-and-steam plume possibly containing some of ash extended 80 km (figure 2). Two more ash plumes were observed on 14 and 17 December, the latter of which extended 15 km SE. Sentinel-2 satellite images show gas-and-steam plumes rising from the North Cerberus crater intermittently at the end of 2019 and into early 2020 (figure 3).

Figure (see Caption) Figure 2. Sentinel-2 satellite image showing a gray ash plume extending up to 17 km SE from the North Cerberus crater on 11 December 2019. Image taken by Hannah Dietterich; courtesy of AVO.
Figure (see Caption) Figure 3. Sentinel-2 satellite images of gas-and-steam plumes at Semisopochnoi from late November 2019 through mid-March 2020. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

The month of January 2020 was characterized by low levels of unrest due to intermittent low seismicity. Small explosions were reported during 14-17 February and a gas-and-steam plume was visible on 26 February. Seismic unrest occurred between 18 February-7 March. Gas-and-steam plumes were visible on 1, 9, 14-17, 20, and 21 March (figure 4). During 15-17 March, small explosions occurred, according to AVO. Additionally, clear satellite images showed gas-and-steam emissions and minor ash deposits around North Cerberus’ crater rim. After 17 March the explosions subsided and ash emissions were no longer observed. However, intermittent gas-and-steam emissions continued and seismicity remained elevated through the end of the month.

Figure (see Caption) Figure 4. Satellite image of Semisopochnoi showing degassing within the North Cerberus crater on 22 March 2020. Image taken by Matt Loewen; courtesy of AVO.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


June 2021 (BGVN 46:06) Citation IconCite this Report

Ash emissions in June 2020 and during February-May 2021

The volcanic Semisopochnoi Island in the western Aleutian Islands contains a group of cones within a caldera complex (figure 5). The active Cerberus center has three summit craters, with the current activity originating from North Cerberus. Since September 2018, typical activity has produced minor ash deposits within the vicinity. This bulletin summarizes activity that occurred from April 2020 through May 2021 based on information given by the Alaska Volcano Observatory (AVO), supplemented by satellite data.

Figure (see Caption) Figure 5. This satellite image of Semisopochnoi Island, Alaska, shows the major surface features with an 8-km-wide caldera in the center. As of 2021, Mount Cerberus is the most active of three cones within the caldera complex. The North, East, and South Cerberus craters are indicated, with a faint gas plume dispersing NE from the active North crater on 22 August 2020. Base satellite image from Sentinel-2 using Natural color (bands 4, 3, 2) rendering. Courtesy of Sentinel Hub Playground.

Intermittent small explosions occurred at Semisopochnoi during early 2020. An AVO Volcano Activity Notice for Aviation (VONA) issued on 1 April reported no indication of activity over the previous two weeks and seismicity at background levels. Satellite data show detectable sulfur dioxide (SO2) emission and visible steam plumes. Low-level unrest continued into early June with occasional small earthquakes, including a few small low-frequency events and episodic tremor, occasional steam plumes, and detectable SO2 emissions. An increase in tremor was detected around 12-13 June, and infrasound and seismicity indicated rapid degassing events on 17 and 19 June, with activity declining again by the 20th. AVO noted that clear satellite images acquired on the 21st showed minor ash deposits near the crater, likely from the elevated activity during the previous week, and vigorous gas and steam emission (figure 6). Steam and gas emission continued through to the end of the month then intermittently through July. A 200-km-long SO2 plume was detected on 15 July and low-level unrest continued.

Figure (see Caption) Figure 6. Minor ash deposits are visible on the Semisopochnoi North Cerberus Crater and a steam plume is shown dispersing ESE on 21 June 2020. Sentinel-2 satellite image with Natural color (bands 4, 3, 2) rendering. Courtesy of Sentinel Hub Playground.

A gas plume was reported on 7 August and seismicity was above background to the 9th, after that seismicity was at very low levels with no more significant events detected. Infrequent small earthquakes were detected through September and minor steam emissions on the 22nd. Seismicity remained low throughout October. No eruptive activity had detected since mid-June and seismicity had declined to very low levels prior to seismic data transmission failing on 11 November. Due to the lack of data, on 20 November the Aviation Color Code and Alert Level were reduced to Unassigned.

There were no reports of activity during December 2020 or January 2021. A satellite image acquired on 7 February showed several small ash deposits extending at least 3 km from the North Cerberus Crater, likely produced by a small explosion the previous week (figure 7). Steam emission prevented views into the crater and clouds obscured the volcano over the following week.

Figure (see Caption) Figure 7. This Landsat 8 image acquired on 7 February 2021 at Semisopochnoi shows several linear ash deposits from the North Cerberus Crater. This reflects low-level explosive activity. Landsat 9 true Color – pansharpened scene. Courtesy of Sentinel Hub Playground.

On 10 March a satellite image revealed a recently emplaced ash deposit that extended 1.5 km from the crater, with a steam plume being blown to the E (figure 8). Several similar small ash deposits had been noted by AVO in the previous weeks. No activity was observed or detected through 18 March, other than a possible gas plume that day. At 0350 on the 19th a small explosion was detected by infrasound monitoring. Another small explosion was detected at 0230 on the 21st, followed by a series of smaller explosions. During 22-23 March three explosions were detected. Cloud cover prevented visual observation of these events, but possible SO2 plumes were detected and a confirmed plume on the 23rd indicated further unrest. A probable ash deposit and plume were imaged on the 24th (figure 9). Activity continued with intermittent explosions and SO2 plumes detected through the 27th.

Figure (see Caption) Figure 8. This 10 March 2021 WorldView-3 satellite image shows ash deposits from low-level explosive activity at the Cerberus North Crater at Semisopochnoi. The ash extends to 1.5 km from the vent and has been partly remobilized by wind. A plume emanating from the crater is being blown to the E. Figure by Hannah Dietterich, courtesy of AVO.
Figure (see Caption) Figure 9. An ash deposit is present between the dashed lines, deposited on snow (red) in this Planet Labs near-IR false color satellite image acquired on 24 March 2021. The deposit extends over 8 km ESE across Semisopochnoi from the North Cerberus Crater and a plume is also visible in the same area. Image courtesy of AVO.

Several small low-altitude ash and gas plumes were detected in satellite images on 30 March and 1 April. Cloud cover prevented satellite views until 12 April, when new ash deposits and low-level ash emissions were observed extending at least to the coastline, accompanied by weak infrasound signals. Low-level activity was also detected the following day. Sustained ash emission that began on the morning of the 15th (figure 10) produced a plume extending more than 350 km E to altitudes of 6 km; activity continued through the next day with a change in direction to the N at around 3 km altitude. Ash emission continued over the following days with a VONA released on the 22nd reporting an ash plume reaching 3 km and extending about 75 km S (figure 11). Through to the end of April ash and SO2 plumes were either observed or noted as probably occurring under cloudy conditions.

Figure (see Caption) Figure 10. This Sentinel-3 satellite scene acquired on 15 April 2021 shows plumes from Semisopochnoi dispersed over 330 km from the vent. The insert shows a zoomed-in view of the island and the proximal ash plume. Original image by Hannah Dietterich, AVO.
Figure (see Caption) Figure 11. This Planet Labs satellite image acquired on 22 April 2021 shows an ash plume produced by the North Cerberus Crater and dispersing S. Ash deposits are visible on the flanks of the cone. Figure by Hannah Dietterich, AVO.

The volcano was often obscured during the first week of May, with activity possibly continuing at a low level without detection. A gas plume was detected on the 11th, and an ash plume is visible in satellite images acquired on the 17th (figure 12). Small explosions and SO2 emissions were detected through 21 May. An ash emission reaching 3 km altitude that was seen by an AVO field crew on 29 May was also observed in satellite data moving SW. Elevated temperatures were detected in the North Cerberus Crater. Ash emissions were produced again on the 30th and observed by an AVO field crew (figure 13). Seismic data transmission was restored on 26 May.

Figure (see Caption) Figure 12. Satellite images of Semisopochnoi acquired on 17 and 29 May (top), and a photograph taken on 29 May 2021 (bottom) show weak activity at the North Cerberus Crater, including ash emission, gas emission, and elevated temperature on the crater floor. Sentinel-2 color infrared (vegetation, bands 8, 3, 4) scene at the top left and the false color (urban, bands 12, 11, 4) scene at the top right courtesy of Sentinel Hub Playground. Photo courtesy of Hannah Dietterich, AVO.
Figure (see Caption) Figure 13. Minor ash emissions produced on 30 May 2021 at Semisopochnoi’s North Cerberus Crater around 1320 local time, taken from a helicopter during field work. Both top and bottom-left photos are taken from the SE. Photos courtesy of Hannah Dietterich, AVO.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).


December 2021 (BGVN 46:12) Citation IconCite this Report

Intermittent explosions, ash plumes, and sulfur dioxide emissions during June-November 2021

Semisopochnoi Island, located in the western Aleutian Islands, contains a group of cones within a caldera complex. The Cerberus center has three summit craters, with the current activity originating from North Cerberus Crater (see figure 5 in BGVN 46:06). Recent activity has consisted of intermittent small explosions and ash emissions since February 2021 (BGVN 46:06). This report describes continuing activity of explosions, ash plumes, and sulfur dioxide emissions during June through November 2021 using information primarily from the Alaska Volcano Observatory (AVO) and satellite data.

During the first half of June, AVO personnel reported low-level seismicity, in addition to minor gas-and-steam emissions (figure 14), elevated surface temperatures at the North Cerberus Crater, and low-level ash emissions that rose to 3 km altitude. Ash was also detected in GOES satellite data that showed several thin plumes that extended SW over Amchitka Island. As a result, minor ashfall occurred on the S part of Semisopochnoi Island, but there were no reports of it on Amchitka Island. By the second week of June, there was an overall decline in activity at the North Cerberus Crater; no eruptive activity was detected in infrasound or satellite data, or by AVO field crews; some sulfur dioxide emissions were observed in satellite data on 11 June. On 16 June AVO lowered the Aviation Color Code (ACC) and Volcano Alert Level (VAL) to Yellow and Advisory, respectively because no explosions or ash emissions had been detected since 30 May; seismicity remained relatively low.

Figure (see Caption) Figure 14. Photo of degassing at the North Cerberus Crater at Semisopochnoi on 8 June 2021. Photo by Cyrus Read, courtesy of AVO.

An explosion that produced a small ash cloud rising to 1.5 km altitude was detected in local infrasound sensors and observed in satellite data at 1300 on 12 July, prompting AVO to raise the ACC and VAL to Orange and Watch, respectively. The event lasted about ten minutes. Following the explosion, seismicity declined and was characterized by intermittent and short bursts of tremor. Because of this marked decline in seismicity and no additional explosive events since 12 July, AVO lowered the ACC and VAL to Yellow and Advisory, respectively. Sulfur dioxide emissions were observed in satellite data on 17-19 and 24 July; the plume on 17 July drifted about 200 km N. Seismicity remained elevated during 23-27 July and robust gas-and-steam plumes were observed in webcam images on 22-24, 26, and 30 July (figure 15). A notable increase in activity at 0200 on 31 July prompted AVO to raise the ACC and VAL to Orange and Watch.

Figure (see Caption) Figure 15. Webcam image from the CEPE station showing a gas-and-steam plume at Semisopochnoi during the evening on 21 July 2021. Courtesy of AVO.

Multiple, discrete, and energetic explosions and increased seismicity were detected in August. The explosions ejected small ash clouds up to 3 km altitude and drifted as far as 160 km, according to AVO (figure 16). Ash emissions from the N crater were occasionally visible in webcam images and subsequent light ashfall was reported on the island. Sulfur dioxide emissions continued during the month. Local seismic networks recorded an explosion and an intense burst of seismic tremor that lasted for about 15 minutes at 1015 on 2 August. A small ash cloud was visible in satellite images and drifted 60 km N at an altitude of 1.5-3 km. An ash cloud generated at 2123 on 4 August was observed in satellite data until 0250 on 5 August, extending 180 km SE over Gareloi and S Tanaga Island. A small ash cloud at 2040 on 6 August drifted 50 km and another one at 2103 resulted in ashfall on the webcam 5 km NE. A large infrasound signal was recorded at 0653 on 8 August, although weather conditions prevented visual confirmation. At least three separate explosions were detected at 1714 on 8 August and 0339 and 0417 on 9 August; a small ash cloud rose to 900 m altitude on the morning of 9 August. During 9-10 August, ten explosions were observed in webcam images. According to the Anchorage VAAC, ash plumes rose to 3-3.9 km altitude during 14-16 and 27-29 August, based on GOES 17 and HIMAWARI satellite images. During 29-31 August ash drifted as far as 300 km NW.

Figure (see Caption) Figure 16. Photo of an eruption plume rising above Semisopochnoi on 3 August 2021. Photo by Nora Rojek, R/V Tiglax, courtesy of AVO.

Explosions, ash plumes, elevated seismicity, and intermittent sulfur dioxide emissions continued during September; ash rose to 4.6 km altitude and local ashfall was visible in satellite data (figure 17). Short-lived daily explosions lasted several minutes, according to infrasound data. Sulfur dioxide emissions rose to altitudes no higher than 3 km and sometimes extended downwind for hundreds of kilometers. According to the Anchorage VAAC, ash plumes were detected to 3-4.6 km altitude on 6, 8, 21-23, 26 September. Overnight during 18-19 September small, discontinuous, low-level ash plumes were observed drifting 100 km SE. The frequency and intensity of the explosions increased during 19-20 September when an ash plume rose to 4.6 km altitude and extended as far as 330 km NW and 100 km SE, causing AVO to increase the ACC and VAL to Red and Warning, respectively. The frequency of discrete explosions decreased to a rate of one per hour on 20 September, resulting in lowering the ACC and VAL back to Orange and Watch, respectively; ash plumes continued to rise to 4.6 km altitude and drifted NW. Sulfur dioxide plumes drifted N during 20-21 September. Occasional low-level ash emissions drifted NW, W, and SE during 22-26 September.

Figure (see Caption) Figure 17. Webcam image from the CEPE station of the eruption plume at Semisopochnoi rising above the North Cerberus Crater on 7 September 2021. The black specks on the image are ashfall deposits. Courtesy of AVO.

Similar activity including numerous explosions, ash emissions to less than 3 km altitude, elevated seismicity, and minor sulfur dioxide emissions in the N crater continued in October. Small ash clouds were observed in satellite imagery on 1, 2, and 3 October that rose to below 3 km altitude and dissipated 100 km from the volcano; the plumes drifted ENE on 2 October and N and NW on 3 October. On 3 October and 16 and 19 November an ash plume rose to 2.4-3 km altitude, based on information from the Anchorage VAAC. Webcams located 5-6 km from the Cerberus Crater recorded ashfall during 4-5 October. The plume on 19 October extended up to 250 km, though the direction was not defined, according to AVO. During 26, 27, and 29 October, ash plumes rose to 3.7 km altitude.

During November, activity in the N crater of Mount Cerberus persisted with minor explosions observed multiple times a day in geophysical and remote sensing data and low-level ash emissions that rose to 1.5-3.7 km altitude and extended 50-80 km based on webcam images and satellite observations (figure 18). Minor ashfall on the island was sometimes visible.

Figure (see Caption) Figure 18. Webcam image from the CEPE station of low-level ash emissions rising from Semisopochnoi’s North Cerberus Crater on 10 November 2021. Courtesy of Matt Loewen, AVO.

Sentinel-2 infrared satellite imagery showed a weak but persistent thermal anomaly in the North Cerberus Crater on clear weather days during June 2021, sometimes accompanied by gas-and-steam emissions (figure 19). Natural Color satellite imagery also showed gas-and-steam and ash plumes rising above the North Cerberus Crater throughout the reporting period, drifting in different directions (figure 20).

Figure (see Caption) Figure 19. Sentinel-2 satellite images of a small thermal anomaly at Semisopochnoi during the first half of June on 6 June (top left), 8 June (top right), and 16 June (bottom left) 2021 that became progressively weaker; by 1 September (bottom right), clouds obscured most of the summit crater. Images using Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 20. Gas-and-ash plumes are visible in Sentinel-2 satellite imagery from the Semisopochnoi North Cerberus Crater on 11 June (top left), 14 October (top right), 19 October (bottom left), and 18 November (bottom right) 2021 and drifting N and E. Sentinel-2 satellite images with Natural color (bands 4, 3, 2) rendering. Courtesy of Sentinel Hub Playground.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845 USA (URL: http://vaac.arh.noaa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


June 2022 (BGVN 47:06) Citation IconCite this Report

Numerous weak ash explosions during December 2021-May 2022

Recent low-level unrest at Semisopochnoi, the largest of the western Aleutian Islands, has been confined to the North Cerberus crater, one of three summit craters (see figure 5 in BGVN 46:06). Activity has consisted of intermittent weak explosions and generally weak emissions, along with plumes of ash, gas-and-steam, and sulfur dioxide (BGVN 45:04 and 46:12). This report describes activity during December 2021-May 2022, using weekly updates from the Alaska Volcano Observatory (AVO) and satellite data. AVO monitors the volcano by webcam, infrasound sensors, satellite images, a seismic network, and lightning detections.

According to AVO, low-level eruptive activity continued during the entire reporting period. Seismicity also remained elevated, mostly consisting of periods with small intermittent seismic tremor. During this time, the Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch, the second highest level for both. Weather clouds usually prevented satellite and webcam views.

Multiple ash explosions occurred daily during the first three weeks of December 2021. Minor ash emissions and plumes rose to an altitude of less than 3 km, and often less than 1.5 km (300 m above the summit), drifting about 100 km E on 3-4 December. 185 km SE on 8-9 December, and 100 km NE on 31 December. According to AVO reports, the number of weekly explosions diminished to “occasional” during the last week of December through the first three weeks of January, although ash plumes could still be observed (figure 21).

Figure (see Caption) Figure 21. Webcam image of an ash emission from the N crater of Semisopochnoi’s Mount Cerberus at 1445 on 13 January 2022. Courtesy of AVO/USGS.

During late January through early May 2022 the number of weekly explosions were variously described as daily, almost daily, or occasional. Multiple daily explosions were recorded during the last three weeks of May (figure 22). Ash explosions often had to be inferred from visible low-level ash clouds, because weather clouds obscured ground observations on most days. According to AVO reports, steam plumes drifted as far as 70 km SW during 6-7 April, and to distances of more than 100 km at altitudes below 1.5 km during 7-8 April. An ash plume drifted up to 80 km WNW on 8 April.

Figure (see Caption) Figure 22. Sentinel-2 satellite image of Semisopochnoi in false color (bands 12, 11, 4) showing an ash plume drifting W from the summit crater area on 12 May 2022. Courtesy of Sentinel Hub Playground.

AVO reports indicated the presence of sulfur dioxide plumes on 21 March and the latter part of May 2022. A sulfur dioxide plume drifted 240 km N during 17-18 May, and sulfur dioxide emissions were detected during 23-24 and 27-29 May. NASA’s TROPOMI instrument aboard the Sentinel-5P satellite recorded high sulfur dioxide levels only on 9 April and 29 May, both highly localized above the volcano.

Elevated surface temperatures were identified in satellite images in the N crater of Mount Cerberus during 15-17 and 19-20 December 2021, and 28-29 May 2022. The MIROVA system recorded only two hotspots during the reporting period, in late January and mid-May 2022, both of very low radiative power. No thermal alerts were recorded by the MODVOLC algorithm for MODIS thermal anomalies.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/).


December 2022 (BGVN 47:12) Citation IconCite this Report

Intermittent explosions and ash emissions during June-November 2022

Semisopochnoi is the largest subaerial volcano in the western Aleutians. It is 20-km-wide at sea level and contains an 8-km wide caldera. The three-peaked Mount Cerberus was constructed within the caldera during the Holocene. Each of these peaks contains a summit crater; the lava flows on the N flank appear younger than those on the S side. The current eruption period began in early February 2021 and has recently consisted of numerous weak ash explosions, ash plumes, ashfall, elevated surface temperatures, and sulfur dioxide emissions (BGVN 47:06). This report covers activity during June through November 2022 using daily, weekly, and special reports from the Alaska Volcano Observatory (AVO) and satellite data. AVO monitors the volcano using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

AVO reported low-level activity during June that consisted of elevated seismicity with intermittent tremor and explosions, and frequent gas-and-steam emissions that mostly consisted of sulfur dioxide, that rose above the N crater of Cerberus; weather clouds often obscured satellite and webcam views. Minor ash emissions were visible in webcam images rising to low heights during 6-9 and 11-12 June and extended as far as 40 km from the vent. Similar low-level activity during July prompted AVO to reduce the Aviation Color Code (ACC) and Volcano Alert Level (VAL) to Yellow and Advisory, respectively on 7 July. Low levels of seismicity and elevated surface temperatures were reported. Satellite and webcam images were mostly obscured due to weather clouds, though gas-and-steam emissions were visible from the active crater during 6-7 and 12-14 July.

During August, seismicity consisted of occasional small earthquakes and seismic tremor. Elevated surface temperatures were also recorded. Webcam images, when not obscured by weather clouds, showed gas-and-steam emissions rising from the N crater of Mount Cerberus. A short-lived explosion was detected at 1347 on 21 August, based on observations from local webcams. A low-level ash cloud was observed in webcam data and recorded in seismic and infrasound data that rose no higher than 6 km altitude; specific altitudes were not determined due to weather clouds (figure 23). As a result, the ACC and VAL were raised to Orange and Watch, respectively. Gas-and-steam emissions possibly containing minor amounts of ash were observed in clear satellite images after the explosion.

Figure (see Caption) Figure 23. Photo of a dense ash plume rising above the N active crater at Mount Cerberus at Semisopochnoi nine minutes after the start of an eruption event on 21 August 2022. Photo by Matt Loewen, courtesy of AVO.

Gas-and-steam emissions, and seismicity including volcanic tremor, continued during September and October. Several small ash eruptions from the active crater were visible in webcam images and detected in seismic and infrasound data during 2-3 September. During 13-15 September explosions generated ash emissions that rose no higher than 1.2 km altitude and drifted up to 8 km SE. Some local ashfall was observed in cloudy webcam images during 16-17 September. On 3 October an explosion was detected in infrasound data, though no accompanying ash emission was reported. Another small explosion was detected in geophysical data on 31 October.

The active crater continued to emit gas-and-steam emissions during November, and volcanic tremor and small earthquakes persisted, based on geophysical data, since weather clouds often obscured clear views. Small explosions were detected in geophysical data during 7 November; however, ash emissions were not visible in satellite or webcam images. After 7 November seismicity decreased and no explosive activity or ash emissions were observed.

Sentinel-2 satellite imagery showed occasional white gas-and-steam plumes rising above the crater, which sometimes contained ash (figure 24). The plumes drifted in different directions. A small thermal anomaly was detected in the crater on 6 October due to clear weather.

Figure (see Caption) Figure 24. Sentinel-2 satellite imagery showed gas-and-steam plumes rising above the active N crater of Mount Cerberus at Semisopochnoi on 6 June 2022 (top left), 13 July 2022 (top right), and 13 November 2022 (bottom right). A weak thermal anomaly was visible in the active crater on 6 October 2022 (bottom left). Plumes drifted NW and S in these images. Images using “Natural color” (bands 4, 3, 2) and “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://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://dggs.alaska.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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.

Eruptive History

There is data available for 6 confirmed Holocene eruptive periods.

2021 Feb 2 ± 2 days - 2023 May 5 Confirmed Eruption Max VEI: 2

Episode 1 | Eruption Episode North Cerberus
2021 Feb 2 ± 2 days - 2022 Nov 7 Evidence from Observations: Reported

List of 4 Events for Episode 1 at North Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
2021 Feb 7    - - - - Ash
2021 Sep 19 2021 Sep 21 Ash Plume 4.6 km altitude
2021 Sep 19    - - - - VEI (Explosivity Index) VEI 2
Episode 2 | Eruption Episode
2022 Dec 27 - 2023 May 5 Evidence from Observations: Reported

List of 3 Events for Episode 2

Start Date End Date Event Type Event Remarks
2023 Jan 28 2023 Jan 29 Explosion Discolored snow observed at the summit in webcam images during 28-29 January 2023 possibly indicated minor, low-level explosive activity at the vent.
2023 Jan 28    - - - - VEI (Explosivity Index) VEI 1
2023 May 7    - - - - Ashfall Minor deposits on the NW flank of N crater.

2019 Dec 7 - 2020 Jun 19 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode North Cerberus
2019 Dec 7 - 2020 Mar 15 (?) Evidence from Observations: Reported

List of 1 Events for Episode 1 at North Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - VEI (Explosivity Index)
Episode 2 | Eruption Episode North Cerberus
2020 Jun 12 - 2020 Jun 19 Evidence from Observations: Reported

2019 Jul 16 - 2019 Aug 24 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode
2019 Jul 16 - 2019 Aug 24 Evidence from Observations: Reported

List of 1 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - VEI (Explosivity Index)

2018 Sep 8 - 2018 Oct 31 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode
2018 Sep 8 - 2018 Oct 31 Evidence from Observations: Reported

List of 1 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - VEI (Explosivity Index)

1987 Apr 13 Confirmed Eruption Max VEI: 2 (?)

Episode 1 | Eruption Episode Sugarloaf ?
1987 Apr 13 - Unknown Evidence from Observations: Reported

List of 3 Events for Episode 1 at Sugarloaf ?

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Eruption cloud
1987 Apr 13    - - - - VEI (Explosivity Index)

1873 Confirmed Eruption  

Episode 1 | Eruption Episode Cerberus
1873 - Unknown Evidence from Observations: Reported

[ 1830 ] Uncertain Eruption

Episode 1 | Eruption Episode Cerberus
1830 - Unknown Evidence from Unknown

List of 1 Events for Episode 1 at Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Volcanic "smoke"

[ 1792 ] Uncertain Eruption

Episode 1 | Eruption Episode Cerberus
1792 - Unknown Evidence from Unknown

List of 1 Events for Episode 1 at Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Volcanic "smoke"

[ 1790 ] Uncertain Eruption

Episode 1 | Eruption Episode Cerberus
1790 - Unknown Evidence from Unknown

List of 1 Events for Episode 1 at Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Volcanic "smoke"

[ 1772 ] Uncertain Eruption

Episode 1 | Eruption Episode Cerberus
1772 - Unknown Evidence from Unknown

List of 1 Events for Episode 1 at Cerberus

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Volcanic "smoke"
Deformation History

There is data available for 1 deformation periods. Expand each entry for additional details.


Deformation during 2004 - 2010 [Subsidence; Observed by InSAR]

Start Date: 2004 Stop Date: 2010 Direction: Subsidence Method: InSAR
Magnitude: 6.000 cm Spatial Extent: 4.00 km Latitude: 52.000 Longitude: 180.000

Remarks: Deformation centered on Mt. Cerberus is probably caused by surface processes such as contraction of volcanic deposits, gravitational sliding, and mechanical compaction.

Figure (see Caption)

a Average line-of-sight surface displacement rate map for Mount Cerberus from SBAS processing of 11 ascending-track Envisat images, some of which are shown in Fig. 6.13. Arrows in (a) and (b) indicate flight and look directions of Envisat SAR when images were acquired. b Deformation interferogram for the time period August 1, 2008?August 21, 2009 from Envisat descending track 459. c Time-series of LOS surface displacement at the peak of deformation in (a)

From: Lu and Dzurisin 2014.


Reference List: Lu and Dzurisin 2014.

Full References:

Lu Z, Dzurisin D, 2014. InSAR imaging of Aleutian volcanoes: monitoring a volcanic arc from space. Springer-Verlag Berlin Heidelberg. https://doi.org/10.1007/978-3-642-00348-6

Emission History

There is no Emissions History data available for Semisopochnoi.

GVP Map Holdings

The Global Volcanism Program has no maps available for Semisopochnoi.

Smithsonian Sample Collections Database

The following 16 samples associated with this volcano can be found in the Smithsonian's NMNH Department of Mineral Sciences collections, and may be availble for research (contact the Rock and Ore Collections Manager). Catalog number links will open a window with more information.

Catalog Number Sample Description Lava Source Collection Date
NMNH 118209-1 Basalt -- 12 Sep 2015
NMNH 118209-10 Scoria -- 12 Sep 2015
NMNH 118209-11 Lapilli tephra -- 12 Sep 2015
NMNH 118209-12 Scoria -- 12 Sep 2015
NMNH 118209-13 Lapilli tephra -- 12 Sep 2015
NMNH 118209-14 Scoriaceous tephra -- 12 Sep 2015
NMNH 118209-15 Scoriaceous tephra -- 12 Sep 2015
NMNH 118209-16 Scoria -- 12 Sep 2015
NMNH 118209-2 Basalt -- --
NMNH 118209-3 Lapilli tephra -- 12 Sep 2015
NMNH 118209-4 Basalt -- --
NMNH 118209-5 Basalt -- 12 Sep 2015
NMNH 118209-6 Fine ash -- 12 Sep 2015
NMNH 118209-7 Fine ash -- 12 Sep 2015
NMNH 118209-8 Pyroclastic flow -- 12 Sep 2015
NMNH 118209-9 Pyroclastic flow -- 12 Sep 2015
External Sites