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Semisopochnoi

Photo of this volcano
  • United States
  • Alaska
  • Stratovolcano
  • 2018 CE
  • Country
  • Volcanic Region
  • 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: 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)


Most Recent Bulletin Report: 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.

Weekly Reports - Index


2018: September | October | November
2015: April | May
2014: June


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




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.

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 7 Holocene eruptive periods.

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2018 Sep 8 2018 Sep 8 Confirmed   Historical Observations
1987 Apr 13 Unknown Confirmed 2 Historical Observations Sugarloaf ?
1873 Unknown Confirmed   Historical Observations Cerberus
[ 1830 ] [ Unknown ] Uncertain     Cerberus
[ 1792 ] [ Unknown ] Uncertain     Cerberus
[ 1790 ] [ Unknown ] Uncertain     Cerberus
[ 1772 ] [ Unknown ] Uncertain     Cerberus
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:

Lubis, A. M., 2014. Uplift of Kelud Volcano Prior to the November 2007 Eruption as Observed by L-Band Insar. Journal of Engineering and Technological Sciences, 46(3), 245-257.

Emission History

There is no Emissions History data available for Semisopochnoi.

Photo Gallery

An aerial view of the SE coast of Semisopochnoi Island shows conical Sugarloaf peak (left-center) with its double parasitic cone (foreground) that was the source of one of the more recent flows. Sugarloaf was erupted outside the southern margin of an 8-km-wide caldera cutting Semisopochnoi. Cloud-draped Mount Cerebus was constructed within the caldera and forms the left horizon. Pre-caldera Ragged Top (right) shows a remnant constructional surface on its seaward face.

Photo by U.S. Navy (published in U.S. Geological Survey Bulletin 1028-O).
See title for photo information.
The western slopes of symmetrical Sugarloaf Peak (left) rise above tundra-covered Semisopochnoi Island. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. Three-peaked Mount Cerberus volcano was constructed within the caldera during the Holocene, along with symmetrical Sugarloaf Peak volcano outside of the caldera to the SSE. Most documented historical eruptions have originated from Cerberus.

Photo by Steve Ebbert, 1997 (U.S. Fish and Wildlife Service).
See title for photo information.
GVP Map Holdings

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.


Title: Rat Islands
Publisher: US Geological Survey
Country: United States
Year: 1951
Series: AK Recon Topo 250
Map Type: Topographic
Scale: 1:250,000
Map of Rat Islands
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
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