Semisopochnoi

Photo of this volcano
  • United States
  • Alaska
  • Stratovolcano
  • 1987 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 51.93°N
  • 179.58°E

  • 1221 m
    4005 ft

  • 311060
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Weekly Report: 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)


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


2015: April | May
2014: June


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.

Eruptive History


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


Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
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

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.

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.

Smithsonian Sample Collections Database


There are no samples for Semisopochnoi in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

Affiliated Sites