No eruption and typical monitoring levels.
Volcano profile · Aleutian Islands, Alaska
Great
Sitkin
A remote Aleutian volcano known for slow crater-filling lava, difficult weather and monitoring that often depends on satellites and instruments.
Latest activity and alert level
Check the live status hub
Great Sitkin can change gradually or with little visual warning. View the Volcoholics volcano directory for the latest verified official position from the Alaska Volcano Observatory.
View latest Great Sitkin status →A remote Aleutian eruption
Slow lava, deep snow and a watchful sky
Great Sitkin rises from a small island in the central Aleutians, more than 40 kilometres east of Adak.
The present eruption began with an explosion in May 2021, followed by slow lava effusion from July that year. Since then, lava has filled most of the summit crater, overridden older domes and advanced into valleys outside the crater.
Unlike the explosive ash crises associated with many Aleutian volcanoes, Great Sitkin's recent behaviour is primarily effusive. Its remoteness makes satellites, local instruments and aviation monitoring especially important.
1,740 mElevation
WATCHVolcano alert level
ORANGEAviation colour code
2021–presentRecent eruptive period
Great Sitkin quick facts
- Volcano type
- Stratovolcano
- Location
- Andreanof Islands, Alaska
- Characteristic style
- Slow summit lava effusion
- Nearest community
- Adak
- Official agency
- Alaska Volcano Observatory
Activity and behaviour
Slow lava growth inside a remote crater
Evergreen profile
How Great Sitkin behaves
Great Sitkin is known for prolonged episodes of slow lava effusion, crater-filling dome growth and low-level seismicity. Cloud, snow and darkness often obscure the summit, so satellites and instruments are essential.
Check the latest verified status →Typical recent styleSlow lava effusionCrater-filling growth can persist for years
VisibilityFrequently obscuredCloud, snow and darkness limit direct observation
SeismicityOften low levelSmall earthquakes and rockfall signals may occur
Main toolsSatellite and seismicRemote sensing is central to monitoring
Official sourceAVO / USGSAuthoritative alert and aviation information
US volcano alert system
What WATCH and ORANGE mean
WATCH indicates heightened or escalating unrest or an eruption with limited hazards. ORANGE means an eruption is underway or likely, but ash emissions are absent or minor at aviation altitudes.
Activity is above background but hazards remain limited.
Great Sitkin's current slow lava eruption fits this operational category.
Significant ash emissions or severe ground hazards are underway or imminent.
Inside the summit crater
A volcano rewriting its own crater
Great Sitkin's eruption is slow enough to reveal each stage of lava emplacement.
Fresh lava emerges inside the 2021 explosion crater, thickens across the crater floor and gradually pushes outward. The eruption has transformed the summit without the sustained ash production seen in many Aleutian crises.
Summit ventFresh lava rises inside the 2021 explosion crater.
Crater fillingThick lava spreads across older summit deposits.
Rim crossingActive lobes move beyond the crater edge.
Slow advanceFlow fronts creep east–southeast with minor rockfalls.
How Great Sitkin is erupting
From crater explosion to years of slow lava
Monitoring
Monitoring Great Sitkin
Through cloud, snow and darkness
AVO combines local instruments with satellite radar and thermal imagery because Aleutian weather often hides the summit from direct view.
Seismic networkTracks earthquakes, rockfalls and changes in eruptive activity.
InfrasoundDetects explosive pressure waves locally and regionally.
Satellite radarMaps lava growth even through cloud and darkness.
Thermal imageryIdentifies active, snow-free areas on the dome and flows.
WebcamsProvide visual confirmation when Aleutian weather allows.
Lightning networksHelp detect ash-rich explosive activity across the region.
Why Great Sitkin matters
A natural laboratory for slow lava emplacement
Great Sitkin gives scientists an unusually long view of how lava spreads, thickens and advances inside a summit crater. Because the eruption evolves gradually, satellite radar, thermal imagery, seismic instruments and remote cameras can measure subtle changes over months and years rather than minutes.
That slow pace allows AVO to compare radar scenes across weeks and seasons, tracking flow-front movement, crater filling and snow-free thermal areas in a way that would be impossible during a short, fast-moving eruption.
A volcano through time
Great Sitkin eruption timeline
1945
Wartime-era eruption
Explosive and lava-dome activity left deposits later overridden by the recent eruptive period.
1974
Short explosive eruption
Ash emission and dome activity created another important layer in the summit crater.
Recent eruptive period begins25 May 2021
Explosion opens the new eruptive phase
An explosion sent ash and gas to roughly 4.6 kilometres above sea level, after which activity shifted toward long-lived lava effusion.
Explosion → effusion
Within weeks, Great Sitkin changed from an explosive eruption to one of the world's clearest modern examples of long-lived crater-filling lava effusion.
Jul–Aug 2021
Lava fills and overflows the crater
Fresh lava spread over the 1945 and 1974 domes, overrode summit ice and moved beyond the crater rim.
2022–25
Persistent slow effusion
The crater-filling lava field expanded gradually, with intermittent thermal anomalies and rockfalls.
Current phase2026
East–southeast lava growth continues
Satellite radar confirms continued expansion while seismicity remains low and no new explosions have occurred.
What matters most
Great Sitkin's main hazards
☁
Aviation ash
A renewed explosion could inject ash into busy central Aleutian air routes.
↘
Lava flows and rockfalls
Slow lava can destabilise steep margins and send blocks down summit valleys.
⌁
Snow and ice interaction
Hot lava over snow and ice creates steam, meltwater and unstable ground.
✈
Aviation disruption
Remote air routes require rapid detection of any ash-producing change.
Volcoholics InsightGreat Sitkin demonstrates that an eruption can remain significant even when it is slow, quiet and almost entirely hidden by Aleutian weather.
Myths and reality
Great Sitkin myths, separated from the science
No explosions means the eruption is over.
Reality: lava has continued to erupt slowly since 2021 despite the absence of new explosions.
Low seismicity means no magma is moving.
Reality: slow effusion can continue with only weak earthquake and rockfall signals.
Cloud cover means the volcano cannot be monitored.
Reality: satellite radar can map lava growth through cloud and darkness.
A remote volcano creates little risk.
Reality: ash-producing changes could affect aviation even when few people live nearby.
Volcoholics Insight
An eruption measured in years, not minutes
Great Sitkin is the opposite of a brief volcanic spectacle. Its present eruption is a slow transformation of the summit crater, documented through thermal pixels, radar images and small rockfall signals across a remote island landscape.
Questions answered
Great Sitkin explained
What type of activity is Great Sitkin known for?
Great Sitkin is known for prolonged slow lava effusion, crater-filling dome growth and low-level seismicity. The intensity and visibility of activity vary over time.
When did the recent eruptive period begin?
An explosion occurred on 25 May 2021, followed by sustained lava effusion beginning in July 2021.
Why is the aviation colour code Orange?
An eruption is underway, although the current phase is primarily effusive and has not produced significant ash since May 2021.
How can AVO monitor through cloud?
Satellite radar, thermal data, seismic instruments and infrasound continue working when visual observations are limited.
Where is Great Sitkin?
On Great Sitkin Island in Alaska's Andreanof Islands, east of the community of Adak.
Official science, made readable
Built from the agencies watching Great Sitkin
Operational status belongs to the Alaska Volcano Observatory and USGS. Volcoholics provides context and never replaces official aviation or hazard notices.