Far out along Alaska’s Aleutian chain, a volcano has been quietly building itself higher for years. Great Sitkin continues to ooze lava into its summit crater in a slow eruption that shows no sign of ending, while small earthquakes rumble beneath its growing dome and keep scientists watching closely.
A slow eruption that keeps going
The Alaska Volcano Observatory has reported that a slow eruption of lava continues within Great Sitkin’s summit crater, accompanied by low-level seismic activity. Rather than erupting explosively, the volcano has been extruding thick lava that piles up and spreads gradually, a process that has continued over an extended period.
The current lava eruption began in July 2021 and has since filled much of the summit crater and pushed into the valleys below. There have been no explosions at Great Sitkin since an event in May 2021, making the ongoing activity a steady effusion rather than a violent blast.
Effusive eruptions of this kind can persist for years, adding lava layer by layer as long as the supply of molten rock continues from below. That longevity makes Great Sitkin a long-running subject of study, offering scientists an extended look at how a lava dome grows and how its behavior shifts over time.
A dome that keeps expanding
Satellite observations show the lava dome gradually expanding, with monitors noting growth toward the east and east-southeast. When cloud cover clears enough for instruments to see the summit, they have detected slightly elevated surface temperatures consistent with the fresh lava at the surface.
That steady enlargement is the visible signature of the eruption. As new lava reaches the surface, the dome broadens and advances, reshaping the summit of the volcano over months and years.
Because the volcano sits in a remote and often cloud-covered part of the Aleutians, satellites and remote sensors do much of the observational work. Clear windows through the clouds are precious, giving scientists the chance to capture thermal images and measure how far the dome has crept since the last look.
The small quakes beneath the surface
Beneath the growing dome, seismic instruments continue to detect activity. The observatory has characterized seismicity as low, marked by occasional small volcanic earthquakes and signals associated with minor rockfalls as loose material tumbles from the steep, evolving lava surface.
Volcanic earthquakes differ from the tectonic quakes generated by shifting faults, arising instead from the movement of magma and gases and the fracturing of rock as the dome grows. Reading those signals is a core part of how scientists infer what is happening out of sight, deep within the volcano.
These small tremors are part of the routine behavior of an active lava dome. Scientists track them closely because changes in the pattern or intensity of seismic activity can offer early clues about whether an eruption is intensifying or shifting.
A sudden increase in earthquakes, or a change in the type of seismic signals, can precede a shift in eruptive behavior, which is why continuous monitoring matters even during long stretches of steady activity. Rockfalls from the steep dome, meanwhile, can send hot debris and small ash clouds down the flanks, adding another hazard for observers to watch.
How scientists keep watch
Great Sitkin is monitored through a combination of tools. Local seismic, geodetic, and infrasound sensors sit on and around the volcano, supplemented by satellite data, web cameras, and regional infrasound and lightning networks that can detect volcanic activity from a distance.
As of late August 2026, the observatory maintained the volcano’s alert level at Watch and its aviation color code at Orange, reflecting ongoing eruptive activity. Those designations signal that the volcano is erupting or could escalate, warranting continued vigilance even during periods of relative calm.
The alert system uses a ladder of levels so that responders and the public can quickly gauge a volcano’s status. The Watch level and Orange color code sit below the highest warnings, indicating heightened activity that falls short of a major hazardous eruption but still calls for close attention from monitoring agencies.
Why a remote volcano still matters
Great Sitkin sits on an uninhabited island in the Aleutians, far from population centers, so the immediate risk to people on the ground is limited. The greater concern from Aleutian volcanoes is often the ash they can send into the sky, because the region lies beneath busy North Pacific air routes.
The Aleutian arc is home to dozens of volcanoes, many of them monitored precisely because of the air-traffic risk. An ash cloud lofted high enough to reach cruising altitudes can force flights to reroute, disrupting travel and cargo across the North Pacific even when no one lives near the volcano itself.
Volcanic ash can damage jet engines, which is why aviation color codes are part of the monitoring system. Continuing updates on the volcano’s status are published by the U.S. Geological Survey, and broader tracking of Alaska’s many active volcanoes is maintained through the Alaska Volcano Observatory.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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