Two Alaskan volcanoes are venting steam right now

Great Sitkin and Shishaldin, two volcanoes roughly 250 miles apart in Alaska’s Aleutian chain, have both been venting visible steam through clear stretches of weather for days running. Neither is showing signs of an imminent explosive eruption, and the Alaska Volcano Observatory has kept both at the same elevated status for weeks: routine monitoring conditions, not an emergency.

What makes the pair worth tracking together is that they represent two different flavors of the same underlying story, an active lava eruption on one island and slow-building unrest on another, both expressed on the surface as the same plume of white vapor rising off a summit.

Two volcanoes, two different kinds of unrest

Great Sitkin sits under a Volcano Alert Level of WATCH and an Aviation Color Code of ORANGE, a status AVO’s September 18 weekly update attributed to a slow effusive lava eruption that has been continuous since July 2021, with no explosions recorded at the volcano since May of that year. The lava has already filled most of the summit crater and advanced into the valleys below, and the observatory’s webcam and satellite imagery that week showed steaming directly from the exposed lava surface whenever cloud cover cleared.

Shishaldin, on Unimak Island in the eastern Aleutians, sits one notch lower at ADVISORY and YELLOW. AVO’s daily update for September 17 recorded clear webcam images showing steam emissions from the summit crater, alongside minor seismic and infrasound activity. The pattern repeated on subsequent days: a September 16 update described steam visible from the crater with only weak seismicity behind it, and by September 19 the observatory was recording minor sulfur dioxide emissions in satellite data even as clouds obscured the rest of the view. AVO’s own volcano background notes that Shishaldin has had at least 54 episodes of unrest and more than 28 confirmed eruptions since 1824, and that its frequency and magnitude of earthquakes, infrasound signals and gas emissions have actually been declining in recent months rather than building toward anything larger. Most of those eruptions have been small, though the observatory’s records show the volcano’s 1999 and 2023 eruptions each produced ash columns that climbed as high as 46,000 feet, a scale of event nothing in the current data set of steam and minor gas emissions resembles.

What WATCH/ORANGE and ADVISORY/YELLOW actually communicate

Those four labels follow a fixed federal system, not an informal description. The U.S. Geological Survey’s explainer on its volcano alert framework, published under its Hawaiian Volcano Observatory, lays out the same four-tier scale AVO uses in Alaska: NORMAL marks non-eruptive background activity, ADVISORY means activity elevated above that background, WATCH applies when an eruption is likely or already underway with limited hazards, and WARNING is reserved for a hazardous eruption that is imminent, underway or suspected. The Aviation Color Code runs in parallel specifically to warn pilots and air traffic controllers about volcanic ash, with ORANGE meaning an eruption is either likely or occurring with no or minor ash, and RED reserved for eruptions producing significant ash.

The color-code half of that system did not originate in Hawaii at all. It was developed by the Alaska Volcano Observatory itself in the 1990s to give pilots flying near the Aleutian arc’s dozens of volcanoes rapid warning of ash hazards, and the International Civil Aviation Organization later adopted it worldwide as recommended practice. Applied to the current status of these two volcanoes, ORANGE and YELLOW both fall well short of the RED and WARNING combination reserved for an eruption actually producing hazardous ash, which is why neither volcano has triggered aviation restrictions over the Aleutians despite the ongoing venting.

How a remote observatory keeps watch on both

Neither volcano sits anywhere near a population center large enough to observe it directly day to day, so AVO leans on instruments instead. Great Sitkin is monitored with local seismic, geodetic and infrasound sensors, satellite data and web cameras, backed up by regional infrasound and lightning networks, according to the observatory’s weekly and daily notices; Shishaldin’s monitoring network follows the same pattern, adding a telemetered geodetic array to track any ground deformation around the summit.

Matt Haney, the Scientist-in-Charge for AVO within the USGS, is listed as the primary point of contact on each of the observatory’s recent notices for both volcanoes, with University of Alaska Fairbanks scientists Ronni Grapenthin and David Fee rotating as coordinating scientist on the geophysical side. Their joint program, run by the USGS, the University of Alaska Fairbanks Geophysical Institute and the Alaska Division of Geological and Geophysical Surveys, is what turns satellite passes and webcam snapshots from two of the more than 50 historically active Aleutian volcanoes into the same steady stream of updates that has tracked steam rising off Great Sitkin and Shishaldin through most of September.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.