Alaska’s Great Sitkin is the only American volcano the USGS has above an advisory

Great Sitkin, a 5,709-foot volcano in Alaska’s Aleutian Islands, sits at alert level WATCH with aviation color code ORANGE, the only entry above ADVISORY on the USGS list of elevated volcanoes. The Alaska Volcano Observatory sent that status at 19:39 UTC on October 29. Three other American volcanoes share the list, all one rung lower, and between them they cover Alaska, Hawaii and the Mariana Islands.

Save more, waste less: The Cool Down’s newsletter sends smart, simple changes that help you and the planet in your everyday life.

Subscribe to The Cool Down →

We may earn a commission if you sign up.

A WATCH does not mean an explosion is expected. For Great Sitkin it describes a slow eruption that has been running for more than five years.

An eruption of lava, not ash

Alaska Volcano Observatory’s daily update for October 29 says lava is erupting slowly within the summit crater. The eruption began in July 2021, and the lava has filled most of the crater and spilled into the valleys below. The update adds that there have been no explosions since May 2021, and that a few small earthquakes were recorded over the previous day while clouds hid the volcano from satellites and webcams.

The observatory’s Great Sitkin page, dated October 30, gives more texture. Satellite images showed minor growth of the active lava dome over the past week, and its south flank is creeping southward and shedding occasional small rockfalls. Seismic activity is low, limited to small volcanic earthquakes and rockfall signals from the growing lava, and webcams caught minor steaming. Kristi Wallace, the USGS acting scientist-in-charge, is the listed contact on the update.

The observatory behind the status is a cooperative program of the USGS, the University of Alaska Fairbanks Geophysical Institute and the Alaska Division of Geological and Geophysical Surveys. Its update lists Kristi Wallace of the USGS and David Fee of the Geophysical Institute as the contacts. The volcano itself lies at about 52.08 degrees north and 176.11 degrees west, far out along the Aleutian chain.

What WATCH and ADVISORY mean on the USGS scale

The USGS defines the tiers on its page about how alert levels characterize conditions at American volcanoes. An ADVISORY marks unrest above a volcano’s known background, or activity that has dropped after a higher level but is still being watched for a renewed rise. A WATCH marks unrest that is escalating toward an eruption whose timing is unknown, and it also covers an eruption that is underway but poses limited hazards. A WARNING is reserved for a dangerous eruption that is imminent, in progress or suspected.

The second clause of the WATCH definition, an eruption underway with limited hazards, is the one that matches a slow lava flow like Great Sitkin’s. It explains how a mountain with low seismicity can outrank Shishaldin, whose observatory reports elevated seismic activity but no eruption.

The three volcanoes one step below

The status feed that ranks them is the USGS elevated-volcanoes listing. It carries four entries. Shishaldin, also in Alaska, is at ADVISORY and YELLOW, with the observatory reporting continuing low-level unrest, elevated seismic activity, small earthquakes, tremor and weak steaming from a summit that rises 9,373 feet. Kilauea is at ADVISORY and YELLOW with its summit eruption paused after episode 55 in its summit eruption, according to the Hawaiian Volcano Observatory update, which expects the next fountaining episode between November 1 and 7.

Kilauea’s update gives the most granular picture of any of the four. Episode 55 of the Halemaʻumaʻu eruption ran from 3:19 to 9:03 a.m. Hawaii time on October 17, with fountains near 720 feet and a plume to about 25,000 feet. Since then the summit has refilled slowly, with tilt recovering about 14.9 microradians, sulfur dioxide output typical of a pause at 1,000 to 5,000 tonnes a day, and three earthquakes below magnitude 1.5 in 24 hours. Episode 55 followed a long, 39-day run-up of overflows fed by a shallow dike under the summit. The forecast window for episode 56 was pushed back because of a recent tilt decline.

The fourth is Ahyi Seamount in the Northern Mariana Islands, an underwater volcano whose summit lies 180 feet below the sea surface. The USGS weekly update reports greenish discolored water over the summit on October 16 and 21, probably from degassing and hydrothermal activity, and warns that an eruption there may endanger mariners. Without local real-time data, the notice says, USGS cannot forecast or warn of an eruption.

Beyond Ahyi, the Northern Mariana notice reports no unrest at any other volcano in the chain. Several of them, among them Anatahan, Sarigan, Maug, Agrigan and Pagan, carry no alert level at all because no geophysical instruments watch them, so a quiet status there reflects missing data as much as missing activity. The open question for Great Sitkin is when, or whether, the observatory lowers it: the lava has been flowing for five years, and the single data point that would settle it, the next daily update, comes from an observatory that could see nothing through the clouds on October 29.

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

Save more, waste less: Subscribe to The Cool Down →

We may earn a commission if you sign up.