USGS Volcano Notice - DOI-USGS-AVO-2026-10-02T17:42:35+00:00

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, October 2, 2026, 12:07 PM AKDT (Friday, October 2, 2026, 20:07 UTC)

GARELOI (VNUM #311070)
51°47'21" N 178°47'46" W, Summit Elevation 5161 ft (1573 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Summary: A single brief explosion detected in geophysical data on October 1 prompted a change in the Aviation Color Code/Volcano Alert Level to YELLOW/ADVISORY. No further signs of unrest have been detected.

A single, brief explosion was detected in geophysical data on October 1 at 07:27 AM AKDT (15:27 UTC). In response, AVO raised the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. Cloudy conditions obscured the volcano at the time of the event, so it is unclear whether a volcanic ash cloud was produced. If ash was generated, it was likely minor given the very short duration of the explosion (less than one minute). Infrasound data indicate the explosion originated from the south crater of Mount Gareloi, and satellite radar data from yesterday shows a small crater‑like feature near the fumarole field on the volcano’s south flank. No additional signs of unrest have been detected since the event.

Gareloi volcano persistently emits magmatic gases from a fumarole field in the south crater and commonly exhibits low-level seismic activity. These observations suggest the presence of shallow magma and potential interaction with a hydrothermal system. The explosion on October 1 likely reflects a change to the magmatic-hydrothermal system, but it is not clear that the likelihood of a volcanic eruption has increased. AVO will continue to monitor activity to determine if the recent changes are related to influx of new magma or other changes to the magma system.

Mount Gareloi is monitored by a local seismic and infrasound network, satellite data, and regional infrasound and lightning-detection networks.

Mount Gareloi, which makes up all of Gareloi Island, is a stratovolcano located in the Delarof Islands group of the Aleutian Islands, about 1,242 miles (2,000 km) west-southwest of Anchorage and about 93 miles (150 km) west of Adak, the westernmost community in Alaska. This small volcano is 6.2 x 5.0 miles (10 × 8 km) in diameter at its base with two summits, separated by a narrow saddle. The northern, slightly higher peak contains a crater about 1,000 ft (300 m) across. The southern summit has a crater open to the south and a persistent degassing vent (fumarole) on its western rim. Gareloi has been one of the most active in the Aleutians since the 1740s, with 16 reports of eruptive activity at Gareloi since 1760. In 1929, its largest historical eruption produced sixteen small south- to southeast-trending craters that extend from the southern summit to the coast, as well as lava flows and pyroclastic deposits on the southeastern flank of the volcano. Eruptions of Gareloi commonly produce ash clouds and lava flows, and the primary hazard is airborne clouds of ash that could affect aircraft. Since seismic instruments were installed in 2003, they have detected small but consistent seismic signals from beneath Mount Gareloi’s edifice.

GREAT SITKIN (VNUM #311120)
52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Summary: Slow eruption of lava continues within the summit crater associated with low-level seismicity and steaming.

Cloudy conditions over the past week have limited most satellite and webcam observations. However, satellite data from September 28 revealed a small collapse on the south side of the lava dome and minor steaming from the summit area. Seismic activity remains low, characterized by occasional small volcanic earthquakes and signals from minor rockfalls associated with continued lava‑flow growth.

The current lava eruption began in July 2021 and has filled most of the summit crater and advanced into the valleys below. There have been no explosions at Great Sitkin Volcano since an event in May 2021. The volcano is monitored using local seismic, geodetic, and infrasound sensors, satellite data, and web cameras, and regional infrasound and lightning networks.

Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 26 miles (42 km) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a ~1 mile (1.6 km)-diameter summit crater. A steep-sided lava dome, emplaced in the crater during an eruption in 1974, has been mostly buried by the ongoing eruption. The 1974 eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft (7.6 km) above sea level. A poorly documented eruption also occurred in 1945, producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.

SHISHALDIN (VNUM #311360)
54°45'19" N 163°58'16" W, Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Summary: Unrest continues with small earthquakes, tremor, infrasound signals, and gas emissions.

Volcanic activity remains slightly elevated. Small earthquakes, ongoing tremor, and occasional infrasound signals have continued over the past week. During periods of clear weather, webcam views showed steaming from the summit area, and satellite data indicated minor sulfur dioxide emissions through much of the week. Overall, the frequency and magnitude of earthquakes, infrasound signals, and gas emissions have declined over recent months.

Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. In addition to the local monitoring network, the Alaska Volcano Observatory uses nearby geophysical networks, regional infrasound and lightning data, and satellite data to monitor the volcano. 

Shishaldin Volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a conical stratovolcano with a base diameter of approximately 10 miles (16 km). It is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest, including over 28 confirmed eruptions since 1824. Most eruptions are relatively small, although activity during the 1999 and 2023 eruptions generated ash columns that reached up to 46,000 ft (16 km) above sea level.

CONTACT INFORMATION:

Matt Haney, Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (907) 378-5460

Contact AVO: https://avo.alaska.edu/contact

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.