USGS Volcano Notice - DOI-USGS-AVO-2025-08-15T18:14:16+00:00

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, August 15, 2025, 12:45 PM AKDT (Friday, August 15, 2025, 20:45 UTC)

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

Lava eruption continues at Great Sitkin Volcano. Satellite observations from this week show that lava is erupting from the vent area and spreading slowly south, with some rockfalls occurring along the south and east parts of the dome. All activity remains confined within the summit crater. Occasional small earthquakes and rockfall, probably from the steep flow margins, continue to be detected in seismic data. A steam plume was visible in clear webcam images.  

The current lava eruption began in July 2021 and has filled most of the summit crater and advanced into valleys below. There have been no explosions at Great Sitkin Volcano since an event in May 2021. The volcano is monitored using local seismic 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. 

SPURR (VNUM #313040)
61°17'56" N 152°15'14" W, Summit Elevation 11070 ft (3374 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Unrest continues to decline at Mount Spurr. Earthquake activity was at a low rate with about 17 located earthquakes over the past week. All had magnitudes less than 0.6. Earthquakes near Pothole Glacier, 10–15 km (6–9 miles) to the west of Spurr, are not related to the volcano.  

Clear weather this week showed little to no visible degassing from the summit, and the level of the summit crater lake remained stable. No sulfur dioxide gas was detected from satellite images. The CP2 gas sensor at Crater Peak continues to detect carbon dioxide from the Crater Peak vent, suggesting that degassing of a deep, but stalled, magma body continues. Ground deformation, as measured by GNSS (GPS) stations, remains paused as it has been since about mid-March 2025. 

AVO continues to monitor activity at Mount Spurr using local seismic, infrasound, and GNSS (GPS) stations, web cameras, airborne and satellite gas measurements, regional infrasound, lightning networks, and satellite images. A gas-measurement flight is scheduled for Sunday, August 17. 

Livestreams of Mount Spurr are available from a station located approximately 8 miles south of Mount Spurr [Mount Spurr Live Stream (SPCL)] and as viewed from Glen Alps above Anchorage [Mount Spurr Live Stream (ANCG)]. 

Mount Spurr is an ice- and snow-covered stratovolcano located on the west side of Cook Inlet approximately 80 miles (129 km) west of Anchorage. The only known historical eruptions occurred in 1953 and 1992 from the Crater Peak flank vent located 2 miles (3.5 km) south of the summit of Mount Spurr. These eruptions were brief, explosive, and produced columns of ash that rose up to about 65,000 feet (20 km) above sea level and deposited minor ashfall in southcentral Alaska (up to ¼ inch or 6 mm). The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. In 2004, Mount Spurr experienced an episode of increased seismicity, surface uplift, and heating that melted a large hole in the summit ice cap and generated debris flows. Primary hazards during future eruptions include far-traveled ash clouds, ash fall, pyroclastic flows, and lahars or mudflows that could inundate drainages on all sides of the volcano, especially on the south and east flanks.

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.