Iliamna

Satellite radar data through July 3 show continued slow eruption of lava in the summit crater of Great Sitkin on the southwest and southeast margins of the lava dome. Rock falls from the steep flow margins continue. Elevated surface temperatures related to this activity were observed in satellite data throughout the week during periods of clear viewing conditions. Occasional small earthquakes continue.

The lava eruption that began in July 2021 is ongoing. It 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. 

Matt Haney, Scientist-in-Charge, USGS [email protected] (907) 786-7497
 

Jessica Larsen, Acting Coordinating Scientist, UAF [email protected] (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.

Repairs to the seismic monitoring network were completed over a week ago. There are now sufficient data available to monitor activity at Iliamna Volcano so the Aviation Color Code and Volcano Alert Level were changed to GREEN/NORMAL from UNASSIGNED/UNASSIGNED on July 1, 2025. 

Iliamna Volcano is located on the western side of lower Cook Inlet in the Lake Clark National Park. Iliamna is a snow-covered stratovolcano which rises 10,020 feet above sea level. Although steam plumes occur on its eastern flanks, there has been no historic volcanic activity at Iliamna. Iliamna is located 225 km (140 miles) southwest of Anchorage and 113 km (70 miles) northwest of Homer.

Matt Haney, Scientist-in-Charge, USGS [email protected] (907) 786-7497
 

Jessica Larsen, Acting Coordinating Scientist, UAF [email protected] (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.

Unrest continues at Mount Spurr. The level of activity remains slightly above background but continues to decline since the peak of unrest earlier this year.  The decrease in activity suggests that the magma intrusion beneath Mount Spurr has stalled and that the likelihood of an eruption has declined.

Earthquake activity continues, with a small number located beneath the summit of Mount Spurr and beneath Crater Peak. The number of earthquakes and their magnitudes continue to show some variability from week to week but are following a decreasing trend. Ground deformation, as measured by GNSS (GPS) stations, remains paused as it has for the last two months. Volcanic gas emissions continue, as would be expected from a passively degassing body of stalled magma.

Fluctuations in unrest are common at volcanoes and eruptive activity remains possible, but unlikely. Should unrest escalate towards an eruption, we expect to observe increases in seismic activity, gas emissions, surface deformation, and surface heating

AVO continues to closely monitor activity at Mount Spurr for signals indicating the volcano is moving closer to an eruption using local seismic, infrasound, and GNSS (GPS) stations, web cameras, airborne and satellite gas measurements, regional infrasound, lightning networks, and satellite images. Livestream camera video from station SPCL located south of Mount Spurr can be viewed at: Mount Spurr Live Stream (SPCL). A livestream of Mount Spurr, as viewed from Glen Alps in Anchorage, is available here: 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 all sides of the volcano, but primarily on the south and east flanks.

Matt Haney, Scientist-in-Charge, USGS [email protected] (907) 786-7497
 

Jessica Larsen, Acting Coordinating Scientist, UAF [email protected] (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.