USGS Volcano Notice - DOI-USGS-AVO-2025-01-03T18:01:23+00:00

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, January 3, 2025, 12:12 PM AKST (Friday, January 3, 2025, 21:12 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

Activity at Great Sitkin Volcano has remained unchanged over the past week, with lava continuing to erupt at a slow rate in the summit crater. Intermittent, small volcanic earthquakes continue. When the weather was clear, the snow-free lava dome was visible in webcam views, and satellite images showed hot ground, consistent with new lava.
  
Since the May 2021 explosion, there have been no other explosions at Great Sitkin Volcano. The lava eruption that began in July 2021 is ongoing. It has filled most of the summit crater and advanced into valleys below. 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 during the 1974 eruption, occupies the center of the crater. That 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 occurred in 1945, also 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 persists at Mount Spurr, with ongoing shallow earthquake activity and surface deformation.

Although data processing continues, our current estimate is that over 260 earthquakes were located at Mount Spurr this past week. Most (more than 90%) were very small, with magnitudes less than 1. Three earthquakes had magnitudes larger than 2, with the largest being a M2.9 from January 2. Many of the earthquakes occurred in clusters on December 28 and January 2. Most of the events continue to be shallow and located under Mount Spurr's summit region. The kind of waxing and waning we saw this week is not uncommon for volcanic earthquake swarms.

The local network of GNSS (GPS) stations continues to record slow but steady ground movement upward and outward, which has been ongoing since March 2024. This is consistent with a pressure increase between 2 to 3 miles (3 to 5 km) depth about 2 to 2.5 miles (3-4 km) west of the summit, which is the general area of ongoing earthquake activity.

Mostly clear weather this past week allowed many views of the volcano. No unusual surface activity or changes were observed, though an occasional steam plume was visible from the summit in webcam images and could sometimes be seen from Anchorage during optimal viewing conditions. The lake in the summit crater is mostly covered with ice, though a small area of open water persists.

AVO continues to closely monitor activity at Mount Spurr for signals that would indicate that the volcano is moving closer to an eruption using local seismic, infrasound, web camera, and GNSS stations along with regional infrasound, lightning networks and satellite data. Based on previous eruptions, additional changes in earthquakes, ground deformation, the summit lake, and fumaroles would be expected if magma begins to move closer to the surface. Therefore, it is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning.

Mount Spurr volcano is an ice- and snow-covered stratovolcano located on the west side of Cook Inlet approximately 120 km (75 mi) west of Anchorage. The only known historical eruptions occurred in 1953 and 1992 from the Crater Peak flank vent located 3.5 km (2 mi) south of the summit of Mount Spurr. These eruptions were brief, explosive, and produced columns of ash that rose up to 20 km (65,000 ft) above sea level and deposited several mm of ash in south-central Alaska, including approximately 6 mm of ash in Anchorage in 1953. The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. 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.

CONTACT INFORMATION:

Dave Schneider, Acting Scientist-in-Charge, USGS, djschneider@usgs.gov (907) 786-7497

Ronni Grapenthin, Acting Coordinating Scientist, UAFGI, rgrapenthin@alaska.edu (907) 378-5460

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.