USGS Volcano Notice - DOI-USGS-AVO-2024-02-23T06:20:09+00:00

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 23, 2024, 11:39 AM AKST (Friday, February 23, 2024, 20:39 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

The eruption of lava within the summit crater of Great Sitkin Volcano continues. Cloud cover inhibited most views of the volcano during the last week. Satellite imagery from February 19 showed continued growth of the active northwest flow lobe. Seismic activity remains relatively low with occasional small volcanic earthquakes.

The current prolonged period of lava eruption at Great Sitkin Volcano began in July 2021. No explosive events have occurred since a single event in May 2021.       

The volcano is monitored by local seismic, geodetic, and infrasound sensors and web cameras, as well as regional infrasound and lightning networks and satellite data.  

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 (43 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 (1.5 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.

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

No significant eruptive activity occurred over the past week and the Aviation Color Code and Volcano Alert Level for Shishaldin were lowered to Yellow/Advisory on Saturday, February 17. Seismicity remains slightly elevated but unchanged throughout the week with small volcanic earthquakes continuing. Cloud cover inhibited most views of the volcano in satellite images during the past week but minor collapses in the upper drainage areas and associated debris runouts were observed on the southeast and northeast sides of the volcano in satellite data on February 17 and February 19. There were clear views of the volcano in webcam images early in the week showing minor steaming from the summit. AVO detected no sulfur dioxide emissions during the past week. 

No significant eruptive activity has been observed since November 2023. 

Local seismic and infrasound sensors, web cameras, and a geodetic network are used to monitor Shishaldin Volcano. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to monitor the volcano. 

Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone 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 the April-May 1999 event generated an ash column that reached 45,000 ft. (14 km) above sea level.

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

 No eruptive activity or other changes have been detected at the volcano in cloudy satellite and webcam imagery. Seismicity has declined over the past several days but remains slightly elevated with possible tremor observed early in the week and small low frequency earthquakes throughout the week.

Mount Gareloi persistently emits magmatic gases from a fumarole field on 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 current increase in seismicity 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.

Gareloi is monitored by local seismic and infrasound sensors, satellite data, a web camera, and distant infrasound and lightning 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 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.

KANAGA (VNUM #311110)
51°55'27" N 177°9'44" W, Summit Elevation 4288 ft (1307 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Cloud cover inhibited most views of the volcano last week, but no changes were observed in satellite radar imagery The level of seismicity has declined with only a few volcanic earthquakes observed on Saturday, February 18. 

The explosion on December 18, 2023 indicates sudden explosions could occur without warning. These explosions may produce ash clouds exceeding 20,000 feet above sea level. Before the current activity, the last unrest at Kanaga Volcano was in February 2012 when a steam-driven explosion occurred together with a fissure opening on the southern crater rim. 

Kanaga Volcano is monitored by local seismic and infrasound sensors and web cameras, regional infrasound and lightning networks, and satellite data. 

Kanaga Volcano occupies the northern corner of Kanaga Island, one of the most southerly members of the central Aleutian chain. It is a symmetric composite cone 4288 ft (1307 m) high and 3 miles (4.8 km) in diameter at sea level, built of interbedded basaltic and andesitic lava flows, scoria layers, and pyroclastic rocks. Kanaga Volcano’s last significant eruption was in 1994–1995. At least two significant ash plumes were recorded over the course of this eruption: the first, to ~25,000 ft (7.5 km), occurred on February 21, 1995 and the second on August 18, 1995, when an eruption cloud reached ~15,000 ft. (4.5 km). A light dusting of ash fell on the community of Adak and air traffic was disrupted due to continuing low-level activity and cloudy conditions which prevented visual approaches to the Adak air field.

CONTACT INFORMATION:

Matt Loewen, Acting Scientist-in-Charge, USGS mloewen@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAFGI dfee1@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.