ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 1, 2024, 11:25 AM AKST (Friday, March 1, 2024, 20:25 UTC)
The eruption of lava within the summit crater of Great Sitkin Volcano continues. Cloud cover inhibited most views of the volcano throughout much of the week. However, satellite radar data, which can observe the ground through the clouds, showed continued growth of the active northwest flow lobe on February 24 and 26. 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.
Low-level unrest continues at Shishaldin Volcano. Seismicity remains slightly elevated and intermittent minor steaming from the summit crater continues. Satellite data show no evidence of elevated surface temperatures or emissions of sulfur dioxide gas, further indicating that unrest remains at a low level. Minor rock falls or collapse events from the unstable ground in and near the summit crater remain likely. These events may generate very small clouds of fine-grained ash that dissipate quickly in the immediate vicinity of the summit.
No significant eruptive activity has occurred 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.
Low-level unrest continues at Mount Gareloi. Seismicity remains slightly elevated. Clouds obscured satellite and web camera images throughout most of the week, and there was no evidence of activity visible during occasional periods of clear viewing conditions.
Mount Gareloi 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 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.
Hannah Dietterich, Acting Scientist-in-Charge, USGS hdietterich@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.