USGS Volcano Notice - DOI-USGS-AVO-2024-08-16T18:04:44+00:00

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, August 16, 2024, 11:35 AM AKDT (Friday, August 16, 2024, 19:35 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

No significant change occurred this week at Great Sitkin Volcano, where the ongoing effusive eruption continues to gradually fill the summit crater with lava. Recent satellite imagery shows lava flow growth near the eruptive vent and trending roughly east-northeast. Weakly elevated surface temperatures and steaming from the active lava flow surface were also observed when the weather was clear. Seismic activity was low and unchanged from previous weeks, with occasional small volcanic earthquakes.

The current, prolonged period of lava eruption at Great Sitkin Volcano began in July 2021 and has mainly been observed using satellite radar images that can view the volcano through cloud cover. A single explosive event occurred in May 2021; no other explosions have been detected since that time.

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

Low-level unrest continues at Shishaldin Volcano. A steam and gas plume from the summit area was observed in webcam and satellite imagery throughout the week when viewing conditions afforded clear views. Occasional small volcanic earthquakes, weak seismic tremor, and weak infrasound signals were detected. These observations are consistent with the degassing of magma deep within the vent. Such activity has characterized the post-eruption period of unrest over the past several months.

No significant eruptive activity has occurred since November 2023. Minor rock falls associated with collapse events from the unstable ground in and near the summit crater may generate small clouds of fine-grained dust that dissipate quickly near the summit.

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, lightning data, and satellite images to monitor the volcano.

Shishaldin Volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a conical stratovolcano 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 activity during July – November, 2023 generated ash columns that reached between 30,000 ft (9 km) and 42,000 ft (13 km) above sea level.

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

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.