ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 5, 2024, 12:45 PM AKDT (Friday, July 5, 2024, 20:45 UTC)
The eruption of lava within the summit crater of Great Sitkin Volcano continues, as observed by satellite images through June 30. Seismic activity was low, with occasional small volcanic earthquakes. This level of seismicity is typical of the slow lava eruption phase of the ongoing unrest. The volcano was obscured by clouds much of the week and slightly elevated surface temperatures were seen in satellite images on July 1 and 2.
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.
Low-level unrest continues at Shishaldin Volcano, with occasional small volcanic earthquakes and weak seismic tremor observed throughout the week. Small infrasound signals were detected on July 1–5, resulting from very small explosions occurring deep in the volcanic conduit. Minor sulfur dioxide gas emissions were observed in satellite data on July 1–3. Web camera images of the volcano show a persistent steam plume at the summit. Low-level seismicity and infrasound, sulfur dioxide gas emissions, and minor steaming, as observed this week, have characterized the post-eruption period of unrest over the past several months.
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. 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 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.
An Information Statement describing new observations of a small lake in the summit crater of Mount Spurr and an update on low-level unrest was released on July 3. While the formation of the lake is new, gas emissions remain low and seismic activity is declining, suggesting the probability of an eruption in the near future has not significantly increased. No surface changes have been observed at Crater Peak, the vent 2 miles (3 km) south of the summit associated with all historical eruptions.
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 on 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.
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.