ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, October 18, 2024, 11:12 AM AKDT (Friday, October 18, 2024, 19:12 UTC)
There have been no significant changes in the ongoing eruption at Great Sitkin Volcano this week. Satellite imagery through October 15 confirms that the slow eruption of lava in the summit crater continues. Intermittent small volcanic earthquakes persist and satellite images from occasional periods of clear viewing conditions show slightly elevated surface temperatures due to the active lava flow.
Since the single explosive event in May 2021, there have been no other explosions at Great Sitkin Volcano. The ongoing lava eruption began in July 2021, and the lava has filled most of the summit crater and advanced over the crater rim into valleys below. The Alaska Volcano Observatory (AVO) monitors Great Sitkin using seismic, infrasound, 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.
AVO has observed a gradual increase in volcanic unrest over a period of several months at Mount Spurr, located about 120 km (75 miles) west of Anchorage. GNSS receivers have detected sustained upward and outward ground deformation since March 2024 and an increase in seismic activity has also been noted since April. Due to this gradual increase in volcanic unrest at Mount Spurr (described in the Information Statement released on October 9) and the subtle increase in the rate and size of earthquakes over the past few weeks, AVO raised the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY on October 16. The largest magnitude earthquake detected in this current period of unrest is a M2.3 earthquake on October 6th. There are no indications that an eruption is imminent. Often this type of seismicity and ground deformation will decline without producing an eruption. Collectively, the observations suggest that a new batch of magma has been emplaced beneath the volcano. The rate of activity indicates that the probability of an eruption in the near future is low. No surface changes have been observed at Crater Peak, the vent 2 miles (3 km) south of the summit associated with all historical eruptions.
AVO continues to closely monitor activity at Mount Spurr for signals that would indicate that the volcano is moving closer to an eruption. Based on previous eruptions, changes from current activity in the earthquakes, ground deformation, summit lake, and fumaroles would be expected if magma began 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 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.