ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, October 25, 2024, 12:15 PM AKDT (Friday, October 25, 2024, 20:15 UTC)
There have been no significant changes in the eruption at Great Sitkin Volcano this week. Satellite radar imagery through October 23 confirms the slow eruption of lava in the summit crater continues. Intermittent small volcanic earthquakes consistent with the eruption of lava persist. Cloudy weather blocked views of the volcano most of the week.
Since the May 2021 explosion, there have been no other explosions at Great Sitkin Volcano. The lava eruption that began in July 2021 is ongoing. It has filled most of the summit crater and advanced 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.
There have been no significant changes in unrest at Mount Spurr over the past week. Seismicity is elevated slightly from last week with numerous small earthquakes detected daily or about 80 earthquakes over the past week. No unusual activity was observed in mostly clear satellite or web camera data. On October 24, an AVO field crew visited Mount Spurr to perform pre-winter work to harden the network and ensure all systems are operational. They also flew over the summit crater and Crater Peak, a vent 3.5 km (2 mi) south of the summit, to make observations. They saw vigorous steam from the fumaroles in the summit crater. The Crater Peak vent was snow-covered.
AVO is closely monitoring Mount Spurr for signs of an impending eruption. We would expect changes in the earthquakes, ground deformation, summit lake, and fumaroles if magma began to move closer to the surface. Thus, 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.
On October 19, strong northwesterly winds near Katmai and the Valley of Ten Thousand Smokes picked up loose volcanic ash from the 1912 Novarupta-Katmai eruption and carried it southeast. The National Weather Service issued a SIGMET for this low-level event and suggested that the maximum cloud height is 6,000 ft (1.8 km) above sea level. Residents reported hazy skies and a dusting of ashfall in the city of Kodiak.
This phenomenon is not the result of recent volcanic activity and occurs during times of high winds and dry snow-free conditions in the Katmai area and other young volcanic areas of Alaska. No eruption is in progress. All volcanoes of the Katmai area (Trident, Snowy, Griggs, Katmai, Novarupta, Mageik, Martin) remain at color code GREEN. Resuspended volcanic ash should be considered hazardous and could be damaging to aircraft and health.
Resuspended volcanic ash should be considered hazardous and could be damaging to aircraft and health. For more information on volcanic ash and human health, visit the following website: http://volcanoes.usgs.gov/ash/. Official warnings about these ash resuspension events are issued by the National Weather Service: http://www.weather.gov/afc. Forecasts of airborne ash hazard to aircraft: http://www.weather.gov/aawu . Volcanic Ash Advisories: http://vaac.arh.noaa.gov/ . Forecasts of ash fall: http://www.weather.gov/afc. Air quality hazards and guidance from Alaska Department of Environmental Conservation, Division of Air Quality: http://dec.alaska.gov/Applications/Air/airtoolsweb/Advisories/Index
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.