USGS Volcano Notice - DOI-USGS-AVO-2023-04-13T11:07:25-08:00

This Information Statement provides an update on ongoing volcanic unrest at Aniakchak volcano. 

Summary  

• Current unrest at Aniakchak volcano suggests that magma is intruding at a depth of 2 to 2.5 mi (3 to 4 km) below sea level, centered under Aniakchak caldera. This increases the likelihood of an eruption over the coming months to years.  

• If Aniakchak volcano does erupt, additional signs of volcanic unrest are likely to precede it as magma rises to the surface, providing advance warning.  

• Some magma intrusions do not result in an eruption, and sometimes unrest can last for months or years prior to an eruption.  

• If an eruption were to occur, the primary hazard would be from volcanic ashfall and drifting ash clouds, which could impact local communities and infrastructure and disrupt air travel.  

• The Alaska Volcano Observatory (AVO) continues to monitor the volcano for changes and will issue further updates as needed.  

Current observations 

Due to low-level unrest, AVO raised the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY at Aniakchak volcano on February 22, 2023.   

Elevated seismicity was first detected in October 2022, characterized by an increase in the rate of earthquakes and a shallowing of earthquake depths to less than 5.6 miles (9 km) below sea level. The earthquake rate increased in mid-February, with dozens of earthquakes detected per day, including a magnitude 3.3 earthquake on February 17.  Measurements of the earthquake rate were disrupted by a partial network outage that began in March and reduced AVO’s ability to detect smaller earthquakes. However, analysis shows that seismicity remains above background, with the largest recent event a magnitude 3.3 on April 6. 

Map showing earthquake locations: http://www.avo.alaska.edu/images/image.php?id=194294 

Figure showing earthquake numbers through time: http://www.avo.alaska.edu/images/image.php?id=194295 

High rates of ground uplift have also been detected with satellite radar data. Although snow cover limits observations before early February, a zone of uplift centered within the eastern side of Aniakchak caldera was first detected between February 4 and 27. The ground uplift rates in February and March were about 1.6 in (4 cm) per week. The most recent image pair from March 23 to April 4 shows that this rate has declined to about 1.2 inches (3 cm) per week. These uplift rates are at the high end of those observed for restless volcanoes worldwide. 

Figure showing recent surface uplift at Aniakchak: http://www.avo.alaska.edu/images/image.php?id=194292 

There have been no visual changes to the ground surface or hydrology. No gas emissions or temperature changes have been observed. 

Prognosis  

The presence of earthquakes and ground uplift at the same time and in the same general area suggests that magma is moving upwards beneath Aniakchak caldera, and the likelihood of an eruption has increased. Initial modeling of the uplift signal shows that it is consistent with an intrusion of new magma 2 to 2.5 miles (3 to 4 km) below sea level. The earthquakes likely are caused by increased stresses in the Earth’s crust due to this intrusion and the substantial uplift that it is causing.  

Based on the current observations and comparison to other episodes of unrest at similar volcanoes, the following scenarios are considered most likely: 

• An eruption occurs that is similar to, or smaller than, the eruption of Aniakchak volcano that occurred in 1931. That eruption spanned six weeks, including strong explosive activity for the first ten days or so that produced measurable ashfall more than 124 miles (200 km) from the volcano. Later stages of the eruption produced smaller explosions and a lava flow in the caldera. Strong earthquakes were reported throughout.  

• No eruption occurs. The magma that has intruded beneath the caldera stalls and unrest declines.  

The following scenario is considered unlikely: 

• An eruption much larger than 1931 occurs. While there have been rare larger eruptions in the geologic history of Aniakchak volcano, the amount of surface uplift currently observed does not suggest a body of magma is accumulating that is much larger than what erupted in 1931.  

Intrusions of new magma under volcanoes do not always result in volcanic eruptions. The ground uplift and earthquake activity at Aniakchak volcano may cease with no eruption occurring. Similar episodes of unrest at other volcanoes worldwide end in eruptions about half the time. Unrest at calderas such as Aniakchak sometimes lasts for many months or even years. Unrest could wax and wane, and if an eruption were to occur, it could be after a period of months or years. 

If an eruption were to occur, it would likely be preceded by additional signals that would allow AVO to provide advance warning. Prior to an eruption, we expect the rise of magma closer to the surface would lead to changes in the ground uplift pattern and an increase in earthquake activity, as well as increased ground surface temperatures, and possible gas emissions.   

Potential hazards 

If an eruption were to occur at Aniakchak volcano, the primary hazard would be from volcanic ashfall and drifting ash clouds, which could disrupt air and marine travel, and impact local communities and infrastructure. The areas that would be impacted by ashfall and drifting ash clouds would depend on the wind direction at the time of the eruption.  

Areas closer to the eruption site, especially within the caldera, could experience additional hazardous phenomena, such as ballistics (flying rocks) or pyroclastic flows.  

It is possible that during a particularly large eruption, hot ash could fall on snow-covered slopes outside the caldera, leading to volcanic mudflows, or lahars, in drainages around the volcano.  

For a full description of volcanic hazards associated with Aniakchak volcano, please see the following report: https://pubs.usgs.gov/of/2000/0519/

Current monitoring 

AVO monitors Aniakchak with a local network, which consists of six seismometers, a web camera, and an infrasound sensor, as well as with satellite remote sensing data and regional infrasound and lightning networks. Several of the seismic stations stopped transmitting data on March 4 due to low power levels caused by snow burial. Two stations remain in operation, but we currently are unable to locate smaller earthquakes due to the outage. 

AVO recently installed an additional seismic station and web camera in Port Heiden, which is 16 miles (26 km) from Aniakchak. Field work at the volcano is planned for late June to service stations on the volcano and add new geophysical equipment to measure ground uplift with higher precision and during times of heavy snow cover. 

For current monitoring data, please see the Aniakchak Activity Page: https://avo.alaska.edu/activity/Aniakchak.php 

Web camera in Port Heiden that shows Aniakchak: https://avo.alaska.edu/webcam/aniakchak_pth.php